User:A-Hrafn/Wheel motor

For information on wheel motors, see Wheel motor.

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.

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.

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. Gearing within the wheel overcomes this objection but with an increase in complexity, cost, noise and likely weight (a smaller, higher speed motor is lighter in weight but this is offset by the weight of the gears).

• 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 and the better the roadholding, 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 (hopefully) cost, and frees up room aboard the chassis of the vehicle.

• Each wheel motor 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. Regenerative braking is one form of dynamic braking. It uses the drive motors as generators to provide braking effect. The (electrical) energy generated is applied to charging the propulsion batteries. When the batteries are fully charged the power generated is diverted into resistance grids to dissipate the braking energy.

History

• First wheel motor concept: Wellington Adams of St. Louis first conceived of building an electric motor directly in the vehicle wheel though it was attached via some complicated gearing. The Adams patent is US # 300,827 in 1884.

• First practical wheel motor: Albert Parcelle of Boston, MA developed the first fully incorporated Wheel hub motor in his "Electro-Motor Traction Wheel" and patented it in patent US # 433,180 in 1890.

• High torque low RPM wheel motor invented: The motor was incorporated into the wheel without gearing and addressed torque considerations through the use of a new high torque, low rpm motor invented by Edward Parkhurst of Woburn, MA in patent # 422,149 in 1890 (and mismentioned in Parcelle's patent as #320,699).

• Electric wheel motor advantages revealed in patent: An early Wheel hub electric motor was invented by Frenchman Charles Theryc and patented in 1896 as US patent 572,036 entitled Wheel with Electric Motor hub for Vehicles. In the patent he explained all advantages including no transmission losses because of the absence of classic transmission rods from engines to wheels.

• Diesel wheel motor: Not all wheel hub motors were electric. C F Goddard in 1896 invented a piston hub motor for horseless carriages patented in US # 574,200. He envisoned it powered by expanding gas of some kind and amazingly his offcenter flexible bent spoke designs later showed up in the Apollo moon lander rovers wheels in 1960's.

• Using cams, another type of combustion wheel motor:In patent # 593,248 W C Smith in 1897 developed another explosive gas expansion motor inside a wheel hub that utilized cams on a track in the hub to transmit power to the wheel.

The electric wheel hub motor was raced by engineer Ferdinand Porsche in 1897 in Vienna, Austria. Porsche later became famous for designing Hitler's "peoples car" the Volkswagen and later the sportscar that bears his name -Porsche.

Porsche's first engineering training was electrical not internal combustion based. As a result he developed his first cars as electric cars with electric wheel hub motors that ran on batteries . 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.

Porsche recognized the efficiencies of power transmission of the electric wheel hub motor over a central engine driving a transmission then the wheels. In an effort to overcome the low battery capacities of the day, he developed a electrical wheel hub motor car that got its electric power from a gasoline driven generator in the car effectively inventing the hybrid auto he called the "System Mixt". He set many speed records of the day in this gasoline powered generator car with two front wheel electric hub motors. He won Austria's Automotive Engineering prize with that car and his career took off. Eventually the growth in power of the gasoline engine overtook the power of the electric wheel hub motors and this made up for any losses through a transmission. As a result autos moved to gas engines with transmissions however they were never as efficient as electric wheel hub motors.

External links

PML Flightlink a UK based company that currently designs and builds the highest power density electric wheel motors in the world. Currently working with Volvo on the ReCharge, a vehicle released at the 2007 Frankfurt Motor Show that uses 4 of PML's in-wheel motors.

e-traction, a Dutch-American company that has several wheel motors in production. Also the manufacturer of the Whisper, a serial hybrid bus with wheel hub motors.

TM4 Inc. a subsidiary of the Hydro-Québec power company in Canada develops and produces wheel motors for automobiles. They claim to have 20 years' experience.

Freepistonpower.com conceived of an engine with valves in the crown of the piston, whose reciprocal movement generated electricity when two opposed pistons were attached to permanent magnets moving through coils wrapped around the shared cylinder. A working model (2004) portends greater efficiencies for HEV designs.

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.

L2ES lab staff and topics french staff working on wheel motor

A new type of motorcycle wheel motor

An electric motor wheel in a bicycle.