Variable compression ratio 2.0T in next QX50!!!!

[12,000 RPM]

http://www.autoblog.com/2016/08/14/infiniti-vc-t-engine-variable-compression-official/

Instead of having the pistons connected to the crankshaft, Infiniti's engine has a pivot arm with a connection on each end. One end connects to the piston, the other connects to a second lower shaft, which is controlled by an actuator arm. At any given time the engine's pistons move up and down according to the lobes on the crankshaft. But the actuator arm can change the angle of the pivot arm up and down. That is, the pistons still move in the same motion with the same stroke, but phase the entire stroke up or down. Move the pivot up and there's less room at the top, which means a higher compression ratio. Move the pivot down and the compression ratio goes down, too. As an added bonus, the lower shaft eliminates the need for counter-rotating balance shafts.

http://pdfaiw.uspto.gov/.aiw?PageNum=0&docid=20130327302

I still have problems visualizing Nissan's VVL but it looks like this applies the same concept to the crankshaft.

On one hand my inner geek is 

On the other hand I'm highly skeptical that this will be as
- cheap
- reliable
- practically effective (i.e. beyond a test lab) in fuel economy and emissions

as a simple hybrid setup. Lubrication? How tall is this engine block going to be? Who's gonna take a gamble on these things out of warranty? I think this speaks more to the strides metallurgy has made for such a complex system to be able to withstand the rigors normally relegated to a crankshaft... but it's hardly an elegant solution.

Still though we will at least see how effective variable compression can be in the real world.... hopefully one day they figure out how to make it simpler

[MrH]

Pretty cool stuff.  I'm excited for it too.

I'd be curious what the response time is.  How fast can it go from 8 to 14 CR? etc

Makes a whole lot more sense than what Saab tried doing for variable compression ratios.

[12,000 RPM]

I need to see an animation of it... though an animation didn't help me grasp their VVL system

Another thing that could be problematic is max rev speed... though that's largely irrelevant with these dieselesque 2.0Ts. So many questions....

[MX793]

Don't we already have a thread for this?

And, yes, it looks a lot like the workings of Nissan's VVL system.

[MrH]

I need to see an animation of it... though an animation didn't help me grasp their VVL system

Another thing that could be problematic is max rev speed... though that's largely irrelevant with these dieselesque 2.0Ts. So many questions....

It's goofy.  There's a video out there showing it.  Once you see it, you'll get it.  It's simpler than I thought it would be.  I just don't know how they're going to seal it off.  Are the actuators and linkages all sitting inside the crank case in oil?

[giant_mtb]

Is it this?  Useful animation starts at 1:55.

https://youtu.be/9dLxHOuWErI

[MrH]

Well, it works on the same principle.  But it's not a cylinder running parallel to the combustion chamber like that.  It sits like below and to the side of the crankshaft and uses a magnetic actuator I think.

[12,000 RPM]

OK, I saw another animation of it. Someone made an animation of this exact setup 2 years ago Pretty simple, kind of brilliant. But I think the whole thing could be a little more space efficient... instead of having the control linkage come up, they could have it come down and hinge under the intake manifold or something. This thing is gonna need like 8 quarts of oil though. Now that I see it it's pretty elegant and simple; we will see how well it works. I figure since the linkages don't have much load they won't need a ton of lubrication actually.

[shp4man]

Usually this kind of stuff doesn't turn out well, but who knows. 

Customer: My car's engine is making noise.
Mechanic: Let's have a look.

Mechanic: Well sir, looks like something came apart inside the motor and damaged other parts. Needs a new motor.
Customer: At 60,000 miles? Ok, how much?   
Mechanic: Uhhhh....$9000...

Customer: OMFG! #$&^*$#!!!!

[12,000 RPM]

Usually this kind of stuff doesn't turn out well, but who knows. 

This is based on technology that has worked for decades. When has "stuff like this" not turned out well?

[shp4man]

Would the benefits of this outweigh the added mechanical complication? It's like electronically operated valves. 

[Laconian]

I wonder how quickly the system can change its compression ratio. MultiAir spooks me a lot more, that system must be fluttering all over the place.

[CaminoRacer]

Would the benefits of this outweigh the added mechanical complication? It's like electronically operated valves. 

The only benefits are for off-boost driving, which is for pussies

[MX793]

It wouldn't need to react especially quickly.  Just faster than the turbo can spool to stay ahead of the boost curve.  Also, the mechanism wouldn't have to move very far to swing the CR.  My biggest concern would be what would happen if the system failed while in the high CR setting.

[Laconian]

It wouldn't need to react especially quickly.  Just faster than the turbo can spool to stay ahead of the boost curve.  Also, the mechanism wouldn't have to move very far to swing the CR.  My biggest concern would be what would happen if the system failed while in the high CR setting.

Aren't wastegates controlled electronically? Just dump the b00st

[12,000 RPM]

It wouldn't need to react especially quickly.  Just faster than the turbo can spool to stay ahead of the boost curve.  Also, the mechanism wouldn't have to move very far to swing the CR.  My biggest concern would be what would happen if the system failed while in the high CR setting.

Yea the mechanism looks like it can respond as fast as a throttle. It should be fine in that regard. There are a shitload of failure modes that aren't present in a regular motor though. Maybe Nissan's VVEL was a stress analysis study for this.