Principles of Operation
The speed control system is designed to maintain a selected vehicle speed between 48 and 200 km/h (30 and 125 mph).
The electronic stepper motor (internal to the speed control servo) is controlled by turning the three phases of the motor ON and OFF in sequence. The sequence determines the motor direction (open throttle or closed throttle based on vehicle speed).
- Output shaft speed (OSS) sensor (except diesel)
- Vehicle speed sensor (VSS) (diesel only)
- Speed control switches
- Brake pedal position switch (BPP)
- Speed control servo
Whenever the system is engaged and active, a speed control set indicator will be illuminated in the instrument cluster.
The brake pedal position (BPP) switch is a normally open switch. When the brake pedal is applied with the speed control system engaged, the BPP switch closes, putting the speed control in stand-by mode.
Normally, when the brake pedal is depressed, the speed control module deactivates the speed control system. Under increased brake pedal effort, the deactivator switch, a normally closed switch, will open and remove power to the speed control servo clutch, releasing the throttle independent of the speed control module.
The air bag sliding contact provides the electrical interface between the steering column wiring and the speed control switches in the steering wheel.
The inputs to the speed control servo are:
- Vehicle speed signal
- Speed control switches
- Brake pedal position (BPP) switch
- Deactivator switch
The output of the speed control servo is:
- Speed control cable controlled throttle position