The engine mechanically supercharges the supercharger, which is called supercharger. When the engine is supercharged, the supercharger is usually driven by the crankshaft of the engine through gears. Turbochargers commonly used centrifugal or Roots compressors, individual use of screw compressors. In recent years, foreign countries have begun to adopt a new type of mechanical scroll turbocharger. Because the driven compressor consumes a certain amount of output power from the engine, the thermal efficiency of the supercharged engine may not necessarily improve, sometimes even lower than with non-pressurized internal combustion engines. The choice of supercharging pressure, first of all to ensure that you can achieve the required average effective pressure, and secondly to obtain the lowest possible fuel consumption. These two demands are often contradictory to supercharging. If the pursuit of the average effective pressure, it will inevitably lead to lower mechanical efficiency, fuel consumption rate. Therefore, the selection of boost pressure values should seek the best compromise between power and fuel consumption. The supercharger system is currently used more commonly in European cars. Because supercharged supercharger is driven by the crankshaft continuous operation, so do not produce turbocharged turbine hysteresis phenomenon. Although the supercharger can only improve about 10% of the 20% power output, but the smooth continuity of the turbocharged engine can not.