LR3/Disco 3
at the same speed.
Lock-Up Clutch Mechanism
The Torque Converter Clutch (TCC) is hydraulically controlled by an electronic pressure regulating solenoid (EPRS4)
which is controlled by the TCM. This allows the torque converter to have three states of operation as follows:
Fully engaged
Controlled slip variable engagement
Fully disengaged
The TCC is controlled by two hydraulic spool valves located in the valve block. These valves are actuated by pilot
pressure supplied via a solenoid valve which is also located in the valve block. The solenoid valve is operated by PWM
signals from the TCM to give full, partial or no lock-up of the torque converter.
The lock-up clutch is a hydro-mechanical device which eliminates torque converter slip, improving fuel consumption. The
engagement and disengagement is controlled by the TCM 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 lock-up
clutch comprises a piston and a clutch friction plate.
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 lock-up of the clutch plate with the body. In this condition there is direct mechanical drive
Item Part Number
Description
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
