Research On Real Time Performance And Reliability Of Can Bus In Automobile

With the development of automotive electronics and the increasing communication between components, automotive on-site bus has been higher demanded in real-time and reliability. At the beginning of the design, CAN bus has a good real-time and reliability, so that the CAN bus has widely used in automotive electronic field. However, with the increasing of the network CAN bus load, CAN Bus arbitration agreement itself would induce network congestion and decrease real-time performance. Moreover, the interactions of CAN-protocol verification mechanisms could also reduce the reliability of CAN bus.According to the basic features of CAN bus, combined with the classification of automotive electronic nodes, this paper analyzes some typical CAN bus system. Then in the respect to real-time, this paper use the concept of network real-time control and some indicators to study the problem of the real-time performance in automotive CAN network. By establishing a mathematical model of CAN bus network and through theories analyzing, a function has been derived between the average delay of CAN bus data frames and network load rate. This paper has also analyzed the limitations of CAN bus protocol arbitration mechanism in the heavy network load conditions. Finally, in the reliability aspect, it researched the definition of the reliability and evaluating scale and elicited the reliability of several bus topologies by theoretical analysis. Against previous analysis, it proposed some optimal design solution for automotive CAN network to improve the real-time and the reliability. Optimization is divided into two areas. On one hand, classified nodes based on the bus nodes data nature and used high-speed, low-speed CAN bus combination method. The methods could reduce the bus load effectively and improve the data's real-time. By using redundancy design in controller lever, effectively improve the system reliability. On the other hand, by using TDM TTCAN protocol in the high-speed CAN Bus, eliminate the impact of arbitration mechanisms on system real-time. Low-speed CAN bus with dynamic priority management mechanism, which saves cost and effective reduction the impact of the traditional CAN bus load on real-time. Finally, by choosing the TI's chips TMS320LF2407A and Microchip's chips MCP2515, made research on the realizing of TTCAN protocol and finished nodes design of TTCAN protocol. Also, analysis the difference between the traditional CAN BUS and the bus made in this article in serial network load environment.By analyzing the experimental data, it can be concluded that TTCAN protocol's delay is far less than traditional CAN bus in the heavy network load conditions. In the same bit error rate network condition, reliable running time of the redundant bus has nearly twice a non-redundant bus. By the realization the solutions proposed in this paper through DSP chips, it shows the technical feasibility. Experiments show that the proposed solutions are also superior to the traditional CAN bus in large network load conditions, real-time performance and reliability and reached the expected results.