Unit 2 Lesson 2

1、Professional English for Mechanical Engineering Lecture: Xiaobin CuiPart I Mechanical DesignLesson 2 GearsLesson 2 Gears Gears are toothed, cylindrical wheels used for transmitting motion and power from one rotating shaft to another. Mesh 相嚙合perpendicular ,p:pndikjl adj. 垂直的Definition & UsesThe teet

2、h of a driving gear mesh accurately in the spaces between teeth on the driven gear. The driving teeth push on the driven teeth, exerting a force perpendicular to the radius of the gear. Thus, a torque is transmitted, and because the gear is rotating, power is also transmitted. 齒輪是齒輪是有齒的圓柱輪輪，用來把一根旋轉(zhuǎn)軸

3、的運(yùn)動和動力傳遞到另一根軸上。cylindrical slindrikl adj. 圓柱的；圓柱體的 Lesson 2 Gears 1. Spur Gear Geometry & Involute Tooth Form The most widely used spur gear tooth form is the full-depth involute form. Its characteristic shape is shown in Figure 2.1. The involute is one of a class of geometric curves called conjugat

4、e curves. involute invlu:t adj. 漸開線geometric ,di:metrik adj. 幾何學(xué)的conjugate knd,geit adj. 共軛的漸開線是漸開線是幾何共軛曲線曲線中的一種。Spur Gear Geometry & Involute Tooth Formdisengagement ,disingeidmnt n. 脫離Lesson 2 Gears當(dāng)具有漸開線齒廓的兩個齒輪的輪齒嚙合并且旋轉(zhuǎn)時，在兩者兩者之間具有具有恒定的角速度比值比值。From the moment of initial contact to the moment of di

5、sengagement, the speed of the driving gear is in a constant proportion to the speed of the driven gear. 從最初接觸一直到分開，主動輪的速度速度與從動輪的速度速度的比值比值是恒定的。When two such gear teeth are in mesh and rotating, there is a constant angular velocity ratio between them.Spur Gear Geometry & Involute Tooth FormThe resulti

6、ng action of the two gears is very smooth. Otherwise there would be speeding up or slowing down during the engagement, with the resulting accelerations causing vibration, noise, and dangerous torsional oscillations in the system. acceleration k,selrein n. 加速度vibration vaibrein n. 振動oscillation ,slei

7、n n. 振蕩；振動；擺動Lesson 2 Gears若情況并非如此，齒輪嚙合時會出現(xiàn)出現(xiàn)時而加速加速、時而減速減速的情況，產(chǎn)生的加速度會引起系統(tǒng)中振動、噪聲以及危險(xiǎn)的扭轉(zhuǎn)振蕩。Spur Gear Geometry & Involute Tooth Form An involute curve by taking a cylinder and wrapping a string around its circumference can be seen. Tie a pencil to the end of the string. Then start with the pencil tight

8、 against the cylinder, and hold the string tautly. Move the pencil away from the cylinder while keeping the string tautly. The curve drawn is an involute. The circle represented by the cylinder is called the base circle. wrap rp vt. 包；纏繞circumference skmfrns n. 圓周；周長taut t:t adj. 拉緊的；緊張的 Lesson 2 Ge

9、arsSpur Gear Geometry & Involute Tooth FormLesson 2 Gears注意到注意到曲線的任意位置上，繩子代表與基圓相切的一條直線，并且同時此直線與漸開線垂直。Notice that at any position on the curve, the string represents a line tangent to the base circle and, at the same time, perpendicular to the involute. tangent 相切Spur Gear Geometry & Involute Tooth F

10、ormLesson 2 Gears在中心線上找到一個位置再繪制一個基圓，并保證生成的漸開線與第一個漸開線相切，可以證明可以證明在接觸點(diǎn)處，與各自基圓相切的兩條線重合，并且隨著基圓的旋轉(zhuǎn)，線的位置保持不變。Drawing another base circle along the same centerline in such a position that the resulting involute is tangent to the first one, it demonstrates that at the point of contact, the two lines tangent

11、to the base circles are coincident and will stay in the same position as the base circles rotate. This is what happens when two gear teeth are in mesh.demonstrate 證明coincident 重合Spur Gear Geometry & Involute Tooth FormIt is a fundamental principle of kinematics, the study of motion, that if the line

12、 drawn perpendicular to the surfaces of two rotating bodies at the point of contact always crosses the centerline between the two bodies at the same place, the angular velocity ratio of the two bodies will be constant.Lesson 2 Gears 這是這是用來研究運(yùn)動的動力學(xué)的基本原理原理，即在兩個旋轉(zhuǎn)體接觸點(diǎn)處繪制一條與接觸面垂直的直線，若此直線同兩個旋轉(zhuǎn)體間的中心線相交于固定

13、點(diǎn)，那么兩個旋轉(zhuǎn)體的角速度比值為常數(shù)。 kinematics kinimtiks n. 運(yùn)動學(xué)；動力學(xué) Spur Gear Geometry & Involute Tooth FormThis is a statement of gearing. As demonstrated here, the gear teeth made in the involute-tooth form obey the law.2. Helical Gear Geometry Helical and spur gears are distinguished by the orientation of their

14、teeth. On spur gears, the teeth are straight and are aligned with the axis of gear. On helical gears，the teeth are inclined at an angle with the axis, that angle being called the helix angle.Helix angle 螺旋角Lesson 2 Gearsorientation ,:rientein n. 方向；定向be aligned with 與對準(zhǔn)helical helikl adj. 螺旋的incline

15、d inklaind adj. 傾斜的Spur Gear Geometry & Involute Tooth FormHelical Gear GeometryLesson 2 Gears如果齒輪非常寬，就會出現(xiàn)會出現(xiàn)輪齒沿螺旋線方向連續(xù)環(huán)繞在齒輪毛坯上。However, practical considerations limit the width of the gears so that the teeth normally appear to be merely inclined with respect to the axis.然而，出于實(shí)際使用考慮考慮，對齒輪寬度寬度做出限限制制，

16、所以與軸線相比輪齒通常是傾斜的。If the gear was very wide, it would appear that the teeth wind around the gear blank in a continuous, helical path. Helical Gear GeometryFigure 2.2 shows an example of commercially available helical gear. The forms of helical gear teeth are very similar to those discussed for spur ge

17、ars. The basic task is to account for the effect of the helix angle.Lesson 2 Gearscommercially km:li adv. 商業(yè)上spur gear 直齒圓柱齒輪Helical Gear Geometry3. Helix Angle The helix for a given gear can be either left-hand or right-hand. The teeth of a right-hand helical gear would appear to lean to the right

18、when the gear is lying on a flat surface. Conversely, the teeth of a left-hand helical gear would lean to the left. In normal installation, helical gears would be mounted on parallel shafts. Lesson 2 GearsLean to 傾向于， 傾斜于Conversely 相反parallel 平行Helix AngleLesson 2 Gears為完成裝配，要求要求嚙合的兩齒輪，其中之一為右旋，而另一個為

19、左旋，并且應(yīng)具有相同螺旋角。If both gears in mesh are of the same hand, the shafts will be at 90 degrees to each other. Such gears are called crossed helical gears. To achieve this arrangement, it is required that one gear should be of the right-hand design and that the other be left-hand with an equal helix angl

20、e. achieve 達(dá)到，獲得Helix AngleLesson 2 Gears 對于斜齒輪來說，應(yīng)優(yōu)先選用優(yōu)先選用平行軸安裝安裝方式方式，因?yàn)閷ν瑯映叽绲凝X輪而言，這一安裝方式比交錯軸斜齒輪安裝方式的傳遞效率要高很多。 The parallel shaft arrangement for helical gears is preferred because it results in a much higher power-transmitting capacity for a given size of gear than the crossed helical arrangement.

21、Helix AngleLesson 2 Gears The main advantage of helical gears over spur gears is smoother engagement because a given tooth assumes its load gradually instead of suddenly. 相對于直齒圓柱齒輪而言，斜齒輪的主要優(yōu)勢優(yōu)勢是是更為平穩(wěn)的嚙合嚙合過程過程，因?yàn)檩嘄X在嚙合過程中逐漸受載，而非突然加載。assume sju:m vt. 承擔(dān)；假定gradually grjuli adv. 逐漸地；逐步地 Helix AngleContac

22、t starts at one end of a tooth near the tip and progresses across the face in a path downward across the pitch line to the lower flank of the tooth, where it leaves engagement. Lesson 2 Gears接觸接觸從輪齒頂端一側(cè)開始開始，然后在齒面上穿過穿過齒輪節(jié)線到達(dá)輪齒的底部側(cè)面，然后脫離嚙合。tip tip n. 頂端 flank flk n. 側(cè)面Helix AngleLesson 2 Gears同時，在一對輪齒脫離嚙合前另一對輪齒輪齒開始開始嚙合嚙合。這樣，與直齒圓柱齒輪相比，斜齒輪同時嚙合且承受外載的平均齒數(shù)更多。Simultaneously, other teeth are coming into engagement before a given tooth leaves engagement, with the result that a larger average number