Cruise Control: Description and Operation
Design and Function
Introduction
The cruise control is controlled by sensors at various points throughout the car. The sensors send signals to the microprocessor in the control module, which processes their states and values. When a signal reads the appropriate value, a relay in the control module closes to feed power to the vacuum pump and regulator. During constant operation, the control module monitors and adjusts the system for optimum performance. The cruise control will not be activated at speeds less than approx. 22 mph.
Cruise Control System Consists Of The Following Components:
A. Speedometer(I/P)
B. SET switch on turn indicator lever
C. Selector switch on turn indicator lever
D. Vacuum valves: behind brake/clutch pedals.
E. Control module: located in the central relay module in the center console inside the car.
F. Stop (brake) light switch: brake pedal.
G. Vacuum pump with built-in regulator; in engine compartment.
H. Park/Neutral Position switch (automatic transmission only)
I. Vacuum servo: located in engine compartment.
Component Description
Cruise Control Switch
The cruise control selector switch is on the turn indicator lever. In order to set the desired speed, the selector switch must be in the ON position.
Adjust the speed of the car to the desired value, press the SET switch and the mise control will be activated. The car will maintain this speed until the brake/clutch pedal is pressed or the cruise control selector switch is set to the OFF position.
A temporary acceleration, such as when overtaking another car, does not affect the function of the cruise control. The car will maintain the speed that was set before the acceleration.
To change the speed setting, use the SET switch. Pressing the + or - switch corresponds to about 1 mph of acceleration or deceleration. The speed of the car when the SET switch is released is programmed into the cruise control system. 960, model year 1992 or later, has a switch with SET- and SET+; other cars have only the SET+ function.
To return to the last speed setting from the cruise control system, move the selector switch to the RESUME setting. The cruise control system will then automatically adjust the car speed to the previously programmed speed.
ON Turns on the cruise control.
OFF Turns off the cruise control.
RESUME Resumes last programmed speed.
SET Activates cruise control and sets programmed speed.
SET- Reduces programmed speed, pressing once corresponds to -1 mph.
SET+ Increases programmed speed, pressing once corresponds to +1 mph.
Vacuum Pump And Regulator
The vacuum pump with built-in regulator is located in the engine compartment.
The vacuum pump is driven by an electric motor controlled by a relay, activated by the control module when all conditions are met. The vacuum pump adjusts the vacuum in the vacuum servo to correspond to the programmed speed. Current speed is monitored by the speedometer, which sends a constant signal to the control module.
When an increased throttle opening is required, for example when driving uphill, the vacuum pump will supply the regulator with more vacuum until the programmed speed is reached. When driving downhill, on the other hand, the regulator will open its release valve to reduce the vacuum and decrease the throttle opening.
Vacuum Servo
The vacuum servo is located on the engine. It consists of a case and a diaphragm. Under vacuum, the rubber diaphragm is pulled into the case to control the throttle opening.
Vacuum Valves (pedal valves)
Older Valve
The older type of valve is adjusted by turning the threaded piston sleeve in or out to achieve the desired disengagement position.
New Valve
A spring-loaded piston activates a microswitch and a vacuum valve. The valve is self-adjusting, using small plastic tabs hook into the piston and adjust it to the proper position.
Identical vacuum valves are located on the pedal assemblies. During adjustment, the pedal is depressed to allow the piston to be pulled out. The pedal is then carefully released so that the piston is not pushed back too far. In the normal position, with the pedal up, the spring is compressed, the switch is on and the vacuum valve is closed.
When the pedal is depressed, when braking or releasing the clutch, the spring pushes the piston back, breaking the switch contact and thereby breaking the control module ground and opening its relay. Simultaneously, the vacuum valve is opened to allow atmospheric pressure into the system, disengaging the cruise control.
Stop (brake) Light Switch
The stop light switch is an extra safety device, in case the brake pedal is depressed and the vacuum valve does not open.
The stop light switch is normally open, but closes when the brake pedal is depressed. The control module is then grounded through the stop lights, and the cruise control system regulates the vacuum in the system.
Since the control module is grounded through the stop lights, they must be functioning in order for the system to work.
The stop light switch is located on the pedal assembly at the brake pedal. Newer model years 1995- have a new type of stop light switch, but it functions in the same way.
Schematic Description Of Disengagement Of The Cruise Control System
Disengagement is achieved by cutting power to the vacuum pump relay in the control module simultaneously with breaking the ground to the vacuum pump so that regulation of the system pressure ceases.
Disengagement:
Selector switch set to OFF.
Car speed falls below 22 mph.
Brake or clutch pedal is depressed, activating a control circuit through the pedal valve's electric switch.
Brake pedal is depressed, activating a control circuit through the stop light switch.
Park/Neutral Position (PNP) switch on car equipped with automatic transmission. In the P or N position, the PNP switch is closed, disengaging the cruise control system.
Safety disengagement provided by control module, occurs in the event of excessive acceleration (wheel spin) and excessive deceleration (locking of wheels after wheel spin). Disengagement also occurs when the engine is unable to maintain the set speed on a steep uphill (less than 75% of programmed speed).
Control Module
The control module of the cruise control is located in the central relay module in the center console inside the car.
1B Power supply
Control module power supply.
3B Ground
Control module ground connection
4B Diagnostics
Binary signals that can be both input and output
6B Stop (Brake) light
Battery power when brake pedal is depressed. When brake pedal is up the connection should be grounded via the stop light bulbs. The connection can also have supply voltage when the ignition is in the OFF position.
7B Vacuum pump
Activated when system is being controlled and speed is to be increased. Non-continuous ground with the frequency controlled by the control module.
8B Speed signal
Signal originates at the speedometer in the form of a sine wave. Transformed in the speedometer to a square wave with a frequency proportional to the speed.
9B Regulator
Activated constantly when the system is active and the speed is to be increased or held constant. When speed is to be reduced there is a non-continuous ground signal with a frequency regulated by the control module.
3E Park/Neutral position switch
Body ground through starter when gear selector is in the N or P position in a car equipped with automatic transmission. Battery power during starting.
4E SET+
Battery power when switch is in the SET+ position.
6E RESUME
Battery power when selector switch is in RESUME position.
7E Power supply to vacuum pump and regulator
A relay in the control module feeds battery power to the vacuum pump and regulator. The relay is operated when the system is operational, that is to say all input signals and internal safety functions have the value and status for approval by the control module.
8E SET-
Battery power when switch is in the SET- position.
9E Brake and clutch valve
Battery power when selector switch is set to ON or RESUME and brake and clutch pedals are up.