Distributor type fuel injection pump adapted for partial cylinder operation of an internal combustion engine

Claim 1

In a distributor type fuel injection pump for combination with an internal combustion engine having a plurality of cylinders, said pump including: a plunger having an outer peripheral surface; a plunger housing having an inner peripheral surface along which said plunger is received therein and defining therein a pump working chamber in cooperation with a head portion of said plunger; means for causing simultaneous reciprocating and rotative motion of said plunger; a low pressure space in which a portion of said plunger is located; a first port formed in said plunger in communication with said pump working chamber and opening in a portion of said outer peripheral surface of said plunger located in said low pressure space; a second port formed in said plunger in communication with said pump working chamber and opening in another portion of said outer peripheral surface of said plunger located within said plunger housing; a plurality of outlet pressure channels corresponding in number to said cylinders of said engine and connected to respective injection nozzles, said second port being disposed for successive engagement with said outlet pressure channels during said simultaneous reciprocating and rotary motion of said plunger; and a fuel injection quantity setting member having an inner peripheral surface slidably fitted on said portion of said outer peripheral surface of said plunger located in said low pressure space for engagement with said first port, and controllable in axial position relative to said plunger; whereby pressure feeding of fuel caused by movement of said plunger through delivery stroke thereof is terminated upon disengagement of said first port from said fuel injection quantity setting member; the improvement comprising: a third port formed in said plunger in communication with said pump working chamber, said third port opening in a portion of said outer peripheral surface of said plunger which is in permanent slidable engagement with said fuel injection quantity setting member; and a plurality of fourth ports formed in said fuel injection quantity setting member in circumferentially spaced relation and smaller in number to said outlet pressure channels, said fourth ports each communicating at one end with said low pressure space and opening at the other end in said inner peripheral surface of said fuel injection quantity setting member at a predetermined axial location thereof; wherein said third port and said fourth ports are arranged relative to each other such that each time said second port engages a predetermined one of said outlet pressure channels, said third port engages a corresponding one of said fourth ports, during each delivery stroke of said plunger in a predetermined low load region of said engine.