Design

Design

Control module




The differential electronic module (DEM) is secured directly to the coupling unit housing and forms a single unit with the axial solenoid. The axial solenoid controls the control valve.
The differential electronic module (DEM) receives signals from the engine control module (ECM), the central electronic module (CEM) and the brake control module (BCM) via the high speed side of the control area network (CAN). The differential electronic module (DEM) uses these signals to determine the oil pressure required for the multi-plate clutch in the coupling unit. The oil pressure for the multi-plate clutch determines the amount of torque which can be transferred to the rear wheels.
Four wheel drive is not available if there is a fault in the differential electronic module (DEM).

Oil pressure and temperature sensor




The oil pressure and temperature sensor in the clutch unit are close to the axial solenoid in the housing for the differential control module (DEM). The sensor is flushed with hydraulic fluid. The sensor gauges the temperature and pressure of the hydraulic fluid (measurement range 0-4 MPa). The sensor transmits signals about temperature and pressure to the control module. The control module uses the temperature and pressure signals to adapt the function of the system, changing the temperature, and therefore the viscosity, of the fluid as required.
If the temperature of the fluid exceeds 100 °C there is no pressure in the coupling and all wheel drive is disengaged. When the temperature falls below 100 °C the coupling is pressurized again. If the oil pressure exceeds 7.4 MPa, the safety valve in the coupling opens. The coupling is pressurized again when the oil pressure drops below 7.4 MPa.
Four wheel drive is not available if there is a fault in the pressure and/or temperature sensor.
There are diagnostics for the oil pressure and temperature sensor.

Control valve/axial solenoid




The control valve/axial solenoid are in the coupling unit for the active on demand coupling (AOC).
The 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 is disabled if there is a fault in the control valve/axial solenoid.
There are diagnostics for the control valve/axial solenoid.

Electrical feed pump




The electrical feed pump is integrated in the coupling unit and is powered by the differential electronic module (DEM). When the engine is started and exceeds 400 rpm, the electrical feed pump receives power from the control unit.
The feed pump pumps oil to the annular pistons, whose rollers move into contact with the cam disc. 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 is disengaged if there is a fault in the feed pump.
There are diagnostics for the feed pump.