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 directly secured onto the clutch unit and together with the axial solenoid and control valve constitutes one unit. Amongst other things the Differential Electronic Module (DEM) communicates with the Engine Control Module (ECM) and the Brake Control Module (BCM) via the Controller Area Network (CAN). Conducted by the sensor signals, the Differential Electronic Module (DEM) controls the oil pressure to the clutch driven plates by adjusting the axial solenoid. The axial solenoid has variable control over the control valve by means of a pulse width modulated (PWM) signal. The basic pressure in the system is built up by the electrical feed pump. The oil pressure to the clutch driven plates is decisive for how much torque 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) is equipped with an oil pressure and temperature sensor, which measures the prevailing temperature and pressure in the hydraulic oil. The oil pressure and temperature sensor informs the Differential Electronic Module (DEM) on the temperature and the pressure. If the temperature is too high, above 105° C, then the four-wheel drive is disconnected to protect the clutch unit from damage. When the temperature falls below 101° C the clutch unit is reconnected with full functionality.
To protect driveshafts and joints, the Differential Electronic Module (DEM) has functions that reduce the torque that is transferred to the rear wheels in certain situations.
"Trailer detection" is an example of one of these functions. This function is based means that if a trailer is coupled to the vehicle and the driving conditions are such that the front wheels slip on the surface, the Differential Electronic Module (DEM) will transfer less torque to the rear wheels than it would have done without a trailer.
This results in most of the torque remaining on the front wheels, which protects the rear wheel driveshafts and drive joints from extreme loads.
Mechanical function, overview
1. Pressure plate
2. Rollers for axial piston
3. Rollers for working piston
4. Axial piston
5. Working piston
6. Input shaft
7. Cam disc
8. Housing for outer clutch driven plates
9. Outer clutch driven plates
10. Inner clutch driven plates
11. Compression springs
12. Output shaft
The engine torque is transferred to the propeller shaft via the transmission. The input shaft is separated from the output shaft. The disc package must be applied to transfer torque to the rear axle. Inner and outer wet clutch plates are the power transmission points between the input and output shafts.
The cam disc, which is sine shaped, rotates at the same speed as the propeller shaft. The axial piston rollers run on the cam disc's roller coaster and press the axial piston in and out, which creates an oil pressure which acts on the working piston, which in turn applies the disc package.
Hydraulic function, overview
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 strainer
11. Electrical feed pump
12. Oil filter
13. Suction valves
14. Piston pump
15. Working piston
16. Wet disc package
17. Bearings
18. Compression springs
Active On demand Coupling (AOC) can be explained as a hydraulic pump.
The basic pressure in the system is built up by the electrical feed pump. This way the axial pistons are pressurized with oil so that they are pressed against the cam disc via the rollers. The axial piston builds up a working pressure which is conducted to the working piston via the pressure valves. 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 proportional in accordance with the oil pressure to the axial pistons. A large difference in speed between the input and output shafts provides high oil pressure to the axial pistons. The same speed on the input and output shafts provides lower oil pressure to the axial pistons. The oil pressure on the clutch driven plates is controlled by the control valve. The axial solenoid controls the control valve. A closed control valve provides maximum pressure to the clutch driven plates, which provides maximum power transmission. An open control valve provides minimum pressure to the clutch driven plates, which provides a limited power transmission.
The accumulator maintains the basic pressure in the system. The oil filter keeps the oil free from dirt and small particles which can 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 is obtained by means of the feed pump building up a basic pressure. A pretensioning of the clutch unit is generated by means of this increase in pressure, and the engine torque can be transferred to both rear and front wheels. The pretensioning functionality is controlled by software so that activation only takes place when necessary.