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UK transmission engineering and control specialist Vocis will show off its electric vehicle-specific, two-speed transmission during the Low Carbon Vehicle Event 2011 at Rockingham Motor Speedway over in the UK.
This will be the first public demonstration of the Vocis two-speed trans, which will be fitted to a prototype electric minibus developed in conjunction with powertrain supplier Zytek.

Vocis transmission guru Andy Turner explains, in simple terms, why two-speeds supposedly beat one:
Electric motors have a very wide operating range, but that doesn't mean that they are equally efficient at every speed. The torque curve of a typical traction motor is well suited to vehicle propulsion, having maximum torque from zero speed and a wide constant power region. However, there is a sweet spot, typically at medium speed and medium to high loads, where the delivery of power is most efficient. A choice of gear ratios allows the motor to be kept in this operating region during more of the drive cycle.
Simulations have shown that Vocis' two-speed unit could reduce energy consumption by up to 10 percent, compared to a single-speed trans. Furthermore, Vocis says that its twin-speed setup doesn't cost much more than a one-speed unit and could even extend battery life. What's interesting is that Tesla learned the exact opposite lesson back in 2008.


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    • 1 Second Ago
  • 33 Comments
      Arun Murali
      • 3 Years Ago
      I wish they had pitched it differently. Think of one gear transmission for speeding up and two gear transmission for slowing down. A really short low gear might help you extend the speed at which the car can regenerate, efficiently. You dont really get any regeneration below 12-15 mph. So, while slowing down. It can shift to the lower gear below 25 mph, meaning you can extend the regeneration to about 4-5 mph. Obviously if you want to race off the red light with futuristic sound effects, you should be able to engage the lower gear. Should give sport car like 0-40 on a normal electric car. This should be able to get you more than 10% boost in range and lower physical break usage.
      Dave D
      • 3 Years Ago
      No, what Tesla learned was that trying to design and build your own transmission without people who had done it for years and already knew how to deal with special, high-torque motors/engines...didn't work. These people know how to do that.
        squngy
        • 3 Years Ago
        @Dave D
        From what I know, Tesla didn't try to make the 2 speed trans themselves. They hired people who had done it for years but weren't able to make one that could withstand the forces Tesla needed it too (at least not within the budget).
          • 3 Years Ago
          @squngy
          that's what i recall
          letstakeawalk
          • 3 Years Ago
          @squngy
          "Tesla is being sued by Canadian supplier Magna for breach of contract. The suit alleges that Tesla failed to pay Magna for development work on its troubled transmission system. Transmission woes have long been the Achilles heel of the Tesla Roadster's development. Initial plans called for a two-speed transmission to be supplied by X-Trac, That unit was quickly proven incapable of reliably handling the EV's zero-RPM grunt. Tesla then went to Magna for a replacement two-speed– which proved equally unsuccessful. After attempting an in-house development, Tesla has given-up on the whole multiple gears thing in favor of the golf-cart elegance of a single-speed box. But wait, says Magna, we told you to try a single-speed solution in the first place. Not only did Tesla not listen, but according to the suit filed California, they didn't pay some $5.6m in development fees that Magna claims it was owed under the development contract." quote from ttac, link to ABG with updates: http://green.autoblog.com/2008/04/15/tesla-now-on-the-receiving-end-of-a-lawsuit-magna-sues-for-brea/
          krona2k
          • 3 Years Ago
          @squngy
          Sales and marketing types rarely bother to check with engineering whether or not something is actually possible, after all what concern would that be to them? As Bill Hicks once stated "If you're in Sales or Marketing, kill yourself." I'm not even kidding ;-)
          Dave D
          • 3 Years Ago
          @squngy
          They hired people after it was way too late for them to get it working right in production. they tried to do it themselves first. By that time it was delaying them getting to market and driving their costs through the roof. So they backed down to something that would work just fine for a top speed of 125mph and went to market.
        letstakeawalk
        • 3 Years Ago
        @Dave D
        Glad to see yet another transmission being developed for EVs!
        Jim McL
        • 3 Years Ago
        @Dave D
        My recollection was that the failed two speed transmission that Tesla used was designed by Borg Warner, am I mistaken? They are not exactly new to the business. However, I do recall a Borg Warner 3 speed automatic in my 1970 Datsun 510 that was quite unreliable.
          Jim McL
          • 3 Years Ago
          @Jim McL
          Looks like I recalled incorrectly
        Chris M
        • 3 Years Ago
        @Dave D
        Tesla didn't try to make their own 2 speed transmission, they tested 2 different models from 2 different suppliers - and neither one held up to the high torque load. There really aren't many companies making 2 speed transmissions, so there weren't many options. The problem is that nobody really has experience making multi-speed transmissions for electric motors, because until now there simply wasn't a market for them. Here's hoping that this new design can actually work as advertised, and is reliable. I wouldn't be at all surprised if Tesla is already testing this new design for use in a future model.
          letstakeawalk
          • 3 Years Ago
          @Chris M
          Perhaps you missed my quote above: "After attempting an in-house development, Tesla has given-up on the whole multiple gears thing in favor of the golf-cart elegance of a single-speed box..." Tesla had transmissions from outside suppliers (which actually worked, but Tesla couldn't get the software to work properly), and Tesla also tried their own internally-designed transmission, which also failed. "According to Siry there were never actually any mechanical failures of the X-Trac transmission, it was simply a matter of Tesla not being able to get their control strategy to work adequately with the hardware." http://www.autoblog.com/2008/04/16/tables-turned-tesla-motors-sued-by-transmission-supplier-magna/ Tesla couldn't develop software to work with an outside supplier's transmission, nor could they design their own transmission.
          letstakeawalk
          • 3 Years Ago
          @Chris M
          My apologies squngy, if I used the wrong terminology. Tesla has some way of controlling their electric motor output (I assumed computer or electronic control, hence using software to manipulate the motor's behavior) but however they do it, their "control strategy" for manipulating the electric motor's output during shifting couldn't be adjusted to work properly with the X-Trac transmission. Siry said it himself - it was Tesla's failure, not X-Trac's. Tesla was trying to manipulate torque from the motor, but couldn't. From the same link above: "Tesla VP Darryl Siry contacted us to clarify the issue with the original X-Trac gearbox. Apparently the problem was not one of actual durability of the transmission itself. Tesla evidently spec'ed out a two speed unit with no clutches. The design intent was to do clutch-less shifting and manage the torque output of the motor during the shifts. Unfortunately the rotational inertia of the motor made this plan unworkable as the torque output couldn't be changed fast enough." Do notice that this was before Magna even stepped in.
          squngy
          • 3 Years Ago
          @Chris M
          @letstakeawalk Software for transmissions? Are you insane? The only way what you wrote could even remotely make sense, is if Magna wanted them to limit the torque while changing gears in software and I can see why Tesla wouldn't want to do that.
          letstakeawalk
          • 3 Years Ago
          @Chris M
          Also squngy, you should be aware that many modern automotive transmissions have a degree of software controlling them. Nothing insane about it at all.
        2 Wheeled Menace
        • 3 Years Ago
        @Dave D
        Exactly Dave. This was during the early years of Tesla. Of course there are transmissions that can take the power. And there are now controls to limit the initial jolt of torque as well. I believe it was all the matter of fitting a heavy duty transmission into a small car like that, more than anything. People in the eBike world are experimenting with 2 speed transmissions and having good results.
      Justin Forposting
      • 3 Years Ago
      In terms of drive cycles for fuel economy/range, the majority of the operating points tend to be very low torque which are also a poor efficiency area (smack in the center of the torque speed map is where you want to be). With a single speed gear ratio, you have to balance these points against the maximum speed requirements, the higher the speed the lower the torque points for the drive cycle. With a second ratio, you can get many of those points up in torque and improve cycle as well as cruising efficiency and increase max torque at lower speeds as a bonus. It's hard to get big gains here with only 2 gears, but gains are available. The extended battery life claim is a bit out there though: the energy is still going to be cycled out of the battery (just over a longer range) and the DC power into the power electronics isn't going to be sufficiently different to make any such claim.
      John R
      • 3 Years Ago
      Electric motors also offer an alternative solution: the electronic transmission. By placing the coils inside a motor in a specific way so they can be split up differently (I think they do this by switching between series and parallel connections), the RPM for the motor's "sweet spot" can be altered electronically. No mechanical transmission needed.
        nbsr
        • 3 Years Ago
        @John R
        That's one solution. It is fairly common in larger motors (for example in trains) but it has some problems too: - "gear" ratios are not very convenient - if you simply split windings in half you get something like 4:1 ratio between first and second gear, and other combinations require more windings. - magnetic cores don't scale - they have to be big enough to carry magnetic flux produced by the parallel connection. Other than driving slowly on a 2nd gear they would be mostly unused. Not that these are unsolvable problems but since every EV already *has* a mechanical transmission, adding one gear to it is "free". This solution could potentially work well with hub motors, except that it would make them *even* bigger (which is an issue already).
      krona2k
      • 3 Years Ago
      Yeah it should be good if this works, might it be only really needed for sports cars though?
        • 3 Years Ago
        @krona2k
        Yeah, more than anything, the two speed will give you either (or both) higher torque for quick launching or/and higher top speeds, depending on your gearing. It's not really that different to needing a gearbox for an ICE vehicle only because a much larger RPM range is useful you need only two gears instead of five. It's also useful in vehicles with smaller motors to give them a bit better performance.
        nbsr
        • 3 Years Ago
        @krona2k
        Sure it will survive. There are many strong cars on the roads I've never heard of design issues with their transmissions. Tesla doesn't use a transmission for two reasons: - It doesn't need one as badly as commuter cars as it already has an overgrown motor plenty of torque. It needs such a motor anyway (for max. power) and they are not overconcerned with its efficiency. - They started early and at a small scale and developing a new transmission costs lots of money. Even large manufacturers don't design a new transmission for each model they make. It didn't stop them from blaming transmissions for all their problems but that's a different story.
      Dan Frederiksen
      • 3 Years Ago
      it'll be interesting to see once people's heads actually get in gear, what solutions will be tried. 2 gears can probably work well and be quite simple but for the most part I'm guessing the single gear will be too appealing. even race cars might do it because they can just gear it for high speed since standstill is never really significantly in play. if it's strong from 50-300km/h there is no great need for another gear even if you could shave 0.1 second off the initial acceleration. road cars that you also want to race might be the ones in most need of multiple gears.
        nbsr
        • 3 Years Ago
        @Dan Frederiksen
        > 2 gears can probably work well and be quite simple but for the most part I'm guessing the single gear will be too appealing. 2 gears are exactly as easy to use as 1 - if you are not speeding down the motorway you could simply drive on the first gear at all times and enjoy better efficiency and acceleration. Although, it probably makes sense to switch to second when you are about to join the motorway - think of it as of a "mode switch" rather than a gear.
        EJ
        • 3 Years Ago
        @Dan Frederiksen
        "no great need for another gear even if you could shave 0.1 second off the initial acceleration." F1 guys would sell their children for .1 sec.
      2 Wheeled Menace
      • 3 Years Ago
      I hope this makes it into production cars soon. Lower speeds are very inefficient in electric motors; you want to keep that motor as high a RPM as possible. It really is the opposite of a gas motor. You could cut the energy use in traffic / city driving conditions by a notable amount.
        JP
        • 3 Years Ago
        @2 Wheeled Menace
        "in electric motors; you want to keep that motor as high a RPM as possible" Not exactly, efficiency drops off near the top end, as does power. I doubt this transmission will do much for efficiency.
        EVSUPERHERO
        • 3 Years Ago
        @2 Wheeled Menace
        I did not know that, guess I better keep it wrapped right around 40 mph on the side streets in town. My motor is probably pushing 10,000 rpms at 55 mph. 12,000 rpms at 70 mph. It is a small motor so it does more rpms.
          Dan Frederiksen
          • 3 Years Ago
          @EVSUPERHERO
          it isn't quite true either though. it's not just about max rpm. the ACPropulsion AC induction motor seems to be most efficient at 8000 at 1/3 power with a good range from 6-11k so for that one it's sort of true but the AFM140 EVO permanent magnet motor is most efficient at 1800rpm (above 96%) that's quite a gearing you got there. is it the azure AC24?
      nbsr
      • 3 Years Ago
      What exactly is this "up to 10%"? If that figure is given for a mixed driving cycle (city and motorway) it could be substantially higher in the city only traffic. Anyway, the "EVs don't need transmission" meme was useful for demonstrating properties of electric motors to the ICE crowd but in a long term it is harming development of electric cars. 10 percent (or more?) longer range is not to be sneezed at.
      paulwesterberg
      • 3 Years Ago
      Strap it onto a tesla motor and take it to the racetrack if it survives then we have a winner.
      mchlrus1
      • 3 Years Ago
      THow about a CVT wouldn't that work, but not for high torque motors like the Tesla, but for the Leaf, Volt, and Focus?
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