The data buses designed by the standardized in-vehicle network can carry out data conversion between different micro-control systems or between micro-control systems and sensors, and can share the resources of other micro-control units especially during vehicle control. . Under the control of a ring area network, if one of dozens of microcontrollers fails, the vehicle can still operate normally, and the reliability of the lifting control system plays an important role in the development of the vehicle network.
However, in order to achieve different functions and purposes, in-vehicle electronic systems must be designed for the characteristics of different electronic systems in the vehicle-mounted network. In general, aspects such as the data rate and the need for safety and reliability should be considered. Various on-board networks develop according to the characteristics of different system requirements.
The development of in-vehicle networks, which involves vehicle bodies, standards opening, chip design, system integration, etc., are usually formed through alliances or forums. Participating members are nothing more than leading depots and Tier 1 automotive electronic systems. Semiconductor chip vendors, system developers and other four kinds of roles. An on-board network starts from the alliance. It takes 5 to 10 years to reach the actual application and then into the car. Due to the current development of semiconductor technology, the time has been significantly shortened compared to before, and resources are required for initial development. Therefore, in the initial period of vehicle applications and chip solutions, alliance manufacturers are the main players. Semiconductor manufacturers outside the alliance develop or use chips for the vehicle network. You must pay for the alliance.
Car network functions
The vehicle-mounted network can be divided into copper-based electrical communication and optical fiber-based optical communication depending on the transmission medium. Figure 2 shows the vehicle-mounted network standards and transmission speed characteristics used in current vehicle electronic systems.
The electrical communication part is mainly based on CAN (Controller Area Network) and LIN (Local Interconnect Network), and the transmission speed is from 10Kbps to 1Mbps. With the development of vehicle communication and multimedia entertainment systems, the demand for high bandwidth is increasing. The industry began to look for fiber-optic communication methods to increase the transmission rate, reduce the length and weight of vehicle beam lines, and reduce electromagnetic interference (EMI), including FlexRay, MOST (Media Oriented System Transport), IDB-1394, and Byteflight. Mainly. In the part of transmission speed, optical fiber transmission can reach more than 10Mbps, and even reach 100Mbps. Under the increasing length of the wiring harness in the car and the drive of the vehicle communication entertainment system, it is foreseeable that the era of fiber optic network in the car is approaching.
All kinds of vehicle networks have their main vehicle electronic systems at the beginning of development. Among them, part of the CAN is mainly for the electronic system around the body, such as electric doors, windows, rearview mirrors, seat control, etc., FlexRay is for the engine control, transmission and drive-by-wire (Drive-by-wire) vehicles The core control system is operated, and the recently developed MOST is mainly responsible for the data transmission protocol of the in-vehicle audio/video multimedia entertainment system and the wireless communication connection of the in-vehicle equipment. Different communication protocols will also share data through the gateway, and the various vehicle information will be centralized to the information center for processing and interpretation.
Automotive semi-conductor suppliers play a role as supplier of chip solutions in the development of in-vehicle networks, and play an increasingly important role in the automotive electronics field. Many semiconductor manufacturers have been invited to participate in the initial stage of the agreement. Including Freescale, Infineon, Philips, Renesas, etc., they have successively released chip solutions supporting various communication standards.
Looking at the development of vehicle communication protocols
The development of in-vehicle networks is derived from the needs of automotive electronic systems. Therefore, different in-vehicle networks have their own development backgrounds. The following is a brief introduction of the current developments of major global in-vehicle network protocols.
CAN application has matured
At present, Controller Area Network (CAN) is the most widely used vehicle bus standard. Germany's Robert BOSCH developed CAN in 1983 and optimized the design of the serial system for vehicles. The design aims to reduce the number of connection lines and increase the transmission function. At the same time, it focuses on practicality, adopts multi-task serial design and has fault tolerance. At present, major car manufacturers worldwide have adopted CAN as a vehicle bus standard.
Byteflight Standard Open Delay
In view of the importance of vehicle safety enhancement, BMW and Motorola, Infineon, Siemens and other manufacturers jointly developed a high-speed network using plastic optical fiber (POF) as a transmission medium in 1996. Communication protocol Byteflight, data transmission rate of 10Mbps. The agreement deals with the compatibility of different bandwidths and the increase of electronic systems in a more flexible manner and is fault-tolerant. Since the development of Byteflight was dominated by BMW, the opening of protocol standards was not very positive. Therefore, Byteflight has not seen any examples of vehicles used outside of BMW.
LIN meets low-cost bus system requirements
In order to meet the needs of low-cost bus systems, several major European car manufacturers, including Audi, BMW, Daimler Chrysler, Volvo, and VW, have jointly developed a LIN vehicle-mounted communication bus, which will provide a low-cost serial communication concept and development environment. Standardization enables depots and their associated factories to design, implement, and handle complex multi-tasking systems with relatively low-cost methods. The communication cost of each node of LIN bus is lower than CAN by 2-3 times, even can share the data through the gateway and connect with existing CAN. LIN is mainly used in vehicle electronic peripheral system controls such as doors, steering wheels, seats, air conditioners, lights, rain sensors, or alternators (Figure 4).
FlexRay system combines flexibility
BMW, Daimler Chrysler, Philips and Freescale jointly developed the FlexRay communication protocol for vehicle control security. This protocol is based on Time-Triggered design and uses FTDMA deterministic access method with Flexible Time Division Multiple Access. Fault tolerance function and fixed communication transmission time, support Event-Triggered and time-triggered communication, ensure the success rate and stability of signal transmission in a fixed time, and have high-speed communication capabilities.
FlexRay can be compatible with different network topologies in the system flexibility section, and can customize the data transmission rate and various priority or identification information, and can diagnose and react appropriately when an error occurs on the line. The communication layer of FlexRay is shown in Figure 5, in which the Protocol Execution Layer plays a central role. On the one hand, the control interface (CHI) communicates with the stored data and controls it appropriately. On the other hand, it uses a voice codec (Codec) and an external physical bus. Make a connection.
MOST meets multimedia high-frequency transmission requirements for vehicles
With the application of automotive multimedia systems, the German carmaker BMW and Daimler Chrysler, the semiconductor company Oasis Silicon Systems and automotive electronics manufacturer Harman/Becker established the MOST alliance to provide high-speed bandwidth bus processing including audio, video, and data. Figure 6 illustrates MOST's main in-vehicle multimedia system, including mobile phones, radios, DVD and CD players, flat panel displays, GPS navigation systems, laptops, cameras, security systems, etc., covering almost all car multimedia applications.
MOST uses optical fiber networks. Its main feature is that it allows Synchronous Data and Asynchronous Data. Since MOST uses a ring architecture, if a problem occurs, the ring connection will be broken, causing the bus to stop operating. Therefore, the bus can only be applied to non-powered systems or security systems, such as audio-visual entertainment systems. At present, MOST has been applied to BMW premium models.
IDB-1394 Serial Consumption and Automotive Electronics
IDB-1394 is a high-speed, multimedia network based on IEEE 1394. In 2002, the 1394 Alliance's Automotive Working Group (AWG) established the IEEE 1394 protocol for automotive electronics. Its goal is to modify the FireWire (IEEE 1394) standard to suit the automotive industry environment. Especially for the power management of automotive electronic systems, automotive application protocol stacks, and physical layers, IDB-1394 enables data to be transmitted over copper wires while supporting optical transmission and electrical signal transmission at transmission speeds up to 400 Mbps. IDB-1394 application connection shown in Figure 8, can be seen from the figure IDB-1394 role is mainly to connect and handle the car multimedia related equipment, external IEEE1394 devices (iPod, Game, 802.11, etc.), and the car Serial control network (CAN, LIN, FlexRay, MOST, etc.)
To ensure compatibility with 1394-related consumer electronics products already used in other markets, IDB-1394 fully defines the ISO/OSI 7-layer interface. The embedded network includes DVD players, video displays, navigation systems, broadcast, and telematics systems ( Telematics) devices, mobile phones and other multimedia applications. Renault, a French car manufacturer, has announced the use of IDB-1394 in the 2006 model, but because IEEE-1394 is widely used in consumer electronics in Japan, Japanese car makers may use IDB-1394 earlier in the car. The license fee for IDB-1394 is US$0.25 per vehicle. However, in the face of more and more European depots supporting the MOST standard, the subsequent development of IDB-1394 remains to be seen.
Vehicle Communication Protocol Standard Organization Fosters Network Technology
There are many organizations around the world that work on the development and opening of in-vehicle network protocol standards. Some of them are based on the demand side of vehicle manufacturers, and some of them are supplied by the first-class automotive electronics manufacturers. However, both organizations must exchange information and conduct forums. Look for applicable standard protocols. Table 2 summarizes the organization that promotes the development of major vehicle network standards and standards.
Car network role will become increasingly important
In the computer's development history, due to the standardization of data transmission and communication protocols, leading the wave of the computer revolution, but also let the entire information industry develop into a brand-new situation.
Between the vehicle electronic systems, a large number of harnesses are used for data transmission. At present, it is estimated that the harnesses in a general vehicle body can reach more than 3,800 meters and the weight can reach 70-80 kilograms. Therefore, how to achieve faster transmission speed and lighter quality by updating materials is a key direction for the development of vehicle networks.
The development of the on-board network at this stage has a complete impact on the automotive electronics and even the entire vehicle industry. In addition to breaking the ecological environment of the original depots, it also increases dialogue through organizations and forums, and further promotes a standardized platform. The development of vehicle platforms is more open and it also accelerates the development and competition of products.
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