Wheel hub motor
Encyclopedia
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
that is incorporated into a hub of a wheel and drives it directly.
Uses in current and future vehicles
- They are commonly found on electric bicycleElectric bicycleAn electric bicycle, also known as an e-bike, is a bicycle with an electric motor used to power the vehicle. Electric bicycles typically cost between and , use rechargeable batteries and can travel up to...
s. - Wheel motors are applied in industry, e.g. driving wheels that are part of assembly lines.
- They have been little applied in cars, yet that is what they were invented for. (See History)
- Hub motors can also be found on buses.
Concept cars
Several concept carConcept car
A concept vehicle or show vehicle is a car made to showcase new styling and or new technology. They are often shown at motor shows to gauge customer reaction to new and radical designs which may or may not have a chance of being produced....
s have been developed using in-wheel motors:
- PML FlightlinkPML FlightlinkPML Flightlink were a Hampshire based firm specialising in the design and manufacture of "pancake" electric motors. The company operated for over 30 years in a number of markets including defense, aerospace, mobility, motion control, processing and printing...
's Mini QED in 2006, and other cars using its Hi-Pa DriveHi-Pa DriveThe Hi-Pa Drive system is an electric in-wheel motor power delivery system.-Demonstration vehicles:In 2006, PML Flightlink demonstrated the Hi-Pa Drive in a series-hybrid car at the British Motor Show in London, using a Mini dubbed the "Mini QED" with its in-wheel motor at all four wheels... - MitsubishiMitsubishiThe Mitsubishi Group , Mitsubishi Group of Companies, or Mitsubishi Companies is a Japanese multinational conglomerate company that consists of a range of autonomous businesses which share the Mitsubishi brand, trademark and legacy...
MIEVMIEVMIEV or MiEV is the name given by Japanese automaker Mitsubishi Motors to its alternative propulsion technologies....
concept model in 2005 - SiemensSiemensSiemens may refer toSiemens, a German family name carried by generations of telecommunications industrialists, including:* Werner von Siemens , inventor, founder of Siemens AG...
VDO (bought by ContinentalContinental AGContinental AG, internally often called Conti for short, is a worldwide leading German manufacturer of tires, brake systems, vehicle stability control systems, engine injection systems, tachographs and other parts for the automotive and transport industries. The company is based in Hanover, Germany...
) eCorner concept in 2006 - HeuliezHeuliezHeuliez is a French company that works as a production and design unit for various automakers. It specializes in producing short series for niche markets, such as convertibles or station-wagons....
WILL using the MichelinMichelinMichelin is a tyre manufacturer based in Clermont-Ferrand in the Auvergne région of France. It is one of the two largest tyre manufacturers in the world along with Bridgestone. In addition to the Michelin brand, it also owns the BFGoodrich, Kleber, Riken, Kormoran and Uniroyal tyre brands...
Active Wheel (which incorporates motorized active suspensionActive suspensionActive or adaptive suspension is an automotive technology that controls the vertical movement of the wheels with an onboard system rather than the movement being determined entirely by the road surface...
as well) in 2008 - The ZAP-XZAP (motor company)ZAP is an electric vehicle company that designs, produces and markets vehicles including automobiles, motorcycles, bicycles, scooters, personal watercraft, hovercraft, ATVs, neighborhood electric vehicles and commercial vehicles. The name stands for Zero Air Pollution...
in 2007 "would use high-tech electric hub motors at all four wheels, delivering 644 horsepower to the ground from a lithium-ion battery pack. The hub motors would eliminate the need for transmission, axles and conventional brakes, opening up space beneath the floor for a giant battery pack." - The Peugeot BB1Peugeot BB1Peugeot BB1 is a full-electric concept car presented by Peugeot in September 2009 at the Frankfurt Motor Show.It incorporates rear in-wheel motors designed with Michelin each with maximum power output of and torque on each wheel of ....
in 2009 incorporates rear in-wheel motors designed with MichelinMichelinMichelin is a tyre manufacturer based in Clermont-Ferrand in the Auvergne région of France. It is one of the two largest tyre manufacturers in the world along with Bridgestone. In addition to the Michelin brand, it also owns the BFGoodrich, Kleber, Riken, Kormoran and Uniroyal tyre brands...
. - The Protean Ford F-150 All-Electric Pickup Truck by Protean Electric uses four in-wheel motors.
Mechanism
Hub motor electromagnetic fields are supplied to the stationary windings of the motor. The outer part of the motor follows, or tries to follow, those fields, turning the attached wheel. In a brushed motor, energy is transferred by brushes contacting the rotating shaft of the motor. Energy is transferred in a brushless motor electronically, eliminating physical contact between stationary and moving parts. Although brushless motor technology is more expensive, most are more efficient and longer-lasting than brushed motor systems.Electric motors have their greatest torque at startup, making them ideal for vehicles as they need the most torque at startup too. The idea of "revving up" so common with internal combustion engines is unnecessary with electric motors. Their greatest torque occurs as the rotor first begins to turn, which is why electric motors do not require a transmission. A gear-down arrangement may be needed, but unlike in a transmission normally paired with a combustion engine, no shifting is needed for electric motors.
Wheel hub motors are increasingly common on electric bikes and electric scooters in some parts of the world, especially Asia.
Comparison with conventional EV design in automobiles
Compared with the conventional electric vehicleElectric vehicle
An electric vehicle , also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion...
design with one motor situated centrally driving two (sometimes four) wheels by axles, the wheel motor arrangement has certain advantages and disadvantages:
Drive by wire
Cars with electronic control of brakes and acceleration provide more opportunities for computerized vehicle dynamics such as:- Active cruise control, where the vehicle can maintain a given distance from a vehicle ahead
- Collision avoidance, where the vehicle can automatically brake to avoid a collision
- Emergency brake assist, where the vehicle senses an emergency stop and applies maximum braking
- Active software differentials, where individual wheel speed is adjusted in response to other inputs
- Active brake bias, where individual wheel brake effort is adjusted in real time to maintain vehicle stability
- Brake steer, where individual wheel brake bias is adjusted to assist steering (similar to a tracked vehicle like a BulldozerBulldozerA bulldozer is a crawler equipped with a substantial metal plate used to push large quantities of soil, sand, rubble, etc., during construction work and typically equipped at the rear with a claw-like device to loosen densely-compacted materials.Bulldozers can be found on a wide range of sites,...
)
While some of these features have started to appear as options for some internal combustion engine vehicles, optional ABS brakes can add up to $2,000 dollars to the cost of a base model.
As wheel motors brake and accelerate a vehicle with a single solid state electric/electronic system many of the above features can be added as software upgrades rather than requiring additional systems/hardware be installed like with ABS etc. This should lead to cheaper active dynamic safety systems for wheel motor equipped road vehicles.
Weight savings
Eliminating mechanical transmission inc. gearboxes, differentials, drive shafts and axles provides a significant weight and manufacturing cost saving, while also decreasing the environmental impact of the product.Unsprung weight concerns
The major disadvantage of Wheel hub motors are that the weight of the electric motors would increase the unsprung weightUnsprung weight
In a ground vehicle with a suspension, the unsprung weight is the mass of the suspension, wheels or tracks , and other components directly connected to them, rather than supported by the suspension...
, which adversely affects handling and ride (the wheels are more sluggish in responding to road conditions, especially fast motions over bumps, and transmit the bumps to the chassis instead of absorbing them). Most conventional electric motors include ferrous material composed of laminated electrical steel
Electrical steel
Electrical steel, also called lamination steel, silicon electrical steel, silicon steel, relay steel or transformer steel, is specialty steel tailored to produce certain magnetic properties, such as a small hysteresis area and high permeability.The material is usually manufactured in the form of...
. This ferrous material contributes most of the weight of electric motors. To minimize this weight several recent wheel motor designs have minimized the electrical steel content of the motor by utilizing a coreless design with Litz wire
Litz wire
Litz wire is a type of cable used in electronics to carry alternating current. The wire is designed to reduce the skin effect and proximity effect losses in conductors used at frequencies up to about 1 MHz...
coil windings to reduce eddy current losses. This significantly reduces wheel motor weight and therefore unsprung weight.
Another method used is to replace the cast iron friction brake assembly with a wheel motor assembly of similar weight. This results in no net gain in unsprung weight and a car capable of braking up to 1G. A good example of this is the Michelin Active Wheel motor as fitted to the Heuliez
Heuliez
Heuliez is a French company that works as a production and design unit for various automakers. It specializes in producing short series for niche markets, such as convertibles or station-wagons....
Will that results in an unsprung weight of 35 kg on the front axle which compares favorably to a small car such as a Renault Clio that has 38 kg of unsprung weight on its front axle.
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 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 envisioned it powered by expanding gas of some kind. His offcenter flexible bent spoke designs later appeared in the Apollo moon rovers' wheels in 1960s.
- 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 Ferdinand Porsche
Ferdinand Porsche
Ferdinand Porsche was an Austrian automotive engineer and honorary Doctor of Engineering. He is best known for creating the first hybrid vehicle , the Volkswagen Beetle, and the Mercedes-Benz SS/SSK, as well as the first of many Porsche automobiles...
in 1897 in Vienna
Vienna
Vienna is the capital and largest city of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.723 million , and is by far the largest city in Austria, as well as its cultural, economic, and political centre...
, Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
. 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
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
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.
External links
- Mitsubishi' experimental car, presented in May 2005, is fitted with wheel motors at the rear.
- A Proposal to adapt wheel motors to MagLev Vehicles