Thesis defense of Aitor Arana

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Thesis defense of Aitor Arana

THESIS

Thesis defense of Aitor Arana

Title of the thesis: Thermal Distortion Effects on Cylindrical Gear Teeth Contact. Obtained the SOBRESALIENTE qualification and the CUM LAUDE mention.

2019·07·24

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  • Title of the thesis: Thermal Distortion Effects on Cylindrical Gear Teeth Contact.
  • PhD programme: DOCTORATE PROGRAMME IN MECHANICAL ENGINEERING AND ELECTRICAL ENERGY
  • Thesis directors: Ibai Ulacia Garmendia, Jon Larrañaga Amilibia
  • Court:
    • President: Dr. D. Philippe Velex (Institut National des Sciences Appliquées de Lyon (INSA))
    • Vocal: Dr. D. José Ignacio Pedrero Moya (Universidad Nacional de Educación a Distancia (UNED))
    • Vocal: Dr. D. Javier Echávarri Otero (Universidad Politécnica de Madrid)
    • Vocal: Dr. D. Jon Ander Esnaola Ramos (Mondragon Unibertsitatea)
    • Secretary: Dr. D. Mikel Izquierdo Ortiz de Landaluce ( Mondragon Unibertsitatea)

Abstract

The thermal behaviour of geared transmissions has been one of the mechanical issues receiving the least amount of attention in the last century. Although the origins of heat generated in gearboxes is already understood, its analysis has been limited to the prediction of steady-state oil temperature, which has a direct influence in gear failure. However, scientific literature review has shown that the effects of thermal expansion have been hardly analysed. Meanwhile, field experience in turbo-machinery industry, proofs that thermally-induced geometry distortion does play a significant role on contact pattern shift leading to tooth breakage if no counter-measures are provided. The main objective of the present thesis is to predict, evaluate and correct uneven mechanical behaviour of spur and helical gears due to thermally-induced flank geometry distortion. For this purpose, heat generated in the gear mesh needs to be quantified and resulting steady-state temperature distribution must be predicted. Then, a model to determine thermal deformation of gear teeth must be developed and implemented on common load distribution calculation flowcharts. The understanding of the type and amount of thermal distortion, along with its effects on loaded behaviour, will allow to correct tooth geometry and compensate for undesired contact behaviour. In the first chapters of the present thesis, a brief description of the origins of thermal distortion is presented and current state of art is reviewed. Then, spur and helical gear teeth geometry and kinematics are described and an analytical load distribution model following the so called “thin-slice” approach is developed. Next, sliding friction behaviour in meshing gears is analysed, the amount of heat generated in the mesh is quantified and temperature distribution is predicted based on the thermal-network concept. New models are developed within each of these chapters and results are validated with experimental measurements from literature. The thermal distortion model is introduced in chapter six, a parameter analysis is carried out and a test case is fully analysed, from geometry distortion to full thermo-mechanical behaviour. At the end of this chapter, design recommendations to cope with thermally-induced deformations are gathered and tooth modification rules are proposed. Finally, an experimental study on thermallyinduced transmission error behaviour is carried out, conclusions are withdrawn and future work in the field is pointed out. Results show that, contrary to common belief, thermal distortion in steel gears does affect load distribution and transmission error and therefore it should be considered in gear tooth contact.