Time-optimal Design and Control of Electric Race Cars Equipped with Multi-speed Transmissions

Abstract: This paper presents a framework to jointly optimize the design and control of an electric race car equipped with a multiple-gear transmission, specifically accounting for the discrete gearshift dynamics. We formulate the problem as a mixed-integer optimal control problem, and deal with its complexity by combining convex optimization and Pontryagin's Minimum Principle in a computationally efficient iterative algorithm satisfying necessary conditions for optimality upon convergence. Finally, we leverage our framework to compute the achievable lap time of a race car equipped with a fixed-gear transmission, a continuously variable transmission and a multiple-gear transmission with 2 to 4 speeds, revealing that a multiple-gear transmission can strike the best trade-off in terms of electric motor control, and transmission weight and efficiency, ultimately yielding the overall best lap time.