字幕表 動画を再生する 英語字幕をプリント - We've talked about engines before, and I don't know if I'll ever get tired of it. The air gets compressed by the piston, and the spark... What? No, stop it! There's no piston here! What if I told you we could skip all of that crap? Not worry about turning downward force into rotational force and cut the size of the gall dang engine in half? That's the Wankel rotary engine! In 1951, Felix Wankel got this idea in his head that if you put a triangular rotor in a well-designed circely, oval-ish shape, you could make an engine that took care of intake, compression, combustion, and exhaust, just like the traditional piston-drive Otto Cylce engine. And because it's a spinning motion, you wouldn't need to worry about crankshafts and valves and timing belts and lifters and all that crap that other people are goofin' around with. He had some trouble getting it right, though. So it was in 1961 that Mazda, intrigued by this idea, helped him out, and here's how it works. A curved triangle sits in the engine. It's what'll drive the driveshaft, which is also weird. Instead of a piston, this magic triangle is called a rotor, because it spins. The rotor sits inside of a housing and rotates around a fixed gear attached to the housing. This gear makes sure that the rotor follows the right path, so it's not just floating around in there. The rotor then spins an eccentric output shaft, and this is what'll give the car moving. You can call it a driveshaft if you want, I'll know what you're talking about. But just the names of the parts should let you know that the Wankel rotary engine plays by its own rules. Now that we know the parts, let's see how they fit together and make the boom. We'll start with the intake. As the triangle-shaped rotor draws away from the wall of the housing, it's creating a vacuum. As it passes the intake hole, it continues to pull away from the wall, drawing the air-fuel mixture into the chamber it's creating, just like a piston would draw air in on its intake stroke. When the peak of the rotor passes the intake port, well, now that chamber's sealed. The rotation of the triangle, still sealed against the housing, begins to compress the air-fuel mixture as it continues its rotation. When the air is as compressed as it can be and the rotor has just a bit more mass on the other side of the chamber, a spark triggers the combustion. The combustion chamber is long. If there's only one plug, the flame would spread too slowly to be effective at producing power. Most rotary engines have two sparkplugs. When the sparkplugs ignite the air-fuel mixture, kapow! It forces the rotor to move in a direction that allows the combustion reaction to expand, continuing the rotor's journey around the housing. The combustion gasses continue to expand, moving the rotors and creating power, until the peak of the rotor passes the exhaust port. Just like the rotor compressed the air-fuel mixture against the wall with the sparkplugs, on this side of the housing, the rotor pushes the exhaust gasses out of the exhaust port. And if you look at the other point of the triangle, the rotor is beginning to draw air into the intake chamber just as it's finishing with the exhaust down here! So the cycle continues, over and over and over and over and over and over, and it continues to go over and over and over. But unlike the jerky up-and-down motion of the pistons, the rotor moves, just like my favorite band, in one direction. ♪ You don't know you're beautiful ♪ There's so much rubbing going on between the rotor and the housing that that gave Wankel a lot of problems as he was designing. Engineers realized that a hole to let in the engine oil would reduce wear on the rotor and housing. Also, to make sure that no chamber of the combustion cycle loses pressure, apex seals cap the point of the triangle. These tweaks are what took Wankel's early underwhelming experiments from curiosity to practicality. And look at this triangle! With three sides, as soon as one side begins, let's say, combustion, another side is completing exhaust while the third side is drawing in air and gas! So, unlike a traditional piston-driven engine, which would need three cylinders to do that, like the rare but very real in-line three, you only need one active component, the rotor, to have three stages of engine combustion occurring simultaniously. The way Mazda did it on their engines, like what powered the RX7 and RX8, was to put two rotors that complimented each-other, so when one rotor was entering combustion, the other was about to enter combustion. You can see how evenly a Wankel rotary engine can deliver power versus the herky-jerky up and down of a piston-driven engine. This evenly-driven rotational force spinning the rotors drives the output shaft. The output shaft has round lobes mounted eccentrically, meaning they're offset from the center line of the shaft. Each rotor fits over one of these lobes. The lobes act sort of like the crankshaft in a piston engine. As the rotor follows its path around the housing, it pushes on the lobes. Since the lobes are mounted eccentric to the output shaft, the force that the rotor applies to the lobes creates torque in the shaft and makes it spin. This makes the eccentric shaft move three turns for each turn of the rotor, and that's why these engines can create such high rev. (engine revving) And if you check out the horsepower versus torque video, you'll know horsepower is how quickly force can be produced. A high-revving engine doesn't need as much torque to generate more horsepower, because it's delivering it so quickly. And, like Mazda did with the RX7, they can be turboed, just like any other engine. And again, because they're revving so high, a turboed Wankel doesn't have to worry half as much about lag! Some lag! So, what are some other benefits of a rotary engine? First, there's fewer moving parts. No lifters, no push rods, no camshafts. All those little things that can go wrong in a traditional engine simply aren't there in a Wankel, so they can't break. In a two-rotor Wankel, you got two rotors and one e-shaft to worry about, that's it. And that means these engines can rev higher and not bust any of those intricate parts. And also? You don't need four, five, six cylinders, you've got an engine delivering consistent power, making awesome noises! (engine revving) And taking up half the room of other engines! Oh! And sometimes, when it gets moving really quick, you get this! (backfiring) That is pretty cool! But that's also a drawback. Wankels use a lot of gas because they have a low compression ratio. When they get moving like that, they make those sweet-ass flames 'cause they're shooting out exhaust gasses with unburnt hydrocarbons. That's not good for fuel economy, and it's not good for the air! Also, remember how they're lubed with oil throughout the housing? That oil burns when it's hot. That means more burnt less clean hydrocarbons, which is tough for emissions. You remember how they sealed up the different chambers created by the rotor. Remember, from before? Uh, yeah. You can blow an apex seal, and if that happens... (screaming) Those chambers bleed into one another and you lose most of the benefits that made you fall in love with your screaming rotary engine in the first place. Between being different and being good, Wankel rotaries are pretty rad. Wankel rotary engines! If you like the way we show how things work on Science Garage, then you really need to check out Brilliant.org. Brilliant is math and science enrichment learning. It's engaging, and instead of just getting talked at about how thing worked, Brilliant is set up to let you really get in there and apply what you're learning. The sequences lead you to thought-provoking, challenging problems, and that helps you understand concepts at a deeper level. Actively solving problems becomes an addictive, interactive experience, and I gotta tell you, it's pretty cool. How do you think the brain trust we just talked about created the Wankel rotary engine? They had a deep understanding of physics and practical application and problem-solving, just like the courses at Brilliant.org. A great place to start is with Physics of the Everyday. This course gets into how things work, things you use every day, just like we do here on Science Garage! To learn more about Brilliant, go to Brilliant.org/sciencegarage and sign up for free! Also, the first 200 people to go to the link will get 20% off their annual premium subscription! I'll see you there! Brilliant! And follow me on Instagram, @bidsbarto, and follow Donut, @donutmedia. We got shirts like this, and we got new designs comin' soon. Guys, we do this every Wednesday! Make sure you subscribe, hit the yellow button so you get notifications! Like the RX7, you can learn about turbochargers here, and you can learn about the RX7 in this episode of Up to Speed! Don't tell my wife these engines can be a hassle, 'cause I'm trying to get one.