Research On Energy Recovery Performance Of Parallel Hydraulic Hybrid Vhicles In Urban Cycle Conditions

As a kind of energy-saving vehicle,the hydraulic hybrid vehicle has the characteristics of high-power density and rapid energy conversion.It can efficiently recover braking energy in the condition of frequent energy exchange,and is suitable for vehicles with frequent starting and stopping conditions.In order to solve the problems of slow pressure build-up and complicated control in the regenerative braking process of the traditional hydraulic hybrid system,a new scheme of hydraulic hybrid vehicle with pressure decoupling of hybrid system based on electro-hydraulic proportional throttle valve was proposed.Simulation and experimental research on the energy recovery and utilization characteristics of hydraulic hybrid vehicle was carried out.This thesis takes the parallel hydraulic hybrid vehicle as the research object.The mainly carried out research is as follows:(1)The deficiencies of the hydraulic system of the traditional parallel hydraulic hybrid vehicle are analyzed.Aiming at the characteristics of the hydraulic circuit of the hydraulic hybrid system,a new scheme of pressure decoupling hydraulic hybrid system based on electro-hydraulic proportional throttle was proposed.The solution realizes the decoupling between the working pressure of the accumulator and outlet pressure of the pump/motor,and the outlet pressure can quickly build pressure to the target pressure.According to the characteristics of the pressure decoupling hydraulic system scheme and the actual needs of the test,the key components of the hydraulic system such as hydraulic pump/motor,accumulator and proportional throttle valve were selected and matched,and the parameters of each key component were obtained.(2)The control strategy of the hydraulic hybrid power system was proposed,and the energy recovery and utilization simulation model of the hydraulic hybrid vehicle with urban cycle conditions and constant braking strength conditions was established.The energy recovery and utilization effects of pressure decoupled hydraulic hybrid system and traditional hydraulic hybrid system were compared and analyzed.The simulation results show that the pressure decoupling hydraulic hybrid system can quickly build pressure during the braking process.Under the braking condition with the braking strength below0.15,the braking force can be completely provided by the hydraulic system,which avoids the participation of mechanical braking and simplifies the control of the braking process.Under the cyclic condition of NEDC,the hydraulic hybrid vehicle saves 27.6%compared with the traditional vehicle.The pressure decoupling scheme and the conventional scheme have the same braking energy recovery rate and utilization rate.The energy recovery rate under the conditions of constant braking strength 0.1 and 0.15 were 90%and 65.6%respectively,and the energy utilization rate was 78.1%under a constant acceleration of0.98 m/s~2.(3)A parallel hydraulic hybrid simulation test bench was established,and a simulation experiment method for hydraulic hybrid system was proposed.The hydraulic hybrid experiment under urban cyclic conditions and constant braking strength conditions was carried out.The experimental results show that the hydraulic pump/motor displacement change and the accumulator pressure change of the hydraulic hybrid vehicle under urban cycling conditions were basically consistent with the simulation results.The pressure decoupling scheme and the traditional scheme energy recovery rate and utilization rate under constant braking conditions were basically consistent with the simulation results.