The term "filter" means an accessory used to filter impurities or gases through a filter paper. It is to point to car filter commonly, it is the fittings of engine.
　　According to the different filtering functions are divided into: oil filter, fuel filter (gasoline filter, diesel filter, oil and water separator, hydraulic filter), air filter, air conditioning filter, etc.. Engine air, oil, fuel three filters, generally known as the "three filters", plus air conditioning filters, commonly known as the four filters. They are responsible for the filtration of lubrication system, medium in combustion system, engine intake system and air circulation system of the carriage.