Function
Function
Electronic function
1. Oil pressure and temperature sensor
2. Differential electronic module (DEM)
3. Control valve/axial solenoid
4. Electrical feed pump.
The differential electronic module (DEM) is secured directly to the coupling unit and forms a single unit with the axial solenoid and control valve. The differential electronic module (DEM) receives signals from 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 oil pressure for the multi-plate clutch determines the amount of torque which can be transferred to the rear wheels.
Note! If the car has dynamic stability and traction control (DSTC), the required stability control is applied before four wheel drive.
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 97 °C. The coupling unit is re-engaged at full function when the temperature falls below 93 °C.
Mechanical function, overview
1. Pressure plate
2. Rollers for the annular piston
3. Rollers for the operating piston
4. Annular piston
5. Operating piston
6. Input shaft
7. Cam disc
8. Housing for the outer plates
9. Outer plates
10. Inner plates
11. Springs
12. Output shaft.
The gearbox transfers engine torque to the propeller shaft. The input shaft is separate from the output shaft. 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 rotates at the same speed as the propeller shaft. The annular piston rollers act on the cam disc to press the annular piston in and out. This creates an oil pressure which affects the operating piston, which in term engages the multi-plate clutch unit.
Hydraulic function, overview (-2005)
1. Cam disc
2. Rollers
3. Pressure valves
4. Pressure limiting valve
5. Control valve cover
6. Oil pressure and temperature sensor
7. Differential electronic module (DEM)
8. Control valve/axial solenoid
9. Accumulator
10. Oil screen
11. Electrical feed pump.
12. Oil filter
13. Suction valves
14. Piston pump
15. Operating piston
16. Wet plate unit
17. Bearing
18. Springs.
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 cam disc via rollers. The annular piston generates a working pressure which is led to the operating piston via the pressure valve. This pressure creates a fixed connection between the input and output shafts. The maximum pressure is limited by the pressure limiting valve. The difference in speed between the input and output shafts is in proportion to the oil pressure fed to the annular pistons. A large difference between the input and output shafts results in high oil pressure to the annular pistons. If the input and output shafts are at the same speed, the oil pressure to the annular pistons is less. The oil pressure at the multi-plate clutch is regulated by the control valve. The axial solenoid controls the control valve. A closed control valve gives maximum pressure to the multi-plate clutch, resulting in maximum power gearbox. An open control valve gives minimum pressure to the multi-plate clutch, resulting in limited power gearbox.
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.
Hydraulic function, overview (2006-)
1. Cam disc
2. Rollers
3. Pressure valves
4. Pressure limiting valve
5. Control valve cover
6. Oil pressure and temperature sensor
7. Differential Electronic Module (DEM)
8. Control valve/axial solenoid
9. Accumulator
10. Oil screen
11. Electrical feed pump.
12. Oil filter
13. Suction valve
14. Piston pump
15. Operating piston
16. Wet plate unit
17. Bearing
18. Springs.
19. Relief and by-pass valve
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 cam disc via rollers. The annular piston generates a working pressure which is led to the operating piston via the pressure valve. This pressure creates a fixed connection between the input and output shafts. The maximum pressure is limited by the pressure limiting valve. The difference in speed between the input and output shafts is in proportion to the oil pressure fed to the annular pistons. A large difference between the input and output shafts results in high oil pressure to the annular pistons. If the input and output shafts are at the same speed, the oil pressure to the annular pistons is less. The oil pressure at the multi-plate clutch is regulated by the control valve. The axial solenoid controls the control valve. A closed control valve gives maximum pressure to the multi-plate clutch, resulting in maximum power gearbox. An open control valve gives minimum pressure to the multi-plate clutch, resulting in limited power gearbox.
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 in there being a difference in speed between front and rear wheels. This difference in speed can affect traction performance in certain driving situations. The role of the pretensioning function is to improve traction performance, primarily in starting off from being stationary, without affecting other properties of the system to achieve this.
The pretensioning function has been achieved by replacing one of the AOC unit suction valves with a new combined relief and by-pass valve, extra oil ducts in the housing and adapted software in the differential electronic module (DEM).
As before, the electronic feed pump starts as soon as the engine has started. Running the pump at a higher speed than before generates increased oil flow. The increased oil flow combined with the new relief and by-pass valve results in a pressure increase that can work on the clutch discs. Greater engine torque can thereby be transferred to the rear axle. The pretensioning function is controlled by software so that it is only activated when necessary.