Module 3 Gears - Classification PDF

M ACHINE ELEMENTS MODULE 3 Gears  Module 2 LEARNING OUTCOMES 1. Identify the different classification of gears and familiarize the gear nomenclature. 2. Apply gear design formulas in designing a gear....

M ACHINE ELEMENTS MODULE 3 Gears  Module 2 LEARNING OUTCOMES 1. Identify the different classification of gears and familiarize the gear nomenclature. 2. Apply gear design formulas in designing a gear. M ACHINE ELEMENTS GEAR DEFINITION Gears are toothed wheels used in transmitting motion and power from one rotating shaft to another eliminating the slippage during turning. M ACHINE ELEMENTS CLASSIFICATION OF GEARS Gears are classified according to the nature of their axes. Parallel Axes Intersecting Axes Nonparallel & Nonintersecting M ACHINE ELEMENTS  Classification of Gears Parallel Axes Intersecting Axes Nonparallel & Nonintersecting Axes External Spur Gear – cylindrical gears with a tooth line which is straight and parallel to the shaft. Most widely used. Can achieve high accuracy with relatively easy production process. No loading in the axial direction (thrust load). The larger of the meshing pair is called the gear, the smaller called pinion. GEAR PINION M ACHINE ELEMENTS  Classification of Gears Parallel Axes Intersecting Axes Nonparallel & Nonintersecting Axes Internal Spur Gear – Internal gear is a gear with its teeth cut in the internal surface of a cylinder and meshes with spur gears. Primarily used for planetary gear drives. The larger is called the annular. M ACHINE ELEMENTS  Classification of Gears Parallel Axes Intersecting Axes Nonparallel & Nonintersecting Axes Twisted Spur or Helical Gear – cylindrical gears with winding tooth lines. Better meshing than spur gears. Superior quietness and can transmit higher loads. Suitable for high speed applications. Requires thrust bearing due to axial load. M ACHINE ELEMENTS  Classification of Gears Parallel Axes Intersecting Axes Nonparallel & Nonintersecting Axes Herringbone Gear – side to side combination of two helical gears of opposite hands. Unlike helical gears, they do not produce an additional axial load. Like helical gears, they have the advantage of transferring power smoothly. The side thrust of one half is balanced by that of the other half. M ACHINE ELEMENTS  Classification of Gears Parallel Axes Intersecting Axes Nonparallel & Nonintersecting Axes Rack and Pinion – Consists of gear rack and a pinion. The gear rack is a cylindrical gear with the radius of the pitch cylinder being infinite. Converts rotational motion into linear motion. M ACHINE ELEMENTS  Classification of Gears Parallel Axes Intersecting Axes Nonparallel & Nonintersecting Axes Pin Gearing – one of the wheels carries cylindrical pins which mesh into the spaces between the teeth of the other wheel. M ACHINE ELEMENTS  Classification of Gears Parallel Axes Intersecting Axes Nonparallel & Nonintersecting Axes Bevel Gears – cone shaped appearance and are used to transmit force between two shafts which intersect at one point. Makes it possible to change the operating angle. Used in differential drives which can transmit power to two axles spinning at different speeds. M ACHINE ELEMENTS  Classification of Gears Parallel Axes Intersecting Axes Nonparallel & Nonintersecting Axes Miter Gears – special case of bevel gears that have equal numbers of teeth. The shafts are positioned at right angles from each other. Used for transmitting rotational motion at a 90-degree angle with a 1:1 ratio. M ACHINE ELEMENTS  Classification of Gears Parallel Axes Intersecting Axes Nonparallel & Nonintersecting Axes Spiral Bevel Gears – have curved teeth at an angle allowing tooth contact to be gradual and smooth. Superior to straight bevel gears in efficiency, strength, vibration, and noise. More difficult to produce Produces axial loads. M ACHINE ELEMENTS  Classification of Gears Parallel Axes Intersecting Axes Nonparallel & Nonintersecting Axes Crown Gears – a type of bevel gear with pitch cone angle of 90 degrees. The teeth project at right angles to the face of the wheel. M ACHINE ELEMENTS  Nonparallel and Parallel Axes Intersecting Axes Nonintersecting Axes Worm Gears – a screw shape cut on a shaft is the worm, the mating gear is the worm wheel, and together on non- intersecting shafts is called a worm gear. Due to sliding contact, it is necessary to reduce friction. Rotation is quite and smooth. M ACHINE ELEMENTS  Nonparallel and Parallel Axes Intersecting Axes Nonintersecting Axes Screw Gears – also sometimes called crossed helical gears, are helical gears used in motion transmission between non- intersecting shafts. Have lower efficiency than parallel or perpendicular shafts. Cannot transmit heavy loads. M ACHINE ELEMENTS  Nonparallel and Parallel Axes Intersecting Axes Nonintersecting Axes Hypoid Gears – a type of bevel gear whose axis does not intersect with the axis of the meshing gear. Unlike the shape of bevel gear which is conical, hypoid gears are have hyperboloid pitch surface. Special gear oils are required due to extreme pressure between the teeth. Considerably stronger because the load is conveyed though multiple teeth simultaneously. M ACHINE ELEMENTS  Nonparallel and Parallel Axes Intersecting Axes Nonintersecting Axes Hyperboloidal Gears M ACHINE ELEMENTS  Nonparallel and Parallel Axes Intersecting Axes Nonintersecting Axes Hyperboloidal Worm Gears M ACHINE ELEMENTS