| In order to improve the performance of automobile braking system,domestic and foreign researchers proposed to integrate electromagnetic braking and frictional braking system,so as to give full play to the advantages of electromagnetic braking and frictional braking to improve the stability,smoothness and environmental protection of automobile.Looking at the current research on the integrated braking system of electromagnetic and friction by domestic and foreign scholars,the current research results pay more attention to the structural design and parameter optimization of the integrated system,the analysis of the combined braking performance of the integrated braking system,the thermos magnetic effect of the electromagnetic braking performance,the analysis of the dynamic characteristics of the frictional braking system and the stability control of the integrated braking system.At present,the research focuses more on the performance of integrated braking system,but less on the dynamic problems caused by the change of working mode of integrated braking system.Due to the different dynamic characteristics of electromagnetic brake and frictional brake torque,and the change of brake demand torque in the process of brake mode switching,the stability and smoothness of automobile braking are affected.For this reason,this paper studies the dynamic problem of the mode switching process of the electromagnetic and friction integrated braking system.The specific work is as follows:Taking the dual disc electromagnetic and friction integrated braking system as the research object,this paper analyzed the structural characteristics of the integrated braking system,divided the integrated braking system into pure electromagnetic braking mode,composite braking mode and pure friction braking mode,established the hydraulic braking system model,and analyzed the change trend and influencing factors of the electromagnetic braking torque.The braking torque of the electromagnetic brake was divided into two parts: the low speed positive proportional linear region and the high speed reverse proportional linear region.The driver’s braking intention was analyzed by using the ANFIS method,the front and rear axle braking force distribution strategy of the automobile braking process was formulated,and the response performance of the electromagnetic brake and hydraulic brake were analyzed.In order to solve the problems that the hydraulic system can not intervene quickly when the brake mode was switched,which affected the smoothness of the automobile braking,the hydraulic braking response strategy of feed forward compensation was proposed.Using the driver’s brake intention model,the pre-start strategy of the hydraulic brake was designed to eliminate the hydraulic pressure crawling of the main brake cylinder.The influence of the integrated braking system on vehicle braking stability was studied by quantitative analysis calculation,and the measures to improve braking stability were proposed.Based on the hybrid system theory,the dynamic characteristics of the integrated electromagnetic and friction brake system were analyzed,and the cause of the dynamic problem of mode switching was revealed.The discrete events,the continuous dynamic process and the coupling relationship between them was described using the hybrid dynamic model,and the hybrid characteristics of the six mode switching conditions were analyzed.The switching performance of the six modes was analyzed from three aspects of responsiveness,smoothness and stability according to the control objectives of the different switching conditions,and three typical mode switching conditions were studied in detail.In the process of mode switching of integrated braking system,there were these phenomena that the electromagnetic brake torque and hydraulic brake torque would have a side or two of the "cut" or "cut out" caused by smoothness problems,the mode-switching smoothness control strategy based on model prediction control method for the integrated braking system was proposed.Based on the principle of sliding mode variable structure control,the anti-lock control strategy of electromagnetic and friction integrated braking system is designed.The simulation of typical mode-switching conditions was carried out using Matlab,and the effectiveness of the proposed control strategy was verified.Based on the analysis of the mode switching dynamic characteristics of the integrated braking system,the evaluation indexes of the mode switching quality of the integrated braking system were determined from three aspects: the response of the mode switching,the smoothness of switching and the environmental protection.Based on expert test data,the weight of evaluation index was determined by joint analysis method,and the evaluation strategy of mode switching quality was put forward by multi-objective optimization method.the influence mechanism of mode switching response,switching smoothness and environmental protection of integrated braking system was analyzed.It was found that the relationship between braking intensity,impact and switching time is "spoon" shape,the relationship between the braking strength and the following of the braking force presents a flat "w" shape,and the relationship between the braking strength and the impact degree presents an approximate linear shape.It was proposed that the proportion of non-contact braking action time is used to characterize the environmental protection effect of vehicle braking mode switching,and the conversion coefficient was used to convert the proportion of electromagnetic braking force in the composite braking mode into action time,to describe the environmental protection performance of the compound braking mode.The calculation method of braking environmental protection was put forward.On the basis of a specific car brake system parameters,the hardware-in-the-loop test platform of integrated brake system was designed based on the modular layering method,and the mode switching test system of integrated brake system based on NI was developed.The verification test of integrated braking system mode switching was carried out,and the hardware-in-the-loop simulation test of braking mode switching under different road conditions was done,the effectiveness of the mode switching of the electromagnetic and friction integrated brake system proposed in this paper is verified. |
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