Efficiency Optimization Of Hybrid CVT Drivetrains

Energy and pollution become two of the most serious problems arounding the world,car manufactures are facing the challenge of supplying vehicle with dramatically reduced CO2 emissions in response to the increasing environmental regulations released by goverments.To be able to meet these future regulations in a cost effective manner,powertrains will need some form of electrification,hybrid vehicles are widely recognized as the most promising solutions,it can improve engine torque setpoints.Push-belt type continuous variable trainsmission(CVT)can change seamlessly through a continuous range of effective gear ratios,it can improve engine speed setpoints.Taking advantage of the combination to reduce emissions and fuel consumptions is the core of energy management strategy regarding CVT type hybrid powertrains.In this paper,Equivalent Consumption Control Strategy(ECMS)choose torque and speed setpoints considering both motor and CVT impactions.Apart from that,energy flow analysis was implemented to have an insight view of the mechanisms under simulation datas.This includes:(1)Decided hybrid typology and performed powertrain parameters matching with benchmark imformations.After that vehicle physical simulation model was built in GT-SUITE,while vehicle controller was built in MATLAB/SIMULINK,co-simulation was performed with some standard test driving cycles.(2)In order to have the theoreticlly global optimal fuel consumption under NEDC driving cycle for a specific hybrid powertrain,Dynamic Programming was utilized.Mathematic equations of each component were derived and used to construct standard optimal problem in the form of Matlab language.Optimal fuel consumption was found and as well as optimal torque and speed setpoints which were set as a referent case during the next step.(3)To make the best usage of both CVT and motor,a new type of Equivalent Consumption Control Strategy was developed.By varying both primary speed setpoint and torque split ratio in the meantime,it will choose speed setpoint and torque setpoints with respect of three different efficiency maps,engine,motor and CVT,to improve the entire fuel economy.(4)Energy flow analysis was introduced to get an insight view of what happened during the simulations.A comparison between DP based simulations energy flow datas and ECMS based simulation energy flow datas was conducted to give a better view of where does the benefit comes from and draw a conclusion that the new ECMS is good enough comparing to global optimal solutions.