Design

Design

Control module




The differential electronic module (DEM) is secured directly to the coupling unit's housing and makes up unit with the pressure reducing valve. The control module and the pressure reducing valve are calibrated together at the factory and can therefore only be replaced together.
Via the controller area network (CAN), the differential electronic module (DEM) receives signals from:
- Engine control module (ECM)
- Central electronic module (CEM)
- Brake control module (BCM)
- driver information module (DIM).
Conducted by these signals, the Differential Electronic Module (DEM) determines how high the oil pressure to the clutch unit should be. The oil pressure to the clutch driven plates is decisive for how much torque can be transferred to the rear wheels.
In case of Differential electronic module (DEM) failure, four-wheel drive may be reduced or lost completely.

Pressure reducing valve




The pressure reducing valve is located in the Differential electronic module (DEM).
The pressure reducing valve receives a constant pulse width modulated (PWM) signal from the control module. The control signal from the control module changes the position of the pressure reducing valve. This regulates the pressure to the discs' operating piston.
In case of diagnostics failure of the pressure reducing valve, four-wheel drive is lost.
The pressure reducing valve can be diagnosed.

Electrical feed pump.




The electric feed pump is located on the clutch unit and is supplied with voltage from the Differential electronic module (DEM).
The pump starts at ignition on and then works up a max. oil pressure of 35 bar. This is to always enable request for full torque. Then the pump is shut off until the pressure has dropped to 50%, then it starts again. If the pump does not reach max. pressure within 15 seconds, it is shut off and is then started again. This is calculated via a current measuring algorithm in the Differential electronic module (DEM). The pump works in intervals so that it is not damaged in case of a malfunction, e.g., leakage, in the system. The time interval that the pump works between depends on the temperature. At normal room temperature the pump runs at approx. 20-30 second intervals.
Four-wheel drive does not function in the event of a fault in the feed pump.
The feed pump can be diagnosed.

Oil filter with non-return valve




The hydraulic oil is pumped to the accumulator tank via an oil filter. The oil filter keeps the oil free from dirt and small particles that can damage the system. There is a non-return valve installed in the oil filter.
In case of oil filter malfunction, a trouble code may be generated.
The oil filter can be diagnosed