In reality, the “status” of automobiles in people’s lives is rising, and the reason for this is that automobiles are intelligent and networked. A variety of comfort, safety and technology function modules are applied to the car. The traditional point-to-point electronic control unit control method is no longer applicable to the development of modern cars. The invention of in-vehicle network system is not only a good solution to the control of each electronic control unit, but also more conducive to the development of automobile modernization. This paper discusses the development status, function, application and development trend of in-vehicle network system.
As the automotive electronic control system enters the era of intelligence and networking, the application of automotive electronic equipment in vehicles is gradually increasing, such as: electric seat adjustment, anti-lock braking system (ABS), body stability system (ESP), traction control system (TCS), active suspension, infotainment multimedia and so on. Most traditional electronic devices use a single point-to-point communication method, and there is basically no information sharing and transfer between different functional ECUs. The increasing number of automotive electronic devices can lead to a thick automotive wiring harness. According to statistics, using the traditional point-to-point wiring method, the wire length of a luxury vehicle can reach more than 2,000 meters and the number of nodes can reach 1,500. In this way, not only does the huge wiring harness occupy the limited space in the cockpit, but it also poses greater difficulties for maintenance. With the increase of electrical equipment, the traditional wiring method gradually no longer brings reliability, stability and safety to the car. In order to develop light weight and miniaturization of vehicles, automotive network system was born. The in-vehicle network system can simplify the wiring harness and improve the sharing of data and signals among electronic control units, avoiding unnecessary waste and space saving.
2.The development status of in-vehicle network system
In-vehicle network systems have been in use since the 1980s. In 1983, Toyota Motor Corporation was the first to apply the door control system of bus system. The system adopts a centralized control method, and the body ECU centrally controls the opening and locking of the four doors and tailgate door locks.
In 1986, the body system began to gradually adopt copper wire as the connection wire of the network system because copper wire has the advantages of low resistivity, high load capacity and good stability. In 1987, the centralized network control system of Nissan and General Motors had started mass production. During this period, Bocsh proposed the protocol of in-vehicle local area network which is, CAN bus (Control Area Network). Then the American Society of Automotive Engineers proposed another network communication protocol: SAE-J1850. Japan Toyota, Nissan, Mitsubishi, Honda and Mazda companies have been designed in their own way to mass production of body network control systems. European automobile manufacturers, on the other hand, use CAN bus to control in each controller. At present, CAN bus system is the most widely used network system.
3.Introduction of the functions of the in-car network system and its advantages
3.1 The functions of the in-vehicle network system are as follows
· Realization of multiplex transmission
Multiplexing means transmitting multiple signal sources or information on the same runway at the same time. In the communication system, the transmission of signals is very fast and the transmission capacity of the channel is very strong. If a channel transmits only one signal, this will be a great waste of resources. Multiplexing can integrate multiple signals in a logical order of the system and transmit them in one channel, and then separate the integrated signals when they reach the control unit that receives them, thus realizing the ability to transmit multiple signals in one channel. The three common ways of multiplexing are time division multiplexing, frequency division multiplexing and code division multiple access.
· System Failure Protection
To ensure that the system can serve the vehicle more reliably, the system should have the ability to handle itself when part of the in-vehicle network system function is lost. The self-processing function includes software self-processing and hardware self-processing. Software fail-safe function means that when a control device in the system fails, the fail-safe is triggered and the corresponding electronic control unit will not receive the signal from the failed device to achieve self-protection; hardware fail-safe means that when the ECU in the system sends a failure, the hardware fail-safe opens and makes it output with a fixed signal set in the system, so as to better guarantee the system to continue working.
·System “hibernation” and “wake-up” hibernation
This function is designed to reduce the extra drain on the battery of the whole system when the ignition is switched off. When the system hibernates, the channel will stop transmitting signals to save power; when the system is operated, the system is instantly woken up and ready to transmit signals.
When the ignition switch is turned on, the system is energized to first complete the self-monitoring of the whole system. If there is no fault, each function of the car can operate normally; if there is a fault in a function, the instrument panel outputs a fault light. This function can self-diagnose both the transmission line and the relevant electronic control components.
3.2 Advantages of in-vehicle network system
The transmission method of the car network signal is to connect various function modules or ECUs through the data bus in order to realize the transmission of the car network signal. Among them, the function modules that control the signals and send data encode and translate the signals and data and send them to the bus. The function modules receiving data are decoded and translated to obtain the corresponding commands and data. The transmission advantages of the system are as follows.
(1) The in-vehicle network system can replace multiple wires by two wires, solving the problem of thick and long wiring harnesses and space-occupying parts;
(2) The in-vehicle network system connects the control units of different functions, which makes the signal transmission more convenient and reliable;
(3) The speed of the signal of shared resources within the LAN is faster than the traditional point-to-point transmission method, thus improving the corresponding speed of the vehicle and providing more efficient services to the occupants;
(4) The system can directly realize the function change and upgrade of the control system through the system software, with high flexibility of mobility;
(5) The system provides fault detection port, which can be used to detect each function of the system directly by the fault detector to improve the efficiency of maintenance personnel.
4.Application of vehicle network system
In-vehicle network system is mainly applied to four systems, namely, body control system, power transmission system, multimedia infotainment system and vehicle safety system.
4.1 Application in the body control system
The body system components are spread all over the vehicle body, so the bus bundle of body control elements is very long, and the transmission signal is also susceptible to interference. The body system has five main control units that perform five functions. The control units are central door locking, power windows, lighting switches, mirror adjustment and heating and self-diagnostic functions.
4.2 Application in the powertrain system
The power data bus connects three electronic control units: engine control unit, ABS control unit and automatic transmission control unit. the CAN data bus transmits data signals at a rate of 500 kbit/s, and the transmission time of each group of data signals is 0.25 ms. Each electronic control unit sends data signals once in 7-20 ms, and each electronic control unit will send them in order within Each electronic control unit sends data signals once in 7-20 ms, and each electronic control unit sends them in the corresponding time in sequence. The sequence is ABS electronic control unit, engine electronic control unit and automatic transmission electronic control unit.
4.3 Application in multimedia infotainment systems
The signal capacity in infotainment system is large and requires fast signal transmission rate. The in-vehicle network uses optical fiber as the transmission channel to meet the various requirements of the infotainment system.
4.4 Application in the security system
According to the signals of each sensor, the reliable operation of each safety equipment is accurately controlled. The number of nodes used in this system is high, so the system is required to have low cost, high communication reliability and fast communication speed.
5 Trends in in-vehicle network systems
Currently, all major automobile manufacturers have their own designed network control systems for body and power systems. Most of the vehicles on sale now adopt the control system of in-vehicle network. Looking ahead, the application of in-vehicle network system in vehicles will become more and more common. In-vehicle network technology will gradually develop towards intelligence, high speed and unification.
The car can be set according to the driver’s goals, the network system will provide the optimal choice for the driver: comprehensive consideration of weather, traffic flow, traffic congestion, etc. to provide the best path for the driver; according to past driving habits, to provide the most appropriate sitting position, suspension comfort, chassis tuning, etc. Intelligent control of vehicle travel time to improve safety and efficiency.
X-by-Wire (wire control) is another direction of the new automotive reform. Under this system, most of the mechanical operation and intermediate transmission mechanisms are omitted, such as the gearshift lever, steering column and various transmission linkages, etc., and replaced by various sensors. The X-by-Wire system is more intelligent and technological, and can win the favor of the public.
The future automotive network will be a high-bandwidth, responsive and mobile network system. Mobility is only a small part of the reason people use cars. With the high-speed development of car network, people can use the car for real-time office, entertainment, and communication with friends. In addition, the high speed of the car network will allow the system to carry more electronic control components to allow the car to achieve more functions, and at the same time, it will improve the reliability of the whole car system and the response speed of the electronic control unit.
5.3 Network protocol unification
In-vehicle network system is the mainstream development direction of today’s automobiles, and all major automobile manufacturers have developed their own network systems. The network protocol standards applied by their respective network systems are different, which will inevitably increase the production cost of automobiles and also bring difficulties in mismatching maintenance equipment. Auto manufacturers and network system suppliers have gradually reached an agreement that LAN is used in Class A network, in Class B network low-speed controller LAN has become the de facto standard protocol, and in Class C network, for traditional real-time distribution control, high-speed controller LAN will be the de facto standard.
In modern cars, in-vehicle network system has been commonly used. With the development of electronic components, more automotive electronic control units are installed into the network system. The development of in-vehicle network systems will reduce the waste of more wiring harnesses and resources, while improving the comfort, safety and reliability of the car. In the near future, the car will develop into a partner that integrates office, leisure and entertainment.