Cruise Control: Description and Operation

The Cruise Control system maintains a driver selected speed by operating the throttle through the Cruise Control Servo. The Cruise Control Servo contains a Vacuum Motor, a normally closed Vacuum Valve solenoid and a normally vented to atmosphere Vent Valve solenoid. When the solenoids are energized, vacuum is applied to the Vacuum Motor which pulls the throttle linkage. Once the desired speed is obtained, the Vacuum Valve solenoid de-energizes, cutting off the vacuum source from the Vacuum Motor. If vehicle speed exceeds the driver selected speed or the cruise system is turned off, the Vent Valve solenoid de-energizes, venting the Vacuum Motor to atmosphere and releasing the throttle linkage. A safety feature of the system is the Brake Cruise Valve which will vent the Vacuum Motor if the brake pedal is depressed.

The operation of the Cruise Control Servo is controlled by the Cruise Control Module or Engine Control Module. The module interprets the servo position and adjusts the servo based on input it receives from the SET Switch, R/A Switch and Vehicle Speed Sensor. The module adjusts servo position by cycling the Vacuum Valve and Vent Valve solenoids on and off. The module will not allow cruise operation if vehicle speed is or falls below 25 mph or above 90 mph. The module will also disable the system when voltage applied to the brake input terminal is removed. This will occur whenever the brake pedal or clutch pedal is depressed, causing the respective switch to open.