Motion Control of a 6WD/6WS Wheeled Platform with In-wheel Motors to Improve Its Maneuverability

Abstract

Multi-axle driving mobile platform that are favored in special environments require high driving performance, steering performance, and stability. Among these, six wheel drive and six wheel steering vehicles hereinafter called 6WD/6WS, gain structural safety by distributing the load and reducing the pitching motion during rapid acceleration and braking. 6WD/6WS mobile platforms are favorable for military use, particularly in off-road operations because of their high maneuverability and mobility on extreme terrains and obstacles. 6WD vehicles that use in-wheel motors can generate independent wheel torque without a need for additional hardware. Conventional vehicles, however, cannot generate an opposite driving force on wheels on both sides. In an independent steering and driving system six-wheel vehicles show better performance than conventional vehicles. This paper discusses the improvement of the cornering performance and maneuverability of 6WD/6WS mobile platform using independent wheel torque and independent steering on each wheel. 6WD/6WS vehicles fundamentally have satisfactory maneuverability under low speed, and sufficient stability at high speed. Consequently, there should be a control strategy for improving their cornering performance using the optimum tire forces that satisfy the driver's command and minimize energy consumption. From the driver's commands (i.e., the steering angle and accelerator/brake pedal stroke), the desired yaw moment with virtual steering, desired lateral force, and desired longitudinal force are obtained. These three values are distributed to each wheel as torque and steering angle, based on the optimum tire force distribution method. The optimum tire force distribution method finds the longitudinal/lateral tire forces of each wheel that minimize cost function, which is the sum of the normalized tire forces. This paper describes a 6WS/6WD vehicle with improved cornering performance and the results are validated through TruckSim simulations.