Hybrid shaft seal assembly for movable shafts

1. A fluid consumer comprising:

a housing for containing an operating fluid;

a shaft movable relative to the housing; and

a shaft seal assembly configured to seal against a mating surface of the shaft to restrict leakage from a fluid-side of the consumer, the shaft seal assembly comprising:

a seal case movable relative to the mating surface of the shaft;

a biasing force that biases the seal case towards the mating surface of the shaft; and

a seal at least partially disposed in the seal case, the seal being configured to seal against the mating surface of the shaft;

wherein the consumer is configured such that:

when in use, fluid pressure from the fluid-side exerts a fluid force against the seal case that is opposite the biasing force,

when fluid pressure exerted against the seal case is equal to or greater than a threshold pressure, (i) the fluid force against the seal case overcomes the biasing force such that the seal case sealingly separates from mating surface of the shaft, and (ii) the fluid pressure from the fluid-side also exerts a force against the seal that forces the seal into sealing engagement against the mating surface of the shaft to form a dynamic seal; and

when fluid pressure exerted against the seal case is less than the threshold pressure, (i) the seal is sealingly engaged against the mating surface of the shaft to form a static seal, and (ii) the biasing force overcomes the fluid force against the seal case, such that a sealing surface of the seal case is sealingly engaged against the mating surface of the shaft to form an additional static seal.

2. The fluid consumer according to claim 1 ,

wherein the biasing force is provided by a biasing member; or

wherein the biasing force is provided by a source of fluid pressure.

3. The fluid consumer according to claim 1 ,

wherein the movable seal case has an interior portion and an exterior portion; and

wherein fluid pressure in the interior portion supplies at least part of the fluid force that is opposite the biasing force.

4. The fluid consumer according to claim 2 ,

wherein the biasing member is located outside of the interior portion of the seal case.

5. The fluid consumer according to claim 2 ,

wherein the seal case includes a wall that at least partially forms an internal fluid chamber of the seal case, the internal fluid chamber configured to contain fluid from the fluid-side in which the fluid force is exerted in a first direction against the wall, and

wherein the biasing member is mounted outside of the seal case on an opposite side of the wall as the fluid chamber, and the biasing member is configured to exert the biasing force against the wall in a second direction opposite the first direction.

6. The fluid consumer according to claim 2 ,

wherein the threshold pressure is based at least partially upon the biasing force of the biasing member and an area of the seal case exposed to the fluid pressure.

7. The fluid consumer according to claim 2 ,

wherein the biasing member is a spring.

8. The fluid consumer according to claim 1 ,

wherein the seal case includes a radially inner wall, a radially outer wall, and a back wall connecting the radially inner and outer walls, the respective walls having an interior portion and an exterior portion, the interior portion forming an annular channel that at least partially contains the seal; and

wherein the radially inner wall has an end face which includes the sealing surface that engages the mating surface of the shaft to form the static seal.

9. The fluid consumer according to claim 8 ,

wherein the seal case is made of a material that forms the sealing surface and the seal case enables sealing engagement with the mating surface to provide the static seal.

10. The fluid consumer according to claim 1 ,

wherein the sealing surface of the seal case includes a separate seal that is operatively coupled to the seal case.

11. The fluid consumer according to claim 1 ,

wherein the seal at least partially disposed in the seal case is a nose seal having an axially projecting nose portion and a radially enlarged portion axially offset from the nose portion, the nose portion having a flat sealing surface that is configured to sealingly engage the mating surface of the shaft.

12. The fluid consumer according to claim 1 ,

wherein the seal at least partially disposed in the seal case includes a radial seal groove that contains a separate seal that sealingly engages an interior surface of the seal case.

13. The fluid consumer according to claim 1 ,

wherein the shaft seal assembly further includes a second biasing member located in a chamber between a wall of the seal case and the seal, the second biasing member being configured to apply a biasing force to the seal to at least partially form the static seal.

14. The fluid consumer according to claim 1 ,

wherein the shaft seal assembly is mounted in an annular space of the housing of the fluid consumer that surrounds the shaft about a longitudinal axis of the shaft.

15. The fluid consumer according to claim 1 ,

wherein the fluid consumer is a hydraulic pump.