Exploring assumptions and requirements for continuous modification of vehicle handling using non-linear optimal control and a new exponential tyre model

An iterative simulation-based nonlinear optimisation technique is used here to explore optimally controlled behaviour of a large RWD vehicle with rear steer and idealised differential actuators. A novel tyre model is also introduced, which uses simple analytic functions for separated calculation of lateral and longitudinal force, with both based on the combined slip and vertical load. By first considering suitable transient and steady-state targets for the yaw rate, optimal control is simulated which is effective throughout the lateral acceleration range. Interestingly this can be closely emulated under stable conditions using PID control of rear steer only, according to the yaw rate target and without the need for separate lateral velocity control. PID is no longer successful when stabilising control is considered, so future research will consider an extension to the nonlinear optimisation method for such cases.