Mitsubishi Motors was one of the first automakers to start research into and development of the electric vehicle as an alternative fuel vehicle. In recent years, the company has turned its attention to the practical application of high-performance lithium-ion battery power to propel FTO EV and Eclipse EV experimental vehicles in 24-hour distance and public road test programs.
Exploiting the benefits of lithium-ion battery and in-wheel motor technology, the MIEV concept opens up new possibilities in terms of alternative fuel vehicle development. As well as seeking further possibilities for the EV, Mitsubishi Motors is also looking at the application of the MIEV concept to hybrid and fuel cell vehicles.
1. In-wheel motor
(1) Further evolution of all-wheel control technology
A major benefit of the in-wheel motor is that it enables drive torque and braking force to be regulated with high precision on an individual wheel basis in both two- and four-wheel drive systems without requiring transmissions, drive shafts, differential gears or other complex and heavy components. The in-wheel motor therefore holds great promise in terms of the contribution to the further evolution of Mitsubishi's all-wheel control technology that enjoys high critical acclaim on such production models as the Lancer Evolution and Pajero.
(2) Greater freedom in layout design
Housing the drive system in the wheels gives greater freedom in designing the layout. This will facilitate the conversion of IC engine-powered vehicles into hybrid vehicles without requiring the introduction of complex hybrid power systems. It will also make it easier to provide room for space-consuming components such as fuel cell stacks and hydrogen tanks in fuel cell vehicles. The space-saving benefits of the in-wheel motors also offer exciting possibilities in terms of body design. Designers will be able to create innovative exteriors, improve dynamic performance through weight distribution optimization, provide roomier interior space and improve crash worthiness through optimization of the structural framework.
2. Lithium-ion battery
Lithium-ion battery technology offers advantages of specific energy, specific power, and life over other types of rechargeable batteries. Mitsubishi Motors has already built several test vehicles using lithium-ion battery systems, including the Mitsubishi HEV in 1996, the FTO-EV in 1998 and the Eclipse EV in 2000. The FTO-EV set a multiple-charge 24-hour distance world record on a proving ground, while the Eclipse EV covered over 400 km on public roads on a single battery charge. These and other testing programs have enabled the company to verify the practical applicability of this type of battery.
Lithium-ion battery has made major advances in performance over the past few years and offers much promise in terms of higher speeds, extended cruising range and weight reduction for electric, hybrid and fuel cell vehicles in the future.
MIEV Schematic - Colt EV profile
The in-wheel motor test car, Colt EV, is based on the standard compact vehicle, Colt. After removing the combustion engine, fuel tank and transmission, two in-wheel motors were fitted to the rear wheels and powered by a floor-mounted lithium-ion battery system.
Rigorous proving ground tests are now being conducted on the Colt EV. The test car is scheduled to undergo a tuning program with independent control of drive torque and braking force for left and right wheels to improve dynamic performance. After receiving vehicle type certification, Colt EV will undergo verification testing on public roads. Mitsubishi Motors will use the on-road testing program to identify and resolve any problems unique to the in-wheel motor vehicle, including any deterioration in road holding and ride comfort due to increases in un-sprung weight, as well as reliability and durability issues in the in-wheel motor system and its peripheral components (suspension, wheels, tyres).
Mitsubishi Motors is continuing its motor and battery research and development programs as it seeks to improve performance while reducing size and weight. The company is currently working on a 50kW in-wheel motor for 4WD vehicle use that will eventually feature individual drive torque and braking force control for each wheel.Published 13 May 2005