机械工程专业英语Ageardrivesystemisonewhereamotorturnsaseriesofgearstodowork.Itplaysaveryimportantroleoftransmittingpower,achievingconveyingandadjustingtorqueinnumerousindustrialequipmentlikemachinetool,automobile,engineeringmachinery,agriculturemachineryandconstructionmachinery.Typically,shaftorientation,efficiency,andspeeddeterminewhichofthesetypesshouldbeusedforaparticularapplication.Thissectionongearingandgeardrivesdescribesthemajorgeartypes;itevaluates(评估，评价)howthevariousgeartypesarecombinedintogeardrivesandconsiderstheprincipalfactorsthateffectgeardrive.轴的方位、效率和速度决定了在实际应用中应该采用上述哪一类齿轮。这一节主要介绍齿轮传动中的主要齿轮类型。它评定了不同类型的齿轮是如何组合起来构成齿轮驱动以及影响齿轮驱动的主要因素。Neartherootofthetooth,however,thetooltracesatrochoidal(摆线)path,Fig.9.2,providingaheavier,andstronger,rootsection.Becauseofthisgeometry,contactbetweentheteethoccursmostlyasrollingratherthansliding.在接近齿根处，刀具轨迹呈摆线，这使齿根处更厚实。由于采用这种几何曲线，齿轮接触处主要是滚动摩擦而不是滑动摩擦。Andbecausecontactissimultaneouslyacrosstheentirewidthofthemeshing（啮合）teeth,acontinuousseriesofshocksisproducedbythegear.由于接触是沿着整个啮合齿宽同时发生，因此齿轮就会产生连续冲击。External-toothgears.Themostcommontypeofspurgearhasteethcutontheoutsideperimeter(周边的)ofmatingcylindricalwheels,withthelargerwheelcalledgearandthesmallerwheelthepinion(小齿轮).Thesimplestarrangementofspurgearsissinglepairofgearscalledasinglereductionstage(一级减速装置),whereoutputrotationisinadirectionoppositethatoftheinput.图9.3所示的是最普通的直齿轮类型，其轮齿是切削加工在配对齿轮的外圆周上。大齿轮称为gear，小齿轮称为pinion。直齿轮最简单的布置就是一级减速装置，其输入转向于输出转向相反。Highernetreductionisproducedwithmultiplestagesinwhichthedrivengearisrigidlyconnectedtoathirdgear.Thisthirdgearthendrivesamatingfourthgearthatservesas(充当，担任)outputforthesecondstage.Inthismanner,severaloutputspeedsondifferentshaftscanbeproducedfromasingleinputrotation.更大的减速比可以采用多级减速来实现，齿轮的第四个齿轮以实现二级减速。采用这种方式，输入一个旋转运动就可以在不同的轴上获得不同的输出转速。Internal(ring)gears.Asthenameimplies(顾名思义),teetharecutontheinsidesurfaceofacylindricalring,insideofwhicharemountedasingleexternal-toothspurgearorsetofexternal-toothspurgears,typicallyconsistingofthreeo