Study On Shifting Without Driving Force Interrupt Based On Double-Motor Hybrid Electric Bus

HEV has limited competition in private family car market because of its high cost.So urban bus becomes the breakthrough point for developing HEV technology because of the financial support from government.In his context,Jilin university HEV studying team cooperating with FAW has developed single-motor double shafts parallel hybrid urban bus,which could achieve the expected performance target.But as traditional vehicle using transmission with class driving force will be interrupted while shifting,which could affect vehicle performance,especially dynamic and smoothness.So the issue of shifting without driving force interrupt (SWDFI) should be solved for automobile in future developing process.With the development of transmission,DCT and CVT were invented to solve the issue of SWDFI for traditional vehicle.While traction motor for HEV could drive automobile without transmission.Using this characteristic of traction motor could achieve SWDFI for HEV.SWDFI is investigated,while working on the Jilin Province governor fund for the project of Double-Motor Hybrid Electric Bus.The scheme of double-motor double shafts parallel structure that designed in a particular integrated powertrain structure provides the necessary condition to deal with SWDFI.Firstly,this paper presents the scheme of double-motor double shafts parallel structure.It has three power sources,one engine and two motors.Main motor is attached to output shaft of transmission through torque coupling,while assisted motor is attached to input shaft of transmission through torque coupling too,which integrated into transmission becomes a new style driving system.The theory of SWDFI:Engine load is reduced while shitfing,and main motor boosts simultaneously.After shifting is finished,engine load is restored,and main motor load is reduced simultaneously.In the process of shifting main motor could compensate the engine power interrupted with limited torque fluctuation.Secondly,this paper presents evaluating indicators of SWDFI.And the process of SWDFI for double-motor structure is set,which could be divided into 7 phases:1)Run before shifting;2)Reduce engine load to zero,simultaneously start motor to boost;3)Separate clutch,select Neutral and new gear;4)Sync and engage new gear;5)Engage clutch;6)Restore engine load ,simultaneously reduce motor load;7)Run in new gear.There are two key problems:how much torque did motor supply and coordinate control of mode-switch,which are got through dynamics analysis to the process of SWDFI.The control algorithm is presented to solve these two key problems after the deep study to them.Lastly,the dynamic model of SWDFI and the vehicle in-situ starting in full load acceleration model are built by MATLAB/SIMULINK/STATEFLOW.The result of contrast simulation between buses with and without SWDFI shows that SWDFI of double-motor structure could improve vehicle dynamic and smoothness through evaluating indicators(alteration of velocity while shifting,accelerating time from zero to a certain velocity and jerk).And then co-simulation model is built(the vehicle model is built by AVL Cruise and control strategy model is built by MATLAB/SIMULINK) to analyze the effect of SWDFI to fuel economy.Conclusion could be got qualitatively through the result of contrast simulation between buses with one motor and two:Double-motor bus could improve fuel economy from two ways,shifting process and recuperation (electric braking),but the effect is limited.