Twin Rod Avadi Engine - Perfect Balance in a Single Cylinder - Genius or Just Another Pipedream?

What's up

engine

heads! Today it's time to review and explain

another

novel and supposedly revolutionary

engine

design, and our topic today is the Avadi engine which you can see here. A very unique and very interesting design. We have two crankshafts, two connecting rods for one piston and the entire

cylinder

rotates. And today, as always, we're going to explain why it was designed this way, what the advantages of this design are, as well as the drawbacks and weaknesses, and of course, we're going to discuss the potential for this design to actually break through. mass production So, let's get started.

Now, the first thing that came to mind when I saw this motor was "hey, this is like a gyroscope because". When you think about it, the

cylinder

rotates and then the two crankshafts rotate inside the cylinder as the cylinder rotates, kind of like a gyroscope. Well, that's funny, but why? Because there really is no inherent benefit to the engine in terms of performance, efficiency, weight or size, or anything really significant when spinning the cylinder. So why would you do it? To answer the “why,” all we have to do is look at the “how.” So how did they spin the cylinder?

The answer is in the gears. As you can see, each of the crankshafts has a gear attached to it. As the crankshafts rotate, the gears rotate and ride on a fixed, stationary ring gear. The fixed ring gear is attached to the outer casing of the motor. Because the fixed gear does not move and the crankshafts travel along it with their gears, it causes the entire cylinder to rotate. And the engine's torque output is actually on an attached shaft that is part of the cylinder, so the entire cylinder rotates at the same RPM as the engine's output RPM.

This is our torque and output RPM. So why do it with gears? Because if you want to make something rotate relative to anything else, there are ways that are simpler, cheaper, and even more efficient than gears. Because gears add substantial mass to a system, they also add friction. So why gears? If we look at the Avadi website and some of their other online sources, you will see how they state that gearing allows the motor to increase its torque, and yes, that is certainly true, because manipulating the gearing and gear ratios allows you to manipulate the torque output of a motor.

If we take two gears, we will use the same gear sizes and ratios as in the Avadi engine. So if we take two gears, a small gear and a large gear, and if we say that the small gear is half the size of the large gear, then we have a gear ratio of 2:1. Now in Avadi, our small gear has 20 teeth and our big gear has 40 teeth, so the gear ratio is 2:1. What that does is if we have an input RPM of, say, 1000 RPM in the entry gear, then our output RPM in the big gear will be half that, it will be 500 RPM.

Of course, because the circumference of the large gear is twice as large, the large gear can only make one revolution while the small gear makes two, so the output speed is cut in half. But the larger circumference of the big gear also means we have double the leverage between the output, the gear center and the teeth, and this gives us double the torque. So if the input torque is, say, 50 Nm in the small gear, then the output torque will be 100 Nm in the large gear. So yes, the gear present at the heart of the Avadi engine increases torque, but so does any gear transmission ever made, because of course all gear transmissions work on the same principle, that's how they manipulate the output. of torque and the output speeds of a vehicle, with gears So why put gears inside the engine when you'll probably have to hook up a gear transmission to it anyway?

And besides, if you really

just

want to increase torque production, why double it? Why go with a 2:1 gear ratio when you can quintuple the torque output with a 5 to 1 gear ratio? So Avadi's explanation doesn't make much sense to me because they don't answer why they go for a 2:1 gear ratio. Well, the answer to that question lies in the very nature of how the four-stroke reciprocating piston internal combustion engine works. To answer why the Avadi engine has a gear like that, why 2:1, why the cylinder rotates, we

just

have to ask ourselves: What else in a four-stroke engine has a 2:1 gear or ratio?

There is no need for gears. Think about it, what else does one revolution mean and something else in relation to it connected to it, two revolutions? Yes, they are the crankshaft and camshaft. The crankshaft and camshaft in a four-stroke engine have a 2:1 ratio. For each revolution of the camshaft, the crankshaft completes two revolutions in the same amount of time, in a 2:1 ratio. This must be done because the four-stroke engine needs 720° or 2 * 360° to complete a full combustion cycle. Each stroke: intake, compression, combustion and exhaust is a top-down or bottom-up piston and each stroke is 180°. ° of crankshaft rotation.

Now the problem is that if you want the intake valves, which are operated by the camshaft, and the exhaust valves, to also be operated by the same or

another

camshaft, you want them to be open only during their respective careers. You want the intake valves to open only during the intake stroke and close during all other strokes. You want the exhaust valves to open only during the exhaust stroke and close during all other strokes. What you have to do to achieve this is convert half the crankshaft rotation into a quarter camshaft rotation. You have to convert 180° of crankshaft rotation into 90° of camshaft rotation and a 2:1 gear ratio does exactly that.

And once you've done that, all you need to do is size and position the camshaft accordingly so that it opens the desired valves only during the desired strokes and the other three quarters of the camshaft rotation the valve will be closed. . And you do the same with the intake and exhaust and voila, you have a properly functioning four-stroke engine. But if we go back to the Avadi we are going to observe that this engine has no valves or camshafts or valve springs or cam lobes, anything like that. In fact, it has one of the simplest valvetrains you'll ever see on any engine because the Avadi's valvetrain consists of nothing more than three holes, that's all.

We have the inner rotating cylinder and there is a hole in it. The fixed outer shell has two holes. As the inner cylinder rotates, the hole aligns at certain times with one of the holes in the outer fixed cylinder. When the holes align, air is allowed to enter or exit the chamber, the engine. When the holes do not line up, the chamber is sealed and air cannot enter or leave. Now, what the engine gears and the 2:1 gear ratio do is convert 180° of engine crankshaft rotation into 90° of cylinder rotation. So what essentially happens with the cylinder is that each quarter of the cylinder is one stroke, so all you have to do is place the holes accordingly and have them match up at the correct time for the correct stroke.

And the gears ensure this because they create a constant and consistent rotational relationship between the position of the piston and the position of the cylinder in relation to the outer casing. That's why the cylinder rotates and that's why we have gears, because they allow this extremely simple valve train to work. This extremely simple valve train, which does not have a large, heavy cylinder head or many moving parts nor does it take up much space is the reason this engine is so light and compact. The Avadi is a 250cc air-cooled engine that weighs only about 10kg and as far as I know there is no equivalent 250cc conventional four-stroke engine. which weighs 10 kg.

They all weigh a little more. Some weigh much more. So what's really been done is added complexity to the bottom end to allow for great simplicity and weight reduction at the top end of the engine's valvetrain, but that's not the only benefit of employing this system.  There are other very fortunate consequences of the anatomy of the Avadi engine. The main benefit of the Avadi anatomy is that it has greatly improved

balance

compared to a conventional

single

barrel design. Let's first look at the conventional design to see and understand why Avadi is better. As you know, in a conventional

single

cylinder, we will have a piston, a rod and a crank.

The piston goes up and down. It has mass, it constantly accelerates and decelerates, quickly, so we have a force that does this constantly and that must be

balance

d if we want to avoid massive vibrations in the engine. We can try to do it in a conventional design with the crankshaft counterweight. At the top and bottom of the crankshaft counterweight, at the top and bottom dead center, the crankshaft counterweight can balance the mass of the piston if we make the mass of the counterweight equal to the mass of the piston. But the problem is that at 90 and 270° the crankshaft counterweight points in a completely different direction than the direction of piston movement, so it can't balance anything and instead the counterweight creates a side-to-side sway and vibration. side. of the engine and we really haven't solved anything.

We simply moved the vibration up and down and converted it to a side-to-side vibration with the crankshaft counterweight. So this doesn't work.  What we can try is to add a balance shaft to the single cylinder design, the conventional design, and a balance shaft is simply a shaft that rotates together, is geared with the crankshaft, or otherwise rotates with the crankshaft and on he has a compensated weight that can balance something. Now what we are going to do is make the crankshaft counterweight be 50% of the piston mass and the counterweight will be the other 50% of the piston mass.  Thus, at the top and bottom dead center, as before, the crankshaft counterweight, now together with the counterweight, balances the piston.

But at 90 and 270 degrees of rotation, the counterweight now balances the crankshaft counterweight, so we've improved the balance, but we haven't made it ideal. Because if we go back to top and bottom dead center, you can see how below the piston, at the piston line, we have a net downward force because the crankshaft counterweight balances only 50% of the piston mass, so 50 % still. remains, and there is a net downward force. On the other hand, on the line or above the counterweight we have a net upward force. So we have these two forces of equal magnitude and opposite direction, so they should cancel each other out and restore balance.

Yes, but the problem is that they are separated by a displacement, a physical distance, and when you have an object and you apply forces of equal magnitude, in opposite directions separated by a distance, you get what is known as an oscillating couple. Basically, you're trying. to turn the object over.  You can easily try this yourself with any type of object and you will see how it works, it is quite intuitive. That's why we've improved the balance with a balance shaft, but now we also have a new type of vibration. The engine is trying to turn. Therefore, the balance is not optimal.

To achieve optimal balance with a conventional single cylinder, we actually have to add two balance shafts located on each side of the crankshaft. We make the crankshaft counterweight 50% of the piston mass and each of the counterweights is now 25% of the piston mass and as you can see from the top and bottom dead center, we now have no oscillating torque because the distribution of forces is now even. As before, at 90 and 270° of rotation, the two counterweights balance the crankshaft counterweight. So to get the

perfect

balance with a single conventional cylinder, we need two balance shafts. When you add two balance shafts to the motor and the gears and everything necessary for them, the bearings, the lubrication and everything, you realize that, first of all, you not only increased the size of the motor, but you added complexity and friction to the engine. to the point that a

twin

-cylinder engine could have been manufactured.

And this is the reason why two balance shafts on individual cylinders are not used very often, for practical reasons. But if we go to the Avadi now we will see that the two crankshafts guarantee practically

perfect

balance from the first moment. On the upper and lower dead teeth, each crankshaft counterweight is equal to 50% of the piston's mass and together they balance the piston.  At 90 and 270°, the two crankshaft counterweights balance each other, so we have practically perfect balance. I say "more or less" because although the crankshaft counterweights are very, very close to each other they still have a little distance between them, so if you look at them from above we can see that there is a littleof swinging. couple here.

But as I said, the distance is extremely small, so I think this is quite imperceptible and, for all practical purposes, this is a single-cylinder engine with practically perfect balance, while being much more compact in its anatomy than a conventional single cylinder. It would be a cylinder with

twin

balance shafts. But Avadi's anatomy has one more benefit: reduced friction. If we look at the conventional design, we can see that when the combustion force acts on the piston and pushes it down, the connecting rod forms an angle. Because of this, a part of the mass of the connecting rod is outside the line of force of the main combustion force and the direction of piston movement.

So what happens is that when the piston pushes down on the connecting rod, the connecting rod in turn tries to flip over. As it attempts to rotate, it pushes the piston against the cylinder wall, thus increasing the friction between the piston and the cylinder and creating greater wear on what is known as the thrust side of the cylinder. Now in Avadi we don't have this problem because we have two rods, so as each rod acts on the piston, each rod tries to rotate in its own direction. So what they do is they cancel each other out and the piston stays more stable in the bore and we've reduced friction and wear.

So far things are looking pretty good for Avadi. We have a design that offers greater compactness and reduced weight compared to a conventional design, while giving us much better balance and less friction. What's not to like? Well, that's what we'll talk about next. The not-so-nice things about the Avadi engine. And to see them we are going to look at the statistics, the specifications of the Avadi that we can find on their website, and Avadi claims that its 250 cc air-cooled engine generates 15.8 horsepower at 3700 RPM and 30.2 Nm of torque at 3500. RPM and, according to Avadi, this makes its engine "twice as powerful and half the weight of the closest competitor engine." So we have to ask ourselves what is the closest equivalent competitor to Avadi?

It is surely not a motorcycle engine, because if we take a modern, air-cooled, very simple, single camshaft and very economical motorcycle, a 250 cc motorcycle, we can see that it generates more power than the Avadi. Obviously, that's not the closest competitive driver. Let's look at something a little more humble. Let's go down the category to find the closest competitor. Here is the Honda GX270. A little more cc than the Avadi. It is an electric equipment engine and if we compare the statistics and specifications we can see that this is where Avadi's claim makes sense. Twice the power and half the weight Because this weight of the gx270, it is with the fuel tank and accessories, I think it is a dry fuel tank but there is still some mass in it, in the tank itself.

So if we drop the accessories and the tank, I think Avadi claims this is it. Double the power half the weight. So the closest competitor is the electric equipment motor? Not really.  The Avadi surpasses this typical representative of an electric equipment engine only because it is a kind of cheat. The engine specifications quoted by Avadi are on the output shaft, remember it is reduced.  So quoting numbers on the Avadi's reduced output shaft would be pretty much the same as quoting numbers on a conventional engine after the transmission and no one does that. We give power to the crankshaft, torque to the crankshaft and if we do that for the Avadi, remember the 2:1 gear ratio, we will see that the engine actually has to rev to 7400 RPM to generate this kind of power. 15.8 horsepower and the torque at the crankshaft is actually around 15 Nm of torque.

The Avadi surpasses the GX only because it accelerates twice as much. Like almost any other power equipment motor, the GX270 is limited to around 3600 RPM. The GX on the crank actually makes more torque than the Avadi. Horsepower is torque multiplied by RPM. If you accelerate twice as much with similar torque, you will generate more power. But to accelerate enough to have a redline of 7400 or more RPM, the Avadi needs a lot more, much stronger internal components, better materials, better bearings, a much more advanced and expensive lubrication system and, in general, that does the engine is much more expensive. probably puts it somewhere in the comparable cost range of a motorcycle engine.

So, you need money for a motorcycle engine but are you going to get the engine performance for an electrical equipment? Yes, nobody wants that. So why is Avadi's performance so poor? Well the answer is very obvious if we go back to the valve train, the culprit is the valve train. In a conventional engine we have the entire engine bore area available for breathing. We can place two intake valves and two exhaust valves, so that the entire orifice area is available for breathing. In the Avadi only half of the hole area is available for breathing; The other half, remember, we need to keep the cylinder sealed.

We cannot fit valves or cavities or orifices in the other half of the Avadi orifice area. So half the area of ​​respiratory capacity means drastically reduced performance and this is inherent to the anatomy. It can't be improved, which means Avadi is destined to have, at least in this design, fairly poor performance. The last major drawback of Avadi is that this design is not scalable. Avadi claims it is, but it isn't. Because, remember, the cylinder rotates. If the cylinder rotates, we cannot stack multiple cylinders on a single crankshaft as we can with a conventional design. For example, a 4-cylinder Avadi engine would have 8 connecting rods, 8 crankshafts, and 12 large gears.

So that's really not practical, it would make the engine very complex, with too many moving parts, too much friction and definitely very expensive. So the Avadi is really scalable only up to the practical displacement of a single-cylinder engine, which is around 800 cc. . Beyond that, Avadi doesn't make much sense, which means that in cars it can only be a range extender. For motorcycles it is of no use, because even for single-cylinder motorcycles it is not a good idea because it has the little power that we mentioned. What else? For electrical equipment it is too expensive. So what is this engine for?

Well, that's actually a very good question and I think I found the answer after looking at a lot of different novel engine designs on this channel and I think the answer is the rise of drone warfare or unmanned aerial vehicles. I believe this is the main driving force behind this recent emergence of so many novel engine designs. Because when you think about it, the Liquid Piston, the INNengine and now the Avadi all focus on one thing: being light and compact. As light and compact as possible. They don't really surpass conventional design in anything else. Not in performance, not in emissions, not in efficiency, not in reliability, sure, nothing.

When you look at the Avadi, for example, does the valve train seal? The holes, how do you seal everything? We don't know anything about whether it works, but none of that really matters for drones. The important thing is that the motor is as light and compact as possible. It doesn't even have to last that long because many drones are suicide drones and what this means is that the rise of this drone war around the world has leveled the playing field between engine companies with a lot of knowledge and a lot of R&D. and new people in the game.

Because drone motors, the motors that are needed for drones, don't really benefit from almost a century of R&D invested in conventional design, which, as I said, levels the playing field in terms of access to potential to obtain financing from armies. And armies have a lot of money and are willing to spend it to fund the development of these engines because they hope to have better drones than other armies. Motivated by this prospect of getting money from the military, we are developing new engine designs and trying to get them to the point where they can be presented to the military in the hope of obtaining funding.

And if you look at all the novel engine designs and how they appeared and how they evolved their presentation online, it's very similar. Usually at first it all starts with this phase of generating buzz and hype. We have a sort of simple, crude prototype at this stage, and we have claims like "twice the power, half the weight better in every possible way", and so on. Most of these statements are usually half-truths or only true under certain conditions, but they are important because they set the stage for the next phase, which is usually the crowdfunding phase, where the engine designers are trying to get some kind of initial funding to develop the design a little more to hopefully mature enough to present to the military so that they can apply for significant funding from the military, running into millions or tens of millions of dollars, and realistically, that It is the amount of money. a novel engine design needs to be brought to true maturity.

And when you investigate, everything starts to make sense. The Avadi was actually designed and developed in the '90s, back in the '90s by a man named Michel Arsenaeu, but it wasn't commercialized until a few years ago, when drone warfare became important. The engine was pretty dark before that. Because it didn't fit very well with any other application, but for drones it might work, so we have a campaign. Also what is worth noting is that Avadi on their website, in the news section, now states that they have abandoned their valvetrain design because they have seen that it is a limiting factor in terms of performance.

I think that was obvious from day one, but they needed that valvetrain design to give them the starting numbers and a very low initial weight and now they're abandoning it in favor of a more performance-oriented design. Also, here they state, in this article, how they are actually targeting the military's money, so yeah, it all really adds up. So yes, we will probably never see this motor in a car or a motorcycle, probably never even in an electrical equipment application. But we may one day see it in a drone, even if it happens we probably won't know. some confidential things or whatever.

But despite this, I don't think this makes this engine any less exciting. I think it's a very interesting and very elegant design and I think analyzing novel engine designs is not only fun but also very useful because it definitely deepens our understanding of engine mechanics and physics in general. And who knows, it might inspire you to create a novel design of your own and try to bring out the greens from the greens. Yes, I'm going to stop here, that's all for today. As always, thank you very much for watching. See you soon with more fun and useful things on the D4A channel.