This article mainly elaborates on the role of wiring harnesses in the field of autonomous driving, mainly discussing the working principle, layout composition, material selection, and crimping technology of automotive autonomous driving wiring harnesses. It is hoped that through the use of technological means, the quality of wiring harnesses can be improved, so as to occupy a place in the future automotive market.
1. Current status of autonomous driving technology
With the deep development of autonomous driving technology, cars with autonomous driving technology of L0~L2 level have been preliminarily implemented in the market. Some manufacturers have already reached the standard of L3 level autonomous driving, but there are still many aspects that need to be improved if L3 level autonomous driving is to be popularized, and the most important one is reliability. Due to being a new technology that has not undergone extensive time testing, it is difficult to guarantee that there are no safety hazards. Imagine, for L3 level autonomous driving technology, if a vehicle encounters an unrecognizable situation and requires the driver to take over the vehicle, but the driver cannot take over in a timely manner, then a traffic accident is likely to occur. Therefore, a reliable auto drive system is crucial, and the connection between software and functions requires wiring harness, which also faces severe challenges for the wiring harness known as the blood of the automobile.
Working principle of wiring harness for autonomous driving
The main components of autonomous driving are composed of the main controller ADU, gateway, front and rear cameras, front and rear radars, etc. Both radar sensors and cameras require advanced sensors and actuators. The radar and camera can collect road information from 1 to 200m and transmit it back to the main controller. The main controller ADU analyzes and calculates the data transmitted back from the radar and camera, and the calculation results interact with various systems of the car through the gateway, achieving comprehensive monitoring of the driver, driving vehicle, and driving road conditions, Enable vehicles to keenly perceive the surrounding environment and independently analyze their operation and potential hazards, making them safer during operation and achieving a dual effect of safety and smoothness. The wiring harness serves as a bridge, which needs to smoothly and quickly transmit the signals recorded by the camera to the host. After the host calculates the results, it quickly transmits them to the gateway through the wiring harness. The gateway receives the results and sends the instructions to the vehicle controller through the wiring harness. After the vehicle controller receives the results, it responds and needs to transmit them to various functional components through the wiring harness, The wiring harness is like a human blood vessel, conveying various power sources and signals.
1) Power supply for autonomous driving. The power supply of the autonomous driving host is usually KL30+KL15. KL30 is mainly used to provide power for various functional components, and KL15 is a wake-up power supply that cannot be turned off when starting the vehicle. Currently, most cars use millimeter wave radar as the front and rear radar. Millimeter wave radar has the characteristics of strong penetration, mature technology, and low cost, but its disadvantage is that the detection distance is short, it cannot perceive pedestrians, and it cannot accurately recognize targets, Therefore, millimeter wave radar usually uses KL15 electricity, which can meet performance requirements and reduce static energy consumption; Lidar is the main dynamic obstacle detection sensor for intelligent driving vehicles, characterized by high detection accuracy, minimal impact from lighting, and can be used to describe surrounding environmental parameters. It also requires a combination of KL30 and KL15 power sources, where KL30 can be continuously powered and KL15 is only used for wake-up purposes. The remaining cameras are generally powered by the host.
2) Ground connection for autonomous driving. The grounding of intelligent driving is an important system and is susceptible to interference from other electrical appliances. It is best to set the grounding point separately and relatively close to the electrical equipment. The grounding position should be set in a corrosion-resistant place. As the grounding point at the rear radar position is susceptible to corrosion from sewage and dust, it should be set on the vehicle body inside the cabin through the main wire harness.
3) The signal line for autonomous driving. The signal transmission of autonomous driving uses CAN network for transmission, usually with terminal resistors on the left and right radars. The terminal resistance of the CAN line is 120 Ω. As the main unit serves as a branch of the CAN line, the branch point cannot exceed 1m, and the distance between the main unit and the radar is far, which cannot meet the design requirements of the wiring harness. Therefore, the method of winding the CAN line is often used to deal with it.
Autonomous driving requires high safety and reliability. In the face of complex driving situations and electrical conditions inside the vehicle, signal transmission requirements are also very high. As the transmission process cannot be disturbed, the performance requirements of the wiring harness are particularly important. The wiring harness needs to shield interference from all parties while ensuring its own reliability, and the level of material and process selection needs to be improved.
Layout of 3 autonomous driving wiring harnesses in the entire vehicle
The automatic driving harness needs to run through the front, rear and left and right sides of the car. At present, due to the imperfect technology, most car enterprises are still in the L2~L3 stage of automatic driving, and still need driver control. The autonomous vehicle on the market have retained DMS and OMS cameras, so the harness layout also involves the inside of the car. The layout of the autonomous driving wiring harness is shown in Figure 1.
picture
Figure 1 Layout of Autonomous Driving Wiring Harnesses
1) Autonomous driving ADUs are generally arranged inside the dashboard. The interior space of the dashboard is narrow, making it difficult to arrange wiring harnesses. Therefore, wiring harnesses will be considered to be arranged in sections, adding a pair of inlines in a wide area to connect the instrument wiring harness and autonomous driving related wiring harness, or separating some functions and integrating autonomous driving related wiring harnesses into the main line.
2) The front camera and front radar are arranged on the front bumper. The connection from the ADU inside the cockpit to the front bumper requires crossing the front panel of the cabin and cockpit. Therefore, it is the best choice to use a pair of inlines to connect the two, and since the outside of the cabin is a wet area, it is best not to place the inlines outside the cabin.
3) The cameras on both sides are usually arranged on the left and right rearview mirrors. To transition from the host to the camera, it is necessary to go through the docking between the door and the vehicle body. The rubber part design of the door line is particularly important, and the bending angle of the rubber part cannot be too large, and it must have elasticity.
4) The rear view camera and rear radar are usually arranged on the back door and rear bumper. The distance from the rear bumper to the front of the car needs to pass through the entire body, which is very long. In terms of layout, fixed points need to be added every other distance, and if necessary, protective plates need to be added for protection. In order to ensure the convenience of assembly, an inline connection is added between the instrument harness and the body harness. The inline near the dashboard is usually integrated together and fixed with protective plates for easy management and maintenance.
4. Selection of autonomous driving wire
Based on the high reliability requirements of autonomous driving, ordinary copper wires cannot achieve high-definition transmission of video signals, which is a fatal flaw for autonomous driving. They cannot accurately recognize road features, distance and other image processing, and cannot accurately detect the surrounding environment of the car and locate the car. Therefore, the FAKRA coaxial line is chosen as the video line. The connection structure of FAKRA coaxial cable is shown in Figure 2, mainly including FAKRA connector, AKRA inline connector, coaxial cable, and PCB board end connector.
picture
Figure 2 FAKRA Coaxial Cable Connection Structure Diagram
1) The section size standards that FAKRA connectors mainly refer to include ISO 20860-1 and USCAR-18, while the testing standards mainly include ISO 20860-2, USCAR-17, and USCAR-2. The size standards define the main dimensions of FAKRA connectors in the axial and radial directions. The standard cross-sectional dimensions of the male connector are shown in Figure 3.
picture
Figure 3 Cross section size standard for male connectors
In the products of different companies, there are situations where the insulation medium materials are not the same. Matching tests should be conducted on connectors with different insulation materials and cross-sectional structures, while meeting the standards, to verify whether the relevant electrical performance indicators are within the specified numerical range.
2) The FAKRA inline connector provides an effective segmentation method, but when using the FAKRA inline, try not to use it too much because there will be insertion loss during inline docking. The more inline, the more loss. Therefore, the FAKRA inline should be used as little as possible, and the selected pair of inline should be from the same manufacturer as much as possible, which can ensure performance and reduce the evaluation and testing of performance after switching manufacturers.
3) The coaxial cable conductor used by FAKRA is copper wire, which is wrapped with a layer of foam filler. The shielding is mainly metal copper mesh or aluminum magnesium alloy woven mesh, and the insulation material is generally PVC. At present, the cable standard used by the country is GBT14864-1993, and the quality of the cable also requires testing and terminal retention.
4) The FAKRA board end connector and line end connector must meet the design requirements of connecting the plug tail and PCB. It is also recommended that the harness end and board end be products from the same manufacturer to avoid performance defects caused by structural differences.
Crimping of 5 autonomous driving wiring harnesses
The main crimping method used for traditional wiring harnesses is U-shaped terminal connection. The traditional cold crimping method is simple and cost-effective, and most non critical parts still use U-shaped terminal cold crimping. Due to the fact that U-shaped terminals rely on high punching pressure to compress copper wires together, mainly relying on friction between copper wires for connection, there will inevitably be certain voids after crimping, resulting in an increase in voltage drop and a decrease in conductivity. However, under the high requirements of autonomous driving, especially when using CAN communication, ultrasonic welding is required.
The principle of ultrasonic welding is to weld wire harness materials and workpieces through high-frequency mechanical vibration. During the welding process, the ultrasonic wire harness welding machine is tightened in three directions simultaneously to the ultrasonic welding end face, and vibrates cyclically on its surface at a frequency of 20kHz. At the same time, pressure is applied to the workpiece to form a strong bond between the workpieces, thereby achieving the welding effect. For ultrasonic wire harness welding, the entire welding process can be precisely controlled without generating excess heat on the metal surface, resulting in strong welding fastness. Due to the fact that ultrasonic welding completely welds copper wires together, the conductivity is much better than cold pressing of U-shaped terminals. Ultrasonic welding, with its excellent welding fastness and stable conductivity, must be able to meet the needs of autonomous driving.
6 Conclusion
With the rapid development of artificial intelligence, visual computing, radar, monitoring devices and global positioning systems, autonomous vehicle use advanced technology, and believe that in the near future, they will be able to create automatic and safe motor vehicles without human active operation. Therefore, automotive wire harness professionals also need to constantly explore advanced technologies, use technological means to improve the quality of wire harnesses, and vigorously put advanced production equipment into use in order to occupy a place in the future.