Definition

1. Noun:
   • The central gear in an epicyclic train: In mechanical engineering, a "sun gear" is the gear at the center of a planetary gear system. It is typically surrounded by and meshes with multiple "planet gears," which in turn rotate within an outer "ring gear."

Usage Examples

• Noun:
  • The power from the engine is transmitted directly to the sun gear.
  • In this design, the sun gear is held stationary to achieve a specific gear reduction ratio.
  • A worn sun gear can cause noise and vibration in the transmission.

Advanced Usage

• "Sun-and-planet gear": A term sometimes used to describe the entire epicyclic gear system, emphasizing the relationship between the central sun gear and the surrounding planet gears.
  • The early steam engines used a sun-and-planet gear arrangement to convert motion.

Variants and Related Words

• Planet gear (or pinion) (n): One of the smaller gears that orbit around the sun gear within a planetary gear set.
• Ring gear (or annulus) (n): The outer internal-toothed gear that encloses the planet gears and meshes with them.
• Planetary gearset (n): The complete assembly consisting of a sun gear, planet gears, and a ring gear.
• Epicyclic gear train (n): The formal engineering term for a gear system where gears rotate about a central axis, synonymous with a planetary gear system.

Synonyms

• Central gear: A descriptive synonym emphasizing its position.
• Sun wheel: An alternative, less common term.

Related Phrases

• To drive the sun gear: To apply input power to the central sun gear.
  • In this configuration, the motor drives the sun gear.
• To lock the sun gear: To prevent the sun gear from rotating, a common method for changing gear ratios in an automatic transmission.
  • The brake band locks the sun gear to the transmission case.

Noun

1. the central gear in an epicyclic train