Modeling and Experimental Validation of Flow Ripple in a Variable Displacement Linkage Pump

Abstract

The optimal operation of hydraulic systems heavily relies on the performance of their pumps and motors. However, these machines often encounter a phenomenon known as flow ripple that causes periodic fluctuations in the outlet flowrate of the pumps, negatively impacting system components and contributing to operational inefficiencies. This prevalent challenge highlights the need for accurate flow ripple modeling and the development of effective mitigation strategies. This paper presents a combined modeling and experimental approach to characterize the influence of the velocity trajectory of pistons in a positive displacement pump on the flow ripple. The study considers a three-cylinder variable displacement linkage pump (VDLP). The model combines the kinematics of the pump linkage mechanism, the pressure dynamics in its piston chambers, and the dynamics of the inlet and outlet check valves to predict the cylinder pressures and individual cylinder flow rates. A prototype VDLP was instrumented and tested to validate the simulation models. Two cylinders of the pump were deactivated, enabling the pump to run with a single pumping element to isolate the flow profile from a single cylinder, allowing for a more direct comparison of simulation versus experimental data. Experiments were run across a range of operating pressures and pump displacements. The results demonstrated a good agreement between the simulation and experimental data, with a normalized mean absolute error (NMAE) between 7% and 30% at the corner conditions. The validated models enable future optimization of the piston trajectory in the VDLP design used as an example architecture in this study to minimize flow ripple.