How to Design Automotive Wire Harness System _ Design Method of Automotive Wiring Harness System

The harness system serves as the nerve of the car and serves as the responsibility for connecting the central control components and the various electrical appliances of the vehicle. The design quality of the harness system is directly related to the safety of the vehicle. With the rapid development of the automotive market, the rapid development of the electrical and electronic industry, the rapid increase in automotive electronics and electrical appliances, coupled with the increase in automotive safety, comfort, economy, and emission requirements, the use of wiring harnesses in automobiles is increasing. Extensively, the design of automotive wiring harness systems has become more important and rigorous.

First, the design process

The design of the wiring harness system is a rigorous project, step by step, Figure 1 is the design flow of the automotive wiring harness system.

Figure 1 Automotive Wiring System Design Flow

Second, the layout principle

2.1 Preliminary planning

In the conceptual design and structural design phase of the vehicle, we must integrate the overall layout awareness of the wiring harness and do a good job in planning. The battery, the fuse box, and the central control unit can be arranged in a centralized manner, which not only saves the cost of the trunk wiring harness, reduces the overall quality of the entire vehicle, improves the beauty of the wiring harness arrangement, but also greatly reduces the risk of fired vehicles.

2.2 Modular

The wiring harness system should be modularized according to the functions and characteristics of the complete machine, which is convenient for disassembly and assembly, and is convenient for maintenance. It also saves vehicle maintenance and repair time. 2 is a three-dimensional wiring diagram of a passenger car harness system, which is divided into engine harness, starting cable harness, front harness, instrument harness, ceiling light harness, left front door harness, left center door harness, right front door harness, right There are 11 modules in the door harness, tailgate harness and chassis harness.

Figure 2 3D wiring diagram of a passenger car harness system

2.3 layout environment

When wiring harness is arranged, sharp edges, high temperature, oil paths, water pipes, and moving parts should be avoided to ensure the reliability of the layout. If you cannot avoid it, you must take appropriate protective measures. If the engine compartment, engine wiring harness should fully consider the engine vibration, heat radiation around the exhaust manifold, a fixed point must be set every 200mm, the distance from the heat source should not be less than 100mm, before the wiring harness and heat source additional heat shield, wiring harness External high-temperature bellows dressing. The wiring harness of the door should focus on the factors such as vias, sealing, and assembly. When the via holes are used, plastic protective sleeves are used to prevent the function failure of the wiring harness due to wear; try to arrange on the dry side of the door to prevent the impact of water leakage on the wiring harness; use as little as possible. Get buckled to secure as many harnesses as possible, reducing the opening and assembly complexity on the body.

2.4 Electromagnetic Interference Protection

In areas with strong electromagnetic interference or signal-sensitive areas, attention should be paid to adding anti-magnetic protection to the wiring harness and setting the wires to twisted-pair or shielded wires, such as a CAN bus. Because the internal electronic control component of the car interferes with the CAN bus, it is in the external electromagnetic environment that changes from low frequency to high frequency, so the anti-jamming capability of the CAN bus has put forward higher requirements. As a CAN bus with reliable data transmission, it is particularly important to ensure its good anti-electromagnetic interference characteristics.

2.5 Grounding Design Principles

Most of the automotive electrical faults are caused by the failure of grounding, which is usually caused by bad ground connection or broken wire. Therefore, the design of the crowbar points of various electrical equipment in the automotive circuit must be rationally arranged according to the nature and function of the electrical equipment in order to ensure the good working conditions of all electrical equipment on the vehicle.

(1) The traction points of electrical appliances that have a large impact on the vehicle's performance and safety and are vulnerable to interference with other electrical appliances must be set up separately, such as engines, ECUs, ABS, etc.; weak-signal sensors or appliances that are subject to interference should be separated Set up a ground point, try to make the shortest electrical circuit, to ensure the real signal transmission, such as radio systems such as audio; high current electrical appliances have to be set up separately, to ensure that the loop near the ground, shorten the loop length, reduce the voltage drop Electromagnetic interference is safe and economical.

(2) In order to improve the reliability of key electrical appliances that affect people's safety in automobiles, dual-type ground irons, such as airbag systems, are used to ensure accurate and timely operations.

(3) General use of electrical appliances can be based on its three-dimensional layout of the location, the environment, optional common ground, reducing the complexity of the assembly and material costs.

Three, two-dimensional harness design

3.1 2D Drawing Design Overview

The parameters of the interface control files, such as car sensors, actuators, and central control components, and the car circuit schematics are used to select the harness components. The two-dimensional wiring harness diagram is then combined with the three-dimensional wiring diagram. The two-dimensional wiring harness diagram is mainly for debugging and maintenance and includes in detail: wiring harness fixing method, fixed position, packing method; local special protection measures; connector model and manufacturer; wiring harness part number, wiring harness version; type of each loop conductor , wire diameter, color, loop start and end position; harness technical requirements. Ensure that the harness has sufficient margins to avoid pulling or tensioning the harness. Since the harness is a deformed part of an automobile component, its actual length and branch position are verified by the actual vehicle's actual measurement.

3.2 Line Color and Line Labeling

With the increase of automotive electrical appliances, the number of wires continues to increase. For ease of maintenance, low-voltage wires are often distinguished by different colors. There are two kinds of wire colors: monochrome and two-color. Monochrome is the best, followed by two colors. The color of the wire is marked with the color code. The first color is the main color in the two-color label, and the second is the auxiliary color. The black wire is used for the ground wire of various automotive electrical appliances. The black wire is not used for any other purpose except for the ground wire. Because the total number of power cords for each appliance is large, two-color lines with red as the main color are generally used. Specifically refer to Table 1 and Table 2. In the actual production of drawings, taking into account the number of harnesses and production accuracy, you can use Excel and Solid Edge to generate electrical circuit tables.

3.3 Selection of conductor cross-sectional area

The allowable voltage drop of a typical 12V power line is not more than 1V, and the calculation of the cross-sectional area of the conductor may be as follows:

S= IρL/U

Where: S-wire cross-sectional area, mm2; I-current flowing through the wire, A; ρ-wire resistivity, the general value of 0.0185Ω · mm2 / m; L-wire length, m; U-wire allowable voltage drop. It should be pointed out that the larger the wire diameter is, the larger the current that can pass, and the harder the wire harness is, the higher the safety factor of the wire harness is, but the larger the wire diameter is, the higher the cost of the wire harness is, and the weight of the vehicle is not good. . After rounding the conductor cross-sectional area size should also consider the voltage drop, wire bundle after the heat and mechanical strength, cost and other factors, the general wire area should not be less than 0.5mm2. There are also differences between the relevant standards and experience values for different types of wires. Refer to Table 3 for details.

3.4 Connector Selection

(1) The vehicle harness system should use as few plug connectors as possible to improve reliability. There is poor contact between the connectors due to vibration, friction, oxidation of the plating layer, and influent water, and there are also electrical function interruptions due to human factors.

(2) The quality of the connector directly affects the overall performance of the harness. For the selection of the connector, it is firstly necessary to ensure good contact and good reliability. In the selection, an appropriate connector should also be selected according to the number of wires, the size of the line current, and the layout space. The material of the connector terminal is generally brass, and the plating is selected according to the specific butt-end electrical device terminal plating. There is no special requirement, and tin plating is generally selected. With the intelligentization of automobiles, the number and types of connectors are also increasing day by day, causing a lot of inconvenience to maintenance and assembly, and the integration of connectors will become a trend in the future.

Fourth, design verification

The harness connector needs to be tested according to its mechanical performance, electrical performance and environmental performance, such as terminal joining force, terminal pulling out force, oscillating current, dielectric strength, heat aging resistance, high temperature resistance, salt spray resistance, temperature/humidity cycle, etc. Conductors need to do insulation stripping performance, insulation wear resistance, hot pressure related inspections and tests. Mass production of the front harness assembly must also complete relevant tests, including resistance to vibration, salt spray resistance, voltage drop, resistance to industrial solvents, temperature and humidity cyclic change performance, electrical performance test tests, due to customer demand, relevant tests in various countries and regions Different project and compliance standards, the experimental requirements will be different.

Conclusion

The intelligent and lightweight automotive development has brought unprecedented challenges to automotive wiring harnesses. From the electrical schematic diagram to the two-dimensional harness diagram, from the design concept to the completion of the harness design, there must be reasonable evidence, and the selection and matching of the relevant components of the harness It is necessary to strictly calculate and check and do a good job of designing the harness system so that the failure of the harness is no longer the chief culprit of the automobile fault.