A set of portal gearboxes was designed for the Society of Automotive Engineers (S.A.E.) Baja challenge, an international collegiate competition where students design, build and compete in a series of off-road racing challenges. The introduction of the new mandatory four-wheel drive rule has prompted an influx of research and development into different four-wheel-drive designs. A set of portal gearboxes were designed to serve as the main final drive reduction for the 2022-2023 car. A portal gearbox is a gear set located within the profile of each wheel that increases the height of the driveshaft input. This portal gearbox design increases the effective ground clearance by 3.2”, improves steering geometry, and houses a set of sprag clutch bearings. Sprag clutch bearings allow for free rotation in one direction and can transmit torque in the other. The sprag bearings were utilized in the design to create a mechanically biased all-wheel-drive (AWD) system. They also greatly decrease the rolling resistance of the drivetrain system when coasting. The portal gearboxes feature a 3:1 reduction to supply a peak torque of 433 ft-lbs to the wheel. The gearboxes were designed to fit within a standard 10” x 5” aluminum wheel, allowing for no compromise in tire selection or off-road performance. The main challenges of the design were the large loadings seen at the wheel, the slim profile required, the manufacturability, and the integration with multiple other components like braking and suspension. The portal gearboxes are to be implemented on the 2022-2023 Union College Baja car and compete in Oshkosh Wisconsin on May 4th-7th.
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