第八章链传动.

第八章Chaindrives链传动§8－1Generalconsiderations概述§8－2Motionfeaturesofchaindrives链传动的运动特性§8－3Designofrollerchaindrive套筒滚子链设计计算§8－4Forcesinchaindrive链传动受力分析§8－5Replacementandtensionofchaindrive链传动的布置与张紧Characteristicsandapplications特点和应用Typesofchaindrives链传动分类§8-1Generalconsiderations概述回总目录1、Advantages优点★Incomparisontobeltdrive与带传动相比：①Absenceofslippage无滑动②Smalleroverallsize尺寸小一、Characteristicsandapplications特点和应用BACK③Smalltensionforce→Smallforcesactingontheshaft张紧力F0小→压轴力小④Highefficiency工作效率高，η≈98％⑤Canbeusedunderhighertemperatureandhumidity能在较高温度和湿度下工作★IncomparisontotootheddriveCanbeusedforlargercentre-to-centredistances与齿轮传动相比：中心距a可以很大（8m）2、Drawbacks缺点①Usedonlyforparallelshafts只用于平行轴②Thevelocityofthechainisnotconstant→Leadingtolargerimpact,vibrationandnoisei瞬变化→高速时冲击、振动、噪音大.3、Applications应用（Forlowspeedandsevereoperationcondition适用于低速，胜任恶劣工况）二、Typesofchaindrives链传动分类①传动链：Powertransmissionchains传递动力Bushingchains套筒链：Higherslidingspeeds、SeverewearRollerchains套筒滚子链：Areextensivelyapplied应用广泛Silentchains齿形链（无声链）：Lessnoise无噪音，Highcost价格高BACK②Liftingchain起重链：Suspendingloads提升重物③Haulingchain曳引链：Carryingloads移动重物三、Rollerchains套筒滚子链1、Structure结构：Bushings套筒4、insidelinkplates内链板1：Pin销轴3、Outsidelinkplates外链板2：Interferencefit过盈配合Bushings套筒、Rollers滚子：Tolerancefit间隙配合Thepinpassthroughthebushingsofadjacentlinkstoformswiveljoints套筒、销轴相对转动链节屈伸元件结构图Withanevennumberoflinks链节数Lp是偶数：Largepitch大节距P：Cotterpins开口销Smallpitch小节距P：Springclamp弹簧夹2、Joints接头形式Withanunevennumberoflinks:Offsetlink链节数Lp是奇数：过渡链节（Which,however,isweakerthanthemainlinks.Therefore,designerstrytousechainswithanevennumberoflinks附加弯矩，导致链条抗拉强度下降，最好不用）BACK§8－2Motionfeaturesofchaindrives链传动的运动特性Variationinspeedratio运动不均匀性Dynamicload动载荷回总目录Thevelocityofthechainandspeedratioisnotconstantuponuniformrotationalspeedofthesmallsprocket.小链轮转速ω1是常数时，瞬时链速V和瞬时传动比i都是周期性变化的。一、Variationinspeedratio运动不均匀性BACK1、Thechainvelocity瞬时链速V（为便于分析，设紧边处于水平位置）①Thevelocityofthejointofthelink销轴中心VA＝ω1R1②Thevelocityofchain链速V＝VAcosβ＝ω1R1cosβ（Thevelocityofverticalmotionofthechain链条上下垂直运动速度V′＝ω1R1sinβ）③2φsinωRV'2φcosωRV2φβ0V'ωRV0β2φsinωRV'2φcosωRV2φβZ360φ2φ,2φβ111max111min1min11maxo111max111min11o111Sinceangleβvaries,thechainvelocityvaries.周期性变化，导致V不均匀性2φsinωRV'2φcosωRV2φβ0V'ωRV0β2φsinωRV'2φcosωRV2φβZ360φ2φ,2φβ111max111min1min11maxo111max111min11o111振动不平稳，忽快忽慢忽上忽下，：加速下降：减速上升2φ,0,02φ:'11V④DecelerationinrisingAccelerationinfallingWhenrising,thechainsuddenlyfallsandvice-versaQuickmotionsuddenlychangesintoslowmotionandvice-versaUnsteadymotionandvibration链速不均匀性11o1ZZ360φ⑤Nununiformityofthevelocityforthechain2、Instantaneousspeedratio瞬时传动比①②βcosRcosγRωωcosγRVω12211222i不均匀，变化212121ωconstωii③Onlyat：Z1＝Z2（R1＝R2）Thereisexactlyawholenumberoflinksinthedrivingsideofthechain只有当Z1＝Z2,紧边长度恰为P的整数倍时i12≡1（ω1≡ω2）（β，γ随时相等）－节距－齿数＝＝）过链长为（链轮转一周，随之转）（＝PZZnniZPsm100060PnZ100060PnZV12212211Z3、Averagevelocityofthechain&averagespeedratio平均链速V和平均传动比iWhenthesprocketturn3600,thelengthofthechainrunningoverthesprocketiszp.NumberofteethofasprocketChainpitchBACK二、Dynamicload动载荷1、Nouniformityofthemotion→Dynamicload运动不均匀性→动载荷V，i，ω2Periodicchange→Acceleration→Dynamicload周期性变化→加速度→动载荷BACKβsinωββsinω211RdtdRdtdVa①2max111o21121max1111ω2P2P2φsinZ180sinω2φsinω2φβ＝，则＝＝＝时，aRRRa②③ω1↑P↑(Z1↓)→Itisfavorabletoselectsmallpitchandlargenumberofteethfromthepointofviewofdecreasingdynamicload动载荷↑宜采用小节距P大齿数Z12、PeriodicchangeV′周期性变化→Crossvibration横向振动→Dynamicload动载荷3、Meshimpact→Dynamicload冲击→动载荷Impactsofthechainlinksonthesprocketteethasnewlinkscomeintoengagement链节进入链轮时，以一定相对速度相啮合→冲击→动载荷constCCnqPU23Inordertoreduceimpact为减小冲击Reduce减小P，nReduce减小q（Massperm线密度）Impactenergyofmotion冲击动能BACK§8－3Rollerchaindrivedesign套筒滚子链设计计算Principalparameters参数选择Typesoffailure失效形式Limitpowercurveandallowablepowercurve极限功率曲线和许用功率曲线Design设计计算回总目录1、i≤8（Usually2～3.5）i↑→α1↓→Numberofmeshingteeth啮合齿数↓→Wearofthesprocket轮齿磨损→Shiftoutwarduponthesprocketteethprofiles跳链α1≥120°→i＝2～3.5一、Principalparameters参数选择Nonuniformityofthemotionanddynamicsload运动不均匀性、动载荷↑Thelinksturn增大链节相对转角→Powerlosses功率损耗↑pressureincreasedactingonthepins增大铰链承压面压强→Wear磨损↑⑴Z1Z1↓→2、Z1，Z2Z1≥9Z1＝f（i）⑵Z2＝iZ1≤120Z2↑→易跳链易跳链△△△△△ddddZconst,PZ180sinPZ180sinPZ180sinPP'oooChainiseasilyfalloutoffsprocket⑶Whenthenumberofthechainlinksistheevennumber，Inordertofacilitatemoreuniformwear,Itispreferabletoselectanunevennumberofteethforthesprocketsortoselectthenumberofteethfromtheseriesofprimenumbers.链节数Lp为偶数时，为均匀磨损，Z最好为质数或不能整除链节数的数3、P（pitch节距）P↑→Size尺寸↑Loadcarryingincreases承载能力增大Nonuniformityofthemotionanddynamicloadincrease运动不均匀性、动载荷增大Highspeedandheavyload：Smallpitchandmultiple-widthchaindrive高速重载:小节距P多排Lowspeedandlightload：Largepitchandsingle-widthchaindrive低速重载:大节距P单排Itisbestpracticetoelectachainwiththeminimumallowablepitchforthegivenload节距P尽量小，但排数≤3～4（均匀）a↓→V不变时，单位时间内同一链节屈伸次数↑→磨损↑a↑→松边上下颤动，不平稳4、Centre-to-centredistance中心距aThenumberofthechainlinks链节数Lp⑴a＝（30～50）P（amax＝80P）21221p)D(D4a12a2)DDπLPLL（⑵Lp（链条长度用链节数表示）L＝LpPaP)2πZZ(Pa22ZZLπPZD2