The lubricating gaps are the primary source of energy dissipation in piston machines. The paper presents results of a simulation study that investigates the effect that a wave-like micro surface shape variation applied to the valve plate gap surface has on power loss in the cylinder block-valve plate interface. Special attention is given to the relation between gap height, operating parameters, surface design and power loss. The effect of waved surface amplitude and frequency is also studied. Results indicate that power loss in the cylinder block-valve plate interface can be reduced by over 50 % on account of the waved surface compared to the standard cylinder block-valve plate interface design. The effect of the waved surface is most significant at low operating pressures. A special in-house code has been used for this research study. The simulation model covers fluid-structure interaction and micro motion of the cylinder block resulting from oscillating piston forces. Details of the model are explained. The model predicts the pressure and velocity fields generated in the lubricating film and calculates leakage, viscous friction and power loss.

Keywords: lubricating gaps, cylinder block-valve plate, axial piston pump, waved surface, energy dissipation