High-voltage wiring harness design for new energy vehicles

With the rapid development of new energy vehicle technology, in order to actively respond to the national policy of promoting the use of green new energy vehicles, various OEMs have launched a series of new energy vehicle products in recent years, including pure electric vehicles, hybrid vehicles, hydrogen fuel vehicles, etc. The technology of new energy vehicles is also gradually improving, and it is a general trend for electricity to replace traditional fuels as the power source of automobiles. High-voltage wire harnesses are the main connection and transmission system for the power supply of the whole vehicle and the realization of vehicle functions. Due to the high voltage of new energy vehicles, the design of high-voltage wire harnesses faces challenges in design schemes, layout trends, etc.

1. High voltage wiring harness design

1. Double-track design of wiring harness

The high-voltage wiring harness design of new energy vehicles adopts a dual-track design. Since the output voltage of the power battery is high voltage, which exceeds the safety voltage of the human body, the body cannot be used as the grounding point of the high-voltage wiring harness. In the high-voltage wiring harness system, the DC high-voltage circuit must be strictly designed according to the dual-track system. Commonly used high-voltage wiring harnesses can be divided into drive system high-voltage wires, power battery high-voltage wires, charging seat high-voltage wires, air-conditioning compressor high-voltage wires, steering oil pump high-voltage wire harnesses, etc.

2. High-voltage connector selection and design

High-voltage connectors are mainly responsible for the connection and transmission of high voltage and high current, and are important components for ensuring human safety on the vehicle. Therefore, when selecting high-voltage connectors, it is necessary to fully consider functions such as high voltage resistance, protection level, loop interlocking, and shielding. At present, when selecting high-voltage connectors, the industry's more advanced, mature, and reliable suppliers are used first, such as: AVIC Optronics, Tyco, Yonggui, Amphenol, and Record, etc.

3. High-voltage wiring harness shielding design

High-voltage wiring harnesses will generate strong electromagnetic interference when transmitting changing high-voltage electricity, so wires with braided shielding mesh are required. When selecting connectors, try to use shielding designs, which can achieve a closed loop connection with the shielding layer of the high-voltage wiring harness during crimping, thereby suppressing the electromagnetic interference generated by the high-voltage wiring harness.

High voltage wiring harness cross-section

2. High-voltage wiring harness layout design

1. Principles of high voltage wiring harness layout

Principle of nearby layout: When arranging the high-voltage wiring harness of new energy vehicles, the path of the high-voltage wiring harness should be shortened as much as possible. This can not only avoid the voltage drop caused by the long path, but also conform to the design of cost reduction and weight reduction.

Safety principle layout: In addition to meeting the principle of proximity, the layout of high-voltage wiring harnesses must also meet the principles of concealment, safety collision regulations, and maintenance convenience. At the same time, the high-voltage wiring harnesses also need to be effectively protected. The unreasonable layout of high-voltage wiring harnesses may cause leakage, fire, and endanger the safety of drivers and passengers.

2. High-voltage wiring harness layout type

The layout types of high-voltage wiring harnesses are currently generally divided into two types: layered layout and parallel layout. Both methods are based on separating the high-voltage wiring harness from the low-voltage wiring harness to reduce the electromagnetic interference of high voltage on low-voltage communication.

(1) Layered layout design

As the name implies, layered layout means that the high-voltage wiring harness and the low-voltage wiring harness are arranged at a certain distance, so as to avoid the electromagnetic interference generated by the high voltage on the power supply and signal transmission of the low-voltage control unit. The design diagram of the layered layout of high and low voltage wiring harnesses is as follows:

(2) Parallel layout design

Parallel arrangement means that the wiring harnesses have the same direction but are arranged in parallel by attaching to the frame or body. The parallel arrangement ensures that the high and low voltage wiring harnesses are parallel and do not cross. The following figure shows the parallel design layout, with the high voltage wiring harness arranged on the left frame and the low voltage wiring harness arranged on the right frame:

Due to the differences in vehicle structure, layout of electrical components and limitations of layout space, the above two layout forms will be reflected in the daily wiring harness layout design of new energy vehicles, and different layout forms will be combined to minimize or avoid the interference of high voltage on low voltage wiring harness communication.

3. Design of safe layout principles for high-voltage wiring harnesses

On the basis of the above two high-voltage wiring harness arrangements, we should also consider the safety and maintainability of the high-voltage wiring harness arrangements.

(1) Design of vibration avoidance area

When arranging and fixing high-voltage wire harnesses, they should avoid areas with severe vibration (such as vibration sources such as air compressors and water pumps), and the high-voltage wire harnesses should be connected to the high-voltage equipment without relative vibration. When it is impossible to avoid due to factors such as structural layout, sufficient margin of high-voltage wires should be left according to parameters such as the vibration amplitude of the wiring harness layout and the maximum motion envelope of the moving parts to avoid the wiring harness being subjected to pulling or tension.

When a vehicle is driving on bumpy roads for a long time, it is easy for the fixing points of the high-voltage wiring harness to move or fall off, which will cause the distance between the two fixing points to increase instantly. Pulling the wiring harness will cause the internal nodes to be pulled off or poorly connected, resulting in a short circuit. Therefore, the length of the high-voltage wire should be controlled reasonably. There should be enough length to offset the stress caused by movement and drag, but it should also avoid being too long to cause the wiring harness to twist.

(2) Design to avoid high temperature areas

When arranging the wiring harness, avoid high-temperature components on the vehicle to avoid high temperatures that may cause the wires to melt or accelerate aging, resulting in the risk of the core wires being exposed and short-circuited with the frame. Common high-temperature components of new energy vehicles include: air compressors, brake air pipes, steering oil pumps, oil pipes, etc.

(3) Design of high-voltage conductor bending radius

Whether it is to avoid squeezing or to avoid areas with excessive vibration amplitude, you need to pay attention to the bending radius of the high-voltage harness when arranging it. This is because the bending radius of the high-voltage harness has a great influence on the resistance of the high-voltage harness. If the high-voltage harness is excessively bent, the resistance of the bent part of the harness will increase, which will cause the line voltage drop to increase; at the same time, excessive bending for a long time will also cause the harness insulation rubber to age and crack; as shown in the following figure, the wrong design diagram (Note: Generally, the minimum inner bending radius of the high-voltage wire should not be less than four times the outer diameter of the wire):

Example of correct joint arrangement (left) Example of incorrect joint arrangement (right)

Therefore, we need to avoid excessive bending of the wires in the connector both in the early design and in the assembly process, otherwise leakage paths may occur in the seal at the rear of the connector. The high-voltage wire harness at the tail of the high-voltage connector must be kept straight, and the high-voltage wires near the tail of the connector must not be bent or rotated.

4. High-voltage line sealing and waterproof design

In order to improve the mechanical protection and dust and water resistance of the high-voltage wiring harness, sealing rings and other protective measures are used between the plugged connectors and at the location where the connectors connect to the cables to prevent the entry of water vapor and dust, thereby ensuring a sealed environment for the connectors and avoiding safety issues such as short circuits between contacts, sparks, and leakage.

At present, most high-voltage wire harnesses are protected by coverings. The main functions of the coverings are wear resistance, noise reduction, radiation heat isolation, and aesthetics. Generally, orange high-temperature resistant flame-retardant corrugated tubes or orange high-temperature resistant flame-retardant cloth-based sleeves are used to completely cover them. As shown in the following figure:

3. Sealing measures

The high-voltage wires and high-voltage connectors are sealed using wire seals, heat shrink tubing, rubber parts and other methods to meet the IP67 level of waterproof and dustproof requirements.

Examples of various types of seals and precautions:

Heat shrink tubing with adhesive for sealing protection (left) Plug-in with blind plug for sealing protection (right)

The tail of the connector is sealed with a rubber sleeve for protection (left) and the wiring harness is arranged in a U-shaped manner for prevention (right)