Study On The Design Optimization Theory Of Highway Continuous Downhill Based On Brake Heating

Continuous downhills have been frequent areas of highway accidents for many years.In recent years,with the rapid increase in the proportion of semi-trailer in road freight travel,traffic accidents related to them are not uncommon.The phenomenon of adaptation has become prominent,becoming the focus of industry and society.Therefore,based on the downhill performance of the semi-trailed truck,it is of great significance to deeply study the continuous downhill traffic safety issues.In this paper,the temperature of the brake hub is used as the link between the truck and the road.Through the combination of theory and experiment,a break heating model of the semi-trailed truck is established.In-depth study of the influencing factors of the break heating,and construct the relationship between the break heating and the longitudinal profile continuous downhill.Based on the break heating attribute of longitudinal slope,taking longitudinal slope parameters as the object,the continuous downhill design optimization method is studied.The thesis carried out the following work:(1)Background analysis and theoretical modeling of brake heating.Based on the relevant survey data,the adaptability status between continuous downhill and semi-trailed truck was analyzed from the road level and the vehicle level,and the necessity of studying the continuous downhill road safety based on the temperature rise of the truck brake hub was explained.The modeling method and applicability of the existing break heating model was analyzed.Taking the six-axle semi truck as the dominant vehicle model,the driving dynamics theory was used to analyze the stress of the downhill freight truck.And theb established the torque balance relationship between the tractor driving wheels.The thermodynamic theory was used to solve the heat dissipation of the hub,and the theoretical break heating model was established.(2)Real vehicle test design and model modification.Three downhill slopes of Ya-lu Expressway,the most representative continuous longitudinal slope in China,were used as the research sections.Dongfeng Tian-long Heavy Truck DFL4251A15(6 × 4)was used as the test vehicle to carry out downhill tests under extreme conditions to obtain vehicle performance characterization data and driver braking data.The defects of the theoretical model were explored through real vehicle data.Then introduced the concept of critical longitudinal slope to modify the break heating model.And the cluster analysis,error analysis and correlation analysis were used to verify the revised model from the critical longitudinal slope and model temperature aspect.(3)Basic theoretical analysis of continuous downhill break heating.Taking the temperature rise sensitivity coefficient as the analysis index,the sensitivity degree of vehicle factors,longitudinal slope factors and environmental factors to the rise and fall of the brake hub were explored through the sensitivity analysis.Under the premise of fixed vehicle conditions,the temperature gradient was used as the microscopic temperature rise attribute of longitudinal slope,and the brake hub temperature was used as the macroscopic temperature rise attribute of longitudinal slope.The two together constituted a continuous downhill brake heating attribute,which can quantify the safety of a certain type of truck brake from the road level,and build a bridge for continuous downhill design optimization through the brake heating.(4)Theoretical research on continuous downhill design optimization.Based on the relatively extreme driving conditions,the safety of the average longitudinal slope extension and the steep combination extension in the continuous downhill design wered analyzed by the brake heating model.Then the break heating properties of the longitudinal slope combination were analyzed,and the longitudinal slope combination parameter optimization method was proposed from three aspects: transitional slope gradient,slope difference between of steep-transitional slope,and slope length combination: According to the characteristics of the single longitudinal gradient temperature gradient,the control value of class Ⅰ and class Ⅱ transitional slope wered proposed;A safe temperature gradient was used to construct the maximum slope difference control equation of adjacent slope sections corresponding to different average longitudinal slopes;the safety of the combination of short-steep slope and long transitional slope,equal slope lengths,and long steep slope and short transitional slope wered analyzed.(5)Application example of continuous downhill design optimization method in the actual design stage.The preliminary design plan for a continuous downhill slope of a newly built super-high bridge-to-tunnel expressway in the southwest mountainous area was optimized,and the safety of the optimized plan was analyzed and evaluated.