Component Overview

The cruise control system consists of electro-mechanical devices and comprises of the following components.

Electronic Control Unit (ECU)
The microprocessor based ECU evaluates the signals received from the driver controls, BeCM (vehicle speed signal), brake pedal switch and clutch pedal switch on manual vehicles. The ECU activates a vacuum pump as required. The ECU has a memory function to store desired cruise speed. The memory is cleared when power to the cruise ECU is cut, i.e. when the main cruise control switch is turned off.

Driver operated switches
The driver controls cruise operation from 3 switches. The main cruise control switch is located on the centre switch pack and activates the cruise control system. 2 further switches are located in the steering wheel. 'Set/+' informs the ECU of the required cruise speed. 'Res' temporarily switches cruise control off but retains the previously set cruise speed. Pressing 'Res' a second time resumes the previously selected cruise speed.

Vehicle speed signal
The cruise control ECU receives a road speed signal from the BeCM, which in turn receives the signal from the ABS ECU. The cruise control ECU compares the road speed signal with the required cruise speed and adjusts the output to the vacuum pump as necessary. Cruise control will not operate below the low speed threshold of 28 mph or above the high speed threshold of 125 mph.

Brake pedal switch
The vehicle utilised 2 brake pedal switchs, mounted on the pedal box. One switch is normally closed with the brake pedal released while the other is normally open. The normally closed switch also incorporates a vent valve to rapidly deplete actuator vacuum when cruise control is disengaged. When the brake pedal is pressed, the signal from each brake switch is monitored by the cruise control ECU which switches the vacuum pump off.

Clutch pedal switch
The clutch pedal switch is located on the pedal box and is identical to the previously described brake pedal switch with vent valve.

Vacuum pump
When cruise control is active and cruise ECU inputs are acceptable, the ECU energises the vacuum pump motor. The vacuum pump creates a vacuum in the actuator which operates the throttle linkage. When the required speed has been achieved, the ECU switches off the vacuum pump. The ECU also controls a dump valve which allows system vacuum to vent to atmosphere.

Actuator
The actuator provides the servo mechanical link between the cruise control system and the throttle linkage.

Neutral lock-out - automatic vehicles
Cruise control is disengaged when neutral or park is selected in the main gearbox. The cruise control ECU receives a signal from the BeCM.

Engine overspeed - manual vehicles
Cruise control is disengaged if the engine speed exceeds 5000 rpm. The cruise control ECU receives the engine speed signal from the BeCM.