汽車車門有限元分析設(shè)計
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譯文題目： Automotive engine
汽車發(fā)動機(jī)
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年01 月15 日
AUTOMOTIVE ENGINE
1 Engine Classification and Overall Mechanics
The automobile engines can be classified according to: (1) cycles, (2) cooling system, (3) fuel system, (4) ignition method, (5) valve arrangement, (6) cylinder arrangement, (7) engine speed.
Engines used in automobiles are the internal combustion heat engines. The burning of gasoline inside the engine produces high pressure in the engine combustion chamber. This high pressure force 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 car moves.
The engine requires four basic systems to run (Fig. 2-1). Diesel engines require three of these systems. They are fuel system, ignition system (except diesel), lubricating system and cooling system. However, three other related systems are also necessary. These are the exhaust system, the emission-control system, and the starting system. Each performs a basic job in making the engine run.
Fig. 2-1 The engine construction
2?Engine?Operating Principles
Fig. 2-2 Engine terms
The term “stroke” is used to describe the movement of the piston within the cylinder. The movement of the piston from its uppermost position (TDC, top dead center) to its lowest position (BDC, bottom dead center) is called a stroke. The operating cycle may require either two or four strokes to complete. Most automobile engines operate on the four stroke cycle (Fig. 2-2).
In four-stroke engine, four strokes of the piston in the cylinder are required to complete one full operating cycle. Each stroke is named after the action. It performs intake, compression, power, and exhaust in that order (Fig. 2-3).
Intake stroke Compression stroke Power stroke Exhaust stroke
Fig. 2-3 Four-stroke-cycle gasoline engine
1. The intake stroke
The intake stroke begins with the piston near the top of its travel. As the piston begins its descent, the exhaust valve closes fully, the intake valve opens and the volume of the combustion chamber begins to increase, creating a vacuum. As the piston descends, an air/fuel mixture is drawn from the carburetor into the cylinder through the intake manifold. The intake stroke ends with the intake valve close just after the piston has begun its upstroke.
2. Compression stroke
As the piston is moved up by the crankshaft from BDC, the intake valve closes. The air/fuel mixture is trapped in the cylinder above the piston. Future piston travel compresses the air/fuel mixture to approximately one-eighth of its original volume (approximately 8:1 compression ratio) when the piston has reached TDC. This completes the compression stroke.
3. 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 3-5MPa or even more. This terrific push against the piston forces it downward, and a powerful 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.
4. Exhaust stroke
At the end of the power stroke the camshaft opens the exhaust valve, and the exhaust stroke begins. Remaining pressure in the cylinder, and upward movement of the piston, force the exhaust gases out of the cylinder. At the end of the exhaust stroke, the exhaust valve closes and the intake valve opens, repeating the entire cycle of events over and over again.
3 Engine Block and Cylinder Head
3.1 Engine Block
The engine block is the basic frame of the engine. All other engine parts either fit inside it or fasten to it. It holds the cylinders, water jackets and oil galleries (Fig. 2-4). The engine block also holds the crankshaft, which fastens to the bottom of the block. The camshaft also fits in the block, except on overhead-cam engines. In most cars, this block is made of gray iron, or an alloy (mixture) of gray iron and other metals, such as nickel or chromium. Engine blocks are castings.
Fig. 2-4 V6 engine block
Some engine blocks, especially those in smaller cars, are made of cast aluminum. This metal is much lighter than iron. However, iron wears better than aluminum. Therefore, the cylinders in most aluminum engines are lined with iron or steel sleeves. These sleeves are called cylinder sleeves. Some engine blocks are made entirely of aluminum.
3.2 Cylinder Sleeves
Cylinder sleeves are used in engine blocks to provide a hard wearing material for pistons and piston rings. The block can be made of one kind of iron that is light and easy to cast while the sleeves uses another that is better able to stand up wear and tear. There are two main types of sleeves: dry and wet (Fig. 2-5).
Dry sleeve Wet sleeve
Fig. 2-5 Cylinder sleeve
3.3 Cylinder Head
The cylinder head fastens to the top of the block, just as a roof fits over a house. The underside forms the combustion chamber with the top of the piston. In-line engine of light vehicles have just one cylinder head for all cylinders; larger in-line engines can have two or more. Just as with engine blocks, cylinder heads can be made of cast iron or aluminum alloy. The cylinder head carries the valves, valve springs and the rockers on the rocker shaft, this part of valve gear being worked by the pushrods. Sometimes the camshaft is fitted directly into the cylinder head and operates on the valves without rockers. This is called an overhead camshaft arrangement.
3.4 Gasket
The cylinder head is attached to the block with high-tensile steel studs. The joint between the block and the head must be gas-tight so that none of the burning mixture can escape. This is achieved by using cylinder head gasket. Gaskets are also used to seal joins between the other parts, such as between the oil pan, manifolds, or water pump and the blocks.
3.5 Oil Pan
The oil pan is usually formed of pressed steel. The oil pan and the lower part of 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 run down into the pan. Thus, there is a constant circulation of oil between the pan and the working parts of the engine.
4 Piston Assembly, piston?rings , The?piston?pin ,Connecting Rods, Crankshafts And Flywheel
4.1 Piston
Piston rings and the piston pin are together called the piston assembly (Fig. 2-6).
Fig. 2-6 Piston, piston rings and connecting rod
The?piston?is?an?important?part?of?a?four-stroke?cycle?engine.?Most?pistons?are?made?from?cast?aluminum.?The?piston,?through?the?connecting?rod,?transfers?to?the?crankshaft?the?force?created?by?the?burning?fuel?mixture.?This?force?turns?the?crankshaft.?
To?withstand?the?heat?of?the?combustion?chamber,?the?piston?must?be?strong.?It?also?must?be?light,?since?it?travels?at?high?speeds?as?it?moves?up?and?down?inside?the?cylinder.?The?piston?is?hollow.?It?is?thick?at?the?top?where?it?takes?the?brunt?of?the?heat?and?the?expansion?force.?It?is?thin?at?the?bottom,?where?there?is?less?heat.?The?top?part?of?the?piston?is?the?head,?or?crown.?The?thin?part?is?the?skirt.?Most?pistons?have?three?ring?grooves?at?the?top.?The?sections?between?the?ring?grooves?are?called?ring?lands.?
4.2 ?piston?rings
?piston?rings?fit?into?ring?grooves?near?the?top?of?the?piston.?In?simplest?terms,?piston?rings?are?thin,?circular?pieces?of?metal?that?fit?into?grooves?in?the?tops?of?the?pistons.
?In?modern?engines,?each?piston?has?three?rings.?(Piston?in?older?engines?sometimes?had?four?rings,?or?even?five.)?The?inside?surface?of?the?ring?fits?in?the?groove?on?the?piston.?The?ring's?outside?surface?presses?against?the?cylinder?walls.?Rings?provide?the?needed?seal?between?the?piston?and?the?cylinder?walls.?That?is,?only?the?rings?contact?the?cylinder?walls.?The?top?two?rings?are?to?keep?the?gases?in?the?cylinder?and?are?called?compression?rings.?The?lower?one?prevents?the?oil?splashed?onto?the?cylinder?bore?from?entering?the?combustion?chamber,?and?is?called?an?oil?ring.?
4.3 The?piston?pin
The?piston?pin?holds?together?the?piston?and?the?connecting?rod.?This?pin?fits?into?the?piston?pin?holes?and?into?a?hole?in?the?top?end?of?the?connecting?rod.?The?top?end?of?the?rod?is?much?smaller?than?the?end?that?fits?on?the?crankshaft.?This?small?end?fits?inside?the?bottom?of?the?piston.?The?piston?pin?fits?through?one?side?of?the?piston,?through?the?small?end?of?the?rod,?and?then?through?the?other?side?of?the?piston.?It?holds?the?rod?firmly?in?place?in?the?center?of?the?piston.?Pins?are?made?of?high-strength?steel?and?have?a?hollow?center.?Many?pins?are?chrome-plated?to?help?them?wear?better.A?piston?pin?fits?into?a?round?hole?in?the?piston.?The?piston?pin?joins?the?piston?to?the?connecting?rod.?The?thick?part?of?the?piston?that?holds?the?piston?pin?is?the?pin?boss.
4.4 Connecting Rods
?The?connecting?rod?little?end?is?connected?to?the?piston?pin.?A?bush?made?from?a?soft?metal,?such?as?bronze,?is?used?for?this?joint.?The?lower?end?of?the?connecting?rod?fits?the?crankshaft?journal.?This?is?called?the?big?end.?For?this?big-end?bearing,?steel-backed?lead?or?tin?shell?bearings?are?used.?These?are?the?same?as?those?used?for?the?main?bearings.?The?split?of?the?big?end?is?sometimes?at?an?angle,?so?that?it?is?small?enough?to?be?withdrawn?through?the?cylinder?bore.?The?connecting?rod?is?made?from?forged?alloy?steel.?
4.5 Crankshafts
The crankshaft is regarded as the “backbone” of the engine (Fig. 2-7). The?crankshaft,?in?conjunction?with?the?connecting?rod,?converts?the?reciprocating?motion?of?the?piston?to?the?rotary?motion?needed?to?drive?the?vehicle.?It?is?usually?made?from?car-bon?steel?which?is?alloyed?with?a?small?proportion?of?nickel.?The?main?bearing?journals?fit?into?the?cylinder?block?and?the?big?end?journals?align?with?the?connecting?rods.?At?the?rear?end?of?the?crankshaft?is?attached?the?flywheel,?and?at?the?front?end?are?the?driving?wheels?for?the?timing?gears,?fan,?cooling?water?and?alternator.?The?throw?of?the?crankshaft,?i.e.?the?distance?between?the?main?journal?and?the?big?end?centers,?controls?the?length?of?the?stroke.?The?stroke?is?double?the?throw,?and?the?strokelength?is?the?distance?that?the?piston?travels?from?TDC?to?BDC?and?vice?versa.?
Fig. 2-7 The crankshaft
4.6 Flywheel
?????The?flywheel?is?made?from?carbon?steel.?It?fits?onto?the?rear?of?the?crankshaft.?As?well?as?keeping?the?engine?rotating?between?power?strokes?it?also?carries?the?clutch,?which?transmits?the?drive?to?the?gearbox,?and?has?the?starter?ring?gear?around?its?circumference.?There?is?only?one?working?stroke?in?four?so?a?flywheel?is?needed?to?drive?the?crankshaft?during?the?time?that?the?engine?is?performing?the?non-power?strokes.?
5 Valve System
Fig. 2-8 Parts of the valve train
The valve operating assembly includes the lifters or cam followers, pushrods, rocker arms and shafts or pivot, valve and springs etc. The purpose of this to open and close the intake and exhaust ports that lead to the combustion chambers as required (Fig. 2-8). Valve mechanisms vary depending on the camshaft location. When the camshaft is positioned in the engine block, valve lifters are mounted in the openings above the camshaft. Pushrods are connected from each valve lifter to a pivoted rocker arm mounted above each valve. A lobe on the camshaft is positioned directly below each valve lifter. A typical camshaft drive has a sprocket bolted to the end of the camshaft, and a matching sprocket is attached to the end of the crankshaft. Those two sprockets may be meshed together or surrounded a steel chain to have the camshaft drive. When the lower part of the camshaft lobe is rotating under the valve lifter, the valve spring holds the valve closed.
汽車發(fā)動機(jī)
1發(fā)動機(jī)的分類和整體力學(xué)
汽車發(fā)動機(jī)可根據(jù)如下因素進(jìn)行分類：（1）循環(huán)系統(tǒng)，（2）冷卻系統(tǒng)，（3）燃油系統(tǒng)，（4）點火方式，（5）氣門布置，（6）氣缸排列，（7）發(fā)動機(jī)轉(zhuǎn)速。
用于汽車的發(fā)動機(jī)是內(nèi)燃機(jī)。汽油在發(fā)動機(jī)內(nèi)部燃燒，產(chǎn)生的高壓力使活塞移動，這一運(yùn)動通過連桿傳遞到曲軸，使它旋轉(zhuǎn)。動力通過動力總成傳遞到車輪，從而帶動汽車前進(jìn)。
發(fā)動機(jī)需要四個基本系統(tǒng)來運(yùn)行（圖2-1）。柴油發(fā)動機(jī)需要其中的三個基本系統(tǒng)來運(yùn)行。它們是燃油系統(tǒng)、點火系統(tǒng)（柴油除外）、潤滑系統(tǒng)和冷卻系統(tǒng)。然而，其他三個相關(guān)系統(tǒng)也是必要的。這些是排氣系統(tǒng)，排放控制系統(tǒng)，啟動系統(tǒng)。每個系統(tǒng)執(zhí)行一項基本工作，使發(fā)動機(jī)正常運(yùn)行。
圖2-1發(fā)動機(jī)結(jié)構(gòu)
2發(fā)動機(jī)工作原理
“沖程”一詞是用來形容汽缸內(nèi)活塞的運(yùn)動?；钊麖淖罡呶恢茫═DC，上止點）運(yùn)動到其最低位置（BDC上，下止點）的運(yùn)動過程被稱為一個沖程。做功周期可能需要兩個或四沖程來完成。大多數(shù)汽車發(fā)動機(jī)為四沖程循環(huán)。
在四沖程發(fā)動機(jī)中，活塞在汽缸內(nèi)的動作都需要完成一個完整的運(yùn)行周期。每個行程按所完成的動作命名。分別是進(jìn)氣，壓縮，做功，和排氣（圖2-3）。
進(jìn)氣沖程 壓縮沖程 做功沖程 排氣沖程
圖2-3四沖程循環(huán)汽油發(fā)動機(jī)
1、進(jìn)氣沖程
進(jìn)氣沖程開始運(yùn)動到活塞行程的頂端附近。當(dāng)活塞開始下降，排氣門完全關(guān)閉，打開進(jìn)氣門，創(chuàng)造一個真空，燃燒室里進(jìn)氣量開始增加。當(dāng)活塞下降，空氣/燃料混合物從化油器通過進(jìn)氣歧管進(jìn)入氣缸。活塞已經(jīng)開始上行后，進(jìn)氣行程結(jié)束進(jìn)氣門即將關(guān)閉。
2、壓縮行程
當(dāng)活塞通過曲軸從BDC位置開始移動，進(jìn)氣門關(guān)閉。在汽缸中活塞上面的空氣/燃料混合物被壓縮。活塞行程壓縮空氣/燃料混合物約為原體積的1/8（大約8:1的壓縮比）時，這時候活塞已經(jīng)達(dá)到TDC的八分之一。這就完成了壓縮沖程。
3、做功沖程
在壓縮沖程中當(dāng)活塞到達(dá)TDC時，火花塞產(chǎn)生電火花。點火系統(tǒng)提供給火花塞一個高壓脈沖使產(chǎn)生火花?；鸹c燃（放火）空氣/燃料混合物，開始迅速燃燒，氣缸壓力增加多達(dá)3-5MPa。這壓力推動活塞下降，并通過連桿曲軸的曲柄銷傳送到一個強(qiáng)大的沖動?；钊厦娴膲毫ν苿铀鼜亩骨S旋轉(zhuǎn)。
4、排氣沖程
在動力沖程結(jié)束時，凸輪軸打開排氣門，排氣沖程開始?；钊蛏线\(yùn)動，氣缸內(nèi)的壓力迫使廢氣排出氣缸。在排氣沖程結(jié)束時，排氣門關(guān)閉進(jìn)氣打開，一遍又一遍地重復(fù)整個循環(huán)。
3發(fā)動機(jī)缸體和缸蓋
3.1發(fā)動機(jī)缸體
發(fā)動機(jī)缸體是發(fā)動機(jī)的基本框架。所有其他發(fā)動機(jī)零部件裝進(jìn)或擰緊在缸體上。它擁有冷卻回路、潤滑油道（圖2-4），發(fā)動機(jī)缸體，還擁有曲軸，機(jī)油底殼。除了頂置凸輪發(fā)動機(jī)外，凸輪軸也屬于這部分。在大多數(shù)汽車中，此缸體是由灰鑄鐵和其他金屬，如鎳或鉻，合金（混合物）鑄造成的。
圖2-4 V6發(fā)動機(jī)缸體
有些發(fā)動機(jī)缸體，尤其是那些小型車使用鑄鋁，這種金屬比鑄鐵輕得多。然而，鐵的耐磨性比鋁好。因此，在大多數(shù)鋁制發(fā)動機(jī)汽缸內(nèi)襯有鐵或鋼材質(zhì)的套管。這些軸套叫做氣缸套。一些發(fā)動機(jī)缸體完全由鋁做成。
3.2氣缸套
氣缸套用于發(fā)動機(jī)缸體內(nèi)，用來防止活塞和活塞環(huán)對缸體的磨損。缸體可以由一種既輕也易于成型的金屬制成，而缸套則用來承受活塞跟活塞環(huán)的磨損。有兩種主要類型的缸套：干缸套和濕缸套（圖2-5）。
干缸套 濕缸套
圖2-5缸套
3.3缸蓋
氣缸蓋是缸體的頂部，相當(dāng)于一所房子的屋頂與活塞頂部形成燃燒室。直列式輕型車輛的發(fā)動機(jī)氣缸只有一個缸蓋;較大的直列式發(fā)動機(jī)可以有兩個或兩個以上。正如發(fā)動機(jī)缸體，缸蓋也可由鑄鐵或鋁合金制成。氣缸蓋攜帶閥門，氣門彈簧，搖臂軸，搖臂，推動氣門齒輪工作的推桿。有時，凸輪軸直接安裝在缸蓋上，不用搖臂控制氣門工作。這被稱為頂置凸輪軸布置。
3.4墊片
缸蓋與高強(qiáng)度鋼螺栓連接缸體。缸體和頭部之間的聯(lián)合，必須不透氣，使燃燒的混合物不能泄漏。這是通過使用氣缸蓋墊片實現(xiàn)。密封墊片還可以用于連接的其他部分，如油底殼，歧管，或水泵和缸體之間。
3.5油底殼
油底殼通常由鋼沖壓形成。油底殼和缸體下部一同被叫做曲軸箱;它們把曲軸封閉起來。潤滑系統(tǒng)中的油泵，抽出油底殼中的油，并把它傳送到發(fā)動機(jī)的所有工作部件。機(jī)油流出再通過管道流回油底殼。因此，機(jī)油要在發(fā)動機(jī)的工作部件不斷地循環(huán)流動。
4活塞，活塞環(huán)，活塞銷，連桿，曲軸和飛輪
4.1活塞
活塞、活塞環(huán)和活塞銷在一起稱為活塞總成?；钊撬臎_程發(fā)動機(jī)的重要部件。大多數(shù)活塞由鑄鋁制成?；钊?，通過連桿，與曲軸相連并將燃燒混合氣產(chǎn)生的力傳給曲軸。這種力量使曲軸轉(zhuǎn)動。
為了經(jīng)得住燃燒室的高溫，活塞必須有足夠的強(qiáng)度。同時活塞必須很輕，因為它在氣缸內(nèi)以很高的速度上下移動?；钊强招牡??；钊敳亢瘢惺苤邷厝?xì)獾膸в袥_擊性的高壓力。底部薄，在那里熱量少?；钊捻敳渴腔钊^或者活塞頂。薄的部分是裙部。大多數(shù)活塞的頂部有3個活塞環(huán)槽。活塞環(huán)槽之間的部分稱為環(huán)帶。
4.2 活塞環(huán)
活塞環(huán)裝在活塞頂部附近的活塞環(huán)槽里。簡單地講，活塞環(huán)就是裝在活塞頂部的凹槽里的薄，圓的金屬。
現(xiàn)代的發(fā)動機(jī)，每個活塞有3 道環(huán)。(在更舊的發(fā)動機(jī)里活塞有4道環(huán)甚至5道環(huán)。)這些環(huán)的內(nèi)表面和活塞上的凹槽相配合。環(huán)的外表面推擠氣缸壁。環(huán)為活塞和氣缸壁之間提供了必要的密封?；钊c汽缸壁不接觸，只有環(huán)與氣缸壁接觸。最頂?shù)膬傻辣ＷC活塞與氣缸壁間密封的環(huán)叫做氣環(huán)。底下的一道防止機(jī)油飛濺到缸筒從而竄入燃燒室的環(huán)叫做油環(huán)。
4.3活塞銷
活塞銷把活塞和連桿連接在一起。這個銷裝在活塞銷座孔和連桿小頭襯套孔內(nèi)。連桿的小頭比安裝在曲軸的大頭小得多。小頭裝在活塞的底部?；钊N貫穿活塞，把連桿小頭與活塞連在一起，并將連桿保持在活塞中心的適當(dāng)位置處。銷由高強(qiáng)度的鋼做成并且是空心的。很多銷都是鍍鉻的以使他們更加耐磨?；钊N裝在活塞的環(huán)形的孔里。活塞銷把活塞和連桿連接起來。用來支撐活塞銷的活塞厚的部分稱為活塞銷凸臺。
4.4連桿
連桿小頭連接著活塞銷。軸瓦由軟金屬制成，例如青銅常被用于這種連接。在連桿大頭安裝曲柄軸頸。這被稱為連桿大頭。對連桿大頭軸承來說，使用的是鉛的鋼背或錫的軸瓦式軸承。這些軸承與那些被用作主要軸承的軸承相同。大頭的裂口有時有一個角度，以便足夠小通過氣缸。連桿由鍛造的合金鋼制成。
4.5曲軸
曲軸被視為發(fā)動機(jī)的“脊梁”（圖2-7）。 曲軸，和連桿一起，把活塞的往復(fù)運(yùn)動轉(zhuǎn)化為駕駛車輛需要的旋轉(zhuǎn)運(yùn)動。通常由小比例的鎳熔成的碳鋼制成。主要軸承曲頸安裝在氣缸體和與連桿大頭末端匹配的曲頸上。曲軸的后端連接著飛輪，前端是連接著定時齒輪，風(fēng)扇，冷卻水和交流發(fā)電機(jī)的驅(qū)動輪。 曲軸的擺幅，即在主要曲頸和連桿大頭末端中心之間的距離，控制著沖程的行程。一個沖程等于兩個擺幅的行程是活塞從上止點運(yùn)動到下止點的距離，反之亦然。
圖2-7曲軸
4.6飛輪
飛輪由碳鋼制成。它安裝在曲軸的后面。除了保持發(fā)動機(jī)在作功沖程時旋轉(zhuǎn)，它還通過離合器將動力傳給變速箱并且在飛輪的圓周上還有起動齒輪。因為4個工作沖程中只有一個沖程作功，所以發(fā)動機(jī)處于非作功沖程時，飛輪帶動曲軸旋轉(zhuǎn)。
5配氣機(jī)構(gòu)
氣門的操作組件包括挺桿或凸輪從動件，推桿，搖臂和軸或樞軸，氣門，彈簧等，這樣做的目的是打開和關(guān)閉所需的燃燒室的進(jìn)氣門和排氣門。根據(jù)凸輪軸的位置，氣門的機(jī)制也有所不同。當(dāng)凸輪軸被定位在發(fā)動機(jī)缸體時，氣門挺桿安裝在凸輪軸上方的開口。推桿連接每個氣門挺桿到每個氣門以上的一個支點搖臂。一個凸輪軸凸角直接被定位低于每個氣門挺桿。一個典型的凸輪軸鏈輪驅(qū)動裝置都有一個螺栓凸輪軸，一個匹配的鏈輪是連接到曲軸末端。這兩個鏈輪可能嚙合在一起，或包圍鋼鏈從而使凸輪軸轉(zhuǎn)動。當(dāng)凸輪軸凸角下部旋轉(zhuǎn)時，氣門挺桿，氣門彈簧保持氣門處于關(guān)閉狀態(tài)。
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