GF28.60-P-3100GZ Interaxle Differential Lock, Function

GF28.60-P-3100GZ Interaxle differential lock, function
- with CODE (430) Offroad package

Component Identification:

The driver can use a differential lock selector wheel (N72s34) located in the lower control panel control unit (N72) to select between three different differential stages.

The following differential settings are available in the "High" on-road ratio:
^ 1st stage: The transfer case differential (interaxle differential lock) is locked automatically
^ 2nd stage: The transfer case differential (interaxle differential lock) is locked manually (100 %)
^ 3rd stage: The transfer case differential (interaxle differential lock) and the rear axle differential (interwheel differential lock) are locked manually (100 %)

The following differential settings are available in the "Low" off road ratio:
^ 1st stage: The transfer case differential (interaxle differential lock) is locked automatically
^ Setting 2: The transfer case differential (interaxle differential lock) is manually locked (100 %) and the rear axle differential (interwheel differential lock) is automatically locked
^ 3rd stage: The transfer case differential (interaxle differential lock) and the rear axle differential (interwheel differential lock) are locked manually (100 %)

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

Pre-control of the locking torque
When the lock is actuated, the transfer case control unit (N15/7) calculates an initial locking torque according to the current operating state.

This pre-control of the locking torque has the following advantages:
^ Ensuring traction for moving off
^ Avoiding overbraking of the rear axle during manual downshifts
^ Reducing the load change shock
^ Avoiding oversteer or understeer under load

To allow pre-control of the locking torque, the transfer case control unit requires the following information:
^ Vehicle speed
^ Engine torque
^ Accelerator pedal position
^ Cornering recognition
^ Wheel speeds

Lock control
The interaxle differential lock regulates the distribution of the engine torque between the front and rear axles.

The transfer case control unit actuates the transfer case switchover magnet (Y108). The transfer case switchover magnet switches between the "High/Low shift" function and the interaxle differential lock function. When the transfer case motor is actuated by the transfer case control unit, the transfer case actuator motor turns the lock control disk (9).

The turning of the lock control disk produces a contra rotation of the front and rear lock levers (10, 11). As the lock levers turn, the balls (2) in the ball ramp mechanism run up to the ramps (1), producing an axial movement of the rear lock lever (11). This causes an axial displacement of the lock piston (3). This axial displacement produces a defined friction torque in the disk pack (5). The differential housing (7) and the front differential side gear (8) are mutually locked.

Safety concept
In the de-energized state (power failure), the transfer case switchover magnet interrupts the connection between the transfer case actuator motor and the front and rear lock levers, and the disk pack is pushed back to the starting position by the disk spring pack (4).

Slip-dependent lock control
While lock control is active, the transfer case control unit, in combination with the pre-control, calculates a suitable range for the slip threshold and the optimum locking torque in order to avoid oversteer and understeer under load.

For this the transfer case control unit requires the following information:
^ Vehicle speed
^ Engine torque
^ Cornering recognition
^ Tire tolerances
^ Wheel speeds

Lock actuation on ABS/ESP control
The transfer case control unit must respond to the requirements of the ABS and ESP systems in order to avoid negative influences on directional stability and road adhesion. For this purpose the transfer case control unit is capable of opening the interaxle differential lock.

To guarantee this function, the following information is required:
^ Stop light signal
^ Deceleration at the rear axle
^ Vehicle speed
^ Signal ABS "active"
^ ESP requirement

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

After ignition "OFF/ON" for greater than 10s the 1st. stage of the differential lock is automatically activated, at less than 10 s the currently selected differential stage remains active.