[en] 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 Finally, an experimental study on thermallyinduced transmission error behaviour is carried out, conclusions are withdrawn and future work in the field is pointed out.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 analysis.

[eu] Engranajeen portaera termikoa arreta gutxien jaso duen arazo mekanikoetako bat izan da azken mendean. Sortutako beroaren jatorria dagoeneko ulertu arren, bere analisia olioaren tenperatura egonkorraren iragarpenera mugatu da, engranajeen hutsegitean eragin zuzena baitu. Alabaina, literatura zientifikoaren berrikuspenak erakutsi du dilatazio termikoaren ondorioak ia ez direla aztertu. Bitartean, turbo-makinen industriako esperientziak frogatu du termikoki eragindako geometriaren distortsioak zeregin garrantzitsua duela karga banaketaren aldaketan hortzen haustura eragiten duelarik neurririk hartzen ez bada. Doktorego tesi honen helburu nagusia termikoki eragindako engranaje zuzen eta helikoidalen geometriaren distortsioak sortutako portaera mekaniko irregularra aurreikustea, ebaluatzea eta zuzentzea da. Asmo horrekin, engranaje parean sortutako beroa kuantifikatu egin behar da eta tenperatura egonkorraren banaketa aurreikusi behar da aldez aurretik. Ondoren, hortzen deformazio termikoa zehazteko eredu bat garatu behar da karga banaketa kalkuluen ohiko fluxuan inplementatuz. Distortsio termiko mota eta zenbatekoa jakiteak, kargapean duen portaeraren ulermenarekin batera, hortzaren geometria zuzenketa ahalbidetuko du kontaktuaren portaera desegokia konpentsatuz. Tesiaren lehen ataletan distortsio termikoaren jatorria deskribatzen da eta gaur egungo egoera berrikusten da. Ondoren, engranaje zuzen eta helikoidalen geometria eta zinematika aztertzen dira eta karga banaketa kalkulatzeko eredu analitiko bat garatzen da "thin slice" izeneko metodoa erabiliz. Segidan, engranaje pareen irristaketa marruskaduraren portaera aztertzen da, kontaktuan sortutako beroa kuantifikatzen da eta gurpil parearen tenperatura-banaketa aurreikusten da sare termikoen kontzeptuan oinarrituta. Kapitulu bakoitzean eredu berriak garatzen dira eta emaitzak literatura zientifikoko datu esperimentalekin baliozkotzen dira. Distortsio termikoa aurreikusteko eredua seigarren kapituluan aurkezten da, parametro ezberdinen analisia egiten da eta adibide praktiko bat goitik behera aztertzen da, geometriaren distortsiotik abiatuta portaera termomekanikoa ikusi arte. Kapitulu honen amaieran, termikoki eragindako deformazioei aurre egiteko diseinu gomendioak biltzen dira eta hortzak zuzentzeko arauak proposatzen dira. Azkenean, transmisio errorearen portaera termomekanikoa esperimentalki aztertzen da, ondorioak laburbiltzen dira eta etorkizuneko ildoak azpimarratzen dira. Emaitzen arabera, eta ohiko ustearen aurka, altzairuzko engranajeen distortsio termikoak karga banaketan eta transmisio errorean eragina du eta, ondorioz, kontuan hartu behar da haien kontaktu analisian.