Servo controlled timing advance for unit pump or unit injector
AssigneeStanadyne, Inc.
InventorsMark Duquette, Kenneth Klopfer
Life of this patent
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Abstract
A hydraulically actuated servo piston and hydraulic advance piston are integrated into the cam follower of a unit pump or injector to provide variable advance for an injection event produced by the pump or injector. The servo piston is nested in the advance piston with fluid passageways in the advance piston selectively opened or closed by movement of the servo piston. The full pressure of a hydraulic pump is available to the advance piston for powering the advance function, while stepwise reduced levels of hydraulic pressure from the same hydraulic pump are applied to control movement of the servo piston. A damping orifice restricts flow of hydraulic fluid to and from the servo piston.
Claims19
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.
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.
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.
Dependencies are inferred from the claim text.