Theoretical investigation of the effect of a relief groove on the performance of a gerotor oil pump

To improve the performance of a gerotor oil pump used in transmission of an automobile, the effect of adopting a relief groove is investigated using the CFD (computational fluid dynamics) method. The main performance factors of models 1 (without the relief groove) and 2 (with the relief groove) are analyzed and compared with regard to the rotation speed and oil temperature. Results show that the volumetric efficiency of models 1 and 2 increases from 86.5 to 89.6 % and from 82.1 to 90.6 %, respectively, as the rotation speed increases from 1500 to 4500 rpm. By contrast, the volumetric efficiency of models 1 and 2 decreases from 89.6 to 76.3 % and from 90.6 to 79.3 % as the rotation speed increases from 4500 to 6500 rpm. In addition, it increases from 68.2 to 79.5 % and from 67.1 to 80.5 %, respectively, as the oil temperature increases from 20 to 120 °C. The increase of rotation speed increases the pressure in the chamber. However, the pressure ripple and average pressure decrease when the relief groove is used. Using a relief groove decreases the torque difference between the inner and outer rotor because the velocity of fluid is uniformed in the chamber. Besides, the potential damage of gerotor pump is reduced because the cavitation is suppressed and the damage power from the cavitation is decreased.