The Vehicle Four-wheelindependent-steering Control Method Based On Linear Programming

Four-wheel-independent-steering(4WIS) technology is able to enhance vehicle flexibility at low speed, and can improve handling stability at high speed, direct yaw torque control technology can improve vehicle handling stability at extreme condition,which have become hotspots.At first, according to related parameters of the experimental prototype, this paper establishes a two-degree-of-freedom and five-input vehicle model taking the four-wheel steering angles and yaw torque as inputs, sideslip angle and yaw rate as outputs. At the same time, the ideal reference model is established according to the front-wheel steering vehicle, with the wheel angle and speed as inputs, sideslip angle and yaw rate as outputs.Feed-forward controller adopts the strategy of combining 4WIS control with direct yaw torque control, the performance index function is built with the minimum sum of the four-wheel side slip angles absolute values, which with absolute values is translated into containing no absolute values, the dynamic model static expressions, ideal sideslip angle and ideal yaw rate are used to obtain feed-forward controller constraint conditions, and then the solution of the feed-forward controller is conducted using the linear programming theory. Simulation under different conditions show feed-forward controller can optimally allocate steering angels, make full use of road friction condition and enhance vehicle stability effectively. However, the system has overshoot, and needs a long time to reach steady states.The performance index function of feed-back controller is the minimum sum of four-wheel side slip angles absolute values under the action of feed-forward controller and feed-back controller, the linear control system is built with four-wheel side slip angles and yaw torque as inputs, vehicle control model and ideal tracking model are set up to get feed-back control constraints, according to the theory of region pole assignment and simulation analysis, the unknown parameter values are solved. Simulation under different conditions verify controller character of fast response speed, suppressing overshoot and optimizing steering angels distribution.To build coordinate transformation equation, the driver model and road function,driver-vehicle-road closed-loop system is established. Selecting different trajectories and road, simulation under different conditions show that vehicle has good tracking character and handling stability, the designed controllers have good effect.