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Design of Baja SAE Gearbox for Optimal Performance and Minimum Weight
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on November 30, 2020 by SAE International in United States
Baja SAE is an intercollegiate competition where teams design and build a single-seat off-road vehicle that is powered by a small 10 HP Briggs & Stratton engine. Due to this power constraint, it is crucial to optimize the vehicle's weight and performance. The purpose of this paper is to demonstrate the process of simulating, designing, manufacturing, and testing the gearbox of the vehicle. The design process began by creating a vehicle dynamics simulation, which included engine performance, CVT Shifting, tire slipping, vehicle mass, rotational inertia, air drag, rolling resistance, weight shift, and drivetrain efficiency. These calculations predicted acceleration times, top speed, and optimal gear ratio. An often-neglected parameter that was analyzed was the rotational inertia in the drivetrain system. The results showed the effective mass of the vehicle increased 12% above the weight of the vehicle, primarily due to the weight and size of the CVT primary pulley. The analysis also tests the sensitivity of the calculations by lowering and raising specific parameters to see the outcome and performance of the vehicle. This was followed by designing a compound gear train with a minimum diameter and face width of all the gears to reduce the maximum amount of weight. The calculations used to minimize the gear footprint took into consideration fatigue and contact stresses. The gearbox housing, shafts, and bearings were also designed and manufactured and integrated into the vehicle. The vehicle was then put through testing, and the vehicle simulation was validated. The results were a gearbox that weighed 36% lighter than previous designs and 4% performance increase.