Once the best trajectory has been determined (both in terms of best track and best speed profile), it is necessary to identify the driver’s inputs to follow the given trajectory. The driver’s inputs are the following: the gear, the clutch, the brake, the accelerator and the steer wheel.
In order to simplify this identification problem, it was decided to implement an automatic gear shift mechanism: during acceleration/braking manoeuvres the gear is incremented (in 0.1s) when the engine speed reaches a value related to the characteristic curve of the engine.
Accelerator and brake inputs, as well as steer wheel inputs, are instead determined using two PID controllers. The accelerator/brake controller, determines the driver’s inputs on the base of the actual reference speed as well as the reference speed that will be required some distance in advance. This “visual distance” is a function of the vehicle speed (an of the vehicle acceleration): the higher the speed the longer the distance. To improve the promptness, a feed-forward contribution based on a simplified vehicle model is also added. Also the steer wheel controller determines the steer wheel angle adding two contributions: a feed-back PID contribution and a feed-forward contribution. For what concerns the feed-back contribution not only the position of the cog of the vehicle with respect to the ideal trajectory is taken into account but also the orientation of the vehicle with respect to the ideal track tangent.
The proposed race driver model has been compared to IPG Driver model on several circuits. The lap time reduction achieved about 10% on any circuit.