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

Electronic control of body systems 145

must be pressed and held until the stored Finally, the system is protected against open or

seat position has been carried out com­ short circuit sensor leads and faults in the relay

pletely. At speeds above 5 mph the control output stages. A stop button is provided to switch

unit does not allow seat positioning using off the entire system in case of malfunction. The

either the programmable or manual stop button can also be used to interrupt each

switches. unwanted seat position action.

A LED gives a visual indication of the control

action taking place:

• storage of seat position when the memory Electronic control of interior temperatures
button is being pressed - the LED flashes

at a high frequency The use of micro-electronic heater control tech­

• seat being adjusted under program con­ niques has increased the accuracy of vehicle tem­

trol - LED on continuously until the seat perature regulation, consequently improving

position has been reached driver and passenger comfort. Electronic control

• seat reaches stored position - LED can compensate for temperaturefluctuationsdue

flashes at a slow frequency. to different engine speeds, driving speeds and

Certain safety precautions are provided to protect outside temperatures. It can provide rapid heating

the system against incorrect operation. Operating of the interior after a cold start and reacts quickly

a different recall button during programmed seat to the desired change in temperature. Control may

adjustment immediately stops the system: the also be extended to an air conditioning system

appropriate button must then be pressed to com­ which both cools the air and removes moisture

plete seat adjustment. Manual control always takes from it, so maintaining an even more constant

precedence over programmed control. interior environment - particularly in hot weather.

Cold air

Interior sensor

Heat exchanger
Discharge sensor1

Warm air

Fig 10.31 Electronic heating control system

146 Automotive Electronic Systems

Heater control two sensors are fed to the control unit for com­
parison with the desired temperature.
Vehicle heating systems regulate the interior tem­
perature simply by changing the amount of hot The desired interior temperature is selected by
water passing through a heater radiator (heat ex­ rotation of a potentiometer, which incorporates a
changer). A control valve regulates the flow rate limit switch for continuous heat and an off switch
of the hot water. An electronic automatic heater for no heat (i.e. cool air).
system is shown in Fig 10.31 and comprises
sensors, actuators, control unit and a temperature Control unit
selection potentiometer.
Fig 10.32 shows a block diagram of the system,
Temperature sensors illustrating the control unit in detail. The two
temperature sensor signals are evaluated with the
Quality of control depends mainly upon the pos­ desired temperature signal, and are then compared
ition and response time of the temperature with a reference voltage provided by the sawtooth
sensors. Two NTC thermistors are used: one to voltage generator. The electrical pulses obtained
measure the interior temperature (located so that by this comparison are amplified in the driver
air from the vehicle interior is continually being circuit to operate the power output transistor.
forced over the sensor to ensure a rapid response); The power transistor earths the regulated voltage
the other to monitor the temperature of the air supplied to the solenoid valve.
being discharged from the heat exchanger into the
interior (located as close to the discharge vent of Actuator
the exchanger as possible). The signals from these
The hot water solenoid valve actuator (Fig 10.33)

Hot-water
valve

Φ4

Interior JΓ^>f J Γ^ T>Hteemapt eerxacthuraenaer Power Switch position to the
temperature LJ L_l sensor output left stop: heating system
sensor stage gives maximum cooling

Switch position to the
right stop: heating system
gives maximum heating
Limit switch
on the
potentiometer

Fig 10.32 Electronic control unit for automatic heater

Electronic control of body systems 147

Armature Spring Ventilation control
Coil
Sealing cone Two additional functions are adjusted in the ven-
Bore tilation system:
1 air flow
Main sealing 2 air distribution.
cone Potentiometers are used to signal the driver's
desire for air flow rate and distribution to the
Fig 10.33 Hot water solenoid valve actuator control unit. By means of an electronic pulse gen-
erator, whose output frequency is proportional
is operated by pulses from the control unit. Pulse to the air flow rate potentiometer's position, the
length (and so the valve open time) depends on the rotational speed of the fan motor can be con-
difference between the actual interior temperature tinuously varied. DC motor actuators, or solenoid
and the desired temperature. When the valve is operated pneumatic actuators, are used to adjust
open, hot water from the engine passes to the heat the position of air flaps for air distribution (Fig.
exchanger. 10.34).

Pushing the defrost button instructs the control
unit to adjust the heating system for maximum
heat, and to direct the whole air flow to the wind-
screen with the blower at maximum speed.

Pressing the ambient air button interrupts the
supply of fresh air from outside the vehicle, while
heating and blowing continue to function as
requested by the driver.

Heating and air conditioning

Interfacing the heating and ventilation system
with an air conditioning system provides a total

Outside
air inlet

Defroster door

Blower fan Floor door
motor Foot area

Fig 10.34 Ventilation control

148 Automotive Electronic Systems

system that will accurately maintain a desired level, thereby preventing 'fogging' on the wind-
interior temperature level, whatever the environ- screen. As the engine coolant temperature rises
mental conditions. In effect, cooling as well as high enough for the heater to be used, the outlet
heating is controlled. flaps are automatically actuated, and the control
unit maintains temperature of the desired level.
Air conditioning systems operate on the same
principle as domestic refrigerators. A refrigerant When defrost is switched on, manually, the air
coolant gas is alternately compressed and flow is automatically set to maximum by pulsing
expanded (Fig 10.35). The gas is first compressed the blower. This can, however, be overridden and
switched to minimum, manually. Signal lamps
Condenser indicate the mode of heating and ventilation being
used.
jifpCompressor Orifice
Pressure switch tube Air conditioner (A/C) systems generally have
*/ three main switches, one to turn the A/C on and
u off, a fan switch to turn the blower on and off and
the temperature select switch. When the A/C is
Dehydrator/ ^ switched on the control unit maintains the desired
accumulator temperature by engaging or disengaging an elec-
tromagnetic clutch in the compressor. When
Evaporator engaged the refrigerant is pumped around the
circuit to maintain the coolness of the interior.
Fig 10.35 Refrigeration process as used in air The compressor clutch is automatically dis-
conditioning systems engaged when the outside temperature is below
0°C. Air flow direction flaps are also automatically
by a pump (the compressor) and cooled in a con- controlled (Fig 10.36(b)).
densor, where it liquefies. It is then passed into an
evaporator where it expands and boils, absorbing Some A/C systems have a feature which
heat from the surroundings - the evaporator is advances the vehicle's ignition timing when the
thus cooler than the environment - and back to A/C automatic mode is selected. This improves
the compressor. engine torque and compensates for the increased
load on the engine due to the A/C. If switched to
By blowing air across the evaporator the vehicle economy mode, interior cooling is carried out by
interior can thus be made cooler than the external simple ventilation using the outside air only (or
temperature - something which an ordinary heater interior air if the recirculation switch is used) and
and ventilation system cannot do. the compressor is switched off.

Vehicle interior temperature sensors are Safety circuits
installed at head and foot height. An exterior A refrigerant leak warning device is built into the
sensor is mounted at the front of the vehicle to A/C system. Its purpose is to prevent damage due
monitor the ambient air temperature, while the to continued operation when there is a shortage
amount of sunlight is monitored from a solar of refrigerant, and also to indicate when to replen-
sensor attached to the outside surface of the ish the refrigerant. The sensor for the leak warning
vehicle body (Fig 10.36(a)). system (Fig 13.37) is generally located in the pres-
sure switch.
When starting the engine in cold weather the
system immediately operates in the defrost mode If there is insufficient refrigerant, then what
until the coolant temperature rises to a preset refrigerant is inside the evaporator vaporises much
more quickly, with a corresponding increase in
temperature and pressure of the refrigerant at the

(α) Potentio balance resistor 2 (PBR2)
Potentio balance resistor 1 (PBR1)

Temperature setting switch | O- l i ^ — - N Co mpressor Fan motor
—►^2225 magnetic clutch
ί Intake door
Set temperature adjuster o-czf>*| Fan control unit
Sunload sensor S Ventilator door
Solenoid valve Air mix door
Vacuum actuator
ft Floor door
(foot) -^3-Control Power servo Air mix door
In-vehicle sensorC unit —£3- Power servo
Vacuum actuator ί Ventilator door
(head) -w Vacuum actuator Air mix door

Water temperature switch ff Floor door

Ambient temperature sensono-

Duct • In-floor ft Water cock
temperature duct sensor
sensor Digital indicator ι c . . 7" Data no]
i —* — H Set temperatL
· In-vent When
checking Data |
duct sensor|
C

• During self-diagnosis

When
co mpressorn
is ON
...lights

Refrigerant leak E§>ft WxWhen ambient When flowing from defroster...lights
warning lamp When flowing from ventilator...Ughts
When refrigerant is air enters... lights When flowing from floor nozzle...lights
insufficient ...lights A/C A/C 5>
When recirculating 2^
inside air... lights U£A2J ///

r*gS

When intaking both inside Air flow indicator
(b) and outside air... lights

Fig 10.36 Typical electronically controlled air conditioner

(a) Control system block diagram
(b) Schematic layout of input switched and controlled actuators

150 Automotive Electronic Systems

occurs, however, when the amount of refrigerant
is low.

Self diagnosis

A self diagnosis mode is typically provided to

Adjusting locate simple faults in the input and output
nut circuits. When switched to diagnostic mode the

temperature display is used to indicate the sensor

and circuit being checked, and a coded message

of their conditions (Table 10.1). The temperature

set buttons are used to switch to the input circuits

to be checked.

The diagnostic mode checks the operation of

the output circuits by sequentially operating the

Refrigerant Temperature six actuators; moving them between stoke ends or
(gas) sensor changing all positions. Satisfactory operation can
be determined by applying a hand to the outlet

Fig 10.37 Temperature and pressure sensor used iadnnoldoorwl,oookbisnegrvaitngthethoepeariratfiolonw, oirnbdyicamtoera,sulrisintegnitnhge
refrigerant warning system ofan air conditioner applied voltage.

outlet. Whenever the coolant temperature exceeds New developments
40-45°C a time delay circuit is activated. If acti-
vated for more than 60 seconds the time delay Air conditioning compressors which automatically
turns on a warning light. This delay prevents vary displacement to match cooling demands are
incorrect signals being displayed as would occur, now being fitted to new vehicles. No on-off cycling
say, during rapid acceleration when there is a of a magnetic clutch is necessary in such com-
corresponding rapid rise in refrigerant tempera- pressors and fewer circuit variations are required
for cutting out the compressor load to match com-
ture. A steady state increase in temperature only binations of operating conditions - giving up to
2mpg improvement in fuel economy.

Table 10.1 Self-diagnosis fault display code and associated component part.

Display no. Item of input signal Parts name

0 Temperature of inside air temperature sensor In-vehicle sensor (foot)
(foot)
1 In-vehicle sensor (head)
2 Temperature of in-vehicle sensor (head) Floor duct temperature sensor
3 Temperature offlooroutlet Ventilator duct temperature sensor
4 Temperature of ventilator outlet Defroster duct temperature sensor
5 Temperature of defroster outlet Water temperature SW
6 Water temperature SW display ON-OFF Sunload sensor
7 Sunload Set temperature adjuster
8 Width of objective temperature PBR2
9 PBR 1
10-15 Position of A/M door 2 No meaning
Position of A/M door 1
No meaning

11

On-board diagnostic techniques

The complexity of many electronic control sys­ Self diagnostics is not without its own peculiar
tems requires that self-diagnosis of system failures problems and could itself be a source of a fault.
be included in the software program. Basically the As a first step in establishing the self diagnostic
diagnostic routine alerts the driver, through a requirements, the failure modes and their effect
warning indicator, that a failure has occurred and on the vehicle must be analysed:
service is required. The diagnostic system can also •
be an aid to the service technician in pinpointing disabling - a failure which prevents oper­

the problem area. This is useful because fault­ • ation of the vehicle

finding in microprocessor-based systems is detectable degradation - a failure that

different to that in analogue and other digital logic • results in poor vehicle performance

circuits, and a number of problems are decidedly undetectable degradation - a failure

peculiar to microprocessor-based systems: which causes the system to operate out­

1 operation depends on the flow of a side the normal parameters, but is not

sequence of instructions. If a single pro­ • discernible

gram bit or byte is in error the whole inconsequential - a failure which has no

system may lock out - noise and bad effect on performance under normal con­

memory bits are common sources oferror. ditions but could result in poor per­

These failures are difficult to pinpoint formance under a multiple failure situ­

ation.
because the whole system may operate Self-test diagnostic software, though requiring
incorrectly.
additional memory, provides a flexible and low
2 signals within the system can be in excess cost solution to fault-finding. Most systems, how­
of 5 MHz, which makes it difficult to ever, still use a degree of hardware to minimise
obtain meaningful results
the functions which would disable the system if
3 use of bus structures makes it possible software problems occur. Typical fail-safe hard­
to connect many complex devices to a ware solutions are found in electronic fuel and
common line - any error signals are thus ignition systems, to maintain operation (albeit
routed to all devices
to a limited degree) when failure occurs in the
4 the faults can either be software or hard­ microprocessor due to software problems.
ware induced, though if the system has In general, self-test diagnostic routines:
been in use for some time the fault is more 1
likely to be due to a hardware component inform the driver a fault has occurred, by

failure. illuminating an indicator.

2 store a specific code for the fault in non-

152 Automotive Electronic Systems

volatile memory for later read-out by the operation. This is done by establishing a precise

service technician, as a fault location aid. set of operating conditions.

3 maintain system operation and bypass the

faulty element by either substituting a

fixed value for the failed element (e.g. if Service diagnostic techniques
the temperature sensor system fails a fixed

temperature is used) or by placing the Most on-board systems have to be switched to

control function units in normal operating diagnostic mode to enable the service technician

state and thus disabling the faulty sub­ to read out the faults logged by the self-diagnostic

system (e.g. if the oxygen sensor fails the routine. Read-out is by flashing the stored error

closed-loop fuel control is disabled). codes via the fault indicator display, or (where off-

In most systems value substitution is usually board computer interfaces are used) by presenting

made to maintain the basic vehicle functions. the error codes numerically. Using the fault code

Function disablement is only used to prevent documentation the fault can then be isolated to a

abnormal operating conditions. specific element.

Transient and intermittent faults are a sig­ Additionally, discrete input and output tests

nificant problem for on-board fault diagnosis: as can be initiated by the service technician which

they are usually very difficult to trace, particularly cause the input to be activated in a prescribed

when relying on the driver to describe the symp­ sequence. An indication is provided for each cor­

toms. The memory which would be required to rect input. In the output test mode output signals

record all transient faults and their characteristics are generally cycled on and off to check the proper

would be huge and thus very expensive, therefore operation of the actuators.

only limited facilities for this are provided: In vehicles with digital displays diagnostic rou­

• all major faults are recorded in memory tines are often provided to evaluate the sensor

• self diagnostic test failures are recorded subsystems from transducer through the control

only if detected over a number of specific unit itself. Certain performance data such as spark

tests advance, fuel delivery, number of engine starts

• all short duration transients are ignored etc, since last recorded fault may be available, also,

• fault indication is only used for active for display.

faults Self-test diagnostics are not usually provided

• memory is cleared if no additional faults for system failures where it is not possible to
are detected within a number of specified establish test conditions due to insufficient data,
cycles.
and for which it would be impractical to collect
Obviously, the diagnostic software must dis­ the data. These tests, though, are usually covered
tinguish between a fault condition and normal by the service technician's input and output tests.

Index

Acceleration sensor, 114 Ball-in-race flowmeter, 22
Accelerometer, 29 Body roll, 113
Accumulator, 109 Bosch-Pierburge carburettor, 72
A/C safety circuit, 148
A/C temperature pressure sensor, 150 operating features, principles, 73
Active suspension, 113 Brake pressure actuator, 107
Actuators, 33 Brake pressure cycle, 111
Brake pad wear warning, 137
DC motor, 35 Brakes, 8
electro-pneumatic, 38 Brake solenoid valve, 107
linear motor, 36
relay, 35 Carburettor, 4
servo motor, 36 Capacitive sensor, 16, 21
solenoid, 35 Capacitor action, 15
stepper motor, 37 Choke actuator, 68
torque motor, 37 Clockwise torque action, 38
Adaptive suspension, 113 Clutch, 7
Advance mechanism, timing, 6 Cold start injection, 78
Air conditioning system, 148 Coolant level sensor, 31
Air-flow sensors, 17, 18 Coolant temperature measurement, 129
Air-fuel ratio, 121 Coolant temperature sensor, 61, 69
Air quantity, 80 Comparator, 55
Air pressure sensor, 20, 21 Constant energy ignition, 54
Air temperature sensor, 69
Alternator control characteristics, 42 characteristics, 56
DC dwell bias, 56
three phase voltage curves, 39 CPU, 10
field diodes, 41 Crankshaft position sensor, 61
condition monitoring, 139 Cruise control, 99
Alternator voltage generation, 39 Current regulations, 83
Aneroid pressure sensor, 15, 20
Anticlockwise torque action, 38 Darlington transistor, 43, 44, 52
Antilock braking system (ABS), 101 DC dwell bias, 56
Antiskid braking system, 102, 103 DC motor, 35
Automobile component parts, 1 Demultiplexer, 129
Automobile layout, 1 Detonation, 28
Automobile system, 1 Detonation sensor, 62

154 Index hot wire, 30
reed switch, 31
Diesel engine, 2 resistive fuel volume, 29
Differential, 7 Four stroke cycle, 3
Digital fuel injection, 84 Fuel consumption graph, 65
Digital ignition system, 57 Fuel cut-off, 70, 75
Digital speedometer, 127 control principle, 71
Diode, power, 42 solenoid, 34, 70
Distributor, 6 Fuel distributor pipe, 89
Dive, 112 Fuel filter, 88
Drive shaft, 7 Fuel flow sensor, 21, 22
Driver information, 127 ball in race, 22
Duty cycle signal, 38 gear, 22
Dwell period control, 50, 51, 55, 59 piston, 22
turbine 21
Electronic accelerator, 119 Fuel ignition control, 91
Electronic carburettor, 66 Fuel injection, 75
Electronic choke control, 66 Fuel injection systems, 75
Electronic controller, brakes, 103 electronic control, 77
Electronic fuel control, 65 multipoint, 77
Electronic gear box throttle body, 76
Fuel injector, 89
automatic, 93 Fuel injector solenoid, 34
manual, 92 Fuel level measurement, 129
Electronic ignition maps, 59 Fuel metering, 4
Electronic ignition system, 46, 48, 49, 53 Fuel pressure regulator, 88, 89, 122
Electronic suspension, 113, 114 Fuel pump, 87
Electronic voltage regulators, 43 Fuel supply, 4
high voltage operation, 44 Fuel system performance comparison, 76
low voltage operation, 43 Frequency divider, 80
Electro-pneumatic actuator, 38
construction, 38 G-ball, 104
operating principle, 38 Gearbox, 7
Engine details, 2 Gear change schedule, 98
CI engine operation, 2 Gear type flowmeter, 22
fixed parts, 2 Generalised control system, 9
IC,SI classification, 2 Generator system, 39
Engine management, fuel/ignition, 91
Engine management systems, 117 Hall effect principle, 15, 16
Equivalence ratio, 26 Hall generator, ignition, 53
Excess air factor, 26 Hall generator, signal, 54
Execute cycle, 11 Heating and air conditioning, 147
Exhaust emission, graph, 65 Heating control, 145
Exhaust gas composition, 26 Hot wire airflow sensor, 18, 87
Exhaust gas oxygen sensor, 26 Hybrid voltage regulator, 44, 45
Exhaust gas regulator (EGR), 120 Hydraulic actuator, 109
Hydraulic modulator brakes, 109
Fetch cycle, 11
Field excitation current, 43 Idle speed control, 74, 79
Filtering, 42 Ignition advance/retard, 6
Final drive, 7 Ignition capacitor action, 6
Fluid level management, 134
Fluid level sensors, 29

AC impedance, 30
capacitive, 30

Ignition coil, 46 Monolithic integrated circuit, 44
winding/voltage ratio, 46 Motion sensors, 22

Ignition coil action, 5 Hall type, 23
Ignition, constant energy, 55 optical, 23
Ignition, digital, 57 Wiegand, 23
Multiplier, 79, 80
distributorless, 63 Multivibrator, 79
microprocessor signal processing, 58, 59
Ignition, electronic control unit, 49, 50 Oil level sensing, 31
operation, 54 Oil pressure measurement, 130
Ignition, push pull coil, 64 Oil pressure sensing, 21
Ignition spark energy, 46 Optical displays, 126
Ignition system, 5
capacitor action, 6 Piezo-electric accelerometer, 29
coil action, 5 Piezo-electric effect, 39
Kettering principle, 5 Piston flow meter, 22
Ignition timing, 6 Potentiometer sensor, 17, 20
Inductive sensors, 24 Power diodes, 42
AC excited, 25 Power seats, 144
D C excited, 25 Power switching, 52
quenched oscillator, 25 Pressure sensors, 15
variable reluctance, 24
Inertia switch, 88 aneroid, 15
Information management, 142 capacitor, 16, 20
Instruction register, 11 Hall effect, 15, 16
Instrumentation, 126 LVDT, 15,61
Instruments (electrical), 8 oil pressure, 21
Interior heating control, 146 piezo-electric, 17
Interrupts, 11 semiconductor, 17, 21
Wheatstone bridge, 17
Kettering ignition principle, 5, 46, 47, 48 Primary winding, 47
Knock control, 62 Programme counter, 11
Knock sensor, 28, 62 Propellor shaft, 7
Pulse control, 81
Lambda oxygen (02) sensor, 26, 121 Pulse shaping, 50, 56, 80
Light failure monitoring, 137, 138
Linear variable differential transformer, 15 Quenched oscillator, speed sensor, 25
Logic levels, 136
Lotus active ride, 116 Random access memory (RAM), 58
Read only memory (ROM), 58
Map displays, 138 Rectification, 40
Mask programmable, 10
Measurand, 9 bridge rectifier, 41
Memorized seat position, 144 full wave, single phase, 40
Memory, 11, 84 half-wave, single phase, 40
Memory tables, 11 three phase, bridge, 41
Microprocessor based brake control, 104 Refrigeration process, 148
Microprocessor based cruise control, 100 Register, 11
Microprocessor based system, 10 Relays, 34
Microprocessor based transmission, 99 Reluctance, 49
Microprocessor, fuel injection, 85 effect of air gap, 49
Microprocessor operation, 11, 84 reluctor signal, 49
Mixture supply, 4 Retard mechanism, 6
Roller cell, 87

156 Index Three phase windings, 39
delta connected, 40
Rotary solenoid, 38 star connected, 40

Schmitt trigger, 50 Throttle actuator, 101
Secondary winding, 46 Throttle body, 87
Self-diagnosis, 151 Throttle body injector, 76

software, 151 fuel injector system, 76
test routine, 151 Throttle speed sensor, 115
Self-induction, 43 Titanium oxide EGO sensor, 27
Self-limiting, 43
Semiconductor sensor, 17 construction, 28
Sensors, 9 Top dead centre (TDC), 6
Siesmic mass, 29 Torque, clockwise duty cycle, 38
Signal conditioning (ignition), 54
Signal generator, 48, 49 anticlockwise duty cycle, 38
Hall effect, 53 Torque motor, 38
magnetic, 49 Torque motor duty cycle, 38
photo-electric, 50 Transmission control, 95, 99
Solenoid actuators, 33 Trip data systems, 131
flat faced, 33 Trip ECU, 133
plunger type, 33 Trip operation, 132
Solenoid characteristics, 34 Turbine flowmeter, 21
Solenoid principle, 33 Turbocharger control, 91
Speech memory, 141
Speech synthesis, 141 solenoid actuator, 92
Squat, 112
Steering sensor, 114 Valve timing actuator, 93
Steering system, 7 Variable reluctance, 24
Stepper motor, choke action, 66, 70 Variable valve timing control, 93
Stroke sensor, 114 Vehicle handling, 123
Subroutine, 11 Vehicle condition monitoring, 134
Suspension actuator, 114 Vehicle service monitoring, 139
Suspension control, 112 Ventilation control, 147
Suspension system, 7 VLSI, 10
Systems, 9 Voice synthesis, 141
cause, 9 Voltage correction, 82
closed loop, 10 Voltage stabilising ignition, 51, 52
effect, 9 Volumetric efficiency, 87
input, 9 Vortex airflow sensor, 19
open loop, 10
output, 9 Wastegate, 91
process, 9 Water solenoid actuator, 147
Wheatstone bridge, 17
Tachometer, 129
T E M C S , 117 Zener controlled dwell period, 52
Temperature sensor, 13 Zener diode, 43, 83, 84
Thermistors, 13 Zirconion oxide cell, 26
Thermocouples, 14 Zirconion oxide E G O sensor, 26

construction, 28