| Revision as of 14:52, 24 July 2012 editEbikeguy (talk | contribs)Extended confirmed users, Rollbackers3,965 edits Reverted 1 edit by 86.131.167.23 (talk): IP editor continues to insert improperly-cited language against clear consensus. (TW)← Previous edit | Revision as of 15:08, 24 July 2012 edit undo86.131.167.23 (talk) Undid revision 503956217 by Ebikeguy (talk) no such consensus even discussed or entered into. no entries in the talk page seen, recording such discussion. reverting. again. with tedium.Next edit → | ||
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| 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 ] technology is more expensive, most are more efficient and longer-lasting than brushed motor systems. | 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 ] 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.{{Citation needed|date=March 2011}} | Electric motors have their greatest torque at startup, making them ideal for vehicles as they need the most torque at startup too, but at the cost of exposing the motor to risk of burn-out<ref>]</ref> or requiring forced-air or liquid cooling<ref>http://www.yobykes.in/pdf/tech_liquid_cooled_hub_motor.pdf</ref><ref>http://www.rockymountaintechnologies.com/articles/E-Drive%20article%202009-08.pdf</ref><ref>http://epg.eng.ox.ac.uk/users/robert-camilleri</ref><ref>http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=5951766&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D5951766</ref>. 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.{{Citation needed|date=March 2011}} | ||
| Wheel hub motors are increasingly common on electric bikes and electric scooters in some parts of the world, especially Asia.<ref>http://www.ebikes.ca/hubmotors.shtml</ref><ref>http://www.electricrider.com/crystalyte/motordimensions.htm</ref> | Wheel hub motors are increasingly common on electric bikes and electric scooters in some parts of the world, especially Asia.<ref>http://www.ebikes.ca/hubmotors.shtml</ref><ref>http://www.electricrider.com/crystalyte/motordimensions.htm</ref> | ||
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| ===Weight savings=== | ===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.{{cn|date=October 2011}} | 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.{{cn|date=October 2011}} However, although there are clear benefits from removing differentials, drive shafts and axles, the removal of the transmission may be a step too far as the burden of efficiency under a wide range of conditions is placed exclusively on the motor. | ||
| ===Motor inefficiency concerns=== | |||
| Electric motors have different efficiency characteristics from combustion engines; their efficiency varies with RPM and power, just in a different way. For example, at low RPM (stall torque) and high power, electric motors can be as low as 15% efficient<ref>http://kellycontroller.com/mot/downloads/CarHubMotor72v7kwCurve.xls</ref>. The efficiency of electric motors typically rises to its peak (published) efficiency only around the middle of its RPM and load range, and the efficiency typically tails off slightly towards the higher RPMs. Thus, removing the gearbox entirely from a vehicle design exposes the motor to worst case scenarios, as the motor must now cope on its own with all possible conditions. | |||
| These worst-case scenarios include potential overheating at low RPMs<ref>]</ref> especially on steep gradients, requiring designs in large vehicles to have liquid cooling or forced-air cooling<ref>http://www.enstroj.si/Electric-products/emrax-motors.html</ref>, or the hub motors simply having insufficient power to climb steep gradients. To compensate for the lack of available power to climb steep gradients, the entire drivetrain - motors, controllers and batteries - would need to be uprated to cope with the worst case scenario, but doing so not only drastically increases the cost and overall weight of the vehicle but also doesn't solve the problem: the uprated motor is still operating under worst possible efficiency conditions ], but is now placed under even heavier load, and the heat losses are far greater than an equivalent geared electric motor that is geared to operate within its best RPM range. | |||
| In order to keep to the hub motor concept and also cover a wide range of conditions, a gearbox would need to be added within the hub itself, in order to avoid the motor operating at its worst efficiency conditions (low RPM, high power). However to add a multi-speed gearbox into the already-limited space of the hub would immediately increases the weight of the hub motor, which is already of some concern. Some manufacturers of wheel hub motors therefore provide two versions of the same product: one with higher torque but a limited top speed<ref>http://kellycontroller.com/hub-motor-72v-45kw-high-torquedisc-brake-p-811.html</ref>, and one with lower torque but a higher maximum RPM<ref>http://kellycontroller.com/hub-motor-72v-45kw-high-speeddisc-brake-p-144.html</ref>, but the mutually-exclusive use of one type or the other then limits the vehicle's usefulness. | |||
| Overall, then: whilst hub motors are perfectly suited to bicycles (which have a limited top speed), and some larger motors<ref>http://www.electricmotorsport.com/store/ems_ev_parts_motors_enertrac_mhm602-603.php</ref> are available at an affordable price for use in motorbikes and trikes, hub motors are not yet ready for general-purpose use in larger vehicles, just on the efficiency concerns alone. With prices of Neodymium and Dsyprosium increasing sharply<ref>http://www.magnet-shop.net/Aktuelle-Preisentwicklung:_:340.html</ref> and with production of EVs and Hybrids expected to rise<ref>http://www.frost.com/prod/servlet/press-release.pag?docid=260357048&ctxixpLink=FcmCtx1&ctxixpLabel=FcmCtx2</ref> it is debatable as to whether ungeared wheel hub motors will ever be viable for general-purpose affordable mass-volume vehicles (in their present form) at all. | |||
| ===Unsprung weight concerns=== | ===Unsprung weight concerns=== | ||
| Line 79: | Line 89: | ||
| *, presented in May 2005, is fitted with wheel motors at the rear. | *, presented in May 2005, is fitted with wheel motors at the rear. | ||
| *A Proposal to adapt | *A Proposal to adapt | ||
| * Article describing the challenges that the EV Hub motor faces, outlining the advantages as well as disadvantages. | |||
| {{DEFAULTSORT:Wheel Hub Motor}} | {{DEFAULTSORT:Wheel Hub Motor}} | ||
Revision as of 15:08, 24 July 2012
 | This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Wheel hub motor" – news · newspapers · books · scholar · JSTOR (August 2009) (Learn how and when to remove this message) |
The wheel hub motor (also called wheel motor, wheel hub drive, hub motor or in-wheel motor) is an electric motor that is incorporated into the hub of a wheel and drives it directly.
Uses in current and future vehicles
- They are commonly found on electric bicycles.
- 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 cars have been developed using in-wheel motors:
- Protean Electric's Mini QED in 2006, and other cars using its Hi-Pa Drive
- Mitsubishi MIEV concept model in 2005
- Siemens VDO (bought by Continental) eCorner concept in 2006
- Heuliez WILL using the Michelin Active Wheel (which incorporates motorized active suspension as well) in 2008
- The ZAP-X 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 BB1 in 2009 incorporates rear in-wheel motors designed with Michelin.
- 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, but at the cost of exposing the motor to risk of burn-out or requiring forced-air or liquid cooling. 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 vehicle 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 Bulldozer)
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. However, although there are clear benefits from removing differentials, drive shafts and axles, the removal of the transmission may be a step too far as the burden of efficiency under a wide range of conditions is placed exclusively on the motor.
Motor inefficiency concerns
Electric motors have different efficiency characteristics from combustion engines; their efficiency varies with RPM and power, just in a different way. For example, at low RPM (stall torque) and high power, electric motors can be as low as 15% efficient. The efficiency of electric motors typically rises to its peak (published) efficiency only around the middle of its RPM and load range, and the efficiency typically tails off slightly towards the higher RPMs. Thus, removing the gearbox entirely from a vehicle design exposes the motor to worst case scenarios, as the motor must now cope on its own with all possible conditions.
These worst-case scenarios include potential overheating at low RPMs especially on steep gradients, requiring designs in large vehicles to have liquid cooling or forced-air cooling, or the hub motors simply having insufficient power to climb steep gradients. To compensate for the lack of available power to climb steep gradients, the entire drivetrain - motors, controllers and batteries - would need to be uprated to cope with the worst case scenario, but doing so not only drastically increases the cost and overall weight of the vehicle but also doesn't solve the problem: the uprated motor is still operating under worst possible efficiency conditions (stall conditions), but is now placed under even heavier load, and the heat losses are far greater than an equivalent geared electric motor that is geared to operate within its best RPM range.
In order to keep to the hub motor concept and also cover a wide range of conditions, a gearbox would need to be added within the hub itself, in order to avoid the motor operating at its worst efficiency conditions (low RPM, high power). However to add a multi-speed gearbox into the already-limited space of the hub would immediately increases the weight of the hub motor, which is already of some concern. Some manufacturers of wheel hub motors therefore provide two versions of the same product: one with higher torque but a limited top speed, and one with lower torque but a higher maximum RPM, but the mutually-exclusive use of one type or the other then limits the vehicle's usefulness.
Overall, then: whilst hub motors are perfectly suited to bicycles (which have a limited top speed), and some larger motors are available at an affordable price for use in motorbikes and trikes, hub motors are not yet ready for general-purpose use in larger vehicles, just on the efficiency concerns alone. With prices of Neodymium and Dsyprosium increasing sharply and with production of EVs and Hybrids expected to rise it is debatable as to whether ungeared wheel hub motors will ever be viable for general-purpose affordable mass-volume vehicles (in their present form) at all.
Unsprung weight concerns
The major disadvantage of Wheel hub motors are that the weight of the electric motors would increase the unsprung weight, 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. 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 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 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 in 1897 in Vienna, Austria. 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.
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, but they were never as efficient as electric wheel hub motors.
See also
References
- http://www.electricrider.com/crystalyte/
- "Wheel Motors to Drive Dutch Buses". Technology Review. 23 March 2009. Retrieved 23 November 2009.
- "SIEMENS VDO'S BY-WIRE TECHNOLOGY TURNS THE eCORNER". VDO. 16 October 2006. Retrieved 15 September 2009.
- "Car motors will disappear – into the wheels". VDO. 8 August 2006. Retrieved 15 September 2009.
- "MICHELIN ACTIVE WHEEL Press Kit". Michelin. 26 September 2008. Retrieved 15 September 2009.
- Ulrich, Lawrence (23 September 2007). "They're Electric, but Can They Be Fantastic?". The New York Times.
- "Peugeot Shows Two HYbrid4 Concepts, New BB1 EV Concept at Frankfurt". Green Car Congress. 15 September 2009. Retrieved 31 May 2010.
- "Test drive of new in-wheel electric motored pickup truck". 15 September 2009. Retrieved 31 May 2011.
- Stall_torque#Electric_motors
- http://www.yobykes.in/pdf/tech_liquid_cooled_hub_motor.pdf
- http://www.rockymountaintechnologies.com/articles/E-Drive%20article%202009-08.pdf
- http://epg.eng.ox.ac.uk/users/robert-camilleri
- http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=5951766&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D5951766
- http://www.ebikes.ca/hubmotors.shtml
- http://www.electricrider.com/crystalyte/motordimensions.htm
- http://www.openroad.com.au/motoring_roadsafety_priceofsafety.asp
- http://kellycontroller.com/mot/downloads/CarHubMotor72v7kwCurve.xls
- Stall_torque#Electric_motors
- http://www.enstroj.si/Electric-products/emrax-motors.html
- http://kellycontroller.com/hub-motor-72v-45kw-high-torquedisc-brake-p-811.html
- http://kellycontroller.com/hub-motor-72v-45kw-high-speeddisc-brake-p-144.html
- http://www.electricmotorsport.com/store/ems_ev_parts_motors_enertrac_mhm602-603.php
- http://www.magnet-shop.net/Aktuelle-Preisentwicklung:_:340.html
- http://www.frost.com/prod/servlet/press-release.pag?docid=260357048&ctxixpLink=FcmCtx1&ctxixpLabel=FcmCtx2
- http://www.youtube.com/watch?v=i1uTR-8KarE
- http://www.causecast.org/news_items/7667-michelin-unveils-active-wheel-in-affordable-electric-car
- http://www.porsche.com/usa/aboutporsche/porschehistory/milestones/
External links
Media related to In-wheel motors at Wikimedia Commons
- Mitsubishi' experimental car, presented in May 2005, is fitted with wheel motors at the rear.
- A Proposal to adapt wheel motors to MagLev Vehicles
- Article describing the challenges that the EV Hub motor faces, outlining the advantages as well as disadvantages.