Car harness is the main body of car circuit. Without harness, there is no car circuit. With the improvement of people's requirements for vehicle safety, comfort, economy and emission, the electrical configuration and functions of vehicles are more and more, and the wiring harness connecting various electrical components is also more and more complex, which has become a link of frequent failures in modern vehicles. The frequent occurrence of failures in the design and manufacture of vehicles is also increasingly valued. How to improve the overall performance of automobile wiring harness has become the focus of attention. In the overall design of automobile wiring harness, three-dimensional layout is the premise.

1、 Design process of automobile harness

The design process of automobile harness is analyzed in detail as follows:

1) The electrical engineer of the main engine plant shall provide the functions of the electrical system of the whole vehicle, electrical load and relevant special requirements, the status and installation position of electrical components, and the connection form of harness and electrical components.

2) According to the electrical schematic diagram, power distribution is carried out for all electrical subsystems and circuits, including the distribution of grounding points. And draw the corresponding electrical schematic diagram of the whole vehicle.

3) Draw a 3D harness layout.

4) Determine the wiring form and direction of the harness on the vehicle according to the distribution of electrical components of each subsystem; Determine the external protection form of the harness and the protection of the vias; According to the connectors of the electrical equipment itself, determine the type of connecting terminal and sheath of the harness: draw a two-dimensional harness diagram.

5) Check the 2D harness diagram according to the frozen 3D harness layout and schematic diagram; The drawings can be issued only after they are confirmed to be correct, and can be trial-produced only after they are approved.

2、 Harness 3D layout and trend design

The arrangement and division of wire harness is comprehensively considered according to the specific situation of body sheet metal and the distribution of electrical components of the whole vehicle. The direction segmentation of the harness should not be limited to a certain form, but on the premise that the body sheet metal can meet the harness layout, the distribution direction of the vehicle should be considered from the perspective of vehicle electrical.

1. Main principles of 3D harness layout

The following describes in detail the main principles to be considered in the 3D layout of the harness.

1) Good assembly process

The trend and segment design of the harness must meet the premise of easy assembly. Try not to add too many processes in the later assembly, and consider sub-assembly, such as door line, instrument panel line, etc.: at the same time, do not use special tools to complete the assembly.

2) Good maintainability

This point corresponds to the first point. It is not only easy to assemble, but also easy to disassemble in terms of after-sales maintenance. It is impossible to remove a section of the harness for the maintenance of an electrical equipment, but also to remove other parts, otherwise it will increase unnecessary maintenance time.

Based on this, the following points need to be considered when designing harness:

① All connectors of the harness shall be arranged at the place accessible by hand. Or simply disassemble some parts. The connector can be touched;

② For connectors that can only be inserted and pulled out with one hand, the other end of the connector shall be fixed on the body;

③ The color, size, internal positioning and other methods of connectors at the same position shall be adopted to prevent incorrect installation;

④ A certain length should be reserved for the harness at the end of the connector to facilitate the insertion and removal of the connector. It is recommended to reserve 80~100mm electrical components with high maintenance rate such as instrument, audio, air conditioning panel, etc. for the harness at the switch end. The reserved length of the rear harness is convenient for plugging;

⑤ The harness of fuse box shall have enough margin to facilitate the disassembly of fuse box.

3) The circuit should be as short as possible

After considering the disassembly and assembly process, it is necessary to consider how to shorten the circuit of the wire as much as possible, because the circuit has the following advantages: ① low voltage drop on the wire, high voltage obtained by the appliance or low signal attenuation; ② It will reduce the vehicle mass; ③ It can reduce the harness cost.

4) Minimize harness segments

This sometimes conflicts with the assembly process, because sometimes it is necessary to divide the harness which can be a section into two sections for the convenience of installation. This needs to be weighed in the actual 3D design of the harness. As the number of harness segments increases, it is bound to increase the number of butt joints between harnesses. The following points should be considered when adding connectors: ① increase the voltage drop on the harness or increase the signal attenuation; ② Increase the potential unreliable points of electrical connection; ③ It is necessary to add mounting points or mounting brackets to fix the butt pieces; ④ Increase harness assembly labor and material cost.

Therefore, we often see a large line running through the engine compartment, passenger compartment and luggage compartment on some German cars. This is a typical less segmented design.

5) Consider electromagnetic compatibility and anti-electromagnetic interference.

Not only from the selection of wire (such as using twisted pair, shielded wire, etc.), but also from the wiring direction of the harness. For example, some European models with battery trunk must transmit current to the engine compartment electrical box and starter, so there will be a large-diameter wire running through the whole vehicle and always carry strong current. At this time, if you still use the traditional wiring method to separate this high-current line and other signal lines in the same bundle, it will inevitably cause interference to the signal line, so this high-current line is usually arranged separately. It is required to make a groove on the sheet metal to fix the wire, which can play a certain role of electromagnetic shielding. Although this treatment will increase the cost, it is necessary.

2. Other details to be noted when wiring harness layout

In addition to the above five basic principles, the harness layout also needs to pay attention to the following details to ensure the reliability of the harness layout.

1) Under the condition of maximum assembly tolerance of wire harness, all wire harnesses arranged near moving parts shall keep sufficient distance from moving parts. The distance is determined by the amount of motion of moving parts.

2) Under the maximum assembly tolerance of the harness, a gap of at least 6mm shall be maintained between the harness and the relatively stationary component, unless the harness is fixed on the component.

3) The harness branch must have enough relaxation so that the harness will not increase the stress of the equipment connected to it. We should show this relaxation on the 3D digital model of the harness to make the 3D state closer to the actual state.

4) In order to prevent the tower iron sheet from damaging any harness on the trunk, the minimum gap between the tower iron sheet on the trunk of the harness and any harness on the trunk of the harness should be kept at 25mm or more during loading.

5) Generally, a fixed point needs to be added at 120mm of the offline harness connector. The purpose is to minimize the harness vibration and quality burden caused by terminals in connectors.

6) The wire harness branch from the engine body to the body should be arranged in a relatively open place as far as possible, with sufficient length allowance. To prevent harness abrasion or tensile stress damage during engine operation.

7) The wiring harness shall be arranged away from the fuel pipeline, and the length between the two fixed points on the wiring harness shall be less than 300mm. In addition, you need to add a fixed point at the corner.