Leontiev D. The theoretical foundations of braking multi-axle vehicles with an electro-pneumatic braking system

Based on the analysis and research, the first proposed method of determining the coordinates of the center of gravity of a multi-axle wheeled vehicle makes further development in the theory of operational properties of a wheeled vehicle. Based on theoretical and experimental studies, it was found that the longitudinal coordinates of the center of gravity of a multi-axle wheeled vehicle depend not only on the loads on its axis, but also on the location of the axes of the multi-axle vehicle relative to each other. For the first time, unified methods for determining the braking coefficient of a multi-axle wheeled vehicle according to its belonging group are proposed, which differ from those known in that they take into account the influence of the axle position of a multi-axle wheeled vehicle relative to its center of gravity. Comparison of theoretical and experimental studies of the braking dynamics of a multi-axle wheeled vehicle showed a qualitative convergence of the calculation results with the performed experimental studies (simulation error did not exceed 5 %). The development of vehicle brake systems is due to the use of electronic control systems for pneumatic brake devices, so the paper develops theoretical prerequisites for assessing the braking dynamics of multi-axle vehicles with electro-pneumatic brake drive. Based on the analysis of existing theoretical approaches and experience in the design of pneumatic devices with electronic control, for the first time generalized functional relationships to determine the dynamics of braking dynamics of multi-axle vehicle with electro-pneumatic brake drive operating in cyclic mode, offers recommendations for selection rational parameters of the axle load of a multi-axle vehicle and a method for determining the initial parameters of the vehicle during the investigation of traffic accidents. The generalized functions of air flow to determine the transients in the brake actuator, allowed to create a universal software for calculating the dynamic properties of electro-pneumatic actuators. Studies have shown that with a decrease in the length of the brake drive or with a decrease in the volume of the drive links, the dynamic processes in them become more intense. Therefore, the choice of the method of determining the air flow in the drive links is important for modelling electro-pneumatic pressure apparatus, as the error in the calculations can reach 50-80 %. The obtained new functional connections of the structural elements of the electro-pneumatic pressure modulator with indirect air flow allowed to form the concept of modelling such devices. Simplify the simulation of the working processes of the electro-pneumatic brake system by taking into account the peculiarities of the hysteresis of pneumatic devices when modelling the braking process of a multi-axle wheeled vehicle using a simple mathematical apparatus. On the basis of the "on-off"method, which was used in the implementation of the concept of organizing a spare brake system with electro-pneumatic brake drive, it was found that the number of combinations of combinations of brake drive contours with brake mechanisms of corresponding matching connection of contours to brake mechanisms. Are proposed criteria of definition of rational schemes realization brake actuator of a multi-axle wheeled vehicle allow to select acceptable variants of realization schemes of connection contours brake actuator to brake mechanisms respective bridges of a multi-axle wheeled vehicle, which provide a deviation efficiency braking of the vehicle by the average of its value is not more than 20 %. The theoretical provisions set out in the work allowed to improve the mathematical model of braking of a multi-axle wheeled vehicle in the adaptive mode during emergency braking, which differs from the known ones in that it takes into account the inconsistency of adhesion between the tires of its wheels and the road surface. The control system of the electro-pneumatic drive adjusts the pressure in the drive by the criterion of the ratio of the realized adhesion force to the limit value of the adhesion force. Based on the simulation modelling of the braking process of a multi-axle wheeled vehicle in the adaptive mode, it was established and confirmed by experimental studies that depending on the potential of the adhesion between the tires of road wheels and the road surface, the pressure in the can be increased by no more than 0.04 MPa in the event of failure of one of the drive circuits during braking of the car on the verge of locking its wheels. Developed and implemented guidelines for determining the axial loads of vehicles on the road surface allow with an accuracy of 10 % to take into account the peculiarities of load redistribution between the axles of multi-axle vehicles during the design of roads in Ukraine.