Experimental investigation of the influence of axis misalignments in stepped planetary gear stages on the excitation and displacement behavior

With the increasing electrification of vehicles, the demand for suitable transmission concepts is growing. The high volume and weight of batteries require savings in other areas. Furthermore, due to the differing output characteristic curves of electric motors, shiftable transmissions are often unnecessary. Instead, a single gear transmission is sufficient. High-speed electric motors offer a weight advantage due to lower torques, which creates a need for especially high transmission ratios. Stepped planetary gearboxes meet these requirements while also delivering high power density. The elimination of masking noises from the combustion engine further highlights the acoustics of the transmission. Consequently, excitation behavior is increasingly seen as a quality criterion. The excitation behavior of planetary gear systems has already been the subject of numerous research studies. In contrast, there are only a few investigations regarding stepped planetary gear systems. Previous simulation studies indicate that stepped planetary gearboxes are sensitive to axis misalignments [1]. However, sufficient experimental results are not yet available. This paper presents the results of investigations conducted on a stepped planetary gearbox test rig with a sequential mesh sequence in both the sun-planet and planet-ring gear contact and a floating sun. The measurement setup allows the investigation of transmission error, structure-borne noise, and displacement of the sun gear shaft and the planet carrier. Using eccentric bushings, defined misalignment states can be imposed on the otherwise rigid gearbox. This enables the investigation of the influence of axis misalignments of the stepped planets and the carrier on the excitation and dynamic displacement behavior. The investigations show frequency and amplitude modulations that had previously only been observed in planetary gear systems. Additionally, long-wavelength excitations in the range of the rotational frequencies of the shafts were identified, occurring either exclusively in the transmission error or in the structure-borne noise. The displacement behavior is analyzed based on the sun gear trajectory. A trochoidal path of the sun gear can be seen. The loops superimposed on the circular sun trajectory can be attributed to geometric deviations in the gears. The investigations demonstrate that planet pin position errors have the greatest influence on the sun gear trajectory. For these cases, it is shown that the sun gear is deflected by the reaction forces from the tooth contacts until a load balance is established.