Different approaches on how to improve braking performance in M3 vehicles to meet secondary brake requirements from ECE R13 regulation through low cost solutions

The braking system of any road vehicle is subject to extensive legislative standards and requirements in many regions around the world. In buses, which belong to M3 category, one of the most critical demands is occupancy rate of passengers that leads to affect Gross Vehicle Weight (GVW). More and more, customers are pushing the manufactures to increase the GVW of buses to allow more passengers inside and consequently increase profitability of the operation. By increasing GVW braking system has to present better performance to fulfill requirements. ECE R13 regulation establishes 2.5m/s² as minimum Mean Fully Developed Deceleration (MFDD) and 64,4meters as maximum Stopping Distance (SD) acceptable to secondary brake performance. In a 4x2 vehicle with GVW of 19.5 tons fitted with disc brakes these requirements are actually fulfilled, but by adding 600 kg it became out of requirements. Based on the parameters which might affect braking performance, three different approaches were studied, tested and disposed in a decision matrix to choose most feasible in terms of performance, costs, manufacturing and time to implementation: a new protecting valve setup, increasing residual pressure at port 21 and 22; a new pneumatic scheme using a Double Check Valve (DCV) to share residual pressure from non- failed circuit to failed circuit; and finally an exchange of 24” service brake chambers by a 27” in both axles, being those solutions preselected as feasible solutions in terms of less impacts to brake system. Tests were performed considering failure at front (FA) and rear (RA) axles. By taking baseline results with MFDD 5.49% and 1.63%, and SD 3.09% and 4.72% out of requirements for FA and RA failures respectively, test results for proposed solutions showed in a ranking: DCV solution as the best performance, which had improved MFDD by 50.56% and 51.92%, and SD had decreased by 67.51% and 59.44%; 27” service chambers as second best solution, which had improved MFDD by 17.80% and 16.23%, and SD had decreased by 24.52% and 18.87%; and finally new protecting valve setup in third place with improving of MFDD by 19,30% and 10.87%, and decreasing of SD by 28.60% and 11.22% overcoming baseline results. Therefore, all three solutions fulfilled the regulation requirements and could be selected by the manufacture according to its needs.