Torque Converter Lock-up Clutch (TCC)
The converter lock-up clutch is a device, which eliminates converter slip and thus helps to improve fuel consumption.
The previous control principle for converter lock-up clutch operation has been replaced by a controlling function on the 4 HP 16. The converter lock-up clutch is engaged and released in a controlled manner. During the controlled phase, a slight speed difference between the impeller and turbine wheel is established. This ensures that the engine's rotating vibration is not phased on to the transaxle. The result is optimum shift quality.
An electronic pressure-regulating valve determines pressure regulation of the lock-up converter clutch's piston.
When open (conversion range), the oil pressure behind the converter lock-up clutch piston and in the turbine zone is equal. The direction of flow is through the turbine shaft and through the space behind the piston, to the turbine chamber.
To engage the lock-up clutch, the direction of flow is modified (reversed) via a valve in the hydraulic selector unit. At the same time, the space behind the lock-up clutch piston is vented. The oil pressure passes from the turbine chamber to the lock-up clutch piston and presses it against the converter's cover. The turbine is thus blocked by way of the linings between the piston and cover, and permits rigid through drive with no slip (or reduced slip if controlled) to the mechanical stage of the transaxle.