Did you know? Your variable valve timing direct injection turbocharged engine is outdated! And it doesn't have a crankshaft or connecting rods; it runs directly through the reciprocating motion of the pistons!
Toyota is developing a Free Piston Engine Linear Generator (FPEG), which promises to make all of this a reality. It's easier to understand if you think of it as a free piston engine plus a linear generator. But is it an engine or a generator?
Simply put, the FPEG engine is like a gasoline generator. Currently, Toyota's prototype uses a single-cylinder design, which has a larger combustion chamber and piston compared to traditional internal combustion engines. The piston moves back and forth under the thrust generated by the combustion of fuel, but this time its task is not to output power to the wheels, but to generate electricity.
Toyota developed the FPEG to create a compact device specifically designed for range-extended electric vehicles. Compared to the engines and generators used in current range-extended electric vehicles, the FPEG will significantly reduce the size and weight of the engine.
The FPEG engine eliminates the crankshaft mechanism, allowing for freer piston movement.
In fact, FPEG is not a new technology, because the world's first FPEG was patented as early as 1959. FPEG is a device that is an extension of FPE (Free Piston Engine).
So, what is an FPEG engine? As the name suggests, this type of engine has a high degree of piston freedom. But how does it allow the piston to move so freely? The reason lies in eliminating the crankshaft and connecting rod structure and replacing them with an air spring. The piston movement is entirely controlled by the gas in the combustion chamber and the air spring. Designers can determine the air pressure and volume themselves, thus allowing for greater design freedom. Simply put, when the piston reaches bottom dead center (BDC), it encounters resistance from the air spring and bounces back, causing the piston to move towards top dead center (DDC). Upon reaching DDC, it is then propelled back down to bottom dead center by the gas thrust generated by the combustion of fuel, and the cycle repeats continuously.
The biggest difference between range-extended electric vehicles (REEVs) and hybrid electric vehicles is that the gasoline engine only charges the battery and does not directly drive the vehicle. The world's first REEV, the Chevrolet Volt, was simply a modified version of a traditional 1.4L gasoline engine.
Toyota gives FPEG ultra-high thermal efficiency
Toyota's FPEG technology is a power generation device that extends from the operation of FPE. In traditional hybrid systems, the generator is separate from the engine body and is connected to the engine crankshaft, using its kinetic energy to generate electricity; but Toyota's FPEG is different. Since FPEG does not have a crankshaft, the piston body becomes the generator, and because there is no crankshaft mechanism, the size of the engine body is reduced, and the structure is relatively simple.
The Toyota FPEG generates electricity through a linear generator system consisting of a permanent magnet mounted on the piston and a coil assembly outside the magnet. On the opposite side of the combustion chamber, the manufacturer fills a sealed space with air to create an air spring. This device replaces the crankshaft design, allowing the piston to rebound and move in the opposite direction when it reaches bottom dead center. The magnet on the piston repeatedly moves and interacts with the coil assembly, generating electricity.
The working principle of FPEG is the same as that of a two-stroke engine. When the piston moves downward, it completes the power stroke and uses the air-fuel mixture to expel the exhaust gas. When the piston moves upward, it draws in fresh air at the bottom of the piston and completes the compression stroke. After reaching top dead center, it completes the work of fuel injection and ignition.
Toyota states that the FPEG engine achieves 42% thermal efficiency under continuous use. Currently, only the best, most complex, and most expensive gasoline engines in the world can achieve close to this percentage, and even then, only under specific conditions. Even more remarkable is that the FPEG engine is only 60 centimeters long and 20 centimeters in diameter. This small engine produces 13 horsepower, making it unsuitable for large vehicles, but sufficient to power micro electric vehicles. Furthermore, the FPEG engine can collaborate with other systems, such as kinetic energy recovery systems, for even better performance.
FPEG can be powered by almost any fuel, not just gasoline.
Toyota stated that a production schedule for the FPEG has not yet been determined. However, they also noted that because the FPEG lacks a crankshaft and relies entirely on air springs for control, the compression ratio of the internal combustion engine can be freely controlled by the volume of the air springs. This means that in addition to gasoline, hydrogen fuel is also a viable option for the FPEG. Once the FPEG officially enters the automotive market, the development of hybrid vehicles will have more possibilities, which is undoubtedly a major benefit for consumers.
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