Cruise Control: Description and Operation

CIRCUIT OPERATION

The cruise control system operates a mechanical linkage to the throttle by means of a vacuum motor. This is a diaphragm moved by a vacuum applied to one side. A solenoid operated valve connects the vacuum motor to a vacuum tank. Another solenoid valve vents the vacuum to reduce suction. The BCM controls the vacuum motor and the throttle by pulsing these solenoid valves on and off.

One input to the BCM is vehicle speed. This input comes from the vehicle speed sensor. If the actual speed signal is different from the speed that was set into and remembered by the BCM, the module generates pulses to change the vacuum and return the vehicle to the set speed. The vehicle speed sensor is mounted on the transaxle. Other inputs to the BCM are from the cruise on/off switch, the set/coast switch, the resume/accelerate switch and the transaxle position switch. A separate vacuum shut down of the cruise control comes from the vacuum release valve on the brake pedal.

The two outputs of the BCM operate the coils of the vacuum valve and the vent valve. Both valves are located within the cruise control servo. These valves move the throttle by means of the vacuum motor. The servo position sensor coil senses the position and motion of the vacuum motor. It feeds this information back to the BCM, to provide smooth acceleration while the vehicle is in cruise control.