Depending on the manufacturer, an in-wheel motor may contain a variety of components, but most have the same basic parts. We're using Michelin's Active Wheel system as our example.
The outside of an in-wheel motor has very little variation compared to a standard wheel. However, once the wheel is taken off the vehicle, the main elements of the in-wheel electric motor system are exposed. That relatively small area contains the braking system, an active suspension system and the electric motor that actually drives the wheel. The in-wheel active suspension system is an electrically operated system that can react in a mere 3/1,000ths of a second to automatically correct pitching and rolling motions.
Some in-wheel motor designs offer what's called regenerative braking as well. That means the system captures some of its own kinetic energy while braking and sends it back to charge the battery. Some hybrids, such as the Toyota Prius and Tesla Roadster, already incorporate this regenerative braking technology, which provides the automobiles with a longer driving range.
One of the greatest advantages of in-wheel electric motors is the fact that the power goes straight from the motor directly to the wheel. Reducing the distance the power travels increases the efficiency of the motor. For instance, in city driving conditions, an internal combustion engine may only run at 20 percent efficiency, meaning that most of its energy is lost or wasted via the mechanical methods employed to get the power to the wheels. An in-wheel electric motor in the same environment is said to operate at about 90 percent efficiency [source: Lepisto].
Sounds pretty good, right? Well, keep reading to find out how an in-wheel electric motor doesn't sacrifice power while increasing efficiency.