Toyotas Free Piston Engine Linear Generator (FPEG)
A new engine has been developed called the free piston engine linear generator (FPEG) from Toyota Central in Maine
The reason behind the “free” is because the piston here has no crankshaft, instead on the power stroke of the engine the piston releases energy into fixed windings which surround it. This generates a shot of three-phase AC electricity, making it sparkles!
The piston is decelerated and reaccelerated upon each stroke and Toyota have had to make sure that all the combustion and electromagnetic power is effectively absorbed to give the best possible efficiency.
You could say the device is much like the alternator of a car as it also generates AC power, however in contrast with most cars today using 3 phase induction or 3 phase brushless DC motors. This car could run entirely off this alternator like design, only needing some current and voltage conditioning.
There will also be a lithium ion battery back added to this car with an AC bridge rectifier to alternate the signal back to DC to add power to it and so you can use the features the car has to offer. Unless Toyota has achieved the AC battery this seems the most probable option.
This can be used with diesel or petrol based engines, however one of the real achievements here is that the engine has a “claimed” 42% thermal efficiency. This completely overtakes any cars today judging by this standard.
However while linear generators and combustion engines are nothing new such as wind up torches or shakeable batteries, and single-acting power pistons have also been found in the Russian military within their power assist boots, the accomplishment here is that linear generators and combustion engines have never been utilised in such a unison.
Liner alternators are close to resemble liner motors, however it’s not as simple as swapping one for the other without having many issues to tackle. However that does not mean a versatile linear electric power device could not be created.
Toyota’s demo engine, just 8 inches around and 2 feet long, and was able to generate 15 hp. A two-cylinder model would be self-balancing and have much reduced vibration.
Having the valves electrically operated can give the user some real advantages to the user as they can control the engine more precisely and accurately. However the video above indicates a two stroke design which could further present problems for the system. Toyota visualises that a twin unit design pumping out 20 kW could power a light electric vehicle at a cruise speed of 120 kph (75 mph).