内燃机专业英语英文

内燃机专业英语英文 内燃机专业英语自编讲义部分: 1. Engine Classification and Overall Mechanics The automobile engines can be classified according to: 1. number of cylinders; 2. arrangement of cylinders; 3. arrangement of valves; 4. type of cooling; 5. number of cycles (two or four); 6. type of fuel burned; 7. type of ignition. The engine is the source of power that makes the wheels go around and the car move. The automobile engine is an internal-combustion engine because the fuel (gasoline) is burned inside it. The burning of gasoline inside the engine produces high pressure in the engine combustion chamber. This high pressure forces piston to move, the movement is carried by connecting rods to the engine crankshaft. The crankshaft is thus made to rotate; the rotary motion is carried through the power train to the car wheels so that they rotate and the moves. The engine requires a fuel system to supply it with a mixture of air and fuel. The fuel system does this by pumping liquid gasoline from a tank into the carburetor, a mixing device that mixes the gasoline with air. The mixture is delivered to the engine where it is burned. The engine also needs a cooling system, the combustion of the air-fuel mixture in the engine creates a very high temperature (as high as 2000 to 2700 ?). The cooling system takes heat away from the engine by circulating a liquid coolant (water mixed with antifreeze) between the engine and a radiator. The coolant gets hot as it goes through the engine. It cools off as it goes through the radiator. Thus, the coolant continually takes heat away from the engine, where it could do damage, and delivers it to the radiator. Air passing through the radiator takes heat away from the radiator. The engine also includes a lubricating system. The purpose of the lubricating system is to supply all moving parts inside the engine with lubricating oil; the oil keeps moving parts from wearing excessively. The engine requires a fourth system, the ignition system. The ignition system provides high-voltage electric sparks that ignite, or set fire to, the charges of air-fuel mixture in the engine combustion chambers. The fifth is starting system and its purpose is to change the electrical current into the mechanical energy to push the crank-shaft around. By means of this, the engine can be started. These five systems are discussed briefly in following sections. 1 Words and Expressions combustion chamber 燃烧室,ignition. 点燃,power train 动力传动系统,carburetor 化油器,antifreeze 防冻的,coolant 冷却剂,液态,,crankshaft 曲轴 2 2. Four-stage-engine Operation The action taking place in the engine cylinder can be divided into four stages, or strokes. “Stroke” refers to piston movement; as stroke occurs when the piston moves from one limiting position to the other. The upper limit of piston movement is called TDC ,top dead center,. The lower limit of piston movement is called BDC (bottom dead center). A stroke is piston movement from TDC to BDC or from BDC to TDC. In other words, the piston completes a stroke each time it change its direction of motion. Where the entire cycle of events in the cylinder requires four strokes (or two crankshaft revolutions), the engine is called a four-stroke-cycle engine, or a four-cycle engine. The four piston strokes are intake, compression, power, and exhaust. Intake stroke. On the intake stroke, the intake valve has opened, the piston is moving downward, and a mixture of air and vaporized gasoline is entering the cylinder through the valve port. The mixture of air and vaporized gasoline is delivered to the cylinder by the fuel system and carburetor. Compression stroke. After the piston reaches BDC, or the lower limit of its travel, it begins to move upward. As this happens, the intake valve closes. The exhaust valve is also closed, so that the cylinder is sealed. As the piston moves upward (pushed now by the revolving crankshaft and connecting rod), the air-fuel mixture is compressed. By the time the piston reaches TDC, the mixture has been compressed to as little as one-tenth of its original volume, or even less. This compression of the air-fuel mixture increases the pressure in the cylinder. When the air-fuel mixture is compressed, not only does the pressure in the cylinder go up, but the temperature of the mixture also increases. Power stroke. As the piston reaches TDC on the compression stroke, an electric spark is produced at the spark plug. The ignition system delivers a high-voltage surge of electricity to the spark plug to produce the spark. The spark ignites, or sets fire to, the air-fuel mixture. It now begins to burn very rapidly, and the cylinder pressure increases to as much as 3-5 MPa or even more. This terrific push against the piston forces it downward, and a power impulse is transmitted through the connecting rod to the crankpin on the crankshaft. The crankshaft is rotated as the piston is pushed down by the pressure above it. Exhaust stroke. As the piston reaches BDC again, the exhaust valve opens. Now, as the piston moves up on the exhaust stroke, it forces the burned gases out of the 3 cylinder through the exhaust-valve port. Then, when the piston reaches TDC, the exhaust valve closes and the intake valve opens. Now, a fresh charge of air-fuel mixture will be drawn into the cylinder as the piston moves down again toward BDC. The above four strokes are continuously repeated. Words and Expressions stroke 行程～冲程,BDC 上止点,TDC 下止点,surge 冲击～脉动,terrific 了不起的～绝妙的,crankpin 曲柄销～连杆轴颈,intake stroke 吸气冲程, compression stroke 压缩冲程,power stroke 做功冲程,exhaust stroke 排气冲 程,fresh charge ,发动机,吸入的新鲜混合油气 4 3. Two-stage-engine Operation In the four-stroke-cycle engine, already discussed in lesson 1、2, the complete cycle of events requires four piston strokes (intake, compression, power, and exhaust). In the two-stroke-cycle, or two-cycle, engine, the intake and compression strokes and power and exhaust strokes are in a sense combined. This permits the engine to produce a power stroke every two piston strokes, or every crankshaft rotation. In the two-cycle engine, the piston acts as a valve, clearing valve ports in the cylinder wall as it nears BDC.A fresh air-fuel charge enters through the intake port, and the burned gases exit through the exhaust port. The complete cycle of operation is as follows: As the piston nears TDC, ignition takes place. The high combustion pressures drive the piston down, and the thrust through the connecting rod turns the crankshaft. As the piston nears BDC～it passes the intake and exhaust ports in the cylinder wall. Burned gases, still under some pressure, begin to stream out through the exhaust port. At the same time, the intake port, now cleared by the piston, begins to deliver air-fuel mixture, under pressure, to the cylinder. The top of the piston is shaped to give the incoming mixture an upward movement. This helps to sweep the burned gases ahead and out through the exhaust port. After the piston has passed through BDC and stars up again, it passes both ports, thus sealing them off. Now the fresh air-fuel charge above the piston is compressed and ignited. The same series of events takes place again and continue as long as the engine runs. We mentioned that the air-fuel mixture is delivered to the cylinder under pressure. In most engines, this pressure is put on the mixture in the crankcase. The crankcase is sealed except for a leaf, or reed, valve at the bottom. The reed valve is a flexible, flat metal plate that rests snugly against the floor of the crankcase. There are holes under the reed valve that connect to the engine carburetor. When the piston is moving up, a partial vacuum is produced in the sealed crankcase. Atmospheric pressure lifts the reed valve off the holes, and air-fuel mixture enters the crankcase. After the piston passes TDC and starts down again, pressure begins to build up in the crankcase. This pressure closes the reed valve so that further downward movement of the piston compresses the tapped air-fuel mixture in the crankcase. The pressure which is built up on the air-fuel mixture then causes it to flow up through the intake port into the engine cylinder when the piston moves down far enough to clear the intake port. The two-stroke engine is not only very simple but gives nearly twice the power 5 of a four stroke engine from a cylinder of given size, but it is wasteful of gasoline, as some mixture inevitably finds its way into the exhaust system on the combines intake/exhaust stroke, and there are always some combustion products left in the cylinder which reduce the rapid burning of the fuel. This kind of engine is always used in motorcycles. Words and Expressions sweep 扫气,connecting rod 连杆,crankcase 曲轴箱,seal off 密封,leaf ,reed, valve 片簧阀,air-fuel charge 可燃混合油气 6 4. Diesel Engine Operating Features We all know that diesel engines, in principle, work in the same way as gasoline engines do. Both kinds of engines are internal-combustion engines, but each of them has its characteristic features. As their names suggest this type of engines burn their fuel inside the working parts of the engines. “Internal” means “inside”, “combustion” means “catching fire or burning”. In any internal combustion engine, burning fuel heats air which consequently expands, and in expanding exists a push to a piston which, in turn, rotates the engine crankshaft through a connecting rod. Now let us compare the diesel engine with the gasoline engine. Firstly, the explosive mixture of the gasoline engine is provided by a carburetor, but in the case of the diesel engine the supply is affected by an injection or “jerk” pump which forces a “short” of fuel into each cylinder in turn according to the correct firing sequence. Secondly, the fundamental difference between gasoline and diesel engines is that in the gasoline engine the source of the heat for igniting the charge, namely, an electric spark, is generated outside the engine, and is taken, as it were, into the waiting charge at the required instant. In the diesel engine the source of heat for igniting the charge is created within the engine by compressing pure air to a degree that will initiate combustion and then injecting the fuel at the right time in relation to the movement of the crankshaft. Both classes of engines are of very similar construction. But as the diesel engine is called upon to withstand very much greater stresses due to higher pressures in cylinders, it has to be of more substantial construction, and is thus heavier. In general, the diesel engine may weigh about 9.25 kilograms per kilowatt. The most important advantage of the gasoline engine is its lower weight per kilowatt. The gasoline engine for automobiles weighs about 6.17 kilograms per kilowatt, and gasoline engines for airplanes may weigh as little as 0.77 kilograms per kilowatt. This advantage prevents the diesel engine from replacing the gasoline engine in some automobiles and airplanes. However, the diesel engine is more efficient, because it has higher compression ration. Its ratio may be as high as 16 to 1. Up to 40 percent of the chemical energy of the burning fuel may be changed into mechanical energy. In addition, the diesel engine runs cooler than the gasoline engine. This advantage is especially obvious at lower speeds. Diesel oil is not only cheaper than gasoline, but also safer to store. Words and Expressions:diesel:柴油机, internal-combustion engines:内燃机, jerk pump:脉动史喷油泵,compression ration:压缩比 7 5. Engine Cylinder Block Crankcase We have seen how the mixture of air and fuel is delivered by the fuel system to the engine cylinder, where it is compressed, ignited, and burned. We have noted that this combustion produces a high pressure that pushes the piston down so that the crankshaft is rotated. Now let us examine the various parts of the engine in detail. Engine cylinder block The cylinder block of liquid-cooled engines forms the basic framework of the engine. Other parts are attached to the cylinder block or are assembled in it. The block is cast in one piece from gray iron or iron alloyed with other metals, such as nickel or chromium. Some blocks are cast from aluminum. The block contains not only the cylinders but also the water jackets that surround them. In aluminum blocks, cast-iron or steel cylinder sleeves (also called bore lines) are used. These metals have better wearing qualities than aluminum and can better withstand the wearing effect of the pistons and ring moving up and down in the cylinders. For most engines, cast iron has been found to be a satisfactory cylinder-wall material. However, in some small engines, the cylinder walls are plated with chromium, a very hard metal, to reduce wall wear and lengthen their life. Cylinder Head The cylinder head is usually cast in one piece from iron, from iron alloyed with other metals, or from aluminum alloy. Aluminum has the advantage of combining lightness with high heat conductivity. That is, an aluminum head tends to turn cooler, other factors being equal. There are two types of head, L head and I head. Cylinder head contains water jackets for cooling; in the assembled engine, these water jackets are connected through openings to the cylinder-block water jackets. Spark-plug holes are provided, along with pockets into which the valves can move as they open. Gaskets The joint between the cylinder block and the head must be tight and able to withstand the pressure and heat developed in the combustion chambers. The block and head cannot be machined flat and smooth enough to provide an adequate seal. Thus, gaskets are used. Head gaskets are made of thin sheets of soft metal or asbestos and metal. All cylinder, water, valve, and head-bolt openings are cut out. When the gasket is placed on the block and the head installed, tightening of the head bolts (or nuts) squeezes the soft metal so that the joint is effectively sealed. Gaskets are also used to seal joints between other parts, such as between the oil pan, manifolds, or 8 water pump and the block. Oil Pan The oil pan is usually formed of pressed steel. It usually holds 5 to 10 litres of oil, depending on the engine design. The oil pan and the lower part of the cylinder block together are called the crankcase; they enclose, or encase, the crankshaft. The oil pump in the lubricating system draws oil from the oil pan and sends it to all working parts in the engine. The oil drains off and runs down into the pan. Thus, there is constant circulation of oil between the pan and the working parts of the engine. Words and Expressions cylinder block 气缸体,block crankcase 曲轴箱,framework 结构～车架, gray iron 灰铸铁,water jacket 水套, plate……with 镀金属,cylinder head 气缸盖,gaskets 密封垫,asbestos 石棉,manifold 岐管,oil pan 油盘, pocket 凹槽,bore liner 气缸衬套 9 6. Piston Connecting Rod Piston The piston is essentially a cylindrical plug that moves up and down in the engine cylinder. It is equipped with piston rings to provide a good seal between the cylinder wall and piston. The piston absorbs heat from the gas, and this heat must be carried away if the metal temperature is to be carried away if the metal temperature is to be held within safe limits. The constant reversal of the piston travel sets up inertial forces, which increase both with the weight of the piston and with its speed. For this reason, designers try to keep piston weight low, particularly in high-speed engines. As lower hood lines and over-square engines became popular, the semi-slipper and full-slipper pistons came into use. On these pistons the number piston rings was reduced to three, two compression and one oil-control. One reason for the slipper piston is that, on the short stroke, over-square engine, the piston skirt had to be cut away to make room for the counterweights on the crankshaft. Also, the slipper piston, being shorter and having part of its skirt cut away, is lighter. This reduces the inertial load on the engine bearings and, in addition, makes for a more responsive engine. The lighter the piston, the less the bearing load and the longer the bearings will last. Another way to lighten the piston is to make it of light metal. The idea piston material would be light and strong, conduct heat will, expand only slight when heated, resist wear, and be low in cost. Thus, most automotive-engine pistons today are made of aluminum, which is less than half as heavy as iron. Iron pistons were common in the earlier engines. Aluminum expands more rapidly than iron with increasing temperature, however, and since the cylinder block is of iron, special provisions must be made to maintain proper piston clearance at operating temperatures. To take care of it, the crown is machined on slight taper, the diameter being greatest where the crown meets the skirt and becoming less toward the top. Piston Rings A good seal must be maintained between the piston and cylinder wall to prevent blow-by. “Blow-by” is the name that describes the escape of burned gases from the combustion chamber, past the piston, and into the crankcase. In other words, these gases “blow by” the piston. It is not practical to fit the piston to the cylinder closely enough to prevent blow-by. Thus, piston rings must be used to provide the necessary seal. The rings are installed in grooves in the piston. Actually, there are two types of rings, compression rings and oil-control rings. The compression rings seal in the 10 air-fuel mixture as it is compressed and also the combustion pressures as the mixture burns. The oil-control rings scrape off excessive oil from the cylinder wall and return it to the oil pan. The rings have joints (they are split) so that they can be expanded and slipped over the piston head and into the recessed grooves cut in the piston. Rings for automotive engines usually have butt joints, but in some heavy-duty engines, the joints may be angles, lapped, or of the sealed type. The rings are somewhat larger in diameter than they will be when in the cylinder. Then, when they are installed, they are compresses so that the joints are nearly closed. Compressing the rings gives them an initial tension; they press tightly against the cylinder wall. Connecting Rod The connecting rod is attached at one end to a crankpin on the crankshaft and at the other to a piston, through a piston pin or wrist pin. The connecting rod must be very strong and rigid and also as light as possible. The connecting rod carries the power thrusts from the piston to the crankpin. At the same time, the rod is in eccentric motion. To minimize vibration and bearing loads, the rod must be light in weight. To maintain good engine balance, connecting rods and caps are carefully matched in sets for engines. All rods in an engine must be of equal weight; if they are not, noticeable vibration may result. In original assembly, rods and caps are individually matched to each other and usually carry identifying numbers so they will not be mixed if the engine is disassembled for service. They must not be mixed during any service job, since this could result in poor bearing fit and bearing failure. Words and Expressions counterweight 平衡重,groove 凹槽,recess 凹口,lap 搭接,eccentric 偏 心的,lower hood lines 低发动机罩,over-square engine 短行程发动机, semi-slipper piston 半裙式活塞,full-slipper piston 全裙式活塞,match in set 配套,blow-by 漏气,initial tension 初张力,poor bearing fit 轴承不配套, bearing failing 轴承故障。 11 7. Crankshaft Flywheel Crankshaft The crankshaft is a one-piece casting or forging of heat-treated alloy steel of considerable mechanical strength. The crankshaft must be strong enough to take the downward thrusts of the pistons during the power strokes without excessive distortion. In addition, the crankshaft must be carefully balanced to eliminate undue vibration resulting from the weight of the offset cranks. To provide balance, crankshafts have counterweights opposite the cranks. Crankshafts have drilled oil passages through which oil can flow from the main to the connecting-rod bearings.The front end of the crankshaft carries three devices, the gear or sprocket that drives the camshaft, the vibration damper, and the fan belt pulley. The pulley drives the engine fan, water pump, and generator with a V belt. Flywheel The flow of power from the engine cylinders is not smooth. Although the power impulses overlap (on six-and eight-cylinder engines), there are times when more power is being delivered than at other times. This tends to make the crankshaft speed up and then slow down. However, the flywheel combats the tendency. The flywheel is a comparatively heavy wheel bolted to the rear end of the crankshaft. The inertia of the flywheel tends to keep it turning at constant speed. Thus, the flywheel absorbs energy as the crankshaft tries to speed up and gives back energy as the crankshaft tries to slow down. In effect, the flywheel absorbs power from the engine during the power stroke (or speedup time) and then gives it back to the engine during the other three strokes (or slowdown time) of the cycle. Words and Expressions forging 锻件,sprocket 扣链齿,链轮上与链条结合的齿,,damper 减震器, flywheel 飞轮,bolt 螺栓,one-piece 整体 12 8. Valves and Vales Train Valves and Valve Train There are two openings, or ports, in the enclosed end of the cylinder. One of the ports permits the mixture of air and gasoline vapor to enter the cylinder. The other port permits the burned gases, after combustion, to exhaust, or escape, from the cylinder. The two ports have valves assembled into them. These valves close off one or the other port, or both ports, during the various stages of engine operation. That is to say, each cylinder has two valves, an intake valve and exhaust valve. The cam lobes on the camshaft are so related to the crankshaft crankpins through the gear or sprockets and chain as to cause the valves to open and close with the correct relationship to the piston strokes. The valves are nothing more than accurately machined metal plugs (on long stems) that close the openings when they are seated (have moved up into the openings). When the valve closes, it moves up so that the outer edge rests on the seat. In this position, the valve port is closed so that air or gas cannot escape from the cylinder. A spring on the valve stem tends to hold the valve on its seat (closed). The lower end of the spring rests against the cylinder head. The upper end rests against a flat washer, or spring retainer, which is attached to the valve stem by a retainer lock (also called a keeper). The spring is under compression, which means that it tries to expand and therefore spring-loads the valve in the closed position. A valve-opening mechanism opens the valve, or lifts it off its seat, at certain times. On most engines, this mechanism, called the valve train, includes a cam on the camshaft, a valve lifter, a push rod, and a rocker arm. As the camshaft turns, the cam lobe comes around under the valve lifter. This raises the lifter, which in turn pushes upward on the push rod. The push rod, as it is lifted, causes the end of the rocker arm to move up. The rocker arm pivots around its supporting shaft so that the valve en of the rocker arm is forced downward. This downward movement forced the valve to move downward off its seat so that it opens. After the cam lobe moves out from under the valve lifter, the valve spring forces the valve up onto its seat again. In the other kind of valve mechanism for an engine, the valves are located in the cylinder block instead of the head. With this arrangement, the camshaft is directly below the valve lifter, and no push rods or rocker arms are necessary. Although the valve-in-block arrangement is a simple design, most automotive engines are 13 valve-in-head type. The valve-in-head engine has certain advantages. Cam and Camshaft A cam is a device that can change rotary motion into linear, or straight-line, motion. The cam has high spot, or lobe; a follower riding on the cam will move away from or toward the camshaft as the cam rotates. In the engine, cams on the camshaft cause the intake and exhaust valves to open. There is a cam on the camshaft for each valve, or two cams per cylinder. The camshaft is driven by gears, or by a chain, from the crankshaft. It turns at one-half crankshaft speed. In the four-cycle engine, every two revolutions of the crankshaft produce one revolution of the camshaft and one opening and closing. The cam lobes are so positioned on the camshaft as to cause the valves to open and close in the cylinders at the proper time with respect to the actions taking place in the cylinders. In addition, the camshaft has an eccentric to operate the fuel pump and a gear to drive the ignition distributor and oil pump. stem:柄～堵住,seat:气门座,rest:安放,spring:弹簧,washer:垫圈,lifter: 气门挺杆,push:推杆,valve train:气门组,cam rod:凸轮凸角,rocker arm: 气门摇杆臂,valve-in-head:顶置式气门,valve-in-block:到置式气门 14 9. Engine Fuel System The fuel system has the job of supplying a combustible mixture of air and fuel to the engine. The fuel system must vary the proportions of air and fuel to suit different operating conditions. When the engine is cold, for example, then the mixture must be rich (have a high proportion of fuel). The reason for this is that the fuel does not vaporize rapidly at low temperatures. Therefore, extra fuel must be added to the mixture so that there will be enough vaporized fuel to form a combustible mixture. The fuel system consists of the fuel tank, fuel pump, fuel filter, carburetor, intake manifold, and fuel lines, or tubes, connecting the tank, pump, and carburetor. Some gasoline engines use a fuel-injection system; in this system, a fuel-injection pump replaces the carburetor. The fuel tank, in which gasoline is stored, is normally located at the rear of the vehicle. It is made of sheet metal and is attached to the frame. A fuel pump delivers fuel from the tank to the carburetor. There are two general types of fuel pump, mechanical and electric. The fuel system has filters and screens to prevent dire in the fuel from entering the fuel pump or carburetor. Dirt could, of course, prevent normal operation of these units and cause poor engine performance. The carburetor is essentially a mixing device which mixes liquid gasoline with air. In this process, it throws a fine spray of gasoline into air passing through the carburetor on its way to the engine. The gasoline vaporizes and mixes with the air to form a highly combustible mixture. This mixture then enters the engine combustion chambers, where it is ignited. It burns, causing the engine to produce power. The mixture must be of varying degrees of richness to suit engine operating conditions. It must be rich (have a higher percentage of fuel) for starting, acceleration, and high-speed operation. And it should lean out (become less rich) for operation at intermediate speed with a warm engine. The carburetor has several different circuits, or passages, through which fuel and air-fuel mixture flow under different operating conditions to produce the varying richness of the air-fuel mixture. Words and Expressions combustible:易燃的,filter:过滤器,manifold:多种的,sheet:薄片,dirt:污 垢,fine:细小的,spray:雾状,richness:可燃成分高的混合燃料,throw into: 喷入,lean out:,内燃机的混合燃料等,可燃成分降低 15 10. Engine Lubricating System There are a great many moving metal parts in the engine. These 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 have 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. The oil is thrown upward as droplets or fine mist and provides adequate lubrication to valve mechanisms, piston pins, cylinder walls, and piston rings. In the combination splash and pressure feed 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 support rotating shafts and the different moving parts in the engine. It covers the surfaces of the moving parts in the engine. It covers the surfaces of the moving parts to prevent metal- to- metal contact and undue water of the parts. In this system, cylinder walls are lubricated by splashing oil thrown off from the connecting-rod bearing. The lubricating oil circulating 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 as a cooling agent. 4) Absorb shocks between bearings and other engine parts, thus reducing engine noise and extending engine life. 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 dirt to protect them from corrosion. A satisfactory engine lubricating oil must have certain characteristics, or properties. It must have proper viscosity (body and fluidity) and must resist oxidation, carbon formation, corrosion, rust, extreme pressure, and foaming. Also, it must act as a good cleaning agent, must pour at low temperatures, and must have good viscosity at extremes of high and low temperature. Any mineral oil, by itself, does not have all these properties. Lubricating-oil manufacturers therefore put a number of additives into the oil during the 16 manufacturing process. An oil for severe 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. Words and Expressions agent:,化学,剂,oxidation:氧化,additive:添加的～添加物,improver:促进剂,depressant:抑制剂,添加剂,,inhibitor:抑制剂～防腐剂,detergent:净化剂～去垢剂,dispersant:分散剂,splash lubricating:飞溅式润滑,combination splash and pressure feed lubricating:飞溅压力结合式润滑,valve:气门机构,cleaning agent:清洁剂,chemical deposits:化学沉淀。 17 11. Engine Cooling System The purpose of the cooling 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 host gases left after the gasoline is burned). But enough remains in the engine to cause serious trouble unless removed by some other means. The cooling system takes care of this additional heat. The cooling system is built into the engine. There are hollow spaces around each engine cylinder and combustion 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 sets of passages. One set carries water. The other set carries air (pulled through by car motion and 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, water continuously circulates between the engine and radiator, carrying heat from 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. The liquid cooling system consists of water pumps, water jackets, engine fan, radiator, and so on. The water pump, driven 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 added to the water during the winter. The water jacket is 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 radiator core is divided into two separate and intricate compartments; water passes through one, and air passes through the other. Words and Expressions:radiator:散热器～水箱,antifreeze:防冻剂,compound: 混合物,draught:气流,compartment:间隔。 18 12. Engine Ignition System The ignition system is part of the electric system of the automobile. Its purpose is to produce high-voltage surges (up to 20,000 volts) and to deliver them to the combustion chambers in the engine. These high-voltage surges then cause electric sparks in the combustion chambers. The sparks ignite, or set fire to, the air-fuel mixture in the combustion chambers so that it burns and causes the engine to operate. The ignition system consists of three basic parts: the ignition distributor, the ignition coil, and the spark plug, together with the connecting wires. When the engine is turning, the ignition coil is repeated connected to and disconnected from the battery. Every time the coil is connected, it becomes loaded with electrical energy. Then, when it is disconnected, the “load” of electrical energy is released in a high-voltage surge. This surge flows through the wiring to the spark plug in the engine cylinder that is ready to fire. You must understand that all this takes place very rapidly. At high speed, the whole series of events happens in less than one three-hundredth o a second. That is, there will be as many as 300 of these events every second that the engine is running at high speed. Some systems use transistors to reduce the load on the distributor contact points. Other systems do not have contact points but use instead a combination of transistors and a magnetic pick-up in the distributor. The ignition distributor has two jobs. First, it closes and opens the circuit between the battery and ignition coil. The distributor’s second job is to distribute each high voltage surge to the correct spark plug at the correct instant by means of the distributor rotor and cap and secondary wiring. There are two basic types of distributor: (1) the type using contact points to close and open the coil primary circuit; (2) the type using a magnetic pick-up and a transistor control unit to interrupt the current flow of the coil primary circuit. Words and Expressions voltage:电压～伏特数,surge:冲击,disconnect:分离～断开,the electric system: 电气系统,ignition distributor:点火分电器,ignition coil:点火线圈,spark plug: 火花塞,high-voltage surge:高压电脉冲,magnetic pick-up:电磁传感器,contact point:触点,the coil primary circuit:初级线圈,transistor control unit:晶体管控 制装置,distributor rotor and cap:分电器分火头和旁电极,secondary wiring:次 级线圈～辅助线路。 19 13. Engine Starting System Automobile engines are not self-starts. In order to start them, the engine crankshaft must be turned over by some outside means so as to (a) admit air-fuel mixture to the cylinder, and (b) cause the mixture to fire. In the case of automobile engines, the mixture in the cylinder, after being compressed, must be not enough to ignite. This requires that the engine be turned over with sufficient speed. If the engine is turned over too slowly, the unavoidable small leaks past the piston rings and also through the intake the exhaust valves of four-cycle engines will permit a substantial part of the fuel-air mixture to escape during the compression stroke. Also, the heat loss from the compressed air to the cylinder walls will be greater at low speed because of the longer exposure. The escape of air and the loss of heat both result in a lower temperature at the end of compression. Therefore, there is a minimum speed which the engine must attain before ignition will occur and the engine will begin firing. The starting speed depends upon the type and size of the engine, its condition, and the temperature of the air entering the engine. The starting system contains a cranking, or starting, motor, and other accessories. The starting motor electrically cranks the engine for starting. It is a special direct-current motor operating on battery voltage and is mounted on the engine flywheel house. The starter changes the electrical current into the mechanical energy to push the crank-shaft round. By means of this, the engine can be started. The cranking motor consists of the commutator end head, holding the brushes; the field frame, into which the field windings are assembled around pole shoes; the drive housing, which houses the drive assembly the supports the motor on the engine flywheel housing; the armature; and the drive assembly. Some cranking motors also have a solenoid that operates the shift lever. Cranking-motor controls have varied from a simple foot-operated pedal to automatic devices that close the cranking-motor circuit when the accelerator pedal is depressed. The present system that has been almost universally adopted for passenger cars and many other vehicles has starting contacts in the ignition switch. When the ignition key is turned against spring pressure past the ON position to START, the starting contacts close. This connects the cranking-motor solenoid or magnetic switch to the battery. After the engine starts and the ignition key is released, spring pressure returns it to the ON position. The starting motor should not be operated more than 5 seconds 20 during each starting operating, for the sake of recovering the energy of battery. It will not be allowed to start it again until it’s stopped for fifteen second. Words and Expressions accessory:附件,commutator:换向器,brush:电刷,armature:电枢,solenoid:螺丝管,cranking motor:起动电机,foot-operated pedal:脚踏板,for the sake of:为了…起见,direct-current motor:直流电机,flywheel house:飞轮壳,commutator end head:换向器端头,the field frame:磁场框架,field windings:励磁线圈,pole shoes:电枢,drive housing:传动箱,the drive assembly:传动总成,shift lever:换档操纵杆,accelerator pedal:加速器踏板,starting contact:启动触点器。 21 14. Locomotives 1. Steam Locomotive The speed of railways, which transformed life in the nineteenth century, is linked inextricably with the steam locomotive. To its devotees the steam locomotive was one of the most romantic and beautiful machines ever built. It first appeared in 1804 in a simple version invented by an Englishman Richard Trevithick. The first steam locomotives to do useful work were ordered and used by coal mines in northeast England in 1813-20. in 1825 a public railway was opened between the English towns of Stockton and Darlington. It had been planned for horse traction, but George Stephenson (1781-1848), a leading builder of colliery locomotives, persuaded the directors to operate a steam locomotive hauling trains heavier than horses could manage. The success of this line led to the much bigger and more important railway between Liverpool and Manchester. It was opened in 1830 after bitter opposition from landlords, coachmen, canal bargees and the large sector of the population that abhorred any change and considered smoke-spouting locomotives to be engines of Satan. Against spirited competition, Stephenson’s Rocket was chosen to provide the motive power. It was small and light enough to run on only four wheel without breaking the flimsy iron track. Thanks to steady improvements in manufacturing, it became possible to make boilers stronger, cylinders and pistons more accurate and better fitting, and the whole locomotive capable of developing more power at higher speeds. For a century steam locomotives provided nearly all the traction for the world’s railways. There were no dramatic technical advances but size, power and speed grew constantly. In Europe many rail systems used excellent track, capable of bearing 100 tonne locomotives running at up to 160km/h (100mph). But in the United States in early days, and in most other young, developing countries, track was lighter, and often badly laid by men racing to complete more miles each day. This called for more wheels to spread the load. Speeds were limited and seldom exceeded 80km/h (500mph), apart from one or two short record-setting runs. The steam locomotive has reached its zenith by the 1930s. European “steamers” were clean, splendidly painted in the livery of their operating companies and, when designed for express passenger haulage, often capable of reaching 160km/h (100mph). American locomotives tended to be more utilitarian. Demands for greater power led to increases in size until they became the biggest land vehicles in history. 22 2. Electric Locomotive The first rival to steam came in the form of the direct-current electric motor, adopted in cities (especially in underground railways), to avoid smoke pollution. The first electric train ran at an exhibition in Berlin in 1879. Soon countries such as Switzerland and Norway found that it was cheaper, with the development of hydroelectric power, to generate electricity than to burn brown coal or wood, and their networks became all electric. Today the electric motor with its linear form under development, is regarded as the best from of traction for railways but the huge capital costs impede its introduction except on the busiest routes. As long ago as 1955, French Railways demonstrated that electric trains of conventional type could run at more than 320km/h (200mph), but average speeds of public trains have risen only slowly. The Japanese New Tokaido line achieved a sudden jump in speed because the line was laid for high speed. Even so , track and trains need constant maintenance. 3. Diesel Locomotive About 1920, the first diesel locomotives and railcars came into general use, powered by compression-ignition oil engines developed by the German Rudolph Diesel (1858-1913)。Though often noisy, diesel engines pick up speed faster and convert 25 to 45 per cent of their fuel energy into useful haulage, whereas the fuel efficiency of steam traction seldom exceeded eight per cent. Despite greater capital cost, diesel locomotives gradually ousted steam from 1935 onwards, until today steam engines are confined to a shrinking number of railways in Africa and Asia and a few local lines elsewhere. Diesels can be started and stopped easily, burn no fuel when not working, and can run at close to maximum power for hours at a time with no strain on either machines or crew. Many diesel locomotives run more than 160 000 km (100 000 miles) a year and modern examples are highly reliable, versatile and relatively efficient, as well as being fast. Only in the smallest sizes does the diesel engine drive the wheels through a mechanical gearbox, as on a lorry. Generally the two are linked hydraulically or electrically. Hydraulic transmissions are arrangements of turbines linked by oil under high pressure, and they can transmit smoothly 2 000 horsepower with any ratio between input and output speeds. In the diesel-electric locomotives the engine drives a generator or alternator. This is used to supply current to traction motors similar to those of electric locomotives. 23 15. Diesel Traction We have now to consider the characteristics of the diesel engine, and the way in which it is used in railway traction. As we saw earlier, in an engine of this type the high temperature needed to ignite the fuel is produced by the piston, which compresses the air in the cylinder to between 650 and 850 lb. per sq. in., raising its temperature to between 1,500 and 1,800 degrees Fahr. When the maximum compression has been reached, the oil, at a pressure of from 2,000 to as much as 5,000 lb. per sq. in., is injected in the form of a finely divided spray, and ignites with explosive force, diving the piston backwards under a pressure of 850 to 1,000 lb. per sq. in.. Injection continues for long enough during the piston stroke to ensure that combustion and the pressure on the piston correspondingly even. Many modern diesel engines are “supercharged” by an increase in the pressure of the air before it is passed into the cylinders. The most common application is by the turbo-supercharger, in which the exhaust gases from the cylinder drive a gas turbine coupled to an air-compressor. The latter fills the cylinder with air at from 147 to 22 lb. per sq. in. above atmospheric pressure, and this high pressure encourages a proportionately greater consumption of fuel, so boosting the power output by as much as 50 per cent. In Great Britain the type of diesel engine in most common use is the four-stoke. The first stoke of the piston compresses the air; just before the end of it the fuel is injected and combustion begins, continuing during the return stroke; the third stroke is the one during which the cylinder is “scavenged” of its spent gases; and in the fourth stroke-that is, the second return stroke-the exhaust port closes, and the inlet valve is opened to admit the air for the next compression stroke. It is during one stroke only out of the four, the second, that the engine develops its power, and this is why the diesel engine requires a number of cylinders, from four in a small shunter to sixteen or more in a main unit of high power, with their cranks set at angles which divide up the circle into a corresponding number of equal parts, so ensuring a perfectly even torque of the crankshaft. In the V-type cylinder arrangement, often adopted in the larger diesel engines, setting the cylinders alternately at an angle right or left the centre-line, in a “V” formation, makes possible a reduction in total length as compared with an engine that has all the cylinders in line. There is also the two-stroke engine, in which the cycle of operation is completed in a single return stroke of the piston. Near the end of the combustion stroke the 24 piston uncovers an exhaust port, which allows the spent gases to escape, and a further piston movement uncovers the inlet port, through which a charge of air under pressure enters the cylinder behind the piston. As soon as the piston has passed the two ports on return stroke compression begins, and the oil is injected just before the piston reaches the top of the stroke. The power of a two-stroke engine does not go up in proportion to the fact that combustion takes place on every return stroke of the piston, instead of on every alternate return stroke, because the two stroke engine is less efficient than the four-stroke. Of the complicated equipment of a diesel engine, the most important constituent-in effect, the nerve centre is the fuel injection pump. It is driven off the main crankshaft by a series of cams on an independent shaft, and each cam actuates the plunger of one of the cylinders. This plunger traps a small quantity of fuel oil, and delivers it as fine spray into the cylinders above the piston, after which a spring restores the plunger to its out-of-action position. The amount of fuel delivered per stroke can be varied, with a proportionate variation in the power developed by the engine. In a two-stroke engine the camshaft is rotated at the same speed as the main crankshaft, and in a four-stroke engine at half the speed. Another camshaft works the valves which open and close the cylinder ports at precisely the right moments. Correct timing is of the utmost importance, and also extreme accuracy, down to a twenty-thousandth part of an inch, in the grinding of certain parts of the fuel injection pump and the valves. The cylinders of a diesel engine would become dangerously overheated if effective measures were not taken to cool them. Each cylinder therefore is encased in a water jacket, which forms part of a circuit through which water is pumped continuously, and cooled by means of air drawn in from the outside atmosphere by large rotary fans, worked off the main crankshaft, or, in the larger diesel-electric locomotives, by auxiliary motors. The fans are often fitted with movable shutters to their air intakes, which open and close automatically, under the control of thermostats, to keep the cylinder temperatures as even as possible, admitting more air when the engine is working hard, and less when it is idling. A second cooling circuit is needed for the lubricating oil, of which a considerable amount is used, and a third, in the case of a diesel-electric locomotive, as with a straight electric locomotive, to prevent overheating in the generators and traction motors. Special measures are necessary for starting up a diesel engine, seeing that no 25 combustion of the fuel can take place without initial air compression in the cylinder. In the smaller diesels this can be done by hand cranking, or by the use of compressed air, or by a device similar to the self-starter of a motor-car, supplied with current from batteries. In a diesel-electric locomotive, however, the general practice is to use current from the storage batteries to drive the generator as though it were a motor, so completely reversing its function; a few moments usually suffice to work the engine by means of the main crankshaft until combustion begins. After this the engine is idled until the locomotive is required to start. Transmission of power from the diesel engine to the locomotive axles is a simple matter in the smaller diesels. In low-powered railcars and shunters, up to, say, 250 or 300 h.p., a gearbox similar to that of a road motor-car serves the purpose, with a gear selector, a forward and reverse lever, a clutch and accelerator for control. To enable the drive to be taken up smoothly, some form of fluid coupling is often inserted between the engine and the gearbox. Diesel-mechanical transmissions may include as many as eight speeds, both forward and reverse. There is a limit, however, to the range of power which can be transmitted mechanically, and this was the reason why electricity was chosen, at a relatively early date, as the intermediary between diesel engine and rail in the more powerful diesel locomotives. In a diesel-electric locomotive plant the diesel engine dries an electric generator, normally mounted on the same bedplate, and it is customary for an auxiliary generator to provide for charging the batteries, lighting and electric control. The d. c. current from the main generator drives the traction motors, mounted on the axles in most modern diesel-electric locomotive, and this part of the equipment is exactly the same as that of the electric locomotives. In a diesel locomotive, while an electric transmission is ideal so far as fineness of control is concerned, it adds greatly to the weight, the cost and the complication of the locomotive as a whole. In recent years, however, such advances have been made in the design of hydraulic transmissions that they are being used successfully in diesel locomotives of up to 2,000 h. p. . The core of a hydraulic transmission is what is known as a “fluid flywheel”. This comprises, first, a driving member, which is a circular chamber fitted with vanes somewhat resembling those of a turbine, and filled with lubricating oil; and, second, the driven member, similarly provided with vanes and driving the output shaft. Rotation of the vanes of the driving member causes the oil to exert centrifugal 26 pressure against those of the driven member, which rotate at increasing speed until the two, in effect, are locked as one, although the speed of the latter, because of friction, is always very slightly less than that of the former. There is no wear and tear in a fluid flywheel comparable to that in a clutch, and the former has the advantage also that if any seizure should take place, say in the engine, no serious damage is likely to result, because the oil pressure in the chamber would break down. The diesel-hydraulic locomotive in future is likely to prove a serious rival to the diesel-electric, and hydraulic transmissions also are being used increasingly in diesel railcar power plants. Words and Expressions diesel engine:柴油机,lb.(pound):磅,sq.in.(square inch):平方英寸, Fahr.(Fahrenheit):华氏温标,supercharge:增压,scavenge:扫除～清除,main line unit:干线机车,shunter:调车机车,fuel injection pump:喷油泵,plunger:柱 塞,grind:研磨,shutter:百叶窗,idle:空转,traction motor:牵引电机,hand cranking:手摇起动,railcar:动车,gear selector:变档杆,forward and reverse lever: 前进及倒车控制杆,gearbox:变速箱,clutch:离合器,hydraulic transmission: 液传动,diesel-electric locomotive:电传动内燃机车,bedplate:底盘,charging: 充电,vane:叶片,power plant:发动机组,coupled to:联结到 27 28