Design

Design

Control module




The differential electronic module is mounted directly onto the housing for the coupling unit. It forms part of a unit with the stepper motor and the control valve.
The control module receives signals from the engine control module (ECM), central electronic module and brake control module via the control area network (CAN). The control module uses these signals to determine the oil pressure for the clutch pack in the coupling unit. The oil pressure on the multi-plate clutch determines the torque that can be transferred to the rear wheels.
All wheel drive is disengaged if there is a fault in the differential electronic module.

Temperature sensor




The temperature sensor in the coupling unit is mounted close to the control valve in the housing for the control module. The sensor is immersed in the hydraulic fluid. The sensor measures the temperature of the hydraulic fluid and transmits a signal to the differential electronic module. The differential electronic module uses the temperature signal to adapt the system when the temperature, and therefore the viscosity, of the fluid changes.
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.
All wheel drive is disengaged if there is a fault in the temperature sensor.

Stepper motor




The stepper motor (4) is built into the housing for the differential electronic module.
The differential electronic module supplies the stepper motor with power. A control signal to the stepper motor from the differential electronic module changes the position of a control spindle (3) in the control valve (2) via a small gear wheel (5). The position of the control spindle alters the cross section of a return duct (1) in the valve. This controls the pressure to the operating piston for the multi-plate clutch.

Electric feed pump




The electric feed pump is built into the coupling unit. The pump is supplied with power by the differential electronic module. When the engine is started and exceeds 400 rpm the differential electronic module supplies the feed pump with power.
The feed pump pumps fluid to the annular pistons. This pushes the rollers for the pistons into contact with the cam disc. At the same time hydraulic fluid flows to the operating piston. This eliminates play in the multi-plate clutch pack. The coupling is now able to react and regulate torque distribution rapidly.
All wheel drive is disengaged if there is a fault in the feed pump.