汽车实用英语(已整理).doc

Valves and Valve TrainThe valve gear of an internal combustion engine provides timely admission of the fresh charge into the cylinders and exhaust of spent gases from them. For this purpose the valves at definite moments open and close the intake and exhaust ports in the cylinder head, through which the cylinders communicate with the intake and exhaust manifold.The valve gear is composed of timing gears, a camshaft, tappets, valves, spring with fasteners and valve guides.The timing gears in most engines are housed in a special case fitted at the front end of the engine. These are necessary to transmit rotation from the crankshaft to the camshaft, fuel injection pump shaft, and to oil pump and other mechanisms.The gears are made of steel and use helical teeth to reduce noise.Camshafts function is to open the engine valves positively and timely, in a definite sequence, and to control their closing against the return action of the valve springs. The shaft is made integral with its cams and bearing journals. Each cam controls a single valve, either intake or exhaust. In some automobile engines, the camshaft is made integral with fuel pump eccentric wheel and oil pump drive gear. The camshaft bearings are lubricated with oil supplied under pressure from the main gallery in the cylinder block.The tappets serve to transmit the force from the camshaft to the push rods. The tappets are small cylindrical bores receiving the push rods. They are made of cast iron or steel and located in the guides, which may be made integral with the cylinder block or removable as in the engine. When the engines operate, the tappets continuously rotate about their axes for uniform wear. The rotation is ensured by a convex surface of their bottoms and a slanted surface of the cams.The push rods transmits the force from the tappets to the rocker and are made as steel stems with hardened tips or duralumin tubes with spherical steel tips press-fitted at. both ends. The push rod tips bear against the tappet hollow at one end against the spherical surface of rocker adjusting screw at other.The rockers transmit the force from the push rod to the valve. The rockers are made from steel and are installed on a hollow fulcrum. A bronze bush is press fitted into the rocker hole to reduce friction. The hollow fulcrum is supported by standards on the cylinder head. Endplay of the rocker is prevented by a coil spring.The rocker arm is a bell crank made of steel. At the middle of the rocker arm, there is a boss with a bore into which is pressed the bushing. A hardened curved pad is provided on the end of the rocker where it contacts the valve stem tip, while a threaded hole is machined in its other end to receive the adjusting screw used to set the valve clearance, the clearance between the rocker contact pad and the valve stem tip, so that the valve will be tightly pressed against its seat when hot. The rocker arm freely oscillates about the rocker-arm shaft supported by a series of pedestals or brackets, which are bolted to the top deck of the cylinder head.An engine valve is a device designed to open a passage when moving in one direction and to close it when moving in the opposite direction. Each cylinder of a four-stroke-cycle diesel or gasoune engine is commonly equipped with an intake valve and an exhaust valve. The purpose of the intake valve is to allow the air fuel mixture or air to enter the cylinder. After the combustion process has been completed, the burned gases are permitted to escape from the cylinder though the exhaust valve. To obtain sufficient valve area, some automobiles have two intake valves and two exhaust valves.A valve consists of a head and stem. The valve head has a narrow chamfer of 45 or 30 referred to as valve face. The valve face fits tightly against the seat, which is achieved by grinding.For better engine breathing, the inlet valve has a larger diameter than the exhaust one. As the valves are not equally heated in the running engine, they are made from different materials. The inlet valves are made from chromium steel, the exhaust valves are of silchrome heat-resistant steel.The cylinder stem of the valve has a recess at the upper end for fastening the valve spring. The valve stems slide in the cast-iron or cerametallic valve guides.The valve spring provides the force necessary to close the valve and hold it tightly against its seat.Some engines use two springs on each valve, which reduce the size of the springs, improves their reliability, and makes their operating conditions less arduous.Valve guide supports the valve stem and guides its movement so that the valve face remains perfectly concentric with the valve seat and fits it without any skewing. Replaceable valve guides are fabricated from cast iron or a cermets material and pressed in the cylinder head.To decrease oil penetration along the valve stem to the combustion chambers, the seating collars are fitted with rubber rings or the seats are provided with rubber caps. More uniform heating and wear of the valve are ensured with the valves rotating during the operation of the engine. In general, there are two ways of rotating: one is free rotate the other is positive rotate.As the valve is opened, spring is compressed and its increasing load causes the flexible washer to flatten out and force balls down their ramps against the resistance offered by their return springs .As the balls roll down, they turn through some angle the flexible washer, seating collar and valve spring together with the valve; when the valve is closed, the valve spring load decrease, the flexible washer deflects to acquire its initial conical shape and abutting against a shoulder in housing, releases the balls which are then forced by their coil springs to return to their starting position.配气机构 内燃机的配气机构保证新鲜混合气可以适时进入汽缸，同时燃烧后的废气及时排出。为实现这一目的，气门在一定的时刻打开和关闭汽缸盖上的进排气道，汽缸通过进排气歧管与进排气管相沟通。 配气机构由正时齿轮、凸轮轴、挺柱、气门、带有锁紧装置的弹簧和气门导管组成。 大多数发动机的正时齿轮装在专门的壳体内，正时齿轮壳体位于发动机前端。必须使用正时齿轮将曲轴的旋转传递到凸轮轴，驱动喷油泵轴、机油泵和其他的装置。正时齿轮由钢制成，采用螺旋状齿以减少噪声。 凸轮轴的功用是按特定的顺序准确适时地打开气门并通过气门弹簧的回位作用控制气门的关闭。凸轮轴与凸轮、轴颈制为一体。每个凸轮控制一个气门:进气门或排气门。有些汽车发动机的凸轮轴也与驱动燃油泵的偏心轮和机油泵的驱动齿轮做成一体。缸体内主油道的机油在压力作用下到达凸轮轴轴颈提供润滑。 挺柱用来把凸轮轴的作用力传递给推杆。挺柱为圆柱形小筒，里面插入推杆。挺柱材料为铸铁或钢，定位于导管内，挺柱导管可以是与缸体一体的或者是可拆卸的。发动机工作时，为使磨损均匀，挺柱总是绕其轴线旋转。挺柱的旋转是由挺柱凸起的下表面和凸轮倾斜面所保证的。 推杆将挺柱传来的推力传给摇臂。推杆由顶部淬火的钢柱或由两端压入配合的带球形钢头的硬铝管制成。推杆的两端一头支撑在挺柱的空腔内，另一头与摇臂调整螺钉端的球形表面配合。 摇臂把推杆的作用力传递到气门。摇臂由钢制成，安装于空心的枢轴。摇臂空内装有青铜衬套以减少摩擦。中空的摇臂轴通过支架固定于汽缸盖。摇臂上的螺旋弹簧防止产生轴向窜动。摇臂是钢制的双臂杠杆。摇臂中部有一带孔的凸台，孔内压装有衬套。摇臂的一端是经过淬火的圆弧状长臂，与气门杆尾端接触，而车有螺纹孔的另一端安装有调整螺钉，用来调整摇臂与气门杆尾端之间的气门间隙，从而保证气门在受热后紧紧压在气门座上。摇臂可以绕摇臂轴自由摆动，摇臂轴通过一系列支座支撑，支座用螺栓固定于汽缸盖上表面。 发动机气门向某一万向运动时开启-通道，而它向相反方向移动时则关闭此通道。四行程汽油机或柴油机的每缸一般都装有进气门和排气门。%气门的作用是使空气燃油混合气进入汽缸。燃烧过程完成后废气通过排气门排出汽缸。为了获得足够的充气面积，有些发动机采用两个进气门和两个排气门。 气门由头部和杆身组成。气门头部相对于气门平面之间存在45。或30。的锥角。通过研磨使气门平面与气门座紧密贴合。 为使发动机更好地换气，进气门(头部)直径大于排气门。在发动机工作时由于进、排气门受热不均等，因此它们采用不同的材料制成。进气门采用铬钢，排气门采用耐热硅铬钢。 圆柱气门杆身的上部有一凹槽用来固定气门弹簧。气门杆身在铸铁或金属陶瓷气门导管内运动。 气门弹簧提供气门关闭时所需要的作用力，保证气门与气门座紧密贴合。 有些发动机的每个气门装有两根弹簧，可以减小所使用的弹簧大小，增加可靠性，使工作更平稳。 气门导管支撑气门杆身，对其运动起导向作用，以保证气门X闭时能准确地与气门座贴合而不产生偏移。可拆卸式气门导管采用铸铁或金属陶瓷材料制成，压入汽缸盖上的(气门导管。 为防止机油从气门杆渗进燃烧室，在气门导管上装有橡胶环或橡胶皮碗。发动机工作时通过气门的旋转可以使气门获得更均匀的受热和磨损。通常有两种实现气门旋转的方式：自由旋转和强制旋转。 当气门开启时，弹簧被压缩，弹力增加，将弹性垫圈压平，迫使钢球克服回位弹簧的阻力沿斜坡滚动。当钢球滚下时，带动弹性垫圈、气门弹簧与气门一起转过一个角度;当气门关闭时，气门弹簧弹力减小，弹性垫圈变形为原来的圆锥状，支撑于壳体的支撑板，钢球在回位弹簧作用下回到原来位置。Engine Cooling SystemThe purpose of the cooling system is to keep the engine at its most efficient operating temperature at all speeds under all driving conditions. As fuel is burned in the engine, about one-third of the heat energy in the fuel is converted into power. Another third goes out through the exhaust pipe unused, and the remaining third must be handled by the cooling system. This means that the engine can work effectively only when the heat energy is equally handled so as to keep the engine temperature in balance:So, the temperature is quite essential for an engine to produce power. No engine can work well without suitable operating temperatures. If the engine runs too hot, it may suffer from pre-ignition, while the air-fuel charge is ignited prematurely from excessive combustion chamber temperature. Viscosity of the oil circulating in an over heating engine is reduced. Hot oil also forms varnish and carbon deposits may be drawn into the combustion chamber where it increases HC emission. This also causes poor performance and premature wear, and may even result in engine damage. Whats more, the behavior of the metals at excessively high temperature also differs from that at normal temperatures. If the engine runs too cold, the fuel will not vaporize properly. If liquid fuel reaches the cylinders, it will reduce lubrication by washing the oil from the cylinder walls and diluting the engine oil. This causes a loss of performance, an increase in HC emissions, and premature engine wear. For these reasons, a cooling system of some kind is necessary in any internal combustion engine.There are generally two different types of cooling system: water-cooling system and air-cooling system. Water-cooling system is common. The cooling medium, or coolant, in them is either water or some low-freezing liquid, called antifreeze. A water-cooling system consists of the engine water jacket, thermostat, water pump, radiator, radiator cap, fan, fan drive belt and necessary hoses.A water-cooling system means that water is used as a cooling agent to circulate through the engine to absorb the hot 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 burned in 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 C, the thermostat valve open fully, its slanted edge shutting off the shorter circuit so that the coolant circulates through the longer one: water-pump-cooling jacket -thermostat -radiator top -tank -radiator core -bottom tank -pump.Water pumps have many designs, but most are the centrifugal type. They consist of a rotating fan, or impeller, and seldom are of the positive displacement type that uses gear or plungers. Many water pumps have a spring-loaded seal to avoid leakage of water around the pump shaft. Some V-type engines have a pump on each cylinder block.The radiator is a device designed to dissipate the heat which the coolant has absorb from the engine; it is constructed to hold a large amount of water in tubes or other passages which provide a large area in contact with the atmosphere.The radiator usually mainly consists of the radiator core, radiator bottom tank, and radiator top tank. Radiator cores are of two basic types, the fin and tube type (fins are placed around the tube to increase the area for radiating the heat) and of the ribbon cellular or honey comb type. The popular fin and tube type of radiator core has the advantage of fewer soldered joints and is therefore a stronger construction. 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 ribbons together along their edges. These tubes are separated by fins of metal ribbon, which help dissipate the heat.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 front end of the crankshaft. Usually the same belt drives the alternator, and belt tension is adjusted by swinging the alternator on its mounting.An air-cooling system contains a centrifugal fan, thermostat, fan drive belt, radiator fin, 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 from the moving parts. When the engine is running, force 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 circulation 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 radiator.The engine cooling system actually is a temperature-regulation system. For a late-model engine, the cooling system must maintain a temperature that is high enough for efficient 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 through the engine. These requirements are very critical for an engine with electronic controls that must maintain precise air-fuel ratios for economy and emission control.发动机冷却系统 冷却系统的功用是保证发动机在任何行车条件、任何车速保持最有效的工作温度。燃料在发动机中燃烧，约三分之一的热能转化为动力，还有三分之一的热能从排气管排出，剩下的三分之一热能由冷却系统来处理。这就意味着只有当热能被均衡地控制，保持发动机温度平衡，发动机才能有效地工作。 因此，温度对于发动机产生动力来说是至关重要的。如果没有合适的工作温度，发动机就不能正常工作。如果发动机过热，过高的燃烧室温度会过早点燃混合气，机油黏度会下降，热机油也会形成机油氧化膜，燃烧室会形成积碳，增加HC排放。过热还会造成发动机性能下降、早期磨损，甚至导致发动机损坏。再者，金属材料在过高温度和正常温度下的性能是截然不同的。如果发动机温度过低，燃油汽化不好。若液态燃油进入汽缸，燃油将冲刷缸壁的机油、稀释机油而降低润滑效果。这也将导致发动机性能下降、HC排放增加、发动机早期磨损。基于这些原因，内燃机必须有某种形式的冷却系统。 通常有两种形式的冷却系统:水冷系统和风冷系统(汽车发动机)普遍采用水冷系统。其中的冷却介质或冷却液为水或某些低凝点液体，被称为防冻液。水冷系统由发动机水套、节温器、水泵、散热器(水箱)、散热器盖、风扇、风扇驱动皮带和必要的软管组成。 水冷系统是指以水作为冷却剂在发动机内循环吸收热量，然后到水箱散热。发动机的冷却主要通过热量的交换和消耗。混合气燃烧产生的热量必须从铸铁或铝制汽缸传递到水套中的水。水套外侧将部分热量发散到周围的空气中，但大部分热量通过冷却液到达水箱进行散热。当冷却液温度达到g0C时，节温器完全打开，节温器倾斜边缘关闭小循环，冷却液大循环流动:水泵+冷却水套+节温器+散热器进水室+散热器心部+散热器出水室+水泵。 水泵的设计各异，但多数采用离心式。水泵由旋转的叶轮组成，少数容积式水泵采用齿轮或柱塞。许多水泵带有弹性密封件，防止水泵轴周围漏水。一些V型发动机两侧缸体都有水泵。 散热器用于散发由冷却液所吸收的发动机的热量，因此散热器的构造保证水管内可以容纳大量的水，并且保证尽量大的散热面积。 散热器通常由心部、上储水室和下储水室组成。散热器心部有两种基本类型:管片式(散热片位于水管周围以增加散热面积)和管带式或蜂窝型。常见的管片式散热器心部优点是焊接点少，因此强度高。管片式心部由一系列从上储水室延伸至下储水室的平行水管组成。蜂窝型心部由大量的窄的水道组成，每对细金属带的两端焊接起来就形成了水道;这些水管通过金属散热片隔开以利于散热。 散热器盖不仅防止冷却液从加水口溅出，也防止冷却液蒸发。 风扇把冷空气吸进散热器心部。风扇通常安装在水泵轴的延伸处，曲轴前端的一皮带轮通过v形皮带驱动风扇。这根皮带一般也驱动交流发电机工作，皮带的张紧度通过在支座上摆动发电机的位置来进行调整。 风冷系统包括离心式风扇、节温器、风扇驱动皮带、散热片、导流板、空气控制罩等。风冷系统使用空气作为冷却剂，空气在发动机内循环流动，带走运动部件的热量。当发动机工作时，空气流经散热片进行散热。为了通过控制冷却空气的体积来调节发动机的温度，围绕在发动机周围的金属壳体内装有节温器。 节温器与空气控制罩相连。发动机温度升高时，空气控制罩开度增加，以进入更多空气;发动机冷却后，空气控制罩关闭，空气的循环便停止，这样冷机能够迅速走热。由于风冷发动机没有水套和散热器，因此迅速热机是其特点之一。 发动机冷却系统实质是温度调节系统。新型发动机的冷却系统使发动机保持在足以获得高效燃烧的高温下工作，但又不致损坏发动机。冷却系统的两项工作就是带走过度热量和维持发动机一定的工作温度。这些要求对于保证精确空燃比、追求好的燃油经济性和良好排放的电控发动机而言是非常关键的。Engine Lubrication SystemAn 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 lubrication oil so that the automobile can move smoothly with proper friction.The engine lubrication is mainly conducted by the lubrication 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. Finally, the oil absorbs shocks between bearings and other engine parts, and forms a good seal between piston ring and cylinder walls.Engine lubricating systems are divided into two types: splash, pressure feed. In the splash lubricating 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 parts of the engine. The oil is thrown up as the oil sprays, which provides adequate lubrication to valve mechanisms, cylinder walls, piston rings and bearings.The splash system of lubrication is a simple method and only works successfully if the oil in the sump 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 bearings and connecting rod bearings.In modern engine designs, these two methods are often combined. Pressure is developed by the oil pump, which delivers oil to the filter for cleaning before it is sent to the camshaft and valve train components at the top of the engine. Other components are lubricated by splashing oil and by a network of passages, or galleries.The lubricating system, no matter what type, has the job if supplying adequate amounts of oil to all moving 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 radiator much like the cooling system radiator, through which the oil passes; this cools the oil. All engines have some sort of level indicator, which usually consists of a dipstick, or oil lever stick, that enters the crankcase from the side of the block. To check the oil