Research on the application of the hottest fieldbu

Research on the application of fieldbus network in the control system of pure electric vehicles

the rapid increase in the number and use of cars today makes the problem of atmospheric environmental pollution increasingly serious. Coupled with the crisis of oil resources, the automotive technology driven by electric energy has become a hot spot in the technical competition of automobile manufacturers all over the world. However, the industrialization of electric vehicles is still in the initial stage of preparation, and the related technologies and products have not yet formed an industrial system. In this new field, China is at a similar level with foreign countries. Therefore, the Ministry of science and technology has set up a major special project for electric vehicles in the "863" plan of the tenth five year plan to further promote the industrialization of electric vehicles and realize the leapfrog development of China's automotive industry

with the rapid development of modern automobile industry and electronic technology, there are more and more electronic devices in automobiles. The number of electrical nodes of a high-end car has reached thousands. If the traditional method is used for wiring, the number of connections is very amazing and there are great hidden troubles. In order to solve this problem, major automobile manufacturers have to comprehensively consider energy efficiency, environmental protection and product quality since the last century. In the 1970s, they began the research on vehicle networks and made great progress, forming a variety of network protocols suitable for different transmission rates and special purposes, such as can bus, Lin bus, KWP2000 for supply side reform and accelerated capacity clearing diagnosis, TTP for X-by-wire Most protocol for multimedia applications, etc. Can (controller area network) was proposed by Bosch Company in the 1980s. A serial data communication protocol developed to solve the data exchange between many control and test instruments in modern vehicles can well solve the above problems. Now many automobile companies in the world, such as Mercedes Benz, BMW, Volkswagen and so on, have adopted can bus to realize the internal data communication of automobiles

in China, the new two-component decomposition solution of vehicle network, bus and communication Hexion company aims to solve this challenge. The research on communication protocol started relatively late, but it has developed rapidly in recent years, especially in electric vehicle projects, bus network has been widely used

2 technical characteristics of automobile bus

automobile bus transmission must ensure the following points: ensure that information can be accurately transmitted; The bus node can access the bus at any time; The node accesses the bus according to the predetermined priority; It has the ability to solve the bus access competition according to the information content, and after the competition is solved, the winning site can access the bus and continue to transmit information; The node successfully accesses the bus in the shortest possible time; Optimized transmission rate (baud rate); Fault diagnosis capability of nodes; The bus has certain scalability and so on

2.1 coding of digital signals

in order to ensure the reliability of information transmission, it is very important to correctly code digital signals. Pulse width modulation (PWM) and non return to zero (NRZ) are mostly used for local data signals of automobiles. When PWM is used as the coding scheme, the upper bound of baud rate is 3 × 105kbps, for low transmission rate occasions. Using NRZ for information transmission can reach 1Mbps, which is used in occasions with high transmission rate

2.2 network topology

practical automotive local area networks are bus topologies, such as can, SAEj1850, advanced palmnet, etc. their advantages are: short cables, easy wiring; The bus structure is simple, and it is a passive component with high reliability; It is easy to expand. To add a new node, you only need to connect it at a certain point of the bus. If you need to increase the length, you can add an additional segment through the repeater

2.3 bus access protocol

the access protocol of automobile bus is generally a contention protocol, and each node can independently decide the transmission of information frames. If two or more nodes send information at the same time, there will be an error, which requires each node to be able to judge whether the conflict occurs. When the conflict occurs, wait for a random time interval according to a certain law and resend it to avoid conflict again. Most of the anti-collision monitoring measures used in the network protocol are carrier monitoring multiple access, such as can, SAEj1850, advanced palmnet, etc. carrier monitoring multiple access/conflict detection + lossless arbitration (csma/cd+nda) are adopted

3 characteristics of CAN bus

can bus communication protocol is formulated under the background of considering the industrial field environment. It adopts three layers in the iso-osi model of Open Systems Interconnection formulated by the international organization for standardization, namely, the physical layer, the data link layer and the application layer. Can bus specification has been formulated as the international standard iso11898 by the international organization for standardization, and is recognized as one of the most promising fieldbus, which has been widely used in industrial fields. With the support of famous semiconductor device manufacturers such as Motorola, Philips, Intel, Siemens, etc., various products with integrated can protocol have been rapidly launched. Compared with the general bus, can bus has the advantages of reliability, flexibility and strong real-time

(1) the CAN bus adopts a multi master structure. Any node on the network can send information to other nodes at any time, and the communication mode is flexible

(2) according to the access to the bus, the nodes on the network can divide carbon nanotubes into two categories: single wall and multi wall, with different priorities (depending on the message identifier), which can be as fast as 134 μ Response within s

(3) using non-destructive bus arbitration technology can greatly save the bus conflict arbitration time, and the network will not be paralyzed in crowded situations

(4) the CAN protocol abolishes the station address coding, but encodes the communication data, which can make different nodes receive the same data at the same time, and can easily realize the transmission and reception of data in the ways of point-to-point, point to multipoint and global broadcasting, which is easy to form a redundant structure to improve the reliability and flexibility of the system

(5) can adopts NRZ coding, and the maximum direct communication distance can reach 10km (rate 5Kbps), and the maximum communication rate can reach 1Mbps (at this time, the maximum communication distance is 40m)

(6) adopt short frame structure, with short transmission time and low probability of interference. Each frame of can information has CRC validity and other error detection measures to ensure a very low data error rate

(7) the communication medium can be twisted pair, coaxial cable or optical fiber, which can be selected flexibly

(8) the CAN node has the function of automatically closing the output in case of serious errors, so that the operation of other nodes on the bus will not be affected

4 application of CAN bus in pure electric vehicles

the biggest difference between pure electric vehicles and traditional vehicles is that they are driven by electric energy, that is, the combination of battery and motor is used to replace the traditional engine. In this way, the drive control of the motor and the management of the battery become electricity