variable compression ratio engines
 

Infiniti is offering it's 4 cyl turbo'd cars with variable compression ratio engines starting in 2018....per Car and Driver.
Just when you think there is no more room for improvements, some new tech comes out!
They say the comp ratio can be changed from 8.8:1 to 12.0 in .2 second...giving better mpg and allowing more boost to be added.
According to their preview..an eccentric bushing is used on each connecting rod at the piston end. A small ram turns the bushing to control the compression ratio.

Seems prone to catastrophic failure...but would imagine that was accounted for in the R&D.

I think Volvo was messing around with variable compression a while ago. In their system the block itself was on a cam that would move the block/head in relation to the static crankshaft position. Did not hear much about it since.

Sorry. It was Sabb and their SVC system. Bankruptcy killed it along with the company.

They never said what the small piston/ram is controlled by. My Honda has var valve timing and it's controlled by oil pressure. I imagine with todays tech, they could prob control it electronically.

Seeing that it's set to be in all their 4 cyl engines, I'm sure it went thru lots of testing.

Ummm, isn't every engine with forced induction (Turbo / Supercharged) variable compression?

Another way to think of forced induction is variable displacement. At 1 bar of boost, you are burning twice as much fuel and air as at ambient temperature / pressure so it is equivalent to having double the displacement.

I prob should have said that as..variable compression "ratio" engine ...meaning the engine is able to vary the distance of the piston from the cylinder head.

This is a better explanation of how it works. I didn't know Porsche has the patent on it.

Porsche patents Variable Compression Ratio Engine Technology - Ferdinand

That's a different mechanism. There are many ways to achieve a variable compression ratio. Including valve timing.

Same as the Infiniti system in the OP

How could valve timing vary the compression ratio?

No, it is not the same. Porsche one is a 2 position, Inifiniti is an analog adjustment.

http://forums.pelicanparts.com/uploa...1486266211.jpg
http://forums.pelicanparts.com/uploa...1486266216.jpg

You could also vary the height of the cylinder head which is how a CFR engine works (that is the engine used as the standard test for octane rating).

Valve timing- late closing of the intake valve aka Miller Cycle. You push some of the fresh air back out and this gives you a longer expansion ratio than the effective compression ratio, at the cost of some displacement.

I have no idea how the extra complexity and mass gives a big enough thermodynamic benefit over the Miller Cycle to justify itself.

Personally, I find this more interesting.
http://www.thedetroitbureau.com/2017/01/mazda-aiming-to-first-with-breakthrough-hcci-engine/

Saab made one back in the late 1990's and showed it off in 2000. They were going to put it in the 9-5 but that was right about the time GM bought the remaining 50% of Saab and shelved the engine due to cost.
Saab's version used a tilting cylinder head with the goal of matching CR to forced induction boost. Interestingly (and very non-Saab like) this engine used 5 cylinders instead of 4 and used a supercharger instead of a turbocharger.

http://saabplanet.saabplanet.netdna-...on-624x429.jpg

http://www.spannerhead.com/wp-conten...Saab_SVC_2.jpg

http://www.spannerhead.com/wp-conten...Saab_SVC_3.jpg

https://en.wikipedia.org/wiki/Saab_Variable_Compression_engine

This is from the Car and Driver Mag

http://forums.pelicanparts.com/uploa...1486269320.jpg
Selectable Squish

Raising an engine’s compression ratio improves fuel efficiency during low-load operation, but it can also lead to catastrophic detonation when maximum power is requested. Engineers have long sought to navigate this challenge with a variable-compression-ratio engine, and Infiniti promises to implement its solution in early 2018 with a complex system of links in the crankcase.

There’s more than one way to skin this cat, though. German powertrain engineering company FEV proposes a piston wrist pin that passes through an eccentric bushing at the top of the connecting rod. As the bushing rotates, the piston moves vertically relative to the rod, in turn adjusting the compression ratio. The position of the bushing is determined passively by a pair of miniature pistons inside the connecting rod that rotate the cam in reaction to combustion and inertia forces. FEV’s 1.7-liter turbocharged inline-four demonstrator can adjust its compression ratio from 8.8:1 to 12.0:1 in 0.2 to 0.6 second.

An old family friend has been working on that concept for some time (15+ years)
VCREngine
He holds a patent of some sort. His has the crank main bearing journals in an eccentric carrier. Not sure how it's actuated.

This.^

Toyota has been doing this for a while with an Atkinson cycle engine. (Prius)

edit: here we go...

Available now in the 2018 Infiniti's

http://forums.pelicanparts.com/uploa...1524348927.jpg

not really.

The term compression has never been used to describe forced induction.
Merc is the only brand that use the term Kompressor as a marketing name for it's superchargers.. but they didn't use the term compression.. it's just a brand name that nobody else used.

Turbo/supercharge just forces more air in the chamber
And then more fuel is injected via a seperate process.
Sure on a physics level, the air is compressed. the Fuel isn't. Not by the Forced induction it ain't.

It's just forced induction.. Nobody calls it compressed induction
Forced induction is about air only.


Compression points to the piston compressing the Air/fuel mixture.

The Saab system seems so simple. I assume it hasn't been adopted is that moving all that mass gives a slow response time.

from C&D
Back at the turn of the 21st century, Saab revealed a supercharged 1.6-liter inline-five engine with a hinged two-piece block. The engine lowered its compression ratio from 14.0:1 to 8.0:1 by pivoting the top of the block, including the cylinders and the head, around a beefy hinge on the intake side. A set of mini connecting rods riding on an eccentric shaft on the exhaust side did the lifting. Since the crankshaft position is fixed, tilting the block’s top changed the combustion-chamber volume and thus the compression ratio. Saab claimed 225 horsepower and a fuel-economy bump of 30 percent over an engine with similar output. Development costs and Saab’s redheaded-stepchild status within GM meant the capital and interest weren’t there to bring the technology to production.

I understand all that. But the concept is so simple I wonder why it has not been adopted by Lexus or anyone else interested in VCR. putting two pistons in each connecting rod seems like an overly complicated way to accomplish the same thing. Either Saab wanted too much money for the patent or there is some technical problem with it. I suggest that rocking the the mass of the block back and forth would not happen fast enough to respond to the changes in compression required by a modern computer controlled engine.

This is my thought.

I agree the Saab system seems so less complicated. The Infinity system seems like a nightmare for long term reliability. I'd guess GM ended up with the patent on the Saab system.

Sent from my Samsung Tablet using Tapatalk

At first I thought it sounded like my SC engine with broken head studs. But after having read the details I love the sound of it. A high compression engine for running around town, then drops the compression to handle the turbo on boost.

I would think that if you do have variable compression and boost, you would not program it based on user mode, but simply tune it over in combination of a wide variation of parameters.


Just like Variocam and ram and ignition is now varied across the rev range.
Think High compression at low revs for low end power then the turbo kicks in and the compression is dropped accordingly.

You can fit 1 bigger turbo instead of ninnying about with a smaller one for less turbo lag. and a bigger one for top end boost.

You could even opt to
turn on HC for initial spool up,
then turn it off & use the boost to accelerate,
once on cruising speed at the highway, turn boost off in favor for HC for reduced fuel cost at cruise.

To be honest the amount of variables now become so complicated that they are probably going to look at Self learning engine DME's running off Big Data.

Eg all the engines send their feedback to the DME,
the DME will still work closed loop off some basic programming,
but the DME's will then send their data to the cloud
Big Data will send back optimisations to the DME

Yes.

And it would be a good idea to avoid the new technology for a couple of years until it got some maturity and reliability (limp home mode :( )

hmm, this would be perfect for HCCI engine. Currently, Mazda needs to use low-boost supercharger and spark plug in order to keep combustion in line across whole range. With variable compression they could probably get rid of supercharger.


https://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition

Not sure, but Mazda seems to be claiming variable compression with their SkyActive technology. I think it is just a variable cam based on engine loading though.

Yupp. It is amazingly clever but still needs low boost supplied by Roots SC to cover certain marginal areas of ignition map.

With fully variable geometrical compression ratio, HCCI would be the death of small diesel.

To me, the simplest system is the one shown in post #13
The idea of raising and lowering the whole cyl head..seems way too bulky.

The Infiniti gets pretty darn near diesel compression at full efficiency - wow!