0134-乘用轎車驅(qū)動(dòng)橋設(shè)計(jì)
0134-乘用轎車驅(qū)動(dòng)橋設(shè)計(jì),轎車,驅(qū)動(dòng),設(shè)計(jì)
原文：
Engine Lubricating System
There are a great many moving metal parts in the engine . These parts must be protected by lubricating oil so that there will be protected by lubricating oil so that there will be no actual metal-to-metal contact . The moving parts , in effect , float on films of oil .
Two types of lubricating systems have been used on four-cycle automotive engines , splash and combination splash and pressure feed .
In the splash lubricating system , oil is splashed up from the oil pan or oil trays in the lower part of the crankcase .The oil is thrown upward so droplets or fine mist and provides adequate lubrication to valve mechanisms , piston pins , cylinder walls , and piston rings .
In the splash lubricating system , oil is splashed up from the oil pan or oil trays in the lower part of the crankcase . The oil is thrown upward as droplets or fine mist and provides adequate lubrication to valve mechanisms , piston pins , cylinder walls , and piston rings .
In the combination splash and pressure feed lubricating system , an oil pump takes oil from the oil from the oil pan and forces it through holes drilled in the engine block and crankshaft .
This oil thereby reaches the various bearings that support rotating shafts and the different moving parts in the engine . It covers the surfaces of the moving parts to prevent metal-to-metal contact and undue wear of the parts .
In this system , cylinder walls are lubricated by splashing oil thrown off from the connecting –rod bearing .
The lubricating oil circulating through the engine to all moving parts requiring lubrication performs other jobs .
(1)?? Lubricate moving parts to minimize wear .
(2)?? Lubricate moving parts to minimize power loss from friction
(3)?? Remove heat from engine parts by acting as a cooling agent .
(4)?? Absorb shocks between bearings and other engine parts , thus reducing engine noise and extending engine life .
(5)?? Form a good seal between piston rings and cylinder walls .
(6)?? Act as a cleaning agent , washing the working surfaces free of chemical deposits , dust and dirt to protect them from corrosion .
A satisfactory engine lubricating oil must have certain characteristics , or properties . It must have proper viscosity (body and fluidity ) and must resist oxidation , carbon formation , corrosion , rust , extreme pressures , and foaming . Also , it must act as a good cleaning agent , must pour at low temperatures , and must have good viscosity at extremes of high and low temperature .
Any mineral oil , by itself , does not have all these properties . Lubricating-oil manufacturers therefore put a number of additives into the oil during the manufacturing process .A oil for severe service may have many additives , as follows :
(1)?? usually a viscosity-index improver ;
(2)?? pour-point depressants;
(3)?? oxidation inhibitors ;
(4)?? corrosion inhibitors ;
(5)?? rust inhibitors ;
(6)?? foam inhibitors ;
(7)?? detergent-dispersants ;
(8)extreme-pressure agents.
Valves and Valves Train
Valves and Valve Train
There are two openings , or ports , in the enclosed end of the cylinder . One of the ports permits the mixture of air and gasoline vapor to enter the cylinder . The other port permits the burned gases , after combustion , to exhaust , or escape , from the cylinder . The two pores have valves assembled into them . These valves close off one or the other port , or both ports , during the various stages of engine operation . That is to say , each cylinder has two valves , an intake valve and exhaust valve . The cam lobes on the camshaft are so related to the crankshaft crankpins through the gears or sprockets and chain as to cause the valves to open and close with the correct relationship to the piston strokes .
The valves are nothing more than accurately machined metal plugs (on long stems ) that close the openings when they are seated ( have moved up into the openings ) . When the valve closes , it moves up so that the outer edge rests on the seat . In this position , the valve port is closed so that air or gas cannot escape from the cylinder .
A spring on the valve stem tends to hold the valve on its seat ( closed ) . The lower end of the spring rests against the cylinder head . The upper end rests against a flat washer , or spring retainer which is attached to the valve stem by a retainer lock ( also called a keeper ) . The spring is under compression , which means that it tries to expand and therefore spring-loads the valve in the closed position .
A valve-opening mechanism opens the valve , or lifts it off its seat , at certain times . On most engines , this mechanism , called the valve train , includes a cam on the camshaft , a valve lifter , a push rod ,and a rocker arm . As the camshaft turns , the cam lobe comes around under the value lifter . This raises the lifter , which in turn pushes upward on the push rod . The push rod , as it is lifted , causes the end of the rocker arm to move up . The rocker arm pivots around its supporting shaft so that the valve end of the rocker arm is forced downward . This downward movement forces the valve to move downward off its seat so that it opens . After the cam lobe moves out from under the valve lifter , the valve spring forces the valve up onto its seat again .
In the other kind of valve mechanism for an engine , the valves are located in the cylinder block instead of the head . With this arrangement , the camshaft is directly below the valve lifter , and no push rods or rocker arms are necessary . Although the valve-in-block arrangement is a simple design . Most automotive engines are the valve-in-head type . The valve-in-head engine has certain advantages .
Cam and Camshaft
A cam is a device that can change rotary motion into linear , or straight-line , motion . The cam has a high spot , or lobe ; a follower riding on the cam will move away from or toward the camshaft as the cam rotates . In the engine , cams on the camshaft cause the intake and exhaust valves to open . There is s cam on the camshaft for each valve , or two cams per cylinder . The camshaft is driven by gears , or by a chain , from the crankshaft . It turns at one-half crankshaft speed . In the four –cycle engine , every two revolutions of the crankshaft produce one revolution of the camshaft and one opening and closing . The cam lobes are so positioned on the camshaft as to cause the valves to open and close in the cylinders at the proper time with respect to the actions taking place in the cylinders .
In addition , the camshaft has an eccentric to operate the fuel pump and a gear to drive the ignition distributor and oil pump .
Piston Connecting Rod
Piston
The piston is essentially a cylindrical plug that moves up and down in the engine cylinder . it is equipped with piston rings to provide a good seal between the cylinder wall and piston . The piston absorbs heat from the gas , and this heat must be carried away if the metal temperature is to be held within safe limits . The constant reversal of the piston travel sets up inertia forces , which increase both with the weight of the piston and with its speed . For this reason , designers try to keep piston weight low , particularly in high-speed engines . As lower hood lines and over square engines became popular , the semi-slipper and full-slipper pistons came into use . On these pistons the number piston rings was reduced to three , two compression and one oil-control . One reason for the slipper piston is that , on the short-stroke , over square engine , the piston skirt had to be cut away to make room for the counterweights on the crankshaft . Also , the slipper piston , being shorter and having part of its skirt cut away , is lighter . This reduces the inertia load on the engine bearings and , in addition , makes for a more responsive engine . The lighter the piston , the less the bearing load and the longer the bearings will last . Another way to lighten the piston is to make it lf light metal . The ideal piston material would be light and strong , conduct heat well , expand only slight when heated , resist wear ,and be low in cost .Thus , most automotive-engine pistons today are made of aluminum , which is less than half as heavy as iron . Iron pistons were common in the earlier engines . Aluminum expands more rapidly than iron with increasing temperature , however , and since the cylinder block is lf iron , special provisions must be made to maintain proper piston clearance at operating temperatures. To take care of it , the crown is machined on slight taper , the diameter being greatest where the crown meets the skirt and becoming less toward the top .
Piston Rings
A good seal must be maintained between the piston and cylinder wall to prevent blow-by . “ blow-by ” is the name that describes the escape of burned gases from the combustion chamber , past the piston , and into the crankcase . In other words , these gases “blow by ” the piston .It is not practical to fit the piston to the cylinder closely to prevent blow-by . Thus , piston rings must be used to provide the necessary seal . The rings are installed in grooves in the piston . Actually , there are two types of rings , compression rings and oil-control rings , The compression rings seal in the air-fuel mixture as it is compressed and also the combustion pressures as the mixture burns. The oil-control rings scrape off excessive oil from the cylinder wall and return it to the oil pan.
The rings have joints (they are split ) so that they can be expanded and slipped over the piston head and into the recessed grooves cut in the piston . Rings for automotive engines usually have butt joints , but in some heavy –duty engines , the joints may be angled ,lapped , or of the sealed type .
The rings are somewhat larger in diameter than they will be when en the cylinder . Then ,when they are installed , they are compressed so that the joints are nearly closed . Compressing the rings gives them an initial tension ; they press tightly against the cylinder wall .
Connecting Rod
The connecting rod is attached at one end to a crankpin on the crankshaft and at the other end to a piston , through a piston pin or wrist pin . The connecting rod must be very strong and rigid and also as light as possible . The connecting rod carries the power thrusts from the pioton to the crankpin . At the shame time , the rod is in eccentric motion . To minimize vibration and bearing loads , the rod must be light in weight . To maintain good engine balance , connecting rods and caps are individually matched to each other and usually carry identifying numbers so they will not be mixed if the engine is disassembled for service . They must mot be mixed during any service job , since this could result in poor bearing fit and bearing failure .
Crankshaft Flywheel
Crankshaft
The crankshaft is a one-piece casting or forging of heat-treated alloy steel of considerable mechanical strength . The crankshaft must be strong enough to take the down ward thrusts of the pistons during the power strokes without excessive distortion . In addition , the crankshaft must be carefully balanced to eliminate undue vibration resulting from the weight of the offset cranks . To provide balance , crankshafts have counterweights opposite the cranks . Crankshafts have drilled oil passages through which oil can flow from the main to the connecting-rod bearings .
The front end of the crankshaft carries three devices , the gear or sprocket that drives the camshaft , the vibration damper , and the fan belt pulley . The camshaft , the vibration damper , and the fan belt pulley . The pulley drives the engine fan , water pump ,and generator with a V belt .
Flywheel
The flow of power from the engine cylinders is not smooth .Although the power impulses cylinders is not smooth . Although the power impulses overlap ( on six-and eight-cylinder engines ) , there are times when more power is being delivered than at other times . This tends to make the crankshaft speed up and then slow down . However , the flywheel combats the tendency . The flywheel is a comparatively heavy wheel bolted to the tear end of the crankshaft . The inertia of the flywheel tends to keep it turning at constant speed . Thus , the flywheel absorbs energy as the crankshaft tries to slow down . In effect , the flywheel absorbs power from the engine during the power stroke( or speedup time ) and then gives it back to the engine during the other three strokes ( or slowdown time ) of the cycle .
譯文
發(fā)動(dòng)機(jī)潤滑系統(tǒng)
發(fā)動(dòng)機(jī)中有大量的運(yùn)動(dòng)的金屬零件。要保護(hù)這些零件就必須進(jìn)行潤滑，這樣可以避免金屬零件之間的直接接觸。實(shí)際上，在運(yùn)動(dòng)零件的表面總是覆蓋著一層油膜。
四行程發(fā)動(dòng)機(jī)使用兩種潤滑系統(tǒng)：飛濺式潤滑和飛濺壓力結(jié)合送油式潤滑。
在飛濺潤滑系統(tǒng)中，油從機(jī)體下部的油盤或油底殼中飛濺上來。飛濺上來的油形成油滴或油霧，使氣門機(jī)構(gòu)、活塞銷、氣缸壁和活塞環(huán)得到充分的潤滑。
在飛濺壓力結(jié)合送油潤滑系統(tǒng)中，油泵從油盤中把油抽上來并壓入發(fā)動(dòng)機(jī)機(jī)體上和曲軸上的油道，被輸送到發(fā)動(dòng)機(jī)的曲軸和各種運(yùn)動(dòng)的零件的每個(gè)軸承上。潤滑油在運(yùn)動(dòng)零件表面形成油膜，以防止金屬零件表面直接接觸以及零件的過度磨損。
在這一系統(tǒng)中，氣缸壁是由連桿軸承運(yùn)動(dòng)飛濺起來的油進(jìn)行潤滑的。潤滑油在發(fā)動(dòng)機(jī)的所有活動(dòng)部件之間循環(huán)流動(dòng)，其作用為：
1.??? 潤滑運(yùn)動(dòng)零件，減少磨損。
2.??? 潤滑運(yùn)動(dòng)零件，減少因磨損因素起的功率損耗。
3.??? 其冷卻劑作用，帶走發(fā)動(dòng)機(jī)零件產(chǎn)生的熱量。
4.??? 吸收軸承和其他發(fā)動(dòng)機(jī)零件之間產(chǎn)生的沖擊力，減少發(fā)動(dòng)機(jī)的噪音，并延長其壽命。
5.??? 在活塞環(huán)和氣缸壁之間形成良好的密封。
6.??? 起清潔劑作用，沖洗運(yùn)動(dòng)零件表面的化學(xué)雜質(zhì)、灰塵和污物，以避免部件受到腐蝕。
理想的發(fā)動(dòng)機(jī)潤滑油必須具有某些特性：必須具有一定的粘性（粘稠度和流動(dòng)性），并且必須具有抗氧化、防止碳膜生成、防腐、防銹、抗極壓和防泡沫等作用，潤滑油必須具有良好清潔作用和良好的低溫流動(dòng)性，以及在高溫和低溫時(shí)都具有良好的粘性。
任何礦物油自身都不具備所有這些特性。因此，潤滑油廠家在制造潤滑油的過程中，加入了許多添加劑。高級(jí)潤滑油中可能加入以下這些添加劑：
（1）常常加入黏度指數(shù)添加劑；(2)抗凝劑；（3）抗氧劑；（4）防腐劑；（5）防銹劑；（6）抗泡劑；（7）凈化分散劑；（8）極壓擠。
氣門與氣門傳動(dòng)組
氣門和氣門機(jī)構(gòu)
在汽缸封閉的一端，有兩個(gè)開口，或稱為孔。一個(gè)開口使可燃混合氣可以及時(shí)進(jìn)入氣缸。另一個(gè)開口是讓燃燒后的氣體從氣缸內(nèi)排出。這兩個(gè)開口都裝有氣門。這些氣門在發(fā)動(dòng)機(jī)工作順序的不同階段，關(guān)閉一個(gè)開口，（或另一個(gè)開口），或者同時(shí)關(guān)閉兩個(gè)開口。也就是說，每個(gè)氣缸有兩個(gè)氣門，即進(jìn)氣門和排氣門。凸輪軸上的凸輪凸角通過齒輪或鏈輪和鏈條與曲軸軸頸相連，這樣，可以使氣門按照活塞行程的正確順序開啟和關(guān)閉。氣門不過是裝在閥桿上加工精細(xì)的金屬塞而已。當(dāng)氣門就位時(shí)（向上移動(dòng)閥口）時(shí)，即可將氣門關(guān)閉。氣門關(guān)閉時(shí)，氣門向上移動(dòng)，這樣氣門的邊緣就正好落在氣門座上。在這一位置上，氣門口關(guān)閉，混合氣就不會(huì)從汽缸中逸出。
氣門桿上的彈簧使氣門保持在氣門座上（關(guān)閉狀態(tài)）。彈簧的下端抵在氣缸蓋上。上端抵在彈簧座上，在彈簧座的下面有栓銷（或叫做定位銷）加以定位。彈簧處于“壓縮”狀態(tài)時(shí)，意味著彈簧試圖伸展，氣門受彈簧作用而處于關(guān)閉狀態(tài)。
使氣門開啟的機(jī)械裝置在恰當(dāng)?shù)臅r(shí)刻開啟氣門或者將氣門從氣門座上提起。在大多數(shù)發(fā)動(dòng)機(jī)中，這套裝置的中包括凸輪軸上的一個(gè)凸輪，一個(gè)氣門挺桿，一個(gè)氣門推桿和一個(gè)搖臂。當(dāng)凸輪軸轉(zhuǎn)動(dòng)時(shí)，凸輪凸角轉(zhuǎn)到氣門挺桿下面，使挺桿上舉，挺桿推動(dòng)推桿。當(dāng)推桿升起時(shí)，搖臂的端部向上移動(dòng)。搖臂圍繞支撐軸旋轉(zhuǎn)，氣門與搖臂相對(duì)應(yīng)的一端壓下。向下的運(yùn)動(dòng)使氣門向下移動(dòng)離開氣門座，氣門被打開。當(dāng)凸輪凸角離開氣門挺桿，氣門彈簧使氣門重新回到氣門座上。
另一種氣門機(jī)構(gòu)的氣門是裝在汽缸體上，而不是汽缸蓋上。在這種裝置中，凸輪軸直接裝在氣門挺桿下，并且不必有推桿或搖臂。雖然側(cè)置氣門發(fā)動(dòng)機(jī)結(jié)構(gòu)設(shè)計(jì)簡單，大多數(shù)汽車發(fā)動(dòng)機(jī)卻都是頂置氣門，因?yàn)轫斨檬綒忾T發(fā)動(dòng)機(jī)的確有優(yōu)點(diǎn)。
凸輪和凸輪軸
凸輪是能夠使旋轉(zhuǎn)運(yùn)動(dòng)變?yōu)榫€性或直線運(yùn)動(dòng)的裝置。凸輪有一個(gè)頂點(diǎn)，或叫做凸輪凸角。當(dāng)凸輪轉(zhuǎn)動(dòng)時(shí)，凸輪上的從動(dòng)件也隨著凸輪軸來回移動(dòng)。在發(fā)動(dòng)機(jī)中，凸輪軸上的凸輪控制進(jìn)氣門和排氣門的開啟和關(guān)閉。每個(gè)氣門有一凸輪，每一個(gè)氣缸就有兩個(gè)凸輪。凸輪軸由曲軸通過正時(shí)齒輪或鏈條來驅(qū)動(dòng)。凸輪軸的轉(zhuǎn)速為曲軸轉(zhuǎn)速的一半。在四行程發(fā)動(dòng)機(jī)中，曲軸上凸輪凸角的位置使氣門在恰當(dāng)?shù)臅r(shí)候開關(guān)，以便與氣缸的工作順序相一致。
此外，凸輪軸還帶動(dòng)一個(gè)驅(qū)動(dòng)燃料泵的偏心輪和一個(gè)帶動(dòng)分電器和油泵的齒輪。
活塞 連桿
活塞
實(shí)質(zhì)上活塞是一個(gè)在氣缸中上下移動(dòng)的圓筒狀的塞子，面裝有活塞環(huán),從而使活塞和氣缸之間具有良好的密封性?；钊麖臍怏w中吸熱，假如要使金屬的溫度保持在安全限度以內(nèi)，就必須散熱?；钊牟粩嗤鶑?fù)運(yùn)動(dòng)產(chǎn)生了慣性力，慣性力隨活塞的重量及其速度的增加而增大。為此，設(shè)計(jì)者設(shè)法使活塞造的輕些，特別是高速度發(fā)動(dòng)機(jī)。由于低發(fā)動(dòng)機(jī)罩和短行程發(fā)動(dòng)機(jī)的進(jìn)一步普及，半圍延裙活塞和滑裙式活塞開始使用。在這些活塞中，活塞環(huán)的數(shù)量減少到三個(gè)，即兩個(gè)氣環(huán)，一個(gè)油環(huán)。使用滑裙活塞的原因是：短行程發(fā)動(dòng)機(jī)需除去部分活塞裙部，從而為曲軸的平衡重讓出空間?；瑒?dòng)活塞長度較短，由于裙部被部分切除后而重量較輕。這就減少了發(fā)動(dòng)機(jī)軸承上的慣性負(fù)荷，使動(dòng)機(jī)反應(yīng)更加靈敏?；钊捷p，軸承的負(fù)荷越小,軸承的工作壽命就越長.還有一種可使活塞質(zhì)量減小的方法,就是用輕金屬制造活塞.理想的活塞材料應(yīng)該重量輕,強(qiáng)度高,導(dǎo)熱好,熱膨脹小,耐磨，價(jià)格低廉。因此今天大多數(shù)的汽車發(fā)動(dòng)機(jī)活塞都是鋁制成的，鋁的重量還不到鑄鐵的一半。鑄鐵活塞在早期的發(fā)動(dòng)機(jī)中廣泛使用。隨著溫度的增加，鋁比鑄鐵膨脹量更大。然而，由于氣缸體是鑄鐵制的，必須采用特殊的措施，以維持工作溫度下正常的活塞間隙。考慮到這一點(diǎn)，活塞頂部要加工成略成錐狀體，即活塞頂部與活塞裙部交接處直徑最大，愈向頂部，直徑愈小。
活塞環(huán)
在活塞與氣缸壁之間必須保持良好的密封以防止漏氣。“漏氣”這一名秤是指燃燒氣體從燃燒室溢出，經(jīng)過活塞進(jìn)入曲軸箱。換句話說，這些氣體是通過活塞溢出的。實(shí)際上，活塞與氣缸間再嚴(yán)密也免不了漏氣。所以活塞環(huán)就用來提供必要的密封?；钊h(huán)裝在活塞的凹槽中。事實(shí)上有兩種活塞環(huán)，氣環(huán)和油環(huán)。當(dāng)可燃混合氣壓縮時(shí)，氣環(huán)密封可燃混合氣；當(dāng)可燃混合氣燃燒時(shí)氣環(huán)可阻止所產(chǎn)生的壓力不外溢。油環(huán)的作用是刮去氣缸壁上多余的機(jī)油，使之流回油底殼。
活塞環(huán)有接口（也就是有一縫隙）。這樣可以使端部擴(kuò)張并滑入活塞上的凹槽中。汽車發(fā)動(dòng)機(jī)上的活塞環(huán)通常是有接口。但在一些重型發(fā)動(dòng)機(jī)上，活塞環(huán)的接口可以使斜角接口，搭接式或是密封式的。
活塞環(huán)的直徑要略大于裝入氣缸時(shí)直徑。這樣，在活塞裝入氣缸中時(shí)，活塞環(huán)就會(huì)被壓縮，接頭幾乎閉合了。受壓使之具有預(yù)張力，活塞環(huán)就緊緊的壓在氣缸壁上。
連桿
連桿的一端與曲軸的連桿軸頸相連，另一端通過活塞銷與活塞相連。連桿必須具有足夠的強(qiáng)度和剛度，并且要盡可能輕。連桿的作用是將活塞承受的壓力傳給連桿軸頸。同時(shí)，連桿做偏心運(yùn)動(dòng)。為了把振動(dòng)和軸承負(fù)荷減小到最低限度，連桿的重量必須盡可能的輕。為了保持發(fā)動(dòng)機(jī)的良好平衡，連桿和連桿蓋都要精心配套。發(fā)動(dòng)機(jī)連桿的質(zhì)量都必須相等，否則，就會(huì)產(chǎn)生明顯的振動(dòng)。在進(jìn)行裝配時(shí)，連桿和連桿蓋都必須一一相互匹配。為了防止拆裝發(fā)動(dòng)機(jī)是發(fā)生匹配錯(cuò)誤，通常在部件上刻上標(biāo)號(hào)。在維修過程中，千萬不能弄混，因?yàn)檫@會(huì)造成軸承不配套及軸承的損壞。
曲軸 飛輪
曲軸
曲軸是由合金鋼鑄造或鍛造，經(jīng)過熱處理，具有一定的機(jī)械強(qiáng)度的整體結(jié)構(gòu)。曲軸必須就有足夠的強(qiáng)度，以承受活塞在做功行程期間向下運(yùn)動(dòng)產(chǎn)生的沖力，而不會(huì)產(chǎn)生過度的扭曲。另外，曲軸必須仔細(xì)地給予平衡，以避免曲柄重力偏移而引起過度振動(dòng)。為了保持平衡，曲軸必須具有與曲軸相對(duì)應(yīng)的平衡重。曲軸上鉆有油道，潤滑油可以從主軸承流到連桿軸承上。在曲軸的前端有三個(gè)裝置：驅(qū)動(dòng)凸輪軸的齒輪或鏈輪，減震器和風(fēng)扇皮帶輪。皮帶輪通過V型皮帶驅(qū)動(dòng)發(fā)動(dòng)機(jī)風(fēng)扇，水泵和發(fā)電機(jī)。
飛輪
發(fā)動(dòng)機(jī)氣缸所產(chǎn)生的動(dòng)力是不均勻的。盡管在六缸或八缸發(fā)動(dòng)機(jī)中，動(dòng)力沖擊重疊發(fā)生，但是有時(shí)產(chǎn)生的動(dòng)力會(huì)大些。這會(huì)使曲軸的運(yùn)轉(zhuǎn)速度忽快忽慢。然而飛輪可以克服這種傾向。飛輪是一個(gè)很重的輪子，用螺栓固定在曲軸的后端。飛輪的慣性使飛輪保持恒速運(yùn)動(dòng)。這樣，飛輪在曲軸加速時(shí)把能量儲(chǔ)存起來，當(dāng)曲軸速度減慢時(shí)再釋放出來。事實(shí)上，飛輪在做功行程（或加速過程）中貯存動(dòng)能，而在其它三個(gè)行程（或減慢過程）中，把動(dòng)能釋放出來。
第一章 方案論證
1.1 概 述
驅(qū)動(dòng)橋處于動(dòng)力傳動(dòng)系的末端，不僅是汽車的動(dòng)力傳遞機(jī)構(gòu)，也是行走機(jī)構(gòu)。其基本功能是增大由傳動(dòng)軸或變速器傳來餓轉(zhuǎn)矩，并將動(dòng)力合理地分配給左、右驅(qū)動(dòng)功能。
驅(qū)動(dòng)橋是汽車傳動(dòng)系中的主要總成之一。驅(qū)動(dòng)橋的設(shè)計(jì)是否合理直接關(guān)系到汽車使用性能的好壞。因此，驅(qū)動(dòng)橋設(shè)計(jì)應(yīng)當(dāng)滿足以下基本要求：
1） 所選擇的主減速比應(yīng)能滿足汽車在給定使用條件下具有最佳的動(dòng)力性和燃油經(jīng)濟(jì)性；
2） 差速器在保證左、右驅(qū)動(dòng)車輪能以汽車運(yùn)動(dòng)學(xué)所要求的差速滾動(dòng)外并能將轉(zhuǎn)矩平穩(wěn)而連續(xù)不斷（無脈動(dòng)）地傳遞給左右驅(qū)動(dòng)車輪；
3） 當(dāng)左右驅(qū)動(dòng)車輪與地面的；
4） 在各種轉(zhuǎn)速和載荷下，具有高的傳動(dòng)效率；
5） 在保證足夠的強(qiáng)度、剛度條件下，應(yīng)力求質(zhì)量小，尤其是簧下質(zhì)量應(yīng)盡量小，以改善汽車平順性；
6） 與懸架導(dǎo)向機(jī)構(gòu)運(yùn)動(dòng)協(xié)調(diào)；
7） 結(jié)構(gòu)簡單，加工工藝性好，制造容易，折裝、調(diào)整方便。
驅(qū)動(dòng)橋一般由主減速器、半軸和驅(qū)動(dòng)橋殼組成。各部分功用如下：
主減速器：將低由傳動(dòng)軸傳來的轉(zhuǎn)速并增大扭矩。
差速器：在兩輸出軸間分配轉(zhuǎn)矩并保證兩輸出軸可能以不同的轉(zhuǎn)速旋轉(zhuǎn)。
半軸：接受并傳遞轉(zhuǎn)矩到兩邊驅(qū)動(dòng)車輪。
驅(qū)動(dòng)橋殼：支承汽車整體質(zhì)量，并承受由車輪傳來的由路面不平引起的反力和反力矩，并經(jīng)懸架傳遞給支架或車身。
1.2 驅(qū)動(dòng)橋結(jié)構(gòu)型式及選擇
驅(qū)動(dòng)橋的結(jié)構(gòu)形式與驅(qū)動(dòng)車輪的懸架形式密切相關(guān)。當(dāng)車輪采用非獨(dú)立懸架時(shí)，驅(qū)動(dòng)橋應(yīng)為非斷開式；當(dāng)車輪采用獨(dú)立懸架時(shí)，驅(qū)動(dòng)橋應(yīng)為斷開式?，F(xiàn)把它們各自的結(jié)構(gòu)特點(diǎn)分析（如：表1）：
表 1驅(qū)動(dòng)橋結(jié)構(gòu)型式及選擇
形式
非斷開驅(qū)動(dòng)橋
斷開驅(qū)動(dòng)橋
特點(diǎn)
結(jié)構(gòu)特點(diǎn)
橋殼是一根支承在左、右驅(qū)動(dòng)輪上的剛性空心梁，而主減速器、差速器和半軸等傳動(dòng)部件都裝在其內(nèi)；整個(gè)驅(qū)動(dòng)橋通過懸架與支架或車身連接
橋殼分段，彼此之間用鉸鏈連接，可作相對(duì)運(yùn)動(dòng)；主減速器、差速器等固定在支架或車身上，兩側(cè)驅(qū)動(dòng)輪通過獨(dú)立懸架與支架或車身連接，兩輪可彼此獨(dú)立地相對(duì)于支架或車身上下跳動(dòng)
優(yōu)點(diǎn)
結(jié)構(gòu)簡單，制造工藝性好，成本低，工作可靠，維修和調(diào)整容易
減低簧下質(zhì)量從而改善汽車通過性，提高行使平順性，平均車速提高。降低車輪和車橋上的動(dòng)載荷，提高了零部件的使用壽命。與地面接觸良好，抗側(cè)滑能力提高，汽車的持縱穩(wěn)定性更好
缺點(diǎn)
簧下質(zhì)量大，對(duì)降低動(dòng)載荷不利，平順性差，Hmin小，通過性不好
結(jié)構(gòu)復(fù)雜，成本較高
應(yīng)用
各種貨車、客車及多數(shù)越野車和部分轎車
越野車、轎車
轎車行使的路面條件較好，故采用非斷開式驅(qū)動(dòng)橋
1.3 主減速器設(shè)計(jì)
1.3.1 主減速器結(jié)構(gòu)方案分析
汽車的主減速器有單級(jí)主減速器和雙級(jí)主減速器，減速型式的選擇與汽車的類型及使用條件有關(guān)，有時(shí)也與制造廠已有的產(chǎn)品系列及制造條件有關(guān)，但它主要取決于由動(dòng)力性、經(jīng)濟(jì)性等整車性能所要求的主減速比i0的大小及驅(qū)動(dòng)橋下的離地間隙、驅(qū)動(dòng)橋的數(shù)目及布置型式等。
本車型采用單級(jí)主減速器，由于單級(jí)主減速器具有結(jié)構(gòu)簡單、質(zhì)量小、尺寸緊湊及制造成本低等優(yōu)點(diǎn)，因而廣泛地用在主減速比i0≤7.6的各種中小型汽車上。例如：轎車、輕型載貨汽車都是采用單級(jí)主減速器，大多數(shù)中型載貨汽車也采用這種型式。
而雙級(jí)主減速器由兩級(jí)齒輪副組成，結(jié)構(gòu)復(fù)雜、質(zhì)量加大，制造成本也顯著增加，因此僅用于主減速比較大（7.6＜i0≤12）且單級(jí)減速不能滿足既定的主減速比和離地間隙要求的重型汽車上。以往在某些中型載貨汽車上雖有采用，但在新設(shè)計(jì)的現(xiàn)代中型載貨汽車上已很少見了。這是由于隨著發(fā)動(dòng)機(jī)功率的提高車輛整備質(zhì)量的減小以及路面狀況的改善，中等以下噸位的載貨汽車往往具有更高車速的方向發(fā)展，因而需采用較小主減速比的緣故。
1.3.2 單級(jí)主減速器傳動(dòng)形式分析
單級(jí)主減速器傳動(dòng)形式主要有四種：螺旋錐齒輪傳動(dòng)、雙曲面齒輪傳動(dòng)、圓柱齒輪傳動(dòng)和蝸輪蝸桿傳動(dòng)。它們的傳動(dòng)形式如圖：
（a） (b) (c) (d)
螺旋錐齒輪傳動(dòng) 雙曲面齒輪傳動(dòng) 圓柱齒輪傳動(dòng) 蝸輪蝸桿傳動(dòng)
圖1單級(jí)主減速器傳動(dòng)形式
（一） 螺旋錐齒輪傳動(dòng)
螺旋錐齒輪傳動(dòng)的主、從動(dòng)齒輪軸線垂直相交于一點(diǎn)，齒輪并不同時(shí)在全長上齒合，而是逐漸從一端連續(xù)平穩(wěn)地轉(zhuǎn)移向另一端，另外，由于輪齒端面重疊的影響，至少有兩對(duì)以上的輪齒同時(shí)齒合，所以它工作平穩(wěn)，能承受較大的負(fù)荷，制造也簡單。但在工作中噪聲大，對(duì)齒合精度很敏感，齒輪副錐頂稍有不吻合便會(huì)使工作條件急劇變壞，并伴隨磨損增大而噪聲增大。為保證齒輪副的正確齒合，必須將支承軸承預(yù)緊，提高了支承剛度，增大殼體剛度。
（二） 雙曲面齒輪傳動(dòng)
雙曲面齒輪傳動(dòng)的主、從動(dòng)齒輪的軸線相互垂直而不相交，主動(dòng)齒輪軸線相對(duì)從動(dòng)齒輪軸線在空間偏移一距離E（偏移距），由于偏移距的存在，使主動(dòng)齒輪螺旋角β1大于從動(dòng)齒輪螺旋角β2，從而使雙曲面齒輪傳動(dòng)比大于相同尺寸的螺旋錐齒輪傳動(dòng)比。
（三） 圓柱齒輪傳動(dòng)
圓柱齒輪傳動(dòng)一般采用斜齒輪，廣泛應(yīng)用于發(fā)動(dòng)機(jī)橫置且前置前驅(qū)動(dòng)的轎車驅(qū)動(dòng)橋和雙級(jí)主減速器置通式驅(qū)動(dòng)橋。
（四） 蝸桿蝸輪傳動(dòng)
蝸桿蝸輪傳動(dòng)比較大（i0﹥7）在任何轉(zhuǎn)速使用下均能工作非常平穩(wěn)且無噪聲，便于汽車的總布置及貫通式多橋驅(qū)動(dòng)的布置，能傳遞大的載荷，使用壽命長，結(jié)構(gòu)簡單，折裝方便，調(diào)整容易。但制造成本高，傳動(dòng)效率低，應(yīng)用于重型多橋驅(qū)動(dòng)汽車和具有高轉(zhuǎn)速發(fā)動(dòng)機(jī)的大客車上。
1.3.3 雙曲面齒輪傳動(dòng)與螺旋錐齒輪傳動(dòng)比較選擇
表2從動(dòng)輪的選擇
類型
雙曲面齒輪
螺旋錐齒輪
優(yōu)點(diǎn)
兩者尺寸相同時(shí)，此種齒輪傳動(dòng)比i0大，當(dāng)i0一定且從動(dòng)齒輪尺寸相同時(shí)，此類齒輪直徑大，輪齒強(qiáng)度大，剛度大。當(dāng)i0一定，主動(dòng)齒輪尺寸相同，此類齒輪Hmin較大。此類齒輪有側(cè)向滑動(dòng)和縱向滑動(dòng)，縱向滑動(dòng)可使其運(yùn)轉(zhuǎn)平穩(wěn)。β1>β2，重合度大，可提高傳動(dòng)平穩(wěn)性和彎曲強(qiáng)度。其主動(dòng)齒輪較大，加工時(shí)所需刀盤刀頂距較大，因而切削刃壽命較長。
由于螺旋角較大，摩擦損失較小，傳動(dòng)效率高達(dá)99%，抗膠合能力強(qiáng)，軸承負(fù)荷小，潤滑成本低。
缺點(diǎn)
縱向滑動(dòng)增加摩擦損失，傳動(dòng)效率較低約為96%，抗膠合能力低，軸向力大，軸承負(fù)荷大，潤滑成本高。
同尺寸時(shí)傳動(dòng)比小，同傳動(dòng)比時(shí)齒輪強(qiáng)度和剛度較小。Hmin小。
選取
螺旋錐齒輪傳動(dòng)
1.4 主減速器主、從動(dòng)錐齒輪的支承方案
主減速器中心須保證主、從齒輪具有良好的齒合狀況才能使它們很好地工作，齒輪的正確齒合除與齒輪的加工質(zhì)量、裝配調(diào)整及軸承、主減速器殼體的剛度有關(guān)外，還與齒輪的支承剛度密切相關(guān)。
1.4.1主動(dòng)錐齒輪的支承方案
現(xiàn)代汽車的主動(dòng)錐齒輪的支承型式有懸臂式和騎馬式。懸臂式一其齒輪大端一側(cè)的軸頸支承在相距比齒寬中點(diǎn)的懸臂長大兩倍以上的一對(duì)軸承上；騎馬式在齒輪小端前增裝一個(gè)稱為導(dǎo)向軸承的圓柱滾子軸承，且大端一側(cè)的軸承靠近，也稱兩端支承式和跨置式。
懸臂式支承通常用在傳動(dòng)轉(zhuǎn)矩較小的轎車、輕型貨車上。在中型和重型貨車上的雙級(jí)主減速器中，由于布置空間的困難，也采用這種支承方式。
采用跨置式支承時(shí)齒輪承載能力較懸臂式支承提高10%左右，提高了支承剛度，并使軸承負(fù)荷減小，改善齒輪嚙合條件。此外，由于齒輪軸頸上的兩個(gè)圓錐滾子軸承間距很小，可以縮短主動(dòng)齒輪軸的長度，使布置更緊湊，并可減少傳動(dòng)軸夾角，有利于整車布置。但是，由于主、從動(dòng)錐齒輪間的空間有限，致使主動(dòng)錐齒輪小端處的支承座和軸承尺寸受到限制。增加了主動(dòng)錐齒輪小端前支承后也給主減速器殼體的鑄造及機(jī)械加工帶來了困難。目前，跨置式支承主要用在需要傳遞較大扭矩的情況下，在中型和重型的單級(jí)主減速器中得到廣泛的應(yīng)用。
參考所選車型屬于轎車，因此主減速器主動(dòng)錐齒輪采用懸臂式支承。
1.4.2從動(dòng)錐齒輪的支承選擇
影響因素：軸承的支承形式，軸承間的距離，軸承上的載荷分布。因?yàn)檩d貨汽車主動(dòng)錐齒輪的支承采用懸臂式支承。從動(dòng)錐齒輪的支承采用圓錐滾子軸承支承，兩軸承的圓錐滾子大端向內(nèi)，以增加支承剛度。這樣即滿足了要求又節(jié)約了成本。
1.5 差速器設(shè)計(jì)
汽車在行駛過程中，左右車輪在同一時(shí)間內(nèi)所滾過的路程往往是不相等的，特別是在轉(zhuǎn)彎時(shí)外車輪比內(nèi)車輪滾過的路程多，如果兩車輪剛性連接，則會(huì)引起車輪在路面上滑拖或滑轉(zhuǎn)，這樣，一方面會(huì)加劇車輪磨損、功率和燃料消耗，另一方面會(huì)使轉(zhuǎn)向沉重，通過性和操作穩(wěn)定性變壞。為此，在左右車輪間裝有輪間差速器。差速器用來在兩輸出軸間分配轉(zhuǎn)矩，并保證兩輸出軸有可能以不同角度轉(zhuǎn)動(dòng)。
差速器結(jié)構(gòu)形式選擇：汽車差速器的結(jié)構(gòu)形式很多，用得最廣泛的是對(duì)稱式圓錐行星齒輪差速器，大多數(shù)汽車都屬于公路運(yùn)輸車輛，對(duì)于在公路上和市區(qū)行駛的汽車來說，如大客車，由于路面較好，各驅(qū)動(dòng)車輪與路面的附著系數(shù)變化很小，因此幾乎都采用了結(jié)構(gòu)簡單、工作平穩(wěn)、制造方便，用于公路汽車也很可靠的普通對(duì)稱式圓錐行星齒輪差速器，作為安裝在左右驅(qū)動(dòng)輪間的所謂輪間差速器作用，對(duì)于經(jīng)常行駛在泥濘、松軟土路或無路地區(qū)的越野汽車來說，為了防止因某一側(cè)驅(qū)動(dòng)車輪滑轉(zhuǎn)而陷車，則可采用防滑差速器，后者又可分為強(qiáng)制鎖止式和自鎖式兩類。自鎖式差速器又有多種結(jié)構(gòu)形式的高摩擦式和自由輪式的以及變傳動(dòng)式的。
選?。浩胀▽?duì)稱式圓錐行星齒輪。
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