Development of a novel miniature high-pressure fuel pump with a low specific speed

Whenever a small amount of fluid has to be pumped against a high differential pressure, various types of piston pumps are typically used. However, the need for excellent suction behaviour, for the possibility of a dry run and for minimal manufacturing costs requires the development of alternative pump concepts. This paper presents the development of a novel miniature high-pressure fuel gear pump to replace the feed pump as well as the high-pressure pump in gasoline direct-injection fuel systems. It was found that the clearance between the housing and the rotating gears has to be reduced to a minimum in order to keep the internal leakage at a reasonable level. Based on theoretical predictions a radially and axially pressure-compensated pump concept was developed by incorporation of a floating sealing element able to minimize the tip and face leakages. The design of this sealing element was optimized in the course of experimental investigations. The experiments were carried out using a specifically developed test rig, and the obtained results prove that the optimized pump is able to generate the required differential pressure Δp = 40–50 bar at a specific speed nq = 0.005–0.400 r/min. The measured Δp–Q curves were almost vertical beyond a certain pressure level, yielding a nearly pressure-independent volumetric efficiency of approximately 75%. The developed pump concept finally offers outstanding performance characteristics in an operation range where conventional gear pump concepts usually lose importance owing to unacceptably high volumetric losses.