南京理工大学机械原理chapter6ppt课件.ppt
《南京理工大学机械原理chapter6ppt课件.ppt》由会员分享,可在线阅读,更多相关《南京理工大学机械原理chapter6ppt课件.ppt(159页珍藏版)》请在三一文库上搜索。
1、Theory of Machines and Mechanisms (机械原理),Chapter1 Introduction Chapter2 Structural Analysis of Planar Mechanisms Chapter3 Kinematic Analysis of Mechanisms Chapter4 Planar Linkage Mechanisms Chapter 5 Cam Mechanisms Chapter 6 Gear Mechanisms Chapter 7 Gear Trains Chapter 8 Other Mechanisms in Common
2、Use Chapter 9 Balancing of Machinery Chapter 10 Motion of Mechanical Systems and Its Regulation Chapter 11 Efficiency of Machine,Chapter 6 GEAR MECHANISMS,circular gears :constant transmission ratio,non-circular gears :the ratio varies,In this chapter, only circular gears are considered.,6.1 Types o
3、f Gear Mechanisms,Depending on the relative shafts positions,parallel shaftsplanar gear mechanism (平面),nonparallel shafts spatial gear mechanism (空间),6.1.1 Planar Gear Mechanisms,External gear pair,Internal gear pair,Rack and pinion (齿条和齿轮),External gear:,Spur gear (直齿轮),Helical gear(斜齿轮),Double Hel
4、ical gear (人字齿轮),Internal gear pair:,1. Spur internal gear 2. Helical internal gear,6.1.2 Spatial Gear Mechanisms,1. Bevel gear mechanism(锥齿轮),2. Crossed helical gear mechanism(螺旋齿轮机构),3. Worm and worm wheel mechanism (蜗杆蜗轮机构),6.2 Fundamentals of Engagement of Tooth Profiles (齿廓啮合基本定律),6.2.1 Fundame
5、ntal Law of Gearing (啮合基本定律),VP1=VP2,1O1P=2 O2P,P12 is the instant centre of the gears 1 and 2.,P12,P - the pitch point(节点).,If a constant transmission ratio i12 is required.,Wherever(无论何处) the teeth contact, the common normal n-n of the tooth profiles through the contact point must intersect the ce
6、nter line at a fixed point。,Pitch circle(节圆): the locus of the pitch point P on the motion plane of the pinion or the gear.,Pitch circles are tangent and roll without slipping each other纯滚动. The gear pair is represented by two chain dotted(点划线) circles tangent to each other. 一对齿轮传动可看成两个节圆做纯滚动。,6.2.2
7、 Conjugate Profiles(共轭齿廓),Meshing(啮合的) profiles of teeth that can yield a desired transmission ratio(传动比) are termed conjugate profiles. 满足啮合基本定律的一对齿廓称为共轭齿廓。,轭,两头牛背上的架子称为轭,轭使两头牛同步行走。共轭即为按一定规律相配的一对。,For any specific tooth profile, we can find its conjugate profile.,Involutes(渐开线) are used most widely
8、 since they can be manufactured and assembled easily.,共轭齿廓曲线的选择,通常采用渐开线、摆线、变态摆线,1.满足定传动比的要求;2.考虑设计、制造等方面。,6.3 The Involute(渐开线) and Its Properties,6.3.1 Generation of Involute,An involute is the curve generated by any point on a string which is unwrapped(展开) from a fixed circle.,当一直线n-n沿一个圆的圆周作纯滚动时,
9、直线上任一点K的轨迹,rb The radius of base circle(基圆).,n-nGenerating line(发生线),K unfolding angle (展角) of the involute at point K.,6.3.2 Properties of the Involute,1.The length of the generating line(发生线) segment unrolled from the base circle is equal to the arc length of the base circle rolled.,NK为渐开线在K点的法线,N
10、K为曲率半径,渐开线上任一点的法线与基圆相切。,2. The length of segment NK is the radius of curvature of the involute at the point K.,A =0,3. The normal distance between two involutes of the same base circle remains the same.,4. The shape of an involute depends only on the radius of its base circle.,As the radius rb of th
11、e base circle approaches infinity, the involute becomes a straight line.,5. No involute exists inside its base circle.,6.3.3 Equation of the Involute 渐开线方程,Pressure angle K,F,VK,=NOK,The polar parametric equation of the involute 渐开线方程 with K as a parameter is,6.3.4 Gearing(啮合) of Involute Profiles,I
12、nvolute gears have constant transmission ratio.,constant,1. Locus of contact point, the line of action(啮合线) =common normal to the involute profiles = the common tangent to the base circles,渐开线齿廓啮合的特点,Since O1PN1 O2PN2,2、 Involute gears have separability(可分离性) of the centre distance.,中心距略有变动时不影响传动的大小
13、。,3、渐开线齿廓啮合的啮合角Working pressure angle 不变, is defined as the angle between the velocity of pitch point P (on both gears) and the line of actionN1N2 . N1N2与节圆公切线之间的夹角, =渐开线在节点处啮合的压力角,6.4.1. External Gears,6.4. Standard Involute Spur Gears,The tooth number of a gear - Z (齿数),Parameters of gear:,the fac
14、ewidth(齿宽) - B,addendum circle (or tip circle) (齿顶圆) -da, ra,dedendum circle (or root circle) (齿根圆)-df, rf,base circle -db, rb,an arbitrary circle (任意圆) -di, ri,The tooth space (齿槽) -the space between the profiles of two adjacent(相邻的) teeth.,The spacewidth(齿槽宽) ei-the arc length of the tooth space a
15、long an arbitrary circle.,The tooth thickness (齿厚) si- the arc length of the tooth along an arbitrary circle.,The pitch(齿距,周节) pi -arc distance between corresponding points of adjacent teeth along an arbitrary circle. pi = ei + si,pressure angle K,Different point on the involute has different pressu
16、re angle K .,The circle the point on which has 20 pressure angle is defined as reference circle (分度圆).,K,Any parameter on the reference circle has no subscript(下标), r, e, s, p, =20 ,pi = ei + si,p= e + s,The module m (模数)- a basic parameter on the reference circle.,Different module needs different c
17、utter. The module m has been standardized.,m, Z, are three basic parameters of a gear.,Tab 6-1 modules of Involute Cylindrical Gears (GB/T1357-1987),Modules of the first series are preferable.,同模数不同齿数,The addendum (齿顶高) ha- radial distance between the reference circle and the addendum circle.,The de
18、dendum (齿根高) hf -radial distance between the reference circle and the dedendum circle.,The tooth depth (齿全高) h -radial distance between the dedendum circle and addendum circle.,For standard gears:,c* - the coefficient of bottom clearance(顶隙系数),ha* - the coefficient of addendum(齿顶高系数),ha*=1 and c*= 0
19、.25 for the normal tooth(正常齿) ha*= 0.8 and c*= 0.3 for the shorter tooth(短齿),c=c* m- bottom clearance顶隙,Base pitch(基节)pb- the pitch on the base circle.,Normal pitch(法节)pn-The distance between corresponding sides of adjacent tooth profiles along the common normal.,pb=pn,Review: The normal distance be
20、tween two involutes of the same base circle remains the same.,),pb=pn=,The fundamental parameters:,Z, m, , ha*, c*,A standard gear means: m, , ha*, c* take the standard values and e = s,一个齿轮:,d=mz da=d+2ha=(z+2 ha*)m df=d-2hf=(z-2 ha*-2 c*)m db=dcos,ha= ha*m hf=( ha*+ c*)m h=ha+hf=(2 ha*+ c*)m P=m,一
21、对标准齿轮正常安装:,m、z决定了分度圆的大小,而齿轮的大小主要取决于分度圆,因此m、z是决定齿轮大小的主要参数,轮齿的尺寸与m, ha* , c* 有关与z无关,至于齿形,与m,z,有关,模数制齿轮,Involutes,straight lines,6.4.2 The Rack(齿条),i ,pi p m,On the reference line(分度线), e=s.,For standard rack, ha=ha*m, hf=(ha*+c*)m,6.4.3 Internal Gears,The tooth thickness the tooth space,To ensure a co
22、ntinuous transmission, there must exist such situation that two pairs of teeth contact simultaneously(同时地) .,6.5.1 Proper Meshing Conditions(正确啮合条件) for Involute Gears,6.5 Gearing of Involute Spur Gears,两对齿分别在K1,K2点啮合 根据啮合基本定律,K1在N1N2上 K2在N1N2上,K1K2法向齿距,在齿轮1上: K1K2 =Pb1,在齿轮2上: K1K2 =Pb2,Pb1=Pb2,The
23、proper meshing condition for involute gears:,The modules and pressure angles of two meshing gears are the same respectively.,The centre distance a is equal to (r1+r2), the reference circles coincide with their pitch circles. 节圆,The two reference circles are tangent and roll without slipping.,6.5.2 C
24、entre Distance and Working Pressure Angle of a Gear Pair,要求:一、侧隙应该为零 二、顶隙为标准值,To keep zero backlash, it holds: 无侧隙啮合条件,the bottom clearance(顶隙) c : the radial distance from the dedendum circle of one gear to the addendum circle of another,标准安装,标准顶隙,Therefore, when two standard gears are assembled at
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 南京理工大学 机械 原理 chapter6ppt 课件
链接地址:https://www.31doc.com/p-2610351.html