5 Facts: Electric In-Wheel Motors

1. What are In-Wheel Motors?
In-wheel motors, also called hub motors, are now commonly used in electrically-assisted bicycles and some concept or one-off electric cars. As the name suggests, propulsion is provided by an electric motor built directly into the wheel hub of a vehicle, bicycle, or scooter.

2. An Old Idea
The idea of in-wheel motors is almost as old as the automobile itself. Jacob Lohner & Co. of Vienna, Austria, produced what is considered the first series hybrid between 1898 to 1906. Designed by a young Lohner employee who would soon make a name for himself far beyond the Lohner Co. - Ferdinand Porsche - it featured an electric motor in each of the front wheels, and became known as the Lohner-Porsche.

3. How They Work
In the traditional gasoline or diesel vehicle, engine output is delivered to the wheels through several mechanical components. These includes a transmission, driveshaft and differential. This is because mechanical power is being transferred. With electric powered vehicles, it is possible to eliminate these mechanical components because electric power can be transferred by wires. In a battery powered vehicle the standard traction motors can be replaced with in-wheel hub motors, with electricity transferred by cables from the batteries to the wheel motors. They can also be used in series hybrid vehicles where electricity created by a gasoline or diesel engine-generator, plus electricity from batteries, is sent to electric motors that drive the wheels. In-wheel motors can also be used in fuel cell vehicles.

4. Advantages of In-Wheel Motors
A big advantage of hub motors is that they can eliminate the need for a transmission, driveshaft, differential, and axle shafts. If gear reduction is needed this can be done within the motor. This not only reduces complexity, but reduces weight and leaves more room for people, cargo, and for electric vehicles, more batteries. These are important factors in smaller, lightweight, fuel-efficient cars. Also electric motors are usually more efficient than other mechanical components, so they can help increase vehicle range. It's quite easy to include regenerative braking in hub motors and they are especially attractive for all-wheel-drive vehicles.

5. Why Aren't They in Cars Now?
While in-wheel motors are appropriate for use with either battery electric or series hybrid vehicles, there have been serious challenges to their commercialization. The only series hybrids around now are a few buses. And while battery electric vehicles appear to be on their way to market, there have been no full-function electric vehicles of this type being mass produced. Integrating everything into a compact wheel for use in a stylish car without looking funky is still a challenge. Finally, there are cost and safety issues that need to be resolved. Not the least of these safety concerns is the routing of high voltage in electrical cables adjacent to drive wheels that are constantly in motion.