an engine which enables/disables cylinders on the fly

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Haven't BMW been doing this for years?

I couldn't open the url but daimler benz were working on this 10 years ago. The idea is that the energy cost of rotating the engine with some cylinders disabled but just bouncing against the gas in the cylinders was a little less than the pumping losses. The gain is that the active cylinders work better thermodynamically. This is because they are having to work a bit harder than when the load is shared between all cylinders, hence they take in a larger charge of air which means compression pressure is higher. Expanding a hot gas from a higher pressure means you get more work out of it if you dump it at a similar pressure and temperature as before.

A similar concept was used on old stationary engines, the engine had no throttle so took a full charge of air in, like a diesel, but differed in that it was premixed with gas or petrol. So each time it fired it ran flat out. Once the engine started to overspeed a governor moved a lever or changed the pivot on the inlet valve control, holding the valve shut. As revs dropped the governor then enabled the inlet valves again for the cycle to continue, they are known as "hit and miss" engines.

AJH

I think the big mercs do this anyway they shut off cylinders both fuelling and sparking when you are cruising

am i understanding correctly? an engine which configures the number of cylinders in use on the fly? anyone understand if this really saves fuel/money (i am imagining friction/wear and tear/incredibly complex valvetrain etc). if it really does save money then i would be truely impressed.

GM's Northstar V8s (I think that's the one anyway) have been doing this for a while, they just turn of the petrol squirting things and magical spark generators to the relevant 4 cylinders. Nothing too complicated.

Dunno how much improvement to fuel consumption it contributes, but I think it has no effect on engine longivity, iirc these engines also have the 100,000 mile service interval.

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The Septics have been trying to get this to work since around 1977. They've released a few onto the market. ISTR Cadillac, or someone similar, releasing a V8-6-4 in around 1979. Didn't work.

Didn;t teh old Alfa twinspark's do something similar - on the overrun you were running using no fel at all.

there was a v12 concept car on topgear or sumat that did it , think it was a cadilac

am i understanding correctly? an engine which configures the number of cylinders in use on the fly? anyone understand if this really saves fuel/money (i am imagining friction/wear and tear/incredibly complex valvetrain etc). if it really does save money then i would be truely impressed.

Fords 4.6 , 5.0 and 6.3 litre Northstar V8 has been doing this for 2 years.

Tim..

if this idea works why cant it be extended to all motor cars through an aftermarket addon: you replace your injectors with a set of special fuel injectors which have another wire to actuate a small valve which can let the compression escape to the outside

when you want to cruise, you just press a button and it disables (or windmills, in aero engine terminology) half of the engine.

there you have it, my second patenable idea in 24 hrs!!!

though i think the most sensible compromise between power and economy would be super/turbocharged sub 1000cc engines like that in the Smart Car or japanese K cars.

to me the variable cylinder idea is like trying to walk on one leg to save energy

Don't know to be honest, but i think most modern cars have that kind of overrun thing. Interesting you say Alfa Romeo though, apparently thier North-American Kamal (SUV I think) will be using the 'Premium V8' (i.e. the Northstar).

It's quite an interesting engine really (as far as engines are interesting...)

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Bollocks to that, engines should be as huge as possible.

Out of all the stuff I drive on a regular basis, the smallest motor is the

1.8 in the Golf.

Otherwise it's either a 2.6 straight 6, 3.2 flat six, 4.6 V8, 6.8 V10, or

7.2 V8.

Little stuff just isn't fun, and doesn't sound anywhere near as good.

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So did the wife's old S-series 1600 Maestro.

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The valve would have to be quite big - after all, it can't be much smaller than the valve that allowed the air in to start with.

you wouldnt need to have another valve...there are perfectly good valves already there to do the job...just cut off the fuel and spark and it wil just process air...as someone earlier said, it will "bounce" off the air it compresses on the compression stroke...

Vettes but fitted with a UK designd engine, maybe in the v late 80's or 90's ha da special key for parkling attendants that cut down the engine. Also didnt the NSX have vtec?

Chrysler C300 5.7L V8. An oil-pressure switch deactivates the pushrods operating the valves on the temporarily inoperative four cylinders.

yes but thats just to do with the cams...

complicated.

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Indeed - and opening a valve would just waste energy, but I thought I'd point out that a tiddly valve wouldn't work anyway.

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Don't plan on retiring off the back of that patent...

Two-smokes have had a decompressor lever for decades - my '62 VeloSlowlex has one - and IIRC older (and I'm thinking 1900s) four-strokes did, too.