Mechanical Power Transmission: Shafts, Gears, and Belts

Mechanical Power Transmission Systems

Shafts and Couplings

A shaft is a rotating machine element that transmits power or energy. A shaft can also be cylindrical and support rotating parts without transmitting power. Couplings connect two shafts:

• Rigid Coupling: Shafts are aligned and maintain their position during rotation (using flanges and couplings).
• Flexible Coupling: Allows for slight misalignment between shafts during operation.

Gear Trains and Powertrains

A gear train refers to a pair of meshing gears. A powertrain consists of two or more gear pairs that alter the rotational speed of the final shaft.

Joints

Joints transmit motion and forces. These forces can be in opposite, same, or different directions.

Chains and Belts

• Chain: Ideal for dusty environments requiring durability. Can be noisy and requires lubrication.
• Timing Belt: Quiet and requires no lubrication, but needs periodic replacement.

Gear Transmission

Friction-Based Transmission

Movement is relayed between two wheels by friction.

• External Gearing: Two discs make contact at their peripheral areas. The driving wheel (pinion) rotates the driven wheel (gear).
• Internal Gearing: Inner and outer wheels rotate in the same direction.
• Bevel Gearing: Used to transmit motion between shafts with intersecting axes, shaped like truncated cones.

Belt and Pulley Transmission

• Pulley: A wheel used in belt transmission.
• Belt: A flexible band connecting two pulleys to transmit torque.

Gear Drives

Used for high-torque applications or when a constant gear ratio is required. Consists of two wheels with teeth.

Transmission Between Parallel Axes

• Spur Gears: Easy to manufacture but noisy. Used for high-speed, high-power applications.
• Helical Gears: Teeth are inclined, resulting in quieter operation and less vibration.
• Herringbone Gears (Double Helical): Two helical gears joined to compensate for axial forces.

Transmission Between Intersecting Perpendicular Axes

• Bevel Gears: Straight or helical teeth.

Transmission Between Non-Parallel, Non-Intersecting Axes

• Worm Gears: Used for high gear ratios and non-reversible transmission.
• Hypoid Gears: Similar to spiral bevel gears but with offset axes.