With the rapid popularization of electric vehicle, the design and layout of high-voltage wiring harness, as the "lifeblood" of vehicle power transmission, has become increasingly important.
Unlike the low-voltage system of traditional fuel vehicles, the high-voltage wiring harness carries hundreds of volts, which is directly related to the safety, reliability and electromagnetic compatibility of the vehicle.
Whether it is endurance performance, charging efficiency or driving experience, high-voltage wiring harness plays a vital role in it. However, this system hidden inside the car body is often ignored by consumers, only when there are faults or potential safety hazards, it will cause widespread concern.
This paper will systematically analyze the technical points of this "invisible guardian" from the classification of high-voltage wiring harness, layout requirements to electromagnetic compatibility design, and help engineers and industry enthusiasts to better understand the design logic of high-voltage wiring harness and the scientific principles behind it.
1 Classification of high voltage harness
EV high voltage wiring harness is generally divided into power battery high voltage wiring harness, motor controller high voltage wiring harness, fast charging socket wiring harness, slow charging socket wiring harness, air conditioning system wiring harness and charging high voltage wiring harness, wherein the charging high voltage wiring harness refers to the wiring harness connecting the high voltage distribution box to the on-board charger, air conditioning compressor and power battery pack heater.
Generally speaking, there are three categories:
1.1 Charging harness
- Fast charging harness: The fast charging harness is specially connected to the fast charging port and the high-voltage battery, and its mission is to realize the rapid replenishment of electric energy.
- Slow charging harness: The slow charging harness is used to connect the AC charging port and the high-voltage battery. It plays an important role in home charging piles or some low-power AC charging scenarios.
1.2 Power harness
The power harness connects the battery and the motor, which can be called the "highway" for the power output of new energy vehicles. The motor controller cable is an important part of the power harness, which connects the high-voltage box and the motor controller. The motor controller is responsible for adjusting the speed and torque of the motor, while the motor controller cable is responsible for transmitting the high-voltage electricity of the battery to the motor controller, and then the motor controller distributes it to the motor.
1.3 High-voltage accessory harness
The high voltage accessory harness is mainly used to connect the high voltage distribution box and other high voltage components. For example, provide high voltage for the air conditioning compressor, so that the air conditioning system can cool or heat normally, bring cool to the car in hot summer, and create a warm environment in cold winter; Power accessories such as PTC heaters (positive temperature coefficient thermistor heaters) for functions such as window defrosting, seat heating, etc.
2 Layout requirements for high voltage harness
2.1 General arrangement requirements of high-voltage wiring harness
The voltage of the high voltage system in the hybrid electric vehicle is hundreds of volts, and the unreasonable arrangement may cause fire or endanger the safety of passengers. The arrangement of high voltage components not only meets the requirements of safety collision regulations, ergonomics and convenience of maintenance, but also needs to formulate effective protective measures for high voltage.
The following points shall be considered during wiring:
- The arrangement of high voltage components shall reserve enough buffer space for the capacity source and the relevant components on its transmission path, increase the distance between the high voltage components and the vehicle body as far as possible, and ensure that the minimum dimension of any non-external high voltage component and the outline of the vehicle shall be kept above 110mm.
- Avoid crossing and winding between high voltage harnesses. The positive and negative high-voltage harnesses shall be routed in the same path to avoid or shorten the bifurcation distance as far as possible;
- The clearance between adjacent parts shall be ≥ 15mm, and the dynamic clearance shall be ≤ 25mm;
- Due to the material and diameter of the high-voltage line, the front and rear ends of the bending part shall be provided with fixing points to avoid large deviation between the actual trend and the design trend;
- The impact of vehicle scraping and sand splashing on the high-voltage wiring harness shall be fully considered;
- The high voltage harness shall be prevented from crossing the sharp edges. If it cannot be avoided, corresponding protective devices shall be added to the sharp edges such as vias.
- The turning radius of the harness shall be ≥ 6D (D is the diameter of the high-voltage harness);
- Ambient temperature shall be lower than 125 ℃;
- The clearance between two adjacent fixed points shall meet the following requirements:
- The sectional area of high-voltage harness shall be more than 16mm2, and the clearance between two fixed points shall be ≤ 300mm;
- The sectional area of high-voltage harness is less than 16mm2, and the clearance between two fixed points is ≤ 200mm;
2.2 General requirements for EMC of high-voltage wiring harness
When designing the wiring harness, in order to improve the electromagnetic compatibility of the whole vehicle, it is generally recommended to follow the following principles:
- It is recommended to keep the interference source and its connecting harness away from the components prone to interference and its connecting harness, and arrange them separately as far as possible. It is recommended that the distance between the connecting harness of the interference source and the connecting harness of the components susceptible to interference shall not be less than 10 cm.
- When the connecting harness of the interference source cannot be far away from the connecting harness of the components susceptible to interference, it is recommended to arrange the two (geometric shapes) vertically and crosswise as far as possible.
- When arranging the harness, the harness shall be arranged in the included angle and groove of the metal body as far as possible, or arranged close to the metal body.
- It is recommended not to hang the harness far away from the metal body. It is recommended that the distance between the harness and the metal structure of the body should not exceed 10 cm. In principle, the closer the better.
- Equipment that do not affect each other can be arranged together.
- Non-sensitive components with strong anti-interference capability and very small electromagnetic interference generated to the outside can be arranged between the components prone to interference and the interference source to form a decoupling barrier and reduce crosstalk between the interference source and the components prone to interference. Non-sensitive parts shall be evaluated and confirmed by the EMC engineer.
- In order to reduce the influence caused by electromagnetic radiation coupling, the area of the current loop of the interference source and the components susceptible to interference and the length of the wiring harness shall be reduced as much as possible. This is also the most basic principle to reduce electromagnetic radiation coupling in the design of vehicle wiring harness.
- The length of the harness should be just connected to the connector of the component. The harness should not be too long and should be coiled into a circle.
2.3 EMC layout influence and requirements of high-current wiring harness
- The wire with large current will form a strong magnetic field around it, so it is not recommended to use the vehicle body as the current loop of the large current component. In the case of using the vehicle body as the current circuit, it is recommended that the positive wire of the power supply should be arranged as close as possible to the vehicle body to reduce the area of the current circuit.
- The distance between the load and the power supply of the high-current circuit should be as short as possible, and the high-current harness should be arranged close to the body metal plate, so as to reduce the area of the circuit and reduce the external radiation of the magnetic field.
- It is recommended to arrange the high-current harness separately, and avoid arranging the high-current harness near the easily interfered parts and their harnesses as far as possible. It is recommended that the distance between the large current harness and the components susceptible to interference and its harness should not be less than 10 cm, so as to prevent the magnetic field generated by the large current harness from affecting the components susceptible to interference.
- The positive line and negative line of the power supply of the large current circuit shall be arranged in parallel.
- It is not recommended to arrange the large current loop near the RF related components (such as antenna, wireless sensor, radio/amplifier, etc.). If it is close to the RF components (above, below and behind them), it is recommended that the positive and negative wires of the power supply of the high-current circuit be laid in parallel.
From the aspects of physical layout space, heat hazard protection, collision safety protection, electromagnetic shielding and high voltage safety, the matters needing attention in the layout of high voltage wiring harness and its basic layout principles are summarized. The layout principle described in this paper comes from the design experience, which needs to be verified, adjusted and optimized in the future work.
The design and layout of high-voltage wiring harness is not a simple "wiring" task, but a complex system engineering that integrates electrical engineering, materials science, mechanical structure design and electromagnetic compatibility technology.
From avoiding cross winding, controlling the distance between fixed points, to calculating the turning radius and shielding interference, every detail directly affects the high-voltage safety and performance stability of the whole vehicle.
Especially in the context of rapid iteration of electric vehicle technology, high-voltage wiring harness also needs to constantly adapt to higher voltage platforms, lighter materials and more compact layout space.
In the future, with the development of automatic driving and ultra-fast charging technology, the intellectualization and integration of high-voltage wiring harness will become new challenges and opportunities. Only by adhering to safety as the cornerstone and innovation as the driving force, can we move forward steadily in the wave of technology and truly make high-voltage wiring harness an indispensable "golden rule" in the development of electric vehicle.