Fuel injection pump plunger

Claim 1

A fuel injection pump plunger which moves reciprocally within a plunger chamber of a plunger barrel to suck in fuel through a fuel port in the barrel and expel fuel from a fuel outlet, the plunger comprising: a plunger head provided with a sloping lower lead formed sloping downward on a peripheral surface of the plunger head; a longitudinal groove connecting the lower lead to the plunger chamber; an upper lead formed sloping downward from an upper face of the plunger head facing the plunger chamber at a position of vertical opposition to the lower lead; an orifice constituted by a cut portion which extends parallel with an axis of the plunger between an end of the upper lead and the plunger chamber; means for rotating the plunger to vary the relative positional relationship between the upper lead and the fuel port to advance or retard the fuel injection timing and to vary the relative positional relationship between the lower lead and the fuel port to control the fuel injection amount; and wherein within the range of rotation of the plunger the orifice cut portion corresponds to a full-load operating region of an engine and the relationship between a width F of the orifice cut portion and a width L of the upper lead is L>F, whereby the timing of the fuel injection can be advanced through an orifice effect produced by the orifice cut portion during the delivery of fuel accompanying the elevation of the plunger.