The FlexRay Bus Message Retransmission Scheduling Strategy And Its Application On Brake-by-wire

With the continuous improvement of people’s requirements on the maneuverability,safety and comfort of automobiles,the traditional throttle,steering and braking systems that are mechanically and hydraulically driven have been transformed into the electronic control system by electric energy driving.The traditional in-vehicle networks(LIN,CAN,etc.)cannot meet the performance requirements of the Brakeby-Wire system due to the shortage of bandwidth and real-time performance.The FlexRay bus technology with the advantages of high transmission rate,flexible topology,time determinism,redundancy and fault tolerance is generated to adapt to timing.It is particularly suitable for automotive X-by-Wire systems that require high real-time and safety reliability.This article analyzes and compares the error handling mechanism of the common vehicle network and FlexRay bus,and builds the failure probability model of the communication system.The following research has been done on the static segment scheduling strategy of FlexRay bus and its application to Brake-by-Wire system:(1)A static segment message retransmission scheduling strategy based on reliability goals is proposed.Firstly,on the premise of satisfying the global reliability goal,an optimization mathematical model of message retransmission numbers is established to reduce the bandwidth occupation of retransmission of static segment messages.Then,with the goal of minimizing the total delay time of message transmission for all messages,a mixed-integer linear programming mathematical model is established to allocate corresponding transmission time slots and periods,using the modeling language AMPl and related solver to solve the above two mathematical models.Experimental results show that compared with existing methods,different messages belonging to the same sending node are combined and sent in the same time slot during scheduling,which can improve message schedulability and bandwidth utilization,realize the minimization of message transmission delay and enable the communication system to meet the corresponding functional safety requirement level.(2)The functional safety standard ISO26262 is used to analyze the safety integrity level and safety objectives of the Brake-by-Wire,A Brake-by-Wire communication experiment platform based on FlexRay bus is built.According to the optimal scheduling results obtained by message retransmission scheduling strategy,the whole system simulation,semi-physical simulation,and system integration test are performed.Firstly,the CANoe.FlexRay software is used to carry out functional modeling and simulation analysis of the communication network.Then the real FlexRay physical node is developed based on the simulation model.The physical node is simulated and tested using the bus interface hardware VN7600 and CANoe.FlexRay software in the semi-physical simulation and system integration test phase.Finally,the oscilloscope is used to test and analyze the physical signals on the FlexRay bus of the communication system.The total test results show that the transmitted data frames meet the design requirements,each communication node operates in accordance with the pre-designed transceiver relationships and the normal operation at the moment,and the physical signal waveforms are regular,and there are no missing frames and error frames within the specified time in the laboratory environment.