Steering Optimization of an 8x8 Vehicle

Abstract

In this work, a method for obtaining optimal steering angles for a multi-axle vehicle is proposed. The tire maximum steering angles are optimized for low turning radius and low lateral slip angles. The optimization process is conducted for the low-speed steady-state maneuver. Another method is proposed to investigate the high-speed handling behavior of the vehicle with the optimized wheel steering angles in a double lane change (DLC) maneuver. The vehicle considered in this work is a prototype 8x8 vehicle with all-wheel steered (AWS) and all-wheel drive (AWD). The 8x8 vehicle has a minimum curb-to-curb turning radius requirement, and the minimum turning radius requirement cannot be met using slip-free turning due to the wheel steering angle limitations. To achieve a turning radius, that is lower than the requirement, tire lateral slip angles must occur. A multi-body dynamics model of the all-wheel steered 8x8 vehicle was created in Adams Car. Adams model was parametrized and automated using a Python code. For the optimization process a genetic algorithm code was written in Python language. The optimization problem is multi-variable constraint optimization, each of the tire maximum steering angle is an optimization parameter and there are physical constraints on the wheel steering angles. For the DLC maneuver, a general open loop steering input function for DLC maneuvers was derived. The genetic algorithm created for the optimization of the wheel steering angles for the turning radius optimization section of the work was revised to optimize the parameters of the general open loop steering input function for the DLC maneuvers. By using this method the steering angles for the tires that results in minimum turning radius and tire lateral slip angles which are capable of performing DLC maneuver at high speeds can be obtained. The methodology developed is especially useful for determining the tire steer angles of the vehicle early in the vehicle design and to create design specifications for the steering system.