The function of air filter is to remove dust and sand particles from the air into carburetor, so as to reduce the wear of cylinder, piston and piston ring, prolong the service life of engine, and eliminate the intake noise. (Tests show that the wear of cylinder, piston and piston ring will increase 8 times, 3 times and 9 times without air filter in truck.) The installation of air filter increases the intake resistance and reduces the output power.

　　按滤清方式，汽油机用的空气滤清器可分为三类：惯性式、过滤式和综合式（前两种的综合）。根据滤芯方式，可分为干式、湿式和半湿式。干式空气滤清器是在圆形筒中放人纸、布或合成纤维过滤材料；湿式空气滤清器即油盘式空气滤清器；半湿式空气滤清器采用在发泡体聚氨醋中渗人油的方式。

　　According to the way of filtration, the air filters used in gasoline engines can be divided into three types: inertia type, filtration type and synthesis type (the first two kinds of synthesis). According to the way of filter element, it can be divided into dry type, wet type and semi-wet type. Dry air filter is to put human paper, cloth or synthetic fiber filter material in a circular cylinder; wet air filter is oil dish air filter; semi-wet air filter is to infiltrate human oil into foamed polyurethane vinegar.

　　综合式空气滤清器的工作情况是：发动机工作时空气以极高的速度从盖与壳之间的夹缝处流人，并沿壳的内壁向下流至油面处，再绕向上方。由于流动方向的急骤改变，较大的尘沙因惯性作用，即冲向机油面而被粘住留下；而较轻的尘沙，随空气一同进人浸机油的滤网，又被滤网粘附。这样经过再次过滤，较干净的空气就从气管流人化油器。

　　The working condition of the integrated air filter is that when the engine works, the air flows from the crack between the cover and the shell at a very high speed, and flows down to the oil surface along the inner wall of the shell, and then goes upward. Because of the sudden change of the flow direction, the larger dust is sticky because of inertia, i.e. rushing to the oil surface; while the lighter dust is sticky because it enters the oil-soaked filter with air. After re-filtration, cleaner air flows from the trachea to the carburetor.