Study On Reliability Improvement Technology Of CVT Sliding Friction Transmission Considering Oil Film State

The new generation of metal belt type continuously variable transmission(CVT)adopts a clamping force control strategy based on the slip ratio,which can significantly improve the transmission efficiency of the CVT,but the relative sliding between the metal sheet and the pulley affects the oil film traction condition of the CVT working,and the oil film state involved in the sliding friction driving condition involves more parameters,which makes it difficult to measure the reliability of the transmission in the state of metal belt slip.In view of this,this paper considers the state of the oil film under slippage of the metal belt,and calculates the oil film characteristic parameters through the elastohydrodynamic lubrication.Based on the non-probabilistic set theory,the reliability model of the sliding friction drive is established,and Monte Carlo method is used to obtain the reliability of CVT sliding friction transmission.Finally,the CVT clamping force compensation control is used to increase the reliability of the sliding drive.The main work of this paper is as follows:(1)Based on the working principle and sliding mechanism of sliding and friction drive of metal belt type CVT,the influence of slip on transmission efficiency and transmission reliability is analyzed.The clamping force control strategy based on the slip ratio can effectively improve the transmission efficiency,but the transmission reliability is difficult to guarantee.According to the state of the lubricant film between the metal belt and the pulley in the slip state,the working conditions of the oil film such as the contact load and the relative sliding speed are analyzed.(2)The mathematical model of the state of the oil film was established based on the actual working conditions of the lubricant film and the elastohydrodynamic lubrication theory between the metal plate and the pulley.Through mathematical derivation,the relationship between the four parameters of torque,speed,speed ratio,and slip ratio and the oil film pressure and oil film thickiness vwas established.The method and process for solving the oil film pressure and oil film thickness were determined and calclulated and analyzed.(3)The inlluence of oil film state on CVT sliding transmission is analyzed,and whether the oil film shear stress reaches its limit is used as the failure criterion of CVT sliding friction drive.Based on the non probability set theory,the super ellipsoid model of CVT sliding transmission is established,and the interval of uncertain variables in the model is determined.Finally,the relationship between the parameters of the CVT and the reliability of the sliding friction drive is obtained by using the Monte Carlo method,and the influence of the relative velocity and load on the reliability is emphatically analyzed.(4)According to the biggest influence factor of reliability and combining the clamping force control strategy based on slip ratio,a clamping force compensation control strategy based on reliability is put forward.A bench test is designed to verify the clamping force compensation control strategy.The results show that the reliability of the clamping force compensation control strategy,compared with the original clamping force control strategy,effectively improves the reliability of the CVT sliding friction drive.