Factors that Influence the Determination of Adhesion Utilization of the ABS in Commercial Vehicles: A Case Study

The anti-lock braking system (ABS) plays a fundamental role in preventing wheel lockup and preserving vehicle steerability and stability during braking. In Brazil, ABS is mandatory for commercial vehicles since 2014, following CONTRAN Resolution 380/11, with the objective of improving traffic safety and reducing road accidents. The performance of an ABS is directly influenced by the characteristics of the vehicle’s braking system, including its pneumatic architecture and mechanical component sizing, which determine brake-force distribution and the frequency of ABS intervention. Regardless of these characteristics, developers must ensure that ABS efficiency complies with applicable regulatory requirements. For performance assessment, NBR 10966 Part 6 establishes procedures for measuring and calculating the adhesion utilization of ABS. Represented by the letter epsilon (ε), adhesion utilization quantifies the relationship between the braking performance achieved with ABS active and that corresponding to the vehicle’s maximum braking capacity without wheel slip. This metric provides an indirect evaluation of system efficiency. This work presents a case study conducted during the development of the ABS for a medium-heavy truck equipped with more than two axles. The study consisted of the analysis of results obtained following the adhesion utilization determination methodology defined in NBR 10966 Part 6, and of the evaluation of its applicability to multi-axle vehicles. Despite the braking system and vehicle configuration meeting all minimum static and dynamic performance requirements, the measured adhesion utilization fell below expectations. This outcome prompted a detailed investigation of both the measurement approach used for this vehicle category and the factors affecting the tire–road friction coefficient, which are independent of the braking system itself. The analysis indicated potential improvements in the test methodology for vehicles with more than two axles and highlighted the significant influence of test-track surface conditions on the results obtained.