Body Control Modules 439
Courtesy of Sullivan Training Systems should always be used when back-probing a terminal.
This will minimize damage to the wire seals and
Figure 13-41 LOADpro1 dynamic voltmeter leads. terminals compared to paper clips and similar non-
approved methods, such as piercing wire insulation
available, some technicians may back-probe the ter- with a sharp probe.
minals of a connector that is still connected to the
device or the mating harness connector to avoid A special set of enhanced DMM test leads called
making open circuit voltage measurements. Some LOADpro1 dynamic voltmeter leads have been de-
OEMs indicate that terminals should not be back- signed for automotive technicians that causes a 510O
probed because doing so may damage wire seals and parallel resistance to be switched on across the DMM’s
terminals. However, special curved probes, known as internal resistance when a pushbutton on the lead is
diagnostic spoons, designed for back-probing terminals depressed (Figure 13-41). If you observe a sizable
decrease in the open circuit voltage indicated by the
DMM when the button is depressed (i.e., greater than
0.5V decrease), there is a high amount of series re-
sistance present somewhere in the circuit, or the open
circuit voltage that you are measuring is caused by
leakage current through an electronic component, such
as an FET, that is not switched on.
Summary
n The body control module on International High Per- lamps, and windshield wipers. The various switches
formance Vehicles is called the electrical system act as inputs to the body controller through either
controller (ESC) on model year 2001–2006 trucks hardwiring or multiplexing. The body controller
and the body controller on 2007 and later year trucks. microprocessor makes decisions based on its pro-
The body controller or ESC contains a microproces- gramming and provides an output in the form of
sor. The body controller or ESC uses information energizing a high side driver, energizing a low side
obtained from the input sources to control the outputs. driver, or transmitting a data link message.
n Outputs of the body controller include high side n Self-diagnostics assist in troubleshooting the body
drivers, low side drivers, and messages on the J1939 controller. Diagnostic trouble codes may be logged
data link. to indicate a circuit that is out of range high or out
of range low.
n Input sources for the body controller include mes-
sages from the J1939 data link, messages from the n The Freightliner SmartPlex system uses two or more
switch data link, and hardwired inputs such as separate modules to control body electrical features.
switches and sensors. The bulkhead module (BHM) controls the chassis
module (CHM) via the J1939 data link.
n A reference ground scheme is commonly used in
automotive electronics to minimize the effects of n The Freightliner SmartPlex uses optional smart
electromagnetic interference and to improve mea- switches to control electrical system features. Each
surement accuracy for sensor circuits. smart switch contains two identification resistors
that uniquely define the switch function.
n A diagnosable switch is a special switch that pro-
vides specific values of resistance, unlike a con- n The instrument cluster in the Freightliner SmartPlex
ventional switch, which is either an open circuit or system is called the ICU. The ICU acts as the input
near 0O. A diagnosable switch is connected to an device for the stalk-mounted multifunction switch.
analog input. This permits circuit failures such as an The ICU transmits the status of the multifunction
open circuit or a shorted-to-ground circuit to be switch inputs onto the J1939 data link.
diagnosed.
n Diagnostic trouble codes (DTCs) are used to indicate
n The body controller controls several electrical sys- that an electronic module has detected an abnormal
tem features, including headlamps, turn signals, stop condition. DTCs may indicate a sensor in-range
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
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440 Chapter 13
operating condition, such as engine coolant tempera- n Ghost voltage describes open-circuit measurement
ture is too high. DTCs may also indicate sensor out of of a voltage by a DMM in a circuit with high re-
range conditions, such as open circuits or shorts to sistance. Ghost voltage can result in misdiagnosis.
ground. A J1939 DTC consists of an SPN and an FMI.
Suggested Internet Searches http://www.freightliner.com
http://www.brighterideas.com
Try the following web sites for more information:
http://www.internationaltrucks.com
Review Questions
1. Which of the following is a true statement concerning an International truck with an electrical system
controller (body controller)?
A. The headlamp ground circuit C. An electric horn circuit that is shorted to ground will result
is completed through the in a blown body controller fuse.
body controller ground.
D. A high side driver in the body controller supplies +12V directly
B. A low side driver in the body to the electric horns when the body controller detects that the
controller is used to control horn input is active.
the horn relay coil low side.
2. The body controller reference ground should not be connected to chassis ground or used as a chassis ground
for what reasons?
A. To prevent eddy currents and C. To prevent back EMF from damaging body controller internal
to prevent interfering with components and to keep digital inputs from becoming logic 0.
the CB radio reception.
D. The body controller reference ground is the same as chassis
B. To reduce electromagnetic ground and can be used as a ground for low-current devices
susceptibility and reduce (under 5A).
voltage measurement
inaccuracies at inputs.
3. A diagnosable switch would typically be connected to which type of input?
A. J1939 data link input C. Pulled-down digital input
B. Pulled-up digital input D. Analog input
4. The resistance across a diagnosable switch is found to be approximately 1200O with the switch closed and
approximately 2400O with the switch open. What does this indicate?
A. The switch is defective C. The switch has probably been exposed to moisture and has
because open switch corrosion on the contacts.
resistance should be near 0O
and closed switch resistance D. The switch may be working as designed.
should be near infinite ohms.
B. The switch is defective
because closed switch
resistance should be near 0O
and open switch resistance
should be near infinite ohms.
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Body Control Modules 441
5. The mirror heat does not work on an International truck with a body controller. The mirror heat switch is
located in a switch pack. The switch pack communicates with the body controller through the switch data
link. Which of the following would not be a cause of the inoperative mirror heat?
A. There is an open circuit B. There is an open circuit between the mirror heat switch and the
between the body controller body controller mirror heat digital input.
high side driver and the
heated mirrors. C. The switch pack is not communicating with the body controller.
D. The mirror heat circuit is shorted to ground.
6. The left side turn signals, both front and rear, do not work on an International truck with a body controller.
The left side turn signals also do not work with the hazard switch in the ON position. The truck has
combination stop/turn rear lamps and the left rear stop lamp illuminates when the brake is depressed. What
could be a possible cause?
A. A defective left turn-signal C. An open circuit between the body controller left turn-signal input
flasher. and the turn-signal switch.
B. The left turn-signal message D. The left rear turn-signal circuit is shorted to ground.
is not being sent by the body
controller over J1939.
7. The windshield wipers on an International truck with a body controller operate at high speed anytime the key
is in the ignition position, regardless of wiper switch position. What is a possible cause?
A. A defective wiper park C. The body controller wiper high-speed input circuit is shorted
switch. to ground.
B. A disconnected wiper switch. D. The wiper-off command is not being received by the body
controller over the J1939 data link.
8. The air pressure gauges, fuel level gauge, and voltmeter do not work on an International truck with a body
controller. All other gauges, such as tachometer and engine oil pressure, are operating correctly. Which of
the following is the most likely cause of the inoperative gauges?
A. The EGC is not B. The engine ECM is not communicating with the EGC.
communicating over the
J1939 data link. C. The J1939 CAN + circuit is shorted to ground.
D. The body controller is not communicating with the EGC over
the J1939 data link.
9. The cruise control does not work on an International truck with a body controller. Which of the following is
not a likely cause?
A. A disconnected stop switch C. No J1939 communication between the body controller and the
connector engine ECM
B. A broken clockspring D. All of the above are possible causes
10. Two technicians are discussing the HVAC system on a 2001 International truck with an ESC. Technician A
says that one purpose of the high side pressure sensor is to act as a high-pressure cut-out switch. Technician B
says that one purpose of the high side pressure sensor is to cause the ESC to switch on a viscous-type fan
clutch to increase high side pressure in cold weather. Who is correct?
A. A only C. Both A and B
B. B only D. Neither A nor B
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442 Chapter 13
11. The multifunction switch on the Freightliner Business Class M2 is hardwired to which device?
A. AMU C. BHM
B. CHM D. ICU
12. Smart switches used on the Freightliner Business Class M2 are identified by the BHM through which
method?
A. Binary on-off combination of B. A unique J1939 source address is transmitted by each smart
two switches inside the smart switch.
switch that are connected to
two BHM digital inputs. C. Two specific values of resistance inside the smart switch that are
connected to two BHM analog inputs.
D. Time-division multiplexing.
13. An out-of-range low DTC might be set for which condition?
A. A digital input circuit is C. An analog input circuit is open.
shorted to ground. D. Both B and C could cause this DTC to be set.
B. An analog input circuit is
shorted to ground.
14. Which best describes ghost voltage?
A. The low internal resistance of C. The rules of a series voltage divider circuit as it relates to the
a DMM ammeter causing a high internal resistance of a DMM voltmeter
false voltage to be displayed
on the DMM D. High DMM internal resistance in parallel with a low value of
circuit resistance
B. The voltage supplied by the
DMM ohmmeter interacting
with other voltage sources on
the truck
15. Two technicians are discussing DTC 110-03. The service information indicates that this DTC is set for an
out-of-range high condition of the engine coolant temperature sensor circuit. Technician A says this DTC is
set due to abnormally high coolant temperature, which could be caused by poor airflow through the radiator.
Technician B says that this DTC can be set due to abnormally high coolant temperature caused by a stuck
thermostat. Who is correct?
A. A only C. Both A and B
B. B only D. Neither A nor B
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
CHAPTER
14 Diesel Engine
Electronics
Learning Objectives
After studying this chapter, you should be able to:
n Discuss the various types of electronically controlled diesel fuel systems.
n Describe why the current flow through an inductor cannot instantly change.
n Explain the fundamentals of a closed loop control system.
n Discuss how an in-range failure might not cause a DTC to be set.
n Explain the difference between in-cylinder emissions reduction and exhaust aftertreatment.
n Discuss how a variable geometry turbocharger can be used to regulate EGR flow rate.
n Explain how particulate matter and NOx exhaust emissions are controlled.
n Describe the requirements of HD-OBD and discuss some of the benefits of this regulation for
technicians.
Key Terms in-range failure permanent DTC
injection control pressure (ICP)
aftertreatment injection pressure regulator (IPR) previous MIL-on DTC
closed loop control learn cycle
confirmed DTC lookup tables proportional solenoid
derate malfunction indicator lamp (MIL)
desired output measured output readiness
error measurement error
exhaust gas recirculation (EGR) open loop control selective catalytic reduction
freeze frame oxides of nitrogen (NOx) (SCR)
H-bridge particulate matter (PM)
heavy-duty on-board diagnostics pending DTC smart actuator
(HD-OBD) smart sensor
hydraulically actuated unit
variable geometry turbocharger
injector (HEUI) (VGT)
virtual sensor
443
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
444 Chapter 14
INTRODUCTION electricity and electronics will be explored as they
apply to a modern diesel engine and truck.
A diesel engine wiring harness from a 1970s truck
may have consisted of one wire for the fuel cut-off so- THE ELECTRONICALLY
lenoid, not including the wiring for the starter motor and CONTROLLED DIESEL ENGINE
alternator. Compare this single wire to the Volvo VE-
D16 engine wiring harness shown in Figure 14-1. One of The central component in modern diesel engines is
the primary reasons for the addition of electronic controls the engine electronic control module (ECM). Some
to diesel engines was the reduction of exhaust emissions, OEMs refer to the ECM as an engine control unit
as required by agencies such as the U.S. Environmental (ECU) or as an engine electronic control unit (engine
Protection Agency (EPA). Diesel engines have always ECU). These terms all mean the same thing in the
had a reputation for being reliable and efficient. How- context of this chapter, an electronic component that
ever, diesel engines of the past were also smelly, noisy, contains a microprocessor. For simplification, the ac-
and polluting. Figure 14-2 illustrates the reduction in ronym ECM will be used throughout this chapter to
EPA-mandated on-road diesel engine exhaust emissions refer to this device or, in some cases, multiple devices.
since 1970. The most visibly evident change is partic-
ulate matter (PM) reduction, which includes all types of The microprocessor in the ECM is programmed to
exhaust smoke. It is now rare to observe an on-highway make logical ‘‘decisions’’ on how it will control its
truck belch out black smoke (soot), although this was a outputs based on the information it receives from its
common sight just a few years ago. The reduction of inputs. This concept was introduced in Chapter 13 for
oxides of nitrogen (NOx), one of the pollutants re- body control modules. The ECM inputs include a va-
sponsible for the formation of smog, has also required riety of sensors, such as those that would connect to the
substantial changes in diesel engines. It is estimated that engine wiring harness shown in Figure 14-1. However,
one model year 1988 HD truck produced the same the primary ECM input is the crankshaft position and
amount of pollutants as 65 model year 2010 trucks. speed, which is typically obtained from the combination
of camshaft and crankshaft position sensors, as ex-
From an electrical perspective, there is not much plained in Chapter 11. The truck operator’s torque or
new material in the final two chapters. Instead, the speed request, obtained from the accelerator position
application of some of the fundamental concepts of sensor (APS), is also an important ECM input.
Wiring Diagram
Coolant Turbo SRA Humidity
level sensor speed sensor sensor
VGT actuator
Intake air Injector Engine brake
pre-heater solenoids solenoid
Cam speed
Boost Coolant sensor
pressure/temp temp sensor
sensor
EGR MFS
Fan control EM vehicle
interface
J1939 CAN2 bus
termination Oil pressure
Crankcase sensor Crank
pressure sensor
Fuel filter speed sensor © Cengage Learning 2014
Air valve
unit Fuel pressure and heater
sensor
Oil level/temp
sensor
Figure 14-1 Typical 2010 engine wiring harness.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 445
Steady- 2010 rule 20
0.2 g/HP-h NOx (100%) 15
state 0.01 g/HP-h particulate 10
20 test 5
2007 final rule
1.1 g/HP-h NOx (ave)
0.01 g/HP-h particulate
Pull ahead
NOx + NMHC
Transient and
new steady-
state test
NOx
Oxides of nitrogen (g/HP-h)15 NOxNOx + HC Transient
Particulate matter (g/HP-h)
test
© Cengage Learning 2014
(unregulated) NOx NOx
10
PM (unregulated)
5 PM
0 1975 1980 1985 1990 1995 PM 0
1970 Model year 2000 2005 2010
Figure 14-2 EPA heavy-duty diesel exhaust emissions for PM and NOx.
The primary ECM outputs are related to the control of the port is closed. The pressure increases within the
the fuel system and the exhaust emission control system. injector or nozzle until the nozzle opening pressure
(NOP) is reached and fuel is injected into the dense,
FUEL SYSTEMS compressed air in the combustion chamber. Combus-
tion then occurs after an ignition delay or lag. The
There are three basic tasks of any diesel fuel system: injector continues to inject fuel under pressure until the
nozzle closure. In a strictly hydromechanical fuel
1. Provide injection metering (quantity of fuel). system, all of these events are controlled without any
2. Atomize the fuel into a fine mist that is capable electrical components. In an electronically controlled
fuel system, these events are controlled by a combi-
of penetrating the densely packed air in the nation of hydromechanical and electrical means.
combustion chamber.
3. Provide injection timing control. The earliest electronic diesel engine controls were an
adaptation of the existing system; that is, electronic con-
Diesel fuel systems of the past were strictly hydrome- trol was added to the existing fuel system. As the exhaust
chanical systems and performed these three tasks rea- emissions standards became increasingly more stringent,
sonably well. These mechanical systems provided good entirely new electronically controlled diesel fuel systems
engine performance and reliability, but poor exhaust have been introduced as outdated designs became obso-
emissions control. To reduce exhaust emissions as well as lete. Examples of this progression will be reviewed.
provide improved performance and fuel economy, the
fuel system must also be capable of performing these Electronically Controlled
basic tasks with extreme precision and at much higher Pump-Line-Nozzle Systems
injection pressures. In addition, the fuel system must:
Pump-line-nozzle (P-L-N) fuel systems include port-
1. Control fuel delivery independent of engine helix and rotary distributor pump systems. These
speed and camshaft geometry (rate shaping). hydromechanical fuel systems were enhanced with
electronic controls permitting these systems to meet
2. Perform multiple injection events per cycle. EPA standards for a few more years of production. P-L-N
systems were not used much in on-highway engines
To perform these tasks with the necessary precision, much after 1997 because they could not deliver the fuel
electronic control of the fuel system is necessary. economy and emissions reduction of more advanced
fuel systems. Although these fuel systems are simple by
Figure 14-3 shows the phasing of diesel delivery, today’s standards, they permitted advances such as
injection, and combustion events. These events are
applicable to most types of diesel fuel systems with
some minor differences. During the delivery phase, the
pressure within the injector or nozzle increases after
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
446 Chapter 14
20° BTDC TDC ATDC
0°
Delivery–fuel pump effective stroke Injection pump
Injection–injection pulse Injection nozzle
Combustion Engine
cylinder
Port NOP ignition Port Nozzle Flame
closure opening closure quench
Injection Ignition Nozzle Afterburn © Cengage Learning 2014
lag lag closing
delay
Figure 14-3 Phasing of delivery, injection, and combustion events.
© Cengage Learning 2014
Figure 14-4 Bosch port-helix injection pump with RE30 rack actuator.
cruise control and road speed limiting. Fuel temperature stroke of each pump plunger. In a conventional port-helix
and air temperature compensation were also made system, a hydromechanical governor controls the rack
possible by these electronic enhancements. position, thus controlling fuel metering. In the elec-
tronically controlled version of the port-helix system,
Port-Helix Injection Pumps. Port-helix injection the hydromechanical governor is replaced by an elec-
pumps utilize a control rack to regulate the effective tronic governor (rack actuator) as shown in Figure 14-4.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 447
Return spring
Linear magnet
Control rod
Control rod 7-way plug
travel sensor
Bearing sleeves
Speed sensor
© Cengage Learning 2014
Figure 14-5 Bosch RE30 electronically controlled rack actuator.
Details of the rack actuator are shown in Figure 14-5. 1 Courtesy of Robert Bosch LLC
The control rod is attached to the pump control rack. The 2
control rod travel sensor provides an indication of the
control rod position to the ECM. The ECM causes the 3
control rod to move to the desired position by controlling 4
the current flow through a proportional solenoid or
linear magnet as shown in Figure 14-5. A conven- 65
tional solenoid like that used in a starter motor is an 1. Control-collar position sensor
on-off (two-position) digital-type device, like a switch. 2. Solenoid actuator for the injected fuel quantity
Unlike a conventional solenoid, a proportional sole- 3. Electromagnetic shutoff valve
noid is an analog device that can be moved and held at 4. Delivery plunger
any position throughout its range of travel based on the 5. Solenoid valve for start-of-injection timing
amplitude of current flowing through the solenoid’s 6. Control collar
electric windings. The control rod is spring applied in
the zero fuel position. Therefore, an interruption of Figure 14-6 Bosch electronically controlled VE distri-
electric current flow through the proportional solenoid’s butor injection pump used on smaller diesel engines.
windings results in engine shutdown. The rack actuator electronically controlled version of a Bosch VE pump.
also contains a variable reluctance speed sensor and The ECM controls the position of the control collar by
timing event sensor, which act as inputs to the ECM. regulating the position of the rotary electrical solenoid
actuator. A potentiometer is used as a control collar
Rotary Distributor Injection Pumps. Rotary distrib-
utor pumps were also adopted for electronic control,
such as the Bosch VE rotary distributor injection pump
shown in Figure 14-6. The hydromechanical governor
is replaced by a rotary solenoid actuator in the
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
448 Chapter 14
position sensor and is an ECM input. The control Sensor signals Courtesy of Robert Bosch LLC
collar is used to regulate the opening and closing of the
spill/cutoff ports to control injected fuel quantity. A 1
start of injection solenoid valve in the pump is con-
trolled by the ECM to regulate injection timing. 2
The pintle-type nozzles may also contain a nozzle 3
valve motion sensor, shown in Figure 14-7, which is
an input to the ECM. The nozzle valve motion sensor 4
is used to determine precisely when the start of in-
jection has occurred. A variable reluctance engine 5
speed sensor also acts as an ECM input. Figure 14-8 1. Untreated signal from the needle-motion
illustrates the waveforms generated by the needle
valve motion sensor, identified as NBF (waveform 1), sensor (NBF)
and the engine speed sensor (waveform 3). The ECM 2. Signal derived from the NBF signal
converts or conditions these raw analog signals into 3. Untreated signal from the engine-speed signal
their respective digital representations in waveforms (2) 4. Signal derived from untreated engine-speed
and (4) shown in Figure 14-8. The raw analog signals
produced by these sensors are not usable by the ECM’s signal
microprocessor until they are converted to a digital 5. Evaluated start-of-injection signal
signal. Figure 14-8 NVMS and engine speed sensor waveforms.
The ECM can be programmed to respond to spe-
cific failures, such as the loss of information from a
Nozzle-and-holder assembly with
needle-motion sensor (NBF)
4 sensor, by applying a derate which is a reduction of
maximum allowable engine torque or speed or initi-
1 ating a limp-home (default) strategy. An interruption
25 of current flow through the fuel metering solenoid
3 results in engine shutdown.
1. Setting pin 4. Cable Courtesy of Robert Bosch LLC Electronic Unit Injector Systems
2. Sensor winding 5. Plug
3. Pressure pin Unit injector systems describe diesel fuel systems
where the pump and the injection nozzle are combined
Figure 14-7 Nozzle valve motion sensor (NVMS). into one unit. The pump can be actuated by the cam-
shaft, as shown in Figure 14-9, or high-pressure en-
gine oil can be used to generate injection pressures, as
described in the next section.
Cam-actuated electronic unit injectors (EUIs) were
introduced in the North American market in 1987.
These single actuator EUIs with two electrical termi-
nals (one solenoid) were widely utilized in North
America until 2007. The electronically controlled ac-
tuator replaces the mechanical rack system used to
control metering in previous mechanical unit injector
(MUI) systems. To increase injection pressures and to
more precisely control timing and metering, dual ac-
tuator EUIs with four electrical terminals (two sol-
enoids) were introduced in 2007. Both of these
systems will be described.
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 449
Electromagnet Piston
Valve
Outlet
Intake
Injector tip © Cengage Learning 2014
Injector needle
Figure 14-9 Camshaft actuated EUI.
Single Actuator EUI. Single actuator EUIs, like that effective stroke. This would have been controlled me-
shown in Figure 14-10, utilize a normally open spill chanically on a typical unit injector system of the past.
valve (4) which is closed when an electric current
flows through the solenoid valve assembly (2). The It is important to note that there is no injection
ECM injector drivers (FETs) supply the control current pressure sensor within the unit injector and there is no
for the solenoid valve assembly. Alternately, some direct measurement of the quantity of fuel being in-
OEMs utilize a separate injector drive module to jected. In addition, there is no direct measurement of
supply this current. when the nozzle actually opens and closes. However,
all of this information is vital for the ECM to be able to
The ECM determines when to energize the solenoid provide precise fuel metering and injection timing.
valve based on its inputs and programming instructions. Therefore, the ECM is programmed to ‘‘know’’ pre-
Energizing the solenoid valve causes the spill valve to cisely when current should be switched on to source
close. Once the spill valve is closed, the pressure within the solenoid valve assembly and when it must be
the pumping element increases rapidly until the nozzle switched off to meter a precise amount of fuel at the
opening pressure (NOP) is reached, at which time fuel exact time. The OEM has determined all of this in-
is injected into the combustion chamber. The NOP is formation through extensive testing in a laboratory
determined by mechanical means in the same manner as a environment during the fuel system development.
mechanical unit injector system. Typical NOP is 5000 psi
(34 MPa), but the injection pressures can rise to as high as Figure 14-11 illustrates the relationship between
30,000 psi (207 MPa). the voltage sourced by the ECM, the current that flows
through the injector solenoid, the spill valve move-
Once the ECM has determined that the desired fuel ment, and the fuel injection rate (all with respect to
quantity has been metered, the ECM shuts off the time on the horizontal axis). Notice in Figure 14-11
current flow through the solenoid valve assembly, that although the voltage supplied by the ECM in-
which causes the normally open spill valve to open. stantly rises from 0V to some level (often 50V or
This causes the pressure within the pumping element more), the current flow through the control valve so-
to rapidly decrease. The nozzle will then close once lenoid gradually ramps up from 0A to some value.
the pressure decreases below the nozzle closing pres- Inductors were introduced in Chapter 3. Recall that
sure resulting in the end of injection. Looking back at when current flows through an inductor, a magnetic
Figure 14-3, the ECM is only controlling the port field is generated. This magnetic field passes through
closure and the port opening to control the pump the windings of the inductor (coil), which cause a
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
450 Chapter 14
1 13 6O resistor. The graph below the circuit in Figure 14-12
2 3 shows the circuit current on the vertical axis and time on
the horizontal axis, which is the same as would be
14 displayed on an oscilloscope using a clamp-on current
probe. When the switch closes, the current flow through
4 5 the circuit instantly increases from 0A to 2A, as pre-
dicted by Ohm’s law. In Figure 14-13, the resistor is
15 6 replaced with an inductor that has 6O of wire resistance.
16 7 Both the inductor and the resistor would each indicate
Fill 6O if an ohmmeter were used to measure their resis-
Spill port tance. Notice in the graph shown in Figure 14-13 that
port 8 the current does not instantly increase from 0A to 2A
9 when the switch is closed but rather the current ramps
10 17 up to 2A over time. However, the voltage across the
11 inductor does instantly change from 0V to 12V when
12 18 the switch is closed. Figure 14-14 illustrates the op-
position of the induced voltage generated by the ex-
1. Solenoid connection 8. O-ring Reprinted Courtesy of Caterpillar Inc. panding magnetic field cutting through the inductor to
(to the multiplex 9. Spring the applied voltage. The result is that until the ex-
enable circuit) 10. Spacer panding magnetic field becomes stationary, the current
11. Body flow through the inductor will be reduced. The time that
2. Solenoid valve 12. Check it takes for the current to rise to the peak value is de-
assembly 13. Tappet pendent upon the value of inductance (henries).
14. Spill duct
3. Spring 15. Spill control circuit Looking again at the injector voltage and current
4. Valve (shown in the 16. Calibration port traces shown in Figure 14-11, the current through the
17. Fuel duct solenoid does not instantly rise to the peak value (IP)
closed position) 18. Pressure chamber but instead ramps up to this peak value over time. The
5. Plunger ECM must take this current rise time into account, as
6. Barrel well as the time for the spill valve to actually close, the
7. O-ring time for the pressure to rise to the NOP, and other
mechanical time constants. The OEM has factored all
Figure 14-10 Single actuator EUI. of these electrical and mechanical lag times into the
ECM programming instructions so that the nozzle
voltage to be induced. The polarity of this induced opening pressure is reached at precisely the optimal
voltage is such that it opposes the voltage that caused time for injection to begin.
the original current flow through the inductor. This
was defined as self-inductance or CEMF in Chapter 3. The injector solenoid current rise time is also im-
To simplify, inductors resist a change in current flow portant for failure detection. The injector solenoid re-
through the inductor. sistance as measured by an ohmmeter may be less than
1O on some injectors and is very dependent on tem-
This leads to an important fact: perature because copper has a positive temperature
coefficient. If the insulation coating on the injector
Important Fact: The current flow solenoid windings becomes damaged by heat and vi-
through an inductor cannot instantly change bration and causes windings to be shorted together, the
from one level to another. However, the resistance of the solenoid as measured with an ohm-
voltage measured across an inductor can meter may not decrease much at all, but the inductance
instantly change from one level to another. of the solenoid will be decreased substantially. The
inductance of a coil cannot be easily measured without
To illustrate this concept, Figure 14-12 shows a sim- specialized test equipment. The decreased inductance
ple electrical circuit with a battery, a switch, and a due to the shorted windings can cause the strength of
the magnetic field to be reduced such that the solenoid
cannot cause the spill valve to close and the cylinder
will misfire. However, the ECM may be programmed
to monitor the time that it takes for the injector current
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 451
BAT
Voltage V-reg 5 V
OV IP
IHOLD
Current Open IRT Injector response time
PW Pulse width
OA BOE Beginning of energizing
BOI Beginning of injection
Control EOE End of energizing
valve EOI End of injection
lift
Closed
Injection IRT BOI EOI Courtesy of Detroit Diesel Corporation
rate tEOI
PW tEOE
tBOE tBOI
Figure 14-11 EUI voltage and current waveforms.
+12V 6 Ohms +12V Inductor
Battery Battery with 6Ω wire
resistance
2 Amps © Cengage Learning 2014 2 Amps © Cengage Learning 2014
0 Amps
0 Amps
Current flow Current flow
Figure 14-12 Instantaneous current rise in resistor Figure 14-13 Ramped current rise in inductor circuit.
circuit.
to rise to the peak value. If the injector solenoid has peak current has been reached (IP). Recall from
failed such that the windings have shorted together, the Chapter 8 the discussions on solenoid pull-in and
peak current rise time will be reduced to resemble that hold-in current. The peak injector current serves as the
of a resistor. The ECM detects this reduced peak solenoid pull-in current. Once the solenoid armature
current rise time and may set a DTC indicating that the has moved to the closed position, the current through
injector is shorted. For example, a J1939 DTC with the solenoid can be reduced to minimize self-heating
SPN 652 and FMI 06 might be set if injector #2 is of the injector solenoid and to reduce the stress on the
detected as being internally shorted. FETs in the ECM. A reduced average hold-in current
(IHOLD) sustained by PWM of the supply voltage is all
One other item of interest in Figure 14-11 is the that is necessary to hold the spill valve closed.
PWM of the voltage sourced by the ECM once the
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
452 Chapter 14
Applied Induced controlled by a second electrical coil. The NCV is
voltage voltage designed to keep the nozzle closed at pressures above
the hydromechanical NOP. Energizing the NCV causes
+12V Expanding © Cengage Learning 2014 the nozzle control pressure to vent, which allows the
Battery magnetic nozzle to open and inject as shown in Figure 14-16. To
field end injection, both the NCV and SV are de-energized
by the ECM.
Figure 14-14 Induced voltage (CEMF) opposes the
applied voltage. The main advantage of the dual actuator EUI is that
the ECM has control over the NOP. This permits much
Dual Actuator EUIs. One disadvantage of single ac- higher injection pressures, which reduces the fuel
tuator EUIs is that the NOP is still mechanically droplet size (better fuel atomization). The dual actua-
controlled. Dual actuator EUIs have two solenoids and tor EUI can also be used for multiple injection events
two control valves; thus, these injectors typically have (multipulse injection) by cycling the NCV off and on
four electrical terminals. Dual actuator EUIs were in- during the injection event. One type of multipulse in-
troduced in North America in 2007. Figure 14-15 jection is pilot injection. Pilot injection reduces the
illustrates a Delphi E3 dual actuator EUI. The elec- familiar diesel engine knock heard at low engine
trically controlled spill valve (SV) works in the same speeds and reduces white smoke at cold starts by re-
way as described in the previous section for a single ducing ignition delay. A small quantity of pilot fuel is
actuator EUI. The needle control valve (NCV) is injected into the combustion chamber a few hundred
microseconds before the main injection pulse. The
Injector Plunger pilot fuel is ignited after a brief ignition delay. The
spring main fuel charge is then injected into the ignited pilot
Electrical fuel. Pilot injection has been described as injecting fuel
O-ring connector into fire. The result is smooth combustion resulting in
High-pressure reduced noise and emissions.
Solenoid valve
fuel duct assembly Figure 14-17 illustrates a variation of the EUI
called the electronic unit pump (EUP). The EUP is a
Spill valve (SV) unit injector that is separated into the pumping com-
O-ring ponent and the injector nozzle component. A tube
Body SV closed
(energized)
SV NCV
electrical coil electrical coil
SV armature NCV closed
SV electrical coil (energized)
NCV electrical coil
Needle control valve (NCV)
Nozzle spindle © Cengage Learning 2014
Needle spring © Cengage Learning 2014
Tip assembly Nozzle valve
Figure 14-15 Delphi E3 dual actuator EUI. Figure 14-16 Nozzle opens when NCV is energized.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 453
ECM
To nozzle Terminals
4
Solenoid
O-rings Fuel
supply
Fuel gland
return
gland Plunger
O-ring
Roller lifter © Cengage Learning 2014
Roller
Figure 14-17 Electronic unit pump.
connects the nozzle to the unit pump element. The engine speed permitting high injection pressures and
ECM controls the valves in the nozzle and the pump in injection rate shaping. Details of a HEUI injector can
a manner similar to EUIs. be found in most diesel fuel system textbooks.
Hydraulically Actuated Unit The main components of the HEUI system shown
Injector System in Figure 14-18 include:
Hydraulically actuated unit injectors (HEUI) 1. High-pressure oil pump, which develops the
describe unit injectors that utilize engine lubrication high-pressure engine oil called the injection
oil under pressure to actuate the pumping element control pressure (ICP).
similar to the action of a hydraulic jack. The internal
HEUI injector components cause fuel to be pressurized 2. An electric injection pressure regulator (IPR),
up to seven times greater than the pressure applied to which is controlled by the ECM.
the lubrication oil, as will be explained later in this
section. The HEUI system is still in use by Navistar as 3. An ICP sensor, which acts as an input to the
of 2012. The main advantages of the HEUI system ECM.
over camshaft actuated unit injectors is the injection
cycle is not limited to camshaft lobe profile and in- 4. The electronic unit injectors, which are con-
jection pressures can be controlled independent of trolled by the ECM.
5. A high-pressure oil manifold, which supplies
engine oil under high pressure to each injector.
The component locations on a typical Navistar DT
engine are shown in Figure 14-19.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
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454 Chapter 14
Injectors Drilled module, but a separate electronic module may control
supply some specific tasks, such as exhaust aftertreatment.
passage
Since injection control pressure (ICP) has a direct
Injection Oil correlation to fuel injection pressure, the ECM is
control manifold programmed to drive the ICP to a specific pressure for
pressure the engine’s current operating conditions. The injec-
sensor Oil line tion pressure regulator (IPR) shown in Figure 14-21 is
an on-off type solenoid, which is controlled by the
From main ECM. The ECM provides a 400 Hz PWM signal to the
gallery IPR and varies the duty cycle (percentage of on-time)
to control the ICP. When the IPR is not energized, the
Injection Courtesy of Navistar, Inc. ICP decreases; when the IPR is energized, the ICP
pressure regulator increases. Therefore, a disconnected IPR results in a
High-pressure oil pump no-start condition because without sufficient ICP, fuel
Oil reservoir injection pressure cannot be developed by the unit
injectors. Conversely, if the IPR becomes physically
Figure 14-18 Navistar HEUI injection pressure control stuck in the energized position, the ICP will increase
system components. rapidly until a mechanical pressure relief valve in the
high-pressure oil manifold opens at 4000 psi (28 MPa)
Injection control High-pressure High-pressure to dump the high-pressure lubrication oil back into the
oil manifold sump. Either of these conditions will result in a cor-
pressure sensor oil hose responding DTC being set by the ECM.
Oil Closed Loop Control. The ECM is programmed to be
reservoir able to determine the desired ICP based on a variety of
inputs and operating conditions. The ECM determines
High- the measured ICP in the high-pressure oil manifold
pressure based on the voltage that the ICP sensor supplies to the
ECM. The ECM converts this voltage into a pressure
pump based on its programming instructions, as explained in
Chapter 11. Therefore, the ECM knows the measured
Injection control Courtesy of Navistar, Inc. ICP and the desired ICP. If the measured ICP is dif-
pressure regulator ferent from the desired ICP, the ECM is able to in-
crease or decrease the ICP by increasing or decreasing
Figure 14-19 HEUI component locations. the duty cycle of the PWM voltage that the ECM is
supplying to the IPR. This is referred to as closed loop
The engine ECM inputs and outputs for a pre-2004 control or feedback control.
HEUI DT engine are shown in Figure 14-20. Navistar
has introduced several generations of the HEUI control An example of a simple closed loop control system
system over the years. These have been known infor- is shown in Figure 14-22. In this system, a clear
mally in part by the number of electronic control plastic tank of water is being used for some industrial
modules used. The first generation was a three-box process. The water exits the tank at a varying rate
system and had a separate ECM, an injector drive through a pipe at the bottom of the tank. A desired
module (IDM), and a vehicle personality module level of water in the tank has been established. To
(VPM). The next generation was a two-box system maintain the level of water in the tank at the desired
with an ECM and an IDM. The third-generation con- level, the amount of water entering the tank must be
solidated engine controller (CEC) is a single module regulated. The person shown in Figure 14-22 has been
system. The separation of tasks into individual elec- given a task of maintaining the tank at the desired level
tronic modules was common practice throughout the shown by opening or closing the valve in the overhead
industry during the early years of electronic controls. fill pipe. If the level of water in the tank drops below
Most OEMs now consolidate engine control into one the desired level, the valve must be opened to add
water to the tank. Conversely, the valve must be closed
if the level of water in the tank is above the desired
level. A closed-loop control system consists of three
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 455
DT 466E & International @ 530E Electronic Engine Controls
Engine-Mounted Components Truck-Mounted Components Cab-Mounted Components
ECT EOT EOP ICP MAP ECM connector Deutch
(optional) IAT pin numbers connector (cowl)
1 (97J) KAM V BAT (ECM fuse)
20 (97-GB) CASE GRD
40/60 (97-GC/97-GD) PWR GRD APS/IVS
AB AB ABC ABC Deutch AB 47 (99B) APS signal 19 (99B) A
Starter connector (97D) IVS signal 2 (99A) B
harness (engine) BCA IAT signal (97AX) 8 (99C) C
MAP signal (97AY) 25 (97X) signal ground 21 (97W) (99D) D
A 45 (97AA) V REF 12 (97U) E
A V IGN
A 46 (97CD) BARO signal (F4) F
A 26
(97GW) (97GU) A (97GT) (97DC) 15 Signal ground (97X) 27 (97M) BNC
A (97ND) (97CY) 24 V REF (97AA) 42
(97BG) 28 (97BG) 14 (97N) BNO (97Z) BARO
(97CE) N/A ICP signal (97BK) 7 (97BL)
(97CE) 5 EOP signal (97CE) 5 (97F) EDL
(97NF) (97BF) 16 EOT signal (97BF) 31 (98) STI
(97DA) 13 ECT signal 56 (97T) STO/WARN
(97-GA) 26 V IGN (F2) (97-GR) 43 27 (97CD)
CMP ground (97AT) DCL- Brake switch
23 (97AS) DCL+ relay
(97BE) 27 CMP signal (97BE) 18 (97D) TACH IN
7 VPM connector
Packard connector IDM 32 (97A) DDS
(thru valve cover) connector 2 (97AM) signal GRD 48 Brake 1 (47) VSS-
(97H) ECI
Inj. # 1 (97AB) B 26 (97GM) PWR GRD 17 (97AF) OWL switch 2 (47A) VSS+
Inj. # 2 22 (97AC) SCCS
ABC (97BR) C 2 (97AB) 6 24 (97CF) SC GRD 11 5 (97AR) TACH OUT1
8 34 (99F) R APS
B CLS (34B) 9 (97DD) R VREF 6 (48) TACH OUT2
28
(97BR) 8 module 36 V IGN V BAT 8 (97E) V BAT (ECM fuse)
9 (93A) TSA
Open 3 (97MV) 33 Self test switch 10 (97B) V IGN (F4)
15 PWR GRD
INJPWR (97MY) A 20 (97AK) 24 EDL 10 6
circuit 37
B 115 volts (97F) 57
35
(97BP) D 9 (97BP) 21 21 14 V IGN 18 (47B) VSS OUT2
59 20 (47C) VSS OUT3
CMP Inj. # 3 3 FDCS (97BB) 50
39
4 EF (97AZ) 30 15 (97GE) PWR GRD
44
16 CI (97BA) 23 (97GF) CASE GRD
B (97AD) M 22 (97AD) 19 1 14
Open 11 (97MS)
Inj. # 4 INJPWR (97MM) 21 (97BM) 14 (97AG) 8 13
115 volts L
(97BN) 10 (97BN) 23 IDM PWR 15 4 EST connector
N relay IDM_EN
12 (98C) ATA-
Neutral switch 11
B 22 15 A (98A) ATA+
Inj. # 5 (97AH) (jumpered w/manual)
(97AP) P 30 (97AP) 7 V BAT ECM PWR Clutch switch V BAT F28
relay (jumpered Crank inhibit
B w/auto)
B 6 (97A-DW) 18 relay V IGN
30
Inj. # 6 Shield grid (97AJ) Courtesy of Navistar, Inc.
(97AL)
(97DA) 15 A Starter meg switch
A (97BH) 25 V IGN F6 5 Start switch
B IPR control (97BH) V BAT
20 V IGN (F1)
IPR valve 17
13 PTO/cruise circuits
9
(Dotted lines = Frequency or switch function) 28 Remote accelerator circuit/
Body builder connector
Figure 14-20 Navistar 3-box HEUI electronic control system.
Spool valve main components: a controller, a plant or process re-
Drain port ferred to as a system, and a means of measuring the
actual system output. The actual system output as
Drain Drain port Return spring determined by the measurement device is referred to as
Engine Off the measured output. In this case, the person’s brain
Poppet movement is the controller, the system is a tank with a valve in a
ECM pressure Control orifice water inlet pipe, and the means of output measurement
regulating and filter are the eyes of the person. The other components of a
signal closed loop control system are a desired output, also
known as setpoint, and a means for the controller to
change the system, such as an actuator. In the example
shown in Figure 14-22, the desired output is the
Valve
Solenoid Pump outlet Courtesy of Navistar, Inc.
winding Spool valve drain port © Cengage Learning 2014
Desired
Poppet Level
Drain Engine Running Figure 14-22 Closed loop control system. Water
Out
Spool chamber pressure
Pump outlet pressure
Figure 14-21 Injection pressure regulator (IPR) valve.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
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456 Chapter 14
established desired tank level, the measured output is the IPR signal if the measured ICP is less than the
the actual tank level observed by the person, and the desired ICP. Conversely, the ECM will decrease the
means for the controller to change the system is a duty cycle of the IPR signal if the measured ICP is
combination of the person’s muscles and the valve. greater than the desired ICP.
Figure 14-23 shows a block diagram for a typical The block diagram shown in Figure 14-23 can be
closed loop control system. In a closed loop control applied to many other types of closed loop control
system, the difference between the desired output and systems in modern trucks. Other examples include
the measured output is referred to as the error. In cruise control, automatic HVAC cab temperature con-
other words: trol, and exhaust aftertreatment temperature control.
error ¼ desired output À measured output Open Loop Control. If the ECM detected some
problem with the ICP sensor, such as an out-of-range
The error can be positive or negative, depending upon low condition caused by a disconnected ICP sensor
the desired output being greater or less than the mea- connector, the ECM would not have any knowledge of
sured output. For example, if the measured level in the the ICP. Without the ICP sensor information, there can
tank in Figure 14-22 were above the desired level, the be no closed loop control of the injection control
error would be negative. The controller uses the am- pressure. In this case, the ECM could still attempt to
plitude and sign of the error input to determine what it drive the IPR with some set duty cycle sufficient to
needs to do with its controller output to cause the error still permit the engine to run. This is referred to as
to go to zero. An error of zero indicates that the desired open loop control. The ECM could be programmed to
output and the measured output are the same, which is drive the IPR at a varying duty cycle dependent upon
the goal of a closed loop control system. engine speed and load. The disconnected ICP sensor
would likely result in a DTC and an engine speed or
In the case of the injection control pressure closed torque derate, but the engine should still provide suf-
loop control system, the following specific definitions ficient power to permit the truck to limp-in to the next
apply: repair facility.
n System = Regulation of the injection control Open loop control can be described as the use of
pressure by the IPR lookup tables within the ECM software. The mileage
chart at the bottom of a roadmap is an example of a
n System Output = Injection control pressure lookup table. If you wanted to find the distance from
n Measurement = ICP sensor one city on a map to another, you could use the lookup
n Measured Output = Measured pressure as indi- table. Through extensive testing, the OEM populates
various lookup tables and programs these into the
cated by the ICP sensor ECM software. For example, at an engine speed of
n Desired Output = Desired ICP determined by 1200 rpm and at 50 percent load, driving the IPR at a
fixed duty cycle of 30 percent should provide suffi-
the ECM cient control of ICP.
n Error = Difference (+/–) between the desired
Open loop control is often used on other truck
and measured ICP systems besides instances where a failure has been
n Controller = ECM detected. For example, open loop control of a system is
n Controller Output = PWM duty cycle of the IPR common during transient (changing) engine load
control signal
The ECM attempts to make the error go to zero, which
will occur when the measured ICP is the same as the
desired ICP. The ECM will increase the duty cycle of
Desired Error Controller System System
Output + Output Output
– Controller
Measured Measurement © Cengage Learning 2014
Output
Figure 14-23 Closed loop control block diagram. When measured output and desired output are equal, error
is zero.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 457
Valve Electronic Oil
seat solenoid discharge port
area Oil
discharge Oil
port inlet
Poppet
valve
return
Oil spring
inlet Poppet
valve
Amplifier
piston
Amplifier
piston
return
spring
Fuel
inlet
Energized Injector De-Energized Injector
Atmospheric pressure Courtesy of Navistar, Inc.
Oil pressure
Fuel supply pressure
Fuel injection pressure
Figure 14-24 Navistar single coil HEUI injector internal components.
conditions and before the engine has reached operating the other to cause the spool to move one way or the
temperature. other.
HEUI Injectors. There have been two major versions The voltage supply is reduced to 48V DC for these
of HEUI injectors used by Navistar. Figure 14-24 second-generation injectors. Figure 14-26 shows the
shows a single-coil version of the injector. The ECM high side and low side drivers (FETs) inside the ECM,
(or IDM) supplies 115V DC to the solenoid to open a which are used to control the injector solenoids. The
port to permit high-pressure oil to act on an amplifier 12V supplied by the truck’s batteries is stepped up to
piston. This piston has a larger diameter on the ICP 48V or 115V by a DC-to-DC converter within the
engine lubrication oil end (top) than the fuel end ECM or IDM. DC-to-DC converters were introduced
(bottom). The piston downward movement causes the in Chapter 7.
fuel to be pressurized seven times greater than the ICP.
For example, if the ICP is 3000 psi (21 MPa), the fuel WARNING Follow the OEM’s specific safety
injection pressure will be 21,000 psi (145 MPa).
recommendations when trou-
Figure 14-25 shows the second-generation Navistar bleshooting any electronically controlled diesel fuel
HEUI injector produced by Siemens, which has two system to prevent fatal electric shock.
electrical coils. The two coils are used to control the
position of a spool valve. The spool valve shuttles Common Rail Fuel Systems
horizontally to permit high-pressure engine oil to act
on the intensifier piston in one direction and to dump If you are familiar with sequential port fuel injec-
this oil back to sump in the other direction. There is tion systems found on many current gasoline engines,
no return spring on the injector spool. The ECM al- then you already understand some of the fundamentals
ternately energizes one solenoid while de-energizing of a diesel common rail fuel system. In both systems,
each injector is supplied by a common fuel rail.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
458 Chapter 14
Injector spool A typical common rail fuel system is shown in
Figure 14-27. The ECM controls the high-pressure
pump solenoid(s) (Figure 14-28) and the electric sol-
enoids within each injector nozzle (Figure 14-29). A
fuel rail pressure sensor is an input to the ECM. Closed
loop control by the ECM, as described in the previous
section, is used to maintain the desired rail pressure.
The ECM programming makes use of all of the ECM
sensor inputs to determine the optimal injection timing
and fuel metering quantity.
WARNING Never crack common rail fuel
lines open with the engine run-
ning for any reason, including checking for a
misfiring cylinder. Doing so could cause fuel under
extreme pressure to penetrate your skin resulting in
death or serious injury. Follow OEM’s instructions for
rail pressure bleed down before loosening any
component in the high-pressure fuel system. Never
install a standard pressure gauge in a common rail
system. The extreme pressures will cause the gauge
to explode.
Oil pressure Courtesy of Navistar, Inc. Measurement Error in Closed Loop Control Sys.tems
High-pressure oil Because of the extreme fuel pressures in a common
Atmospheric pressure rail system, a pressure relief valve (PRV) is typically
located in the fuel rail. This mechanical relief valve
Fuel pressure opens to dump fuel back through the return if rail
Fuel supply pressure pressure exceeds a predetermined value. The me-
Less than 3,100 psi chanical relief valve should never open during normal
Above 3,100 psi operation, but problems such as an in-range failure
of the fuel rail pressure sensor can cause the ECM to
Figure 14-25 Navistar second-generation two-coil not be able to determine the actual fuel rail pressure
HEUI injector. correctly. An in-range failure describes a condition
where the voltage measured at the input of the con-
The injectors are electrically actuated in both systems at troller is not out-of-range high or out-of-range low
a specific time resulting in an injection event. However, (defined in Chapter 13) but is within the acceptable
the biggest difference between gasoline sequential port normal operating range for the sensor. An in-range
fuel injection and common rail diesel injection is the fuel failure is a voltage that is within the acceptable range,
pressure. In a gasoline port injection system, the fuel but it does not accurately represent the actual pres-
pressure is typically not higher than 100 psi (690 kPa) sure, temperature, or flow rate that an accurate gauge
while in a diesel common rail system, the pressures can or other measurement device would indicate. In other
exceed 35,000 psi (241 MPa). In addition, the solenoid words, an in-range failure is a measurement error.
actuator in a diesel injector does not directly lift the For example, excessive resistance on the terminals of
needle to start injection as it does in a gasoline port fuel the rail pressure sensor and the wiring harness ter-
injector. Details on the internal workings of an electro- minals caused by fretting corrosion can cause the rail
hydraulic injector are provided in most diesel fuel sys- pressure sensor to incorrectly indicate that the pres-
tem textbooks. sure within the rail is much lower than the actual rail
pressure. The ECM only ‘‘knows’’ the measured rail
pressure based on voltage supplied by the sensor at
the applicable ECM input terminal. If an electrical
problem causes this voltage to be incorrect but still
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 459
48V Injection Control Injector solenoid (open coil)
Injector solenoid (closed coil)
Microprocessor Injector high
control side driver
48V (open coil)
Injector low Courtesy of Navistar, Inc.
side driver
(open coil)
Injector high
side driver
(closed coil)
Injector low
side driver
(closed coil)
Figure 14-26 High and low side drivers in ECM control injector coils.
High-pressure Fuel rail Pressure relief valve
fuel sensor
2m
10m Reprinted Courtesy of Caterpillar Inc.
ULSD To CRS
system
Injectors
Figure 14-27 Caterpillar common rail fuel system.
within the normal operating range for the sensor, no failures can be some of the more difficult electrical
DTC will likely be set indicating a problem with that problems to resolve because a measurement error of
particular sensor circuit. However, DTCs indicating a temperature, pressure, or flow rate can cause a variety
potential problem with some other system may ac- of unexpected problems in any closed loop control
tually set due to the in-range failure. These in-range system.
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
460 Chapter 14
Pump solenoid #1 12 4
connector (from ECM)
CReprinted Courtesy of Caterpillar Inc.3
Pump solenoid #2 Courtesy of Robert Bosch LLC4
connector (from ECM)
5
Return to tank 6
7
Low-pressure inlet 8
(from 2m secondary
filter) 9
High-pressure outlet
(to rail)
Oil inlet
Low-pressure inlet
(from 10m primary filter)
Transfer pump
Low-pressure outlet
(to 2m filter & CRS
system)
Figure 14-28 Common rail high-pressure pump with
control solenoids.
A phrase borrowed from computer science, which 10
describes in-range failures, is ‘‘garbage in, garbage
out.’’ If fretting corrosion causes high resistance in the 11
rail pressure sensor circuit, the actual value of rail
pressure is unknown by the ECM. Therefore, the mea- a. Injector closed b. Injector opened
sured rail pressure may be much less or much greater (at-rest status) (injection)
than the actual value of rail pressure. The ECM could
control the high-pressure pump such that the actual rail 1. Fuel return 6. Bleed orifice
pressure increases to the point that the mechanical
pressure relief valve in the rail opens to prevent damage 2. Electrical connection 7. Feed orifice
to the fuel system. In this case, the incorrectly measured
rail pressure due to the in-range failure could be con- 3. Triggering element 8. Valve control chamber
sidered as garbage in and the ECM’s control of the
high-pressure pump could be considered as garbage out. (solenoid valve) 9. Valve control plunger
In many cases, observing the pressure, temperature, 4. Fuel inlet (high 10. Feed passage
or other parameter using an electronic service tool (as
described later in this chapter) with the key on, engine pressure) from the rail to the nozzle
off and determining if the value displayed is plausible
(believable) can be excellent clues indicating a possi- 5. Valve ball 11. Nozzle needle
ble in-range failure. For example, if the rail pressure is
indicated as 3000 psi (21 MPa) on an engine that has Figure 14-29 Solenoid-controlled common rail injec-
not been running for quite some time, you may suspect tor nozzle.
a rail pressure measurement error. In another example,
if engine coolant temperature indicates 2008F (938C) Some common rail fuel systems may utilize an
and manifold air temperature and all other temperature electrically actuated PRV in the fuel rail. The ECM
sensors on the engine indicate close to 708F (218C) on controls the PRV to cause rail pressure to rapidly de-
a cold engine, you may suspect a measurement error of crease when zero fuel is being commanded, such as
coolant temperature (provided no electric block heater when the truck is coasting down a hill.
is currently being used).
Piezo Injectors. The latest generation of common rail
Some OEMs may perform such plausibility checks injectors contain a piezo actuator instead of an electro-
at engine start up and while the engine is running to magnetic solenoid actuator. These injectors are often
cause a DTC to set indicating a possible sensor mea- called piezo injectors. Piezoelectric pressure sensors
surement error. were introduced in Chapter 11. Piezo injectors contain
a stack of crystal wafers as shown in Figure 14-30.
Recall form Chapter 11 that if a crystal is squeezed, it
will produce a proportional voltage. This process is also
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 461
De-Energized Energized EUI is stored in the ECM. The ECM decrypts this
calibration code and modifies the pulse width ac-
cordingly for each injector to reduce fuel-metering
errors caused by manufacturing tolerances. If injectors
or EUIs that have calibration codes are replaced, the
new calibration information must be written to the
ECM using the appropriate electronic service tool.
Piezo © Cengage Learning 2014 DIESEL EXHAUST EMISSIONS
actuator CONTROL
Figure 14-30 Piezo-actuated common rail injector. Looking back at Figure 14-2, the EPA mandated
reduction in diesel exhaust emissions has led to an
reversible. If a voltage is applied to a crystal, the crystal influx of technology into on-highway diesel engines.
will expand. Piezo injectors take advantage of this The advances in fuel delivery systems discussed in the
principle. Although the stack of crystal wafers may only previous section are responsible for a large percentage
expand by perhaps 0.004 in. (0.16 mm) when 100V is of the overall exhaust emissions reduction. The ability
applied by the ECM, this movement can be translated of modern fuel systems to meter a precise amount of
through an internal hydraulic system within the injector atomized fuel at just the right time permits engine
to cause the injector to actuate and inject. manufacturers to balance performance, fuel economy,
and exhaust emissions. However, the fuel system is
The advantage of piezo actuators over solenoid just one aspect of exhaust emissions reduction as will
actuators is the reduced response time. Recall in be discussed in this section. Exhaust emissions re-
Figure 14-11 the time that was necessary for the duction can be divided into two major areas: in-
current level through the solenoid to increase to a cylinder and aftertreatment.
value sufficient for the solenoid actuator to respond.
Since piezo injectors contain no inductor, there is no In-Cylinder Exhaust Emissions
associated current rise time permitting very fast actu- Reduction
ation and multiple injection events per cycle. One
diesel engine manufacturer indicates that up to seven In-cylinder exhaust emissions reduction refers to
separate injection events per combustion cycle can be reduction of emissions in the combustion chamber.
performed using piezo injectors. Piezo injectors also The two main regulated diesel engine pollutants are
require less electric power to operate than solenoid PM and NOx. It would be relatively easy to reduce one
actuated injectors. or the other of these pollutants within the combustion
chamber. However, almost anything that is done in-
Piezo injectors are currently used on many auto- cylinder that causes a reduction in soot (PM) results in
motive diesel engines and some smaller truck engines. an increase in NOx and vice versa. For example, ad-
However, piezo injectors will likely come into more vancing the injection timing increases peak combus-
widespread use in on-highway truck engines as the tion temperatures resulting in reduced soot, but causes
technology matures. higher NOx creation. Conversely, retarding injection
timing reduces peak combustion temperatures, which
Injector Replacement. Most EUIs or common rail reduces NOx creation but causes higher levels of soot
injectors have a calibration or trim code. This cali- to be generated. This dilemma is known as the soot-
bration code indicates specific flow characteristics for NOx tradeoff.
the component and compensates for manufacturing
tolerances. The calibration code for each injector or Exhaust Gas Recirculation (EGR). Exhaust gas re-
circulation (EGR), as the name implies, is recircula-
tion of exhaust gasses back into the combustion
chamber. The exhaust gas is somewhat inert and dis-
places combustion oxygen, resulting in a decrease in
peak combustion temperature and a resulting reduction
in NOx. Exhaust gas also contains water vapor, which
has a very high specific heat. Therefore, the water
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
462 Chapter 14
VGT-turbo Exhaust
EGR valve
EGR cooler
Air © Cengage Learning 2014
Check Valve
Charge air cooler
Figure 14-31 Typical cooled EGR system with VGT.
vapor in the recirculated exhaust gas acts as a heat sink Piston ring Piston ring seals Bushing
to further reduce peak combustion temperatures. The Cam gear
exhaust gas is taken from the exhaust manifold and Crank seal
directed through plumbing to the intake manifold, as Crankshaft Control valve
shown in Figure 14-31. An EGR valve, which is Unison ring
controlled by the ECM, is used to only permit EGR to
flow when specified by the ECM. The exhaust gas Turbine Reprinted Courtesy of Caterpillar Inc.
passes through an EGR cooler to reduce the gas tem- wheel
perature and increase the gas density.
Pin
The intake manifold pressure on a turbocharged
diesel engine may be nearly the same as the exhaust Vanes
manifold pressure. Therefore, it is necessary to cause
the exhaust manifold pressure to become greater than Figure 14-32 Electrohydraulic VGT actuator.
the intake manifold pressure for sufficient EGR to
flow. This can be accomplished using a variable ge- cycle of the PWM output supplied to the solenoid to
ometry turbocharger (VGT). The term variable tur- attain the desired VGT vane position.
bine geometry (VTG) is also used to describe the
technology. The operation of a VGT turbocharger is An electric VGT actuator is shown in Figure 14-33.
described in detail in most diesel engine textbooks. These actuators typically contain a stepper motor and
VGTs are also used to control the air-to-fuel ratio, es- the control circuitry for the stepper motor. The earliest
pecially at low engine speeds. In the case of using a versions of these actuators received the desired VGT
VGT for EGR control, driving the VGT vanes closed position from the ECM by way of an ECM provided
increases the exhaust manifold pressure (backpressure). PWM signal or with some other simple digital signal.
This also increases the intake manifold pressure, but This was one-way communication; the actuator only
the increase in the exhaust manifold pressure is more received a desired VGT position from the ECM but
than the increase in intake manifold pressure due to the could not communicate any information back to the
inherent inefficiencies of the system. ECM. The latest versions of VGT actuators are capa-
ble of communicating with the ECM via a J1939 data
The ECM controls the VGT vane position using an link. This permits the actuator to detect problems such
actuator, like that shown in Figure 14-32. This ex- as stuck vanes, a common problem on variable ge-
ample uses a control valve that contains an electric ometry turbochargers, and provide this information
solenoid, which regulates the flow of engine lubrica- back to the ECM. The ECM may then set a DTC
tion oil under pressure to control the VGT vane posi- indicating that the desired VGT position could not
tion. A VGT vane position sensor is an input to the
ECM. The ECM may use a PWM output to control the
electric solenoid. Therefore, this is a closed loop
control system. The ECM determines a desired VGT
position, the vane position sensor indicates the mea-
sured VGT position, and the ECM regulates the duty
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 463
© Cengage Learning 2014 some diesel exhaust emission estimations. The use of
virtual sensors throughout a truck electrical system
Figure 14-33 Electronic VGT smart actuator. will likely expand in the future as the processing
power of microprocessors continues to increase.
be attained. This type of actuator may be known as a
smart actuator. A smart actuator is an actuator that Smart actuators, such as a VGT actuator, typically
contains electronic circuitry such as a microprocessor perform a learn cycle at initialization (power-up). A
and a communications interface. A smart actuator is learn cycle can be described as a zero and span cali-
typically managed by another controller, such as the bration; the actuator is driven to the minimum position
engine ECM. A J1939-based smart actuator would (zero) and then driven to the maximum position. In the
typically only require four wires: +12V, ground, and case of a stepper motor controlled actuator, the num-
the two J1939 circuits. ber of steps necessary to travel from the minimum to
the maximum position is the span or operating range.
Most VGTs have a speed sensor. This may be a For actuators directly controlled by the ECM, the
variable reluctance or Hall effect type sensor. The ECM may perform an initial learn cycle of applicable
sensor measures the speed of the shaft connecting the actuators when the engine is new and store the ac-
turbine and compressor wheels. A flat section milled tuator’s position sensor minimum and maximum
on the shaft acts as the target for the turbocharger voltage information in non-volatile memory. The
speed sensor. The turbocharger speed is an input to the ECM then performs a learn cycle of the actuator at
ECM and is used to prevent the turbocharger from each initialization (or at engine shutdown for some
exceeding the maximum design speed. The ECM actuators) and compares these values to the values
monitors the turbocharger speed and will adjust the stored in memory. If the most recent learn cycle values
vane position or derate to reduce the turbocharger deviate by more than some allowable tolerance, the
speed to prevent damage to the turbocharger. ECM may set a DTC indicating an invalid learn cycle
of that component. This invalid learn cycle may be
The turbocharger speed, along with the intake air caused by a mechanical problem such as stuck vanes
density, can also be used by the ECM to estimate the on a VGT or by heavy carbon deposits on an EGR
intake manifold absolute pressure (MAP). Although valve that prevent the valve from fully closing. The
most 2004 and later diesel engines with EGR have a invalid learn cycle may also be due to an electrical
MAP sensor, the estimated manifold pressure can be problem, such as wiring harness failures like shorted
compared to the value indicated by the sensor. If the and open circuits.
ECM determines a large discrepancy between the es-
timated and measured values for intake manifold Performing a learn cycle on an actuator permits the
pressure, a DTC can be set indicating such. Possible ECM to compensate for manufacturing tolerances of
causes include large boost leaks or sensor measure- the actuator and to verify that the actuator is capable of
ment error caused by a wiring harness problem or an moving throughout its full range of travel. Replace-
in-range MAP sensor failure. The estimation of MAP ment of some engine electrical components that have
by the ECM using turbocharger speed and intake air stored initial learn cycle values may require the use of
density is known as a virtual sensor. A virtual sensor an electronic service tool to inform the ECM that the
is an estimated value obtained from mathematical component has been replaced so that the ECM can
models of the system. These mathematical models are perform a new initial learn cycle calibration of the
developed using physical sensor readings installed on component. Consult the specific OEM’s service liter-
engines during development to calculate the estimated ature for more information.
value for a virtual sensor. Virtual sensors are used for
An EGR valve is typically an electric motor oper-
ated device with an integral valve position sensor
which acts as an input to the ECM. The EGR valve is
typically a normally closed valve and may be a poppet
or a butterfly-type valve. The ECM controls the EGR
valve position by supplying current to the motor in the
valve. For the circuit shown in Figure 14-34, the ECM
is able to drive the EGR valve to the open or the closed
position by reversing the current flow through the
motor. This type of circuit is known as an H-bridge
because the layout looks like the letter ‘‘H’’. The
ECM switches on only high side driver A and low
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
464 Chapter 14
+12V +12V flowing out of the faucet (manifold air temperature), it
is not difficult to calculate the percentage of hot water
A and D making up the warm water flowing from the faucet.
On EGR flow rate is typically under closed loop con-
AB trol by the ECM. The ECM determines the desired
EGR flow rate based on its program instructions. The
M measured EGR flow rate is determined by the ECM
based on the applicable sensor input values. On en-
C B and C D © Cengage Learning 2014 gines so equipped, the ECM then controls the EGR
On valve position and VGT position to attain the desired
EGR flow rate for the current operating conditions.
Figure 14-34 H-bridge used to control EGR valve.
The percentage of EGR compared to the percentage
side driver D as shown in Figure 14-34 to cause of air in the combustion chamber is an important
conventional current to flow through the motor from measurement for a modern diesel engine. Too much
left to right to cause the motor to turn clockwise, EGR results in reduced air-to-fuel ratio, which causes
which opens the EGR valve. To reverse the direction poor performance, black exhaust smoke (soot), and
of the motor and close the EGR valve, the ECM high exhaust manifold temperatures. Conversely,
switches on only high side driver B and low side driver too little EGR causes the engine to produce excessive
C. This same H bridge type control may be applied to NOx, resulting in non-compliance with exhaust
other devices, such as an intake air throttle. emissions standards. An in-range failure caused by a
defective sensor or a wiring harness problem can
On many diesel engines, the ECM controls the cause the ECM to incorrectly calculate the percentage
amount of EGR flowing into the intake manifold by of EGR.
opening the EGR valve to a specific position and
regulating the VGT position to increase or decrease the Diesel Exhaust Aftertreatment
exhaust manifold pressure. Some engines have an ex-
haust manifold pressure sensor, which is an input to Since it is not possible to sufficiently reduce
the ECM. This sensor along with the intake MAP both soot and NOx with in-cylinder techniques alone,
sensor can be used by the ECM to determine EGR the 2007 EPA emissions standards resulted in the
flow rate. Several 2007 and later diesel engines make addition of exhaust aftertreatment devices to most
use of an EGR flow rate sensor. The EGR flow sensor on-highway diesel engines. As the name implies, af-
measures the differential pressure (delta pressure) tertreatment is modification to the exhaust gasses
across a venturi in the EGR plumbing. The ECM then outside of the combustion chamber.
calculates the EGR flow rate based on this differential
pressure. This is similar to the calculation of electric 2007 EPA Emissions. For the 2007 EPA require-
current flow by measuring the voltage drop across a ments, most North American OEMs chose to control
known resistance. Some engines may use three tem- NOx in-cylinder and handle the PM (mostly carbon-
perature sensors to determine EGR flow rate. The based soot) reduction using aftertreatment. A diesel
temperature sensors measure the charge air cooler particulate filter (DPF) is an aftertreatment device used
outlet air temperature (temperature of the air that is to trap the soot particles in a porous ceramic filter
entering the intake manifold), the post EGR cooler material. The soot in the DPF is periodically removed
exhaust gas temperature, and the manifold air tem- through a process referred to as regeneration. In a DPF
perature. The ECM can calculate EGR flow rate using regeneration, high temperatures of up to 11658F
these three temperatures. This is analogous to a water (6308C) are used to cause the soot to oxidize. This
faucet with separate controls for the hot and cold water oxidation process is similar to what happens when
that flow out of one faucet. If you know the temper- barbequing with charcoal briquettes. Fire is initially
ature of the hot water (exhaust gas temperature) and used to heat the charcoal briquettes. Once the fire
the cold water (charge air cooler outlet temperature) burns out, the briquettes continue to glow orange for a
and the temperature of the resulting warm water prolonged period of time as the charcoal (carbon ma-
terial similar to soot) combines with oxygen in the air
(oxidizes) to form CO2 gas and heat. Eventually, all of
the carbon is oxidized and nothing remains of the
charcoal briquettes except for a small amount of ash.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 465
There are two primary methods of creating the heat exhaust upstream of the DOC, the DOC temperature
in the diesel exhaust system necessary to cause DPF must be greater than approximately 5758F (3008C) to
regeneration. Most North American OEMs use a diesel make sure that most of the fuel will be converted into
oxidation catalyst (DOC) upstream of the DPF to heat in the DOC. This is known as the DOC light-off
generate heat. A DOC is similar to a catalytic con- temperature. If the engine is sufficiently loaded, the
verter found in automobiles. A catalyst is a substance DOC temperature may already be above the light-off
which increases the rate of a chemical reaction. The temperature. Otherwise, many 2007 and later diesel
catalyst material in a DOC is typically a platinum engines have an intake air throttle at the intake man-
metal. The DOC converts hydrocarbons (HC) and ifold inlet. The ECM has control over this normally
exhaust oxygen (O) into CO2, H2O, and heat energy. open butterfly-type throttle valve. Reducing the air-to-
Note that there is no flame or ignition involved. Since fuel ratio of a diesel engine by supplying less air to the
diesel fuel is a hydrocarbon compound, a system of engine results in an increase in exhaust temperatures.
injecting diesel fuel into the exhaust stream is used to Some engines may use an exhaust throttle instead of an
create the heat necessary to regenerate the DPF. This intake air throttle for the same purpose.
hydrocarbon injection system is controlled by the
ECM or by a separate aftertreatment control module in Once the DOC light-off temperature is reached, the
some systems. Temperature sensors at the DOC inlet, ECM can start the injection of diesel fuel into the ex-
the DOC outlet (or DPF inlet), and the DPF outlet are haust. This is referred to as fuel dosing. Many 2007 and
typically used as inputs to the ECM. These tempera- later engines utilize electric solenoids, which are con-
ture sensors are thermocouples, thermistors, or RTDs trolled by the ECM to meter diesel fuel under moderate
(PRTs), as described in Chapter 11. Thermocouple pressure, typically less than 250 psi (1.7 MPa), through
type sensors are typically hardwired to a remote a dosing injector into the exhaust upstream of the DOC.
aftertreatment temperature module instead of being Here is another closed loop control system—the desired
wired directly to the ECM. This module communicates DOC outlet temperature and the measured DOC outlet
temperature information to the ECM using a CAN temperature.
network or some other digital network system such as
a local interconnect network (LIN). A typical DOC/ A fuel dosing system supplied by Bosch called the
DPF system is shown in Figure 14-35. Departronic1 system is used by many OEMs. This
system has the fuel dosing control components all
The ECM monitors the soot loading of the DPF contained in a single block, as shown in Figure 14-36.
to determine when DPF regeneration is necessary. A This assembly contains an inlet and outlet pressure
differential (delta) pressure sensor across the DPF is sensor, a fuel temperature sensor, and an inlet and
typically an input to the ECM to assist in this calcu- outlet control solenoid. The pressure sensors can be
lation of DPF soot loading. As the soot loading in- utilized for fuel dosing system diagnostics permitting
creases, the differential pressure increases. However, the ECM to set a DTC if a problem is detected.
most ECMs also calculate the soot in the DPF based on The dosing injector used with this system is a
fuel consumption and many other factors. When the
calculated soot level increases above a threshold, the
ECM will initiate the DPF regeneration. One funda-
mental of chemistry is that the rate of a chemical
reaction increases as the temperature increases.
Therefore, prior to diesel fuel being injected into the
© Cengage Learning 2014
© Cengage Learning 2014
Figure 14-35 DOC/DPF system. Figure 14-36 Bosch Departronic fuel dosing system.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
466 Chapter 14
hydromechanical injector, which opens and closes up ignite the diesel fuel to produce a flame in a burner
to 1000 times per second to atomize the fuel. Other unit within the exhaust upstream of the DPF. Com-
systems may use an electric solenoid-actuated dosing pressed air is also introduced into the exhaust to aid
injector, which is controlled by the ECM. combustion. The spark plug and ignition coil are
similar to those found in gasoline engines. An igni-
The ECM will steadily increase the DOC outlet tion coil is a type of transformer, as discussed in
temperature to approximately 11008F (6008C) using Chapter 3.
closed loop controlled metering of the dosing fuel. At
this temperature, the soot in the DPF is typically oxi- The preceding described active DPF regeneration.
dized within 20 minutes without flame, similar to Another form of DPF regeneration is passive regen-
glowing barbeque charcoal briquettes. eration. Passive regeneration is described as natural
regeneration. Soot in the DPF will oxidize at a slow
Some OEMs utilize in-cylinder dosing as the source rate at temperatures as low as 5008F (2608C) in an
of exhaust hydrocarbons instead of using a separate environment containing moderate levels of nitrogen
dosing injector in the exhaust. In-cylinder dosing refers dioxide (NO2). One additional function of the DOC is
to a late charge of fuel injected into the combustion to convert the nitric oxide (NO) that makes up the
chamber after combustion is complete. This charge of exhaust NOx into nitrogen dioxide to promote passive
unburned fuel is pushed out by the piston during the regeneration, thus reducing the need for active DPF
exhaust stroke and is oxidized in the DOC. regeneration. Ideally, an engine that is operated under
load will naturally produce sufficient exhaust tem-
Caterpillar used a different approach for 2007– peratures in the DPF to permit all of the soot that is
2009 engines compared to most other North Ameri- being created by the engine to be passively oxidized.
can OEMs called the Caterpillar Regeneration System Additional information on passive DPF regeneration
(CRS) as shown in Figure 14-37. Instead of using a can be found in the Internet links at the end of this
DOC to generate heat necessary for DPF regenera- chapter.
tion, CRS uses a spark plug near the fuel injector,
shown as the central component in Figure 14-38, to
Single electrical DPF sensor box
connection 280-1616/17/18
PWM VMAF Flame detect DPF DPF DPF
driver delta P temp intake delta P outlet
temp temp
IVA/Cat brake —early Turbo out Air tubing
exhaust opening (exhaust) temp 12" out DPF Outlet exhaust
Compressor out temp flame
Combustion 1.25" containment
Pilot/main fuel air valve
pressure sensor (2)
Pilot/main fuel press ctrl Purge air VMAF
valve (2) w/ 1 PWM driver on/off
Fuel injector CRS Engine exhaust .
Swirl plate
3 way fuel enable Fuel Ignition Valve block Spark plug
Fuel pump coil
Spark plug wire (M18 electrode CGI Reprinted Courtesy of Caterpillar Inc.
only)
Cat
engine
Dual stacks Dual stacks require
600/625 bHp dual DPFs
ratings
Figure 14-37 Caterpillar CRS system. Compressed air is used to purge the injector and to aid in combustion.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Diesel Engine Electronics 467
Flame Spark plug
detect sensor
A1 Purge air
F2 Pilot fuel
Main fuel
F4
C3 Coolant out
C5
Coolant in © Cengage Learning 2014
Figure 14-38 Caterpillar CRS injector and spark plug details. Engine coolant is used to cool the injector.
2010 EPA Emissions. The 2010 EPA emissions reg- by the system. However, the nitrous oxide (N2O) and
ulations required a further reduction in NOx emissions. nitric oxide (NO) are regulated exhaust emissions so
To meet this requirement, most North American this is not a desirable condition.
on-road diesel engine manufacturers opted to use
selective catalytic reduction (SCR) aftertreatment Most 2010 systems still have a DOC and DPF for
systems. As of 2013, all North American truck man- PM emissions. However, most 2010 and later diesel
ufacturers will use SCR. The term selective means that engines have substantially less soot emissions because
only the oxygen in the exhaust bonded with nitrogen is of the soot-NOx tradeoff discussed earlier in this
targeted. SCR uses ammonia (NH3) passing through a chapter. SCR has permitted OEMs to mostly control
catalyst in the exhaust system to convert most of the soot in-cylinder and control NOx in the aftertreatment
NOx into harmless nitrogen (N) and water (H2O). The system. Model year 2010 and later engines using SCR
ammonia is created by the injection of a urea-water are said to rarely require DPF regeneration and
compound into the exhaust called diesel exhaust fluid achieve improved fuel economy compared to 2007
(DEF) in North America and AdBlue1 in other parts engines.
of the world. DEF may also be referred to as a re-
ductant, which means an NOx reducing agent. A typ- The DEF that is injected into the exhaust dis-
ical SCR system diagram is shown in Figure 14-39. sociates or breaks down into ammonia in the hot ex-
Note that there are three components shown within the haust stream upstream of the SCR catalyst. A mixer
catalyst assembly. The SCR catalyst and hydrolysis swirl plate is typically placed in the exhaust down-
catalyst are utilized for the NOx and DEF conversion stream of the DEF dosing injector to assist in breaking
processes. The oxidation catalyst located at the exit of down the DEF into ammonia. Temperature sensors at
the catalyst assembly converts any excess ammonia the SCR catalyst inlet and outlet act as inputs to the
that remains or slips through the SCR catalysts into ECM to make sure the temperature is sufficient for
nitrogen (N), nitrous oxide (N2O), and nitric oxide decomposition of the DEF into ammonia. The SCR
(NO). This prevents ammonia from being exhausted temperature sensors may be thermocouples, thermis-
tors, or RTDs. Two NOx sensors are also typically
used in an SCR system. A NOx sensor in the exhaust
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468 Preoxidation catalyst Chapter 14
Engine Mixer
ECM Exhaust gas
Oxidation catalyst
Hydrolysis catalyst
SCR catalyst
Urea pump © Cengage Learning 2014
Urea tank
Figure 14-39 SCR system components.
upstream of the SCR catalyst inlet and another NOx NOx sensors, see the Internet links at the end of this © Cengage Learning 2014
sensor at the SCR catalyst outlet are inputs to the chapter.
ECM. The ECM or a separate aftertreatment control
module has control of the DEF dosing system. The To meter the DEF, many OEMs use the Bosch
inlet NOx sensor is typically used by the ECM to de- Denoxtronic1 DEF injection system shown in
termine the quantity of DEF to be dosed. The outlet Figure 14-40. The DEF injection module for this
NOx sensor may be utilized for diagnostics, such as the system contains an electric motor driven DEF pump,
detection of poor quality or diluted DEF. Alterna- electric heating element, temperature sensor, and a re-
tively, some OEMs may use a virtual sensor for the versing valve. Because DEF is mostly purified water, the
inlet NOx sensor, meaning that there is no physical freezing temperature of DEF is about 128F (À118C).
inlet NOx sensor and that the NOx present at the SCR Therefore, it is necessary to evacuate DEF from the lines
catalyst inlet is estimated by the ECM using mathe- and the pump to prevent expansion damage caused by
matical models. frozen DEF. The reversing valve in the DEF injection
module is controlled by the ECM. At engine shutdown,
NOx sensors are typically smart sensors. A smart the reversing valve is actuated causing DEF to be
sensor is a sensor that contains signal processing and a evacuated from the system and returned to the DEF tank.
communication interface. The communication inter-
face is often J1939, permitting the smart sensor to Figure 14-40 Bosch Denoxtronic system.
communicate directly with the ECM over a J1939 data
link. Thermocouple type aftertreatment temperature
sensors are also typically smart sensors. The output of
a smart sensor is a message indicating NOx informa-
tion, aftertreatment temperature, DEF quality, or other
parameter. Some OEMs may have a proprietary (pri-
vate) J1939 data link used for smart sensors and other
engine-based components, such as a VGT actuator,
instead of connecting these components to the vehicle
J1939 data link. Other networks such as LIN may also
be used for smart sensors to communicate with the
ECM. A J1939-based smart sensor typically requires
four wires: 12V power, ground, and the J1939 circuits.
NOx sensors operate on principles similar to
wideband oxygen sensors. For more information on
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Diesel Engine Electronics 469
Electrically heated DEF supply and injection lines© Cengage Learning 2014 Ammonia sensors will also be used in SCR systems
to thaw a frozen DEF system are common and most in the near future. Ammonia sensors are similar to NOx
DEF tanks are heated by an engine coolant heater sensors. The ammonia sensor is located within the
(Figure 14-41). An electric control valve in the tank SCR catalyst and is used by the ECM for closed loop
header is controlled by the ECM. A temperature sensor control of the DEF injection quantity. The ammonia
in the DEF tank is an ECM input. The ECM only sensor will also reduce the possibility of excess am-
permits coolant to flow through the DEF heater if the monia being generated and passing through the SCR
tank temperature sensor indicates the DEF might be catalyst. Excess ammonia is falsely detected as NOx by
frozen. DEF is not damaged if it is frozen and it can the outlet NOx sensor.
typically be thawed by the system within a few mi-
nutes of operation. However, DEF rapidly deteriorates Soot sensors are also likely in the future. A cracked
if its temperature exceeds 1408F (608C) so it is im- or melted DPF can cause excessive PM emissions. To
portant that the DEF not be overheated. detect this condition, a soot sensor will be placed in the
exhaust downstream of the DPF outlet. A soot sensor
Typical problems with SCR systems include poor contains two closely spaced electrical conductors. As
quality DEF caused by dilution with water. The water soot (carbon) particles accumulate in the sensor, the
used in DEF is purified and deionized. The use of tap electrically conductive carbon causes a change in the
water to dilute DEF can cause the SCR catalyst to be resistance between the electrical conductors. This re-
permanently contaminated by the minerals in the tap sistance indicates the amount of soot in the exhaust. To
water. DEF dilution is a form of emissions tampering. remove the accumulated soot from the sensor, an
electric heater in the sensor is switched on periodically
Sulfur contamination is another SCR system to burn off the soot particles.
problem. The use of ultra-low sulfur diesel fuel is
critical for aftertreatment devices. The sulfur in the HD On-Board Diagnostics
fuel contaminates both the DOC and the SCR catalyst
rendering them ineffective. In some cases, the sulfur Heavy-duty on-board diagnostics (HD-OBD)
can be removed with heat by performing a DPF re- describes the ability for a diesel engine to monitor if its
generation. The heat during the regeneration may also exhaust emissions exceed EPA thresholds and then to
dissolve DEF deposits in the SCR mixer, another alert the vehicle operator by means of a malfunction
common problem with SCR systems. indicator lamp (MIL). A DTC consisting of the SPN
and FMI must also be stored in the ECM memory
DEF quality sensors are used on some trucks out- indicating the detected malfunction. The MIL graphic
side of North America and their use will likely become is defined by the EPA as an amber-colored ISO engine
mandated in the United States by 2014 to reduce the symbol. You are likely familiar with the term OBD II,
likelihood of intentional DEF dilution. These sensors which refers to passenger car exhaust emissions. The
determine if the DEF has been diluted with water or term OBD has been utilized in the past by some OEMs
other contaminates by measuring the viscosity, spe- to define non-emissions related system self-diagnostics
cific gravity, or conductivity of the DEF. Information such as a body controller setting a DTC for headlamp
on DEF quality sensors can be found in the Internet current being too low. Since HD-OBD requirements
links at the end of this chapter. for on-road diesel engines started coming into effect in
2010, most OEMs now reserve the term OBD for EPA
Figure 14-41 DEF tank header with engine coolant mandated exhaust emissions on board diagnostics. By
heater. 2014, all EPA on-highway diesel engines will be
subject to some form of HD-OBD regulations.
HD-OBD may also include cylinder misfire de-
tection because a misfire can cause large amounts of
unburned fuel (hydrocarbons) to be present in the
exhaust. Currently, this detection is limited to lower
engine speeds only, but will likely expand to all speeds
and loads in the future. The hydrocarbons that are
present in the exhaust due to a misfire can cause
damage to the DOC and DPF. The hydrocarbons due
to a misfire are oxidized in the DOC and generate heat,
as discussed earlier in this chapter. Hydrocarbons (HC)
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470 Chapter 14
are also a regulated exhaust emission so any excess The readiness status indicator is also useful for
hydrocarbons that pass through or slip through the technicians. After performing an emissions related
DOC and DPF cause the engine to be non-complaint. repair, confirmed DTCs can be cleared using an
Cylinder misfire is typically detected by changes in the electronic service tool. However, since two drive cy-
crankshaft speed as indicated by the crankshaft posi- cles are required to cause the MIL lamp to illuminate,
tion sensor. just clearing the confirmed DTCs, starting the engine,
and checking for an illuminated MIL lamp is typically
In addition to exhaust emissions, HD-OBD also not sufficient to verify the repair has fixed the prob-
addresses engine crankcase emissions (blow-by). lem. The readiness indicator and pending DTCs can be
Crankcase filters and closed crankcase systems are used to validate the repair. A road test of 20 minutes or
used to control crankcase emissions. Cooling system more may be necessary to cause the readiness indicator
thermostat performance is also monitored in HD-OBD to indicate ‘‘ready.’’ If a pending DTC is indicated, the
systems. repair may have not fixed the problem even though the
MIL lamp is not yet illuminated.
HD-OBD DTC Types. There are several types of HD-
OBD DTCs. When the ECM first detects most types HD-OBD also requires the ECM to store a snap
of emissions related malfunctions, a pending DTC is shot of specific engine operating conditions in non-
stored in the ECM memory, but this will not illumi- volatile memory when the MIL lamp has been illu-
nate the MIL lamp. If the same malfunction is not minated. This information, known as a freeze frame
detected during a second EPA defined drive cycle, data, can be retrieved by an electronic service tool with
the ECM erases the pending DTC. However, if the the intent of assisting a technician in the diagnosis of
same malfunction is detected on a second consecutive the problem. Freeze frame data includes engine
drive cycle, the MIL lamp must be illuminated and parameters that were recorded when the failure was
the pending DTC will become a confirmed DTC, detected such as engine speed, load, and coolant
which is also referred to as a MIL-on DTC. A con- temperature among others.
firmed DTC also results in the ECM storing a per-
manent DTC in non-volatile memory. A permanent Additional HD-OBD Provisions. Unlike the two
DTC cannot be cleared with an electronic service tool consecutive trip MIL illumination process described
or by disconnecting the vehicle batteries. The MIL earlier, some failures of the SCR system may result in
lamp will remain illuminated until the problem is no the ECM imposing severe derate penalties and illu-
longer detected by the ECM for three consecutive minating the MIL upon the first detection of the fail-
drive cycles, at which time the confirmed DTC and ure. This includes an empty DEF tank and
permanent DTC will be erased by the ECM and be- disconnected SCR system electrical connectors. The
come a previous MIL-on DTC. Previous MIL-on derate penalties are necessary because an empty DEF
DTCs are erased by the ECM after 40 engine warm- tank or many other types of emissions system failures
up cycles, provided the same problem has not been may not otherwise result in any operator detectable
detected again. engine performance issues.
Although some locales have existing truck emis- HD-OBD also has provisions for access to OEM’s
sions inspection and maintenance (I/M) programs such service information and diagnostic tools including
as smoke opacity tests, as of 2012 emissions in- electronic service tools. This permits non-OEM inde-
spections for on-road trucks are not required in most of pendent repair facilities to purchase the OEM’s service
the United States. However, these I/M inspections will information and tools necessary to diagnose and per-
likely become mandated in the future. The inspection form repairs of the HD-OBD system. Much of HD-
on HD-OBD vehicles would likely consist of verifying OBD as it pertains to service information is still under
with an electronic service tool that the MIL lamp is not discussion as of 2012.
being commanded on by the ECM and that no pending,
confirmed, or permanent DTCs are stored. Prior to an DIESEL ENGINE DIAGNOSIS
emissions inspection, the engine must have been op-
erated long enough and under the required conditions As complicated as a modern diesel engine may
for the ECM to have performed all internal emissions appear to be, checking the fundamentals such as fuel
systems tests. This is referred to as readiness status or and air filters, boost leaks, and fuel quality are still
I/M readiness. The OBD readiness status indictor in essential for proper engine performance. Battery state
the ECM must indicate ‘‘ready’’ before an emissions of charge and charging system voltage are other basic
test can be performed.
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Diesel Engine Electronics 471
items that cannot be overlooked. Once the funda- Pro-Link 9000
mentals are ruled out, more advanced diagnostic
techniques and tools may be necessary to find the Data readout window 15-pin vehicle cable
cause of the problem.
Soft touch keypad and power cable
Electronic Service Tools
Data and power cable connector
Electronic service tools (ESTs) refer to devices that
read information from the various electronic modules RS232 serial data port Power cable
connected to the vehicle data link. Early ESTs were
often handheld display devices known as scan tools, such Pushbutton
as the popular Pro-Link 9000 shown in Figure 14-42.
This tool is still widely used today to diagnose legacy Data
electronic diesel engines as well as some vehicle sys- cable
tems such as ABS.
Data Not needed for SERIAL LINK
Most OEMs now use a PC-based EST, as shown in cartridge Mack Truck JUMPER
Figure 14-43. These tools can display ECM parame- applications Mack Truck
ters, such as the measured intake manifold air tem- use only!
perature or the measured intake manifold pressure. Vehicle 404000 Courtesy of NEXIQ Technologies
This can be very useful in diagnosing in-range mea- adapter
surement errors, which may not be causing a DTC
to be set. For example, an engine that has not been Figure 14-42 Pro-Link 9000 scan tool.
operated for several hours should indicate similar
temperatures for all temperature parameters such as A variety of tests can be performed with most
coolant temperature, manifold air temperature, or other ESTs, such as a cylinder cutout test. This test causes
similar parameter with ignition on and engine off. A fueling to each cylinder to be disabled resulting in that
substantial difference in one reading may indicate a cylinder not firing. When a cylinder that is contribut-
measurement error due to a wiring harness problem or ing is disabled, a change in the way the engine sounds
a defective sensor. will be evident along with increased vibration.
© Cengage Learning 2014
Figure 14-43 PC-based electronic service tool.
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472 Chapter 14
However, disabling a cylinder that is misfiring due to Therefore, Figure 14-44 indicates a problem with the
an injector problem or some mechanical issue will number 2 cylinder.
not cause a noticeable change in the engine sound or
vibration. Engine parameters such as injection pulse Most PC-based ESTs can command an active DPF
width may also be displayed on the EST during the parked regeneration on applicable engines, which is
cutout test. The example shown in Figure 14-44 in- useful for diagnosing DPF regeneration problems. The
dicates that when the number 2 cylinder was cut out, graphical display of a DPF regeneration shown in
the injection pulse width for the other five cylinders Figure 14-45 is an example of the type of information
did not increase as would be expected. If a contributing that can be displayed by a PC-based EST.
cylinder is cut out, the load on the engine increases and
the ECM responds by supplying more fuel to all of the Oscilloscopes
cylinders to compensate. If a dead or minimal con-
tributing cylinder is cut out, the load on the engine Portable hand-held oscilloscopes have become an
does not change so there is minimal change in the essential tool for truck technicians. Oscilloscopes
quantity of fuel that is supplied to the other cylinders. permit a rapidly changing electrical signal to be
evaluated. Modern oscilloscopes are sometimes
Figure 14-44 Injector cutout test results indicate a referred to as digital storage oscilloscopes (DSO)
problem with the #2 cylinder. because these are digital devices with the capability
of storing waveforms in memory for later reference.
Oscilloscopes display voltage amplitude on the ver-
tical axis and time on the horizontal axis. Current can
also be displayed using a clamp-on ammeter. The
volts per amp setting of the clamp-on ammeter can be
entered into the oscilloscope settings so that properly
scaled current is displayed on the oscilloscope
screen.
Multiple-channel (multiple input) oscilloscopes per-
mit two or more signals to be evaluated relative to each
other at the same time as shown in Figure 14-46. For
example, the engine crankshaft position sensor and
camshaft position sensor signals could both be displayed
on an oscilloscope at the same time to detect problems
such as a slipped or loose target. When combined with a
clamp-on ammeter, voltage and current can both be
displayed at the same time, such as injector supply
Courtesy of Detroit Diesel Corporation
Courtesy of Detroit Diesel Corporation
Figure 14-45 DPF parked regeneration parameters monitored with electronic service tool.
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Diesel Engine Electronics 473
Freeze Control 05/27/2011 01:59:34 AM
Example <
Waveform
Print Run 1
Save Recall
2
Time/Div T Ch 3: OFF © Cengage Learning 2014
20 mSecs Ch 1: 5.00 V DC Ch 4: OFF
Ch 2: 5.00 V DC Level: 0.25V
T Source: Ch 1
Nrml
Rising Edge
Figure 14-46 Two-channel oscilloscope displays two different signals.
4.00
3.50
3.00
2.50
2.00
1.50
1.00 Y Scale = 500 mV/Div © Cengage Learning 2014
0.50 X Scale = 20 μs/Div
0.00 20 40 60 80 100 120 140 160 180 200
0
Figure 14-47 Typical J1939 voltage levels using two-channel oscilloscope referenced to ground.
voltage and injector current draw. Comparing the J1939 data link. Intermittent open or shorted circuits
waveforms from a properly running engine with those cause a change in the signal pattern, as does elec-
observed on an engine that is exhibiting a problem can trical noise. The oscilloscope can be monitored for
be very useful information. change while wiggling the wiring harness containing
the data link circuits and while switching on and off
Another use of an oscilloscope is to diagnose potential electrical noise sources. Figure 14-47
problems on a communication network, such as the
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
474 Chapter 14
4.00
3.00
2.00
1.00 © Cengage Learning 2014
Y Scale = 1 V/Div
0.00 X Scale = 20 μs/Div
–1.00 20 40 60 80 100 120 140 160 180 200
0
Figure 14-48 Intermittent open J1939 circuit causing communication problems.
illustrates the typical voltage levels observed with a © Cengage Learning 2014
two-channel oscilloscope monitoring J1939 data link
activity with no problems present. One channel is
connected between CAN+ and ground and the other
channel is connected between CAN– and ground. In
Figure 14-48, an intermittent open circuit has been
captured.
Hand-held battery-powered oscilloscopes are rea-
sonably priced, but another option is a PC-based
oscilloscope, such as the PicoScope1 shown in
Figure 14-49. This oscilloscope uses the PC as the
display screen via a USB connection. Waveforms can
be stored on the PC and viewed later.
Figure 14-49 PicoScope PC-based oscilloscope kit.
Summary
n Vehicles with diesel engines sold in the United n Self-inductance prevents the current flow through
States are subject to EPA exhaust emissions regu- an inductor from changing instantly.
lations. These regulations have resulted in substantial
decrease of particulate matter (PM) and oxides of n Hydraulically actuated electronic unit injectors
nitrogen (NOx) emissions. To attain these require- amplify engine lubrication oil under pressure to
ments, electronic engine controls were necessary. generate fuel injection pressures.
n Electronic unit injector (EUI) systems with single n A closed loop control system compares a desired
actuators control the spill valve opening and clos- output to the measured output with the difference
ing. Dual-actuator EUIs control both the spill valve being referred to as the error. A controller drives
and the nozzle opening. the output such that the error becomes zero, indi-
cating the desired output and the measured output
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
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Diesel Engine Electronics 475
are the same. Closed loop control systems are used n Soot is captured in the diesel particulate filter
in a variety of truck systems. (DPF). A periodic regeneration of the filter to oxi-
dize the soot is sometimes necessary. Heat for the
n An in-range failure is a condition where the input regeneration is produced either by diesel fuel being
voltage at an electronic control module is within the injected over a diesel oxidation catalyst (DOC) or
normal operating voltage range, but does not cor- by igniting the fuel in a burner in the exhaust.
rectly represent what is being measured.
n Selective catalytic reduction (SCR) uses ammonia to
n Exhaust emissions can be controlled by a combina- reduce NOx. The ammonia is produced when a urea
tion of in-cylinder techniques and by exhaust after- water solution called diesel exhaust fluid (DEF) is
treatment systems. injected into the exhaust stream.
n A variable geometry turbocharger (VGT) can be used n HD-OBD describes the ability of a diesel engine to
to regulate EGR flow. determine that its exhaust emissions have exceeded
a threshold and to illuminate a malfunction indicator
n An H-bridge is an electronic circuit that causes the lamp (MIL) to alert the operator.
polarity of two wires to reverse to permit directional
control of an electric motor.
Suggested Internet Searches
Try the following web sites for more information:
http://cumminsemissionsolution.com
http://www.bosch.com
http://factsaboutscr.com
http://www.conti-online.com
http://www.epa.gov
http://www.picotech.com
Review Questions
1. Technician A says that cam-actuated unit injectors use a common high-pressure pump to develop injection
pressures. Technician B says that a single-actuator EUI typically has four electrical terminals. Who is
correct?
A. A only C. Both A and B
B. B only D. Neither A nor B
2. The ICP of an HEUI fuel system is controlled by which device?
A. HEUI regulator C. Camshaft control regulator
B. Open loop control valve D. IPR
3. Which of these is a true statement regarding a closed loop control system?
A. The desired output and the C. If the desired output and the measured output are the same
measured output are never the value, the error is zero.
same value.
D. The desired output is always greater than the measured
B. When the error is zero, the desired output.
output and the measured output
must both also be zero.
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476 Chapter 14
4. Technician A says that the current flow through an inductor can instantly change. Technician B says that an
in-range failure always causes a DTC to be set. Who is correct?
A. A only C. Both A and B
B. B only D. Neither A nor B
5. A high-pressure common rail injector is being replaced. Which of the following may be necessary?
A. Switch the ignition on with engine C. Adjust injector preload and rack timing.
off for 5 minutes to permit the
ECM to perform a learn cycle of D. No specific action is ever required when replacing any
the new injector. electronic injector.
B. Use an EST to enter the specific
calibration data for the new
injector.
6. An active DPF regeneration is occurring on an EPA 2007 engine equipped truck that has a DOC. Which of
the following is likely not present in this system:
A. DPF C. DOC inlet temperature sensor
B. Spark plug and ignition coil D. DPF differential (delta) pressure sensor
7. Which of these is most likely to be a smart sensor?
A. Coolant temperature sensor with C. Virtual exhaust manifold temperature sensor
two electrical terminals D. NOx sensor with four electrical terminals
B. Manifold temperature sensor with
two electrical terminals
8. HD-OBD includes which of the following?
A. Permanent DTC C. Confirmed DTC
B. Pending DTC D. All of the above
9. Which of the following would be the most likely device to be controlled by an H-bridge?
A. Smart sensor C. DEF injector
B. HEUI injector D. EGR valve
10. Technician A says that a rail pressure sensor wiring problem can cause the pressure relief valve in a high-
pressure common rail system to open. Technician B says that DEF that has been diluted with water may
result in a DTC. Who is correct?
A. A only C. Both A and B
B. B only D. Neither A nor B
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
CHAPTER
15 Modern Truck
Electrical System
Learning Objectives
After studying this chapter, you should be able to:
n Explain the basic functionality of an electronically controlled automatic transmission.
n Discuss the functionality of an automated manual transmission.
n Define the terms PRNDL, NSBU, VIM, chuff test, differential braking, and ABS modulator.
n Explain how an air ABS system and traction control operates.
n Test an ABS wheel-speed sensor circuit.
n Describe how a fault detected by a trailer ABS ECU causes the trailer ABS warning lamp to illuminate
in the truck instrument panel.
n Discuss the operation of an Eaton electric hybrid system.
n Describe the difference between a series hybrid and a parallel hybrid.
n List the steps to troubleshoot a wiring problem with the J1939 data link.
Key Terms drive-axle ABS event power line carrier (PLC)
dual-mode hybrid system series hybrid system
anti-spin regulation (ASR) electronic on-board recorder telematics
automated manual torque-speed control (TSC)
(EOBR) vehicle onboard radar (VORAD)
transmission (AMT) linear Hall effect sensor
automatic traction control (ATC) modulators
chuff test parallel hybrid system
data mining
differential braking
INTRODUCTION TRANSMISSIONS
This chapter discusses details of major systems on Historically, most truck transmissions were manually-
a modern truck not already covered in previous shifted standard transmissions with the only electrical
chapters and how these systems interact. Emerging components being a reverse lamp switch and perhaps a
technologies, such as hybrid electric trucks, are also vehicle speed sensor. However, electronically con-
discussed along with general troubleshooting tips for trolled automated manual transmissions and electronic
modern truck electrical and electronic systems. automatic transmissions can now be found in trucks of
all weight classes.
477
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478 Chapter 15
Electronic Automatic Transmissions ground for the transmission ECU is typically made
directly at the batteries in the same manner as in most
Electronically controlled automatic transmissions electronic engine ECMs. Some OEMs refer to this
are common in vocational trucks and school buses. direct battery power and ground connection for elec-
Although Caterpillar has entered the electronic auto- tronic modules as ‘‘clean power’’ or similar termi-
matic transmission market in recent years, most auto- nology. Many trucks use the Allison vehicle interface
matic transmissions found in North American built module (VIM) shown in Figure 15-2 as a means of
trucks are manufactured by Allison Transmission1. isolating the transmission ECU from the truck wiring.
Details on the most common models of Allison The VIM contains relays, fuses, and jumper wires.
transmissions will be discussed, but these principles
can be applied to most other electronic automatic The World Transmission uses an electronic shifter
transmissions. to permit the truck operator to select the desired range.
This shifter may be a pushbutton-type shifter or a
Allison World Transmission. The Allison World lever-type shifter (Figure 15-3). There is no mechanical
Transmission (WT) 3000/4000 series is widely used in connection, such as a shift cable, between the shifter
medium-duty vocational trucks, but may also be found and the WT automatic transmission. The electronic
in some heavy-duty applications. A larger 5000/6000 shifter is hardwired to the transmission ECU. The range
series is used in heavy-duty off-highway trucks. This selected by the truck operator is communicated from
transmission can be described as a full-authority the electronic shifter to the transmission ECU via four
electronically controlled automatic transmission be- hardwired circuits. The four circuits are connected to
cause the transmission will only shift into a range four transmission ECU digital inputs. These four digital
when commanded by the transmission ECU. Solenoid inputs make up a 4-bit binary number corresponding to
valves in the transmission valve body are controlled by the selected range. The shifter causes the voltage
the transmission ECU to provide the various trans- present on the four ECU inputs to be high or low,
mission ranges. The electronic control system is corresponding to the selected range.
known as the World Transmission Electronic Controls
(WTEC). A simplified WTEC block diagram is shown The transmission ECU may also use information
in Figure 15-1. The WTEC ECU has three 32-pin from the J1708/J1587 or J1939 data links to obtain
electrical connectors that are color-coded gray, black, engine load information. This engine load information
and blue for identification. Three generations of includes accelerator-position information and is used
WTEC systems have been used; the last being the by the transmission ECU to determine shift points.
WTEC III. Alternatively, an accelerator-position sensor may be
hardwired directly to the transmission ECU in some
Typical electrical layout for a World Transmission applications.
is shown in Figure 15-2. The +12V power supply and
The transmission has three variable reluctance–type
speed sensors, which are used to measure engine speed,
Shift selector
Speed sensors ECU Oil level sensor
Solenoids
Throttle position sensor
Retard modulation C3 pressure switch
Vehicle/engine Temperature sensor
communication links (sump/retarder)
VIM © Cengage Learning 2014
Inputs Outputs
Figure 15-1 Allison WTEC block diagram.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Modern Truck Electrical System 479
Blue Throttle
connector position
sensor
Electronic
control unit
Black Vehicle harness
connector
Gray Vehicle
Diagnostic connector interface
data reader (DDR) module
connector (VIM)
Selector harness
Diagnostic DD Transmission harness
data reader
R MODE
N
D
Remote D Transmission
push button
R feed through
selector
DN
1D
2 D harness
5
N
3 MODE 4 connector
DR 3
N
R 2
Strip push button 1
shift selector
Remote © Cengage Learning 2014
(European OEM) lever selector
Figure 15-2 World transmission components.
turbine speed, and output shaft speed (Figure 15-4). transmission fluid flow to the clutch packs within
The transmission ECU determines shift points based on the transmission. There are two types of solenoids:
all of its hardwired information, and information ob- normally closed (Figure 15-6) and normally open
tained from the data links indicating accelerator position (Figure 15-7). The transmission ECU supplies a pulse
and engine load. width modulation (PWM) control voltage, like that
shown in Figure 15-8, to the applicable combination
The main output of the transmission ECU is the of solenoids to obtain the desired range. For example,
control of several electric shift solenoids within the Figure 15-9 illustrates the elements in use to obtain
electrohydraulic control module located inside the trans- third range. Solenoids B, C, F, and G are energized by
mission (Figure 15-5). These solenoids control the
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
480 Chapter 15
1D DD Digital display D R
2 D N
R MODE Mode D
N N MODE 5
3 D Display/diagnostic 4
DR mode 3
2 © Cengage Learning 2014
N 1
R
Strip pushbutton Pushbutton Six-speed
lever selector
selector selector
Figure 15-3 Allision WT electronic shift selectors.
Output
MD 3070PT
Engine Turbine © Cengage Learning 2014
All WT MD/B 300B 400
Turbine
HD/B 500
Output Output © Cengage Learning 2014 Figure 15-5 WT electrohydraulic control module.
All WT MD/B 300B 400
(except MD/B 300/B 400 often used by the engine ECM or electronic speed-
retarder units) ometer to determine vehicle speed. Transmission out-
put shaft speed is provided by the transmission ECU as
Figure 15-4 WT speed sensors. a pulsing 12V signal (square waveform). The fre-
quency of the square waveform produced by the ECU
the transmission ECU to apply clutches C1 and C3, is proportional to the vehicle speed. It is important to
and the lockup torque converter clutch. note that this output shaft speed signal is produced by
the transmission ECU, not the transmission’s output
J1939 message outputs of the transmission ECU speed sensor. The transmission output speed sensor is a
include transmission output shaft speed, selected variable reluctance sensor, which produces an AC sine
range, current attained range, and transmission oil wave. This AC signal is an input to the transmission
temperature. There are also typically two or more ECU. The transmission ECU then produces a variable
transmission indicator lamps that the transmission frequency output shaft speed signal based on the in-
ECU can cause to illuminate if a failure or other formation the transmission ECU receives from its
condition is detected. Much of this information is output shaft speed sensor. This square waveform
transmitted on the J1939 data link by the transmission transmission output shaft speed signal produced by the
ECU for use by other electronic modules. transmission ECU is typically hardwired to the engine
ECM or electronic speedometer. The engine ECM or
The transmission ECU also provides a hardwired electronic speedometer then converts the frequency of
indication of transmission output shaft speed that is this square wave into vehicle speed. The engine ECM
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Modern Truck Electrical System 481
Magnetic Supply On
coil port
Off
Exhaust 25% 75%
1 cycle
Metal core Control main © Cengage Learning 2014
pressure to On
solenoid regulator
Off
valve 50% 50%
1 cycle
Figure 15-6 WT normally closed solenoid.
On
Magnetic Supply © Cengage Learning 2014
coil port Off
75% 25%
Exhaust 1 cycle
Figure 15-8 Pulse width modulation (PWM) voltage
supplied by transmission ECU controls WT solenoids.
Metal core Control main © Cengage Learning 2014 medium-duty trucks. This transmission uses a cable-
pressure to type shifter that controls a manual selector valve in the
solenoid regulator transmission valve body. Unlike the World Transmis-
sion series, a complete loss of electrical control of the
valve automatic transmission still permits a forward range
(third range) and reverse to permit the truck to ‘‘limp
Figure 15-7 WT normally open solenoid. home.’’ The 2000 series transmission ECU has two
32-pin electrical connectors that are color-coded red
or electronic speedometer is able to convert transmis- and gray for identification. The ECU controls electric
sion output shaft pulse frequency into vehicle speed solenoids located in the valve body in a manner similar
through a pulses-per-mile value that has been pro- to the WTEC series.
grammed into the engine ECM or electronic speed-
ometer. The engine ECM can then transmit this vehicle A multifunction switch assembly located on the
speed information onto the J1939 and J1708/J1587 side of the transmission known as the NSBU (neutral-
data links for use by all other electronic modules on start back-up) switch provides an indication of re-
the truck, including the instrument panel cluster (IPC). quested gear to the transmission ECU. The NSBU
contains four switches that are hardwired to the
The transmission ECU also provides an indication transmission ECU to provide an indication of shifter
of neutral by supplying +12V at a specific output position. The NSBU also contains two additional
terminal if the transmission is in neutral. FMVSS re- switches that are typically connected to the truck’s
quirements indicate that the cranking motor in a truck chassis wiring harness. One switch provides an indi-
with an automatic transmission can only be operated cation of park or neutral position for engine crank
if the transmission is in park or neutral. This ECU inhibit. The other switch is used to control the back-up
neutral indication terminal is used in the engine crank lights. The NSBU does not contain any electronic
inhibit control circuit on most trucks with automatic components.
transmissions.
The 2000 series transmission ECU is connected to
Allison 2000 Series. A lighter-duty Allison 2000 the J1939 data link. Information is exchanged with
series automatic transmission is also used in some other electronic modules on the truck, such as the
engine ECM via the J1939 data link.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
482 Chapter 15
Lube
filter
Torque Cooler
converter
Lube
Converter in
Converter out Lube
Converter flow Lube
regulator
Lockup Overdrive knockdown
EX
G EX
FWD
N/C F LU A C1 B C2 C C3 D C4 E CS
on-off N/C N/O N/O N/C N/C N/C
Main
C2 EX Control Main
Main filter
C1 C1 Exhaust
backfill main reg. Main filter
C4 C5 Main Pressure
EX relief
C2 C3 C4 C5 regulator
C1 C3 Accumulator Pump
latch relay valve
Pressure switch
C2 EX © Cengage Learning 2014
latch Solenoids energized
Clutches applied Suction filter
B-C-F-G Sump
C1, C3, Lockup
Figure 15-9 WT hydraulic schematic—third range attained.
Allison 4th Generation Controls. In 2006, Allison mounted on the external shift linkage in prior 2000
electronic automatic transmission systems were up- series transmission has been eliminated on these
dated and are referred to as 4th Generation Controls. models. Switches inside the transmission are hard-
All 2000, 3000, and 4000 series 4th Generation wired to the transmission ECU to provide an indication
transmissions use a common transmission ECU. The of shifter position based on the manual selector valve
calibration (programming) in the ECU varies for each position.
model. The 4th Generation transmission ECU has a
single 80-pin electrical connector. Allison Transmission Diagnostics. Allison Trans-
mission’s Diagnostic Optimized Connection (DOCTM)
The electronic shifter on 3000 and 4000 series 4th PC-based electronic service tool (EST) is the best
Generation transmissions is connected to the truck’s method of troubleshooting an Allison automatic
J1939 data link and communicates with the transmis- transmission. The interface device is connected to the
sion ECU via the J1939 data link. A hardwired circuit truck’s diagnostic connector and uses J1708/J1587
between the transmission ECU and shifter also pro- (World Transmission) or J1939 (2000 series and all 4th
vides a confirmation of requested range using a PWM Generation Controls) to communicate with the trans-
signal. mission ECU. The DOC electronic service tool permits
diagnostic trouble-code retrieval and observation of
A cable shifter is used on 2000 series 4th Genera- the status of the transmission’s inputs and outputs as
tion transmissions to control a manual selector valve in
the transmission. However, the external NSBU switch
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Modern Truck Electrical System 483
well as providing some transmission tests and cali- VOLUME R Courtesy of Eaton Corporation
bration procedures. CONTROL N
D
The Pro-Link 9000 and other hand-held EST can SERVICE H
also be used to troubleshoot the World Transmission L
series. Additionally, the World Transmission series SHIFT
and 4th Generation Controls models with electronic Eaton Fuller
shifters permit the retrieval of diagnostic trouble codes Transmissions
stored in the transmission ECU on the shifter’s digital
display when a combination of buttons on the shifter is Pushbutton Shift Control Eaton Shift Lever
depressed.
Figure 15-11 Eaton driver interface.
Automated Manual Transmissions
Courtesy of Roadranger Marketing. One great drive
An electronically controlled automated manual train from two great companies – Eaton and Dana Corporations.
transmission (AMT) can be thought of as a standard
manual transmission without a shift lever. The shift lever
has been replaced by two electric motors (Figure 15-10)
that are controlled by an electronic transmission ECU.
AMTs can be divided into two main types: two-
pedal and three-pedal systems. This refers to the
presence of a clutch pedal in the cab of the truck. In a
two-pedal system, the clutch is controlled by the
transmission ECU. A three-pedal system has a stan-
dard clutch pedal and is controlled by the truck oper-
ator, although the clutch is only used for start-up and
stopping the vehicle.
Several manufacturers now produce AMTs, but the
most common are the Eaton Fuller Roadranger family
of AMTs. Details on some models of these trans-
missions will be discussed.
Eaton AMT Inputs. An electronic truck operator in- Figure 15-12 Eaton AMT speed sensors.
terface shift control, like those shown in Figure 15-11,
communicates with the transmission ECU via a private Courtesy of Roadranger Marketing. One great drive train from
J1939 communication network called the EPL. The two great companies – Eaton and Dana Corporations.
primary hardwired inputs to the transmission ECU are
Shift Select Motor Shift Finger Courtesy of Roadranger Marketing. One great drive train from two great
Gear Select companies – Eaton and Dana Corporations.
Yoke
Shift
Shaft
Rail Select Motor
Rail Sensor Figure 15-13 Gear and rail select position sensors.
Yoke
obtained from three transmission-mounted speed sen-
Figure 15-10 Eaton AMT electric shift control sors (Figure 15-12) and the rail select and gear select
assembly. position sensors (Figure 15-13). These position sen-
sors may be potentiometers on early Generation 1
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
484 Chapter 15
V-Ref
V-Ref
N O
SENSOR
S
AIRGAP GND OUTPUT © Cengage Learning 2014
TARGET MAGNET
Figure 15-14 Linear Hall effect position sensor principle.
AMTs, or linear Hall effect sensors in later gen- clutch (although this practice is not recommended).
erations. A linear Hall effect sensor produces a linear The J1939 message used to reduce the engine torque or
output voltage relative to the location of a target speed is called torque-speed control (TSC).
magnet, as shown in Figure 15-14. Additionally, en-
gine load information is also obtained by the trans- Eaton UltraShift. The Eaton UltraShift is a two-
mission ECU through a J1939 network connection, as pedal version of AMT. The transmission ECU con-
well as information from the ABS ECU and body trols the clutch. There have been several types of
control module, if applicable. clutches throughout the various generations of Ul-
traShift including centrifugal and wet clutches.
The primary outputs of the transmission ECU are However, the latest (2012) version of UltraShift Plus
the control of the rail select motor and the shift select uses a conventional disc-type clutch, which is oper-
motor, shown in Figure 15-10. The motors drive ball ated by an electronic clutch actuator (ECA). An ECA
screws, which move the internal transmission shift is shown in the section on Hybrid Electric Trucks
yokes in the same way as a standard transmission (Figure 15-39). The ECA is controlled by the trans-
shift lever operated by the truck operator. The rail mission ECU via a private communication network.
select and gear select position sensors are used by the The ECA contains a brushless DC electric motor and
ECU to determine the rail and shift ball screw posi- planetary gear set to produce the torque necessary to
tions to control the two motors to obtain the desired release and engage the clutch. The transmission ECU
range. can release the clutch during each upshift and
downshift, as well as during initial start-up and when
The transmission ECU calibrates the shift control stopping the truck.
system each time the ignition is switched off. A series
of clicking noises can be heard as the shift and rail Eaton AMT Diagnostics. Eaton ServiceRangerTM is
select motors are driven to each end of their available the PC-based EST used to diagnose an Eaton AMT.
travel. This calibration information is stored in the ServiceRanger permits AMT DTCs to be viewed and
transmission ECU non-volatile memory for use at the cleared. Various transmission parameters, such as shift
next key cycle. rail position and shaft speeds, can be viewed in real
time and tests and calibrations can also be performed
Eaton AutoShift. The Eaton AutoShift is a three- using ServiceRanger.
pedal version of AMT. The truck operator controlled
clutch is only used for start-up and stopping. Once the ANTILOCK BRAKING SYSTEMS
vehicle is in motion, the transmission ECU commands
the engine ECM to reduce torque via a J1939 message Antilock braking systems (ABS) have been re-
to shift, by matching engine speed to the transmission quired in the United States for many years for both air
speed. The truck operator can leave his foot on the and hydraulic truck brake systems and for trailers with
accelerator throughout the shift. The J1939 message air brakes.
controls engine speed much in the same way that a
skilled truck operator feathers the accelerator to shift
once the truck is underway without depressing the
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Modern Truck Electrical System 485
Courtesy of Bendix Commercial Vehicle Systems LLC. All rights reserved.
Figure 15-15 ABS schematic for straight truck.
Tractor and Truck Air ABS wheel-speed sensor with an integral wiring harness and
an electrical connector is shown in Figure 15-16.
An ABS electronic control unit (ECU) is the elec-
tronic module that controls the air ABS system. Var- The wheel-speed sensor target for drum brakes is
iable reluctance–type speed sensors are used to typically constructed of stamped metal and is installed
measure individual wheel speeds at both front wheels on the wheel hub, as shown in Figure 15-17. The
and at least two of the rear wheels on tandem-axle target may be known by several names, including tooth
trucks. Electrically controlled ABS valves are used to wheel, tone wheel, tone ring, reluctor wheel, and ex-
control the air supplied to the service brake chambers citer ring. A typical truck ABS target has 100 teeth.
to prevent wheel lockup. The electrical and pneumatic The wheel-speed sensor is installed in a mounting
layout for a straight truck ABS application is shown in block on the axle so that the target will pass in close
Figure 15-15. proximity to the tip of the wheel-speed sensor when
the hub is installed. A sensor clamping sleeve is typ-
Wheel-Speed Sensors. Most ABS wheel-speed sensors ically used to retain the sensor in the mounting block.
are variable reluctance sensors containing a permanent
magnet with a coil of wire wrapped around the magnet. The target passing in front of the tip of the wheel-
A variable reluctance sensor is a two-wire sensor that speed sensor causes an AC voltage to be produced by
generates an AC voltage signal when a low-reluctance the variable reluctance wheel-speed sensor, as de-
target passes in front of the sensor. The wheel-speed scribed in Chapter 11. The frequency and amplitude
sensors are inputs to the ABS ECU. A typical ABS of the voltage produced by the wheel-speed sensor is
directly proportional to wheel speed. The ABS ECU
measures the frequency of the AC waveform produced
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
486 Chapter 15
Courtesy of Bendix Commercial Vehicle Systems LLC. All rights reserved. by the sensor to determine the speed of each wheel that
is equipped with a wheel-speed sensor.
Figure 15-16 Typical ABS wheel-speed sensor with
integrated wiring harness and connector. The electrical resistance of an ABS wheel-speed
sensor is typically between 1000 and 2000 ohms. This
Courtesy of Bendix Commercial Vehicle Systems LLC. is the resistance of the coil of very small gauge wire
All rights reserved. inside the sensor. The wheel-speed sensor is connected
to the ABS ECU through two wires that are twisted
together to reduce electrical interference caused by
changing magnetic fields near the wiring. Neither of
these wires is directly connected to ground or to bat-
tery positive inside the ABS ECU or inside the sensor.
The ABS ECU continuously monitors the integrity
of the individual wheel-speed sensor circuits for
opened or shorted circuits. If the ABS ECU detects a
faulted wheel-speed sensor circuit, the ABS ECU sets
a diagnostic trouble code (DTC) indicating which
sensor circuit is faulted. The ABS ECU then disables a
portion of the ABS system due to the faulted sensor
circuit and causes the ABS warning lamp in the in-
strument panel cluster (IPC) to be illuminated.
Wheel-speed sensors are typically installed in each
of the two front (steer) axle wheel ends. Trucks with
tandem rear axles often only have wheel-speed sensors
in one of the rear axles. The two rear sensors are in-
stalled at the wheel ends of the forward-rear axle or
rear-rear axle, depending on the truck’s rear suspen-
sion type. This four-sensor four-ABS valve system
shown in Figure 15-18 is known as a four-channel
ABS system. Other trucks with tandem rear axles may
have sensors in each of the rear-axle wheel ends for a
total of six sensors and six ABS valves; this is known
as a six-channel ABS system.
Figure 15-17 ABS tone wheel and wheel-speed Modulators. ABS modulators, also known as ABS
sensor for a drum brake system. valves, are used to control the air in the service brake
Tooth wheel Tooth wheel
Sensor
Sensor
ECU
ABS ABS
valve valve
ATC valve © Cengage Learning 2014
Tooth wheel Sensor Diagonal 1 Sensor
Diagonal 2 Tooth wheel
Figure 15-18 Four-channel ABS with ATC.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Modern Truck Electrical System 487
Exhaust Brake
solenoid valve
Inlet Control
solenoid
Reservoir Piston
Inlet
Supply valve
Delivery © Cengage Learning 2014
Air brake
chamber
Exhaust Exhaust
valve
Figure 15-19 Air ABS brake modulator with integral relay valve.
chambers to prevent wheel lockup. The modulators Courtesy of Bendix Commercial Vehicle Systems LLC.
contain two solenoids (coils) referred to as the inlet All rights reserved.
solenoid and the exhaust solenoid. The two solenoids
may also be known as the hold and dump solenoids, Figure 15-20 Pair of air ABS brake modulators for
respectively. The two solenoids control the inlet and front axle plumbed to a quick-release valve.
the exhaust valves inside the modulator as shown in
Figure 15-19. The modulator depicted is a combina- Air brake modulators are designed so that if the
tion modulator-relay valve. ABS system is not functional, normal braking is not
impacted. The modulator inlet valve is normally open,
Modulators on modern trucks are typically plumbed and the modulator exhaust valve is normally closed.
in series with each of the truck’s service brake chamber When neither modulator solenoid is energized, the
supply lines. These modulators have an air supply port, truck’s brake system is like a traditional non-ABS
air delivery port, an air exhaust port, and an electrical system due to the normal state of the modulator sole-
connector. Two modulators that are plumbed to a quick- noid valves. Air passes directly through the modulator
release valve for a front-axle installation are shown in
Figure 15-20. The air supply ports for these modulators
are plumbed to the quick-release valve shown in the
center of the assembly. The modulator air delivery ports
are the openings at the opposite ends of this assembly
and are plumbed to the service brake chambers. The air
exhaust ports are at the bottom of the modulator. Some
modulators are also designed to act as quick-release
valves, permitting the elimination of standard quick-
release valves from the air brake system.
Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
488 Chapter 15
to the respective service brake chamber with neither outside or inside the cab. If the ABS ECU is located
modulator solenoid energized. outside of the cab, the ECU is a sealed-type module
that uses sealed connectors. ABS ECUs mounted in-
Energizing the modulator’s normally open inlet so- side the cab may be non-sealed modules. An example
lenoid causes the modulator to block the flow of air into of a sealed ABS ECU is shown in Figure 15-22. A
the respective service brake chamber. Energizing the non-sealed ABS ECU designed for interior mounting
normally closed exhaust solenoid then causes some of is shown in Figure 15-23. Most ABS ECUs are con-
the compressed air in the respective service brake nected to the J1939 data link to permit communication
chamber to be vented to atmosphere through the mod- with other electronic modules on the truck.
ulator’s exhaust port. This action reduces the brake force
on the wheel that is locking up. The ABS ECU controls Typical ABS Operation. The ABS ECU monitors the
these solenoids as necessary to prevent wheel lockup. speed of each wheel that has a sensor to determine if
wheel speed is decreasing too rapidly, indicating that
The two coils in each modulator are typically wheel lockup is about to occur. If wheel speed is
connected together on one end inside the modulator so decreasing too rapidly, the ABS ECU controls the
that they share a common terminal (Figure 15-21). modulators to prevent wheel lockup. The action in
Therefore, the typical modulator only has three elec- which the ABS ECU is controlling the modulators is
trical terminals. This is similar to the three terminals of known as an antilock event or ABS event.
a combination high-beam low-beam headlamp. Unlike
a headlamp, though, none of the modulator terminals is If the ABS ECU determines that wheel lockup is
connected directly to ground. The three wires of each about to occur based on the frequency generated by a
modulator are hardwired to the ABS ECU. The ABS wheel-speed sensor, the ABS ECU energizes the cor-
ECU supplies power and ground to the modulator coils responding modulator inlet valve solenoid to block the
only when a modulator coil is to be energized. When flow of air into the service brake chamber. The ABS
neither modulator solenoid is being energized by the
ABS ECU, neither battery positive voltage nor ground Courtesy of Bendix Commercial Vehicle Systems LLC. All rights reserved.
is being supplied to any of the three modulator ter-
minals. Because both the power and the ground for the
modulator solenoids are controlled, a shorted-to-
ground or shorted-to-battery-positive circuit between
the modulator and the ABS ECU will not interfere
with normal braking.
The ABS ECU continuously monitors the modulator
wiring for shorted and opened circuits. If a modulator
circuit is detected as shorted or open, the ABS ECU
disables that modulator and causes illumination of an
ABS warning lamp in the instrument panel.
ABS ECU. The air brake ABS ECU controls the ABS Figure 15-22 Bendix EC30/EC17 ABS electronic con-
system. The air brake ABS ECU may be located trol unit connector view. This unit is sealed and can
be mounted outside of the cab.
ABS Inlet © Cengage Learning 2014 Courtesy of Bendix Commercial Vehicle Systems LLC.
ECU solenoid All rights reserved.
Exhaust
solenoid
Figure 15-21 Each brake modulator has three Figure 15-23 Bendix EC60 ABS electronic control unit
electrical terminals. The common circuit may be with advanced features designed for interior mounting.
positive or negative, depending on the ABS system.
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
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