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The output of a fuel injection pump plunger is alternately directed to a pair of injection nozzles by a hydraulically actuated shuttle valve. A shuttle housing incorporated into the high pressure circuit includes a bore containing the valve shuttle which is reciprocated by alternating fuel pressure introduced at each end of the bore. The alternating pressurized fuel is supplied to the bore in timed relationship with the reciprocation of the pump's plunger by a rotary distributor driven by the pump cam shaft. Means are provided in the shuttle to interconnect the shuttle actuating and the injection pump high pressure passages during the intervals between fuel injection to establish a controlled low pressure level in the high pressure passages prior to the next injection.
The present invention is directed to the type of fuel injection system wherein the injection nozzles are supplied with fuel which is pumped and metered at a central fuel injection pump remote from the nozzles. In this type of system, the timing as well as the metering is controlled by the pump, and the nozzles valve opens, usually against spring pressure, only during the brief pumping interval to admit the pumped fuel quantity to a combustion chamber. The fuel is pumped at extremely high pressures, commonly between 5,000 and 20,000 psi, in order to effect the proper nozzle operation and fuel atomization.
Fuel injection pumps of the category described enjoy commercial popularity in three general types. In a first type, a separate single plunger pump is provided for each combustion chamber. This type is particularly adapted for use with large stationary diesels wherein the distance between cylinders would preclude the use of a single centrally located pump with its fuel distribution conduits.
In a second type of pump, a single pumping element actuated by a multilobed cam shaft is utilized to supply a plurality of engine cylinders by combining a distributor arrangement into the high pressure circuit. Typically, the pumping plunger is rotated and reciprocated, and suitable distributor slots in the rotating plunger direct the pump output sequentially to the engine cylinders. The fuel metering function is carried out by a fuel control sleeve on the plunger to selectively uncover a port communicating with the pumping chamber.
The third type of pump, and that to which the present invention is directed, is characterized by a central pump unit from which fuel is distributed through conduits to the individual combustion chambers, and wherein a separate pumping plunger is provided for each engine cylinder, the plungers commonly being arranged in line and driven by a common cam shaft. Fuel metering is accomplished by rotation of the plungers to vary the beginning or ending (or both) points of the plunger stroke utilized for high pressure pumping. This type of pump, while more expensive to build than the rotating distributor-plunger type pump described above, is recognized as a more dependable, longer lasting and generally superior pump and is preferred for engine fuel control where cost is not an overriding factor.