The manufacturing development of axial piston pumps usually takes the trend of high speed and miniaturization, and increases power density. Axial piston pumps are usually characterized as high speed to improve the power density; thus, high-speed churning losses caused by the internal rotating components stirring the oil can increase significantly. In order to improve the efficiency, more attention should be given to the churning losses in axial piston pumps, especially in high-speed conditions. Using the method of least-squares curve fitting, this paper establishes a series of formulas based on the churning losses test rig over a wide range of speeds, which enable accurate predictions of churning losses on the cylinder block and pistons. The reduction coefficient of flow resistance of multi-pistons as calculated. The new churning losses formula devoted to the cylinder block and rotating pistons was validated by comparison with experimental evidence in different geometries of axial piston pumps. According to the prediction model of churning losses, some valuable guidance methods are proposed to reduce the energy losses of the axial piston pump, which are the theoretical support for the miniaturization of axial piston pump manufacturing.

Raising the rotational speed of an axial piston pump is useful for improving its power density; however, the churning losses of the piston increase significantly with increasing speed, and this reduces the performance and efficiency of the axial piston pump. Currently, there has been some research on the churning losses of pistons; however, it has rarely been analyzed from the perspective of the piston number. To improve the performance and efficiency of the axial piston pump, a computational fluid dynamics (CFD) simulation model of the churning loss was established, and the effect of piston number on the churning loss was studied in detail. The simulation analysis results revealed that the churning losses initially increased as the number of pistons increased; however, when the number of pistons increased from six to nine, the torque of the churning losses decreased because of the hydrodynamic shadowing effect. In addition, in the analysis of cavitation results, it was determined that the cavitation area of the axial piston pump was mainly concentrated around the piston, and the cavitation became increasingly severe as the speed increased. By comparing the simulation results with and without the cavitation model, it was observed that the cavitation phenomenon is beneficial for the reduction of churning losses. In this study, a piston churning loss test rig that can eliminate other friction losses was established to verify the accuracy of the simulation results. A comparative analysis indicated that the simulation results were consistent with the actual situation. In addition, this study also conducted a simulation study on seven and nine piston pumps with the same displacement. The simulation results revealed that churning losses of the seven pistons were generally greater than those of the nine pistons under the same displacement. In addition, regarding the same piston number and displacement, reducing the pitch circle radius of piston bores is effective in reducing the churning loss. This research analyzes the effect of piston number on the churning loss, which has certain guiding significance for the structural design and model selection of axial piston pumps.