Recent advances in chassis systems promise to greatly improve the performance of autonomous vehicles and new energy vehicles. By adopting the brake-by-wire technology, the fast response and precise pressure control of an electro-hydraulic brake system (EHB) can enhance the longitudinal control performance for trajectory tracking of autonomous vehicles. The lateral controller for trajectory tracking is generally presented in the previous studies. However, the longitudinal control is rarely considered, since the tire force longitudinal-lateral coupling is neglected. To address this issue, this work proposed a longitudinal control algorithm, involving of the longitudinal tire force constraint mechanism, the load-transfer active control strategy, the coordination mechanism, the demand calculation of actuators, and the actuator control strategy. The longitudinal tire force constraint mechanism is utilized to remain the lateral stability at the friction limits of vehicle handling. Based on the tire force longitudinal-lateral coupling characteristics, the tire longitudinal force constraint can be derived to meeting the tire lateral force requirements. The load-transfer active control strategy aims at improve the steering response. The cornering stiffness of front wheels can be increased owing to the longitudinal load transfer implemented by the active brake of EHB. After the longitudinal tire force constraint mechanism and the load-transfer control strategy being developed, the coordination mechanism is designed for correcting the desired longitudinal action given by the upper planning layer. The demand of actuators is derived by the vehicle dynamics. The actuator control can guarantee the fast response and precise regulation with the assistance of the x-by-wire technology. The effectiveness of the longitudinal control system is demonstrated via the high-fidelity Carsim-AMESim-Simulink co-simulation under the typical situations.

CICTP