Research and Application of Automotive Wiring Harness Design
The wiring harness product serves as a connection carrier for automobile electrical functions, and realizes circuit connection between various electrical components. The starting point and ending point of each circuit connection constitute the loop in the wiring harness product. It can be said that the wiring harness circuit is the core of the wiring harness product. The quality of the wiring harness circuit design directly determines the safety and reliability of the entire vehicle wiring harness. With the increase of the degree of electrification of vehicles, the data of electrical components increases, the signal interaction between electrical appliances is getting closer and closer, and the number of automobile wiring harness circuits has also increased sharply. The wiring harness data of general vehicle models has reached nearly 1,000 .
How to optimize and coordinate such a large number of circuits is a difficult problem for automotive wiring harness design.
Existing automotive wiring harness design and technical materials mainly provide design guidance for wiring harness design in the selection of wiring harness materials and manufacturing and processing. However, the planning and design concepts of wiring harness circuits lack systematic analysis. The key points of the design are explained, and the specific control path is provided, which has a certain guiding effect on the wiring circuit design.
Cost-based circuit design method
The wiring harness circuit accounts for about 90% of the material cost of the wiring harness, including wires and connectors. To control the design cost of the wiring harness, we must start with the optimization of the wiring harness circuit design. For the use of wires, how to realize the circuit connection function with the minimum wire length is the first issue to be considered in circuit design. This involves two aspects of design elements: the placement of electrical components and the choice of wiring harness routing. These two elements are independent and interrelated, and have a significant impact on the use of wire length.
First of all, it is necessary to determine the connection method of the circuit based on the principle of components, and then determine the initial position of each component in the vehicle environment. The choice of the wiring harness routing is based on the position of the components, and the shortest wiring harness length is used. Covering as many parts layout areas as possible, this is also the prototype of the entire vehicle electrical topology.
After completing the topology construction of the entire vehicle, it is necessary to check the design and determine whether the placement position of components and the wiring path of wiring harnesses are reasonable by calculating the specific amount of wires (currently there are a lot of software on the market to implement this function). The specific method is to compare the components one by one, and design the different layout positions of the BCM to check the length of the wire used in the vehicle, and then determine where the BCM is arranged.
In this process, mutual influences often occur: the adjustment of the layout of component A will affect the selection of the location of component B. Therefore, after determining the influence of each component and the path of the harness on the length of the conductor one by one, the first round of the preferred solution will be the one that has a greater impact on the length of the conductor. On this basis, the topology is rebuilt, and other secondary solutions are compared and analyzed again. , So as to achieve the most economical topology design platform.
The perfect topology can ensure the least amount of wires. At the same time, for the use of wires, the traditional design concept has clear requirements for the selection of wires. In order to avoid confusion of terminal connection, more wire colors are often used to distinguish However, with the continuous improvement of manufacturing level and inspection methods, in fact, the wire color of the wires can be appropriately designed to adjust the circuit function with the least number of wire types, and it is also a way to reduce the cost of circuit design from a design perspective.
For connectors, how to minimize the use of connectors and reduce the number of transfer loops is the focus of circuit design. Here the wiring harness design engineer needs to be transformed into a system design engineer, and the design work to reduce the use of connectors and transfer circuits is moved to the design and planning of electrical components. There are two main aspects to consider.
On the one hand, the functional circuit of electrical components can be distinguished according to the vehicle configuration. For example, airbag controllers, the basic functional circuit can be designed in the same connector, and the high-profile or extended functions can be arranged in another connector. On low-profile models, only one connector can be used to implement the electrical circuit function.
Performance-based circuit design method
The wiring harness circuit is the core to realize the circuit connection. The safety and reliability of the circuit connection must meet the requirements. The wires and connectors in the circuit design must comply with the requirements of the load and the environment. These contents have been included in other design materials. There is a detailed description, this article only explains how to ensure the performance of the circuit from the path selection of the circuit.
First of all, the design of the circuit must avoid the failure mode that cannot be detected. The circuit behind the fuse is connected in parallel with the relay coil terminal and the contact terminal. This design is common in the vehicle circuit design. When the point terminal is different, this design is obviously reasonable, but when the relay coil terminal and the contact terminal are the same, such a design cannot be recognized by current electrical inspection equipment when the terminal is inserted into the relay hole. This way of failure.
Therefore, this circuit design method cannot be adopted in some cases. Of course, the design environment and manufacturing environment that different design engineers face are different, and the specific failure modes will be different, but the avoidance of failure modes in circuit design must be considered first.
On the other hand, the current level of automotive electronics has increased significantly. As an electronic carrier, the electromagnetic environment facing automobiles is also more complicated, and how to reduce electromagnetic interference in the design of wiring harness circuits is an inevitable subject. Wire coupling interference, power supply interference, grounding interference, radiation interference, etc. will adversely affect the normal operation of electrical devices, and the loops in the wiring harness are bundled together. The wiring coupling interference between the wiring harness loops and between the wiring harness and the metal conductor is online. The beam is particularly prominent.
To reduce wire coupling interference in loop design, we must first distinguish between interference loops and sensitive loops. To put it simply, inductive load circuits such as ignition coils, horns, and motors are interference circuits, while images, radar probes, low-power LED lights, various sensors and other circuits are sensitive circuits. During the design process, interference circuits and sensitive circuits Need to be arranged separately. Tests have shown that increasing the lead spacing can reduce high-frequency interference. In the case where it is impossible to distinguish between them, a function test must be performed by way of lead injection interference to determine the correct circuit design.
At the same time, in order to reduce the influence of the radiation and coupling of the wiring harness, the circuit loop area and the length of the wiring harness should be reduced as much as possible. In the design of the entire vehicle, the loop area of the wiring harness needs to be minimized, especially the power cord and ground wire. The wiring harness in the loop is required to run as close as possible, and at the same time, it is fixed as close to the metal body as possible to reduce the loop area. More than 50cm.
In addition to the layout of interference circuits and sensitive circuits, the twisted-pair wires and shielded wires used in the wiring harness also need to be paid attention to in the loop design to achieve the shielding expectations: the two wire diameters of the twisted-pair wires The length should be the same, and the twist length is preferably 10 ~ 20mm. The specific twist length is subject to the test test. The shield ground terminal should connect the shield 360 ° and the shield shell at both ends. The signal lines form a complete shield. For the shell of the component connected by the shielded cable is not a metal structure, the shield can be laminated on a metal plate that is reliably connected to the vehicle body using a metal conductive clip, and the shielding effectiveness should reach 60dB.
In conclusion
How to optimize and coordinate such a large number of circuits is a difficult problem for automotive wiring harness design.
Existing automotive wiring harness design and technical materials mainly provide design guidance for wiring harness design in the selection of wiring harness materials and manufacturing and processing. However, the planning and design concepts of wiring harness circuits lack systematic analysis. The key points of the design are explained, and the specific control path is provided, which has a certain guiding effect on the wiring circuit design.
The wiring harness circuit accounts for about 90% of the material cost of the wiring harness, including wires and connectors. To control the design cost of the wiring harness, we must start with the optimization of the wiring harness circuit design. For the use of wires, how to realize the circuit connection function with the minimum wire length is the first issue to be considered in circuit design. This involves two aspects of design elements: the placement of electrical components and the choice of wiring harness routing. These two elements are independent and interrelated, and have a significant impact on the use of wire length.
First of all, it is necessary to determine the connection method of the circuit based on the principle of components, and then determine the initial position of each component in the vehicle environment. The choice of the wiring harness routing is based on the position of the components, and the shortest wiring harness length is used. Covering as many parts layout areas as possible, this is also the prototype of the entire vehicle electrical topology.
After completing the topology construction of the entire vehicle, it is necessary to check the design and determine whether the placement position of components and the wiring path of wiring harnesses are reasonable by calculating the specific amount of wires (currently there are a lot of software on the market to implement this function). The specific method is to compare the components one by one, and design the different layout positions of the BCM to check the length of the wire used in the vehicle, and then determine where the BCM is arranged.
In this process, mutual influences often occur: the adjustment of the layout of component A will affect the selection of the location of component B. Therefore, after determining the influence of each component and the path of the harness on the length of the conductor one by one, the first round of the preferred solution will be the one that has a greater impact on the length of the conductor. On this basis, the topology is rebuilt, and other secondary solutions are compared and analyzed again. , So as to achieve the most economical topology design platform.
The perfect topology can ensure the least amount of wires. At the same time, for the use of wires, the traditional design concept has clear requirements for the selection of wires. In order to avoid confusion of terminal connection, more wire colors are often used to distinguish However, with the continuous improvement of manufacturing level and inspection methods, in fact, the wire color of the wires can be appropriately designed to adjust the circuit function with the least number of wire types, and it is also a way to reduce the cost of circuit design from a design perspective.
For connectors, how to minimize the use of connectors and reduce the number of transfer loops is the focus of circuit design. Here the wiring harness design engineer needs to be transformed into a system design engineer, and the design work to reduce the use of connectors and transfer circuits is moved to the design and planning of electrical components. There are two main aspects to consider.
On the one hand, the functional circuit of electrical components can be distinguished according to the vehicle configuration. For example, airbag controllers, the basic functional circuit can be designed in the same connector, and the high-profile or extended functions can be arranged in another connector. On low-profile models, only one connector can be used to implement the electrical circuit function.
On the other hand, it can also be planned according to the connection area of the circuit. For example, it is also an airbag controller. Some designers will consider designing the function of the chassis in the same connector and the function of connecting the instrument panel to another connector. In the plug-in, such a plan can reduce the mutual transfer of the regional circuits. This area-based functional circuit design is particularly effective for electrical components (such as BCM controllers) with more pins.
The wiring harness circuit is the core to realize the circuit connection. The safety and reliability of the circuit connection must meet the requirements. The wires and connectors in the circuit design must comply with the requirements of the load and the environment. These contents have been included in other design materials. There is a detailed description, this article only explains how to ensure the performance of the circuit from the path selection of the circuit.
First of all, the design of the circuit must avoid the failure mode that cannot be detected. The circuit behind the fuse is connected in parallel with the relay coil terminal and the contact terminal. This design is common in the vehicle circuit design. When the point terminal is different, this design is obviously reasonable, but when the relay coil terminal and the contact terminal are the same, such a design cannot be recognized by current electrical inspection equipment when the terminal is inserted into the relay hole. This way of failure.
Therefore, this circuit design method cannot be adopted in some cases. Of course, the design environment and manufacturing environment that different design engineers face are different, and the specific failure modes will be different, but the avoidance of failure modes in circuit design must be considered first.
On the other hand, the current level of automotive electronics has increased significantly. As an electronic carrier, the electromagnetic environment facing automobiles is also more complicated, and how to reduce electromagnetic interference in the design of wiring harness circuits is an inevitable subject. Wire coupling interference, power supply interference, grounding interference, radiation interference, etc. will adversely affect the normal operation of electrical devices, and the loops in the wiring harness are bundled together. The wiring coupling interference between the wiring harness loops and between the wiring harness and the metal conductor is online. The beam is particularly prominent.
To reduce wire coupling interference in loop design, we must first distinguish between interference loops and sensitive loops. To put it simply, inductive load circuits such as ignition coils, horns, and motors are interference circuits, while images, radar probes, low-power LED lights, various sensors and other circuits are sensitive circuits. During the design process, interference circuits and sensitive circuits Need to be arranged separately. Tests have shown that increasing the lead spacing can reduce high-frequency interference. In the case where it is impossible to distinguish between them, a function test must be performed by way of lead injection interference to determine the correct circuit design.
At the same time, in order to reduce the influence of the radiation and coupling of the wiring harness, the circuit loop area and the length of the wiring harness should be reduced as much as possible. In the design of the entire vehicle, the loop area of the wiring harness needs to be minimized, especially the power cord and ground wire. The wiring harness in the loop is required to run as close as possible, and at the same time, it is fixed as close to the metal body as possible to reduce the loop area. More than 50cm.
In addition to the layout of interference circuits and sensitive circuits, the twisted-pair wires and shielded wires used in the wiring harness also need to be paid attention to in the loop design to achieve the shielding expectations: the two wire diameters of the twisted-pair wires The length should be the same, and the twist length is preferably 10 ~ 20mm. The specific twist length is subject to the test test. The shield ground terminal should connect the shield 360 ° and the shield shell at both ends. The signal lines form a complete shield. For the shell of the component connected by the shielded cable is not a metal structure, the shield can be laminated on a metal plate that is reliably connected to the vehicle body using a metal conductive clip, and the shielding effectiveness should reach 60dB.
In conclusion
This article analyzes the automotive wiring harness circuit design method from two aspects of cost and performance, and explains the application of specific methods in combination with working practices. Guiding significance.
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