Research Of High-Precision Clock Synchronization In Automotive CAN Network

Owing to strong communication and high reliability,Controller Area Network (CAN) is widely used in automobile bus. With the growing number of automotive electronic control unit (ECU), accurate clock reference is the impact of high performance automotive network system which is one of the important factors. Therefore, the research of vehicle CAN network and clock synchronization problem, bulding the clock synchronization algorithm of low consumption, high precision has important practical significance. Based on the analysis of the characteristics of CAN bus, hierarchical structure, bus message format, communication mechanism and error detection and fault definition and other aspects of the foundation, the related research of the automobile CAN network control system clock synchronization method and its realization had been carried out.First, the paper introduces the present situation and development trend of CAN bus, clock synchronization research status at home and abroad, meanwhile the specific details of the CAN bus layered structure, four kinds of message format, communication mechanism, error detection and other aspects are also introduced.Then,in view of clock synchronization in vehicle CAN network application, the research was carried out. First of all, the basic concept of the clock drift rate and clock synchronization mechanism are introduced, then through the analysis of advantages and disadvantages in master and slave and its improved algorithm and consultation clock synchronization methods, this paper proposes the "clock drift rate" clock synchronization method based on the alternate synchronization master node priority list. In order to reduce the network redundant load problems because of the periodic consultation,in the condition of the main node failure,this method determines the standby host node by using the alternate synchronization master node priority list node negotiation and gives the corresponding synchronization algorithm.Finally, the simulation experiments was carried out based on "the clock drift rate" clock synchronization algorithm in CANoe simulation software. This paper analyzses the result of the simulation after the detail description of clock synchronization method model, database and CAPL programming design. The simulation experiment shows that when in failure of the host node, each node scan alternate synchronization master node priority list and select the highest priority node as the master node meanwhile the system operates normally, it’s explained that the algorithm can effectively prevents the master-slave clock synchronization of single point failure, and enhance system stability. In addition, There are common places existing between synchronization and existing master-slave synchronization, but in the same conditions clock synchronization overhead is reduced, which can effectively solves the problem of single point failure occurs; In addition, the precision of clock synchronization is effectively improved according to the current CAN network running status by modifying the value of weight factor λ, to better meet the vehicle CAN network real time requirement.