Wet clutch actuation piston and method of use

1. A method of operating a piston clutch system, comprising:

selectively delivering pressurized fluid along a fluid conduit within a shaft to a location adjacent a first circumferential groove in a piston, said shaft located through said piston;

using a seal plateau to define a radial fluid boundary of said first circumferential groove;

rotating said piston wherein said seal plateau prevents centrifugal forces from moving said fluid radially outward beyond said seal plateau; and

axially translating said piston into a clutch pack against a biasing member to selectively lock a plurality of interleaved plates in said clutch pack.

2. The method of claim 1 , wherein said piston has a planar outboard surface radially outboard from said seal plateau that extends to an outer circumferential surface of said piston.

3. The method of claim 1 , wherein a prefill fluid pressure in said conduit is insufficient to move said piston against said biasing member and cause said piston to engage said clutch pack, said prefill fluid pressure not incurring sufficient centrifugal fluid forces to cause said piston to engage said clutch pack.

4. The method of claim 1 , wherein an engagement pressure in said conduit is sufficient to move said piston against said biasing member and cause said piston to engage said clutch pack.

5. The method of claim 1 , wherein the seal plateau comprises a continuous radial face extending in a circumference around a shaft side radial face of the piston.

6. The method of claim 1 , wherein a second circumferential groove is positioned radially outside of the first circumferential groove and the seal plateau.

7. The method of claim 1 , wherein a second circumferential groove and oil port are positioned radially outside of the seal plateau.

8. The method of claim 1 , further comprising preventing fluid from escaping past a shaft, wherein the shaft contacts an inner circumferential surface of the piston.

9. The method of claim 1 , further comprising preventing fluid from escaping past a groove in an outer circumferential surface of the piston, wherein the outer circumferential surface of the piston contacts a housing.

10. A method of operating a piston clutch system, comprising:

delivering fluid from within a piston to a shaft side radial face of the piston, and delivering the fluid to a location adjacent to a first circumferential groove in the shaft side radial face;

rotating the piston; and

using a seal plateau circumferentially surrounding the first circumferential groove to prevent the delivered fluid from moving radially outward past the seal plateau during rotation of the piston.

11. The method of claim 10 , wherein the first circumferential groove forms a transition from an inner circumferential surface of the piston to the seal plateau.

12. The method of claim 10 , wherein a second circumferential groove is positioned radially outside of the first circumferential groove and the seal plateau, and the seal plateau transitions into the second circumferential groove.

13. The method of claim 10 , further comprising using a groove within the seal plateau to prevent the fluid from moving radially outward past the seal plateau.

14. The method of claim 10 , further comprising delivering an amount of fluid to the shaft side radial face to prefill the first circumferential groove but not to displace the piston.

15. The method of claim 14 , further comprising delivering more fluid to the shaft side radial face to displace the piston toward a clutch pack.