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河南理工大學(xué)萬方科技學(xué)院本科畢業(yè)論文
The machine piston connecting rod set- detailed exposition of piston
?
The piston connecting rod set is composed of the piston, piston wreath, piston pin, connecting rod, connecting rod axle bush, etc.
Ⅰ. effect: The effect of the piston is to bear the air pressure, and pass to connecting rod to drive the bent axle to revolve through connecting rod axle bush, the piston coping is still a part of the burning room. The work condition: Piston works under the condition of heat, high pressure, high speed, and bad lubrication .Piston directly contacts with the heat air. The temperature can amount to above 2500 Ks in a moment .The piston is heated severely, but the condition of spreading the hot is bad .So while the piston works, the temperature is very high and the coping is up to the 600-700 Ks: And the temperature distributes asymmetrically; The piston coping bears great air pressure, especially the pressure is greatest in the route of doing efficacy. The gasoline machine is up to the 3-5MPas, the diesel engine is up to the 6-9MPas.This makes the piston produce pound, and ????bear the function of the side pressure. Therefore, the piston should have enough heat-proof, try to decrease the heating area,, strengthen the cooling of the piston, to make the highest temperature of the coping descend .The piston moves at very high speed(8-12 ms/ s) back and forth in the air cylinder, and speed changes constantly, This produces very great inertial dint, making the piston bear great additional load working under such bad condition, the piston will become deformed heating power. At the same time ,it slitters the chemical corrosive power of the burning gas .In order to descend the inertial dint of back and forth, we must ease the weight of the piston as possible .Piston works under the condition of the heat, high pressure, high speed(the average speed can amount to the 101115 m/ s), and its lubricant condition is bad and the frication between the piston and the air cylinder wall is very great. In order to descend the friction, the surface of the piston surface must be wear-resistant..
Request:
(1) To have enough rigidity and strength, and the reliable dint;
(2) Transmit heat well, bear the high pressure, bear the heat and bear to wear away;
(3) the quantity is small, the weight is light, descend the inertial dint of back and forth as possible
The aluminum metal alloy material satisfies the top requests basically, therefore, the piston generally adopts the high strength aluminum metal alloy, but some low speed diesel engines adopt high class iron casting or heat-proof steel?
Ⅱ, structure: The piston can be divided into three parts, piston coping, the piston head and piston skirt departments.
1. The piston coping
The piston coping bears the air pressure, it is a part of the burnable room .Its shape, position, size are relevant to the concrete from of the burnable room. They are made to satisfy the combustible hybrid spirit formation and burnable requests. Its coping shape can be divided into four major types, a flat coping piston, a convex coping piston, a concave coping piston and model piston. ?
A convex coping piston is usually used on the two blunt distance I.C. engines, It is good to improve the process exchanging the gas .Modern four blunt the distance gasoline machine also adopts the convex coping piston in order to strengthen the effect of pushing the gas or extend the ratio of compressing .Convex of a piston coping presents a form of ball, its coping strength is high, having an effect of leading, being advantageous to improve the process of exchanging the gas, two route of travel gasoline machines often adopt the convex coping piston
A piston coping presents the hollow form, the shape and positions of the cave pit must be advantageous to the combustion of the combustible and hybrid gas, having a pair of eddies concave pit ball, concave pit, U concave pit, and so on.
2.Piston head
The piston refers to the first piston wreath to the part above the piston pin.It has several wreath slots, which are used to install the piston wreath and have an effect of sealing completely. It is also called the leak proof department .The diesel engine’s compress ratio is high, and generally have four wreath slots, The three upper wreaths are used to install, the lower part installs the oil wreath. The gasoline machine has three wreath slots generally, which are two jet of gas wreath slots and an oil wreath slots. At the bottom of oil wreath slot many paths toward eyelet are drilled to make the quilt oil wreath flow from the air cylinder wall? to the oil bottom hull through these eyelets. The working condition of the wreath slot is the worst and should leave the coping generally a little farther.
Above the gas wreath, a narrow insulating slot is usually set to cut off the heat flow which is spread from the piston coping to the first gas wreath and make parts of calories from a piston wreath spread, thus easing the hot burden of the first gas wreath. On some engines small wreathe slots are often made between the coping head and the first gas wreathe, sometimes till a few more wreath. This kind of small wreath can adsorb the lubricant because it accumulates the carbon. It can keep piston and the air cylinder walls from biting to match when it work in the condition of losing oil, so it is called accumulating the carbon slot.
? The calories that the piston coping absorbs also mainly passes the air cylinder wall through the piston wreath to leak proof department, again spread by the cool water.In a word, the function of the piston head is in addition to install the piston wreath, still seal completely function and transmit heat function, sealing completely the air cylinder together with the piston wreath, keeping combustible admixture spirit from leak crankcase, at the same time pass the(70-80)%calories to the air cylinder wall through the piston wreath.
3. Piston skirt department
The piston skirt department refers to the parts from the bottom of the oil wreathe slot. It includes the pin which is used to pack the piston. The piston skirt department exercises to rise to lead to the function to the piston in the back and forth in the air cylinder, and bear the side pressure. The length of the skirt department is decided by the size and the piston diameter of the side pressure. The so-called side pressure mean in the compression route of travel and make route of travel of efficacy .The level component of the gas pressure which take effect on the piston coping presses the piston to the air cylinder wall. Compress the route of travel and make the side pressure direction of the efficacy route of travel air exactly the opposite, because of the combustion pressure consumedly high in compress the pressure, so, make the side in the route of travel of efficacy pressure also consumedly high in compress the side in the route of travel pressure. Two on the sides that bear the side pressure of the piston skirt department be called to push the dint to face, they be placed in to sell the mutually perpendicular direction of the stalk line with piston up.
Structure characteristics:
? (1) make into oval in advance:
The wall thick of the piston skirt department is bigger along the direction of the pin and the hot inflation have great capacity. While working under the common function of hot burden and the side pressure the skirt ministry becomes the oval pillar form. Following the piston to pin direction it has the elongation slightly, but the perpendicularity pin direction it has slightly short. In order to make piston in working condition still keep the cylinder form and prevent from resulting in piston choked to death or the part wore away big because of oval transform, the piston skirt department processes generally and in advance oval, its major axis and pistons sell the stalk direction perpendicular. In order to reduce the heat transform around the piston, we can also make the surface of skirt cast into bottom to sink the 0.5-1 mms
In order to make both sides of skirt bear the air pressure and keeping with air cylinder small but safety of cleft, while working the piston must have right of cylinder form. But, because the thickness of the piston skirt department is very asymmetry, the piston pin the metals of a bore part thick, be subjected to the hot inflation to have great capacity, follow the piston to sell a stalk line direction of transform to have great capacity in other directions. Moreover, the function that bears the air side pressure, causes the piston to transform the more perpendicular piston of quantity pin the direction big.
Thus, if the piston in cold state hour skirt department is a circular, while working the piston will become on oval, making a circumference cleft of the piston and air cylinder not equal, resulting in piston block in the air cylinder and the machine can't work normally. Therefore, while processing we make the piston skirt department into the oval shape in advance. The direction of oval major axis is perpendicular with the pin. The direction of the minoraxis follows the direction of the pin. Thus while working the piston work tend the near positive circle.
(2)The temperate of the piston along the direction of the length is very asymmetry. The temperature of the upper part of the piston is high, the lower part is low, it is upper part that the inflation quantity also correspond big, the lower part is small. In order to make the piston top and bottom diameter tend equal, that is to say the cylinder form, must make the piston into the top smaller the bottom the big stairs form in advance, taper.
(3) In order to reduce the calories of the piston skirt department ,we usually open the hot slot horizontally in the skirt department. In order to compensa the skirt department after be subjected to the heat of transform the quantity, the skirt department opens lengthways of inflation slot. The shape of the slot contain" T" form or" Π " form slots. The horizontal slot opens generally under most the underneath of a wreath slot, both the edge pin sides ( also opened in the oil wreath slot) of on the skirt department so as to reduce the head calories delivered toward the skirt department, so it is called separating the hot slot. The vertical slot will make the skirt department have the certain flexibility so as to the possibly small cleft with the air cylinder while thus making piston assemble, but at hot state have the in expiation of function again, result in piston choked to death in the air cylinder unlikely, past be called vertical slot inflation slot. The skirt department will make it open a side of the slot after open the vertical slot just the degree diminish, bearing the side a side that pressure is smaller in assemble should make it locate make route of travel of efficacy .The diesel engine piston is subjected to the dint big, the skirt department does not open the slot generally.
(4) In order to ease the weight some pistons slice one part in both sides that opens the bore or is free from the side pressure to the skirt department, to eliminate the inertial dint, to reduce neighborhood of heat transform the quantity, and form drag along the plank type piston or short piston.The flexibility between of the plank structure skirt is good, the quantity is small, the matching cleft between the piston and air cylinder is smaller, so it is applicable to the high speed engine.
(5)In order to reduce the hot inflation degree of the aluminum metal alloy? piston skirt department, some gasoline? machine piston imbeds the steel slice in the piston skirt department or pin. The structure characteristics of the permanent model steel is as the permanent model steel is the low carbon iron nickel metal alloy with33% ～ 36% nickel, its coefficient of expansion is only 1/10 of that of aluminum metal alloy. But pin through the permanent model steel slice and the skirt departments connect with each other and curb the degree of the coefficient of expansion.
(6) the gasoline that have is on board, the center line of the piston pin is to deviate the piston center? line flat surface, subjected to the main side in the route of travel of efficacy a square of the pressure partial to move the 1-2 mms. This kind of structure can make piston compare in from compress route of travel go to make route of travel of efficacy mildly from press toward air cylinder of a the noodles transfer to press toward air cylinder of another one side, reducing the sound of knocking the urn. While installing, the direction that this kind of piston pin is partial to place can't pack anti-, otherwise change to pound the dint and will enlarge, making the skirt department damaged
中文翻譯：
發(fā)動(dòng)機(jī)活塞連桿組—活塞詳解
活塞連桿組由活塞、活塞環(huán)、活塞銷、連桿、連桿軸瓦等組成。
一、功用：
活塞的功用是承受氣體壓力，并通過活塞銷傳給連桿驅(qū)使曲軸旋轉(zhuǎn)，從而氣缸里面的吸氣、排氣等過程?；钊敳窟€是燃燒室的組成部分。
活塞的工作條件：活塞在高溫、高壓、高速、潤(rùn)滑不良的條件下工作?；钊苯优c高溫氣體接觸，瞬時(shí)溫度可達(dá)2500K以上，因此，受熱嚴(yán)重，而散熱條件又很差，所以活塞工作時(shí)溫度很高，頂部高達(dá)600～700K，且溫度分布很不均勻；活塞頂部承受氣體壓力很大，特別是作功行程壓力最大，汽油機(jī)高達(dá)3～5MPa，柴油機(jī)高達(dá)6～9MPa，這就使得活塞產(chǎn)生沖擊，并承受側(cè)壓力的作用，因此，活塞應(yīng)有足夠的耐熱性，要盡量減小活塞的受熱面，加強(qiáng)活塞的冷卻，適當(dāng)增大傳熱面，使活塞頂部的最高溫度下降，以便保護(hù)活塞頭。活塞在氣缸內(nèi)以很高的速度(8～12m/s)往復(fù)運(yùn)動(dòng)，且速度在不斷地變化，這就產(chǎn)生了很大的慣性力，使活塞受到很大的附加載荷?；钊谶@種惡劣的條件下工作，會(huì)產(chǎn)生變形并加速磨損，還會(huì)產(chǎn)生附加載荷和熱應(yīng)力，同時(shí)受到燃?xì)獾幕瘜W(xué)腐蝕作用。因此， 為了減小往復(fù)慣性力，必須盡可能地減輕活塞的重量。活塞是在高溫、高壓、高速（活塞平均速度可達(dá)101115m/s）的條件下工作的，其潤(rùn)滑條件較差，活塞與氣缸壁間摩擦嚴(yán)重。為減小摩擦，活塞表面必須光滑、耐磨。
要求：(1) 要有足夠的剛度和強(qiáng)度，傳力可靠；
(2) 導(dǎo)熱性好，耐高壓、耐高溫、耐磨損；
(3) 質(zhì)量小，重量輕，盡可能減小往復(fù)慣性力。
鋁合金材料基本上滿足上面的要求，因此，活塞一般都采用高強(qiáng)度鋁合金，但在一些低速柴油機(jī)上采用高級(jí)鑄鐵或耐熱鋼也符合要求。
2、 構(gòu)造：
活塞可分為三部分，活塞頂部、活塞頭部和活塞裙部。
1.活塞頂部
活塞頂部承受氣體壓力，它是燃燒室的組成部分，其形狀、位置、大小都和燃燒室的具體形式有關(guān)，都是為滿足可燃混合氣形成和燃燒的要求，其頂部形狀可分為四大類，平頂活塞、凸頂活塞、凹頂活塞和成型頂活塞。
加工最簡(jiǎn)單的是平頂活塞，它的頂部是一個(gè)平面，結(jié)構(gòu)簡(jiǎn)單，制造起來較容易，受熱面積小，加工簡(jiǎn)單，頂部應(yīng)力分布較為均勻，一般用在汽油機(jī)上，柴油機(jī)很少采用。
凸頂活塞多用于二沖程內(nèi)燃機(jī)上，它有利于改善換氣過程?，F(xiàn)代四沖程汽油機(jī)為了增強(qiáng)擠氣效果或增大壓縮比也有采用凸頂活塞。凸頂活塞頂部凸起呈球頂形，其頂部強(qiáng)度高，起導(dǎo)向作用，有利于改善換氣過程，二行程汽油機(jī)常采用凸頂活塞。
凹頂活塞頂部呈凹陷形，凹坑的形狀和位置必須有利于可燃混合氣的燃燒，從而提高燃料的利用率。他的內(nèi)型有雙渦流凹坑、球形凹坑、U形凹坑等等。
1. 活塞頭部
活塞頭部是活塞環(huán)槽以上的部分。其主要作用是承受氣體壓力，并傳給連桿；與活塞環(huán)一起實(shí)現(xiàn)對(duì)氣缸的密封；將活塞頂所吸收的熱量通過活塞環(huán)傳給氣缸壁。?它有數(shù)道環(huán)槽，用以安裝活塞環(huán)，起密封作用，又稱為防漏部。柴油機(jī)壓縮比高，一般有四道環(huán)槽，上部三道安裝氣環(huán)，下部安裝油環(huán)。汽油機(jī)一般有三道環(huán)槽，其中有兩道氣環(huán)槽和一道油環(huán)槽，在油環(huán)槽底面上鉆有許多徑向小孔，使被油環(huán)從氣缸壁上刮下的機(jī)油經(jīng)過這些小孔流回油底殼。第一道環(huán)槽工作條件最惡劣，一般應(yīng)離頂部較遠(yuǎn)些。
在第一道氣環(huán)的上方往往開有一道較窄的隔熱槽，隔斷由活塞頂部傳向第一道氣環(huán)的熱流，使部分熱量由第二、三道活塞環(huán)傳出，從而減輕第一道氣環(huán)的熱負(fù)荷。有的發(fā)動(dòng)機(jī)，在活塞頂面至第一道環(huán)槽之間，有時(shí)一直到以下幾道環(huán)槽處，常加工出細(xì)小的環(huán)行槽。這種細(xì)小的環(huán)行槽可以因積碳而吸附潤(rùn)滑油，在失油工作時(shí)可防止活塞與氣缸壁的咬合，故稱之為積碳槽。
活塞頂部吸收的熱量主要也是經(jīng)過防漏部通過活塞環(huán)傳給氣缸壁，再由冷卻水傳出去?？傊?，活塞頭部的作用除了用來安裝活塞環(huán)外，還有密封作用和傳熱作用，與活塞環(huán)一起密封氣缸，防止可燃混合氣漏到曲軸箱內(nèi)，同時(shí)還將(70～80)%的熱量通過活塞環(huán)傳給氣缸壁，以免氣缸內(nèi)的溫度過高，減小對(duì)缸體材料所產(chǎn)生的不利。
2.活塞裙部
活塞裙部指從油環(huán)槽下端面起至活塞最下端的部分，它包括裝活塞銷的銷座孔?；钊共繉?duì)活塞在氣缸內(nèi)的往復(fù)運(yùn)動(dòng)起導(dǎo)向作用，并承受缸體的側(cè)壓力。裙部的長(zhǎng)短取決于側(cè)壓力的大小和活塞直徑。所謂側(cè)壓力是指在壓縮行程和作功行程中，作用在活塞頂部的氣體壓力的水平分力使活塞壓向氣缸壁。壓縮行程和作功行程氣體的側(cè)壓力方向正好相反，由于燃燒壓力大大高于壓縮壓力，所以，作功行程中的側(cè)壓力也大大高于壓縮行程中的側(cè)壓力?；钊共砍惺軅?cè)壓力的兩個(gè)側(cè)面稱為推力面，它們處于與活塞銷軸線相垂直的方向上。
結(jié)構(gòu)特點(diǎn)：
(1）預(yù)先做成橢圓形：
活塞裙部沿銷座方向壁厚較大，熱膨脹量大。工作時(shí)在熱負(fù)荷和側(cè)壓力的共同作用下裙部會(huì)變成橢圓柱形，沿活塞銷軸方向略有伸長(zhǎng)，而垂直銷軸方向略有所短。為了使活塞在工作狀態(tài)下仍保持圓柱形，防止因橢圓變形而造成活塞卡死或局部磨損過大，活塞裙部一般預(yù)先加工成橢圓形，其長(zhǎng)軸與活塞銷軸方向垂直。為了減小活塞銷座附近的熱變形，還可以將銷座的裙部表面鑄成下陷0.5—1mm。
為了使裙部?jī)蓚?cè)承受氣體壓力并與氣缸保持小而安全的間隙，要求活塞在工作時(shí)具有正確的圓柱形。但是，由于活塞裙部的厚度很不均勻，活塞銷座孔部分的金屬厚，受熱膨脹量大，沿活塞銷座軸線方向的變形量大于其他方向。另外，裙部承受氣體側(cè)壓力的作用，導(dǎo)致沿活塞銷軸向變形量較垂直活塞銷方向大。這樣，如果活塞冷態(tài)時(shí)裙部為圓形，那么工作時(shí)活塞就會(huì)變成一個(gè)橢圓，使活塞與氣缸之間圓周間隙不相等，造成活塞在氣缸內(nèi)卡住，發(fā)動(dòng)機(jī)就無法正常工作。因此，在加工時(shí)預(yù)先把活塞裙部做成橢圓形狀。橢圓的長(zhǎng)軸方向與銷座垂直，短軸方向沿銷座方向。這樣活塞工作時(shí)趨近正圓，從而減小活塞與缸體的摩擦力。
(2）預(yù)先做成預(yù)先做成階梯形、錐形
活塞沿高度方向的溫度很不均勻，活塞的溫度是上部高、下部低，膨脹量也相應(yīng)是上部大、下部小。為了使工作時(shí)活塞上下直徑趨于相等，即為圓柱形，就必須預(yù)先把活塞制成上小下大的階梯形、錐形，有利于活塞的運(yùn)動(dòng)。
(3）為了減小活塞裙部的受熱量，通常在裙部開橫向的隔熱槽，為了補(bǔ)償裙部受熱后的變形量，裙部開有縱向的膨脹槽。槽的形狀有"T"形或"Π"形槽。橫槽一般開在最下一道環(huán)槽的下面，裙部上邊緣銷座的兩側(cè)(也有開在油環(huán)槽之中的)，以減小頭部熱量向裙部傳遞，故稱為隔熱槽。豎槽會(huì)使裙部具有一定的彈性，從而使活塞裝配時(shí)與氣缸間具有盡可能小的間隙，而在熱態(tài)時(shí)又具有補(bǔ)償作用，不致造成活塞在氣缸中卡死，故將豎槽稱為膨脹槽。裙部開豎槽后，會(huì)使其開槽的一側(cè)剛度變小，在裝配時(shí)應(yīng)使其位于作功行程中承受側(cè)壓力較小的一側(cè)。柴油機(jī)活塞受力大，裙部一般不開槽。
（4）有些活塞為了減輕重量，在裙部開孔或把裙部不受側(cè)壓力的兩邊切去一部分，以減小慣性力，減小銷座附近的熱變形量，形成拖板式活塞或短活塞。拖板式結(jié)構(gòu)裙部彈性好，質(zhì)量小，活塞與氣缸的配合間隙較小，適用于高速發(fā)動(dòng)機(jī)。短板式結(jié)構(gòu)裙一般用于低速發(fā)動(dòng)機(jī)。
（5）為了減小鋁合金活塞裙部的熱膨脹量，有些汽油機(jī)活塞在活塞裙部或銷座內(nèi)嵌入鋼片。恒范鋼片式活塞的結(jié)構(gòu)特點(diǎn)是，由于恒范鋼為含鎳33%～36%的低碳鐵鎳合金，其膨脹系數(shù)僅為鋁合金的1/10，而銷座通過恒范鋼片與裙部相連，牽制了裙部的熱膨脹變形量，有利于保持活塞的基本尺寸，減小摩擦。
（6）有的汽油機(jī)上，活塞銷孔中心線是偏離活塞中心線平面的，向作功行程中受主側(cè)壓力的一方偏移了1～2mm。這種結(jié)構(gòu)可使活塞在從壓縮行程到作功行程中較為柔和地從壓向氣缸的一面過渡到壓向氣缸的另一面，以減小敲缸的聲音。在安裝時(shí)，這種活塞銷偏置的方向不能裝反，否則換向敲擊力會(huì)增大，使裙部受損。
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