Auto Electricity and Electronics, 6th Edition Page 406 (406 of 768)

406 Auto Electricity and Electronics
Copyright by Goodheart-Willcox Co., Inc.
Figure 21-15. Note how the large servo motor mounts on a rack-and-pinion steering assembly. ECM can drive the motor to reduce
steering effort or to even steer the vehicle with an automatic parking system. (Honda Motor Co.)
Ground
Terminal
O-Ring
Motor
Torque Sensor
Assembly
O-Ring
Rack Guide
Disc Washer
Locknut
Rack Guide Screw
Spring
Gearbox Mount Cushion
Gearbox Housing
Mount Cushion
Torque Sensor
Figure 21-16. This is one type of steering sensor. It uses two
light emitting diodes (LEDs) and two photo transistors. Slotted
disc rotates with the steering wheel and steering shaft. As holes
pass between the LEDs and photo transistors, the photo transis-
tors are energized and produce electrical signals that represent
steering action.
Photo
Transistors
Light Emitting
Diodes
Steering
Action
Slotted Disc
Connected to
Steering Shaft
Figure 21-17. Auto park system normally uses an infrared sen-
sor to measure distances behind the vehicle to allow the parking
ECM to steer and drive the vehicle into the parking space auto-
matically. (Siemens)

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406 Auto Electricity and Electronics
Copyright by Goodheart-Willcox Co., Inc.
Figure 21-15. Note how the large servo motor mounts on a rack-and-pinion steering assembly. ECM can drive the motor to reduce
steering effort or to even steer the vehicle with an automatic parking system. (Honda Motor Co.)
Ground
Terminal
O-Ring
Motor
Torque Sensor
Assembly
O-Ring
Rack Guide
Disc Washer
Locknut
Rack Guide Screw
Spring
Gearbox Mount Cushion
Gearbox Housing
Mount Cushion
Torque Sensor
Figure 21-16. This is one type of steering sensor. It uses two
light emitting diodes (LEDs) and two photo transistors. Slotted
disc rotates with the steering wheel and steering shaft. As holes
pass between the LEDs and photo transistors, the photo transis-
tors are energized and produce electrical signals that represent
steering action.
Photo
Transistors
Light Emitting
Diodes
Steering
Action
Slotted Disc
Connected to
Steering Shaft
Figure 21-17. Auto park system normally uses an infrared sen-
sor to measure distances behind the vehicle to allow the parking
ECM to steer and drive the vehicle into the parking space auto-
matically. (Siemens)

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Chapter 21 Chassis System Electronics 407
Copyright by Goodheart-Willcox Co., Inc.
When the car body is at a normal or riding height,
the electronic height control system is off. Air pressure in
the shocks is adequate to keep the car body the correct
distance from the road surface. The height sensor does not
feed current to the compressor or solenoid.
If the trunk is loaded with heavy luggage for example,
the added weight will compress the rear air shocks. This
will make the ride height too low. When the car is started,
the sensor link “mechanically informs” the height sensor of
the low ride height condition by closing the sensor switch
contacts. The compressor motor turns on and pumps more
air pressure into the rear shock absorbers. This extends the
shocks and raises the car body.
When the specifi c ride height is reached, the height sen-
sor switch opens to turn off the compressor. This restores the
previous ride height, even with extra weight in the trunk.
When the weight is removed from the trunk, the car
body would tend to rise. The height sensor switch is then
moved in the other direction by the link. This closes another
set of contacts in the switch and energizes a pressure release
solenoid valve. Air pressure is then expelled from the rear
shocks until the body drops down to the correct ride height.
Electronic Shock Absorber Systems
An electronic shock absorber system uses various vehi-
cle sensors, an ECM, and shock absorber actuators to control
ride stiffness. It is designed to increase comfort and safety by
matching suspension system action to driving conditions. See
Figure 21-19.
Although exact designs vary, the major components of
a typical electronic shock absorber system are:
Steering sensor—detects steering wheel rotational
direction and speed to feed data about the vehicle
direction to the ECM.
Brake sensor—usually a brake light switch that reports
when brakes are applied.
Acceleration sensor—usually a throttle position sen-
sor that detects when the car is accelerating rapidly.
Mode switch—dash switch that allows the driver to
input the desired shock action or ride stiffness.
Figure 21-18. Infrared sensor sends out invisible light that
bounces off of objects behind or in front of bumpers. The time
it takes for the light to refl ect off of objects is used by the park-
ing ECM to avoid hitting objects while automatically parking the
vehicle. (Bosch)
Parking Assistance
(Parkpilot)
Figure 21-19. Block diagram shows how various sensors feed electrical data to the ECM. ECM can then energize the shock actuators
to control ride stiffness and shock action. (Toyota)
Sensors
Selector Switch
Speed Sensor
Steering Sensor
Stop Lamp Switch
Neutral Start Switch
(A/T Vehicle)
Throttle Position Sensor
ECU
Shock Absorber
Control
Computer
Shock Actuator
Shock Actuator
Shock Actuator
Shock Actuator
TEMS Indicator

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Chapter 21 Chassis System Electronics 405
Copyright by Goodheart-Willcox Co., Inc.
Figure 21-14. Study the major parts of an electric assist power steering system. (Honda Motor Co.)
Under-Hood Fuse Relay Box
Data Link
Connector (DLC)
Battery
Steering ECM
Rack-and-Pinion
Assembly
Motor
Under-Dash
Fuse Relay Box
Gauge Control
Module (TACH)
EPS Indicator
Since the time between sending a pulse and the time
it takes for the pulse to bounce off objects, the ECM can
calculate the distance between the car and the object. Four
ultrasonic or video sensors are mounted in the four corners
of the bumpers. They all work together to allow the ECM to
move, steer, and stop the vehicle when parking.
Electronic Height Control
An electronic height control system uses a height
sensor to control the operation of a small electric air com-
pressor. This type of system is used on the rear of the car to
compensate for loads placed in the trunk or when passengers
fi ll the back seat. These parts include:
Height sensor—lever-operated switch that reacts to
changes in car body height and suspension movement.
Compressor assembly—electric motor-powered air
pump that produces pressure for the system.
Pressure lines—air hoses that connect the compressor
with air shock absorbers.
Air shocks—air-filled shock absorbers that can act on the
suspension system to alter the ride height of the car.
Sensor link—linkage rods that connect the height sen-
sor to the suspension system.
Solenoid valve—solenoid-operated air valve that can
release air pressure from the system.

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