The student Aurea Iñurritegui Marroquin obtained an OUTSTANDING CUM LAUDE qualification
The student Aurea Iñurritegui Marroquin obtained an OUTSTANDING CUM LAUDE qualification
The student Aurea Iñurritegui Marroquin obtained an OUTSTANDING CUM LAUDE qualification
Thesis title: Crowned spherical gear couplings working at high misalignment applications: Geometry generation, loaded tooth contact analysis and experimental validation
Court:
- Chairmanship: José Ignacio Pedrero Moya (UNED)
- Vocal: Francesca Maria Cura (Politecnico di Torino)
- Vocal: Víctor Roda Casanova (Universitat Jaume I)
- Vocal: Marcos Louredo Casado (JAURE – Regal Beloit Spain S.A.)
- Secretary: Miren Larrañaga Serna (Mondragon Unibertsitatea)
Abstract:
Spherical gear couplings are commonly used mechanical components to transmit power between highly misaligned rotating shafts. Their main geometry characteristic is the appearance of undercut sections on the hub when machining a high amount of longitudinal crowning. This possibility is even more significant when gear couplings with a low number of teeth are manufactured directly on the shaft.
Most of the geometry generation models in the literature avoid the generation of undercut sections. Moreover, it is a matter of disagreement among the existing models, since the generated tooth surfaces of the hub vary depending on the analytical model employed. In fact, these variations influence the contact characteristics and the load distribution of the gear coupling.
Moreover, the working high misalignment angles cause a drastic decrease in the number of teeth in contact, which imply high tooth-root stresses and result in the failure by tooth root breakage. However, the scientific literature is focused on gear couplings working in applications where the misalignment angles are below 1°, thus mainly centered on failures other than bending fatigue, such as fretting fatigue failure or surface wear. Thus, there is a lack of sizing methods oriented to higher misalignment angles, therefore current components working at these conditions may be oversized, or which is even more critical, sometimes undersized.
This thesis covers the existing gap in the generation of the crowned hub tooth surface geometry, with the development of a novel mathematical model which assesses the complete thread surface of the cutting tool and considers its cutting tool path. Moreover, this model can accurately generate undercut profiles that may appear on the hub.
Furthermore, the achievable misalignment angle of this type of gear coupling is discussed, assessing the influence of the geometry and manufacturing variables on this value. It gives an overview of the preliminary design phase and helps the designer choose an appropriate gear coupling to avoid as much as possible further geometrical issues, without compromising the achievable misalignment angle.
Finally, a loaded tooth contact analysis is carried out with a finite element model to understand the load distribution among the teeth and the bending tooth root stress in terms of the applied torque and the working misalignment angle. Moreover, the results are experimentally correlated with a real gear coupling which works in such high misalignment applications.
The results from the geometry generation model reveal that deviations between the generated crowned tooth surfaces with models existing in the literature are significant and modify the undercut cross sections beginning or even the contact conditions. At the same time, it is proved that the generated geometry is in good agreement with experimental data and highlights that the existing models in the literature to determine the maximum misalignment angle are not applicable for highly crowned gear couplings. Moreover, from the loaded tooth contact analysis, different mechanical behaviours arise at low or high misalignment angles since teeth in the pivoting position lose contact. This results in a tooth root stress history change from a sinusoidal cycle to a pulsating cycle.
In conclusion, this research analysis in depth the geometrical and mechanical behaviour differences that arise when applying current generating and rating standards to gear couplings working in applications at high misalignment angles (above 3°), with the definition of analytical and numerical models suitable for them.