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> but an appropriate gear ratio should handle that. See Prius's "Powersplit Device". I'd describe the Powersplit device to be a combination of generator/alter

> but an appropriate gear ratio should handle that. See Prius's "Powersplit Device". I'd describe the Powersplit device to be a combination of generator/alternator, starter/electric motor, reversed-differential (2x power inputs -> 1x driveshaft), and effective gear-ratio. All in one planetary gearset. EV motor2 determines the speed of the car. The ICE motor can spin at any speed that the computer determines to be useful. If EV Motor2 is 0-rpm, then the ICE is 100% in generator mode (2000rpm but the car isn't moving: all the energy goes to charging the battery). If the EV motor is at 10mph but ICE is off (0-rpm), then its 100% electric drive mode. And any combination in-between is possible. EV Motor1 (a smaller, weaker motor) controls the 3rd set of gears (I think the planet gears?? I forget), which determines how ICE relates to EV (changes the effective gear-ratio) https://eahart.com/prius/psd/ https://eahart.com/prius/psd/ --------- So yeah, the PSD allows the ICE to always function at the appropriate speed (which is either 0rpm or ~2500rpm for efficiency). While the combination of EV-motor1 (changes effective gear ratio of ICE) and EV-motor2 (hard-wired to the final speed) handle the different speeds the user wants in practice. All in like, 15 gears or so. https://www.youtube.com/watch?v=jofycaXByTc https://www.youtube.com/watch?v=jofycaXByTc --------- I do think that the Prius (and Prius Prime) have surpassed the Volt's design, and the proof is in the pudding. Prius Prime has 52mpg, a figure far more efficient than the Volt ever had. Prius Prime also has 220 horses today for a 0-to-60 time of 6.6 seconds. So today's Prius Prime is a lot faster than the Volt too. Volt was good when it came out, but technology has gotten better since then. Toyota has seemingly perfected this "power split device", and its beginning to lead into exceptional acceleration and good driving feel (as opposed to being 100% economy focused like before). Volt had better feel than the 2010-era Prius, but 2024-Prius is a totally different car. I think all Volt fans are in "but what if GM didn't kill the Volt and kept investing in the technology?". And... yeah... that's a fun what-if. But... GM killed the Volt. It sucks, because it seemed like great tech. Apparently GM has kept the drivetrain technology ("Ultium") and has continued to provide R&D, but Toyota's recent advancements are jawdroppingly good.

rootusrootus 3y ago
The Volt was a great idea, but I couldn't make it work for me. I need a four door car which regularly holds four people, and the Volt (especially the newer one, which was when I was shopping) has a low roofline. Only time I've hit my head harder on a car roof was when I tried to sit in a new Supra. So I ended up finding something where the physics of getting in and out were more agreeable. Still a sedan, just with fewer headaches. I wish they had offered that same powertrain design in something other than a Cruze.
akira2501 3y ago
> All in one planetary gearset. In the first version. In later versions they added a second separate gear set. Then even later they merged the two gear sets back into one but with two separate planetary arrangements. I'm not a particular fan of EVs in general, but I do very much like the Prius and the careful engineering that went into this drive train. This video[0] does a great job of explaining the overall system in the context of an operating vehicle. [0]: https://www.youtube.com/watch?v=PIYNAroYEk0 https://www.youtube.com/watch?v=PIYNAroYEk0
labcomputer 3y ago
> I do think that the Prius (and Prius Prime) have surpassed the Volt's design, and the proof is in the pudding. Prius Prime has 52mpg, a figure far more efficient than the Volt ever had. This is partly because the Prius is optimized as a hybrid-first design, while the Volt is optimized as a BEV-first design. The difference is in the gear ratios of the planetary CVTs: Prius is optimized to minimize the amount of energy transmitted electrically, which maximizes overall efficiency. However, that design is sub-optimal for a car that you want to act like an EV. As your link shows, the Prius must have the ICE spinning at speeds greater than 42 mph. Not a problem for a hybrid, but that doesn't work for a "range-extender EV" like the Volt. Additionally, (before the current model year) Toyota's plug-in hybrids can't provide full acceleration in EV mode--they always kick in the ICE when you floor it. That's again a consequence of how the transmission is optimized for hybrid operation. By making compromises to the gasoline efficiency, GM was able to create a car which acts like a real EV most of the time: A 1st gen Volt will go at least 80 mph in EV mode, and won't turn on the ICE (come hell or high water) until the battery is below 5%. And, it will do that for an honest 35 miles of freeway driving. The second generation Volt uses GM's "2 mode" hybrid transmission, which closes some of the MPG gap by adding one fixed ratio (100% mechanical transmission) as well as high and low speed eCVT ratios (to minimize electrical power in those two speed ranges). https://www.gm-volt.com/threads/gen-2-volt-transmission-operating-modes-explained.337644/ https://www.gm-volt.com/threads/gen-2-volt-transmission-oper...
- dragontamer 3y ago
  > However, that design is sub-optimal for a car that you want to act like an EV. As your link shows, the Prius must have the ICE spinning at speeds greater than 42 mph. Not a problem for a hybrid, but that doesn't work for a "range-extender EV" like the Volt. Additionally, (before the current model year) Toyota's plug-in hybrids can't provide full acceleration in EV mode--they always kick in the ICE when you floor it. That's again a consequence of how the transmission is optimized for hybrid operation. True in 2007. But 17 years later, the Prius Prime 2024 has 100% EV mode even at highway speeds. Toyota has improved the design since that webpage was made in 2007. Despite this change, the Prius still achieves 57 mpg, even better than ever before. Prius Prime is a proper EV-only mode, albeit a touch underpowered but its EV mode now covers all possible driving conditions. ------ I believe the modern Prius 2024 has 17,000 RPM limits now, as well as tweaked gear ratios and far larger EV and ICE engines. Despite the larger 220hp aggregate engine, the Prius remains absurdly efficient. Both in EV mode and in ICE mode. This is why I was saying that the Volt has wasted it's opportunity. GM was ahead in many respects 10 years ago, but Toyota has caught up. The GM advantage has been squandered. > By making compromises to the gasoline efficiency, GM was able to create a car which acts like a real EV most of the time: A 1st gen Volt will go at least 80 mph in EV mode, and won't turn on the ICE (come hell or high water) until the battery is below 5%. And, it will do that for an honest 35 miles of freeway driving. Prius Prime added a button to enter EV-only mode in this 5th generation design starting in 2023. It took Toyota too long to add this feature, but now that it's here the 5th generation Prius is a far better choice. Especially because Prius still has it's trademarked 50+ MPG and 130+MPGe ratings. Top of the line efficiency. It's somewhat frustrating to see Toyota catch up when GM was so far ahead for so long. Also because GM killed the Volt.

rootusrootus 3y ago

The Volt was a great idea, but I couldn't make it work for me. I need a four door car which regularly holds four people, and the Volt (especially the newer one, which was when I was shopping) has a low roofline. Only time I've hit my head harder on a car roof was when I tried to sit in a new Supra. So I ended up finding something where the physics of getting in and out were more agreeable. Still a sedan, just with fewer headaches. I wish they had offered that same powertrain design in something other than a Cruze.

akira2501 3y ago

> All in one planetary gearset. In the first version. In later versions they added a second separate gear set. Then even later they merged the two gear sets back into one but with two separate planetary arrangements. I'm not a particular fan of EVs in general, but I do very much like the Prius and the careful engineering that went into this drive train. This video[0] does a great job of explaining the overall system in the context of an operating vehicle. [0]: https://www.youtube.com/watch?v=PIYNAroYEk0 https://www.youtube.com/watch?v=PIYNAroYEk0

labcomputer 3y ago

> I do think that the Prius (and Prius Prime) have surpassed the Volt's design, and the proof is in the pudding. Prius Prime has 52mpg, a figure far more efficient than the Volt ever had. This is partly because the Prius is optimized as a hybrid-first design, while the Volt is optimized as a BEV-first design. The difference is in the gear ratios of the planetary CVTs: Prius is optimized to minimize the amount of energy transmitted electrically, which maximizes overall efficiency. However, that design is sub-optimal for a car that you want to act like an EV. As your link shows, the Prius must have the ICE spinning at speeds greater than 42 mph. Not a problem for a hybrid, but that doesn't work for a "range-extender EV" like the Volt. Additionally, (before the current model year) Toyota's plug-in hybrids can't provide full acceleration in EV mode--they always kick in the ICE when you floor it. That's again a consequence of how the transmission is optimized for hybrid operation. By making compromises to the gasoline efficiency, GM was able to create a car which acts like a real EV most of the time: A 1st gen Volt will go at least 80 mph in EV mode, and won't turn on the ICE (come hell or high water) until the battery is below 5%. And, it will do that for an honest 35 miles of freeway driving. The second generation Volt uses GM's "2 mode" hybrid transmission, which closes some of the MPG gap by adding one fixed ratio (100% mechanical transmission) as well as high and low speed eCVT ratios (to minimize electrical power in those two speed ranges). https://www.gm-volt.com/threads/gen-2-volt-transmission-operating-modes-explained.337644/ https://www.gm-volt.com/threads/gen-2-volt-transmission-oper...

dragontamer 3y ago
> However, that design is sub-optimal for a car that you want to act like an EV. As your link shows, the Prius must have the ICE spinning at speeds greater than 42 mph. Not a problem for a hybrid, but that doesn't work for a "range-extender EV" like the Volt. Additionally, (before the current model year) Toyota's plug-in hybrids can't provide full acceleration in EV mode--they always kick in the ICE when you floor it. That's again a consequence of how the transmission is optimized for hybrid operation. True in 2007. But 17 years later, the Prius Prime 2024 has 100% EV mode even at highway speeds. Toyota has improved the design since that webpage was made in 2007. Despite this change, the Prius still achieves 57 mpg, even better than ever before. Prius Prime is a proper EV-only mode, albeit a touch underpowered but its EV mode now covers all possible driving conditions. ------ I believe the modern Prius 2024 has 17,000 RPM limits now, as well as tweaked gear ratios and far larger EV and ICE engines. Despite the larger 220hp aggregate engine, the Prius remains absurdly efficient. Both in EV mode and in ICE mode. This is why I was saying that the Volt has wasted it's opportunity. GM was ahead in many respects 10 years ago, but Toyota has caught up. The GM advantage has been squandered. > By making compromises to the gasoline efficiency, GM was able to create a car which acts like a real EV most of the time: A 1st gen Volt will go at least 80 mph in EV mode, and won't turn on the ICE (come hell or high water) until the battery is below 5%. And, it will do that for an honest 35 miles of freeway driving. Prius Prime added a button to enter EV-only mode in this 5th generation design starting in 2023. It took Toyota too long to add this feature, but now that it's here the 5th generation Prius is a far better choice. Especially because Prius still has it's trademarked 50+ MPG and 130+MPGe ratings. Top of the line efficiency. It's somewhat frustrating to see Toyota catch up when GM was so far ahead for so long. Also because GM killed the Volt.