Simulation Study On The Transmission Characteristics For V-belt CVT

The V-belt continuously variable transmission is an optimal device of the transfer motion for vehicle. It has been the research focus of automatic transmission with some characters of non-impact shifting, driving comfort, and good performance of powertrain matching, etc. At present, the key area of CVT study centers on the control of electro-hydraulic system, basically including clamping force control and ratio control. In this paper, the dynamic model of transmission system would be built and the simulation test for the two types of control procedure would be conduct.In the first, it was acknowledged that the constant of ratio depended on the equilibrium of clamping force of the primary and secondary pulley, and the process of speed ratio change was the transition from one steady state to another in essence by means of learning inner mechanical structure of CVT, analyzing operation theory, and understanding the coupling relationship between the two types of control.Secondly, researched on the relationship between slip rate and transmission stability through conducting the slip characteristic test and the CVT efficiency test,and it was concluded that the clamping force was the key factor of slip behavior. In consideration of the low efficiency of traditional strategy, a new one based on the slip was proposed by obtaining the optimal slip cure. For increasing the precision of the clamping control, the PI controller was adopted. It was shown that there had a improvement on efficiency and no excessive slip occurred with the new strategy.Finally, Ratio control made a great effect on the vehicle dynamic performance. It was found that ratio change rate was the key for the ratio matching. Introduced the ratio change rate control into the research of ratio control with the analysis of geometrical structure of transmission process. Combining the new clamping force strategy, a comprehensive simulation model integrated two types of control was built.The ratio change rate was adjusted through PD controller. With selecting the proper parameters, the following performance of ratio and the adjusting property of control process was improved on the basis of high efficiency.