Control of transfer case/rear axle differential lock, function - GF28.19-P-3050VG

MODEL 164.1 with ENGINE 156, 272, 273, 629, 642 with TRANSMISSION 722.9 as of Model Year 09/Modification Year 08 model refinement package with CODE (430) Off-road package 

MODEL 164.8 with ENGINE 273, 629, 642 with TRANSMISSION 722.9 as of Model Year 09/Modification Year 08 with CODE (430) Off-road package 

Shown on model 164.1 

Function requirements for transfer case/rear axle differential lock control, general 

• Ignition ON
• Transmission in position "N"

Control of transfer case/rear axle differential lock, general information 

The electronically controlled transfer case combines the "High/Low shift" function and the center differential lock (interaxle differential lock). The transfer case is actuated and monitored by the transfer case control unit.

Control of transfer case/rear axle differential lock, function sequence 

The function sequence is subdivided into the following steps:

• Function sequence for "High/Low shift" (on-road and off-road ratios) 
• Function sequence for interaxle differential lock 
• Function sequence for interwheel differential lock 

Function sequence for "High/Low shift" (on-road and off-road ratios) 

The transfer case is equipped with a planetary gear set which permits the driver to shift between the on-road ratio "High" and the off-road ratio "Low" while the vehicle is moving. The planetary gear set is located in the central differential module. The on-road ratio "High" is 1:1, the off-road gear ratio "Low" is 2.93:1.

The off-road ratio allows the driver to drive extremely slowly off-road or when pulling a trailer. The transfer case control unit monitors and shifts the transfer case according to:

• Vehicle speed
• Position of transfer case actuator motor (M46/2)
• Additional CAN signals

If all the shift conditions are satisfied, the transfer case control unit actuates the transfer case actuator motor and the ratio in the transfer case is changed.

Function sequence for interaxle differential lock 

The engine torque is distributed 50:50 between the front and rear axles via a differential.

In order to ensure optimum torque distribution to each wheel in all driving situations, the transfer case is equipped with an electronic control system.

The transfer case control unit detects wheel slip and locks the differential by means of a multi-disk clutch according to the driving situation.

The transfer case control unit calculates the optimum locking torque (pre-control) depending on the operating condition. In order to avoid oversteer and understeer under load, a suitable slip range for the multi-disk clutch (interaxle differential lock) is calculated in addition to the optimum locking torque.

The interaxle differential lock is activated by the transfer case control unit via the transfer case switchover magnet and the transfer case actuator motor.

For this the transfer case control unit requires the following information:

• Vehicle speed
• Engine torque
• Cornering recognition
• Tire tolerances

The transfer case control unit also considers requirements associated with the antilock brake system (ABS) and Electronic Stability Program (ESP), to help prevent any negative influence on braking stability. To guarantee functionality, the interaxle differential lock is opened when required by the ABS and ESP systems.

For this purpose the following parameters are available to the transfer case control unit on the CAN data bus:

• Stop light signal
• Deceleration at the rear axle
• Vehicle speed
• ABS request
• ESP requirement

The lock overload protection guards the interaxle differential lock against damage and guarantees the maximum possible availability of the lock function.

Function sequence for interwheel differential lock 

The electronically controlled differential lock (interwheel differential lock) in the rear axle differential is actuated and monitored by the rear axle differential lock control unit.

For the controlled distribution of the engine torque between the left and right rear wheels, the rear axle differential lock control unit requires the following information, which is made available on the CAN data bus:

• Pre-control of the locking torque
• Slip-dependent lock control
• ESP requirement
• Lock overload protection

The rear axle differential lock control unit actuates the interwheel differential lock according to its input signals via the rear axle differential actuator motor.

	Electrical function schematic for transfer case/rear axle differential lock control		PE28.19-P-2053-97MAB
	Component description of transfer case control unit	N15/7	GF28.19-P-3200VG
	Component description of rear axle differential lock control unit	N15/9	GF28.19-P-3500VG