Torque Converter

DESCRIPTION

Fig. 3:

The torque converter is located in the bellhousing area of the transaxle, between the engine and transaxle. The torque converter is a fluid coupling that transmits torque from the engine drive plate to the input shaft of the transaxle. The torque converter consists of four main components (Fig. 3):
- Impeller
- Turbine
- Stator
- Converter Clutch assembly

OPERATION
The converter impeller (driving member) which is integral to the converter housing and bolted to the engine drive plate, rotates at engine speed. The converter turbine (driven member) which reacts from fluid pressure generated by the impeller, rotates and turns the transmission input shaft.
Torque is transmitted by fluid passing through curved vanes in both the impeller and turbine. Since the coupling is produced by transmission fluid, the turbine can slip or turn slower than the impeller.
The stator contains a one-way overrunning clutch, which free-wheels when the impeller and turbine are rotating at the same speed. However, the stator stops when speed reduction or torque increase take place. When the stator stops, it changes the direction of the fluid leaving the turbine vanes. This directs fluid back into the impeller with greater force, resulting in torque multiplication.
The torque converter clutch is hydraulically operated and controlled by the TCM. It consists of a piston and a frictional disc that form a direct mechanical link between the impeller and turbine when slippage is inefficient or unnecessary.
The torque converter hub drives the transmission oil pump.

ELECTRONICALLY MODULATED CONVERTER CLUTCH
In order to reduce heat build-up in the transmission and buffer the powertrain against torsional vibrations, the TCM can duty cycle the LR/CC solenoid to achieve a smooth application of the torque converter clutch. This function, also referred as "Electronically Modulated Converter Clutch (EMCC), can occur at various times depending on the following variables:
- Shift lever position
- Current gear range
- Transmission fluid temperature
- Engine coolant temperature
- Input speed
- Throttle angle
- Engine speed
The TCM controls the torque converter by way of internal logic software. The programming of the software provides the TCM with fine control over the LR/CC solenoid. There are four output logic states that can be applied as follows:
- No EMCC
- Partial EMCC
- Full EMCC
- Gradual-to-no EMCC

NO EMCC
Under No EMCC conditions, the L/R Solenoid is OFF. There are several conditions that can result in NO EMCC operations. No EMCC can be initiated due to a fault in the transaxle or because the TCM does not see the need for EMCC under current driving conditions.

PARTIAL EMCC
Partial EMCC operation modulates the L/R Solenoid (duty cycle) to obtain partial torque converter clutch application. Partial EMCC operation is maintained until Full EMCC is called for an actuated. During Partial EMCC some slip does occur. Partial EMCC will usually occur at low speeds, low load and light throttle situations.

FULL EMCC
During Full EMCC operation, the TCM increases the L/R Solenoid duty cycle to full ON after Partial EMCC control brings the engine speed within the desired slip range of transaxle input speed relative to engine rpm.

GRADUAL-TO-NO EMCC
This operation is to soften the change from Full or Partial EMCC to No EMCC. This is done at mid-throttle by decreasing the L/R Solenoid duty cycle.