Fuel injection apparatus for internal combustion engines

Claim 1

A fuel injection pump-and-nozzle assembly forming part of a fuel injection apparatus serving an internal combustion engine, said assembly being of the type that has (a) a hydraulically operated pump piston having two opposite radial faces, (b) a pump work chamber bounded by one of said radial faces of said pump piston, (c) a servo pressure chamber bounded by the other of said radial faces of said pump piston, (d) a pressure source externally of said assembly for pressurizing fuel to a supply pressure, (e) first supply conduit means extending from said pressure source to said pump work chamber, (f) a supply valve disposed in said first supply conduit means, (g) second supply conduit means extending from said pressure source to said servo pressure chamber, (h) discharge or return conduit means extending from said servo pressure chamber, (i) a solenoid control valve for controlling the flow in said second supply conduit means and in said discharge conduit means for intermittently causing fuel to be admitted at said supply pressure from said pressure source into said servo pressure chamber to effect the delivery strokes of said pump piston, and (j) a fuel injection valve in communication with said pump work chamber, said fuel injection valve being biased closed with an opening pressure greater than the charging pressure prevailing in said pump work chamber at the end of the charging period, the improvement comprising A. a throttle member disposed in said first supply conduit means between said pressure source and said supply valve, said throttle member being so dimensioned as to substantially lengthen the charging period, during which fuel is supplied from said pressure source to said pump work chamber, with respect to the injection period during which fuel is injected into the engine from said pump work chamber, and B. spring means urging said supply valve towards a closed position against the flow of fuel from said pressure source, the supply valve closing pressure exerted by said spring means being so designed that taken together with the maximum charging pressure in the pump work chamber it at most equals said supply pressure, said supply pressure being greater than the opening pressure of said fuel injection valve, wherein the radial faces of said pump piston define identical pressure receiving areas, and wherein said pump piston is displaceable in order to effect the delivery strokes and the charging strokes of the pump-andnozzle assembly by the pressurized fuel delivered into said servo pressurE chamber and said pump work chamber.