Braking compatibility between motorvehicle and trailer: identification of impacts on braking behavior under different types of predominance pressure 2024-36-0308

In recent decades, it can be noted an advance in new technologies applied to commercial vehicles. This advancement led to the development of new functions making products more efficient and safer, benefiting the society in general. Commercial vehicle manufacturers brought their products to levels higher than those required by current legal resolutions. Among the various resolutions applied to the braking system, in CONTRAN #915/22, which specifies minimum requirements of performance of vehicles brakes, the part 7 of NBR 10966 stands out. This standard determines requirements for compatibility between towing and towed units combined as a vehicle. The purpose of this study was to evaluate the thermal balance between the brakes of a motor vehicle combined with a semi-trailer. The tests were carried out by varying the pneumatic pressure that controls the service brake of towed units during braking. Some of the pressure levels were complying with compatibility requirements, others were not. Results showed better thermal balance between the brakes of towing and towed units when using control pressures complying with the legislation. Pressures outside the limits stated in the NBR 10966, resulted on thermal imbalance between the brakes. At times, temperature gradients between the brakes of the semi-trailers were detected, indicating that the response and the releasing time of the brakes increase as the distance between their brake chambers and the towing unit increases, agreeing with previous works. In addition, tests also showed that there are differences between the pressure provided by the towing unit and the towed unit braking pressures. It was concluded that to obtain adequate thermal balance, what guarantee safe driving, good braking performance, comfort and stable braking, the pneumatic pressure provided by the towing unit in the control glad hand must be within the limits established by the applicable resolutions.