Scroll-type supercharger

The scroll-type supercharger is a positive displacement orbiting-spiral supercharger. It is a compromise between the more rugged rotating lobe and the more efficient sliding vane type superchargers and is considered to offer the highest potential in regard to efficiency, noise and pressure fluctuation [cite book | last = | first = | authorlink = | coauthors = | title = Fuel Cell Power for Transportation | publisher = Society of Automotive Engineers | date = 2000 | location = | pages = | url = | doi = | id = | isbn = 0768007364]

History

The basic concept of the scroll-type supercharger was invented by Léon Creux of France in 1905, originally for aircraft use, though Creux did consider it as a possible form of steam engine. However, Creux's supercharger failed due to the relatively poor casting techniques available at the time. This type of supercharger has not seen widespread use in the aviation role, but has been used on a small number of automobile applications.

Description

The moving parts of the supercharger is a disc-shaped displacer with identical spirals (or scrolls) projecting from each side, and manufactured from light alloy to reduce inertia. A pair of fixed scrolls supported by the end walls of the compressor chamber are interleaved with the moving scrolls. Rather than rotating, the displacer is driven in an orbital motion to create a pumping action between the pairs of scrolls.Air is pulled into the device when the moving scrolls are at their furthest from the fixed scrolls, leaving a large gap. As the shaft rotates the gap closes, and the point of widest opening rotates to a point further "into" the charger. As the process continues the gap eventually ends up on the middle of the housing, at the point where the higher pressure air exhausts into the engine. The scrolls are shaped so the gap slowly decreases in size as it moves to the center, thereby compressing the air.

The edges of the scrolls are sealed by strip-type seals, while the supercharger's main shaft bearings use radial seals to prevent the charge air from becoming contaminated with oil. [cite book | last = Nunney | first = M.J. | authorlink = | coauthors = | title = Light and Heavy Vehicle Technology | publisher = Butterworth-Heinemann | date = 2006 | location = | pages = | url = | doi = | id = | isbn = 0750680377]

Volkswagen G-Lader

The most common and well known scroll-type supercharger is the G-lader ("lader" is German for "charger"), designed by Volkswagen for use in a version of the Mk2 Polo called the GT G40. Launched first as a limited batch of about 500 cars in 1987, most were sold to VW workers. A normal production version of the G40 was launched as part of the Mk3 (or Mk2f) range. The name comes from the "G" shape of its compression channels. It was mounted on a 1272cc engine, which offered performance about that of a 2 litre normally-aspirated engine.

A similar, but larger G60 became available in the VW Corrado during the early 1990s and was also available in limited numbers in the VW Passat and VW Golf. The G60 won International Engine of the Year when it was introduced in 1989.The 40 and 60 denote the displacer scroll width in mm.

All supercharger types benefit from the use of an intercooler to get rid of the heat produced during compression.

Notes

References

*cite web | last = | first = | authorlink = | coauthors = | title = G-Lader Arbeitsweise (G-Lader Function) | work = | publisher = Die G-Laderseite.de | date = | url = http://g-laderseite.de/g-lader_arbeitsweise.php | format = | doi = | accessdate = 2008-02-09
*cite web | last = | first = | authorlink = | coauthors = | title = Patent number: 801182 "ROTARY ENGINE" | work = | publisher = US Patent Office | date = 1905 | url = http://www.google.com/patents?id=ls1cAAAAEBAJ&dq=801182 | format = | doi = | accessdate = 2008-02-09