Operating principles of an active clutch (Freelander 2)

3rd generation couplings

An internal electronically controlled pump provides hydraulic pre-charge pressure to the clutch. Pre-charge pressure ensures that the required working pressure is supplied to the clutch discs, which eliminates initial wheel slippage when accelerating the vehicle from a standstill.

In combination with the pre-charge pressure, a mechanical hydraulic pump acts on the clutch discs, providing the main hydraulic working pressure of the clutch. The mechanical pump operates on the "inlet side" and "outlet side" of the clutch:

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

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

This primary hydraulic pressure serves to transmit torque and provide the traction needed off-road, as well as to provide the required lock-up.

4th generation couplings

The 4th generation clutch still uses an electric pump to create the hydraulic pre-pressure to eliminate wheel slip when starting off. However, the same pump is also used to provide the main working hydraulic pressure to the clutch.

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