Claims
- 1. An actuator having a variable length extending between an energy receiving end and an energy transmitting end, said actuator comprising:
a body defining a first bore; an actuator piston disposed in said first bore and defining a second bore, said actuator piston movable relative to said body to define a variable volume first hydraulic chamber between said body and said actuator piston; and a servo piston disposed in said second bore and movable relative to said actuator piston to defined a second variable volume hydraulic chamber between said actuator piston and said servo piston; wherein the length of said actuator is dependent upon the volume of said first hydraulic chamber, movement of said servo piston relative to said actuator piston controls delivery of a first hydraulic pressure to said first hydraulic chamber and movement of said servo piston is controlled by delivery of a second hydraulic pressure to said second hydraulic chamber, said second hydraulic pressure being modulated from said first hydraulic pressure.
- 2. The actuator of claim 1, wherein said second hydraulic pressure is modulated in discrete steps from a maximum hydraulic pressure substantially equal to said first hydraulic pressure to a minimum hydraulic pressure between said maximum hydraulic pressure and zero, each discrete step producing a different actuator length.
- 3. The actuator of claim 1, wherein a known spring force acts in opposition to movement of said servo piston away from said actuator piston so that a net pressure in said second hydraulic chamber is substantially proportional to the known spring force applied to the servo piston.
- 4. The actuator of claim 1, further comprising body pressure passageways penetrating said body to communicate with said first bore, said body pressure passageways selectively alignable with actuator piston pressure passageways penetrating said actuator piston to communicate with said second bore, said actuator piston pressure passageways selectively alignable with pressure transfer channels on the outside of said servo piston.
- 5. The actuator of claim 1, wherein said first and second hydraulic pressures are generated by a single source.
- 6. The actuator of claim 1, wherein said actuator comprises a cam follower assembly for translating rotary motion of an engine-driven cam into reciprocating linear motion and delivering said reciprocation linear motion to a pumping plunger for a unit pump or injector, said energy receiving end comprising a cam roller supported by said body and said energy transmitting end comprising a piston cap in contact with said first piston and moving relative to said body with said first piston.
- 7. The actuator of claim 1, wherein said second hydraulic chamber includes a damping orifice which restricts flow of hydraulic fluid into and out of said second hydraulic chamber.
- 8. A cam follower assembly for translating rotary motion of an engine-driven cam into reciprocating linear motion, said cam follower assembly disposed between the cam and a pumping plunger of a unit pump or injector to apply said reciprocating linear motion to said pumping plunger, said cam follower assembly having a variable length extending from the cam to a plunger actuation surface in contact with said plunger, said cam follower assembly comprising:
a cam follower body defining an advance piston cavity; an advance piston disposed in said advance piston cavity for axial movement therein, said advance piston defining a servo piston cavity; and a servo piston disposed in said servo piston cavity such that relative movement is permitted between said advance piston and said servo piston, wherein a first hydraulic chamber is defined between said cam follower body and said advance piston and a second hydraulic chamber is defined between said servo piston and said advance piston and the length of said cam follower assembly is dependant upon a volume of said first hydraulic chamber.
- 9. The cam follower assembly of claim 8, wherein movement of said servo piston relative to said advance piston controls a flow of hydraulic fluid to said first hydraulic chamber and movement of said servo piston is dependent upon a variable hydraulic pressure delivered to said second hydraulic chamber.
- 10. The cam follower assembly of claim 9, further comprising:
means for mounting one end of a servo piston spring in fixed relation to said follower body, with the other end of said servo piston spring acting on said servo piston in opposition to the hydraulic pressure applied to said second hydraulic chamber such that the net pressure in said second hydraulic chamber is proportional to the force exerted by said servo piston spring.
- 11. The cam follower assembly of claim 8, wherein said advance piston defines a fluid passage into said second hydraulic chamber and said fluid passage comprises damping means for restricting the flow of hydraulic fluid into and out of said second hydraulic chamber.
- 12. The cam follower assembly of claim 11, wherein said damping means comprises a restricted flow orifice in said fluid passage.
- 13. The cam follower assembly of claim 8, wherein a constant hydraulic pressure is applied to said first hydraulic chamber and a modulated hydraulic pressure is applied to said second hydraulic chamber, said constant and modulated hydraulic pressures being derived from a single hydraulic source.
- 14. The cam follower assembly of claim 8, further comprising:
follower body hydraulic ports and passageways penetrating a cylindrical wall of said follower body surrounding said advance piston cavity; advance piston hydraulic ports and passageways penetrating a cylindrical wall of said advance piston surrounding said servo piston cavity; and annular fluid transfer channels on an outer surface of said servo piston, wherein said follower body passageways are alignable with said advance piston hydraulic ports and said advance piston passageways are alignable with said annular fluid transfer channels, alignment of said follower body passageways with said advance piston hydraulic ports being dependent upon the position of said advance piston relative to said follower body and alignment of said advance piston passageways with said annular fluid transfer channels being dependent upon the position of said servo piston relative to said advance piston.
- 15. The cam follower assembly of claim 8, wherein said plunger actuation means comprises:
a piston cap having a lower portion in contact with a shoulder of said advance piston and axially extending to a central projection in contact with said plunger, said piston cap moving in concert with said advance piston such that the reciprocating linear motion of said cam follower assembly is transmitted to said plunger by said advance piston.
- 16. A method for hydraulically adjusting the timing of an injection event comprising:
axially moving a timing advance piston disposed in a cam follower body relative thereto in response to hydraulic pressure in an advance chamber defined between the cam follower body and the advance piston; axially moving a servo piston disposed in the timing advance piston relative thereto in response to hydraulic pressure in a servo chamber defined between the advance piston and the servo piston; applying a substantially constant hydraulic pressure to one of said advance or servo chambers; and applying a modulated hydraulic pressure to the other of said advance or servo chambers, wherein said substantially constant hydraulic pressure and said modulated hydraulic pressure are derived from a single hydraulic pressure source.
- 17. The method of claim 16, wherein said step of applying a substantially constant hydraulic pressure comprises:
applying said substantially constant hydraulic pressure to said advance chamber; and said step of applying a modulated hydraulic pressure comprises:
applying said modulated hydraulic pressure to said servo chamber, said modulated hydraulic pressure being a stepwise reduced value of said substantially constant hydraulic pressure.
- 18. The method of claim 16, comprising the step of:
mounting one end of a servo piston spring in fixed relation to the follower body with the other end of the servo piston spring exerting a known force on the servo piston on opposition to the hydraulic pressure in the servo chamber, wherein the pressure in the servo chamber is proportional to the known force exerted on the servo piston by the servo piston spring.
- 19. The method of claim 16, comprising the step of:
restricting the flow of hydraulic fluid into and out of said servo chamber.
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Application No. 60/247,825, filed Nov. 9, 2000.
Provisional Applications (1)
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Number |
Date |
Country |
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60247825 |
Nov 2000 |
US |