Characterization of the Brake Linings Coefficient of Friction by Means of Instrumented Suspensions Equipped on a Hybrid Race Vehicle

<div>The knowledge of the brake linings coefficient of friction (BLCF) is crucial for the control of the braking moment in modern vehicles equipped with electric powertrains. In the case of race vehicles equipped with carbon–carbon brakes, the coefficient of friction exhibits great variations as a function of the main influencing factors, namely the pressure, the temperature, and the sliding speed at the pad–disc interface. In this work, a Le Mans Hypercar instrumented with more than 150 sensors was adopted to perform the characterization of the BLCF from racetrack acquisitions. The front and rear left suspensions of the vehicle were instrumented with strain gauge channels and position transducers to acquire the reaction loads at the upright and the orientation of the arms. Then, the geometric matrix method was implemented for calculating the moments at the upright from which the braking torque was derived without the need to know any of the wheel inertia, nor the driveshaft torque. Data from multiple acquisitions across different racetracks, operating temperatures, and ambient conditions were used to characterize the BLCF of the front and rear carbon brakes equipped on the vehicle. After implementing pre-processing steps aimed at improving data homogeneity, two friction maps were characterized for the front and rear systems, respectively. The friction maps were validated against new experimental data showing an average 3% error reduction over assuming a constant BLCF. Accordingly, the characterized friction maps can be integrated in the brake-by-wire system of the vehicle for accurate caliper pressure control through real-time estimation of the BLCF from commonly available sensor signals, such as caliper pressure, wheel speed, and disc temperature. In this context, the effectiveness of the friction maps was demonstrated by comparing the predicted brake moments with the torques measured by the instrumented suspensions, highlighting the advantages over assuming a constant BLCF.</div>