Turbocharger system with turbine bypass valve actuated by multiple-rate fluid pressure actuator

1. A turbocharger system, comprising a turbocharger having a turbine driven by exhaust gas from an internal combustion engine and a compressor driven by the turbine for compressing air for delivery to the engine, a turbine bypass valve arranged with respect to the turbine such that the turbine bypass valve is movable between an open position and a closed position for regulating flow of exhaust gas to the turbine, and motive device connected to the turbine bypass valve and operable to provide motive force for moving the turbine bypass valve between the open and closed positions, wherein the motive device comprises a fluid pressure actuator comprising a piston slidable in a cylinder, the piston dividing an internal space in the cylinder into first and second chambers, one of said chambers containing a compression spring assembly operable to exert a spring force on the piston in a first direction, the cylinder defining a port into one of said chambers through which the chamber can be selectively subjected to a vacuum or pressure for exerting a fluid pressure force on the piston in a second direction opposite from the first direction such that the piston will move in the second direction when the fluid pressure force exceeds the spring force, and wherein the spring assembly comprises a first spring arranged to be compressed by the piston throughout a first range of motion of the piston, a second spring arranged to be compressed by the piston throughout a second range of motion that is smaller than and co-terminal with the first range of motion but to be uncompressed during an initial part of the first range of motion of the piston in the second direction, and a third spring arranged to be compressed by the piston throughout a third range of motion that is smaller than and co-terminal with the second range of motion but to be uncompressed during an initial part of the second range of motion of the piston in the second direction.

2. The turbocharger system of claim 1 , wherein the second spring has a spring constant differing from that of the first spring.

3. The turbocharger system of claim 2 , wherein the spring constant of the second spring is greater than that of the first spring.

4. The turbocharger system of claim 3 , wherein the spring constant of the second spring is at least two times that of the first spring.

5. The turbocharger system of claim 3 , wherein the spring constant of the second spring is at least four times that of the first spring.

6. The turbocharger system of claim 3 , wherein the spring constant of the second spring is at least six times that of the first spring.

7. The turbocharger system of claim 1 , wherein at least one of the second and third springs has a spring constant differing from that of the first spring.

8. The turbocharger system of claim 7 , wherein the spring constant of the second spring is greater than that of the first spring.

9. The turbocharger system of claim 8 , wherein the spring constant of the third spring is greater than that of the second spring.

10. A fluid pressure actuator for providing motive force to move a turbine bypass valve of a turbocharger system that includes a turbocharger having a turbine driven by exhaust gas from an internal combustion engine and a compressor driven by the turbine for compressing air for delivery to the engine, the turbine bypass valve being arranged with respect to the turbine such that the turbine bypass valve is movable between an open position and a closed position for regulating flow of exhaust gas to the turbine, the fluid pressure actuator comprising:

a piston slidable in a cylinder, the piston dividing an internal space in the cylinder into first and second chambers, one of said chambers containing a compression spring assembly operable to exert a spring force on the piston in a first direction, the cylinder defining a port into one of said chambers through which the chamber can be selectively subjected to a vacuum or pressure for exerting a fluid pressure force on the piston in a second direction opposite from the first direction such that the piston will move in the second direction when the fluid pressure force exceeds the spring force, and wherein the spring assembly comprises a first spring arranged to be compressed by the piston throughout a first range of motion of the piston, a second spring arranged to be compressed by the piston throughout a second range of motion that is smaller than and co-terminal with the first range of motion but to be uncompressed during an initial part of the first range of motion of the piston in the second direction, and a third spring arranged to be compressed by the piston throughout a third range of motion that is smaller than and co-terminal with the second range of motion but to be uncompressed during an initial part of the second range of motion of the piston in the second direction.

11. The fluid pressure actuator of claim 10 , wherein the second spring has a spring constant differing from that of the first spring.

12. The fluid pressure actuator of claim 11 , wherein the spring constant of the second spring is greater than that of the first spring.

13. The fluid pressure actuator of claim 12 , wherein the spring constant of the second spring is at least two times that of the first spring.

14. The fluid pressure actuator of claim 12 , wherein the spring constant of the second spring is at least four times that of the first spring.

15. The fluid pressure actuator of claim 13 , wherein the spring constant of the second spring is at least six times that of the first spring.

16. The fluid pressure actuator of claim 10 , wherein at least one of the second and third springs has a spring constant differing from that of the first spring.

17. The fluid pressure actuator of claim 16 , wherein the spring constant of the second spring is greater than that of the first spring.

18. The fluid pressure actuator of claim 17 , wherein the spring constant of the third spring is greater than that of the second spring.