摘要
随着电子技术和控制技术的飞速发展,汽车故障诊断已经发展到使用专用的故障检测仪来进行。现在的汽车在线故障诊断系统已经可以对车辆电控系统参数实行连续监控和故障自诊断,这种系统能记录电控系统的间歇故障,查找故障更加方便及时。OBD-Ⅱ标准详细规定了汽车在线故障诊断系统所使用的通信协议,规定了车外诊断设备和车内电子控制单元进行通信时所要遵循的规范,还规定了汽车发生相应故障时所应该产生的故障代码及获取这些故障代码的方法。OBD-Ⅱ汽车在线故障诊断系统标准已经被世界上绝大多数的汽车生产厂家采用。
汽车车载故障监控诊断平台是配合OBD-Ⅱ在线故障诊断系统使用的车外诊断设备。它通过汽车的OBD-Ⅱ故障诊断接口与车内电子控制单元建立起通信连接,用规定的通信模式和车内电子控制单元进行对话,获取汽车故障诊断代码和实时状态数据,进过分析处理得出故障诊断结果,并对结果进行存储和实时显示。
本文通过对OBD-Ⅱ汽车在线故障诊断系统所使用的通信协议和诊断模式的深入研究,提出了基于OBD-Ⅱ的车载故障监控诊断平台的设计方法。
故障监控诊断单元进行故障数据的提取、分析和显示。硬件平台设计方面,本文提出了以S3C2410处理器为中心的设计方案,并给出了主要外围电路的设计。软件设计方面,给出了故障监控诊断单元的软件设计框架。
车载故障监控诊断平台的OBD-Ⅱ接口单元是车载故障监控诊断单元和车内电子控制单元进行通信的桥梁。它将OBD-Ⅱ系统的信号转换成RS232信号供给故障诊断平台。通过对OBD-Ⅱ通信协议的研究分析,提出了两种多协议自适应式网络接口单元的设计方法。深入探讨了以单片机为基础设计网络接口的方法,给出了相应的软件硬件设计。以专用协议转换芯片为基础,完成了网络接口的单元的设计工作。
With the development of electric technology and control technology, special fault diagnostic tools are used in automobile’s fault diagnosis. Now, the on broad diagnostic system can monitor the systemic parameters of automotive electronic control system continuously. This kind of diagnostic system can memorize the intermittent problems. So it would be easier and faster to find out the faults. The communication protocols used by diagnostic system, the communication criterions which shoud be followed, and the trouble codes and how to get them are described in detail in OBD-Ⅱstandard. Most of the automobile manufactures have adopted the OBD-Ⅱfault diagnostic system.
The on-vehicle fault diagnostic platform is used to get diagnostic information and real-time status messages from the electronic control units. It communicates with the electronic control units through the OBD-Ⅱelectrical connector, acquire trouble codes and datas. The diagnostic results will be displayed on the LCD.
This dissertation based on in-depth study of the protocols and methods which defined by OBD-Ⅱstandard. It puts forward how to design the on-vehicle fault diagnostic platform.
The fault diagnostic cell is responsible to get and analyse the trouble codes. The hardware core is S3C2410, the peripherally auxiliary circuit design is carried out in this dissertation. The sofeware framework also carried out in this dissertation.
The interface cell of the on-vehicle fault diagnostic platform is the gateway between the automobile and the diagnostic equipment. It convertes the code schemes between OBD-Ⅱand RS232. Two different methods for interface cell design are presented in this dissertation. One bases on the microcontroller and the other bases on the ASIC special for protocol converting. Some design works, such as the hardware and software design in both methods are carried out in this dissertation.
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