Types of gears

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  • 1. Gears Mechanical Engineering Dept. 1

2. Applications of Gears Toys and Small Mechanisms small, low load, low cost Appliance gears long life, low noise & cost, low tomoderate 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. Mechanical Engineering Dept. 3 4. Types of GearsGear (large gear)Spur gears tooth profile is parallel tothe axis of rotation, transmits motionbetween parallel shafts. Internal gearsPinion (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. Types of GearsBevel gears teeth are formed on aStraightconical surface, used to transferbevel gearmotion between non-parallel andintersecting shafts. Spiral bevel gearMechanical Engineering Dept.5 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 specialPinioncase of spur gears with the gearhaving an infinitely large diameter,the teeth are laid flat.Rack Mechanical Engineering Dept.6 7. Types of gears 7 8. Nomenclature of Spur Gear Teeth Clearance Fillet radiusPitch circlegear diam. Base CircleBacklash = (tooth spacing)driven gear (tooth thickness)driver , measured on the pitch circle. Mechanical Engineering Dept.8 9. Useful Relations P=N/dP = diametral pitch, teeth per inchN = number of teethd = pitch diameter (gear diameter)p (circular pitch) = d / N Pp = Metric systemm (module, mm) = d / NMechanical Engineering Dept. 9 10. Standard Tooth SpecificationsPressure angleBase tion of accircleLinePitch Pressure angle circle PitchPitchcircleline Base circleLine of centersStandard pressure angles, 14.5o (old), 20o, and 25o Two mating gears must have the same diametral pitch, P, and pressure angle, . Mechanical Engineering Dept.10 11. Template for teeth of standard gears 11 12. Standard Gear Specifications ParameterCoarse pitch Fine pitch(pd=N/d20) Pressure angle, 200 or 250 (not common)200 Addendum, a1/pd1/pd Dedendum, b 1.25/pd1.25/pdWorking depth2.00/pd2.00/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/pdNot standardizedClearance0.25/pd 0.25/pd+0.002Minimum width at top 0.25/pdNot standardized land Circular pitch /pd/pd 12 13. Kinematics of Gear Trains Conventional gear trains3 N25 N4, 3 = 4 ,2 = N34 = N5Speed ratio5 output== input2 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. Planetary (or Epicyclic) Gears Gears whose centers can move Used to achieve large speed reductions incompact space Can achieve different reduction ratios byholding different combinations of gearsfixed Used in automatic transmissions of cars14 15. Planetary gear 15 16. Components of a planetary gear Planet CarrierInput shaft Sun gear Ring gear 16 17. A variant of a planetary gearCarrier17 18. Connecting the main engine to the propeller through a reduction gearPropeller,Output flangeoperates at about 100RPM EngineGear Engine operates at about 400 RPM18 19. Gear box Stick shift SynchronizersThe gear box is in first gear, second gear 19 20. Planetary gears in automotivetransmission Planetary gears20