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Is this a variable Atkinson style ICE?

One of the new ICE platforms from Infiniti (The MCE-5 ICE) has a variable compression internal combustion engine.

The compression ratio can automatically adjust from 14.0:1 to 8.0:1.

How has Infiniti achieved this?

Is this an evolution of an Atkinson style ICE?

How quickly can the engine adjust to variables such as throttle position to produce MOAR power?

It seems this would have to be done at the crank with an Atkins arm that could change angles but seems extremely complex. Although there is probably not very much data regarding reliability at this point but added complexity would seemingly reduce reliability.

Can someone provide an explicit explanation of how Infiniti has achieved this marvel of engineering?

Any visual examples to explain the process are desirable.

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    youtu.be/kV2ApRM_Pi8 – Zaid Sep 10 '16 at 11:14
  • @Zaid watched a bunch of vids on it earlier so I thought I would ask the question. – DucatiKiller Sep 10 '16 at 11:16
  • @JasonC as are the answers to many questions here... With that said, this video explains how the CR theory is applied. I'm not sure where I stand on the reliability issue - most of the mechanicals are reusing proven elements in a well-lubricated area. The downside is similar to the BMW variable lift system - what happens when the VCR solenoid fails? My guess is they've engineered a limp-mode for that inevitable scenario. – Lathejockey81 Sep 10 '16 at 14:43
  • @Lathejockey81 - I'd suggest almost any mechanical failure in Infinitis system would more than likely cause catastrophic failure ... but that's my thinking. – Pᴀᴜʟsᴛᴇʀ2 Sep 10 '16 at 16:12
  • As an aside, Wankel engines are a good example of poor reliability not being associated with added complexity -- on the other hand Nissan's VCR engines are using pretty run-of-the-mill components, control arms and cams and shafts and such, there's just more of them. So more things to go wrong I suppose, but at least the engineering is well-understood. We shall see. On the bright side the fundamental concept seems to be in public domain, so there's a good opportunity for competition to drive improvements in the future. – Jason C Sep 10 '16 at 16:52
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Infiniti MCE-5 VC-T

This engine does not exist. MCE-5 is a French R&D company that is working on VCR engines (I think they're associated with Peugeot, possibly even a spin-off but don't quote me on that). Nissan (Infiniti) also worked on similar technology independently. So there is the MCE-5 engine, the Infiniti's VC-T, Saab was working on one, Yamaha had two-stroke ones in the 90's, Lotus, Porsche, Volvo, Renault, Gomecsys, and probably a few other companies, too. But there's no "Infiniti MCE-5", which would be like a "Toyota Subaru".

How has Infiniti achieved this?

This is pretty readily available information so I won't reproduce it fully here. However, the general gist of the VC-T (and other similar types) is that variable compression ratios are accomplished by adjusting the stroke on the fly through various crankshaft linkages. There are other types, for example, the Lotus Omnivore adjusts the displacement on the fly by moving the top wall of the combustion chamber (interactive demo), and the Gomecsys engines adjust the stroke on the fly by using magic.

Complete details are available at:

The MCE-5 and Nissan engines are very similar except the MCE-5 uses a piston to change the lower link's pivot point / movement range, and the Infiniti uses a rotating control shaft (you'll want to click those links). All of the VCR variants use different methods of achieving the same variable compression effect (the Lotus changed the size of the compression chamber, the Gomecsys system uses some geared magic contained entirely within the crankshaft that they claim to be a drop-in replacement for any standard crankshaft, etc.).

Is this a variable Atkinson style ICE?

Is this an evolution of an Atkinson style ICE?

You don't have to use the Atkinson cycle with a VCR engine (Saab used the Otto cycle, for example), Nissan just happens to do that.

The only difference between Otto and Atkinson is the Atkinson cycle holds the intake valves open during part of the compression stroke. According to the R&T article it switches between cycle types as needed (which is no surprise as Nissan has been pretty in to variable valve timing since the late 80's, which I guess was the golden age of valve timing -- VTEC came to be in the 80's, too):

The engine's electronic valve timing and port-plus-direct fuel injection allow it to switch between normal and Atkinson cycle operation on the fly.

I suppose you could call it Miller instead of Atkinson if it's supercharged, maybe (I'm always fuzzy on these details, all I know is it's apparently super trendy to have an ICE cycle named after you). Whether you want to consider it to be an "evolution" of whatever cycle is a matter of perspective, it's merely another variant of an ICE.

It's probably worth mentioning here that this type of engine has been around for roughly 100 years, but limited to lab test benches. Nissan just happened to win the public production and marketing race recently so, you know: you go, Nissan.

How quickly can the engine adjust to variables such as throttle position to produce MOAR power?

Well it's all computer controlled so it can adjust immediately, limited by how fast the control shaft can rotate (Nissan), the piston can move (MCE-5), or whatever. Whether or not there's intentional delays and transitions, I don't know, you'd have to look at the ECU's firmware.

I'm positive that at the bare minimum, if there are any feedback loops involved, then there is at least some damping / filtering going on to prevent oscillations / noise in the compression ratio, and this may place some constraints on response time (although those constraints can most likely be viewed as beneficial).

Can someone provide an explicit explanation of how Infiniti has achieved this marvel of engineering?

Yes, all of the links above as well as all of these links can provide explicit explanations with visual aids.

It's a pretty straightforward and very old concept, it's just that it took a long time for the tech to be in a state that was ready for public use. Since that just happened recently all of a sudden it's getting media attention, but there's tons of readily available info about these types of engines if you want to find out more.

As for reliability most of the modern variants have been under development for decades, and the first VCR prototype is about a century old. They're used in labs a lot, so they're probably off to a good start but of course there's not a lot of real-world data yet. Hopefully they don't go the way of the Wankel engine.

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