The latest version of the shutting-down of both of the middle cylingers in a four-cylinder occurs pretty drastically. In this case, both the valves in a cylinder and the injection valve are closed, even the current for the ignition spark is cut off. At least the air in the two cylinders is still compressed and expanded, which helps to maintain the temperature here.
This shutting-down is actually a product of the adjustment possibilities of the cam-shafts. Originally, the idea was to have two different cam-throws on the cam-shaft and to switch over during the running operation. Thus giving an economic engine a second wind, if the driver should want it.
There were two cams, close to each other, a normal- and a sport cam. The cam-pair had a fixed position on it's shaft but could be shifted longitudinally. Thus would, e.g., when shifting in one direction, the normal cam be used, and in the other direction, the sport cam would take over. In the case of the cylinder shut-down however, it would alternate between the normal- and the zero-lift cam-throw.
This switching back and forth, occurs through two electro-magnetically controlled pins, which are exactly as far apart as the breadth of the cam-throw. With the left pin, the complete sleeve, including the two cams is shifted to the left and the right pin does the same to the right. This means that they can only be operated one at a time.
This electro-magnetic control works by engaging the respective pin into a slot, which after turning about a half a rotation, shifts the sleeve in the desired direction. Thereby, it is assisted by small, spring-loaded balls, which similar to the linkage in the manual gearchange, enable the exact adjustment and position-locking, after the metal-pin has done it's job the current is removed.
Advantage: The two remaining cylinders work more, thus more efficiently.
The disadvantage of this, not all that simple, mechanical construction: The workshop can only exchange the cylinder head completely. Now, when is this fabulous system switched on? Always then, if no great demands are made by the driver or by the environmental conditions, if the engine is warm enough and if the RPMs are distinctly higher than idling speed and lower than the nominal RPMs.
Should you, at this point, still not really understand this construction, it is strongly recommended that you watch the video at the botom of the page. The actual geniality of this construction is, that current is only used during the cam change-over. Also, all it needs is a simple solenoid, so no servo-motor is necessary. Apparently, VW places a great deal of trust in their engines, because now, the two outside cylinders are exposed to more wear and tear.
Who would ever have thought that such narrow cam-throws, together with roller-tappets, would be enough? One can justifiably be curious, if and when this system will also be available for Diesel engines. Also whether, because of the small amount of space available, both would even be possible, the change-over from a zero- to a sport-cam. Whatever the case may be, the relatively small effort involved and the universal application speaks for itself. 05/13