A typical four-stroke engine or Otto cycle engine does intake, compression, combustion, and exhaust. The Atkinson cycle engine and the Miller cycle engine also do intake, compression, combustion, and exhaust, however they differ in one small but very important detail that allows them to be significantly more efficient than the Otto combustion cycle engine. And in this video we're going to dive back into engine history to see and learn about the evolution of the combustion engine and the difference between the Otto, Atkinson, and Miller four-stroke engines. The Otto engine as we know it today was invented in 1876 by German Nicolaus August Otto. Although it may not look like it, the 1876 engine has many of the elements we see in today's engines and is Otto's first true four-stroke engine. There's a crankshaft, a connecting rod, and even a camshaft. Inside we have a piston and the engine does intake, compression, combustion, and exhaust just like any modern engine. Of course, Otto's first engine was an instant commercial success, and of course Otto patented the design. Now this, the patent, is what brings us to Mr. James Atkinson, who, like many of his contemporaries, after seeing the commercial success of the Otto engine, began to develop his own engine. Now the problem is that in order for it to be commercially viable, such an engine had to be sufficiently different from the Otto design so as not to infringe patent rights. Atkinson decided that the compression stroke of the Otto engine was actually something that could be improved, and that was to be done by reducing the length of the compression stroke relative to the length of the combustion stroke, or the expansion stroke as some call it. In other words, the engine would spend more time generating power than wasting it by compressing the fuel-air mixture. In 1957, American engineer Ralph Miller patented the Miller cycle engine. Now the Miller cycle engine is based on the same concept as the Atkinson engine, that is, reducing the power-reducing effects of the compression stroke. The problem is that Ralph Miller chose a much simpler and more elegant solution compared to the extremely complicated set of connecting rods and linkages of Atkinson's original design. And the solution is this: keep the intake valve open for longer. That's it. The construction of the engine remains absolutely the same as that of a conventional Otto engine, the only thing that differs is the valve timing. A conventional Otto engine closes the intake valve before the compression stroke begins. This is done to ensure that the entire length of the cylinder is used to store and compress the air-fuel mixture, leading to optimum power. The Miller engine does not close the intake valve when the compression stroke begins. The intake valve is kept open for the first 20-30% of the compression stroke. An open intake valve, of course, means that the upward movement of the piston simply pushes part of the air-fuel mixture into the intake manifold. The piston cannot compress anything until the intake valve closes. In fact, back in the late 90s, Mazda put this exact concept into practice with its KJ-ZEM engine which it fitted in the Mazda Millenia/Xedos 9/Eunos 800. The KJ-ZEM was a supercharged 2.3-litre V6 that ran on the Miller cycle. Right after the Mazda Millenia was discontinued, Toyota revived the concept behind the Atkinson/Miller cycle. Toyota’s foray into this field began in 1997 with the first generation Toyota Prius and its 1NZ-FXE engine. But this time, instead of a supercharger, we have an electric motor which is used to compensate for the lack of torque and responsiveness. As we know, electric motors produce instant torque and do not drain engine power like superchargers do, meaning that hybrid drivetrains and the Atkinson cycle are a perfect match which was put into practice in all of Toyota’s hybrid vehicles. Another advantage that modern technology has brought is variable valve timing, or VVT. This allows the engine to run on the Atkinson cycle only when desirable, reducing load conditions such as highway driving. 00:00 The Road to Compression 08:15 Atkinson 14:05 Miller 18:04 Mazda and Toyota #d4a #d4aespanol #mechanics