Transmissions: Automatic Transmissions: Torque converters
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Topic IntroductionHelp

Sprag one way clutches

Summary
The stator one way clutch prevents the stator from turning in the opposite direction to engine rotation during torque multiplication. It allows the stator to rotate with the impeller and turbine when coupling point is reached.

In the sprag-type one-way clutch, the inner race has a central spline. It locates on the stator support shaft to hold the race stationary.

The outer race is part of the stator hub. It turns with the stator in the direction of engine rotation.

Equally-spaced sprags between the two races produce a wedging action to stop the stator rotating in reverse. The sprags are held in place by a spring loaded cage.

The cage moves the sprags together so that when the stator is locked, each carries an equal share of the load.

The one-way action is produced by the different radii of the sprags, and the curvature at their outer edges. This gradually increases from the shorter radius, to the larger.

When the stator is turned against engine rotation, it pivots the sprags towards the larger radius and wedges them between the two races, locking them together.

When the effort to the stator is reversed, the sprags pivot towards the smaller radius and the outer race glides freely over them in the direction of engine rotation.

In the roller type one-way clutch, the inner race is splined to the stator support. The outer race has wedge-shaped segments which retain the rollers.

In each segment, a waved compression spring pushes each roller towards the narrow end of the wedge. A force on the stator blades against engine rotation, locks the outer race onto the rollers, wedged between the two races.

Turning the stator with the engine rotation eases the wedging. And the stator rotates with the impeller and turbine.