A Computationally Efficient Control Allocation Method for Four-Wheel-Drive and Four-Wheel-Independent-Steering Electric Vehicles

In this paper, a computationally efficient two-path nonlinear optimal control allocation method is proposed to improve the yaw stability of four-wheel-independent-steering, four-wheel-drive vehicles. The virtual controller output is allocated using an optimization problem to compute each wheel's steering and traction commands at every controller time step. The optimization problem is solved by running a sequential quadratic programming (SQP) procedure, which may take some time to obtain satisfactory results. The proposed two-path control structure is derived from a more complex single-path allocation problem where torque allocation and steering correction optimal solutions are calculated concurrently. In this separated two-path control structure, computational load due to the complexity of the single block problem is reduced. In real applications, each problem can be run in parallel on different controllers of the vehicle controller network, which decreases the execution time with near-optimal results. The performance and speed comparisons of both approaches are studied using detailed vehicle simulations.

Introduction

With increasing government restrictions about carbon emission, automobile manufacturers are forced to use green energy in their products. As a result, EV culture becomes more dominant against the traditional IC engines [1]-[3]. The introduction of new EV powertrain alternatives resulting new opportunities to improve the overall driving performance of attracting more researchers to focus more on vehicle control using mechatronic components such as electric actuators and brakes [4]. Research about stability control for four-wheel steering and four-wheel traction systems is more attractive because of the flexibility of the driveline architecture.