Simplified Hybrids

Mitsubishi Motors Corp. portents a potentially game-changing twist for hybrid-electric vehicles (HEVs) and pure electric vehicles (EVs) with its new generation of in-wheel electric motors.

Mitsubishi's latest in-wheel motor design was displayed at the Detroit and Geneva auto shows this year on separate concept cars designed to highlight the innovative technology.

Powered by under-floor lithium-ion batteries, the pure EV chassis is totally devoid of engine, transmission and mechanical drivetrain, leaving a flat platform with wheels at each corner, maximizing passenger and load space.

The concept was unveiled at the Geneva show as the Concept EZ MIEV (Mitsubishi In-wheel motor Electric Vehicle).

The electric motor-propelled 20-in. (51-cm) wheels are a hollow doughnut construction, with the motor's electrically driven rotor outside the stator, in contrast to the usual electric motor design with the rotor — or armature — inside the fixed stator.

Mitsubishi says the in-wheel design leaves internal space for brake and hub assemblies. Each permanent-magnet synchronous motor is rated at 20 kW (27 hp) for a total of 80 kW (107 hp).

Maximum torque is 295 lb.-ft. (400 Nm). With 4-wheel drive, the car transfers up to 1,180 lb.-ft. (1,600 Nm) of torque to the road. Predictably, the output provides brisk acceleration to 62 mph (100 km/h) in 11 seconds, the auto maker says, with a top speed of 90 mph (150 km/h).

This performance comes without an internal combustion engine.

Speed control works in conjunction with an electronic inverter, using a simple switching arrangement between 4- and 2-wheel drive. The battery pack, weighing 330 lbs. (150 kg), comprises 22 modules delivering 300 volts.

Mitsubishi says the Concept MIEV's driving range is about 72 miles (120 km). Normal recharge time is seven hours, with rapid charge to 80% in 30 minutes. Steering and brakes use an adaptation of drive-by-wire technology.

The Concept EZ MIEV is built on a 108-in. (274-cm) wheelbase and is 144 ins. (366 cm) long. For passenger protection, the engine-less front of the chassis is designed with an ample crumple zone. Curb weight is 2,640 lbs. (1,200 kg).

For the Concept CT hybrid unveiled in Detroit, the vehicle has a front-mounted engine/generator with coolant radiator.

Unlike a conventional HEV, however, the engine is used only to charge the batteries for extended range, as the in-wheel motor does not lend itself to direct drive from an internal-combustion engine.

The fuel tank and an 8-module battery pack are fitted under the rear floor. A fuel cell-powered variant of the MIEV also is envisioned.

Although Mitsubishi sees great promise for the in-wheel electric motor, the possible penalty in road adhesion and handling due to the high unsprung weight of the motor/wheel assembly has yet to be established.

One on-the-road precedent, revealed in 2001, is the KAZ electric motorhome designed in Japan at the Keio University, with one experimental prototype built by an Italian company.

Some 22 ft. (6.7 m) long, it runs on eight wheels that all employ integral 55-kW (73-hp) motors. The six forward wheels are steered by electro-hydraulic servos.

The motorhome's combined 8-wheel-motor output of 590 hp gives the 3-ton (2.7-t) vehicle a stated top speed of 180 mph (290 km/h), while lithium-ion batteries provide a claimed 180-mile (290-km) range between charges.