Improvement of Vehicle Path Tracking by Relaxing the Steering Angle Speed Limit

System constraints have an important influence on the path tracking of vehicles. The steering angle speed limit is a kind of system constraints. But the value of the steering angle speed limit adopted by different researchers is not the same. The influence of different values of the limit on path tracking is not clear. To clarify these influences, we refer to previous work to establish path tracking controllers based on linear model predictive control (LMPC) and nonlinear model predictive control (NMPC). Subsequently, we compare LMPC-based controllers with different steering angle speed limits and then compare NMPC-based controllers with different angle speed limits. According to the simulation results, relaxing the steering angle speed limit can make the error of the LMPC-based controller change from divergence to convergence. And, relaxing the steering angle speed limit can further reduce the error of the NMPC-based controller. When the steering angle speed limit is relaxed from ±10°/s to ±20°/s, the maximum absolute value of the displacement error is reduced from 0.551m to 0.326m, and the maximum absolute value of the heading error is reduced from 0.110m to 0.067m. Besides, we should note that relaxing the steering angle speed limit requires replacing the steering mechanism of the vehicle with a high-power steering mechanism.