Torque converter

DESCRIPTION

The torque converter (Fig. 9) is a hydraulic device that couples the engine crankshaft to the transmission.

The torque converter consists of an outer shell with an internal turbine, a stator, an overrunning clutch, an impeller and an electronically applied converter clutch. The converter clutch provides reduced engine speed and greater fuel economy when engaged. Clutch engagement also provides reduced transmission fluid temperatures. The converter clutch engages in third gear. The torque converter hub drives the transmission oil (fluid) pump.

The torque converter is a sealed, welded unit that is not repairable and is serviced as an assem nbly.

CAUTION: The torque converter must be replaced if a transmission failure resulted in large amounts of metal or fiber contamination in the fluid. If the fluid is contaminated, flush the fluid cooler and lines.

Fig. 9 Torque Converter Assembly

1 - TURBINE

2 - IMPELLER

3 - HUB

4 - STATOR

5 - FRONT COVER

6 - CONVERTER CLUTCH DISC

7 - DRIVE PLATE

IMPELLER

The impeller (Fig. 10) is an integral part of the converter housing. The impeller consists of curved blades placed radially along the inside of the housing on the transmission side of the converter. As the converter housing is rotated by the engine, so is the impeller, because they are one and the same and are the driving member of the system.

Fig. 10 Impeller

1 - ENGINE FLEXPLATE

2 - OIL FLOW FROM IMPELLER SECTION INTO TURBINE SECTION

3 - IMPELLER VANES AND COVER ARE INTEGRAL

4 - ENGINE ROTATION

5 - ENGINE ROTATION

TURBINE

The turbine (Fig. 11) is the output, or driven, member of the converter. The turbine is mounted within the housing opposite the impeller, but is not attached to the housing. The input shaft is inserted through the center of the impeller and splined into the turbine.

The design of the turbine is similar to the impeller, except the blades of the turbine are curved in the opposite direction.

Fig. 11 Turbine

1 - TURBINE VANE

2 - ENGINE ROTATION

3 - INPUT SHAFT

4 - PORTION OF TORQUE CONVERTER COVER

5 - ENGINE ROTATION

6 - OIL FLOW WITHIN TURBINE SECTION

STATOR

The stator assembly (Fig. 12) is mounted on a stationary shaft which is an integral part of the oil pump. The stator is located between the impeller and turbine within the torque converter case (Fig. 13).

The stator contains an over-running clutch, which allows the stator to rotate only in a clockwise direction.

When the stator is locked against the over-running clutch, the torque multiplication feature of the torque converter is operational.

Fig. 12 Stator Components

1 - CAM (OUTER RACE)

2 - ROLLER

3 - SPRING

4 - INNER RACE

TORQUE CONVERTER CLUTCH (TCC)

The TCC (Fig. 14) was installed to improve the efficiency of the torque converter that is lost to the slippage of the fluid coupling. Although the fluid coupling provides smooth, shock-free power transfer, it is natural for all fluid couplings to slip. If the impeller and turbine were mechanically locked together, a zero slippage condition could be obtained. A hydraulic piston was added to the turbine, and a friction material was added to the inside of the front cover to provide this mechanical lock-up.

OPERATION

The converter impeller (Fig. 15) (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.

TURBINE

As the fluid that was put into motion by the impeller blades strikes the blades of the turbine, some of the energy and rotational force is transferred into the turbine and the input shaft. This causes both of them (turbine and input shaft) to rotate in a clockwise direction following the impeller. As the fluid is leaving the trailing edges of the turbine's blades it continues in a "hindering" direction back toward the impeller. If the fluid is not redirected before it strikes the impeller, it will strike the impeller in such a direction that it would tend to slow it down.

Fig. 13 Stator Location

1 - STATOR

2 - IMPELLER

3 - FLUID FLOW

4 - TURBINE

Fig. 14 Torque Converter Clutch (TCC)

1 - IMPELLER FRONT COVER

2 - THRUST WASHER ASSEMBLY

3 - IMPELLER

4 - STATOR

5 - TURBINE

6 - FRICTION DISC

Fig. 15 Torque Converter Fluid Operation

1 - APPLY PRESSURE

2 - THE PISTON MOVES SLIGHTLY FORWARD

3 - RELEASE PRESSURE

4 - THE PISTON MOVES SLIGHTLY REARWARD

STATOR

Torque multiplication is achieved by locking the stator's over-running clutch to its shaft (Fig. 16).

Under stall conditions (the turbine is stationary), the oil leaving the turbine blades strikes the face of the stator blades and tries to rotate them in a counterclockwise direction. When this happens the over-running clutch of the stator locks and holds the stator from rotating. With the stator locked, the oil strikes the stator blades and is redirected into a "helping" direction before it enters the impeller. This circulation of oil from impeller to turbine, turbine to stator, and stator to impeller, can produce a maximum torque multiplication of about 2.4:1. As the turbine begins to match the speed of the impeller, the fluid that was hitting the stator in such as way as to cause it to lock-up is no longer doing so. In this condition of operation, the stator begins to free wheel and the converter acts as a fluid coupling.

Fig. 16 Stator Operation

1 - DIRECTION STATOR WILL FREE WHEEL DUE TO OIL PUSHING ON BACKSIDE OF VANES

2 - FRONT OF ENGINE

3 - INCREASED ANGLE AS OIL STRIKES VANES

4 - DIRECTION STATOR IS LOCKED UP DUE TO OIL PUSHING AGAINST STATOR VANES

TORQUE CONVERTER CLUTCH (TCC)

In a standard torque converter, the impeller and turbine are rotating at about the same speed and the stator is freewheeling, providing no torque multiplication.

By applying the turbine's piston to the front cover's friction material, a total converter engagement can be obtained. The result of this engagement is a direct 1:1 mechanical link between the engine and the transmission.

Converter clutch engagement in third or fourth gear range is controlled by sensor inputs to the powertrain control module. Inputs that determine clutch engagement are: coolant temperature, engine rpm, vehicle speed, throttle position, and manifold vacuum. The torque converter clutch is engaged by the clutch solenoid on the valve body. The clutch can be engaged in third and fourth gear ranges depending on overdrive control switch position. If the overdrive control switch is in the normal ON position, the clutch will engage after the shift to fourth gear, and above approximately 72 km/h (45 mph). If the control switch is in the OFF position, the clutch will engage after the shift to third gear, at approximately 56 km/h (35 mph) at light throttle.