Definition

Noun: A mechanical assembly, specifically a system of gears, where at least one gear (a planet gear) rotates on an axis that itself moves around a central, fixed axis. This creates a compound rotational motion, allowing for complex speed reductions or increases within a compact space.

Usage

An epicyclic gear train is a fundamental component in many mechanical devices. It is primarily used to transmit torque and change speed and direction of rotation in a highly efficient and space-saving manner. - The automatic transmission in a car often uses an epicyclic gear train to achieve different gear ratios. - Astronomical clocks historically employed complex epicyclic gear trains to model the perceived motion of planets.

Advanced Usage

• Planetary Gear Set: This is the most common type of epicyclic gear train. It consists of a central sun gear, multiple planet gears mounted on a rotating carrier, and an outer ring gear (or annulus).
  • In a hybrid vehicle's power-split device, a planetary gear set seamlessly manages power from the engine and electric motors.

Variants and Related Words

• Planetary Gear Train: A synonym often used interchangeably with , emphasizing the sun-and-planets configuration.
• Epicyclic Gearing: The general concept or principle behind an epicyclic gear train.
• Sun Gear: The central gear in a planetary system.
• Planet Gear: A gear that rotates on its own axis while revolving around the sun gear.
• Ring Gear (Annulus): The outer, internally-toothed gear that meshes with the planet gears.
• Planet Carrier: The structure that holds the planet gears and defines their revolving path.

Synonyms

• Planetary Gear Train
• Epicyclic Gearing System

Related Phrases & Concepts

• Gear Ratio: The relationship between the rotational speeds of the input and output shafts in an epicyclic gear train, which can be calculated using the relative speeds of the sun, carrier, and ring gears.
• Power Transmission: The primary function of an epicyclic gear train is the efficient transmission of mechanical power.

Noun

1. a system of epicyclic gears in which at least one wheel axis itself revolves about another fixed axis