Traditional fuel vehicles, the power source is to burn fuel through the engine piston movement, rely on the crankshaft and gear train to transmit the power equipment such as engine flywheel, generator, compressor and cooling water pump, and realize the operation of the vehicle and function through the power transmission device. The new energy vehicles, especially pure electric vehicles, are provided by high-voltage battery packs, and the transmission carrier is high-voltage wiring harnesses, connecting charging port holders, high-voltage battery packs, inverters, motors, on-board chargers and other high-power equipment and DC converters, low-power equipment such as air conditioning compressors, PTCs and heaters.

1、  Design of high voltage wiring harnesses

1.1 Composition of high voltage wiring harnesses

High voltage wiring harnesses mainly include: high voltage connectors, high-voltage cables, grounding terminals and cable ties, covering materials, tapes, heat shrinkable sleeves, rubber sleeves, mounting brackets and other auxiliary materials.

1.2 High voltage connectors

According to the function definition, it can be divided into two types: small current and large current, the high current is mainly used in power systems such as OBC, motors and batteries, and the small current is mainly used in compressors, PTCs, battery heating devices and DCDC and other functional appliances.

1.3 High voltage cables

High voltage cables are mainly divided into shielded wires and unshielded wires, with wire diameters ranging from 2.5mm²~120mm².

1.4  Accessories for auxiliary materials

The auxiliary material accessories are not much different from those used in traditional low-voltage wiring harnesses, but the outer material needs to be covered with an orange covering to serve as a high-voltage hazard warning.

2、  Technical requirements for high voltage wiring harnesses

2.1 Technical requirements for the cable

(1) Structure

The high voltage cable is mainly composed of wire core and insulating materials, and the shielded wire also has a shielding layer and a double-layer insulation structure.

(2) Insulating materials

Insulation materials mainly include core insulation and sheath insulation. The selection of core material is mainly based on the requirements of temperature resistance, mechanical strength and softness, and the sheath material is selected according to the requirements of temperature resistance and mechanical properties. Due to the direct contact with the environment, the environmental properties of sheath insulation, such as liquid resistance and wear resistance, are particularly important to the sheath requirements, and currently there are mainly cross-linked polyethylene and silicone rubber as the basic materials of the insulation layer.

(3) Shield

The shielding is required by EMC (electromagnetic compatibility) and uses multiple copper wires to form a braided shield. Tinned copper wire can make it more resistant to environmental influences such as oxidation. The design can be kept flexible with thin copper wire, and the braided shield can be combined with various other shields, such as aluminum foil. The shield can be wrapped around a layer of non-woven fabric to ensure easy peeling of the sheath during assembly.

(4) Bend radius

Due to the limitation of space, the path through which the cable passes is very narrow and complex, and the cross-sectional area is larger than that of ordinary wire harnesses, resulting in a large bending radius and a high bending force that is difficult to overcome. In order to solve this problem, the high flexibility of the high voltage cable is crucial, usually 5~10 times of the recommended outer diameter of the SR conductor of the cable.

2.2 Precautions for high voltage wiring harness wiring

(1) When the high-voltage cable passes through the sharp edge or through the hole, the protective structure should be designed;

(2) Avoid heat sources or keep sufficient distance from them when arranging;

(3) Avoid large elastic friction between cables;

(4) Generally, the distance between the fixed points of the cable arranged in a straight line is ≤ 300mm, and the distance between the fixed points and the connector is ≤ 120mm;

(5) The motor wiring harness should consider the influence of the movement of the components and the impact on the connector or terminal, and reserve sufficient movement;

(6) Electromagnetic interference should be considered in the wiring harness layout, 90° broken lines should be avoided when wiring, and high and low voltage lines should be arranged separately;

(7) The high voltage wiring harness arrangement should have a suitable space for installation and maintenance;

(8) The aesthetics of the wiring needs to be considered, and the bare chassis hanging wire needs to be considered to increase the wiring harness slot;

(9) The tail of the connector should be kept straight to avoid the failure of the connector seal caused by bending;

2.3 High voltage wiring harness shielding requirements

(1) For high voltage systems, shielding should give priority to the rationality of the layout at the system level, such as the separation of high and low voltages, the specification of wiring, and the distance between interference sources and signal sources. At the same time, it is also necessary to pay attention to the distance between the power source and the output of the high voltage wiring harness, such as the motor and the motor controller on the whole vehicle, if the arrangement is far apart, then the risk of common mode current transmission interference through the cable will be formed;

(2) For the connector itself to have a 360° shielding layer, it must be effectively connected with the cable shielding layer, the shielding layer covers the entire connection length, in order to ensure sufficient shielding function, and minimize the resistance between the shielding interfaces, in the product life cycle, the contact resistance of the shielding connection < 10mΩ, with more and more vehicle electrical equipment, now the general value is to < 5mΩ;

(3) In addition, it is also necessary to consider the reliable grounding of the shield, if the equipment end is connected through the nut, we need anti-corrosion treatment, because if the treatment is not done, it will lead to the increased risk of shielding, as well as the effective shielding connection between the cable or connector and the equipment end, if the surface of the equipment end does not have a surface treatment protective layer, we even need to increase the shielding protection box and other ways to achieve reliable shielding continuity connection;

2.4 Selection of high voltage connectors

The selection of high-voltage connectors mainly considers the electrical principle, use requirements, wiring harness layout, assembly space and assembly method, and also combines the cost for comprehensive consideration. For integrated solutions, through-hole connectors can be considered, mainly considering factors such as cost and concerns about the tripping risk of PCB connectors in the case of vibration. For batteries, motors, etc., which need to be assembled at the vehicle factory, they are usually plug-in connectors; For parts with relatively harsh environmental requirements, high ambient temperature, and large current and instantaneous current, the temperature rise and waterproof level requirements can be considered.

3、  Future development and trend of high voltage wiring harness

3.1 With the modularization and integration of the whole vehicle, the wiring harness will gradually be standardized, and the existence of multiple wiring harnesses with a part number is convenient for management and cost calculation.

3.2 Lightweight trend In order to reduce fuel consumption, a large number of wiring harnesses on the vehicle have become the key goal of enterprise lightweight. At present, the material used in automobile wiring harness is mainly copper, so in addition to reducing the cross-sectional area, aluminum material is used that is lighter than copper in terms of weight reduction. In addition, the price of aluminum is cheaper than copper, and once aluminum wire can be used in wire harnesses, it can not only reduce weight, but also effectively improve the cost performance.

3.3 With the progress of terminal technology, small terminals can carry more current, and the structure of high-voltage connectors is also developing in the direction of increasing precision and lightweight.

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