Design

Design

Control module




The differential electronic module (DEM) is secured directly to the coupling unit housing and forms a single unit with the control valve/axial solenoid. The control module and the control valve/axial solenoid 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 system 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.
Four-wheel drive does not function in the event of a fault in the Differential Electronic Module (DEM).

Oil pressure and temperature sensor




The oil pressure and temperature sensor is located next to the control valve/axial solenoid in the differential electronic module (DEM). The sensor is flushed with hydraulic fluid. The sensor gauges the temperature and pressure of the hydraulic fluid (measurement range 0-8 MPa). The sensor transmits signals about temperature and pressure to the control module. The control module uses the signal to adapt the system when the temperature, and therefore the viscosity, of the fluid changes.
If the temperature of the oil exceeds 105 °C then the clutch is depressurized and four-wheel drive is disconnected. When the temperature falls below 101 °C the clutch is pressurized again. The pressure of the oil is limited to max. 10.3 MPa by the safety valve.
Four-wheel drive does not function in the event of any fault in the temperature sensor, and the function is significantly reduced in the event of a fault in the pressure sensor.
The oil pressure and temperature sensor can be diagnosed.

Control valve/axial solenoid




The control valve/axial solenoid is located in the differential electronic module (DEM).
The control valve/axial solenoid receives a constant pulse width modulated (PWM) signal from the control module. The control signal from the control module is used by the solenoid to change the position of the control valve. This regulates the pressure to the operating piston in the multi-plate clutch.
Four-wheel drive does not function in the event of a fault in the control valve/axial solenoid.
The control valve/axial solenoid can be diagnosed.

Electrical feed pump.




The electrical feed pump is fitted on the clutch unit and is supplied with voltage from the Differential Electronic Module (DEM). When the engine is started and reaches an engine speed of over 400 rpm the electrical feed pump is supplied with voltage from the control module.
The feed pump pumps oil to the annular pistons, whose rollers move into contact with the hub's cam curve. At the same time the oil flows to the operating piston, so that the play in the multi-plate clutch unit is eliminated. The coupling is then able to react rapidly and regulate as required.
Four-wheel drive does not function in the event of a fault in the feed pump.
The feed pump can be diagnosed.