Active On-Demand Coupling Section View

The hydraulic pump 12V electric motor is controlled by the active on-demand coupling control module. The motor is started simultaneously with the vehicle engine to ensure hydraulic pressure is available when the vehicle starts to move. The pump is a six piston axial pump with an integral centrifugal overflow valve. The hydraulic pump generates hydraulic pressure which compresses the clutch plates. Increasing the pressure increases the clutch torque to a maximum of 1160Nm.

The output pressure is determined by the rotational speed of the motor and the centrifugal overflow valve. The active on-demand control module governs the hydraulic pump motor speed by controlling the current supplied to the motor. Three weighted levers and spring loaded ball valves form the overflow valve. As the pump rotational speed increases, the levers are moved outward by centrifugal force. As the levers move, they allow the ball valves to lift from their seats, allowing hydraulic pressure to bleed through the three ball valves and return to the fluid reservoir in the casing. Pressurized hydraulic fluid from the pump is directed via a gallery to the clutch piston.

The clutch comprises the outer drum, a set of friction and steel clutch plates and the input shaft. Torque output from the Power Transfer Unit (PTU) is passed from the driveshaft to the driveshaft flange on the active on-demand coupling. Rotation of the driveshaft flange is passed to the input shaft. When hydraulic pressure is applied to the clutch plates by the piston, the plates lock and torque is passed through the plates to the outer drum which rotates. The outer drum has a splined center bore which mates with the rear differential input shaft. Torque is passed from the outer drum to the rear differential. The outer drum is located on axial needle roller bearings.

The piston is located in the casing. Two seals are fitted to the piston and seal against the casing. A gallery behind the piston distributes hydraulic pressure evenly on the piston full area. When hydraulic pressure is applied, the piston moves to compress the clutch plates. The active on-demand control module operates the electric motor and the hydraulic motor and applies the required pressure to the plates via the piston. The control module can allow slippage of the clutch plates for partial lock-up, or apply full pressure for full lock-up.

A mechanical overflow valve is located in the casing to prevent over-pressure. When the pressure at the piston full area reaches a pre-determined value, the overflow valve is lifted off its seat against spring pressure and hydraulic fluid is allowed to bleed back to the reservoir within the casing.

The input shaft is mounted radially on radial ball bearings. A thread on the outer end of the input shaft provides for the attachment of the driveshaft flange which is secured with a nut. The clutch end of the input shaft is fitted with needle roller bearings, which support the rear differential input shaft.