| With the continuous improvement of Chinese economic strength,the transportation industry has ushered in rapid development.The continuous growth of the total mileage of the road,the continuous improvement of road facilities and equipment,and the development of the automobile industry have made Chinese car ownership increase year by year.The increasing number of road traffic participants leads to various traffic accidents,and traffic safety has gradually become a topic of concern.Semi-trailer trains due to its large load,body length and different braking timing sequence between the shafts,it is easy to collapse,tail flick,rollover and other braking instability phenomena in the braking process.Therefore,it is necessary to study the braking safety of semi-trailer trains.At present,bench test and road test are mainly used to test the braking performance of automobiles.The road test method requires a suitable testing site,and the test results are greatly affected by the environment,usually only as an auxiliary test method.The bench test method requires the application of professional braking detection equipment.The equipment covers a small area,and the test results are less affected by the environment and have good repeatability.It can detect the braking force,braking imbalance and blocking force of the vehicle,and can meet the most basic braking performance testing needs.However,the number of axles of the semi-trailer train is large,and the structure of the braking system is complex.The different braking timing sequences between the axles will lead to braking instability during the braking process.The premature braking of the steering axle will cause the vehicle to brake and deviate.The premature braking of the drive axle will cause the tractor and the semi-trailer to fold,and the premature braking of the semi-trailer axle will cause tail flick.Although the national standard Technical Specifications for Safety of Power-driven Vehicles Operating on Roads(GB7258-2017)puts forward requirements for the braking timing detection of semi-trailer trains,the current dynamic detection method is still in its infancy,and the related research on the braking timing evaluation of semi-trailer trains is still blank.The research on the braking performance of semi-trailer trains at home and abroad mainly focuses on braking stability control.Based on the previous research,by analyzing domestic and foreign regulations and literature,a detection method for indirectly obtaining the braking timing sequence of semi-trailer trains is proposed by using cycloid formula to calculate tire slip rate and monocular vision technology to solve tire braking slip rate.Based on the FAHP and CRITIC combination analysis method,the comprehensive evaluation theory system of braking sequence stability of semi-trailer train is established.Truck Sim simulation software is used to establish a three-axis semi-trailer train simulation model,and the motion characteristics of the semi-trailer train under different braking timing conditions are simulated and analyzed in straight line,curve and single-line braking.The evaluation index parameter data based on the braking timing operation condition is obtained for evaluation.The main research contents of this paper include the following four aspects:(1)Brake timing detection based on tire slip rateThe relationship between road adhesion coefficient and tire slip rate is analyzed,and the solution scheme of tire slip rate based on cycloid formula is proposed.The validity and accuracy of the solution formula of slip rate based on cycloid formula are tested.The hardware layout and connection of monocular vision vehicle train braking timing sequence detection are completed,and the braking timing sequence detection test is designed and completed.(2)Establishment of braking timing evaluation systemThe typical braking conditions and braking instability modes of semi-trailer trains are analyzed.According to the braking stability mode,and referring to the domestic and foreign regulations and literatures on the braking performance of semi-trailer trains,a comprehensive evaluation theory system is established based on FAHP-CRITIC combination analysis method,and the subjective and objective weights of evaluation indexes are calculated.(3)Vehicle kinematics modelingTruck Sim simulation software is used to establish the braking timing model of semi-trailer train,and the motion characteristics of semi-trailer train under different working conditions are analyzed.(4)Experimental designIn order to test the accuracy of the established semi-trailer train simulation model,a test detection system was built and a real vehicle test was designed.The feasibility and rationality of the model were determined by comparing the test and simulation results.(5)Brake timing evaluation and train braking stability analysisAccording to the evaluation system and evaluation index,the braking simulation analysis of semi-trailer train is carried out for the braking sequence experiment scheme under different working conditions.Based on the simulation results and FAHP-CRITIC combination analysis and evaluation theory system,the comprehensive evaluation is carried out.Aiming at the optimal braking timing scheme,in order to further analyze the influence of vehicle structure parameters,use parameters and road conditions on vehicle braking stability under the braking timing,the simulation analysis of the influence parameters of braking stability is carried out,and reasonable improvement suggestions are given according to the simulation results. |
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