Fuel injection pump and timing control therefor

In a fuel injection pump for an associated internal combustion engine, pump plunger means providing sequential pumping strokes, means for changing the timing of the pumping strokes comprising a cylinder, an advance piston movable in said cylinder, means interconnecting said advance piston with said pump plunger means to advance and to retard the relative timing of the pumping strokes, a first source of fluid having a pressure correlated with engine speed, means operatively connected to said advance piston for moving said advance piston in response to said first pressure to change the relative timing of said pumping strokes including a source of operating fluid under pressure to power said advance piston, and gating means responsive to said first fluid pressure for disabling said operation of said advance piston moving means so that said advance piston is in a position corresponding with a fully retarded relative timing of pumping up to a predetermined speed, said advance piston moving means includes a servo mechanism including a servo piston and a servo spring, said first fluid pressure acting on said servo piston in opposition to said servo spring to establish an equilibrium position of said advance piston, a second cylinder, a spring holder piston movable in said second cylinder, said servo spring being mounted for movement with said spring holder piston to vary the reference position of said servo spring thereby to vary the equilibrium positioning of said advance piston, preloaded spring means for biasing said spring holder piston to a position commensurate with advanced relative timing of pumping, and a second fluid pressure connected to said second cylinder to act on said spring holder piston in opposition to said preloaded spring means, said second fluid pressure being correlated with a particular variable engine operated condition other than for said first fluid pressure, and the preload of said spring means being overcome by said second fluid pressure at a predetermined level of said particular operating condition of the engine to move said servo spring holder toward a position commensurate with a relatively retarded timing thereby to modify the timing control of said first fluid pressure.

In a fuel injection pump for an associated engine, pump plunger means providing sequential pumping strokes, means for changing the timing of the pumping strokes comprising a first cylinder, an advance piston movable in said first cylinder, means interconnecting said advance piston with said pump plunger means to advance and to retard the relative timing of the pumping strokes;

• a first source of fluid having a pressure correlated with engine speed, a second source of fluid having a pressure correlated with a variable engine operating condition other than speed, means operatively connected to said advance piston and responsive to said first fluid pressure and said second fluid pressure for moving said advance piston to change the relative timing of pumping strokes, said advance piston moving means comprising a servo mechanism including a servo piston for controlling the flow of an operating fluid to position said advance piston, and a servo spring, said first fluid pressure being connected to act on said servo piston in opposition to said servo spring to establish an equilibrium position of said advance piston;
• a second cylinder, a spring holder piston movable in said second cylinder, said servo spring being mounted for movement with said spring holder piston to vary the reference position of said servo spring thereby to vary the equilibrium positioning of said advance piston, means biasing said spring holder piston to a position commensurate with advanced relative timing of pumping, and said second fluid pressure being connected to said second cylinder to act on said spring holder piston in opposition to said bias means, said second fluid pressure being operative to overcome said bias means to move said servo spring holder toward a position commensurate with a relatively retarded timing thereby to modify the timing control of said first fluid pressure.