外文翻译--汽车的基本机械机构

附 录 The basic mechanisms Of Automobiles The automobile industry is a fast developing industry. From the later 18th century when the first automobile was put on road, this industry has developed tremendously. Now there are thousands of factories all over the world manufacturing. numerous types of automobiles. This industry employs crores of men and women directly and indirectly in allied industries. The automobile engines are also being used in engine powered machines for agriculture, construction and manufacturing processes. Various types of small engines are also being used in lawn movers, power. saws, snow removers and similar equipment. The automobile industry is a developing and demanding industry which does not find its end or saturation point. There is a great demand for varied types of automotive products, vehicles and engines. There is also a great demand for trained and experienced persons in this industry for diagnosing motor vehicle troubles, repairing and replacing engines components, transmissions, propeller shafts, differentials, axles, steering system components,brake system components, suspension components, air-conditioners, heaters, body and glass work. The automobile consists of five basic mechanisms, or components. These are : (1) The engine, which is the source of power, including the fuel, lubricating, cooling, and electric systems. (2) The frame, which supports the engine, wheels, steering and brake systems and body (3)The power train, which carries the power from the engine(through the clutch,transmission, drive shaft, differential, and axles)to the car wheels. (4) The car body . (5)car-body accessories, including heater ,lights, windshield wipers, and so for The engine is the source of power that makes the car move. It is usually called an internal combustion engine because gasoline is burned inside the engine cylinders, or combustion chambers. This is in contrast to external-combustion engines(such as steam engines),where the combustion takes place outside the engine. The burning of gasoline in the engine cylinders produces the power. The power is then carried from the engine through the power train to the car wheels so that the wheels turn and the car moves. The fuel system plays a vital part in the power producing process since it supplies the gasoline to the engine cylinders. In each engine cylinder, a mixture of gasoline vapor and air enters the cylinder, the piston pushes up into the cylinder to compress the mixture, and then an electric spark ignites the compressed mixture so that the piston is forced downward. Of course, in the engine the piston is not blown completely out of the cylinder, the piston simply moves up and down in the cylinder-up to compress as the mixture burns. The piston straight-line motion must be changed to rotary motion before it can be used to make the car wheels rotate. A connecting rod and a crank on the engine crankshaft make this change. The engine valves get the burned gasoline vapor out of the engine cylinder and bringing fresh changes of gasoline vapor and air into the cylinder. There are two openings ,or ports, in the enclosed end of the cylinder ,each containing a valve. The valve are accurately machined plugs on long stems. When they are closed, or seated (that is, moved up into the ports), the ports are sealed off and gas cannot pass through the ports. When the valve is open, gas can pass through the port The valves are opened by cams on the engine camshaft. The cam has a high point,r lobe； every time the cam rotates, the lobe comes around under the valve lifter and move it upward. The lifter then carries this upward movement through the pushrod to the rocker arm. The rocker arm pivots on its support and pushes down on the valve stem, causing the valve to move down, that is, to open. After the cam has turned enough to move the lobe out from under the lifter, the heavy valve spring pulls the valve back into its seat. The spring is attached to the upper end of the valve stem by a spring retainer and lock. There is a cam for each valve (two cams per cylinder) on the engine camshaft. The camshaft is driven off the crankshaft by gears or by sprockets and a chain. When the entire cycle of events requires four piston strokes (two crankshaft revolutions), the engine is called a four-stroke-cycle engine, or a four-cycle engine. The our strokes are intake, compression, power, and exhaust. On the intake stroke, the intake valve is open. The piston moves down, pulled by the rotation of the crankshaft. This piston movement creates a partial vacuum in the cylinder, and air rushes into the cylinder past the intake valve to fill up this vacuum. As the air moves toward the cylinder, it must pass through the carburetor. There it is charged with gasoline vapor. Thus, it is a mixture of air and gasoline vapor that rushes into the cylinder as the piston moves down on theintake stroke. After the piston moves down to the bottom dead center on the intake stroke, the intake valve closes. The lobe on the cam controlling the intake valve has moved out from under the valve lifter. Since the other valve is also closed, the upper end of the cylinder is sealed. Now, as the piston is pushed up by the rotating crankshaft, the mixture of air and gasoline vapor that has been drawn into the cylinder is compressed. By the time the piston has moved up to the top dead center, the mixture is compressed to a seventh or an eighth of its original volume. That is like taking a gallon of air and compressing it to a pint. The result is high pressure in the cylinder. About the time the piston reaches the top dead center on the compression stroke, an electric spark occurs at the cylinder spark plug. The spark plug is essentially two heavy wire electrodes； the spark jumps between these electrodes. The spark is produced by the ignition system. It ignites, or sets fire to, the compressed air-gasoline-vapor mixture. Rapid combustion takes place； high temperatures and pressures result. At this instant, the downward pressure on the top of the piston may amount to as much as 2tons. This powerful push forces the piston down, and a power impulse is transmitted to the crankshaft through connecting rod and the crank. The piston is forced down by the pressure of the burning gasoline vapor during the power stroke. When the piston reaches the bottom dead center, the exhaust valve opens. Now, as the piston starts back up again, it forces the burned gases from the cylinder. By the time the piston has reached the top dead center the cylinder is cleared of the burned gases. The exhaust valve closes and the intake valve opens. Then ,the piston starts back down again on the next intake stroke. The four cycles, or piston strokes, are continuously repeated while the engine is running. A clutch is a friction device used to connect and disconnect a driving force from a driven member. In automotive application, it is used in conjunction with an engine flywheel to provide smooth engagement and disengagement of the engine and manual transmission. Since an internal combustion engine develops little power or torque at low rpm, it must gain speed before it will move the vehicle. However, if a rapidly rotating engine is suddenly connected to the drive line of a stationary vehicle, a violent shock will result. So gradual application of load, along with some slowing of engine speed, is needed to provide reasonable and comfortable starts. In vehicles equipped with a manual transmission, this is accomplished by means of a mechanical clutch. The clutch utilizes friction for its operation. The main parts of the clutch are a pressure plate, and a driven disk. The pressure plate is coupled with the flywheel, while the driven disk is fitted to the transmission input shaft. The pressure plate is pressed to the disk by the springs so that the torque is transmitted owing to friction forces from the engine to the input shaft of the transmission. Smooth engagement is ensured by slipping of the disk before a full pressure is applied. The automobiles are equipped with a dry spring-loaded clutch. The clutch is termed dry because the surfaces of the pressure plate and driven disks are dry incontrast to oil-bath clutches in which the plate and disks operate in a bath of oil. It is called spring-loaded because the pressure plate and the driven disk are always pressed to each other by springs and are released only for a time to shift gears or to brake the automobile. In addition to the plate and disk, the clutch includes a cover, release levers, a release yoke, pressure springs and a control linkage. The clutch cover is a steel stamping bolted to the flywheel. The release levers are secured inside the cover on the supporting bolts. The outer ends of the release levers are articulated to the pressure plate. Such a construction allows the pressure plate to approach the cover or move away from it, all the time rotating with the flywheel. The springs spaced around the circumference between the pressure plate and the clutch cover clamp the driven disk between the pressure plate and the flywheel. The springs are installed with the aid of projections and sockets provided on the cover and pressure plate. The pressure plate sockets have thermal-insulation gaskets for protecting the springs against overheating. The clutch release mechanism can be operated either mechanically or hydraulically. The mechanically-operated release mechanism consists of a pedal,a return spring, a shaft with lever, a rod, a release yoke lever, a release yoke, a release ball bearing with support and a clutch release spring. When the clutch pedalis depressed, the rod and shaft with yoke shift the released bearing and support assembly. The release bearing presses the inner ends of the release levers, the pressure plate is moved away from, the driven disk and the clutch is disengaged. To engage the clutch, the pedal is released, the release bearing thus releasing the release levers so that the pressure plate is forced by its springs towards the flywheel to clamp the driven disk and engage the clutch. The clutch hydraulically-operated release mechanism consists of a clutch pedal, clutch release spring, a main cylinder, a pneumatic booster, pipelines and hoses and a lever of the clutch release yoke shaft. The main cylinder accommodates a piston with a cup. The pneumatic booster serves to decrease the pedal force required to disengage the clutch. The booster includes two housings with the servo diaphragm clamped in between. The housing accommodates pneumatic, hydraulic and servo plungers. When the clutch pedal is pushed, the fluid pressure from the main cylinder is transmitted through the pipelines and hoses to the hydraulic and servo plungers of the pneumatic booster. The servo arrangement is intended for automatic change of the air pressure in the pneumatic cylinder proportionally to the force applied to the pedal. The plunger moves with the diaphragm, the outlet valve closes and the inlet valve opens thus admitting the compressed air to the pneumatic plunger piston. The forces created by the pneumatic and hydraulic plungers are added together and are applied through the push rod to the release yoke shaft lever, the lever turns the shaft and the release yoke shaft disengaging the clutch. After the clutch pedal is released,the outlet valve opens and the inlet closes. Under the action of the springs thepistons return the plungers to the initial position and the air from the cylinder is let out to the atmosphere. Automatic clutches were used in certain U.S. and European cars. American MotorsE-stick clutch eliminated the need for physical operation of the clutch pedal. A German car maker engineered an automatic clutch system called Hydrak, which consisted of a fluid flywheel connected to a single, dry disk clutch. In the E-Stick set up, the pressure plate levers engage the clutch disk rather than release them. Also, the clutch remains disengaged until a servo unit is applied by oil pressure when the shift lever is placed in gear with the engine running. The Hydrak unit also begins operation when the lever is in gear. This activates a booster unit, which disengages the clutch disk. The hydraulic clutch parts are bridged over by a free-wheel unit, which goes into action when the speed of the rear wheels is higher than the speed of the engine. A special device controls ingagement of the mechanical clutch, depending on whether the rear axle is in traction or is pushed by car momentum. A more-or-less unusual clutch pressure plate set-up is used on late model Chrysler and American Motors cars. Called a semi-centrifugal clutch, the pressure plate has six cylindrical rollers which move outward under centrifugal force until they contact the cover. As engine speed increases, the rollers wedge themselves between the pressure plate and cover so that the faster the clutch rotates, the greater the pressure exerted on the pressure plate and disk. A transmission is a speed and power changing device installed at some point between the engine and driving wheel of the vehicle. It provides a means for changing the ratio between engine rpm ( revol utions per minute) and driving wheels rpm to best meet each particular driving situation. Given a level road ,an automobile without a transmission could be made to move by accelerating the engine and engaging the clutch. However, a start under these conditions would be slow, noisy and uncomfortable. In addition, it would place a tremendous strain on the engine and driving parts of the automobile. So in order to get smooth starts and have power to pass and climb hills, a power ratio must be provided to multiply the torque and turning effort of the engine. Also required is a speed ratio to avoid the need for extremely high engine rpm at high road speeds. The transmission is geared to perform these functions. The transmission is designed for changing the torque transmitted from the engine crankshaft to the propeller shaft, reversing the vehicle movement and disengaging the engine from the drive line for a long time at parking or coasting. A higher to rque should be applied to the wheels to set an automobile in motion or move uphill with a full load than to keep it rolling after it gets under way on level stretches of the road, when inertia is high and tractive resistance is low. To meet these variable torque requirements, special gear boxes are used. Such gear boxes are called fixed-ratio transmissions. In a gear train consisting of a driving gear and a driven gear, the torque at the driven gear will increase as many times as the number of teeth of the driven gear is larger than that of the driving gear. The figure obtained by dividing the number of driven gear teeth by that of the driving gear is called gear ratio. If a train consists of several pairs of gears, the overall ratio is the product of the gear ratios of all the gear pairs in the train. To provide the different torques required under the varying operating conditions of a vehicle, the transmission incorporates several pairs of gears with different gear ratios. If an intermediate gear is introduced between the driving gear and the driven gear, the rotation of the driven gear will be reversed. The transmission consists of a housing, an input shaft and gear, an output and gear, an idler shaft, a reverse gear, a cluster of gears and a gear shift mechanism. The cast iron housing has upper and side covers and bores for the installation of shafts. The bottom and side walls are provided with holes for filling and draining oil. The input shaft is made of steel integral with the driving gear and the rim. The front end of the input shaft is installed on the bearing in the bore of the crankshaft, while the rear end rotates in the bore of the front wall of the housing. The input shaft is arranged so that only the driving gear and the rim are accommodated inside the housing while the splined potion of the shaft protruding from the transmission carries the hub of the clutch driven disk. The output shaft is splined and rests with its front end on a roller bearing installed in the bore of the input shaft. The other end of the output shaft rotates in a ball bearing in the transmission housing wall. The output shaft splines carry the sliding gears. The output shaft is coaxial with the input shaft. The idler shaft carries a cluster of gears of different sizes. The cluster is mounted in the roller bearings on an axle or, together with the shaft, on bearings in the housing wall bores. The idler shaft constantly rotates with the input shaft because their gears are in constant mesh. The reverse gear(a single gear or a two-gear cluster) rotates on an axle secured in the holes of the housing walls. The gear shift mechanism is designed for engaging gears, setting them neutral and engaging the reverse speed. The speeds are changed by shifting the gears or sleeves along the output shaft. The transmission type depends on the number of the sliding gears or sleeves. The transmission with two sliding gears or synchronizer sleeves is called two-range, with three gears, three-range. Depending on the number of forward speeds there are three-,four- and five-speed transmissions. The gear shift mechanism is mounted on the top cover. The shift lever is arranged on the cover or on the bracket of the lever support. 汽车的基本机械机构 汽车工业是一种迅速发展的工业。从十八世纪后期第一辆汽车出现在公路上后，这一工业便迅猛发展起来。如今全世界成千上万的工厂生产着各种各样的汽车。汽车行业也汇聚了千千万万的人。汽车发动机广泛地应用于配有巨大动力的机械中，如农业、建筑业、制造业。不同类型的小型发动机也应用于植草机、动力锯、除雪机等类似的设备中。汽车行业是一个发展着的、需求着的行业，似乎永远找不到它的尽头和饱和点。汽车、运输工具 、发动机有着巨大的需求量。这一行业同样需要受过锻炼的、有经验的精英，来诊断这些机动车辆的故障、修理和更新机动车的零件、变速器、推动轴、差分器、车轴、操纵系统、刹车系统、暂停部件、空调装置、发热器、机身以及玻璃制造等。 汽车由五个基本的机械机构或部件组成。它们是： （ 1）发动机，它是动力的源泉，包括燃料、润滑剂、冷却和电气系统。 （ 2）框架，它支持发动机、车轮、操纵和刹车系统，以及机身。 （ 3）传动系，它将来自发动机的动力（经过离合器、调速器、传动轴、差分器和车轴）传送到车轮。 （ 4）机身。 （ 5）机身附件， 它包括加热器、灯光、挡风玻璃擦等等。 发动机是使得汽车运行的动力源泉。它通常叫做一个内置的燃烧发动机，因为汽油是在发动机气缸或燃烧腔内被燃烧的。这是相对于外置的发动机而言的（如蒸汽发动机），其燃烧发生在发动机的外部。发动机气缸内的汽油的燃烧产生了动力。然后动力经过传动系传送到发动机再到车轮，这样车轮转动，汽车便开始运行。 在动力产生的过程中燃料系统起着重要的作用，因为它给发动机气缸提供汽油。在每一个发动机气缸里，蒸发出来的汽油和空气组成的混合体进入气缸，活塞推进气缸，压缩混合体，然后电火花点燃压缩混合体， 这样活塞被迫向下。当然，在发动机内，活塞没有完全推到气缸外面，而是随着混合体的燃烧，在气缸内简单地来回移动。在汽车车轮能够转动之前，活塞的线性运动必须转变成旋转运动。发动机机轴上的连杆和曲柄实现了这一转变。 阀门将燃烧过的汽油蒸气送出气缸外面，同时把汽油蒸气和空气新鲜可燃混合气送入气缸。当他们被关闭或固定时（也就是推到端口上），端口被封闭，这样气体不能流通到端口。当他们被打开时，气体可以流通到端口。 阀门是通过发动凸轮轴上的凸轮被打开的。凸轮有一个最高点，或圆形突出部分；每次当凸轮转动时，突出部分在气门挺 杆之下，使得挺杆向上。挺杆将这个向上的运动传动到推杆再传送到摇杆臂。摇杆臂在它的支撑体上转动并在阀杆上推下去，使得阀移到低处，也就是说阀被打开了。当凸轮转动得足够使突出部分移出挺杆之下时，承重的阀门弹簧将阀门退回到自己的位置。弹簧被弹簧座和锁附在阀杆的下端。在发动机凸轮轴上每个阀门都有一个凸轮（每个气缸两个凸轮）。凸轮轴通过齿轮或链条齿和齿条受到机轴的驱动。 如果整个循环过程需要四次活塞运动，那么该发动机就叫做四冲程发动机，或四行程发动机。这四个行程是输入、压缩、发动、和排气。 在输入行程时，进气阀是被打开 的，活塞受到机轴旋转的推动，移到下面。活塞的这个移动引起了气缸内的局部的真空，同时空气通过进气阀推进气缸，以填补该真空。当空气向气缸移动时，它必须经过气化器。那里充满了汽油蒸气。因此当活塞在输入端移至下端时进入气缸的是空气和汽油蒸气的混合体。 当活塞在进口端移到下止点时，进气阀关闭。控制着进气阀的凸轮的突出部分已经从阀门下面移走。因为另一个阀门也是关闭的，气缸的上端被关闭。现在，当转动着的机轴将阀门推上时，已经进入气缸的空气和汽油蒸气混合体被压缩。直到活塞被推到上止点时，气体被压缩成原来的七分之一或八分之一 。这就类似一加仑的空气被压所成一品托。究其原因是由于气缸内部的高压。 在压缩行程，当活塞到达上止点时，气缸火花塞产生一个电火花。火花塞本质上是两个粗钢丝电极。火花由点火系统产生。它点燃了压缩的空气和汽油蒸气混合体。由于高压和高温，发生了急剧的燃烧。此时，活塞顶端向下的压力达到两吨。这个巨大的推力使得活塞向下，同时巨大的冲力通过连杆和曲柄传送到机轴。 在动力行程，由于汽油蒸气的燃烧使得活塞受迫。当活塞达到下止点时，排气阀被打开。这时，活塞又一次被返回，它推动气缸内被燃烧过的气体。到活塞到达上止点时，气缸内被燃 烧过的气体被清除掉。排气阀关闭，进气阀开启。活塞在下一个输入行程时再次被返回。发动机运行时，这四个行程持续地重复着。 离合器是一种摩擦装置，它用于从从动机构中联合和拆分驱动力。在汽车的应用中，它用于与发动机调速轮相连，以提供发动机和手工传送之间的平滑结合和正常脱离。 因此随着发动机速度的降低，需要渐进装载的应用，以获得一个合理的和舒适的启动。在装配有手工传动的汽车系