机械设计基础 精品课程 链转动

第八章Chain drives链传动§8－1 General considerations概述§8－2 Motion features of chain drives链传动的运动特性§8－3 Design of roller chain drive套筒滚子链设计计算§8－4 Forces in chain drive链传动受力分析§8－5 Replacement and tension of chain drive 链传动的布置与张紧§8-1 General considerations 概述 Characteristics and applications特点和应用Types of chain drives链传动分类回总目录一、Characteristics and applications特点和应用1、Advantages 优点★In comparison to belt drive与带传动相比：①Absence of slippage 无滑动②Smaller overall size 尺寸小③Small tension force→Small forces acting on the shaft小→压轴力小张紧力F④High efficiency 工作效率高，η≈98％⑤Can be used under higher temperature and humidity能在较高温度和湿度下工作★In comparison to toothed drive Can be used for largercentre-to-centre distances与齿轮传动相比：中心距a可以很大（8m）2、Drawbacks 缺点①U sed only for parallel shafts只用于平行轴②The velocity of the chain is not constant→ Leading to larger impact, vibration and noise i瞬变化→高速时冲击、振动、噪音大.3、Applications 应用（For low speed and severe operation condition适用于低速，胜任恶劣工况）二、Types of chain drives链传动分类①传动链：Power transmission chains传递动力Bushing chains 套筒链：Higher sliding speeds 、Severe wear Roller chains 套筒滚子链：Are extensively applied 应用广泛Silent chains齿形链（无声链）：Less noise 无噪音，High cost价格高②Lifting chain起重链：Suspending loads提升重物③Hauling chain曳引链：Carrying loads 移动重物三、Roller chains 套筒滚子链1、Structure 结构：Bushings 套筒4、inside link plates内链板1：Pin 销轴3、Outside link plates 外链板2：Interference fit 过盈配合Bushings 套筒、Rollers滚子：Tolerance fit 间隙配合The pin pass through the bushings of adjacent links to form swivel joints套筒、销轴相对转动链节屈伸元件结构图2、Joints 接头形式With an even number of links链节数L p是偶数：Large pitch 大节距P：Cotter pins 开口销Small pitch 小节距P：Spring clamp 弹簧夹With an uneven number of links: Offset link 是奇数：过渡链节链节数Lp（Which, however, is weaker than the main links. Therefore, designers try to use chains with an even number of links附加弯矩，导致链条抗拉强度下降，最好不用）§8－2Motion features of chain drives链传动的运动特性Variation in speed ratio运动不均匀性Dynamic load动载荷回总目录The velocity of the chain and speed ratio is not constant upon uniform rotational speed of the small sprocket.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、Variation in speed ratio运动不均匀性1、The chain velocity 瞬时链速V（为便于分析，设紧边处于水平位置）①The velocity of the joint of the link销轴中心VA ＝ω1R1②The velocity of chain 链速V＝V A cosβ＝ω1R1cosβ（The velocity of vertical motion of the chain 链条上下垂直运动速度V′＝ω1R1sinβ）③2φsin ωR V'2φcos ωR V 2φβ0V'ωR V 0β2φsin ωR V'2φcos ωR V 2φβZ 360φ2φ,2φβ111max 111min 1min 11max o 111max 111min 11o 111-========-==⎥⎦⎤⎢⎣⎡-=周期性变化，导致V 不均匀性2φsin ωR V'2φcos ωR V 2φβ0V'ωR V 0β2φsin ωR V'2φcos ωR V 2φβZ 360φ2φ,2φβ111max 111min 1min 11max o111max 111min 11o 111-========-==⎥⎦⎤⎢⎣⎡-=振动不平稳，忽快忽慢忽上忽下，：加速下降：减速上升⇒⎪⎭⎪⎬⎫⎥⎦⎤⎢⎣⎡⎥⎦⎤⎢⎣⎡-2φ,0,02φ:'11V ④Decelerationin rising Acceleration in falling When rising, the chain suddenly falls and vice-versa Quick motion suddenly changes into slow motion andvice-versaUnsteady motionand vibration↑↓→=链速不均匀性11o 1Z Z 360φ⑤Nun uniformity of thevelocity for the chain2、Instantaneous speed ratio瞬时传动比①②βcosRcosγRωωcosγRVω12211222===i不均匀，变化212121ωconstωii→=③Only at ：Z 1＝Z 2（R 1＝R 2 ）There is exactly a whole number of links in the driving side of the chain只有当Z 1＝Z 2,紧边长度恰为P 的整数倍时i 12≡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）（＝P Z Z n n i ZP s m100060Pn Z 100060Pn Z V 12212211Z ⨯⨯=3、Average velocity of the chain& average speed ratio 平均链速V 和平均传动比iWhen the sprocket turn 3600, the length of the chain running over the sprocket is z p . Number of teethof a sprocket Chain pitch二、Dynamic load 动载荷1、No uniformity of the motion→ Dynamic load运动不均匀性→动载荷V，i，ω2Periodic change→Acceleration → Dynamic load动载荷周期性变化→加速度→βsin ωββsin ω211R dtd R dt dV a -=-==①2max 111o21121max 1111ω2P 2P 2φsin Z 180sin ω2φsin ω2φβ±±±±=＝，则＝＝＝时，a R R R a ②③ω1↑ P↑(Z1↓) →It is favorable to select small pitch and large number of teeth from the point of view of decreasing dynamic load动载荷↑宜采用小节距P大齿数Z12、Periodic changeV′周期性变化→Cross vibration 横向振动→Dynamic load动载荷3、Mesh impact→ Dynamic load冲击→动载荷Impacts of the chain links on the sprocket teeth as new links come into engagement链节进入链轮时，以一定相对速度相啮合→冲击→动载荷constC C n qP U -=23In order toreduce impact 为减小冲击Reduce 减小P，nReduce 减小q（Mass per m Impact energy of motion 冲击动能§8－3Roller chain drive design套筒滚子链设计计算Principal parameters 参数选择Types of failure 失效形式Limit power curve and allowable power curve 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↓→Number of meshing teeth 啮合齿数↓→Wear of the sprocket 轮齿磨损→Shift outward upon the sprocket teeth profiles跳链α1≥120°→ i＝2～3.5一、Principal parameters参数选择Nonuniformity of the motion and dynamics load运动不均匀性、动载荷↑The links turn 增大链节相对转角→Power losses 功率损耗↑pressure increased acting on the pins 增大铰链承压面压强→Wear 磨损↑⑴Z 1Z 1↓ →2、Z 1，Z 2Z 1≥9 Z 1＝f （i ）⑵Z 2＝i Z 1 ≤120 Z 2↑→易跳链易跳链△△△△△↑→↑→===+=d d d d Z const,P Z 180sin P Z 180sin P Z180sin P P 'o o o Chain is easily fallout off sprocket⑶When the number of the chain links is the even number，In order to facilitate more uniform wear, It is preferable to select an uneven number of teeth for the sprockets or to select the number of teeth from the series of prime numbers.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↑Load carrying increases 承载能力增大Nonuniformity of the motion and dynamicload increase运动不均匀性、动载荷增大High speed and heavy load ：Small pitch and multiple-width chain drive 高速重载:小节距P多排Low speed and light load ：Large pitch and single-width chain drive低速重载:大节距P单排It is best practice to elect a chain with the minimum allowable pitchfor the given load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-centre distance 中心距a The number of the chain links 链节数L p ⑴a ＝（30～50）P （a max＝80P ）21221p )D (D 4a12a 2)D D πL PL L -+++==（⑵L p （链条长度用链节数表示）L ＝L p Pa P )2πZ Z (P a 22Z Z L πPZ D 21221P -+++==代入L p Round →The even number 偶数Lp′→Actual centre-to-centre distance 实际中心距a′⎥⎥⎦⎤⎢⎢⎣⎡--⎪⎭⎫ ⎝⎛+-+⎪⎭⎫ ⎝⎛+-=212221'21')2πZ Z (82Z Z 2Z Z 4P 'P P L L a。