Design

Design

Control module




Differential Electronic Module (DEM) is directly secured onto the clutch unit housing and together with the axial solenoid constitutes one unit. The axial solenoid controls the control valve.

The Differential Electronic Module (DEM) receives signals via the Controller Area Network (CAN) 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.
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 fitted close to the axial solenoid in the Differential Electronic Module (DEM) housing. The sensor is flushed with hydraulic oil. The sensor measures the temperature and pressure (measurement range 0 - 4 MPa) of the hydraulic oil. The sensor sends a signal on temperature and pressure to the control module. The control module uses the signal to adapt the function of the system when the temperature of the oil and its subsequent viscosity is changed.
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) housing.
The control module supplies a variable pulse width modulated (PWM) signal to the axial solenoid. The solenoid changes the position of the control valve in accordance with the control signal. The pressure to the working piston of the clutch driven plates is controlled in this way.
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 axial pistons whose rollers are applied to the cam disc. At the same time oil flows to the working piston so that the play in the disc package is eliminated and the clutch's capacity for rapid reaction and control is prepared.
Four-wheel drive does not function in the event of a fault in the feed pump.
The feed pump can be diagnosed.