

Toyota Central R&D Developing Free-Piston Engine Linear Generator - negativity
http://www.greencarcongress.com/2014/04/20140422-fpeg.html

======
tlb
I predict these won't ever be smaller, lighter and cheaper than traditional
design with an rotating engine and separate generator.

In general, the generator weighs and costs more than the engine for the same
power level. In the linear design, the generator is used inefficiently because
the magnets are moving in a sinusoid instead of a constant velocity past the
windings, and the maximum speed of a piston is lower than the optimum speed of
a generator. So you'll need more magnet & wire for the same power level,
increasing total weight and cost.

~~~
trhway
>I predict these won't ever be smaller, lighter and cheaper than traditional
design with an rotating engine and separate generator.

it most possibly will. The reason is that traditional design was built for
actual mechanical spinning of the wheels with all the trade-offs coming from
it. Generating engine has completely different requirements which would drive
trade-offs and optimizations. For example, you can run free-piston at much
higher rpm, thus mitigating the inefficiency of magnet/wire usage. Higher rpm
would lead to less weight for the same power. The pressure/volume curve can
also be optimized and shaped instead of the sinusoid forced by the rotating
movement. Etc...

~~~
jacquesm
Much higher frequency, not RPM! (there is no flywheel to go around...)

------
userbinator
Oscillating piston generators have been around for a _long_ time, they're
nothing new and based on the same principle of operation as those shake-to-
recharge flashlights; note the date on this one in particular:

[http://www.google.com/patents/US2900592](http://www.google.com/patents/US2900592)

AFAIK they were briefly used in very limited amounts by the Germans in highly-
space-constrained applications like missiles, but otherwise they were quite
inefficient.

------
tsomctl
Interesting. Presumably there will still be just piston rings in the normal
place, although I would like to see more on how they are going to lubricate
it. You don't want the gas spring chamber to fill up with oil. My guess for
how they are going to get it started is by driving the permanent magnets with
the coils. Also, why is it 2 stroke? I'd always assumed that 2 strokes were
smaller and cheaper, but had less power. Possibly because there is no momentum
to do 2 of the 4 strokes. Toyota definitely has the technology to make it a
modern EFI 4 stroke, though. For the fuel intake and compression strokes, the
coils could be disconnected from the load and driven so that the strokes
complete.

~~~
digdugdirk
Two stroke engines are actually smaller, cheaper, and more powerful than four
stroke engines of equal displacement. The issue with two stroke engines is
cleanliness. Because there isn't a spare cycle to push all the extra unburned
particles out of the chamber and let only clean air/fuel into the chamber,
there is some loss of power efficiency due to the attempted combusting of
leftover particles. This is more than mitigated by having double the amount of
power strokes per equivalent displacement. There's actually some really
interesting design techniques that have been used to "coax" the waste
particles out of the chamber, take a look at MotoGP technology circa early
2000's if you want to learn more.

~~~
marvin
All the two stroke engines I have used (light aviation) have been terribly
unreliable and painful to maintain. Won't start, often fires just on one
cylinder, stops randomly, leaks oil everywhere. Is this a "shitty design"
problem rather than an inherent problem with two-stroke engines?

~~~
digdugdirk
Probably a combo of both. You know how I said above that there are some cool
design techniques to get the old waste gases out of the cylinder? Well those
techniques only work over a very narrow band of RPMs, under very specific
air/fuel ratios. Your problem is even worse because you're in an aviation
setting. Your engines are experiencing very different air densities, and this
is causing the air/fuel ratio to change drastically compared to what they've
been tuned for. If they get too rich, they stall. Too lean, they explode.

The leaky oil? Yeah, that's probably just a two stroke being a two stroke. Due
to the design, they aren't "oiled" like a car, you instead shoot the oil in
with the gasoline in the injection cycle, and it just kinda seeps in and
around the engine. That's the main reason why they're dirty - both literally
and environmentally.

~~~
Gravityloss
Diesel engines have less problems when inlet air goes to the exhaust, since in
a diesel, inlet air doesn't contain any fuel. A two stroke diesel has thus
some synergistic advantages.

A direct injection otto engine could also work very well as a two stroke.

------
ScottBurson
Whatever happened to the Mueller wave disc motor? Does anyone know? It seemed
very well-suited as a range extender motor in a series hybrid. Surely there's
a Chevy Volt driving around with one somewhere...

EDITED to add: they seem to have run out of funding without producing anything
commercializable:
[http://newenergyandfuel.com/http:/newenergyandfuel/com/2013/...](http://newenergyandfuel.com/http:/newenergyandfuel/com/2013/09/04/arpa-
e-backing-the-msu-wave-disk-engine/)

------
rasz_pl
Already patented by Bill's trolling patent outfit.

[http://jalopnik.com/5210372/bill-gates-files-patents-for-
ele...](http://jalopnik.com/5210372/bill-gates-files-patents-for-
electromagnetic-engine-plasma-injectors)

