Types of gears


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Types of gears

  1. 1. Gears Mechanical Engineering Dept. 1
  2. 2. Applications of Gears• Toys and Small Mechanisms – small, low load, low cost• Appliance gears – long life, low noise & cost, low to moderate load• Power transmission – long life, high load and speed• Aerospace gears – light weight, moderate to high load• Control gears – long life, low noise, precision gears Mechanical Engineering Dept. 2
  3. 3. Mechanical Engineering Dept. 3
  4. 4. Types of Gears Gear (large gear)Spur gears – tooth profile is parallel tothe axis of rotation, transmits motionbetween parallel shafts. Internal gears Pinion (small gear)Helical gears – teeth are inclined tothe axis of rotation, the angle providesmore gradual engagement of the teethduring meshing, transmits motionbetween parallel shafts. Mechanical Engineering Dept. 4
  5. 5. Types of GearsBevel gears – teeth are formed on a Straightconical surface, used to transfer bevel gearmotion between non-parallel andintersecting shafts. Spiral bevel gear Mechanical Engineering Dept. 5
  6. 6. Types of GearsWorm gear sets – consists of ahelical gear and a power screw (worm),used to transfer motion between non-parallel and non-intersecting shafts.Rack and Pinion sets – a special Pinioncase of spur gears with the gearhaving an infinitely large diameter,the teeth are laid flat. Rack Mechanical Engineering Dept. 6
  7. 7. Types of gears 7
  8. 8. Nomenclature of Spur Gear Teeth Clearance Fillet radius Pitch circle gear diam. Base CircleBacklash = (tooth spacing)driven gear – (tooth thickness)driver , measured on the pitch circle. Mechanical Engineering Dept. 8
  9. 9. Useful Relations P=N/d P = diametral pitch, teeth per inch N = number of teeth d = pitch diameter (gear diameter)p (circular pitch) = πd / N Pp = πMetric systemm (module, mm) = d / N Mechanical Engineering Dept. 9
  10. 10. Standard Tooth SpecificationsPressure angle Base tion of ac circle Line Pitch Pressure angle φ circle Pitch Pitch circle line Base circle Line of centersStandard pressure angles, 14.5o (old), 20o, and 25o Two mating gears must have the same diametral pitch, P, and pressure angle, φ. Mechanical Engineering Dept. 10
  11. 11. Template for teeth of standard gears 11
  12. 12. Standard Gear Specifications Parameter Coarse pitch Fine pitch (pd=N/d<20) (pd=N/d>20) Pressure angle, φ 200 or 250 (not common) 200 Addendum, a 1/pd 1/pd Dedendum, b 1.25/pd 1.25/pd Working depth 2.00/pd 2.00/pd Whole depth 2.25/pd 2.2/pd+0.002Circular tooth thickness 1.571/pd (≅circular pitch/2) 1.571/pd Fillet radius 0.30/pd Not standardized Clearance 0.25/pd 0.25/pd+0.002Minimum width at top 0.25/pd Not standardized land Circular pitch π/pd π/pd 12
  13. 13. Kinematics of Gear Trains Conventional gear trains ω3 N2 ω5 N4 , ω3 = ω4 , ω2 = N3 ω4 = N5 Speed ratio ω5 output = = input ω2 mV = e = train valueReverted gear train – output shaft is concentricwith the input shaft. Center distances of thestages must be equal. Mechanical Engineering Dept. 13
  14. 14. Planetary (or Epicyclic) Gears• Gears whose centers can move• Used to achieve large speed reductions in compact space• Can achieve different reduction ratios by holding different combinations of gears fixed• Used in automatic transmissions of cars 14
  15. 15. Planetary gear 15
  16. 16. Components of a planetary gear Planet Carrier Input shaft Sun gear Ring gear 16
  17. 17. A variant of a planetary gear Carrier 17
  18. 18. Connecting the main engine to the propeller through a reduction gear Propeller, Output flange operates at about 100 RPM Engine Gea r Engine operates at about 400 RPM 18
  19. 19. Gear box Stick shift SynchronizersThe gear box is in first gear, second gear 19
  20. 20. Planetary gears in automotive transmission Planetary gears 20