Cruise Control: Description and Operation

CRUISE CONTROL DESCRIPTION AND OPERATION

System Operation
Cruise control is a vehicle speed control system which maintains a desired vehicle speed without the driver having to continually apply foot pressure to the accelerator pedal.

The cruise control system is an Electro-motor system, i.e. it uses a stepper motor to control vehicle speed. A throttle relaxer servo is fitted as part of the traction control system to provide engine torque control. The throttle relaxer momentarily reduces the throttle opening angle when traction loss occurs. There is no electronic interface between the throttle relaxer and the cruise control module.

The main components of the Electro-motor cruise control system are:
- Cruise Control Module
- Switch Assembly - Cruise Control
- Brake pedal stop lamp switch (Switch A)
- Brake pedal electrical release switch (Switch B)
- Clutch pedal switch and patch harness (manual transmission models)
- Cruise control cable
- Electrical wiring (incorporated into the main wiring harness)

The cruise control module also uses an output from the powertrain control module (PCM) for vehicle speed, and provides an input to the instrument cluster for cruise control status indication.

When the cruise control module is powered up via the cruise control ON/OFF push-button switch, the cruise control module activates an input to the instrument cluster. The instrument cluster sees this line as active and sends a message to the Multi-function Display (MFD) to turn its CRUISE icon on.

Cruise Control System Components:

When the CRUISE switch is rotated to the SET/DECEL position (provided the vehicle speed is above 25 mph and either the brake or clutch pedal is not pressed) the cruise control module activates an input to the instrument cluster. The instrument cluster sees this line as active and sends a message to the MFD to turn its ACTIVE icon on and in turn, the instrument cluster informs the PCM via the serial data interface to use a specific transmission shift pattern. The transmission shift pattern is designed primarily for cruise mode, having fewer transmission down shifts and reduced transmission gear change activity.

The cruise control module is mounted forward of the right-hand strut tower and adjacent to the ABS/TCS module. The cruise control module functionally integrates an electronic controller with an electric stepper motor.

The electronic controller monitors vehicle speed from a signal generated by the PCM which in turn, operates the electric stepper motor.

The stepper motor, in response to the electronic controller, adjusts the throttle position to maintain the desired vehicle set speed. The electronic controller is operated by the cruise control system control switches, located at the tip of the headlamp and turn signal switch assembly.

Two switches, mounted on the brake pedal support, disengage the cruise control system electronically when the brake pedal is pressed.

The upper switch is the cruise control electrical release switch (Switch B). The two rear terminals are used for the cruise control system.

IMPORTANT: Using the front set of terminals will result in the cruise control not functioning.

The lower switch is the brake pedal stop lamp switch (Switch A), and is used to illuminate the stop lamps and signal the cruise control module to disengage. With the brake pedal at rest, the stop lamp contacts in the lower switch are open, and closed when the brake pedal is pressed. With the brake pedal at rest, the electrical release contacts in the upper switch are closed, and open when the brake pedal is pressed. Both switches are used to signal the cruise control module so that if one should fail, the second switch will still generate a signal to the cruise control module to disengage the cruise control function.

For vehicles with a manual transmission, a clutch pedal switch mounted on the clutch pedal support, has been incorporated into the cruise control system. When the driver presses the clutch pedal to change gear, the cruise control is disengaged. When the clutch pedal is pressed, a signal is transmitted to the cruise control module to disengage the cruise control function. With the clutch pedal at rest, the contacts of the clutch switch are closed, and open when the clutch pedal is pressed.

The cruise control module comprises of an electronic controller, electric stepper motor, solenoid operated clutch, gear train assembly, and a connecting strap. The electronic controller receives signals from the cruise control electrical release switch, stop lamp switch, clutch pedal switch and vehicle speed output. It then generates signals to control the stepper motor and solenoid operated cruise control module clutch. The electric stepper motor is a brushless type motor with a four pole permanent magnet armature and three phase stator. The motor provides torque through a mechanical gear train to a control cable, which actuates the throttle linkage. When the brake pedal electrical release switch is activated (brake pedal pressed) the stepper motor begins to spin the motor back to the zero motor position.

If the signal of the cruise control module is pulled high, it will cause the stepper motor clutch to de-energize in about 0.75 second. In most cases, the stepper motor will be in the zero position when the module clutch is disengaged. This time delay period is introduced to prevent the accelerator pedal from slapping while the throttle is still held open. The stepper motor relies on the throttle return spring to return the stepper motor to the zero position as the spring on the drum gear is not strong enough to return the throttle/cruise to zero.

The internal components of the cruise control module are not serviceable.