SOCIETY OFAUTOMOTIVE ENGINEERS, INC. TwoPennsylvania Plaza,NewYork,N.Y.10001 HybridBatterySystem D.H.Brown General ElectricCo. Automotive Engineering Congress Detroit,Mich. January11-15,1971710236 Downloaded from SAE International by University of Wisconsin - Madison , Sunday, September 09, 2018710236 HybridBatterySystem D.H.Brown General Electric Co. INTRODUCTION Batteries forelectric vehicles mustmeetallde mandsmandated bythedriver andbythetraffic patterns heenters.Acceleration fromastandstill andhillclimbing arethegreatest usualdemands. Lead-acid batterycharacteristics aresuchthata greatreserve ofunusedampere-hours willremain whenacceleration performance hasbecomeunac ceptable. Uptofiftypercentgreaterrangecanbe addedbeforethiseffectismanifest ifanaccelera tionbatteryofthenickel-cadmium typeisadded. However, thiscombination ofbatteries cannotbe simplyplacedinparallelelectriccircuits toachieve suchabenefit. Thelead-acid batterymustbepro tectedfromhighcurrentdraindemands. Compari sontocomplete substitution forthelead-acid battery withanickel-cadmium batteryshowsthatthemost economic combination willutilizeaminimum size nickel-cadmium battery, andwillappreciably reduce thesizeandweightoflead-acid batteryrequired for agivenrange. Although thebatterydatausedforthisworkpre datetherecentadvances inbatterytechnology, the attributes ofthehybridbatterysystemthatmatchit sowelltothedemands ofvehicular trafficindicate thatitisanimportant element ofthistechnology. VEHICULAR REQUIREMENTS Theoperator ofavehicledemands torque;forac celeration, forhillclimbing, forsustaining steady speed.Thehorsepower appliedtothewheelsisthe resultofthespeedatwhichthetorqueisapplied; horsepower isasecondary andderivative measure ofperformance; torqueisprimary. Theveryconceptofresponsiveness asappliedtovehiclesispre dominantly relatedtoacceleration andtheavailabil ityofhightorquewhenthedrivercallsforit. Theconvenient measure ofacceleration, unitsof g,hasthevirtueofbeingdirectlyrelatedtograde ability. Intrafficpatternsthelocalroadgradeand expectedacceleration ratesareimposedimpartially onallvehicles. Breakaway torquesareoftheorder of0.1gonthelevel,withgradesaddingtorquede manddirectly. Automobile acceleration of0.2gon thelevelisacceptable. Lowervaluesareaccept ablefortrucks,butwouldgenerally irritateother autoists. Torquewouldbeamaximum astheve hicleapproaches operating speedwhilestillaccel erating. Forsimpleelectricdrivestheelectric currentdemandwouldpeakatsuchtimes.When everthebatterydischarge condition willnotsustain suchapeak,thenthedriverwillsenseafallingoff ofacceleration performance andanincreasing in abilitytosustainhisnormalpositioninthetraffic mix. LEAD-ACID BATTERY CHARACTERISTICS Because ofthevarietyoflead-acid batteries a characteristic forampere-hour capacityversuscur rentwasproduced asinFigure 1thatwasnormal izedwithrespect tothefive-hour continuous drain ratingpoint(1)*.Batterycapacityinkilowatthours refersexclusively tothisratingpoint.Evaluation ofasubcompact electriccarwithlimitedurban rangeandspeedshowedthattheampere-hour limit inoperation wasreduced belowtherating. Thiswas *Numbers inparentheses designate References at endofpaper. ABSTRACT Electric vehicles thatmixwithnormaltraffic mustprovideburstsofhightorqueastheyacceler atefromstandstill tooperating speed.Batterysys temsthataresizedforsustained drivingexperi- enceexcessive drainduringeachacceleration fromrest.Asystemproviding aseparate small batteryforacceleration andthemeanstoisolatethemainbatteryfrombriefpeakcurrentdemands ispresented inthispaperalongwiththebenefits inweight,cost,andrangethatresult.Opera tionoftheGeneral Electric Deltaresearch vehicle withandwithoutthedualbatterysystemdemon stratedthedistinct advantages ofthehybridbat terysystem. Downloaded from SAE International by University of Wisconsin - Madison , Sunday, September 09, 20182 duetothehighercurrentforcontinuous drivingand theevengreatercurrentrequired toaccelerate to speed.Thesepointsareindicated onFigure 1and areta