Análise de desempenho e substituição de um câmbio CVT por câmbio de relações fixas de 3 velocidades para protótipo do tipo BAJA SAE por meio de modelagem numérica computacional

Abstract

The Continuously Variable Transmission concept is defined for allowing the exploration of a determined point of interest (usually best performance or fuel consuption) developed by the engine over a speed range through the continuous variation of its transmission drive ratios. Since this task is commonly accomplished by, among others, a flexible member, the CVT ends up performing lower values of mechanical transmission efficiency, and since in the Baja SAE category all Briggs & Stratton 10 HP engines are standard by rule and therefore not allowed to be tuned by the teams, the most powerful drivetrain is the one that best delivers its engine power to the wheels. In order to enable the performance analysis and comparison between the Bombaja UFSM’s prototype (BJ16) current CVT transmission and a 3-speed sequential gearbox transmission at the very same car, it has been developed a numerical model which simulates the vehicle longitudinal dynamics and enables the user to behold and compare how the new concept would perform over the actual vehicle. Once the results have been compared and verified by overlapping the model results with a comercial lap timing software (OptimumLap) and actual testing results, it was defined the proper transmission drive ratios for a 3-speed sequential gearbox and compared the two transmission concepts performance at BJ16. The results achieved in this project evidence the advantages of replacing the CVT transmission with the new fixed ratio concept at the conditions here analyzed, showing substantial perfornance improvements in tests that recquire longitudinal performance capabilities such as acceleration, which the elapsed time was reduced from 4.75 to 4.32 seconds, as well as a traction test, proving the BJ16 ability and reliability while towing a truck over the old CVT concept, being able to accomplish the task in the most of its speed range in first gear.