Calculation of dynamic torque acted on external gear pump considering relief groove and trapped oil pressure

For research the effect of trapped oil pressure and teeth number on dynamic torque of external gear pump, meshing process was geometrical analyzed by dividing tooth surface into eight meshing point, three different areas and seven meshing stages. With meshing curvature radius of driving gear as a variable in a tooth period, the corresponding static and dynamic torque formula were derived. The special analysis and comparison were achieved with an instance. All results indicated that the higher trapped oil pressure, the more fluctuation of torque and higher value of max amplitude, but the min amplitude of torque was generally unchanged; the quality of meshing torque with the same teeth number of the gears was better than dissimilar teeth number. Static torque formula had a bigger calculation error. A lot of important conclusions were educed, which trapped oil pressure had a great negative influence on torque, and dissimilar teeth number of meshing gears had different influence on various performance of external gear pump, therefore trapped oil pressure should be eliminated as far as possible and the predominance of dissimilar teeth number on uniform teeth number wasn't absolutely positive.