Auxiliary Power Supply System for Electric Power Steering (EPS) and High-Heat-Resistant Lithium-Ion Capacitor "2279
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Article Auxiliary Power Supply System for Electric Power Steering (EPS) and High-Heat-Resistant Lithium-Ion y Capacitor Takumi Mio 1,* , Yukihiro Komatsubara 1, Naoki Ohmi 1, Yusuke Kimoto 1, Kentaro Iizuka 1, Tomoki Suganuma 1, Shun Maruyama 1, Toyoki Sugiyama 2, Fumihiko Sato 2,*, Satoshi Shinoda 2, Tokuaki Hibino 2 and Koji Nishi 1 1 Power Storage Device Dev. Group, BR Electrical Power Storage Device Business Dept., JTEKT Corporation 1-7 Kitajizouyama, Noda-cho, Kariya, Aichi 448-0803, Japan; [email protected] (Y.K.); [email protected] (N.O.); [email protected] (Y.K.); [email protected] (K.I.); [email protected] (T.S.); [email protected] (S.M.); [email protected] (K.N.) 2 Power Supply System Dev. Group, BR Electrical Power Storage Device Business Dept., JTEKT Corporation 1-7 Kitajizouyama, Noda-cho, Kariya, Aichi 448-0803, Japan; [email protected] (T.S.); [email protected] (S.S.); [email protected] (T.H.) * Correspondence: [email protected] (T.M.); [email protected] (F.S.) Presented at EVS 31 & EVTeC 2018, Kobe, Japan, 1–3 October 2018 y Received: 19 April 2019; Accepted: 18 May 2019; Published: 22 May 2019 Abstract: Advanced Driver Assistance System (ADAS) and Automated Driving (AD) are the two major topics for the current and next generations of vehicles. To realize them in full-size vehicles equipped with a 12 V power supply, the need for electric power steering (EPS) is increasing. Currently, the steering system of full-size vehicles is equipped with hydraulic power steering due to electric power shortage. An auxiliary power supply system using a lithium-ion capacitor was developed in order to solve the concern. In addition, to mount the system in the vehicle with no cooling–heating equipment, development of expanding the operating temperature range of the lithium-ion capacitor was conducted. Several improvements have made the capacitor operate stably in high-temperature environments above 100 ◦C. Keywords: electric power steering; temporary power boost; redundant power supply; lithium-ion capacitor 1. Introduction Advanced Driver Assistance System (ADAS) and Automated Driving (AD) are the two major topics for the current and next generations of vehicles. According to the roadmap issued by the Prime Minister’s Office in Japan, Level 4 of the AD level defined by the SAE International in J30162 (September 2016) will be realized around 2025 in limited scenes such as expressways and highways [1,2]. AD functions take over the longitudinal and lateral guidance of the vehicle and must be fail-operational in case of any failure [3–5]. Therefore, it is also essential to improve functional safety in electric power steering (EPS) to protect SAE Level 3 or higher from power failure during driving [6,7]. To realize ADAS and AD functions in full-size vehicles equipped with a 12 V power supply, the need for EPS is increasing. Currently, the steering system of full-size vehicles is equipped with hydraulic power steering due to electric power shortage. In order to steer a 3.5-ton class full-size vehicle, up to about 18 kN of steering rack force is required. Assuming that the overall efficiency of the EPS, including the ECU, motor, and gears, is approximately 50%, the electric power required to output the steering force is about 2000 W. If the necessary power is supplied from a 12 V power supply, World Electric Vehicle Journal 2019, 10, 27; doi:10.3390/wevj10020027 www.mdpi.com/journal/wevj World Electric Vehicle Journal 2019, 10, 27 2 of 13 about 170 A is required, but the current supplied to the EPS is up to 120 A, so the power demand of EPS cannot be satisfied. 12 V power supply can only drive EPS for vehicles weighing less than 3 tons (aboutWorld 12 Electric kN rack Vehicle force). Journal 2019, 10, x FOR PEER REVIEW 2 of 13 The shortage for the electric power required by the EPS must be compensated by the driver’s steeringsupply, force. about This 170 is manifestedA is required, as but an the “EPS current torque-assist supplied delayto the phenomenon”EPS is up to 120 in A, which so the thepower steering wheeldemand suddenly of EPS becomes cannot be heavy satisfied. during 12 V abrupt power steeringsupply can or only stationary drive EPS steering. for vehicles So, inweighing order toless install EPS tothan full-size 3 tons (about vehicles 12 kN equipped rack force). with a 12 V power supply, torque-assist delay phenomenon must The shortage for the electric power required by the EPS must be compensated by the driver’s be solved. steering force. This is manifested as an “EPS torque-assist delay phenomenon” in which the steering In recent years, 48 V mild-hybrid vehicles have been launched, mainly in Europe and the United wheel suddenly becomes heavy during abrupt steering or stationary steering. So, in order to install States,EPS but to 48full V-size is avehicle drives systemequipped power with a source 12 V power only, supply and auxiliary, torque-assist electronics delay phenomenon components must are still conventionalbe solved.12 V [8]. Since EPS belongs to auxiliary electronics components, the electric power shortage cannotIn recent be years, resolved. 48 V Itmild will-hybrid take a vehicles long time have for been the overall launched, voltage mainly of thein Europe vehicle and to rise.the InUnited addition, States, when but 48 installing V is a drive EPS system in a full-size power source vehicle, only, it is and necessary auxiliary to electronics consider thecomponents steering force changeare atstill the conventional time of temporary 12 V [8] power. Since EPS loss. belongs There isto aauxiliary possibility electronics that driving components, cannot the be continuedelectric if EPS assistpower is shortage lost. Even cannot while be resolved. the torque-assist It will take delay a long phenomenon time for the overall occurs, voltage a part of the v steeringehicle to force necessaryrise. for steering a full-size vehicle is output from the EPS, but in the situation of a power supply In addition, when installing EPS in a full-size vehicle, it is necessary to consider the steering failure, all the torque-assist force is lost. It is impossible to satisfy the steering force only with the force change at the time of temporary power loss. There is a possibility that driving cannot be power of the driver. continued if EPS assist is lost. Even while the torque-assist delay phenomenon occurs, a part of the Asidesteering from force the necessary realization for steering of ADAS a full and-size AD,vehicle there is output are benefits from the to EPS, introducing but in the EPSsituation to full-size of vehicles.a power A typicalsupply failure point,is all that the torque it is environmentally-assist force is lost. friendly. It is impossible The conventional to satisfy the steering hydraulic force power steeringonly useswith the power driving of the force driver. of the engine to constantly power the hydraulic pump in order to generate hydraulicAside from power. the realization This creates of ADAS excess and burden AD, there on are the benefits engine andto introducing is one of theEPS reasons to full-size for high fuel consumption.vehicles. A typical The point EPS systemis that it operatesis environmentally the motor friendly. only during The conventional steering, therefore hydraulic reducing power the load onsteering the engine uses the and driving improving force of fuel the consumption engine to constantly by approximately power the hydraulic 2.5% [9]. pump in order to Consequently,generate hydraulic JTEKT power. worked This oncreates development excess burden of the on auxiliary the engine power and is supply one of systemthe reasons for EPS for with high fuel consumption. The EPS system operates the motor only during steering, therefore reducing the following features [10,11]: the load on the engine and improving fuel consumption by approximately 2.5% [9]. 1. EliminationConsequently, of the JTEKT torque-assist worked delayon development during abrupt of the steering auxiliary and power stationary supply steeringsystem for EPS 2. withPeak the cut following of the electric features power [10,11 consumption]: during abrupt steering and stationary steering 1. Elimination of the torque-assist delay during abrupt steering and stationary steering 3. Redundant power supply in case of 12 V power supply failure 2. Peak cut of the electric power consumption during abrupt steering and stationary steering 3. Redundant power supply in case of 12 V power supply failure 2. EPS Electric Power Consumption First,2. EPS FigureElectric1 Pshowsower C theonsumption result of maximum electric power consumption of various electrical componentsFirst, of Figure a vehicle. 1 shows The the electric result powerof maximum consumption electric power of the consumption EPS system of during various abrupt electrical steering is largercomponents than that of a of vehicle. the air The conditioner electric power and consumption headlights. of the On EPS the system other during hand, abrupt the electric steering power consumptionis larger than of the that EPS of during the air straight-lineconditioner and driving headlight is onlys. On 3% the of stationaryother hand, steering. the electric power consumption of the EPS during straight-line driving is only 3% of stationary steering. 1.0 0.8 0.6 0.4 (Normalization) Power consumption 0.2 0.03 0.0 FigureFigure 1. Measuring 1. Measuring result result of maximum of maximum electric electric power consumptionpower consumption of various of electricalvarious electrical components of vehicle.components of vehicle. World Electric Vehicle Journal 2019, 10, 27 3 of 13 World Electric Vehicle Journal 2019, 10, x FOR PEER REVIEW 3 of 13 World Electric Vehicle Journal 2019, 10, x FOR PEER REVIEW 3 of 13 Next,Next, FigureFigure2 2 shows shows the the power power consumption consumption during during abrupt abrupt steering steering of of a a full-size full-size vehicle.