If you haven’t noticed, internal-combustion engines are kind of big – even the three-cylinder unit on the new triumph 675 is too large to carry around in your arms. However, what if you ride a bike that doesn’t necessarily need an engine that big, or an engine that contains all the standard rotating parts? What if your electric car just needs a simple range-extending generator? Well, Toyota has you covered with the FPEG.

FPEG stands for Free Piston Engine Linear Generator (FPELG didn’t have the same ring to it), and it could very well be the first seriously major change to the standard internal-combustion engine in its century-long history. All Toyota had to do was take a look at an older engine design, incorporate a long-standing law of physics, and spend measureless time and money to make everything work. Easy, right?

A two-stroke motor going into a passenger car? What year is this?!

The big change between the FPEG and a standard car engine is the removal of both the crankshaft and the connecting rods. When it comes to providing juice for electric-car batteries, you don’t need the rotational motion of the crankshaft – all it does is add weight and complication. So Toyota ditched the crankshaft (and, by proxy, the connecting rods, since they bolt to the crankshaft). However, that leaves us with an engine and a piston that lacks the ability to move back and forth in the cylinder; the power stroke will push the piston down, but without the crankshaft and con rods, what will push it back up?

To remedy that issue, Toyota created a gas-filled chamber underneath the piston. As the piston moves downwards in the cylinder, it compresses that gas, which acts as a spring to launch the piston back up to the top. That’s all well and good, but again, without the crankshaft, how is power delivered to the vehicle once the air-fuel mixture is ignited?

That’s where the law from physics comes into play. Toyota replaced the crankshaft with a magnet just below the piston (a neodymium-iron-boron magnet, specifically) and a coil of wire built into the cylinder wall. Thanks to the beauty of physics, if you drop a magnet through a coil of wire, it generates a voltage. If that wire is connected in a circuit, current will flow. In more scientific terms, when a magnet is moved relative to a conductor, it creates an electromotive force; what you have there is Faraday’s law of induction.

The biggest downside of losing the crankshaft? Also losing one of the dirtiest-named car parts. That really limits our ribald joke-making.

Toyota’s FPEG takes full advantage of Faraday’s law. As the piston moves through the cylinder, the magnet connected to the piston will move through the coiled wire built into the cylinder. That creates the electromotive force, which will then supply current to batteries or directly to an electric motor. Toyota’s discovered a unique way to turn mechanical energy into electrical energy while simultaneously deleting unnecessary parts of the equation.

The result is a 15-or-so-horsepower engine that, in a balanced two-cylinder configuration, is less than a foot around and about two feet long. That’s a small, light engine – perfect for electric cars, where every bit of weight savings will translate to increased efficiency. 15 horsepower might not seem like much, but it’s enough to keep a small car rolling down the highway at the speed limit.

Toyota’s got one single use in mind for the FPEG, one that we’ve already discussed – range-extending motors for electric cars. 15 horsepower is enough to provide juice to a range-anxious EV driver, and as mentioned before, it would be smaller and lighter than the current slew of range-extender engines, so there are many benefits to be had from the FPEG.

However, since it’s still a prototype, don’t expect it to be in your next Prius plug-in. That said, Toyota and BMW are entering into a new joint-venture based around a new sports car. If that car happens to be a hybrid, you may see this engine right at the heart of that beast.