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1、第 1 页 共 8 页 英 文 翻 译原 文 ：English Lubricating SystemThere are a great many moving metal parts in the engine. There parts must be protected by lubricating oil so that there will be no actual metal-to-metal contact. The moving parts , in effect , float on films of oil .Two types of lubricating systems h
2、ave been used on four-cycle automotive engines , splash and combination splash and pressure feed.In the splash lubricating system , oil is splashed up from the oil pan or oil trays in the lower part of the crankcase .Theoil is thrown upward as droplets or fine mist and provides adequate lubrication
3、to valve mechanisms , piston pins , cylinder walls ,and piston rings.In the combination splash and prcssure fcad lubricating system , an oil pump takes oil from the oil pan and forces it through holes drilled in the engine block and crankshaft.This oil thereby reaches the various bearings that suppo
4、rt rotating shafts and the different moving parts in the engine. It covers the surfaces of the moving parts to prevent metal-to-metal contact and undue wear of the parts.In this system , cylinder walls are lubricated by splashing oil thrown off frem the connecting-rod bearings.The lubricating oil ci
5、rculating through the engine to all moving parts requiring lubricarion through the engine to all moving parts requiring lubrication performs other jobs.(1)Lubricate moving parts to minimize wear.(2)Lubricate moving parts to minimize power loss from friction.(3)Remove heat from engine parts by acting
6、 as a cooling agent.(4)Absorb shocks between bearings and other engine parts , thus reducing engine noise and extending engine life.第 2 页 共 8 页 (5)Form a good seal between piston rings and cylinder walls.(6)Act as a cleaning agent , washing the working surfaces free of chemical deposits , dust and t
7、o protect them from corrosion.A satifactory engine lubricating oil must have certain characteristics . or properties . It must have proper viscosity (body and fluidity) and must resist oxidation , and foaming . Also , it must act as a good cleatning agent , must pour at low temperatures , and must h
8、ave good viscosity at extremes of high and must have good viscosity at extremes of high and low temperature.Any mineral oil , by itself , does not have all there properties . Lubricating-oil manufactures therefore put a number of additives into the oil during the manufacturing process . An oil for s
9、evere service may have many additives , as follows:(1)usually a viscosity-index improver;(2)pour-point depressants;(3)oxidation inhibitors;(4)corrosion inhibitors;(5)rust inhibitors;(6)foam inhibitors;(7)detergent-dispersants;(8)extreme-pressure agents.English Cooling SystemThe purpose of the coolin
10、g system is to keep the engine at its most efficient operating temperature at all engine speeds and all driving conditions . A great deal of heat is produced in the engine by the burning of the air-fuel mixture. Some of this heat escapes from the engine through the exhaust gases ( the hot gases left
11、 after the gasoline is burned ) . But enough remains in the engine to cause serious trouble unless removed by some other means . The cooling bybtem take care 第 3 页 共 8 页 of this additional heat.The cooling system is built into the engine . There are hollow spaces around each engine cylinder and comb
12、ustion chamber . These hollow spaces are called water jackets , since they are filled with water . When the engine is running , the water takes heat from the engine , becoming hot in the process . A water pump pumps the hot water from the engine water jackets into the radiator . The radiator has two
13、 sets of passages . One set carries water . The other set carries aie ( pulled thrugh by car motionand the engine fan ) . As the hot water passes through ,it gives up its heat to the air passing through . The cooled water then reenters the engine , where it can pick up more heat . In operation , wat
14、er continuously circulates between the engine and radiator , carrying heat form the engine to the radiator . By this means , excessive engine temperatures are prevented.Two general types of cooling systems are used , air cooling and liquid cooling . Most automotive engines now employ liquid cooling
15、. The liquid cooling system consists of water pumps , water jackets , engine fan , radiator and so on . The water pump , driver by a belt from the engine crankshaft , circulates the cooling liquid between the radiator and engine water jackets . The cooling liquid is water . Antifreeze compounds are
16、added to the water during the winter . The water jacket are cast into the cylinder blocks and heads . The engine fan is usually mounted on the water pump shaft and is driven by the same belt that drives the pump and the generator . The purpose of the fan is to provide a powerful draft of air through the radiator . The radiator is a device for holding a large volume of water in close contact with a large volume of air so that heat will transfer from the water to the air . The ra
