2 ms·

First Geared CVT [video]

8 points by dsego 2y ago

Onavo 2y ago
How does this compare to Toyota's planetary gear CVT (used in all of their hybrids)?
- CRConrad 2y ago
  A quick Web search seems to indicate that's either a) not actually a CVT at all, or at best b) a planetary gear used as a power-splitting device to connect electric and ICE power sources to a conventional CVT. So this compares rather favourably, by actually being a geared CVT, which Toyota's "eCVT" apparently isn't at all. Sources: https://eahart.com/prius/psd/ https://eahart.com/prius/psd/ (From: https://news.ycombinator.com/item?id=39566938 https://news.ycombinator.com/item?id=39566938 ) https://www.youtube.com/watch?v=O61WihMRdjM https://www.youtube.com/watch?v=O61WihMRdjM (Long, 39 min!) Ooh, aah, now I get it (I think): Yes, the output RPM of the "eCVT" is indeed continuously variable. But that's just how all planetary gearboxes with two power inputs (as here, ICE and e-motor) work: The output RPM is a function of both the input RPMs, a (weighted) average of them if you will. So you can vary the output RPM while holding one of the input RPMs constant, simply by varying the other input RPM. Here Toyota presumably wants to keep the ICE working at the most economical RPM, while allowing the vehicle to move at varying speeds, which they achieve by varying the RPM of the electric motor. (In practice, Toyota uses two electric motors, but AFAICS the principle also applies to just one. TBH I'm not sure why they need two, but then I'm only halfway through that long video.) So yeah, the "eCVT" is kind of "a CVT", but only if you have two power sources simultaneously. It can't apply a continuously varying gear ratio from just one power input to a power output, which is what is usually meant by "power transmission". TL;DR: This can vary the gear ratio from a single power source to your wheels; Toyota's "eCVT" only works for hybrids (or other systems with two independent power sources).
  - CRConrad 2y ago
    More YouTube videos about the eCVT... 1) Better -- much simpler, and above all shorter -- video explanation of the Toyota system: https://www.youtube.com/watch?v=jofycaXByTc https://www.youtube.com/watch?v=jofycaXByTc . 2) Another, a little longer, but very pedagogical and beautifully animated explanation: https://www.youtube.com/watch?v=E_xCssR8qQI https://www.youtube.com/watch?v=E_xCssR8qQI . Eight years old, but apparently the "power split device" worked the same even then. Bonus -- short conversation in the comments, arriving at the same conclusion I did above: @TimpBizkit 3 weeks ago I thought the prius had a cvt 1 reply @aspecreviews 3 weeks ago It doesn't. The "CVT" is electrically simulated. Heh, yeah. 3) Titled something about "Launch Gear", but actually on the whole CVT thing (from a channel I semi-regularly watch): https://www.youtube.com/watch?v=HanImTejIVM https://www.youtube.com/watch?v=HanImTejIVM . 4) A good basic look-through of the various types of CVT and their history: https://www.youtube.com/watch?v=A3CA2oZ2ADM https://www.youtube.com/watch?v=A3CA2oZ2ADM . 5) Long and thorough explanation of the Prius powertrain: https://www.youtube.com/watch?v=PIYNAroYEk0 https://www.youtube.com/watch?v=PIYNAroYEk0 . Uses a cutaway of the actual transmission, so good for getting a more concrete picture than e.g. #2 above. But... Long. 6) Another one from WeberAuto like in my parent comment, this time on the (apparently very similar) Honda system: https://www.youtube.com/watch?v=QLUIExAnNcE https://www.youtube.com/watch?v=QLUIExAnNcE . So likely to be about as good as the previous one, but... 25 minutes more of this? Naah, I've had enough. There were also some from Scotty Kilmer et al, but... The less said, the better. The ones I'd most recommend are #4 for general CVT stuff and #2 for the Prius e-CVT's operating principle specifically. Well well, all in all that was quite the rabbit hole.

8 points by dsego 2y ago

Onavo 2y ago

How does this compare to Toyota's planetary gear CVT (used in all of their hybrids)?

CRConrad 2y ago
A quick Web search seems to indicate that's either a) not actually a CVT at all, or at best b) a planetary gear used as a power-splitting device to connect electric and ICE power sources to a conventional CVT. So this compares rather favourably, by actually being a geared CVT, which Toyota's "eCVT" apparently isn't at all. Sources: https://eahart.com/prius/psd/ https://eahart.com/prius/psd/ (From: https://news.ycombinator.com/item?id=39566938 https://news.ycombinator.com/item?id=39566938 ) https://www.youtube.com/watch?v=O61WihMRdjM https://www.youtube.com/watch?v=O61WihMRdjM (Long, 39 min!) Ooh, aah, now I get it (I think): Yes, the output RPM of the "eCVT" is indeed continuously variable. But that's just how all planetary gearboxes with two power inputs (as here, ICE and e-motor) work: The output RPM is a function of both the input RPMs, a (weighted) average of them if you will. So you can vary the output RPM while holding one of the input RPMs constant, simply by varying the other input RPM. Here Toyota presumably wants to keep the ICE working at the most economical RPM, while allowing the vehicle to move at varying speeds, which they achieve by varying the RPM of the electric motor. (In practice, Toyota uses two electric motors, but AFAICS the principle also applies to just one. TBH I'm not sure why they need two, but then I'm only halfway through that long video.) So yeah, the "eCVT" is kind of "a CVT", but only if you have two power sources simultaneously. It can't apply a continuously varying gear ratio from just one power input to a power output, which is what is usually meant by "power transmission". TL;DR: This can vary the gear ratio from a single power source to your wheels; Toyota's "eCVT" only works for hybrids (or other systems with two independent power sources).
- CRConrad 2y ago
  More YouTube videos about the eCVT... 1) Better -- much simpler, and above all shorter -- video explanation of the Toyota system: https://www.youtube.com/watch?v=jofycaXByTc https://www.youtube.com/watch?v=jofycaXByTc . 2) Another, a little longer, but very pedagogical and beautifully animated explanation: https://www.youtube.com/watch?v=E_xCssR8qQI https://www.youtube.com/watch?v=E_xCssR8qQI . Eight years old, but apparently the "power split device" worked the same even then. Bonus -- short conversation in the comments, arriving at the same conclusion I did above: @TimpBizkit 3 weeks ago I thought the prius had a cvt 1 reply @aspecreviews 3 weeks ago It doesn't. The "CVT" is electrically simulated. Heh, yeah. 3) Titled something about "Launch Gear", but actually on the whole CVT thing (from a channel I semi-regularly watch): https://www.youtube.com/watch?v=HanImTejIVM https://www.youtube.com/watch?v=HanImTejIVM . 4) A good basic look-through of the various types of CVT and their history: https://www.youtube.com/watch?v=A3CA2oZ2ADM https://www.youtube.com/watch?v=A3CA2oZ2ADM . 5) Long and thorough explanation of the Prius powertrain: https://www.youtube.com/watch?v=PIYNAroYEk0 https://www.youtube.com/watch?v=PIYNAroYEk0 . Uses a cutaway of the actual transmission, so good for getting a more concrete picture than e.g. #2 above. But... Long. 6) Another one from WeberAuto like in my parent comment, this time on the (apparently very similar) Honda system: https://www.youtube.com/watch?v=QLUIExAnNcE https://www.youtube.com/watch?v=QLUIExAnNcE . So likely to be about as good as the previous one, but... 25 minutes more of this? Naah, I've had enough. There were also some from Scotty Kilmer et al, but... The less said, the better. The ones I'd most recommend are #4 for general CVT stuff and #2 for the Prius e-CVT's operating principle specifically. Well well, all in all that was quite the rabbit hole.