Longitudinal Vehicle Stability Control Based on Modified Sliding Mode Control

In order to improve speed tracking accuracy and ensure longitudinal stability control in vehicles under conditions of parameter uncertainty and external interference, this study introduces a modified sliding mode control (SMC) method. The proposed method replaces the reaching rate function in conventional SMC with a saturation function, which effectively reduces the chattering phenomenon in the control process. The longitudinal modified SMC method consists of two stages for both driving and braking control, designed according to the longitudinal vehicle dynamics model. Within the first stage, the control law determines the engine torque or brake torque; while the second stage oversees the modulation of throttle opening or brake pressure. To ensure a smooth transition between driving and braking modes, switching rules are defined predicated on predefined thresholds governing the driving or braking torque and speed errors. The stability of this control system is verified through Lyapunov stability analysis. To validate the effectiveness and practicality of the algorithm, simulations are performed using CarSim/Simulink, and experiments are conducted on a hybrid Lincoln MKZ. Results from both simulations and experiments demonstrate that the modified SMC method improves speed tracking accuracy and longitudinal control stability, even when dealing with rapidly changing speeds. Moreover, the algorithm exhibits a remarkable ability to resist external interference, making it a reliable solution for real-world applications.