毕业论文设计：三级圆柱圆锥齿轮减速器设计

北京化工大学毕业设计PAGE34毕业论文(设计)三级圆柱圆锥齿轮减速器设计1绪论通过查阅一些文献我们可以了解到带式传动装置的设计情况，为我所要做的课题确定研究的方向和设计的内容。1.1带传动带传动是机械设备中应用较多的传动装置之一，主要有主动轮、从动轮和传动带组成。工作时靠带与带轮间的摩擦或啮合实现主、从动轮间运动和动力的传递。带传动具有结构简单、传动平稳、价格低廉、缓冲吸振及过载打滑以保护其他零件的优点。1.2圆锥-圆柱齿轮传动减速器YK系列圆锥-圆柱齿轮传动减速器适用的工作条件：环境温度为-40～40度；输入轴转速不得大于1500r/min,齿轮啮合线速度不大于25m/s，电机启动转矩为减速器额定转矩的两倍。YK系列的特点：采用一级圆弧锥齿轮和一、二、三级圆柱齿轮组合，把锥齿轮作为高速级（四级减速器时作为第二级），以减小锥齿轮的尺寸；齿轮均采用优质合金钢渗碳淬火、精加工而成，圆柱齿轮精度达到GB/T10095中的6级，圆锥齿轮精度达到GB/T11365中的7级；中心距、公称传动比等主要参数均采用R20优先数系；结构上采用模块式设计方法，主要零件可以互换；除底座式实心输出轴的基本型外，还派生出输出轴为空心轴的有底座悬挂结构；有多中润滑、冷却、装配型式。所以有较大的覆盖面，可以满足较多工业部门的使用要求。减速器的选用原则：（1）按机械强度确定减速器的规格。减速器的额定功率P1N是按载荷平稳、每天工作小于等于10h、每小时启动5次、允许启动转矩为工作转矩的两倍、单向运转、单对齿轮的接触强度安全系数为1、失效概率小于等于1%等条件算确定.当载荷性质不同，每天工作小时数不同时，应根据工作机载荷分类按各种系数进行修正.减速器双向运转时，需视情况将P1N乘上0.7～1.0的系数，当反向载荷大、换向频繁、选用的可靠度KR较低时取小值，反之取大值。功率按下式计算：P2m=P2*KA*KS*KR，其中P2为工作功率；KA为使用系数；KS为启动系数；KR为可靠系数。（2）热功率效核.减速器的许用热功率PG适用于环境温度20℃，每小时100%连续运转和功率利用律（指P2/P1N×100%）为100%的情况，不符合上述情况时，应进行修正。（3）校核轴伸部位承受的径向载荷。2结构设计2.1V带传动带传动设计时，应检查带轮的尺寸与其相关零部件尺寸是否协调。例如对于安装在减速器或电动机轴上的带轮外径应与减速器、电动机中心高相协调，避免与机座或其它零、部件发生碰撞。2.2减速器内部的传动零件减速器外部传动件设计完成后，可进行减速器内部传动零件的设计计算。齿轮材料的选择应与齿坯尺寸及齿坯的制造方法协调。如齿坯直径较大需用铸造毛坯时，应选铸刚或铸铁材料。各级大、小齿轮应该可能减少材料品种。蜗轮材料的选者与相对滑动速度有关。因此，设计时可按初估的滑速度选择材料。在传动尺寸确定后，校核起滑动速度是否在初估值的范围内，检查所选材料是否合适。传动件的尺寸和参数取值要正确、合理。齿轮和蜗轮的模数必须符合标准。圆柱齿轮和蜗杆传动的中心距应尽量圆整。对斜齿轮圆柱齿轮传动还可通过改变螺旋角的大小来进行调整。根据设计计算结果，将传动零件的有关数据和尺寸整理列表，并画出其结构简图，以备在装配图设计和轴、轴承、键联结等校核计算时应用。联轴器的选择减速器的类型应该根据工作要求选定。联接电动机轴与减速器，由于轴的转速高，一般应选用具有缓冲、吸振作用的弹性联轴器，例如弹性套柱销联轴器、弹性柱销联轴器。减速器低速轴（输出轴）与工作机轴联接用的连周期，由于轴的转速较低，传递的转距较大，又因为减速器轴与工作机轴之间往往有较大的轴线偏移，因此常选用刚性可以移动联轴器，例如滚子链联轴器、齿式联轴器。对于中、小型减速器，其输出与工作机轴的轴线便宜不很大时，也可以选用弹性柱销联轴器这类弹性可移式联轴器。联轴器型号按计算转距进行选择。所选定的联轴器，起轴孔直径的范围应与被联接两轴的直径相适应。应注意减速器高速轴外伸段轴径与电动机的轴径不得相差很大，否则难以选择合适的联轴器。3设计计算过程及说明3.1选择电动机3.1.1电动机类型和结构型式选择Y系列笼型三相异步电动机,卧式闭型电电动机。3.1.2选择电动机容量工作机所需功率SKIPIF1<0=SKIPIF1<0=7.98kwSKIPIF1<0=80.7r/min电动机的输出功率SKIPIF1<0=SKIPIF1<0=10.4kwη=SKIPIF1<0*…..*SKIPIF1<0=0.82*0.98*0.95*0.98*0.97*0.98*0.98*0.97*0.98*0.98*0.99*0.96=0.77确定电动机的额定功率Ped>=Pd3.1.3选择电动机的转速同步转速1500r/min。3.1.4确定电动机型号选择Y160M-4额定功率11kw转速1460r/min3.2传动装置的总传动比及其分配i=SKIPIF1<0=18.1带传动i=2圆锥i=2.5圆柱i=43.3计算传动装置的运动和动力装置参数各轴转速:电动机轴SKIPIF1<0=1460r/min减速箱输入轴SKIPIF1<0=SKIPIF1<0=486.7r/min高速轴SKIPIF1<0=SKIPIF1<0=235.1r/min低速轴SKIPIF1<0=SKIPIF1<0=58.8r/min各轴输入功率:SKIPIF1<0=SKIPIF1<0=11kwSKIPIF1<0=SKIPIF1<0*0.95=10.45kwSKIPIF1<0=SKIPIF1<0*0.98*0.97*0.98=9.73KWSKIPIF1<0=SKIPIF1<0*0.98*0.97*0.98=9.07KW各轴转矩:T0=9550*SKIPIF1<0/SKIPIF1<0=72.0N*mT1=9550*SKIPIF1<0/SKIPIF1<0=205.0N*mT2=9550*SKIPIF1<0/SKIPIF1<0=395.2N*mT3=9550*SKIPIF1<0/SKIPIF1<0=1493.1N*m3.4带传动设计3.4.1定v带型号和带轮直径工作情况系数SKIPIF1<0=1.1计算功率SKIPIF1<0=SKIPIF1<0SKIPIF1<0=1.1*11=12.1kw选带型号A型小带轮直径SKIPIF1<0=100mm大带轮直径SKIPIF1<0=(1-0.01)*100*3=297mm大带轮转速SKIPIF1<0=SKIPIF1<0=481.8r/min3.4.2计算带长求SKIPIF1<0SKIPIF1<0=(SKIPIF1<0+SKIPIF1<0)/2=198.5mm求ΔΔ=(SKIPIF1<0-SKIPIF1<0)/2=98.5mm2(SKIPIF1<0+SKIPIF1<0)>=a>=0.7*(SKIPIF1<0+SKIPIF1<0)初取中心距a=600mm带长L=πDm+2*a+SKIPIF1<0=1839.5基准长度SKIPIF1<0=2000mm求中心距和包角中心距a=SKIPIF1<0+SKIPIF1<0=344.18+337.06=681.24<700mm小轮包角α1=180°-(D2-D1)*60°=180°-(297-100)*60°/681.24=162.6>120°数求带根v=3.14*SKIPIF1<0*SKIPIF1<0/(60*1000)=7.64m/s传动比i=SKIPIF1<0/SKIPIF1<0=2带根数SKIPIF1<0=1.32kwSKIPIF1<0=0.95SKIPIF1<0=1.03ΔP=0.17kwz=SKIPIF1<0/((SKIPIF1<0+ΔSKIPIF1<0)*SKIPIF1<0*SKIPIF1<0)=12.1/((1.32+0.17)*0.95*1.03)=8.3取9根求轴上载荷张紧力SKIPIF1<0=500*SKIPIF1<0/v*z(2.5-SKIPIF1<0)/SKIPIF1<0+qv*v=500*12.1/(7.64*9)*(2.5-0.95)/0.95+0.10*SKIPIF1<0=149.3N轴上载荷SKIPIF1<0=2*SKIPIF1<0sin(SKIPIF1<0/2)=2*9*149.3*sin(162.6°/2)=2656.5N

3.5齿轮传动设计直齿锥齿:轴交角∑=90°传递功率P=10.45kw小齿轮转速SKIPIF1<0=486.7r/m传动比i=2.07载荷平稳,直齿为刨齿,小齿轮40Cr,调质处理,241HB~~286HB平均260HB,大齿轮用45号钢,217HB~~255HB平均230HB齿面接触疲劳强度计算齿数和精度等级取SKIPIF1<0=24SKIPIF1<0=i*SKIPIF1<0=48EQSKIPIF1<0SKIPIF1<0SKIPIF1<0选八级精度使用系数SKIPIF1<0=1.0动载荷系数SKIPIF1<0=1.15齿间载荷分配系数SKIPIF1<0估计SKIPIF1<0*Ft/b<100N/mmcosSKIPIF1<0=u/SKIPIF1<0=2/SKIPIF1<0=0.89cosSKIPIF1<0=1/SKIPIF1<0=1/SKIPIF1<0=0.44SKIPIF1<0 =SKIPIF1<0/cosSKIPIF1<0=24/0.89=26.97SKIPIF1<0=SKIPIF1<0/cosSKIPIF1<0=48/0.44=109.1SKIPIF1<0αv=(1.88-3.2(1/(2*SKIPIF1<0)+1/(2*SKIPIF1<0)))cosSKIPIF1<0=1.85SKIPIF1<0=SKIPIF1<0=0.85SKIPIF1<0=SKIPIF1<0=1.4齿向载荷分布函数SKIPIF1<0=1.9载荷系数SKIPIF1<0=SKIPIF1<0SKIPIF1<0SKIPIF1<0SKIPIF1<0=1*1.5*1.4*1.9=3.99转矩SKIPIF1<0=9.55*SKIPIF1<0*SKIPIF1<0=9.55*SKIPIF1<0*10.45/486.7=20505N.mm弹性系数SKIPIF1<0=189.8SKIPIF1<0节点区域系数SKIPIF1<0=2.5接触疲劳强度SKIPIF1<0=710MpaSKIPIF1<0 =680Mpa接触最小安全系数SKIPIF1<0=1.5接触寿命系数SKIPIF1<0=SKIPIF1<0=1.0许用接触应力[SKIPIF1<0]=SKIPIF1<0*SKIPIF1<0/SKIPIF1<0=710*/1.05=676Mpa[SKIPIF1<0]=SKIPIF1<0*SKIPIF1<0/SKIPIF1<0=680*/1.05=648Mpa小轮大端分度圆直径SKIPIF1<0SKIPIF1<0=0.3SKIPIF1<0SKIPIF1<0=70mm验算圆周速度及Ka*Ft/bSKIPIF1<0=(1-0.5SKIPIF1<0R)SKIPIF1<0=(1-0.5SKIPIF1<0R)70=59.5mmSKIPIF1<0=SKIPIF1<0=3.1459.5*486.7/60000=1.5m/sSKIPIF1<0=SKIPIF1<0

b=SKIPIF1<0*R=SKIPIF1<0*d/(2*sinSKIPIF1<0)=SKIPIF1<0*SKIPIF1<0/(2*SKIPIF1<0=20.4mmSKIPIF1<0*SKIPIF1<0/b=1.0*689.2/20.4=33.8N/mm<100N/mm确定传动尺寸大端模数m=SKIPIF1<0/SKIPIF1<0=70/24=2.9mm实际大端分度圆直径dSKIPIF1<0=mSKIPIF1<0=3*24=84SKIPIF1<0=mSKIPIF1<0=3*48=144b=SKIPIF1<0*R=0.3*80.5=24.15mm齿根弯曲疲劳强度计算齿面系数SKIPIF1<0=2.72SKIPIF1<0=2.38应力修正系数SKIPIF1<0=1.66SKIPIF1<0=1.78重合度系数SKIPIF1<0=0.25+0.75/SKIPIF1<0=0.25+0.75/0.85=0.66齿间载荷分配系数SKIPIF1<0SKIPIF1<0*SKIPIF1<0/b<100N/mmSKIPIF1<0=1/SKIPIF1<0=1/0.66=1.56载荷系数SKIPIF1<0=SKIPIF1<0SKIPIF1<0SKIPIF1<0SKIPIF1<0=1*1.15*1.56*1.9=3.4弯曲疲劳极限SKIPIF1<0SKIPIF1<0=600MPaSKIPIF1<0 =570MPa弯曲最小安全系数SKIPIF1<0=1.25弯曲寿命系数SKIPIF1<0=SKIPIF1<0=1.0尺寸系数SKIPIF1<0=1.0许用弯曲应力[SKIPIF1<0]=SKIPIF1<0limSKIPIF1<0SKIPIF1<0/SKIPIF1<0=600*1.0*1.0/1.25=480MPa[SKIPIF1<0]=570*1.0*1.0/1.25=456MPa验算SKIPIF1<0=SKIPIF1<0=SKIPIF1<0=152<[SKIPIF1<0]EQEQSKIPIF1<0SKIPIF1<0=SKIPIF1<0=152*2.38*1.78/(2.72*1.66)=142.6MPa标准斜齿圆柱齿轮小齿轮用40Cr调质处理,硬度241HB~~286HB平均260MPa大齿轮用45号钢,调质处理,硬度229HB~~286HB平均241MPa初步计算转矩SKIPIF1<0=9.55*SKIPIF1<0SKIPIF1<0*9.73/235.1=39524N.mm齿数系数SKIPIF1<0=1.0SKIPIF1<0值取SKIPIF1<0=85初步计算的许用接触应力[SKIPIF1<0H1]=0.96SKIPIF1<0Hlim1=0.9*710=619MPa[SKIPIF1<0H2]=0.9SKIPIF1<0Hlim2=1.9*580=522MPa初步计算的小齿轮直径SKIPIF1<0=AdSKIPIF1<0=85*SKIPIF1<0=48.1mm取d1=50mm初步尺宽b=SKIPIF1<0d*SKIPIF1<0=1*50=50mm校核计算圆周速度v=SKIPIF1<0=0.62m/s精度等级选九级精度齿数z和模数m初步齿数SKIPIF1<0=19;SKIPIF1<0=i*19=4*19=76和螺旋角SKIPIF1<0SKIPIF1<0=SKIPIF1<0/SKIPIF1<0=50/19=2.63158SKIPIF1<0=2.5mmSKIPIF1<0=arcosSKIPIF1<0=arccos2.5/2.63158=18.2°使用系数SKIPIF1<0=1.10动载系数SKIPIF1<0=1.5齿间载荷分配系数SKIPIF1<0SKIPIF1<0=SKIPIF1<0=2*39524/50=1581NSKIPIF1<0=1.1*1.581/50=34N/mm<100N/mmSKIPIF1<0=[1.88-3.2[1/SKIPIF1<0+1/SKIPIF1<0]cosSKIPIF1<0=[1.88-3.25*(1/19+1/76)]cos18.2°=1.59SKIPIF1<0=SKIPIF1<0==2.0SKIPIF1<0=SKIPIF1<0=1.59+2.0=3.59SKIPIF1<0=arctanSKIPIF1<0=arctanSKIPIF1<0=20.9°cosSKIPIF1<0=cos18.2°20cos°/20.9cos°=0.95齿向载荷分布系数SKIPIF1<0=A+B[1+0.6*SKIPIF1<0]SKIPIF1<0+c*b/1000=1.36SKIPIF1<0=SKIPIF1<0*SKIPIF1<0*SKIPIF1<0*SKIPIF1<0=1.10*1.05*1.76*1.36=2.76弹性系数SKIPIF1<0=189.8SKIPIF1<0节点区域系数SKIPIF1<0=2.5重合度系数SKIPIF1<0取SKIPIF1<0螺旋角系数SKIPIF1<0=SKIPIF1<0许用接触应力SKIPIF1<0验算SKIPIF1<0=189.8*2.38*0.97SKIPIF1<0=647MPa<690MPa齿根弯曲疲劳强度验算齿行系数YFaSKIPIF1<0=SKIPIF1<0SKIPIF1<0YSKIPIF1<0=2.72YSKIPIF1<0=2.2应力修正系数SKIPIF1<0SKIPIF1<0=1.56SKIPIF1<0=1.79重合度系数SKIPIF1<0SKIPIF1<0=1.61SKIPIF1<0螺旋角系数SKIPIF1<0SKIPIF1<0SKIPIF1<0SKIPIF1<0齿向载荷分配系数SKIPIF1<0SKIPIF1<0SKIPIF1<0=1.76<SKIPIF1<0齿向载荷分布系数SKIPIF1<0b/h=50.(2.25*2.5)=8.9SKIPIF1<0=1.27载荷系数K=SKIPIF1<0*SKIPIF1<0*SKIPIF1<0许用弯曲应力SKIPIF1<0SKIPIF1<0验算SKIPIF1<0SKIPIF1<03.6轴的设计输入轴选用45钢调质SKIPIF1<0SKIPIF1<0取d=35mm计算齿轮受力SKIPIF1<0=84mmSKIPIF1<0=(1-0.5SKIPIF1<0SKIPIF1<0=689.2NSKIPIF1<0=SKIPIF1<0tanSKIPIF1<0SKIPIF1<0=SKIPIF1<0计算支反力水平面反力SKIPIF1<0=1102.7NSKIPIF1<0=-413.5N垂直面反力SKIPIF1<0=-1235.7NSKIPIF1<0=4115.5N水平面受力图垂直面受力图水平面弯矩图垂直弯矩图合成弯矩图转矩图许用应力许用应力值SKIPIF1<0应力校正系数SKIPIF1<0当量弯矩图SKIPIF1<0SKIPIF1<0轴径SKIPIF1<0SKIPIF1<0高速轴轴材料选用45钢调质,SKIPIF1<0SKIPIF1<0SKIPIF1<0取d=40mm计算螺旋角SKIPIF1<0齿轮直径小轮SKIPIF1<0=SKIPIF1<0大轮SKIPIF1<0小齿轮受力转矩SKIPIF1<0=9.55*SKIPIF1<0圆周力SKIPIF1<0=2*SKIPIF1<0/SKIPIF1<0=2*39524/50=1581N径向力SKIPIF1<0画小齿轮轴受力图水平反力SKIPIF1<0=1358.1NSKIPIF1<0=912.1N垂直反力SKIPIF1<0=594.7NSKIPIF1<0=103.3N水平受力图垂直受力图水平弯矩图垂直弯矩图合成弯矩图画转矩图应力校正系数SKIPIF1<0画当量弯矩图SKIPIF1<0SKIPIF1<0=50220N.mm校核轴径SKIPIF1<0=20.3<40mm低速轴材料同前两轴SKIPIF1<0SKIPIF1<0画大齿轮受力图计算支反力水平反力SKIPIF1<0=1185.8SKIPIF1<0=395.2N垂直反力SKIPIF1<0=21.2NSKIPIF1<0=584.6N垂直受力图水平弯矩图垂直弯矩图合成弯矩图转矩图当量弯矩SKIPIF1<0SKIPIF1<0校核轴径SKIPIF1<0=26<60mm3.7轴承的选择输入轴轴承选择:选用圆锥滚子轴承30208e=0.37Y=1.6Cr=63000NSKIPIF1<0 =1177.7NSKIPIF1<0=4297.0NSKIPIF1<0 =SKIPIF1<0/(2*Y)=368NSKIPIF1<0=SKIPIF1<0/(2*Y)=1342.8NSKIPIF1<0=1228.4NSKIPIF1<0=1342.8NSKIPIF1<0/SKIPIF1<0=1.0>eSKIPIF1<0/SKIPIF1<0=0.3<e查表SKIPIF1<0=0.4SKIPIF1<0=1.6SKIPIF1<0=1SKIPIF1<0=0当量动载荷SKIPIF1<0=SKIPIF1<0*(SKIPIF1<0*SKIPIF1<0+SKIPIF1<0*SKIPIF1<0)=1.0*(0.4*1177.7+1.6*1228.4)=2436.5NSKIPIF1<0=SKIPIF1<0*(SKIPIF1<0*SKIPIF1<0+SKIPIF1<0*SKIPIF1<0)=4297.0N轴承寿命SKIPIF1<0=SKIPIF1<0同样,高速轴承和低速轴承分别用选用圆锥滚子轴承30210和30213。3.8键的选择SKIPIF1<0输入轴SKIPIF1<0L=20(mm)高速轴SKIPIF1<0L=20低速轴SKIPIF1<0L=30T=SKIPIF1<03.9减速机箱体的设计名称符号尺寸关系结果箱座壁厚SKIPIF1<0SKIPIF1<0=0.025*a+3SKIPIF1<08箱盖壁厚SKIPIF1<0SKIPIF1<0=0.02*a+3SKIPIF1<08a=SKIPIF1<0箱体凸缘厚度SKIPIF1<0,SKIPIF1<0,SKIPIF1<0b=1.5=15;SKIPIF1<0=1.5SKIPIF1<0=15;SKIPIF1<0=2.5=25加强肋厚度SKIPIF1<0,SKIPIF1<0m=0.85=8.5;SKIPIF1<0=0.85SKIPIF1<0=8.5地脚螺栓直径SKIPIF1<0SKIPIF1<014地脚螺栓数目nSKIPIF1<04轴承旁连接螺栓直径SKIPIF1<00.75SKIPIF1<0箱盖,箱座连接螺栓直径SKIPIF1<0SKIPIF1<0;螺栓间LSKIPIF1<0轴承盖螺钉直径数目SKIPIF1<0,nSKIPIF1<0SKIPIF1<0=8n=4轴承盖外径SKIPIF1<0SKIPIF1<0=s(两连接螺栓间的距离)观察孔螺钉直径SKIPIF1<0SKIPIF1<0轴承旁凸台高度和直径h,SKIPIF1<0h由结构决定,SKIPIF1<0=SKIPIF1<0箱体外壁至轴承座端面距离SKIPIF1<0SKIPIF1<0+SKIPIF1<0+SKIPIF1<03.10减速器附件设计3.10.1窥视孔和视孔盖窥视孔应该在箱盖顶部,以便观察,应在凸台上以便加工。3.10.2通气器在箱盖顶部,要适合环境,其尺寸要与减速器大小相合适。3.10.3油面指示器应该设在油面比较稳定的地方,如低速轴附近。用圆形油标,有标尺的位置不能太高和太低,以免溢出油标尺孔座。3.10.4放油孔和螺塞放在油的最低处,平时用螺塞塞住,放油孔不能低于油池面,以免排油不净。3.10.5起吊装置吊环可按起重重量选择,箱盖安装吊环螺钉处设置凸台,以使吊环螺钉有足够的深度。3.10.6定位销用圆锥销作定位销,两定位销的距离越远越可靠,常设在箱体连接凸缘处的对角处,对称布置。直径d=0.8d2。3.10.7起盖螺钉装在箱盖连接凸缘上,其螺纹长度大于箱体凸缘厚度,直径可与连接螺钉相同。3.11密封与润滑轴承采用接触式密封。传动采用浸油润滑,尽量使各传动浸油深度相同。轴承润滑采用刮油润滑。4设计小结通过这次设计让我了解到机械设计是从使用要求等出发，对机械的工作原理、结构、运动形式、力和能量的传递方式，以及各个零件的材料和形状尺寸等问题进行构思、分析和决策的工作过程，这种过程的结果要表达成设计图纸、说明书及各种技术文件。通过带式输送机传动装置的设计,了解了带式输送机传动装置的原理以及其结构。从带式输送机传动装置的设计，我学到了机械设计的思想--以最少的成本达到最好的目的,以最简单的结构达到所需的功能。设计思想中最突出得的是—-合理二字。整个设计过程使我受益非浅。5参考文献1王昆等主编,机械设计课程设计,武汉:高等教育出版社,1995。2邱宣怀主编,机械设计.第四版,北京:高等教育出版社,1997。3濮良贵主编,机械设计.第七版,西安:高等教育出版社,2000。4任金泉主编,机械设计课程设计,西安:西安交通大学出版社,2002。5许镇宁主编,机械零件,北京:人民教育出版社,1959。6TragfahigkeitsberechnungVonStirn-undKegelradern(DIN3990),1970。目录目录第一章总论 1一、项目概述 1二、可行性研究报告编制依据和范围 2三、项目主要经济技术指标 3四、******国家森林公园概况 3第二章项目背景及必要性 8一、项目背景 8二、项目建设的必要性与可行性 10第三章项目选址分析 13一、项目选址 13二、项目城市概况 13三、经济发展概况 14四、公共设施依托条件及施工条件 17第四章需求分析与建设规模 18一、****国家森