| The lubricating oil film between the planet and the pulley bears the tasks of power transmission and lubrication at the same time.So,it is the most important link in the power transmission chain of metal belt CVT.The characteristics of oil film determine the transmission quality and lubrication effect,but they can not be measured directly under actual operating conditions.So it is difficult to control the characteristics of oil film accurately.To solve this problem,a numerical simulation method was put forward in this thesis.Based on the theory of TEHL(Thermal Elasto-Hydrodynamic Lubrication),a mathematical model was established to get the characteristic parameters of lubricant oil film.And then,the effects of slip ratio,transmission torque and transmission ratio on the oil film were studied.It provides the basis for designing the CVT structures,and also provides the basis for developing an clamping force control method based on the oil film characteristic parameters.The main works of this thesis are as follows:(1)The theoretical analysis of CVT structures and the theoretical analysis of dynamic transfer process were carried out.The forming mechanisms of various kinds of sliding friction during the transmission process were studied,and the influence of macro slide of metal belt on the transmission efficiency was analyzed.According to the analysis of working conditions of the oil film which existed the clearance between planet and pulley,the lubricant film is in elasto-hydrodynamic lubrication,and the influence of temperature on oil film can not be ignored.(2)Based on the theory of TEHL,a mathematical simulation model of lubricating oil film was established.According to the geometric parameters of CVT,the relations between torque,speed ratio,slip ratio and relative velocity,load,synthetic curvature radius were derived.The boundary conditions were determined according to the actual working conditions.The characteristics of each equation in the model were analyzed,and then the process of numerical solution was determined.(3)The distribution of oil film pressure,oil film thickness and oil film temperature were obtained by numerical simulation.The effects of various working parameters on the pressure,temperature and film thickness were studied by numerical simulation model.This thesis had designed an orthogonal experiment which interaction was taken into account.Finally,The sensitivity of pressure extreme value,minimum film thickness and maximum temperature to various working parameters was obtained.(4)An experiment aimed to obtain the temperature of oil film at different level parameters was designed and finished.Although there is an difference between thetemperature get from experiment and the temperature get from numerical simulation,the maximum up to 12?,but the trend is basically the same.It can be taken as a basis for designing the CVT structures and developing a control method based on the characteristics of oil film after corrected. |
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