Planetary gears are used commonly in many power transmission systems in automotive, rotorcraft, industrial, and energy applications. Powertrain efficiency concerns in these industries create the need to understand the mechanisms of power losses within planetary gear systems. Most of the published work in this field, however, has been limited to fixed-center spur and helical gear pairs. An extensive set of experiments is conducted in this research study to investigate the mechanisms of spin power loss caused by planetary gear sets, in an attempt to help fill the void in the literature.
A test set-up was designed and developed to spin a single-stage, unloaded planetary gear set in various hardware configurations within a wide range of carrier speeds. The measurement system included a high-resolution torque sensor to measure torque loss of the gear set used to determine the corresponding spin power loss. Repeatability of the test set-up as well as the test procedure was demonstrated within wide ranges of speed and oil temperature.
A test matrix was defined and executed specifically to measure total spin loss as well as the contributions of its main components, namely drag loss of the sun gear, drag loss of the carrier assembly, pocketing losses at the sun-planet meshes, pocketing losses at the ring-planet meshes, viscous planet bearing losses, and planet bearing losses due to centrifugal forces. Multiple novel schemes to estimate the contributions of these components of power losses were developed by using the data from tests defined by the test matrix. Fidelity of these schemes was tested by comparing them to each other. Based on these calculations, major components of power losses were identified and rank ordered. Impact of the rotational speed and oil temperature on each component was also quantified.