Some manufacturers of electric drivetrains, to improve performance, use two electric motors; and, at least one automobile manufacturer, Mitsubishi, maker of the MIEV, uses four advanced electric motors, one for each wheel. Engineers can provide cost-effective anti-lock braking, traction control and vehicle stability systems by installing electronic control over the electric motor that drives each wheel independently.
Nissan has taken a somewhat different, although no less innovative, approach. Each wheel is independently driven electrically and a sophisticated system controls the power of each shaft separately. Seems the same so far, doesn't it?
The difference is that this is accomplished using only two motors, thus achieving dramatic improvements in compactness and efficiency. Each Super Motor has two shafts; the right and left act independently. (Two shafts per Super Motor times two electric motors equals four wheel electric drive.)
Green Car Congress shows us the inner workings of the innovative Nissan Super Motor (see above a cut away view of the Nissan Super Motor taken from GCC article)
The Super Motor features dual rotors on both the inside and outside of a single stator. To avoid torque interference between the rotors, magnets having different numbers of pole pairs are used for the inner and outer rotors.
What does that do? The Super Motor can output power through two shafts. The design of the motor allows for the application of a compound current. Thus, an inverter can control the power output of each shaft separately.
Note: The motor also can work as a generator, which means it affords regenerative braking and potential use as an emergency generator. Since the Super Motor offers greater power density than a conventional electric motor, there also increased heat generation. To address that issue, Nissan engineers who designed the Super Motor included a cooling system. between the stator teeth.
In simple terms, one Super Motor does the job of two motors, because the Super Motor can drive the right and left wheels independently. Nissan has built their enviromentally-friendly, concept cars with four wheel drive using two Super Motors. Each wheel is driven independently, which can enhance the dynamic performance and stability. While the Super Motor alone is innovative, Nissan has added two other innovations. The electric drivetrains of their concept cars since 2003 have utilized fuel cells and lithium batteries.
What we have yet to see from Nissan, as possible from them as from Toyota, is a plug.
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[...] Currently, one of the more interesting designs for an electric drivetrain, the motor-wheel assembly is an elegant integration of an electric motor and other components into a package that fits inside a regular-size tire. Mounting the wheel directly on the rotor provides for direct transmission of torque, enhanced freewheeling, regenerative braking, and more economical inclusion of vehicle control, e.g., braking, traction, and stability systems. (Nissan has an even more economical approach: two motors doing the job of four, nevertheless, this design relies upon a more traditional four wheel drive arrangement.) [...]
[...] The point that I want to make is that in this post I avoided discourse about fuels cells and robot navigation systems, or even speculating as to how far they will get this year. Instead, I have expressed appreciation for a modular approach taken by transportation engineers that is facilitating crossover. For instance, how similar would electronic control over a Nissan Super Motor in a two-wheel, personal mobility device be to that in a six-wheel van? [...]