Principles Of Operation: Notes

The following vehicle sub-system control modules are used for the Terrain Response system:

Engine management - Engine Control Module (ECM)
Transmission control - Transmission Control Module (TCM) (automatic transmission only)
Active on-demand coupling control module
Brake system - Anti-lock Brake System (ABS)/Dynamic Stability Control (DSC)/Electronic Traction Control (ETC)/Hill Descent Control (HDC) - ABS module

Each sub-system operates in different ways in relation to the selected Terrain Response program to achieve the optimum traction, stability and ease of control for the terrain encountered.

ENGINE MANAGEMENT SYSTEM (EMS)

The EMS can change the accelerator pedal maps to change the amount of torque per percentage of pedal travel.

Each terrain program uses a combination of operating parameters for each sub-system. Changing between terrain programs initiates a different set of operating characteristics which will be noticeable to the driver, for example; if the accelerator pedal is held in a constant position and the terrain program is changed from Grass/Gravel/Snow to Sand, the driver will notice the torque and engine speed increase.

If the terrain program is changed from Sand to Grass/Gravel/Snow, the driver will notice a reduction in torque and engine speed.

NOTE: The change in torque and engine speed can take approximately 30 seconds and care must be taken not to confuse the Terrain Response system operation with an EMS fault.

TRANSMISSION CONTROL (AUTOMATIC TRANSMISSION ONLY)

The transmission control module changes the shift maps for the Terrain Response program selected. This changes the shift points providing early or late upshifts and downshifts.

For example, in the Grass/Gravel/Snow program, the transmission will perform early upshifts and very late downshifts to ensure the transmission is in the highest gear possible. The hill detection function of the Transmission Control module (TCM) will lock the torque converter and hold whichever gear is selected to the engine speed (RPM) limit if necessary when descending a steep incline. This provides maximum engine braking before the driver needs to apply the brakes.

Sport mode is only available when the general program is selected. Sport mode is disabled in all Terrain Response special programs. 'CommandShift™' is available in any program.

ACTIVE ON-DEMAND COUPLING CONTROL

The active on-demand coupling control module has 2 operating strategies; pre-emptive and reactive.

The pre-emptive strategy anticipates and predicts the locking torque value required to minimize slip and maximize stability. Each Terrain Response program has a different threshold and input criteria for the pre-emptive strategy. For example, a higher locking torque would be applied on slippery surfaces.

The reactive strategy varies the amount of locking torque in response to the actual slip level and the dynamic behavior of the vehicle. Each Terrain Response program has a different threshold and input for the reactive strategy. The reactive strategy improves vehicle traction and composure by eliminating any wheel spin which has occurred after the pre-emptive strategy was applied. The locking response applied is applicable to the terrain program selected. For example, very sensitive on slippery surfaces to provide maximum traction and minimize surface damage.

The locking torque calculations use various signals from other sub-systems, for example, engine torque, accelerator pedal position, selected gear, steering angle, vehicle speed, lateral acceleration, yaw behavior.

The DSC function of the ABS system can override the active on demand coupling control and reduce any applied locking torque during DSC action.

ABS SYSTEM CONTROL

The ABS module controls several functions and adjusts the operating parameters of these functions to optimize the selected Terrain Response program.