Abstract

To accurately calculate the flow rate of cycloid rotary pump as well as to correctly understand its trapped oil phenomenon, firstly the instantaneous flow rate formula of cycloid rotary pump was established based on the method of swept area, and then it was compared with the two present approximate formulas by an example. Secondly, based on the established flow rate formula and the created trapped oil model in the present literature, the trapped oil pressure of a single cavity near the minimum volume position was simulated. It was pointed that for cycloid rotary pump as an example, the flow non-uniform coefficient was 6.45%, and in contrast, the flow non-uniformity coefficient of external gear pump was 21.2%. Relative to the accurate results, the two present approximate errors of flow rates were 1.93% and 2.90%; and the present approximate error of flow non-uniform coefficient was 7.13%; when the minimum position angle was added by 0.5° or 1° or 2°, relative to discharge pressure of the pump, the corresponding maximum peak of trapped oil pressure increased by 1.6% or 6.0% or 21.7%. The results indicate that the flow characteristics of cycloid rotary pump are better than the external gear pump, the two present approximate errors of flow rate are little but the present approximate error of flow non-uniform coefficient is higher. Also, there is a trapped oil phenomenon in cycloid rotary pump which is not obvious.