STUDY OF MOTION AND POWER TANSMISSION

ELEMENTS-BY SIMRANJEET BHATIA

-130120119017-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 CHAIN

DRIVEDRIVE

Easier to remove/replace than beltsCompactSomewhat flexibleRelatively inexpensiveCan handle heat, dirt, weather exposure (when

properly lubricated)

EXAMPLES OF CHAIN DRIVE

GEAR GEAR DRIVEDRIVE

Gears are most often used in transmissions to convert an electric 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 motor’s high speed and low torque to a shaft’s requirements for low speed high torque:speed high torque:

Gears essentially allow positive engagement between teeth so high Gears essentially allow positive engagement between teeth so high forces can be transmitted while still undergoing essentially rolling forces can be transmitted while still undergoing essentially rolling contactcontact

Basic Law of Gearing:Basic Law of Gearing:

––A common normal (the line of action) to the tooth profiles at A common normal (the line of action) to the tooth profiles at their point of contact must, in all positions of the contacting their point of contact must, in all positions of the contacting teeth, pass through a fixed point on the line-of-centers teeth, pass through a fixed point on the line-of-centers called the pitch pointcalled the pitch point

––Any two curves or profiles engaging each other and satisfying Any two curves or profiles engaging each other and satisfying the law of gearing are conjugate curves, and the relative the law of gearing are conjugate curves, and the relative rotation speed of the gears will be constantrotation speed of the gears will be constant

EXAMPLE OF GEAR

SPUR GEARSPUR GEAR BEVEL GEARBEVEL GEAR

Teeth are parallel to the Teeth are parallel to the axis of the gearaxis of the gear

AdvantagesAdvantages– CostCost

– Ease of manufactureEase of manufacture

– AvailabilityAvailability

DisadvantagesDisadvantages– Only works with mating Only works with mating

geargear

– Axis of gear is parallelAxis of gear is parallel

Gear axis at 90°, based Gear axis at 90°, based on rolling coneson rolling cones

AdvantagesAdvantages– Right angle drivesRight angle drives

DisadvantagesDisadvantages– Get axial loading which Get axial loading which

complicates bearings complicates bearings and housingsand 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 GEARSHELICAL GEARS

Teeth are at an angle to the gear axis (usually Teeth are at an angle to the gear axis (usually 10° to 45°) – called helix angle10° to 45°) – called helix angle

AdvantagesAdvantages• Smooth and quiet due to gradual tooth Smooth and quiet due to gradual tooth

engagements (spur gears whine at high speed due engagements (spur gears whine at high speed due to impact). Helical gears good up to speeds in to impact). Helical gears good up to speeds in excess of 5,000 ft/minexcess of 5,000 ft/min

• More tooth engagement allows for greater power More tooth engagement allows for greater power transmission for given gear size.transmission for given gear size.

DisadvantageDisadvantage• More expensiveMore expensive• Resulting axial thrust componentResulting axial thrust component