EXAMENSARBETE I ELEKTROTEKNIK 300 HP, AVANCERAD NIVÅ STOCKHOLM, SVERIGE 2015 An integrated brake disc and electric drive for vehicle propulsion A FEASIBILITY STUDY JOHAN LINDER KTH KUNGLIGA TEKNISKA HÖGSKOLAN SKOLAN FÖR ELEKTRO- OCH SYSTEMTEKNIK An integrated brake disc and electric drive for vehicle propulsion -A feasibility study JOHAN LINDER Master of Science thesis in Electrical Machines and Drives at the School of Electrical Engineering KTH Royal Institute of Technology Stockholm, Sweden, February 2016. Supervisor: Oskar Wallmark Examiner: Oskar Wallmark TRITA-EE 2016:019 An integrated brake disc and electric drive for vehicle propulsion -A feasibility study JOHAN LINDER c JOHAN LINDER, 2016. School of Electrical Engineering Department of Electric Power and Energy Systems KTH Royal Institute of Technology SE–100 44 Stockholm Sweden Abstract In this thesis, the feasibility to integrate an brake disc and electric machine is investigated. In wheel motors (IWMs) have several advantages, such as saving space in the vehicle, individual and direct control at the wheels and the absence of a mechanical transmission. However, today’s IWMs are heavy and, thus, negatively affect the driving performance of the vehicle due to the increase of the unsprung mass. By integrating an already existing part in the wheel, this increase of the unsprung mass can be minimized. The brake disc manages high temperatures, a significant wear in rough environ- ment, which puts high demands on the rotor. The second part of the machine, the stator, will be significantly affected by the high temperatures of the rotor. The temperatures of the stator are transferred by convection, conduction and radiation from the rotor or brake disc. Liquid cooling of the stator back is analyzed as a potential solution for handling the high temperatures. In order to analyze the feasibility of the concept, thermal, electric and mechanical modelling has been used. The evaluation whether it is possibleor not to integrate the brake disc has been with regard to the results of weight, cost, thermal tolerance and electric performance. Key words: Axial flux, brake disc, core less rotor, in wheel motor, hub motor, quarter car model, segmented rotor, switch reluctance machine, single teeth winding. iii iv Sammanfattning I detta arbete unders¨oks m¨ojligheten att integrera en bromsskiva med elmaskin. Hjul- motorer har flera f¨ordelar, bland annat sparas utrymme i sj¨alva bilen, individuell kon- troll samt drivning av hjulen utan mekaniska transmissioner. Men hjulmotorer som kan anv¨andas idag v¨ager oftast s˚apass mycket att den od¨ampade massan ¨okar kritiskt och k¨oregenskaper av fordonet d˚ablir lidande. Genom att integrera en befintlig del i hjulet kan ¨okningen av od¨ampade massan minskas. Att anv¨anda bromsskivan som rotor, kr¨aver att denna t˚al temperaturer ¨over 500◦C samt p˚afrestningar och slitage som en vanlig mekanisk friktionsbroms m˚aste uth¨arda. Den andra delen av maskinen, statorn kommer ¨aven denna att p˚averkas av de h¨oga tem- peraturerna av bromsskivan som kommer ledas via konvektion, konduktion och str˚alning. M¨ojligheten att kyla statorn med v¨atska och om detta ¨ar tillr¨ackligt unders¨oks. F¨or att analyserna genomf¨orbarheten av projektet har termiska, elektriska och mek- aniska modeller anv¨ants. Resultaten har analyserats d¨ar maskinens vikt, kostnad, termisk t˚alighet och elektrisk prestanda har legat till grund f¨or bed¨omningen om l¨osningen; att integrera en broms-skiva med elmaskin ¨ar rimlig eller ej. Nyckelord: Axialfl¨odes, bromsskiva, enkeltandad lindning, hjulmotor, hub motor kvartfordonsmodell, ryggl¨os rotor, segment rotor, variabel reluktansmaskin. v vi Acknowledgements/Forfattarens¨ tack F¨orst och fr¨amst vill jag tacka Doktor Oskar Wallmark som har handlett mig genom hela detta arbete genom alla dess niv˚aer och sv˚arigheter. Jag vill ocks˚atacka alla inblandade p˚aVolvo som varit mycket hj¨alpsamma och framf¨or allt S¨oren Eriksson som handlett och inspirerat mig samt Quintus Jalkler som hj¨alpt mig med kontakter och ¨ovriga fr˚agor under arbetet. Dessutom vill jag passa p˚aatt tacka alla mina goda v¨anner som gjort studietiden p˚a KTH minnesv¨ard. Ett speciellt tack till Anna Larsson som ¨agnade tid ˚at att granska min rapport. Samt Noj Kazemi, Sebastian H˚akansson, Erik Hallqvist och Alexander Sj¨oberg som jag ¨agnat ˚atskilliga timmar att studera med. Utan den kamratskapen och st¨odet hade min studietid blivit betydligt jobbigare och framf¨orallt tr˚akigare. Jag vill tacka alla d¨ar hemma, mor, far, syster och morfar, som st¨ottat och m¨ojlig- gjort mina studier under ˚aren. Mina v¨anner som under alla dessa ˚ar fortfarande h˚aller samman som det j¨arng¨ang vi alltid varit. Samt min mycket gode v¨an Viktor Andersson som delar mitt st¨orsta intresse och som introducerat mig till flertalet av fordonsv¨arldens alla h¨orn. Avslutningsvis vill jag tacka min K¨araste Lisa f¨or allt personligt st¨od hon har givit mig under detta examensarbete. Johan Linder Stockholm, Sweden February 2016 vii viii Contents Abstract iii Sammanfattning v Acknowledgements/Forfattarens¨ tack vii Contents ix 1 Introduction 1 1.1 Background................................. 1 1.2 Objectives.................................. 2 1.3 Thesisoutline................................ 3 2 Previous work 5 2.1 Patents.................................... 5 2.2 VolvoReChargeConcept . .. .. .. .. .. .. .. 5 2.3 Hybridelectricvehicles. 6 2.4 Inwheelmotors............................... 7 3 Influence of unsprung mass 9 3.1 Suspension ................................. 9 3.2 Quartercarmodel.............................. 10 3.3 Simulinkquartercarmodel . 11 3.3.1 Increasingtheunsprungmass . 15 3.4 Resonancefrequency ............................ 19 3.5 Summaryofchapter............................. 20 4 Brakes 23 4.1 Thefunction................................. 23 4.2 Thedisc................................... 24 4.3 Brakeregulation............................... 24 4.4 Brakeforcedistribution. 25 ix Contents 4.5 Heattransfer................................. 25 4.5.1 Conduction ............................. 25 4.5.2 Convection ............................. 26 4.5.3 Radiation .............................. 26 4.6 1Dthermalmodels ............................. 27 4.6.1 Powerappliedonmass . 28 4.6.2 Powerappliedonsurface. 28 4.7 3Dthermalmodels ............................. 30 4.7.1 Forcedconvection . .. .. .. .. .. .. .. 31 4.7.2 Naturalconvection . 33 4.8 Summaryofchapter............................. 35 5 Electrical machine 39 5.1 Designchallenges.............................. 39 5.2 Choiceofmachine ............................. 40 5.3 Segmentalrotor ............................... 41 5.4 Linearmodel ................................ 42 5.5 Thewheelmotor .............................. 44 5.6 Solidrotorinductionmachine . 46 5.7 Summaryofchapter............................. 47 6 Implementation of brake disc 51 6.1 Heattransferbetweenthestatorandrotor . ..... 51 6.2 3Dmodel .................................. 52 6.3 Summaryofchapter............................. 53 7 Conclusion and further work 59 7.1 Conclusion ................................. 59 7.2 Furtherwork ................................ 60 A Parameters of quarter car model 63 B Parameters of 1D thermal models 65 C Parameters of 3D thermal model 67 D Parameters and specification of the electrical machine 69 E Parmaters of implementation of machine thermal model 73 References 75 x Chapter 1 Introduction In this part the background, the aim and goals of the project are presented. 1.1 Background Hybrid electric vehicles (HEVs) and electric vehicles (EVs) are more than ever an impor- tant topic in the vehicle industry. Manufactures, such as Tesla, Volkswagen, Chevrolet and Toyota are only a few that offers EVs and/or HEVs to the market. However, the batteries used in the vehicle today has an upper limit of driving range. Even if there are supercharg- ers available that charge the batteries in 30 minutes and deliver a cruising range of around 270 km [10], the charging of the batteries is still considerable more slow than an ordinary refuel of a vehicle with internal combustion engines (ICEs). HEVs combining the ICE with an electric drive are one opportunity to overcome the limits of the pure EV. It offers the cruising range as ordinary cars thanks to the ICE and the fast refuels of fossil fuel. Compared to pure ICE propelled vehicles it (potentially) offers lower fuel consumption thanks to regeneration of brake energy to electric energy and the possibility to keep the ICE operating at points with high efficiency. Development of electric machinery and associated powertrain componets has opened up for a lot of opportunities. In wheel motors (IWMs) enable the possibility to direct and individual drive and control the wheels without expensive and difficult mechanical transmission and drive shafts. However, a drawback is the increasing of unsprung mass due to more weight in the wheel, effecting driving performance and comfort of the vehi- cle [46], [29]. By integrating the already existing brake disc as a rotor in an IWM, there is a possibility to reduce the total increase of unsprung mass. Today, Volvo XC90 and V60 are two HEV models using the Volvo Twin Engine which use an electric machine placed on the rear axle Fig. 1.1. The electric machine is using two drive shafts for driving each rear wheel. Recently Volvo introduced a new vehicle platform, the Scalable Product Platform (SPA). Presently the XC90 is the only manufactured model using SPA and therefore