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A path following control strategy for a four-wheel-independent-drive electrical vehicle (4WID-EV) based on backstepping and model predictive control is presented, which can ensure the accuracy of path following and maintain vehicle stability simultaneously. Firstly, a 2-DOF vehicle dynamic model and a path following error model are built and the desired yaw rate is obtained through backstepping. Then, a model predictive controller is adopted to track the desired yaw rate and obtain the optimal front wheel steering and external yaw moment. Meanwhile, an optimal torque distribution algorithm is carried out to allocate it to each tire. Finally, the effectiveness and superiority of the strategy is validated via CarSim–Simulink joint simulation. Results show that the strategy has higher following accuracy, smaller sideslip angle, and better yaw rate tracking.

The braking stability has significant importance for commercial vehicles, especially tractor-semitrailer. However, the brake lag of air brake system brings serious safety risk to the vehicle. To improve the braking stability of tractor-semitrailer, an optimized air brake system is proposed. Using characteristic of the fast exhaust response of spring brake cylinder of composite brake chamber, a normally open solenoid valve and a normally closed solenoid valve are connected with the spring brake cylinder of composite brake chamber of semitrailer to control the spring brake force, which responds more quickly than service brake force. A strategy is proposed to control the difference between the actual braking torque of the semitrailer brake and the target braking torque and is simulated based on AMESim and SIMULINK. An experiment is made to verify the effectiveness of the optimized system. The simulation shows that the improved scheme reduces the response time of semitrailer brake system by 0.19 s, and effectively restrains the lateral movement of the vehicle downhill braking and improves the stability of the braking direction of the vehicle. And the experiment indicates that the brake of semitrailer responds earlier than tractor, which means the brake lag is improved significantly.

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Brake time delay, which is a major shortcoming of air brake systems, may lead to precarious situations. In this study, the structure of an air brake system of a tractor–semitrailer was optimized by adding a shuttle valve and a two-position-three-port electromagnetic valve between the control pipeline and the charging pipeline downstream of the trailer control valve. The new electronically controlled structure clearly ensures that the semitrailer brakes faster, as validated by a simulation, bench test, and real-vehicle test. The simulation results reveal considerable improvements in the braking time, braking distance, longitudinal kinetic energy, lateral kinetic energy, and β phase plane. The bench test indicates that in the proposed structure, the average response time of service brake cylinders of the first and third axles of the semitrailer are 0.12 and 0.17 s, respectively. In addition, the real-vehicle test indicated that the service brake cylinders of the first and third axles responded 0.12 and 0.18 s earlier than those in the original system, respectively.