【作者】 李海龙；

【导师】 黄海珍；

【作者基本信息】 吉林大学 ， 工程硕士（专业学位）， 2018， 硕士

【摘要】 CAN总线技术是电动汽车上应用最为广泛的通信技术,但是随着网联和智能技术采用,电动汽车上的通信数据量越来越大,CAN总线的负载率也越来越高,传统的报文仲裁方案已经渐渐难以满足如此多的通信量需求,CAN总线通信的可靠性也越来越低。汽车动力系统直接关系到汽车的行驶性能及安全性,因而对于报文的实时性要求很高,这就要求我们找到一种解决方案来保证报文及时、可靠地传输。提高电动汽车CAN总线通信实时性能的方案主要有两种:一是使用传输速率更高的总线技术,二是在现有CAN总线基础上进行优化,使报文在高总线负载率的情况下,也可以及时、准确地传输。目前,虽然有FlexRay和IDB-C等技术可以大幅提高总线的传输速率,但是由于成本问题,无法在短时间内普及。TTCAN、FTTCAN等技术可以提高CAN总线的报文传输能力,保证报文传输的实时性,但是TTCAN、FTTCAN对硬件提出了更高的要求,也会增加成本。所以在目前CAN总线技术上进行优化是一种不增加成本,亦可满足电动汽车总线报文传输性能要求的技术方案。本文对CAN通信提出三点优化方案:1.提出了实时调整仲裁窗大小的方案。本文在CAN通信协议的基础上,提出通过设计仿TTCAN调度矩阵,实现模仿TTCAN的通信方式,并在利用MATLAB编写遗传算法优化仿TTCAN调度矩阵的基础上,根据汽车动力系统中非周期报文的数量自动调整仲裁窗的方案,并结合已有的EDF截止优先级算法,形成了对仿TTCAN的综合优化方案。然后利用Stateflow搭建通信模型验证了优化方案的有效性。该优化方案可以在保证周期报文正确、及时传输的前提下,优化了汽车动力系统中散热器温度、进气口温度等非周期报文的传输,使这些报文的丢帧及延时都得到了一定的改善。发动机、电机、电池中非周期报文实时性的提升可以提升动力系统的响应速度,进而提高车辆的性能。最后在真实硬件条件下对将该方案进行对比分析,优化后的非周期报文的延迟和丢帧都得到了一定程度的改善,进一步验证了优化方案的可行性及提高总线通信实时性的效果。2.提出了合并非周期报文数据场的方案。根据非周期报文周期不确定且数据长度较短的现象,提出了将同一节点在同一基本周期内发送的非周期报文合并的方案,合并之后可以省去一个仲裁场、CRC场等所占据的字节,提升了数据帧中有用信息的占比。利用Stateflow搭建模型,验证了方案的可行性与有效性。结果表明该方案可以降低散热器温度、进气口温度等报文的延迟及总线的负载率,提高了总线通信的实时性。3.提出了缩短数据场长度的方案。针对目前车企CAN总线协议数据帧存在大量空白数据字节的情况,提出了将CAN报文数据帧中的空白数据字节在传输过程中去除的方案。通过仿真分析,验证了该方案的可行性,并提出了该方案实现的流程。本文从多个方面对CAN总线提出了优化方案,并在仿真和真实硬件实验条件下,对其可行性及有效性进行了验证,希望可以对CAN总线的优化研究提供参考。更多还原

【Abstract】 CAN bus technology is widely used communication technology in electric vehicles.However,with the adoption of network connection and smart technologies,the amount of communication data on electric vehicles are increasing,and the load rate of CAN buses is also getting higher and higher.The traditional message arbitration scheme has gradually been difficult to meet so many traffic demands,and the reliability of CAN bus communication is getting lower and lower.The automotive power system is directly related to the driving performance and safety of the vehicle.Therefore,the requirement of the real-time nature of the message is very high.This requires us to find a solution to ensure timely and reliable transmission of the message.There are two main solutions for improving the real-time performance of electric vehicle CAN bus communication performance:one is that use the bus technology with a higher transmission rate,and the other is that optimize on the basis of the existing CAN bus,so that the message can be transmitted in a timely and accurate manner under a high bus load rate.Currently,although technologies such as FlexRay and IDB-C can significantly increase the bus transfer rate,they cannot be popularized in a short time due to cost issues.TTCAN,FTTCAN and other technologies can improve the CAN bus message transmission capability and ensure the real-time transmission of messages.However,TTCAN and FTTCAN not only impose higher requirements on hardware,but also increase costs.Therefore,optimization on the current CAN bus technology is a solution that does not increase the cost and satisfy the transmission performance requirement of the electric vehicle bus message.This article proposes three optimization schemes for CAN communication:Firstly,a scheme for adjusting the size of the arbitration window in real time was proposed.Based on the CAN communication protocol,this paper proposes to design the TTCAN scheduling matrix to implement the TTCAN communication.And on the basis of using MATLAB to write genetic algorithm to optimize the TTCAN scheduling matrix,a comprehensive optimization scheme for TTCAN is formed.This method is based on the scheme of automatically adjusting the arbitration window according to the number of non-periodic messages in the automotive power system,and is combined with the existing EDF cut-off priority algorithm.Then use Stateflow to build the communication model to verify the effectiveness of the optimization scheme.The optimization scheme can optimize the transmission of non-periodic messages such as radiator temperature and inlet temperature in the automotive power system under the premise of ensuring correct and timely transmission of periodic messages.So the frame loss and delay of these packets have been improved.The improvement of the real-time performance of non-periodic packets in engines,motors and batteries can increase the response speed of the powertrain system and thus improve the performance of the vehicle.Finally,under the real hardware conditions,this program is compared and analyzed.The delay and frame loss of the optimized aperiodic packets are improved to a certain extent,which further validates the feasibility of the optimized scheme and the effect of improving the real-time performance of the bus communication.Secondly,a scheme for merging data fields of aperiodic messages was proposed.According to the phenomenon that the period of non-periodic messages is uncertain and the data length is short,a scheme for combining the aperiodic messages sent by the same node in the same basic period is proposed.After the merger,bytes occupied by an arbitration field,CRC field,etc.can be saved,and the proportion of useful information in the data frame can be increased.Using Stateflow to build the model,the feasibility and effectiveness of the scheme are verified.The results show that this scheme can reduce the delay of the message and the load rate of the bus such as radiator temperature and inlet temperature,so it can improve the real-time performance of the bus communication.Finally,proposed to shorten the length of the data field program.In view of the fact that there are large number of blank data bytes in the data frame of the CAN bus protocol in the car company,a scheme to remove the blank data bytes in the CAN message data frame during the transmission process is proposed.Through simulation analysis,the feasibility of the scheme is verified,and the process of the scheme is proposed.This paper proposes an optimization scheme for CAN bus from many aspects.And under the conditions of simulation and real hardware experiments,the feasibility and effectiveness of the CAN bus are validated.It is hoped that it can provide reference for the optimization research of CAN bus.更多还原