带传动的类型和特点

PAGEPAGE99第八章带传动第一节带传动的类型和特点带传动由主动带轮1、从动带轮2和挠性带3组成，借助带与带轮之间的摩擦或啮合，将主动轮1的运动传给从动轮2，如图8-1所示。图8-1图8-1带传动示意图根据工作原理不同，带传动可分为摩擦带传动和啮合带传动两类。1.摩擦带传动摩擦带传动是依靠带与带轮之间的摩擦力传递运动的。按带的横截面形状不同可分为四种类型，如图8-2所示。(1)平带传动。平带的横截面为扁平矩形（图a），内表面与轮缘接触为工作面。常用a)b)c)d)图8-2a)b)c)d)图8-2带传动的类型(2)V带传动。V带的横截面为梯形，两侧面为工作面（图b），工作时V带与带轮槽两侧面接触，在同样压力FQ的作用下，V带传动的摩擦力约为平带传动的三倍，故能传递较大的载荷。(3)多楔带传动。多楔带是若干V带的组合(图c),可避免多根V带长度不等,传力不均的缺点。(4)圆形带传动。横截面为圆形(图d),常用皮革或棉绳制成,只用于小功率传动。2.啮合带传动啮合带传动依靠带轮上的齿与带上的齿或孔啮合传递运动。啮合带传动有两种类型，如图8-3所示。(1)同步带传动。利用带的齿与带轮上的齿相啮合传递运动和动力，带与带轮间为啮合传动没有相对滑动，可保持主、从动轮线速度同步（图a）。(2)齿孔带传动。带上的孔与轮上的齿相啮合，同样可避免带与带轮之间的相对滑动，使主、从动轮保持同步运动（图b）。二、带传动的特点摩擦带传动具有以下特点：(1)结构简单，适宜用于两轴中心距较大的场合。(2)胶带富有弹性，能缓冲吸振，传动平稳无噪声。(3)过载时可产生打滑、能防止薄弱零件的损坏，起安全保护作用。但不能保持准确的传动比。(4)传动带需张紧在带轮上，对轴和轴承的压力较大。(5)外廓尺寸大,传动效率低(一般0.94~0.96)。a)同步齿形带传动b)齿孔带传动图8-3啮合带传动根据上述特点，带传动多用于①中、小功率传动（通常不大于100KW）；②原动机输出轴的第一级传动（工作速度一般为5~25a)同步齿形带传动b)齿孔带传动图8-3啮合带传动第二节V带和带轮带的构造和标准a)帘布结构b)线绳结构图8-4V带剖面结构标准V带都制成无接头的环形，其横截面由强力层1、伸张层2、压缩层3和包布层4构成，如图8-4所示。伸张层和压缩层均由胶料组成，包布层由胶帆布组成，强力层是承受载荷的主体，分为帘布结构（由胶帘布组成）和线绳结构（由胶线绳组成）两种。帘布结构抗拉强度高，一般用途的V带多采用这种结构。线绳结构比较柔软，弯曲疲劳强度较好，但拉伸强度低，常用于载荷不大，直径较小的带轮和转速较高的场合。Va)帘布结构b)线绳结构图8-4V带剖面结构V带和带轮有两种尺寸制，即有效宽度制和基准宽度制。基准宽度制是以V带的节宽为特征参数的传动体系。普通V带和SP型窄V带为基准宽度制传动用带。按GB/T11544-97规定，普通V带分为Y、Z、A、B、C、D、E七种，截面高度与节宽的比值为0.7；窄V带分为SPZ、SPA、SPB、SPC四种，截面高度与节宽的比值为0.9。带的截面尺寸如表8-1所示，基准长度系列如表8-2所示。窄V带的强力层采用高强度绳芯，能承受较大的预紧力，且可挠曲次数增加，当带高与普通V带相同时其带宽较普通V带小约1/3,而承载能力可提高1.5~2.5倍。表8-5V带轮的基准直径系列（摘自GB/T13575.1-92）(mm)基准直径dd(c11)带型基准直径dd(c11)带型YZSPZASPABSPBCSPCDEYZSPZASPABSPBCSPCDE外径da(h11)外径da(h11)2022.4252831.535.5404550566371758085909510010611211812513214015023.225.628.231.234.738.743.248.253.259.266.274.283.293.2103.2115.2128.2*54*606775798494104116129136144154*80.5*85.5*90.595.5100.5105.5111.5117.5123.5130.5137.5145.5155.5*132*139147157160170180200212224236250265280300315335355375400425450475500530560600630670164184204228254284319359404504634165.5185.5205.5229.5255.5285.5320.5360.5405.5455.5505.5565.5635.5167177187207231257287322362407457507567607637*209.6*221.6233.6245.6259.6289.6309.6324.6344.6364.6409.6459.6509.6569.6609.6639.6371.2391.2416.2441.2466.2491.2516.2572.2616.2646.2519.2549.2579.2619.2649.2689.2注:*只用于普通V带第三节V带传动工作能力分析一、带传动的受力分析带以一定的预紧力套在带轮上。静止时带轮两边的拉力相等，均为预紧力F0，如图8-7a)所示。负载转动时，由于带与带轮接触面摩擦力的作用，带绕上主动轮的一边被拉a)b)图8-7带传动的受力分析紧，称为紧边，紧边的拉力由F0增加到F1；另一边被放松，称为松边，拉力由F0降至F2。如图8-7b)所示。紧边与松边拉力的差值a)b)图8-7带传动的受力分析F=F1－F2(8-1)若带传递功率为P（KW）、带速为v（m/s）则：N(8-2)如果近似的认为工作前后胶带总长不变，则带的紧边拉力增量应等于松边拉力的减少量，即F1－F0＝F0－F2，即：(8-3)由式（8-1）、（8-3）得：(8-4)二、带传动的应力分析带在工作过程中主要承受拉应力，离心应力和弯曲应力三种应力。三种应力迭加后，最大应力发生在紧边绕入小带轮处，其值为：≤（8-5）式中：σ1=F1/A为紧边拉应力(MPa),A为带的横截面积(mm2)；σb1=Eh/dd为带绕过小带轮时发生弯曲而产生的弯曲应力,E为带的弹性模量(MPa),h为带的高度(mm),dd为带轮的基准直径(mm)；σC=qv/A为带绕带轮作圆周运动产生的离心应力，q为每米长带的质量（kg/m），见表（8-1）。在带的高度h一定的情况下，dd越小带的弯曲应力就越大，为防止过大的弯曲应力对各种型号的V带都规定了最小带轮直径dmin如表8-6所示。表8-6V带轮的最小基准直径型号YZSPZASPABSPBCSPCDEddmin(mm)2050637590125140200224355500三、带的弹性滑动和打滑1.弹性滑动由于带传动存在紧边和松边，在紧边时带被弹性拉长，到松边时又产生收缩，引起带在轮上发生微小局部滑动，这种现象称为弹性滑动。弹性滑动造成带的线速度略低于带轮的圆周速度，导致从动轮的圆周速度v2低于主动轮的圆周速度v1,其速度降低率用相对滑动率表示。相对滑动率＝0.01~0.02,故在一般计算中可不考虑，此时传动比计算公式可简化为：（8-6）2.打滑与极限有效拉力当外载较小时，弹性滑动只发生在带即将由主、从动轮离开的一段弧上。传递外载增大时，有效拉力随之加大，弹性滑动区域也随之扩大，当有效拉力达到或超过某一极限值时，带与小带轮在整个接触弧上的摩擦力达到极限，若外载继续增加，带将沿整个接触弧滑动，这种现象称为打滑。此时主动轮还在转动，但从动轮转速急剧下降，带迅速磨损、发热而损坏，使传动失效。所以必须避免打滑，在设计时应限制带的最大拉力。当带有打滑趋势时，带与带轮间的摩擦力达到极限值，即有效拉力达到最大值，这时可由欧拉公式推导得极限有效拉力为：（8-7）式中：e为自然对数的底，；f为摩擦系数（V带用当量摩擦系数代替，）；为包角，即带与带轮接触弧对应的中心角（rad），因大带轮包角总是大于小带轮包角，故这里应取为小带轮包角。第四节普通V带传动设计计算一、设计准则和单根V带的额定功率1.设计准则根据带传动工作能力分析可知，带传动的主要失效形式有：①带在带轮上打滑，不能传递动力；②带发生疲劳破坏（经历一定应力循环次数后发生拉断、撕裂、脱层）。因此带传动的设计准则为：①带在传递规定功率时不发生打滑,即满足式（8-7）。②具有一定的疲劳强度和寿命,即满足式（8-5）。2.单根V带所能传递的额定功率。经推导可得单根V带所能传递的额定功率为：（8-8）式中：v为带速m/s。在特定带长、使用寿命、传动比(i=1、)以及在载荷平稳条件下，通过疲劳试验测得带的许用应力后，代入式（8-8）便可求出特定条件下的P0值，见表8-7。表8-7包角=180o、特定带长、工作平稳情况下，单根V带的额定功率P0(KW)型号小带轮直径dd1(mm)小带轮转速n1(r/min)20040073080098012001460160020002400280032003600Z5663718090－－－－－0.060.080.090.140.140.110.130.170.200.220.120.150.200.220.240.140.180.230.260.280.170.220.270.300.330.190.250.310.360.370.200.270.330.390.400.250.320.390.440.480.300.370.460.500.540.330.410.500.560.600.350.450.540.610.640.370.470.580.640.68A75901001121251401600.160.220.260.310.370.430.510.270.390.470.560.670.780.940.420.630.770.931.111.311.560.450.680.831.001.191.411.690.520.790.971.181.401.662.000.600.931.141.391.661.962.360.681.071.321.621.932.292.740.731.151.421.742.072.452.940.841.341.662.042.442.873.420.921.501.872.302.743.223.801.001.642.052.512.983.484.061.041.752.192.683.163.654.191.081.832.282.783.263.724.17B1251401601802002240.480.590.740.881.021.190.841.051.321.591.852.171.341.692.162.613.063.591.441.822.322.813.303.861.672.132.723.303.864.501.932.473.173.854.505.262.202.833.644.415.155.992.333.003.864.685.466.332.643.424.405.306.137.022.853.704.755.676.477.252.963.854.895.766.436.952.943.834.805.525.956.052.803.634.464.924.984.47续表8-7630.200.350.560.600.700.810.931.001.171.321.451.561.66710.250.440.720.780.921.081.251.351.591.812.002.182.33SPZ750.280.490.790.871.021.211.411.521.792.042.272.482.65800.310.550.880.991.151.381.601.732.052.342.612.853.06900.370.671.121.211.441.701.982.142.552.933.263.573.841000.430.791.331.441.702.022.362.553.053.493.904.264.58900.430.751.211.301.521.762.022.162.492.773.003.163.261000.530.941.541.651.932.272.612.803.273.673.994.254.42SPA1120.641.161.912.072.442.863.313.574.184.715.155.495.721250.771.402.332.522.983.54.064.385.155.806.346.767.031400.921.682.813.033.584.234.915.296.227.017.648.118.391601.112.043.423.704.385.176.016.477.608.539.249.729.941401.081.923.133.353.924.555.215.546.316.867.157.176.891601.372.474.064.375.135.986.897.338.389.139.529.539.10SPB1801.653.014.995.376.317.388.509.0510.3411.2111.6211.4310.772001.943.545.886.357.478.7410.0710.7012.1813.1113.4113.0111.832242.284.186.977.528.8310.3311.8612.5914.2115.1015.1414.22—2502.644.868.118.7510.2711.9913.7214.5116.1916.8916.44——2242.905.198.388.9910.3911.8913.2613.8114.5814.01———2503.506.3110.2711.0212.7614.6116.2616.9217.7016.69———SPC2804.187.5912.4013.3115.4017.6019.4920.2020.7518.86———3154.979.0714.8215.9018.3720.8822.9223.5823.4719.98———3555.8710.7217.5018.7621.5524.3426.3226.8025.3719.22———4006.8612.5620.4121.8425.1527.3329.4029.5325.81————型号小带轮直径d1(mm)小带轮转速n1(r/min)10020030040050060073098012001460160018002000C200224250280315400——————1.391.702.032.422.863.911.922.372.853.404.045.542.412.993.624.325.147.062.873.584.335.196.178.523.304.125.006.007.149.823.804.785.826.999.3411.524.665.897.188.6510.2313.675.296.718.219.8111.5315.045.867.479.0610.7412.4815.516.077.759.3811.0612.7215.246.288.009.6311.2212.6714.086.348.059.6211.0412.1411.95D3554004505005603.013.664.375.085.915.316.527.909.2110.767.359.1311.0212.8815.079.2411.4513.8516.2018.9510.9013.5516.4019.1722.3812.3915.4218.6721.7825.3214.0417.5821.1224.5228.2816.3020.2524.1627.6031.0017.2521.2024.8427.6129.6716.7020.0322.4223.2822.0815.6318.3119.5918.8815.1312.9714.2813.349.59——————E5005606307108006.217.328.7510.3112.0510.8613.0915.6518.5221.7014.9618.1021.6925.6930.0518.5522.4926.9531.8337.0521.6526.2531.3636.8542.5324.2129.3034.8340.5846.2626.6232.0237.6443.0747.7928.5233.0037.1439.5639.0825.5328.4929.1725.9116.4616.2514.52——————————————————二、带传动设计步骤和参数选择设计V带传动的原始数据为带传递的功率P,转速n1、n2（或传动比）以及外廓尺寸的要求等。设计内容有：确定带的型号、长度、根数、传动中心距、带轮直径以及带轮结构尺寸等。设计步骤一般为：1.确定设计功率Pc（8-9）式中：P为带传递的额定功率（KW）；KA为工况系数，见表（8-8）。表8-8工况系数KA载荷性质工作机原动机空、轻载启动重载启动每天工作小时数h<1010～16>16<1010～16>16载荷变动微小液体搅拌机、通风机和鼓风机（≤7.5KW）、离心式水泵和压缩机、轻型输送机1.01.11.21.11.21.3载荷变动小带式输送机（不均匀负荷）、通风机（>7.5KW）旋转式水泵和压缩机（非离心式）、发电机、金属切削机床、旋转筛、锯木机和木工机械1.11.21.31.21.31.4载荷变动较大制砖机、斗式提升机、往复式水泵和压缩机、起重机、磨粉机、冲剪机床、旋转筛、纺织机械、重载输送机1.21.31.41.41.51.6载荷变动很大破碎机（旋转式、颚式等）、磨碎机（球磨、棒磨磨、管磨）1.31.41.51.51.61.8注：①空轻载启动—电动机（交流启动、三角启动、直流并励）、四缸以上的内燃机、装有离心式离合器、液力联轴器的动力机；②重载启动—电动机（联机交流启动、直流复励或串励）、四缸以下的内燃机；③反复启动、正反转频繁、工作条件恶劣等场合，KA应乘以1.2。2.选择V带的型号根据设计功率Pc和主动轮转速n1由图8-8、9选择带的型号。3.确定带轮的基准直径dd1和dd2小带轮直径dd1应大于或等于表8-6所列的最小直径dmin。dd1过小则带的弯曲应力设计功率Pc设计功率Pc/（KW）图8-8普通V带选型图图8-8普通V带选型图设计功率Pc/设计功率Pc/（KW）图8-9窄V带选型图dd1、dd2均应符合带轮直径系列尺寸，见表8-5。4.验算带速v(8-10)带速太高离心力增大，使带与带轮间的摩擦力减小，容易打滑；带速太低，传递功率一定时所需的有效拉力过大，也会打滑。一般应使普通V带5m/s＜v＜25m/s窄V带5m/s＜v＜35m/s否则重选dd1。5.确定中心距a和带的基准长度Ld在无特殊要求时，可按下式初选中心距a0：≤ao≤mm(8-11)由带传动的几何关系，可得带的基准长度计算公式：mm(8-12)按查表8-2得相近的V带的基准长度Ld，再按下式近似计算实际中心距：a≈a0+（8-13）当采用改变中心距方法进行安装调整和补偿初拉力时，其中心距的变化范围为（8-14）6.验算小带轮包角≥（8-15）1与传动比有关，愈大（dd2－dd1）差值愈大，则1愈小。所以V带传动的传动比一般小于7,推荐值为2~5。速比不变时，可用增大中心距a的方法增大1。7.确定V带根数zz≥（8-16）式中：Pc为设计功率，按式（8-9）计算；P0为特定条件下单根V带所能传递的功率（KW），查表（8-7）；ΔP0为i＞1时的额定功率增量（KW），查表（8-9）；K为包角系数，考虑不是特定长度时，对传动能力的影响，查表（8-10）。8.确定单根V带初拉力F0（8-17）9.计算带对轴的压力FQFQ（8-18）表8-9考虑i≠1时，单根V带的额定功率增量△P0(KW)型号传动比i小带轮转速n1(r/min)20040073080098012001460160020002400280032003600Z1.00～1.01—1.02～1.04—0.000.021.05～1.08—1.09～1.12—0.011.13～1.18—0.031.19～1.24—1.25～1.34—0.021.35～1.51—1.52～1.99—.0.040.05≥2.0—带速v(m/S)51015A1.00～1.010.001.02～1.040.020.020.020.030.030.040.040.051.05～1.080.010.020.020.030.030.040.040.060.070.080.090.101.09～1.120.020.030.030.040.050.060.060.080.100.110.130.151.13～1.180.020.040.040.050.070.080.090.110.130.150.170.191.19～1.240.030.050.050.060.080.090.110.130.160.190.220.241.25～1.340.020.030.060.060.070.100.110.130.160.190.230.260.291.35～1.510.020.040.070.080.080.110.130.150.190.230.260.300.341.52～1.990.020.040.080.090.100.130.150.170.220.260.300.340.39≥2.00.030.050.090.100.110.150.170.190.240.290.340.390.44带速v(m/S)51015202530续表8-91.00～1.010.000.000.000.000.000.000.000.000.000.000.000.000.001.02～1.040.010.010.020.030.030.040.050.060.070.080.100.110.131.05～1.080.010.030.050.060.070.080.100.110.140.170.200.230.251.09～1.120.020.040.070.080.100.130.150.170.210.250.290.340.381.13～1.180.030.060.100.110.130.170.200.230.280.340.390.450.51B1.19～1.240.040.070.120.140.170.210.250.280.350.420.490.560.631.25～1.340.040.080.150.170.200.250.310.340.420.510.590.680.761.35～1.510.050.100.170.200.230.300.360.390.490.590.690.790.891.52～1.990.060.110.200.230.260.340.400.450.560.680.790.901.01≥2.00.060.130.220.250.300.380.460.510.630.760.891.011.14带速v(m/S)5101520253035401.00～1.010.000.000.000.000.000.000.000.000.000.000.000.000.001.02～1.050.000.000.010.010.010.010.020.020.020.030.030.040.041.06～1.110.010.010.020.030.030.040.050.050.070.080.090.110.121.12～1.180.010.020.040.050.060.070.080.090.120.140.160.180.201.19～1.260.020.030.060.060.080.090.110.130.160.190.220.250.28SPZ1.27～1.380.020.040.070.080.090.110.140.150.190.230.270.310.341.39～1.570.020.040.080.090.110.130.160.180.220.270.310.360.401.58～1.940.030.050.090.100.120.150.180.200.250.300.350.400.461.95～3.380.030.060.100.110.130.160.200.220.270.330.380.440.49≥3.390.030.060.100.120.140.170.210.230.290.350.410.470.52带速v(m/S)51015201.00～1.010.000.000.000.000.000.000.000.000.000.000.000.000.001.02～1.050.000.010.020.020.030.030.040.040.050.060.070.080.101.06～1.110.020.030.050.060.070.090.100.120.140.170.200.230.261.12～1.180.030.050.090.100.120.150.180.200.250.300.350.400.451.19～1.260.030.070.120.140.160.210.240.270.340.410.480.540.62SPA1.27～1.380.040.080.150.170.200.250.300.330.410.500.580.660.751.39～1.570.050.100.170.200.230.290.350.390.490.590.680.780.881.58～1.940.050.110.190.220.260.330.400.440.550.660.770.880.991.95～3.380.060.120.210.240.280.360.430.480.600.720.840.951.07≥3.390.060.130.220.250.300.380.460.510.630.760.891.011.14带速v(m/S)51015202530351.00～1.010.000.000.000.000.000.000.000.000.000.000.000.000.001.02～1.050.010.020.040.040.050.070.080.090.110.130.150.170.201.06～1.110.030.060.110.120.150.180.220.240.300.360.420.470.531.12～1.180.050.100.190.210.250.310.380.410.520.620.720.830.931.19～1.260.070.140.260.280.340.420.510.560.700.840.981.131.27SPB1.27～1.380.090.170.310.340.420.510.620.680.851.021.191.361.531.39～1.570.100.200.360.400.490.600.730.801.001.201.401.601.801.58～1.940.110.220.410.450.550.680.820.901.131.351.581.812.031.95～3.380.120.250.450.490.600.740.890.981.231.471.721.962.21≥3.390.130.260.470.520.640.780.951.041.301.561.822.082.34带速v(m/S)5101520253035401.00～1.010.000.000.000.000.000.000.000.000.000.00———1.02～1.050.030.050.100.110.130.160.190.210.260.32———1.06～1.110.070.140.260.290.350.430.530.580.720.86———1.12～1.180.130.250.460.500.620.750.921.001.251.51———1.19～1.260.170.340.620.680.841.021.241.361.712.05———SPC1.27～1.380.210.410.750.831.011.241.511.652.072.48———1.39～1.570.240.490.890.971.191.461.771.942.432.92———1.58～1.940.270.551.001.101.341.642.002.192.743.28———1.95～3.380.300.591.081.191.461.782.172.382.973.57———≥3.390.320.631.151.261.551.892.302.523.153.79———带速v(m/S)10152025303540续表8-9型号传动比i小带轮转速n1（r/min）100200300400500600730980120014601600180020001.00～1.01—0.000.000.000.000.000.000.000.000.000.000.000.001.02～1.04—0.020.030.040.050.060.070.090.120.140.160.180.201.05～1.08—0.040.060.080.100.120.140.190.240.280.310.350.391.09～1.12—0.060.090.120.150.180.210.270.350.420.470.530.591.13～1.18—0.080.120.160.200.240.270.370.470.580.630.710.78C1.19～1.24—0.100.150.200.240.290.340.470.590.710.780.880.981.25～1.34—0.120.180.230.290.350.410.560.700.850.941.061.171.35～1.51—0.140.210.270.340.410.480.650.820.991.101.231.371.52～1.99—0.160.240.310.390.470.550.740.941.141.251.411.57≥2.0—0.180.260.350.440.530.620.831.061.271.411.591.76带速v(m/S)5101520253035401.00～1.010.000.000.000.000.000.000.000.000.000.000.000.00—1.02～1.040.030.070.100.140.170.210.240.330.420.510.560.63—1.05～1.080.070.140.210.280.350.420.490.660.841.011.111.24—1.09～1.120.100.210.310.420.520.620.730.991.251.511.671.88—1.13～1.180.140.280.420.560.700.830.971.321.672.022.232.51—D1.19～1.240.170.350.520.700.871.041.221.602.092.522.783.13—1.25～1.340.210.420.620.831.041.251.461.922.503.023.333.74—1.35～1.510.240.490.730.971.221.461.702.312.923.523.894.98—1.52～1.990.280.560.831.111.391.671.952.643.344.034.455.01—≥2.00.310.630.941.251.561.882.192.973.754.535.005.62—带速v(m/S)5101520253035401.00～1.010.000.000.000.000.000.000.000.000.000.00———1.02～1.040.070.140.210.280.340.410.480.650.800.98———1.05～1.080.140.280.410.550.640.830.971.291.611.95———1.09～1.120.210.410.620.831.031.241.451.952.402.92———1.13～1.180.280.550.831.001.381.651.932.623.213.90———E1.19～1.240.340.691.031.381.722.072.413.274.014.88———1.25～1.340.410.831.241.652.072.482.893.924.815.85———1.35～1.510.480.961.451.932.412.893.384.585.616.83———1.52～1.990.551.101.652.202.763.313.865.236.417.80———≥2.00.621.241.862.483.103.724.345.897.218.78———带速v(m/S)510152025303540表8-10小带轮的包角修正系数包角1180°175°170°165°160°155°150°145°140°135°130°125°120°110°100°90°10.990.980.960.950.930.920.910.890.880.860.840.820.780.740.69例8-1设计某机床上电动机与主轴箱的V带传动。已知：电动机额定功率P=7.5KW,转速n1=1440r/min,传动比i12=2,中心距a为800mm左右，三班制工作，开式传动。解：计算项目计算与说明计算结果1.确定设计功率PC由表8-8取KA=1.3得：PC=1.3×7.5=9.75KWPC=9.75KW2.选择带型号根据PC=9.75KW，n1=1440r/min,由图8-8选A型V带选A型V带3.确定小带轮基准直径dd1由图8-8、表8-4、表8-6取dd1=140mmdd1=140mm4.确定大带轮基准直径dd2dd2=i12dd1=2×140=280mm由表8-4取dd2=280mmdd2=280mm5.验算带速vv=πdd1n1/(60×1000)=3.14×140×1440/(60×1000)=10.55m/s5m/s<v<25m/s符合要求v=10.55m/s符合要求6.初定中心距a0按要求取a0=800mma0=800mm7.确定带的基准长度LdL0=2a0+π(dd1+dd2)/2+(dd2－dd1)2/4a0=2×800+π(140+280)/2+(280－140)2/(4×800)=2265.53mm由表8-2取Ld=2240mmLd=2240mm8.确定实际中心距aa≈a0+(Ld－L0)/2=800+(2240－2265.53)/2=787.24mm中心距变动调整范围：amax=a+0.03Ld=787.24+0.03×2240=854.44mmamin=a－0.015Ld=787.24－0.015×2240=753.64mma=787.24mmamax=854.44mmamin=753.64mm9.验算小带轮包角=169.81o1>120o合用1=169.81o合用10.确定单根V带的额定功率P0根据dd1=140mm,n1=1440r/min由表8-7查得A型带P0=2.27KWP0=2.27KW11.确定额定功率增量ΔP0由表8-9查得：ΔP0=0.17KWΔP0=0.17KW12.确定V带根数z由表8-10查得：Kα≈0.98由表8-2查得：KL=1.06取z=4根Z=4根13.确定单根V带的初拉力F0≈191.42NF0=191.42N14.计算带对轴的压力FQFQ＝2zF0sin(1/2)＝2×4×191.42sin(169.81/2)≈1525.31NFQ=1525.31N15.确定带轮结构绘工作图（略）第五节同步带传动一、同步带传动的特点和应用同步带是以细钢丝绳或玻璃纤维为强力层，外覆以聚氨脂或氯丁橡胶的环形带。由于带的强力层承载后变形小，且内周制成齿状使其与齿形的带轮相啮合，故带与带轮间无相对滑动，构成同步传动。如图8-10所示。同步带传动具有传动比恒定、不打滑、效率高、初张力小、对轴及轴承的压力小、速度及功率范围广、不需润滑、耐油、耐磨损以及允许采用较小的带轮直径、较短的轴间距、较大的速比，使传动系统结构紧凑的特点。一般参数为：带速v≤50m/s；功率P≤100KW；速比i≤10；效率η=0.92~0.98；工作温度－20~80℃。图8图8-10同步带结构与同步带传动二、同步带的参数、类型和规格1.同步带的参数(1)节距Pb与基本长度Lp。在规定张紧力下，同步带相邻两齿对称中心线的距离，称为节距Pb。同步带工作时保持原长度不变的周线称为节线，节线长度Lp为基本长度（公称长度），轮上相应的圆称为节圆。如图8-10所示。显然有Lp=Pbz。(2)模数m。与齿轮一样，也规定模数m=Pb/。图8-11图8-11梯形齿和圆弧齿同步齿形同步带分为梯形齿和圆弧齿两大类，如图8-11所示。目前梯形齿同步带应用较广，圆弧齿同步带因其承载能力和疲劳寿命高于梯形齿而应用日趋广泛。同步带按结构分为单面和双面同步带两种型式。双面同步带按齿的排列不同又分为对称齿双面同步带（DA型）和交错齿双面同步带（DB型）两种，如图8-12所示。此外还有特殊用途和特殊结构的同步带。本节仅讨论单面梯形齿同步带。较常用的梯形齿同步齿形带有周节制和模数制两种，其中周节制梯形齿同步齿形带已列入国家标准，称为标准同步带。标准同步带按节距大小分为七种类型。带的齿形和带宽如表8-11所示，节线长度系列如表8-13所示。标准同步带的标记包括：型号、节线长度代号、宽度代号和国标号。对称齿双面同步带在型号前加“DA”，交错齿双面同步带在型号前加“DB”。图8-12对称双面齿和交错双面齿同步齿形带标记示例：图8-12对称双面齿和交错双面齿同步齿形带橡胶同步带980H200GB/T11616-89带宽代号200，带宽50.8mm型号H,节距12.7mm长度代号980，节线长2489.20mm聚氨酯同步带DA900H200GB/T11616-89带宽代号200，带宽50.8mm型号H,节距12.7mm长度代号900，节线长2286mm对称齿双面同步带模数制梯形齿同步带以模数为基本参数，模数系列为1.5、2.5、3、4、5、7、10，齿形角2为40°，其标记为：模数×齿数×宽度。例如聚氨酯同步带2×45×25表示：模数m=2,齿数z=45，带宽bs=25mm的聚氨酯同步带。三、同步带轮(1)同步带轮的材料及轮辐、轮毂结构同V带轮。为防止齿形带工作时从带轮上脱落，一般推荐小带轮两边均有挡圈，而大带轮则无挡圈；或大小带轮均为单面挡圈，但挡圈各在不同侧，如表8-12所示。(2)同步带轮轮齿形状有渐开线齿廓和直边齿廓两种（用于梯形齿同步齿形带），其中渐开线齿廓的同步带轮可借用齿轮刀具展成加工，齿廓具体尺寸请参阅有关手册。(3)周节制同步齿形带轮的宽度如表8-12所示，直径如表8-14所示。(4)周节制同步带轮标记由带轮齿数、带型号、轮宽代号和标准代号组成。标注示例：带轮32H075GB/T11361-89轮宽代号075，轮宽19.1mm带型号H,节距12.7mm轮齿数32表8-11周节制梯形齿同步齿形带的齿形与带宽型号节距pb(mm)齿形角2β(º)齿根厚s(mm)齿高ht(mm)带高h(mm)齿根圆角半径rr(mm)齿顶圆角半径ra(mm)带宽bS(mm)及代号MXL最轻型2.032401.140.511.140.130.13公称尺寸3.04.86.4代号012019025XXL超轻型3.175501.730.761.520.200.30公称尺寸3.04.86.4代号012019025XL特轻型5.080502.571.272.30.380.38公称尺寸6.47.99.5代号025031037L轻型9.525404.651.913.60.510.51公称尺寸12.719.125.4代号050075100H重型12.700406.122.294.31.021.02公称尺寸19.125.438.1代号075100150公称尺寸50.876.2—代号200300—XH特重型22.2254012.576.3511.21.571.19公称尺寸50.876.2101.6代号200300400XXH超重型31.7504019.059.5315.72.291.52公称尺寸50.876.2101.6代号200300400公称尺寸127——代号500——表8-12周节制梯形齿同步齿形带带轮的宽度(GB/T11361－89)(mm)型号轮宽代号轮宽基本尺寸型号轮宽代号轮宽基本尺寸MXL0120190253.04.86.43.85.37.15.67.18.94.76.28.0H07510015020030019.125.438.150.876.220.326.739.452.879.024.831.243.957.383.522.629.041.755.181.3XXL0120190253.04.86.43.85.37.15.67.18.94.76.28.020050.856.662.659.60256.47.18.98.0XH30076.283.889.886.9XL0317.98.610.49.5400101.6110.7116.7113.70379.510.712.211.120050.856.664.160.4L05007510012.719.125.414.020.326.717.023.329.715.521.828.2XXH30040050076.2101.612783.8110.7137.791.3118.2145.287.3114.5141.5表8-13周节制梯形齿同步齿形带的节线长度、齿数(GB/T11616-89)长度代号节线长Lp(mm)齿数z长度代号节线长Lp(mm)齿数z长度代号节线长Lp(mm)齿数zMXLXXLXLLXLLHXHHXHXXH3640444850566064707280889010011011212012413014015016017018018719020091.44101.60111.76121.92128.02142.24152.40162.56177.80182.88203.20223.52228.60254.00279.40284.48304.80314.96330.20355.60381.00406.40431.80457.20476.25482.60508.00455055606370758090100110125140155175200225250485664728088961041121201281441603035404550556065707580859095100334050210220225230240250255260270285300322328330345360367390420450480507510540560570600533.40558.80571.50584.20609.60635.00647.70660.40685.80723.90762.00819.15833.12838.20876.30914.40933.45990.601066.801143.001219.201289.051295.401371.601422.401447.801524.001051101151201251305660646872768086879298104112120128136144160485460667278849096102108114120586463066070075077080084085090098010001050110011201200125012601400154016001700175018001600.201676.401778.001905.001955.802032.002133.602159.002286.002489.202540.002667.002794.002844.803048.003175.003200.403556.003911.604064.004318.004445.004572.00126132140150160170180200210220250280340728088961121281441601762005664728096112128144表8-14周节制梯形齿同步齿形带带轮的直径(GB/T11361-89)（mm）注：括号内尺寸尽量不采用。四、同步带传动设计已知条件：①传动功率；②小带轮和大带轮转速；③传动用途、载荷性质、外廓尺寸、原动机种类以及工作制度等。设计计算步骤如表8-15所示。表8-15同步带传动设计计算项目符号公式及数据说明选择带型确定节距PcPc=KAPKA—工况系数，见表8-16P—传递的功率选择带型确定节距Pb根据Pc和n1由图8—13查取带型，表8-11确定节距Pb。为使传动平稳，提高带的柔性以及增加啮合齿数，节距应尽可能取较小值。n1—小带轮转速。小带轮齿数、节圆直径z1d1z1≥zminzmin见表8-17d1=z1Pb/π带速v和安装尺寸允许时，z1尽可能选用较大值，并取表8-14中的标准值。大带轮齿数、节圆直径z2d2z2=iz1=z1n1/n2d2=z2Pb/πz2取表8-14中的标准值带速vv=πd1n1/(60×1000)XL、L型，vmax=50m/s；H型，vmax=40m/sXH、XXH型，vmax=30m/s；若带速超过上述范围，应重选d1初定中心距a00.7(d1+d2)≤a0≤2(d1+d2)或按结构要求定带的节线长及齿数Lp、zLp0≈2a0+π(d1+d2)/2+(d2-d1)2/4a0按表8-14取接近的标准值LP及其齿数z理论中心距a中心距可调时：a≈a0+(LP-LP0)/2中心距不可调时：a≈(d2-d1)/2cos(1/2)inv(1/2)=(LP-πd2)/(d2-d1)中心距a的偏差见表8-181为小带轮包角。inv(1/2)为1/2角的渐开线函数。根据算出的inv(1/2)值，由渐开线函数表查得1/2值，即可求得精确的a值。d1=d2时，无法用渐开线函数，此时：a=Pb(z-z1)/2最好采用中心距可调结构。续表8-15小带轮啮合齿数zm对MXL、XXL、XL型zmmin=4,其他型zmmin=6。基本额定功率P0Ta—带宽为bS0的许用工作拉力N,见表8-19。m—带宽为bS0单位长度的带的质量kg/m见表8-19。带宽bSbS0—选定型号的带的基准宽度mm,见表8-19。KZ—小带轮啮合齿数系数zm≥65432Kz1.000.800.600.400.20作用在轴上的力FR表8-16同步带的工作情况系数KA工作机原动机交流电动机(普通转矩鼠笼式、同步电动机)直流电动机（并激），多缸内燃机交流电动机（大转矩、大滑差率、单相、滑环），直流电动机（复激、串激）单缸内燃机每天运转时间,h3～58～1016～243～58～1016～24电传打字机、计算机、复印机、录音机、照相机、放映机、计测仪器、医疗器械1.01.21.41.21.41.6清扫机械、办公机械、缝纫机、木工机械1.21.41.61.41.61.8轻载荷运输机、包装机、筛子1.31.51.71.51.71.9液体搅拌机、食品机械、印刷机械、造纸机械、洗衣机、钻床、车床、镗床1.41.61.81.61.82.0搅拌机（水泥、粘性体）、带式输送机、纺织机械、铣床、刨床、磨床、振动筛、离心压缩机、离心泵、齿轮泵、往复式压缩机1.51.71.91.71.92.1悬挂式输送机、洗衣机、离心鼓风机、发电机、励磁机、卷扬机、起重机、橡胶机械、