零件相对运动就会产生摩擦。一些表面上看起来很光滑的零件,在放大镜下看却是凹凸不平的。如果这些凹凸不平的表面直接接触,甚至互相嵌合,在运动时,不但阻力增大,而且磨损加剧。当负荷较大时,因摩擦产生的热量大,会使零件烧损甚至粘咬在一起,使发动机不能工作。为了避免这种情况,就要在两个相对运动的零件间加入润滑油,用润滑油内部的液体摩擦来代替或者 Part relative movement will produce friction. Some seemingly smooth parts, under the magnifying glass but it is uneven. If these uneven surfaces are in direct contact with each other, or even fit in with each other, not only the resistance increases, but also the wear increases during the exercise. When the load is large, due to the heat generated by the friction, the parts will burn even stick together, so that the engine can not work. In order to avoid this situation, it is necessary to add lubricant between two relatively moving parts, with liquid friction inside the lubricant instead of or