Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

Body Accessory Systems Operation 347
From fuse
panel
On
Off
Resume
Coast
Speed
control
switch
assembly
Speed
control
amplifier
Stop light
switch
Speed
sensor
From fuse
panel
From fuse
panel
Set
Accelerate
Speed
control
servo
Actuator
Connects ot
throttle linkage
Figure 15-49. Cruise control system component circuit.
(GM Service and Parts Operations)
Figure 15-48. Cruise control system schematic. (GM
Service and Parts Operations)
A vacuum-release valve is also used to disengage
the system when the brake pedal is
depressed.
Electrical and Vacuum Circuits
Figure 15-48 shows an electrical and vacuum circuit
diagram. The system operates by controlling
vacuum to the servo through various solenoids
and switches.
Electronic Cruise Control
Components
Cruise control can also be obtained by using
electronic components rather than mechanical
components. Depending on the vehicle manufacturer,
several additional components may
be used.
The electronic control unit is used to control
the servo unit. The servo unit is again used to
control the vacuum, which in turn controls the
throttle. The vehicle speed sensor (VSS) buffer
amplifier is used to monitor or sense vehicle
speed. The signal created is sent to the electronic
control module. A generator speed sensor may
also be used in conjunction with the VSS. The
clutch switch is used on vehicles with manual
transmissions to disengage the cruise control
when the clutch is depressed. The accumulator is
used as a vacuum storage tank on vehicles that
have low vacuum during heavy load and high
road speed.
Figure 15-49 shows how electronic cruise
control components work together. The servo
unit controls the throttle position, using a vacuum
working against spring pressure to operate
an internal diaphragm. The controller controls
the servo unit vacuum circuit electronically.
The controller has several inputs that help
determine how it will affect the servo, including
a brake-release switch (clutch-release switch),
a speedometer, a buffer amplifier (generator
speed sensor), a turn signal lever mode
switch, and speed-control switches on the steering
wheel.
SUPPLEMENTAL
RESTRAINT SYSTEMS
A typical supplemental inflatable restraint
(SIR) or air bag system (Figure 15-50) includes
three important elements: the electrical system,
air bag module, and knee diverter. The electrical
system includes the impact sensors and the electronic
control module. Its main functions are