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Mechanical Transmissions

Mechanical Transmissions. Belts. Chains. Gears. CONTENTS GEAR TYPES OF GEARS NOMENCLATURE APPLICATIONS OF GEARS VELOCITY RATIO GEAR TRAINS EXAMPLE PROBLEMS AND QUESTIONS. Gears – What are they?.

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Mechanical Transmissions

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  1. Mechanical Transmissions Belts Chains Gears

  2. CONTENTS GEAR TYPES OF GEARS NOMENCLATURE APPLICATIONS OF GEARS VELOCITY RATIO GEAR TRAINS EXAMPLE PROBLEMS AND QUESTIONS

  3. Gears – What are they? Gears are wheels with teeth. Gears mesh together and make things turn. Gears are used to transfer motion or power from one moving part to another.

  4. Gears – The Purpose Sports cars go fast (have speed) but cannot pull any weight. Big trucks can pull heavy loads (have power), but cannot go fast. Gears cause this. Gears increase or decrease the power or speed, but you cannot generally speaking.

  5. Gears are generally used for one of four different reasons: • To reverse the direction of rotation • To increase or decrease the speed of rotation • To move rotational motion to a different axis

  6. 1. According to the position of axes of the shafts. Parallel 1.Spur Gear 2.Helical Gear 3.Rack and Pinion b. Intersecting Bevel Gear c. Non-intersecting and Non-parallel worm and worm gears TYPES OF GEARS

  7. Types of Gears

  8. SPUR GEAR Teeth is parallel to axis of rotation Transmit power from one shaft to another parallel shaft Spur Gears in any transmission system are employed for changing the speed and the torque and are fixed on shafts Gear ‘A’ is called the ‘driver’ because this is turned by a motor. As gear ‘A’ turns it meshes with gear ‘B’ and it begins to turn as well. Gear ‘B’ is called the ‘driven’ gear.

  9. Spur Gears Pinion Gear

  10. Spur Gears - Types External Set: Opposite Movement Internal Set: Movement in the same direction

  11. The teeth 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 Helical Gear

  12. Helical Gear… Helical Gears can be used for transmitting motion between parallel shafts as between perpendicular shafts. Helical gears used for transmission at an angle are called SPIRAL GEARS.

  13. Herringbone gears HERRING-BONE Gears are pairs of Helical Gears. These gears are used for large power transmission. • Herringbone gears are mostly used on heavy machinery.

  14. 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 The rotary motion of pinion 1 (small gear) is transformed into linear motion of the rack 2. For transmitting large power worm & worm rack transmission is employed.

  15. A ‘rack and pinion’ gears system looks quite unusual. However, it is still composed of two gears. The ‘pinion’ is the normal round gear and the ‘rack’ is straight or flat. The ‘rack’ has teeth cut in it and they mesh with the teeth of the pinion gear. The pinion rotates and moves the rack in a straight line - another way of describing this is to say ‘rotary motion’ changes to ‘linear motion’.

  16. Bevel gears Bevel gears can be used to change the direction of drive in a gear system by 90 degrees. A good example is seen as the main mechanism for a hand drill. As the handle of the drill is turned in a vertical direction, the bevel gears change the rotation of the chuck to a horizontal rotation

  17. Straight and Spiral Bevel Gears

  18. 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 WORM AND WORM GEAR

  19. Types of Gears“According to the position of axes of the shafts” Parallel Helical Gears Spur Gears Herringbone Gears B. Perpendicular Axis C. Planetary Intersecting Non Intersecting Planetary Gears Bevel Gears Worm Gears

  20. Planetary Gears“suited for highly dynamic drives” • With their weight advantage, planetary gearboxes are also well established for extremely high output torque and for mobile applications. • The maximum ratio that can be achieved in a single stage is approximately i = 12. Larger ratios are then achieved by adding further downstream stages. • Alongside the increased load capacity, it is also reduce noise emissions.

  21. Base Circle Pitch circle gear diam. Backlash = (tooth spacing)driven gear – (tooth thickness)driver , measured on the pitch circle. Nomenclature of Spur Gear Teeth Clearance Fillet radius

  22. Face of a tooth: That part of the tooth surface lying outside the pitch surface. Flank of a tooth: The part of the tooth surface lying inside the pitch surface. Circular thickness (also called the tooth thickness): The thickness of the tooth measured on the pitch circle. It is the length of an arc and not the length of a straight line. Tooth space: pitch diameter The distance between adjacent teeth measured on the pitch circle. Backlash: The difference between the circle thickness of one gear and the tooth space of the mating gear. Circular pitch (Pc) : The width of a tooth and a space, measured on the pitch circle. NOMENCLATURE….

  23. NOMENCLATURE OF SPUR GEARS

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