Assignment

It sounds very tempting. One has a powerful engine with lots of cylinders under the bonnet, and, they only need more fuel if one requires higher performance. Otherwise, some cylinders are simply switched off. In theory, one can avoid throttle losses because now one must give the engine more gas.

Function

Unfortunately, making this a reality was more difficult than the idea behind the invention. In the history of the combustion engine, there have been any number of engines with more than one crankshaft, in which one could simply switch off certain parts mechanically. Technically however, these engines were complicated and heavy. For the engines of today, the switched off cylinders must carry on running, when the injection (and the ignition) is switched off, they function like an air pump, which can somewhat confuse the Lambda regulation.

All cylinders working ...

Because mostly six-cylinder engines are affected anyway, one could (e.g., with V-engines) shut down entire cylinder-banks. This again, can lead to the ideal running temperature not being reached. Possibly the compression and following expansion of the air is not sufficient to maintain the engine temperature. What then, if these engine parts have to suddenly deliver full performance? Perhaps the regulation can continuously change the working cylinders, and divert the coolant and/or exhaust gases accordingly. There are even systems which, with the help of a variable valve control, change over very quickly, keeping the hot exhaust gas in the cylinders for as long as possible.

Cylinder 2 and 3 switched off ...

In any event, it is important that the driver notices as little as possible. In the case of a four-cylinder, this may be a little difficult. In some engines additional complexity in the shape of compensation shafts is required. When shutting off cylinders the effort required may be more than the reasonable advantage is worth. There is also the problem of marketing. E.g., if one takes a Diesel engine with only few cylinders, a high amount of torque and a low consumption. If one wishes to avoid the disadvantages of rough running, then an engine with a large number of cylinders is not the solution to the problem, if, through the shutting off of cylinders means that it loses some of it's smooth running character.

Special feature

Shutting off of cylinders is even used in racing car engines to maintain control of the torque delivery, in this case however, without influencing the valves.