Torque converter lockup clutch including axial one-way clutch

1. A lockup clutch for a torque converter comprising:

a clutch plate including a friction material;

a piston including a first wedge surface; and

a support supporting the piston, the piston being axially slidable along the support in a first axial direction to cause engagement of the lockup clutch by contacting the friction material; and

a wedge including a second wedge surface, the wedge being axially movable along the support, the first wedge surface being arranged and configured with respect to the second wedge surface such that contact between the first wedge surface and the second wedge surface limits axial movement of the piston in a second axial direction opposite the first axial direction,

the piston including a stop surface for contacting a further surface of the wedge, the stop surface configured for contacting the further surface of the wedge when the piston is moved in the first axial direction to cause engagement of the lockup clutch,

the wedge and piston being arranged and configured such that the wedge maintains a consistent liftoff distance from the friction material as the friction material thins out,

wherein the piston includes a groove formed in a surface thereof, the groove being defined by the stop surface and an angled surface forming the first wedge surface,

wherein the groove is formed in an inner circumferential surface of the piston and the wedge is a ring held on an outer circumferential surface of the support,

wherein the piston includes a radially extending section configured for contacting the clutch plate and an axially extending section extending axially from a radially outermost end of the radially extending section, the inner circumferential surface of the piston that the groove is formed in being at a radially innermost end of the radially extending section.

2. The lockup clutch as recited in claim 1 wherein the ring is a conical ring.

3. The lockup clutch as recited in claim 1 further comprising a seal between the radially innermost end of the radially extending section and the outer circumferential surface of the support.

4. The lockup clutch as recited in claim 1 further comprising an inner axial surface of a torque converter front cover, the clutch plate being sandwiched axially between the inner axial surface and the piston, the piston being axially slidable in the first axial direction to force the clutch plate into the inner axial surface to cause the engagement of the lockup clutch, the first wedge surface being arranged and configured with respect to the second wedge surface such that contact between the first wedge surface and the second wedge surface limits axial movement of the piston away from the clutch plate.

5. The lockup clutch as recited in claim 1 further comprising a leaf spring connected to the piston biasing the piston in the second axial direction.

6. The lockup clutch as recited in claim 1 wherein the support is a front cover hub section.

7. The lockup clutch as recited in claim 6 wherein the front cover hub section includes a first radial extension and a second radial extension, the piston being slidable along the first radial extension and the second radial extension.

8. The lockup clutch as recited in claim 7 wherein the radially innermost end of the piston is axially slidable along the first radial extension and the axially extending section of the piston is axially slidable along the second radial extension.

9. The lockup clutch as recited in claim 8 further comprising a leaf spring connected to the piston and the second radial extension biasing the piston in the second axial direction.

10. A torque converter comprising:

the lockup clutch as recited in claim 1 ,

a damper assembly configured for transferring torque from the lockup clutch to a transmission input shaft when the lockup clutch is locked.

11. The torque converter as recited in claim 10 wherein a radially outer end of the clutch plate drivingly engages the damper assembly.

12. The torque converter as recited in claim 11 wherein the radially outer end of the clutch plate includes drive projections extending into circumferential spaces between springs of the damper assembly.

13. The lockup clutch as recited in claim 1 wherein the wedge has a triangular shape.

14. A method of forming a lockup clutch comprising:

providing a piston with a first wedge surface;

providing the piston and a wedge including a second wedge surface on a support such that the piston is axially slidable along the support in a first axial direction to cause engagement of the lockup clutch and the first wedge surface is arranged and configured with respect to the second wedge surface such that contact between the first wedge surface and the second wedge surface limits axial movement of the piston in a second axial direction opposite the first axial direction to maintain a controlled liftoff over a life of the lockup clutch,

forming a stop surface on the piston for contacting a further surface of the wedge, the stop surface configured for contacting the further surface of the wedge when the piston is moved in the first axial direction to cause engagement of the lockup clutch,

wherein the forming of the stop surface on the piston includes forming a groove in an inner circumferential surface of the piston, the groove being defined by the stop surface and an angled surface forming the first wedge surface,

wherein the wedge is held on an outer circumferential surface of the support,

wherein the piston includes a radially extending section configured for contacting a clutch plate of the lockup clutch, the inner circumferential surface of the piston that the groove is formed in being at a radially innermost end of the radially extending section; and

further comprising providing a seal between the radially innermost end of the radially extending section and the outer circumferential surface of the support, the seal being held in a further groove in the inner circumferential surface of the piston at the radially innermost end.

15. The method as recited in claim 14 further comprising providing the wedge in the groove before the piston is provided on the support.

16. The method as recited in claim 15 wherein the wedge is a conical ring.

17. The method as recited in claim 14 further comprising providing the clutch plate axially sandwiched between an inner axial surface of a torque converter front cover and the piston, the piston being provided on the support such that the piston is axially slidable in the first axial direction to force the clutch plate into the inner axial surface to cause the engagement of the lockup clutch, the first wedge surface being provided with respect to the second wedge surface such that contact between the first wedge surface and the second wedge surface limits axial movement of the piston away from the clutch plate.

18. The method as recited in claim 14 further comprising connecting a leaf spring to the piston biasing the piston in the second axial direction.

19. A lockup clutch for a torque converter comprising:

a clutch plate including a friction material;

a piston including a first wedge surface; and

a support supporting the piston, the piston being axially slidable along the support in a first axial direction to cause engagement of the lockup clutch by contacting the friction material;

a wedge including a second wedge surface, the wedge being axially movable along the support, the first wedge surface being arranged and configured with respect to the second wedge surface such that contact between the first wedge surface and the second wedge surface limits axial movement of the piston in a second axial direction opposite the first axial direction,

the piston including a stop surface for contacting a further surface of the wedge, the stop surface configured for contacting the further surface of the wedge when the piston is moved in the first axial direction to cause engagement of the lockup clutch,

the wedge and piston being arranged and configured such that the wedge maintains a consistent liftoff distance from the friction material as the friction material thins out; and

a leaf spring connected to the piston biasing the piston in the second axial direction, the leaf spring being at a radial height of the clutch plate,

wherein the support is a front cover hub section including a first radial extension and a second radial extension, the piston being slidable along the first radial extension and the second radial extension, the leaf spring being fixed to the second radial extension.