Automotive Electricity and Electronics 5th Edition by James D. Halderman (z-lib.org)

8

Vehicle control electronics

An engine will operate most efficiently when the maximum road speed suffers, down by about 5 to
gear ratio is such that fuel consumption is mini­ lOmph. There is negligible effect on acceleration
mised while the engine power is sufficient to main­ characteristics.
tain the required road speed. Transmission elec­
tronic control units are designed to optimise the Beside providing precise transmission control
selection of a gear ratio, either in continuously responding to both driving and engine conditions,
variable or stepped transmission units. They can the control unit can be programmed to adjust the
also be used to engage higher gear ratios (over­ gear change points and clutch lock-up operation to
drive) during cruising to bring about considerable provide the driver with a choice of three different
fuel savings. Widespread gear ratios give the best driving modes:
possible fuel economy, and a 5-speed gearbox 1 normal - for almost all urban driving
leaves much smaller variants between its per­
formance curve than, say, a 3-speed gearbox. conditions and motorway driving
2 economy - allows more fuel-efficient driv­
The electronic control is usually based on a
single chip microprocessor and separate memor­ ing by increasing the operational range of
ies. Input information comes from a variety of the lock-up clutch
operational sources including engine speed, road 3 power - provides the engine's full power
speed, throttle angle and a digital code for gear characteristics, so that the driver can have
selection. Output circuits are used to drive stepper a little extra acceleration for, say, over­
motors or solenoids to control various actuators taking, or power when pulling heavy
including clutches, hydraulic pressure lines and loads.
oil pump feeds. Many advanced transmission control systems
are equipped with a self-diagnostic capability to
The actual transmission control is achieved detect malfunctions in the sensors, electrical sys­
through a system of memory mapped parameters tem and in other areas.
including gear ratio, rate of ratio change and
hydraulic line pressure. Clutch control is based on Electronically controlled automated manual
the functions of throttle angle and engine speed, gearbox
stored in memory and summed to bring an output
signal to the actuator. Usually an automatic trans­ The main advantage ofa direct-drive manual gear­
mission system down-rates the vehicle per­ box is its fuel efficiency when compared to
formance figures. But, with electronic control (in hydraulic torque converters and automatic trans­
comparison with a manual system) only the mission systems. The application of electronic
control to a manual gearbox, however, combines

96 Automotive Electronic Systems

Input Programme Safety Throttle valve
sequence circuit %, control
m-1 3 5 Selector position
Acceleration pedal ac Vehicle KH>I
* depression en data Gear
Throttle valve change
position El·
(d==n n
Engine speed h*cz3—y

Coolant temperature Gate selector

-Φ- Clutch stroke Microprocessor h0Clutch control
Gear position
5 Vehicle speed H indicator
cQ

(a)

Sensor inputs the benefits and virtues of manual transmission
and the 'easy-to-drive' fully automatic trans-
Programme sequence mission.
for optimum engine
and gear matching The basic transmission is usually a straight-
forward two-shaft, fully synchronised five-speed
Clutch Gear select gearbox. The clutch is a conventional single dry-
control and change plate type with a diaphragm spring. Both clutch
operation and gear changing are done by hydraulic
Stepping Throttle open­ Accumulator actuators, one actuator for the clutch, one for the
motor ing control gear gate selection and a third for the actual gear
changing, each of which is actuated by a solenoid
®- valve controlled by an 8-bit microprocessor. An
electronic pump provides hydraulic pressure and
Clutch R * H « ' Reservoir an accumulator stores and controls the oil pres-
r sure. The control unit also controls the opening
V- o—Φ) [ of the throttle valve by means of a stepping motor,
& and directs the actuators and stepping motor to
Engine ■y- do all the clutch engagement and disengagement,
Hydraulic gear changing and throttle synchronisation. Sen-
Gearbox u-fyy-J pump sors provide the input signals related to: engine
speed; gear lever position; accelerator pedal
Electro-hydraulic depression travel; throttle valve opening; coolant
actuator temperature; gearbox input shaft speed; vehicle
speed; and the amount of clutch stroke in current
(b) use. The control unit controls the the clutch and
gear operations by programmed instruments, and
Fig 8.1 Electronically controlled automated manual performance and specification maps, choosing the

gearbox
(a) Block diagram
(b) Operation

Vehicle control electronics 97

optimum clutch operating speed and timing and Fig 8.1 shows in block diagram form the

the best engine/gear combination for the operating microcomputer system control and functions.

condition, as well as preventing over-revving.

The control programs allow fully automated Automatic transmission electronic control
and manual gear changes. Safety circuits are built- system
in to prevent accidentally moving the gear lever

into reverse position while travelling at speed, Current electronic control units whether intended

and to cover the failure of sensors. The software for constant velocity (CV) or stepped automatic
program provides a 'kickdown' function based on transmissions, have much in common with the
a vehicle speed map and the throttle position

sensor indicating full throttle. Dependent upon t Torque converter

the speed of throttle movement the ratio will be ( Lock-up clutch
changed down by one (light throttle) or two (heavy

throttle) gears.

The interface between the driver and the con­

trol system is by either a console selector lever

moving through the familiar H-plus-a-leg gate or Gears

by push-button selection. Both provide manual

and fully automated gear changes. There are four Oil pressure circuit Solenoid valves
forward gear positions: 1 and 2 - which hold first

and second gears respectively; 3 - an automatic

mode in which the gears change from 1 to 2 and Inputs from Electronic
down through the same gears; D - fully automatic sensors control
using all five forward gears; and R - reverse hold.
unit

The final selection is N - neutral. (a)

Throttle control
stepper motor

Sensor -► Solenoid — ► Lock-up
Throttle opening -► Electronic valves
1 Vehicle speed
Water temperature control -β

1 Pattern select switcrΠ + unit Oil
pressure
Engine speed > -* circuit —► OD
Brake lamp switch >
-* — ► Gears
Gear lever l
ik

Diagnosis

(b)

Fig 8.2 Electronic transmission control system
(a) Construction of gearbox
(b) Block diagram

98 Automotive Electronic Systems

vehicle systems already encountered. Where conditions, stored as a digital code mask - pro­
designs are microprocessor-based and the main grammed into the ROM during manufacture. The
features include sensors for: engine speed; engine point of gear-change is defined by the parameters
load; road speed; intermediate speed; throttle which are addressed by lines of load and speed.
angle; brake input; and a digital code sensor for Clutch control is based on functions of throttle
indicating gear selection, as well as output circuits angle and engine speed. Both functions are stored
suitable for driving stepper motors or solenoids to in the memory and are summed to give an output
control; clutch; gear ratio; hydraulic pressure signal: this time proportional to the clutch pres­
lines; oil pump feed; and engine braking (Fig sure required.
8.2(b)).
A kick-down facility gives a lower gear ratio for
The electronic controlled transmission system high acceleration needs. The kick-down control
(Fig 8.2(a)) comprises a torque converter with a also prevents the kick-down function from taking
lock-up clutch, epicyclic gearbox and a control place while driving in overdrive gear at speeds
unit which calculates optimum points for gear over 100 km/h, to prevent the engine from over-
change and lock-up action, and controls gear revving.
changes, overdrive selection and clutch lock-up
with corresponding solenoid valves. Overdrive (OD), is selected with a control
switch and an indicator lamp informs the driver
Control action of overdrive operations. The control unit only
allows OD to be selected, however, under certain
Transmission control is achieved through a system driving conditions. A solenoid controls OD
of memory mapped parameters such as gear- engagement.
change characterisation, rate of ratio change and
hydraulic line pressure. Fig 8.3 shows a typical Sensor input signals are conditioned in the per­
gear ratio change schedule for all operating ipheral unit (Fig 8.4) to limit voltage amplitudes,
filter out noise and convert the analogue input
signals into digital form. By processing the input

Kickdown range

13-3

E 267- Upshift
Downshift
o AO-OH
Έ£o
■S 53-3-

1000 2000 3000 4000
90 100
30 Propeller shaft revolutions (rpm) (60)
Ί
km/h 0 10 20 (20) 40 50 60 70 80 110 120 130
I ' 1—' i' _I -I^1 u _IT Ii (70) (80)
(30) (40)
MPH (0) (10) (50)

Vehicle speed km/h (MPH)

Fig 8.3 Gear change schedule including kickdown and torque converter lock-up. The full-load gear change points
are reached at higher speeds than in the economy programme

Vehicle control electronics 99

Reference- _^ r ~l ♦Electronic control unit
mark () I/O
sensor v - ^ Ignition
fuel injection Ignition
Output stage ΨL·, coil

Engine O
speed
sensor

Engine u Output stage Injection
temperature valves

Battery RAM/ROM

Idle signal 2Έ Fault
full load signal co indicator
_Ofc' - ΌcP Safety
relay
Air-flow
sensor Oil
pressure
o Microprocessor regulator
Solenoid
Output Output stage valves,
speed clutch,
gears
Position | P|R|N [ D|3 J2 11 I/O Output stage overdrive
switch Transmission
Programme - engine actions j
switch
Kickdown
switch
Overdrive
switch

Fig 8.4 Block diagram of typical microprocessor-based automatic transmission system

quantities of engine load and transmission output erate an output to the ignition and fuel control
speed, as well as the switch signals of full-load, units, to influence their operation. The advantage
kickdown, OD and programme selection, the of such outputs is that the engine torque can be
microprocessor determines a speed for changing controlled by retarding the ignition timing during
down or up a gear ratio using the gear change gear changing (to cut out the 'jerk') to ensure a
characteristic map stored in ROM. smooth gear change. By retarding the ignition
timing the engine torque achieved is only equal to
The microprocessor then compares the vehicle the part-load value. After the gear change has been
speed code with the look-up table speed code. completed the ignition timing is returned to its
Should there be a difference an error speed code normal value.
is computed from which the microprocessor ener­
gises the solenoid valves; to select the calculated The output to the fuel system is used to indicate
gear by directing hydraulic pressure to the control when the vehicle is stationary for more than a few
clutches and brake band servo. To ensure smooth seconds; interrupting the fuel injection to conserve
and easy gear changing the control unit modu­ fuel and reduce exhaust emissions.
lates oil pressure using a pressure regulator. The
microprocessor determines the most appro­ Electronic cruise control system
priate modulation pressure using the engine load
signal and stored characteristic map. A system which allows the driver to select and
automatically maintain or resume a constant
Many electronic transmission control units gen­

100 Automotive Electronic Systems

speed, independent of road conditions, is popu­ speed sensor (positioned in the transmission line
larly called cruise control. or speedometer cable), the throttle position switch
and potentiometer, and the driver select switch.
The driver initially sets up the electronic con­ The control unit compares the stored speed with
trol unit to store the vehicle speed at that moment the actual speed and produces a throttle control
and start the automatic control procedure. The signal relative to the difference between the two
selected speed is stored in memory and compared which is applied to the throttle actuator. The
continuously with later vehicle speeds. Any vari­ throttle actuator sets the engine throttle butterfly
ation between the two speed signals causes the valve position to cause the vehicle to speed up or
control unit to adjust the throttle to counteract slow down to the desired speed. The actuator
the difference so maintaining the required vehicle control signal is the sum of the control voltage
speed. It is also possible to resume to the stored and the signal position of the throttle.
speed after, say, braking or acceleration.
Principle of operation
The cruise control cuts out automatically when
the brake or clutch pedal is depressed, thus The majority of control units are of a digital
enabling engine braking on overrun and pre­ nature, generally microprocessor-based, although
venting excessive revving on gear changes. Also, analogue systems do exist.
to ensure a progressive and steady change in speed
and to be responsive to changing road conditions When digital techniques are used the stored
in a way that is comfortable to driver and pas­ speed and the actual vehicle speed are processed
sengers the system restricts the rate of acceleration directly as binary digital numbers. The speed
to an acceptable level. sensor's input signal is in the form of a pulsed AC
voltage whose frequency is proportional to vehicle
Most cruise systems employ an electro-pneu­ speed. After amplification and conversion to a
matic system for the mechanical operation of the square wave, the signal is counted by a binary
throttle. Fig 8.5 shows a block diagram of a typical
system. Input signals are taken from a magnetic

Speed
signal

Cancel Input /output Actuator
switches buffer Overdrive
solenoid
Control box ej
Acceleration
resume/set I/O
coast
toggle switch i ,1 Microprocessor
Preset A-D converter
push button
Preset ] ΓΗPower supply RAM Counter
speed dial
Main
push button

Electronic control unit

Fig 8.5 Typical microprocessor-based cruise control

Vehicle control electronics 101

counter over a given time period. The number Electronic anti-lock braking systems
of pulses counted during the period is directly
proportional to the vehicle's speed. Anti-lock brake systems (sometimes called anti­
skid systems), through constant monitoring of
The two digital numbers, stored speed and wheel speeds, intermittently regulate brake fluid
actual vehicle speed, are then compared and (by pressures to prevent the brakes from locking-up
subtraction) the difference is obtained. The the wheels and causing the tyres to lose grip, i.e.
difference is used to generate a control signal for skid on the road. Fig 8.7 shows block diagrams of
the actuator. an electronic anti-lock system.

Fig 8.6 shows a cross-section of a typical When the wheel speed decreases rapidly, a
electro-pneumatic actuator. When the solenoid is wheel speed sensor detects the condition and the
energised the armature is attracted to the core, control unit intermittently actuates a solenoid
pressure controller, effectively turning the brake
Air valve fluid pressure to that wheel off and on. The
reduced brake pressure prevents the wheel from
locking.

Actuator Basic principle of operation

Thottle lever The basic system shown in block diagram form in
Fig 8.7(a) shows that each 'braked' assembly has
Fig 8.6 Solenoid-operated throttle actuator a sensor which constantly monitors the rotational
speed of the road wheel. This sensor generates an
closing the air valve and opening the vacuum electrical signal and sends a stream of pulses to
valve. Vacuum from the inlet manifold draws the the electronic control unit (ECU). These sensor
diaphragm into the actuator chamber, producing signals are constantly monitored and compared
the force for throttle actuation. The force exerted with the other wheel speed signals by the elec­
by the piston can be varied by rapidly opening tronic devices in the ECU.
and closing the valves, thus changing the average
pressure in the chamber. If during braking lock-up of one wheel becomes
imminent the sensor signal from that wheel will
The actuator is mounted on the engine and differ from the sensor signals from the other road
connected directly to the throttle. The control wheels. The ECU reads this difference in speed
function remains stable in all driving conditions and outputs another electrical signal to the pres­
and produces a smooth gentle response. sure control actuator to reduce the hydraulic pres­
sure to the affected wheel. Constant adjustment
Some cruise control systems may use an actu­ (pumping) of the hydraulic pressure at the affected
ator unit comprising an electric motor with wheel is maintained until the ECU interprets the
integral gearing and electromagnetic clutch. The same rate of deceleration (same wheel speeds) by
rotary motion is converted into linear motion with all the sensed wheels (Fig 8.7(b)).
the clutch, a selector gear and a lever.
A warning lamp system is included to indicate
when the brakes are under the control of the
ECU and to monitor brake fluid level and actuator
pressure.

102 Automotive Electronic Systems

Wheel speed Input amplifier Digital signal Valve drive Power output Solenoid
sensors ♦ filter processing current regulator and switching actuators
stage
Φ Ch 1 1 apressure control
0 a
Ch 2 ICC,
ICB, 0

Front axle

ICD [>h£
Warning
Ch3 lamp
ChA
Rear axle ICB2 j Relay
Processing
ΦMagnet c> - a
and coil 0—"0
Input ICA
ICCi

Output Actuation

reluctor ring mounted on the revolving pinion

Electronic shaft-flange. A magnetic field within the sensor
is interrupted by the variable reluctance of the
brake control toothed reluctor ring, producing an electrical
logic

Master Wheel Wheel pulse whose frequency is related to speed.
cylinder speed If there are 45 'teeth' on the reluctor ring a

Pressure signal every 8 degrees (360/45 = 8) will be gen­
controller erated by the sensor. This ac signal varies in

Wheel frequency and amplitude according to the
cylinder rotational speed of the reluctor. The sensor gap is

very precise and care must be taken to ensure the
(b) sensor mounting faces are clean and not damaged

Fig 8.7 Typical electronic anti-lock braking systemor distorted. The sensor is also magnetic and
(a) Block diagram ofwhole system precautions should be taken to ensure it is not
(b) Block diagram ofa single wheel showing feedbacsukbjected to demagnetising conditions.
control
Under normal driving conditions the actuator

solenoid valve is switched off. In the off position

Anti-skid braking system (single line) the actuator pressurisation spring, via the piston
and plunger, holds the fluid-pressure cut-ball off
In this system only the rear braking pressure is its seat, allowing brake fluid under pressure from
electronically controlled (Fig 8.8).
the brake master cylinder to be applied to the
The wheel speed sensor is located on the rear rear wheel cylinders in the normal way, without
axle housing and is positioned close to the toothed interruption.

Vehicle control electronics 103

Intake
manifold

Chamber B

Speed
sensor

Cylinder

Pressurization spring
Fig 8.8 Single line actuator operation

<£ Input Digital Valve drive >
amplifier signal processing Channels 1 +2
<^M Channels 1-4 Channels 1 + 2 Bipolar ICA.1 D>
MOSIC2.1
<£ X Actuator
<S3 Digital solenoid
Wheel pulse Bipolar IC1 signal processing Valve drive valves
generators Channels 3+4 Channels 3*4
MOSIC2.2 Bipolar IC 42 >

L TT— B Warning light

Oscillator tfäiDigital monitoring -Δ Memory D>^—(S>—i

Motor > Vstab <*- Memory circuit H> [>hB Valve relay
Voltage Clock generation
voltage regulator MOS IC3 > | Motor relay
Battery
voltage z Voltage
monitoring

¥

A Input function
B Digital calculation function
C Power output function
D Monitoring and safety function

Fig 8.9 Block diagram of an electronic control unit

104 Automotive Electronic Systems

Under heavy braking conditions or when the a single piston master cylinder and the rear brakes
rate of deceleration is more than l g (9.8 m s 2 ) , by controlled accumulator pressure. Another sys-
the G-ball is accelerated down the ramp closing tem utilises a dual piston master cylinder for front
the vacuum port, connected to the inlet manifold. and rear brake operations, and an electrical return
The ECU, having sensed a significant change in pump to feed the brake fluid which is released by
wheel speed, outputs a control signal to the solen- the wheel brake cylinder during pressure reduc-
oid actuator valve, which opens allowing atmos- tion back into the appropriate brake circuit. The
pheric air pressure to enter chamber A of the return pump is of the double piston type in order
actuator. The increase in air pressure forces the that the dual-circuit braking system remains fully
power piston to move against the pressurising isolated from each other.
spring, in the direction of the arrow. This action
allows the cut-ball to seat on the valve face and Electronic control unit
cut the brake fluid pressure being applied to the
rear brake wheel cylinders. This action maintains Signals from the wheel speed sensors are evaluated
the current level of braking pressure in the rear by the ECU which then computes the permissible
brake line to continue the present braking effort, wheel slip for optimum braking. It controls the
and prevent the rear brakes from locking. fluid pressure in the wheel cylinders via solenoid
valves in the actuator.
The frequency of the signal from the ECU
controls the period of pressure difference between At the start of a journey, the system will auto-
chambers A and B, and hence the cycle of matically carry out a self check of all the functions
hydraulic pressure adjustment. in accordance with a stored programme. The sys-
tem is continually monitored during a journey
The anti-skid control is applied to the rear and if any system or component is not operating
wheels only because they are more likely to lock satisfactorily the anti-lock part of the braking sys-
during heavy braking, due to the weight transfer, tem is shut down and the system reverts to a non-
from rear to front, unloading the rear wheels and anti-lock system. A warning lamp is used to alert
reducing adhesion. the driver that the anti-lock system is non-oper-
ational.
Anti-lock braking system (ABS)
The ECU is a complex unit, comprising some
The majority of cars use a dual-circuit (two-line) seven ICs of the latest digital technology, on which
braking system, where the front brakes are on a many demands are made. For the purpose of
separate hydraulic circuit to the rear brakes. explaining the ECU's functional operation these
can be divided into four functional areas.
With ABS as part of the braking system three-
and four-line hydraulic systems are in common 1 Input - amplifying and signal conditioning
use, to give independent wheel braking under (ICA).
anti-lock control.
2 Computing - digital signal processing (ICB).
In a four-line system each of the four braked 3 Output - valve drive and power stage (ICC).
wheels has a separate and independent hydraulic 4 Safety - monitoring and fault detection (ICD).
fluid pressure pipeline, whereas in the three-line
system the two rear brakes share a hydraulic fluid Fig 8.9 shows a block diagram of the basic con-
pressure pipeline, and possibly a common speed struction of the ECU.
sensor as in the anti-skid system. There are vari-
ants which measure the rear wheel speed inde- Input section
pendently, even though they share the same pipe-
line. In this section the electrical signals from the four
wheel-speed sensors are fed through for filtering
In one system the front brakes are activated by

Vehicle control electronics 105

and amplification. The input interface usually uses actuator assembly, by energising the respective
bipolar technology, and the input amplifier is pro- relays.
vided with special interference suppression and
self-test circuitry. The output section uses current regulators
within the valve drive ICs. By way of these current
Computing section regulators the output signals from the logic circuit
cause different currents to flow in the power out-
The heart of the controller is formed by the two put stages. With the result that the desired pos-
digital LSI circuits, with each employing two itional operation of the solenoid valve is obtained.
channels for processing the signals and executing
the logic process. Some 16,000 transistors are Under ABS braking on road surfaces with
accommodated on a chip area of approximately different friction coefficients, left and right, some
37 mm2. Silicon gate N-channel technology is used vehicles may experience a yawing moment which
and the controllers are custom designed for this is difficult for the driver to control. The yawing
task. moment causes a sideways movement of the
vehicle due to a torque acting about the vertical
The digital controller, which is similar in design axis of the vehicle. To counteract this the output
to a microprocessor, contains special computing drive signals for the solenoid valves on the steering
modules. These modules are better suited to the axle are processed so as to reduce the build up of
ABS task than microprocessors, at this stage of these yawing moments. This is done by using an
development, especially with regard to computing algorithm that produces a drive signal for the
speed and accuracy. solenoid valve of the front wheel with the higher
friction coefficient that delays the build up of
A digital phase lock loop circuit is used to braking pressure to the optimum required for
measure the speed of two wheels, filter the signal retardation. The gain in stability is paid for with
and convert it into a digital word. A serial arith- longer stopping distances.
metic unit then calculates the wheel slip and the
wheel deceleration or acceleration which are then The amplifying and filtering, differentiating
integrated in the following logic circuit to form and calculating wheel slip, deriving the commands
command signals for the actuator valves in order for the actuators and outputting them takes
to obtain brake pressure modulation. approximately 0.5 ms.

The slip value is obtained by comparing the Each of the functional areas described above
vehicle speed with the speed of wheel rotation. An which makes up the digital controller (computer)
optimum braking force which gives 8-30% slip is contains a monitoring circuit for the detection of
used as a reference value for vehicle speed. This faults.
vehicle reference speed is derived from each of the
diagonally opposed wheels. The two wheel speeds Monitoring and safety section
are processed by two separate digital modules
which are then compared in turn to give a vehicle The basic function of this section is to detect
reference speed. This speed value is used in any incorrect electrical or electronic signals. The
the logic circuits as if it were the vehicle's road section uses a digital monitoring circuit, a voltage
speed. monitor, a voltage regulator, a fault memory with
relay and lamp driver.
Output section
A fault signal from the monitoring circuits sets
When all the relevant signals and/or information the fault memory and switches off the system via
has been processed the output section is used to the cut-off relay and the voltage regulator. The
send commands to the solenoid valves, in the driver is informed by means of the warning lamp
that the control is inoperative and that normal
braking is available 'failed safe'.

106 Automotive Electronic Systems

Brake master cylinder

Fig 8.10 Electronic antilock braking systems
(a) With hydraulic modulation assembly
(b) With actuator assembly

The safety circuit can also transmit a self-test below a pre-set value, the ABS will be shut down.
signal to check that all is in working order. The The system will be restored when the voltage rises

self-test cycle begins when the wheel speed at all above the pre-set value again.
the speed channels exceeds 5-7 km/h. After the This ensures that the battery's state of charge
self-test has verified that the system is in good
order, the warning light goes out. does not affect the value of current flowing
through the solenoid windings, and hence valve
Another function ofthe safety circuit is to moni- position, when the ABS is in operation.
tor the battery voltage and if the voltage falls

Vehicle control electronics 107

Actuator The solenoid valves are actuated by the ECU
and depending on the driving signal's control cur­
There are two types of actuator assemblies in rent and switching state they connect the wheel
common use, one is a separate assembly to the cylinder with the brake master cylinder or the
brake master cylinder unit (hydraulic modulator electrical return pump. They can also close off the
assembly) (Fig 8.10(a)) and the other is integral wheel cylinder from both circuits and the pump.
with the master cylinder (actuation assembly)
(Fig. 8.10(b)). Pre-tensioned springs are located on the arma­
ture of the solenoid valve to limit the armature
Hydraulic modulator assembly movements during the different control currents.
The solenoid valves increase, hold steady or
The hydraulic modulator consists of a solenoid decrease the brake line fluid pressure between 4
valve and accumulator for each brake line, a return and 10 times per second depending upon the state
pump and the control relays. of the road conditions.

Master Rear brake line
cylinder
Actuator
A
Solenoid valve
6 -Λ/νφ—j Rear wheel
Γ Τ ΤΖΓ cylinder
A/vi T Motor Fluid return lines
from wheel cylinders
<> pump Front wheel
cylinder
r^w)—[

P-Master cylinder Accumulator 2r§ Reservoir

fluid return lines'

τ- Γ - ^ \ Λ Λ ) — w\A)--—Γ-

0 ~ζ> I-

tt .aΛΛ/1 1_L ΓΝ3 /wj IT n
A I Solenoid valve Solenoid valve
Ö

Near side front brake line Off side front brake line

I— To wheel cylinder (open) • To wheel cylinder (closed) From wheel cylinder
I—To returTi circuit (closed)
3- r rI—To return circuit (closed) tii To return circuit (open)
/ws r^n ΛΛΛ

T IT LFrom master cyl inder (closed) LFrom master cylinder (closed)

l-From master cylinder

Increase position Hold position Decrease position

Fig 8.11 Hydraulic control circuit diagram

108 Automotive Electronic Systems

When the pressure is reduced, the return pump wheel deceleration or the ECU detects that the
pumps the brake fluid released from the wheel wheel rotation is out of phase with the other
cylinders back to the appropriate circuit of the wheel, due to heavy braking or different frictional
brake master cylinder, by way of an accumulator. surfaces, and the wheels are likely to lock. To
The accumulator, temporarily, stores the fluid prevent this the braking pressure at the wheel(s)
from the wheel cylinder which occurs following a concerned is initially kept constant. This is
drop in line pressure. Whenever time line depres- achieved by the ECU outputting a signal to the
surisation takes place a back pressure is produced appropriate power transistor which in turn
in the master cylinder fluid line which causes the allows battery current to be supplied to the
brake pedal to raise slightly. Because of this the solenoid winding.
functional operation of the ABS can be felt by
the pulsing of the brake pedal as the pressure in The current supplied causes the valve to move
the master cylinder fluid lines is cycled on and off. to a position that closes both the inlet and outlet
ports and the braking system is in the hold phase,
Principle of operation and the valve in the hold position.

When braking with an ABS the ECU's output Decrease pressure position
signal has three different conditions to control
the position of the solenoid valve. Under these If the wheel rotation continues to decelerate at an
conditions the following pressures positions are abnormal rate, the ECU will then, via the current
involved: regulators, allow an increase in current to flow
through the solenoid winding, moving the arma-
• Pressure increasing position (normal brake ture still further and open the port to the return
condition). pump. The pressure in the wheel cylinder is
reduced so that the wheel is not braked excess-
• Maintained or pressure hold position. ively.
• Pressure decreasing position.
At the same time the motor relay is closed by
Fig 8.11 shows a schematic line diagram of a another ECU's signal so that the motor pump can
hydraulic modulator controlling three brake lines, operate and draw fluid from the wheel cylinder
and as can be seen there are as many actuating via the accumulator. The pump then transfers the
solenoids as there are brake lines. In a four line fluid to the master cylinder fluid line against the
system there would be four of these solenoid pressure applied to the brake pedal.
valves - one for each wheel cylinder.
When the wheel rotational speed accelerates
Increase pressure position again the ECU having processed the sensor signals
will cause the pump motor to be switched off and
During normal braking, fluid from the master move the solenoid valve to the increased position
cylinder flows through the solenoid valves to the permitting the fluid pressure to be restored. This
wheel cylinders. The wheel speed sensors have not cycle of operation between the three positions
transmitted any abnormal or rapid deceleration takes place between 4 and 10 times every second
signal to the ECU. Consequently, no actuating the ABS is in operation.
current will be supplied to the solenoid valves,
and the armature spring holds the valve in the 'at- The actuator relay for the solenoid valves is
rest' position. always energised (closed) by an ECU signal when-
ever the system operates, except in the case of a
Hold pressure position fault (Fig 8.12).

When a wheel-speed sensor signals a high rate of The fault detecting circuit is always monitoring
the system operations and produces the fault sig-
nal for the failsafe circuit whenever faults occur.

Vehicle control electronics 109

Ignition switch give a visual indication of what components have
malfunctioned.
ECU -®-
Actuation assembly
-*o | Motor
relay This type of ABS actuation assembly contains a
number of interactive components (Fig 8.13).
From M ) Motor pump
current Integral brakefluidreservoir.
regulator Actuator relay Reservoir warning unit, used to indicate when
and output —o o the brake fluid level is low and to switch the
ABS control off in the event of low fluid level.
-3ramplifier fBattery ; Electric pump, an electric pump is used to draw
fluid from the reservoir and send it at high
HL pressure to the lower region of the accumu­
lator. The pump is of the double piston type
Fig 8.12 Electrical control circuit so that the brake circuit of the dual-line system
remain fully isolated from each other.
The failsafe circuit opens the actuator relay and Accumulator, the pressure accumulator has
switches the failure indicator lamp on. a gas filled chamber behind a flexible
diaphragm. As the pump continues to supply
When used, at this stage of development, the fluid to one side of the diaphragm, the nitrogen
self diagnosis display consists of 8 light-emitting- gas on the other side is compressed so that a
diodes mounted on the surface of the ECU. Each
LED turns on according to the fault signal to

Reservoir

Solenoid valve Main valve
block assembly

Fig 8.13 Hydraulic actuator assembly Electric pump and
motor assembly
Pressure warning
switch solenoid

110 Automotive Electronic Systems

reservoir of brake fluid under high pressure is Principle of operation
established.

5 Pressure switch, this is used to monitor the As with the modulator type, the actuation

pressure in the accumulator so that the pump assembly is controlled by different output signals

can be switched on and off. When the pressure to provide alternative operating conditions (Fig

reaches a maximum threshold of 180 bar the 8.14).

pump is switched off. When the pressure falls

below 140 bar the pump is switched on again. Normal brake operation
Should the pressure fall below 105 bar the

pressure switch acts as a safety device sig- When the brake pedal is pushed down the control

nalling the ECU to switch the ABS system valve is moved to open and fluid under pressure

off, and illuminate the warning lamps. from the accumulator is made available in the

6 Main valve, this electromagnetic switching boost chamber. The value of the fluid pressure

valve is used to open the connecting channel being proportional to the amount of control valve

between the pressure region of the brake movement. This booster pressure acts on the

power booster and the pressure region in front brake power booster piston (12) and via the open

of the master cylinder, and to close the flow inlet solenoid valve (13) provides the braking

of fluid to the reservoir during ABS control. pressure for the rear wheel cylinders. At the same

This ensures a continuous supply of high time the master cylinder piston (4) displaces brake

pressure brake fluid during ABS control. fluid and builds up the pressure in the brake lines

When the ABS is not in operation the main to the front wheel cylinder, again via the open

valve is closed by the ECU and the return to inlet valves in their brake lines.

the reservoir is reopened. Throughout this condition the outlet valves

7 Valve block, the valve block contains six solen- stay closed preventing any ABS action.

oid valves, two for each brake line. These are

used as the inlet and outlet valves for the ABS controlled brake operation
flow of brake fluid. Under normal braking the

valves are in the 'at rest' position where the The ABS control comes into operation when the

inlet solenoid valve is open and the outlet deceleration of one or more road wheels show

solenoid valve is closed. With the brake fluid abnormal deceleration and the associated tendency

pressure being applied to the wheel cylinder to lock. Under these conditions the ECU switches
through the inlet valve when the brakes are on the output transistor to close the electrical
circuit of the inlet solenoid, which moves the
applied.
When abnormal deceleration of a wheel(s) solenoid's armature piston to the closed position
occurs the ECU closes the inlet valve and preventing any more fluid getting to the wheel
opens the outlet valve. So reducing the brake cylinder. At first the pressure in the line is kept
line pressure and preventing the wheel(s) from constant (hold position) with both the inlet and
locking. To achieve an even and controlled outlet valves being closed. If the wheel continues
deceleration of the vehicle the two valves are to decelerate a second signal from the ECU opens
cycled on and off by the ECU at approximately the outlet valve, decreasing the pressure, reducing
the braking efforts and returning the 'excess' fluid
12 times per second.
In the case of a fault in the system the to the reservoir.
solenoid valves are not activated by the ECU As soon as the system enters the anti-lock mode
so that the normal braking function is avail- the main hydraulic solenoid valve (5) is opened
able. by an electrical signal from the ECU. This allows
boost pressure to enter the master cylinder area

Vehicle control electronics 111

Reservoir Pressure
Main valve accumulator

Dntrol valve
Connecting lever

Brake Piston
master cylinder brake power booster

Solenoid- Solenoid-/ \ Solenoid -
outlet valve outlet valve inlet valve
( rear brake)
(rear brake)
®
eVL βWheel brake VR © HA

cylinder - right
front wheel

Fig 8.14 Hydraulic control diagram

by flowing in the reverse direction and over its but the rear brakes can only be bled using the
seal. The front brakes now become dynamically system's own pressure.
powered the same as the rear brakes. The main
valve stays open and the inlet and outlet continue Summary of the control sequence
to cycle on and off adjusting the brake pressure
until the wheel sensors indicate equal braking on With reference to Fig 8.15, when a wheel speed
all four wheels. sensor signals a high rate of deceleration such
that the wheels are likely to lock, the electronic
The reason for opening the main solenoid valve controller acts to prevent any further increase in
is to ensure that there is an adequate supply of
high pressure fluid, even under prolonged ABS 3t 1 !
braking, is available to compensate for the fluid
released from the wheel cylinder back to the res­ Ό </> 1
ervoir. ^ N|
&>&)'
Because this type of actuator operates at a high N-.
working pressure (180 bar), the system must be in σ* 1
depressurised before any work is done on the —£n*ώ2σc, /ΓQ1^L ,..,
system. The system can be depressurised by \
pumping the brake pedal some 20 times until the ! I Time —*-
pedal feels hard.
(a)
The front brakes can be bled in the normal way,
Fig 8.15 Graphs showing the variation in braking
pressure under controlled braking

112 Automotive Electronic Systems

braking pressure. The braking pressure of the distance above ground level. Weight transfer
wheel(s) concerned is initially kept constant (point causes the vehicle to lean outwards on its springs,
A), and prevented from increasing. which results in an interaction with the steering
linkage and changes the camber angles of the tyres.
If the wheel continues to decelerate abnormally, Energy is stored in the springs, which must be
the pressure in the wheel cylinder is reduced so dissipated by the dampers as the vehicle leaves the
that the braking effort is reduced (point B). corner. The moment of inertia of the vehicle about
the roll axis and the role stiffness govern the
The wheel will then accelerate again due to the resonant frequency of the suspension system. If
reduced pressure. Once a specific threshold has the dampers are ineffective or if the vehicle is high
been reached the fluid pressure is increased again and heavy, the roll resonance can turn it over
(point C), causing the wheel to decelerate, and (Fig 8.16). At constant speeds vehicle weight is
the control cycle repeats again at a frequency
of between 4 and 10 seconds depending on the Roll
condition of the road surface.

Microcomputer based control system

The electronic control unit includes the micro­ Fig 8.16 Body roll when cornering
computer components, fault detecting mechan­
ism, failsafe circuits and self diagnosis circuitry. distributed evenly (Fig 8.17(a)), but during heavy
braking, deceleration or acceleration weight is
The microcomputer calculates the wheel transferred to the front or rear wheels (Fig.
rotation speed from the input pulse signal fre­ 8.17(b)), which affects vehicle safety, ride, hand­
quency. Evaluation of the wheel rotational situ­ ling and comfort. Yet the car must give the driver
ation produces the output signal to prevent the a good ride on a smooth surface, it has to handle
wheel from skidding wherever slip is detected. well in corners, and it has to give a reasonable ride
on a rough road. Conventional suspension systems
As with the previous system the micro­ are a compromise design not fully satisfying every
computer's output signal has three different con­ one of those conditions.
ditions.
Electronically controlled suspension systems
1 output signal controls the activating have been developed which can fully satisfy every
solenoid valve in the pressure increase
position for normal braking.

2 pressure hold signal.
3 pressure decrease signal.

The fault detecting mechanism is always moni­
toring the system's operation and produces the
fault signal for failsafe circuit whenever a fault
occurs.

The selfdiagnosis mechanism consists of 6 eight
LEDS on the ECU surface. Each LED turns on
according to the fault to give a visual indication
of the faulty components.

Electronic suspension systems (b) (c)

When a vehicle corners, the force accelerating it Fig 8.17 Suspension and handling
towards the centre of turn acts at ground level, (a) Even distribution
but the centre of mass of the vehicle is some (b) Dive when braking
(c) Squat on acceleration

Vehicle control electronics 113

one of the above conditions, by manual or auto­ will become compressed and the other extended,
matic selection. The suspension design is based and the vehicle is prevented from experiencing
on active suspension principles. body roll. Active suspension systems can be
implemented by mechanical or hydro-pneumatic
As Fig 8.18(a) shows, an active suspension means, but as the complexity rises electronic con­
system interposes hydraulic rams between springs trol is the most effective way.
and body and the wheel position is monitored
with a sensor. If the wheel moves towards the Electronic control unit
body, the movement is sensed and causes the ram
to extend until the wheel is back in the original An electronically controlled suspension system,
position, which compresses the spring. When a illustrated in Fig 8.19, uses a microprocessor-
vehicle is cornering as in Fig 8.17(b) one spring based control unit to adjust the damping force of
the four shock absorbers. Table 8.1 lists the main
(a) (b) components of the system and their functions and
Fig 8.18 Principle of an active suspension system locations.
(a) Active suspension interposes rams between springs
The control unit adjusts the system such that
and body two levels of damping take place, switched auto­
(b) When vehicle corners, rams counteract weight matically depending on the driving conditions:

transfer • soft - normal driving conditions, eg con­
stant speed on a level, straight road, or
slow and steady acceleration or decel­
eration, slow speed town driving

Steering Microprocessor Suspension movement
sensor control unit sensor
Brake
Speed sensor Rear suspension
sensor unit

Throttle
sensor

Hydraulic pump Front suspension
Control valve unit

Fig 8.19 Adaptive suspension system with electronic control

114 Automotive Electronic Systems

Table 8.1 Main components and their functions

Name of component Function Location

Shock absorber Incorporates 2-way switching valve to change Front and rear suspensions
damping force

Actuator Drives 2-way valve of shock absorber At top of shock absorber

Mode select switch Switches the damping force mode At right of steering column on
instrument panel

Mode indicator lamp Indicates damping force selected In the meter

Suspension control computer Controls the system depending on the selected mode Inside left quarter-panel

Ignition switch Supplies power to suspension control computer when Steering column
turned on

Steering sensor Detects steering direction and angle of the steering Bottom of the steering column
wheel turn

Stop lamp switch Sends braking signal to the computer Brake pedal bracket

Throttle position sensor Sends degree of accelerator pedal depression to Throttle body
computer

Car speed sensor Sends car speed signal to computer In the meter

Neutral start switch (A/T Sends P (parking) and N (neutral) range signals to Transmission
only) computer

• hard - harsh or sports driving conditions, has independent threshold sensitivities in the
eg cornering at speed, hard acceleration three directions:
or deceleration, high speed 1 longitudinal - over 0.3 g
2 lateral- over 0.5g
When the system switches from soft to hard damp- 3 vertical - over 1.0 g.
ing, the spring constant increases by about 50%
and the damping coefficient increases by about A light beam between a source and detector
150%. The driver has the option to override auto- detects pendulum movement: when the beam is
matic control, and switch permanently to either broken, the pendulum has exceeded one or more
of these two damping settings. of the threshold sensitivities and the control unit
switches to hard suspension mode, to counteract
The five sensors around the vehicle allow the the accelerating force.
control unit to monitor vehicle speed, rate at which
the steering wheel turns, acceleration or decel- Steering sensor
eration, throttle operating rate, and suspension
stroke. A change in driving conditions causes the The steering wheel sensor is an angular velocity
monitored signals to change and, if the signal sensor, which allows the control unit to monitor
change is sufficient, the control unit switches the the rate of change of steering wheel angle. A
suspension accordingly. slotted disc rotated by the steering mechanism
separately interrupts two infra-red beams: The
Acceleration sensor angular velocity is determined by the control-unit
from the difference in time between the first beam
The acceleration sensors are of the pendulum-type interruption and the second. When the steering
detecting acceleration changes in three directions: wheel angular velocity exceeds a threshold the
longitudinal, lateral, and vertical. The pendulum control unit switches to its hard suspension mode,
sensor, due to its pivot and weight arrangement,

Vehicle control electronics 115

so that greater damping force is automatically 8.20(a)). The oil passage orifices are located in a
provided to, say, prevent rolling when cornering rotary valve, which is integrated with the control
or give easier handling when pulling out to over- rod driven by the actuator. Under normal, soft
take. driving conditions the control rod opens the valve
orifices, allowing a greater flow of oil between the
Suspension stroke sensor
Orifice Orifice
The suspension stroke sensor uses photo inter- (open) (closed)
rupters to monitor the relative positions between
the body and suspension. The control unit moni-
tors the sensor signals and changes the suspension
to hard mode if it determines that either the upper
or lower limits of the suspension stroke are
approached. This helps prevent the incidence of
full bump and/or full rebound.

Vehicle speed sensor When When When
extending extending compressing
Located in the transmission or speedometer cable, Soft cushioning (damping)
this sensor is a typical inductive pick-up, and Hard cushioning (damping)
provides a train of pulses whose frequency is pro-
portional to vehicle speed. (a)
Motor
The control unit monitors the speed and auto-
matically switches to hard suspension mode at Solenoid Stopper
speeds above 120 km/h.

Throttle speed sensor

The throttle speed sensor is used to detect the
speed at which the accelerator pedal is being oper-
ated. It may take the form of a pedal pressure
sensor or a simple potentiometric sensor. When
the sensor signals indicate that the throttle move-
ment speed (accelerating or decelerating) is over
preset threshold limits, the control unit auto-
matically switches to hard suspension mode, so as
to maintain a more level vehicle condition under
acceleration or deceleration.

Actuators Electric motor

There are two main types of activator/damper (b)
arrangements available. The first has a damper
with a twin-chamber construction, whose oil pass- Fig 8.20 Twin-chamber electrically actuated suspension
ages between the two cylinders may be opened damper
and closed to give soft and hard damping (Fig {a) Construction ofdamper
(b) Construction ofactuator

116 Automotive Electronic Systems

top and bottom chambers. In the hard sports Negative^ feed back signal Load
mode the control rod closes the valve preventing cell
oil flow. The dampers resemble large diameter Hydraulic supply
ordinary suspension dampers and are normally Sensor
installed in the same place as conventional vehicle USPump Control valve
dampers. Tank Accumulator!

The actuator used to drive the rotary valve is a Wheel
permanent magnet DC motor (Fig 8.20(b)). The
DC motor is controlled directly by the control e Loa d Servo
unit, taking approximately 0.1s to actuate, thus cell valve
providing a fairly rapid change in suspension Servo
mode.
v;afl3ve-OCHTankl
The second type of actuator/damper arrange­ Pump f
ment is described by its manufacturer, Lotus, as
a synthetic electronic spring. The actuator is, in (b)
fact, a hydraulic ram powered by a small engine
driven pump and controlled by varying the vol­ Fig 8.21 The Lotus active ride suspension system
ume of oil in the actuators (via a servo valve). (a) Principle
The system is inherently self-levelling and can be (b) Block diagram
controlled to eliminate roll in corners and to be
exceptionally soft or hard. The hydraulic actuator
also replaces the road springs, dampers and anti-
roll bars.

Fig 8.21 shows the Lotus active ride suspension
system and the electro-hydraulic suspension dam­
pers in detail.

A mode lamp is normally provided in active
electronic suspension systems to indicate whether
the damping force is set soft or hard. When a
failure occurs, an alarm light is also used to inform
the driver of the malfunction and of the measures
taken by the control unit (eg fixed to hard mode).
Data regarding the malfunction are provided on
a harness check terminal as coded signals to help
diagnosis of failure.

9

Total management systems

The trend towards more advanced and more inte- functions which help the vehicle to continue to
grated engine control systems has resulted in total operate even in the event of a fault. Fig 9.1(a)
management systems, combining ignition, fuel- shows a block diagram of the TEMCS principle
ling function, automatic transmission and other and Fig 9.1(b) illustrates a typical system.
key engine functions into a single centralised Although most control categories have been dis-
engine management and control system. Rightly cussed in earlier chapters, a brief description of
so: such systems afford many advantages; fully each category follows.
optimised engine performance and lower overall
cost from the use of common components being Electronic fuel injection (EFI)
only two. A single microprocessor, single power
supply and single housing are used in a single Electronic fuel injection (Fig 9.2) is based on the
control unit - rather than having separate control intermittent fuel injection principle; using sensor
units each with microprocessor, supply and hous- signals and data maps stored in an electronic mem-
ing, for each function. Common sensors are used ory to compute the optimum injection timing and
to provide input signals, too. fuel discharge duration. The fuel is discharged
exactly to the engine's various operating con-
Total electronic management control systems ditions of: cold starting; warm-up phase; idling;
(TEMCS) provide highly integrated and precise part-load; full-load; acceleration; deceleration; air
control of engine and transmission functions density; battery voltage fluctuation; fuel pump
through the use of a common microprocessor- control.
based computer. Precision control is achieved not
only for engine idling speed, fuel injection volume, Electronic ignition control
and ignition timing, but also the computer link-
up with an automatic transmission system means The TEMCS control unit is programmed with
optimum gear-changing points and control of data to provide optimum ignition characteristics
lock-up clutch operation, so providing a more (Fig 9.3) under all operating conditions. Many
efficient transmission of power, improved driving features are included: ignition triggering; spark
performance and higher fuel economy. advance and retard; constant coil energy; variable
dwell periods; ignition advance under idling con-
TEMCS are designed to combat the increasing ditions; knock control allowing the ignition point
complexity of today's engines and strict emission to be set for maximum torque at full load without
legislation. They also have an advanced self-diag- knocking.
nostic capability for the instant detection of a
malfunction; together with fail-safe and self-repair

118 Automotive Electronic Systems

< Items detected by individual sensors> <Microcomputer> <Control categories> < Effects >

• Throttle position TEMCS Steering and 1 Improved vehicle
• Coolant temperature Electronic suspension handling
• Induction air volume control Fuel injection |
• Engine speed Ignition timing 2 Improved driving
unit Idling speed performance
• Air conditioner Gear changes 1
operation Clutch lock-up | 3 Impnroved fuel
Diagnostics e f f!iicc i e n c y
• Vehicle speed
• ECT shift position U Improved comfort
• ECT pattern selection 5 Improved
• Starter operation
• Brake operation serviceability

(a)

|^ ^ ECT
ECU

Gear change/
clutch lock-up

(b)

Fig 9.1 Total electronic management control systems
(a) Block diagram
(b) Typical TEMCS

Total management systems 119

Crank angle sensor Engine speed and piston position TEMCS ► Injector
Air flew meter Amount of intake air control
Cylinder head temperature sensor Temperature of engine
Throttle valve switch Throttle valve idle position unit
Neutral /park switch Gear position
Vehicle speed sensor Vehicle speed
Ignition switch Start signal
Battery Battery voltage

Fig 9.2 Electronic fuel injection

Crank angle sensor Engine speed and piston position TEMCS Power
Air flow meter Amount of intake air control transistor
Cylinder head temperature sensor Temperature of engine
Throttle valve switch Throttle valve idle position unit
Vehicle speed sensor Vehicle speed
Ignition switch Start signal
Detonation sensor Engine knocking
Battery Battery voltage

Fig 9.3 Electronic ignition timing control

The last feature also allows the ignition point pulses are suppressed to limit the engine speed to
to run close to the engine's knock threshold, and a preset maximum. A TEMCS may also provide
retards the ignition should the threshold be cruise control features.
breached. Knock in turbo-charged engines can
also be prevented by reducing boost pressure and Electronic accelerator
retarding the ignition timing as soon as knock is
detected. An integrated potentiometer is attached to the
accelerator pedal to provide information on the
Speed control pedal's position to the control unit. This is used
in conjunction with data from other sensors to
The control unit is programmed with target calculate the optimum throttle butterfly valve pos-
engine speed values to respond to different engine ition and so set the throttle actuator. The use of
condition and operating requirements (Fig 9.4). an electronic accelerator eliminates a mechanical
Via the idle speed actuator, the control unit adjusts source of error due to play, friction and wear.
idle speed to the target value. Also, fuel injection

120 Automotive Electronic Systems

Ignition switch Start signal ► Idle- up solenoid
Battery voltage TEMCS
Battery Load signal control
unit
Headlamp switch (a)
Cooling fan switch
Power steering oil pressure switch

Crank angle sensor Engine speed TEMCS Auxiliary
Cylinder head temperature sensor Engine temperature control ► air control valve
Ignition switch Start signal
Throttle valve switch Throttle valve idle position unit
Neutral/park switch Neutral position
Air conditioner switch Air conditioner operation
Battery Battery voltage

(b)

Limiting maximum engine speed n0 by
suppression of fuel injection pulses

rpm i n' Injection I
interrupted
6000 "

ί 80min-'----

4500 Engine speed TEMCS Fuel injector
c sensor control ► solenoid

a 3000 Γ / — Engine speed unit
.5 1500 h limiter on

Time t (0

Fig 9.4 Engine speed control
(a) Idle-up control
(b) Idle speed control
(c) Maximum engine speed control

Exhaust emissions control and reducing the nitrogen oxide density in the
exhaust gas. When the EGR valve is open, exhaust
Exhaust gas recirculation (EGR) gas can flow from the exhaust manifold to the
In an EGR system, some exhaust gas is returned intake manifold. The EGR valve is regulated by
to the combustion chamber (Fig 9.5), thus low- the control valve (solenoid operated) to govern the
ering the flame temperature during combustion amount of exhaust gas that flows.

Total management systems 121

Control Intake manifold EGR EGR control
valve closed vacuum source control valve solenoid valve

Solenoid

Control
current

intakToe ULUiJ ciosea Engine speed Crank EGR
T Exhaust gas(in) Engine temperature angle sensor ► control solenoid
(a) Throttle valve idle position
Start signal (O
Crank angle sensor
Cylinder head temperature sensor TEMCS
Throttle valve switch control
Ignition switch ► circuit

(b)

Fig 9.5 Exhaust gas recirculation control Air filter >l Carburettor Engine
(a) Actuator details
(b) Block diagram

(c) Layout

Generally EGR only occurs when the engine is Extra air TEMCS Lambda Exhaust
at normal temperature and running at medium control control se0n2sor gas
speed. valve
unit
Air-fuel ratio
The air-fuel ratio control circuit regulates the air Feedback control
volume entering the inlet manifold, or the volume
of fuel discharged through the injector valves: (a)
helping to keep the actual air-fuel ratio close to
the stoichiometric (i.e. when λ= 1) air-fuel ratio. Air Air flow Engine LamDaa |
This results in a complete combustion which sensor
minimises the production of carbon monoxide o2
(CO) and unburned hydro-carbons (HC). + + t IInjector valves
sensor
In an air supply feedback control system, the i I IFuel-*[[
main air supply enters the inlet manifold from the ▲ i k ki ▲
air filter and carburettor, as in Fig 9.6(a). After
combustion a lambda oxygen sensor attached to TEMCS
the exhaust manifold detects the air-fuel ratio in
the exhaust, signalling this information to the 1 unit

(b)

Fig 9.6 TEMCS control ofair-fuel ratio
(a) Using an extra air control valve
(b) Using fuel injection

122 Automotive Electronic Systems

computer. On the basis of this information the 29A- Fuel
control unit adjusts the extra air control valve to ^ 196- pressure
maintain the ideal air-fuel ratio. Alternatively, in
a fuel injection system the control unit increases 98-
or decreases the fuel volume injected (Fig. 9.6(b))
and so maintains the ideal air-fuel ratio.

Electronic transmission control o 984 Time —

Electronic transmission control (Fig 9.7), Pressure regulator
improves fuel economy and gear-change quality, control system is
and increases a given transmission torque and in operation
reliability. The control unit directly controls the
gearbox's pressure regulator, solenoid valves and (a)
clutch actuators. Gear-change characteristic
curves, stored in memory, are used to effect the i Start
best change schedule for fuel economy or power
performance. Ignition On
switch

Off

On

Off 1 off

About 3minutes

Throttle opening (b)

Vehicle speed ► Lock-up
solenoid
TEMCS ► Pressure
control regulator
Coolant temperature [ Battery voltage —► control circuit
unit Ignition /start
Mode select switch ► ÖD Temperature sensor TEMCS 1
— ► control
> solenoid Pressure
unit regulator
Gear position switch control 1
—► solenoid
Gear change
Gear lever | ► solenoid

[Brake signal (0

Fig 9.7 Block diagram transmission control Fig 9.8 Fuel pressure regulator - electronic control
system
Fuel pressure regulator (a) Showing pressure variations
(b) Control pulse
(c) Block diagram

Electronic control may be added to the fuel injec- manifold absolute pressure changes. But, when
tion pressure control circuit, so as to increase fuel the electronic control system is in operation the
pressure and make it easier to start a hot engine. fuel pressure is increased, for the duration of the
This is achieved by shutting off the manifold control pulse. Fig 9.8(b) shows the control pulse,
vacuum supply to the pressure regulator during while Fig 9.8(c) illustrates the control circuit and
starting, and for 3 minutes after starting when the system.
water temperature is above 100°C.
Self diagnostics
Fig 9.8(a) shows graphically how the pressure
regulator normally maintains a constant pressure An on-board diagnostic function is provided in
difference between manifold absolute pressure and the control unit to detect, memorise and display
fuel pressure, by changing the fuel pressure as

Total management systems 123

system malfunctions. Typically, fourteen diag­ abnormal signal, the system may ignore the signal;
noses are available, one normal state and 13 mal­ instead using a predetermined value thus main­
function states. The majority of the diagnoses taining vehicle operation, albeit now under open
concern sensor malfunctions. loop control.

When a system fault is detected an instrument Vehicle handling management system
panel warning light is switched on. The diagnosed
state is logged into memory and stored, even after As automotive technology advances, chassis and
the ignition is switched off. This memory function suspension systems are becoming increasingly
is helpful in locating a problem which otherwise complex - now with electronic control features
may be extremely hard to find. Service personnel helping to provide superior handling and comfort.
can later read these logged malfunctions which Working on a similar concept to TEMCS, vehicle
appear as a repeatable display of sequenced error handling management systems integrate several
code numbers. Table 9.1, for example, lists the control functions into one central electronic con­
self-diagnosis code in the Nissan ECCS engine trol unit. The block diagram in Fig 9.9 shows the
management system. The code number needed to concept of such a control system; based on seven
identify a fault is determined from the frequency input signals and the activation of steering, sus­
by which two coloured indicator lamps (one red, pension and antilock braking devices.
one green) go on and off. The red lamp refers to
the tenth digit while the green lamp refers to the Suspension and anti-lock braking systems have
unit digit. For example, if the red lamp blinks already been discussed, but speed responsive rack
twice and the green lamp three times the code and pinion steering systems need mention (Fig
number is 23: indicating the throttle valve switch 9.10). The control unit controls the current in the
is malfunctioning. solenoid valve so that the power-assistance ratio
is light at low speeds, heavier at high speeds.
When such self diagnostic systems detect a very

Table 9.1 Self diagnostic error codes in the Nissan ECCS engine management system

Indication method

The light goes out Red light The light goes Green light Error code Malfunction area
out no.

4.8 sec 2.4 sec 2.4 sec 2.4 sec

• 11 Crank angle sensor

·· 12 Air flow meter
···
·• · · · 13 Water temperature sensor
··
14 Vehicle speed sensor
·· ···
• 21 Ignition signal

··· 23 Throttle valve switch

Air conditioner switch

31 (with Nissan air
conditioner)

OK (without Nissan air
conditioner)

··· ·· 32 'Start' signal
··· ·• · · ·
···· 34 Detonation sensor
···· ···
···· 41 Air temperature sensor
····
43 Battery voltage

44 OK (with Nissan air
conditioner)

124 Automotive Electronic Systems

Mode selection switch Control mode signal CRT Situation display
| Steering sensor display Diagnosis
| Brake light switch
Steering wheel angle signal 'c
Throttle position sensor
Vehicle speed sensor Brake activation signal ZJ ^ Spring rate adjustment
Neutral start switch
Vehicle height sensor Accelerator angle signal "o ► Actuator Shock absorber damping |
Vehicle speed signal ► force adjustment
* "ouc

o Vehicle height adjustment
ΙωΛ
Park/neutral position signal oo Steering resistance II
ao adjustment ||

U

Vehicle height signal

► Awheel ESC(ABS) ]

(a)

Hydropneumatic suspension Rear I
Front suspension |

suspension

Accumulator

Levelling
valve

Levelling □ HJ
valve
Reserve Pump
tank r—1 Priority
valve
Tl ■

(b)

Fig 9.9 A vehicle handling management system
(a) Block diagram
(b) Hydraulic diagram

Total management systems 125

Vehicle speed
sensor

Bypass

Mode select
switch

(a) (b)

Fig 9.10 Speed responsive power steering
(a) Layout
(b) Solenoid control valve, varying steering effort

according to mode and vehicle speed

10

Electronic control of body systems

You only need sit behind the steering wheel of a ing parts, construction is modular and
modern car and turn on the ignition to see that the
micro-chip has arrived: all-electronic dash panels there are fewer sub-assemblies
and instrumentation systems are commonplace, more comprehensive instrumentation
with their large and easy to read displays (Fig while clarity is maintained through
10.1). Compared with traditional electro­ flexibility in display area and format,
mechanical instruments, microelectronic dis­ using dotmatrix, alphanumeric, ISO
plays are able to provide: symbols and bargraph displays
greater freedom in display location for
• Faster and more accurate information
• increased reliability - there are no mov­ better visibility
attractive customised displays

Voltmeter Speedometer Rev counter
Oil pressure gauge

Warning
(amps

Water temperature
gauge

Fig 10.1 Digital electronic instrumentation display panel

Electronic control of body systems 127

• easier accommodation in the dash panel but this is only one factor of an electronic driver
due to shallow depth of electronic panel information system.

• clearer and more extensive instru- Fig 10.2(a) shows a block diagram of a single
mentation information display system. When a micro-
processor is used to process signals, however, it
• increased vehicle safety, operating may be as the central processor for several input
efficiency and driver convenience. signals, and the operation of several display
devices. Fig 10.2(b) illustrates a typical electronic
Electronic display systems can be separated into information display system combining the oper-
active and passive types. Active displays; LED, ations of many instrumentation systems into one.
vacuum fluorescent etc, are triggered, reliable,
easy to read and are easy to multiplex. Passive Digital speedometer (Fig 10.3)
displays such as LCD, have good visibility in
strong light, consume very little power even over Vehicle speed is monitored by a sensor fitted in
a large display area. the transmission train; usually the gearbox, in
place of the more conventional speedometer drive
Driver information and display systems gear (Fig. 10.4(a)). Inside the sensor is a pulse
generator, working on induction, Hall effect, or
There have been several changes in the methods photo-interruption principles, producing 2 to 8
oftelling the driver what needs to be known about pulses per revolution, up to a maximum speed of
the operating condition of the vehicle: about 4,000 rev/min.
• combinations of analogue dials with
The frequency of the generated pulses is pro-
digits portional to the number of interrupters on the
• modular digital dash units drive rotor and the vehicle speed (Figure 10.4(b)).
• 'space-age' panels of numbers/bar/ If the sensor is geared to revolve at say, 1500
rev/mile then for each mile travelled a four pole
graphs, climbing streams of light, col- interrupter will produce 6000 pulses. The sensor
oured warning symbols, and CRT 'tele- signal is conditioned by an interface amplifier
vision' screens.
There is no denying that it is the colourful
displays themselves which have the most appeal;

Physical Input Electronic
measurand interface controller Output
Sensor interface Display
►
Observed
action

Sensor 1 Engine speed (a) Tachometer Display 1 j
Microprocessor
Sensor l \ Vehicle speed Speedometer -►I Display 2 |
controller
Sensor 3 Oil pressure Oil pressure & warnin^g | Display 3 |

Sensor A Fuel level Fuel tank content Display 4 |

Sensor 5 Coolant temperature Engine temperature Display 5 |

(b)

Fig 10.2 Instrumentation control system
(a) Block diagrams of a generalised instrumentation
(b) Microprocessor-based instrumentation control system

128 Automotive Electronic Systems

Speed ► Multiplexer ► Sample Gate ► Demultiplexer — ► 7 segment
sensor gate on-off decoders
4
^Γ^ Reset Microprocessor
Digital 4
counter 1r

C-I uQMPH\I

Display

Fig 10.3 Generalised speedometer electronic instrumentation system

Multiplexer Demultiplexer

Light 0 0-
detector 1
(a) 2 1
3
U 1 output 2
5 line
8 input 6 1 input 3 8a output
lines 7
line 5 lines

6

7

Vo Input select code Output select code
High from microprocessor from microprocessor
speed
Fig 10.5 Digital selection devices multiplexer and
demultiplexer

the microprocessor, turning on and off a sample

Vo gate. After a set of pulses have been counted, the
Low digital counter is reset to zero in readiness for the
speed next count cycle.

Frequency After performing necessary computations on
the counted number of pulses, the microprocessor

(b) indicates the speed on the display.

Fig 10A Speed sensor The display driver circuit selects the display

(a) Typical construction segments to display numerals representing the

(b) Voltage/frequency characteristic vehicle's speed, according to the number of pulses

device to a squarewave and sampled (typically) received from the speed sensor.

through a multiplexer. The multiplexer is an elec­ Electronic tachometer
tronic switching device through which the mic­

roprocessor can select one of several sensor inputs The tachometer operation is similar to the speed­
for processing. The output is typically switched ometer except that the signal pulses originate from
through a demultiplexer (Fig 10.5). The electronic the vehicle ignition system. The number of
speedometer operates by counting the number of rev/min of an engine is directly proportional to
pulses received from the speed sensor in a given the sparking frequency and a signal wave-form of
time and from this computes the speed to be this frequency is readily available from the pri­
displayed. The time slot over which the sensor mary ignition coil circuit. After counting these
pulsed signal is counted is controlled directly by pulses over afixedtime period, the microprocessor

Electronic control of body systems 129

Engine speed Signal Microcomputer Display '"■ -►
sensor conditioning driver
^ Display

Fig 10.6 Electronic engine speed indicating system (tachometer)

calculates the engine speed and displays the result value by the analogue-to-digital converter, then

accordingly; representing the number of 100s of multiplexed to the microprocessor. The micro-

engine revolutions per minute. processor uses the binary number to address a

For example, a four cylinder, four stroke engine particular memory location. Another binary num-

fires twice per revolution of the crankshaft and ber which corresponds to the actual temperature

therefore at, say 6,000 rev/min, the sparking fre- value for the sensor voltage is stored in that mem-

quency will be 12,000 sparks/min i.e. 200 Hz. The ory location. The microprocessor uses the number
pulses are counted for 0.3s, so the result is '60' from memory to generate the appropriate output
hundreds. Fig 10.6 shows an engine speed signal to activate the display driver circuit to dis-
measurement system.
play the temperature value.

If the coolant temperature exceeds a limit then

Coolant temperature measurement an output signal is generated which activates a
warning indicator.

The engine coolant temperature is sensed by a

thermistor, mounted on the engine block close to Fuel volume measurement
the thermostat (Fig 10.7). The resistance of this

sensor decreases with increasing temperature. To measure fuel quantity the microprocessor sam-
Sensor output voltage converted to a binary ples the sensor signal via the analogue-to-digital

k— Me mory ]

Analogue to digital —► Multiplexer ►1Microprocessor M— High temperature |
converter limit

i

Coolant temperature _kJ Output stage light
sensor
1' vfö9\

J Character Display
Ί generator
i n n °\

1UU

Fig 10.7 Coolant temperature indicating system

. }—* Multiplexer Microprocessor uMemory
Quantity 9
converter
/ Quantity 10
ii

vv Float Sensor Address Quantity 11 LED or LCD or

lFevueel l^A)T..τ—·ι^Μ/—,<ψό»LΡ'-;^λλΗ μ1r \ / C « - Λ Λ« « , Λ« * ^
^0Μϊψ-*k:i:J*yS( .-;ii
Demultiplexer -1JlEi I . F l |

1' Display 1

de<:oders Fiiunuel |

Fig 10.8 Fuel volume measurement system

130 Automotive Electronic Systems

converter and multiplexer as shown in Fig 10.8, readings over a few seconds and computes the
and generates a signal to display the contents of average sensor voltage value. The averaged output
memory at the address indicated. The sensor is a is used as the memory address for determining
thick-film variable resistance device controlled by the fuel volume value.
a float. The resistor is used as a voltage divider so
that the voltage at the caliper arm is related to Oil pressure measurement
float position which, in turn, is dependent upon
Oil pressure is measured by a piezoresistor sensor
TTEmpty Vo (Fig 10.10). A piezoresistor is attached to a dia­
phragm whose deflection causes a change in the
Float - ^ > 1 Lto*CPU piezoresistor's resistance. The piezoresistor is con­
Mechanical nected into a simple voltage divider circuit and
linkage Sensor Full the voltage across a fixed value resistor is pro­
element portional to oil pressure. The analogue sensor
(potentiometer) voltage is converted to a digital code and used by
the microprocessor to address a table of voltage
Regulated Regulated and oil pressure codes stored in ROM. The output
voltage voltage signal generated is used to drive the display and
thus give a digital representation of the engine oil
(a) (b) pressure.

Fig 10.9 Fuel volume sensor Engine <>j Regulated
(a) Construction block voltage
(b) Circuit

fuel level (Fig 10.9). A table of binary codes equi­ Rp 'Piezo­
valent to the fuel volume and the sensor voltage resistor
for the fuel tank is stored in ROM.
Piezo-resistor i Vo
When the fuel volume level drops to a minimum (a)
preset limit the microprocessor also generates an (b)
output to activate an audible and/or visual low-
fuel warning.

To compensate for fuel movement in the tank
the microprocessor samples and stores several

Analogue to digital Multiplexer Memory
converter Low pressure
Microprocessor li mit

Oil pressure Demultiplexer Character Warning |
sensor generator
Demultiplexer Λ1
Fig 10.10 Oil pressure indicating system Decoder
(a) Sensor details (0 inn 1
(b) Circuit ofsensor
(c) Oil pressure measurement system 1 UU

Electronic control of body systems 131

Trip computers journey. Or the average speed over the same dis­
tance. Or the estimated distance to the next fuel
Microprocessor-based trip computers are a major stop; taking into account the way the vehicle has
development in vehicle electronics, and with care­ been driven. It may also function as a stopwatch,
ful use allow more economical driving. A trip as well as giving the outside temperature.
computer monitors performance during a journey,
displaying a variety of information from fuel con­ Sophisticated trip computers are available
sumption to the vehicle's average speed. which offer some 12 functions, some of which
require manual input from the driver or passenger.
For example, press a button and the vehicle's Key in the desired travel time and the trip distance
instantaneous fuel consumption is displayed. Or and the computer will calculate the average speed.
the average fuel consumption since beginning the Or it can determine the fuel consumption over a
particular stretch of road.
Input signals > Control ► Trip data
unit display Trip computers can be used to help save fuel
Fuel used and make motoring a more enjoyable time.
Vehicle speed
Engine speed A block diagram of a trip computer system is
Fuel level shown in Fig 10.11. A diagram showing the trip
Air temperature computer control unit in more detail is shown in
Keyboard select Fig 10.12. The trip computer system can either
be implemented as a set of special functions of
Fig 10.11 Block diagram of trip computer system the main microprocessor-based instrumentation
system or it can be a stand-alone system employing
its own microprocessor.

Commands

Speed sensor ζ%
(induction type
or Hall)

Fuel flow sensor

. Battery
Fig 10.12 Details of trip computer control system

132 Automotive Electronic Systems

Trip computer operation Function 2 - stopwatch
The stopwatch can be started, stopped and reset
The trip computer receives input signals from to zero using the appropriate button. This elapsed
four sensors, which measure vehicle speed, fuel time function can be used for, say, measuring
flow rate, fuel volume and outside air temperature. acceleration or finding out how long a journey has
Using these input signals in conjunction with the taken.
internal trip computer clock, a number of func­
tions may typically be calculated and displayed in Function 3 - instantaneous fuel consumption
digital form, all illustrated in Fig 10.13. When this function is selected the computer takes
a reading of the pulse frequency from the fuel flow

sensor i.e. fuel flowing per unit of time. This

11 Function 1 Π Γι ~« Γι quantity is used by the computer to determine the
Time fuel consumed per mile or per kilometre and to
31§ Function 2 give an instantaneous consumption display. On
I Stopwatch fuel injection systems the pulse time is used as a
basis for this calculation, which is proportional to

the amount of fuel injected. The pulse time of

only one injector may be measured, this is then

multiplied by the number of cylinders to give the

Function 3 Function 4 total amount of fuel used. The computer deter­

Fuel Fuel mines the fuel consumption by comparing the fuel
consumption consumption flow rate in gallons (litres) per hour to the vehicle
(instantaneous) (average)

speed in miles (kilometres) per hour, defined by:

mcc speed (in mph)

I§ consumption (in mpg) = ;

fuel flow rate (in gph)

Function 5 Function 6 At speeds up to 5 or 6 mph the display may be in
Average speed Range
gallons per hour; above this preset minimum

speed it is in mpg.

The instantaneous fuel consumption is updated

Function 7 LwJar Ίij Function 8 frequently, say every second, and as a consequence
Distance °F Outside air the display changes rapidly as the operating con­
covered temperature ditions vary, depending upon accelerator position;
cruising, climbing or descending hills, or acce­
lerating etc. By displaying information on the

Fig 10.13 Typical trip computerfunctions exact amount of fuel being used at any given

moment, the trip computer helps driving tech­

Function 1 - time niques to be adopted which show useful gains in

The accuracy of a quartz crystal combines with fuel economy.

microprocessor technology to provide an easily Function 4 - average fuel consumption

read display of time regardless of whether the When the average fuel consumption function is
ignition is on or off. The clock may have a 12- selected the trip computer divides the distance
hour or 24-hour cycle and is easily reset after the travelled from the start of the trip by the total fuel
battery or supply has been disconnected. The time which has been used.
distance travelled
is initially entered by pressing the appropriate Average fuel consumption = total fuel
buttons as specified by the manufacturers.

Electronic control of body systems 133

Both variables are recorded as part of the com- is usually displayed in steps of 0.5°C. Outside air
puter's normal functions; distance travelled is temperature is a source of interesting information
obtained from the speedometer circuit and the for cars fitted with air conditioning. This function
fuel used from the fuel flow rate. The calculation can also make a real contribution to road safety;
can be started and restarted at any time and is not because black ice forms on the road surface at a
affected if the ignition is switched off. The display temperature just above freezing point, and an
shows the figure in mpg or kilometres per litre. accurate reading of outside air temperature could
give advance warning of black ice conditions.

Function 5 - average speed

This value is calculated using the speed pulses,

averaged over the time of the journey. The trip Trip electronic control unit
computer can show the vehicle's average speed, in
mph, at any time during the trip. The function The microprocessor used in the trip computer is
can be restarted at any time, providing useful provided with memories for the various functional
journey time information for either complete trips programmes, tables and data. Typically, a 32-
or individual sections of a trip. Breaks in the channel input/output device is provided for com-
journey with the ignition off are not included. munication with the peripheral units, sensors and
displays (Fig 10.14). The analogue input quan-

Function 6 - range tities are digitized in an analogue-to-digital con-

This programme is used to show how far the car verter and fed to the microprocessor through a
is able to travel using the fuel remaining in the multiplexer. Digital input signals are fed to the
tank. The calculation is determined using the con- microprocessor after filtering by the input devices.
tents of the fuel tank and the average fuel con- Current consumption is kept down to about 5 mA
sumption. The display shows the distance possible which means that the battery is subjected to only
in miles or kilometres. a slight electrical load. It is also because of this
low current consumption that continuous realtime

Function 7 - distance covered operation of the display and control electronics is
The distance covered since the last reset is cal- made possible. Additionally, the system will still
culated by summing the speed pulses derived from function reliably even if the supply voltage falls
the measurement of the vehicle's speed. below 5v.

Display driver circuits are used to generate

Function 8 - outside air temperature the characters on the liquid crystal or vacuum

The outside air temperature is measured using the fluorescent display. With the LCD type, one of
NTC thermistor. The temperature range dis- the driver IC contains the oscillator required for
played ranges typically from 40°C to 170°C, and generating the alternating voltage.

Voltage 1 o+V
regulator Display
Sensor 'r
inputs i aooo 1
» Analogue
m j Protection Clock U Li U LI
. £ circuits to digital *t
converter ROM
and RAM Display driver
► Multiplexer
buffer » Control i
amplifier registers Microprocessor
Input/output
_ intejfp£e_.
M—1

Fig 10.14 Block diagram configuration of trip computer control unit

134 Automotive Electronic Systems

Calibration providing the driver with compliance with the
law, safe driving, indication of potential costly
When the trip computer or any of the sensors faults and advising routine maintenance checks -
have been replaced or in the event of incorrect the integration of service interval indicators
functional displays, it is necessary to calibrate the inform the driver when the time has arrived for
system to ensure matching of components. the next service, rather than being fixed by time
or mileage.
Vehicle condition monitoring
Systems are available for monitoring single and
Vehicle condition monitoring (VCM) systems multi-functions, with each monitoring channel
provided the driver with an indication of the oper- comprising a sensor, electronic control unit and
ational state of various systems and functions that display. The principles of operation and design of
are the subject of legislation and/or are vital to the each system varies according to the parameter
safety and operation of the vehicle. A VCM system being monitored and the operating environment.
generally monitors all functions automatically and The construction and operation of the control
constantly, and makes an active display of any unit, incorporating the input device, signal pro-
malfunction. cessing and the display drive circuitry, also varies
with the application. Single channel systems (Fig
The following systems/functions can be moni- 10.15) use standard integrated circuits, while the
tored: multi-channel systems are based on micro-
• coolant level processors (Fig 10.16). The display drivers use
• fluid level, clutch and brake fluid, screen- depend on the type of display technology; fila-
ment-bulb, VFD, LCD, or LED, and the display
wash water level format (i.e. dot matrix, alphanumeric, bar graph
• engine oil level or symbolic) and, in turn, these depend on the
• lights parameters being monitored.
• brake pad wear
• oil contamination
• engine operating conditions,

Sensor Electronic control IC Display levels
Timer 1 Continuous
Display 2 Switch telltale
Channel 3 Failure-event warning
monitor

Switched change
in resistance level

Fig 10.15 An individual monitoring channel comprises a sensing element, electronic circuit and illuminated
warning display

Multi-sensor ROM JOutput device * Display
inputs RAM
Display driver
Signal Microprocessor
conditioning
and filtering

frl

Fig 10.16 Multichannel microprocessor-based condition monitoring system

Electronic control of body systems 135

Fig 10.17 Typical vehicle condition monitoring system
(a) Circuit
(b) Display cluster

136 Automotive Electronic Systems

Typical system operation (Fig 10.17) checked. If the status is within limits the display
lamps will go out after the 5 seconds.

The sensors used to monitor each particular However, if an open circuit or earth fault is

vehicle function do so by switching between high detected on any of the sensor supply leads, the

and low resistance values when preset functions electronic monitoring circuit causes the warning

limits are exceeded. The use of resistors avoids lamp of the affected channel to flash for a preset

false readings due to a wiring fault (Fig 10.18). period (40 seconds) and then go out. This warning

The two main types of sensors used: a float-swit- is repeated following each subsequent warning
ched magnet and reed switch sensor - used for lamp test period until the sensor lead fault has
low fluid level detection (for coolant, wash bottle, been corrected.

If, on the other hand, a low level condition is

present on a sensor, the appropriate warning lamp

Open = high resistance is illuminated continuously.

° Closed = low resistance Following the initial start-up all sensors, with

the exception of the oil sensor, are monitored

(a) Resistance based sensor. Normally closed with short continuously while the ignition is on and if a low
and/or open circuit detection. Normal logic 0; Failure level occurs at any time the corresponding warning
logic 1 is illuminated. The oil level is checked only once

during each ignition on period: at the very begin-
V ning. This is because there is no point in con-

stantly monitoring oil level: as soon as the engine

V, -■ Logic 1 turns oil is pumped out of the sump and a low-

level would be sensed. Further, if the engine

Logic 0 stands for less than about three minutes between

running periods the oil does not have enough time

Time to drain completely back to the sump - most VCM

(b) Typical condition monitoring sensor signals systems simply use the previous sensed level and

Fig 10.18 Principle of sensor switching action andedliasppslaeyd.thOaitl unless more than three minutes has
signal levels level sensing often has its own dedi-

(a) Resistance based sensor normally closed with schaotretd monitoring IC.
andIor open circuit detection. Normal-logic 0; The coolant, fuel and screen wash sensors are
failure-logic 1
(b) Typical condition monitoring sensor signals interrogated for a continuous 8 seconds before a
warning is displayed. This is to prevent lamp

flicker due to fluid movement in the container.

hydraulic fluid, fuel level) and a hot-wire resist- When the vehicle's side lights are on the warning

ance sensor (for oil level) and their operation in a lights are automatically dimmed - for night driv-

VCM system have already been described in the ing. One of the channels on the control assembly
chapter on sensors.
has a dual input and can be used for monitoring

The control assembly integrated circuit pro- a system with two sensors but only one warning

vides timing signals and monitoring channels. display (for example, a brake fluid level sensor and

Timing signals automatically provide a check a brake pad wear sensor may be used to drive a

on the operation of all display lamps by generating single brake warning lamp).
a test signal ofa predetermined duration (normally The brake pad wear sensor is, in fact, a small
5 seconds) each time the ignition is turned on wire loop, embedded in the brake pad at a depth
which illuminates all the warning lamps. At the of about 1.5 mm from minimum thickness of pad
same time the status of each sensor assembly is (Fig 10.19). Two resistors, of resistance 180 ohm

Electronic control of body systems 137

To ance increases to 1380 ohm, activating the warning
control circuit.
assembly
The monitoring capacity of the control unit can
Harness be increased with the addition of a further two ICs
connector dedicated to purely monitoring functions. These
additional monitoring ICs are dependent upon
(a) Friction the main assembly for the various timing signals
material which control the operating modes of warning
Brake pad lamps. Where a VCM system has or needs more
than twelve monitoring channels, however, it is
more economic and reliable to replace the discrete
ICs with a microprocessor.

Light defects (Fig 10.20)

material The monitoring of pertinent lights: stop lights;
tail lights; number plate light; low beam etc, may
(b) be done by separate or combined monitoring
units. Monitoring in these units is accomplished
Fig 10.19 Brake pads sensor either with electromagnetically operated reed
(a) When brake pad is not worn switches or with semiconductor devices (Fig
(b) When brake pad is worn 10.21).

and 1200 ohm, are housed in the wiring harness Reed switch monitoring (Fig 10.21(a))
connector to help differentiate between a dis- When the light circuits are operating the light's
connected sensor and a worn brake pad. current, flowing through the coil winding of the
monitoring unit, is sufficient to create an elec-
When the pad thickness is greater than 1.5 mm tromagnetic force to hold the normally closed
the resistance between the terminals is 180 ohm. reed. Switch contacts open, breaking the earth
When the pad is worn down, on the other hand, circuit of the monitor display lamp. If a light
the wire loop becomes open circuit and the resist- filament fails or an open circuit occurs in the
wiring no current can flow through the coil wind-

Warning lamp legend Feed in
Feed in
ii 1A 'i i Graphic ii Feed out
display

unit
it A

■\ 1 *r i ' 1r fi

12 sensors Vehicle condition w
monitoring
controller Lamp failure
monitor

1 "^

_ ! a r lit on fe ec

Fig 10.20 Condition monitoring system which includes lights failure detection

138 Automotive Electronic Systems

i A/1
n Pi-t__J[>-J
Φ1 8A

Ί Γp-O-O—i i Ö-

jßy φ/ φ/ φ/ φ/ e^j J-/

_4Tn 55W CXJ55W
5W 5W J21W 21W 5W I5W

Light switch Lights being Low beam control
monitored unit

(a)

Light being
P5 monitored

Fig 10.21 Light failure monitoring
(a) Reed switch
(b) Semiconductor

ing, closing the reed switch contacts, making the main beam and dipped beam blue
earth circuit of the monitor display lamp. side, tail and number plate white
rear fog, brake red
Semiconductor monitoring (Fig 10.21(b)) turn indicators green
When the light circuits are operating, transistor doors open red
Tj is on, preventing LED D2 from lighting up.
With a failed light filament or broken wiring Consists of:
circuit, transistor Tx is off and D2 lights up.
Headlamp main beam lamps -2 segments
VCM map displays Headlamp dipped beam lamps -2 segments
Side lamps - 2 segments
The vehicle map (Fig 10.22) is shaped like a car Tail lamps - 2 segments
viewed from the top, and graphically displays the Brake lamps - 2 segments
following information; door open; boot open; side Rear number plate lamp -1 segment
lamps; dipped beam; mean beam; turn indicators; Rear fog guard lamps- 2 segments
brake lamps; rear fog lamps; rear number plate Direction indicators- 4 segments
lamp. The various map functions illuminate when
their circuits are activated in different colours to Fig 10.22 MAP display layout
the outline colour (yellow) when the ignition is
switched on. Typical colours are:

Electronic control of body systems 139

provided there are no faults in the circuits. If a Service indicator
circuit or lamp is faulty the related map segment
is not activated, and is accompanied by other Oil service or service inspection intervals are usu-
VCM warnings drawing the driver's attention to ally determined by evaluating and storing input
parameters and summing their cumulative effects
the map for corrective action.
until the system decides a service is required.

Alternator monitoring In their simplest form service indicators take
account only of vehicle mileage and time since the

The condition of the alternator is monitored by last service. The more advanced, however, also

tapping into one of the phase windings to sense take account of the operating conditions to which
the phase output voltage comparing it with the the engine is subjected by including engine speed
battery output voltage, and generating a square and temperature as input parameters.

wave signal pulse (Fig 10.23). The VCM control Typical input parameters to the service indi-

cator control system are:

• engine speed - all speeds greater than

Battery 4500 r/min are recorded

output • engine temperature - each cold start is

Comparison monitored and all temperatures below

Phase Alternator 50°C are recorded, as measured by the
output pulse Ignition coolant temperature sensor

nJUUL pulse • time - the service due condition is always
displayed after approximately 11-12
Alternator Frequency counter months from the date of resetting after
and comparator

Warning the last service
display • distance - derived from the vehicle speed

Fig 10.23 Alternator condition monitoring system sensor: The distance driven since the last

service inspection.

unit compares the frequency of this square wave Turning on the ignition causes the electronic dis-

with the frequency of ignition pulses. There play to indicate the instantaneous state until the

should be a ratio of 7.5 alternator pulses for each next oil service or inspection (Fig 10.24). Initially

ignition pulse, because the alternator is geared, the interval to the next service may be 12,000

through the pulley ratio, to revolve 7.5 times as units; this decreases at the rate of 1 unit per mile

fast as the engine. If there are more ignition pulses travelled, or at a faster rate if high engine speeds

it means that the alternator drive belt is slipping; or low temperature starts occur. When more than

either through wear, incorrect tension or the rotor about 1200 units remain, the interval left until a

is starting to seize up, and the alternator is rotating service is due is displayed in green. Below 1200

at a slower than normal speed. If there are more yellow or orange segments display the interval.

alternator pulses this could be an indication of a When the service interval has been exhausted red

battery fault. segments and a 'service due' symbol is displayed.

DDDDDDDDDD <2r=*z&

Service

Fig 10.24 Typical service interval illuminating segments

140 Automotive Electronic Systems

The display is reset to full scale after the vehicle Ensure that these buffer batteries are fully charged
has been serviced. To ensure correct operation of before disconnecting. The resetting procedure
the service interval gauge (SIG) the calendar must must follow the manufacturer's instructions in
always be set properly before the SIG is reset, order to cancel the memory.
and after each battery disconnection. Some SIGs
employ the use of buffer batteries to ensure having Voice synthesis
the same display as before, after removing the
instrument panel or disconnecting the car battery. The voice synthesiser is an electronic device which

laSensors Radio

(O) Electronic control unit FT1■■ ■·'-1i

pr j^_■

£/* 1 Speech 1
ROM
Speaker
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harness socket
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Relay
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γΐ ι ^ Radio contact

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OK Ύ1 ^χ Synthesis contact

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(b)

Fig 10.25 Typical voice synthesiser VCM system
(a) Block diagram
(b) Circuit to allow voice message to cut-off audio output

Electronic control ofbody systems 141

uses a synthesised voice to warn the driver of Start address^ . Address bus
information or conditions which might not other­ Data bus
wise be noticed. Driving a vehicle imposes a very «=3
heavy visual load on the driver. The driver's hear­ Write Chip enable
ing is, however, less heavily involved and can be Busy Speech Speech
used as an information channel to support visual processor ROM
displays in conveying warnings to the driver of
critical vehicle operating conditions and/or trip ¥
computer information. This results in improved
safety as the driver is free to concentrate on obser­ Filter wLoudspeaker
vation ofthe traffic and road conditions, and better
driver information through the use of verbal mess­ Amplifier
ages accompanied by advice. ►

The voice synthesiser comprises an electronic Fig 10.27 Speech synthesis system
control unit fed by some 20 sensors (Fig 10.25) and
broadcasts its messages through either a separate The following functions are usually monitored
loudspeaker or the audio equipment fitted to the by voice synthesis VCM systems, with messages
vehicle. If the latter, the voice synthesiser message coming in three categories: 1 attention alerts; 2
takes precedence over the audio output. warnings; 3 information.

Messages can be synthesised in a number of Attention alerts
ways. A common way is to record, digitally, each Fall in oil pressure, engine overheating, charging
possible human voice sound (known as a system failure, braking circuit failure (repeated
phoneme) in ROM memory (Fig 10.26). Repro- every few seconds).

y - ^ Microphone Accoustic Warnings
y laboratory Low coolant level, low fuel level, stop light defec­
0=! tive, brake pads warning, side light failure, low oil
^ level (once after ignition is turned on, or every 10
Recorder minutes).

1 Information
Door not closed, light left on, handbrake not
Analogue to digital released, all functions working normally, or ser­
converter vice required (once only).

1r ► IC manufacturer The messages are also listed in order of broad­
cast priority. The low priority messages can be
Digital restricted from use, but not the high priorities.
speech analyser All phrases stored in the speech ROM can be
checked out by pressing the appropriate test keys.
1r To avoid unnecessary interruption while driving,
defects are announced only after a repeated
Speech ROM monitoring of the sensors. If the driver is to
be informed, a gong-type sound precedes the
Fig 10.26 Memorising speech data announcement. Important warnings begin with
words such as: attention; alert; or warning.
duction of a message is now possible by addressing
in turn each phoneme required to make up the
message, converting them all back to analogue
form, filtering to smooth out the stepped changes,
and finally amplifying (Fig 10.27). Special speech-
processor microprocessors and speech memories
are used.

142 Automotive Electronic Systems

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Computer and voice synthesis Main package

S O DL I STEAT

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LED 7ΓΤ TH <®>0<D» IF
driver Display multiplex drivers
Display rc—
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Keyboard
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Quartz /M
time
reference Microprocessor

Data Microprocessor Display L o 9 i c
highway Filaments
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English . Select Supply f
memory Voice » language 1
Power
31German synthesizer! Signal conditioning supply
Audio
French output —x—r

Italian

On/off Fuel level —
volume 1/1
Temperature—
Radio speaker
Speed — Switches Battery Ignition
Fuel
Engine speed - flow

(b)

Fig 10.28 A typical integrated driver information management system
(a) Display layout
(b) Circuit details

Electronic control of body systems 143

Driver information management 1I

Memory
software

Experience in vehicle electronics and advanced Sensors Signal TV
display technologies is leading to the implemen­ conditioning
tation of total information systems for the auto­ Microprocessor —► Character and
mobile. The first step is the addition of a trip 1i generator
computer to a vehicle's VCM system, common in
many of today's top-of-the-range models. Inte­ Timer 1 1Tf A I controller
grating all driver information functions into a T
single display is the next step. Indeed, a number 1 1
of examples of integrated systems already exist
(Fig 10.28). Keyboard 1 | v - CRT

Driver

The integrated driver information centre uses Fig 10.29 CRT-based driver information management
microprocessor-based control systems to selec­ centre block diagram

tively manage what the instrument panel displays.

It can also monitor conditions and give trip infor­ shown by climbing streams of green light, and bar

mation. Information can be backed up and pro­ graphs give information on fuel level and water

vided in speech form, and display of information temperature. There are also appropriately col­

can be either VFD, LCD or cathode ray tube oured warning symbols on oil pressure, water and

(CRT). oil temperature, low fuel level, battery condition,

Generally, the use of VFD or LCD means that icy conditions, supplemented by a verbal message
the style of the display and the symbols etc are from a voice synthesiser. Symbolic warnings for
predetermined and cannot be altered. The use of seat belts, heated rear window and bulb failure
CRT instrumentation, on the other hand, allows are provided, but these can be made inoperative
the use of computer controlled graphic displays by means of a delete switch.

and gives the benefits of both digital and analogue

instrumentation. Electronic controlled power seats
The CRT display has the appearance of a small

television tube, and indeed is based on the same In this application the microprocessor system is

principles except that it has specially formulated capable of storing four different seat positions in

phosphors and a special electron gun which make its memory, so that at the touch of a button it will

it suitable for use in automobiles. Data and graph­ move the seat backward and forward, up or down,

ics are presented on the screen in a sharp, clear back rest inclination and headrest height, repro­

format that is easily readable. When used with ducing exactly the position stored in memory.

filters information can be displayed in up to six The programmable memory registers 10
colours. A block diagram of a typical CRT-based different combinations of seat adjustments for
driver information management centre is shown each of the positions stored, enabling a single
in Fig 10.29. The centre monitors some 30 vari­ driver to code in a number of positions suitable
ables, has a 100K memory, and adjusts the inten­ for different types of driving, eg motorway and
sity of the displayed information according to town, or each of several drivers can code in their
ambient light. Although only one CRT is shown, own favourite position. In addition, the seat pos­
the centre can be used with more (some vehicle ition can be changed manually.
manufacturers are using the centre with three, Fig 10.30 shows the system in detail. Sensors
120 mm CRTs) to display more information.
are attached to the electric motor actuators which
A whole mass of information can be displayed. control seat movement and adjustment. With each
Typically, vehicle speed and engine rev/min are revolution of actuator gear the corresponding

144 Automotive Electronic Systems

Ι^,β Memory buttons +V Seat
switch
rmn tEuJ­ ^ M a n u a l adjustments 1 > —►Relay |
1000- Amplifier

[ Stopj Microprocessor

H3 H3 ""^■'i k

Recall
button

Analogue l—>
to digital
J | \ ^—<5>J
Pr><;itim1 ΐ
potentiometer
sensors

Seat lifting
device

(c)

Fig 10.30 Programmable power-seat positioning system
(a) Functional control diagram
(b) Block wiring diagram
(b) (c) Motors and actuating mechanism

sensor sends position information to the micro­ processor, and stored in RAM as a digital code if
processor, via an analogue-to-digital converter. the position memory key is then pressed.
The microprocessor compares the actual position
with the position requested by the driver, adjust­ If a position recall button is pressed the micro­
ing the seat accordingly until the difference processor assigns the corresponding seat pos­
between is zero. The position motors are driven ition codes to the program command and then
by signals from the output stage which operate compares these codes one after the other to the
the relays connecting the motors to the battery. corresponding sensor signals. If they are not the
The motors are arranged in two groups for seat same, the motors are driven in their appropriate
positioning: directions, until all match exactly. The seat will
then be in the correct position as memorised.
• group 1 - backward, forward, front
cushion height and the head restraint Two programs are provided to recall the four
stored seat positions:
• group 2 - backrest inclination and rear 1 recalling a memorised seat position auto­
cushion height.
matically: by pressing the pertinent recall
When one of the manual adjustment buttons is push button. The ignition switch must
pressed the control unit directly activates the be at position 1 (battery auxiliary) or 2
appropriate relay connecting battery voltage to the (ignition on) and the engine not running
motor, causing the seat to move position for as 2 recalling a memorised seat position with
long as the button is depressed. During this action the engine running and vehicle speeds
sensor signals are monitored by the micro- below 5mph: the position recall button