Cruise Control: Description and Operation
DESCRIPTIONThe speed control system is composed of ON-OFF, SET-ACC, COAST and RESUME switches. The system contains vacuum hoses, servo (throttle actuator) assembly, speed sensor, amplifier, check valve assembly, and depending on model and year, a clutch switch, a manual lever position switch, stop light switch, or vacuum dump valve, an actuator (servo) and an actuator cable.
OPERATION
To operate speed control system, engine must be running and vehicle speed must exceed 30 mph. When ON-OFF switch is actuated, the system is ready to accept a set speed signal. When vehicle speed stabilizes (above 30 mph), and the ON switch is engaged, the operator may depress or release the SET-ACC button. This speed will be maintained until a new speed has been set, brake pedal has been depressed, or the system is turned off.
The vehicle speed may be reduced by applying the brake or clutch pedal and then resetting the speed using the method outlined above or by depressing the COAST switch. When the vehicle has slowed to the desired speed, the COAST switch is released and the new speed is set automatically. If the vehicle speed is reduced below 30 mph (48 km/h), the operator must manually increase the speed and reset the system.
When activated, the Speed Control System maintains vehicle road speed at a driver-selected rate. Using input information form the Vehicle Speed Sensor and the Speed Control Servo feedback potentiometer, the Speed Control Amplifier varies the level of vacuum applied to the Speed Control Servo. The Speed Control Servo, in turn, operates the engine throttle linkage to speed up or slow down the vehicle.
Voltage is present at the Speed Control Switch Assembly ON contacts at all times through the STOP Fuse, the Horn Relay coil and the Slip Ring Assembly.
With the Ignition Switch in START or RUN, voltage is present at the Speed Control Amplifier through the METER Fuse.
SPEED CONTROL AMPLIFIER INPUTS
Speed Control Switch Assembly
The Speed Control Switch Assembly signals the Speed Control Amplifier to turn the system on, turn the system off, set and hold the vehicle speed accelerate or coast. With the Switch held ON, voltage is applied to pin E, C234, of the Amplifier. In OFF, pin E is grounded. With the Switch held in SET/ACCEL, a 680 ohm resistor is placed in the ground circuit. In RESUME, a 2200 ohm resistor is placed in the ground circuit; and in COAST, a 120 ohm resistor is used.
Stop Lamp Switch
With the brake pedal depressed, the Stop Lamp Switch contacts close and voltage is present at pin F, C234, of the Speed Control Amplifier. This input causes the Amplifier to disengage the System.
Clutch Interrupt Switch (Manual Transaxle)
With the clutch pedal depressed, the Clutch Interrupt Switch contracts open, interrupting the ground circuit that the Amplifier monitors through the Clutch Interrupt Switch and the Stop Lamps. this input causes the Amplifier to disengage the System.
Vehicle Speed Sensor
The Vehicle Speed Sensor is a small, permanent magnet generator that is driven by a transaxle gear. Sensor output is proportional to vehicle road speed. With Sensor output indicating that vehicle road speed is above 30 mph, the Speed Control Amplifier enables the Speed Control System. The Vehicle Speed Sensor is signal is also used to maintain vehicle speed when the System is operating.
Speed Control Servo
The Speed Control Servo contains a potentiometer that is connected to the throttle linkage. The Speed Control Amplifier applies a reference voltage of the return signal. This feedback circuit provides information about throttle linkage position.
SPEED CONTROL AMPLIFIER OUTPUTS
Speed Control Servo
With the Speed Control System turned ON and vehicle road speed above 30 MPH, the Speed Control Amplifier energizes the Vacuum and Vent Valves in the Speed Control Servo. The Vacuum Valve passes vacuum to the Speed Control Servo, the Vent Valve controls the level of vacuum applied to the Servo.
The Vacuum Dump Valve provides a mechanical means of disengaging the Speed Control System. With the brake pedal released, the Valve is closed, and the vacuum level in the System is determined by the Vent Valve. With the brake pedal depressed, the Valve opens, disabling the vacuum circuit.