Power Transmission Systems

Power Transmission

• Rotating elements with mechanical energy need to be utilized at the required place by transmitting power from one shaft to another or from a prime mover to a machine.

Transmission System

• A system used to transmit power from one mechanical element to another mechanical element.

Types of Transmission Systems

• Belt drives
• Rope drives
• Chain drives
• Gear drives

Factors to Select Transmission System

• Distance between driver and driven pulley shaft
• Operational speed
• Power to be transmitted

Belt Drive

• Power is transmitted between parallel shafts
• Consists of two pulleys with an endless belt passed over them
• Rotary motion is transmitted from driving pulley to driven pulley
• Friction is a helpful agent in belt drives

Terminology of a Belt Drive

• Driver: supplies power to another mechanical element
• Driven: receives power from the driver
• Tight side: portion of the belt with maximum tension (denoted by T1 Newton)
• Slack side: portion of the belt with minimum tension (denoted by T2 Newton)
• Arc/Angle of contact: portion of the belt in contact with the pulley surface

Belt Materials

• Rubber
• Leather
• Canvas
• Cotton
• Steel

Classification of Belt Drives

• Open belt drive
• Closed belt drive

Open Belt Drive

• Both driver and driven pulleys rotate in the same direction
• Belt is passed over driver and driven pulleys
• Driver pulley pulls the belt from one side and delivers to the other side
• Tension is more on the lower side than the upper side

Cross Belt Drive

• Driven rotates in the opposite direction to that of the driver
• Belt rubs against each other at the point where it crosses, causing wear
• To avoid this, the speed of the belt should be less than 15 m/s

Comparison between Open Belt Drive and Closed Belt Drive

• Open belt drive: both driver and driven rotate in the same direction, no rubbing point, and requires less length of the belt
• Closed belt drive: driver and driven rotate in opposite directions, has a rubbing point, and requires more length of the belt

Velocity Ratio of Belt Drives

• n1/n2 = d2/d1 (speed of driving shaft to speed of driven shaft = diameter of driven pulley to diameter of driver pulley)
• When thickness of belt is considered: n1(d2 + t) / n2(d1 + t)

Creep and Slip

• Creep: relative motion between belt and pulley surface due to contraction and expansion of the belt
• Slip: relative motion between pulley and the belt passing over it
• Velocity ratio when slip is considered: n1 d2 / n2 d1 (100 - S), where S is the percentage slip

Idler Pulley, Stepped Pulley, and Fast and Loose Pulley

• Idler pulley: used to change the direction of the belt or to increase the arc of contact
• Stepped pulley: used when the centre distance between the pulleys is fixed
• Fast and loose pulley: used when the belt needs to be shifted from one pulley to another

Advantages and Disadvantages of Flat Belt Drives

• Advantages: low running and maintenance cost, possibility to transmit power over a moderately long distance, and efficient at high speeds
• Disadvantages: not preferred for short centre distance, belt joints reduce the life of the belt, and loss of power due to slip and creep

Gear Trains

• An arrangement of gears that mesh with each other to transmit power from one shaft to another
• Types: simple gear train (SGT) and compound gear train (CGT)

Simple Gear Train

• Arrangement of gears in series
• Intermediate gears are provided between the driver and driven gears

This quiz covers the basics of power transmission, including the types of transmission systems and their applications. It explores the concept of transmitting mechanical energy from one element to another.