Twin Rod Avadi Engine - Perfect Balance in a Single Cylinder - Genius or Just Another Pipedream?
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It's time to review another novel engine design and today we are going top inspect the Avadi MA 250 engine. As always I’ll explain what makes it special, how it works, the strengths and weaknesses of the design as well as the potential for it to enter mass production.
So as you can see this is a rotary engine, but it’s not rotary in the way that a Wankel/Mazda rotary engine is. This is still piston based with the big difference between this and conventional engines being that here the entire cylinder rotates within a casing and we have two connecting rods and two crankshafts for one piston. The crankshafts are geared to a stationary ring gear.
When I saw this engine for the first time the first thing that came to my mind was “hey this a big gyroscope. The cylinder spins in this direction, the crankshafts spin within it, kind of like a gyroscope. Ok that’s interesting….but why? There is no inherent benefit to making an engine cylinder together with the piston rotate around an axis so why do it?
To understand why we must observe how is the cylinder spinning. The spinning is done via gears. Why gears? If you want to make something spin there are more efficient ways than gears.
If we look at the Avadi website we will see they claim that the gears provide a reduction or torque increase for the engine. And yes this is of course true. All geared transmissions work on the same principle.
If we take two gears. A small input gear and an output gear that is twice the size we will double our torque output. This is the same arrangement as in the Avadi engine the pinion gears on the crankshaft are half the size or half the number of teeth of the fixed ring gear. So if we imagine that have an input speed of 1000 rpm and 10 Nm of torque at the small gear than our output speed at the large gear will be 500 rpm and the output torque will be 20Nm. A gear that is twice as large halves speed and doubles torque. This happens because the larger gear has a greater circumference and therefore the distance from the teeth to the center is doubled. When we double this distance we double the leverage and thus the torque. The speed is halved because for every two revolutions of the small gear the large gear makes only one revolution, so we have a 2:1 gear ratio.
So yes, the geared arrangement does increase torque as Avadi claims but this is NOT the reason why they implemented this solution. If they were interested only in torque then they could have done a 4:1 gear ratio and quadrupled the torque. So why 2:1? Think about it, what else has a 2:1 gear ratio, what else rotates twice for ever 1 rotation of the other things?
Yes, that’s right! The crankshaft and camshaft in a conventional four stroke engine have a 2:1 ratio. The crankshaft rotates twice for every single rotation of the camshaft. Why?
Because a four stroke engine needs 720 degrees to complete a full combustion cycle. Intake, compression, combustion and exhaust - each stroke is 180 degrees of crankshaft rotation and 4 x 180 equals 720. But during those 720 degrees you want to open the intake valve only once and you want to open the exhaust valve only once. You want the intake valve open only during the intake stroke and the exhaust valve open only during the exhaust stroke. To achieve that all you need is a 2:1 rotation ratio between the crankshaft and the camshaft. A 2:1 ratio means that 180 degrees of crankshaft rotation is only 90 degrees of camshaft rotation. So all you have to do is place your camshaft lobe in the correct position in relation to the crankshaft and the piston and your intake valve will be open only when you want it to be open.
Now if we go back to the Avadi engine we will see that this engine has no camshafts, no valves, no springs no nothing but the four stroke rules still apply, with or without a camshaft. The Avadi engine has an incredibly simple valve train that essentially consists of only three holes. This is one of the main reasons why the engine is so compact and so light.
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#d4a #enginebalance
00:00 How it Works
10:54 Engine Balance
17:17 Breathing Issues
22:67 Drones
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