慶應義塾大学 - 電気自動車研究室
Professor > History of Electric vehicle production
Supervising
Professor Hiroshi Shimizu: History of Electric vehicle production
Supervising
Professor Shimizu was related to development of 8 Electric vehicles during 30 years including Eliica. He has done the effort which makes the triangle made with 3 of value big and have come while continuing such development.
Vehicle A was converted from a gasoline-powered car. Such automobiles can be made by removing the engine and replacing it with an electric motor and batteries. Electric vehicles currently produced by automakers are manufactured in this way.
Vehicle B is an electric two-wheeler. Around this time people came to realize that the most sensible arrangement for electric vehicles was to put the motors in the wheels. This vehicle features in-wheel motors, which enable efficient transmission of energy from the motors to the wheels. Since there is no need to mount an engine in the car body, this vehicle has the following features: 1) more space is available for the passenger compartment, 2) the body structure is simple, and 3) fewer parts are required.
Vehicle B was developed in a joint research project with Tokyo R&D Co., Ltd. and Seiko Epson Corporation.
Vehicle C features motors in four wheels. It was developed jointly with Nippon Steel Corporation.
Called IZA, Vehicle D is an improved version of Vehicle C. This car has a top speed of 176 km/h and a range of 270 km on a single charge. This was a ground-breaking development stage, since it showed that electric cars were capable of performance close to that of gasoline vehicles. Tokyo Electric Power Company organized a research group for IZA, and development work was carried out amid ongoing discussion in this group.
Vehicle E is a large truck, designed to take atmospheric samples at high altitude. Accurate atmospheric readings cannot be made if one’s own vehicle emits exhaust gases, necessitating the use of an electric truck. This vehicle is a series hybrid, capable of travelling approximately 30 kilometers on batteries alone. For longer distances, it runs on electricity generated by a gasoline engine.
Vehicle F was the first to feature a “built-in-battery frame,” where batteries are mounted in a hollow frame under the floor of the car. This structure eliminates the need for space above the floor to install large-capacity batteries. Since the batteries are the heaviest component, placing them under the floor also lowers the center of gravity. Moreover, unit construction of the battery containers and frame enables a lighter car body.
This structure also ensures battery safety. Around 2005 there were a number of incidents where PC and mobile phone batteries overheated and caught fire. This led to growing concern that lithium-ion batteries might be dangerous. Cobalt is used in the anodes of these compact batteries to maximize the amount of power they can store per unit of mass. However, manganese is used in the large lithium-ion batteries installed in electric vehicles. When manganese is used, the possibility of overheating or catching fire is extremely low. Even so, if such batteries are mistakenly charged at several times the specified level, it is possible that internal pressure will build, the safety valve will open, and the liquid inside them will spurt out. Mounting the batteries within a strong frame structure is an effective way of avoiding further damage in such a case.
Vehicle F was developed with a research budget provided under the framework of the MEXT special coordination funds.
Vehicle G is a limousine-style passenger car. When developing Vehicle F, it was hoped that passenger compartment space would be greatly increased, since the in-wheel motors and built-in-battery frame did away with most major components above floor level. When the vehicle was actually built, however, the regular-sized tires took up much of the space intended for the passenger compartment, so available space did not increase as much as anticipated.
Consequently we wanted to make the tires smaller, but simply reducing their size would detract from comfort and make the vehicle unable to carry heavy loads. We therefore hit on the idea of splitting each large wheel into two small wheels. This would minimize the intrusion of the wheel arches into the passenger compartment.
Vehicle G was developed to embody this idea. It has four pairs of compact wheels, making eight wheels and eight motors in all. The suspension for this set-up was termed “tandem wheel suspension.” In addition to the batteries, the inverter (spend controller) was also mounted in the frame under the floor. We therefore changed the name of the frame from “built-in-battery” to “built-in-component.” This platform structure comprising the three elements of in-wheel motors, built-in component frame, and tandem wheel suspension was termed the “integrated platform.”
Vehicle G was developed under the framework of MEXT special coordination funds for strategic basic research.
