If the carrier is the output member of a planetary gear set, the resulting power flow is always a forward reduction or underdrive ratio.

If the carrier is the output member of a planetary gear set, the resulting power flow is always a forward reduction or underdrive ratio.

• A. Technician A
• B. Technician B
• C. Both Technician A and Technician B
• D. Neither Technician A nor Technician B

Answer: (A)

In a planetary gear set, power flows through the sun gear, the planet gears, and the output carrier. When the carrier is the output member, the planet gears must both mesh with the sun and with the ring and also orbit with the carrier. The no-slip constraints on those two gear meshes couple the motions in such a way that, for forward power flow, the carrier’s speed ends up lower than the input speed. In other words, the carrier acts as a reduction path: the output rotates slower than the drive, which is the underdrive behavior. This is the typical arrangement used when the carrier is the output in automotive planetary gear systems—the power path from input to output inherently produces a speed reduction in forward operation. The result is a forward reduction or underdrive ratio, not an overdrive.

In a planetary gear set, power flows through the sun gear, the planet gears, and the output carrier. When the carrier is the output member, the planet gears must both mesh with the sun and with the ring and also orbit with the carrier. The no-slip constraints on those two gear meshes couple the motions in such a way that, for forward power flow, the carrier’s speed ends up lower than the input speed. In other words, the carrier acts as a reduction path: the output rotates slower than the drive, which is the underdrive behavior.

This is the typical arrangement used when the carrier is the output in automotive planetary gear systems—the power path from input to output inherently produces a speed reduction in forward operation. The result is a forward reduction or underdrive ratio, not an overdrive.