Date of Award


Document Type

Union College Only


Mechanical Engineering

First Advisor

William Keat

Second Advisor

Andrew Rapoff




SAE Baja Portal Gearbox sprag clutch bearing awd system


A set of portal gearboxes were 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. 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 location. This portal gearbox design increases the effective ground clearance by 3.2 in, 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 in x 5 in aluminum wheel, allowing for no compromise in tire selection or off-road performance. The main challenges of the design were the rigorous 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 were implemented on the 2022-2023 Union College Baja car and competed in SAE Oshkosh Baja event in Wisconsin on May 4th -7 th



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In Copyright - Educational Use Permitted.