2. Layout principle of automobile wiring harness

In the wiring harness layout of the new energy vehicle, the high voltage wire harness and low voltage wire harness are arranged reasonably according to each function, in order to realize the stability and reliability of the automobile wire harness and the function of each electric device at the same time.

2.1 Structural layout of automobile wiring harness

The automobile wiring harness layout design usually refers to the wiring arrangement of the automobile wire harness according to the position of the automobile electrical parts and fixing it in the appropriate position by using various fixed devices such as clamps and ties to form the automobile electrical network and realize the various electrical functions of the automobile.

The new energy vehicle is characterized by complex electrical functions, narrow space, relatively wide distribution of electrical parts, and the need to separate the high voltage wire harness and low voltage wire harness to reduce mutual interference and ensure the reliable and stable operation of the automobile electrical system. This brings some challenges to the wiring harness layout of new energy vehicles.

The layout design of automobile wiring harness generally follows the considerations of reliability, convenient assembly and maintenance and so on.

In the layout design of automobile wiring harness, the main trunk line and quantity are usually designed by using the principle of topological structure and the module design layout scheme of automobile electrical parts, and then the corresponding branches are designed according to the topology and other electrical parts, this can effectively improve the harness assembly and economy.

From the perspective of automobile topology, the general vehicle wiring harness is divided into one-stage structure, two-stage structure and three-stage structure.

Among them, the one-stage structure mainly designs a main body of the automobile wire harness layout, and then designs many branch layouts from above, which can effectively reduce the wiring harness docking points, connectors, and improve the economy and so on.

The two-stage structure is usually divided into two main bodies according to the design scheme of the electrical parts module of the new energy vehicle, and then connected by additional wire harness connectors. The three-stage structure is similar to the two-stage structure, which mainly divides the wire harness trunk into three for layout and design.

Whether it is a two-stage structure or a three-stage structure, the wiring harness is convenient to maintain, and the assembly can be adjusted with the layout of electrical parts, but increasing the number of wire harness brings inconvenience to the post-market maintenance.

When the layout of the automobile wiring harness exceeds the three-stage structure, the connection points increases, the reliability of the harness decreases, so it is not recommended.

2.2 Design principles of automobile wiring harness

2.2.1 Reasonable length arrangement of automobile wire harness

The length of automobile wire harness is generally calculated based on the distance of the actual wire harness between two electrical device connectors.

If the reserved length of the wire harness is too long, it is very easy to cause the wire harness to be redundant and complicated or to interfere with other automobile parts around it, thus causing automobile failure; if the reserved length is too short, it will have a great impact on the assembly of the wire harness.

Therefore, when designing the automobile wire harness, we need to consider the actual direction, the reserved length is within a reasonable range, and usually the reserved length does not exceed 200mm, in order to ensure the reliability of the actual assembly.

In addition, when the automobile electrical parts are installed in a more hidden position, the corresponding wire harness length needs to be increased in order to facilitate the later maintenance and inspection.

If there are relative moving parts near the automobile wire harness, the design of the length needs to consider the distance of the relative motion and increase the wire harness length appropriately.

2.2.2 Selection principles of automobile wire harness connectors

The automobile wire harness connector is an important device to ensure the normal operation of the electrical parts.

Therefore, the selection of wire harness connectors has a great impact on the reliability of new energy vehicles.

During the docking of the wire harness, the connector can effectively ensure the insulation between the terminal pins of the wire harness and realize the reliable fixed connection between the wire harness and various electrical components, such as sensors and actuators.

In the actual selection of connectors, the following principles should be followed.

1). The size of the wire harness connector needs to be reasonably selected according to the wire diameter of the wire harness and the size of the current, so as to avoid the automobile wire harness can not be fixed in the connector due to the size of the connector.

2). For the electrical parts with high requirements for wire harness connectors, it is recommended to use high reliability wire harness connectors such as gold plating.

3).Connectors need to be distinguished by size, color and other characteristics; in the same area, the same type of connectors suggest to add wire harness color, positioning slots and other error prevention measures, which can effectively prevent the wrong connection of electrical devices.

4). For metal terminals such as high voltage wire harness, corresponding protection should be designed to avoid problems caused by unnecessary contact of wire harness.

5). The insertion and unplugging of the connector needs to leave enough space to ensure the stability of the connector assembly.

6). The automobile connector should be fixed away from the splash or sand impact, and the waterproof connector should be used; if it cannot be changed, the necessary protective equipment for the wire harness connector needs to be added.

2.3 Safety principles for automobile wiring harness

The safety and stability of the automobile wiring harness is one of the prerequisites to ensure the normal operation of the automobile, so the automobile wiring harness needs to follow the corresponding safety principles in the layout, design and assembly.

1). When the wire harness needs to be pierced, special protective devices

such as adding sheath or wrapping tape are needed to avoid damage. It should be noted that protectors should not affect the performance of the wire harness and avoid additional damage to the wire harness.

In addition, when designing the fixed hole of the automobile wire harness bracket, we should not only consider the wire diameter of the wire harness, but also consider the size of the connector through the hole. It is usually required that the diameter of the hole of the automobile wire harness for sheet metal parts is 2 to 3 times that of the connector, while for the cavity, the diameter of the space section is generally greater than 1.3 to 1.5 times of that of the connector. For sheath or wrapping tape, it is generally larger than the diameter of the hole 1~2mm.

2). When there are moving parts in the installation area of the automobile wire harness, there should be at least 50mm distance from the moving parts.

3). When there is a heat source in the installation area of the automobile wire harness, it is necessary to stay away from the heat source as far as possible.

The distance from the parts with a temperature higher than 150C should be greater than 50mm.

If the wiring position can not avoid the hot parts such as the exhaust pipe, the thermal insulation pad should be added to protect the wire harness, and at least keep the distance above 125mm to effectively reduce the temperature around the wire harness.

4). The wire harness grounding needs to be stable and reliable, and the contact surface is flat. It can run reliably when the corrosion part of the grounding point is damaged.

Automobile low-voltage wire harness grounding point is usually selected on the body or chassis, high-voltage wire harness can not choose this part should be set separately.

5). Because of the existence of high and low voltage wire harness in new energy vehicles, it is necessary to keep the distance between the high and low voltage wire harness more than 300mm to avoid electrical interference.