Torque Converter Assembly

TORQUE CONVERTER ASSEMBLY





The torque converter assembly serves three primary functions. First, the torque converter is a fluid coupling that smoothly transmits engine torque to the transaxle gear train. This fluid coupling also allows the vehicle to stop without stalling the engine. Secondly, it multiplies torque from the engine to the transaxle for additional vehicle performance. Finally, the torque converter assembly provides a mechanical (for direct drive) link from the engine to the transaxle with the use of a Torque Converter Clutch (TCC).
The torque converter assembly is a four element torque converter. It consists of a converter pump assembly (driving member), a turbine assembly (driven or output member), a clutch pressure plate assembly splined to the turbine to provide direct drive, and a stator assembly (reaction member). The converter cover is welded to the pump to seal all four members in a fluid filled housing.
The converter pump acts as a centrifugal pump, picking up fluid at its center and discharging this fluid at its rim between the blades. It is the force of this fluid from the pump hitting the turbine blades that causes the turbine to rotate. When the engine is idling in gear, the converter pump is not spinning fast and the force of the fluid leaving the pump is not great enough to turn the turbine and move the vehicle.
As engine speed increases, the fluid force increases and more engine power is transmitted to the gear train. Turbine speed does not reach engine speed until the torque converter clutch (pressure plate) is applied.
The pressure plate is splined to the turbine hub. It applies against the converter cover to provide a mechanical (direct drive) coupling of the engine to the transaxle. This mechanical coupling provides a more efficient transfer of engine torque to the drive wheels by eliminating the small amount of slippage that occurs in a fluid coupling. Thus, with the pressure plate (TCC) applied, the turbine assembly turns at engine speed.
To keep the pressure plate in the released position, TCC release fluid is fed through the turbine shaft in the release circuit. This release fluid then builds up pressure to counteract the converter clutch apply fluid and releases the pressure plate away from the cover. Fluid then leaves the converter by flowing between the turbine and stator shafts, and into the cooler and lubrication circuits.
In the apply position, converter clutch apply fluid flows between the stator shaft and converter hub to feed into the converter. This apply fluid fills the converter and applies the TCC pressure plate against the converter cover.
As the pressure plate applies, fluid between the converter cover and pressure plate is forced into the turbine shaft. The rate of exhausting TCC release fluid is controlled by the converter clutch solenoid to control the feel of the converter clutch. The fluid then flows back through the TCC release circuit.
To aid in controlling torsional shock during converter clutch apply, a damper assembly is incorporated in the converter clutch pressure plate. The spring loaded damper assembly is splined to the converter turbine assembly. The converter clutch pressure plate is attached to the pivoting mechanism of the damper assembly. This pivoting action allows the pressure plate to rotate independent of the damper assembly, up to approximately 18 degrees. The rate of independent rotation is controlled by the pivoting mechanism acting on the springs in the damper assembly. The cushioning effect of the damper assembly springs, aids in reducing converter clutch apply feel, and irregular torque pulses from the engine or road.

TCC Apply:
- Engine temperature above 50°C (122°F).
- Vehicle speed above 26 km/h (16 mph).
- Transaxle fluid temperature above 20°C (68°F).

TCC Release:
- Low engine speed down shift (e.g., light throttle, or steady) throttle with load increase.
- Low end of 3rd gear speed range, brake on = TCC off.
- Fast deceleration, i.e., brake lock on ice = TCC off, gear = manual.