Experimental and Analytical Investigation of Floating Valve Plate Motion in an Axial Piston Pump

The purpose of this investigation was to experimentally measure the motion of the floating valve plate in an axial piston pump under various operating conditions and to develop a model to determine how the floating valve plate motion affected the lubricating pressures between the valve plate and cylinder block. In order to achieve the objectives, a hydraulic circuit was designed and developed to incorporate and operate a floating valve plate axial piston pump. The hydraulic circuit integrating the axial piston pump (axial piston pump apparatus, APPA) consists of a series of valves, pressure sensors, a charge pump, flow meters, temperature sensors, a heat exchanger, and proximity probes. The floating valve plate axial piston pump housing was modified to incorporate three proximity probes to measure the valve plate position and motion relative to the cylinder block, thus allowing for determination of the film thickness within this contact. The results illustrate that as the pump starts up the valve plate experiences vibrations and begins to lift relative to the cylinder block. Then as the pump reaches steady-state operation the valve plate achieves a fixed position and tilt. The results also demonstrate that under steady-state operation, the valve plate vibrates and this vibration correlates well with the speed and the number of pistons in the pump. The measured film thickness results were then used in a lubrication model to determine the pressures generated between the floating valve plate and the cylinder block. The analytical results highlight how the motion of the valve plate directly correlates to the pressure pulsations seen in the lubricating gap.