Electronic Function

Fig 1: Active On Demand Coupling Electronic Function

Courtesy of VOLVO CARS CORPORATION

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.

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.