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Interwheel differential lock, function - GF28.60-P-3200VG

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 

Sectional view of rear axle differential 

Fig 1: Identifying Interwheel Differential Lock Components
G10116015Courtesy of MERCEDES-BENZ USA

Function requirements for interwheel differential lock, general 

Interwheel differential lock, general 

The interwheel differential lock distributes the engine torque between the left and right rear wheel.

Interwheel differential lock, function sequence 

The function sequence is subdivided into the following steps:

Function sequence for differential stages 

The driver can use a differential lock selector wheel (N72s34) located in the lower control panel (N72) to select between three different differential stages. The following differential stages are available in the "High" on-road ratio:

1st stage: Transfer case differential (interaxle differential lock) is locked automatically

2nd stage: Transfer case differential (interaxle differential lock) is locked manually (100 %)

3rd stage: Transfer case differential (interaxle differential lock) and the rear axle differential (interwheel differential lock) are locked manually (100 %)

The following differential stages are available in the "Low" off-road ratio:

1st stage: Transfer case differential (interaxle differential lock) is locked automatically

2nd stage: Transfer case differential (interaxle differential lock) is locked manually (100 %)

3rd stage: Transfer case differential (interaxle differential lock) and the rear axle differential (interwheel differential lock) are locked manually (100 %)

Each differential stage has a red LED to indicate the active state.

Function sequence for specified locking power 

When the lock is actuated, the transfer case control unit (N15/7) calculates a specified locking torque according to the current operating state.

The information about the specified locking torque is sent by the transfer case control unit via the engine-compartment CAN (CAN C) to the rear axle differential lock control unit (N15/9). This pre-control of the locking torque has the following advantages:

To allow calculation of the specified locking torque, the transfer case control unit requires the following information:

Function sequence for locking control 

The rear axle differential lock control unit regulates the distribution of the engine torque between the left and right rear wheels. The multidisk clutch (interwheel differential lock) is actuated via the rear axle differential actuator motor.

When the rear axle differential actuator motor is actuated by the rear axle differential lock control unit, the rear axle differential actuator motor rotates the eccentric with ball ramp mechanism (3) via the spur gear (1). Due to the ball ramp mechanism installed on the eccentric (3), the balls run up their "ramps" when the eccentric (3) is rotated. This produces an axial movement of the eccentric (3). The eccentric (3) pushes the thrust ring (6) against the interwheel differential lock disk pack (5). This produces a defined friction torque in the disk pack (5). The differential housing (4) and the differential side gear (2) are mutually locked.

In order to optimize fuel consumption, the position of the spur gear is maintained by the magnetic brake (7) in the rear axle differential actuator motor if the differential is permanently locked.

Function sequence for safety concept 

In the deenergized state (power failure) the interwheel differential lock is open.

Function sequence for locking actuation on antilock brake system (ABS)/Electronic Stability Program (ESP) control 

The transfer case control unit must respond to the particular requirements of the ABS and ESP systems in order to avoid negative influences on directional stability and road adhesion. These requirements are made available to the rear axle differential lock control unit via the CAN data bus. For this purpose the transfer case control unit is capable of opening the interwheel differential lock. To guarantee this function, the following information is required:

Function sequence for locking overload protection 

The aim of the lock overload protection is to protect the interwheel differential lock against damage and guarantee the maximum possible availability of the lock function.

IMPORTANT After ignition "OFF/ON" for >10 s the 1st stage of the differential lock is automatically activated. The current differential stage selection remains active if the period is less than 10 s.

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 
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