VW quantifies MPG gain of 4- to 2-cylinder deactivation at 31 mph = +16 mpg

[jime57]

Originally Posted by hancock

The valve operating mechanism in any 4 stroke engine is where special attention has to be made to protest 'sliding' surfaces. For instance the introduction of roller followers on cams.

So no hydrodynamic protection and wear protection will be based on the lubricant antiwear properties (ZDDP) and metalurgical considerations such as choice of material and surface treatment to the splines that move the 'collar mechanism' also how this movement interacts with the cams surfaces?.

Don't know that VW has done so, but it isn't difficult from a design viewpoint to provide pressure lubrication to the splines. One only needs an oil galley through the center of the the camshaft. I suspect that VW would have seen spline lubrication as an issue early on.

[NeilBlanchard]

Does it have to be inline? What about splitting into two opposed twins (a la BMW Boxers), or two 90 degree twins (like Ducati or Moto Guzzi)? Each half would have perfect primary balance, and each could have their own counterbalance shafts to reduce secondary vibrations?

[jmcc]

Possible, of course, but unlikely for a major manufacturer to adopt such a layout when *most* platforms are engineered for in-line configurations (speaking from a European perspective here!)

[yostumpy]

could this work on a turbo deisel? with an electric fuel cut off solonoid on , say , the two inner injector pipes. Which would be the best 2, inner or outer cut off. How would the turbo react to only working on 2 cylinders.Would a fuel cut off solonoid work on the high pressure side of a Bosch mech injector pump. The engine is 2500cc, so I wonder if a landrover would drive (on highway) on 1250cc without overheating?

[Frank Lee]

Originally Posted by NeilBlanchard

Does it have to be inline? What about splitting into two opposed twins (a la BMW Boxers), or two 90 degree twins (like Ducati or Moto Guzzi)? Each half would have perfect primary balance, and each could have their own counterbalance shafts to reduce secondary vibrations?

AFAIK there is no such thing as an ICE with perfect balance; it changes with rpms too. It may be minimal, it may be acceptable, but I think if the two are not in synch you will know it!

[shovel]

In that case, we need a four cylinder "boxer" engine that has two different displacements, for example a 1L pair and a 1.5L pair. - then use a slide valve in the intake/exhaust manifolds that turns the larger pair into a supercharger for the smaller pair during deactivation...

[hancock]

Thanks guys, yes we can all make our own decisions! Interesting that Ford are about to launch the 3 cylinder 1.0L gasoline engine for the Ford Focus. A different technical approach to VW but coming up with the same sort of answers on fuel economy and CO2 emissions but with clever turbocharging and reduced engine friction.

Hancock

[Diesel_Dave]

Originally Posted by yostumpy

could this work on a turbo deisel? with an electric fuel cut off solonoid on , say , the two inner injector pipes. Which would be the best 2, inner or outer cut off. How would the turbo react to only working on 2 cylinders.Would a fuel cut off solonoid work on the high pressure side of a Bosch mech injector pump. The engine is 2500cc, so I wonder if a landrover would drive (on highway) on 1250cc without overheating?

Go common rail, and then turning off the fuel is easy--just turn off the injector. As far as the turbo goes, I think I'd be okay. I'm not sure about the overheating concern--you'd be putting less heat into the coolant with half the cylinders.

[Xist]

Once again, I think that I have a genius idea, look into it, and it has been tried and disproven, and then figured out by VW (or at least someone).

In this and other threads you guys talk about vibrations from having an odd number of cylinders firing. Are one-cylinder engines inherently rough? What about those three-cylinder metros that you know and love?

I just kept reading about how ICE engines are most efficient at 90% capacity, but they are never [responsibly] used like that. I do not have any problem with the idea of accelerating hard to highway speeds, but in theory, couldn't one lonely cylinder maintain speed?

Honestly, I do not think this is necessarily one of those things where if it worked automakers would try it. Sure, maybe we cannot figure it out, but do you think that in a few years Volkswagon or someone else might?

[some_other_dave]

Yes, one-cylinder motors are harsh. They usually have very large flywheels to help damp that out to some extent.

The three-cylinder Metro engines are not that bad. In large part because they are designed specifically to be three-cylinder engines, with combustion events equally spaced around the 720-degree four-stroke cycle.

If you take a four-cylinder engine (combustion events every 180 crank degrees) and just turn off one cylinder, you have three "hits" and one "miss", instead of three evenly-spaced "hits". This makes the motor run rougher and makes the vibrations harsher.

If you disable two opposite cylinders, you get alternating "hit" and "miss" events, which should be less vibration than the 3/4 engine.

The best candidates for cylinder deactivation are engines with a bunch of evenly-spaced cylinders, such as V6, V8, and V12 engines. You could shut down one bank of the motor and effectively make an I3, I4, or I6 engine. If the firing order is set up correctly in the first place, all combustion events will be evenly-spaced and not too far apart, and the engine will be reasonably smooth.

Honda has done the V6 single-bank deactivation. Several manufacturers have deactivated various parts of V8 motors, with varying levels of success.

-soD