Dynamic high-frequency behaviour of the swash plate in a variable displacement axial piston pump

Abstract

In variable displacement axial piston pumps and motors, the rotation of the barrel causes a strong vibrating torque load on the variable displacement components, that is, on the swash plate. In most analysis, this vibrating torque is counteracted by a mechanical end stop, thereby forcing a constant swash plate angle. However, in real pump and motor operation, the swash plate is not held mechanically. Instead, the position of the swash plate is defined by a hydraulic control system. The vibrating torque load on the swash block is compensated by the control piston and cylinder, in which the pressure changes dynamically, as a reflection of the dynamic torque load created by the rotating barrel. The variation of the control pressure demands the swash plate to oscillate around the average swash plate position, which is defined by the control system of the pump (or motor). In this study, the vibrating movement of the swash plate is measured in a variable displacement floating cup pump. The floating cup principle features two swash plates, which are operated out of phase. This has given the opportunity to connect the control systems of both swash plates by means of a restriction. The experiments have shown that the swash plate vibration has a significant effect on the displacement of the individual pistons, while commutating in and around the top and bottom dead centres. The study shows that the swash plate vibration needs to be included in the analysis of variable displacement axial piston pumps and motors.