How the Active Clutch Works (Freelander 2)

3rd generation couplings

An internal electronically controlled pump provides hydraulic pre-pressure to the clutch. The preload pressure ensures that the required working pressure is applied to the clutch discs, which eliminates the initial wheel slip when the vehicle accelerates from a standstill.

In combination with the preload pressure, a mechanical hydraulic pump is applied to the clutch discs to supply the clutch's main hydraulic operating pressure. The mechanical pump works on the "inlet side" and "outlet side" of the coupling:

• input side - connection to the cardan shaft from the front axle;
• the output side is the connection with the differential to the rear axle.

Any difference in speed between the front and rear axles initiates the operation of the mechanical hydraulic pump. The amount of hydraulic pressure applied by the pump to the set of clutch discs determines the gap between the discs. For example, the higher the hydraulic pressure, the smaller the gap between the discs and, therefore, the greater the torque transmitted through the clutch from the front axle to the rear axle.

This main hydraulic pressure is used to transmit the torque and traction needed off-road, as well as to provide the required lockup.

4th generation couplings

The 4th generation clutch still uses an electric pump to generate hydraulic pre-pressure to eliminate wheel spin when pulling away. However, the same pump is also used to provide the main operating hydraulic pressure to the coupling.

The principle of transmitting torque through the clutch discs remains the same as described above for the 3rd generation clutch.