Numerical investigation of how piston-chamber dead volume affects the delivery flow ripple in axial piston pumps

Delivery flow ripple is a critical factor limiting the performance of axial piston pumps. Capped pistons with small dead volume have emerged as a promising solution to mitigate the delivery flow ripple. However, the underlying mechanisms by which capped pistons influence delivery flow ripple remain unclear, and potential adverse effects have not been fully understood. This study aims to numerically investigate how the piston-chamber dead volume affects the delivery flow ripple in axial piston pumps. First, a high-fidelity computational fluid dynamics (CFD) model of an axial piston pump is developed and validated by measurement data of delivery pressure ripple. Second, the validated CFD model is used to compare the delivery flow ripples between standard and capped pistons, and to analyze the mechanisms through which the capped piston design affects the delivery flow ripple. Finally, the conditions under which capped pistons have either positive or negative effects are systematically examined and summarized. The numerical results show that the capped piston design generally reduces delivery flow ripple under most conditions. However, it can increase the delivery flow ripple when excessive trapped-volume compression occurs within the piston chamber.