6 ms·

Electric cars don't usually have "gearboxes" proper. They use gears, fixed ratio reductors. This is not expensive nor is it fragile nor bulky nor inefficient.

by yholio 7y ago

Electric cars don't usually have "gearboxes" proper. They use gears, fixed ratio reductors. This is not expensive nor is it fragile nor bulky nor inefficient. The benefits that a very high torque motor could bring are real but marginal, a few percentage points improvements on the respective metrics. They could instantly be negated by, say, the lower initial reliability of a revolutionary design.

IshKebab 7y ago
The article mentions that.
- yholio 7y ago
  And then goes on to make outlandish claims about the benefits of the technology
  - IshKebab 7y ago
    Also true, but I didn't say otherwise.
    - yholio 7y ago
      Meanwhile, I logically built on the same point to present a contrarian opinion, so your initial reply is somewhat pointless nitpicking. It's exactly what the author of the article intended, making a passing reference to the fundamental flaw thet invalidates the rest of the hype contained. It's not even a conspiracy, it's standard clickbaity journalism, a balanced article about a possible 3% efficiency boost would not make it to HN front-page.
Svip 7y ago
I am genuinely curious, why aren't there transmissions for electric engines? Surely the advantage would be the same as for an IC engine. I remember hearing that Tesla tried to build a 2 speed transmission for their Roadster back in the day, but apparently it kept breaking, so they stuck with no transmission. Are there transmissions out there for EVs, and I just haven't been paying attention? And if no, why is it so hard? Is it because of the torque?
- spacenick88 7y ago
  Afaic the upcoming Porsche Taycan has a two speed transmission. In the Taycan it's used for more efficiency at >160 kph or so something an American car really doesn't need and it costs them a slower 0-100 kph. Tesla uses another trick to get better acceleration to 100 kph. They have two motors and one is geared for high efficiency at US highway cruising speeds (so ca 120 kph). In general electric motors have a very wide band of excellent efficiency and an even wider band of great efficiency and they are orders of magnitude more efficient than ICE in any part of their operational torgue/speed range.
- magicalhippo 7y ago
  Electric motors full torque regardless of RPM, unlike an ICE which has the usable torque in a limited RPM range.
  - blattimwind 7y ago
    We have many gears for better efficiency with ICE, because every ICE has very narrow areas of RPM×torque that give you acceptable efficiency (typically those with high mean effective pressure). You could totally get away with three gears and still get to 150 km/h, it's just that it will be a lot less efficient. Electric motors don't have this particular problem, and they don't need a start gear that is a lot shorter than the other gears (1st to 2nd is usually around a factor two, while from 2nd up to the next higher gear the ratio will change by perhaps 30 % or so) because they can deliver nominal torque at low speeds or from zero speed (so they don't need a clutch, either). An ICE can't do that. Here are the transmission ratios of a random six speed transmission: 1st 2nd 3rd 4th 5th 6th R 4.2 2.5 1.7 1.3 1 0.8 3.8
    - hwillis 7y ago
      > every ICE has very narrow areas of RPM×torque that give you acceptable efficiency (typically those with high mean effective pressure). You could totally get away with three gears and still get to 150 km/h, it's just that it will be a lot less efficient. It isn't that narrow[2]. Engines with fewer gears aren't particularly less efficient, they're just MUCH slower. Look at a map of gears[2]: the top gears are in the efficient range, but the lower gears are only there to allow you to rev the engine high while accelerating. In the ratios you gave, you could cut out 1, 3, 4 and only use gears 2, 5 and 6 and be able to get around fine- you start in second and then shift up as soon as you're rolling. You'd have a much more efficient car but you'd be incredibly slow. [1]: https://qph.fs.quoracdn.net/main-qimg-0c6c45106b28601fc1aef4172c08faf1.webp https://qph.fs.quoracdn.net/main-qimg-0c6c45106b28601fc1aef4... [2]: http://www.posterus.sk/wp-content/uploads/p12975_02_obr02.png http://www.posterus.sk/wp-content/uploads/p12975_02_obr02.pn...

by yholio 7y ago

IshKebab 7y ago

The article mentions that.

yholio 7y ago
And then goes on to make outlandish claims about the benefits of the technology
- IshKebab 7y ago
  Also true, but I didn't say otherwise.
  - yholio 7y ago
    Meanwhile, I logically built on the same point to present a contrarian opinion, so your initial reply is somewhat pointless nitpicking. It's exactly what the author of the article intended, making a passing reference to the fundamental flaw thet invalidates the rest of the hype contained. It's not even a conspiracy, it's standard clickbaity journalism, a balanced article about a possible 3% efficiency boost would not make it to HN front-page.

Svip 7y ago

I am genuinely curious, why aren't there transmissions for electric engines? Surely the advantage would be the same as for an IC engine. I remember hearing that Tesla tried to build a 2 speed transmission for their Roadster back in the day, but apparently it kept breaking, so they stuck with no transmission. Are there transmissions out there for EVs, and I just haven't been paying attention? And if no, why is it so hard? Is it because of the torque?

spacenick88 7y ago
Afaic the upcoming Porsche Taycan has a two speed transmission. In the Taycan it's used for more efficiency at >160 kph or so something an American car really doesn't need and it costs them a slower 0-100 kph. Tesla uses another trick to get better acceleration to 100 kph. They have two motors and one is geared for high efficiency at US highway cruising speeds (so ca 120 kph). In general electric motors have a very wide band of excellent efficiency and an even wider band of great efficiency and they are orders of magnitude more efficient than ICE in any part of their operational torgue/speed range.
magicalhippo 7y ago
Electric motors full torque regardless of RPM, unlike an ICE which has the usable torque in a limited RPM range.
- blattimwind 7y ago
  We have many gears for better efficiency with ICE, because every ICE has very narrow areas of RPM×torque that give you acceptable efficiency (typically those with high mean effective pressure). You could totally get away with three gears and still get to 150 km/h, it's just that it will be a lot less efficient. Electric motors don't have this particular problem, and they don't need a start gear that is a lot shorter than the other gears (1st to 2nd is usually around a factor two, while from 2nd up to the next higher gear the ratio will change by perhaps 30 % or so) because they can deliver nominal torque at low speeds or from zero speed (so they don't need a clutch, either). An ICE can't do that. Here are the transmission ratios of a random six speed transmission: 1st 2nd 3rd 4th 5th 6th R 4.2 2.5 1.7 1.3 1 0.8 3.8
  - hwillis 7y ago
    > every ICE has very narrow areas of RPM×torque that give you acceptable efficiency (typically those with high mean effective pressure). You could totally get away with three gears and still get to 150 km/h, it's just that it will be a lot less efficient. It isn't that narrow[2]. Engines with fewer gears aren't particularly less efficient, they're just MUCH slower. Look at a map of gears[2]: the top gears are in the efficient range, but the lower gears are only there to allow you to rev the engine high while accelerating. In the ratios you gave, you could cut out 1, 3, 4 and only use gears 2, 5 and 6 and be able to get around fine- you start in second and then shift up as soon as you're rolling. You'd have a much more efficient car but you'd be incredibly slow. [1]: https://qph.fs.quoracdn.net/main-qimg-0c6c45106b28601fc1aef4172c08faf1.webp https://qph.fs.quoracdn.net/main-qimg-0c6c45106b28601fc1aef4... [2]: http://www.posterus.sk/wp-content/uploads/p12975_02_obr02.png http://www.posterus.sk/wp-content/uploads/p12975_02_obr02.pn...