Vehicle powertrain modeling and ratio optimization for a continuously variable transmission

In this thesis, a systematic methodology is developed for choosing the optimum ratio trajectory of a continuously variable transmission in a passenger vehicle. The methodology embraces and resolves trade-offs between driveability and fuel economy via a constrained optimization problem and its solution. The ratio optimization is set in the context of an intelligent hierarchical control strategy, which is proposed as the methodology for achieving the maximum potential benefits that a CVT has to offer over standard discrete-ratio transmissions. The intelligent hierarchical controller allows additional vehicle and driving environment information to be identified and enhances the functionality and performance of the overall ratio control strategy.; A vehicle powertrain model is developed as a hybrid combination of data-driven neural networks and analytical and heuristic techniques. The engine and torque converter models especially provide novel solutions to complex modeling and simulation problems. These models, and the overall powertrain model are both tractable and sufficiently accurate for use in a support and testing role for the development of the CVT ratio control system. The powertrain model is fully validated with data garnered from a CVT-equipped test vehicle.; The optimum CVT ratio schedule is formulated as a constrained optimization problem with maximum fuel economy as the objective function and driveability concerns and physical limitations included as the constraints. The key notion to achieving good driveability is the introduction and definition of a horsepower reserve function that creates a consistent and desirable vehicle response under different driving conditions. Simulation results compare the optimized schedule's performance with several other possible ratio schedules, including the minimum brake specific fuel consumption map, with favorable results in terms of both driveability and fuel economy. The ratio optimization problem formulation and solution provide a novel and unique approach to systematically addressing driveability and fuel economy considerations associated with a continuously variable transmission.