Roots-type supercharger

The Roots type blower is a positive displacement lobe pump which operates by pumping a fluid with a pair of meshing lobes not unlike a set of stretched gears. Fluid is trapped in pockets surrounding the lobes and carried from the intake side to the exhaust. The most common application of the Roots type blower has been as the induction device on two-stroke Diesel engines, such as those produced by Detroit Diesel and Electro-Motive Diesel. Roots type blowers are also used to supercharge Otto cycle engines, with the blower being driven from the engine's crankshaft via a timing or V-belt, a roller chain or a gear train.

The Roots type blower is named after the American inventors and brothers Philander and Francis Marion Roots, founders of the Roots Blower Company of Connersville, Indiana USA, who 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 blower in a patented engine design, making the Roots-type blower the oldest of the various designs now available. Roots blowers are commonly referred to as air blowers or PD (positive displacement) blowers, and can be commonly called "huffers" when used with the gasoline-burning engines in hot rod customized cars.

The Roots-type blower is simple and widely used. It can be more effective than alternative superchargers at developing positive intake manifold pressure (i.e., above atmospheric pressure) at low engine speeds, making it a popular choice for passenger automobile applications. Peak torque can be achieved by about 2000 rpm. Unlike the basic illustration, most modern Roots-type superchargers incorporate three-lobe or four-lobe rotors; this allows the lobes to have a slight spiral along the rotor axes, which in turn reduces pulsing in the input and output (this is impractical with two lobes, as even a slight spiral could open up a free path through the supercharger at certain angles).

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