Torque Converter With Lock-Up

Lock-up System:

The torque convener is described under "Torque Convener General". This section will deal only with the mechanical lock-up function.

Power transmission is fully mechanical when the torque converter is locked by the lock-up clutch, thereby eliminating the slip which is an inevitable feature of the unit. Engine speed is reduced and a certain fuel saving is achieved.

The mechanism consists of a plate which is pressed into contact with the torque convener housing, the mating surface of which is provided with a friction lining.

Engagement and disengagement are controlled by the signal valve and changeover valve in the control system. (In the illustration below, the control system is shown with the underside facing upward.)

Lock-up Function Disengaged

Pressure Supply:

1st-3rd Gears
Line pressure is supplied at A and the valve moves to the upper position.
The combination of line pressure and spring force prevents the valve from moving downwards when governor pressure B is increased.

Line pressure C applied to the top of the changeover valve holds the valve in the lower position.

4th Gear
Line pressure is now supplied to the middle port D of the signal valve.

Since the governor pressure B is not sufficiently high to move the valve downwards, the valve is held in the upper position by spring force.

The changeover valve remains in the lower position.

Lock-up Function Engaged

Pressure Supply:

4th Gear Only
The signal valve moves downwards when the governor pressure B is sufficiently high (i.e. when the car is driven above a certain speed).

This admits line pressure D to the underside of the changeover valve, which moves upwards and permits oil to flow to the torque converter in the opposite direction. This forces the lock-up clutch plate into contact with the friction lining on the housing, eliminating slip. Since the oil in the torque converter is now almost at rest, it does not require to be cooled.