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KOM-UNIT-4Gear 1
This document provides an overview of gears, discussing their types, advantages, and disadvantages, as well as their functionality in transmitting motion and power. The text covers various gear types including spur, helical, herringbone, bevel, and worm gears, along with their specific applications and characteristics. Additionally, it elaborates on gear nomenclature, backlash, velocity ratios, and types of gear trains, emphasizing the importance of gears in mechanical systems.
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KOM-UNIT-4Gear 1
- 1. GEAR….. • Gears aretoothed wheels used for transmitting motion and power from one shaft to another when they are not too far apart and when a constant velocity ratio is desired
- 2. Advantages of GearDrive • Since there is no slip, so exact velocity ratio is obtained. • Larger power can be transmitted.(Compare to Belt & Chain) • Its more efficient (upto 99%) • Its require less space
- 3. Dis-Advantages of GearDrive • Need special machines and tools for manufacturing Gear. • High maintenance cost • Chances of vibration & Noise in operation • It require precise alignment of shafts for power transmission.
- 4. TYPES OF GEARS Accordingto the position of axes of the shafts. a. Parallel 1.Spur Gear 2.Helical Gear 3. Herringbone Gear 4.Rack and Pinion b. Intersecting Bevel Gear - Straight bevel Gear - Spiral beval Gear c. Non-intersecting and Non-parallel worm and worm gears
- 5. SPUR GEAR • Teethis parallel to axis of rotation • Transmit power from one shaft to another parallel shaft • Used in Electric screwdriver, oscillating sprinkler, windup alarm clock, washing machine and clothes dryer
- 6. External and Internalspur Gear…
- 7. Helical Gear • Theteeth on helical gears are cut at an angle to the face of the gear • This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears • One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees
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- 9. Herringbone gears • Toavoid axial thrust, two helical gears of opposite hand can be mounted side by side, to cancel resulting thrust forces • Herringbone gears are mostly used on heavy machinery.
- 10. Rack and pinion •Rack and pinion gears are used to convert rotation (From the pinion) into linear motion (of the rack) • A perfect example of this is the steering system on many cars
- 11. Bevel gears • Bevelgears are useful when the direction of a shaft's rotation needs to be changed • They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well • The teeth on bevel gears can be straight, spiral or hypoid • locomotives, marine applications, automobiles, printing presses, cooling towers, power plants, steel plants, railway track inspection machines, etc.
- 12. Straight and SpiralBevel Gears Straight Bevel Gear Spiral Bevel Gear
- 13. WORM AND WORMGEAR • Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater • Many worm gears have an interesting property that no other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm • Worm gears are used widely in material handling and transportation machinery, machine tools, automobiles etc
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- 20. NOMENCLATURE • Pitch Circle: –The circle, the radius of which is equal to the distance from the center of the gear to the pitch point. • Pitch Diameter: – Diameter of the pitch circle • Pitch Point: – The point of tangency of the pitch circles of two meshing gears, where the Line of Centers crosses the pitch circles. • Pressure Angle: – Angle between the Line of Action and a line perpendicular to the Line of Centers.
- 21. . – Face: • Theworking surface of a gear tooth, located between the pitch diameter and the top of the tooth. – Face Width: • The width of the tooth measured parallel to the gear axis. – Flank: • The working surface of a gear tooth, located between the pitch diameter and the bottom of the space between gear teeth • Addendum: – The radial distance between the Pitch Circle and the top of the teeth. Dedendum: • The radial distance between the bottom of the space between teeth and the pitch circle.
- 22. . • Whole Depth—addendum + dedendum + Clearance • Working Depth — addendum + dedendum • Circular Pitch: – Inches of Pitch Circle circumference per tooth. • Circular Thickness: – The thickness of the tooth measured along an arc following the Pitch Circle • Clearance: – The distance between the top of a tooth and the bottom of the space into which it fits on the meshing gear. Clearance Circle— A circle that is tangent to the addendum circle of the mating gear.
- 23. Back lash ingears • Backlash: The difference between the circle thickness of one gear and the tooth space of the mating gear. • Spur gear backlash is the amount of tooth space between mating gears at the pitch circle diameter
- 24. NOMENCLATURE…. • Diametral pitch(Pd): The number of teeth of a gear unit pitch diameter. The diametral pitch is, by definition, the number of teeth divided by the pitch diameter. That is, Where Pd = diametral pitch N = number of teeth D = pitch diameter • Module (m): Pitch diameter divided by number of teeth. The pitch diameter is usually specified in inches or millimeters; in the former case the module is the inverse of diametral pitch. m = D/N D N Pd
- 25. VELOCITY RATIO OFGEAR DRIVE d = Diameter of the wheel N =Speed of the wheel ω = Angular speed velocity ratio (n) = 2 1 1 2 1 2 d d N N
- 26. Fundamental Law ofGearing • The angular velocity ratio between the gears in a gear-set must remain constant throughout the gear mesh
- 27. GEAR TRAINS • Agear train is two or more gear working together by meshing their teeth and turning each other in a system to generate power and speed • It reduces speed and increases torque • Electric motors are used with the gear systems to reduce the speed and increase the torque
- 28. Types of GearTrains • Simple gear train • Compound gear train • Planetary gear train Simple Gear Train • The most common of the gear train is the gear pair connecting parallel shafts. The teeth of this type can be spur, helical or herringbone. • Only one gear may rotate about a single axis
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- 30. Compound Gear Train •For large velocities, compound arrangement is preferred • Two or more gears may rotate about a single axis
- 31. Planetary Gear Train(Epicyclic Gear Train)
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- 33. Planetary Gear Train… •In this train, the blue gear has six times the diameter of the yellow gear • The size of the red gear is not important because it is just there to reverse the direction of rotation • In this gear system, the yellow gear (the sun) engages all three red gears (the planets) simultaneously • All three are attached to a plate (the planet carrier), and they engage the inside of the blue gear (the ring) instead of the outside.
- 34. Planetary Gear Train… •Because there are three red gears instead of one, this gear train is extremely rugged. • planetary gear sets is that they can produce different gear ratios depending on which gear you use as the input, which gear you use as the output, and which one you hold still.
- 35. Planetary Gear Train… •They have higher gear ratios. • They are popular for automatic transmissions in automobiles. • They are also used in bicycles for controlling power of pedaling automatically or manually. • They are also used for power train between internal combustion engine and an electric motor
- 36. Short Quetions • Whatis power transmission? • Why gear drives are called positively driven? • What is backlash in gears? • What are the types of gears available? • What is gear train? Why gear trains are used? • Why intermediate gear in simple gear train is called idler? • What is the advantage of using helical gear over spur gear? • List out the applications of gears • Define the term ‘module’ in gear tooth • What is herringbone gear?
- 37. Essay type questions •With sketch explain various types of gears • With sketch explain three types of gear trains • With neat sketch explain the nomenclature of spur gear • Write the applications, advantages and disadvantages of gear drives