Torque Converter and Lockup Clutch

Torque Converter and Lockup Clutch: The torque converter is the link for transmitting power from the engine to the gearbox. It converts high speed/low torque into low speed/high torque with a slight slip from the fluid coupling. The integral converter lockup clutch eliminates slip during the transfer of rotational speed.

The torque converter clutch is locked when the control module diverts oil pressure in the converter. The oil flow is reversed to depressurize the area in front of the clutch and apply pressure to the back side of the clutch pushing it against the converter housing. The clutch plate locks the turbine wheel directly to the converter housing allowing it to rotate as a unit without slip.

The lockup clutch is a two-friction surface clutch. It is slip-controlled in all forward gears (1 through 6). The operating points when the lockup clutch is engaged are increased which reduces fuel consumption.




The lockup clutch will not engage until the oil temperature is >35 °C. The control of the lockup clutch depends on various factors such as:

- Load requirement signal
- Engine load status
- Selected gearshift program
- Vehicle speed
- Gearbox oil temperature

Examples:

- Control of the lockup clutch takes place in the XE program (extreme economy) in gears 1 through 6 at a speed of approx. >30 km/h when a load requirement of <50% is present. The lockup clutch is disengaged if the load requirement is >50%.
- The converter clutch is engaged from a speed of approx. 80 km/h in all forward gears. It is engaged at a speed of 20 km/h at full load or kick-down.

There are small oil channels in the lining of the lockup clutch. This oil circuit quickly reduces the temperature in the torque converter after the lock-up clutch engages.

The GA6HP26Z has a new feature of reducing the load on the engine when the vehicle is stationary and the brake pedal pressed. The turbine (input) shaft is uncoupled from the drive so that only a minimum load remains, reducing fuel consumption. The uncoupling phase is achieved by a control feature of the "A" clutch which is called stand By Control (SBC). The pressure is reduced in the A clutch allowing the turbine shaft and torque converter to turn freely until acceleration is requested.