By on July 21, 2011

In my review of the VW Golf blue-e-motion on Tuesday, I noted that “the holy grail of EV development is a multi-speed transmission,” but that nobody has been able to build one that can reliably handle the 100% torque at zero RPM characteristics of an electric drivetrain. Tesla tried two different multi-speed transmissions (from X-Trac and Magna), before giving up and going with the single-speed setup that every production EV now uses. Nobody has even talked about a multi-gear EV since… until now. With Fisker’s Karma about to go to market, CEO Henrik Fisker tells Autocar that his firm is developing a multi-speed EV gearbox, and that it would improve performance in EVs like the Karma, saying

With the torque at the wheels increased by the use of a gearbox, Veyron levels of performance should be possible.

We’re as excited as anyone else by the idea of an EV with shiftable gears, but this sounds more like Fisker trying to drum up some hype for the Karma launch. After all, the Karma launches to 60 MPH in a leisurely 7.9 seconds in “stealth” (EV) mode and 5.9 seconds in “sport” mode with gas power to up the wattage… a far cry from Veyron performance. As C&D puts it:

The Karma’s initial surge is sufficiently potent to avoid damnation as a slug. But the physics conspire against it keeping pace with other $100K sports sedans.

Lugging over 4,000 lbs is certainly easier with a multi-gear transmission, but given the reliability challenge, we’d be more likely to trust an EV transmission from a reliable supplier rather than a boutique luxury PHEV maker. And until Fisker can back up the Veyron reference with some hard evidence, we’re filing this one under “intriguing but unlikely.” Still, it’s exciting to know that this technical challenge is still out there, unconquered by major manufacturer or feisty startup… in a world where cars are becoming increasingly mundane, the multi-gear EV transmission challenge is a throwback to the golden years of automotive development.

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12 Comments on “Fisker: With An EV Transmission, All Things Are Possible...”


  • avatar
    Bytor

    Holy Grail??? Nonsense. Unnecessary complexity is more like it.

    One of the the great things about an EV, is the mechanical simplicity.

    Once you have a Electric motor with a wide enough operating range, a transmission is just superfluous source of mechanical breakdown and efficiency losses.

    If you have bucketloads of torque right from ZERO RPM, why do you need a lower first gear? If you have wide RPM range out past 15000 RPM, why do you need higher gears? Unless you are attempting to set some kind of speed record, an EV transmission is a pointless mechanical complexity and weakness. Gears are only needed to cover weak motors that have narrow power bands.

    Hobbyist conversions usually use stock manual transmissions, but that is because they are stuck with off the shelf, lower RPM DC motors.

    Maybe Fisker will do it because they are building PHEVs and efficiency/range won’t matter as much to them, but for pure EVs expect single speeds to the norm for all production EVs because it just makes perfect sense.

  • avatar
    bumpy ii

    EVs don’t *need* a transmission in most cases, but having a 2-speed does help performance at higher speeds where a 1-speed setup would be pretty far down the torque curve.

    The “holy grail” sought here already exists in the form of a built Powerglide modified to work in an EV (mainly an external pump and a manual shift body). Just a matter of picking a price point and a mtbf number. However, you don’t even need that if you use two motors and switch them electrically to provide two (or more) speed ranges.

    • 0 avatar
      Bytor

      Good motors keep delivering HP, they back off on the torque by design, or the HP would be off the rails at high RPM requiring much more KWs than the battery could deliver and more cooling to keep the motor intact. Torque fall off is expected and largely irrelevant to need to change gears. It is HP falloff that matters.

      Despite the obsession with torque, power is what matters. You only really need to change gears if you reach an RPM where HP has fallen significantly.

      The real holy grail is simply a motor that can keep delivering high HP at high RPMs, removing the need for a transmission. Then you are more efficient, more reliable and you don’t waste time shifting.

      If you deliver 250 HP at 7500 RPM and still deliver 250 HP at 15000 RPM it doesn’t matter at all that you have half the torque and changing gears would just be a waste of time/energy.

  • avatar
    bunkie

    Two things come to mind. First, can’t the torque problem be managed via sofware in the motor controller? Second, using bumpy’s suggestion, a fluid coupling (torque converter) might be a viable solution. Drag racers have been building torque converters that handle monster torque for years.

    BTW, I own a ShopSmith (a multipurpose woodworking tool). It has an AC induction motor and a CVT (using two variable diameter pullies and a belt), producing a usable speed range of 600-6000 RPM. The same basic design has been made for 55 years. They recently replaced this design with a variable reluctance DC motor with an electronic motor controller. The result has been an increase in the operating range to 250-10000 RPM. The drawback is cost which is twice that of the old setup.

    • 0 avatar
      bumpy ii

      Most AC motor setups do limit the initial torque output in software to keep the torque burst from peeling the motor apart. DC controllers tend to operate on the principle of “throw all the elctrons in and hope nothing breaks”, but even that could be mediated with a slipper clutch and a willingness to consider it a maintenance item.

  • avatar
    TR4

    “nobody has been able to build one that can reliably handle the 100% torque at zero RPM characteristics of an electric drivetrain”

    WTF? Something does not compute. A normal car with a manual transmission will apply around 100% torque at zero (or damn close to it) rpm during a spirited take off (rev to 3000, let clutch in quickly while giving it enough gas to keep the revs up). If you “pop” the clutch there will be a momentary torque of >100% engine torque due to the rotational momentum of the flywheel being dumped into the transmission. Typically, either the tires losing traction or the clutch’s max torque will limit this. Similar deal with an automatic. The torque converter multiplies the engine torque by a factor around 2 to 3 at stall. With a high performance (i.e. high stall speed) converter it is easy to get twice the engine’s peak torque applied to the gearbox part of the transmission.

  • avatar
    GS650G

    A transmission could take the strain off the motor at times.

  • avatar
    michal1980

    your DC motors power goes down as rpm goes up.

  • avatar
    Dynasty

    A steam engine has 100% torque at zero RPM.

    An electrical motor has 100% torque above zero RPM.

    • 0 avatar
      golden2husky

      Is that statement correct? An electric motor has the highest current at startup; the torque of a motor is directly related to the current through it. So a stalled motor has far more current demand and maximum torque. Once a motor begins to speed up, a counter electromotive force opposes the current flow through the windings and the current draw drops as the motor’s speed increases. So shouldn’t the motor be developing its maximum torque just before the rotor begins to rotate?

      • 0 avatar
        Dynasty

        I’m not an electrical engineer, but that is what an electrical engineer told me.

        I don’t disagree that an electrical motor has the highest current draw at startup, but the key is the motor needs to begin spinning for there to be any twisting force.

        A stalled electrical motor drawing full amperage is going to catch on fire (assuming the demand placed on it is too great to spin).

        I suppose a steam engine would also have 100% torque just at the point of the crank beginning to spin as well.

  • avatar
    Robert Gordon

    “but the key is the motor needs to begin spinning for there to be any
    twisting force”

    Nonsense. You are confusing Torque with work. Torque is a force, work is resulting effect of applying a force, power is the rate at which work is done. However applying a force to an option does not necessarily result in work. The coffee cup on your desk has a constant force being applied yet it doesn’t go anywhere. Likewise you can apply a torque without anything happening.


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