Analysis And Optimization Research On Delay Characteristics Of Vehicle CAN Bus

The networked control system has a simpler structure,higher efficiency,and stronger stability than the traditional point-to-point communication control system,which is the trend of future technology development.Today,CAN bus is one of the most widely used field bus control networks in the automotive field,it has the advantages of high performance,high reliability,high real-time performance,and relatively flexible design.The CAN bus has a unique non-destructive bit-by-bit arbitration technology,which can effectively avoid competition conflicts that may be caused by a large number of messages simultaneously requested to be sent.However,this technology may cause the transmission delay problem of lower priority messages,and this problem is also one of the key technical difficulties that need to be solved at this stage.Based on the national key research and development plan,this thesis aims to realize the high real-time performance of the control system,and studies the key technology of CAN bus delay optimization.On the basis of introducing the characteristics of the CAN bus and its research status at home and abroad,this thesis points out the importance of reducing the communication delay to the performance of the control system from the perspective of use requirements and technical characteristics.Based on the introduction of CAN bus technical specifications,such as frame type,layered structure,error mechanism,etc.,the communication process delay and error recovery time model of bus delay is established,and the influencing factors of bus delay are analyzed,and several important indicators of delay judgment are studied:burst situation,dense packet transmission situation,jitter situation and worst-case delay time.Aiming at the problem that it is difficult to find the reason for the delay of the bus network,a test and evaluation method for comprehensive analysis of the delay characteristics of the bus is proposed,and the effectiveness of the method is verified by experiments.Aiming at the problem of communication delay,this thesis proposes a hybrid optimization scheme of message offset compensation and identifier coding optimization,starting from both the whole and the part.In the whole part,the message segmentation method is changed,and all the messages are reclassified and give the mapping relationship with the upper layer protocol;in the local part,a reference message is established,the correct arrival time of each message is calculated according to the distribution of the reference message,offset compensation is performed on some messages.This solution not only improves the overall network environment,but also solves the serious delay and even frame loss of some messages,thereby achieving the purpose of reducing the delay time.Real vehicle analysis and simulation research are carried out by using bus simulation development software CANoe and bus time characteristic analysis software Sym TA-S.The experimental results show that the delay characteristic test and evaluation method can effectively find the delay problem;the hybrid optimization scheme using message offset compensation and identifier coding optimization can greatly increase the proportion of low-latency messages,reduce the number of high-latency messages,and increase the subsequent scalability of the bus network,which has important theories significance and practical engineering application value.