What Ever Happened to the Hub Motor BEV?

By · June 23, 2011

Venturi Volage

The Venturi Volage concept.

Back in 1900, Porsche introduced a hybrid vehicle that featured two gas engines and a wheel hub electric motor. Since then, the hub motor has been largely relegated to low-powered, two-wheel electric vehicles. In the mid-2000’s, when battery electric and fuel cell vehicles were starting to show up on the radar (again), the wheel hub motor was seen again, but was clearly not headed for prime time. While shown in numerous car prototypes, wheel hub motors have never really got off the ground in passenger cars. In 2008, Michelin introduced a concept called the WILL with the bold claim that their hub motors would be on the road by 2010. With the introduction of the hand-built Venturi Volage electric sports car (to launch in 2012 for an unspecified price), the Michelin system has found an on-ramp to the road. In 2009, Daimler announced that hub motors were powering their Citaro fuel cell bus. And most recently, in Japan, SIM-Drive Corporation claims to have developed a BEV that has a range of 207 miles using hub motors that they will launch in 2013.

One of the major challenges facing hub motors is the increase in the mass of the wheel. The increased mass at the wheel causes increased inertia which can wreck havoc with vehicle stability, particularly on corners. Additionally, any shock to the wheel (like the pothole that gave me a flat tire not too long ago) could be transferred to the hub mounted motor and is substantially more likely to cause catastrophic damage. Finally, the complexity of the motor controls is substantially higher in hub motors than in chassis mounted motors. Some of this complexity is because turning wheels rotate at different speeds (the wheel inside the turn rotates slower than the outside wheel). While this problem is tacitly solved by the differential gear in vehicles with axles, it must be computerized for hub motor vehicles.

Hub motors do have the advantage of being able to act much more independently to changing road conditions. Plus, removing the motor from the potential passenger compartment will increase vehicle package flexibility (more storage or passenger room). The aforementioned complexity of the system can be overcome, as well, albeit at a cost. Perhaps most importantly to the BEV industry, the elimination of the axle or transmission makes the hub motors more efficient than a chassis mounted electric motor.

Michelin WILL

When I have asked about the hub motor design, most say the design remains too expensive, potentially lower powered, and unreliable for mainstream vehicles. Hub motors are smaller than typical chassis motors (30-50kW vs. 80+kW), which has raised concerns with the amount of power available to the vehicle. The cost of using two 40 kW wheel hub motors is higher than using one 80 kW motor (plus the resulting power is not a simple additive equation as implied by that statement). Add to that a more expensive control unit for the hub motors and you have a drivetrain that pushes the boundaries of cost effectiveness.

That said, hub motors aren’t dead yet. As the SIM-Drive and Michelin Active Wheel shows, there is work that is still being done with new lighter weight and smaller motors. These advances are solving many of the challenges facing hub motors in passenger cars and will likely result in a mainstream hub motor vehicle, though I don’t expect you will see it in your neighborhood showroom this decade.

Comments

· · 2 years ago

I probably lack the proper vocabulary to properly convey this idea but I'll try.

Why not move the motor out of the wheel and onto the frame.

Move the motor from the battery to where the shocks connect to the car's frame. The motor connects to an independent drive shaft that goes from the motor straight to the wheel. This approach would seem to take much of the negatives - like shock from potholes - out of the equation but still retains the pluses - like wheel independence.

· · 2 years ago

omg where's the edit!?
^^^
Move the motor from the wheel to where the shocks connect to the car's frame.

· · 2 years ago

Yes, I think I understand what you are attempting to say, Travisty . . .
get the motors out of the interior of the wheel, but keep them as 4 individual entities and connect them with short axle shafts.

Regardless . . . I agree with the conclusion of the article: that its an interesting idea but, ultimately, a bit too unwieldy for the workaday EVs we'll be driving (or are already driving, as the case may be.) This isn't going to prevent it from invariably showing up one day in a cost-no-object luxury EV, though.

In the mean time - and for the rest of us - 2 wheel / front-wheel-drive via a (simpler in an EV than in an ICE) trans-axle will serve us well for years to come. Modern hydraulic disc braking systems are also very well engineered, reliable and affordable. If I understand the motor-in-the-wheel concept correctly, hydraulics would be replaced by an electronic interface. Without relentlessly overstating it, I'll stand by my premise that EVs shouldn't immediately become more electronically complex as they simultaneously become mechanically simpler.

· Anonymous (not verified) · 2 years ago

There are many advantages.
* Provides 4 wheel drive functionality. If 2 front wheels get struck, power could come from 2 rear wheels.

* Also if 1 motor fails, the other 3 could run the vehicle.

* Power from motors go directly to wheels eliminating transmission related losses. So Well to Wheels efficiency increases

* In heavier vehicles like vans / buses, powerful motors could be fitted in rear wheels to pull the extra load.

* Or front 2 motors could power for cruise while all 4 motors could power during pickup.

* More space is available to passenger/cargo without central motor occupying that space.

Its worth trying a shot.

· Anonymous · 2 years ago

In Electric Trains (Electric Multiple Units) as used in the Cities like Washington DC, Mumbai, Singapore has motors fitted in bogies which joins 2 axles and directly sends power to wheels.

http://en.wikipedia.org/wiki/Electric_multiple_unit

Typically every rail car has 2 bogies (1 in front and another in back). For every car there will be 2 motors. They provide a fast pickup and is also very energy efficient.

Even the High speed trains in China & Japan has this EMU concept. The same can be applied in road vehicles as well.

First lets ensure that Electric vehicles get popular. Then the Hub motors may get popular.

· Charles (not verified) · 2 years ago

My thought has been axle motors would be a good compromise between in wheel motors and chassis mounted motors. Axel motors have some of the same disadvantages as in wheel motors, such as limited power and no transmission. Axel motors have almost all of the advantages of in wheel motors, plus others. Axel motors allow for full hydraulic breaks and most of the mass is not at the wheel.

Just a thought.

· · 2 years ago

So that's what they're called, Axle Motors, makes sense.

I don't view their size as a huge disadvantage. Even if each motor is half / third of the size if you have 2 or 4 motors their combined power is equal to or greater than a single motor.

As for the lack of a transmissions that's a huge advantage IMO. With electric motors there's no need to change gears and in that case all a transmission does is waste energy in heat.

· Spies (not verified) · 2 years ago

Michelin Hub Motor? I am still wondering what ever happened to the Michelin Tweel! The Tweel seemed like a good match for a BEV. http://en.wikipedia.org/wiki/Tweel

· · 2 years ago

While there are purportedly "many advantages" to a wheel/hub/motor setup, I have to wonder if these aren't going to be outweighed by increased complexity and cost. Perhaps electrical multiple units already work well in large rail trains, but scaling it all down to automotive sizes is what is so hard to do. Even Michelin seems to think their system is "not quite ready for prime time" just yet.

There also seems to be some speculative interest here in a hybrid, with individual motors tucked inward, near the frame, and axle shafts protruding to the wheels. Unfortunately, you're probably going to come up with something that is the worst of both worlds . . . adding weight and complexity to the pure wheel/hub/motor system, while not gaining any advantage to the time-tested system of a single, larger and centrally placed motor. Please submit some drawings and perhaps I'll approach that idea with a more open mind. Until then . . .

I'm convinced that the incremental approach to the problem is better.
By simply replacing the ICE under the hood with a single electric motor, you not only save on complexity, you also save on size and weight under there (not to mention heat and dirt.) The conventional transmission that the electric motor is coupled to is also going to be simpler. 4 or 5 forward gears needed for the limited torque range of an ICE are going to be replaced by a far simpler unit with 1, perhaps 2, forward gears. Hence, the tranny will also be smaller and lighter in weight.

It's also is going to be cheaper. It's the high price of current generation batteries that make EVs so expensive these days, not the drive train But battery technology is an entirely different discussion. Maybe when batteries get cheaper and better we'll see renewed justification for more exotic drive trains.

I'm all for progress and I'll be interested in seeing a Michelin-type system in another decade or so (about when they, the inventor/manufacturer, thinks they'll have it perfected.) Until then, I think the single electric motor mated to a generationally advanced (simpler and lighter) conventional drive train is going to be what most automotive engineers are going to suggest for foreseeable future.

· Anonymous (not verified) · 2 years ago

Honestly, Don't be so simple minded.

The unspring weight issue is the ONLY one ever mentioned about wheel motors, yet it's an inconsequential issue. There isn't a car on the road that runs in-board brakes to optimize for unsprung weight.... I rest my case!

The real challenge with electric wheel motors is torque density and packaging which are both directly related to electric motor design with the issues involved being WELL beyond the knowledge of anyone short of an electric motor design engineer. Anyone discussing this subject who ISN'T an electric motor engineer is simply talking shit!

· · 2 years ago

Looking ahead, one of the most important use for hub/in-wheel motors may be for large-scale conversions of existing internal combustion vehicles to all-electric or various flavors of plug-in hybrid (series, parallel, blended modes, depending on the needs of the driver and the economics). See http://www.calcars.org/ice-conversions to understand what we at CalCars call "The Big Fix," and see what existing companies are doing.
As batteries become smaller and cheaper, this solution will, we hope, emerge as the most promising way to reduce transportation fossil fuel use. Wheel motors could be the key to migrating this solution from large gas-guzzlers to smaller vehicles where there is less available space.
I'd be interested to hear any information or forecasts about price trends (in volume) and technology expectations.

· · 2 years ago

Honestly, anon, don't be so arrogant.

You've got real engineers who . . . ah um . . . AREN'T AFRAID TO USE THEIR REAL NAMES who are saying that this thing is still years in the future. Yet you, the mystery man behind curtain number 3, says he has all the answers. Needless to say, I'm not impressed.

You'd have a lot more credibility if you created a real profile on this group instead of hiding and hurling invective. The internet is full of guttersnipes who are afraid of their own shadow. You're not the only one, unfortunately. Merely the latest.

Thanks, Felix, for injecting a bit of civility back into this discussion. My premise isn't that this thing is impossible. But it's not suddenly going to be appearing on every EV 3 to 5 years from now.

· Michael Thomas Sepe (not verified) · 2 years ago

Cant i remove my transmition from the back of my Power Stroke and install a genorator
and run wheel motors and charge a bank of batteries for short runs just like a train lokamotive

· Steve Hack (not verified) · 2 years ago

What do you think of Protean's approach?

We are developing a new concept in energy storage for EV's and we are looking for a good motor platform for our test bed

· Michael Thomas Sepe (not verified) · 2 years ago

I like it and i want some ASAP

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