I predict these won't ever be smaller, lighter and cheaper than traditional design with an rotating engine and separate generator.<p>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.
Oscillating piston generators have been around for a <i>long</i> 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:<p><a href="http://www.google.com/patents/US2900592" rel="nofollow">http://www.google.com/patents/US2900592</a><p>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.
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.
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...<p>EDITED to add: they seem to have run out of funding without producing anything commercializable: <a href="http://newenergyandfuel.com/http:/newenergyandfuel/com/2013/09/04/arpa-e-backing-the-msu-wave-disk-engine/" rel="nofollow">http://newenergyandfuel.com/http:/newenergyandfuel/com/2013/...</a>