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The wheel motor (also called wheel hub motor or hub motor) is an electric motor that is incorporated into a wheel and drives it directly.

Contents 1 Uses 1.1 Application to cars: Comparison with conventional EV design 2 History 3 External links

[edit] Uses

• Wheel motors are applied in industry, driving e.g. wheels that are part of assembly lines.
• They have been little applied in cars, yet that is what they were invented for. See the "History" section.

[edit] Application to cars: Comparison with conventional EV design

Compared with the conventional electric car (EV) design with one motor situated centrally driving two (sometimes four) wheels by axles, the wheel motor arrangement has certain advantages and disadvantages. First the disadvantages:

• Power is the multiplicity of torque and rotational speed, P = τω. With the advent of the brushless dc motor, much higher rotational speeds can be obtained than before. Hence, it has become possible to fit a car with a relatively small and light motor that compensates for its low torque with higher rotational speed. This is obviously not a possibility with a wheel motor, meaning it will generally be heavier.

• By Newton's law of motion, F = ma, the force with which a wheel acts on the vehicle depends on the wheel's mass and acceleration. Whereas the acceleration depends mainly on the road conditions, the mass is an important design variable. The lighter the wheel (strictly: the un-sprung weight) in comparison to the vehicle, the smoother the ride, given equal road conditions. Since a wheel with a motor in it will be heavier than without it, the ride will be bumpier. This effect need not be serious, though, depending on the mass of the vehicle. Realistic mass for a wheel motor in a car lies between 10 and 30 kg.

• For the above reason, a vehicle fitted with wheel motors will generally be designed to have one in each wheel instead of just two, in order to minimize the mass of each wheel. This means that it carries four motors instead of just one in the case of the conventional electric car, making it more complex.

Then the advantages:

• Four wheel drive is a big advantage in and by itself, hence the need for it can be seen as positive.

• Maximal torque is generated. Wheel motors can easily generate 700 Nm (!) This means that under difficult or slippery road conditions, the wheel motor car will have a better chance at getting forward than any other type.

• Every kind of power transmission becomes redundant, such as gearboxes, differentials, drive shafts and axles. This reduces complexity as well as weight and frees room.

• Each wheel motors has to be precisely electronically controlled in any case. Therefore, modern control systems such as ABS, traction control and stability control will be almost automatically included in such a vehicle.

• Regenerative braking is at least as easily applied as in the case of one central electric motor.

[edit] History

The wheel motor was first developed by engineer Ferdinand Porsche in 1897 in Vienna, Austria. In the following three years, he developed the first car using the technology. The Lohner Porsche, fitted with one wheel motor in each of the front wheels, appeared at the World Exhibition in Paris in 1900 and created a sensation in the young automobile world. In the following years, 300 Lohne Porsches were made and sold to wealthy buyers.

[edit] External links

Tech-m4, a subsidiary of the Hydro-Québec power company in Canada develops and produces wheel motors for automobiles. They claim to have 20 years' experience.

GM's experimental car, presented in 2003, is driven by a conventional IC engine at the front while fitted with wheel motors at the rear.

Mitsubishi' experimental car, presented in May 2005, is fitted with wheel motors at the rear.