Abstract CAN bus technology is suitable for the interconnection of industrial process monitoring equipment due to its unique design, high reliability and characteristics. Many well-known brand cars have also adopted CAN bus technology. The paper analyzes the development of CAN bus and the characteristics of automotive CAN bus technology, and discusses the application of CAN bus in the automotive field.
Keywords CAN bus; automotive electronics; intelligent system
The CAN bus is one of the most widely used fieldbuses in the world and can realize the control of the vehicle itself. For the automotive industry, its real-time, flexibility, reliability and low cost have a large market space. For example, the engine management system, the transmission controller, the instrumentation equipment, and the electronic trunk system are all embedded in the CAN bus control device.
1 Development of CAN bus In the current automotive industry, various electronic control systems have been developed for safety, comfort, convenience, low pollution, and low cost. The types of data used for communication between these systems and the reliability requirements are different, and the situation caused by multiple buses is complicated and the number of wire harnesses is increased. Originally thought to be suitable for "reducing the number of wire harnesses" and "high-speed communication of large amounts of data through multiple LANs", in 1986 German electrician Bosch developed a CAN communication protocol for automobiles. Since then, CAN has been standardized by IS011898 and IS0 11519. It is a standard protocol for automotive networks in Europe. The high performance and reliability of CAN have been recognized and widely used in industrial automation, marine, medical equipment, industrial equipment, etc. aspect.
2 Characteristics of automotive CAN bus technology (1) Design goals.
For automotive CAN bus transmission, the following aspects must be guaranteed: the logical "0" of the signal should be clearly distinguished from the logical "1" of the signal; the ability to use the information content to solve the bus access congestion; with optimized transmission Rate; node automatic fault diagnosis and the ability of the node to successfully access the bus quickly; the car CAN bus can have certain scalability as the data transmission rate increases.
(2) Encoding of digital signals.
Correctly encoding digital signals plays an important role in ensuring reliable transmission of information. There are two basic methods for car LAN data signals: non-return-to-zero (NRZ) and pulse width modulation (PWM). The non-return-to-zero system is used for information transmission. Generally, it is used in the case of high transmission rate, and the upper limit is 1 Mb·s-1. When pulse width modulation is used as the coding scheme, it is generally used in the case of low transmission rate. The upper limit is 3 x 105 kb·s-1.
(3) Network topology.
The automotive CAN bus has the following advantages: the bus structure is simple, the reliability is high, the cable is short, the passive components, the wiring are easy, and the expansion is easy. If you need to increase the CAN bus length, you can use the repeater to add an additional segment. To add a new node, simply plug it in at some point on the car's CAN bus. CAN can use a variety of physical media, such as twisted pair, fiber, and the like. The most common is the twisted pair. The signal is transmitted using differential voltage. The two signal lines are called “CAN_H†and “CAN_Lâ€. When static, they are both about 2.5 V. At this time, the state is represented as logic “1â€, which can also be called “recessiveâ€. The CAN_H is higher than CAN_L to indicate a logic “0â€, which is called “dominantâ€. In this case, the voltage values ​​are usually CAN_H=3.5 V and CAN_L=1.5 V.
3 CAN bus application in the automotive field (1) Application of CAN bus technology.
Most well-known foreign cars have adopted CAN bus technology, such as Volvo, Lincoln, Audi, BMW, etc., and domestic car brands, such as Chery, have already applied bus technology to several models. CAN bus technology is to send various driving data of the car to the "bus" through sensors all over the body. On this information sharing platform, all the receiving ends that need these data can read the required information from the "bus". Therefore, the various systems of the car can coordinate operation, share information, ensure safe driving, comfortable and reliable. In general, the more high-end cars are equipped with more CAN_BUS, the higher the price, such as Touran, Passat and other models are equipped with multiple CAN bus.
(2) Hardware design of automotive CAN bus node ECU.
The core technology of automotive CAN bus research and development is to design the ECU with CAN interface. The CAN bus module of ECU is composed of CAN controller and CAN transceiver. The CAN controller performs a complete CAN protocol and completes communication functions, including information buffering and receive filtering. The CAN transceiver is required as an interface between the CAN controller and the physical bus, which implements the conversion of the logic level signal between the CAN controller and the bus.
(3) The application of CAN bus in domestic independent brand cars.
Due to cost control, technical strength and other factors, CAN_BUS bus technology generally appears in foreign high-end cars. In the A-class and below models, most of this technology appears in joint venture brands, such as POLO, New Bora and so on. Among the self-owned brands, there are few models using CAN bus technology, and Fengyun 2 is the representative model. Fengyun 2 CAN bus technology can realize the communication of engine, gearbox, ABS, body, instrument and other controllers, so that the whole vehicle information can be shared in time. In Fengyun 2's combination instrument panel, more than 20 pieces of information such as stage mileage, accurate door display, and seat belt reminder are all displayed, which is doubled compared with the same level products, which increases the safety during driving.
In addition, with the help of CAN bus technology, after the internal sensors realize information sharing, the number of interfaces of the wiring harness and the controller in the vehicle body is greatly reduced, and the mutual interference and wear of the excessive wiring harness are avoided, and the automobile electrical power is reduced. The failure rate of the system. Open the bonnet and see a clear and concise interior layout. In terms of maintenance, the application of CAN bus technology also makes the most convenient guarantee for troubleshooting. The CAN bus intelligent butler system complies with European and American OBDII standards and regulations, and realizes the function of online diagnosis. After the vehicle fails, each controller stores the fault code through the CAN bus intelligent housekeeping system. The professional diagnoses the fault status for the vehicle through the diagnostic instrument, quickly and accurately finds the fault point, and eliminates the fault in the first time. The use of CAN bus technology to achieve system integration of information transmission, greatly improve the response speed of various components, reduce the incidence of accessory wear, and correspondingly reduce maintenance costs; Moreover, the application of advanced integration technology has also greatly improved the vehicle itself The scientific and technological content enhances the competitiveness of products.
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