A study on tribo-dynamic model for ball piston pairs of vehicle ball piston pump

Ball piston pump has a good development potential and application prospect due to its small volume, high power density and the ease of expanding displacement. In this paper, a tribo-dynamic model for ball piston is developed through coupling friction lubrication model and dynamic model, with consideration of the effects of oil-film lubrication and structural deformation of ball piston. Then the changing law of oil-film pressure and film thickness of two point-contact pairs (ball-outer ring pair and ball-cylinder bore pair) are analyzed, with the friction force and torque of ball piston obtained. Finally a test bench is built to conduct test verification. The results indicate that the lubrication condition of ball-cylinder bore pair shifts between elasto-hydrodynamic lubrication and hydrodynamic lubrication. Under the same operating pressure, the friction torque of ball piston pump shows a linear rising trend with the increase of operating speed.