Suction controlled pump for HEUI systems

This invention relates generally to multiple piston pumps and more particularly to a high pressure pump used in a hydraulically actuated electronically controlled unit injector (HEUI) fuel control system. The invention is particularly applicable to and will be described with specific reference to a constant flow, fixed displacement pump and the integration of the fixed displacement pump into a HEUI system. However, those skilled in the art will appreciate that the invention may have broader application and may be integrated into other hydraulic pump driven systems, such as vehicular steering systems. A HEUI system uses a fixed displacement, piston pump to provide a generally constant pump flow of high pressure hydraulic fluid over the operating speed range of the pump to minimize parasitic power drains on the engine. The piston pump includes an orificing suction slot to vary the pump displacement over the operating speed of the pump. A throttling valve at the pump inlet may be provided to starve inlet fluid feed if reduced flow to the injectors is additionally required.