Closed-loop energy equivalence for transient brake tribometer testing: methodology and validation against the WLTP cycle

: This work proposes a closed-loop energy-equivalent methodology for reproducing transient braking cycles on a tribometer, addressing the inability of conventional tribometers to control the frictional energy dissipated at the pad–disc contact under transient loading. The methodology combines kinematic translation of the cycle into tribometer-compatible inputs with a normal-force recalibration strategy based on the energetic coefficient of friction, updated between cycle repetitions to converge on the prescribed dissipated energy. Sample miniaturisation criteria are also derived from tribometer operational constraints, and the particle-emission characterisation setup is aligned with the procedure prescribed by UN GTR No. 24, the regulatory reference for brake emission testing. The methodology is implemented on a commercial tribometer and benchmarked against a certified inertia-dynamometer test of the WLTP-Brake cycle, using a grey cast iron disc and a low-metallic pad representative of a large SUV. The braking distance was reproduced within 2% and the dissipated energy within 7%, with disc temperature trends consistent between tribometer and dynamometer. PM 10 mass emissions agreed within 5% (mg/km), well below the 17–27% inter-laboratory variability reported for full-scale dynamometer testing.