At present, new energy vehicles are developing in the direction of high voltage and high current. Some high-voltage systems can withstand voltages as high as 800V and currents as high as 660A. Such large currents and voltages will produce electromagnetic radiation, which will interfere with the normal operation of other electronic components.
There are some commonly used shielding electromagnetic interference methods for high-voltage wiring harness:
（1）The conductor has its own shielding layer
Below is a schematic diagram of the structure of a single-core high-voltage wire with its own shielding layer, which is usually composed of two layers of metal conductive material and two layers of insulating material, from the inside to the outside is the core, insulation layer, shielding layer, insulation layer. The wire core is generally made of copper or aluminum, which is the carrier of current. When the current passes through the wire core, electromagnetic interference will be generated, and the role of the shielding layer is to shield electromagnetic interference, so that the electromagnetic interference starts from the wire core and stops at the shielding layer, and will not be emitted to interfere with other electronic devices.
The common shielding layer structure can be divided into three cases,
① Braided shielding with metal foil
It is usually composed of two parts: metal foil and braided shielding layer. The metal foil is usually aluminum foil, and the braided shielding layer is usually braided with tinned copper wire, and the coverage rate is ≥85%. The metal foil is mainly used to prevent high-frequency interference, and the braided shield is to prevent low-frequency interference. The shielding performance of a high-voltage cable consists of two parts, transfer impedance and shielding attenuation, and the shielding efficiency of the wire harness usually needs to reach ≥60dB.
The conductor with shielding layer only needs to peel off the insulation layer when stripping the wire, and then crimp the terminal, which is easy to realize automatic production. The wire with its own shielding layer generally adopts a coaxial structure design, if you want to achieve the peeling treatment of the two layers of insulation on a device, the wire itself is required to have a very ideal coaxial degree, but this is difficult to achieve in the actual production process of the wire, so in order not to damage the wire core when stripping the wire, it is necessary to treat the two layers of insulation separately. In addition, the shielding layer also needs some special treatment. For the wire with its own shielding layer, the wiring harness processing and manufacturing process involves more steps such as peeling, cutting aluminum foil, cutting shielding mesh, flipping mesh, and crimping shielding ring, as shown in Figure 3. Each step requires increased equipment and manual input. In addition, if there are omissions when handling the shield layer, resulting in contact between the shield layer and the core, it will cause serious quality problems.
② Single braid shield
This high-voltage cable structure is the same as the braided shield and metal foil structure mentioned above, but the shield layer only uses braided shield and no metal foil, as shown in the following figure. Since metal foil is mainly used to prevent high-frequency interference, the shielding effect of this structure for high-frequency electromagnetic interference is worse than that of braided shielding and metal foil, and the application range is not as extensive as braided shielding and metal foil shielding, and for the wiring harness production process, it is only less steps to cut aluminum foil, and the entire production process is not well optimized.
In order to improve the processing difficulties caused by the traditional shielding method, some scholars are studying a high-voltage cable shielding made of copper foil with a width of 13~17mm and a thickness of 0.1~0.15mm at an Angle of 30~50, and 1.5~2.5mm winding between each other. This shield only uses metal foil, eliminating the steps of cutting the net, turning the net, pressing the shield ring, etc., which greatly simplifies the wire harness production process, reduces the wire cost, and saves the equipment investment of crimping the shield ring.
③ Single metal foil shield
The above several methods are the design of the shielding layer of the high voltage wire. If you consider from the perspective of reducing costs and optimizing connector design and wiring harness production process, you can directly remove the shielding layer of the wire itself, but for the entire high-voltage system, EMC has to consider, so it is necessary to add components with shielding functions in other places. At present, the common solution for high voltage wiring harnesses is to add a shielding sleeve outside the wire or add a filter to the device.
(2)Add shielding sleeve outside the wire;
This shielding method is realized through the wire outer shielding sleeve. The structure of the high-voltage wire at this time is only the insulation layer and the conductor. This wire structure will reduce costs for wire suppliers; For wire harness manufacturers, it can simplify the production process and reduce the input of equipment; For the design of high-voltage connectors, the structure of the entire high-voltage connector has become simpler because of the need to consider the design of shielding rings.
The 2024 Beijing Automotive Wiring Harness and Connector Exhibition will also hold the Automotive wiring harness and Connector Summit Forum at the same time, inviting industry associations and corporate executives to share hot topics such as the landing application of automotive wiring harness in the development of the intelligent connected automotive industry and future development trends. Through the participation, people can quickly understand the development status and cutting-edge trends of the industry.
New energy vehicles put forward different and even higher requirements for automotive wiring harnesses and connectors. As an important part of automobile parts, wiring harnesses and connectors need to use more wire control technology to achieve a higher degree of intelligent driving control. The control harness carrying digital signals replaces the traditional hydraulic or wire control components to achieve faster and more accurate vehicle control such as braking and steering. As the system becomes more complex, the vehicle harness is more vulnerable to collision, friction, various solvents and other external environment erosion and short-circuit and other failures, so the safety and durability of the harness is also one of the important properties that it needs to meet.
The 2024 Beijing Automotive Wiring Harness and Connector Exhibition will also hold the Automotive wiring harness and Connector Summit Forum at the same time, inviting industry associations and corporate executives to share hot topics such as the landing application of automotive wiring harness in the development of the intelligent connected automotive industry and future development trends. Through the participation, people can quickly understand the development status and cutting-edge trends of the industry.
Post time: Dec-15-2023