By on April 19, 2013

Protean Electric In-Wheel Electric Motor

It’s April, when automotive engineers from all over the world gather in Detroit for the SAE World Congress. Protean Electric, which has been promoting the electrification of cars with their in-wheel mounted direct drive motors for the past few years, used the occasion of the World Congress to introduce the production version of their motor, which will start being assembled in a Protean owned factory in China next year.

Protean is also looking to license their technology to OEMs. The Protean motor can fit on standard hubs inside wheels that are 18 to 24 inches in diameter and the power units are also compatible with disk brakes, with mounting bosses for calipers. They can be used as part of a hybrid system, or since they have a continuous output rating of 86 HP per motor, they are powerful enough when used in pairs to drive pure battery electric vehicles. A self-contained unit with integral electronics and controls, the Protean motor can even be retrofitted to used cars. Protean is selling the fact that it’s a bolt on solution to turn a conventional combustion powered car into a hybrid. It’s actually pretty nifty and the motors allow for reverse torque so with the proper electronic controls torque vectoring is possible, allowing for very sophisticated traction and stability control. Theoretically, with a motor at each wheel it could also make parallel parking a snap by turning on the car’s own axis. Their in-wheel motor, though, is not why I’m writing about Protean. The real reason why I’m writing about Protean is a study the company commissioned Lotus Engineering to do on the real world impact of unsprung mass. A study with a somewhat counter-intuitive conclusion.

Surprisingly, Lotus, which knows a thing or two about chassis dynamics, said that tires and suspension tuning have a greater impact on ride and handling than adding the 68 lbs per wheel that the Protean system weighs. That sounds like heresy in an automotive world that has chanted “reduced unsprung mass” as a mantra for the past 50 years, at least. Reducing the mass of the parts of the car not supported by the suspension, in other words the mass of the suspension itself, has long been considered essential to better handling. Since they’re mounted in the wheel, hub motors are on the wrong side of the unsprung mass equation. Lotus says that while adding weight to the wheel has an effect on ride and handling, that effect can be offset by normal suspension tuning procedures.

The choice of Lotus Engineering to do the testing was not coincidental, because of Lotus Cars’ reputation for making what are arguably the best handling cars in the world. Cars that have supple road manners in addition to their cornering grip. The fact that Lotus cars can deliver that kind of cornering performance while still maintaining a comfortable ride on real world loads has not been lost of reviewers and car enthusiasts. Essentially, Protean was thinking that if Lotus gives them a pass, so will all the car guys who are asking, “But what about unsprung weight?”

Here’s what Steve Williams of Lotus Engineering said:

Whilst it is true to say that the vehicle dynamic performance was degraded by the increase in unsprung mass, the degree to which this was noticeable was small and could be said to have moved the overall dynamic performance of the test vehicle from class leading to mid class. Further more, the understanding gained from this study has led Lotus to believe that the small performance deficit could be largely recovered through design changes to suspension compliance bushings, top mounts, PAS characteristics and damping, all part of a typical new vehicle tuning program.

Add the powerful benefits of active torque control and Lotus’s finding make a strong argument for the vehicle dynamics benefits of hub motors as an EV drivetrain.

White paper (PDF) on the study here. Powerpoint presentation here.

Ronnie Schreiber edits Cars In Depth, a realistic perspective on cars & car culture and the original 3D car site. If you found this post worthwhile, you can dig deeper at Cars In Depth. If the 3D thing freaks you out, don’t worry, all the photo and video players in use at the site have mono options. Thanks – RJS

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35 Comments on “Heresy Unsprung, Lotus Engineering: Unsprung Weight Doesn’t Really Matter Much...”

  • avatar
    Dr. Kenneth Noisewater

    I’m thinking compact motors (like the Axiflux) with short shafts to the wheels may be the way to go?

    • 0 avatar
      bumpy ii

      Yar, but it would need some sort of reduction gear in there. Could use long sausage-looking motors, since you have pretty much the entire width of the car inside the wheels to work with. Wouldn’t need brake calipers either, except to satisfy the DOT.

      • 0 avatar
        Dr. Kenneth Noisewater

        Axiflux is quoting ~2000 lbft of torque, so a reduction gear may not be needed ;)

        Either way, a fixed reduction gear from the motor to the axle would not be horrible, and if you could save weight and didn’t care about torque vectoring you could fit their motor inside a traditional diff (or at worst cap the diff off and save the weight and space of a driveshaft).

  • avatar

    It sound to me that there are simply “ways around excessive unsprung mass” and that, in this application, it’s a worthwhile tradeoff for the benefits of independent motors.

    Just as it’s beneficial to have an overall car that weighs less, it doesn’t mean there aren’t technological ways to compensate, nor that our safety and cost expectations would allow for ultralight cars today. Again, a worthwhile tradeoff to most people. For others, there’s always Lotus or a Miata or FR-S, etc.

  • avatar

    Great. One more hair-brained idea to offer for the EV mantra.

    Did anyone every think that placing an electric motor in an area most prone to salt-water and slush penetration in NE Winters might be a bad thing?
    “Oh, it will be sealed tightly.” Yeah. Right.


    • 0 avatar

      Just like your head……

      If it’s sealed, it’s sealed. It probably will need yearly maintenance to maintain the seals. But as it stands if this is offered at a reasonable cost it could be a great innovation because it go between vehicles on trade-in and extremely useful on fleet vehicles.

    • 0 avatar

      At the SAE convention they had a demonstration unit inside a water bath. Between the unsprung weight question, and your point about water penetration, it looks like Protean has anticipated some of the possible objections too wheel motors.

      • 0 avatar

        Hi Ronnie – – –

        Thanks for your comment. I read superficially through the “.pdf” above, and looked at your referenced YouTube. The former helped me review some engineering bygones.

        It is difficult to tell exactly where the water level was in that demonstration, even using the 3D glasses I have. But by halting the video, I found that it seems the water is actually a little puddle at the bottom, which is being splashed up on the rest of the Protean motor, WITHOUT exerting hydraulic pressure on the motor.

        So, not only is there an unsprung weight issue (which Porsche would say is huge), there are these issues:

        1) First, there are ultimately no such things as perfectly tight seals where motive shafts exit any device;

        2) Acceptable levels of relatively pure water penetration will not have the same effect as the much lower acceptable level of electrolytic water penetration that comes from a salt solution;

        3) Riding through water that is 1/2 the wheel diameter WILL exert hydraulic pressure, forcing water to be squeezed into the smallest pores and channels;

        4) Slamming the vehicle through 6-inch deep pothole with a tire/wheel/brake/motor/suspension assembly that is now 68 lbs per wheel heavier, — well, you can just imagine what that will mean for longevity of those components, or the increased structural mass that has to be built in;

        5) And speaking of longevity, what Protean can show in a demo unit will not be the same as any leak- free condition that could be assured for 11 years (average car life) and 120K miles later;

        6) As with the added expense that comes from doing an alignment on a FWD car, what will be the even more added expense from an alignment caused by sliding your Protean-wheeled car into a curb?

        7) What is the replacement cost of one of these motors, easily damaged in this fragile location;

        8) How does the presence of the motor affect the cooling of brakes, since that wheel location is now more tightly packed?

        IMHO, if you’re going the Hybrid route, do the Porsche 918 or LaFerrari method: keep the electric motors housed safely INBOARD (even inside), not outboard. Xeranar’s less than gracious personal reference notwithstanding, this concept does not appear tested enough nor robust enough over the long term, and will no doubt add even more $$$ to the purchase price of a hybrid vehicle.


        • 0 avatar

          “8) How does the presence of the motor affect the cooling of brakes, since that wheel location is now more tightly packed?”

          Funny you should mention cooling. The engineering white paper shows a coolant line going directly to the wheel.

          I assume it’s there to cool the power electronics, because I don’t think they can get the coolant to the disc in their design.

          As excited as I am about these things, I agree that there are a lot of unknowns. Heck, even the super-reliable Prius was still a beta test in its first generation, and many of thew 1st generation Prius traction batteries were replaced. The “iconic” Prius is one if the more reliable cars I’ve ever owned, and gets great marks from people who measure these things. I would be shocked if something as new new and innovative as these hub motors got everything thing right the first time.

          • 0 avatar

            Luke 42 – – –

            You said: “I would be shocked if something as new new and innovative as these hub motors got everything thing right the first time.”

            Yes, there are some “awkward” designs that can continually be worked into improvements such that they are made robust (e.g., your Prius; the rear-engined Porsche’s).

            But there are other designs that are so inherently flawed that no “improvements” will matter (e.g., a rear-engine car with FWD). I am not saying the latter is definitely the case with in-wheel electric motors for general-use vehicles, but rather that there is such a mountain of fundamental issues to be overcome, one can only ask,”Why do it?” That which works on a Martian Rover is not necessarily a virtue on planet Earth.

            After all, new light-weight gears, drive-shafts, and differentials do serve the purpose of delivering power exactly where it’s needed; be almost immune to road hazards and water damage; and have a long history of reliability with relatively low cost.


          • 0 avatar

            Sometimes there is hidden simplicity that isn’t obvious. For instance, the Prius’s transmission is basically a beefed up differential. It’s far simpler than any conventional transmission. Mechanical simplicity can be gained when electronics are added. As a computer guy, I can troubleshoot electronics easier than an automatic transmission, so this is win for me.

            It seems like the same thing is happening with these hub motors. You trade 3 mechanical subsystems for one unsolved problem. Its high risk but it could be a big win, if they get it right.

            I really hope they get it right eventually! But there is a lot of real world miles that need to be driven to tell if it’s any good first….

        • 0 avatar

          Hey, the saltwater problem is easy to solve. The EPA will just ban the use of salt on the roads. Think of the billions slugs that’ll save.

  • avatar

    Jet engines sucked in the 1940’s

  • avatar

    Your characterization of Lotus’s analysis is grossly misleading.

    The difference between “class leading” and “class average” is enormous. It represents the difference between the automakers who know what they’re doing (GM RWD, Ford FWD, Porsche, Mazda, Honda double-wishbone) and the ones who never knew in the first place or were too cheap to do a good job (recent Hondas, GM FWD, Hyundai). If one change can undo the work of a top-notch vehicle dynamics department, it’s not a “small” decline.

    The 10″ Hoosier LC0 offers slightly less peak grip than the 13″ Hoosier R25B, and is more load-sensitive and flexible. We’ve built cars that use both tires. The 10s save about 20 lbs of unsprung weight on their own. The cars we’ve built using the 10s are visibly faster through transitions, tight corners, and bumpy sections than the older ones.

    Unsprung weight’s been treated like it matters for seventy years because it does.

    • 0 avatar

      I quoted a Lotus spokesperson and linked to the paper so I don’t think it’s quite fair to say that I was “grossly misleading”. They’re talking about road cars, not track cars, like your Hoosier shod cars are. What makes a difference on the track may not be even noticeable to the average driver.

      I suppose the question will be resolved if Protean can make a car go like that electrified M-B SLS that got Chris Harris laughing like a madman.

      Regarding class leading and class average, the difference between, let’s say, a Mazda 3 and other cars in its class that don’t ring car guys’ bells when it comes to handling and feel is mostly tuning, since almost all of those cars have essentially the same suspension layouts with lower control arms, McPherson struts and rack & pinion steering.

      • 0 avatar
        Adrian Clarke

        “handling and feel is mostly tuning”

        You say that like it’s almost inconsequential compared to the actual layout of the suspension – when in fact it’s the whole ball game.

        Types of suspension for a given vehicle are rarely dictated by desired handling characteristics – they are determined by packaging constraints and cost (helloooo Mustang!) and sometimes marketing.

        It’s the tuning and the components that define driving feel and road manners. For example the E60 M5 has basic strut front suspension.

        • 0 avatar

          ” “handling and feel is mostly tuning”

          You say that like it’s almost inconsequential compared to the actual layout of the suspension – when in fact it’s the whole ball game.”.

          Not at all. What I was saying was that when most cars in any one class have similar suspension layouts, tuning will be the primary difference in how those cars handle and ride. I really don’t think that we’re disagreeing much.

          A well tuned live axle can handle better than a poorly tuned IRS. Hell, a well tuned live axle can sometimes handle and corner better than a well designed and tuned IRS. A Boss 302 Laguna Seca can get around a track at least as fast as a BMW M3 or M5. The first Lotus Cortinas had really trick multi-link rear ends but they found that there weren’t any practical advantages over just picking the correct leaf springs and shocks.

          Speaking of Lotus, I just heard a lecture at the SAE convention by Karl Ludvigsen on Colin Chapman. He pointed out that Chapman experimented with solid axle de Dion setups, front and rear, well into the 1970s.

          • 0 avatar

            Ronnie – –

            Having studied both the “White Paper” and the PP/pdf a bit more, I can make some observations:
            1) No mention was made of differences in braking;
            2) No comparisons were done in trail braking;
            3) Standard skidpad and slalom tests were not used;
            4) The sedan’s identity was not revealed (although, it is not too hard to surmise that it may have been a BMW 3-series).

            Rather than the subjective scoring, and then the elaborate computer-derived measurements from obscure methods, all that is necessary to be side-by-side with the “standard” vehicle (to which 136 lbs has been added in the passenger’s seat and two weights of 68lbs each have been added on the back-seat floor) is this:
            1) Acceleration, 0 to 60 mph, in seconds;
            2) Skid-pad, 200-foot radius, max g’s obtainable;
            3) Braking, 60 to 0, in feet;
            4) Slalom, 700-ft total, 100-ft spacing, in mph.

            BTW: Yes, live axles (LA’s) can do as well as IRS under some conditions, but not universally. The killer for LA’s is washboard surfaces on curves with an outside camber. Bye-bye.
            I have tried to get Nordschleife lap times for ANY version of Mustang, and seem not to be able to do that. Maybe you can help me. They certainly exist for Porsche 911’s and BMW M3’s/M5’s.


  • avatar

    As long as braking is done by real brakes I have no qualms with that.
    Simply dont like the idea of braking from the hub motor.

    They can be fitted to 18 or bigger wheels which none of the cars or truck I have is that size. Parhaps a smaller size coming in the future.

    • 0 avatar
      bumpy ii

      Henry Ford didn’t like those untrustworthy hydraulic brakes either.

    • 0 avatar

      I encourage you to read the white paper on Pretean’s site.

      The wheel has disc brakes, but they’re unusual. In order to make room for the in-wheel inverter, they use an inside-out disc and two calipers.

      Their reasoning for including a disc brake at all is basically that cars need to be able to slow down way faster than they can accelerate, so building an electric motor powerful enough to do a panic stop would have meant they needed a much bigger motor, wiring, and battery to absorb the charge of a panic stop. Or, they could put this unusual disc brake on it. They chose the disc brake.

      The white paper walks through their reasoning. Its an interesting engineering case study, even if you wouldn’t want to own an EV.

      Personally, I’ve been reading up on it because I thought it would be fun the build an electric Jeep Wrangler Unlimited. I’d originally thought of replacing the transmission and transfer case with a pair of Netgain Transwarp motors, but I decided to check up on these guys and they had posted some interesting reading. It would require a custom suspension, and I know that both the Jeep guys and the EV guys should be appalled, but what does a Jeep stand for if you can’t make turning it into whatever floats your boat an interesting hobby… :-)

    • 0 avatar

      @ blowfiSh

      who aRE you .
      an d what you did blowfish to?

  • avatar

    Maybe they figure they can throw enough software at it to make it handle like something sporty. It’s the future you know.

    • 0 avatar

      That’s more or less the idea!

      According to Protean’s white papers, that really is what they’re doing.

      Having driven an EV, though, I really want one for my commute. I’d also like to build a range-extended electric jeep with an electric power takeoff box. Who care about unsprung weight on a Jeep!

      This stuff may not be your idea of a good time or of the ideal car, but it gets me excited!

  • avatar

    I still have some question as to the setup of the inwheel motor though. Are majority of the motor mass part of the rotating or non-rotating components? I feel while the ride aspect can probably be tuned out with suspension(and frankly I think we are doing this already with the advent of cars of ginormous wheel/tire combo), the rotational inertia effect, and possibly gyroscopic effect is more pronounced if it is a rotating component. Even the previous example cited by the comment regarding the heavier and lighter Hoosier, the rotational effect I feel might be an even bigger contributor as it’ll affect accelerating in both direction, as well as potential gyroscopic effect…

  • avatar

    I’m not quite sure if this article is calling them out on a bunch of marketing BS, or if it is simply reporting a fact that unsprung weight does not matter so much as people have made out in the past. I think it is the latter…

    68 lbs per wheel is huge. I am sure it will have a noticeable effect. However, I can also see that if you do a good job with suspension tuning, it might not be that noticeable to most people, especially if you increase the sprung weight with a bunch of batteries as well.

    Now, go back and ask the same suspension engineers if reducing unsprung weight will improve the ride. There is only one answer… You can find out for yourself by driving two BMWs back to back. One with runflats, and one without. The one with the runflats will ride and handle quite nicely, and even better than many other cars. The one without will ride and handle noticeably better than that.

    • 0 avatar

      I’m sure you’re right, if your goal is to build the ultimate sports car. But I’m not particularly interested in driving one BMW, much less two BMWs back to back.

      For the transportation appliances that get me excited, there really is such a thing as “smooth enough”. The EVs I’ve driven have superior NVH, on account of the explosion engine being removed from the car, so you have a lot of room to make compromises while still making an appliance that is a pleasant way to get to your cube…

  • avatar

    Good white paper at the Protean link discussing issues with putting a motor in the wheel, but I’ll wait for the paper describing the results of durability testing – transportation random noise spectra applied for, say, 2000-3000 hours for fatigue testing, shock spectra simulating high speed impact with our northeastern winter potholes and, say, a 1000 hours of road salt mist. I’m familiar with Mil specs like 810, but SAE or similar orgs must have their own homegrown versions with appropriate load levels and durations. I’m not rooting against the concept, but they need to prove it’s robustness to get my money.

    • 0 avatar

      I’m very interested in this, too.

      They’re making a good case that they’ve thought it through, but we won’t really know until these things get abused in the real world for a few years. Assuming they’re ever made at all!

  • avatar

    Regardless of whether someone at Lotus claims the effect is “less” than “many” expect, competition will lead to less compromised locating of those 68 pounds than at the wheel hubs. Any motor compact enough to located there, can be located plenty of more opportune places as well.

    • 0 avatar

      COnsidering the amounts of SUV:s and pickups alone that run ridiculous off road tyres or 28 inch chrome monstrosities I’d think it’s safe to assume that many drivers are prepared to suffer from unneeded unsprung weight. The packaging advantages of having the motors where they take up no space at all in the car is not exactly negligible, and, I do struggle to find another place in a car were that would be achieved.

  • avatar

    It’s sort of like after the upheavals of the past decade all Lotus had left to sell was their credibility as masters of handling perfection. These were the people that once could make two generations of Isuzu-badged GM T-bodies and R-bodies into exceptional handling cars and use the money to make a FWD sports car that drove so well it shut up naysayers. If you can put a price tag on the brand equity they built, it is whatever they were paid to endorse hub motors.

  • avatar

    Micheline did this about a decade ago together with one of the French car manufacturers. Always seemed like a nifty idea as it opens up the packaging of a car’s drive train to new layouts by not requiring difs, gearboxes, drive shafts and what not. Crab walking cars that turn on the spot would be a god send for delivery businesses in cities with tight streets. Imagine a AWD delivery van or ambulance with a level floor that sits meer inches above the pavement that can get into almost any spot, it might even be worth the inefficiency hit of running a ICE coupled to a generator without a battery pack. Another use might be logging or construction trucks with on demand AWD trailers with the added advantages of having ECS working on all axles when on road.

    • 0 avatar

      Ferdinand Porsche did this 115 years ago, when battery electrics were actually competitive with IC powered cars. The next year he built the first series hybrid to address the weight of batteries. Soon geared transmissions were developed that could transfer power without the drawbacks of the generator and hub motors, and the technology was cast on the ash-heap of history until the current era of repeating the mistakes of the past. Check out the Lohner-Porsche if you’re curious.

  • avatar

    I don’t buy it.

    How is the wheel going to follow a divet in the road at speed? Doubling the spring rate and adding an ton of suspension insulation?

    I don’t buy it.

    Maybe lay people won’t notice. People don’t seem to notice that new cars are tuned MUCH more stiffly (too stiff, imo) in 2013 than they were in the 90s.

    It’s really hard for “worse but good enough” to give me a boner.

    Just put them inboard and use half shafts.

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