Search

To study the oil film performance, a multi-physical coupling model considering the elastohydrodynamic lubrication effect of the piston–cylinder interface is established and verified. The oil film thickness is obtained by solving geometric formulae, and the dynamic pressure model is derived by solving the Reynolds equation. Considering the oil film thickness and pressure distribution of the piston–cylinder interface, the elastic deformation model is solved. Both theoretical and experimental results show that the oil film morphology is influenced by the elastic deformation of the piston surface. The impact of the minimum fluid film thickness and its influence on the piston surface are well analyzed and discussed. When taking elastic deformation into account, the viscous friction reduces greatly, especially during the oil discharging process. Based on the theoretical research, a unique test rig was designed and established for testing and measuring the oil film thickness and the viscous friction of the piston.

This paper discovers how the surface texture of micro-dimples impacts the tribological performance of the interface between cylinder block and valve plate. For this, a mathematical model which considers the cavitation effect for calculating oil film pressure and oil leakage is established. The radius of the micro dimples is considered for studying the influence of the pressure field and the leakage flow. Then a simulation model is built up according to the mathematical model. Meanwhile, a particular test rig was designed and established to verify the theoretical results. Both simulation and experimental results show that a good designed surface texture of micro-dimples could improve the lubrication performance a lot and the structure parameters could be optimized. The leakage flow of the port plate pair will be greatly decreased by micro dimples and it is positive correlated with the radius of the micro dimples.

The fluid film between piston and cylinder works simultaneously as bearing and lubricating functions, its thickness determines the lubrication efficiency and performance of an axial piston pump. Because of the thickness is usually micron level, and its change in the whole cycle is difficult to observe directly. In order to reveal it particularly, this paper present a mathematical model which considering structure, piston kinematics and a dynamic piston load to predict the film thickness in a cycle. The minimum thickness is used as an index to evaluate lubrication performance and its variation are studied under different load pressure, rotating speed and length ratio between cylinder and piston. A special test rig with four displacement sensors placed through the cylinder surface allows measuring the film thickness at these points. The model was verified by comparing the numerical results with measurements taken on the test rig. Results indicate that: (1) The mathematical model could effectively predict the film thickness trend and the position of the minimum thickness; (2) The minimum thickness in pressure phase is greater than in suction phase, and increases with the increase of load pressure and decreases with the increase of rotation speed, the influence of load pressure on film thickness is much greater than that of rotational speed. (3) Increasing the length ratio reduces the piston eccentric and raises the minimum film thickness, and in order to obtain the better lubrication, the length ratio should be greater than 0.5.