Helical Gears3 ME350 .Helix is either right or left-handed. >Opposite-hand helical gears with the same helix angle mesh 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. 16
ME 350 16 Helical Gears3 •Helix is either right or left-handed. ¾Opposite-hand helical gears with the same helix angle mesh with their axes parallel. ¾Same-hand helical gears mesh with their (nonintersecting) 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 Gears3 ME350- .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. 17
ME 350 17 Helical Gears3 •Advantages: ¾Quieter running ¾Greater strength for the same size gear. •Disadvantages: ¾Greater cost than spur gears ¾Introduction of axial component of force = Requires thrust bearings on the shaft. •Parallel-axis helical gears used extensively in vehicle transmission ¾Both manual and automatic-shifting ¾Principally because of their quiet running
Helical Gears3 MF350 Edge of paper Base helix angle E13- Base cylinder (a)Opposite-hand pair meshed on parallel axes Section B-B (b)Same-hand pair meshed on crossed axes FIGURE 13-22 18 Nomenclature of helical gears. SectionA-A
ME 350 18 Helical Gears 3
Bevel Gears3 ME350- .Straight Bevel >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. 19
ME 350 19 Bevel Gears3 •Straight Bevel ¾Usually used for pitch-line velocities up to 1000 ft/min = When the noise level is not an important consideration. ¾Available in many stock sizes ¾Less expensive to produce than other bevel gears, especially in small quantities
Bevel Gears3 ME350- Spiral >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 20
ME 350 20 Bevel Gears3 •Spiral ¾Similar to bevel gears ¾However, teeth are angled with respect to axis at a spiral angle (analogous to the helix angle of helical gears). ¾Recommended for higher speeds and where noise level is an important consideration. ¾Have less vibration ¾Stronger than straight bevel gear of same diameter and pitch. = Because spiral’s tooth is thicker in direction of loading