汽车专业英语（第2版普通高等院校汽车工程类规划教材）

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UNIT3AUTOMOTIVE LUBRICATION SYSTEM 3.1The Basics An automobile could not move itself without the aid of friction. However， excessive friction in the engine would mean rapid destruction. Of course，we cannot eliminate friction，but we can reduce it to a considerable degree by the use of lubricating oil so that the automobile can move smoothly with proper friction. The purpose of the lubrication system is to circulate oil through the engine. Many parts inside the engine， such as the camshaft，crankshaft， connecting rods，and pistons are connected to other metal parts. When parts rub together，friction is created. Friction produces heat. Although two metal surfaces may appear smooth to the naked eye，they may look rough when seen through a microscope. An engine must have a good lubrication system. Without it，the friction heat from the contact of the moving parts would wear the parts and cause power loss. Oil，when placed between two moving parts，separates them with a film. This oil film prevents the parts from rubbing against each other. This oil film also cushions the parts， giving quieter and smoother engine operation. Shafts and bearings rotate while in contact with other engine parts. Oil between them forms a film that completely encircles the rotating part. As a result，that part will not directly touch a stationary(nonmoving)part. 3.2Parts of the Lubrication System The main parts of a lubrication system are： pump，main oil gallery， relief valve and filters(Fig.31). Fig.31Lubrication system 3.2.1Oil Pump In most cars，the oil pump is in the crankcase above the sump. It draws oil through a tube that extends downward into the sump. This tube，called the oil