Dynamics of planetary drivetrains accounting for time-varying mesh stiffness

Abstract

Planetary gear trains (PGTs) are widely used due to their exceptional load distribution ability which significantly improves their reliability. Despite this, PGTs can be subject to high vibrations as a result of many dynamically interacting bodies and high loads. This can lead to excessive wear and premature failure. This thesis work aims to provide further insight into the dynamic behavior of PGTs by developing a comprehensive dynamic model. Accuracy of the model is improved by using analytically obtained time-varying mesh stiffness. Modal analysis is used to obtain natural frequencies and mode shapes which are then used to find the forced response of the system. All models used in the work are individually tested and validated against reference works with very good accuracy. Effects of time-varying mesh stiffness are studied on different gear geometries. It is found that in some cases constant mesh stiffness is an appropriate simplification, however for some other geometries, the effects of time-varying stiffness can become much greater, with errors up to 18–26%. For gears with small helix angle and especially spur gears the stiffness tends to vary much more significantly, leading to large discrepancies between constant and time-varying stiffness models.