Application and Fault Analysis of Automobile Special Conductor Assembly

With the rapid development of the automobile industry, cars have entered thousands of households, changing people's way of travel and bringing great convenience to people's lives. With the iterative development of new technologies such as regional chain, intelligent network and Internet of Things, new technologies are applied to automobile products, especially the subversive application of intelligent cockpit, which greatly improves the satisfaction of user experience. At the same time, the number of automobile controller modules is increasing, and the signal delivery between modules is gradually increasing, which puts forward higher requirements for automobile signal transmission frequency and anti-interference. Therefore, it is necessary to have a deep understanding of the basic characteristics and application scenarios of automobile special wire assemblies in the future, especially to apply what you have learned. When the automobile network system fails, theoretical analysis and experimental verification will be carried out to get a solution.

Introduction

The Wiring Harness is not only an integral part of the automobile, but also an important part for connecting the electric appliances and modules of the whole vehicle, the carrier for ensuring the functional operation of the automobile, and the core hardware for ensuring the comfort and reliability of the whole vehicle. With the rapid development of automobile science and technology, the car engine and controller chip are iteratively upgraded, and the traditional LIN and CAN wiring loom can't meet the requirements of automobile signal delivery rate. HSD, FAKRA high-frequency plug-in and special cables are born and developed vigorously. Compared with the traditional wiring harness plug-in, HSD and FAKRA plug-in are more demanding on high-frequency performance, so the terminal crimping and processing technology are particularly important, otherwise, the characteristic impedance of the product will be affected, which may lead to market problems such as signal intermittent loss and abnormal display of instrument display.

1. Application and Characteristics of Special Conductor Assembly

1.1 Application of Special Wire Assembly

With the upgrade of automobile configuration, the proportion of normal use of special conductor assembly becomes larger, and the proportion of cost increases accordingly. The main applications are: mainframe to large screen (separated), 360 module to front, back, left and right cameras, TBOX to mainframe, and face recognition to front, back, left and right cameras. Take the configuration of about 100,000 self-owned brand cars as an example. Generally, the number of special wires is 10~15, which accounts for a large proportion.

The special conductor assembly consists of high-frequency plug-in, cable and wrapping tape. Plug-ins are divided into HSD and FAKRA plug-ins. Among them, the mainstream foreign plug-in manufacturers are Rosenberg and Tyco, and the domestic manufacturers are Xinhan and Dianlian. The interface of plug-ins of different brands are the same, but the design concepts of different manufacturers are different, and the physical structures of terminals and sheaths are slightly different. Example: Different insertion and withdrawal forces of terminals. Therefore, when plug-ins of different brands are used with each other, care should be taken and they must be fully verified in our company, Kable-X. The process control of special wire terminal crimping and cable processing is closely related to product reliability, so the production and processing of special wire requires high automation equipment.

1.2 Characteristics of Special Wire Assembly

Among the auto parts, the special wire assembly is a "small piece" with relatively few secondary materials, and the assembly is relatively simple, mainly consisting of connectors and cables. According to the physical structure and transmission rate, plug-ins are divided into HSD and FAKRA, and cables are mainly divided into RG174, RTK031, RG174LL, Dacar535, Dacar636 and Dacar566. Different cables have different core diameters and different bending times.

Main Performance of HSD:

1. Transmission frequency: 0-2GHz, characteristic impedance of 100ω, maximum carrying current 3a;

2. Commonly used cables: Dacar535, Dacar636(0.14), Dacar566(0.4), etc.

3. Hole position: 4 PIN pins.

Main performance of FAKRA:

According to the physical structure, it can be divided into conventional FAKRA and Mini FAKRA. Compared with conventional Fakra, Mini Fakra has more space advantages, relatively less usage, and single port has no cost advantage for the time being; Processing technology: the mainstream of conventional Fakra includes the second generation machining, the third generation stamping, and the third generation matching the automatic production design with low cost.

1. Conventional Fakra transmission frequency: 0-6GHz, characteristic impedance 50ω; The Mini Fakra transmission frequency is 0-20GHz, and the characteristic impedance is 50ω;

2. Commonly used cables: RG174(0.14), RTK031(0.4), etc.

3. Hole position: conventional one PIN, four pins for four-in-one Mini Fakra;

4. Due to the bandwidth demand, cost and other factors, the conventional Fakra is basically used except the Mini Fakra used in 4-in-1.

1.3 Key Characteristics of High-Frequency Performance

Characteristic impedance refers to the impedance when the cable is infinitely long. The characteristic impedance of a cable is a complex characteristic, which is determined by the values of various physical parameters of the cable, such as inductance, capacitance and resistance, which in turn depend on the shape and concentricity of conductors, the distance between conductors and the material of cable insulation. Impedance determines the transmission effect, and it is also the key to signal integrity. In addition, insertion loss, return loss, near-end crosstalk performance and temperature vibration are also key performances, which are important indicators of reliability.

2. Fault Analysis of Special Conductor Assembly

The technology of special conductor assembly is relatively mature, and the reliability of products is stable. There are few market problems caused by special conductor assembly, and occasionally. Take occasional multimedia black screen and flash screen as examples to discuss. Obviously, there are many abnormal problems in multimedia display, such as abnormal host software bug, large screen single piece damage, etc. Next, it introduces the fault caused by the quality of single cable and the cable troubleshooting method when the host and large screen function are normal.

2.1 Replacement Elimination Method

Occasional failures, which are difficult to reproduce and difficult to troubleshoot, require engineers to have a solid theoretical knowledge and clear their thinking to troubleshoot.

On-site inspection of multimedia display system: host, large screen, wiring harness, check whether the surface of a single piece is damaged by "looking", find out the working condition and scene of the fault by "asking", analyze the potential failure reasons by "thinking" theory combined with the fault parts, sort out the troubleshooting ideas, lock in the root cause, and quickly solve the fault.

Replace the new host and large screen in turn, and continue to operate to see if the function is normal. If necessary, carry out periodic bumpy road test certificate to eliminate the quality problems of single host and large screen caused by chip and software bugs, and further focus on the problems of special wires.

2.2 High-Frequency Characteristic Impedance Test of Faulty Parts

The physical characteristics and high-frequency performance of the special conductor assembly, especially the impedance and resistance, will directly affect the stability and reliability of the display system. First, remove the audio and video switching harness of the harness, and visually identify whether the surface of the harness is damaged, whether the wire core is exposed, whether the terminal hole position is abnormal, and whether it is obviously enlarged. If the abnormality cannot be fully judged, the performance of the faulty harness can be tested by auxiliary equipment for further judgment.

Characteristic impedance testing equipment: impedance tester. Test method: LVDS harness length is 860mm, and two board connectors are used to test high-frequency parameters, and two special PCBs for HSD high-frequency test are welded. Test requirement: 100 10 mω is required. If the test result exceeds the requirement by 100 10 mω, it is a fault of the special conductor assembly.

2.3 Physical Characteristics Test of Faulty Parts

Testing equipment: terminal planer. Test method: The terminal of the fault part is analyzed in profile. Test requirements: All crimping is qualified (there is no cavity in the crimping section of the terminal fault part, and the compression rate of the wire in the terminal meets the crimping requirements). If the test results show that there are holes in the crimping section of the terminal fault parts, the crimping is not good. For example, other common poor crimping are: the crimping wing is not closed, the crimping is insufficient, the conductor is not deformed at the end, the crimping wing does not wrap the conductor, and the terminal crimping wing is turned out.

Characteristic impedance is essentially different from characteristic resistance only by one word, and there is also a close relationship. Abnormal resistance leads to abnormal impedance. It can be seen that the terminal crimping quality directly affects the terminal transmission performance, and the crimping tooth length and crimping height affect the characteristic impedance, which has a great influence on the product quality.

Above, replace the new host and large screen in turn, simulate the operation when the fault recurs, run bumpy road verification when necessary, and check the single problem of the host and large screen when the function is normal; Secondly, by checking the physical structure of the terminal with naked eyes, analyzing the terminal crimping and testing the characteristic impedance with the help of electronic equipment, the characteristic impedance difference caused by the improper crimping of the locking terminal leads to the mismatch of the characteristic impedance of the display system and the system abnormality.

3. Conclusion

With the improvement of the supporting facilities of the national automobile industry, the perfection of laws and regulations, and the recovery of the global economy, the automobile industry will develop in a subversive way in the future. The application of electric vehicles, autonomous driving and other technologies will be the standard of automobiles, and at the same time, the application of special conductor assemblies will be more and more. FAKRA, because of its low cost and small volume, will be extended in common use, and HSD may be replaced by FAKRA in the future. At the same time, networking, intelligence and sharing have been highly integrated, and the requirements for the speed and bandwidth of signal delivery between modules have been improved. The application of 100-megabit and Gigabit Ethernet is also a development trend in the future.