What gear set was originally a three-speed gear set able to provide an overdrive with minor modification?

What gear set was originally a three-speed gear set able to provide an overdrive with minor modification?

• A. ZF
• B. Ravigneaux
• C. Wilson
• D. Simpson

Answer: (B)

In a planetary gearset, multiple forward speeds come from selecting which elements—sun gear, planet carrier, or ring gear—are held or driven. An overdrive means the output speed exceeds the input, giving a final drive ratio of less than 1:1. The Ravigneaux gearset uses two sun gears of different sizes sharing a common set of planets, which allows three forward ratios to be produced in a compact package. Because this arrangement already provides multiple power paths through a single gearset, a small modification—such as changing which element is held or where the output is taken—can create an overdrive stage without a complete redesign. That makes a three-speed transmission based on a Ravigneaux set able to offer overdrive with only minor modification. The other gearset types aren’t as naturally suited to adding overdrive in a simple three-speed layout without more substantial changes.

In a planetary gearset, multiple forward speeds come from selecting which elements—sun gear, planet carrier, or ring gear—are held or driven. An overdrive means the output speed exceeds the input, giving a final drive ratio of less than 1:1. The Ravigneaux gearset uses two sun gears of different sizes sharing a common set of planets, which allows three forward ratios to be produced in a compact package. Because this arrangement already provides multiple power paths through a single gearset, a small modification—such as changing which element is held or where the output is taken—can create an overdrive stage without a complete redesign. That makes a three-speed transmission based on a Ravigneaux set able to offer overdrive with only minor modification. The other gearset types aren’t as naturally suited to adding overdrive in a simple three-speed layout without more substantial changes.