In this paper, results from an experimental study on power losses of planetary gear sets are presented. The experimental set-up includes a specialized test apparatus to operate a planetary gear set under tightly-controlled speed, load and oil temperature conditions, and instrumentation for an accurate measurement of power losses. The test matrix consisted of gear sets having 3 to 6 planets under loaded and unloaded conditions in order to separate load independent (spin) and load dependent (mechanical) power losses. The test matrix also included tests with planet gears having two levels of tooth surface roughness amplitudes as well as tests at varying oil inlet temperature. The results clearly indicate that spin power loss decreases with both reduction of number of planets and increase in oil temperature. Meanwhile, the mechanical power loss decreases with a decrease in oil temperature and reduction in gear surface roughnesses. Results also indicate that mechanical losses can be described by the power transmitted and lost by each planet branch.

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