710235 AnElectromechanical Transmission forHybrid Vehicle Power Trains -Design and Dynamometer Testing G.H.Gelb, N.A.Richardson, T.C.Wang, and B.Berman TRW Systems Group PREVIOUS STUDIES conducted byTRW Systems Group (1,2)*showed that ahybrid power train consisting ofaheat engine, batteries, generator, andtraction motor connected in anappropriate manner offered ameans ofachieving goodur banandhighway performance, reducing engine emissions, while maintaining highfueleconomy. Ref. 2described theresults ofanextensive computer simula tionofaparticular transmission system. Thispaper willde scribe thatsystem indetail andpresent theresults ofaseries ofdynamometer testsperformed onaproof-of-principle hard ware implementation. GENERAL DESCRIPTION OFTHE ELECTRO MECHANICAL TRANSMISSION There areavariety ofways inwhich theelements ofahybrid power train canbeassembled. However, allconfigurations canbegrouped intotwocategories-series andparallel con figurations. Basic parallel andseries configurations areshown inFig. 1.Theseries configuration hasseveral shortcomings.First, alloftheengine-produced power must flowthrough the generator, suffering theinefficiency ofthatconversion; like wise, alltractive energy must flowthrough themotor, suffer ingtheinefficiency ofthatconversion. Inaddition, both machines must berated forthecontinuous power level asso ciated with highway operation, andtherefore their sizeand weights may beexcessive. Theparallel configuration, ontheother hand, provides a direct mechanical pathfrom theheatengine totherearwheels, using theelectrical paths onlyfortorque conversion and/or power peaking. Overall system efficiency canbeimproved by elimination ofthose mechanical-to-electrical-to-mechanical conversion steps forasignificant partoftherequired propul sivepower. Several alternative parallel configurations arepossible. How ever,itisclearthattheconfiguration which minimizes power andspeed excursions oftheprime mover willoffer maximum engine design flexibility and,consequently, lowest emissions andhighest fueleconomy. Aparticular configuration wasde veloped byTRW Systems Group which iscalled theElectro mechanical Transmission (EMT). Itisaparallel arrangement ofagenerator, traction motor, batteries, power conditioning, control equipment, andappropriate gearing. Thetransmission operates intwomodes, accommodating thedual nature ofve* Numbersin parentheses designate Referencesat endof paper. ABSTRACT Thedesign ofatransmission forheatengine-battery hybrid vehicles, theElectromechanical Transmissions, isdescribed. Re sultsofthetesting ofabreadboard EMT power train onadynamometer arediscussed interms ofemission reduction, fuel consumption, andpower flow efficiencies. Sources ofsystem inefficiency andareas offurther investigation areidentified. 915 Downloaded from SAE International by University of New South Wales, Sunday, September 16, 2018916 G.H.GELB, ETAL. hicular propulsion requirements (2),thatis,urban stop-and-go operation andhighway cruising. TheEMT configuration anditsbasic power andinformation flow paths areshown inFigs. 2and3.Power produced by theengine isdelivered totheinput (sun gear) ofaplanetary gearsystem. Theplanetary gearsystem algebraically divides theinput power between theplanet carrier andtheringgear indirect proportion tothespeeds ofthose elements. The speeds inturn arerelated through thesystem gearratios to theinput shaft speed. Inthepresent implementation, the planet carrier gear isconnected toagenerator-termed the Speeder-while theringgeardrives thepropeller shaft ofthe vehicle. Atraction motor-termed theTorquer-is coupled directly through afixed gearratio tothepropeller shaft. Inmode one(Fig. 2),theengine isrunatconstant throttle, constant speed atapower setting consistent with theaverage power required ofthevehicle inurban operation. Thecon stant-torque output oftheengine isdelivered totheSpeeder andpropeller shafts, thusthese twoshafts receive aconstant torque input indirect relationship totheplanetary gea