Apparatus for adjusting the timing of a fuel injection pump

Claim 1

In a fuel injection pump having a housing, a charge pump having pumping plungers to deliver measured charges of liquid fuel in successive pumping strokes to the cylinders of an associated engine, timing means to vary the timing of the pumping strokes relative to the operation of the associated engine, and actuating means for actuating the timing means for advancing and retarding the timing of the pumping strokes in response to the operating conditions of the associated engine, said actuating means comprising a piston for actuating the timing means and having its ends exposed to fluid chambers at the opposite ends thereof, spring means engaging the piston and a fluid supplied under pressure to one chamber at one end of the piston to bias the piston in the direction to retard the timing, a source of fluid under a regulated pressure correlated with engine speed in communication with the other chamber at the other end of the piston and acting against the bias of the spring means and fluid pressure in said one chamber to advance the timing of the pumping strokes with increased engine speed, said one chamber being connected to said housing, a drainage passageway for draining fluid from the housing to control the pressure in both the housing and said one chamber, valve means between said drainage passageway and the housing for maintaining the fluid pressure in both the housing and said one chamber at a predetermined generally constant pressure and pressure dump means selectively operable to connect the housing to said drainage passageway to dump the said predetermined generally constant pressure in both the housing and said one chamber without affecting the fluid pressure in said other chamber and thereby advance the timing by a predetermined amount.