Principles of Operation

PRINCIPLES OF OPERATION

The speed control system is controlled by the powertrain control module (PCM).

The speed control system is enabled/disabled by the speed control switches, the speed control deactivator switch, the stoplamp switch, and the parking brake switch.

The speed control switch functions:
- turn on the speed control system.
- set and maintain the desired vehicle speed.
- accelerate the vehicle speed.
- decelerate the vehicle speed.
- tap-up/tap-down the vehicle speed.
- resume the prior vehicle speed.
- turn off the vehicle speed control system.
- cancel the speed control.

Pressing and releasing the ON switch turns the system on. Pressing and releasing the SET/ACCELERATE switch while the vehicle is traveling, sets the desired speed.

Tapping the SET/ACCELERATE or COAST/DECELERATE buttons, while in the set mode, increases or decreases the maintained vehicle speed by 1.6 km/h (1 mph) per tap for US instrument clusters, or 2.0 km/h (1.24 mph) per tap for metric instrument clusters. If the respective button is pressed and held, the vehicle speed continues to accelerate or decelerate until the button is released.

Pressing the OFF switch, or positioning the ignition switch in the OFF position, turns the speed control off. Pressing the brake pedal puts the system in the standby mode. Pressing the RESUME button when the system is in standby mode causes the vehicle to accelerate or decelerate until the last set speed is resumed. Resume does not function if the OFF button is pressed, the ignition switch is in the OFF position, or if the current vehicle speed is below the minimum operational speed.

The inputs to the PCM for the speed control system are the:
- parking brake signal from the instrument cluster.
- anti-lock brake system (ABS) module.
- speed control deactivator switch.
- stoplamp switch.
- speed control switches.

The outputs from the PCM for the speed control system are the:
- Instrument cluster
- Throttle command

When the gasoline motor is powering the vehicle and the speed control is active, the speed control system does not require an electronic actuator for electronic throttle control (ETC) vehicles. The throttle position is completely controlled by the PCM. The speed control electronics are contained entirely within the ETC subsystem.

When the electric traction motor is powering the vehicle and the speed control is active, the electronic actuator corrects for deviations in the actual vehicle speed by proportionally applying wheel torque. The control electronics modulate the wheel torque to minimize error between the actual vehicle speed and the desired speed.

The PCM strategy uses the powertrain control for smooth accelerations.

The PCM sends a requested controller area network (CAN) vehicle speed control set speed status (enable/disable) to the instrument cluster whenever the speed control set telltale should be turned ON or OFF.

The driver commands the speed control system by pressing the steering wheel mounted switches. The steering wheel switches are hardwired to the PCM.

The speed control system operates in the following modes:
- ON
- OFF
- SET/ACCELERATE
- COAST/DECELERATE
- RESUME
- SOFT DEACTIVATE
- STANDBY
- HARD DEACTIVATE

When the speed control is in the ON mode and the PCM receives a SET/ACCELERATE or COAST/DECELERATE switch input, the speed control system enters the SET mode and maintains the present vehicle speed (provided the vehicle speed is within the system operating range). When the PCM receives an SET/ACCELERATE switch input, the speed control system will accelerate the vehicle 1.6 to 2.7 km/second (1.00 to 1.68 miles/second) on level roads. The speed control system continues to accelerate the vehicle until the switch is no longer pressed and then maintains that vehicle speed. If the duration of the switch input is less than 640 ms the speed control system increases the vehicle speed by 1.6 km/h (1 mph) for US instrument clusters, or 2.0 km/h (1.24 mph) for metric instrument clusters. When the system is in the STANDBY mode and a RESUME switch input is received, the speed control system transitions into the SET mode and modifies the vehicle speed to resume the last set vehicle speed, provided the speed control system has previously been in the SET mode in the current ON cycle.

When the PCM receives a COAST/DECELERATE switch input, the speed control system decreases the vehicle speed 1.6 to 2.7 km/second (1.00 to 1.68miles/second) on level roads. Once the switch is no longer pressed, the speed control system ceases vehicle deceleration and maintains the present vehicle speed. If the duration of the switch input is less than 640 ms, the speed control system decreases the vehicle speed by 1.6 km/h (1 mph) for US instrument clusters, or 2.0 km/h (1.24 mph) for metric instrument clusters.

In the event of an OFF command or a deactivation request from any source except a brake pedal tap, the system carries out a hard deactivation and immediately returns control to the accelerator pedal.

The accelerator pedal can be used to override the set speed control. Once the speed control is SET and the operators foot is removed from the accelerator pedal, the accelerator pedal will fully return to its at rest (idle) position. The operator may override the speed control by pressing the accelerator pedal to a position that represents a wheel torque command greater than the speed control demand. A certain amount of free-play (dead space) may be felt by the driver in this mode.

The speed control system provides self-diagnostics. The speed control is disabled anytime an error is detected in the system. No cluster telltale or message center messages are displayed when faults occur. Fault codes are logged by the PCM.