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Journal of Environmental Sciences 21(2009) 745749 Research and development of electric vehicles for clean transportation WADA Masayoshi Department of Human-Robotics, Faculty of Development, Saitama Institute of Technology, Saitama 369-0293, Japan. E-mail: mwadasit.ac.jp Abstract This article presents the research and development of an electric vehicle (EV) in Department of Human-Robotics Saitama Institute of Technology, Japan. Electric mobile systems developed in our laboratory include a converted electric automobile, electric wheelchair and personal mobile robot. These mobile systems contribute to realize clean transportation since energy sources and devices from all vehicles, i.e., batteries and electric motors, does not deteriorate the environment. To drive motors for vehicle traveling, robotic technologies were applied. Key words: electric vehicle; robot technology; converted electric vehicle; clean transportation DOI: 10.1016/S1001-0742(08)62335-9 Introduction The infl uences of internal combustion systems such as cars with gas engines become a serious social problem because of the environment pollution. To alleviate the problems, automobile manufacturers forced to shift their part of productions from pure internal combustion systems to hybrid systems or electric systems. An electric system provides the best solution to the problem, however, weight andenergycapacityofelectricbatteriesarestillnotenough for the substitution of the internal combustion system with gasoline. Therefore, a hybrid system might be a reasonable solution for the substitute of pure internal combustion system so far. Toyota Motor Corp. provided their fi rst hybrid car “PRIUS” (Toyota Motor Corporation, 1997), and the hybrid technology has been extended to large class of cars, such as “Estima hybrid” and “Harrier hybrid”. It is estimated that electric systems will be widely used in the near future. To get initiative in this direction of development, Mitsubishi Motors developed a pure electric vehicle, “i-MiEV” and Fuji Heavy Industry also developed “R1e”, both of which will be commercially available soon. Electric drive systems are relatively simple compared with an engine. It needs no cooling system, lubricant system, timing control between electric and gas responses. In our electric vehicle (EV) project, the fi rst stage of the research has been started in which we study the fundamen- tal capabilities of EV. For the objective, we developed a converted EV (electric mini, E-MINI) in our laboratary. In thisarticle, the procedure of conversionand results of basic tests including road tests are reported. * Corresponding author. E-mail: mwadasit.ac.jp 1 Electric vehicle development 1.1 Developments of electric vehicle in laboratory or as personal project Good features of EVs are clean and easy to handle not only in driving but also in the development in university laboratory or as personal project. To develop a gas engine, a large space with expensive facilities is needed for testing engine, such as an isolated room with a noise reduction system, an air ventilations, a safety system for eliminating the damages of engine explosion, etc. Unlike the development of engine, a drive system with an electric motor is quite simple and easy to handle. No special facility for noise reduction is needed, because electric motor is very quiet compared with engine. No air ventilation system is needed since electric system does not contaminate the environments, and smelly or volatile chemistry such as gasoline is not used. 1.2 Base car As a base car for converted EV, a class of light-car (less than 660 cc of gas engine) or a small-car around 10001300 cc might be suitable. Since the light-car shows a better performance in traveling range and acceleration. After the conversion, it would gain 100 kg and sometimes additional weight could reach 300 kg. We chose a Rover Mini (known as a Mini Cooper) as a base car to develope the converted EV because of its relatively small size, rigid monocoque chassis construc- tion, and easily obtainable of parts. The car has been sold for about 40 years without major design change. Additionally, its electric systems are quite simple which has no computers, nor brake-servo system. Figure 1 shows a snap shot of a base car before 746WADA MasayoshiVol. 21 Fig. 1Rover Mini (before conversion to EV). conversion to EV. The base car used was manufactured in 1986 and its specifi cations are shown in Table 1. 1.3 Motor type Some types of motors which can be used for electric vehicle propulsions are now commercially available such as direct current (DC) brash motors, DC brash-less motors, induction motors, etc. However, if a base car with a back gear was chosen, a DC brash motor is a solution with the highest priority when consider the cost, weight, and performances. Currently, digital control technology is applied to drive a such high power motor in which power switching devices such as FETs, IGBTs are used. The full voltage power line is switched on and off in high frequency higher than 10 kHz by the switching devices and the pulse shaped voltage is applied to motor windings. The switching frequency is constant while a ratio between on-time and off -time in one cycle is varied based on the operation value. This drive method is called as a pulse width modulation (PWM). For rotate a DC brash motor in specifi c direction, it needs just one switching device which chops a power line connected to a motor. However, if rotating a motor to drive in multiple directions is needed, namely clockwise (CW) and counterclockwise (CCW), four switching devices are needed to be installed. Compared to DC brash motor, a DC brash-less motor or an alternate current (AC) motor need at least six switching devices which have to be controlled independently. Also, a sensor for detecting rotor angle is essential and can make a motor and a driver to be complicated, heavy and bulky. Table 1 Specifi cations of Rover Mini (1986) Parameter EngineSize 998 cc; max. power: 31 HP; max. torque: 7.1 (kgfm) DimensionLength 3054 mm; width 1440 mm; height 1330 mm; wheelbase 2036 mm Weight680 kg Number of persons4 DriveFront-engine and Front-drive (FF) Transmission4-Speed manual transmission From the discussion, it is clarifi ed that a DC brash motor rotating only in one direction is the simplest confi guration compared with others. The confi guration can be available by installing or remaining a back gear on the vehicle. This is not a diffi cult requirement because a normal gas engine can rotate in one direction as well. It could be an another solution to alter the connection between batteries and a motor using circuit contactors to provide a current fl ow in negative direction. In this case, the moving direction, forward or back, is controlled by an electric switch, unlike a usual automobile which moving direction is controlled by a mechanical gear transmission. However, this is a unique solution only applicable for EVs. 1.4 Battery type We have to consider the type of drive batteries for propelling EV. A Li-ion battery may present the best per- formance among the existing batteries in its energy/weight ratio. However, the strict current control in charging and discharging situations is required and a special ordered battery charger has to be used in many cases. If the battery confi guration has been fi xed, it would be diffi cult to change it for a new specifi cation, such as changing voltage, increasing the number of batteries to enlarge maximum current, etc. Beside the inconveniences, Li-ion battery systems are extremely expensive which are 10100 times of lead type battery in cost. In addition, it has not been accepted by the public that the safety of the Li-ion batteries has been established. Due to above reasons, lead based batteries was chosen for drive EV. Optima yellow top, the deep cycle battery from Optima batteries, Inc., provides quite high perfor- mances compared with standard lead batteries. 2 Electric vehicle design 2.1 Components for electric vehicles Most important components for EV are a drive motor and a motor controller as discussed in the previous section. A motor used for converted EV is a series-wound DC brash motor which is available on 72120 VDC and 400 A current at most. A motor controller with power switching devices can turn on and off 120 VDC power at most in 15 kHz frequency. Some of the important components used in EV are shown in Table 2 together with photos of a motor and a controller in Fig. 2. 2.2 Design of drive unit The major subjects of the conversion are a design and Table 2EV components (important components only) MotorL91-4003Advanced DC motors Controller1221C7401CURTIS ThrottlePB-6CURTIS BreakerTQD-200General electric Electric contactorEV-200-AAANAKILOVAC E-meterLink10 model900092Zantrex BatteryYT-4.2LSOptima batteries Battery chargerBL-20K (b) 1221C7401. assembling of a drive unit which consists of a drive motor, a clutch, a fl y wheel and a transmission. A transmission is not always needed to an EV, however, we utilize the original transmission to extend the limited motor torque and velocity to adapt various drive situations together with for remaining a back gear to realize back drive using DC motor rotating only in one direction. Figure 3 shows a snap shot of removing the gas engine from the vehicle. The case of the transmission was partly removed by machining process to locate the motor shaft to the exact location of a crank shaft of the original engine. Figures 4 and 5 show an original transmission, a machined transmission case, and the drive unit assembly with a drive motor mounted on the top of the transmission, respectively. The weight of the original engine was 141 kg including small peripheral Fig. 3Removal an engine from Rover Mini. devices such as a generator, a starter motor, etc., while the drive unit with a motor weights 87 kg. The maximum torque of developed drive unit is 6.91 kgfm and maximum power is 22.70 kW (30.45 HP). 2.3 Battery confi guration Various available combinations exist for connecting a multiple batteries to a drive motor for an EV. Most of motors and motor drivers are available for the power range DC 72144 V. The appropriate battery confi guration is one of the most important subjects for developing EV. It depends on the size and weight of the original car, the weight of batteries, and motor performances. For generating 72 V, at least 6 batteries (12 V each) are needed to connect them in series. However, the batteries providing 4.32 kWh power under the assumption require one battery pack has 60 Ah capacity. Normally, an EV can travel 7 to 10 km per 1 kWh energy, it is obvious that the energy is not enough for a car in normal use. If 72 V is believed the best for system, the next solution for the system is to install 12 batteries in a car, in which a pear of 6 batteries are connected in parallel. Table 3 shows the possible connections for EV drive with lead type 12 V batteries. For driving E-MINI, a DC power is generated by 8 batteries connected in series which rated voltage is 96 V. The capacity of a battery is 60 Ah, total energy on a car becomes 5.76 kWh. The batteries can be charged by an on-board battery charger with plugging it in an AC 100 V socket which is found at every home in Japan. Since the Fig. 4Transmission of E-MINI. (a) a transmission separated from an engine block; (b) a transmission case after machining. 748WADA MasayoshiVol. 21 Fig. 5A drive unit assembly with motor, transmission and clutch. Table 3Possible solutions of the number of batteries, voltages and total capacities. TotalSingle connectionDouble (parallel) connection voltage (V) Num. ofCapacityNum. ofCapacity batteries(kWh)batteries(kWh) 7264.32128.64 8475.041410.08 9685.761611.52 10896.481812.96 120107.22014.4 132117.922215.84 144128.642417.28 maximum current for battery charge is limited at 8 A, no special wiring or large breaker is required. 2.4 Installation Figure 6 shows the location of components and the wiring of E-MINI. A motor, a motor controller and a throttle are located in an engine compartment. The throttle is connected to a gas pedal by wire, driver can operate the car in an identical manner with a standard gas car. Batteries are placed in separated locations including an engine compartment, a space under the back seats and a rear luggage room. A battery charger is installed also in luggage room which electric cord is pulled out from the cap of gasoline tank for battery charging. Figures 6b and 6c show engine compartment and the overview of E-MINI respectively. The total weight of the car reaches 760 kg which is 80 kg gained from the car before conversion. 2.5 Meters and indicators To manage and get information of drive batteries, an E- mater is installed on a cockpit of E-MINI which provides a total voltage, a current fl ow, a remained energy in kWh, and the estimated possible time for driving (Fig. 7). Tacho- meter, and ampmeter are also installed around the cockpit for getting instantaneous information of drive motor. A speedo-meter works as a standard car. 3 System test 3.1 Road test E-MINI has been authorized to drive on public roads with a license plate. E-MINI could travel 35 to 38 km distance by one charge where approx. 3.5 to 4 kWh energy had been consumed. Therefore, effi ciency is in the range of 8.7510.85 km/kWh. Figure 8 shows the energy consumption and the voltage drop as travel distance increased from 0 (start) to approximate 30 km. 3.2 Battery charge Figure 9 shows the change of the stored energy in battery charging using on-board charger. E-MINI has an on-board battery charger which is available for 100 V AC using home power lines, because the maximum current is restricted at 8 A. F