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."
Re:so how is it different from diesel electric loc (Score:4, Informative)
RTFS.
A diesel locomotive as a traditional diesel engine with a crankshaft that turns a generator. The rotational energy is converted in to electricity by moving coils past alternating magnetic fields.
If move a single magnet back and forth through a coil it will also produce electricity.
If you attach the magnet to the piston and the coil around the cylinder walls you don't need a crankshaft anymore. I guess in theory, less friction = less loss = more efficient. Without a crankshaft there isn't any side load put on the cylinder either, so that experiences less friction too.
You still need mechanical movement to run values though, or you've just an inefficient 2-stroke cycle.
Perhaps they need to develop decent electronic valves before they go telling everyone how efficient it is.
Re:Efficiency? (Score:5, Informative)
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.
Re:Efficiency? (Score:5, Informative)
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:
http://www.greencarcongress.co... [greencarcongress.com]
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)...
Re:The vibration must suck (Score:5, Informative)
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.
Re:Efficiency? (Score:4, Informative)
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.
Re:Efficiency? (Score:5, Informative)
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.
Re:Efficiency? (Score:5, Informative)
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.
Re:so how is it different from diesel electric loc (Score:4, Informative)