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Here is a video demonstrating a (possibly less elegant) electrically controlled CVT called the D-Drive: https://www.youtube.com/watch?v=F6zE__J0YIU https://www

Here is a video demonstrating a (possibly less elegant) electrically controlled CVT called the D-Drive: https://www.youtube.com/watch?v=F6zE__J0YIU https://www.youtube.com/watch?v=F6zE__J0YIU The concept is straightforward if you visualize mechanical advantage. A high torque at low RPM is the same power output as a low torque at high RPM. If you picture an asymmetric differential with primary power going into it where one wheel is geared higher than the other, then a weaker motor on one of the wheels could control the torque and RPM of the other wheel. So we probably could have been using electrically assisted CVTs decades ago where a small fraction of the power could have gone into a generator/motor pair at about 90% conversion efficiency to control the output RPM. I can't help but feeling that most of the gains in things like 6 speed automatic transmissions to increase fuel economy have largely been a waste of time. We could have gotten rid of traditional transmissions and gone with a design like the Prius that are simpler, more efficient and more durable. By now economies of scale probably would have made them less expensive as well. I’m actually a little curious why this hasn’t happened with supercars.

motoboi 12y ago
What is the benefit in using this scheme opposed to a gearbox? Is most efficient to use two electric motors (powered by the combustion engine through a generator) or use gears in a gearbox, but without the power penalty of the generator? Is this more efficient than a gasoline drive system only if the energy to drive the electric motors come from an external source (the power grid, though the batteries)?
- lsaferite 12y ago
  Well, a simple reason is a CVT can keep the ICE in a very narrow RPM band where it's operating at maximum efficiency.
  - motoboi 12y ago
    Agreed. But there are many others CVT schemes without electric motors.
    - lsaferite 12y ago
      And most of those will have problems with high torque motors.
choppaface 12y ago
Supercars generate 5x-10x more torque, which would likely break this sort of transmission. Most automatic transmissions have a similar planetary gear design but use clutches to control power delivery (from the single motor). These clutches will burn up under lots of torque. Furthermore, it would be hard to implement a way of shifting the CVT to a predictable ratio and holding it there while in a tight turn. (Holding the ratio might not be hard, but the driver will probably want a predictable ratio before going into the turn).
- rodgerd 12y ago
  > Supercars generate 5x-10x more torque, which would likely break this sort of transmission Perhaps, perhaps not. Williams had a working CVT in the FW14C F1 car, which was pre-emptively banned at the behest of their competitors. It probably set back CVT research by a couple of decades, and marked the end of F1 as a tech testbed. Currently it's worth noting the Toyota are running the Lexus 450h in racing, and the Lexus LS600h runs a 327HP/520Nm V8 though a CVT mated to an electric motor running over 200 HP.

motoboi 12y ago

What is the benefit in using this scheme opposed to a gearbox? Is most efficient to use two electric motors (powered by the combustion engine through a generator) or use gears in a gearbox, but without the power penalty of the generator? Is this more efficient than a gasoline drive system only if the energy to drive the electric motors come from an external source (the power grid, though the batteries)?

lsaferite 12y ago
Well, a simple reason is a CVT can keep the ICE in a very narrow RPM band where it's operating at maximum efficiency.
- motoboi 12y ago
  Agreed. But there are many others CVT schemes without electric motors.
  - lsaferite 12y ago
    And most of those will have problems with high torque motors.

choppaface 12y ago

Supercars generate 5x-10x more torque, which would likely break this sort of transmission. Most automatic transmissions have a similar planetary gear design but use clutches to control power delivery (from the single motor). These clutches will burn up under lots of torque. Furthermore, it would be hard to implement a way of shifting the CVT to a predictable ratio and holding it there while in a tight turn. (Holding the ratio might not be hard, but the driver will probably want a predictable ratio before going into the turn).

rodgerd 12y ago
> Supercars generate 5x-10x more torque, which would likely break this sort of transmission Perhaps, perhaps not. Williams had a working CVT in the FW14C F1 car, which was pre-emptively banned at the behest of their competitors. It probably set back CVT research by a couple of decades, and marked the end of F1 as a tech testbed. Currently it's worth noting the Toyota are running the Lexus 450h in racing, and the Lexus LS600h runs a 327HP/520Nm V8 though a CVT mated to an electric motor running over 200 HP.