3 gear trains(1)

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3 gear trains(1)

  1. 1. 3/14/2013 1 ME‐205 : Element of machine dynamics and design Dr. Muhammad Wasif Assistant  Professor – I.M.D. Ph.D. (CAD/CAM – Canada), M.Engg. (Mfg. Engg. – NEDUET),  B.E. (Mech. Engg. – NED UET). Member ASME and PEC Room : 1st on LHS of main corridor, ground floor – IM Building Machine dynamics : Gear Trains 1 Gear Drives • Are more efficient and durable than the flexible power drives. • Due to different designs of gears, these can used to transmit torque and angular velocity in a wide variety of applications. • Due to no slippage between two gear, power loss in the gear drives are negligible. • Gear drives are used for precise velocity ratios and high power transmission applications. • These are used in compact machines with less center distances. 2ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET)
  2. 2. 3/14/2013 2 Gear Drives ‐ Limitation • Machining of gears are much costlier than the manufacturing of flexible power drives. • It requires proper method of lubrication, for longer life and efficient operation. • Machining error and misalignment cause the noise and vibrations, which result in failure of the gear drives. 3ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Classification of Gear Drives 4ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET)
  3. 3. 3/14/2013 3 Classification of Gear Drives 5ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Differential of  engine Wind turbine Engine  Transmission Opposite direction Same direction Linear direction Gear Drives for Parallel Shafts   6ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Spur Gears • Lengthwise teeth direction is parallel to the gear rotation axis (uniform cross section). • Easy to machine, • High quality gears can be produces. • Available in different types of tooth design and pressure angles. In a gear pair, gears exerts only thrust force on each other. Applications : Watches, toys, transmission drives etc. Spur Gears
  4. 4. 3/14/2013 4 Gear Drives for Parallel Shafts   7ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Helical Gears • Teeth lengthwise direction is oblique to the gear rotation axis (increase length of teeth) • Carry more load due to long teeth. • Gear pair exert axial as well as thrust fore to each other. • Can also be used for non‐parallel shafts. • These gears are more expensive than the spur gear and slightly less efficient. • Applications : Transmission of car, motorcycle. Helical  Gears 8ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET)
  5. 5. 3/14/2013 5 Gear Drives for Non‐Parallel Shafts   9ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Bevel Gears • Are used for non‐parallel, intersecting and non‐ intersecting shafts. • Straight, zerol and spiral bevel gears are different types of bevel gear, based on different curvatures of teeth. • Spiral bevel gears are more durable, produce less vibration, due to gradual contact b/w curved teeth. • Hypoid gear is a special type of spiral bevel gear with pinion at an offset. Straight Bevel Gears Spiral Bevel Gears Gear Drives for Non‐Parallel Shafts   10ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Bevel Gears • Spiral bevel gears provide high reduction ratio. • Have high contact ratio with less noise, than the straight or zerol bevel gears. • Spiral bevel gears are more expensive and machined by complex machine tools. • Applications : Vehicle transmission, choppers. Miter Gears • Special type of bevel gear used for 90 degree shaft with 1:1 velocity ratio. Miter Gears
  6. 6. 3/14/2013 6 11ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) 12ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET)
  7. 7. 3/14/2013 7 Gear Drives for Non‐Parallel Shafts   13ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Worm Gears • Worm is a shank having at least one complete tooth (thread), which drives the wheel having teeth in helical direction, to be driven by a worm. • Provides high reduction ratio • Worm pair rotates in one direction and restrict the rotation in opposite direction. i.e. worm drives the wheel, wheel cannot drive a worm, therefore, it locks the mechanism in one direction. • Noiseless operation. • Applications : chain block, speed reducer. Worm Gears 14ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET)
  8. 8. 3/14/2013 8 15ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Gear Nomenclature 16ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Pitch Point • The basic requirement of gear‐tooth  geometry is the provide the velocity ratios  exactly constant. • The action of a pair of gear teeth satisfying  this requirement is termed conjugate  gear‐tooth action. • Law of gearing states; “As the gears rotate, the common  normal to the surfaces at the point of contact  must always intersect the line of centers at  the same point P, called the pitch point.”
  9. 9. 3/14/2013 9 Gear Nomenclature 17ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Pitch Circles • A Circle passing through the pitch point, with the center at the rotation axis of the gear is called pitch circle. • A gear with larger pitch circle is called member gear, whereas, other gear with smaller pitch circle is called pinion. No matter which one is driver or driven. • The velocity ratio and center distance are; . . 0.5 = Where, p=pinion, g=gear, =angular velocity d=pitch diameter, r=pitch radius. Gear Nomenclature 18ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Pressure Angle • Circle passing through the pitch point, with the center at the rotation axis of the gear is called pitch circle. • The gear with larger pitch circle is called member gear, whereas, gear with smaller pitch circle is called pinion. No matter which one is driver or driven. • The velocity ratio between two gear is; . . Where, p=pinion, g=gear, =angular velocity d i h di f h
  10. 10. 3/14/2013 10 Gear Nomenclature 19ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) • For a 3D spur gear, pitch cylinder is considered, which is formed by pitch circle pulled about the rotation axis of the gear. • The tooth surface above the pitch cylinder is called “face”, whereas, tooth surface below the cylinder is called ” flank”. • Circular pitch (p) : Distance measured on the circumference of the pitch circle from a point of one tooth to the corresponding point on the next tooth. • Pressure angle () : It is the angle between the common normal to two gear teeth at the point of contact and the common tangent at the pitch point.  Gear Nomenclature 20ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) Profile
  11. 11. 3/14/2013 11 Gear Nomenclature 21ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) • For a 3D spur gear, pitch cylinder is considered, which is formed by pitch circle pulled about the rotation axis of the gear. • The tooth surface above the pitch cylinder is called “face”, whereas, tooth surface below the cylinder is called ” flank”. • Circular pitch (p) : Distance measured on the circumference of the pitch circle from a point of one tooth to the corresponding point on the next tooth. ∙ ∙ • Diametral pitch (P) : No. of teeth per inch.  Gear Nomenclature 22ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) • Module (m) : Pitch diameter in mm. 1 • Addendum : It is the radial distance of a tooth from the pitch circle to the top of the tooth. • Dedendum : It is the radial distance of a tooth from the pitch circle to the bottom of the tooth. • Addendum circle : It is the circle drawn through the top of the teeth and is concentric with the pitch circle. • Dedendum circle : It is the circle drawn through the bottom of the teeth. It is also called root circle. • Total depth : It is the radial distance between  the addendum and the dedendum circle of a • gear.
  12. 12. 3/14/2013 12 Gear Nomenclature 23ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) • Clearance : It is the radial distance from the top of the tooth to the bottom of the tooth, in a meshing gear. • Working depth. It is radial distance from the addendum circle to the clearance circle. It is equal to the sum of the addendum of the two meshing gears. • Tooth thickness : It is the width of the tooth measured along the pitch circle. • Tooth space : It is the width of space  between the two adjacent teeth measured  along the pitch circle. • Backlash : It is the difference between the  tooth space and the tooth thickness, as  measured on the pitch circle. Gear Nomenclature 24ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET) • Top land : It is the surface of the top of the tooth. • Face width : It is the width of the gear tooth measured parallel to the axis of rotation. • Profile : It is the curve formed by the face and flank of the tooth. • Fillet radius : It is the radius that connects the root circle to the profile of the tooth. • Path of contact : It is the path traced by the point of contact of two teeth from the beginning to the end of engagement.
  13. 13. 3/14/2013 13 Refernces 25 • R.S. Khurmi, G.K. Gupta, 2005, A text book of machine design, New Dehli‐ India,  EURASIA PUBLISHING HOUSE. • R. G. Budynass, J.K. Nisbett, 2005, Shigley’s Mechanical Engineering Deisgn, New  York –USA, McGraw Hill. • R.C. Juvinall, K.M. Marshek, 2012, Fundamental of Machine Componenet Design,  NJ, John Willey and Sons. • http://www.mae.ncsu.edu/eischen/ • http://www.khkgears.co.jp/en/gear_technology/pdf/gearabc_b.pdfB. J. Hamrock • http://www.xtek.com/pdf/wp‐gear‐terminology.pdf • http://www.khkgears.co.jp/en/gear_technology/pdf/gearabc_b.pdf

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