Lubrication characteristics between a cylinder block and a valve plate in axial piston pumps play an important role in volumetric efficiency and durability of a hydraulic unit. In this paper, the finite element method is used for the computation of the pressure distribution between a cylinder block and a valve plate of the axial piston pump. Also, the Runge-Kutta method is applied to simulate the dynamics of a cylinder block of three-degrees of freedom motion. From the results of computation, two major conclusions are drawn. One is related to the fluid film characteristics between a cylinder block and a valve plate, and the other is related to the average leakage flow rate which is determined by the pressure gradient and the clearance near the discharge port. To confirm results of numerical simulation of cylinder block dynamics, experiment is conducted using three eddy-current type gap sensors, which are imbedded at the pump housing. Finally, a revised shape of a valve plate is proposed which increases the stability of the cylinder block dynamics and the volumetric efficiency of the pump based on numerical simulation.

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