The compressor still plays a role in the petrol engine. As a rule, the compressors are driven by the crankshaft and function after the principle of the displacement pump. There have also been isolated compressors, e.g., where the compressor part of a turbo-charger, is driven by the engine itself (see last picture). This would however fall into the category of flow-pumps.

In the case of the displacement pump, the increase in engine RPM results directly in the improvement of the air supply to the engine. Any acceleration delays appear only in a very diminished manner. They are basically found in three different forms:

1. Classic Roots-blower (see picture 8),
2. Rotary-type screw-compressor (see pictures 1 - 5),
3. Spiral-type supercharger (see pictures 6, 7).

Nowadays, the charger is generally driven by a belt from the crankshaft. This may also, at the same time, drive ancillary components. In the meantime, it's important to have a relatively high charging pressure in the low RPM regions, the normal incline of which, is clearly cut by the regulation.

In the past, the compressor provided more a higher performance, nowadays however, it raises or increases the maximum tourque. The charger in fact, is responsible for the horizontal line shown over a wide RPM- range. The regulation takes place either through a changeable bypass and/or through an electrically operated clutch in the drive wheel.

The compressor has been around for a long time (see the last picture). It was successfully used in the racing cars of the 1930s. What is new though, is that it can be installed serially, together with a turbo-charger (see picture 9). It is then responsible more for the lower RPM and for the the delay-free acceleration, whereas afterwards, the turbo-charger takes over with the advantage of drawing less power from the engine. 01/14