Ratio Optimization And Control Of Metal Belt CVT Based On Power Demand

Energy conservation and environment protection is the main theme of the development of the modern automobile industry.With the development of the national economy and the car entering the family,the convenient automatic transmission is more popular with customers,and it has been popularized and developed rapidly.Continuous Variable Transmission can achieve continuous change of ratio.And it can match the power system better and reach the best fuel efficiency.It is an ideal form of automatic transmission.The variable speed characteristic curve of CVT based on the characteristic of steady state engine can,t take account of the power and economy of the whole vehicle,and can,t directly reflect the driver's driving intention and adapt to the change of driving conditions.The response of traditional PID control is slow,and it is difficult to realize real-time speed ratio accurate control.Aiming at the above problems,combined with the National Natural Science Fund "automatic transmission gear power demand a realtime optimization and decision making based on online technology(51575220)" and the Project of Industry and School and Research Institution “research and development of CVT/DCT control function ",this paper presents an optimization method for speed ratio of CVT based on power demand and the speed ratio control method of pre control plus PID.The goal is to improve fuel economy effectively from the two aspects of online optimization and accurate control of speed ratio under the constraints of dynamic demand.The main research contents are as follows:(1)This paper systematically analyzes the mechanism and hydraulic system of CVT and its working principle.And a transmission system model of metal belt continuously variable transmission(CVT)is established,including engine model,CVT dynamics model,CVT transmission efficiency model and vehicle dynamics model.(2)Based on AMESIM and MATLAB,the model of dynamic and hydraulic system of CVT is built,and the hardware in loop simulation platform is established by compiling and integrating LABCAR.(3)This paper has solved the speed regulation characteristic curve of the best economy and the best dynamic CVT.The Markov forecast model of driver's dynamic demand is set up,and the dynamic optimization algorithm of CVT is studied based on the dynamic demand of prediction.And then the best economic target speed ratio under the demand of dynamic demand is obtained.(4)The speed ratio control algorithm of pre control plus PID is developed based on the optimal speed ratio obtained.The PID pressure control method based on Simth correction is proposed in view of the control precision of the hysteresis of hydraulic system.Then the speed ratio control precision is improved,the system control development time is shortened and the system development cost of CVT is saved.(5)Based on the developed speed ratio control strategy,the bench and vehicle tests are carried out to verify the rationality and advantages of the speed ratio control strategy and the pressure control strategy.The speed ratio control algorithm and the pressure control algorithm are debugged and verified on the bench.At the same time,the speed ratio control algorithm verification and test experiment are carried out on the whole vehicle under the Power on and Power off operating mod.