Unit injector for internal combustion engines

Claim 1

In a unit fuel injector for an internal combustion engine, including: a plunger barrel unit which has a plunger barrel, a pumping plunger slidably received within said plunger barrel for reciprocating motion therein and controllable in circumferential position, said plunger having one end face and an outer peripheral surface, a fuel intake passage and a fuel overflow passage both opening into said plunger barrel and blockable by the outer peripheral surface of said plunger, a plunger chamber definable within said plunger barrel and by said one end face of said plunger, and communication passage means formed in the outer peripheral surface of said plunger for communicating said plunger chamber with said fuel intake passage and said fuel overflow passage; and an injection nozzle unit combined in one body with said plunger barrel unit; the improvement wherein: a solenoid valve is arranged across said fuel overflow passage for closing same to determine the injection timing and the injection quantity; said communication passage means comprises a first longitudinal slit for communicating said fuel intake passage with said plunger chamber, a second longitudinal slit for communicating said fuel overflow passage with said plunger chamber, and a circumferentially extending suction slit communicating with said first longitudinal slit and registrable with said fuel intake passage when said plunger is in an extreme position remote from said plunger chamber; said second longitudinal slit axially extending beyond said fuel overflow passage toward an opposite end of said plunger remote from said plunger chamber so as to maintain comminucation of said fuel overflow passage with said plunger chamber throughout substantially the whole stroke of said plunger when said second longitudinal slit is circumferentially aligned with said fuel overflow passage; said fuel intake passage, said fuel overflow passage, said first and second longitudinal slits, and said suction slit being so disposed that said plunger can assume selectively a normal operating position and a starting position, at respective first and second circumferential positions thereof; wherein in said normal operating position of said plunger, one of said first longitudinal slit and said suction slit is circumferentially aligned with said fuel intake passage to communicate same with said plunger chamber, and said second longitudinal slit is circumferentially aligned with said overflow passage to communicate same with said plunger chamber whereby said fuel overflow passage is maintained in communication with said plunger chamber throughout substantially the whole stroke of said plunger; and in said starting position of said plunger one of said first longitudinal slit and said suction slit is circumferentially aligned with said fuel intake passage, but said second longitudinal slit is circumferentially out of alignment with said fuel overflow passage to maintain said fuel overflow passage disconnected from said plunger chamber.