Optimization And Control Of Clamping Force Of CVT For System Energy Saving

Because of its unique physical structure and transmission principle,metal belt continuously variable transmission can realize continuous change of speed ratio and better match the power system,among which clamping force control is one of the key control technologies.The traditional clamping force control uses engine output torque instead of pulley input torque,so the calculation of pulley input torque is not accurate;the clamping force control technology based on slip ratio is immature and costly,and can not be applied to engineering;the traditional method does not consider the transmission efficiency and other factors when solving the target speed ratio.In view of the above problems,this paper proposes a method for calculating the basic clamping force based on the maximum friction coefficient,the estimation of the input torque of the pulley and the double-fuzzy rule to determine the dynamic safety factor,calculates the optimal economic target speed ratio considering the efficiency of the gearbox,and designs a double-layer speed ratio controller and a feed-forward-fuzzy PID pressure controller,combining with the research and development of the control function of CVT/DCT in the school-enterprise cooperation project.The research results have important reference value for improving the transmission efficiency of metal belt continuously variable transmission and the fuel economy of the whole vehicle,and have certain engineering application prospects for the development of domestic metal belt automatic transmission.The main contents are as follows:(1)Building vehicle simulation platform.The power transmission route and working principle of the hydraulic system are analyzed in detail.The hydraulic system and longitudinal dynamics simulation model of the vehicle are established by AMESim.The control model of the metal belt continuously variable transmission is built by Maltab/Simulink tools.The accuracy of the model is verified by the bench test data,which lays a foundation for the optimization and control of clamping force of CVT for system energy saving.(2)A method for calculating the basic clamping force based on the estimation of the input torque of the pulley is proposed.The theoretical calculation method of clamping force is analyzed.Compared with the existing calculation method of clamping force,the theoretical minimum clamping force is determined based on the maximum friction coefficient and the input torque of the pulley is estimated.The dynamic safety factor is determined by the double-fuzzy rule,and the basic clamping force is determined,which provides the basis for the speed ratio control.(3)Design a double-layer speed ratio controller.The shortcomings of traditional method for calculating target speed ratio are analyzed,and the target speed ratio is calculated according to the output power of wheels.A double-layer speed ratio controller with clamping force correction as output variable is proposed.The pulley pressure control method with pre-control and fuzzy PID is adopted to ensure the control accuracy of pressure and speed ratio.(4)Bench test and simulation analysis are carried out.A bench test platform was built to verify the control effect of the pressure controller.A test method of the key control parameter kpks of metal belt continuously variable transmission was designed.The parameters of kpks were extracted from the test.Based on the simulation platform,the control effects of the input torque estimation method,clamping force control method and speed ratio control method of the pulley in this paper were studied based on the starting condition and NEDC cycle condition.The simulation results show that the control method in this paper has some optimization in energy saving compared with the traditional control method.