A fuel injection system for an engine comprising, in combination:
- a fuel source;
- a plunger pump adapted to be driven by the engine and having a barrel in which a plunger is sealingly slidable, the barrel and plunger defining a pressure chamber, the barrel being formed with a first and a second hole through the circumference thereof, the plunger being formed with a longitudinal passageway opening at one end into the pressure chamber and a circumferential groove connected to the other end of the longitudinal passageway, the first hole being connected to the fuel source;
- a fuel injection nozzle adapted to be operatively connected to the engine and connected to the pressure chamber, the plunger pump being connected to supply fuel from the fuel source to the nozzle at high pressure, the nozzle having a valve element biased to block fuel flow through the nozzle, the valve element having a first surface exposed to pressurized fuel from the pump so that the valve element is urged by the pressurized fuel applied to the first surface in a direction opposite to the biasing force so that the force of the pressurized fuel on the first surface overcomes the biasing force during the injection stroke of the pump plunger to move the valve element to allow fuel flow through the nozzle and thereby fuel injection into the engine, the valve element having a second surface connected to the second hole and arranged so that the pressurized fuel from the pump applied to the second surface urges the valve element in the same direction as the biasing force;
- and,
- a valve connected to feed pressurized fuel from the pump to the second surface of the valve element near the end of the injection stroke of the plunger whereby the biasing force and the force of the pressurized fuel applied to the second surface of the valve element in combination move the valve element against the force of the pressurized fuel applied to the first surface of the valve element to move the valve element to block fuel flow through the nozzle and terminate the fuel injection, said valve including the plunger and the barrel formed with the second hole, the first and second holes being arranged so that in sequence during the injection stroke of the plunger, the second hole is covered by the end of the plunger defining the pressure chamber thereby blocking communication between the pressure chamber and the second surface of the valve element, the first hole is covered by the end of the plunger defining the pressure chamber thereby blocking communication between the pressure chamber and the fuel source, the second hole is uncovered by the circumferential groove of the plunger thereby allowing communication between the pressure chamber and the second surface for the valve element and the first hole is uncovered by the circumferential groove of the plunger thereby allowing communication between the pressure chamber and the fuel source, said valve further including a check valve unit connected between the second hole of the barrel and the second surface of the valve element of the nozzle to permit fuel flow only from the second hole to the second surface, said check valve unit comprising a chamber formed therewithin, a passageway connected between the chamber and the second hole of the barrel, and a valve element urged by a compression spring disposed in the chamber to block the passageway and formed with a longitudinal constricted passageway to bypass the passageway.