STUDY OF MOTION AND POWER TANSMISSION ELEMENTS - BY SIMRANJEET BHATIA SR NO.:24

GEAR TERMINOLOGY PITCH DIAMETER ROOT DIAMETER CENTER DISTANCE OUTSIDE DIAMETER DIAMETRAL PITCH = TOOTH SIZE

MATING SPUR GEARS CENTER-TO-CENTER DISTANCE TANGENT PITCH CIRCLES D1 + D2 2 = CC DIST D1 D2

CHAIN DRIVE Easier to remove/replace than belts Compact Somewhat flexible Relatively inexpensive Can handle heat, dirt, weather exposure (when properly lubricated)

EXAMPLES OF CHAIN DRIVE

GEAR DRIVE Gears are most often used in transmissions to convert an electric motor’s high speed and low torque to a shaft’s requirements for low speed high torque: Gears are most often used in transmissions to convert an electric motor’s high speed and low torque to a shaft’s requirements for low speed high torque: Gears essentially allow positive engagement between teeth so high forces can be transmitted while still undergoing essentially rolling contact Gears essentially allow positive engagement between teeth so high forces can be transmitted while still undergoing essentially rolling contact Basic Law of Gearing: Basic Law of Gearing: –A common normal (the line of action) to the tooth profiles at their point of contact must, in all positions of the contacting teeth, pass through a fixed point on the line-of-centers called the pitch point –Any two curves or profiles engaging each other and satisfying the law of gearing are conjugate curves, and the relative rotation speed of the gears will be constant

EXAMPLE OF GEAR

SPUR GEAR BEVEL GEAR Teeth are parallel to the axis of the gear Advantages –Cost –Ease of manufacture –Availability Disadvantages –Only works with mating gear –Axis of gear is parallel Gear axis at 90°, based on rolling cones Advantages –Right angle drives Disadvantages –Get axial loading which complicates bearings and housings

WORM GEAR RACK AND PINION Gears that are 90° to each other Advantages –Quiet / smooth drive –Can transmit torque at right angles –No back driving Disadvantage –Most inefficient due to excessive friction (sliding) –Needs maintenance The rack and pinion gear is used to convert between rotary and linear motion. –Could have straight or bevel teeth –Provides less backlash –Greater feedback

HELICAL GEARS  Teeth are at an angle to the gear axis (usually 10° to 45°) – called helix angle  Advantages Smooth and quiet due to gradual tooth engagements (spur gears whine at high speed due to impact). Helical gears good up to speeds in excess of 5,000 ft/minSmooth and quiet due to gradual tooth engagements (spur gears whine at high speed due to impact). Helical gears good up to speeds in excess of 5,000 ft/min More tooth engagement allows for greater power transmission for given gear size.More tooth engagement allows for greater power transmission for given gear size.  Disadvantage More expensiveMore expensive Resulting axial thrust componentResulting axial thrust component