Function
Function
Electronic function
1. Control module for all wheel drive (differential electronic module)
2. Stepper motor
3. Control valve
4. Pressure flow
5. Control valve cover.
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 differential electronic module communicates with the engine control module (ECM) and brake control module via the control area network (CAN). The differential electronic module uses the sensor signals to control the oil pressure on the multi-plate clutch by adjusting the control valve. The oil pressure on the multi-plate clutch determines the torque that can be transferred to the rear wheels.
Note! If the car has DSTC (dynamic stability and traction control), the stability control function has priority over all wheel drive.
The Active On Demand Coupling has a temperature sensor. This measures the temperature of the hydraulic fluid and transmits it to the differential electronic module. All wheel drive is disengaged if the temperature is too high. This prevents damage to the coupling unit.
Mechanical function, overview
1. Pressure plate
2. Rollers for annular pistons
3. Rollers for the operating piston
4. Annular piston
5. Operating piston
6. Input shaft
7. Cam disc
8. Housing for the outer clutch driven plates
9. Outer clutch driven plates
10. Inner clutch driven plates
11. Springs
12. Output shaft.
The engine torque is transferred to the propeller shaft via the gearbox. The input shaft is separate to the output shaft. The multi-plate clutch pack in the coupling must be loaded for torque to be transferred to the rear axle. The inner and outer wet plates are the points at which drive is transferred between the input and output shafts.
The sinusoidal cam disc rotates at the same speed as the propeller shaft. The rollers for the annular piston act on the peaks and troughs of the cam disc. This presses the annular piston in and out, generating an oil pressure which acts on the operating piston, causing it to engage the multi-plate clutch pack.
Hydraulic function, overview
1. Cam disc
2. Rollers
3. Pressure valves
4. Overload protection valve
5. Control valve cover
6. Control valve
7. Stepper motor
8. Accumulator
9. Oil screen
10. Electric oil pump
11. Oil filter
12. Suction valves
13. Piston pump
14. Operating piston
15. Wet multi-plate clutch pack
16. Bearing
17. Springs.
Active On Demand Coupling can be described as a hydraulic pump.
The basic pressure in the system is generated by the electric oil pump. This puts pressure on the annular pistons pressing them against the cam disc via the rollers. The annular piston generates an operating pressure which is supplied to the operating piston via the pressure valve. This pressure connects the input and output shaft. Maximum pressure is limited by the overload protection valve. The difference in speed between the input and output shafts is in direct proportion to the oil pressure on the annular pistons. The greater the difference in speed between the input and output shafts, the higher the oil pressure on the annular pistons. If the speed of the input and output shafts is the same, the oil pressure on the annular pistons is less. The oil pressure on the multi-plate clutch is controlled by the control valve. The stepper motor operates the control valve. The pressure on the multi-plate clutch is greatest when the control valve is closed. This provides maximum torque to the rear wheels. The pressure on multi-plate clutch is lowest when the control valve is open. This limits the torque transferred to the rear wheels.
The accumulator maintains the basic pressure in the system. The oil filter keeps the oil clean and free of small particles which could damage the system.