Kongsberg Automotive is developing a brand-new actuator for engaging and disengaging a clutch for different driveline applications. This master thesis research improves the concept design of the shift fork for the new Dog-Clutch Actuator using Design for Manufacturability (DFM). Initially, the knowledge about the mechanism of the product is gained with the aid of the design team and the proper boundary conditions for the boundary value problem are obtained. The conventional die-cast materials are investigated, and appropriate material is selected to create the material model. Most of the traditional HPDC aluminum alloys are aluminum-silicon system; therefore, a detailed study on the nucleation of Silicon in the melt and how it influences the mechanical properties of the alloy is conducted. During gear engagement, the two rotating gears of the dog-clutch collide and synchronize the angular velocity of the hub and the input gear. The synchronization force is dynamic; therefore, explicit time integration is used to capture the system's response with the assistance of FEM software. As the shift fork undergoes cyclic load during the gear shift, the fatigue analysis is performed to evaluate the life (Nf) of the component using Wohler's curve. The value of the maximum principal stress at the critical spots like notch and its direction are determined using the 3D Mohr's circle. In this analysis, the endurance limit correction factors and notch factor (Kf) are used for the S-N curve correction, and Goodman's criteria are used to incorporate the mean stress effect. Fatigue analysis requires a very fine mesh to estimate the precise stress magnitude at the critical locations and, the structural optimization algorithm requires many iterations to determine the optimal layout of the shift fork. Therefore, the explicit integration scheme is not efficient as it will be computationally expensive and time-consuming to solve the problem. Hence, the equivalent static load is determined for the gear shift force at the peak load and used for calculations and product development. As the initial concept design of the shift fork is asymmetrical, it requires varying stiffness in its structure to transfer the force efficiently to the shift sleeve. The FEA results state that one prong of the shift fork experience up to 75% of the total load, which increases the overall stress of the component (up to 0.9Sy). The shift fork also doesn't have adequate torsional stiffness, and as a result, stress concentration has occurred in one of the fillets in the shift fork. The iterative design is set up to improve the design of the shift fork by optimizing the stiffness of the two prongs which provided the key observations that describe the design changes which improved the design. In this phase, the overall stress of the component is reduced by 20% and minimizes the difference in the load between the two prongs by 27.5% compared to the initial design. The shift fork needs to be light to achieve the necessary acceleration during the gear shift. Therefore, topology optimization using the projected subgradient method is implemented to optimize the mass and compliance of the improved design in the iterative design phase. Then the design realization phase is set up to implement the results obtained from the topology optimization to conceptualize the viable product. The optimized result decreased the overall stress and maximum deflection by 20%. It also reduced the load difference in the two prongs of the shift fork by 35% by maintaining the same mass as the initial concept design.

Hypoid gears have been used extensively in automobiles, aerospace, marine and other applications for decades. The special advantages of hypoid gears come with inherent contact complexities of varying curvature and sliding in both profile and lengthwise direction. Spalling failure is catastrophic and needs to be addressed with deeper roots in gear design. Analytical methods present several limitations. Iterative development from experimentation is expensive and time consuming with different nonlinear parameters difficult to interpret. This thesis aims to develop a method to calculate contact fatigue life for initiation of spalling using finite element methods. Experiments have played a major role in understanding the causal factors for failure, determining the fatigue life and to study the major system design parameters. A failure analysis of the fractured flank is performed. It clarified the design causal factors for failure and the mechanism of failure. Pinion being the vulnerable part is the focus of this thesis, a finite element model was developed on ANSOL HFM and the residual stresses were superposed on MSC Marc. A finite element fatigue analysis is performed on FEMFAT and the component fatigue life is determined. The calculated fatigue life is compared with physical testing results using Weibull statistical analysis in combination with probabilistic bearing life models to formulate emphatical correlation methods. The goal of this thesis is to establish a method to estimate fatigue life by taking up example of computing subsurface fatigue life of a hypoid pinion. The influence factors like the method of contact analysis, different types of residual stresses due to case hardening and shot peening, fatigue criteria, friction, material properties are studied in this thesis to develop a conscience for the methodology to computing contact fatigue life. The bulk material properties based on hardness represented fatigue properties more accurately. Scaled normal stress in critical plane fatigue criteria was found more suitable for contact analysis with pre-stresses and multi-axial non-proportional contact stress state on FEMFAT. Finite element based contact analysis method was found to be more suitable for subsurface fatigue life estimation despite the inherent advantages of the hybrid surface integral method and its accurate representation of friction. It was found that inclusion of friction in model did not change the fatigue life significantly, showing that the influence of hardness, surface topographies lubrication and contact temperature on shear stresses are too large to be neglected. Contact fatigue life increased by a factor of 4.4 times due to shot peening of gears in comparison with case hardening indicating the influence of residual stresses. For the estimation of fatigue life at the initiation of failure, a complete correlation with the fatigue test results could not be achieved and reasons for deviations were clearly identified. The area of damage indicated by this computation method correlated with the damage observed during tests. The observations and calculations indicated premature failure of pinion with explanation of mechanism of failure of pinion flank using contact conditions. / Hypoidväxlar har använts i stor utsträckning i bilar, flyg-, marin- och andra applikationer under årtionden. De speciella fördelarna med hypoidväxlar kommer med inneboende kontaktkomplexitet med varierande krökning och glidning i både profil och längdriktning. Spallingfel är katastrofala och måste hanteras med grundlig redskapsdesign. Analytiska metoder har flera begränsningar. Iterativ utveckling baserad på experiment är dyrt och tidskrävande med olika icke-linjära parametrar som är svåra att tolka. Denna avhandling syftar till att utveckla en metod för att beräkna kontaktutmattningslivslängden för initiering av spalling med finitaelementmetoden. Experiment har spelat en viktig roll för att förstå orsaksfaktorerna för fel, bestämma utmattningslivslängden och för att studera de viktigaste systemdesignparametrarna. En felanalys av den skadade kuggflanken utfördes, vilket förtydligade felens orsaksfaktorer och den underliggande felmekanismerna. Driften är fokus för denna avhandling, en finitaelementmodell utvecklades med ANSOL-HFM och restspänningarna överlagrades med FEM-verktyget MSC-Marc. En slutlig elementutmattningsanalys utfördes med FEMFAT och komponentens utmattningstid bestämdes. Den beräknade utmattningslivslängden korrelerades med fysiska provningsresultat genom att tillämpa statistisk Weibullanalys i kombination med probabilistiska livslängdsmodeller. Målet med denna avhandling är att utveckla en metod för att uppskatta utmattningslivslängden och att tillämpa metoden för att beräkna bulkmaterialets utmattningslivslängd för ett hypoidrev. Påverkningsfaktorer som metoden för kontaktanalys, olika typer av restspänningar på grund av ythärdning och kulblästring, utmattningskriterier, friktion, materialegenskaper studeras i denna avhandling för att utveckla denna metod för att prediktera kontaktutmattningslivslängden. Bulkmaterialegenskaperna för hårdhet representerade utmattningsegenskaperna mera exakt. Skalad normalspänning i kritiska planutmattningskriterier befanns vara mer lämplig för kontaktanalys med förspänningar och multi-axiell icke-proportionell kontaktspänningsstatu än andra egenskaper med FEMFAT. Metodbaserad kontaktanalysmetod visade sig vara mer lämplig för uppskattning av ytutmattningslivslängd trots de inneboende fördelarna med hybridytaintegralmetoden och dess mera exakta friktionsrepresentation. Det visade sig att inkludering av friktion i modellen inte markant förändrade livslängden, vilket visade att påverkan av hårdhet, smörjning av ytorna och kontakttemperatur på skjuvspänningarna är för stor för att försummas. Kontaktutmattningslivslängden ökade med en faktor 4,4 gånger på grund av kugghjulning jämfört med ythärdning, vilket indikerar restspänningspåverkan. För att uppskatta utmattningslivslängden vid inledningen av ytfel kunde en fullständig korrelation med utmattningstestresultaten inte uppnås och orsakerna till avvikelser identifierades tydligt. Det skadade område som indikeras av denna beräkningsmetod korrelerade väl med den skada som observerades under testerna. Observationerna och beräkningarna indikerade tidigt fel i kuggen med förklaring av mekanismen för fel hos kuggflanken med hjälp av aktuellt kontaktförhållande.