Mitsubishi's Electric Car Achieves 160km Cruising Range

Jan 24, 2008
Tatsuhiko Hayashi, Nikkei Automotive Technology
"i MiEV" test vehicle
"i MiEV" test vehicle
[Click to enlarge image]
Battery under the floor
Battery under the floor
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A battery pack composed of a number of cells in a metal container is mounted on the body with four cross members.
A battery pack composed of a number of cells in a metal container is mounted on the body with four cross members.
[Click to enlarge image]
Meidensha's 47kW motor
Meidensha's 47kW motor
[Click to enlarge image]
Lithium Energy Japan's Li-ion rechargeable battery
Lithium Energy Japan's Li-ion rechargeable battery
[Click to enlarge image]

Mitsubishi Motors Corp unveiled its electric vehicle "i MiEV," which has been remodeled for use in a field test scheduled for February 2007 in cooperation with electric companies throughout Japan.

Compared to the model used in the preliminary test conducted in January 2008, the latest model has a longer cruising range. Mitsubishi will provide a fleet of 40 cars to five electric companies.

Mitsubishi aims to launch mass-production of electric vehicles in 2009. And, in the field test, the company plans to investigate such issues as the "preferable length of time for charging from the viewpoint of users" and "compatibility with rapid rechargers under development by electric companies."

Two major improvements in the new test vehicle are the adoption of new Li-ion rechargeable battery and the cruising range extended from 130 to 160km in the 10-15 Japanese test cycle. The longer range was achieved by the redesigned motor, control system, etc.

In December 2007, Mitsubishi Motors, GS Yuasa Corp and Mitsubishi Corp set up Lithium Energy Japan, a joint company specializing in the development, production and distribution of large Li-ion rechargeable batteries. Lithium Energy Japan plans to produce 200,000 cells (equivalent to the demand for 2,000 units of electric vehicles) in the FY2009.

The test vehicle will mount the new company's battery for the first time. Thus far, Mitsubishi has used a battery manufactured by Litcel in its existing models.

The performance of new battery is the same as that of its predecessor, ie, a voltage of 330V and a capacity of 16kWh. It also has the same setup composed of 22 modules obtained by combining four cells, each of which has a voltage of 3.3V and a current capacity of 50Ah. But the new battery as a whole has a slightly larger capacity, because the variation in capacity of the cells is reduced.

In addition, the new battery uses a cell container made of metal to enhance safety, in contrast to the existing battery that uses a plastic cell container. A Mn-based material is used for the positive electrode in the new battery.

A battery pack is prepared by placing the battery modules composed of 88 cells in total on a plastic tray that has four cross members on its lower side before mounting the pack on the vehicle body. The pack also has a stronger structure. The existing battery modules are placed in an aluminum case directly attached on the vehicle body. Thus, an undesired force is applied on the module in a case of collision.

In the new battery pack, the cross members are designed to receive the force, thereby preventing the modules from being deformed.

The cruising range was prolonged because the company aimed to develop an electric vehicle that runs about 100km with the air conditioner turned on. The company extended the range by improving the motor efficiency and regeneration capability as well as reducing the rolling resistance of tires.

Despite using the same structure as before, ie, an interior permanent magnet (IPM) motor, the company improved the efficiency in the low-speed rotation range. In addition, the amount of regeneration is increased, while reducing the use of friction brakes in the 10-15 Japanese test cycle.

The rolling resistance of tires is also reduced by nearly 10%. The test showed that the vehicle can drive 108 km with the air conditioner turned on to cool the car, and 100km with the heater on.

The company also made efforts to reduce the size and weight of the components in consideration of mass production. For example, the motor size has been reduced by 10% by a reduction in the number of parts. In addition, a rib is installed on the motor housing to reduce kilohertz-order noise. As a result, the radiated noise is reduced by about 5dB(A).

The inverter size is also reduced by 30% by placing the electronic parts closer to one another to increase mounting density. The recharger size is reduced by 10%. The motor and the inverter are manufactured by Meidensha Corp.

The time required to recharge the battery pack is about 14 hours at AC 100V/15A, about 7 hours at AC 200V/15A and about 30 minutes by rapid charging (80% recharge). The company standardized the communication protocol of the rapid recharger before use so that it can also be utilized in Fuji Heavy Industries Ltd's electric vehicle "R1e."