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New energy vehicles generally work in the voltage range of B level, so it is required that the high-voltage Wiring Harness also needs to meet the working voltage range requirements of 60V Kramp-Karrenbauer 1500. At present, the common wire harness voltage requirements are AC30V Kramp-Karrenbauer Dimensity 1000 or AC30V-1000V according to the provisions of GB/184384.3 for B level voltage.
As the main energy transmission channel, the new energy high-voltage cable bundle of automobile needs to bear a large current, and the rated working current of DC bus can reach 300A yuan A or above.
Due to the characteristics of high voltage and high current of high-voltage wiring loom, there are also high requirements for the tightness of cable harness. Generally, waterproof and dustproof tests and airtight tests are required. If the sealing is not good, it will cause moisture or water ingress, which will lead to rapid aging or damage of wires and connecting parts. If the sealing performance of the Connector is poor, the insulation resistance will be reduced, and the whole vehicle will report insulation failure.
Because the high-voltage Wire Harness passes through a large current for a long time, it generates a lot of heat. Therefore, the wire temperature resistance of the high-voltage wire harness generally reaches 125℃ (150 yuan℃), and the terminal temperature resistance generally reaches 140 yuan℃.
EMC (Electromagnetic Compatibility) refers to the ability of equipment or system to operate in accordance with the requirements in its electromagnetic environment without causing intolerable electromagnetic interference to any equipment in its environment. Simply put, EMC includes EMI (Electromagnetic Interference) and EMS (Electromagnetic Susceptibility). EMI refers to the electromagnetic interference caused by equipment to its environment during normal operation; EMS refers to a certain degree of immunity of appliances to electromagnetic interference in their environment. EMI is active, that is, it interferes with the outside world, while EMS is passive, that is, it resists the outside interference. Therefore, the EMC requirement for the equipment is to reduce the interference to others, and at the same time, it can resist a considerable degree of external interference.
The electromagnetic compatibility of parts is the foundation and premise of the whole vehicle electromagnetic compatibility. The parts used in new energy vehicles should not only meet the requirements of the electromagnetic compatibility of parts, but also the parts suppliers are obliged to support and carry out relevant rectification when the electromagnetic compatibility of the whole vehicle occurs. Theory and practice have proved that the occurrence of any electromagnetic disturbance must have 3 conditions: the source of disturbance, the way of spreading disturbance and sensitive equipment. Parts of new energy vehicles should be optimized as much as possible from two aspects: first, try to reduce the intensity of harassment; The second is to improve the ability to resist harassment as much as possible.
Within the scope of the whole vehicle, firstly, ensure that the EMC of parts meets the standard requirements, and connect all control units together through wiring harnesses. The emphasis of shielding design of new energy vehicle should be the layout of high-voltage system, shielding design and anti-interference treatment of CAN communication network. First of all, the high-voltage wiring harness should be arranged along the vehicle body as far as possible to optimize the electromagnetic radiation loop of the whole vehicle, and at the same time, the vehicle body should be used to form a closed shielded cabin. At the same time, shielding high-voltage cables and connectors is also an economical and effective method to reduce unnecessary electromagnetic interference. A series of standard experiments conducted by us Kable-X show that shielding cables and connectors can effectively reduce unnecessary interference in the frequency range from KHz in 100 to MHz in 200 . At present, all domestic models use shielded high-voltage lines, and Japanese cars also use shielded nets to cover the outside of high-voltage lines, and the plug-in parts are processed to realize shielded connection. In order to avoid the risk of electromagnetic interference caused by the transmission of strong current by the high-voltage harness, which leads to the power supply of the low-voltage harness to the control unit and the electromagnetic interference of signal transmission, the high-voltage harness and the low-voltage harness are generally designed in layers, and the distance is guaranteed to be within mm of 300 yuan, Kramp-Karrenbauer, 200 yuan.
The following is the introduction of several common cables to EMC solutions.
The experimental results show that the shielding effect of the combination of aluminum tube and woven mesh segments is the best in the GHz frequency range of 0, Kramp-Karrenbauer.
The power supply and various electrical parts of the new energy vehicle are physically connected with each other through wiring harnesses, which are distributed all over the vehicle. If the power system is compared to the heart of an automobile, then the wiring harness is the neural network system of the automobile, which is responsible for the information transmission among the electrical parts of the whole vehicle. With the continuous improvement of people's requirements for comfort, economy and safety, the types of electronic products on automobiles are also increasing, and the failure rate of increasingly complex wiring harnesses in automotive wiring harness is also increasing correspondingly. This requires improving the reliability and durability of the wire harness. Terminal connector is an important part to determine the reliability of the system, and it is also an important part of the whole wiring harness. Due to the harsh working environment of some terminals and connectors, all kinds of faults are easy to occur in terminals and connectors, such as corrosion, aging and loosening under the action of vibration. Electrical circuit failures caused by the damage, loosening, shedding and failure of terminals and connectors account for more than 8% of the failures of the whole electrical system, so the reliability design of terminals and connectors should be fully emphasized in the reliability design of the electrical system of the whole vehicle. In order to improve the reliability of terminal and connector design, the failure modes should be analyzed first, so as to do the corresponding preventive work. And terminal connectors usually have three main failure modes: poor contact, poor insulation and fixed falling off. Among them, for poor contact, static contact resistance, dynamic contact resistance, single hole separation force, vibration resistance of connecting points and components can be used to judge. For poor insulation, the insulation resistance of insulators, time degradation speed of insulators, dimensions of insulators, contacts and other parts can be detected to judge. For the reliability of the fixed-off type, it can be judged by testing the assembly tolerance, torque resistance, retention force of connecting pin, insertion force of connecting pin, retention force under environmental stress and other indicators of terminals and connectors. After analyzing the main failure modes and failure forms of terminals and connectors, the following measures can be taken to improve the reliability of terminal and connector design:
A) Select the appropriate connector. The selection of connectors should not only consider the type and quantity of connecting circuits, but also be beneficial to the composition of equipment. For example, the circular connector is less affected by climate and mechanical factors than the rectangular connector, and has less mechanical wear, so it can be reliably terminated with wires or cables. Therefore, the circular connector should be selected as much as possible.
B) The more the number of contacts in the connector, the lower the reliability of the system. Therefore, if space and weight permit, try to choose the connector with fewer contacts.
C) When selecting connectors, 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 allowable heat when working at the highest temperature of the surrounding environment. At the same time, in order to reduce the working temperature of the connector, the heat dissipation conditions of the connector should be fully considered. For example, the contact piece far 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 is working in corrosive gas and liquid environment, in order to prevent corrosion, attention should be paid to horizontal installation from the side as much as possible during installation. When conditions require vertical installation, water should be prevented from flowing into the connector along the lead, and waterproof connectors are generally used.
F) Terminal pull-off force and shield ring pull-off force need to meet the standard requirements.
G) In the design process of high-voltage wiring harness, it is necessary to consider the bending radius of wiring harness layout. Inappropriate bending radius will cause the cable to pull on the terminal and shielding ring for a long time, which will easily lead to the risk of pulling off. In addition, the working environment of the wiring harness on the vehicle is very bad. The existence of corrosive gas and liquid, humidity, high temperature, vibration, friction and collision with other parts are easy to cause insulator wear, loose joints, wire corrosion and other phenomena, which will lead to open circuit and short circuit. Therefore, in order to make the wiring harness work safely and reliably, we should do a good job in the protection design of the wiring, that is, we should do a good job in binding and fixing the wiring harness.
The wiring harness of the whole vehicle should be protected against corrosion and moisture, and the adverse effects of vehicle vibration should be prevented; The wire hole must be protected, such as flanging design, to prevent the insulation layer from being damaged due to the friction of the wire harness when it passes through. In order to improve the reliability of protection design, environmental screening test should be carried out on wrapping materials before assembly, so as to prevent unqualified products from entering the next link; The accelerated life test of different packaging materials should also be carried out according to the environmental stress of different parts during the design and selection, so as to select the one with the best comprehensive performance.
Definition of high voltage harness voltage: AC:30V
The safety design of high-voltage wiring harness mainly lies in insulation, voltage protection, overload, IP protection requirements of connectors, etc.
Insulation: refers to a safety measure that uses nonconductive substances to isolate or wrap the charged body to protect against electric shock; Under the action of strong electricity, the insulating material may be broken down and lose its insulating property. Therefore, the insulation selection of electrical lines and equipment must be compatible with the voltage level, and it must be compatible with the use environment and operating conditions to ensure the safety of insulation. Generally, high-voltage wire harnesses are double insulated and withstand voltage: apply a voltage higher than the normal working voltage to the insulator of the tested equipment for a specified period of time. If the insulation between them is good enough, the voltage applied to it will only produce a small leakage current. If the insulator of a tested device keeps its leakage current within the specified range within the specified time, it can be determined that the tested device can operate safely under normal operating conditions.
Overload: The amount of current in an electrical line that is allowed to pass continuously without overheating the wire is called safe current carrying capacity or safe current. If the current flowing through the wire exceeds the safe current carrying capacity, it is called wire overload. When the temperature exceeds this temperature, the insulation will age rapidly and even the line will burn.
The main causes of overload are improper selection of conductor section, and the actual load has exceeded the safe current of conductor. And the current carrying capacity of the terminal is not enough, which has exceeded the maximum current it carries.
IP protection requirements of connectors: High-voltage connectors, together with wiring harnesses, are connected to the power train system of HEV/EV, which is not only the key energy transmission line for driving the vehicle, but also a key factor affecting the safety performance, which will cause the vehicle to break down, catch fire, and even generate electric shock, thus the life safety of vehicle users. Tests have proved that high-voltage terminals exposed to humid air are more prone to corrosion and more dangerous. Therefore, if possible, the protection level of all high-voltage plug-ins should be above IP67. Of course, it must be higher in worse situations such as chassis or front cabin.
Anti-finger touch function design: the design of the high-voltage system of the whole vehicle should ensure that the operation will not be affected in the case of single-point failure.
As the key core component of the high-voltage wiring harness, the high-voltage connector has the same characteristics as that of the high-voltage wiring harness, among which the following characteristics are prominent:
Withstand voltage: meet the requirements of creepage distance and electrical clearance, and meet the rated voltage requirements of 750V;
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