Study On Efficiency Characteristics Of The Hydro-mechanical Continuously Variable Transmission And Energy Recovery System

Hydro-mechanical Continuously Variable Transmission has the characteristics of controllable step less speed change,high transmission power,high transmission efficiency,smooth running and simple operation.It can significantly improve the dynamic performance,fuel economy and driving comfort of heavy duty truck.Under the condition of the city,the frequent start and stop of the vehicle reduces the fuel economy of the vehicle.Therefore,it is necessary to analyze the efficiency characteristic of the HMCVT,find the speed range of the high transfer efficiency of the HMCVT,and provide the theoretical support for the reasonable driving operation.In order to recover the kinetic energy of vehicle braking,to start the vehicle,to improve the utilization of energy and to reduce the fuel consumption,the braking energy recovery unit is designed on the basis of the original five stage type of Hydro-mechanical Continuously Variable Transmission,and the recovery and utilization of braking energy are realized.To sum up,the subject is of practical significance.In this paper,a 300 horsepower heavy duty truck is used as the applicable object,and the efficiency characteristics of the five stages Hydro-mechanical Continuously Variable Transmission designed by the five Zheng group are analyzed and studied.The simulation model of the traditional heavy truck vehicle simulation model and the braking energy recovery system are established by using the AMESim simulation software.The efficiency characteristics of HMCVT and the characteristics of the braking energy recovery system are simulated and analyzed.The simulation results of the braking energy recovery unit simulation experiment platform are verified by experiments.The main research contents are as follows:(1)According to the technical parameters of a 300 horsepower heavy duty truck and the speed distribution of the transmission system,the existing five stage output type stepless transmission scheme of the five sign group is analyzed.The analysis and calculation method of power flow and efficiency characteristics is studied,and the conditions of generating power cycle and parameters affecting power cycle are analyzed.The influence rule of power cycle on system efficiency is summarized.It is concluded that HMCVT has high transmission efficiency and the speed range is 40~50km/h.(2)Based on the hydraulic transmission in the HMCVT transmission,the energy recovery unit of the hydraulic brake is designed.In view of the problem that the existing mechanism can't guarantee the variable pump/motor working at the rated speed interval at any speed braking,the speed regulation mechanism is designed.A design plan of adjusting the speed of variable pump/motor by using clutch is put forward.According to the connection mode of the accumulator,by comparing the influence of the single accumulator and the double accumulator on the braking energy recovery,the design scheme of the braking energy recovery system using the dual energy storage as the accumulator is determined.(3)The energy management and control strategy of the braking energy recovery unit are discussed.According to the operating conditions of the vehicle and the principle of ideal braking torque distribution,the braking torque distribution rules based on the ideal distribution torque distribution curve are formulated.On the premise of ensuring the safety of the vehicle,the braking energy is recovered to the maximum,and on this basis,the control strategy of hydraulic brake and the starting control strategy are set up,which provides the basis for the simulation of the vehicle model.(4)Based on the simulation software AMESim,the vehicle simulation model of the braking energy recovery system is established,simulation is carried out under different braking strength,initial braking speed,load and initial pressure of accumulator,the influence of the above factors on the performance and efficiency of the braking energy recovery unit is analyzed.A driving operation proposal that can improve the recovery rate of braking energy is put forward.(5)A simulation experimental bench for braking energy recovery unit is set up.The design scheme of dual accumulator braking energy recovery unit is compared with the design plan of single accumulator braking energy recovery unit.It is verified that the design plan of double accumulator braking energy recovery unit is higher than that of single accumulator braking energy recovery unit.The influence rule of double accumulator braking energy recovery unit on load and braking strength is verified.