Fuel injection apparatus for internal combustion engines

Claim 1

A fuel injection apparatus serving an internal combustion engine and having at least one pump-and-nozzle assembly of the type that includes (a) a hydraulically operated pump piston having two opposite radial faces of identical area, (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 compression spring disposed in said servo pressure chamber and exerting a force on said pump piston, (e) a pressure source externally of said assembly for pressurizing fuel, (f) first supply conduit means extending from said pressure source to said pump work chamber, (g) a check valve disposed in said first supply conduit means to permit a fuel flow from said pressure source to said pump work chamber, (h) second supply conduit means extending from said pressure source to said servo pressure chamber, (i) discharge conduit means extending from said servo pressure chamber, (j) a control valve for controlling the flow in said second supply conduit means and in said discharge conduit means for intermittently causing pressurized fuel to be admitted from said pressure source into said servo pressure chamber to effect, together with said compression spring, the delivery strokes of said pump piston, (k) a throttle member disposed in said discharge conduit means downstream of said control valve and (1) a spring-biased fuel injection valve communicating with said pump work chamber, the improvement comprising A. means defining a permanently set throttle opening in said throttle member, B. a solenoid valve situated immediately adjacent said servo pressure chamber and constituting said control valve, said solenoid valve adapted to assume a closed position and an open position, C. means establishing communication between said servo pressure chamber and said discharge conduit means through said throttle member in the closed position of said solenoid valve, D. means establishing communication between said servo pressure chamber and said pressure source in the open position of said solenoid valve and E. means controlling the periods of closed and open positions of said solenoid valve for determining the duration of the charging strokes of said pump piston during which fuel is supplied to said pump work chamber from said pressure source, said duration determining the fuel quantity readied for injection in said pump work chamber.