| ▲ | theshrike79 2 days ago |
| This is the thing with good hybrids. The "gas pedal" becomes a "I want to go faster/slower" pedal, its position has zero impact on the RPM. As an anecdote: A security company I know only buys Toyota Hybrids for their guards just because of that. They have a habit of driving cars like they stole them and normal ICE cars break down from that kind of abuse. Hybrids won't let you abuse them, they pick the RPM and you deal with it. (They also swap the passenger seat for a plastic box because the guards threw heavy crap like safety boxes on it, wearing down the seat in months) |
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| ▲ | taeric 2 days ago | parent | next [-] |
| This is less a hybrid thing and more a new transmission thing. It, of course, isn't free. The efficiency of a CVT is a good 10-20 percent lower than previous transmissions. That said, currently, the win from keeping the engine at either the max power or the max efficiency speed is substantial. There are some really good videos out there going over how newer CVTs work. Looks like some people are working on ones that are teeth driven, to reduce the loss from being free belt driven. Borderline magical stuff, all told. (Obviously, not magic magic. But very very impressive designs.) |
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| ▲ | roelschroeven 2 days ago | parent | next [-] | | The post you commented on was talking about Toyota hybrids though, who don't use a CVT in the sense you're talking about. They use a series-parallel hybrid transmission which is sometimes called eCVT, but works completely different from a classic CVT. There are no pullies, belts, chains, none of that. What they do have is a couple of motor-generators and a differential to link the system up with the engine and the drive shaft. No friction losses like CTVs have. See https://prius.ecrostech.com/original/PriusFrames.htm, or look up "Hybrid Synergy Drive" on Wikipedia or Youtube or your favorite search engine. | | |
| ▲ | taeric 2 days ago | parent [-] | | Ah, totally fair in that this particular transmission is better than the belt driven CVT stuff. I had thought they were still a bit worse than other transmissions, but it looks like if they are, it is on the order of 1% or so. Is fascinating to watch these things work. |
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| ▲ | klaff 2 days ago | parent | prev [-] | | I have a Subaru (ten years old w/ >200k miles on it's chain-type CVT), and I thought the justification for it was that it was more efficient than previous systems. From a mechanical engineering standpoint, the Subaru CVT uses a fairly conventional lock-up torque converter at the input, but that gets locked as you pass something like 15-20 mph (once the lowest gear ratio is satisfactory w/o the torque converter function) and beyond that all shifting of the CVT is done w/ the torque converter locked. In addition, the clamping force of the sheaves is adjusted per the torque load of the transmission to minimize the frictional losses. Anyway I'm curious about data comparing efficiency of conventional and CVT automatics. | | |
| ▲ | taeric 2 days ago | parent [-] | | My understanding is that the overall system is more efficient. It is only the transmission that is less so. The videos online that look at various CVT systems is truly an amazing resource that I regret not having when I was younger. :D | | |
| ▲ | klaff 2 days ago | parent [-] | | If overall efficiency is what you see reflected in the EPA mileage numbers (or similar European tests), in what scenario would a lower efficiency transmission (lower Pout/Pin over some range of operating points?) lead to or even allow better overall efficiency? | | |
| ▲ | taeric 2 days ago | parent [-] | | I'm not sure I understand the question? You get the engine to hit its sweet spot and to hold it there. That gain outweighs the loss from the new transmission. This would be similar to hitting the optimal torque point. The idea there would be that you can get out of the acceleration phase faster, so that you can transition to a more efficient gear to maintain the speed for longer. The wikipedia looks to cover this well. One of the cites is specific on the efficiency of the CVT. I think I overstated how much higher the loss is, so maybe that is confusing things? I thought it was 10-20, but the cite on the page shows it solidly around 10. | | |
| ▲ | klaff 2 days ago | parent [-] | | Ah, thank you, I see the argument. I'm still a bit skeptical though when many non-CVT automatics are 6 or 8-speed models that there would be much "sweet spot" benefit left by being able to make relatively small changes in engine speed. Like many things probably depends on exactly what comparison is being made. | | |
| ▲ | taeric 2 days ago | parent [-] | | I mean, we are comparing 6-8 to effectively infinite? Question then comes into just how much is lost by being outside of the sweet spot for an engine. Which, I agree that I would not have thought it would be that big of a deal. Just going off modestly paying attention in my car, I see massive benefits keeping the car around 300 rpms lower. Interestingly, my car gets better gas mileage around the 40ish speeds than I do at full highway speeds. That somewhat surprises me. It is very dependent on not having a heavy foot, of course. | | |
| ▲ | klaff a day ago | parent | next [-] | | Best efficiency speed can be understood by considering impact of fixed losses like HVAC, lights, computing, which consume more energy the longer you drive (so the total energy for those would be minimized by going faster) and the aerodynamic losses in which force goes with speed squared, power w/ speed cubed, energy over a fixed distance back to squared because at higher speeds time is reduced (this component is theoretically minimized by going very slowly). In between is rolling resistance which requires a fixed energy per distance, so it doesn't care about speed. For EVs, the drivetrain efficiency is so high that it's variability with operating point doesn't affect this calculation much, and so the most efficient speed of an EV is around the speed at which the fixed losses equal the aero ones. This will vary greatly with environmental conditions since AC or heating load can be large in hot or cold conditions but at the right temperature will go to near zero. In ICE cars, the drivetrain efficiency is much lower and so the drivetrain efficiencies are a much more significant part of the optimization problem, but the basic physics of the aerodynamics are the same. The model I used to use in my head is that for an ICE, the most efficient operating point is probably around the lowest speed the car can operate in the highest gear, so maybe around 40 mph / 60 km/h? Obviously a rough heuristic though. | |
| ▲ | vel0city 2 days ago | parent | prev [-] | | Generally speaking your car will get better fuel economy at 40mph than it will at 60 or 70mph. Your car gets so much more wind resistance the faster you go. The main reason why city mileage is usually lower is because of all the stopping. | | |
| ▲ | taeric a day ago | parent [-] | | I think I just mentally had this idea shifted up about 10-15 mph. I'd expected 55 to be the sweet spot, for some reason. |
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| ▲ | vladvasiliu 2 days ago | parent | prev | next [-] |
| Do all Toyotas do that? I'm pretty sure that my dad's Corolla will rev the engine when I press the gas if the engine is already running. I'm also surprised for the first few minutes when I drive it how little "engine braking" it has (my habit is from riding a big motorbike). |
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| ▲ | trklausss 2 days ago | parent | next [-] | | Depends on the configuration. If they are equipped with a CVT+electric engine on the shaft, then that's the case: they rev to the sweet spot (which on gas engines is 4000-5000 rpm on acceleration? Depending on expected engine load I assume) and the speed is controlled by hydraulic force applied on the CVT. With other hybrids: depends on the generator they have installed, but it matches the consumption in amps by the engine in order to "go" if it is not directly coupled with the transmission, or they just downshift to accelerate with help of the electric engine. I am assuming a lot here: Toyotas (specially RAV4) mount CVTs among others, assuming pure electric generator by the ICE or coupled to it... So it depends a lot on specific configuration. | | |
| ▲ | taeric 2 days ago | parent [-] | | Even CVTs will rev the engine if you floor it, no? They typically allow for wanting to be in a few sweet spots. I prefer to keep it near the max efficiency speed. That said, my wife is a bit more aggressive and spends more time in the max power mark. It has a predictable change on the MPG reported by the vehicle. |
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| ▲ | MSFT_Edging 2 days ago | parent | prev | next [-] | | I know for a fact you can neutral-drop a prius. I know it's not exactly the same, but I was a teenager and curious, and you can rev them and shift into drive with some heel-toe finesse. Not sure if this works on the newer ones, this one was an early 2010s model. | | |
| ▲ | kstrauser 2 days ago | parent [-] | | Thank you for performing the experiment I didn’t even know I wanted to know the results of before now. | | |
| ▲ | MSFT_Edging 2 days ago | parent [-] | | I performed many experiments on that family prius and with complete honestly, my experiments weren't even in the top ten worst things that car survived. Trees, multiple motorcycles, final destination esque road debris, an accident that should have totalled it if not for an insurance mistake, leading to repairs worth more than the car. Three teenage drivers and two adult drivers with heavy feet. Not to mention many many hardware store runs hauling various sacks of yard materials, baby trees, lumber, etc. My favorite times were rallying on compacted un-plowed snow. The thin tires and light weight meant it absolutely shredded. It's my opinion that the Toyota Prius is one of the greatest vehicles ever built and they should be respected and feared. | | |
| ▲ | kstrauser 2 days ago | parent [-] | | That's an amazing testimony to its grit. I could stand to hear more of those stories over the appropriate beverage. |
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| ▲ | theshrike79 2 days ago | parent | prev | next [-] | | Dunno. My both Priuses did it and the company was specifically using the Yaris Hybrid. Both will rev on neutral, but when the gear selector is on Drive there is no link between the pedal and RPM. | | |
| ▲ | bonzini 2 days ago | parent [-] | | And on Brake it's even the opposite: above a certain speed, you press the accelerator and the RPM decreases to remove engine braking. |
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| ▲ | coryrc 2 days ago | parent | prev | next [-] | | They're programmed to rev in situations like that, because people are used to it. Under normal operation, RPM is decided by power needs. If you start accelerating on the freeway, for example, the engine might jump from 1100 RPM to 3000 RPM with just some pedal, while a manual transmission obviously changes very little. | |
| ▲ | adgjlsfhk1 2 days ago | parent | prev [-] | | it's possible that the engine rev is just the speakers. a lot of cars are doing fake engine sounds. | | |
| ▲ | vladvasiliu 2 days ago | parent [-] | | The dash has an RPM gauge which moves. Also, the noise is horrendous, not sure why they would have chosen that when they could have used a nicer-sounding tone. This is a tame small car, not something you'd buy to impress your friends. |
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| ▲ | RegnisGnaw 2 days ago | parent | prev [-] |
| The whole "pas pedal" becomes faster/slower (one pedal driving) is coming to an end. Its being banned as default in the world's largest EV market (and largest EV export country). |
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| ▲ | HPsquared 2 days ago | parent | next [-] | | Huh, that's interesting. Apparently China will be banning cars from having one-pedal driving as the default. Losing muscle memory of pressing the brake pedal. Makes sense, actually. | |
| ▲ | taeric 2 days ago | parent | prev | next [-] | | I'm curious what you mean? I'm fairly confident the post you are responding to was only talking about newer transmissions. Which, I can't imagine those are going away? | | |
| ▲ | RegnisGnaw 2 days ago | parent [-] | | The post is talking about most people drive with BEV , which is one pedal driving. My Tesla does one pedal driving my default. China has banned "one pedal driving" as a default. | | |
| ▲ | taeric 2 days ago | parent [-] | | I took it to be people that are far more aggressive with the gas pedal than they really need to be. That is, it was more the heavy foot than it was letting off to brake. Regardless, your point stands. People that have gotten used to not directly using brakes to indicate you are slowing down is a dangerous thing with how reliant we are on the standard indications that you are slowing. All the more so if you need to rapidly lose a ton of speed, where even regenerative brakes often fall back to friction. | | |
| ▲ | Sohcahtoa82 2 days ago | parent [-] | | > People that have gotten used to not directly using brakes to indicate you are slowing down is a dangerous thing with how reliant we are on the standard indications that you are slowing. Most, if not all, EVs will light up the brake lights when you're slowing via regen braking as long as the deceleration rate is above a certain threshold. I know my Tesla does. | | |
| ▲ | taeric 2 days ago | parent [-] | | This addresses the signalling to the people behind you problem. You still should have the foot nearer the brake so that you can fully stop, if you need to do so rapidly. Emergency brake systems probably help a lot with this problem, of course. Still seems wise to follow some of the older practices that we used to drill into people. |
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| ▲ | stretchwithme 2 days ago | parent | prev [-] | | So you just type in the speed you want and hit enter? |
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