Axial piston pump leakage modelling and measurement

This thesis is concerned with the dominant leakage characteristics of an axial piston pump. Results have been obtained from a combination of analysis, Computational Fluid Dynamics (CFD) and experimental work, and have added to existing knowledge in this field. The measurement of slipper leakage within an axial piston pump is impossible due to additional leakage from the pistons and between the cylinder barrel and port plate. It may only be determined by analysis and this aspect has been studied via a new CFD simulation. Further progress has been made experimentally on slipper leakage. A new test apparatus was designed and developed by the author and comparisons have been made with parallel analytical work. Previous research in this area has concentrated on single-landed slippers and leakage rates from such slippers have been examined, however only under static conditions. The work in this thesis is the first to consolidate experimental studies on multiple-land slippers, and the first to measure slipper leakage under dynamic conditions. These results have been compared with both CFD simulations and a new theoretical study undertaken in parallel with this work. The new test apparatus allowed measurement of both leakage and groove pressure under a range of operating conditions. It was established that the presence of a groove reduces the restoring moment produced, and hence enables the slipper to operate with an appropriate angle of tilt, thus permitting hydrodynamic lift to more readily exist. However, this occurs at a cost of increased leakage. In addition to the experimental work on slippers, the time-varying pressures within selected cylinders of an axial piston pump were measured. In parallel, a fully dynamic CFD model of a pump was produced. This model included all leakage paths from the pump. It was discovered that the port plate leakage dominated the overall leakage, with slipper leakage still being significant, but with piston leakage insignificant. This model was also used to predict the flow and pressure ripple from the pump and the predictions were compared with experimental measurements.