Improvement of Battery Charging Efficiency using 2- Clutch System for Parallel Hybrid Electric Vehicle

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1 EVS7 Symposium Barcelona, Spain, November7-0, 03 Improvement o Battery Charging Eiciency using - Clutch System or Parallel Hybrid Electric Vehicle Minseok Song, Seokhwan Choi, Gyeonghwi Min, Jonghyun Kim, Hyunsoo Kim * School o Mechanical Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon , Korea(aneol3@skku.edu) Hybrid Electric Vehicle Design Team, Hyundai-Kia R&D Center, 77- Jangduk-dong, Hwasung-si , Korea Abstract A battery charging control using a driving motor is proposed or an AT based parallel HEV. To charge the battery using the driving motor, a -clutch system control is proposed which uses the engine clutch and the clutch inside the transmission. The battery charging eiciency is estimated rom the engine uel consumption and eiciency o the power electronics. To evaluate the perormance o the suggested battery charging control, HEV perormance simulator is developed and simulations are perormed or FTP-7 mode. Simulation results show that battery charging using the driving motor has a higher charging eiciency and aster charging speed compared with the conventional battery charging system using the ISG. Keywords: -clutch system, ISG(integrated starter generator), driving motor Introduction The currently developed or mass-produced hybrid electric vehicle(hev) are classiied as the series type, parallel type and power split type. In parallel type HEV, transmission plays the key role, which combines and distributes the power o the engine and the motor. Automatic transmission(at), continuously variable transmission, dual clutch transmission, automated manual transmission have been adopted as the transmissions or HEVs. In Fig. an AT based parallel HEV is shown, which is under study[]. The target HEV has an engine clutch that connects or disconnects the engine with the motor, which provides the electric vehicle (EV) mode or the hybrid electric vehicle (HEV) mode. The HEV starts in EV mode and the operation mode is shited to HEV mode when the driver wants to accelerate the vehicle []. The mode shit is perormed by the ISG(integrated starter generator). The ISG o the HEV under EVS7 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium

2 study (Fig. ) is connected to the engine through a belt drive. When the mode shit begins, the ISG operates to increase the engine speed to the target speed or the engagement o the engine clutch[3]. Another important role o ISG is to charge the battery as a generator The battery SOC(state o charge) might be lower than the lower-limit. In this case, the EV mode is limited until the battery SOC is recovered to the normal state. Moreover, i the battery SOC drops below the lower limit requently, durability o the battery might be reduced. However, since the ISG uses a small motor with relatively low eiciency compared with driving motor, this charging process may decrease the total system eiciency. In this study, a battery charging control is proposed using a driving motor during vehicle stops to obtain the improved charging eiciency. To evaluate the charging eiciency, HEV perormance simulator is developed and uel economy o the -clutch system is investigated. 3) SOC_Low : In this mode, the engine is mostly used and the battery is charged. The engine operation is increased while the motor operation is decreased. Fig. shows the battery energy management strategy. SOC, HtoN SOC, NtoH SOC, NtoL SOC LtoN are used to determine the battery SOC state. I SOC > SOC, the battery SOC state is changed NtoH to SOC_High. I SOC < SOC, the battery SOC NtoL state is changed to SOC_Low. I SOC < SOC < LtoN SOC, the battery SOC state is changed to HtoN SOC_Normal. Battery charging during the vehicle stop is only perormed when SOC_Low. SOC_High Engine clutch SOC < SOCHtoN SOC > SOCNtoH SOC_Normal SOC < SOCNtoL SOC > SOCLtoN Figure: Structure o AT based parallel HEV SOC_Low Battery charging system. Battery energy management strategy For the battery management o the target HEV, the ollowing battery SOC state are deined: SOC_High, SOC_Normal, SOC_Low[4]. ) SOC_High : In this mode, the battery is mostly used. The engine operation is decreased while the motor operation is increased. ) SOC_Normal : In this mode, the engine and motor are working together under normal condition. Figure:Battery energy management strategy. Charge by ISG(Control ) The ISG is used as a generator which has a power capacity o 8.3kw. The engine operates the ISG, which generates the electric power to charge the battery. The engine power is determined depending on the electric load o the ISG. The engine clutch is disengaged (Fig. 3), which means that the engine and ISG are decoupled rom the driveshat. EVS7 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium

3 8.3kW( IS G B attery B attery( c harg ing dis engaged 30kW( Motor Trans mis s ion( c lutc h eng ag ed 6.s peed automatic ( trans mis s ion E OP CL OWC CL3 BK BK R3 R R C3 C C S3 S S OUTPUT CL INPUT Figure4: Structure o the 6-speed AT Figure3:Charge by ISG (Control ).3 Charge by driving motor(control ) Since a 30kW driving motor has a higher eiciency and power generation capacity than the 8.3kW ISG, it can restore the battery SOC to a stable range within a shorter time. Thereore, it is more advantageous to charge the battery by the motor than the ISG during the vehicle stop. To charge the battery using the driving motor, a -clutch system control is proposed which uses the engine clutch and the clutch inside the transmission. Structure o the 6-speed AT and operation o the riction elements are shown in Fig.4 and Table. To transmit the power rom the engine or motor to the driveshat, at least two riction elements should be engaged(fig. 4, Table). However, when the battery is charged by the driving motor, the driving motor and engine should be decoupled rom the driveshat. Thereore, one riction element o AT is disengaged to disconnect the motor rom the driveshat. For example, at st gear, the brake BK and one way clutch are engaged to transmit the power. To charge the battery using the driving motor, BK is disengaged while one way clutch is engaged[5-8] At this moment, dierent rom Control, the engine clutch is engaged and the engine operates the driving motor to charge the battery instead o ISG(Fig. 5). Table:Friction elements operation BK BK CL CL CL3 OWC ST O O ND O O 3 RD O O 4 TH O O 5 TH O O 6 TH O O 8.3kW IS G B attery B attery c harg ing eng ag ed 30kW Motor Trans mis s ion c lutc h dis engaged 6%s peed automatic trans mis s ion E OP Figure5: Charge by driving motor (Control ).4 Eiciency analysis or battery charging system Fig. 6 shows the battery charging eiciency or Control and Control. The battery charging eiciency is estimated rom the engine uel consumption and eiciency o the power electronics such as motor and inverter. Battery charging eiciency is calculated as ollows: Charging_e iciency = Engine _ eiciency PE _ ecinecy () where the unit o the Engine_eiciency is expressed as kwh/g. As shown in Fig. 6, the engine works in high eiciency region in Control since the driving motor has larger power generation EVS7 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium 3

4 capacity than ISG, which provides the improved battery charging eiciency. The proposed battery charging control using driving motor, Control, shows a charging eiciency o 0.4kwh/g which is higher than ISG (A) o 0.kwh/g. Energy(generation(kWh/g (a) Control 6.3kW,(0.kWh/g Torque,(Nm Figure6:Battery charging eiciency 3 HEV Perormance Simulator To evaluate the uel economy o the battery charging control, dynamic models o the relevant HEV powertrain and HEV perormance simulator were developed. Engine: The engine was modeled using the engine characteristic map. The engine output torque was modeled as a irst order system. Motor: The motor is used as electric motor when driving and as a generator during regenerative braking. The ISG cranks the engine during the engine start. The motor and ISG were modeled using characteristic curves and eiciency maps. Battery: The input and output currents o the battery were calculated using the internal resistance model. For the battery internal resistance, the experimental results according to the battery SOC were used (B) (B) Motor generating eiciency (%) Energy generation = SFC (g/kwh) 7kw,(0.4kwh/g 7kW,(0.4kWh/g Energy(generation(kWh/g (b) Control 6.3kw,( 0.kwh/g Torque,(Nm Engine(speed, rpm Engine(speed, rpm AT: The 6-speed AT consisted o two SPPGs (single pinion planetary gears), one DPPG (double pinion planetary gear), two wet-type multiple disc clutches, three wet-type multiple disc brakes, and a one way clutch. The operating elements o the AT such as planetary gears, clutches, and brakes were modeled using the AMESim sotware. The st step gear ratio N is obtained as, N = ω ω _ in _ out ( = R S + )( R S R3 S 3 ) () where is the teeth number o the ring gear(r), R the teeth number o the sun gear(s), S the R3 teeth number o the ring gear(r3), the teeth S3 number o the sun gear(s3), speed, ω _ out ω _ in the AT input the AT output speed. Gear ratios o the nd, 3rd, 4th, 5th and 6th gear steps can be obtained in a similar way. Vehicle: The vehicle model consisted o a drive shat, tires, and a running resistance model. The longitudinal vehicle dynamic equation is represented as, V = m where veh + R ( N t ( N R t N N T ) F F ( J F l is the road load, the engine inertia, AT inertia, w c e e + J ) + N c l b J + J F b the brake orce, J the clutch inertia, J the wheel inertia, e w ) (3) Je J the T the engine torque, m the vehicle mass, veh R t the tire radius, N the inal reduction gear ratio, N the AT gear ratio, and V the vehicle velocity. A HEV perormance simulator was developed based on the dynamic models o the HEV powertrain(fig. 7) EVS7 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium 4

5 (a) (b) (c) Figure7:HEV perormance simulator 4 Simulation results To evaluate the perormance o the suggested battery charging control, simulations were perormed or FTP-7 mode using the HEV perormance simulator. As shown in Fig. 8, in region (a), the battery SOC by Control and Control shows the same perormance since the HEV is travelling. In region (b), Control shows higher battery SOC compared with Control because the driving motor operates with higher eiciency. Battery charging speed o Control (0.8% per sec) is aster than Control (0.08% per sec). As a result, the battery SOC state is recovered to SOC_Normal( SOC > SOC ) while the battery LtoN SOC o Control still remains in the SOC_Low. In region (C), due to the dierence o the battery SOC state, the engine output power o the Control becomes larger than that o Control. Thereore, the battery SOC dierence between Control and Control is reduced. It is seen rom the simulation results that the inal battery SOC o Control (38.8%) has higher value compared with that o Control (37.%). Mo tor% charging Figure8:Battery charging during FTP-7 mode travel 5 Conclusions SOC _ Normal SOC LtoN SOC _ Low Control HS G Control charging 38.8% 37.% A battery charging control using a driving motor was proposed or an AT based parallel HEV. To charge the battery using the driving motor, a - clutch system control was proposed which uses the engine clutch and the clutch inside the transmission. In this control, one riction element o AT should be disengaged to disconnect the motor rom the driveshat. The engine clutch is engaged and the engine operates the driving motor to charge the battery instead o ISG. The battery charging eiciency is estimated rom the engine uel consumption and eiciency o the power electronics. The proposed battery charging control has a charging eiciency o 0.4kwh/g which is higher than ISG charging eiciency o 0.kwh/g. To evaluate the perormance o the suggested battery charging control, a HEV perormance simulator was developed and simulations were perormed or FTP-7 mode. Simulation results show that the battery charging using the driving motor has a higher eiciency and aster speed compared with the conventional battery charging system using the ISG. EVS7 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium 5

6 Acknowledgments This work was supported by the Technology Innovation Program unded by the Ministry o Knowledge Economy(MKE, Korea). Reerences [] The Boston Consulting Group The come back o the electric car, how real, how soon, and what must happen next, BCG report, 009. [] S. Kim et al., A study on control strategy or hybrid electric vehicle during mode change, KSAE 008 Annual Conerence, 008 [3] M. Song et al., Motor control o a parallel hybrid electric vehicle during mode change without an integrated starter generator, Journal o Electrical Engineering & Technology, Vol.6, No., , 03 [4] B. Min et al., Development o uel economy improvement technique or hybrid electric vehicle by using driving condition prediction, KSAE annual conerence, 0 [5] J. Motosugi et al., Development o a slip control system or RWD hybrid vehicle using integrated motor-clutch control, SAE , 0 [6] F. Renken et al., Power electronics or hybrid-drive systems Power Electronics and Applications, 007 European Conerence [7] I. Soliman et al., Control o electric to parallel hybrid drive transition in a dualdrive hybrid powertrain, SAE paper , 00. Authors Minseok Song He received B.S and M.S in mechanical engineering rom Sungkyunkwan University, Suwon, Korea, in 009 and 0, where he has been working toward Ph. D. degree. His research interests include modeling and control o powertrain system or hybrid electric vehicle and plug-in hybrid electric vehicle Seokhwan Choi He received B.S in mechanical engineering rom Sungkyunkwan University, Suwon, Korea, in 0 where he has been working toward M.S. degree. His research interests include modeling powertrain system or hybrid electric vehicle Gyeonghwi Min He studies or a master s degree in mechanical engineering rom Sungkyunkwan University, Korea. His research interests modeling and control o hybrid vehicle. Jonghyun Kim He received a B.S. in mechanical engineering rom Sungkyunkwan University, Suwon, Korea, in 00. Since 006, he has worked as an engineer at Hybrid Transmission part o HEV system engineering team in Hyundai Motor Company. He is in charge o developing oil pump o hybrid transmission including electric oil pump. Hyunsoo Kim He received a B.S. in mechanical engineering rom Seoul National University, Seoul, Korea, in 977, a M.S. degree in mechanical engineering rom the Korea Advanced Institute o Science and Technology (KAIST), Seoul, Korea, in 979, and a Ph.D. degree in mechanical engineering rom the University o Texas at Austin, Texas, USA, in 986. Since 986, he has worked as a Proessor, Chairman, and Dean o the College o Engineering at Sungkyunkwan University. His main research interests include Hybrid Electric Vehicle (HEV) transmission system design, regenerative braking, and optimal power-distribution algorithms or HEV and vehicle stability control or HEV and In-wheel Electric Vehicles. He has authored numerous journal papers and patents. Pro. Kim served as a President o Electric Drive Vehicle Division o the Korea Society o Automotive Engineers and an editor o the International Journal o Automotive Technology rom 005 to 0. He has served the society as a leader in next-generation automotive technology in Korea. EVS7 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium 6