RESEARCH PAPERS: Power Transmission and Gearing

Effects of Planetary Speed-Reduction Ratio on Mean Service Life

[+] Author and Article Information
M. Savage

The University of Akron, Akron, Ohio 44325

K. L. Rubadeux

The Hendrickson Company, Canton, Ohio 44707

H. H. Coe

NASA Lewis Research Center, Cleveland, Ohio 44135

J. Mech. Des 120(1), 113-118 (Mar 01, 1998) (6 pages) doi:10.1115/1.2826662 History: Received October 01, 1996; Online December 11, 2007


Planetary-gear transmissions are compact speed reductions which use parallel-load paths to transmit high power. The range of possible reduction ratios is bounded from below and above by limits on the relative size of the planet gears. For a single-plane planetary transmission, the speed-reduction ratio must be greater than two for planet gears to exist. As the ratio increases, so does the size of the planets relative to the sizes of the sun and ring. Which ratio is best for a planetary reduction can be resolved by studying a series of optimal designs. In this series, each design is obtained by maximizing the service life for a spur-gear planetary with a fixed size, speed-reduction ratio, input speed, power and materials. The planetary-gear reduction service life is modeled as a function of the two-parameter Weibull distributed service lives of the ball bearings and spur gears in the reduction. Planet-bearing life strongly influences the optimal reduction lives which point to an optimal planetary reduction ratio in the neighborhood of four to five.

Copyright © 1998 by The American Society of Mechanical Engineers
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