In the front face of the flywheel, there is a shallow indentation used tu determine the position of the piston in the first cylinder. When this indentation is aligned with a special hole provided in the bell hous ing, the piston is at top dead center(TDC)or indicates the start of fuel injection into the first cylinder The flywheels of some engines also carry marks indicating the serial numbers of the cylinders where the compression (curs. The flywheel marks and indentation are used for setting the valve and ignition sys tems relative to prescribed pOsitions of the crankshaft In conclusion, the connecting rx and crankshaft mechanism of the engine is composed of various units, and each of these units has its own functions in producing power for vehicles New words n,机械机构 ankcase n.曲轴箱 intricate ad.复杂的 坚硬的,不易变形的 变形,扭曲 natw、平的,平坦的 concave: (.叫的,四面的 ambulence e n.紊流,涡流 incra n,惯性,惯量 drainage n.排水系统 serial adi.连续的,一系列的 lamp n.夹子 夹紧 backbone n.脊骨,支柱,骨干 vibration n.振动,颤动 radially adr.径向地 Phrases and Expressions 热能 kinetic energy动能 piston hea活塞顶部 piston land活塞环槽岸 piston pin hule活塞销孔 compression ring压缩环,气环 ng joumal支承轴颈 oi- controf ring控油环,洲环 counter-balanced weight平衡重量,平衡块 crank art曲柄臂 1. This major unit must be strong and rigid enough to withstand any bending or distortion
这一部件必须非常坚固刚硬,才足以抗得住任何的弯曲或扭曲。 2. The piston head or"crown is the top surface against which the explosive force is exerted 活塞头部,即冠部的上表面是承受爆燃所产牛的力。 3. In order to reduce or eliminate such vibration, it must be provided with counter balanced weight that extend radically from the crankshaft centerline in the opposite direction of the crank arms 为了减少或消除振动,它必须装有平衡块,而且平衡块应径向地从曲轴中心线向曲柄相 对的方向延仲安装 4. The heavier the flywheel or the larger its diameter the smaller will be the speed change 飞轮越重或飞轮直径越大,速度变化就越小 Unit Three Valve gear The valve gear of an intemal combustion engine provides timely admission of the fresh charge into the cylinders and exhaust of spent gases fom 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 push rods, rocks with fasteners lve guides, shown in Fig. 1-5) The timing gears in most en gines are housed in a special case fitted at the front end of the en- are necessar mmit rotation from the crankshaft to the camshaft, fuel injection pump haft, and to oil pump, and other mechanisms. The gears are made of Fig. I-5 Valve gear steel and use helical teeth to re- I timing gear 2-eccentrc 3--camshatt 4--jourtels 5-lappels b-vaIve duce noise 12--cams 13-camshaft bushing 14--canshahi fmat erl Camshafts function is to open the engine valves positively and timely, in a definite sequence, and tocontmol their closing against the retum uction of the valve springs. The shaft is made integral with its cams and bearing joumals.Each bile engines. the camshaft is made integral with fuel pump eccentric wheel and oil pump drive gear.The camshaft hearings are lubricated with oil supplied under pressure from the main gallery in the cylinder The tappets serve to transmit the force from the camshaft to the push rods. The tappets are small cy lindrcal brew receive the push rods. They are made of cast iron or steel and located in the guides, which
0 may be marle 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 mation is ensured by a convex sur- face of their bottoms and a slanted suface of the cams ith hardened tips or duralumin tuhes 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 the rocker adjusting screw at the other The nx: kers transmit the: foree from the push rod to the valve. The rockers are made fro steel and are installed on a hollw fulcrum. A bronze bush is press fitied into the rocker hole to reduce friction, The hollow fulerum is supported by standands on the cylinder head. Endplay of the rocker is prevented by rocker where it contacts the valve stem tip, while a threaded hole is machined in its other end to receive the adjusting serew 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 mcke shaft supported by a series of pedestals or brackets, which are bolted to he top deck of the cylinder heal An engine valve is a device desigmed Lo open a passage when moving in one direction and to close it heTI Moving in the: opposite: direction. Each cylinder of a four-stroke-cycle diesel or gasoline engine nly equipped with an intake valve and an exhaust The purpose of the intake valve is to all the air fuel mixture or air to enter the cylinder. After the combustion proeess has been completed, the bumed gases are prnnitte to escape fmm the cylinder thmugh the exhaust valve. To obtain sufficient valve area. some automobiles have two intake and two exhaust valves In the engines, the inlet and exhaust ports are made In the cviloaer he eads sand terminate in inserted alve seats of heat-resistant cast iro A valve consists of a head and stem. The valve head has a narrow chamfer of 45 or 30 referred alve face. The valve face fits tightl The kinds of the: inlet and exhaust valves are of different diameter. For better engine breathing, the inlet valve has a larger dianeter 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 ex haust valves are of bichrome heat-resistant steel The cylindrical stern 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 foree necessary to close the valve and hold it tightly against its seat Valve: springs may have their coils spaced either evenly or variably. a variable coil pitch can lessen the tendency of the spring to vibrate or flutter at high speeds. Where such springs are used, the close- wound end (with less coil spacing)must be installed toward the valve head Some engines use two springs on each valve, which reduce the size of the springs, improves their re- liability ditions less ardu
Valve guide supports the valve stem and guides its movement so that the valve face remaing perfectly concentric with the valve seat and fits it without any skewing. Replaceable or insert, valve guides are fab ricated 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 otating during the operation of the engine. In general, there are two ways of rotating: one is free rotate the other is positive rotate The valves of some automobile engines are made to rotate positively by a special mechanism during engine operation. This mechanism known as the valve rotator, consists of a stationary housing with five ramplike grooves along its circumference that contain five steel balls loaded by return spring. Freely placed on top of the balls is a flexible washer against which rests valve spring through the intermediary of a seating collar e valve Is open spring is compressed and its increasing boad causes the flexible washer to flatten out and force balls down their ramps against the resistance offered by their retum springs. As the balls roll down, they turn through some angle the flexibie 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 retum to their starting position New words manifold 歧管,总管 appet n.(凸轮)挺杆,气门推杆 .螺旋的,螺旋形的 凸的,凸面的,凸圆的 硬铝,杜拉铝 spherical adj.球的,球形的 crum n 支点,支轴,支柱 oscillateυ",摆动,振动,摇摆 pedestal n.轴承座,轴架,支座 terminate 27.终止,结束,终结 amter rI 锥角,切角面,圆角 arduous ad.陡峭的,艰巨的 同心的,同轴的 penetration n.渗透,穿透,侵人 nical adj,圆锥形的,圆锥的 Phrases and Expressions alve gear气门机构,配气机构
fresh charge吸人的新鲜混合气 communicate with与……连通,和……互通 coil spring螺旋弹簧,圈弹簧 camshaft play凸轮轴端隙 valve stem气门杆,阀杆 rocker contact pad摇臂接触部位 silehrome heat-resistant steel徒铬耐热钢 h spring变螺距弹簧 Notes 1. The valve gear of an intemal combustion engine provides timely admission of the fresh charge into the cylinders and exhaust of spent gases from then 内燃机的配气机构能定吋地将新鲜的混合气充入气缸,并且将废气从气缸中排出。 2. The push rods transmits the force from the tappets to the rocker and are made as steel stems wit hardened tips or duralumin tubes with spherical steel tips press-fitted at both ends 推杆将挺杆传来的推力传给摇臂,推杆出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 3. A variable coil pitch can lessen the tendency of the spring to vibrate or flutter at high speeds 变螺距弹簧能减少弹簧的振动趋势或在高速时的“跳动”。 4.The: valves of some. automobile engines are made to rotate positively by a special mechanism dur 有些发动机的气门上安装有特殊的结构,这种结构可使气门在发动机工作时相对转动。 Unit Four Engine Cooling System The 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 ener- gy in the fuel is converted into power, Anothe r thirl goes out through the exhaust pipe unused, and the remaining thind must be handled by the cooling system. This means that the engine can work effectively nly 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 engines can work well thout 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 nit circulating in an over heating engine is reduced. Hot oil also forms vamish 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 and can produce a condition which the metal deforms slowly and continuously at a constant stress. 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