A filter is an accessory that filters impurities or gases through a filter paper. Generally refers to automotive filters, which are accessories for engines.
According to different filtering functions, it is divided into: oil filter, fuel filter (gasoline filter, diesel filter, oil water separator, hydraulic filter), air filter, air conditioner filter, etc. The engine has three kinds of filters: air, oil and fuel. It is generally called "three filters", plus air conditioner filters, commonly known as four filters. Separate the lubrication system, the medium in the combustion system, the engine intake system, and the cabin air circulation system.