Design study of high-voltage wiring harness for electric vehicles

2021-05-15 19:05 admin
1. Introduction
 As the main body of the electric vehicle system, the automobile wiring harness is the carrier of electric vehicle power transmission and signal transmission, which is very important for the driving of electric vehicles. Among the automotive wiring harnesses, automotive high-voltage wiring harnesses are the most critical. It is the assembly of cables and their connectors or terminals and other parts into a whole harness. It handles the electrical transmission between the energy and power devices of electric vehicles. Compared with the wiring harness of other electrical equipment in automobiles, the high-voltage wiring harness of cars needs to ensure that electric cars have higher safety and reliability in various harsh environments and various driving conditions. The design principle of an electric vehicle wiring harness is based on the shortest cable length, the smallest number of cables, and the most suitable cable cross-section, and the correct connector is selected to connect and to ensure the regular and safe operation of all lines: automotive electrical appliances, electronic equipment, and switches.
 The design of high-voltage wiring harness for electric vehicles includes wiring harness design, wire diameter design, high-voltage connector selection, electromagnetic shielding design, high-voltage interlocking HVIL design, and high-voltage wiring harness protection and identification design.
 2, the wiring design of the high-voltage wiring harness.
 The standard distribution positions of high-voltage components of electric vehicles are usually divided into high-voltage wiring harnesses centered on high-voltage electrical appliances, which can be divided into charging high-voltage wires, battery high-voltage wires, and motor high-voltage wires—voltage line. The charging high-voltage cable is connected to the charger and the battery unit, the battery high-voltage cable is connected to the controller and the battery unit, and the motor high-voltage cable is connected to the controller and the motor part. The high-voltage line carries a large current, and the diameter of the wire diameter becomes thicker. This is very important for wiring, electromagnetic interference, and shielding wiring. The high-voltage wiring harness is arranged in the narrow space of the car and must have good flexibility. In the high-vibration environment of the vehicle, the high-voltage wiring harness must have good wear resistance, tensile resistance, and tear resistance.
 3 , wire diameter size design.
 The high-voltage wiring harness is the main body of the electric vehicle circuit. Without the wiring harness, there is no car circuit. The high-voltage wiring harness is a high-safety component in electric vehicles and has undergone special treatment carrying capacity, mechanical strength, insulation protection, and electromagnetic compatibility. Generally speaking, it is entirely different from the requirements of traditional automotive wiring harnesses. The withstand voltage and temperature performance of high-voltage wiring harnesses is much higher than that of low-voltage wiring harnesses. The rated high voltage withstand voltage of conventional passenger cars is 600V, and the voltage of commercial vehicles and buses can be as high as 1,000V. According to the current of the high voltage system components, it can reach 250A-400A. High-temperature resistance grades are divided into 125°C, 150°C, 200°C, and cables with -40°C to 125°C are usually selected. Domestic original equipment manufacturers use generally shielded high-voltage lines, which can reduce or avoid the radiation of high-voltage lines, thereby reducing the impact of EMI and RFI on the entire vehicle system. So, the size of the wire diameter needs to consider the following aspects: the rated current of the load circuit; the allowable temperature of the cable conductor; the ambient temperature when the wire harness is working; when the wire itself is energized, the resistivity change caused by the temperature rise; the bundled wire harness The allowable current-carrying capacity reduction factor, etc.
4. Types and applications of high voltage connectors
(1) Features and applications of high-voltage connectors
High-voltage connectors are used in various modules, such as high-voltage distribution boxes, power batteries, maintenance switches, DC/DC interfaces, air conditioners, power motors, instrumentation and monitoring systems, as well as lighting and audio. Features of high-voltage connectors: 1) Mistake-proof structure (many fool-proof vital positions can be selected) and viewing angle (different colors); 2) Fast and reliable connection; 3) High-voltage interlock and secondary locking design, excellent anti-vibration performance 4) Choose straight/elbow according to the space and wiring of the car; 5) The design of the contact pin can prevent electric shock caused by accidental operation; 6) According to the shielding function, it is divided into unshielded connectors and shielded connectors. The unshielded connector has a simple structure, no shielding function, and low cost. Use in places that do not must shieldings, such as the charging circuit, the inside of the battery pack, the inside of the controller, and other electrical appliances covered by metal casings. The shielded connector has a complex structure, has shielding requirements, and has a high cost. It is suitable for places with shielding function, such as the connection between the exterior of electrical appliances and high-voltage wiring harness. 7) Connection methods include push-pull type, bayonet type, straight-in type, threaded type, etc.; 8) Connection methods include crimping, tail hole, connecting copper bar, thread, etc. The crimping method is suitable for molds of corresponding specifications. The external force connects the connector terminal and the cable contact surface together, which is fast, stable, and reliable and has a long service life. Suitable for batch processing. At present, electric vehicle wiring harness cables and connector terminals are usually connected by crimping.
(2) Function and application of maintenance switch
When the high-voltage system of the electric vehicle needs to be inspected and repaired, the maintenance switch is turned off to disconnect the high-voltage main power supply, thereby ensuring the safety of the operators. So, maintenance switches are essential in high-voltage systems. There are two types of maintenance switches: with fuse and without fuse. The fuse switch has a complicated structure, a simple structure, a large volume, and a high cost. It is usually used in high-current and high-voltage systems, such as high-voltage battery packs. The switch without fuse has a small structure and low cost and is suitable for arranging positions in cars with limited space.
5. Shielding and EMC interference design
Because electric vehicles have high-voltage AC systems, they have large electromagnetic interference. At the same time, electromagnetic waves of different frequency bands emitted by high-voltage components such as motors and controllers can also interfere with vehicle audio, reversing images, and transmission sensors. Thus, all interfaces of each high-voltage wiring harness should be shielded. Shielding needs to consider the rationality of the layout at the system level. For example, when wiring at the system level, you need to pay attention to high and low voltage isolation, wiring specifications, interference sources should be far away from signal sources, and power lines and signal lines should be isolated or wired as much as possible. . The more, the better. Avoid grouping the input and output signal lines together to avoid interference. We also need to consider the reliable grounding of the shielding layer, for example, connecting the equipment terminal through a grounding electrode and anticorrosive treatment of the grounding component to reduce the risk of shielding layer failure. If there is a protective layer on the surface of the device, we even need to add a protected protective box to achieve a reliable shielded continuity connection. The shielding and full shielding of the signal control core is a tinned copper wire braided shielding structure, and the braiding density is not less than 80% [2]. The signal control core shielding layer can shield external electromagnetic waves on the signal transmission of the monitoring core signal and avoid misoperation during work. When the cable is working, the total shielding layer of the line is used as a grounding wire, which can inhibit the charging of electric vehicles. The impact of excessive current on the power grid can also shield the main body of the cable to prevent it from emitting electromagnetic waves and reduce the interference to low-current communication equipment inside and outside the electric vehicle.
6, high-voltage interlock HVIL design
To ensure the reliability of the high-voltage circuit connection, the design of the high-voltage circuit interlock function is proposed. Hazardous voltage interlock circuits, also known as high voltage interlock circuits (HVIL), are a typical interlock system that uses electrical signals to check the electrical integrity of the entire module, wires, and connectors. The high-voltage components are equipped with a high-voltage interlocking humanized safety design, which runs through all the high-voltage parts of the entire vehicle. Before disassembling the high-voltage components, the high-voltage interlock structure must be disconnected to perform the operation and control and feedback through the BMS.
7. Protection and identification design for high-voltage components and high-voltage wiring harnesses
The protection of high-voltage components includes waterproof, mechanical protection, and high-voltage warning signs. The high-voltage wiring harness system must meet the layout and ergonomic requirements of the vehicle. For high-voltage wiring harnesses located in the engine compartment and chassis, special attention should be paid to protecting the wiring harnesses. The high-voltage wiring harness arranged in the chassis components should consider the heavy rain of the vehicle, wading, and chassis scratches. , the wire harness itself is fixed by heat-shrinkable tubes, corrugated tubes, and various sleeves. The wiring harness can be set to the vehicle. Plastic trunking, different suspension clamps, or metal elbows are used to fix high-voltage wiring harnesses. To remind and warn users and maintenance personnel, the high-voltage wiring harness should be protected by orange cables and orange corrugated pipes. The high-voltage connector should also be marked in orange as a warning, and the protection level of the selected high-voltage connector should be at least IP67.
8. Concluding remarks
The development of the new energy automobile industry is an essential breakthrough in the strategic transformation and upgrading of my country's automobile industry. The green and low-carbon development trend characterized by new energy has been launched. High-voltage wiring harnesses are used for the connection and integration of various components of electric vehicles. It is the main body of the electric vehicle circuit network, which provides a strong guarantee for the comfort, economy, and safety of the car's internal network. At the same time, with the modularization, integration, and mass production of vehicles, the many high-voltage wiring harnesses of the vehicle will be optimized and reduced in the form of customized wiring harness fixing parts is convenient for management and maintenance. It is more effective to realize the cost calculation of standardization and lightweight. The price-performance ratio is further developed.