Noise optimization and canceling effects in planetary gear stages depending on topography

The power density of planetary gear stages offers a very compact gearbox design for transmissions with cylindrical gear stages. Due to the close coupling between the gear meshes within planetary gear stages, a design for low noise behavior is laborious. Components of planetary gear stages are a central sun gear, several planetary gears, which may orbit around the sun and an outer ring gear. There are different topographies of planetary gear sets in practical use, which show different mesh behavior. The number of teeth of the ring and sun gear influences the number of planets, which can be mounted equally spaced. This topography, in particular the number of planets and number of teeth of ring and sun gear, determines the meshing phases that occur within the planetary gear meshes. An in-phase gear meshing means, that the planets have the same mesh position at all time, while sequential mesh positions between the planets describe a sequentially phased meshing. There are also combinations of in-phase and sequentially phased meshing possible, e.g. half-symmetrical meshing phase (only for even numbers of planets possible). The meshing phases have significant influence on fluctuations of the transmitted torque moment and on the resulting radial forces. These parameters influence the Transmission Error (TE) and the gear mesh excitation which are main sources of gear noise. In this paper, different topographies and meshing phases for planetary gear stages are evaluated regarding noise behavior. General considerations are discussed to identify advantageous designs.