Design method of automobile wiring harness system

As the nerve of the car, the wiring harness system plays an important role in connecting the central control components and various electrical appliances in the car. The design quality of the wiring harness system is directly related to the safety of the vehicle. With the increasingly popular automobile market, the rapid development of the electronic and electrical industry, the rapid increase in automobile electronic appliances, and the improvement of people's requirements for automobile safety, comfort, economy and emissions, the application of wiring harnesses in automobiles is becoming more and more Extensive, the design of automotive wiring harness systems has become more important and rigorous.

1. Design process

The design of the wiring harness system is a rigorous project that pays attention to step by step. Figure 1 is the design process of the automotive wiring harness system.

Figure 1 Automotive wiring harness system design process

2. Arrangement principles

2.1 Early planning

In the conceptual design and structural design stages of the vehicle, it is necessary to integrate the awareness of the overall layout of the wiring harness and do a good job in early planning. It is best to centrally arrange the battery, fuse box, and central control components. This can not only save the cost of the main wiring harness, reduce the overall quality of the vehicle, improve the aesthetics of the wiring harness layout, but also greatly reduce the risk of vehicle fire.

2.2 Modularization

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

Figure 2 Three-dimensional wiring diagram of a passenger car wiring harness system

2.3 Lay out the environment

When laying out the wiring harness, try to avoid areas with sharp edges, high temperatures, oil lines, water pipes, and moving parts to ensure the reliability of the layout. If it cannot be avoided, appropriate protective measures need to be taken. For example, in the engine compartment, the engine wiring harness should fully consider engine vibration and heat radiation around the exhaust manifold. A fixed point must be set every 200mm, and the distance from the heat source should not be less than 100mm. A heat shield and wire harness should be attached before the wiring harness and the heat source. Wrap with high-temperature-resistant corrugated pipes externally. The door wiring harness should focus on via holes, sealing, assembly factors, etc. Use a plastic protective sleeve when passing through holes to prevent the functional failure of the wiring harness due to wear; try to arrange it on the dry side of the door to prevent the impact of water leakage on the wiring harness; use as little as possible Snaps are needed to fix as many wiring harnesses as possible to reduce openings on the body and assembly complexity.

2.4 Anti-electromagnetic interference

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 pairs or shielded wires, such as CAN bus. Since the internal electronic control components of the car interfere with the CAN bus, putting it in an external electromagnetic environment that changes from low frequency to high frequency, higher requirements are placed on the anti-interference ability of the CAN bus. As a CAN bus for reliable data transmission, it is particularly important to ensure its good anti-electromagnetic interference characteristics.

2.5 Grounding design principles

Automotive electrical failures are mostly caused by ground failure, usually due to poor ground contact or an open circuit in the ground wire. Therefore, the design of the grounding points of each electrical equipment in the automobile circuit must be reasonably arranged according to the nature and function of the electrical equipment to ensure the good working condition of each electrical equipment on the automobile.

(1) The grounding points of electrical appliances that have a great impact on vehicle performance and safety and are susceptible to interference from other electrical appliances must be set up separately, such as engines, ECUs, ABS, etc. Weak signal sensors or electrical appliances that are susceptible to interference must be set up separately. Establish a grounding point and try to keep the electrical circuit as short as possible to ensure the true transmission of signals, such as audio and other radio systems; separate grounding points for high-current electrical appliances should also be established to ensure that the circuit is grounded nearby, shortening the length of the circuit and reducing the voltage drop , electromagnetic interference, safe and economical.

(2) In order to improve the reliability of critical electrical equipment in automobiles that affects personal safety, multiple grounding is used, such as airbag systems, to ensure that they work accurately and in a timely manner.

(3) General electrical appliances can selectively share ground irons according to their three-dimensional layout location and environment, reducing assembly complexity and material costs.

3. Two-dimensional wiring harness diagram design

3.1 Overview of 2D diagram design

The selection of wiring harness components is based on the data parameters of interface control files such as automotive sensors, actuators, and central control components and the automotive circuit schematic diagram, and then combined with the three-dimensional wiring diagram to complete the two-dimensional wiring harness diagram. The two-dimensional wiring harness diagram is mainly for debugging and maintenance, and should include in detail: the wiring harness's fixing method, fixing position, and wrapping method; local special protection measures; connector model and manufacturer; wiring harness part number, wiring harness version; and the type of each loop wire , wire diameter, color, loop start and end position; wiring harness technical requirements, etc. Ensure that the wiring harness has sufficient margin to avoid subjecting the wiring harness to tension or tension. Since the wire harness is a deformed part of the automotive component, its actual length and branch locations must be verified by actual vehicle measurements.

3.2 Line colors and line markings

As automobile electrical appliances increase, the number of wires continues to increase. To facilitate maintenance, low-voltage wires are often distinguished by different colors. There are two types of wire colors: single color and double color. Single color is the best, and double color is the second best. The color of the wire is marked with a color code. In the double color mark, the first digit is the main color, and the second digit is the auxiliary color. Black wires should be used for the ground wires of various automotive electrical appliances. Black wires are not used for other purposes except as ground wires. Because the total number of power cords for each electrical appliance is large, two-color cords with red as the main color are generally used. Please refer to Table 1 and Table 2 for details. When actually making drawings, considering the number of wire harnesses and production accuracy, Excel and Solid Edge can be used directly to generate electrical circuit tables.

3.3 Selection of conductor cross-sectional area

Generally, the allowable voltage drop of a 12V power line is not greater than 1V. The cross-sectional area of ​​the conductor can be calculated according to the following formula:

S= IρL/U

In the formula: S - cross-sectional area of ​​the wire, mm2; I - current flowing through the wire , A; ρ - resistivity of the wire, generally 0.0185Ω·mm2/m; L - wire length, m; U - allowable voltage of the wire drop. It should be pointed out that the larger the wire diameter, the greater the current that can pass through, the less likely the wire harness is to burn out, and the higher the safety factor of the wire harness. However, the larger the wire diameter, the higher the cost of the wire harness, and it is not conducive to the lightweighting of the car. . The size of the cross-sectional area of ​​the rounded wires should also consider factors such as voltage drop, heat generated after the wires are bundled, mechanical strength, and cost. Generally, the wire area should not be less than 0.5mm2. Different wire types have different relevant standards and experience values. Please refer to Table 3 for details.

3.4 Connector selection

(1) The vehicle wiring harness system should use the minimum number of connectors to improve reliability. Poor contact between connectors may occur due to factors such as vibration, friction, coating oxidation, water ingress, etc. There may also be electrical function interruption due to human factors.

(2) The quality of the connector directly affects the overall performance of the wiring harness. When selecting a connector, you must first ensure that it has good contact and good reliability. When selecting, you should also select a suitable connector based on the number of wires, line current, layout space and other constraints. The material of plug connector terminals is generally brass, and the plating layer is selected according to the terminal plating of the specific electrical equipment used at the docking end. There are no special requirements, and tin plating is generally used. As cars become smarter , the number and types of connectors are also increasing, causing a lot of inconvenience to maintenance and assembly. The unification of connectors will become a future development trend.