Page - 273 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 437 Churning loss: To reduce friction between the gear teeth, the final reduction gear rotates in lubricationoil.During thegear rotation, thechurning lossoccurs inproportion to therotational speed. Churning loss iscalculatedas follows[28]: Tloss_churning= 1 2 ρω2Rp3SmCm, (7) whereω is therotationalspeed,ρ is the lubricantdensity,Rp is thegearpitcheffectiveradius,Sm is thecontact surfacecoefficient,andCm is thedimensionlesschurningtorque loss. Brakeandclutch loss: Thebrakeandclutchunloaded losses are thedrag lossesbetween the friction surface and lubricant in thedisengagedstate. Thebrakeandclutchunloaded losseswere modeledusingtheexperimental results (Figure9a). MG1unloadedloss:MG1unloadedloss iscausedbythemechanicalandelectrical components whenMG1rotates freely [29]. For the input split type,MG1doesnotproduce thepower topropel thevehicle in theEV#1modeandis freelyrotatingbecause it is connectedto thevehicle throughthe planetarygear.MG1unloadedlosswasmodeledusingtheexperimental results (Figure9b). Oilpumploss:Theoilpumpprovidesaflowrate for the lubrication, cooling,andthecontrolof theclutchandbrake. Sinceamechanicaloilpump,which isdrivenbythedriveshaftviaagearwas usedin this study, theoilflowissupplied inproportionto thevehiclespeed.While theclutchorbrake isengaged,additionaloilflowisneededtogenerate thecontrolpressure. Therefore, theoilpumploss dependsonthevehicle speedandcontrolpressure. In this study, theoilpumplosswasobtainedfrom PriusTHSexperimental results, showninFigure9c [16]. (a) (b) (c) 6SHHG USP 6SHHG USP 0 0.5 1 Figure9. The torque lossmapderived fromtheexperimental result for: (a)Brake/clutch; (b)MG1 unloaded; (c)Oilpump. Tocalculate thedrivetrain loss, thedesignspecificationandlocationofeachelementarerequired. In Figure 10, a schematic diagramof the reference PHEV, using the design concept described in Figure6b, is shown.The installationpositionsof thebearingsweredeterminedreferringto the3rd generationToyotaPrius. Thebearing losses inside theMG1andMG2wereconsideredinthemotor efficiencymap.MG2wasconnected to theoutput throughtworeductiongears,G1-G2andG3-G4. Thefrictionfaceareaof thebrakeandclutchandthenumberofclutch frictionfacesweredetermined byconsideringthe transmittedtorque[30]. Themagnitudeof thePElossanddrivetrain lossvarydependingonthepowerflowpath,which isdeterminedbytheoperatingmode. InTable3, thecomponentsof thePElossanddrivetrain lossare shownforeachoperatingmode. InEV#1andparallelmode, thePE lossesoccur fromthebatterycharge/discharge,MG2, and HDCoperation. TheMG1 loss needs to be considered in theEV#2mode, power split, and series mode, inaddition to thebattery,MG2, andHDClosses. Thedrivetrain losses come fromthegear, planetarygear,andbearings. Theunloadedlossesoccurdueto thedragwhentheclutchorbrake is freelyrotating. Thechurning lossalwaysexistsat thefinal reductiongear. Inaddition, theoilpump lossneeds tobeconsideredwhentheclutchorbrake isengaged. 273