Explain the construction, working and application of overdrive.
1 Answer

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  • An overdrive is a mechanism that allows an automobile to cruise at sustained speed with reduced engine RPM, leading to better fuel economy, lower noise, and lower wear.
  • It is mounted at the rear end of the gearbox.
  • The gear ratio provided by an overdrive unit is 30% more than the direct top gear.
  • The unit consists of an epicyclic gear train.
  • The planet carrier is connected to the output shaft of the gear box.
  • When the sun gear is locked to the output shaft of the gear box, the planet carrier rotates about the sun gear.
  • The ring gear rotates more slowly than planet gear thus giving more ratio than the direct drive.
  • Overdrive is used in some sports cars and luxury cars.
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