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Toyota Describes Combustion Engine That Generates Electricity Directly 234

cartechboy writes: "While electric cars are now more available than ever, combustion engines will remain for decades to come. Now auto engineers are working to refine combustion power as part of cars that are increasingly electrified, including plug-in hybrids. Toyota's new 'Free Piston Engine Linear Generator' (or FPEG) shows us one potential way. Linear engines eliminate the rotating crankshaft of conventional engines in favor of a single chamber, in which a piston moves forward and backward. A linear engine has no crankshaft, nor connecting rods. In their place is a gas-filled chamber, the compression of which functions like a spring — returning the piston after the expansion / combustion phases of a typical combustion cycle. This back-and-forth motion can be turned into energy, when you haven't got a crankshaft and the mechanically-useful rotation it produces. While linear engines are far from new, and Toyota's test units are only 10 kW (13 horsepower), a pair of them can still produce enough electricity for a Yaris- or Corolla-sized vehicle to cruise on the highway at 75 mph."
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Toyota Describes Combustion Engine That Generates Electricity Directly

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  • Efficiency? (Score:5, Interesting)

    by Dan East ( 318230 ) on Wednesday April 30, 2014 @06:23PM (#46884715) Journal

    The real question is how efficient is it? The article doesn't say. It might be simpler mechanically than using a crankshaft to generate rotational energy, but that doesn't mean it is more efficient than an alternator / generator method of producing electricity.

    • Re:Efficiency? (Score:5, Insightful)

      by Todd Palin ( 1402501 ) on Wednesday April 30, 2014 @06:29PM (#46884765)
      I was thinking the same thing. Efficiency is the real question. I assume the article would have mentioned this if the efficiency was available to the authors. The fact that efficiency figures weren't available means they were not very impressive at this stage. The devil is in the details.
      • 10 kw is an interesting number for another reason, too -- 10 kwh is about the size of the average US home electrical draw. [] An hour of run time, some storage... assuming 10 kw is the output of these things, and various efficiencies, etc. Still, it's an interesting number. Sure seems like you could make an interesting power source from them.

      • Re:Efficiency? (Score:5, Informative)

        by Dahamma ( 304068 ) on Wednesday April 30, 2014 @07:15PM (#46885207)

        Efficiency information was there, I guess the dumbed-down article linked from the post didn't feel like including it. This link (that was in TFA) has much more interesting details: []

        Summary is, not only does it have 42% efficiency (for reference, efficient DI gas engines are about 35%, and diesel about 40%), it allows for a lighter, simpler engine with reduced cooling and lubrication requirements. Higher efficiency, lower weight, fewer moving parts all just generally contribute to a lower TCO, which would be a great thing, as series hybrids are still not particularly cheap (at least without their current subsidies)...

        • Well that, and Toyota is behind this. But I'm rather surprised that it's that efficient. I would think there would be a substantial inductive loss in the form of wasted EM radiation along with heat. At least with mechanical energy, it goes directly from the combustion chamber to where the rubber meets the road; effectively.

          • Re: (Score:3, Interesting)

            by Crayz9000 ( 2783019 )
            Mechanical losses are a major issue with cars, particularly when dealing with power losses through differentials. Friction will quickly make you its bitch, which is why everything must be kept well-lubricated, and even then you have to keep the viscosity to an absolute minimum to avoid fluid load.
            A completely electric drivetrain, if done right, can eliminate almost all of the moving parts that contribute to power loss. Electricity, wires, and motors. It doesn't get much simpler than that.
          • Re:Efficiency? (Score:5, Informative)

            by XNormal ( 8617 ) on Thursday May 01, 2014 @04:41AM (#46887357) Homepage

            The conventional piston-and-crankshaft engine forces the variation of cylinder volume over time to follow a specific sinusoidal curve. This is not the most efficient way to convert the energy of a hot expanding gas to motion. Look at the third picture in the slideshow to see the power-over-time graph of the free piston engine to get an idea of how differently this engine runs.

            This fundamental difference in thermodynamic cycle performance makes the biggest improvement to the efficiency of this engine. It more than makes up for the inherent inefficiencies in converting the mechanical motion to electricity and back. Using electricity lets you use capacitors and batteries to smooth that spiky but efficient power production to a a smooth supply for the electric motors.

        • Does that include using it to drive the wheels?
          I assume the petrol/diesel stats do.

          • Does that include using it to drive the wheels? I assume the petrol/diesel stats do.

            Doesn't make much difference because electric motors are very efficient, nearing 100%.

            • Re:Efficiency? (Score:5, Informative)

              by calidoscope ( 312571 ) on Wednesday April 30, 2014 @10:00PM (#46886099)

              The transmissions on current GE and EMD diesel electric locomotives are about 94% efficient from the output of the prime mover to the driving wheels. I would expect electric car motors to be on the order of 90 to 95% efficient, so this should compare favorably with a mechanical tranny.

              Speaking of locomotives, the free piston gasifier was being heavily researched in the 1950's as a more efficient realization of a gas turbine and something that could compete with diesel engines as prime movers.

              • The numbers I've read are in the range of 95-98% efficient, but I can't find any links right now. In any case, whether it's 90% or 99%, the net is that a linear generator feeding an electric motor should be at least as efficient as a traditional ICE, as well as being lighter and simpler.
      • The devil is in the details.

        Crap, I've spent years hunting him in the boardroom!

    • Efficiency and size/HP. A small one as a backup genny in an EV might be interesting, or larger ones in a hybrid.

      If they are efficient, how about using them as portable generators as well? That nobody has used them in this manner before sparks my critical side.
      • Re:Efficiency? (Score:4, Interesting)

        by Blaskowicz ( 634489 ) on Wednesday April 30, 2014 @08:24PM (#46885611)

        Nobody has used them because they need some high tech. From what I've read free-piston engines need to be computer-controlled at a very high rate, else the technology is unworkable. Something like an Intel 8051 wouldn't keep up, so for that reason alone it was not invented 30 years ago.
        Writing the firmware must be hard, as hinted by the wikipedia article's end. Maybe that requires a lot of computer simulations, which is easier to do in the 2000s and 2010s to say the least.

        I do agree a portable generator would nice, or a lightweight vehicle that doubles as a power plant. 10 kilowatts would be pretty good for audio gear, lighting and an ice machine to keep the beer cool.

        • needs what a low end smart phone or a Raspberry Pi can provide without breaking a sweat?

          Doesn't quite explain the last 10 years. We've had plenty of computing power for ages.

      • As for efficency I read a claim they can do 60%, which is crazy high and pretty much the max for anything. But my source is weak (finding about free-piston engines serendipitously and maybe doing some google searches)

        • As for efficency I read a claim they can do 60%, which is crazy high

          No way ... unless you are using liquid nitrogen for your heat sink. Even a perfect Carnot cycle isn't going to give you efficiencies that high. Maybe they mean "60% of perfect CC" rather than "60% = (electrical energy out)/(fuel energy in)".

          • That must be theoretical efficiency (I thought of that after hitting "submit").
            That makes me think of audio amplifiers. Class D amps have a theoretical efficiency of 100% :), real world results are about 88% to 92%.

    • by grmoc ( 57943 )

      .. and how efficient is at as compared to a turbine?

      • or a free piston engine driving a turbine? I love how I keep seeing the same shit different decade

      • Re: (Score:2, Insightful)

        by Anonymous Coward

        Turbines are really not efficient at all. Even if you made a perfect turbine, the Brayton cycle is inherently less efficient than the Otto/Atkinson cycle used in internal combustion engines.

        They are used in airplanes because nothing beats their power/weight ratio, and in power plants because of their longer MTBF and ability to burn lower quality fuels.

        • Re:Efficiency? (Score:4, Informative)

          by slinches ( 1540051 ) on Wednesday April 30, 2014 @09:33PM (#46885987)

          That's not true in practice. The efficiency of the Brayton cycle may be lower for the same compression ratio, but higher compression ratios are achievable. This is the same reason Diesel engines are more efficient. Also, turbines tend to have lower thermal and mechanical losses.

      • Well, according to the only reference I found before I got bored [] you need recirculation to even reach 30% with a small turbine in the power range we're discussing. That's not really competitive with modern ICEs, let alone this engine.

    • by Zeussy ( 868062 )
      The other thing the article doesn't state, is that the cylinder and head design is similar to 2 stroke diesels. With exhaust ports at the top, and intake ports at the bottom, blocked off as the piston moves up. They generally use a supercharger or a turbocharger to force the exhaust gases out and the fresh intake charge in, so I assume this design is using some sort of electric supercharger in it's place.
      • by AK Marc ( 707885 )
        One thing I didn't see is that with a "free piston" why couldn't you have both sides generate power? A 2-stroke on one end and another 2-stroke one stroke dealyed. Double power in a small/light container. Turn off one of them to save fuel. Have a bank of 3, and run them 1-cyl to 6-cyl for a wide variety of power generation and economy modes.
        • by Zeussy ( 868062 )
          You might need a set of sleeve valves or similar to seal off the intake ports. So the combustion chamber of the deactivated cylinder can act as the air spring.

          I wonder if there is a limitation to how much power you can make from that size of linear generator/stator though, so you wouldn't get much advantage, I don't know that much about that side of things though.
    • Re: (Score:2, Interesting)

      by kimvette ( 919543 )

      The real question is actually, will the car be safe? with 13hp*2, 0-60 will likely be in the high 20s. Not very good for merging, or crossing traffic, or going uphill, or even hauling groceries. Think sub-VW Beetle performance, considering that a Beetle weighed in at less than half the weight of today's nannystate-mandated safety features.

      • They will not be powering the acceleration directly though, they will be charging batteries which power an electric drivetrain. That means you get some extra charge while you are sitting at a red light and you use more when accelerating to highway speed.
      • Re:Efficiency? (Score:5, Informative)

        by im_thatoneguy ( 819432 ) on Wednesday April 30, 2014 @07:13PM (#46885183)

        The real question is actually, will the car be safe? with 13hp*2, 0-60 will likely be in the high 20s. Not very good for merging, or crossing traffic, or going uphill, or even hauling groceries.

        Of course. The great thing about electric cars is that you have tons of torque instantly available. This is just for charging batteries. As long as you aren't accelerating indefinitely they can make up the high power drain from the acceleration while cruising.

      • Acceleration should be just fine. This thing just needs to run constantly producing power to charge the battery. The electric motors will have far more torque and power than this, and be able to (temporarily) discharge the battery, until you lift.

    • The real question is how efficient is it?

      It does not have to be any more efficient if they manage to reduct weight and increase reliability. Efficiency has a big part to play but even a less efficient engine would be desirable if they improve greatly on other aspects.

      Remember that this is being targeted for vehicles that will run mostly on electric power. An ICE is a dead weight when not being used. If someone drives using 90% pure electric then the efficiency gains of carrying less weight could easily outweigh the losses of an ICE that was

    • Even if this is less efficient than a conventional ICE, it's still less moving parts therefore less things to wear out, which should make it last even longer and require less maintenance.

    • by flyneye ( 84093 )

      In their hurry to generate too much excitement and raise investors they neglected to convert the statement: Toyota's test units are only 10 kW (13 horsepower), a pair of them can still produce enough electricity for a Yaris- or Corolla-sized vehicle to cruise on the highway at 75 mph." into a more saleable; Toyota's test units are only 100 kW (130 horsepower), a pair of them can still produce enough electricity for a Yaris- or Corolla-sized vehicle to cruise on the highway at 750 mph."
      Conservatism has no pl

  • Okay. Is there some sort of plan to use these in future vehicles? How do they compare to traditional engines in terms of efficiency, power, maintenance requirements, etc.? How do they compare to electric vehicles in the same regard? Devoid of any such meaningful substance, this story seems like fluff meant to distract from Tesla, Nissan, Ford, etc. who are aggressively pursuing all-electric vehicles.

  • So you're gonna need at least two cylinders. But they'll have to be opposed and they'll have to fire in time, because otherwise they're not going to help you. I don't have any trouble believing they can synchronize them, but this makes the engine a lot longer, and you might as well just build a boxer. If the gas seal on the chamber on the other side of the piston fails, your engine will fail spectacularly. Seals fail all the time. Meh.

    • by Zeussy ( 868062 )
      They can be horizontal opposed in motion in the parallel twin design. This will give some second order imbalance though. Piston rings don't fail all the time, or you would see new cars blowing blue smoke all the time. They gradually wear out.
    • Right, because I'm sure the engineers at Toyota haven't thought about this kind of stuff.

      • Right, because I'm sure the engineers at Toyota haven't thought about this kind of stuff.

        They build stuff they have no intention of producing all the time, they can still afford shit like that because people still want their cars.

        • by mjwx ( 966435 )

          Right, because I'm sure the engineers at Toyota haven't thought about this kind of stuff.

          They build stuff they have no intention of producing all the time, they can still afford shit like that because people still want their cars.

          It's called Research and Development.

          Things like VTEC didn't pop into your Honda overnight, the technology was developed over decades until it became good and cheap enough to be put into everyday use.

    • by Anonymous Coward on Wednesday April 30, 2014 @08:00PM (#46885485)

      Free piston engines have a distinct difference with respect to vibration. They can potentially couple a lot less vibration to the chassis than traditional designs because the vibration is only in one plane and there is no need to couple the engine to the chassis to provide torsional reaction force for the drive train.

      The vibration of any individual component doesn't matter, only the vibration that is coupled to the chassis of the vehicle. With a free piston design, there is no need to couple the engine directly to anything because you have no output shafts to couple to the drive train, and no mechanical reaction forces to contain. That means that the body of the engine can be decoupled from the chassis of the vehicle in the axis of vibration, and *allowed* to vibrate back and forth as much as it needs to. That provides the reaction force to the piston, and the forces coupled to the chassis are only the frictional loss in your mounting system.

      • Why was this modded down? If I had mod points I would mod it up.

        All I can assume is that some anti-green ideological idiot wants to shoot down any thing that makes good sense and saves energy.

        I assume that they are political conservatives, since it fits their typical behavior. I wonder if the Koch (pronounced COCK) brothers are somehow involved.

    • by AK Marc ( 707885 )
      The free piston needs no connection to the car. You could have the engine mounted in a manner that it slides back and forth, giving no net vibration to the chassis. You are thinking of drawbacks to a simple swap. That seems a stupid assumption.
  • How is this not just a one cylinder engine? Based on the description, that's what it sounds like.

    Why don't they just scale down (massively) from diesel electric locomotives [] and be done with it?

    • by jonwil ( 467024 )

      Isn't the Chevy Volt PHEV exactly like that? Its got a gasoline engine that powers a generator that powers an electric motor that powers the wheels. It also has batteries you can plug in and charge up though.

    • Rather than the cylinder driving a crankshaft, they're driving a linear alternator directly (basically an inverse solenoid - turning linear back-and-forth motion into electric current). That ought to lead to less losses from inertia and friction, as well as being more compact.

    • by amorsen ( 7485 )

      Diesel electric locomotives are horribly inefficient and heavy.

      • by AK Marc ( 707885 )
        Yet still much better than direct-drive Diesel.
  •'ve invented the alternator!

    • From the description, it sounds like they invented the weird piston machines that you can see in the Michael Jackson Moonwalker video game.
  • There were 2 of these 10Kw units required to cruise at 75Mph, so the efficiency, assuming 35% thermal efficiency, is 22mpg.

    Given that they're small and easy to maintain, perhaps that doesn't matter if they're only backups, or if this is just a first-iteration technology that may get substantially better.

    The big concern imho, is vibration. Unlike a crankshaft-based engine/motor, there is no physical coupling of the pistons if you deploy two of these in a horizontal configuration (as TFA suggests would counte

    • The synchronization would have to be between the electronic control units. So it can be implemented by running e.g. an ethernet cable between the two engines.

    • How about having two pistons sharing a combustion chamber in a horizontally opposed arrangement? The forces would cancel leaving no net force on the outer casing. Also, to return the pistons, why not just make the other ends a combustion chamber as well, so it's double-acting? Again, forces cancel.

      I would imagine the real tricky thing would be to make the pistons work effectively as magnets within the generator coils - permanent magnets (even very strong rare-earth ones) wouldn't give you enough field - y
  • So chemical energy generates mechanical energy which then generates electricity. This is not what the word "directly" means.

    • Yeah this definitely isn't a direct electrical generator. But it could be far more easily distributed throughout a vehicle. Instead of every piston needing to be mechanically linked you could have them spread throughout the car and arranged somewhat arbitrarily (except for vibration considerations). So from that perspective they are kind of direct in that electricity comes directly out of a self contained unit instead of needing an engine connected to an alternator. Each piston is creating electricity.

  • by 140Mandak262Jamuna ( 970587 ) on Wednesday April 30, 2014 @07:10PM (#46885163) Journal
    The description talks about using a gas chamber as a spring to push the piston back to starting position. Why? There is no crank shaft on the other side? We could imagine a dual acting piston with a combustion chamber on both sides. In a regular IC engine there is a flywheel to do the intake, compression and exhaust strokes soaking up the energy from the power stroke. Even with a dual acting piston, there is an issue there.

    The linear generator is also a motor. We should be able to use the magnetic fields to move the piston back and forth. Mechanical complexity of cams, crankshafts and flywheels and clutches replaced by the electrical complexity. Easier to handle and more reliable too. But still don't see any reason to believe it is going to be more efficient.

  • 10 kilowatts ought to be enough, it's like the output of 50 human beings (unless they're working really hard at pedaling), I also don't feel the need to go over 50 mph.

    In fact it is a good match for the european category of heavy motorised quadricycle : up to 15 kilowatts, up to 1 ton payload (when transporting goods ; max vehicle weight at 550 kg in this case) and top speed not very high.
    If the engine can be scaled down in power as well as size and weight you open up the lightweight category which is max 4

    • I also don't feel the need to go over 50 mph.

      So it YOU! If you're that guy, please, please get out of the fast lane! It's dangerous to have everybody switching to the slow lane to pass you. ;)

      • So you're the guy tailgating me :).
        Driving slowly (slowish) makes it easy to follow the rules.
        On the highway, drive at whatever the speed you wish on the right lane ; if there's traffic riding with the haul trucks might be an option. On a non-highway road, drive at whatever speed but if there's speedy traffic you might be driven to drive faster.. But either way this way of driving works if you consider the speed limit as a maximum instead of a minimum.

        It might be more relevant in Europe with lots of turns o

  • At least, a magnetohydrodynamic generator [] is the only thing I can think of off the top of my head that "directly" converts energy from combustion to electricity. Still doesn't look like it's anywhere close to the efficiency of a good fuel cell, though, and those superconducting magnets would make for an awfully heavy vehicle. (Now, if you used liquid hydrogen for both fuel and cryo-coolant...)

  • by PopeRatzo ( 965947 ) on Wednesday April 30, 2014 @07:29PM (#46885313) Journal

    Felix Wankel is somewhere laughing his ass off.

    • Elegant design, and lots of HP per liters of displacement. The problem is that you often run into carbon fouling and the apex seals break. They also need oil metered in with the fuel as there isn't an oil sump. Now combine the need to burn oil with the fact a combustion cycle doesn't have enough time to stay in the chamber and you have pollution. It's why the entire length of the exhaust system is one giant catalytic converter.

      Now if they can make a diesel Wankel with strong enough apex seals, now you're ta

      • I don't know nothin' about no apex seals, but I drove a '93 RX-7 a few times and that thing would push you down against your seat back when you hit the gas. It was a twin turbo and the owner told me it was getting close to 400 bhp, but I can't say one way or the other, but man, I liked that car.

      • I've seen some amazing prototype demos of magnetic fluids as a sealant. The concept is sound and I don't know why somebody isn't doing anything with them. It can hold quite a lot-- magnets keep the liquid in the gaps and there is minimal friction; much less than any solids. somebody just needs to engineer a synthetic oil that is magnetic... but even if they don't, just the magnetic fluid should be enough...

        not sure of the speeds... but the demo I saw was for an air compressor that used less energy (due t

  • Free piston engines have been around since a least the 50s. Described in detail in Taylor's "The Internal Combustion Engine in Theory and Practice"1977, rev 1985, An excellent set of book on how internal combustion engines work.

    The classic version used a turbine for output and was not very efficient. Using direct electromagnetic output for a hybrid is an interesting idea. One of the great weaknesses of the free piston engine is poor low power performance, and that isn't needed in a hybrid. Not clear though

    • I read about free piston engine about one year ago, and it described a single piston going back and forth.
      Very interesting that the concept was devised in the 50s, it makes me think that the flying car was invented in the 50s as well. Only it was uncontrollable and not worth for anything except hovering over the ground for 30 seconds or such.

    • The classic version used a turbine for output and was not very efficient.

      You know, I just imagined a use for this engine that actually takes advantage of the fact that it's basically a big air compressor. If you added a valve system on the other end, you could bleed off part of the pressure and feed it into the MDI air car system. This is the component that makes plug-in air hybrids efficient to refuel with fuel. Well, if you add engine brake technology to it, that is. And then you feed the engine brake exhaust into the air tank. But since it has this other side to it, it doesn'

      • The original use of free piston engines was as air compressors to drive turbines, so its a good idea. I turned out in practice though that they were not as efficient as expected and they were never widely used despite many years of R*D.

  • A fuel cell is pretty good at converting chemical energy into electrity directly.

    Of course they work best on Hydrogen, but we need to stop burning carbon anyway.

  • it's an old idea, but worth trying now because electric power conversion works very well now. This thing generates AC at some variable frequency and voltage depending on fuel flow and load. The waveform that comes out is awful. (See the article). Two successive cycles can be quite different. There's no flywheel or rotating mass to smooth out the motion.

    Today, converting that irregular electrical output into something more consistent is straightforward. The output is going to be fed into some kind of swit

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