Fuel injection pump and timing control therefor

摘要

A liquid fuel injection pump for supplying timed charges of fuel to an engine by timed pumping strokes includes an adjustable timing mechanism for changing the timing of the pumping strokes. The timing mechanism includes an advance piston which is variably positionable in response to two different hydraulic control pressures. A speed related control pressure operates a servo mechanism associated with the advance piston to provide a component of speed advance. The reference position of a servo spring associated with the servo mechanism is varied by the second control pressure acting against a piston which mounts the spring and which is biased to a position of relatively advanced timing, thereby to add a component of advance which modifies or supplements the speed advance. The second control pressure is correlated with engine load and/or acceleration and in one embodiment is derived from the positioning of the fuel metering means and in another embodiment is derived from the intake manifold air pressure such as that from a turbocharged engine so that the timing is relatively advanced at low loads and during acceleration, and is relatively retarded at higher loads. A gate controlled by the position of a fuel limiting plunger coacts with the advance piston's servo mechanism to prevent advance of the advance piston during engine cranking, and maximum fuel delivery per pumping stroke is controlled according to intake manifold air pressure.