• Aug 6th 2009 at 7:54PM
  • 42
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.

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.

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    • 1 Second Ago
      • 6 Years Ago
      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.
      • 6 Years Ago
      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?
      • 6 Years Ago
      Aren't there some problems with unsprung weight here? What does all this stuff weigh? And will this drive survive being underwater?
      • 6 Years Ago
      "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.
        • 6 Years Ago

        I couldn't agree more. I think the people pushing for this just think that it's cool and really have no idea what they're talking about.

        This is probably a classic example of a non engineer telling the engineer what to do:

        "Hey, lets put the motor in the wheels!"
        "We could, but that wouldn't be very smart. Instead, we could-"
        "Nope. We're putting the motors in the wheels. Just make it work. We need a running concpet in a month so quit wasting time and get to it!"
        • 6 Years Ago
        What an engineer's circle jerk this crap is. You want to solve all the problems of hub motors? It's easy as pie. Just take an normal car design with 4 drive wheels then put the 4 wheel motors in the chassis where they belong. Attach them to the regularly-sprung and infinitely more light wheel assemblies and then off you go. Why in god's name is it deemed worthwhile to do this all for the sake of reducing 4 stub axles?

        This truly is moronic and only eco-yuppies who are too busy with their delusions of grandeur would try to make this when an almost plug and play option with all the benefits and none of the drawbacks is available.
      • 6 Years Ago
      I think most of you are missing the point of the Michelin Active-Wheel system. The suspension inside isn't *in addition to* a normal car's suspension system - it *is* the suspension system. These motors are not suitable to use on converting existing cars to EV, but are designed to replace the normal suspensions of future cars that are designed to use them.
      • 6 Years Ago
      Learn to use css float and clear properly guys -- your text overlays the images on Safari 4.0.2.

      Otherwise, this is a good introductory article. I hadn't realised the patent was so old. So... it's expired now, right? Anyone can do it. Right?

      I'm still not clear why nobody's investigating high torque, low rpm motors with a direct drive, so the motor *is* the hub. Weight reduction, efficiency and cooling would come free; while the suspension could again be a separate component, giving better geometry. With a fully active Bose-style suspension, you don't even need very much in the way of tyres -- but of course you'd want to protect the motor/hub from shock, so it couldn't be Automoblox-style solid rubber.

      Just musing.
        • 6 Years Ago
        Thanks Arend. What you meant to say was http://lmgtfy.com/?q=wheel+motor

        I guess starting a family really *does* erase some memories. I remember reading about the Apeldoorn buses some time ago.

        From your site: "On average TheWheel™ uses only half the electric energy of a typical geared traction motor (see: Mechanical Efficiency and/or Friction Reduction). This means that only half the amount of battery capacity and generative power is required."

        That shows that the Wikipedia article ( https://secure.wikimedia.org/wikipedia/en/wiki/Wheel_motor) is very misleading when it says "A purported advantage of this design is that no additional transmission system is needed, thereby increasing the efficiency of the drive system. However, because electric motors are most efficient at high rates of revolution[citation needed], direct drive hub motors tend to be inefficient[citation needed].". It should say "less efficient", not "inefficient".
        • 6 Years Ago
        "I'm still not clear why nobody's investigating high torque, low rpm motors with a direct drive, so the motor *is* the hub. Weight reduction, efficiency and cooling would come free; while the suspension could again be a separate component,"

        that is what we do at e-traction. the motor is engineered as the hub for the rim and can support the weight of the vehicle. it is direct drive without any gears.

        we are at this moment working on 1 suv and a small passenger car both with rear wheel drive.

        • 6 Years Ago
        A bose style suspension is insanely heavy, expensive, and actively draws a lot of power from the battery. It would kind of negate the original goals of the hub motor.

        Personally, just mounting motors to the frame like in a regular cars seams like it is still the best option.
        • 6 Years Ago
        Thank you Lorena. You are the only sane person to have commented on this so far.
      • 6 Years Ago
      Wouldn't this be a whole lot more expensive than simply mounting 4 motors to the chassis and driving a conventional wheel from each motor?
      • 6 Years Ago
      Another example of integration (on buses):
      • 3 Years Ago
      인 휠 모터 안에 들어가는 모터 오일 혹시 어떤거 사용하는지 아시는 분 있나요? 도요타에 도요타 Fine-X (2005), 도요타 i-unit (2005) 같은 자동차안 내부에 들어가는 오일 혹시 종류 아시는 분 있음 좀 알려주세요~! !
      • 6 Years Ago
      I get excited as to how car archetecture will change when they don't have to envelope a bulky engine
        • 6 Years Ago
        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.
      • 6 Years Ago
      Would there be enough power to drive a car with just two of these motors (for example in the front two wheels)?
        • 6 Years Ago
        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

        • 6 Years Ago
        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.
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