Ch15 - bud21932_ch15_765-804 3:48 AM Page 765 CONFIRMING PAGES 1 5 Chapter Outline 151 152 153 154 155 156 157 158 159 Bevel GearingGeneral 766

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15 Bevel and Worm Gears Chapter Outline 15–1 Bevel Gearing—General 766 15–2 Bevel-Gear Stresses and Strengths 768 15–3 AGMA Equation Factors 771 15–4 Straight-Bevel Gear Analysis 783 15–5 Design of a Straight-Bevel Gear Mesh 786 15–6 Worm Gearing—AGMA Equation 789 15–7 Worm-Gear Analysis 793 15–8 Designing a Worm-Gear Mesh 797 15–9 Buckingham Wear Load 800 765
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766 Mechanical Engineering Design The American Gear Manufacturers Association (AGMA) has established standards for the analysis and design of the various kinds of bevel and worm gears. Chapter 14 was an introduction to the AGMA methods for spur and helical gears. AGMA has estab- lished similar methods for other types of gearing, which all follow the same general approach. 15–1 Bevel Gearing—General Bevel gears may be classified as follows: Straight bevel gears Spiral bevel gears Zerol bevel gears Hypoid gears Spiroid gears A straight bevel gear was illustrated in Fig. 13–35. These gears are usually used for pitch-line velocities up to 1000 ft/min (5 m/s) when the noise level is not an important consideration. They are available in many stock sizes and are less expensive to produce than other bevel gears, especially in small quantities. A spiral bevel gear is shown in Fig. 15–1; the definition of the spiral angle is illus- trated in Fig. 15–2. These gears are recommended for higher speeds and where the noise level is an important consideration. Spiral bevel gears are the bevel counterpart of the helical gear; it can be seen in Fig. 15–1 that the pitch surfaces and the nature of con- tact are the same as for straight bevel gears except for the differences brought about by the spiral-shaped teeth. The Zerol bevel gear is a patented gear having curved teeth but with a zero spiral angle. The axial thrust loads permissible for Zerol bevel gears are not as large as those for the spiral bevel gear, and so they are often used instead of straight bevel gears. The Zerol bevel gear is generated by the same tool used for regular spiral bevel gears. For design purposes, use the same procedure as for straight bevel gears and then simply substitute a Zerol bevel gear. Figure 15–1 Spiral bevel gears. (Courtesy of Gleason Works, Rochester, N.Y.)
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Bevel and Worm Gears 767 Basic crown rack Cutter radius Spiral angle Mean radius of crown rack Circular pitch Face advance ± Figure 15–2 Cutting spiral-gear teeth on the basic crown rack. Figure 15–3 Hypoid gears. (Courtesy of Gleason Works, Rochester, N.Y.) It is frequently desirable, as in the case of automotive differential applications, to have gearing similar to bevel gears but with the shafts offset. Such gears are called hypoid gears, because their pitch surfaces are hyperboloids of revolution. The tooth action between such gears is a combination of rolling and sliding along a straight line and has much in common with that of worm gears. Figure 15–3 shows a pair of hypoid gears in mesh.
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This note was uploaded on 03/22/2010 for the course MEEN ISEN 302 taught by Professor Kim during the Spring '10 term at Texas A&M University–Commerce.

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Ch15 - bud21932_ch15_765-804 3:48 AM Page 765 CONFIRMING PAGES 1 5 Chapter Outline 151 152 153 154 155 156 157 158 159 Bevel GearingGeneral 766

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