[HN Gopher] Mazda's rotary engine in the age of the electric car
___________________________________________________________________
Mazda's rotary engine in the age of the electric car
Author : gascoigne
Score : 67 points
Date : 2024-03-28 12:22 UTC (1 days ago)
(HTM) web link (www.nippon.com)
(TXT) w3m dump (www.nippon.com)
| 486sx33 wrote:
| Does it produce more low end torque verses a traditional gasoline
| combustion engine? If not then why is it better suited for
| electrical generation? Is it more efficient with less load?
|
| The article mostly makes it sound like Mazda just loves the
| wankle and wants to find any possibly way to bring it back - even
| though it has "high" emissions... so coupling it with a hybrid
| electric motor makes it happen..
|
| That can't be the whole story?
| jpgvm wrote:
| Wankels can be made extremely compact so that might have
| something to do with it, i.e it has both very high power to
| weight and power to volume specs. I honestly don't know if that
| is the reason though, perhaps someone more knowledgeable of the
| specifics of range extenders might chime in but I imagine that
| is an important factor.
| sethhochberg wrote:
| They have a pretty narrow power band (produce efficient max
| power at a small range of RPMs) which always somewhat limited
| their use for normal ICE cars, but is a pretty workable
| constraint for an electrical generator.
|
| So you have compact size, good power to weight ratio, and
| power limitations that don't really matter for range extender
| purposes. Lots of potential.
|
| I can't find the article right now, but I'd swear I remember
| discussion here a handful of months ago about a startup
| marketing a similar EV range extender engine design.
| HPsquared wrote:
| They have low compression though, which really hurts the
| thermal efficiency.
| coryrc wrote:
| Then you may as well use a gas turbine, which is pretty
| much better in every way that matters for generating
| purposes.
| iamthirsty wrote:
| Except extremely complex and usually hard to repair and
| inefficiently sized for a consumer car.
| userbinator wrote:
| Actually far simpler than a piston engine; the fuel
| consumption and high production cost was what made them
| become extinct.
|
| https://en.wikipedia.org/wiki/Chrysler_Turbine_Car
| kyleee wrote:
| Of course Jay Leno has one; not sure if he's featured it
| on his youtube channel (I don't recall seeing it).
| Awesome
| 01HNNWZ0MV43FF wrote:
| Yep I've seen it on his YouTube. The "EcoJet"
| https://www.youtube.com/watch?v=10q9_pB6unU
|
| He said that they had to put really big brakes on it. I
| guess for some reason you can't just have a clutch.
| Personally if I was going for eco I'd want something more
| clever than "bigger brakes" but maybe building something
| like a Hybrid Synergy Drive is harder than building a
| turbine.
| WalterBright wrote:
| Gas turbine cars have been built, but they tend to set
| anyone on fire if they walk behind the car.
|
| https://bandimere.com/previewing-the-brakes-plus-jet-car-
| nat...
| coryrc wrote:
| You're probably being silly, but for anyone else, gas
| turbines as used for generators don't have jet exhausts
| on them, i.e. https://www.youtube.com/watch?v=yR5oVn-Fvvg
| philwelch wrote:
| So what do they do with the exhaust?
| elevatedastalt wrote:
| The reason jet engines have that sort of exhaust is
| because the primary purpose of the gas turbine there is
| to dump all the excess energy into the exhaust to make it
| go fast (so that the plane can be pushed ahead by the
| reaction force). They produce very little power, just
| enough to power the Auxiliary Power Unit (that manages
| the plane electronics, air-conditioning etc.).
|
| If you want to use a gas turbine for producing power, you
| will set it up such that most of the energy goes into the
| work generated, rather than the exhaust, so it would be a
| cooler, slower exhaust, similar to an IC-engine.
| 01HNNWZ0MV43FF wrote:
| Depending on the plane and engine. Big jetliners have
| high-bypass turbines where they do intentionally produce
| a lot of torque, to spin a large compressor fan, but most
| of the fan air does not go through the combustion step,
| it's just used to react off of.
| WalterBright wrote:
| It's ironic how propeller airplanes evolved into jets for
| for thrust and back to propellers.
|
| (A ducted fan is still a propeller.)
| pfdietz wrote:
| We may go to unducted fans soon. The latest iteration of
| this concept has two sets of fans, one set of which
| doesn't rotate.
| philwelch wrote:
| Other people have already mentioned the distinction
| between turbojets (what you're describing) and turbofan
| engines, but I think there's another inaccuracy:
|
| > They produce very little power, just enough to power
| the Auxiliary Power Unit (that manages the plane
| electronics, air-conditioning etc.).
|
| The APU is a completely separate gas turbine that doesn't
| rely on the main engines. As a consequence, the APU on an
| airplane will also have its own exhaust.
|
| > If you want to use a gas turbine for producing power,
| you will set it up such that most of the energy goes into
| the work generated, rather than the exhaust, so it would
| be a cooler, slower exhaust, similar to an IC-engine.
|
| Yes, obviously. At the same time, I was under the
| impression that turboprops and turboshafts on airplanes
| and helicopters still produced enough jet exhaust to
| represent a safety hazard, and in those applications you
| would also expect that most of the energy would go into
| the work generated rather than the exhaust. So is it just
| that this residential generator is even more efficient
| than the main engine of a heavy-lift helicopter? Is it
| because it's a less powerful machine in the first place?
| I could continue to speculate about this but I don't
| actually know.
| mrighele wrote:
| Some models do, some others do not:
| https://www.youtube.com/watch?v=b2A5ijU3Ivs,
| https://www.youtube.com/watch?v=CdCudNSti_Q
| JALTU wrote:
| Oh! The Batmobile!
| fodkodrasz wrote:
| Except for consumption, waste heat generated, size.
| mrighele wrote:
| If all you need is power generation, use a nuclear
| reactor. Time to bring back the Ford Nucleon ! [1]
|
| Comes with daily free health checkup (in form of an
| X-Ray).
|
| [1] https://en.wikipedia.org/wiki/Ford_Nucleon
| xattt wrote:
| Aaahktually, the radiation given off the reactor would be
| too "hard" and useless in soft-tissue imaging.
|
| Maybe neutrino imaging?
| user_7832 wrote:
| Apparently they really don't scale well. I found this
| reddit post explaining it better:
|
| > Gas turbines scale extremely poorly. They rely on small
| clearance between the rotating blades and the housings
| for efficiency. The smaller the turbine, the greater the
| relative clearance and the more energy is lost. Gas
| turbines, at least with established technology, make very
| little sense below 300ish HP. As a real life comparison:
| A Robinson R44 piston helicopter and an R66 turbine
| Helicopter have almost identical design, dimensions, and
| weights. Power is around 250 / 300hp. The former burns
| between 50-60L of gas per hour at cruise, the latter
| around 90-110L of Jet fuel.
|
| 1 - https://old.reddit.com/r/cars/comments/s8vkv8/are_wan
| kel_eng...
| bob1029 wrote:
| 300 HP = ~220 kW
|
| I believe a Tesla can charge its battery pack at
| approximately this rate.
| avalys wrote:
| What's your point?
|
| There's no reason to have a generator that charges the
| pack in a hurry. It really only needs to cover the
| maximum sustained average draw - driving up an extended
| grade at high speed. That's a lot less than 300 hp - it's
| probably not more than 80 hp or so at most.
| Baeocystin wrote:
| I remember back in the 90's in auto shop we calculated
| that you'd only need 15-25hp continuous to essentially
| power all of a car's needs if you could smooth demand for
| power from the peaks over the length of the trip. It
| stuck with me as a surprisingly small number, but it
| mathed out, even including heating and AC. Cars are both
| larger and more aerodynamic nowadays; I wonder if the
| amount would still be the same?
| UniverseHacker wrote:
| Thank you, I've wondered for years why we didn't have
| tiny gas turbine engines...
| pfdietz wrote:
| There are companies that have tried, like Capstone
| (formerly Capstone Turbine, then Capstone Green Energy).
| Capstone declared chapter 11 bankruptcy last year (since
| emerged and continuing under new leadership.)
| alexose wrote:
| Cosworth appears to have developed a microturbine for
| this purpose. And it (maybe?) has found a home in Ariel's
| latest insane car:
| https://www.carscoops.com/2022/09/ariel-hipercar-is-
| an-1180-...
| cjbgkagh wrote:
| AFAIK I think there is some difficulty in getting
| turbines to scale down efficiently with a need of a
| recouperator to maintain a higher core temperature for
| better efficiency. The recouperator is additionally
| expensive on top of the already expensive turbine cost.
|
| Having a rotary with a turbo should be able to work
| better at a lower scale for a pretty cheap production
| cost.
| cranky908canuck wrote:
| Want to comment explicitly, though I upvoted a similar
| comment ... a gas turbine in a consumer car will be a
| maintainability nightmare (where do you find the
| technicians that can do anything with it?), at least in
| the current automotive ecosystem.
| eep_social wrote:
| Maybe you're thinking of the Edison kits? They seem to be
| putting a genset into the truck bed to do EV conversions:
| https://news.ycombinator.com/item?id=38893567
| seltzered_ wrote:
| > I'd swear I remember discussion here a handful of months
| ago about a startup marketing a similar EV range extender
| engine design.
|
| Possibly https://liquidpiston.com
|
| Prior discussions: https://hn.algolia.com/?dateRange=all&pa
| ge=0&prefix=true&que...
| speed_spread wrote:
| In a hybrid vehicle, the gas engine can be run mostly as a
| generator, which makes it possible to further optimize it for
| a very specific load. It's possible that such an
| updated+tuned Wankel could be a great fit for certain
| applications where space and weight are at a premium.
|
| They can simulate lots of it but to get real answers, they
| have to build the engine and see how it holds up.
|
| Also Mazda is a small-ish manufacturer at the Japanese scale.
| Since Wankels are part of their identity they could decide to
| build a car with it even though the downsides wouldn't make
| sense for a "rational" brand like Toyota. It can give them
| that creative freedom that help make desirable cars and keep
| Mazda relevant.
| tokai wrote:
| I bet wankle development is also excellent for internal
| education of their engineers.
| porphyra wrote:
| nit: it's spelt Wankel not Wankle.
|
| Also for those who don't know, it's pronounced /'vaNGkl/ or
| /'vaNGk@l/ in the International Phonetic Alphabet (IPA). In
| German, "W" is pronounced as "V" in English, and the "e" in
| the syllable "kel" is reduced to a schwa ([@]) sound, common
| in many German pronunciations of unstressed vowels.
| jpgvm wrote:
| Sadly enough I did know that but wrote it wrong anyway!
| Fixed, thanks. :)
| pengaru wrote:
| > Does it produce more low end torque verses a traditional
| gasoline combustion engine? If not then why is it better suited
| for electrical generation?
|
| What does low end torque have to do with electrical
| _generation_?
| jiveturkey wrote:
| It's not a direct connection.
|
| You do want efficient horsepower to drive a generator. More
| low end torque means the HP comes at lower RPM, which should
| mean less fuel consumption.
|
| Sibling says the achilles heel of the Wankel rotary is low
| end torque, but you don't take the direct output from the
| engine, it goes through gear reduction for final drive
| output. The real achilles heel is the awful emissions. It's
| more or less a 2 cycle engine from that POV.
|
| When driven at variable speeds it's hard to wrangle.
|
| The reason it's well suited for electrical generation is its
| mechanical simplicity, compactness, low weight, low NVH, and
| not least important, "rotary" brand value. I suppose that
| when run at constant RPM and constant or smoothly changing
| load, the emissions is easier to deal with.
| pengaru wrote:
| The side-port exhaust used in the rx-8 generation RE
| substantially improved the emissions situation, but the
| fuel efficiency is still trash by modern ICE standards.
|
| It's been awhile since I gave a damn about wankels (or ICEs
| in general), but ISTR there being a relatively low limit to
| achievable static compression ratio due to the fundamental
| geometry of the swept volume. Modern ICE engines are
| largely exploiting the combination of direct injection and
| the high compression ratios it enables to improve their
| thermal efficiency. Between the relatively low compression
| ratio and sub-optimal combustion chamber shape and the fact
| that it migrates around the housing with the power stroke,
| the wankel is pretty much doomed in a world that cares
| about efficiency.
|
| disclaimer: I've worked hard to discard all my gearhead
| knowledge, but went fairly deep down the rx-7 rabbithole in
| my 20s-30s. Take the above with a big grain of "I may be
| senile and overconfident in stale once-deep knowledge"
| salt.
| WillAdams wrote:
| Pretty much.
|
| One (potential?) advantage not mentioned in the article is
| lighter weight relative to a similar traditional engine.
| joking wrote:
| Would be good as a range extender motor. I think smaller
| battery cars with range extenders should be a better option
| than what we have now.
| thehappypm wrote:
| Oh my God, if Tesla sold a range extender gas generator
| that sat in the frunk, and could add an extra 150 miles..
| take my money.
| jsight wrote:
| Low end torque tends to be the rotary's Achilles heel. I think
| the claim being made is that efficiency is better at high,
| steady RPMs, but tbh, I've always found that claim a bit
| dubious. If you love the rotary engine, this does have some
| nice perks as the electric motor basically fixes the rotary
| engine's main weakness.
|
| Having said that, I'd have been much more excited about this
| 10-15 years ago.
| ianai wrote:
| A YTer said it allows the rotary engine to operate in its
| best circumstances. It's essentially a range extender while
| battery tech improves.
| lostlogin wrote:
| It fixes the terrible efficiency by having an entirely
| different power source?
|
| As others have pointed out, the article doesn't do a great
| job of explaining how the rotary helps.
| suprjami wrote:
| It really isn't. Go and drive a 13BT car. They make almost
| all their torque by 2500rpm and the curve is flat. They're
| more torquey than any 4 cylinder I've driven.
| skellera wrote:
| I don't understand why Mazda doesn't just make a drift-tuned
| electric car. You could do amazing stuff with software focused
| on that driving style.
|
| A true electric successor to the RX-7 would capture so much
| attention.
| HPsquared wrote:
| The unique sound is a key selling point for rotary
| enthusiasts. Kind of raspy, almost like a 2-stroke.
| mikestew wrote:
| _Kind of raspy, almost like a 2-stroke._
|
| That's not what the TV commercials from the 70s told me:
|
| "Piston engine goes 'boing, boing, boing, boing'"
|
| "But the Mazda goes 'hmmmmmmm'"
|
| (Oh, of course there's a YouTube video:
| https://www.youtube.com/watch?v=oHzeGEHWMjo)
| porphyra wrote:
| Sports cars, in general, are much loved but seldom bought.
| kjkjadksj wrote:
| You'd think its a different time now that the kids who grew
| up lusting over these cars now have money for one, enough
| money to create a new car market where even a pickup truck
| can be almost six figures optioned out
| porphyra wrote:
| Yeah but by the time you're able to afford one you will
| be married with kids and therefore prioritize
| practicality over drifting.
| Prcmaker wrote:
| I'm literally waiting for it, have been for quite a while.
| Small cars have numerous benefits over just being sporty.
| An electric, or even a hybrid 86/BRZ or miata would be
| great, but can't be compared to the mini or fiat, and while
| tesla might be fast, it's huge. Even with a price increase
| these could be more affordable than a lot of sports cars.
| The 86/BRZ has been a huge seller too.
| ggreer wrote:
| Several reasons.
|
| First, like most of the Japanese manufacturers, Mazda bet
| against electric vehicles. They focused R&D on improving
| engine efficiency and getting their engines to run on
| hydrogen. If Mazda wants to make electric vehicles now, they
| have to play catch-up, or license key technologies from other
| manufacturers.
|
| Second, batteries are heavy. For sedans and mid-size
| crossovers, this isn't much of a problem. EVs of that class
| are about the same weight as combustion vehicles. But for a
| lightweight sports car with decent range, batteries would be
| a big chunk of the total weight. Tesla's 85kWh battery weighs
| around 1,200lbs. If your desired weight is 2,500lbs, that
| only leaves 1,300lbs for the actual car. Yes you can save
| some weight by making the battery part of the structure, and
| you don't need an exhaust system, engine block, alternator,
| intake, etc, but it's still a tough set of constraints to
| work within.
|
| Why do customers want sports cars to be light? Well all else
| equal, a lighter vehicle will have better performance. But
| even when all else isn't equal, vehicle weight can
| drastically affect driving enjoyment. I have a 4,048lb Model
| 3 Performance and a 2,182lb Mazda Miata. In terms of specs,
| the Model 3 is better in every way. It can accelerate, brake,
| and turn better than the Miata. It even has more range than
| the Miata. But the Model 3 feels like it's using brute force
| to beat inertia into submission. (Don't get me wrong, that
| can be fun.) The Miata is the opposite. Its light weight
| means that there's very little inertia to overcome, and
| something about that is extremely satisfying. It's almost
| like having a street legal go-kart. Until battery technology
| improves, an electric version just won't have the same
| appeal.
| lostlogin wrote:
| Going with this theme, the idea of a battery car with
| longer range is appealing to me. However a smaller battery
| but quick charging would mostly remove the need.
|
| I'm not sure I want to drive around with a capacitor in the
| boot, but a huge battery isn't ideal either.
| gambiting wrote:
| That's the whole thing right - most people don't actually
| care about having 600 miles of range, they care about
| being able to "refuel" quickly. My Mercedes AMG would
| only do like 200 miles on a tank of fuel and I don't ever
| recall having any kind of range anxiety with it, because
| you could gain all of it back within like 5 minutes and
| keep going.
| user_7832 wrote:
| It would be theoretically possible to have a small battery
| ("just a 60 mile/100km range, or even smaller) combined
| with a generator, but I don't know if markets would
| appreciate that.
| 01HNNWZ0MV43FF wrote:
| This company Toyota started a pretty popular line of
| hybrid gas-electric cars, maybe 20 years ago, called
| Priuses. I think they sell pretty well. I see a lot of
| them running as taxis. The new ones can plug in and drive
| a few miles on the highway on pure electric before
| starting the gas engine.
| gambiting wrote:
| Priuses do use the ICE to drive the wheels though, no?
| pfdietz wrote:
| Yes, they are parallel hybrids.
| dragonwriter wrote:
| Its called a series hybrid, there have been a small
| number of plug-in hybrids that used that design, they
| weren't successful in the US and are no longer in the US
| market. But that may not be anything particular about the
| technology; I wouldn't generalize from such a small set.
| narag wrote:
| It seems Mazda is going ahead with an electric Miata, they
| just don't know how electric it will be:
|
| https://www.motortrend.com/news/2026-mazda-mx-5-miata-
| electr...
| eggsboenk wrote:
| The McMurtry Speirling is claimed to be under 1000kg. A
| lightweight electric car may not be an oxymoron after all.
| Just some concessions to make.
| ggreer wrote:
| The McMurtry Speirling is not street legal and it costs
| $1 million.
| fragmede wrote:
| And what a car it is!
| gambiting wrote:
| Our VW e-Up is just below 1200kg and has 150 miles range
| from a 36kWh battery, fits two of us, baby seat, and
| Costco shopping. You can absolutely have a lightweight
| electric car, just be realistic about what you're
| getting.
| discreteevent wrote:
| "Adding power makes you faster on the straights.
| Subtracting weight makes you faster everywhere." - Colin
| Chapman (Lotus)
| ksec wrote:
| >A true electric successor to the RX-7 would capture so much
| attention.
|
| Not entirely sure that would be the case even with a Red Sun
| label on it.
| busterarm wrote:
| As someone who owns a white turbo fc, sans stickers, I
| would be interested.
| porphyra wrote:
| Low end torque is not that relevant to electrical generation,
| which typically involves the motor constantly running at a
| constant rpm. So, since low end torque is a weakness of the
| Wankel engine, that actually makes it more suitable for
| electrical generation than for driving directly.
| dragontamer wrote:
| > Does it produce more low end torque verses a traditional
| gasoline combustion engine? If not then why is it better suited
| for electrical generation? Is it more efficient with less load?
|
| You've got it backwards.
|
| The Prius's Atkinson engine makes low-end torque *worse*, and
| then relies upon the EV Motor to drive the car at low speeds
| (0mph to 10mph) before the ICE kicks back in.
|
| If ICE is operating, its at higher RPMs where the generator can
| still be useful (low RPMs like 500 are too low for the Atkinson
| engine to be effective in any way, the computer instead
| increases the RPM to maybe 2000, and uses all the power to
| drive a generator instead)
|
| ------------
|
| So you see, the name of the game is efficiency at all costs,
| with EV-motors assisting whatever compromise you built into the
| motor. In the case of Toyota, its absolutely undrivable crap
| for low-end torque ICE, but a powerful enough 60hp to 100hp
| electric-motor that can handle the low-speeds and stop-and-go
| traffic, smoothing out any problems.
|
| ------
|
| IE: The engineers build a highly compromised ICE engine (the
| Atkinson engine) that has a far narrower band of usable RPMs
| than a normal vehicle. Then they smooth out those problems with
| electric motors.
|
| It sounds like Mazda is doing the same trick here with their
| Rotary engine, but the Rotary engine doesn't have the crazy-
| good efficiency curves that the Toyota Atkinson engine has.
| Efficiency isn't the "only" name of the game however, but Mazda
| now needs to find out a good way to market this engine /
| highlight its strengths.
| 01HNNWZ0MV43FF wrote:
| It's not like the ICE doesn't do anything at low speeds, HSD
| uses the two motor-generators like a gearbox
| pfdietz wrote:
| Isn't it a Miller cycle engine, not Atkinson? Miller cycle
| exploits variable valve timing to make the compression stroke
| effectively shorter than the expansion stroke (but reduces
| the amount of air being compressed, reducing power); Atkinson
| has some funky extra joints in the rod or crankshaft, I
| think.
|
| Yes: https://en.wikipedia.org/wiki/Atkinson_cycle
|
| However, these modern Miller cycle engines are being called
| Atkinson or Atkinson-Miller cycle for some reason.
| brucethemoose2 wrote:
| Power/Weight is extremely high. A tiny wankel will do the job,
| and weight is everything on cars.
|
| It does prefer a narrow RPM band, which is fine.
|
| Reliability is the biggest concern TBH, but maybe that's not a
| _huge_ bummer if its more of a backup /assistant engine.
| suprjami wrote:
| Reliability for rotaries hasn't been a concern for a long
| time. Modern apex seals work well and last a reasonably long
| time. There is a need to stop parroting facts from the 1980s.
| pavlov wrote:
| It can be the whole story.
|
| Engineering organizations fall in love with superficial
| attributes of solutions that worked especially well for them in
| the past. When RIM/BlackBerry realized the iPhone was a serious
| threat, they built a touchscreen phone where the entire display
| produces a physical clicking effect because they were so
| convinced that what people really want from a smartphone is the
| click of a keyboard.
|
| Mazda is BlackBerry, and the rotary engine is their clicky
| keyboard.
| cpursley wrote:
| > Mazda is BlackBerry
|
| No, they're not. Go test drive a Miata. They make the most
| fun cars to come out of Japan. And also have one of the
| better design languages.
| ryukoposting wrote:
| It has nothing to do with sentimentality.
|
| Wankels have tremendous power-to-weight and power-to-size
| ratios. Their main problem is reliability. The generally
| accepted solution to improve rotary engine reliability (oil
| injection) results in poor emmissions. The wide, flat-ish
| combustion chamber doesn't help the emmissions problem, either.
|
| The Wankel is at its most efficient and its most reliable when
| operating at a constant RPM. Conveniently, the EV generator
| application demands a pretty flat RPM band. As a result, the
| engine doesn't need to lean as hard into those emmissions-
| increasing compromises.
|
| Thus, EVs allow the Wankel's benefits over a reciprocating-
| piston engine to be reaped without the same costs as before. In
| theory, at least. It remains to be seen if the benefits will
| outweigh the drawbacks. I'm glad they're at least going to give
| it a try.
| rootusrootus wrote:
| Almost feel bad for GM, the article did not mention the Volt when
| talking about series hybrids. But I guess it is a Japan-focused
| news source.
| jmspring wrote:
| The funning thing is, people I know who have a Volt love their
| cars. Haven't tried one myself. My family has a couple of paid
| of Toyota gas vehicles that are 8+ years old and will probably
| live longer than we will.
| joking wrote:
| Vehicles with range extenders are the exception, even if they
| seem a good option, they didn't gain market share.
| Tagbert wrote:
| I drive a 2017 Volt gen 2 and love it. I drive about 90+% of
| miles in EV mode and mostly use the gas engine for road
| trips. It is fun to drive and (other than a couple of common,
| and easily fixed issues) has been reliable. I do plan to
| replace it in the next year because it sits very low and has
| a very low roofline. My spouse is uncomfortable getting into
| it so we almost never drive it when together.
| nradov wrote:
| I don't understand why GM never put the Voltec drivetrain
| into a compact SUV. It would have sold much better than an
| odd looking hatchback with little interior space.
| illegalsmile wrote:
| My friend has a few volts from 2013-2018 (that he loves) and
| I usually borrow one for trips to see family and friends
| 12-16 hours away rather than drive my truck. I think they're
| great vehicles. ~40mpg at 80-90mph on the highway is really
| good though it does take premium for that 40+ mpg and it has
| a smallish tank so you have to stop a little more often. Once
| you reach your destination all driving is done on electric
| and charges overnight on a regular outlet/level 1. Their
| maintenance is surprisingly low for what seems like a complex
| system.
|
| Crazy to me that Chevy has abandoned their PHEV platform
| considering others, like Toyota, are in such high demand.
| Speaking of which I spent a week with a Rav4 Prime and found
| that equally as impressive range-wise as a volt.
| tokai wrote:
| The point is the wankle engine. No sense in mentioning the
| Volt.
| rootusrootus wrote:
| They did mention a couple other series hybrids, however,
| neither of which has a Wankel.
| Projectiboga wrote:
| I was always impressed by this engine in my childhood, but it
| never really caught on. Here is a variation I've seen on the
| internet, i'm not sure how practible it would be.
| https://arstechnica.com/cars/2023/11/this-inside-out-design-...
| explorigin wrote:
| https://www.youtube.com/watch?v=X5UOqZn43gY It has longevity-
| issues due to an internal roller bearing on the main shaft.
| knodi123 wrote:
| wow, thanks. I didn't expect to watch the whole thing, but I
| did.
| fragmede wrote:
| Depending on how it's being used. Rotary engines are better
| in some ways when being run hard (ie as a track car) compared
| to more traditional layouts.
| Projectiboga wrote:
| Mazda and Toyota formed an alliance to share technologies to fill
| gaps they each had. I'm guessing this is fruit of that
| partnership.
| vpribish wrote:
| Where do read Toyota into this announcement?
| mattmaroon wrote:
| I have never understood why the Volt Series Hybrid idea never
| took off. It is more efficient to turn gasoline into electricity
| and then drive the car with that than to directly connect the
| engine to the wheels. Is it perhaps that the cost involved is
| just too much more than a plugin hybrid to make the small extra
| fuel savings worth it?
| HPsquared wrote:
| Surely the "generator -> charger -> battery -> inverter ->
| motor" chain is less efficient than a driveshaft. Perhaps the
| only benefit is the engine can run at an optimal speed, but an
| appropriate gear ratio should handle that.
| dragontamer wrote:
| > 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/
|
| ---------
|
| 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
|
| ---------
|
| 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 wrote:
| 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 wrote:
| > 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
| labcomputer wrote:
| > 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-
| oper...
| ch_sm wrote:
| > It is more efficient to turn gasoline into electricity and
| then drive the car with that than to directly connect the
| engine to the wheels
|
| I thought so too, but my research suggested that the efficiency
| is pretty much the same if not worse and power delivery is
| worse. Do you have some links? I'd like to be wrong on this
| one.
| idontwantthis wrote:
| I thought the idea is that the battery acts as a buffer and
| the engine is always either off or at constant rpms in its
| ideal power band.
| callalex wrote:
| You also have to keep in mind that the average consumer
| is...quite stupid, or more charitably quite sensitive.
| There are lots of cars on the market today with CVTs
| (continuously variable transmissions) that enable the motor
| to always be driven in the most optimal RPM. However in
| software, the engines are intentionally driven at less
| efficient rpm's so that the driver can feel steps and
| lurches as the car accelerates which is somehow more
| "correct" to the average car buyer.
| 01HNNWZ0MV43FF wrote:
| Priuses do a power split where the engine drives the wheels
| and the motor-generators act sort of like an electrical
| CVT. You would have to be out of the power band a lot to
| make a series hybrid more efficient than a parallel hybrid.
| The reason locomotives are series hybrids is just that
| mechanically switching that amount of power isn't
| practical. To my surprise, even off-highway mining trucks
| mostly use mechanical transmissions.
| themerone wrote:
| Aside from your suggestion violating the laws of physics,
| that's actually not how the Volt worked.
|
| The original concept for the volt was that the engine would
| only generated electricity, but in production models, the
| engine was connected to the drivetrain.
| Tagbert wrote:
| Almost - In production models the engine does act like a
| series hybrid generator under most circumstances. At high
| speeds, the engine was directly connected to the drive train
| as it is more efficient to do that. the transaxle of the
| Voltec system is a marvel of engineering. It supports a
| dynamic switching between series and parallel hybrid mode as
| well as using the two separate electric motors for either
| power delivery or can switch one to regen and can rapidly
| switch between those modes, too.
| rootusrootus wrote:
| That remains true for more recent "series hybrids" as well,
| such as the Honda mentioned in the article. The efficiency
| gain from engaging the ICE when cruising on the highway is
| just too good to pass up.
| deelowe wrote:
| That seems unlikely. A mechanical coupling should be close to
| near perfect efficiency where as using the engine to drive
| electric motors requires several conversion steps.
| calfuris wrote:
| The trick is having a large buffer, so that typically the
| engine can operate at the point with the best specific fuel
| consumption or shut down entirely. Getting energy from the
| engine to the wheels is less efficient than a mechanical
| transmission, but the increased average efficiency of the
| engine can more than offset that.
| deelowe wrote:
| Still seems like a traditional hybrid would be more
| efficient. I'm not sure what's gained by removing the
| mechanical coupling altogether (other than
| cost/reliability).
| Electricniko wrote:
| Honda has an interesting solution in their latest gen
| hybrids, where the electric motors power the wheels at
| lower speeds, the combustion engine runs at its optimum
| RPMs as a generator while the electric motors are
| working, and at higher speeds a clutch activates that
| changes the coupling so that the combustion engine
| directly drives the wheels.
| 01HNNWZ0MV43FF wrote:
| Whatever the Prius HSD does is great. It'll do 50 MPG
| city and highway. No clutch at all.
| jeremymims wrote:
| This was how the BMW i3 worked. It was a rather novel design
| that included an optional small electric scooter motor in the
| rear that had a 2.5 gallon gas tank. When the battery was low,
| it would be charged by running the small generator.
|
| This was clearly a wonderful idea but it was hamstrung by a
| silly California rule requiring the gas range to be less than
| the electric range to qualify for rebates. With a 6 gallon
| tank, the car would have been able to do ~300 miles instead of
| 170 and would have been parked in everyone's driveway.
|
| An added benefit was that the car could use existing gas
| station infrastructure when you needed to travel long
| distances.
| davewritescode wrote:
| That and the fact that in the US the car is tuned to only
| turn on the range extender when the battery is nearly dead
| and it can't always keep up.
|
| Thankfully it's trivial to change.
| labcomputer wrote:
| > it was hamstrung by a silly California rule requiring the
| gas range to be less than the electric range to qualify for
| rebates.
|
| The problem is that BMW wanted to get the same amount of
| credits as a pure-BEV. California anticipated that a car with
| 300 miles of gas range might spend much of it's life being
| driven on gas if there was no penalty for doing so... and in
| fact that is _exactly_ what happened with many European plug-
| in hybrids sold as company cars.
|
| California never gave BMW the credits, but BMW decided to
| keep the dinky gas tank anyway, so that's on them.
| Tagbert wrote:
| The Volt worked best as an EV with an ICE range extender. As an
| EV, the 40-52 mile range was sufficient for 90+% of daily
| driving. Adding more range would have little true benefit. It
| was a series hybrid, but it was mediocre as a hybrid due to the
| added battery weight.
|
| Nissan has the E-power hybrid that is the pure series hybrid
| that you describe. AFAIK it is not as efficient as a regular,
| parallel hybrid. The advantage is in cost as running the gas
| engine as a generator uses fewer components than running it in
| a parallel hybrid system.
|
| https://www.nissan-
| global.com/EN/INNOVATION/TECHNOLOGY/ARCHI....
| gimmeThaBeet wrote:
| I got my honda partially because it has the closest thing to
| nissan's e-power (in many ways the same, but with a couple
| twists).
|
| At low speeds (< 45 mph) it's either off the battery the
| whole time, or the motor runs and directs power to the
| traction motor or the battery. One wrinkle is that the motor
| assembly has a clutch that can engage the engine direct to
| the wheels, but like in city driving, the engine isn't going
| to be connected to the wheels. But I def would say that at
| least Honda's hybrid doesn't feel as simple as e-power.
|
| Now this probably isn't really accurate, but architecturally
| I think I like it because the only thing keeping it from
| being a BEV is the battery size (only a couple kWh); the
| electric motor is strong enough to be usable on its own.
|
| I think Toyota has increased the power on the normal prius,
| and definitely on the prime, but it used to be as part of the
| power split system, the electric drive motor wasn't sized to
| be enough on its own.
| ryandvm wrote:
| Stellantis (Dodge) has an upcoming version of the RAM 1500 that
| does this. It's an electric truck with a 145 mile range on
| electric battery; once that is expended the gas engine kicks on
| to run a 130 kilowatt generator.
|
| https://www.cnbc.com/2023/11/07/new-ram-pickup-ev-has-gas-po...
| dragosmocrii wrote:
| have a look at the new Mitsubishi outlander EV, it kinda works
| like the volt
| callalex wrote:
| "It is more efficient to turn gas into electricity"
|
| I don't think that's correct. It may be true for highly
| variable/low loads where the pumping losses in the pistons
| dominates. However the majority of fuel consumption in a car
| happens at traveling speed (highway miles). That is the area
| that needs to be optimized for.
|
| My 2015 Honda Accord Hybrid takes this approach. At below-
| freeway speeds the gas motor runs in series to drive an
| electric motor. At highway speeds, it engages a clutch and
| directly connects the engine to a low-loss 1-speed
| transmission.
| darby_eight wrote:
| > However the majority of fuel consumption in a car happens
| at traveling speed (highway miles).
|
| Unless of course you drive primarily in stop-and-go traffic,
| e.g. delivery drivers, taxis, commuter cars, etc. Quite often
| you won't exceed 50 kph. For whatever reason, I've never seen
| (or have and forgotten) a car marketed towards this market--
| probably for exactly the reason that plug-in hybrids perform
| better in this scenario.
| labcomputer wrote:
| > > "It is more efficient to turn gas into electricity"
|
| > I don't think that's correct.
|
| You're right, it's not.
|
| In fact, GM wrote an SAE paper about their "2-mode hybrid"
| transmission (which was used in their 2008-2013 light-duty
| trucks and SUVs, and then in later modified form in the 2nd
| gen Volt), where this is plainly explained.
|
| In the paper they describe exactly the tradeoffs made to
| optimize fuel efficiency in an eCVT... it turns out that you
| want to set up the planetary gears to minimize the energy
| transmitted from input to output via electricity and maximize
| the amount transmitted mechanically because that is most
| efficient. You especially want to avoid a round trip through
| the battery in most cases (except when that allows installing
| a smaller, more efficient ICE).
|
| That has implications for the CVT's mechanical ratio: GM's "2
| mode" which has what basically amounts to an auxiliary
| overdrive integrated in the eCVT so that it can use smaller
| motor-generators over a wider range of speeds. Smaller motor-
| generators means more energy is transmitted mechanically,
| which means higher efficiency.
|
| This is also basically the same reason the 1st gen Volt gets
| _significantly_ worse highway MPG in range-extender mode than
| the (contemporary) Prius Hybrid (~35MPG vs ~50MPG): The 1st
| gen Volt eCVT was envisioned as an EV with a range extender
| (where energy usually comes from a battery), while the Prius
| 's eCVT was optimized for driving primarily on the ICE, with
| the battery only supplementing acceleration.
| Tade0 wrote:
| Both the Chevy Volt and Toyota's hybrids rely on a planetary
| gear set to blend power between the gasoline engine and
| electric motors.
|
| Here are the differences explained in more detail:
|
| http://roperld.com/science/ChevyVolt.htm
| maxerickson wrote:
| At least one version could run as a series hybrid or as a
| torque combining hybrid, depending on which clutches were
| engaged.
| shanusmagnus wrote:
| What was the purpose of using the rotary engine in the first
| place, for ICE cars? From the comments it seems it's maybe
| lighter for a given power output. Is that it, other than just the
| novelty of it?
| 20after4 wrote:
| It's about double the power output for a given size /
| displacement. It's very smooth and high-revving so that makes
| for a really fun driving experience in a light-weight sports
| car.
| jdblair wrote:
| Lighter and mechanically simpler were the selling points. Poor
| fuel efficiency and trouble with the seals were the downsides.
|
| My uncle had an RX-7 back in the 80s when I was a kid. I
| remember when it was idling I could see the exhaust puffing, in
| pulses. It only had a single combustion chamber after all.
| LarsDu88 wrote:
| It's mechanically simpler until the apex seals blow out. Then
| you are fucked
| samdunham wrote:
| I've had three RX-7s. A first generation and two second
| generations. I drove the first until the wheels literally
| fell off (I was a young, stupid kid that ignored the
| crunching sounds of the rear wheel bearings falling apart.
| The rear wheel(s) seized while I was driving down a bridge
| causing the axel to snap in half. That was an interesting
| "drive" down the rest of the bridge). The second was a base
| model second gen that I gave up when I suddenly had two cars
| because of getting married, then divorced. The third was my
| favorite. A late model second gen fully loaded. That one
| eventually caught on fire due to negligence at a tire place.
| I loved that car.
|
| The third generation never got cheap enough for me to
| consider one, but oh, I wanted one badly. The RX-8 never
| really caught me. Plus they had some early issues. That
| Iconic concept definitely has my attention, though.
| aidenn0 wrote:
| Power density is indeed the main advantage. It's also much
| easier to balance; hunks of metal changing direction many times
| per second (6000 RPM is 100Hz) is somewhat mechanically
| exciting.
| dragontamer wrote:
| A good article.
|
| It barely addresses the elephant in the room however: The Toyota
| Prius and its Atkinson engine.
|
| The Atkinson engine is 99% the same as a regular engine (aka:
| Otto cycle), except the timing is different. Instead of closing
| the valves when the piston+cylinder is full of gasoline+air
| mix... the Atkinson engine waits a bit and "leaks" some
| gasoline+air back out before closing the intake valve,
| effectively burning only 70% of the fuel, but getting maybe 85%+
| of the power of a regular Otto-cycle engine. Its a simple and
| cheap tweak to a traditional engine that grossly improves
| efficiency (but at huge costs to low-end torque).
|
| Basically, any regular ol' carmaker who is mass producing Otto
| cycle / regular ICE engines can easily tune their piston timing
| to be an Atkinson engine instead. I believe Toyota even has
| computerized controls today that switches between efficient
| Atkinson (lower-power but higher efficiency) modes and powerful
| Otto cycle (higher power but lower efficiency) modes, though this
| control isn't really used too often in practice.
|
| ---------
|
| This article makes a good point that Mazda has a culture of
| this... rotary engine. It does compare it (somewhat unfairly) to
| the Atkinson engine though (inside the Prius and RAV4), I don't
| think anyone expects any traditional engine (Otto or Rotary) to
| keep up with Atkinson Engine efficiency.
|
| Its a good try however. But it does raise the question of what
| benefits can this rotary engine give over other engine types.
| aidenn0 wrote:
| I am mildly annoyed that Toyota calls late intake valve closing
| (LIVC) an "Atkinson-cycle" Atkinson made 3 engines none of
| which are anything like a 4-stroke with LIVC. The closest is
| perhaps his two-stroke engine, which kept the exhaust valve
| closed during the power stroke and open for part of the
| compression stroke.
|
| The Miller-cycle is much closer to what the Prius uses than
| anything Atkinson made; it was a traditional 4-stroke with
| LIVC, but required a super-charger to generate power at low
| RPMs.
|
| The Prius has a CVT and electric motor, overcoming any issues
| at low RPMs. Also now that VVT is more common, many engines run
| with LIVC under certain conditions.
| jeffbee wrote:
| And, of course, Mazda had been selling LIVC engines for years
| before the Prius appeared. Like all of Mazda's other weird
| engines they were expensive, bad, and unreliable.
| SebFender wrote:
| I have so many bad memories from this engine. I finally brought
| them to court to win. But all this to say Mazda has been out of
| the game so long living on dreams with this engine.
| busterarm wrote:
| Mine went 110k miles without ever blowing up and then I decided
| to rebuild it.
|
| It's got as much longevity as other cars from the era if you
| pay attention to oil/omp and (over)boost (if you have a turbo).
| Everyone puts in at least a downpipe and then neglects all of
| the other mods (wastegate mod, better fuel bump, bigger
| injectors, wideband o2 sensor and new fuel map, better
| intercooler, etc) that you'll be forced to do along the way or
| suffer from boost creep and an eventual grenaded engine.
|
| It's all of the other things under the hood that I've had to
| replace from all that heat though. Three alternators. A wiring
| harness that caught fire...
| ngcc_hk wrote:
| Is the rotary better or worst with pollution ?
| 1970-01-01 wrote:
| The problem with the Wankel is and has always been apex seals.
| You need to rebuild it at least once during a vehicle lifetime. I
| would not say it is safe from this fate, even with modern seals
| and a hybrid application.
| aunty_helen wrote:
| I thought it was the horrible compression and oil burning. Apex
| seals seem to last if you don't do silly things to them but you
| can't solve inherent issues with the cycle design.
|
| For comparison, rotaries get about 100psi of compression, a
| modern gas car can more than double that. More compression,
| more efficient burn.
| 1970-01-01 wrote:
| I've read that oil burning (which is directly tied to the
| apex seals) has been fixed in modern engines. Compression is
| a somewhat configurable matter, and can be high in a low-
| torque generator (battery hybrid) application.
| SeanLuke wrote:
| > Despite all this, though, the MX-30 R-EV still falls somewhat
| short, with a catalog fuel efficiency of 15.4 kilometers per
| liter (as measured in WLTC mode). With no similar vehicles on the
| market, like-for-like comparison is not possible, although the
| Toyota RAV4 plug-in hybrid gets 22.2 km/l, while the Prius plug-
| in hybrid gets 26.0 km/l. The MX-30 R-EV is clearly inferior in
| terms of its fuel economy.
|
| That's because the engine serves an entirely different purpose.
| The Prius plug-in hybrid is a 13.6kWh battery mated to a regular
| engine. The MX-30 R-EV is a 17.8 kWh battery mated to a tiny
| ultralight _emergency range extender_.
|
| As to similar designed cars, um, hello, the BMW I3 Hybrid?
| Exactly the same design.
|
| The failing of the MX-30 R-EV is that its battery size is
| pathetically small for what amounts to an EV with a range
| extender. It is an embarrassment.
___________________________________________________________________
(page generated 2024-03-29 23:00 UTC)