Electronic Continuously Variable Transmission

Every year, the University of Arizona Baja Society of Automotive Engineers team designs and builds an off-road vehicle to race against other schools in competition. The car has a mechanical continuously variable transmission (CVT). It has pulleys, which use internal flyweights and springs for actuation, that vary their diameters depending on engine RPM and load coming from the gearbox.

This project presents a more efficient method that controls the pulley diameter electronically.

The team modeled and designed a system consisting of two pulleys, two motors, two linear actuators, hydraulics, three microcontrollers, an RPM sensor, and a housing to protect the electronics. Additionally, the team implemented a controls algorithm based on modeled vehicle dynamics to determine the proper gear ratios for optimal performance. The students integrated and tested the system on the club’s 2021 Baja competition car, finding that it displayed superior durability, tunability and control.