Roots type supercharger
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The Roots type supercharger or Roots blower is a positive displacement type device that operates by pulling air through a pair of meshing lobes not dissimilar to a set of stretched gears. Air is trapped in pockets between the lobes and carried between the intake side to the exhaust. The supercharger is typically driven directly from the engine's crankshaft via a belt. In order for the Roots supercharger to deliver air at greater pressure than atmospheric, it must be geared so that it turns faster than the engine. It is named for the brothers Philander and Francis Roots, who first patented the basic design in 1860 as an air pump for use in blast furnaces and other industrial applications. In 1900, Gottlieb Daimler included a Roots-style supercharger in a patented engine design, making the Roots-type supercharger the oldest of the various designs now available.
Out of the three basic supercharger types the Roots is considered the least efficient. However, it is simple and widely used and thus is invariably the most cost efficient. It is also more effective than alternative superchargers at developing compression at low engine rpms, making it a popular choice for passenger automobile applications. Peak boost can be achieved by about 2000 rpm. Much work has been done to improve the efficiency of the Roots type supercharger, but because it does not have internal compression (the design can be classified as just a "blower") it will never have the same potential as the twin-screw type supercharger, or the centrifugal type supercharger.
All supercharger types benefit from the use of an intercooler to reduce heat produced during compression.
The Roots design is commonly used on two-stroke diesel engines, which require some form of forced induction since there is no intake stroke. In this application, the blower does not often provide significant compression and these engines are considered naturally aspirated; turbochargers are generally used when significant boost is needed.
References
- (April 5, 2002). Roots Type Superchargers Explained. (http://www.superchargersonline.com/content.asp?id=22) SuperchargersOnline.com. Accessed September 11, 2004.
- Blower Briefing. (http://www.tomhenryracing.com/technical/default.htm) Tom Henry Racing. Accessed September 11, 2004.