The Mechanics of GM's Patent: A Breakdown of the Variable Compression Engine

When examining the inner workings of a modern engine, it's easy to get caught up in the complex systems and technologies that make them tick. However, one of the most innovative engines of our time is actually quite simple in principle. The General Motors (GM) patent for their variable compression engine uses a traditional auto cycle design with a twist - instead of having fixed points, the position of the fixed point can be altered to change the compression ratio.

The Auto Cycle Design: A Simplified System

The traditional auto cycle design features two fixed points: the center of the crankshaft and a pin that allows for back-and-forth motion. This motion is what drives the piston up and down in its stroke. However, by changing where this fixed point is located, the compression ratio can be altered. In traditional engines, this is done using a more complex system of linkages to change the position of the fixed point.

GM's Solution: A Variable Compression Engine

Instead, GM uses a worm gear system that allows for the rotation of the pin that alters the compression ratio. This means that by pulling on the worm gear, the position of the fixed point can be changed, which in turn changes the compression ratio. This clever solution allows for two different modes of operation: efficiency mode and power mode.

Efficiency Mode: Lower Compression Ratio

In efficiency mode, the engine operates with a lower compression ratio, which means that less fuel is burned and more heat is retained inside the cylinder. This results in greater efficiency and reduced emissions. The low compression ratio also makes it easier to achieve high mileage from the engine, as there is less wear on the piston rings.

Power Mode: Higher Compression Ratio

In power mode, the engine operates with a higher compression ratio, which allows for more fuel to be burned and more power to be generated. However, this increases the risk of knocking or pinging in the cylinder, which can damage the engine over time. To mitigate this issue, GM would likely add forced induction - such as a turbocharger or supercharger - to increase the air-fuel mixture and reduce the likelihood of knock.

A Simple yet Clever Solution

So how does GM's patent work? It all comes down to the clever use of the worm gear system. By changing the position of the fixed point, the compression ratio can be altered in an instant. This means that drivers can choose between efficiency mode and power mode with ease. In essence, this engine is a traditional Atkinson cycle engine, but with the added feature of variable compression.

The Future of Engine Design

GM's patent for their variable compression engine marks an exciting development in the world of engine design. By changing the compression ratio at will, drivers can optimize their engine for efficiency or power. While this technology may not be widely available just yet, it represents a significant step forward in terms of innovation and adaptability.

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Skillshare: An Online Learning Community

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"WEBVTTKind: captionsLanguage: enhello everyone and welcome in this video sponsored by Skillshare which we will get into more at the end of the video we are talking about GM's patented variable compression engine with independent compression and expansion ratios what now this all probably looks like a big mess of information but I promise we have a nice logical flow here and we will eventually understand how this engine works by the end of the video the big idea here GM doesn't want to compromise between power and efficiency they want both just like every other car maker out there they both want power and efficiency they don't want to sacrifice one or the other and so this is one solution which GM has come up with this patent dates November of 2018 now GM's engine has independent compression and expansion ratios so the first thing we need to understand is what's the difference so a typical engine will have your four strokes intake compression power exhaust and so here we've got that laid out and we're going to illustrate what the difference is between a compression ratio and an expansion ratio so on that intake your piston moves down to the bottom once it's at the very bottom the volume within that cylinder divided by the volume once that piston goes all the way up to the very top top dead center v1 divided by V 2 that will give you your compression ratio so it's the volume of air with the piston at the very bottom versus the volume of air with the piston at the very top after that compression stroke now your expansion stroke is then the volume after that piston goes down from the power stroke so with the very bottom of its stroke that volume divided by the volume when it's at the top of its compression stroke and so as you can see in the typical engine these are going to be the exact same V 1 is equal to V 3 so the compression ratio and the expansion ratio are exactly the same well this leads us to a problem so if you look inside your cylinder if you've just had that spark ignite you have the power stroke occur it pushes down this piston once this piston reaches the very bottom there's still a very high amount of pressure within the cylinder and then you open your exhaust valve and all that high pressure escapes out your exhaust that's just wasted energy whereas if you could use that pressure to continue push this piston downward if it were able to go down further then you can get more useful work out of that pressure that's built within that combustion chamber as a result of burning that air in fuel so that means you could get more work that means you could have better efficiency so you use the same amount of fuel to go a further distance that would be ideal so engineers are very clever and they came up with a solution in order to have a greater expansion ratio versus the compression ratio and this is called the modern atkinson cycle and so essentially what they're doing here is decreasing the compression ratio and so as that piston pulls in the air it then continues to push up and presses out some of that air without the intake valve yet closing so the piston has already started its compression stroke and your intake valve remains open so by using valve timing they're decreasing the compression ratio because some of that air and fuel is pushed back out and so by doing so now you can see your compression ratio is going to be this volume right here but that piston gets to move all the way down to here and so your expansion ratio is greater and so by doing this that pressure pushes down on that piston for a longer amount of time and you're able to get more useful work out of it so it's more efficient the challenge of course here is as you might notice if you're pushing out some of that air and fuel if you have less oxygen overall to burn then you're not going to make as much power and so that's the challenge while you make power more efficiently you don't make as much of it so great for an engine that's looking for high MPG but not so great for an engine that's trying to get you you know up and cruising up to 60 miles per hour up on the highway real quickly so remember GM's engine wants two things they want independent expansion and compression ratios for efficiency and then they want a variable compression ratio for power and so how do they do this well in order to understand the independent expansion ratio and compression ratio portion of it we need to understand a traditional atkinson cycle engine and this probably looks fairly complicated it's not it's actually pretty simple how this engine works and we're going to get through it so you know just looking at it on the surface here very briefly we have the end of our tech stroke the end of our compression stroke the end of our power stroke and the end of our exhaust stroke and there's really just two main differences between this traditional style Atkinson cycle engine and the engine that you are used to seeing in your car so the first one being is that in our cars were used to this engine going up and down and the bottom that crankshaft just going in a circular motion like so so it just goes up and down and this goes in a circle and we have two rotations of the crank shaft that's what I've drawn here in red so that purple point is fixed this purple point is fixed those two points and never move everything else moves so that purple is fixed and this red crankshaft just rotates in a clock right here now the difference being is that it only rotates once for all four strokes so one of the biggest differences is that the crank shaft only rotates once for all four strokes the second difference being the piston instead of doing this up and down circular motion it's just going like this it's just bouncing back and forth so the piston itself is just doing that and in one rotation of this crank shaft this piston goes over to here back over to there back over to here back over there and every time it's in the center there it pushes up and then it comes back over and so looking at this this right here here's our piston here's our connecting rod very similar to what we have in a traditional engine then you have this crankshaft here which rotates about that fixed purple point fix purple point over here with another link and you have this Center link right here connecting that crankshaft to that connecting rod so that Center link all it's doing is as this red crankshaft rotates around you can see those 90-degree rotations there as it rotates around this Center link just pushes back and forth like so that's all it's doing so this is rotating in a circle that Center length is just kind of going back and forth like this and by going back and forth it's pushing that piston up each time so you can see here it's gonna rotate 90 degrees it's going to start to push that piston up then you're going to have it continue to rotate another 90 degrees your crankshaft it comes back down as that connecting rod is now all the way on this side then it continues to rotate down so as it rotates down it pulls that Center link over that pushes this back up and so you just repeat that with this piston going back and forth like so up and down with a connecting rod going back and forth rather than a circular motion like you see in a traditional auto cycle engine and what this does based on the geometry of where you have these fixed points and that crankshaft is it actually varies your compression ratio from your expansion ratio so you can see that here as it comes over it pushes it up this distance but it's only come down for the intake stroke to this line right here and then for the power stroke it goes down an additional distance so your expansion ratio is greater than your intake ratio remember the only two differences being we have this crankshaft in one rotation this piston will go the connecting rod will go back and forth and that will cause this to go up and down twice so very simple system it just uses this system of linkages in order to make that occur it looks far more complicated than an auto cycle but in principle how it works is actually fairly simple and so if you're to trace the position of that piston you can see it comes down for the intake stroke back up for the compression stroke goes further down than it did for the intake stroke for your expansion stroke and then back up to the beginning of your intake stroke and so you have that independent intake stroke distance versus your power stroke distance which allows for greater efficiency okay so now we can get into the meat of GM's patent and so they have two different modes they want to operate efficiently or they want to operate in power mode and so how do they do it well if we go back to our traditional auto cycle here remember we have these two fixed points the center of your crank shaft right there in purple and then this pin right here which just allows for this back-and-forth motion that that piston is undergoing so remember that bottom pin right here so this little point is just going to rotate like so in order to allow that piston to go up and down and so what if we were to change where this fixed point was what if we could actually anchor this in a different location well if we were to do so we would alter the compression ratio where actually would be just shifting this curve here how we wanted to and so that's where GM's pen come in comes in so they have this true Auto cycles style engine here and then this point right here instead of being completely fixed it's on this worm gear right here so you can use an electric motor you've got a worm gear and you can rotate this gear and so that means you're changing this purple position right here you're pulling it this direction and so by pulling that this direction as you can see the crankshaft has remained in the exact same position but we've rotated where this fixed position is and in doing so we've decreased our compression ratio so very clever little solution here in order to have this have different compression ratios depending on what you're going for so a higher compression ratio would be used for efficiency the reason you can't use a really high compression ratio for power is that you start to run into issues with nuk so you have to limit your ignition timing meaning you're firing that spark plug very late and in doing so you don't make much power so in order to make more power you want to be able to decrease the compression ratio and so that's what they're doing here by changing this position of that fixed point they're decreasing the compression ratio then likely the case would be you would add forced induction and with you know additional forced induction whether it's a turbocharger or supercharger and that lower compression ratio you don't have to worry about knock because you've decreased that compression ratio and then you can make more power because of it and so it's it's a clever solution where you have instead of kind of the the modern style Atkinson cycle you have actually a traditional style ikenson engine but with this modern twist on it where you have a variable compression ratio so fairly neat and what this is doing is just shifting this curve right here in your favor so if you want more efficiency you increase that compression ratio if you want more power you decrease it and you probably would add some boost in order to increase power so a very clever system and ultimately based on something very simple and again you know when you're looking at append don't just assume that this is exactly what it's going to look like patents are kind of going to be the simplified version they will probably have a different system of linkages and how it would actually be put into production if it ever is into production rather than looking exactly like this but this gives the general idea of how that engine style would actually work now again a big THANK YOU to Skillshare for sponsoring this video there's a link in the video description and the first 500 of you to sign up using this link will get two free months of membership now obviously I spend a lot of my own time learning and teaching that's what this channel is all about but I also spend a ton of my time creating and that's really where Skillshare as a platform shines it's an online learning community designed for creators whether you're just about to start out or well into your career whether it's photography video editing script writing animating or even the more business-oriented side of being a creator and they have thousands of classes to help you learn new skills and apply them in the real world again you can sign up using the link in the video description and the first 500 will get two months free if you have any questions or comments of course feel free to leave those below thank you so much for watchinghello everyone and welcome in this video sponsored by Skillshare which we will get into more at the end of the video we are talking about GM's patented variable compression engine with independent compression and expansion ratios what now this all probably looks like a big mess of information but I promise we have a nice logical flow here and we will eventually understand how this engine works by the end of the video the big idea here GM doesn't want to compromise between power and efficiency they want both just like every other car maker out there they both want power and efficiency they don't want to sacrifice one or the other and so this is one solution which GM has come up with this patent dates November of 2018 now GM's engine has independent compression and expansion ratios so the first thing we need to understand is what's the difference so a typical engine will have your four strokes intake compression power exhaust and so here we've got that laid out and we're going to illustrate what the difference is between a compression ratio and an expansion ratio so on that intake your piston moves down to the bottom once it's at the very bottom the volume within that cylinder divided by the volume once that piston goes all the way up to the very top top dead center v1 divided by V 2 that will give you your compression ratio so it's the volume of air with the piston at the very bottom versus the volume of air with the piston at the very top after that compression stroke now your expansion stroke is then the volume after that piston goes down from the power stroke so with the very bottom of its stroke that volume divided by the volume when it's at the top of its compression stroke and so as you can see in the typical engine these are going to be the exact same V 1 is equal to V 3 so the compression ratio and the expansion ratio are exactly the same well this leads us to a problem so if you look inside your cylinder if you've just had that spark ignite you have the power stroke occur it pushes down this piston once this piston reaches the very bottom there's still a very high amount of pressure within the cylinder and then you open your exhaust valve and all that high pressure escapes out your exhaust that's just wasted energy whereas if you could use that pressure to continue push this piston downward if it were able to go down further then you can get more useful work out of that pressure that's built within that combustion chamber as a result of burning that air in fuel so that means you could get more work that means you could have better efficiency so you use the same amount of fuel to go a further distance that would be ideal so engineers are very clever and they came up with a solution in order to have a greater expansion ratio versus the compression ratio and this is called the modern atkinson cycle and so essentially what they're doing here is decreasing the compression ratio and so as that piston pulls in the air it then continues to push up and presses out some of that air without the intake valve yet closing so the piston has already started its compression stroke and your intake valve remains open so by using valve timing they're decreasing the compression ratio because some of that air and fuel is pushed back out and so by doing so now you can see your compression ratio is going to be this volume right here but that piston gets to move all the way down to here and so your expansion ratio is greater and so by doing this that pressure pushes down on that piston for a longer amount of time and you're able to get more useful work out of it so it's more efficient the challenge of course here is as you might notice if you're pushing out some of that air and fuel if you have less oxygen overall to burn then you're not going to make as much power and so that's the challenge while you make power more efficiently you don't make as much of it so great for an engine that's looking for high MPG but not so great for an engine that's trying to get you you know up and cruising up to 60 miles per hour up on the highway real quickly so remember GM's engine wants two things they want independent expansion and compression ratios for efficiency and then they want a variable compression ratio for power and so how do they do this well in order to understand the independent expansion ratio and compression ratio portion of it we need to understand a traditional atkinson cycle engine and this probably looks fairly complicated it's not it's actually pretty simple how this engine works and we're going to get through it so you know just looking at it on the surface here very briefly we have the end of our tech stroke the end of our compression stroke the end of our power stroke and the end of our exhaust stroke and there's really just two main differences between this traditional style Atkinson cycle engine and the engine that you are used to seeing in your car so the first one being is that in our cars were used to this engine going up and down and the bottom that crankshaft just going in a circular motion like so so it just goes up and down and this goes in a circle and we have two rotations of the crank shaft that's what I've drawn here in red so that purple point is fixed this purple point is fixed those two points and never move everything else moves so that purple is fixed and this red crankshaft just rotates in a clock right here now the difference being is that it only rotates once for all four strokes so one of the biggest differences is that the crank shaft only rotates once for all four strokes the second difference being the piston instead of doing this up and down circular motion it's just going like this it's just bouncing back and forth so the piston itself is just doing that and in one rotation of this crank shaft this piston goes over to here back over to there back over to here back over there and every time it's in the center there it pushes up and then it comes back over and so looking at this this right here here's our piston here's our connecting rod very similar to what we have in a traditional engine then you have this crankshaft here which rotates about that fixed purple point fix purple point over here with another link and you have this Center link right here connecting that crankshaft to that connecting rod so that Center link all it's doing is as this red crankshaft rotates around you can see those 90-degree rotations there as it rotates around this Center link just pushes back and forth like so that's all it's doing so this is rotating in a circle that Center length is just kind of going back and forth like this and by going back and forth it's pushing that piston up each time so you can see here it's gonna rotate 90 degrees it's going to start to push that piston up then you're going to have it continue to rotate another 90 degrees your crankshaft it comes back down as that connecting rod is now all the way on this side then it continues to rotate down so as it rotates down it pulls that Center link over that pushes this back up and so you just repeat that with this piston going back and forth like so up and down with a connecting rod going back and forth rather than a circular motion like you see in a traditional auto cycle engine and what this does based on the geometry of where you have these fixed points and that crankshaft is it actually varies your compression ratio from your expansion ratio so you can see that here as it comes over it pushes it up this distance but it's only come down for the intake stroke to this line right here and then for the power stroke it goes down an additional distance so your expansion ratio is greater than your intake ratio remember the only two differences being we have this crankshaft in one rotation this piston will go the connecting rod will go back and forth and that will cause this to go up and down twice so very simple system it just uses this system of linkages in order to make that occur it looks far more complicated than an auto cycle but in principle how it works is actually fairly simple and so if you're to trace the position of that piston you can see it comes down for the intake stroke back up for the compression stroke goes further down than it did for the intake stroke for your expansion stroke and then back up to the beginning of your intake stroke and so you have that independent intake stroke distance versus your power stroke distance which allows for greater efficiency okay so now we can get into the meat of GM's patent and so they have two different modes they want to operate efficiently or they want to operate in power mode and so how do they do it well if we go back to our traditional auto cycle here remember we have these two fixed points the center of your crank shaft right there in purple and then this pin right here which just allows for this back-and-forth motion that that piston is undergoing so remember that bottom pin right here so this little point is just going to rotate like so in order to allow that piston to go up and down and so what if we were to change where this fixed point was what if we could actually anchor this in a different location well if we were to do so we would alter the compression ratio where actually would be just shifting this curve here how we wanted to and so that's where GM's pen come in comes in so they have this true Auto cycles style engine here and then this point right here instead of being completely fixed it's on this worm gear right here so you can use an electric motor you've got a worm gear and you can rotate this gear and so that means you're changing this purple position right here you're pulling it this direction and so by pulling that this direction as you can see the crankshaft has remained in the exact same position but we've rotated where this fixed position is and in doing so we've decreased our compression ratio so very clever little solution here in order to have this have different compression ratios depending on what you're going for so a higher compression ratio would be used for efficiency the reason you can't use a really high compression ratio for power is that you start to run into issues with nuk so you have to limit your ignition timing meaning you're firing that spark plug very late and in doing so you don't make much power so in order to make more power you want to be able to decrease the compression ratio and so that's what they're doing here by changing this position of that fixed point they're decreasing the compression ratio then likely the case would be you would add forced induction and with you know additional forced induction whether it's a turbocharger or supercharger and that lower compression ratio you don't have to worry about knock because you've decreased that compression ratio and then you can make more power because of it and so it's it's a clever solution where you have instead of kind of the the modern style Atkinson cycle you have actually a traditional style ikenson engine but with this modern twist on it where you have a variable compression ratio so fairly neat and what this is doing is just shifting this curve right here in your favor so if you want more efficiency you increase that compression ratio if you want more power you decrease it and you probably would add some boost in order to increase power so a very clever system and ultimately based on something very simple and again you know when you're looking at append don't just assume that this is exactly what it's going to look like patents are kind of going to be the simplified version they will probably have a different system of linkages and how it would actually be put into production if it ever is into production rather than looking exactly like this but this gives the general idea of how that engine style would actually work now again a big THANK YOU to Skillshare for sponsoring this video there's a link in the video description and the first 500 of you to sign up using this link will get two free months of membership now obviously I spend a lot of my own time learning and teaching that's what this channel is all about but I also spend a ton of my time creating and that's really where Skillshare as a platform shines it's an online learning community designed for creators whether you're just about to start out or well into your career whether it's photography video editing script writing animating or even the more business-oriented side of being a creator and they have thousands of classes to help you learn new skills and apply them in the real world again you can sign up using the link in the video description and the first 500 will get two months free if you have any questions or comments of course feel free to leave those below thank you so much for watching\n"