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If you value fuel economy, CVT is good. If you value driving performance, it is bad. Choose one. (Or just buy electric and don't worry about fiddly transmissio

If you value fuel economy, CVT is good. If you value driving performance, it is bad. Choose one. (Or just buy electric and don't worry about fiddly transmissions)

rsj_hn 6y ago
Even in the world of PEV there is a trade off between fuel economy and performance, so this has nothing to do with transmissions. The fact that you use energy stored as electricity does not get around the laws of inertia or air resistance -- accelerating a mass quickly will always require more energy than accelerating it slowly. And in the PEV world, since re-charging can take an hour instead of a minute, the consequences of draining the battery more quickly are going to be more of an annoyance. Transmissions come up in that this is how some automakers meet efficiency requirements -- by taking away some control over acceleration from the driver by using a transmission that is programmed to shift gears in the higher rev ranges, with no manual override. But this makes the car less responsive. Here, Tesla's brilliance shines, not because it doesn't have a transmission -- they can and do put in software that limits acceleration, so they could have done the same thing to improve range, but onlike others that improve efficiency by making the car less responsive to the driver, they improve efficiency by having a more efficent engine or a lighter car, while keepig the car very responsive to the driver. The real brilliance of Tesla is in building cars that are fun to drive (read, responsive), and indeed most of the innovation of electric cars that has been successful in the market was based around improving acceleration and adding more torque, making the car more fun to drive. That's why models like the Tesla or the old Ferrarris with electric assist are much loved by drivers, even though models like the Leaf and Bolt are not. Drivers care about good handling.
- ogre_codes 6y ago
  > Even in the world of PEV there is a trade off between fuel economy and performance, so this has nothing to do with transmissions. CVTs are not efficient because they control the rate of acceleration. You can over-rev a CVT and get as much acceleration as your engine (and it's transmissions losses) will allow. CVTs are efficient because they allow the engine of the car to operate in its most efficient power range more of the time. EVs run into this same issue, but the way Tesla anyhow solved for it is pretty wild. Dual motor Teslas have 2 different motor/ drivetrain gear ratios. The rear wheels are most efficient at lower speeds and when you are driving slower, they get most of the power. The front wheels are most efficient at higher speeds and when you are driving faster, they get the most power. This way the most efficient motor is always doing the most work at any time. This is likely why the AWD Teslas have so much more range than the single engine/ RWD models. There is a good article talking about EV transmissions here, the bit about Tesla's 2 gear ratio setup is about 12 paragraphs in. https://cleantechnica.com/2019/07/22/ev-transmissions-are-coming-and-its-a-good-thing/ https://cleantechnica.com/2019/07/22/ev-transmissions-are-co...

If you value fuel economy, CVT is good. If you value driving performance, it is bad. Choose one. (Or just buy electric and don't worry about fiddly transmissions)

rsj_hn 6y ago

Even in the world of PEV there is a trade off between fuel economy and performance, so this has nothing to do with transmissions. The fact that you use energy stored as electricity does not get around the laws of inertia or air resistance -- accelerating a mass quickly will always require more energy than accelerating it slowly. And in the PEV world, since re-charging can take an hour instead of a minute, the consequences of draining the battery more quickly are going to be more of an annoyance. Transmissions come up in that this is how some automakers meet efficiency requirements -- by taking away some control over acceleration from the driver by using a transmission that is programmed to shift gears in the higher rev ranges, with no manual override. But this makes the car less responsive. Here, Tesla's brilliance shines, not because it doesn't have a transmission -- they can and do put in software that limits acceleration, so they could have done the same thing to improve range, but onlike others that improve efficiency by making the car less responsive to the driver, they improve efficiency by having a more efficent engine or a lighter car, while keepig the car very responsive to the driver. The real brilliance of Tesla is in building cars that are fun to drive (read, responsive), and indeed most of the innovation of electric cars that has been successful in the market was based around improving acceleration and adding more torque, making the car more fun to drive. That's why models like the Tesla or the old Ferrarris with electric assist are much loved by drivers, even though models like the Leaf and Bolt are not. Drivers care about good handling.

ogre_codes 6y ago
> Even in the world of PEV there is a trade off between fuel economy and performance, so this has nothing to do with transmissions. CVTs are not efficient because they control the rate of acceleration. You can over-rev a CVT and get as much acceleration as your engine (and it's transmissions losses) will allow. CVTs are efficient because they allow the engine of the car to operate in its most efficient power range more of the time. EVs run into this same issue, but the way Tesla anyhow solved for it is pretty wild. Dual motor Teslas have 2 different motor/ drivetrain gear ratios. The rear wheels are most efficient at lower speeds and when you are driving slower, they get most of the power. The front wheels are most efficient at higher speeds and when you are driving faster, they get the most power. This way the most efficient motor is always doing the most work at any time. This is likely why the AWD Teslas have so much more range than the single engine/ RWD models. There is a good article talking about EV transmissions here, the bit about Tesla's 2 gear ratio setup is about 12 paragraphs in. https://cleantechnica.com/2019/07/22/ev-transmissions-are-coming-and-its-a-good-thing/ https://cleantechnica.com/2019/07/22/ev-transmissions-are-co...