Many modern off-road construction machines incorporate traction control systems to provide better performance and stability in harsh driving conditions. These systems are capable of controlling wheel slip in such a way that the tractive force is increased, tire consumption is reduced, and the overall safety of the machine is improved. However, the driving surface conditions can have a strong impact on the optimal control parameters for the traction control system. This paper sets forth a method of automatically tuning the controller parameters in real time, so that the system can maximize the tractive force on its own.
Toward this end, a simple longitudinal wheel dynamics model is developed using a construction machine as a reference. This model incorporates considerations for the generation of tire force, wheel slip dynamics and machine transmission. Then, a simple traction control structure using proportional-integral-derivative (PID) control is presented which attempts to keep the machine wheels from slipping excessively. Finally, a real-time optimization scheme using the extremumseeking algorithm was included in the system in order to automatically improve the setpoint of the controller by maximizing the pushing force of the machine. Using the vehicle model of the system, the auto-tuning controller is tested to determine the capability of the system to improve the performance. The optimization scheme allows the controller to find the optimal point, meaning that the output force can be increased when starting at a poor setpoint. Given the availability of a proper feedback signal, this system should be widely applicable to a wide range of different vehicle systems for incorporating traction control.
Keywords: Traction control, electro-hydraulic braking, optimization, automatic parameter tuning