Energy Economic Analysis And Efficiency Optimization Of CVT For Electric Vehicles

Due to the increasingly severe energy problems and environmental pollution,more and more stringent laws have been enacted to limit vehicle energy consumption and exhaust emissions.Electric vehicles are promising as they are sustainable and do not require fossil fuels,which is considered to be a suitable replacement for conventional vehicles,and has received widespread attention.CVT enables infinitely variable speed rate,which can increase the energy economy of electric vehicles.However,the low mechanical efficiency and high hydraulic energy loss limit its application in electric vehicles.This paper takes electric vehicle with CVT as object,and concentrates on energy economy and efficiency optimization of electric vehicle with CVT.The main research contents of this paper is as follows:(1)The configuration of electric vehicle matching different transmission systems is analyzed,and its transmission and shifting characteristics are compared.The electric vehicle model with single-speed transmission,two-speed AMT and CVT is completed,the energy-saving superiority of CVT is investigated by simulation.A electric CVT vehicle configuration and the hydraulic system are proposed.According to the test data,the motor characteristic MAP and the CVT efficiency MAP are drawn in the Matlab environment.Ultimately,the various parts and vehicle models are produced,and the integration of each model is completed.(2)Aiming at the optimal electric drive efficiency,a speed ratio matching strategy considering the CVT efficiency is proposed.The influence of speed ratio range,speed ratio matching strategy and oil supply mode on the energy consumption economy of pure electric CVT vehicle is studied through simulation.The simulation results reveal that speed ratio matching strategy considering the CVT efficiency can lower the energy consumption by 0.983 k Wh in NEDC driving cycle,the CVT efficiency and electric drive efficiency is increased by 2.38% and 8.09%.At the same time,the reasonable selection of the speed ratio range and the use of electric oil pump can improve the energy transmission efficiency of electric vehicle with CVT.(3)A CVT clamping force fuzzy control strategy based on the slip rate is proposed.The feasibility and energy-saving effect of the proposed strategy are investigated through simulations under extreme conditions and standard driving cycles.Under the NEDC driving cycle,the energy consumption per 100 kilometers with the clamping force fuzzy control strategy based on slip rate is 14.90 k Wh,which is 6.67% lower than that of the traditional clamping force control strategy,and the average CVT efficiency and average electric drive efficiency are improved by 3.71% and 6.40%.Under other standard driving cycles,energy consumption and CVT efficiency are also improved to varying degrees.4)The CVT bench test was carried out.The composition of the CVT test bench,as well as the test equipment and process are introduced.The feasibility of the CVT model and the CVT speed ratio control method is verified by experiments,and the slip-efficiency characteristics of CVT under different input conditions are obtained.