What would be the output on the ring gear of a planetary gear set when the carrier is input and the sun gear is the held component?

What would be the output on the ring gear of a planetary gear set when the carrier is input and the sun gear is the held component?

• A. Minimum forward overdrive
• B. Maximum forward overdrive
• C. Maximum forward reduction
• D. Minimum forward reduction

Answer: (D)

In a planetary gear set, the speeds of sun, ring, and carrier are all tied together by how the planets mesh with both sun and ring. When you drive the carrier and hold the sun, the planets must roll around the fixed sun while also turning the ring gear. This constraint causes the ring to rotate in the same general direction as the carrier, but at a slower rate. So the ring output moves forward, but with a reduction in speed. The reduction is determined by the gear tooth counts, but in this arrangement the ring ends up with the smallest (least) forward reduction compared to other fixed-element cases. Hence the ring gear output is minimum forward reduction.

In a planetary gear set, the speeds of sun, ring, and carrier are all tied together by how the planets mesh with both sun and ring. When you drive the carrier and hold the sun, the planets must roll around the fixed sun while also turning the ring gear. This constraint causes the ring to rotate in the same general direction as the carrier, but at a slower rate. So the ring output moves forward, but with a reduction in speed. The reduction is determined by the gear tooth counts, but in this arrangement the ring ends up with the smallest (least) forward reduction compared to other fixed-element cases. Hence the ring gear output is minimum forward reduction.