From the Outside It Looks Like a Single but Inside Four Pistons Mingle! Square Four Engine Explained

Video Description

Try Onshape, the world's most capable in-browser CAD software for free for 6 months: https://Onshape.pro/d4a Support the channel by shopping through this link: https://amzn.to/4hdUdlc Patreon: https://www.patreon.com/d4a Become a member: https://www.youtube.com/channel/UCwosUnVH6AINmxtqkNJ3Fbg/join Today I want to talk about a very rare but also very interesting engine configuration. If you were to observe this engine from the outside you might be tempted to think how it’s just a big single cylinder….but if you lift the cylinder head inside you would find not one, but FOUR pistons packed into a square, hence the name. Square four. This engine configuration is in fact the most compact way possible to arrange four cylinders. It is as narrow as a two cylinder which means that it’s esseenetially half the length of an inline four while at the same time being noticeably shorter than a V-twin. And it achieves all of this while being very smooth and well balanced. Despite these important benefits this engine configuration never became widespread or popular and today it’s largely forgotten, but I think that it deserves a comeback because today we can easily manufacture something that we couldn’t back in the 40’s and 50s when this engine was alive. As you can see what this engine essentially is two 180 degree twin cylinders fused together into a single cylinder block. But these two twins are not mirror images of each other. As you can see when this piston of this pair goes up the opposing piston of the other pair goes down. The result is that diagonally opposed pistons go up and down together. And this tells us that one crankshaft trails the other by 180 degrees of phase shift. So we have two cylinders going up and two cylinders going down together, does this remind you of any other engine configuration? Yes, the inline four also has two pistons going up and two going down and this means that the square four fires every 180 degrees of engine rotation just like the inline four, giving an even firing interval which contributes to a smooth sound and feeling of the engine. But despite the equal firing interval the different anatomy of the square four forces a different exhaust pipe configuration giving the square four a very interesting soundtrack. What about engine balance? As we know primary balance or imbalance primarily stems from the mass of the piston and in the square four, just like in the inline four, when two pistons are at top dead cetner and creating and upward force the other two pistons are at bottom dead center creating a downward force so the two up cancel out with the two down and we have perfect primary balance, just like in the inline four. Almost Whenever you take something and spin it at very high speed, such as a crankshaft, you are creating a gyroscopic effect. This is the reason why certain Ducati V4 motorcycles have a counter-rotating crankshaft. Now in a square four we have two crankshafts. They are geared together which means that they are spinning in opposite directions and that means that the gyroscopic effect or torque of one crankshaft cancels out the other leading to a net zero gyroscopic effect resulting in a more agile motorcycle with better steering feel when ridden at the limit. But here’s the ace up the square four’s sleeve! If we choose to replace the two 180 degree inline twos with two 270 degree inline twos the square four can achieve perfect primary and secondary balance with only four cylinders. In a 270 degree twin when 1 cylinder is at top dead center the other is at mid stroke. So if we implement that into a square four we would have two pistons at top dead center and the other two at mid stroke. That means two primary forces pointing up and no primary forces at mid-stroke because that’s when the piston has achieved peak velocity, it’s not accelerating or decelrating hence no force. This means that we now have imperfect primary balance. But remember, we have two crankshafts and primary vibrations occur at the speed of the crank which means that we can easily restore perfect primary balance with crankshaft counterweights. When it comes to secondary balance it’s perfect out of the box. Secondary forces point up at top dead center and down at mid-stroke which means that on a 270 degree twin they simply cancel out and would do the same thing on the square four. They would create a very slight rotating couple, but honestly it’s so small that it’s not worth mentioning. A special thank you to my patrons: Daniel Zwoa Meda Beda valqk Toma Marini Cole Philips Allan Mackay RePeteAndMe Sam Lutfi Cakeskull #d4a #squarefour #onshape