Research On The Load Spectra Compilation And Application Of Plug-in Hybrid Electric Vehicle Powertrain

With the rise and development of new energy vehicles,the plug-in hybrid electric vehicles(PHEVs)become popular in automotive industries and research institutes due to both good dynamic performance and longer driving range.The popularization of PHEV also leads to more requirements on reliability.Until now,automotive industries and research institutes have developed practicable testing systems for traditional cars and hybrid electric vehicles(HEVs),but no relevant techniques and testing methods for PHEVs.As the core technique of reliability test,the load spectra compilation determines the accuracy and credibility of the test.Compared to traditional car,PHEV adds the motor as its second source of power,which makes differences on the strength and form of load in drivelines;compared to traditional HEV,PHEV has a larger battery and more frequent charging and discharging,which results in more effects from the loads generated by the motor on the driveline,as well as the rules for modes switching.The differences of the drivelines make the forms of load data different,and targeted methods should be used to handle the data due to the different driving modes.This thesis will analyze these differences and develop a set of methods to compile the load spectra of PHEV powertrain,and optimize the bench test procedures of HEV based on equivalent damage principle.This thesis will contain the following works:1)Performing real road load test for PHEV powertrain.Determining the typical roads of Changchun based on the real traffic flow;determining the typical periods when the vehicle flowrate is fairly focused by counting the vehicle flow on typical roads,then determining the test time;determining the test people and parts of powertrain,as well as the amount of the data;analyzing the data.2)Determining the minimum test cycle size based on the multi-criteria decision technology.Dividing the data into 35 types and calculating the mean,the standard deviation and the damage of each type,then calculating the sample size of each type by using relevant formulas;determining the subjective weight coefficient using the subjective weight method,and determining the objective weight coefficient using the entropy method;determining the total weight coefficient by linear weighting method;finally,the minimum sample size is determined by weighting,and the minimum test cycle size is determined,then.3)Compiling the spectra of powertrain.The minimum sample is divided into three types:engine torque,motor positive torque and motor negative torque;then the rainflow counting and nonparametric extrapolation is performed and the full life two-dimensional load spectra for engine and motor is done;then the full life one-dimensional load spectra is developed by non-average stress equivalent transformation;finally,the whole-life eight-grade load spectra is done based on equivalent damage principle and Miner principle.4)Optimizing the bench test procedures of HEV.Through analyzing the Industry Standard QC/T926-2013,which is made for HEV bench reliability test,and calculating the real ratio of damage among all modes in PHEV to modify the duration of each period,which is more suitable for PHEV bench reliability test.