A pneumatic slip control braking system has been demonstrated, which reduces emergency stopping distances of heavy goods vehicles (HGVs) by up to 19%. Solutions are still required to set the optimal reference wheel slip for this system online, so that it can adapt to changing operating conditions. This paper considers whether extremum seeking algorithms (ESAs) could be a feasible alternative approach to online tyre model fitting, the computational expense of which has to date inhibited real-time implementation.

Convergence and stability properties of a first order sliding mode ESA are discussed, and its tuneable parameters are recast as physically meaningful performance metrics. Computer simulations are conducted using a detailed braking system model and hardware-in-the-loop simulations are conducted with prototype pneumatic slip control braking hardware for HGVs. The ESA enables the braking system to achieve at least 95% of the maximum possible braking force for almost the entirety of an emergency stop. Robustness to parameter errors, road roughness and changing friction conditions are all explored.