2012 Mitsubishi i-MiEV EV motor/transmission

Electrifying the Automobile – A “Joule” of an Idea
Highly efficient, lightweight yet powerful, and proven to be reliable to the extreme, the electric powertrain that provides the motive force for the all-new 2012 Mitsubishi i is a paragon of engineering excellence and is an evolution of the Japanese auto manufacturer’s highly developed electric motors and accompanying transmissions that have powered the company's groundbreaking 100% battery-powered electric vehicles through its rich history.

The main components that make up the drivetrain for the North American-spec Mitsubishi i include:

• Electric Motor
• Fixed Reduction Gear Transmission
• Motor Control Unit (MCU)

Electric Motor
Weighing all of 108 lbs., the electric motor powering the 2012 Mitsubishi i features numerous high-tech elements that aid in the area of efficiency, performance and reliability.

Adoption of a synchronous permanent magnetic motor design helps to reduce weight and makes for an electric motor of more compact dimensions. Electric motor reliability is also improved through the use of an advanced neodymium magnet - far and away the strongest type of permanent magnet for use in an electric motor. Also adding to the electric motor’s durability and efficiency are a highly-effective water-cooling system along with a high-performance casing that is not only dust resistant but also completely waterproof.

Noise, vibration and harshness (NVH) produced by the electric motor have been all but eliminated thanks to computer-aided design and analysis.

As a result of its advanced design and extensive testing and development, the electric motor in the Mitsubishi i is completely maintenance-free and backed by 5-year / 60,000 mile power train warranty.

Refined yet Lively Powertrain Performance
In its home market, the diamond-star-badged car builder sells both an electric and gasoline-powered turbocharged version of the subcompact Mitsubishi i. And while the latter version of the vehicle is known for its peppy performance (especially for the small 660cc displacement of its three-cylinder engine) in the tiny kei car vehicle class in Japan with a full 63 bhp and 69 ft.-lb. (47 kW and 94 Nm, respectively) on tap, the all-new North American-spec Mitsubishi i with MiEV technology (Mitsubishi innovative Electric Vehicle) betters its internal combustion sibling thanks to an electric motor that produces nearly 49 kW (66 bhp)  at 3000 to 6000 rpm and 196 Nm (145 ft-lb) of torque from 1 to 300 rpm.  Because all 145 ft-lb of torque are available at any rpm, standing start acceleration is ideal for stop-and-go urban (city) driving conditions. Maximum rotation speed of the electric motor is 9900 rpm.

Yet whether accelerating or decelerating, extremely smooth vehicle operation is assured as a result of the single fixed speed transmission - occupants inside of the 2012 Mitsubishi i will never experience the sort of momentary hesitation/quiver that occurs in a manual or automatic transmission with multiple gears.

Transmission

Compact in size and weight yet offering excellent performance and refined operation, the fixed gear ratio transmission of the 2012 North American-spec Mitsubishi i is engineered to make the most of the electric motor’s high torque output and a wide power band.

The 7.065 gear ratio has been selected for use in this transmission as research and testing has determined this to be the best ratio for optimum dynamic performance from the electric motor. This fixed gear ratio, along with a simplified two-stage parallel shaft reduction and a conventional differential unit, distribute motor torque to the vehicle's rear wheels.
Other technical highlights include a single open-type ball bearing that helps to reduce drag and an output shaft layout position that helps to reduce friction of the transmission.

Strong yet sturdy, this remarkable transmission measures less than 7 inches in length and weighs less than 42 lbs. when mated to the electric motor, the combined transmission/motor measures less than 19 inches long and only weighs 143 lbs - a fraction of the weight of the typical internal combustion engine and transmission pairing.

The Transmission (L) and the Electric Motor (R) weigh a combined 143 lbs.

Motor Control Unit (MCU)
The Motor Control Unit (MCU) is a critical component of a 100% electric-powered vehicle as it manages and regulates the electrical power supply to the electric motor to generate the necessary level of torque to power the vehicle by converting the battery packs DC voltage into three-phase AC. Conversely, the MCU is responsible managing the electrical energy that is produced by the regenerative braking system and is fed back into the lithium-ion battery pack.

In propulsion mode (drive), the MCU generates the three-phase AC current dataset into the coil of the electric motor to generate a magnetic field. The motor is rotated by synchronizing the magnetic-field of magnets with the magnetic-field of coil current and with speed sensing position of the rotor. The MCU controls motor torque by adjusting the magnetic-field of the coil current.

The attraction and repulsion that takes place between the rotating magnetic field and the magnets within the electric motor generates the acceleration torque.

In regeneration mode (braking), the MCU generates deceleration torque by adjusting the phase of electrical current and feeding the regenerative energy back into the main drive lithium-ion battery pack. In this phase, the electric motor essentially becomes a generator.

The critical electrical components housed within the Motor Control Unit are a smoothing condenser to help stabilize the DC current, several insulated-gate bipolar transistors (IGBT) that convert the DC electrical current into AC, a heatsink to provide cooling/heat dissipation and a control board that supervises the electric motor. The control board is located in a separate area within the MCU from the smoothing condenser, the IGBTs and the heatsink to protect it from the heat generated by these components.

The Motor Control Unit measures 11.3 inches wide, 12.2 inches long and 6.7 inches tall and weighs 33 lbs. and, like the vehicle’s electric motor, is housed a completely waterproof and dustproof structure and makes use of water-cooling for temperature control.