Cylinder - on - demand technology

[Burnerman]

What do you make of this latest attempt to reduce emissions?
VAG do away with power to two cylinders as required......by sliding the cam lobes away from the valves! The cams are on splines, and presumably moved by solenoids.
Not sure what to make of that one!
John

 

[Mursal]

Yes the A5 FSI engine has it, think its used to change from 2 to 4 valves per cylinder, but I'd have to check. I think they had to do quite a bit of added engineering when they decided to inject the petrol directly into the cylinder (FSI)

Not sure how it will age, but I said that about the 2.2 Turbo when that girl won all the rallies with it. VAG are pushing the boundaries with an ever more complicated approach to solving problems.

https://www.youtube.com/watch?v=caYQ7TWAOKA

 

[Dave54]

I read something about this, or some similar arrangement a while back. More complexity for very little result IMHO. Manufacturers desperately fiddling at the edges to meet the seemingly random targets set by people who have no idea about anything vaguely technical (politicians)
Meanwhile you have people driving around in huge pickups and SUVs, flying around the world for holidays (and to decide what emissions we should be making), along with all the rest of the things that produce Co2 for no "good" reason.
Nothing personally against any of these things incidentally. I do what I want to as well.
So basically I see it as an over complicated solution, to a problem that doesn't really need addressing this way.

 

[Burnerman]

I couldn't agree more.....boss wife's new Nissan gives a (computered) 64 mpg constant.
I mean, hell, what more can you ask for?
John

 

[Dave54]

I couldn't agree more.....boss wife's new Nissan gives a (computered) 64 mpg constant.
I mean, hell, what more can you ask for?
John

Couldn't agree more John. There are a number of small cars that give this sort of mileage now I believe. I haven't got a clue what sort of efficiency that represents, but I'm pretty sure that smaller is the answer, rather than more complicated.
I had one of the small Skodas as a loan car a couple of years ago. Brand new, never been driven before. Very nice little car it was too. Not cramped for my large 6ft frame, and nippy enough. It had that engine cut out thing though. What a bloody nuisance that is!
Mind you I've had cars that did that in the past!

 

[Avocet]

Yes, I'm sure small-engined, lightweight cars are the best solution (mopeds even better!) but not everybody wants or can use such vehicles. The only way the manufacturers can improve the efficiency of the larger vehicles is with more complex technologies. Either that, or the European Commission could ban the larger vehicles altogether, but that would then reduce consumer choice, which wouldn't be popular either. Besides, often the technologies developed on more expensive vehicles (like partial cylinder shut-down) will filter down to the smaller, cheaper ones when it has been perfected and productionised to the point that the cost is within reach. in a way, the buyers of the larger, more complex vehicles are subsidising future developments for the smaller ones.

 

[xr4x4]

So what would happen to the compression in that cylinder is the valves never open?

Isn't it a waste of energy to compress it if it doesn't need to?

Surly it would be far easier to stop the injector firing fuel and just opening a second valve/valves to stop compression.

 

[Burnerman]

I suppose the theory is, if there's no incoming charge of air then there isn't anything to compress.....hence those cylinders are idling.
There's a fair bit of HP used in opening valves, so if they don't have to be opened, why bother?
Opening valves to allow compression to escape will cause seat burning in a relatively short time.
These are my theories and based on nothing.....all I saw was a new camshaft last time I was in the Audi parts dept, and it caught my attention!
Of course, Honda's V-Tec system has been opening valves on demand for a while now.
John

 

[empip]

...The 2005 Chrysler 300C and Dodge Magnum RT were the first high-volume, modern production vehicles in North America to use cylinder deactivation (though GM was the first to use such a system with the failed Cadillac “four-six-eight” system). Bob Lee, Powertrain Product Team vice president, said, “The MDS was part of the engine's original design. This resulted in a cylinder-deactivation system that is elegantly simple and completely integrated into the engine design. The benefits are fewer parts, maximum reliability and lower cost.”...

First came upon this in Australia - Ocean road trip in Chrysler 300c V8 hemi, one wouldn't know when she dropped into 4 cylinder mode, but floor the loud pedal and the 'two motorbikes' sound soon caressed your lug holes !

Worth a shufty :- http://www.allpar.com/mopar/new-mopar-hemi.html


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[Avocet]

I suppose the theory is, if there's no incoming charge of air then there isn't anything to compress.....hence those cylinders are idling.
There's a fair bit of HP used in opening valves, so if they don't have to be opened, why bother?
Opening valves to allow compression to escape will cause seat burning in a relatively short time.
These are my theories and based on nothing.....all I saw was a new camshaft last time I was in the Audi parts dept, and it caught my attention!
Of course, Honda's V-Tec system has been opening valves on demand for a while now.
John

Yes, I think that's the idea. Don't open EITHER valve and whatever is in there will fluctuate between a low positive pressure at TDC and a partial vacuum at BDC, with a net pressure around zero. I'm sure it won't be quite like that in practice, but maybe close. If you just let air in and out using the valves but switched off the injectors, I think there would be all sorts of problems. Unless it was a direct injection engine, you'd get that cylinder "scavenging" a very weak mixture from adjacent injectors maybe - causing misfires and all sorts. Added to that, I think dumping a load of "cold" air into the exhaust would play havoc with the lambda sensor(s) and cat(s). Another problem with just letting the valves open and close as normal would be the "pumping losses". The engine would still be trying to compress a charge of (almost entirely) air in that cylinder, thus acting as a brake. The efficiency savings wouldn't be that great.

 

[ladylola]

I seem to recall that the Germans tried a similar thing during the war , if I remember correctly it was an eight cylinder engine that could have some ( 4?) cylinders shut down in order to save fuel. Obviously no computer control and not hugely successful , there's still a lot of metal to keep moving losing energy on the way.