Nissan announces 2.0L variable compression ratio engine

[NeilBlanchard]

If the crankshaft rotation was counterclockwise - would the power stroke have better mechanical vectors?

The radius of the crank pin is much smaller, and based on that, the torque would seem to be MUCH lower for the left side diagram.

[niky]

Originally Posted by NeilBlanchard

If the crankshaft rotation was counterclockwise - would the power stroke have better mechanical vectors?

The radius of the crank pin is much smaller, and based on that, the torque would seem to be MUCH lower for the left side diagram.

Interesting thought. I see what you mean... this is basically the reverse of a stroker modification... instead, you're getting the engine to act like a short-stroke one with the same effective movement range. I don't know if it's noticeable, but the piston on the VC-T actually accelerates slower at the start of the downstroke than the standard piston, where all the power is supposed to be made... and contrawise, due to the eccentric movement of the upper link, if you reversed the motion, the VC-T piston would indeed move faster on the downstroke, which *should* give more torque. (...uhh... right?)

But I'm assuming Nissan makes it rotate that way due to side loading and efficiency. Plus, it will probably rev higher (if these other considerations outweigh the extra friction caused by the extra link assemblies) Besides... with a turbo, they can probably cover up any torque deficiency inherent in the design... they're claiming V6-like power... meaning 250-300+ hp... though that's not too terribly far out for a two-liter turbo nowadays.

[California98Civic]

Thanks Daox... interesting bit of news.

[Fingie]

This is certainly interesting.

We'll see how well these will last.

It's amazing how far you'll go with money, many cheaper manufacturers haven't even changed to direct injection, and here we have some manufacturers reinventing the wheel (Or should I say crank)

[NeilBlanchard]

Originally Posted by niky

Interesting thought. I see what you mean... this is basically the reverse of a stroker modification... instead, you're getting the engine to act like a short-stroke one with the same effective movement range. I don't know if it's noticeable, but the piston on the VC-T actually accelerates slower at the start of the downstroke than the standard piston, where all the power is supposed to be made... and contrawise, due to the eccentric movement of the upper link, if you reversed the motion, the VC-T piston would indeed move faster on the downstroke, which *should* give more torque. (...uhh... right?)

But I'm assuming Nissan makes it rotate that way due to side loading and efficiency. Plus, it will probably rev higher (if these other considerations outweigh the extra friction caused by the extra link assemblies) Besides... with a turbo, they can probably cover up any torque deficiency inherent in the design... they're claiming V6-like power... meaning 250-300+ hp... though that's not too terribly far out for a two-liter turbo nowadays.

I was thinking along the lines of what Honda (and I am sure others as well) did, which is to offset the centerline of the cylinder to the down (power) stroke side. This puts the connecting rod in a better position at TDC to push the crank more effectively at the beginning of the power stroke.

[niky]

Originally Posted by NeilBlanchard

I was thinking along the lines of what Honda (and I am sure others as well) did, which is to offset the centerline of the cylinder to the down (power) stroke side. This puts the connecting rod in a better position at TDC to push the crank more effectively at the beginning of the power stroke.

The way I see it... it's already offset that way... but I don't know how much of that vertical push goes into the crank.

Funnily enough, some readers pointed out Honda's EX-link, which I knew nothing about... which uses almost the exact same multi-link system, only with a continuously moving lower pivot, basically making it an atkinson's engine, with a longer intake stroke achieved mechanically rather than through valve trickery:

https://www.youtube.com/watch?v=P68W5jOR0bA

(the animation is a bit off, though... in the final Honda prototype, the connecting rod also pushes straight down on the power stroke)

Thinking of covering this one, also, since it was mentioned... but that's going to be a pain in the butt to animate.

[NeilBlanchard]

That's a different design than the Nissan engine.

[niky]

Originally Posted by NeilBlanchard

That's a different design than the Nissan engine.

Yes, it is, but interestingly, Honda's final engine uses a very similar multi-link geometry:

[rmay635703]

Interesting that Honda uses that engine for natural gas cogeneration and heat.

Its unfortunate that cogeneration systems (which are just a motor and heat exchanger) can't be mass produced and reasonably priced.

If they were priced at the same rate as any other small engine we could produce energy at home more efficiently than the grid with about the same level of reliability. Solar when you have it NG when you don't and need heat.

[RedDevil]

Road&Track had it featured nicely:

Variable Compression Engine - How Infiniti VC-T Works