Lubrication characteristics of ball-cylinder pair in eccentric ball piston pumps

Ball-cylinder pair is the key friction pair of eccentric ball piston pumps. The reliability of ball-cylinder pair is significant to the performance of ball piston pump. The amended point contact elastohydrodynamic lubrication (EHL) model of ball-cylinder pair is developed in this paper. Non-Newtonian behavior of lubricants and slide-roll feature of ball-cylinder pair are considered. Pressure distribution and film profile of ball-cylinder pair are calculated. The characteristics of friction and lubrication are analyzed. The result shows that a film dimple takes place at the inlet of the contact, corresponding to a pressure mutation. For friction coefficient, with the increase of entrainment velocity of ball-cylinder pair, the curve goes down first and then goes up to the peak. After that, the curve decreases slightly to stability. Also, the curve decreases first and increases slowly to stability with respect to the normal load of ball-cylinder pair. Tendency of the curves representing friction coefficient is different from the classical Stribeck curve. The simulating results are validated by test.