Hello everyone and welcome.
In this video we're going to be talking about
Infiniti's new VC-T engine.
Variable Compression Turbocharged Engine
Now, I personally think they should have
called it Variable Compression Ratio
and made VCRs great again
but that's besides the point and not my decision to make.
So the reason why this engine has gotten so much media hype lately
is because what it's doing is trying
to remove compromise from engines.
So traditionally you can have an engine that's really
powerful but it won't be very efficient,
or you can have an engine that's very efficient but it won't be very powerful.
So what Infiniti's trying to do here
is allow you to choose between both of those options
with the same engine.
You're not going to have both at the same time
but you can choose to run it efficiently
or you can choose to run it with a lot of power
depending on where that foot is on that gas pedal.
So the way they do this is
by incorporating this variable compression ratio.
It can be as low as 8:1
with lots of boost for high power
or it can be as high as 14:1 for a very efficiency operating condition
So how does this system work?
How does it do this?
Well it looks like this complex mess
which it kind of is but we're going to break this down,
simply so that we can understand what's going on.
So the way I want to do this is
look at this in two different sections.
This top section here
which is just going to be like a normal engine
and then this lower section here
which is going to be used to adjust the compression ratio.
So for now, let's just ignore everything below this
and look at what we've got going on up top.
So here we have our piston, the connecting rod, the cylinder, everything like usual.
The difference here is this crankshaft,
so you can see there's this rectangular piece called the multilink.
and that's going to be linking up these two sections.
And so your crankshaft, is going to be right here,
the center of rotation, right there.
So, to give you an understanding of what this looks like
here we have a crankshaft,
and so this right here
is this right here
and then the center, this axis which it rotates about
is of course right there, so looking at this
this crankshaft right here how this will be oriented
would be just like that
with the center right here and this will rotate around
This piston will come down and up and down and up
And rotate this section
And now important thing you need to understand is that this multi link right here this rectangular piece
maintains this orientation as it goes around the crankshaft it doesn't rotate
it maintains that orientation and so that's what we're gonna be using
to change the compression ratio is changing the angle of this
rectangular piece right here so you can see if you were to tilt it up that would
cause this piston to move up increasing the compression ratio and if you were to
tilt it down that would decrease the compression ratio pulling the piston
down so what we're looking at right here is top dead center the crankshaft
oriented like that so you've got the top of it right here and then the center of
it right there and it's about to rotate down like that. So how this works on the
compression ratio adjustment system basically all you need to know about
this side of the system the most important piece is that what you're
trying to do is to move this lower link up and down because as you move this
lower link up and down you change the orientation of this rectangular piece
this multi link and so if you were to pull it down you can see it increase the
compression ratio because it pivots about this point pushes the piston up
and if you were to push it up you would pull the piston down decreasing the
compression ratio at top dead center Okay great so how does it do this?
Well, the magic of it really comes down to this central shaft right here but
basically we have a harmonic drive right here you can just think of this as a
device which rotates clockwise or counterclockwise and then you have this
actuator arm which rotates this central shaft. So the central shaft rotates about
this pivot point right here so you can see if this central shaft were to rotate
downward if it were to rotate down that direction it's going to pull this lower
link down and by pulling that lower link down it's pushing the piston up
increasing the compression ratio. I f it were to rotate upward if this piece were
to rotate up like that it's going to push up on here and then that's going to
pull this down and that's going to decrease your compression ratio so it's
all dependent on which way you turn this actuator arm it's linked up and it's
going to cause this to pivot about this point right here so you can see
currently this is the state it's in if you were to rotate it using this linkage
you could rotate it down and you would increase your compression ratio to 14:1
or you could turn it all the way up and that would push this up pivot this
down and that would decrease your compression ratio down to 8:1 so you
know once you kind of see all of this work together it's really not that
complicated but it is kind of a mess looking at all of it together
and so the important thing to just kind of see is that it can rotate
this rectangular piece rotates around the crankshaft about this point right
here and then these two pieces right here these two links keep this
rectangular piece in that orientation as it goes around and you can change that
by changing the height of this lower link using that central shaft great
that's all clear right? And so you know why do you want to do this? Well as I
mentioned you kind of remove that compromise so you can use a low
compression ratio you can put in tons of boost and so why do you need a low
compression ratio well you want to prevent knock and so you know you can start
to get into some tricky scenarios if you have high compression ratio and high
boost so to make it safe reliable you decrease the compression ratio and then
you eliminate, you know, you reduce your chances of knock and you have a safer-running,
more powerful engine well then you can pump it up to that 14:1
to get that really high efficiency not only does 14:1 have a higher
thermal efficiency but they've used this in combination with the Atkinson cycle
so they're using variable valve timing to leave those intake valves open for a
short duration during that compression stroke and that improves the efficiency
I have a whole nother video explaining how that Atkinson cycle works if you're
interested but basically what they're doing is giving you really good
efficiency in one operating condition and lots of power in the other operating condition
So, is it going to be the most efficient two-liter engine out there?
Well no, of course not. And is it going to be the most powerful 2-liter engine out there?
No. but what it's doing is its allowing you to choose between both of
those so if you're cruising down the highway you can get great fuel economy
and then if you're ripping through you know a canyon you can actually have some
fun it'll decrease the compression ratio load it up with boost and you've got
all kinds of power so it is a very cool option to give you efficiency when you
want it and power when you don't so thank you guys for watching and if you
have any questions or comments feel free to leave them below