Simanaitis Says

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RESEARCHERS AT Toyota’s Central R&D Labs in Japan have shared details of generating electricity with an unorthodox internal combustion engine. The engine is a two-stroke design, but with a piston that has no connecting rod nor crankshaft. The free-piston-engine linear generator, FPEG for short, could have application in hybrid cars. Its basic principle is shared with flashlights that operate sans batteries.


The principle of electromagnetic induction: Movement of a magnet through a coil of wire generates an electrical current in the coil. Image from

At the heart of both Toyota’s FPEG and battery-less flashlights is the principle of electromagnetic induction, of generating an electrical current by moving a magnet past a wire.

Electromagnetic induction was discovered independently by two scientists working an ocean apart in 1831. Englishman Michael Faraday published his results first; his reward is the name Faraday’s Law describing the phenomenon of inductance. On the other hand, American Joseph Henry is honored by the System International unit for measuring the same phenomenon, the henry. (Faraday gets abbreviated into the farad, the SI unit for capacitance.)


At left, Joseph Henry, 1797 – 1878, American scientist. At right, Michael Faraday, 1791 – 1867, English scientist. Co-discoverers of electromagnetic induction in 1831.

The electromagnetic aspects of Toyota’s FPEG are best described in the battery-less device known as the “shake” flashlight. Outwardly resembling an ordinary flashlight, its body contains a fixed coil through which a magnet is forced by shaking the flashlight linearly. An ultracapacitor stores the charge electrically, as opposed to a battery’s chemical process.


A “shake” flashlight, aka Faraday flashlight, gets its electrical charge, and its LED illumination, without batteries. Its magnet (here, partly to the right of the copper coil) is shaken between the two black bumpers.

I got my Faraday flashlight several years ago from MBtech Group, a joint venture of Daimler-Benz and French AKKA, an engineering and technology consulting firm. Typical of shake flashlights, thirty seconds of vigorous shaking (the light, not me) gives perhaps five minutes of bright illumination. See for more on these devices.

Toyota’s FPEG replaces shaking with two-stroke internal combustion. A high-strength neodymium-iron-boron magnet is integrated into a piston which moves freely within its cylinder, around which is wound an induction coil.


Toyota’s FPEG engine is a two-stroke, receiving the blue intake air and expelling the red exhaust simultaneously. A video at shows how this is accomplished.

The combustion chamber replaces one bumper of the shake flashlight; a gas-spring chamber replaces the other. See for a video of FPEG operation.

Precise ignition timing and adjustable pressure of the gas-spring are crucial to control the free piston’s reciprocation. Engraved lines on the piston are sensed to identify its location.

Additional subtlety of Toyota’s FPEG  is shown in the design of its W-shape piston.


The FPEG’s piston is shaped like a W, a double-U, as shown in this cross-sectional view.

The combustion chamber is at the center-top of the W. The piston’s exposure to its gas-spring-chamber is at the bottom of the W.

A larger cross-section at the bottom improves thermal efficiency of the gas-spring. Hollow portions of the piston promote cooling and lubrication. The magnet is opposite the piston crown, thus preventing its loss of strength through heat-induced magnetic degaussing.

Toyota researchers first analyzed a computer simulation of the FPEG, followed by building an actual prototype. The prototype was spark-ignited and achieved stable operation for more than 4 hours without problems of cooling or lubrication.

They calculate their FPEG produced 10 kW of output power. Thus, for example, a pair of such devices could be employed to provide cruise capability for a small electric vehicle.


SAE Technical Papers (and gratis Abstracts) on Toyota’s FPEG research can be obtained through

FPEG research was the subject of two technical papers presented at the 2014 SAE World Congress earlier this year in Detroit. SAE Technical Papers No. 2014-01-1203 and 2014-01-1193 give details of FPEG fundamental characteristics and aspects of control, respectively. ds

© Dennis Simanaitis,, 2014


  1. Alfred Lunde
    January 26, 2016

    Where might I find the present status of this engine. I understand they were working on a two cylinder version to smooth it out and gain more power.

    • simanaitissays
      January 26, 2016

      I’ve read nothing about it recently. Which, of course, works both ways. It might have been dismissed. Or it’s promising enough to be near production. Either way, an automaker keeps quiet about it.

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