Analysis of characteristics of high-voltage wire harness of new energy electric vehicles
How much do you know about the characteristics of high-voltage wire harnesses of new energy electric vehicles? Konnra wire harness engineers will focus on introducing you to the characteristics of high-voltage wire harnesses of new energy electric vehicles. We hope that after our introduction, you can learn about the high-voltage wire harnesses of new energy electric vehicles. Features have an in-depth understanding.
New energy vehicles generally work in the B-level voltage range, so the high-voltage wiring harness also needs to meet the operating voltage range of 60V-1500V. The current general wire voltage requirements are AC30V-1000V according to the regulation of B-level voltage in GB/T184384.3 , Or DC60V-1500V.
2. High current
As a main energy transmission channel, the high-voltage wire harness of new energy vehicles needs to withstand a large current, and the rated working current of the DC bus can reach more than 300A.
3. Sealing
Due to the high voltage and high current characteristics of high-voltage wire harnesses, the tightness of wire harnesses is also highly demanded. Generally, waterproof and dustproof tests and airtightness tests are required. If the seal is not good, it will cause moisture or water intrusion, which will cause wires and connection parts. Of rapid aging or damage. If the sealing performance of the connector is poor, it can also lead to a reduction in insulation resistance, and the entire vehicle reports an insulation failure.
4. Heat resistance
Because the high-voltage wire harness passes a large current for a long time, because the power is large, the Joule effect generates a lot of heat, so the temperature resistance level of the wire of the high-voltage wire harness generally reaches 125 ℃ (150 ℃), and the terminal temperature resistance generally reaches 140 ℃.
5. EMC performance
EMC (Electro Magnetic Compatibility) refers to the ability of a device or system to operate in compliance with its requirements in its electromagnetic environment and not cause intolerable electromagnetic interference to any equipment in its environment. Simply put, EMC includes EMI (Electro Magnetic Interference) and EMS (Electro Magnetic Susceptibility). EMI refers to the electromagnetic interference generated by the equipment in the environment during normal operation; EMS refers to the degree of anti-interference that the appliance has to a certain extent to the electromagnetic interference present in the environment. EMI is active, that is, interference to the outside world, EMS is passive, that is, to resist external interference. Therefore, the EMC requirements for the device are: to reduce interference to others, and at the same time to resist a considerable degree of external interference.
Within the scope of the vehicle, first ensure that the EMC of the components meets the standard requirements, and connect the various control units together through the harness. The focus of the vehicle-level shielding design of new energy vehicles should be the layout of high-voltage systems, shielding design, and anti-interference processing of CAN communication networks. First of all, it is required to arrange the high-voltage wiring harness along the car body to optimize the loop of electromagnetic radiation of the whole vehicle, and at the same time use the car body to form a closed shielding cabin. At the same time, shielding high-voltage cables and connectors is also a cost-effective method to reduce unnecessary electromagnetic interference. A series of standard experiments show that shielded cables and connectors can effectively reduce unnecessary interference in the frequency range of 100kHz to 200MHz. At present, all domestic models use shielded high-voltage lines. Japanese vehicles also use shielding nets to cover the outside of the high-voltage lines, and the plug-in parts are processed to achieve shielding connections. In order to avoid the electromagnetic interference when the high-voltage wire harness transmits strong electric current, resulting in the risk of electromagnetic interference caused by the low-voltage wire harness to the power supply and signal transmission of the control unit, the layered design of the high-voltage wire harness and the low-voltage wire harness is generally adopted, and the distance is guaranteed within 200-300mm.
6 durability
The power supply and various electrical parts on the new energy vehicle are physically connected to the circuit through the wiring harness, and the wiring harness is distributed throughout the vehicle. If the power system is compared to the heart of a car, then the wiring harness is the neural network system of the car, which is responsible for the information transmission between the various electrical parts of the car. With the continuous improvement of people's requirements for comfort, economy, and safety, the variety of electronic products on automobiles is also increasing, and the failure rate of automobile wiring harnesses is becoming more and more complicated. This requires improving the reliability and durability of the wiring harness. Terminals and connectors are important parts that determine the reliability of the system and an important part of the entire wiring harness. Due to the harsh working environment of some terminals and connectors, various failure modes are prone to occur in terminals and connectors, such as corrosion, aging, and looseness under the action of vibration. Due to the damage, looseness, shedding, and failure of terminals and connectors, electrical circuit failures account for more than 50% of the failures of the entire electrical system. Therefore, the reliability design of terminals and connectors should be fully paid attention to in the reliability design of the entire vehicle electrical system. In order to improve the reliability of the terminal and connector design, the failure mode should be analyzed first, so as to do the corresponding preventive work. Terminals and connectors usually have three main failure modes: poor contact, poor insulation and fixed dropout. Among them, for poor contact, static contact resistance, dynamic contact resistance, single-hole separation force, connection points and components can be used Vibration resistance and other indicators can be judged; for poor insulation, the insulation resistance of the insulator, the time degradation rate of the insulator, the dimensions of the insulator, contacts and other parts can be judged; for the reliability of the fixed drop-off type, the terminal and the connector can be detected The assembly tolerance, torque resistance, connecting pin holding force, connecting pin insertion force, holding force under environmental stress conditions and other indicators can be judged. After analyzing the main failure modes and failure modes of the terminals and connectors, the following measures can be taken to improve the reliability of the terminal and connector design:
a) Select the appropriate connector. The choice of connectors not only needs to consider the type and number of connected circuits, but also facilitates the composition of the equipment. For example, circular connectors are less affected by climatic and mechanical factors than rectangular connectors, and have less mechanical wear and reliable termination with wires or cables, so choose circular connectors as much as possible.
b) The greater the number of contacts in the connector, the lower the reliability of the system, so as far as space and weight allow, try to choose a connector with a smaller number of contacts.
c) When selecting a connector, the working conditions of the equipment should be considered. This is because the total load current and the maximum working current of the connector are often determined according to the heat allowed when working under the highest temperature conditions of the surrounding environment. At the same time, in order to reduce the working temperature of the connector, the heat dissipation condition of the connector should be fully considered. For example, the contact farther away from the center of the connector can be used to connect the power supply, which is more conducive to heat dissipation.
d) When the plug-in works in a corrosive gas or liquid environment, in order to prevent corrosion, it should be installed horizontally from the side as much as possible during installation. When the conditions require vertical installation, water should be prevented from flowing into the connector along the lead, Generally use waterproof connectors.
e) The pull-out force of the terminal and the pull-out force of the shield ring need to meet the standard requirements.
f) In the design process of the high-voltage wire harness, the bending radius of the wire harness arrangement needs to be considered. An inappropriate bending radius will cause the cable to pull the terminal and the shield ring for a long time, which is likely to cause the risk of pulling off. In addition, the working environment of the wiring harness on the vehicle is very harsh. The presence of corrosive gases and liquids, humidity, high temperature, vibration, and friction and collision with other components are prone to wear and tear of insulators, loose joints, and corrosion of wires. Open circuit, short circuit. Therefore, in order to make the wiring harness work safely and reliably, the protection design of the circuit should be done well, and the wiring harness should be bandaged and fixed.
The vehicle wiring harness should have anti-corrosion and moisture-proof protection measures, and prevent the vehicle vibration from adversely affecting it; the wire hole must be protected, such as flanging design, to prevent the insulation layer from being damaged by the wiring harness friction when the wiring harness passes through. In order to improve the reliability of protection design, an environmental screening test should be carried out on the packing material before assembly to avoid unqualified products from entering the next link; the design materials should also be designed to accelerate the life of different packaging materials according to the environmental stress in different parts Test to select the one with the best comprehensive performance.
7 Security
Definition of high-voltage wiring harness voltage: DC: 60V
The safety design of the high-voltage wiring harness mainly lies in insulation, voltage protection, overload, and IP-level protection requirements of connectors.
Insulation: refers to the use of non-conductive materials to isolate or wrap up the charged body to protect against electric shock. A strong safety measure; under strong electrical effects, the insulating material may be broken down and lose its insulating properties. Therefore, the insulation selection of electrical circuits and equipment must be matched with the voltage level, and must be adapted to the use environment and operating conditions to ensure the safety of insulation. High-voltage wiring harnesses generally use double insulation and withstand voltage: apply a voltage higher than normal to the insulator of the device under test for a specified period of time. If the insulation between them is good enough, the voltage applied to it Only a small leakage current will be generated. If the leakage current of an insulator of a device under test remains within the specified range within a specified time, it can be determined that the device under test can operate safely under normal operating conditions.
Overload: The amount of current in electrical lines that allows continuous passage without overheating the wires is called safe current carrying capacity or safe current. If the current flowing through the wire exceeds the safe current carrying capacity, the wire is called overload. When overloaded, the temperature exceeds this temperature, which will cause rapid insulation aging and even line burning.
The main reasons for overloading are improper selection of wire cross section, the actual load has exceeded the safe current of the wire; and the current carrying capacity of the terminal is not enough to exceed the maximum current it carries.
IP level protection requirements for connectors: high-voltage connectors and wiring harnesses connected to the powertrain system of HEV/EV are not only the key energy transmission lines for vehicle driving, which affect vehicle functions and performance, but also a key factor affecting safety performance. It will cause the vehicle to break down, catch fire, or even cause electric shock, thus the life of the vehicle user is safe. IP protection design. Tests have shown that high-voltage terminals exposed to humid air are more likely to corrode and are more dangerous. Therefore, if possible, the protection level of all high-voltage plug-ins is required to be above IP67. Of course, it is located in a worse situation such as the chassis or the front cabin. The lower must be higher.
Anti-touch finger function design: the design of the high-voltage system of the whole vehicle needs to ensure that the single-point failure does not affect the operation
For the safety of personnel, even if the plug-in is exposed, it is necessary to ensure that the personnel do not cause harm by bare hands. Therefore, the design of the sheath and the terminal prevents the fingers of the person from directly contacting the terminal.
8 Features of High Voltage Connector
As a key core component of the high-voltage wire harness, the high-voltage connector has the same characteristics as most of the high-voltage wire harness. Among them, the following features are more prominent:
Pressure resistance: meet creepage distance and electrical gap requirements, meet 750V rated voltage requirements;
Security: with high-voltage interlocking function, not matching the plug-in to meet the IPXXB requirements, matching the plug-in to meet the IPXXD protection requirements. The electrical clearance and creepage distance meet the design requirements of pollution levels.
9 Features of High Voltage Wire
The biggest feature of high-voltage wires for vehicles is high voltage resistance. At present, high-voltage wires in the market are at 600V AC/1000V DC high voltage resistance level. As the cruising range increases, higher power output is required, and high-voltage wires with higher voltage levels will be required. The withstand voltage level will reach and exceed the level of 1000V AC/1500V DC. In addition, for the high-voltage wires used in high-voltage high-current modules, due to the requirements of high power, interior space and wiring design, high-voltage wires have the characteristics of high current resistance, high temperature resistance, flame retardancy, high flexibility and EMC anti-shielding performance. Meet the application of new energy vehicle market
10Charging port features
Compared with other high-voltage connectors, the charging port is vulnerable to contact terminals after plugging and unplugging, resulting in increased impedance in the contact area, heat generation, and ablation, etc. Because some are used outdoors, the pollution level is 3, and the actual situation is higher than This pollution level, especially the products at the end of the charging pile, is basically unprotected, so the selection of plastic materials needs to consider the characteristics of high temperature and oil resistance. The protection level must meet IP54 before insertion and IP55 after insertion, and the actual application scenario is higher than this. standard.
From the standard point of view, the charging port needs to meet the requirements of GB/T20234.1, and the fast charging interface and the slow charging interface also need to meet the requirements of GB/T20234.2 and GB/T20234.3, respectively. The charging port must also meet the requirements of the interoperability standard GBT34657.2-2015.
At present, the common problems to be solved in the charging port include: there is no better solution for AC 63A heating and ablation, there is no reference standard for the strength of the charging gun hook, and it is easy to break in actual use.
The rationality of the line design length:
Generally, the length of each part of the wire harness is determined according to the actual position of the electrical appliances on the body of the car, and all the places where the wire harness passes have fixed cable ties or holes to fix the wire harness. Therefore, the reliability of the harness is also greatly affected by the size of each branch on the harness assembly. If the wiring harness is too long, it not only wastes space and materials, but also easily leads to friction caused by contact with other components during vehicle travel, which accelerates the wear of the wiring harness and causes problems such as short circuits. Therefore, the design length of the harness must be slightly more than the actual length, and the generally appropriate slack measure is 0.05-5% according to different environments.
High-voltage wiring harness flexibility:
The high-voltage wire harness basically uses a large square, so there is also a certain requirement for the minimum bending radius of the cable. It is usually 5D of the outer diameter of the cable; the color requirement of the high-voltage wire harness: in order to play a warning role, the high-voltage wire harness must be orange; high-voltage warning signs can also be attached.
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