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This Bachelors Thesis, conducted together with Öhlins racing AB, aims to develop a deeper understanding of the vehicle dynamics of snowmobiles, focusing particularly on the behavior of the rear suspension under various motions and applied forces. The rear suspension called the bogie, consists of several linkages, springs, and dampers whose geometry and parameters influence the movement of the bogie. The study aims to attain industry-standard knowledge of snowmobile dynamics by developing a simulation model in Matlab to further understand and examine the behavior of the bogie during heave and pitch, as well as consulting with professionals in snowmobile simulation to understand industry practices.The simulation model is built on two main components, the kinematic- and the dynamic calculations. The kinematics is determined by measuring existing snowmobiles to get data on how the points in the bogie are distanced. Subsequently, the motion of the bogie during heave is calculated by iteratively lifting the rail a small distance upwards from the initial points determined by the measurements. The motion will be dictated by the center arm since the rail is not allowed to rotate and the center arm can't be compressed. The dynamics of the bogie are then modeled by integrating springs to examine how the application of force varies throughout the motion. This, together with the forces exerted on the rail by the arms will result in a net heave force which is the force that is needed to initiate the heave motion.The heave simulation reveals that the application point of the heave force shifts forward during the compression of the bogie, a behavior that positively impacts the vehicle's turning ability by effectively shortening the wheelbase. Additionally, the motion ratios for the center and rear springs were analyzed, showing distinct variations. The motion ratio analysis for the center spring revealed only slight variations in the front, whereas the rear motion ratio exhibited substantial changes due to the rear arm and spring moving in opposite directions.Limitations of the study include the absence of empirical validation as well as simplifications of the suspension linkage, specifically the exclusion of coupled mechanisms. Future work should involve simultaneous pitch and heave movements and incorporate feedback from professional snowmobile drivers to refine the suspension settings. The insights gained from these simulations can guide the design of more efficient and responsive snowmobile bogies, ultimately enhancing the vehicle's performance and safety.

Bottenstycket i en motorcykelframgaffel utsätts för cykliska belastningar med hög mittspänning. Öhlins Racing har vid prövning identifierat att det på grund av dessa kan uppstå mycket höga spänningskoncentrationer i o-ringsspår placerade i bottenstycket, vilka kan leda till högcykelutmattningsbrott. O-ringsspåren är närmst rektangulära med mycket små hörnradier i vilka problematiken uppkommer. För att lösa detta och förhindra brott har ett nytt spår tagits fram. Med hjälp av modellering med finita elementmetoden samt utmattningsanalys utvärderades originalspåret och ett nytt spår utvecklades och simulerades. I den nya geometrin har, utöver hållfasthet, hänsyn tagits till o-ringens tätningsförmåga, klämrisken vid montage, samt produktionstekniska aspekter. Det nya spåret innebär en ökning av den nedre kälradien från 0,4 mm till 0,6 mm jämfört med originalet och åstadkommer en estimerad livslängdsförbättring på över 500 gånger.