Determinação da relação de transmissão para um veículo tipo baja SAE

Abstract

The current work intends to analyze the influence of the transmission ratio of a Baja’s vehicle gearbox in its competition performance. The study was carried out in two strands, one related to the restrictions of force transmission between tire and soil and another related to the limitations of net power. Several values of transmission ratio were simulated and the vehicles performance was assessed in an acceleration test (time to travel a 30m distance) and speed (maximum speed in 100m). Initially the CVT’s characteristic curve was obtained through a data acquisition system with embedded sensors. The torque and power curves were obtained as required by SAE (Society of Automotive Engineers) from the Briggs & Stratton Intek Pro® 10 HP catalog. Afterwards, the vehicle’s drag coefficient was obtained from a computational simulation using the software SolidWorks®, as well as the translational and rotational inertia from the 3D models. From the engine power balance study, the available power was calculated for several rotation ranges and the power consumed by the following resistances: rolling, mechanical, aerodynamic, inertial and ramp. This allowed the vehicle’s maximum performance capped by the net power, comprised of the maximum speed, maximum slope angle, maximum acceleration and maximum driving force. Through the study of the transmission force between soil and tire, the same parameters were obtained, now capped by the tire grip force, with the exception of maximum velocity, obtained only by the power balance. Comparing the values, the most critical, therefore, smaller, values were adopted as maximum for each parameter. Finally, analyzing the theoretical performance in the acceleration and speed tests along with the other performance parameters, the optimal transmission ratio was chosen for the prototype.