oil from the cylinder walls and diluting the engine oil. This causes a loss of perfornance, an increase in HC emissions, and premature engine wear. For these reasons, a cooling system of some kind is necessary They are generally two different types of cooling system: water-cooling system and air-cooling sys tem. Water-caxling system is more common. The cooling medium, or coolant, in them is either water or sutme low-freezing liquid, called antifreeze. A water-cooling system consists of the engine water jacket thermostat, water puInp. radiator, radiator eap, fan, fan drive belt and necessary hose A water- cooling system means that water is used as a cooling agent to circulate through the engine to absorb the heat and carry it to the radiator for disposal. The engine is cooled mainly through heat transfer and heat dissipation. ' The heat generated by the mixture bumed in the engine must be transferred from the iron or aluminum cylinder to the water in the water jacket. The outside of the water jacket dissipates some of the heat to the air surrounding it, but most of the heat is carried by the cooling water to the radiator for dissipation. When the coolant temperature in the system reaches 90, the thermostat valve open fully, its slanted edge shutting off the shorter circuit so that the e cola nt circulates through the longer one: water- pump-cooling jacket-thermostatradiator top-tank-radiator core-bottom tank-pump. ( shown g.16) but most are the centrifugal type. They and seldom are of the positive dis L plungers. Many water pumps have a loaded seal to avoid leakage of ype engine s have a pump on each cyl- The: rad liator is a device designed dissipate the hcat which the coolant has absorbed from the engine; it is constructed to hold a large amount of which Fig 1-6 Cooling system hose 4-thernuostt provide a large area in contact with the 5"water pump fan 7-ylimmer block an head cooling jack atmophere 8-drain eok 9--conmecting The radiator usually mainly consists of the radiator core, radiator bottom tank, and radiator top ank. Radiator cores are of two basic types, the fin and tube type( fins are placed around the tubes to in- crease the area for radiating the heat )and of the ribbon cellular or honey comb type. The populer fin and tube type of radiator core has the advantage of fewer soldered joints and is therefore a stronger construc tion. It consists of a series of parallel tubes extending from the upper to the lower tank. The honeycomb type core consists of a large: number of narrow water passages made by soldering pairs of thin metal rib
bons together along their edges. These tubes are separated by fins of metal ribbon which help dissipate the The radiator cap serves not only to prevent the coolant from splashing out the filler opening, but also to prevent evaporation of the coolant The fan is designed to draw cooling air through the radiator core. The fan is usually mounted on an extension of the water pump shaft and is driven by a v-belt from a pulley mounted on the font end of the erankshaft. Usually the same belt drives the altemator, and belt tension is adjusted by swinging the alter nator on its mounting An air-cooling system contains a centrifugal fan, thermostat, fan drive belt, radiator fins, baffle plates, air control ring, etc. An air-cooling system means that air is used as a cooling agent to circulate through the engine to carry the heat away fmm the moving parts. When the engine is running, forced air is directed over and through the fins to dissipate the heat. In order to regulate the engine temperature by controlling the volume of cooling air, a thermostat is installed inside the metal housing which encloses the engine The thermostat unit is connected to an air control ring. As the engine becomes hotter, the control ring opens wider to admit more air, and closes when the engine is cold With the ring closed, air circula- tion is restricted, and a cold engine warms up more rapidly. Rapid warm-up is one of the characteristics of air-cooled engine, since they do not have heat water in cylinder jackets and radiat The engine cooling system actually is a temperature-regulation system. For a late-model engine, the ooling system must maintain a temperature that is high enough for cficicnt combustion but not so high that the engine will be damaged. The two jobs of the cooling system are to carry excess heat away from the engine and maintain uniform temperature throughout the engine. These requirements are very critical for an engine with electmnic controls that must maintain precise air fuel ratios for economy and emission con lew words premature adj.过早的 viscosIty n.粘度 vamish n.积炭 vaporize t.汽化 polant n.冷却剂 dissipation n.消散,分散 hemostat n.恒温器,温度 impeller 7,叶轮,工作轮,轮子叶片 ribbon n.带,带状物 cellular ad.蜂窝式的,多孔的 mount I.安装,装配,固定 honeycomb 蜂窝结构,蜂窝状物 ulley n.滑轮,带轮,滑车
alternator n.交流发电机,振荡器 Phrases and Expressions water jacket.冷却水套 水泵 cylinder jacket气缸套 radiator cap水箱盖,散热器盖 baffle plate隔板,挡板 radiation fin散热片 centrifugal fan离心式风扇 st pipe排气管 convert .into 把………变成(转变成,转化成) 预热 Notes 1. This means that the engine can work effectively only when the heat energy is equally so as to keep the engine temperature in balance 这意味着只有均等地处理热能以保持发动机温度的均衡,发动机才能有效地工作 2. The behavior of metals at excessively high temperatures also differs from that at normal temper 金属在过高温度中的性能与在正常温度中的性能是有区别的。 3. This causes a loss of performance, an increase in HC emissions and premature engine wear 这将导致工作不正常,碳氢化合物的排放将增加,还会导致发动机过早磨损。 4. The heat generated by the mixture burned in the engine must be transferred from the iron or alu minum cylinder to the water in the water jacket 发动机中可燃混合气燃烧所产生的热量必须从铁制戍铝制的气缸中传送到冷却水套里的 冷却水中。 5. They consist of a rotating fan or impeller, and seldom are the positive displacement type that us gears or plungers 它们(水泵)由一个旋转叶片,即叶轮组成,而很少采用由齿轮或柱塞构成的容积式水 泵 Unit Five Engine Lubrication System An automobile could not mowe itself without the aid of friction. However, exce engine would mean rapid destruction. Of course, we cannot eliminate friction, but we can reduce it to a considerable degree by the use of lubrication oil so that the automobile can move smoothly with proper The engine lubrication is mainly conducted by the lubricating oil, which has several functions in the
lubricating system: first of all, the oil forms a protective coating on the metal surface and prevents a metal to metal contact, thus reducing friction and minimizing wear. Secondly, as the oil is fed to the various moving parts of the engine, it absorbs and carries the heat away from the engine parts. Thirdly, as the oil circulates through the moving parts of the engine, it tends to wash off dirt away from the engine parts. Fi nally, the oil absorbs shocks between bearings and other engine parts, and forms a good seal between pis- ton rings and cylinder walls To do these jobs, lubricants are usually made from the same crude oil from which gasoline is ob- tained. The petroleum oil is unded with animal fats, vegetable oils and other ingredients to pro duce, Satisfactory oils and greases for automotive use, Lubricating oils and greases are also manufactured from silicones and other materials and have no petroleum products in them. Furthermore, the engine oil must function whether the temperature is below zero or above 200deg. I. This is contrary to the nature of petroleum products since they tend to thicken at low temperatures and thin out at high temperatures. The oil must go through many processes during manufacture to reduce this tendency to change viscosity with changes in temperature Engine lubricating systems are divided into two types: splash, pressure feed. In the splash luhricat ing system, there are dippers on the lower parts of the connecting rod bearing caps: these dippers enter oil trays in the oil pan with each crankshaft revolution. 'The dippers splash oil to the upper part of the en- gine. The oil is thrown up as the oil sprays, which provides adeqquate lubrication to valve mechanisms cylinder walls, piston rings and bearings sut The splash system of lubrication is a simple method and only works successfully if the uil in the mp is maintained at the correct level, neither too high nor too low, and the engine is kept horizontal Pressure or forced lubrication is used in practically all engines apart from simple lubrication and splash lubrication, and is characterized by the oil being fed under pressure from a pump to the majority of engine parts, especially to main bea- and connecting rod bea In modem engine desigs, these two methods are often comhined shown in Fig. 1-7. Pressure is devel oped by the oil pump, which delivers the camshaft and valve train components at the top of the en gine. Other components in Fig. 1-7 by a network of passages, or galler The lubricating syster n. no mat ter what type, has the job Fig. 1-7 Labrication syster 1.7-reducing walve 2--oil cooler 3--cooler cock safety valve ing adequate amounts of oil to all mor
17 ving engine parts so that the oil can do the various jobs. In some heavy- duty engines, where the oil has a harder and hotter job to do, oil cooler is included in the lubricating system. The oil cooler has a radi- itor much like the cooling system radiator, through which the oil passes: this cools the oil. All engines have some sort of lever indicator. which usually consists of a dipstick, or oil lever stick, that enters the crankcase iom the side of the block. To check the oil lever in the open pan, the dipstick can he pulled out and the height of thc oil on the stick noted. Oil can then be added if the oil lever is too low for ade te engine protection In general, the lubrication system of an automotive engine apart fron the lubricating also contains a eserver (called the oil pan, sump, or crankcase)to hold the oil supply, a pump to develop pressure, nd the valves for controlling flow and The oil pumps are of the positive displacement type in several designs. Vanes, plungers, rotors and gears are all used to build up the necessary pressure. The pumps of gear and rotor types are always posi tively driven, usually from the camshaft either by means of gears or cams The gear-lypxe: pumps used in engine lubrication systems may be either of duplex type or simplex type. The duplex type oil pump comprises two sections. Each pump section operates independently of the otner The simplex type oil pump consists of an oil pick up, a housing, an cnd cover, and a pair of gears The driving gear of the pump is keyed to the pump drive shaft, which is supported by two bushings pressed in the bousing of the pump and its end cover. The driven gear meshes with the driving gear and is free to rotate on a fixed spindle pressed in the punp housing. Jn operation, the oil entering the pump through the inlet port in the housing becomes trapped between the teeth of the contra-rotating gears and the surrounding wall of the pumping chamber. The oil is thus carried arund the periphery of the gears (not between them)and then discharged through opposite discharge port. At this point, the action of the ntermeshing teeth prevents the oil from retuming to the inlet side of the pump bile, She oil punp in tractor engines is driven from a gear on the nose of the crankshaft; while in automo- engines, it is driven from a gear made integral with the camshaft To remove mechanica impurities fmm the oil circulating though the engine lubrication system,the filter is used. The oil filter can filter dirt and solids out of the oil in lubrication systcm. As these par icles of foreign matter are prevented from entering the engine by oil filter, the rate of wear of engine parts is reduced. Engines of more recent designs use a full-flow centrifugal oil filter, that is, all oil passes through the filter before it reaches the bearings. This is a reaction-type centrifugal filter with which all of delivered by the oil pump is cleaned in the filter rotor. This filter has an oil outlet pipe fitted inside the hollow spindle of the filter rotor and connected to the oil line that distributes the oil to the various parts of the lubrication system In centrifugal oil filters the rotor consists of a body and a bowl. The surface area of the rotor top greater than that of the bottom, because the diameter of the uppcr journal of the mtor spindle is greater than that of the lower joumal. The total oil pressure force acting on the rotor top from below is greater than the force acting on the bottom. Therefore, when the engine is running; the rotor is lifted and its bearing end face is thus relived. The higher the pressure in the rotor, the greater the distance the rotor is