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- Hacker News
- I recently bought a hybrid, and had been trying to wrap my brain around how it had an Atkinson engine in it. Was imagining a solenoid-driven crankshaft linkage or similar. Loved learning from this video that the secret is in valve timing and not fancy linkages.
But. The other points made felt muddled or even contradictory. I either didn't follow the TC guy's explanation closely enough, or the script could have used another pass.
by chancitag - I'm assuming that right now all valves as computer controlled so why we cannot have best of both worlds? cannot we dynamically switch between Otto and Atkinson cycles by just changing valve profiles?
computer could use Otto cycle in case more power is needed in rare situations
by Szpadel - Watching the graphs during the driving segment helped me more than his explanation, but maybe I'm visual about it? It's interesting to see when the battery is being used.
I've seen some modern hybrids just have a visualizer for this on the dash to encourage you to coast more and things, which seems about as helpful in understanding it too.
by nemomarx - I have a conventional (not plug-in) hybrid Toyota Corolla as otherwise I'd have to pay loads to drive it in the city.
It does get crazy mileage and drives well so I can't complain. They are more expensive than standard cars though and you can't leave it in neutral which is a problem in some car washes.
- Can you power off and leave in neutral?by giarc
- Why do you need to put it in neutral in a car wash? Does it push the car forwards?
You can put the Toyotas in neutral, but you need to lift a special hatch and manually unlock the shifter. You need to do that if you're being towed. It's all in the manual, of course. I saw the hatch immediately. It's crazy to me that other geeks haven't checked every knob and hatch in their car or at least skimmed the manual.
- 2021 Corolla hatchback owner, I didn't know anything about the neutral thing until I was given a courtesy car by the dealership (CH-R: big car, tiny boot) and the lady told me twice never to put in neutralby walthamstow
- I don't get it. I put my Toyota hybrid in neutral while going through a car wash all the time.
I just googled this. I had no idea this was a thing some people worry about. I guess it's a problem if the hybrid battery runs out while the car is in neutral, but there's a meter right there to tell you how much charge it's got if you're really worried about it.
by justin66 - The CEO of Toyota Research Institute, Gill Pratt, had some good (albeit self-serving) points about the benefits of hybrids and PEVs to complement EVS a few years back that I bookmarked and keep coming back to:
https://web.archive.org/web/20210727090309/https://medium.co...
https://web.archive.org/web/20210825054702/https://medium.co...
> Maximizing the benefit of every battery cell produced requires that we distribute them smartly.
> This means putting them into a greater number of “right sized” electrified vehicles, including HEVs and PHEVs, instead of placing them all into a fewer number of long-range BEVs, like my model X. This is particularly important because presently it is difficult to recycle the kinds of batteries used in BEVs. If we are to achieve carbon neutrality, we must pay attention to all parts of the “3R” process — Reduce, Reuse, and Recycle.
> For example, we hardly ever put gas into our RAV4 Prime PHEV, which has a battery ⅙ as large as our Model X BEV. For the same investment in batteries as our single Model X, five other RAV4 Prime customers could reduce their carbon footprint too.
by krosaen - I'm not sure about this, because a smaller battery pack with fewer modules needs to work much harder.
PHEV batteries are discharged at higher rate (C) while a BEV can spread the load across many more modules. EV range of PHEV is so small that the battery gets fully cycled daily, while a BEV with similar commute distances and charging can easily keep batteries at a more comfortable state of charge.
The recycling thing doesn't make sense to me. For getting raw materials back the difficulty is the same (get the cells out and grind them), and having more cells per pack should amortize labor cost better.
BEV batteries aren't recycled at scale yet, because there aren't many to recycle. They're easier to reuse for grid storage, since BEV packs already have many modules hooked up to a single BMS.
So this sounds more like Toyota is just supply constrained on batteries.
by pornel - I saw some parts of this video, so I'm not sure it was mentioned, but the key parameter that is optimized at all times in a hybrid is brake specific fuel consumption:
https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio...
This is possible (and done) in any automatic, but in hybrids it was taken to the extreme, with electric motors covering for situations when either the RPM or torque are not where desired.
In fact, my experience is that during highway driving it's actually slightly off the optimal point, charging the battery in the process. I speculate that it's so that the surplus power can be released immediately by just making the electric motor stop acting as a generator and go into, well, motor mode.
by Tade0 - Watched this when it came out. I felt like it had that typical Technology Connections problem where it will take one under explored point along a Pareto frontier and conflate it for the global optimal design.
At least that was my experience with the toaster, microwave, and dishwasher detergent episodes.
While Hybrid System II is very clever and non-intuitive coming from an ICE or EV frame of reference there are reasons even Toyota hasn’t placed all their chips on this bet. In fact as Japan’s largest manufacturer they want to have a bet on every point of Pareto frontier which is why Toyota makes cars with their own competing iForce hybrid design (I’m a big fan of the generator + torque assist), hydrogen cars, electrics, plug in hybrids, diesels, propane and yes gas.
Specifically Hybrid System II is best if you can 1) only have one car 2) don’t have a place to charge it 3) do lots of starts and stops driving around town.
by paulgerhardt - My whole draw to hybrids is low overall cost and longevity. Just two days ago I bought my son a 2007 Prius with 194k miles for $6k; and three weeks ago, a 2008 with 225k miles for my sister for $2.5k. Both should last another 200k if they don’t abuse them.
And if gas goes over $6 I’m buying one for myself, too. I sleep in my car twice a week for work, and being able to run the AC on hot Florida nights will be the cherry on top.
The 2007 is like new except it’s the original battery, so son and I will swap the modules inside the battery pack in a few weeks for some refurbished modules with a warranty. Aside from the battery, the ABS pump is fragile but it is a DIY replacement if you have the time and patience.
Other than that, they just go and go and go, saving money mile after mile.
by cbdevidal - My 2010 Prius has out of the blue started burning oil last year, like it's going out of style.
It's a common problem with them. But otherwise, it's a very reliable car.
by vkou - For anyone who is concerned that this only applies to Toyota drivetrains (which was true for quite some time), Toyota made nearly all of their HEV patents (24,000 of them) completely royalty-free in 2019 [0].
At this point, I assume the only thing stopping manufacturers is their pre-existing investment in other technology.
[0] https://global.toyota/en/newsroom/corporate/27512455.html
- From what I know (granted I’d rather have a bev, but alas) this also applies to the Honda hybrid system, I’m sure there are others.
- Ford Kuga (EU) / Escape (US) is built from those patents. It’s basically a copy of Toyota’s hybrid system. And it’s actually quite great, until it catches on fire.by gregolo
- The toyota hybrid transmission is genuinely brilliant. Probably one of the most important and broadly overlooked innovations in automobile technology this century.by yabones
- So this is specifically about Toyota's hybrid engines (which is very different from e.g. Honda's engine, not to mention plug-in hybrids or "mild hybrids"). The explanation of the mechanics starts around the 36 minute mark.
I always found most explanations of Toyota's Power Split Device too abstract, until I found this page where you can play with the sliders to see how the power is actually split between the ICE and the MG1/MG2 electric generators: https://eahart.com/prius/psd/
by em500 - Note that Ford's plugin hybrids (using the same 2.5L engine as the full hybrids) also use the same technology (due to them having a cooperation and patent sharing agreement with Toyota) though they do differ a tiny bit due to the engine.
The tool is interesting though the Ford system can run independently on MG2/MG1 alone up to about 130kph (~80mph) depending on requested torque and load.
Only thing Ford screwed up is the battery (or Samsung since this time it's the cells).
by consp - The Prius model is basically how the new Honda hybrid power train works. (I'm gearing up to buy a new Civic once my insurance gets me my payout.) It has a two motor system (traction and generator) coupled to an Atkinson cycle engine with a planetary gearbox.
However, it's a 2L engine and the whole thing puts down 200hp, netting acceleration that beats a Civic SI and ~50 miles per gallon.
They first trialed it in Japan and Europe as the Civic EHEV a few years ago, and as of 2025 it has replaced the Sport and Sport Touring trims' former turbocharged 1.5L power train.
by redwall_hp - Fun story: I used to own a Prius, and it turns out they expose the speeds and torque values of MG1, MG2, and the engine independently on the OBDII port.
What this means it that you can set up an app like Torque[0] and add widgets that show you how fast each of the motors are spinning, live, and watch what happens when e.g. the engine starts: MG1 and MG2 both torque the engine forward, MG2 just enough to stop the car from attempting to roll backward in response to MG1's torque through the planetary gearset, and then MG1 spins up with the engine and then stops torquing it once the engine reaches idle.
Battery charging while idling is similar: MG1 turns itself into a generator, fighting the engine and generating electricity in the process. The throttle opens considerably, as if you'd pressed the accelerator halfway to the floor, but MG1 and the engine work together to keep the engine's RPM around ~1,200 so you'd never know it - it's as if you're driving up a really steep hill that stops you from accelerating even though you have the gas pressed halfway down. And then MG2 torques backward to stop the car from rolling forward any more than the Prius's normal "simulate a normal gas car's tendency to roll forward when the user lets their foot off the brake" would have it do.
It was fascinating to watch, and I kind of regret not building an app similar to the parent comment's link that showed what my car was doing in real time with the gears drawn out like that.
by javawizard - The title doesn't match the point of the video. What he is trying to show is the world would be a better place if we could establish that hybrids come in two flavors: Toyota and non-Toyota. There's really no better hybrid design. Unfortunately that means they aren't scrapped after decades, and Mongolia has become a dumping ground for them.[1] So it still is the best hybrid drivetrain in the world, but much like plastic or PFAS or some other very long term problems, the old battery cannot be cheaply scrapped. Toyota's new lithium models like the Sienna in the video have solved that, but now you're just half-assing a conventional EV until solid state systems are ready. By 2030 I expect the last Toyota hybrid to be announced.by 1970-01-01
- africa imports a lot of used Japanese vehicles as well - majority of vehicles on the road in RHD countries r ex-jap.
I think - that's still a good thing though - as long as the used ex-jap hybrid vehicle can still save fuel.
Chinese EVs n hybrids will probably make that less common as they're cheap enough.
by dzonga - Toyota’s system is good but I personally prefer series hybrids which have power delivery more like an EV.by kube-system
- > Since early 2025, the government has made battery exports illegal.
This seems like a self-imposed problem, especially in a country with no advanced battery recycling capacity.
by xattt - Ford's hybrids come from the Toyota tree, although they've diverged.
The new Honda hybrids are more like a generator + ev, which is also pretty interesting.
by klooney - I'm still not sure about the shoehorning of Mongolia into the discussion, but what these sorts of comments often fail to discuss is what the supply chain into new things looks like, because that can be equally destructive to the environment.
Generally, recyclers will pay for scrap that has minerals which can be recovered from the scrap.
Toyota Siennas use liquid Ni-MH batteries. It is likely these batteries as scrap aren't being exported, or, if they are, they are exported to foreign recyclers (in this case, many of those recyclers are actually less polluting that U.S. recyclers simply because they built their plants this century and new technology pollutes less). Also, Ni-MH can be replaced one cell at a time to produce "rebuilt" battery packs sold to economy customers, and "spent" cells, which simply fail performance tests, can often be used in other applications that are less demanding than hybrid vehicles. There is a cottage industry here in the U.S. doing these things. Ni-MH that is exported is usually completely dead cells going to a recycler (smelter), or at least that was my experience when I worked in that supply chain.
Li-ion using Cobalt is highly sought after by recyclers due to the expense of virgin Cobalt, so experiences a similar supply chain to Ni-MH. LMO chemistry batteries were the ones nobody wanted to touch, as they have no value, and they are all of the cheap replacement batteries people buy on Amazon for $15, and likely will be the chemistry people will use in their EU mandated replacement battery phones for some nightmare future mass pollution disasters.
by paulnpace - I always thought the problem with hybrids was the complexity of the drive train, but this video is challenging that notion. It argues that the hybrid pack (minus the battery, perhaps?) is more compact and simpler than a manual gearbox, even. It consists of two electric motors and a planetary gear set, which is seemingly simpler than clutch packs, gear sets and belts of regular transmissions, including CVTs.
Time codes 3:06, 37:07, 43:57, 43:36 (note on the eCVT naming), and 44:17.
by chem83 - There's a lot of memes about how dumb it is to have all of the ICE moving parts, but they're just memes. We know how to make engines and they are cheap to mass produce. The complexity argument is aesthetic.by jeffbee