汽车实用英语已整理.docx

汽车实用英语已整理.docx

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汽车实用英语已整理

ValvesandValveTrain

Thevalvegearofaninternalcombustionengineprovidestimelyadmissionofthefreshchargeintothecylindersandexhaustofspentgasesfromthem.Forthispurposethevalvesatdefinitemomentsopenandclosetheintakeandexhaustportsinthecylinderhead,throughwhichthecylinderscommunicatewiththeintakeandexhaustmanifold.

Thevalvegeariscomposedoftiminggears,acamshaft,tappets,valves,springwithfastenersandvalveguides.

Thetiminggearsinmostenginesarehousedinaspecialcasefittedatthefrontendoftheengine.Thesearenecessarytotransmitrotationfromthecrankshafttothecamshaft,fuelinjectionpumpshaft,andtooilpumpandothermechanisms.Thegearsaremadeofsteelandusehelicalteethtoreducenoise.

Camshaft'sfunctionistoopentheenginevalvespositivelyandtimely,inadefinitesequence,andtocontroltheirclosingagainstthereturnactionofthevalvesprings.Theshaftismadeintegralwithitscamsandbearingjournals.Eachcamcontrolsasinglevalve,eitherintakeorexhaust.Insomeautomobileengines,thecamshaftismadeintegralwithfuelpumpeccentricwheelandoilpumpdrivegear.Thecamshaftbearingsarelubricatedwithoilsuppliedunderpressurefromthemaingalleryinthecylinderblock.

Thetappetsservetotransmittheforcefromthecamshafttothepushrods.Thetappetsaresmallcylindricalboresreceivingthepushrods.Theyaremadeofcastironorsteelandlocatedintheguides,whichmaybemadeintegralwiththecylinderblockorremovableasintheengine.Whentheenginesoperate,thetappetscontinuouslyrotateabouttheiraxesforuniformwear.Therotationisensuredbyaconvexsurfaceoftheirbottomsandaslantedsurfaceofthecams.

Thepushrodstransmitstheforcefromthetappetstotherockerandaremadeassteelstemswithhardenedtipsorduralumintubeswithsphericalsteeltipspress-fittedat.bothends.Thepushrodtipsbearagainstthetappethollowatoneendagainstthesphericalsurfaceofrockeradjustingscrewatother.

Therockerstransmittheforcefromthepushrodtothevalve.Therockersaremadefromsteelandareinstalledonahollowfulcrum.Abronzebushispressfittedintotherockerholetoreducefriction.Thehollowfulcrumissupportedbystandardsonthecylinderhead.Endplayoftherockerispreventedbyacoilspring.Therockerarmisabellcrankmadeofsteel.Atthemiddleoftherockerarm,thereisabosswithaboreintowhichispressedthebushing.Ahardenedcurvedpadisprovidedontheendoftherockerwhereitcontactsthevalvestemtip,whileathreadedholeismachinedinitsotherendtoreceivetheadjustingscrewusedtosetthevalveclearance,theclearancebetweentherockercontactpadandthevalvestemtip,sothatthevalvewillbetightlypressedagainstitsseatwhenhot.Therockerarmfreelyoscillatesabouttherocker-armshaftsupportedbyaseriesofpedestalsorbrackets,whichareboltedtothetopdeckofthecylinderhead.

Anenginevalveisadevicedesignedtoopenapassagewhenmovinginonedirectionandtocloseitwhenmovingintheoppositedirection.Eachcylinderofafour-stroke-cycledieselorgasouneengineiscommonlyequippedwithanintakevalveandanexhaustvalve.Thepurposeoftheintakevalveistoallowtheairfuelmixtureorairtoenterthecylinder.Afterthecombustionprocesshasbeencompleted,theburnedgasesarepermittedtoescapefromthecylinderthoughtheexhaustvalve.Toobtainsufficientvalvearea,someautomobileshavetwointakevalvesandtwoexhaustvalves.

Avalveconsistsofaheadandstem.Thevalveheadhasanarrowchamferof45°or30°referredtoasvalveface.Thevalvefacefitstightlyagainsttheseat,whichisachievedbygrinding.

Forbetterenginebreathing,theinletvalvehasalargerdiameterthantheexhaustone.Asthevalvesarenotequallyheatedintherunningengine,theyaremadefromdifferentmaterials.Theinletvalvesaremadefromchromiumsteel,theexhaustvalvesareofsilchromeheat-resistantsteel.

Thecylinderstemofthevalvehasarecessattheupperendforfasteningthevalvespring.Thevalvestemsslideinthecast-ironorcerametallicvalveguides.

Thevalvespringprovidestheforcenecessarytoclosethevalveandholdittightlyagainstitsseat.

Someenginesusetwospringsoneachvalve,whichreducethesizeofthesprings,improvestheirreliability,andmakestheiroperatingconditionslessarduous.

Valveguidesupportsthevalvestemandguidesitsmovementsothatthevalvefaceremainsperfectlyconcentricwiththevalveseatandfitsitwithoutanyskewing.Replaceablevalveguidesarefabricatedfromcastironoracermetsmaterialandpressedinthecylinderhead.

Todecreaseoilpenetrationalongthevalvestemtothecombustionchambers,theseatingcollarsarefittedwithrubberringsortheseatsareprovidedwithrubbercaps.Moreuniformheatingandwearofthevalveareensuredwiththevalvesrotatingduringtheoperationoftheengine.Ingeneral,therearetwowaysofrotating:

oneisfreerotatetheotherispositiverotate.

Asthevalveisopened,springiscompressedanditsincreasingloadcausestheflexiblewashertoflattenoutandforceballsdowntheirrampsagainsttheresistanceofferedbytheirreturnsprings.Astheballsrolldown,theyturnthroughsomeangletheflexiblewasher,seatingcollarandvalvespringtogetherwiththevalve;whenthevalveisclosed,thevalvespringloaddecrease,theflexiblewasherdeflectstoacquireitsinitialconicalshapeandabuttingagainstashoulderinhousing,releasestheballswhicharethenforcedbytheircoilspringstoreturntotheirstartingposition.

配气机构

燃机的配气机构保证新鲜混合气可以适时进入汽缸，同时燃烧后的废气及时排出。

为实现这一目的，气门在一定的时刻打开和关闭汽缸盖上的进排气道，汽缸通过进排气歧管与进排气管相沟通。

配气机构由正时齿轮、凸轮轴、挺柱、气门、带有锁紧装置的弹簧和气门导管组成。

大多数发动机的正时齿轮装在专门的壳体，正时齿轮壳体位于发动机前端。

必须使用正时齿轮将曲轴的旋转传递到凸轮轴，驱动喷油泵轴、机油泵和其他的装置。

正时齿轮由钢制成，采用螺旋状齿以减少噪声。

凸轮轴的功用是按特定的顺序准确适时地打开气门并通过气门弹簧的回位作用控制气门的关闭。

凸轮轴与凸轮、轴颈制为一体。

每个凸轮控制一个气门:

进气门或排气门。

有些汽车发动机的凸轮轴也与驱动燃油泵的偏心轮和机油泵的驱动齿轮做成一体。

缸体主油道的机油在压力作用下到达凸轮轴轴颈提供润滑。

挺柱用来把凸轮轴的作用力传递给推杆。

挺柱为圆柱形小筒，里面插入推杆。

挺柱材料为铸铁或钢，定位于导管，挺柱导管可以是与缸体一体的或者是可拆卸的。

发动机工作时，为使磨损均匀，挺柱总是绕其轴线旋转。

挺柱的旋转是由挺柱凸起的下表面和凸轮倾斜面所保证的。

推杆将挺柱传来的推力传给摇臂。

推杆由顶部淬火的钢柱或由两端压入配合的带球形钢头的硬铝管制成。

推杆的两端一头支撑在挺柱的空腔，另一头与摇臂调整螺钉端的球形表面配合。

摇臂把推杆的作用力传递到气门。

摇臂由钢制成，安装于空心的枢轴。

摇臂空装有青铜衬套以减少摩擦。

中空的摇臂轴通过支架固定于汽缸盖。

摇臂上的螺旋弹簧防止产生轴向窜动。

摇臂是钢制的双臂杠杆。

摇臂中部有一带孔的凸台，孔压装有衬套。

摇臂的一端是经过淬火的圆弧状长臂，与气门杆尾端接触，而车有螺纹孔的另一端安装有调整螺钉，用来调整摇臂与气门杆尾端之间的气门间隙，从而保证气门在受热后紧紧压在气门座上。

摇臂可以绕摇臂轴自由摆动，摇臂轴通过一系列支座支撑，支座用螺栓固定于汽缸盖上表面。

发动机气门向某一万向运动时开启-通道，而它向相反方向移动时则关闭此通道。

四行程汽油机或柴油机的每缸一般都装有进气门和排气门。

%气门的作用是使空气燃油混合气进入汽缸。

燃烧过程完成后废气通过排气门排出汽缸。

为了获得足够的充气面积，有些发动机采用两个进气门和两个排气门。

气门由头部和杆身组成。

气门头部相对于气门平面之间存在45。

或30。

的锥角。

通过研磨使气门平面与气门座紧密贴合。

为使发动机更好地换气，进气门（头部）直径大于排气门。

在发动机工作时由于进、排气门受热不均等，因此它们采用不同的材料制成。

进气门采用铬钢，排气门采用耐热硅铬钢。

圆柱气门杆身的上部有一凹槽用来固定气门弹簧。

气门杆身在铸铁或金属瓷气门导管运动。

气门弹簧提供气门关闭时所需要的作用力，保证气门与气门座紧密贴合。

有些发动机的每个气门装有两根弹簧，可以减小所使用的弹簧大小，增加可靠性，使工作更平稳。

气门导管支撑气门杆身，对其运动起导向作用，以保证气门X闭时能准确地与气门座贴合而不产生偏移。

可拆卸式气门导管采用铸铁或金属瓷材料制成，压入汽缸盖上的（气门导管。

为防止机油从气门杆渗进燃烧室，在气门导管上装有橡胶环或橡胶皮碗。

发动机工作时通过气门的旋转可以使气门获得更均匀的受热和磨损。

通常有两种实现气门旋转的方式：

自由旋转和强制旋转。

当气门开启时，弹簧被压缩，弹力增加，将弹性垫圈压平，迫使钢球克服回位弹簧的阻力沿斜坡滚动。

当钢球滚下时，带动弹性垫圈、气门弹簧与气门一起转过一个角度;当气门关闭时，气门弹簧弹力减小，弹性垫圈变形为原来的圆锥状，支撑于壳体的支撑板，钢球在回位弹簧作用下回到原来位置。

EngineCoolingSystem

Thepurposeofthecoolingsystemistokeeptheengineatitsmostefficientoperatingtemperatureatallspeedsunderalldrivingconditions.Asfuelisburnedintheengine,aboutone-thirdoftheheatenergyinthefuelisconvertedintopower.Anotherthirdgoesoutthroughtheexhaustpipeunused,andtheremainingthirdmustbehandledbythecoolingsystem.Thismeansthattheenginecanworkeffectivelyonlywhentheheatenergyisequallyhandledsoastokeeptheenginetemperatureinbalance:

So,thetemperatureisquiteessentialforanenginetoproducepower.Noenginecanworkwellwithoutsuitableoperatingtemperatures.Iftheenginerunstoohot,itmaysufferfrompre-ignition,whiletheair-fuelchargeisignitedprematurelyfromexcessivecombustionchambertemperature.Viscosityoftheoilcirculatinginanoverheatingengineisreduced.HotoilalsoformsvarnishandcarbondepositsmaybedrawnintothecombustionchamberwhereitincreasesHCemission.Thisalsocausespoorperformanceandprematurewear,andmayevenresultinenginedamage.What'smore,thebehaviorofthemetalsatexcessivelyhightemperaturealsodiffersfromthatatnormaltemperatures.Iftheenginerunstoocold,thefuelwillnotvaporizeproperly.Ifliquidfuelreachesthecylinders,itwillreducelubricationbywashingtheoilfromthecylinderwallsanddilutingtheengineoil.Thiscausesalossofperformance,anincreaseinHCemissions,andprematureenginewear.Forthesereasons,acoolingsystemofsomekindisnecessaryinanyinternalcombustionengine.

Therearegenerallytwodifferenttypesofcoolingsystem:

water-coolingsystemandair-coolingsystem.Water-coolingsystemiscommon.Thecoolingmedium,orcoolant,inthemiseitherwaterorsomelow-freezingliquid,calledantifreeze.Awater-coolingsystemconsistsoftheenginewaterjacket,thermostat,waterpump,radiator,radiatorcap,fan,fandrivebeltandnecessaryhoses.

Awater-coolingsystemmeansthatwaterisusedasacoolingagenttocirculatethroughtheenginetoabsorbthehotandcarryittotheradiatorfordisposal.Theengineiscooledmainlythroughheattransferandheatdissipation.Theheatgeneratedbythemixtureburnedinenginemustbetransferredfromtheironoraluminumcylindertothewaterinthewaterjacket.Theoutsideofthewaterjacketdissipatessomeoftheheattotheairsurroundingit,butmostoftheheatiscarriedbythecoolingwatertotheradiatorfordissipation.Whenthecoolanttemperatureinthesystemreaches90°