Toyota is developing a unique style of gasoline engine, known as a free-piston engine, in order to have a unit that can be integrated into a range-extender configuration as efficiently as possible.

They’re calling it the Free Piston Engine Linear Generator, or FPEG, and while it may sound like a new thing, these crankless motors were actually among the first kinds of internal combustion engines to be used.

This new design is specifically tailored to be of very compact dimensions, solely to produce electricity; it’s not designed to send any kind of power to the wheels, focusing exclusively on topping up the battery.

Currently, their test units put out around 13 hp, and a pair of them is apparently good enough to ensure a constant cruising speed of 75 mph (120 km/h) for a Yaris-sized vehicle. Instead of using two separate cylinders, perhaps they could use a boxer configuration, ideal if they also want to cull the potential vibrations caused by the one-pot design.