Electrical Overview
Electrical Overview
Control module (1)
The control module compares the selected speed with the actual speed. If necessary, the control module activates a vacuum pump or regulator. These in turn control a vacuum servo. This servo is connected to the accelerator pedal (AP) and therefore controls vehicle speed.
The cruise control module maintains the set speed until it is disengaged. SET+ or SET- changes the speed stored in the memory.
The control module incorporats several safety functions. These prevent damage due to system failures. The vehicle speed must be in excess of 35 km/h (22 mph), the selector switch must be in the ON position, and the SET button must be pressed in before the control module can operate the vacuum pump relay. If the car has an automatic transmission, the control module is switched off when the gear selector lever is in the P or N positions.
In addition to the electrical safety functions, there are several pneumatic safety devices, see Vacuum control.
The control module monitors the system and disengages cruise control during abnormal acceleration (wheel-spin) or deceleration (wheel lock). The control module also disengages the system if the vehicle speed drops below 75% of the selected speed. This may occur when driving up steep slopes when the engine is unable to maintain a constant speed.
Another important control module function is to store diagnostic trouble codes (DTCs). This allows the system to be fault-traced using the VADIS PC. In order to operate correctly, the control module requires several sensors. These are described below with their functions.
Stop (brake) light switch (2)
The stop (brake) light switch acts as an extra safety device in case the brake pedal is depressed and the vacuum valve does not open. When the brakes are used, the control module is no longer grounded via the stop (brake) light bulbs; the system is disengaged. If the bulbs are defective, the cruise control will not operate. Always check the stop (brake) light bulbs first if there is a fault in the system.
Pedal valves (electrical) (3)
These are located above the brake pedal and clutch pedal (manual transmission). They have the same function as the stop (brake) light switch. They cut off the voltage to the pump and regulator in the pump unit. This opens the pump regulator and allows air into the vacuum system. In its normal position, when the pedal is up, the valve is closed.
The pedal valves are combined electrical / vacuum valves. When the pedal is depressed, the vacuum circuit is also broken. See vacuum control.
Switch
The switch incorporates:
- a switch for switching the system off and on
- two buttons to increase and decrease the vehicle speed.
- a sliding switch to resume the selected speed.
Vacuum pump and regulator (5)
If vehicle speed drops below the selected speed, the vacuum pump is turned on and the vacuum in the servo increases. The servo presses down the accelerator pedal (AP) a little and the vehicle speed increases again. If the vehicle speed exceeds the set speed, the regulator allows air into the vacuum system, reducing the vacuum. The vacuum pump is driven by an electric motor. This is switched on when the SET+ button is pressed in and the control module relay is engaged. The motor drives the pump until the vacuum servo has a sufficient vacuum to maintain the selected speed.
When extra power is required, when driving up a hill for example, the vacuum pump is switched on again in order to increase the system vacuum until the selected speed is achieved. When driving downhill, the regulator vacuum valve is opened to allow air into the system, reducing the vacuum to the vacuum servo.
Park / neutral position (PNP) switch (6)
The control module is switched off if the automatic transmission gear selector lever is in the P or N positions. However the selected speed remains in the memory.
Vehicle speed signal (VSS)
The cruise control module requires information about the actual speed of the vehicle. This information is obtained from the speedometer (8). In cars with manual transmissions, the mechanical movement of the speedometer cable is converted into a speed- related pulsed frequency. This signal is then transmitted to the control module. In cars with automatic transmissions, this information is provided by the Aisin Warner transmission (7). This cable is routed to the instrument panel.
Data from all these sensors allow the control module to control the speed of the vehicle. Actual speed control is carried out using a vacuum servo next to the accelerator pedal (AP). The vacuum for this servo is governed by a pump or control valve, the regulator.