Function
Function
Electronic function
The differential electronic module (DEM) is secured directly to the coupling unit and forms a single unit with the control valve/axial solenoid. The differential electronic module (DEM) communicates, among other things, with the engine control module (ECM) and the brake control module (BCM) via the control area network (CAN). The differential electronic module (DEM) uses the sensor signals to control the oil pressure to the multi-plate clutch by adjusting the axial solenoid. The axial solenoid regulates the control valve constantly using a pulse width modulation (PWM) signal. The basic pressure is generated by the electronic feed pump. The oil pressure for the multi-plate clutch determines the amount of torque which can be transferred to the rear wheels.
Active On demand Coupling (AOC) has an oil pressure and temperature sensor, which gauge the prevailing temperature and pressure of the hydraulic fluid. The oil pressure and temperature sensor provide the differential electronic module (DEM) with information about the temperature and pressure. Four wheel drive is disengaged to protect the coupling unit from damage if the temperature becomes too high, above 105°C. The coupling unit is re-engaged at full function when the temperature falls below 101°C. To protect the drive shafts, constant velocity joints and to prevent overheating, the differential electronic module (DEM) has functions that slightly reduce torque transfer to the rear wheels in certain driving situations.
"Trailer detection" is an example of such a function. This functions works on the basis that if a trailer is connected to the vehicle and the driving conditions are such that the front wheels "grip" the surface, the differential electronic module (DEM) opts to transfer a smaller percentage of the total torque to the rear wheels, than it otherwise would have done without a trailer.
This results in the main percentage of torque being at the front wheels. Therefore, protecting the drive line from extreme load.
Mechanical function, overview
The transmission and bevel gear transfers engine torque to the propeller shaft. The input shaft is joined to the clutch's output shaft via the multi-plate clutch pack. The multi-plate clutch in the coupling must be engaged to transfer torque to the rear axle. The inner and outer wet multi-plate clutch are the transfer point between the input and output shafts.
The sinusoidal cam disc with its sinusoidal curve rotates at the same speed as the propeller shaft. The annular piston rollers act on the cam disc's cam curve and press the annular pistons in and out. This creates an oil flow. The oil flow is controlled by the control valve/axial solenoid to create an oil pressure. The oil pressure affects the operating pistons that are applied against the multi-plate clutch pack.
Hydraulic function, overview
The Active On demand Coupling (AOC) can be described as a hydraulic pump.
The basic pressure is generated by the electronic feed pump. This pressurizes the annular pistons with oil so that they are pressed against the hub's cam curve via rollers. The annular pistons generate a working pressure which is led to the operating piston via the check valves on the intake side. This pressure creates a fixed connection between the input and output shafts. The maximum pressure is limited by the pressure limiting valve. Large differences in speed on the input and output shafts enable the annular pistons to create an oil flow. The oil flow is less if the input and output shafts are at the same speed. The oil flow, created by the annular pistons, is controlled by the control valve, which in turn is controlled by the axial solenoid. A closed control valve produces high pressure, which causes maximum pressure on the clutch driven plates. This produces a maximum power transmission. An open control valve produces low pressure, which causes minimum pressure on the clutch driven plates. This produces a limited power transmission.
The accumulator maintains the basic pressure in the system. The oil filter keeps the fluid clean by filtering dirt and small particles which could damage the system.
Pretensioning
The function of the four wheel drive system is based on there being a speed (rpm) difference between the front wheels and the rear wheels. This speed (rpm) difference can affect torque performance in certain driving situations. The task of the pre-tensioning function is to improve torque performance, in particular when pulling off from being stationary, without affecting other properties in the system.
The pre-tensioning function is achieved by the electric feed pump starting as soon as the engine has started. During acceleration, when pulling off, or during other situations that means that the oil pressure's desired value is not achieved by the clutch's flow, the feed pump, together with the check and by-pass valve, builds up a pressure (1.0 MPa). This pressure affects the clutch driven plates and can therefore transfer greater torque to the rear axle. The pre-tensioning function is controlled by the software so that activation only occurs when necessary.