Four Wheel Drive System Operation 1 Speed Torque On Demand

Four Wheel Drive System Operation - 1 Speed Torque On Demand

2H Operation

2H turns on when you select NORMAL or CONSERVE. Power is delivered to the rear wheels only. This mode is appropriate for normal on-road driving on dry pavement and provides the best fuel economy. Torque is passed through the transfer case to the rear drive shaft at a 1:1 ratio. In 2H:

The 4x4 Switch Module sends a 2H mode status to the TCCM via HS2 CAN (4x4_SW = 2H).
The TCCM provides a ground for the IWE solenoid (IWE_OS # = No).
The TCCM outputs a 0% duty cycle to the clutch field coil (4WD_CLTCH_OUT # = 0.00%).
2H will momentarily be displayed in the message center at key up and after a 4A to 2H shift.

NOTE: When shifting to 2H mode in order for the IWEs to completely disengage the vehicle steering wheel must be less than 90 deg and 5 seconds have elapsed since the shift to 2H has been initiated.

4A and 4H OPERATION

4A and 4H OPERATION 4A turns on when you select EXCITE, NORMAL 4x4 AUTO or SLIPPERY. It provides electronically controlled four-wheel drive with power delivered to all four wheels, as required, for increased traction. 4A is calibrated in conjunction with Drive Mode. 4A in EXCITE is less aggressively tuned and is appropriate for dry road surfaces. 4A in NORMAL 4x4 AUTO is appropriate for all on-road driving conditions, such as dry road surfaces, wet pavement, light snow or gravel. 4A in SLIPPERY is more aggressively tuned and is appropriate for slippery surfaces, such as light snow or gravel.

4H turns on when you select DEEP CONDITIONS. It provides electronically locked four-wheel drive power to both the front and rear wheels for use in off-road or winter conditions such as deep snow, sand or mud. This mode is not for use on dry pavement.

Shifts from 2H to 4A can be made at any speed. When performing this shift, release the accelerator pedal prior to the shift and wait until the Shift in Progress message disappears in the IPC before accelerating, this improves the shift performance as the IWEs engage. In 4A:

The 4x4 Switch Module sends a 4A mode status to the TCCM via HS2 CAN (4x4_SW = Automatic).
The TCCM opens the ground for the IWE solenoid (IWE_OS # = Yes).
The TCCM outputs a 0% to 97% duty cycle to the clutch field coil (4WD_CLTCH_OUT # = x.xx%).
In 4H, the TCCM outputs a constant 97% duty cycle to the clutch field coil.
4A or 4H is displayed in the message center.

In 4A, the TCCM continuously monitors conditions and driver input to send torque automatically to the front driveline by controlling the transfer case clutch, providing 4WD capability. The TCCM sends a duty cycle command to the transfer case clutch coil as a torque request based on combination of preemptive and wheel slip response algorithm. Preemptive response is based on steering wheel angle, vehicle speed, throttle positions and available powertrain torque. Wheel slip response is based on monitoring the average front and rear wheel speeds.

When 4WD is no longer needed (during cruising or steady state driving) system defaults back to RWD mode by setting the duty cycle output to 0. The IWEs remain engaged to allow seamless torque transfer to the front driveline when necessary.

TCCM increases the duty cycle to prevent or control slip under any of the following conditions:

Slip is detected.
Heavy acceleration (throttle position).
Straight-ahead steering wheel angle.
Slippery or Deep Conditions drive mode is selected.

TCCM decreases the duty cycle to prevent or reduce vehicle bind under any of the following conditions:

Low speed.
Low acceleration (throttle position).
Tight turn steering wheel angle.
Excite drive mode is selected.

The TCCM has a thermal hardware protection strategy which monitors the amount of energy going through the clutch. This strategy has 2 levels of protections:

AUTOLOCK - If the system is in 4A and TCCM detects driving conditions that require greater 4X4 performance, the TCCM temporarily turns on 4H from 4A after detecting driving condition and informs the customer via the message center indicating 4X4 TEMPORARILY LOCKED. The 4x4 system automatically returns to 4A after the system no longer detects these driving conditions and informs the customer via the message center indicating 4X4 RESTORED.
POWERTRAIN TORQUE PROTECTION - If the system is in 4A and TCCM detects excessive stress or high energy going through the clutch (clutch is slipping excessively while the system is commanding max clutch torque), clutch output will be turned off and message center indicates 4x4 TEMPORARILY DISABLED. When the system had the ability to cool off, 4x4 operation will be automatically restored.

NOTE: The 4x4 Temporarily Disabled message can be dismissed by the customer however it's advisable to let the TCCM clear the message itself, which indicates that the 4x4 system has resumed normal operation.

Torque-On-Demand Clutch

The transfer case is equipped with an electronically controlled clutch which is located inside the case. This clutch is used to transfer torque in 4A mode. The clutch consists of a transfer case field coil, ball and ramp or cam plate, and a multi-disc friction and steel clutch pack.