Numerical and experimental study on the influence of piston combined motion on churning losses in axial piston pumps

As the speed of the axial piston pump increases, the energy loss due to the fluid agitation by the piston increases sharply. This energy loss caused by fluid friction, called churning loss, impedes the piston movement. Currently, most studies on the stirring loss of a piston focus on rotational motion, ignoring the reciprocating motion of the piston. However, improving the efficiency of the piston pump in a high-speed zone requires investigating the churning loss of the combined piston motion. This study establishes a theoretical churning loss model. The shielding effect between multiple pistons and the flow characteristics around the pistons in the compound motion were considered in the theoretical model. The influence of the relative distance S z / d and the swashplate inclination angle β on the shielding effect between multiple pistons is analyzed. The result shows that k z increases as S z / d and β increase. The velocity correction coefficient λ is introduced to modify the velocity term of the traditional centralized parameter model. The λ values are found to be near 1 for different swash plate inclinations. In addition, a churning loss test device that can eliminate the influence of friction losses is designed, and a churning loss test is performed. The theoretical calculation results agree well with the experimental data in the rotation speed range of 1500–7500 r/min. This study is the first to accurately measure and predict the churning losses of multiple pistons in compound motion in an axial piston pump.