Vehicle driveline having torque transfer device that is operated on fluid pressure

A vehicle driveline comprising:

• a clutch having a plurality of first clutch plates and a plurality of second clutch plates that are interleaved with the first clutch plates;
• a reservoir configured to hold hydraulic fluid;
• a hydraulic ram coupled to the clutch, the hydraulic ram having a piston chamber and a piston that is movable in the piston chamber between a first position which is retracted relative to the first and second clutch plates, and a second position in which the piston is extended toward the first and second clutch plates to a greater extent than when the piston is in the first position;
• a first valve coupled for fluid communication with the piston chamber;
• a second valve coupled for fluid communication with the piston chamber, and the reservoir;
• and
• a pump configured to pump hydraulic fluid from the reservoir to the piston chamber via the first valve;
• wherein the first valve is operable in a first position, in which fluid communication is permitted between the pump and the piston chamber, and a second position in which fluid communication between the pump and piston chamber is prevented, wherein the first valve is switched between the first and second positions by a solenoid;
• wherein the second valve is operable in a first position, in which fluid communication is permitted between the piston chamber and the reservoir, and a second position in which fluid communication is permitted from the piston chamber to the reservoir but prevented from the reservoir to the piston chamber;
• and
• wherein the second valve is configured to be in the first position when a pressure within the piston chamber is less than a predetermined pressure, and the second valve is configured to be in the second position when the pressure in the piston chamber is greater than the predetermined pressure.