Yes. Eighty-eight cells are connected in series, and if just one of the cells in the battery lost balance, it could affect and deteriorate the total performance of the battery. Therefore, in order to prevent this phenomenon, we have incorporated the circuit called “balance control”.
The lithium-ion battery has a proper operating voltage range, and so it's very excellent to be used in the operating range. However, once the battery becomes out of the proper range, it will have suddenly deteriorated. So, it has always been monitored so that it will not become out of the range. In short, it is not enough to monitor the battery overall, so the “i-MiEV OS” controls every individual cell's voltages. To use the battery safely for a long time, the control of the battery is absolutely necessary.
Now, we hear the public people think electric vehicles can be easily produced by electric-appliance makers, but there is a big difference in usage between home electric appliances and electric vehicles.
For example, the lithium-ion battery has also been used in mobile phones or personal computers, but the definite difference for electric vehicle use is to need specific considerations for driving. In short, the battery to drive the vehicle must meet various kinds of external factors such as external pressure, collision, vibration, temperature change, etc. For example, in case of collision, the battery may be deformed due to external pressure. So, the secure safety and reliability must be incorporated to cope with such conditions.
In case of vehicle, the battery capacity is not maximized to the limit and the surplus has been considered as a margin for safety.
There is also a protection of the control side and a crash-safety technology of the body side. Of course, these cannot be created without any information of know-how related to car manufacture which has been long cultivated.
I think it's easy just to make an electric vehicle, but it is very difficult to produce the electric vehicles which have combined the safety and reliability.
- Hiroaki Yoshida
- General Manager of the EV/Powertrain System Engineering Department, Joined Mitsubishi Motors Corporation in 1978, belonged to the Research Department, engaged in the development work of electronically controlled suspension, four-wheel steering system, anti-skid brake system, and then transferred to the EV development team of Electronics Engineering Department, where involved in the research and development work of electric vehicles, fuel cells, and hybrid vehicles.
