Evaluation of ABS Braking Performance for Vehicles Descending Slopes under Different Road Adhesion Coefficients

Abstract

Braking safety on downhill roads with varying tire–road adhesion is a critical concern in vehicle dynamics. This paper evaluates the effectiveness of the Anti-lock Braking System (ABS) during downhill braking through a combined simulation and experimental approach. A longitudinal vehicle dynamics model is developed, integrating a driver model, vehicle body dynamics, wheel dynamics, and an ABS model employing a Fuzzy Logic controller. Simulation results are compared with experimental braking data to validate the model, assess controller performance, and evaluate ABS behavior on an actual vehicle. The comparison shows that braking performance parameters follow similar variation trends in both simulation and experiment; however, the Fuzzy controller maintains the wheel slip ratio within its optimal range with noticeably higher stability in simulation than in experiment. Using the validated model, braking performance from an initial speed of 60 km/h is investigated across different road adhesion coefficients and slope angles. When the adhesion coefficient decreases from 0.8 to 0.3, braking distance increases by 354.07% at an 8° slope and 725.50% at a 12° slope. Under low-adhesion conditions (φ = 0.3), increasing the slope from 8° to 12° raises braking distance by 121.16%, whereas under high-adhesion conditions (φ = 0.8), the increase is only 16.03%. These findings highlight the necessity of simultaneously accounting for road grade and adhesion coefficient when assessing ABS braking performance on downhill roads.