What are in-wheel motors?
Have you ever thought that putting motors inside the wheels of a vehicle may a more elegant way of providing propulsion? It would certainly eliminate a number of energy-robbing parts; transmission, driveshafts, differentials and make the drivetrain more modular and provide additional space for other energy storage/creation devices. Like so many things, in-wheel motors have already been done, but technology and our ability to integrate them into wheels has changed a lot since the first in-wheel motor (also called a hub motor) was patented back in 1884 and, after disappearing for decades, they are starting to creep back into vehicles. And why not? Not only do they reduce frictive energy loss and free up space, the tech can be integrated into many different platforms including electric vehicles (EVs), hybrids and fuel cell vehicles (FCV) and they can be installed in something as light as a bicycle or as heavy as a bus. Chances are you'll see an in-wheel motor in action sometime in the near future. Get ready by reading more after the jump.
*Updated with great video of Michelin Active wheel in action.
History
The best-known early vehicle to employ wheel motors was designed by a young Ferdinand Porsche in the employ of coachbuilder Lohner and is known as the Lohner-Porsche Mixte Hybrid (above). Akin to the Chevy Volt, this hybrid had a battery that could take it 30 miles as well as a gasoline engine to supply energy for distances beyond that. Besides cars, the concept was utilized in some early motorcycles but went the gasoline engine route. The 1915 Smith Motor Wheel (right) sold over 60,000 examples before being sold to Briggs & Stratton who continued to sell them. As the more conventional drivetrains we know today came down in price, hub motors mostly disappeared from the landscape until companies such as Crystalyte started putting them in bicycles in more recent times. Earlier this decade, car manufacturers got in the act and GM, Toyota and Mitsubishi all had in-wheel motor programs; more recently, companies such as PML Flightlink (now Protean Electric) and Raser have shown some promising in-wheel motor designs.How they work
The most basic design is a rather simple integration of an electric motor into the hub of the wheel. When power is applied to the stationary coils on the inside of the wheel, an electromagnetic field is generated and the outer part of the motor attempts to follow it and turns the wheel to which it is attached. The Siemens eCorner (video above) and Michelin Active Wheel don't stop with just the motors and also incorporate suspension and other goodies.
Pros & Cons
As we mentioned before, placing the motor in the wheel allows for a simpler drivetrain and reduces energy losses from all the expurgated bits. With all that bulk removed, designers are less constrained, because they don't have to accommodate awkwardly-shaped mechanicals, and can concentrate on aerodynamics and aesthetics. Another benefit is control. Not only can wheel spin can be eliminated but, given a sophisticated computer controller, relative wheel speed can be managed too. When a car is in a turn, every wheel wants to turn at a slightly different rate, causing a loss of traction. If the individual speeds are properly managed, handling and grip should improve.
Not that the hub motor is perfect. One of the traditional shortcomings has been its hefty addition to unsprung weight, so-called because it is not supported by the suspension of the vehicle. This can degrade handling and ride quality. The better, more recent products address this issue somewhat by including dampening and lighter, innovative designs but it is still a concern that needs attention. Another shortcoming is cost. Having two, or in some cases four, state-of-the-art mobilizers can add greatly to the cost of your vehicle, not to mention an increased vulnerability to unfriendly outside forces (i.e., curbs and other cars). Finally, there is the question of durability. Being so close to where the rubber hits the road in an unsprung manner means in-wheel motors need to be able to soak up some pounding. Each manufacturer will have to prove itself when it comes to ticking vs. licking.
Examples of integration
While still it may still be early to declare that in-wheel motors will take over the world, there are several vehicles which use or plan to use this tech. The first that comes to mind is the Vectrix Maxi-scooter. Although the company has recently filed for bankruptcy, the performance of their in-wheel motor is not to blame and owners often boast of the acceleration of their machines. Another impressive machine bound for buyers next year is the Lightning GT. This luxo-sport beast boasts a 0-to-60 time of four seconds and uses the same Hi-Pa Drive wheels used in a certain hybrid MINI prototype and the Volvo ReCharge concept. The company behind that product, Protean Electric, has its own retrofitted all-electric Ford 150 to showcase the Hi-Pa Drive motors.
Another wheel-motor worth looking at is the Michelin Active wheel. These should arrive nicely packaged in the Venturi Volage as well as a more humble Heuliez-constructed affair. If Bee Automobiles follows through on announced plans, they have a promising design licensed from Oxford University intended for a hill-climbing race car as well as a city car, the Bee One.
While it remains to be seen how popular they ultimately become, in-wheel motors have come a long way in the past 20 years and should be around in at least some green motoring applications in the near future. If you can think of any we may have missed, please let us know in the comments section below.
Reader Comments (Page 1 of 3)
gorr 9:23PM (8/06/2009)
Im interrested to buy. This is in my view a green product as it decrease the car weight but before buying i will test drive it carfully because it's complicated and im not sure it will do the job, but im confident.
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jpm 9:26PM (8/06/2009)
Nice video... gotta love solid works.
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T-Bahn 10:05PM (8/06/2009)
Hydro-Québec has also a «moteur-roue» since around 2000-2001 At time they did some test with a Chrysler intrepid, 4 inWheel electric engine, burn rubber !
See: http://www.tm4.com/
Nothing new :)
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barry 11:07PM (8/06/2009)
I get excited as to how car archetecture will change when they don't have to envelope a bulky engine
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locoyocal 12:37AM (8/07/2009)
Yup. I'll also get excited when they reduce car weight and gain electric efficiency. That will totally change architecture since the battery won't have to be as big.
someEEguy 11:07PM (8/06/2009)
Another example of integration (on buses):
http://www.e-traction.com/index.htm
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Lad 12:44AM (8/07/2009)
Toyota build and raced a hybrid enduro race-car with two front in-wheel 10 kw electric motors; Beat the snot out of the other cars
see: http://www.greencarcongress.com/2007/07/toyota-hybrid-r.html
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Matthew 1:03AM (8/07/2009)
You mention the reduction of drivetrain and the potentially more sophisticated wheel speed control. But there is a simpler reason to love hub wheels - they have the potential to make America an automotive power again.
Once the drivetrain (and basic suspension actuation) are simplified into standardized components, the parts that will differentiate the car become:
1. The look - America has great industrial designers (many working for Toyota et al)
2. The batteries - Harder to win, but we still have great nonotechnology resources
3. THE SOFTWARE!!!
#3 is the key. When handling becomes a function of control software, not manufacturing, this plays to the US pre-eminence in creating software for real life. Yes, India and China produce engineers, but the creativity that could be unleashed by an open drivetrain controlled digitally could be unreal - you could download handling packages, small companies could create new arrays of software, communications, and sensor technologies to adapt roads to conditions and geospatial location.
We will not win if electric cars become like standard cars, with loads of manufactured parts. We cannot be the low-cost manufacturer. But if it becomes a question of creative IP, we could rule the roost again.
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Arend 3:37AM (8/07/2009)
here you have some movies about the e-traction bus driven with direct drive wheelmotors
http://www.youtube.com/watch?v=vd4DTzvHBRw
http://www.youtube.com/watch?v=NTCndViiE2k
and the site of the hytruck a wheelmotor driven hydrogen truck.
www.hytruck.eu
best regards
Arend Heinen (e-traction)
www.e-traction.eu
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Guy 6:14AM (8/07/2009)
Michelin is an old big company and I want to believe them. But I scratched my hear when I read this. Comparing the wheel diameter with the diameter of that 30Kw electric motor. We can estimate that the motor is not bigger than 10 Cm diameter (not more than 3.9 inch) This might be the real invention. Not the fact that the electric motor is put inside the wheel, what has been done be so many. Also I see no cooling for that motor. When the efficiency is about 90% than they have 3000 watt of heat to get rid of !!! 3Kw of heat in an object the size of my fist without any cooling ???
I don't like to be the unbelieving Thomas here, but I like to see more before I believe this.
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Domenick Yoney 9:09AM (8/07/2009)
In the Venturi Volage press release it is mentioned that these motors are liquid cooled.
http://www.autobloggreen.com/2008/10/02/paris-2008-venturi-volage-revealed/
Guy 2:10PM (8/07/2009)
Domenick, that's not visible in the above picture. I don't see any tubing to evacuate 3KwH of heat. What amazes me to the max is that nobody in these comments seams to be wondering or asking any questions how it is possible to generate 30Kw of motion from a motor the size of a can of beans !!!
Stu 7:02AM (8/07/2009)
How would these cope in extremely wet conditions? If you happened to drive through water that went a third of the way up the wheel, would you run the risk of shorting the motor out?
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John McPherson 7:13AM (8/07/2009)
Aren't there some problems with unsprung weight here? What does all this stuff weigh? And will this drive survive being underwater?
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jmkpepckid 7:32AM (8/07/2009)
And what happens the first time you hit a sizable chuck hole in the road and bend the rim? What will be the cost to replace it? It can typically cost a couple of hunderd dollars to replace a rim and damaged tire. It looks like with this unit it could cost quite a bit more to replace! I don't see it as viable with some of the road we drive on here in Michigan.
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bvz 4:37PM (8/07/2009)
Well, if you hit hard enough to damage the motor, then you have a problem (and that is a real possibility with hub motors).
But if you just bend the rim, you are no worse off than you would be in a standard car. The rims, as far as I know, just bolt onto the hub the same way current rims bolt onto the hub of a conventional car.
Mark Kiernan 8:24AM (8/07/2009)
Would there be enough power to drive a car with just two of these motors (for example in the front two wheels)?
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Lorena Palin 9:51AM (8/07/2009)
Unsprung weight seams like the biggest issue here, it's going to wreck handling.
Also, why is everyone putting these stupid things in the front wheels? I mean most modern ICE cars are FWD because axles are big (ish), bulky (ish), and heavy (ish), so they can save weight and make things more compact via FWD (thats why the original mini used it).
But, electric motors, of any type, are small and compact. The batteries might be big bulky and heavy, but wire is not- you can run wires from the battery to a motor anywhere in the car, so why are they using the front?
Also, with this in hub motor thing, if you put them up front, you are increasing the mass of the wheels that have to be turned in order to steer- that can't be good. RWD makes much more sense
Richard 12:19PM (8/07/2009)
Why FWD? Probably because while RWD is unquestionably superior (if we're only driving 2 wheels) on the track, FWD excels in low-performance situations where adverse road conditions apply... a situation that a much higher percentage of drivers encounter on a daily basis.
Lemon 9:52AM (8/07/2009)
"Not that the hub motor is perfect. One of the traditional shortcomings has been its hefty addition to unsprung weight, so-called because it is not supported by the suspension of the vehicle. This can degrade handling and ride quality. The better, more recent products address this issue somewhat by including dampening and lighter, innovative designs but it is still a concern that needs attention."
Yeah, it needs a lot of attention. I'd gladly deal with a slight drivetrain loss before I increase my unsprung mass by ten fold. Increasing unsprung mass makes it much harder for the suspension to do its job (aka, keeping the tire in contact with the road). This not only degrades the vehicles performance, but also the safety.
If the motor is somehow damped, like the article suggests, wouldn't there have to be a drive system anyway? Why not mount the motors to the frame just inside the wheels and run a CV shaft to the wheel? It would still have all the advantages of no differentials/transmissions/etc but wouldn't have the disadvantage of increased unsprung mass. There would by plenty of room there so packaging shouldn't be an issue.
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