Vehicle intelligence is an effective way to improve driving safety and comfort and reduce traffic accidents. The trajectory tracking control of unmanned vehicles is the core module of intelligent vehicles. As a redundant system, the X-by-wire electric vehicle has the advantage that the turning angles and driving torque of the four wheels can be precisely controlled and it has a higher degree of controllability and flexibility. In this paper, a trajectory tracking control algorithm based on a hierarchical control architecture is designed based on x-by-wire vehicles. The hierarchical control algorithm architecture includes the trajectory tracking layer, tire force distribution layer, and actuator control layer. The trajectory tracking layer uses the longitudinal force, lateral force, and yaw moment as the control variables; the model predictive control algorithm controls the vehicle to follow the desired trajectory. The tire force distribution layer is solved by transforming the tire force distribution problem into a quadratic programming problem with constraints. Based on the expected resultant force and resultant moment, the longitudinal force and lateral force of each tire in the vehicle coordinate system are obtained. The actuator control layer converts the coordinate system to obtain the longitudinal force and lateral force in the tire coordinate system, which uses the arctangent function tire model to solve the desired tire slip angle, and then obtains the vehicle steer angle and driving torque. To verify the effectiveness of the trajectory tracking control algorithm of the hierarchical control architecture, the proposed trajectory tracking control algorithm is simulated and verified through the variable speed double line change condition and the low road friction coefficient double line change condition. The simulation results show that the control algorithm proposed in this paper has the accuracy to follow the desired trajectory.Definition:

<div class="section abstract"><div class="htmlview paragraph">The rapid development of city traffic makes the driving conditions faced by vehicles increasingly complex. The drive-by-wire chassis vehicle has the characteristics of four-wheel independent steering, four-wheel independent drive and four-wheel independent braking, which has become a current research hotspot because that can meet various complex working conditions. However, it is precisely because of the high degree of controllability of the drive-by-wire chassis that the research on the control strategy has become difficult. In this paper, an integrated control strategy based on the hierarchical algorithm framework is designed for the drive-by-wire chassis vehicle, which includes a centralized control layer, a tire force distribution layer and an actuator control layer. The centralized control layer is based on the model predictive control algorithm, which takes the vehicle longitudinal speed, lateral speed and yaw rate as the control objectives, and solves the total longitudinal force, total lateral force and total yaw moment required by the vehicle. The tire force distribution layer assigns the control objectives to the four wheels, which adopts the optimal control method to transform the tire force distribution problem into a quadratic programming problem, and solves the problem with the tire utilization efficiency as the optimization objective to obtain the longitudinal force and lateral force of each wheel. The actuator control layer obtains the wheel angle and driving torque through the tire inverse model. The performance with the proposed strategy is demonstrated by steering wheel angle step input simulation test under the condition of low road friction coefficient which compared with the direct yaw moment control algorithm. In order to further verify the effectiveness of the strategy under various driving conditions, a simulation test of the sine input of steering wheel angle was carried out to verify that the strategy can improve the driving stability of the vehicle under various driving conditions.</div></div>