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Automotive wiring harness an important overlooked component

by | Mar 26, 2024

What is a car wiring harness

The automobile wiring harness is the network main body of the automobile circuit. Without the wiring harness, there would be no automobile circuit. A wire harness refers to a component in which contact terminals (connectors) punched out of copper are crimped to wires and cables, and then an insulator or metal shell is molded on the outside, and the wire harness is bundled to form a connecting circuit. The wiring harness industry chain includes wires and cables, connectors, processing equipment, wiring harness manufacturing and downstream application industries. Wiring harnesses are widely used and can be used in automobiles, household appliances, computers and communication equipment, various electronic instruments and meters, etc. The body wiring harness connects the entire body , the general shape is H-shaped.

Main specifications and performance requirements of automotive wiring harnesses

1. Cross-sectional area of the conductor

Select the cross-sectional area of the conductor according to the load current of the electrical equipment. The general principle is that electrical equipment that works for a long time can use a conductor with 60% of the actual current carrying capacity. Electrical equipment that works for a short time can use a conductor with an actual current carrying capacity of 60%-100%. between the wires; at the same time, the voltage drop in the circuit and the heating of the wires should also be considered to avoid affecting the electrical performance of the electrical equipment and the allowable temperature of the wires; in order to ensure a certain mechanical strength, generally the cross-sectional area of low-voltage wires is not less than 1.0mm² .

2. Wire color

Automotive circuits are characterized by colors and numbers. With the increase in automotive electrical equipment, the number of wires is also increasing. In order to facilitate the identification and maintenance of automotive electrical equipment, low-voltage lines in automotive circuits are usually composed of different colors, and are coded with color letters on the automotive electrical circuit diagram. Mark out. The color codes of the wires (represented by one or two letters) are usually marked on the automobile circuit diagram. The colors of the wires on the automobile are generally different. There are two commonly used selection principles: single color and double color. Such as: red (R), black (B), white (W), green (G), yellow (Y), black and white (BW), red and yellow (RY). Among the two-color lines, the former is the main color and the latter is the auxiliary color.

3. Physical properties of wires (1) Bending performance. The wires between the door and the body should be composed of wires with good bending properties. (2) High temperature resistance. Wires used in high-temperature areas generally use vinyl chloride or polyethylene-coated wires with good insulation and heat resistance. (3) Shielding performance. In recent years, the number of electromagnetic shielding wires used in weak signal circuits has also continued to increase. 4. Wire harness wrapping (1) Cable half-stack wrapping method, apply insulating paint and dry to increase the strength and insulation performance of the cable. (2) The new wire harness is partially wrapped with plastic and then placed in a plastic corrugated tube with a side cutout, making it stronger, better protected, and easier to find line faults.

Wire harness production process

The first station of wire harness production is the wire opening process. The accuracy of the wire opening process is directly related to the entire production schedule. Once an error occurs, especially if the wire opening size is too short, it will lead to rework of all work stations, which is time-consuming and laborious and affects production efficiency. Therefore, when preparing the wire opening process, the wire opening size and stripping size must be reasonably determined according to the requirements of the drawing.

The second station after opening the line is the crimping process. The crimping parameters are determined according to the terminal type required by the drawing, and the crimping operation instructions are produced. If there are special requirements, it is necessary to indicate them on the process documents and train the operators. For example: some wires need to pass through the sheath before crimping, which requires pre-installing the wires and then returning from the pre-assembly station before crimping; there are also piercing crimping methods that use special crimping tools. This crimping method has good electrical contact performance.

Next comes the pre-assembly process. First, the pre-assembly process operating instructions must be compiled. In order to improve the efficiency of the final assembly, pre-assembly stations must be set up for complex wire harnesses. The reasonableness of the pre-assembly process directly affects the efficiency of the final assembly and reflects a The technical level of craftsmen. If there are too few pre-assembled parts or the wire paths of the assembly are unreasonable, it will increase the workload of the general assembly personnel and slow down the speed of the assembly line. Therefore, craftsmen must always stay on site to summarize. The last step is the final assembly process. Able to design tooling equipment and material box specifications based on the assembly platform designed by the product development department, and affix the numbers of all assembly sheaths and accessories on the material box to improve assembly efficiency. Prepare the assembly content and requirements for each station, and balance the entire assembly station to prevent excessive workload at one point and slow down the entire assembly line.

The composition of the wiring harness

Automotive wiring harness consists of wires, terminals, coverings, connectors and other parts.

1. Wires Wires are the main component of the wire harness, usually called wires. They are the main part of the wire harness. Their main function is to carry the current required by the load. The important parameter of a wire is its current-carrying capacity. The current-carrying capacity of a wire is affected by the wire diameter (the cross-sectional area of the wire conductor), the wire length, the resistivity of the conductor and the ambient temperature.

2. Connector

 Connectors are indispensable components for connecting wire harnesses to other electrical equipment. They are divided into wire harness end connectors and electrical appliance end connectors. We often hear about male connectors (referred to as male terminals) and female connectors (referred to as female terminals). The connector where the male terminal is located is called a male connector, and the connector where the female terminal is located is called a female connector. The ones on our wiring harness end are usually female connectors.

Connectors can be divided into two categories: waterproof and non-waterproof. At the beginning of the design, PIN pins of different widths are selected according to the current that each PIN pin needs to carry, and then a cavity is formed on the connector to accommodate different PIN pins, thereby forming a Housing that accommodates multiple PINs.

(1) CPA-molded shell secondary locking mechanism


Its function is to ensure that the buckle of the primary locking mechanism will not be easily withdrawn after the plastic shell and electrical interface are assembled in place. Due to its special function, CPA must ensure worker operability and legibility when designing. This is CPA is required to be an independent organization on the plastic shell and must also have a special color mark.

(2) Waterproof sealing ring: There are two types of waterproof sealing mechanisms, one is used for sealing between plastic cases, and the other is used for sealing terminal leads.

(3) TPA - terminal secondary locking structure Terminal Position Assurance: Not all terminals require a secondary locking structure. VW requires that TPA should be used when the terminal width is less than 2.8mm (including 2.8). In order to ensure the convenience of installation by wire harness factory workers , the color of TPA also needs to be identifiable, and there must be a clear feel during assembly. In order to ensure that TPA will not automatically enter the locking position during transportation to the wiring harness factory, an anti-locking mechanism is necessary on TPA.

3. Wire harness wrapping The main function of the wiring harness wrapping is to protect the wiring harness. Depending on the material of the wrapping, the main types of wrapping include corrugated pipe, PVC tape, cloth-based tape, flannel tape, sponge tape and aluminum foil tape.

Due to different materials, the material properties of different wrappings are also inconsistent. Correspondingly, their application conditions and methods on the wire harness assembly are also inconsistent. The specific selection should be based on the specific use environment of the wire harness and its wear resistance, Heat resistance.

4. Wire harness fixtures

Unlike other parts on other cars, the wiring harness is a flexible part. The wiring harness cannot be sent in a predetermined shape. Therefore, in order to constrain the layout path of the wiring harness on the entire vehicle, additional parts need to be added to fix the wiring harness. These additional parts The part is the wire harness fixture, which plays the role of fixing the wire harness and constraining the wire harness layout path.

Wire harness fixtures include: cable ties, buckles, rubber sheaths, wire harness brackets, etc. Depending on the installation environment of the wire harness, such as the wiring harness installation space, temperature requirements, waterproof requirements, the shape and shape of each wire harness fixture The materials are not consistent. Even so, the wire harness fixtures also show a trend of standardization, and they are also one of the components that is easier to implement in the selection of wire harness platforms.

5. Wiring harness accessories

Wire harness accessories refer to other smaller products on the wire harness assembly, such as product labels, fuse clips, etc. on the wire harness assembly.