汽車曲柄連桿機構(gòu)設(shè)計及有限元分析
汽車曲柄連桿機構(gòu)設(shè)計及有限元分析,汽車,曲柄,連桿機構(gòu),設(shè)計,有限元分析
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譯文題目： The basic mechanisms Of Automobiles
汽車的基本機械結(jié)構(gòu)
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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 Motors"E-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 ( revolutions 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.
汽車的基本機械機構(gòu)
汽車工業(yè)是一種迅速發(fā)展的工業(yè)。從十八世紀后期第一輛汽車出現(xiàn)在公路上后，這一工業(yè)便迅猛發(fā)展起來。如今全世界成千上萬的工廠生產(chǎn)著各種各樣的汽車。汽車行業(yè)也匯聚了千千萬萬的人。汽車發(fā)動機廣泛地應用于配有巨大動力的機械中，如農(nóng)業(yè)、建筑業(yè)、制造業(yè)。不同類型的小型發(fā)動機也應用于植草機、動力鋸、除雪機等類似的設(shè)備中。汽車行業(yè)是一個發(fā)展著的、需求著的行業(yè)，似乎永遠找不到它的盡頭和飽和點。汽車、運輸工具、發(fā)動機有著巨大的需求量。這一行業(yè)同樣需要受過鍛煉的、有經(jīng)驗的精英，來診斷這些機動車輛的故障、修理和更新機動車的零件、變速器、推動軸、差分器、車軸、操縱系統(tǒng)、剎車系統(tǒng)、暫停部件、空調(diào)裝置、發(fā)熱器、機身以及玻璃制造等。
汽車由五個基本的機械機構(gòu)或部件組成。它們是：
（1）發(fā)動機，它是動力的源泉，包括燃料、潤滑劑、冷卻和電氣系統(tǒng)。
（2）框架，它支持發(fā)動機、車輪、操縱和剎車系統(tǒng)，以及機身。
（3）傳動系，它將來自發(fā)動機的動力（經(jīng)過離合器、調(diào)速器、傳動軸、差分器和車軸）傳送到車輪。
（4）機身。
（5）機身附件，它包括加熱器、燈光、擋風玻璃擦等等。
發(fā)動機是使得汽車運行的動力源泉。它通常叫做一個內(nèi)置的燃燒發(fā)動機，因為汽油是在發(fā)動機氣缸或燃燒腔內(nèi)被燃燒的。這是相對于外置的發(fā)動機而言的（如蒸汽發(fā)動機），其燃燒發(fā)生在發(fā)動機的外部。發(fā)動機氣缸內(nèi)的汽油的燃燒產(chǎn)生了動力。然后動力經(jīng)過傳動系傳送到發(fā)動機再到車輪，這樣車輪轉(zhuǎn)動，汽車便開始運行。
在動力產(chǎn)生的過程中燃料系統(tǒng)起著重要的作用，因為它給發(fā)動機氣缸提供汽油。在每一個發(fā)動機氣缸里，蒸發(fā)出來的汽油和空氣組成的混合體進入氣缸，活塞推進氣缸，壓縮混合體，然后電火花點燃壓縮混合體，這樣活塞被迫向下。當然，在發(fā)動機內(nèi)，活塞沒有完全推到氣缸外面，而是隨著混合體的燃燒，在氣缸內(nèi)簡單地來回移動。在汽車車輪能夠轉(zhuǎn)動之前，活塞的線性運動必須轉(zhuǎn)變成旋轉(zhuǎn)運動。發(fā)動機機軸上的連桿和曲柄實現(xiàn)了這一轉(zhuǎn)變。
閥門將燃燒過的汽油蒸氣送出氣缸外面，同時把汽油蒸氣和空氣新鮮可燃混合氣送入氣缸。當他們被關(guān)閉或固定時（也就是推到端口上），端口被封閉，這樣氣體不能流通到端口。當他們被打開時，氣體可以流通到端口。
閥門是通過發(fā)動凸輪軸上的凸輪被打開的。凸輪有一個最高點，或圓形突出部分；每次當凸輪轉(zhuǎn)動時，突出部分在氣門挺桿之下，使得挺桿向上。挺桿將這個向上的運動傳動到推桿再傳送到搖桿臂。搖桿臂在它的支撐體上轉(zhuǎn)動并在閥桿上推下去，使得閥移到低處，也就是說閥被打開了。當凸輪轉(zhuǎn)動得足夠使突出部分移出挺桿之下時，承重的閥門彈簧將閥門退回到自己的位置。彈簧被彈簧座和鎖附在閥桿的下端。在發(fā)動機凸輪軸上每個閥門都有一個凸輪（每個氣缸兩個凸輪）。凸輪軸通過齒輪或鏈條齒和齒條受到機軸的驅(qū)動。
如果整個循環(huán)過程需要四次活塞運動，那么該發(fā)動機就叫做四沖程發(fā)動機，或四行程發(fā)動機。這四個行程是輸入、壓縮、發(fā)動、和排氣。
在輸入行程時，進氣閥是被打開的，活塞受到機軸旋轉(zhuǎn)的推動，移到下面?；钊倪@個移動引起了氣缸內(nèi)的局部的真空，同時空氣通過進氣閥推進氣缸，以填補該真空。當空氣向氣缸移動時，它必須經(jīng)過氣化器。那里充滿了汽油蒸氣。因此當活塞在輸入端移至下端時進入氣缸的是空氣和汽油蒸氣的混合體。
當活塞在進口端移到下止點時，進氣閥關(guān)閉?？刂浦M氣閥的凸輪的突出部分已經(jīng)從閥門下面移走。因為另一個閥門也是關(guān)閉的，氣缸的上端被關(guān)閉?，F(xiàn)在，當轉(zhuǎn)動著的機軸將閥門推上時，已經(jīng)進入氣缸的空氣和汽油蒸氣混合體被壓縮。直到活塞被推到上止點時，氣體被壓縮成原來的七分之一或八分之一。這就類似一加侖的空氣被壓所成一品托。究其原因是由于氣缸內(nèi)部的高壓。
在壓縮行程，當活塞到達上止點時，氣缸火花塞產(chǎn)生一個電火花?；鸹ㄈ举|(zhì)上是兩個粗鋼絲電極?；鸹ㄓ牲c火系統(tǒng)產(chǎn)生。它點燃了壓縮的空氣和汽油蒸氣混合體。由于高壓和高溫，發(fā)生了急劇的燃燒。此時，活塞頂端向下的壓力達到兩噸。這個巨大的推力使得活塞向下，同時巨大的沖力通過連桿和曲柄傳送到機軸。
在動力行程，由于汽油蒸氣的燃燒使得活塞受迫。當活塞達到下止點時，排氣閥被打開。這時，活塞又一次被返回，它推動氣缸內(nèi)被燃燒過的氣體。到活塞到達上止點時，氣缸內(nèi)被燃燒過的氣體被清除掉。排氣閥關(guān)閉，進氣閥開啟。活塞在下一個輸入行程時再次被返回。發(fā)動機運行時，這四個行程持續(xù)地重復著。
離合器是一種摩擦裝置，它用于從從動機構(gòu)中聯(lián)合和拆分驅(qū)動力。在汽車的應用中，它用于與發(fā)動機調(diào)速輪相連，以提供發(fā)動機和手工傳送之間的平滑結(jié)合和正常脫離。
因此隨著發(fā)動機速度的降低，需要漸進裝載的應用，以獲得一個合理的和舒適的啟動。在裝配有手工傳動的汽車系統(tǒng)中，這可以通過一個機械離合器獲得成功。
離合器是通過摩擦獲得運行的。離合器的主要裝置是一個壓力盤和一個驅(qū)動板。壓力盤外加有調(diào)速輪，而驅(qū)動板和傳動輸入軸相品配。壓力盤通過彈力壓住驅(qū)動盤，這樣扭矩由于發(fā)動機和傳送的輸入軸之間的摩擦力而被傳動。
汽車一般裝有干式彈力離合器。之所以稱之為干的是因為壓力盤和驅(qū)動板是干的，相對于油式離合器，它是浸泡在油中運行的。之所以稱之為彈力的是由于壓力盤和驅(qū)動板是靠彈力相互壓在一起的，同時在某個時刻被釋放到汽車的齒輪或剎車裝置中。
除了壓力盤和驅(qū)動盤，離合器還包含
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