Abstract: With the widespread application of electronic technology in automobiles, the wiring harness in automobiles has become enormous and complex. Statistics show that a high-end sedan can have wiring lengths of up to 2 km and 1500 electrical contacts. Therefore, automotive network technology has emerged as a direction for automotive technology development. Keywords: CAN bus, communication technology, vehicle control, wiring harness, network technology. In modern automobiles, the electronic control system and wiring harness are closely related. If we use the human body as an analogy for the functions of microcomputers, sensors, and actuators, we can say that the microcomputer is equivalent to the brain, the sensors are equivalent to sensory organs, and the actuators are equivalent to motor organs. Clearly, without nerves and blood vessels, the hands and feet of a human body cannot function properly. The wiring harness, which connects the electrical and electronic components of an automobile and enables them to function, acts as the "nerves and blood vessels" of the car. The wiring harness is composed of wires that form circuits. It must ensure the transmission of electrical signals, guarantee the reliability of the connected circuits, supply the specified current value to the electronic and electrical components, prevent electromagnetic interference to surrounding circuits, and eliminate electrical short circuits. Automotive wiring harnesses can be functionally categorized into two types: signal lines that transmit sensor input commands and power lines that carry electricity to drive actuators. Signal lines are thin wires that do not carry electricity (e.g., fiber optic communication), while power lines are thick wires that carry high currents. For example, the cross-sectional area of ​​conductors used in signal circuits is 0.3 or 0.5 mm²; those used in motors and actuators are 0.85 or 1.25 mm²; and those used in power circuits are 2, 3, or 5 mm². Special circuits (starter, alternator, engine ground wire, etc.) have different specifications of 8, 10, 15, and 20 mm². The larger the conductor cross-sectional area, the greater the current capacity. The selection of wires is constrained not only by electrical performance but also by the physical properties required in the vehicle, thus the selection range is wide. For example, the wiring in taxis, which involves frequent opening and closing of doors and crossing between vehicle bodies, should be made of wires with good flexibility. Wires used in high-temperature areas are generally made of polyvinyl chloride or polyethylene-coated wires with good insulation and heat resistance. In recent years, the use of electromagnetic shielding wires in weak signal circuits has been increasing. Furthermore, connectors—key components connecting wiring harnesses to electronic and electrical parts and circuits—have also been continuously improved. For example, automotive connectors manufactured using resistance welding and new wiring harness materials have been successfully applied to roof modules. With the increasing demands for safety, comfort, and environmental protection in modern automobiles, the number of circuits and power consumption in vehicles have increased significantly. Therefore, how to more effectively and rationally arrange a large number of wiring harnesses within the limited space of a vehicle has become a problem facing the automotive manufacturing industry. This article focuses on automotive wiring harnesses and provides a brief overview of the current status and future development trends of in-vehicle communication technology. Overview of Automotive Wiring Harness Development To adapt to the high functionality of vehicles and the diversification of user needs, automotive wiring harnesses are gradually occupying more space in vehicles. In fact, to improve fuel economy and reduce weight, the diameter of the wires themselves has been continuously reduced from the original AV wires, through AVS wires, to AVSS wires. The diameter of the wiring harness is constantly decreasing. Moreover, the application of multiplexing technology (in-vehicle local area network (LAN)) in recent years has greatly reduced the number of circuits. Figure 1 illustrates the variation in the number of circuits and the maximum diameter of the wiring harness in passenger cars with engine displacements of 1800–2000 mL. However, the trend in wiring harness development shows that the number of circuits in vehicles continues to increase, with some high-end cars exceeding 2000 circuits. One effective method to reduce wiring harness weight is to use a 42V power supply. This is considered an effective method for applications requiring high electrical loads, such as electric power steering (EPS) or electric air conditioning, as it allows for increased power supply without increasing current (without increasing wire cross-sectional area). On the other hand, as the power supply voltage increases, safety issues such as electromagnetic noise or leakage occur, necessitating the use of shielded wires or waterproof connectors, thus increasing the weight of the wiring harness. Therefore, with the widespread application of in-vehicle local area networks, there is a demand for wire materials with high shielding properties against electromagnetic interference. Since the 1990s, European, American, and Japanese automakers have been increasingly promoting modular production methods, using planar wiring materials such as flexible printed circuits (FPCs) or flexible flat cables (FFCs) as the wiring medium within modules. In modules, especially in areas with limited wiring space such as the roof, doors, and consoles, this approach is expected to be further adopted to balance maximizing cabin space and improving the efficiency of wiring harness layout. With the application of flexible printed circuits in modules, and the integration of electronic components and sensor components, wiring materials are evolving towards higher functionality. Examples include the application of FPCs in dashboards and the use of membranes to support sensors or in antennas. Regarding multi-channel communication, the increasing volume of communication and its expanded applications in safety features and multimedia information acquisition are driving the development towards higher-speed, higher-reliability communication protocols. It is anticipated that network technology will be further applied not only within vehicles but also between roads and between vehicles. As a communication medium within automobiles, wires are evolving towards higher speeds, resistance to electromagnetic interference, and "opticalization" (i.e., the adoption of optical waveguide technology). The increasing voltage (42V) of automotive wiring harnesses reduces current consumption and wire diameter due to the higher power supply voltage, thus enabling lightweight wiring harnesses and improving assembly convenience in vehicles. However, increasing the power supply voltage from the current 14V to 42V, approximately doubling it, presents many challenges that must be addressed: leakage, short circuits, electrolytic corrosion, electromagnetic noise, and arc discharge. Among these, arc discharge is the most significant and difficult to resolve. Arc discharge refers to the discharge phenomenon that occurs when contacts or terminals separate during energization. In 42V applications, this is known as a stable arc. Compared to a 14V power supply, this arc lasts longer and has significantly higher discharge energy. The center temperature of the arc can reach several thousand degrees Celsius, posing a serious danger. Arc discharge, especially when connectors are pulled out, requires immediate protective measures due to direct contact with the user. The following describes measures to protect connectors from arc discharge. These include: using optimized terminal materials; effectively dispersing the arc discharge energy of the two terminal contacts; improving the connector housing to increase the connector pull-out speed; and using magnets to eliminate arc discharge. Among these, using magnets is considered the most effective way to limit arc discharge in situations with medium to high current flow. This refers to the effect of a magnetic field causing the arc to twist; increasing the gap between contacts also has the same effect. For example, Fujikura has developed this technology, successfully reducing arc discharge energy steadily by adding a magnetic field and optimizing the magnetic flux density. In addition to wiring harness components, the company has also developed fuses and 42V power supply boxes (R/B, J/B) with relays, or 42V three-phase synchronous motor wiring harness assemblies. Using R/B and J/B 42V power supply boxes, especially in areas prone to water contact such as engine compartments, where leakage and electrolytic corrosion are particularly significant, necessitates proper specification of the distance between circuits. When using wiring harness assemblies, limiting electromagnetic noise is a critical issue, necessitating the development of dedicated shielded wiring harnesses and effectively waterproof connectors. While efforts have indeed been made to address these issues with 42V voltage, the use of shielding and waterproofing structures increases weight. Therefore, targeted measures must be taken when adopting 42V power supplies, eliminating unnecessary components and carefully analyzing and categorizing the protection measures implemented. This is an important approach for the future. However, to date, 42V is only used in high-end cars, and development for its application in mainstream cars is still in its early stages. Therefore, a cost-balanced analysis of the entire vehicle must be conducted when applying 42V electrical systems; this can be considered a common challenge for 42V technology. Currently, the international research and development body for 42V is the advisory group of MIT. Fujikura of Japan joined the organization in 1999 and has been involved in its activities. Currently, Japan, Europe, and the United States are collaborating to develop 42V standards. It is expected that the adoption of the 42V standard will reduce component costs, accelerating the widespread adoption of 42V power supplies. The implementation of 42V electrical systems will begin with a dual-voltage (14V, 42V) structure, gradually transitioning to a single 42V electrical system. The time required for this transition depends on the development of automotive electronics technology and consumer affordability. The Current Status and Development Trends of In-Vehicle Local Area Network (LAN) Communication Protocols With the widespread application of electronic technology in automobiles, vehicle wiring has become extensive and complex. Statistics show that a high-end sedan using traditional wiring methods can have wiring lengths of up to 2km and 1500 electrical contacts. Therefore, automotive networking technology has emerged as a direction for automotive technology development. For a long time, multiplexing technology has been seen as a solution to the ever-increasing number of automotive wiring harnesses. Major automobile manufacturers worldwide have developed their own standards. However, due to its high cost, multiplexing technology is only used in high-end vehicles. In recent years, the number of automotive electronic systems has been increasing, data transmission speeds have become insufficient, and even small, economical cars are demanding higher functionality. Furthermore, the increasing number of wiring harnesses has led to their bulkiness. Therefore, against this backdrop, since 2000, the standard communication protocol for Controller Area Networks (CAN) has been used in foreign passenger cars. Currently, the most widely used communication protocol is high-speed CAN, with its most important application being communication between the powertrain and body systems. CAN is characterized by event triggering and CSMA/CA (if the bus is idle, all electronic control units can send signals; when signals conflict, higher priority signals are sent first, followed by others). As the amount of information on the network increases, it becomes difficult to guarantee response time and predictability. Modern high-end cars have more than 70 electronic control units. Due to the continuously increasing amount of information on the network, the network is segmented, with separate networks for each body system or powertrain. Only necessary data is transferred through inter-network gateways (using two communication protocols within the vehicle). The following is a brief overview of the vehicle body system, powertrain system, multimedia system, and in-vehicle local area network used for safety systems (see attached table). 1. Vehicle Body System (1) Low-speed Controller Area Network (CAN, ~125kbps) This is a low-speed version of CAN. Its structure is basically the same as that of high-speed CAN, but in a two-wire bus, communication continues even if a fault occurs on one side (short circuit, open wire). The wire medium is copper wire, using single wire or twisted pair wire. (2) LIN (Local Interconnect Network, ~20kbps) LIN is Local Internet, which is a communication protocol dedicated to low-speed communication of the vehicle body system. It has low cost (I/F is a general-purpose UART), master/slave mode (using a single master controller/multiple slave devices). Rev.2.0 specification has been published (September 2003), and the wire uses copper wire (single wire). 2. Powertrain System (1) High-speed Controller Area Network (~1Mbps) This is currently the most widely used in-vehicle local area network communication protocol. Its features are event trigger, CSMA/CA mode. It is expected that in North America, starting in 2007, high-speed CAN (500kbps) will be standardized and become a regulation as a diagnostic communication protocol. The wire is copper wire, and twisted pair is generally used. (2) FlexRay (~10Mbps) FlexRay is a high-speed fault-tolerant network protocol and a new generation of in-vehicle local area network communication protocol. It is under development, centered in Europe. The Ver.2.0 specification has been released (September 2004). Its features are high speed, TDMA mode (using synchronous mode, managed by communication program), high reliability (equipped with dual wire harness driver, with signal transmission timing monitoring function), and can be considered for application in automotive safety systems. Cars equipped with FlexRay are expected to be launched in 2008. Copper wire is used in Ver.2.0. (3) Multimedia system ① MOST (Media Oriented Systems Transport, ~24.5Mbps) It is centered in European cars and has been put into practical use. The communication wire uses plastic optical fiber (POF: plastic fiber). ②IDB-1394 (~400Mbps) This is the automotive version of IEEE 1394, which is widely used in peripheral devices of personal microcomputers and home appliances. The wires are copper wires and plastic optical fibers (POF), but it has not yet been used in vehicles. However, a prototype vehicle was exhibited in Aichi and Nagoya, Japan at the World Intelligent Transportation Systems (ITS) Conference in 2004. 4. Safety System (1) Safe-by-wire (~160kbps) Safe-by-wire is the electronic drive-by control of the vehicle safety system. It is a special communication protocol used in safety systems such as airbags. The Safe-by-wire Consortium merged with BST to form the Safe-by-wire plus Consortium and announced ASR2.0 (September 2004). Its features are power overlap, TDMA, high reliability (network duplication), and copper wires. Currently, we are analyzing the special communication protocols applicable to various systems of the vehicle body. In the future, due to cost, information volume and required reliability, we must consider using the communication protocol most suitable for each system. For communication wiring harnesses, the rapid advancement of communication speeds necessitates consideration of electromagnetic compatibility (EMC) issues and the implementation of necessary shielding measures. Future development may involve replacing the current twisted-pair cables with shielded cables or even further replacing them with point-of-care (POF) optical fibers. Using POF can solve EMC problems and achieve weight reduction. The application of glass-based optical fibers will further enable higher-speed communication, but issues such as cost, assembly, and environmental friendliness must be addressed. Furthermore, the expanded application of in-vehicle local area networks (LANs) increases the workload of electronic control unit (ECU) software development. Because this is specialized software, it is difficult to reuse it in other vehicle types. Therefore, to address this issue, there is a trend towards the generalization of basic software applications, such as AUTOSAR and JASPAR general-purpose basic software. By applying general-purpose basic software, there is no need to consciously differentiate between hardware, thus improving development efficiency (only for application-oriented development) and enabling the reuse of application software. This can shorten development time, improve quality, and ensure the international competitiveness of automotive OEMs and automotive parts manufacturers. From the perspective of communication infrastructure, the characteristics and challenges of in-vehicle local area networks (LANs) Internet connection services via CATV or ADSL have become the driving force behind the rapid popularization of broadband internet networks. Furthermore, FTTH connections saw an increase of over 80,000 to 90,000 users per month in 2004. Statistics show that approximately 2.74 million households in Japan used CATV, while approximately 12.33 million households used ADSL, exceeding 1.5 million users. This represents a significant increase in a very short period (according to statistics from the Japanese Ministry of Internal Affairs and Communications in July 2004). In addition, due to the increase in network-compatible devices in homes, wireless LANs are becoming increasingly popular not only in offices but also in homes. Moreover, internet access via mobile phones (portable phones), exemplified by i-mode, has become increasingly common. Statistics show that by August 2004, the number of users (joiners) in Japan had exceeded 70 million, making it the largest means of internet application in Japan. Therefore, in today's world where the Internet serves as a primary communication infrastructure for personal information exchange, the use of the Internet, whether while traveling or in any other way, has become a natural demand from users. Even as vehicles change, this trend remains prevalent. In this context, the role of the vehicle is not merely to provide an environment for using a PC inside the car, but rather for the vehicle itself to connect to the Internet and transmit and receive information. For example, many information devices already integrated into vehicles, such as navigation systems, have added Internet functionality to better meet practical needs and enhance the convenience of automobiles. The following is a brief overview of the problems encountered when expanding or adding network functionality to existing in-vehicle information facilities. 1. The challenges of existing in-vehicle local area networks: With the increasing functionality of automobiles, electronic control units (ECUs) have been added. To effectively integrate these units into vehicles and reduce or limit the weight of wiring harnesses, the application of the Internet has been considered. However, the amount of information transmitted has increased simultaneously, and the controller area network, currently the mainstream communication protocol, has reached capacity saturation. Therefore, depending on the application, two (or more) communication protocols are used as a solution. Furthermore, the adoption of new standards such as FlexRay is also being considered. Meanwhile, direct IP communication within existing in-vehicle local area networks is difficult due to limitations imposed by various communication protocols and applications. For example, in CAN, only 8 bytes (bits) of data can be transmitted in one frame. Even the IPv4 header (20 bytes) requires 3 frames to transmit the signal, and if the upper layers of UDP or TCP are also included, the necessary number of frames increases further. These frames cause bus congestion, leading to delays or missing vehicle control data, which must be avoided. On the other hand, MOST, as a communication protocol for multimedia systems, is already partially implemented, and the IEEE 1394 standard is being re-analyzed. Utilizing MOST will also bring IP applications to standard specifications. IEEE 1394 has good compatibility with pocket radios or PCs, as well as information systems sold as standalone devices. If it can meet the diverse environmental conditions of vehicles, various information systems can be installed in vehicles. Because of this situation, the in-vehicle local area network (LAN), along with the communication LAN of control and safety systems such as the Controller Area Network (CAN), is expected to adopt communication protocols suitable for high-capacity transmission, capable of handling IP-based entertainment programs or vehicle navigation information. Furthermore, to adopt a 42V electrical system, the accelerated application of fiber optics with high electromagnetic noise immunity must be considered. Ethernet may also be used between specific information devices, and in the future, Bluetooth may be used to connect to the vehicle's self-diagnostic system, enabling multimedia functionality within the vehicle itself. These possibilities may all emerge. 2. External to the Vehicle: Internet Connection With the widespread adoption of the Internet, wireless LANs such as IEEE 802.11 are increasingly being used not only in companies but also in ordinary homes. Therefore, when connecting to vehicles, currently, special attention should not be paid to specific communication protocols; rather, it is reasonable to use IEEE 802.11b,g, or IEEE E802.1a. In addition, to ensure security and reliability, the application of IPv6 may also be considered. 3. Connectivity on the Move and Vehicle-to-Vehicle Connectivity: Internet connectivity for mobile devices is a unique challenge for automobiles. While mobile phone services have become increasingly practical, issues such as communication speed and cost remain. On the other hand, DSRC services used in Electronic Toll Collection (ETC) systems, which do not necessarily require IP communication, are still under discussion and attract attention. Furthermore, the Car-to-Car Communication Consortium, established in 2004 with the aim of realizing practical wireless vehicle-to-vehicle communication, is also noteworthy.