To accurately study the dynamic characteristics of the spiral bevel gear transmission system in a helicopter tail transmission system, the finite element model of the gear shaft was established by a Timoshenko beam element, and the mechanical model of the spiral bevel gear was created by the lumped mass method. The substructure method is employed to extract the dynamic parameters from the gearbox’s finite element model, and the dynamic model of the spiral bevel gear-shaft-bearing-gearbox coupling system was built according to the interface coordination conditions. In the model, the influences of time-varying stiffness, a time-varying transmission error, gearbox flexibility, unbalance excitation, and a flexible shaft and bearing support on the system vibration were taken into account simultaneously. On this basis, the dynamic differential equations of the full coupling system of the spiral bevel gear were derived, and the effects of the gearbox flexibility, the shaft angle, and the unbalance on the dynamic properties of the system were analysed. The results show that the gearbox flexibility can reduce the gear meshing force and bearing force, in which there is a more significant impact on the bearing force. The shaft angle affects the position, size, and direction of the system’s axis trajectory. Meanwhile, the meshing force and the bearing force of the system are also varied because of the various pitch angles of the driving and driven gears under different shaft angles. The unbalance of the gear shaft has an effect on the vibration of the spiral bevel gear transmission system in all directions, wherein the influence on the torsional vibration is the most significant, and the influence increases as the unbalance rises. The unbalance of the gear shaft also affects the meshing force and bearing force, which increases as the rotational speed rises. This research provides a theoretical basis to optimize dynamic performance and reduce the vibration and noise of a spiral bevel gear full coupling system.
Taking the marine encased differential gear train as an example, the relationship between the journal bearing parameters and the meshing force of the transmission system is analyzed. In this paper, the dynamic model of the encased differential gear train with journal bearing is established considering the factors of time-varying meshing stiffness and comprehensive transmission error. In this dynamic model, four stiffnesses and four damping coefficients are applied to characterize the asymmetry and interaction of the oil film stiffness and damping of planet bearing. The system responses are calculated by the Fourier series numerical algorithm. The results show that the introduction of journal bearing in encased differential gear train can contribute to gearbox vibration reduction. Moreover, the planet bearing parameters (e.g., clearance-to-radius ratio and eccentricity ratio) of the differential stage affect the meshing forces of both the differential and encased stages. In addition, the influence of the planet bearing parameters of the encased stage on the meshing force of the encased stage is more obvious than that of the differential stage. This work may develop a theoretical analysis framework for the design and manufacture of marine transmission systems in the future.
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