A = Unlocked condition B = Locked condition 1 Clutch plate 2 Clutch piston 3 Torque converter body 4 Turbine 5 Impeller 6 Stator 7 Piston chamber 8 Turbine chamber The lockup clutch is a hydro-mechanical device which eliminates torque converter slip, improving fuel consumption. The engagement and disengagement is controlled by the EAT ECU to allow a certain amount of controlled 'slip. This allows a small difference in the rotational speeds of the impeller and the turbine which results in improved shift quality. The lockup clutch comprises a piston and a clutch friction plate. M44 1824 A B 1 4 6 5 7 8 1 4 6 5 7 8 2 3 2 3
AUTOMATIC TRANSMISSION – ZF 5HP24 DESCRIPTION AND OPERATION In the unlocked condition, the oil pressure supplied to the piston chamber and the turbine chamber is equal. Pressurised fluid flows through a drilling in the turbine shaft and through the piston chamber to the turbine chamber. In this condition the clutch plate is held away from the torque converter body and torque converter slip is permitted. In the locked condition, the TCC spool valves are actuated by the electronic pressure regulating solenoid (EPRS4). The fluid flow in the unlocked condition is reversed and the piston chamber is vented. Pressurised fluid is directed into the turbine chamber and is applied to the clutch piston. The piston moves with the pressure and pushes the clutch plate against the torque converter body. As the pressure increases, the friction between the clutch plate and the body increases, finally resulting in full lockup of the clutch plate with the body. In this condition there is direct mechanical drive from the engine crankshaft to the transmission planetary gear train. Fluid Pump The fluid pump is an integral part of the transmission. The fluid pump is used to supply hydraulic pressure for the operation of the control valves and clutches and also to pass the fluid through the transmission cooler. The HP fluid pump is a crescent type pump and is located between the intermediate plate and the torque converter. The pump has a delivery rate of cm per revolution.