Description & Operation: Notes
Cruise control is a speed control system which maintains a desired car speed under normal driving conditions. However, steep grades up or down may cause slight variations in the vehicle speed. The electronic cruise control system has the capability to cruise, coast, resume speed, accelerate, and 'tap-up' and 'tap-down'.
The main parts of the cruise control system are the mode control switches, Engine Control Module (ECM), servo unit, vehicle speed sensor, vacuum supply, electrical and vacuum release switches.
The cruise control system uses vacuum to operate a throttle servo unit. The servo unit maintains a desired car speed by trapping vacuum in the servo unit at the proper servo position. The ECM monitors vehicle speed and servo position to operate the servo vacuum and vent valves to maintain desired speed. The ECM prevents system engagement below a minimum speed, about 25 MPH. The operation of the cruise control function is controlled by mode control switches located on the steering wheel and dash. The system may be disengaged by turning off the dash switch or by activating any of the release switches. See Fig 1 .
An electrical release switch mounted on the brake pedal bracket disengages the system electrically when the brake pedal is depressed. A vacuum release valve, mounted on the brake pedal bracket, vents the trapped vacuum in the servo to atmosphere when the brake pedal is depressed, allowing the servo unit to quickly return the throttle to idle position.