Performance Analysis And Optimization Of Key Pairs In Camshaft And Connecting-rod Type Hydraulic Motor

Combined FEM (Finite Element Method) and computer simulation with fluid mechanics and tribology, the key friction pairs in camshaft and connecting-rod type hydraulic motor are researched in detail on the quantitative analysis of their performances and the structure optimization. The main researches and results can be summarized as follows:(1) The mathematical models of the hydrostatic bearings for the connecting-rod slides are derived which take account of the squeeze effects of the oil films. Based on the mathematical models, the simulating models are built and run under Matlab/Simulink simulation environment. With the derived mathematical models and the built simulating models, ont only the oil film thickness, the pressure drop ratio, the forces and etc. of a single connecting-rod slide can be calculated, but also the overall performance parameters such as the torque, the flow rate, the leakage rate and etc. of the hydraulic motor can be simulated when the all five connecting-rod slides work simultaneously. The simulating results are consistent with the existing analysis and have accuracy over the existing analysis by taking account of the squeeze effects, the leakage, backpressure and etc..(2) The stresses and the distortions of the distributor shaft and the connecting-rod slides are calculated with the FEM under Ansys Workbench. In order to reduce the stress and distortion of the distributor shaft, a group of feasible optimum structure sizes are presented. Applying the contact computing module under Ansys Workbench, the contact stress and the distortion of the connecting-rod slide and ball under nonlinear contact are calculated respectively.(3) First of all, the friction characteristics of the existing spherical hinge pairs are analyzed and calculated based on the oil film squeeze theory. The oil film exist time surface graph of relation with the initial relative eccentricity and the final relative eccentricity, as well as the oil film exist time graph of relation with the difference of radius between the ball and the socket is plotted. From the graphs, the existence conditions of the oil film under squeeze are founded. The results show that the existing structure sizes cannot meet the existence conditions of the oil film under squeeze. Afterwards, in case that the existence conditions of the oil film under squeeze are difficult to be or cannot be satisfied, the friction and wear of the spherical hinge pairs is analyzed and optimized by combining the friction binomial theorem with the theory of elasticity and some rational hypothesis about the contact surfaces. A formula of the optimum surface roughness with the minimum friction factor for the ball and the socket is derived.