汽车专业英语教程多媒体教学课件Unit7ction4

1EngineCoolingSystem
Thepurpoofthecoolingsystemistokeeptheengineatitsmostefficientopertingtemperatureatallenginespeedsandalldrivingcon-ditions.
Section4EngineCoolingandLubricatingSystems
发动机冷却与润滑系统
(一)发动机冷却系统
冷却系统的作用是控制发动机的温度,使发动机在各种转速和各种行驶状态下都能有效地工作。
Agreatdealofheatisproducedintheenginebytheburningoftheair-fuelmixture.Someofthisheatescapesfromtheenginethroughtheexhaustgastokeeptheenginefromover-heating.Butenoughremainsintheenginetocaurioustrouble,thecoolingsystemtakescareofthisad-ditionalheat.Anotherimportantjobofthecoolingsystemistoallowtheenginetoheatupasquicklyaspos-sible,andthentokeeptheengineataconstanttemperature.
Therearetwotypesofcoolingsys-temsfoundoncars:liquid-cooledandair-cooled.
混合气的燃烧在发动机中产生大量的热,其中部分热量通过废气被排出以阻止发动机过热。但是,残留在发动机中的余热仍足以使发动机受到严重损坏,冷却系统就是专门用来消除余热的。冷却系统还有一个重要任务,就是让发动机迅速预热,然后就让发动机保持恒定的温度。
冷却系统有两种:液冷和风冷。
Thecoolingsystemonliquid-cooledcarscirculatesafluidthroughpipesandpassagewaysintheengine.Asthisliquidpassthroughthehoten-gineitabsorbsheat,coolingtheen-gine.Afterthefluidleavestheengine,itpassthroughaheatexchanger,orradiator,whichtransferstheheatfromthefluidtotheairblowingthroughtheexchanger.
Someoldercars,andveryfewmo-demcars,areair-cooled.Sincemostcarsareliquid-cooled,wewillfocusonthatsysteminthisarticle.
液冷系统的流体在发动机中的管路和通道中循环流动。当液体流过发热的发动机时,就吸收了大量热量。当液体流出发动机时,通过热交换器或散热器,将液体变为气体吹走。
有些老式汽车和少数现代汽车采用风冷系统。因为大部分的汽车采用液体冷却,所以我们主要讨论液冷系统。
Theliquidcoolingsystemconsistsofwaterpumps,waterjackets,enginefan,radiator,coolantrervoirtank,radiatorcap,thermostat,hosandsoon,asisshowninFig.7-26.Thecoolingsystemisbuiltintotheengine.Therearehollowspacesaroundeachenginecylinderandcombustionchamber.Thehollowspacesarecalledwaterjackets,sincetheyarefilledwithwater.Whentheengineisrunning,thewatertakesheatfromtheengine,becominghotintheprocess.Awaterpumppumpsthehotwaterfromtheenginewaterjacketsintotheradiator.
液体冷却系由水泵、水套、发动机风扇、散热器(水箱)、副水箱、、压力式水箱盖、节温器、水管等组成,如图7-26所示。冷却系统就设置在发动机中。每个气缸体和燃烧室周围都留有空腔,这些空腔装满了水,称之为水套。在发动机运行过程中水被加热,并以水循环方式把热量从发动机中带走。水泵从发动机水套中把热水抽到散热器中,
Theradiatorhastwotsofpas-sages.Onetcarrieswater.Theothertcarriesair(pulledthroughbycarmotionandtheenginefan).Asthehotwaterpassthrough,itgivesupitsheattotheairpassingthrough.Thecooledwaterthenreen-terstheengine,whereitcanpickupmoreheat.Inoperation,waterconti-nuouslycirculatesbetweentheengineandradiator,carryingheatfromtheenginetotheradiator.Bythismeans,excessiveenginetemperaturesareprevented.
散热器有两条通道:一条是水道,另一条是气道(空气是通过汽车行驶和发动机的风扇抽入的)。当热水流过水道时,气道中流通的空气使热水冷却,冷却后的水又重新进入发动机,再把发动机中的热量传导出去。在这一过程中,水不断地在发动机与散热器之间循环,水携带着热量从发动机流到散热器再散发出去。通过这个方法可避免发动机温度过高。
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Fig.7-26
1—WaterJacket;水套
2—Heater;暖气水箱
3—HeaterHo;暖气水管
4—Thermostat;节温器
5—WaterPump;水泵
6—PressureCap;压力式水箱盖
7—CoolantRervoirTank;副水箱
8—RadiatorCore;散热器芯
9—Hos;水管
10—FanBelt;风扇皮带
Thewaterpumpisasimplecen-trifugalpump.Thewaterpump,drivenbyabeltfromtheenginecrankshaft,circulatesthecoolingliquidbetweentheradiatorandenginewaterjackets.Thecoolingliquidiswater.Antifreezecom-poundsareaddedtothewaterduringthewinter.Thewaterjacketarecastintothecylinderblocksandheads.Theenginefanisus-uallymountedonthewaterpumpshaftandisdrivenbythesamebeltthatdrivesthepumpandthege-nerator,eFig.7-27.
水泵就是个简单的离心泵。水泵由发动机曲轴上的皮带驱动,使冷却液在散热器与发动机水套之间循环流动。冷却液是水,冬季在水中须加入防冻剂。水套被铸入气缸体和气缸盖内部。发动机风扇通常安装在水泵轴上,由驱动水泵和发电机的同一条皮带驱动,参见图7-27。
Thepurpoofthefanistoprovideapowerfuldraftofairthroughtheradiator.Theradiatorisadeviceforholdingalargevolumeofwaterinclocontactwithalargevolumeofairsothatheatwilltransferfromthewatertotheair.Theradiatorcoreisdividedintotwoparateandintri-catecompartments;waterpassthroughone,andairpassthroughtheother.
风扇的作用是向散热器提供强大的空气流,与大量空气密切接触的散热器内可以容纳大量的水,这样热量可以通过水散发到空气中。散热器芯为分离和间隔交错的两部分。冷却水在其中一部分中流过,空气在另一部分中通过。
Fig.7-27
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1—WaterPump;水泵
2—Pulley;皮带盘
3—CoolingFan;冷却风扇
Theradiatoristhelargestpartofthecoolingsystem,mostoftheheatfromtheengineistransferredfromthecoolanttothesurroun-dingair,asisshowninFig.7-28.Therervoirtankisconnectedtotheoverflowho.Whenthehotcoolantexpandsintheradiator,therervoirtankallowscoolanttoflowin.Asthesystemcools,thecoolantwillbedrawnbackintotheradiator.
水箱是冷却系最大的零件,大部分发动机的热量由冷却液散发至周围空气中,如图7-28所示。副水箱连接溢流管,当热冷却液在水箱内膨胀,冷却液便流入副水箱;当冷却系温度下降后,冷却液又再从副水箱流回水箱。