No crankshaft, no problem: Toyota's free piston engine is brilliant

http://www.roadandtrack.com/go/out-of-turn-toyota-engine

by ilamont • 12 years ago

228 105 12 years ago

All it needs to do is generate motion, so they made it like those flashlights you charge by shaking them. Reciprocal! What will be revolutionary will be performing this with some kind of rotary engine.

arethuza2• 12 years ago

The Jaguar C-X75 almost made it into production - and it had miniature gas turbines linked to generators feeding the batteries and wheel motors:

http://en.wikipedia.org/wiki/Jaguar_C-X75

Given the current popularity of hybrid hyper-cars from Porsche, McLaren and Ferrari it would be interesting to see if something like the Jaguar is tried again.

thesz2• 12 years ago

This is what I was thinking about too. Rotation is better than reciprocal line movement.

tomswartz07• 12 years ago

Much older than that was the Chrysler Turbine car:

http://en.wikipedia.org/wiki/Chrysler_Turbine_Car

This was quite literally a lower power jet aeroplane turbine used to power the car.

I would imagine that this would have been great on fuel economy on the highway, but terrible in cities.

marcosdumay• 12 years ago

What will be revolutionary will be performing this with some kind of rotary engine.

You mean, like a turbine?

codfrantic2• 12 years ago

You mean, like a turbine?

I think he means like a Wankel engine:

http://en.wikipedia.org/wiki/Wankel_engine

exDM692• 12 years ago

You mean, like a turbine?

There are rotary internal combustion engines, such as the Wankel engine. It has a triangular "rotor-piston" spinning in a circular cylinder and goes through four "strokes" per revolution.

Mazda is a manufacturer that utilizes rotary engines in production cars today, particularly in their high performance models.

http://en.wikipedia.org/wiki/Wankel_engine

thesz2• 12 years ago

What is forgotten here is a reduction of vibrations.

The crankshaft works as a (cheap) synchronizer for piston movement and can reduce vibrations when phases are aligned in special way.

Motor vibrations are big deal - they take energy and also reduce quality of car.

tankenmate• 12 years ago

This is why they mention that a two cylinder engine is balanced; e.g. a boxer configuration.

maxerickson10• 12 years ago

It's mentioned obliquely:

Even better, a two-cylinder FPEG is inherently balanced

I guess electronic timing is also up to the task of keeping things running smoothly without mechanical synchronization.

yason• 12 years ago

The article mentioned a two-cylinder configuration where the movements of two pistons would be mirroring each other, nullifying the vibrations.

mentos• 12 years ago

Seems like needing the piston to change directions is a waste of momentum. What about a similar design where a ball is propelled around the inside of a circular doughnut to generate electricity?

codfrantic2• 12 years ago

Or a Wankel engine[1]

[1] http://en.wikipedia.org/wiki/Wankel_engine

Zigurd• 12 years ago

A rotary engine isn't free-piston, but it also doesn't have reciprocating parts. But it also shows there are other challenges to efficiency than reciprocating pistons.

sharemywin3• 12 years ago

I think the pressure would go around the donut on both sides and equalize.

yxhuvud• 12 years ago

Wouldn't a more obvious solution be to change the direction by adding a second combustion chamber on the other side?

kabdib2• 12 years ago

That works great until you miss ignition on the opposite side, then wham it bottoms out and destroys the other side of the engine.

A gas spring is a pretty simple mechanism and can't misbehave (too bad you can't put it to work, though -- probably a lot of heat being wasted compressing it).

luch• 12 years ago

Is your question rhetorical ? Because that's how ITER (nuclear fusion reactor) generate electricity in a nutshell, if you replace the ball by plasma.

source : https://www.iter-india.org/images/fusion_experiments2.jpg

fanf2• 12 years ago

That diagram is about the energy inputs to heat the plasma.

Energy output to generate electricity is quite indirect: hot neutrons escape the magnetic containment and are caught in a lithium blanket. This produces tritium from the nuclear reaction between the neutrons and lithium nuclei, and heat. The blanket is cooled with water which is used to drive a conventional steam turbine generator set.

See the last paragraph of the reactor overview at http://en.m.wikipedia.org/wiki/ITER and note that they do not plan to generate electricity from ITER: it is purely experimental.

chiph2• 12 years ago

Too hard to seal. Ask a RX8 owner about rotor apex seals sometime. The bane of their existence.

In this new motor there's nitrogen on the other end of the piston that provides "rebound". It's probably inside the coolant jacket as well to prevent expansion and the loss of efficiency that would bring.

kabdib2• 12 years ago

Ex RX-7 owner here. Not much room in the back of one of those things, but I always had room for cans of oil :-)

Wonderful cars. I'd buy an RX-9 if they ever built one, but they're never going to. So I have to motorcycle instead, could be worse :-)

busterarm7• 12 years ago

The problem with the RX-8s isn't the rotor apex seals (any more so than any other rotary), it's actually injection. A design oversight with how they inject oil in the '04-'06 models causes the engine to not be lubricated properly and this will cause a lot of problems. Even though they fixed it after '06, it's still not perfect. Like the '89 and after RX-7s, the RX-8 needs to run with premix.

But generally you want to avoid buying an '04-'06 RX-8 used.

busterarm7• 12 years ago

The bane of their existence.

Just like spun rod bearings and thrown rods are for Subaru owners, amirite?

At least when a seal goes, I can replace the rotor, walls and side housing; if it even needs that.

pbhjpbhj• 12 years ago

You could have a reciprocating engine instead. Wankel engines have problems due to sealing being difficult (as would your idea, explosive gases escape at the edge of the sphere), as I understand (I've not studied it in depth), but a reciprocating engine would seemingly have no more [in fact less] issues with being sealed than 2 parallel pistons. Have the first combustion chamber push the piston one direction past the coils and have a second chamber at the opposite end push the piston back. Any excess movement might be able to be used for pre-compression?

Of course many people have thought of this before (don't you hate it when that happens! ;0)) - http://www.youtube.com/watch?v=2SlwoBLspTQ shows 2 such engines.

http://www.youtube.com/watch?feature=player_detailpage&v=yV0... shows another idea, 2 pistons either side of a single combustion chamber.

nabla9• 12 years ago

If you follow that line of thought to it's conclusion, you end up with gas turbine (Brayton cycle).

Sami_Lehtinen• 12 years ago

Yes, that's what I thought. Many people seem to ignore gas turbine option, even if those are very reliable and efficient power sources. If there's interest towards different engine designs, it might be a good idea to check this out too: https://en.wikipedia.org/wiki/Wave_disk_engine and another interesting design: https://en.wikipedia.org/wiki/Swing-piston_engine There surely isn't shortage of engine designs, most of these designs are from 1800's. So nothing new.

susi22• 12 years ago

Don't forget that for an electric motor you need a sine shaped AC and not DC so it's pretty convenient that this design produces exactly that. Whereas with a "continuous" design you'd need to make it AC.

randallsquared• 12 years ago

If your motor needs AC, you already have an inverter, since the battery produces DC.

derekp7• 12 years ago

I hear this quite often, but I don't quite see how this is true. Each piston is hooked to a crankshaft, which is hooked to a flywheel. Even with a single piston, the energy of it slowing down and reversing is absorbed in the flywheel, which is in turn used to propel it in the opposite direction. Add multiple pistons, and the energy of slowing down is again used to accelerate another piston.

Just think of any spot on a wheel representing an arbitrary amount of mass. Spin the wheel, and the only thing slowing it down is friction -- not that spot constantly changing direction.

maxerickson10• 12 years ago

This article is specifically about a piston engine that does not have a crankshaft.

bnegreve• 12 years ago

Seems like needing the piston to change directions is a waste of momentum.

It's not, in a closed system momentum is conserved [1] so without friction, a free engine would rotate forever.

Also there is not conceptual difference between an engine and a ball sniping in a donut. In both case, the piston or the ball have to change direction (the piston has to change direction more abruptly though)

[1] http://en.wikipedia.org/wiki/Momentum#Conservation

daraosn• 12 years ago

Reminds me of http://en.wikipedia.org/wiki/Mazda_Wankel_engine Good think this seems to be efficient, but I would like that instead they would be putting more focus on improving batteries rather than gas motors.

sharemywin3• 12 years ago

until you get most of your grid power from solar your still using fossil fuels for power.

wtallis• 12 years ago

About 30% of US electricity is produced from nuclear power or non-solar renewable sources. Solar may be a hot topic, but it's nowhere near being the top alternative to fossil fuels.

nmcfarl• 12 years ago

Sure - but the grid + ev combo is still more efficient than a gas vehicle. And of course the grid uses a wide range of fossil fuels which reduces some of the geopolitical concerns. Finally in some places your power is already quite low on hydrocarbons - Seattle City Light is only 1.3% hydrocarbon.

kalleboo• 12 years ago

95% of my grid power comes from hydro or nuclear, so I'm good.

mikeash3• 12 years ago

Small engines are irrelevant to grid power regardless, even if you get all of your electricity from fossil fuels. Power plant generators are completely different beasts, as the tradeoffs change considerably as you scale up.

sharemywin3• 12 years ago

sorry if your in the midwest...

TheLoneWolfling4• 12 years ago

Wankel engines are great in some ways - but the seals are really difficult to get reliable.

thedz• 12 years ago

Yeah, not like multi-billion dollar corporations can R&D into multiple areas at the same time.

Already__Taken2• 12 years ago

It's also a big deal having electronic controlled valves, you can make them have a square profile for maximum flow rates.

programminggeek• 12 years ago

What people might not think about so much is that weight reduction is as important if not more important than the advancements we make in the engine.

When Rocky Mountain Institiute was working on their hyper car concept, I believe the researcher said that weight reduction was more important than electric or gas engine.

I think he said something like for every pound you save, you actually reduce an extra 2-3 pounds of supporting materials elsewhere. Lighter cars need less HP, you can reduce some of the support bracing as it's not as heavy of a vehicle, etc...

Making cars super light would do a lot of good and so every time I see a giant battery for electric cars or a 2nd engine to act as a backup, I wonder how much that is costing in terms of weight and MPG.

wspeirs• 12 years ago

Along with a weight reduction, they said that, "It can also be run like a diesel, using compression rather than a spark plug to ignite its fuel mixture." This is important as spark plugs require a decent amount of energy to function.

tnorthcutt2• 12 years ago

spark plugs require a decent amount of energy to function

Are you sure about that?

According to [0], "To ignite a stoichiometric air-fuel mixture (14:1) approximately 0.2 milliJoules of spark energy are required. Very rich or lean mixtures can require as much as 3 mJ."

[0] http://www.mr2.com/TEXT/DavidKucharczyk/ignition.html

IgorPartola5• 12 years ago

There are lots of designs where the car is significantly lighter than a typical vehicle driving on American or European roads. The problem with them is that if you get in an accident, you are much more likely to suffer much more damage. There are in fact regulations in the US that effectively require you to build heavier cars. Motorcycles and scooters are great examples of personal transportation that are lightweight and can get ridiculous fuel economy, but in a Vespa vs 18 wheeler, the Vespa will lose every time, which is why you don't see them on the freeway.

mikeash3• 12 years ago

One important question is how much you really care about efficiency if you're getting most of your energy from electricity. Electricity isn't free, and it still pollutes depending on what your local generating capacity looks like, but it's a lot better than even the most efficient gasoline.

The problem with most electric cars right now is range, which is due to the inherent cost of the batteries. But it's largely psychological, as most people's driving in most situations is within the range of a reasonable electric vehicle. It's just exceptional circumstances when it's not enough.

Thus, paradoxically, adding a gasoline range extender to an electric car could really help enable electric driving considerably. And if the car drives 90% on electricity, the efficiency of the gas engine doesn't matter too much. It's just there as a backup.

I almost bought a plug-in hybrid last year. A Volt or similar would let me do a ton of pure electric driving, while still having the option to go farther. A Leaf or similar just wouldn't cut it for me, because a car that covers 90% of my driving isn't good enough. But if it can cover 100%, with 90% on electricity, that's a big gain. Ultimately I didn't get one, because they're still a bit too compromised (the Volt only seats 4, others have tiny cargo space), but range extenders could be an important bridge measure as batteries slowly improve, and the extra weight isn't all that important in many cases.

IgorPartola5• 12 years ago

If you enjoyed this article, check out http://jalopnik.com/what-its-like-to-ride-in-a-car-with-the-...

alkoual• 12 years ago

This could be used as a transition from gas to battery cars. Why? Currently one of the most important reasons holding back companies from producing electric cars is the lack of good batteries, but with this, companies can produce cars that convert gas to electricity in order to drive an electric motor. After a few years, when gas becomes even more expensive and batteries get better, we can switch this mechanism to batteries, and that's it.

adrow• 12 years ago

Previous discussion: https://news.ycombinator.com/item?id=7677197

IgorPartola5• 12 years ago

I believe this is what Chevy Volt does, and it's brilliant. There are two reasons I like this design. First, the fossil fuel engine in the Volt spins at only three pre-defined speeds so it can be optimized better. By contrast, your normal car engine has to run at both 900 RPM and 6500 RPM, with the best fuel economy somewhere between 2000 and 3000 RPM. Heck, you could shut the Volt's engine entirely while it's "idling" and not have to worry about stop & go traffic: the engine is independent of the wheels.

Second, and this is admittedly more long term, it doesn't really matter what type of engine you put into the Volt. This thought was presented to me by one of their dealers, but it makes a lot of sense. The current engine is a "tried and true" gasoline job. But if Chevy found that diesel or bio fuel, or natural gas worked better, they could swap it out without redesigning the rest of the drivetrain.

I may sound like a walking billboard for the Volt, but I am honestly not. I don't own one, and do not work for Chevy/GM. I do happen to think that the Volt is the best compromise between price, range on batteries, and ability to drive long distances. While Tesla's are very cool, I think the Volt is a much more gradual transition from gas to electric.

maxerickson10• 12 years ago

This article is more about using the linear electrical generator on the piston than it is the configuration of the power train. No vehicles on the road today have anything similar to what is discussed in the article.

Also, I'm not sure about the current model, but there was a bunch of kerfuffle over the Volt not really being a strict electric hybrid:

http://www.plugincars.com/exclusive-chevrolet-volt-chief-eng...

Some of the time, at least in the edition discussed there, energy from the engine goes to the wheels without ever becoming electricity. Maybe they changed it in later models (but I sort of doubt it, the capability is there because it can be the most efficient way to use the engine).

IgorPartola5• 12 years ago

I did not know that. Looking at the Wikipedia article for the Volt [1] I can see that the gasoline engine may provide additional mechanical energy to turn the wheels, but it's only to assist the primary and secondary electric motors.

In either case, I am not a purist going after a 100% electric car. I want to get more miles per dollar, and I want to produce less CO2 per mile. The Volt seems to do that, while still letting me drive from NYC to LA and back without having to spend more than three minutes at any given gas station. More importantly, any gas station will do, since it can run on just gas. For a daily commute, it will likely run 100% electric since the battery won't be depleted. To me, this is a great combination.

[1] http://en.wikipedia.org/wiki/Chevrolet_Volt#Drivetrain

mikeash3• 12 years ago

Nothing in your first paragraph is special to the Volt. Any hybrid, aside from the less advanced "motor assist" designs (found in earlier Honda hybrids) get the same advantages. A Prius can keep the engine at a happy RPM throughout due to effectively having a CVT, and it can not only shut off the engine when stopped, but even when moving up to 40+MPH.

There are some interesting consequences of a pure serial hybrid design like the Volt (although the Volt isn't quite a pure serial design), but friendlier RPM and the ability to shut the engine down aren't it.

graycat6• 12 years ago

It's simple: A car needs a source of energy. Then a 15 gallon tank of gasoline is just super tough to beat. Can beat it a little with a 15 gallon tank of Diesel oil. A few hundred pounds of batteries with a charge from the electric grid? You gotta be kidding.

Now, what to do with that liquid in that 15 gallon tank is a question, but the basic fact remains. Did I mention that that fact is simple? A car needs energy, and that 15 gallon tank is tough to beat. For the rest, we have a lot of possibilities, but that 15 gallon tank is tough to beat.

graycat6• 12 years ago

Gee, some people need some help: Did I mention, a 15 gallon tank is tough to beat? Electric power, that is, without a tank of gasoline or Diesel, for the energy for a car, is tough, super tough, for now and a long time, too tough to store. It's tough. Storing electric energy is tough, too tough for a car and likely also for wind and solar to feed the grid. Yes, there are ways to store the energy from wind and solar for the grid, but those ways are too expensive, by a factor of about 2, over other means of electric power generation that do not need storage, even if the power from wind and solar are just free, as in totally free, as in $0.00 per megawatt year.

So, let's look at an example, say, Tesla. I just went to their Web site and looked at charging time and saw

During the work week I charge only at work during an 8hr shift from a 110 outlet. I only live 6 miles from work. I usually get ~30 miles of charge in 8 hours

So, right, 8 hours of charging for 30 miles of driving. Lots of cars can go 30 miles on one gallon of gasoline that takes about, what, 20 seconds, to pump. Diesel, maybe 45 miles.

The car, sure, it can still drive the wheels with electric motors, but, to make any sense, we store little or no electric energy in the car. Instead, the energy for the car is stored in a 15 gallon tank of gasoline or Diesel.

We had electric cars going way back to the beginning of cars. Why? Because lead acid batteries and electric motors were already old things. And, a battery much better than lead acid is still tough to get; indeed, we still use lead acid batteries in cars for, say, the starting motor.

The main problem with electric cars remains the batteries. As a Ford executive said long ago, build me a good battery and I will build you a good electric car. We are still waiting for a good battery, say, comparable with a 15 gallon tank of gasoline, in range, capital expense, operating expense, durability, and 'recharging' time.

So far, a Tesla is a toy for rich people. Sorry 'bout that.

I could like an electric car; it would have a lot of advantages. The problem is the battery. And that's been the problem for about 100 years.

masklinn• 12 years ago

I believe this is what Chevy Volt does

The article's point is not to about "diesel-electric" systems (where the ICE acts solely as a prime mover for a generator and the wheels are always driven electrically). That's old news in both transportation in general (it's been in use in trains and ships since the early 20th century) and in hybrids ("diesel-electric" is sometimes called "series hybrid" or "range-extended electric vehicle" in cars).

It's about a new engine design[0] where electric generation is merged into the piston itself: a "normal" diesel-electric engine has a regular diesel engine (or more generally ICE) with pistons driving a crankshaft which drives the driveshaft, which is connected to a generator.

Here the design does away with the crank and driveshaft: the piston itself is a rotor, and the casing becomes the stator, doing away with mecanical transmission altogether: the piston and its cylinder become a linear generator.

[0] not quite that new, the first patent on free-piston engines[1] for linear generators dates back to 1959. The new part is getting a design to actually work in a vehicle[2].

[1] a free-piston engine is an engine without a crankshaft transforming the piston's linear movement into rotational movement

[2] the crankshaft does not just transform motion and lose energy, it also synchronises pistons and limits the piston's course. But if the piston+cylinder is a self-contained generator, I guess you can treat each piston as a single-piston linear engine? Which would limit the usual issues of multiple free-piston engines.

edit: formatting, footnotes

IgorPartola5• 12 years ago

Thanks for the explanation.

zackmorris• 12 years ago

I drew almost this exact same picture in high school, along with just about every other kid interested in internal combustion engines (before I knew what a horizontally opposed engine was, like the boxer engine in Subarus). I'm just glad to see a car company talking about it, because the way we do it now with transmissions is pretty much ridiculous. This engine is roughly 7 times weaker than it should be, because Nikola Tesla had a 110 horsepower turbine in 1913 https://en.wikipedia.org/wiki/Tesla_turbine which was unfortunately ahead of its time because the country was barely getting wired with electricity at that point.

But today a 95% efficient generator connected to a 95% efficient motor for 90% overall transmission efficiency would be worth it on a turbine or Stirling engine running at 40-50% efficiency (maybe 40% overall at the wheels). Compare that with an old gas guzzler from the 70s running at 25% efficiency with maybe an 85% efficient transmission for 20% efficiency at the wheels. Not to mention that cars used to weigh twice as much which halved city fuel economy again, and lacked regenerative breaking which halved it again, and so on and so forth. It’s no wonder that cars used to get 10 mpg when what I would argue are relatively simple engineering changes could have raised that to 30, 50, even 100 mpg. It’s almost like they were deliberately designed to be as inefficient as possible…

pjc50• 12 years ago

They were designed for cost-effectiveness in an era of cheap fuel. Electric transmission wasn't feasible on the car scale until cheap microelectronics arrived. It was confined to diesel-electric locomotives.

fulafel• 12 years ago

cars used to weigh twice as much which halved city fuel economy

Nit: this is actually the other way around, cars have been gaining weight - so much that it has swallowed most of the mileage improvement we'd otherwise have gotten from other tech improvements.

See eg http://newsoffice.mit.edu/2011/cars-on-steroids-0104

hyperliner• 12 years ago

Pardon my ignorance, but the video does not show and I am interested to see if they modified the system, but what draws the piston back towards the spark plug?

juandopazo• 12 years ago

IIUC, a spring.

phea• 12 years ago

It's a gas spring, similar to a car shock.

tnorthcutt2• 12 years ago

It's not drawn, it's pushed, by the pressure built up in the "gas spring chamber".

snowwrestler• 12 years ago

Anyone know why hybrids don't use turbine generators? As I understand it, they are more efficient than even the best reciprocating engine. Aside from solar and wind, every large-scale generating station uses turbines, for example.

TheLoneWolfling4• 12 years ago

IIRC, turbines are really ineffecient at small scales.

It's only when you get up to large scales that they start making sense.

DigitalJack• 12 years ago

they are slow to get to speed and loud.

Stolpe• 12 years ago

I remember seeing something similar to this a year ago in a documentary series concerning the small Swedish supercar manufacturer Koenigsegg. See it here: https://www.youtube.com/watch?v=Bch5B23_pu0&list=PLHa6PXrV-y.... It sounds really interesting.

ChuckMcM• 12 years ago

Pretty cool, and I wonder if you could build the piston with two "heads" and put a cylinder head on either end and just shoot it back and forth. Magnetics of course have a hard time at high temperatures, so I'm not sure how you generate the stator field reliably.

bradleyland• 12 years ago

The problem would be startup and shutdown timing. Any circumstance where you had a "missed" ignition (which occurs more often than you'd think) would result in a catastrophic failure (pistol slams in to the opposing head).

marknutter• 12 years ago

Why was this article removed from the front page of Hacker News?

zevyoura• 12 years ago

Even better, a two-cylinder FPEG is inherently balanced and would measure roughly 8 inches around and 2 feet long. An engine of that size and type could generate 15 hp, enough to move a compact electric vehicle at highway speed after its main drive battery has been depleted.

Is 15 HP really enough to move a car at highway speeds? I had a CBR250 motorcycle that produced 22-24 HP and weighed around 350 pounds, and it was not particularly great on the highway. It's hard for me to imagine a car that's 3+ times heavier with less horsepower being safe on a highway.

No crankshaft, no problem: Toyota's free piston engine is brilliant

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