圈上海夫通大华 西+口 LECTURE 12-1 ME371/ME337 DESIGN AND MANUFACTURING Gears Introduction Covered: 漏 Ch9 in Design of Machinery SHAN 圈上泽夫通大学 Lectures Power/Energy Conversion (Electrical Motors) Power/Energy Transmission (Gears,Cam,Linkage, Belt Drives, Power Screws Transmission Joints (Fasteners, Support Connectors) (Bearings) Structural Support (Frames) Tools Statics,Dynamics, Stress Analysis,etc. 1
1 Gears Introduction LECTURE 12-I ME371/ME337 DESIGN AND MANUFACTURING Covered: Ch9 in Design of Machinery Lectures Power/Energy Conversion (Electrical Motors) Transmission Support (Bearings) Joints (Fasteners, Connectors) Structural Support (Frames) Tools Statics, Dynamics, Stress Analysis, etc. Power/Energy Transmission (Gears, Cam, Linkage, Belt Drives, Power Screws)
圆上清支大学 Outline Common Types of Gears Fundamental Law of Gearing Gear tooth nomenclature How to manufacture a gear? Interference and undercutting 圆上海文大学 Where can we find gears? 上方肉 2
2 Outline Common Types of Gears Fundamental Law of Gearing Gear tooth nomenclature How to manufacture a gear? Interference and undercutting Where can we find gears?
圈上海文通大华 Why Use Gears? 1.Reduce/lncrease speed 2.Increase torque 3.Move power from one point to another 4.Change direction of power 5.Split power Generally this functionality is accomplished by many gears mounted in a gear box! 圈上泽充大学 Common Types of Gears 3
3 1. Reduce/Increase speed 2. Increase torque 3. Move power from one point to another 4. Change direction of power 5. Split power Generally this functionality is accomplished by many gears mounted in a gear box! Why Use Gears? Common Types of Gears
圈上泽文通大华 Common Types of Gears 圈上泽夫道大学 Spur Gear(直齿轮) These gears have teeth parallel to the axis of rotation and are used to transmit motion and power from one shaft to another parallel shaft. low cost for transmitting motion and power between parallel shafts. 口 Low cost to manufacture. 4
4 Common Types of Gears Spur Gear（直齿轮） These gears have teeth parallel to the axis of rotation and are used to transmit motion and power from one shaft to another parallel shaft. low cost for transmitting motion and power between parallel shafts. Low cost to manufacture
圆上清支美大学 Helical Gears(斜齿轮) Helical gears are similar to spur gears but have teeth inclined to the axis of rotation. ▣ Helix angle can be a few degrees or as much as 450 ▣ Can perform essentially same function as spur gears, connecting parallel shafts for speed reduction/increase and torque increase/reduction. o 周 上海充廷大学 Helical Gears(斜齿轮) 口 Helix is either right or left-handed (左旋、右旋) ▣ Opposite-hand helical gears with the same helix angle mesh(啮合) with their axes parallel. Same-hand helical gears mesh with their (non-intersecting)axes skewed or crossed >Have theoretical point contact between the teeth. >Limits their load-carrying capacity compared to parallel-axis helicals. which mate with a roll-slide motion (a)Opposite-hand pair (b)Same-hand pair similar to spur gears,but engage meshed on parallel meshed on crossed their teeth in a smooth,wiping axes axes action across the face width 5
5 Helical gears are similar to spur gears but have teeth inclined to the axis of rotation. Helical Gears（斜齿轮） Helix angle can be a few degrees or as much as 450 Can perform essentially same function as spur gears, connecting parallel shafts for speed reduction/increase and torque increase/reduction. Helix is either right or left-handed (左旋、右旋) Opposite-hand helical gears with the same helix angle mesh (啮合) with their axes parallel. Same-hand helical gears mesh with their (non-intersecting) axes skewed or crossed Have theoretical point contact between the teeth. Limits their load-carrying capacity compared to parallel-axis helicals, which mate with a roll-slide motion similar to spur gears, but engage their teeth in a smooth, wiping action across the face width Helical Gears（斜齿轮）
圈上泽文通大华 Helical Gears(斜齿轮) Advantages: >Quieter running >Greater strength for the same size gear. ▣ Disadvantages: >Greater cost than spur gears >Introduction of axial component of force Requires thrust bearings on the shaft. Parallel-axis helical gears used extensively in vehicle transmission Both manual and automatic-shifting >Principally because of their quiet running. 圈上泽夫道大学 Bevel Gears(锥齿轮) Bevel gears have teeth formed on conical surfaces and are used mostly to transmit motion and power between intersecting shafts. >Straight Bevel(直齿圆锥齿轮) >Spiral(螺旋锥齿轮) >Hypoid(准双曲面伞齿轮) 6
6 Advantages: Quieter running Greater strength for the same size gear. Disadvantages: Greater cost than spur gears Introduction of axial component of force Requires thrust bearings on the shaft. Parallel-axis helical gears used extensively in vehicle transmission Both manual and automatic-shifting Principally because of their quiet running. Helical Gears（斜齿轮） Bevel gears have teeth formed on conical surfaces and are used mostly to transmit motion and power between intersecting shafts. Straight Bevel（直齿圆锥齿轮） Spiral （螺旋锥齿轮） Hypoid （准双曲面伞齿轮） Bevel Gears （锥齿轮）
圈上海文通大华 Bevel Gears 口Straight Bevel(直齿圆锥齿轮) >Usually used for pitch-line velocities up to 1000 ft/min (When the noise level is not an important consideration) >Available in many stock sizes >Less expensive to produce than other bevel gears,especially in small quantities. 圈上泽夫道大学 Bevel Gears 口Spiral(螺旋锥齿轮) >Similar to bevel gears >However,teeth are angled with respect to axis at a spiral angle(analogous to the helix angle of helical gears). >Recommended for higher speeds and where noise level is an important consideration. >Have less vibration >Stronger than straight bevel gear of same diameter and pitch.(Because spiral's tooth is thicker in direction of loading) 7
7 Bevel Gears Straight Bevel（直齿圆锥齿轮） Usually used for pitch-line velocities up to 1000 ft/min (When the noise level is not an important consideration) Available in many stock sizes Less expensive to produce than other bevel gears, especially in small quantities. Spiral （螺旋锥齿轮） Similar to bevel gears However, teeth are angled with respect to axis at a spiral angle (analogous to the helix angle of helical gears). Recommended for higher speeds and where noise level is an important consideration. Have less vibration Stronger than straight bevel gear of same diameter and pitch.(Because spiral’s tooth is thicker in direction of loading) Bevel Gears
圆上泽文大学 Worms and worm Gears Worms(蜗杆)and worm gears are used to transmit motion and power between nonparallel,nonintersecting axes. Worm is similar to a screw thread. having one or a few teeth Helix angle is very large. Worm mates with a special gear called a worm gear or worm wheel Analogous to a nut being advanced by the thread of the worm. Their axes are typically at 90 degrees to one another. © 上海充廷大学 Worms and worm Gears The worm set can give very large gear ratios(up to about 360:1)in a compact package >Because of the small number of teeth on the worm. If the lead angle of the worm is small enough ( about 6 degree)the worm set can be self-locking In other words,it cannot be back-driven from the worm gear,i.e.it will hold a load. 8
8 Worms （蜗杆） and worm gears are used to transmit motion and power between nonparallel, nonintersecting axes. Worms and worm Gears Worm is similar to a screw thread, having one or a few teeth Helix angle is very large. Worm mates with a special gear called a worm gear or worm wheel Analogous to a nut being advanced by the thread of the worm. Their axes are typically at 90 degrees to one another. The worm set can give very large gear ratios (up to about 360:1) in a compact package Because of the small number of teeth on the worm. If the lead angle of the worm is small enough (< about 6 degree) the worm set can be self-locking In other words, it cannot be back-driven from the worm gear, i.e. it will hold a load. Worms and worm Gears
圈上海文通大华 Worms and worm Gears ▣Disadvantage: >Relatively low efficiency compared to other gear sets. The relative motion at the teeth is sliding rather than rolling > Generates significant heat. Heat transfer from the gearbox,rather than the stresses in the teeth,can limit a worm set's life. The oil temperature in the mesh should be kept below about 200 degree Fahrenheit for long tooth life. 圈上泽夫通大学 Common Types of Gears Type Shaft Orientation Advantages Disadvantages Spur Parallel,Non-Intersecting High efficiency Noisy Parallel,Non-Intersecting Helical Non-Parallel,Non- Lower Noise More expensive Intersecting Bevel Shaft Any angle,intersecting or Greater Thrust and non-intersecting Orientation Loads Hypoid change Worm Perpendicular,non- High Gear Ratio,not Low Efficiency intersecting back drivable 9
9 Disadvantage: Relatively low efficiency compared to other gear sets. The relative motion at the teeth is sliding rather than rolling Generates significant heat. Heat transfer from the gearbox, rather than the stresses in the teeth, can limit a worm set’s life. The oil temperature in the mesh should be kept below about 200 degree Fahrenheit for long tooth life. Worms and worm Gears Common Types of Gears Type Shaft Orientation Advantages Disadvantages Spur Parallel, Non-Intersecting High efficiency Noisy Helical Parallel, Non-Intersecting Non-Parallel, NonIntersecting Lower Noise More expensive Bevel and Hypoid Any angle, intersecting or non-intersecting Shaft Orientation change Greater Thrust Loads Worm Perpendicular, nonintersecting High Gear Ratio, not back drivable Low Efficiency
圆上清支大学 Outline Common Types of Gears Fundamental Law of Gearing Gear tooth nomenclature How to manufacture a gear? Interference and undercutting 圆上清支大丝 Fundamental Law of Gearing Assuming roll without slip at the pitch point,what is the relationship between the angular velocities of the cylinders? From previous knowledge: 02=-生 03 From Instant Centers:Instant Center(2,3)must be located at point of contact.So, 02 ,3-2,3 03 1,2-2,3) 2 10
10 Outline Common Types of Gears Fundamental Law of Gearing Gear tooth nomenclature How to manufacture a gear? Interference and undercutting Fundamental Law of Gearing Assuming roll without slip at the pitch point, what is the relationship between the angular velocities of the cylinders? From previous knowledge: 2 3 3 2 r r From Instant Centers: Instant Center (2,3) must be located at point of contact. So, 2 3 3 2 1,2 2,3 1,3 2,3 r r
