Electric passenger cars, as the name implies, are powered by electric power, so high-power motors, large-capacity batteries must be used, and in order to reduce charging time, high-voltage and high-current charging technologies are utilized, which requires high-voltage electrical systems. The electric high-voltage electric system of the electric passenger car can connect all the components such as the motor, the battery and the power electronic components. The electric high-voltage harness of the electric passenger car is the electrical path connecting the energy source (fuel cell) of the electric passenger car and the power device. . In order to meet the driving requirements of electric passenger cars and the requirements of harness connection reliability and safety under various driving conditions, this paper designs a high voltage and high current (high power) electric passenger car high voltage harness.
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Development at home and abroad
At present, the new energy automobile industry is in the stage of exploration and a small amount of trial production. There is no industrial scale at home or internationally, so the related parts are also in the trial production stage. However, compared with the overall technical level of automobile wiring harnesses, which are mainly lagging behind in wire harness assembly in China, the technical basis of foreign automobile wiring harnesses is solid and there is a solution for high-voltage wire harnesses. For example, Amphenol, the industry leader in the field of charging connectors for electric and hybrid vehicles, has developed a high-voltage harness for electric vehicles with simple structure, excellent performance and high user acceptance. Reliable work in high temperature, vibration, limited space and other harsh environments has been widely adopted by domestic and foreign automobile manufacturers; TYCO, Delphi, LS and other foreign companies followed closely and launched their own High-voltage harness solutions and related products.
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High voltage harness design
In order to make up for the research gap in the field of high-voltage wire harnesses for electric passenger cars in China, and to get rid of the current situation of high-voltage wire harnesses required for electric passenger cars in China, the high-voltage harnesses of high-voltage and high-current electric passenger cars are launched. Research and development. According to the requirements of high-voltage harness for electric passenger car high-voltage electrical system, the designed high-voltage harness for electric passenger car should meet the following requirements a, high-voltage and high-current service requirements. b. Anti-electromagnetic interference, waterproof, anti-vibration, anti-wear, flame retardant and reliable contact and other safety and reliability requirements.
2.1 Design of high voltage cable
The traditional car is powered by a gasoline engine. The traditional car cable is used to transmit control signals. The current and voltage are small. Therefore, the cable diameter is small, and the structure is only the conductor plus insulation. It is very simple. However, according to the requirements of the use of high-voltage cables for electric passenger cars, the high-voltage cables for electric passenger cars mainly function to transmit energy, and the energy of the batteries needs to be transmitted to the various subsystems. Therefore, the designed high-voltage harness for electric passenger cars must meet the high pressure. Current transfer. The electric high-voltage cable of electric passenger car is subject to higher voltage (rated voltage up to 600V), large current (rated current up to 600A), strong electromagnetic radiation, so the diameter of the cable is obviously increased, and at the same time, in order to avoid electromagnetic radiation to surrounding electronic equipment Strong electromagnetic interference is generated, which affects the normal operation of other electronic equipment. The cable is also designed with an anti-electromagnetic interference shielding structure, that is, a coaxial structure is used, and the inner conductor and the outer conductor (shield) work together, and the magnetic field in the cable is concentrically distributed. The electric field is directed from the inner conductor and stops at the outer conductor, so that the electromagnetic field outside the cable is zero, that is, the electromagnetic radiation is shielded, thereby ensuring the normal operation of the electric vehicle.
The insulation materials for early automotive cables were mainly PVC (polyvinyl chloride), but PVC contained lead, which was harmful to human body. In recent years, it has been gradually adopted by LSZH (low-smoke halogen-free material), TPE (thermoplastic elastomer), XLPE (cross-linked). Substituting polyethylene, silicone rubber and other materials. Because the high-voltage cable of electric passenger car meets the requirements of wear resistance and flame retardant while meeting high voltage, high current and anti-electromagnetic interference, the performance of these materials is compared:
a, LSZH can be divided into PO (polyolefin) and EPR (ethylene propylene rubber) two categories, of which PO cable materials as the mainstream. There are a large number of AI(OH)3, Mg(OH)2 inorganic flame retardants in the formulation of PO LSZH flame retardant cable materials, so that the cable material has better flame retardant, low smoke, halogen free, low toxicity, etc. Characteristics, but also makes it different from other non-flame retardant materials and halogen-containing flame retardant materials in terms of physical and mechanical properties, electrical properties and extrusion process properties.
b. TPE is a kind of polymer material with both rubber and thermoplastic properties. It shows high elasticity of rubber at normal temperature and can be plasticized at high temperature. However, this material is not wear-resistant and cannot meet the high-voltage line of electric passenger car. The use of the bundle is required.
c, XLPE is made of ordinary PE (polyethylene) material with temperature resistance of 75 ° C after radiation crosslinking, its temperature resistance can reach 150 ° C, and has excellent physical and mechanical properties, anti-overload capability and Long life and other characteristics, but not flame retardant.
d. Silicone rubber has high breakdown voltage, so it has arc resistance, trace resistance and ozone resistance. It has good resistance to high and low temperature, high temperature resistance up to 200 °C, good insulation performance, high temperature and high humidity. Stable and flame retardant under conditions. After comparing the properties of the above materials, silicone rubber has the advantages of good physical and mechanical properties, long service life and low price, which is the first choice for high-voltage cable insulation materials for electric passenger cars. The structure of the final designed high-voltage cable for electric passenger cars is shown in Figure 1.
2.2 high voltage connector design
2.2.1 Design of high current contacts
Usually connectors (mainly the contacts in them) have temperature limits. Once the temperature exceeds the specified limit, the connector will be safe from heat and even fail. There are two main reasons for the increase in connector temperature:
a, the car itself. The highest temperature on the car is around the engine. For example, the temperature around a conventional car engine can reach above 125 °C.
b, the connector itself. The connector will generate heat during use, and the contact piece inserted in the connector has contact resistance. The larger the contact resistance, the greater the power loss, and the higher the temperature of the contact member, the lower the reliability. In this regard, special attention should be paid to the design of high-voltage and high-current connectors for electric passenger cars. In order to avoid excessive use temperature, the insulation material in the connector is damaged, the insulation performance is lowered, even the burnout failure, and the elastic loss of the contact member after heating, or the formation of an insulating film in the contact area, reduces contact reliability, and increases The large contact resistance, which in turn exacerbates the use temperature rise, so that the vicious cycle eventually leads to the failure of the connection contact, and the large current contact in the high-voltage and high-current connector of the electric passenger car must be rationally designed.
When designing high current contacts, the choice of contact form will directly determine the quality and cost of the connector. Generally, the contact forms of the contacts are mainly three types: a chip type, a leaf spring type and a wire spring type, as shown in FIG.
The jack of the chip contact piece is slotted and closed, and the jack is processed by beryllium bronze wire (rod). The raw material price is relatively expensive, and the subsequent closing process is difficult to control, the product quality consistency is difficult to guarantee, and the cost is high. .
The socket of the leaf spring type contact member is a crown spring hole, and one or two leaf spring rings are arranged in the socket, each leaf spring ring is composed of a plurality of spring pieces, and all the spring pieces are arched inward to form elastic. Spring coil; when the jack and the pin are matched, each spring piece is in contact with the pin and generates a pressing force to ensure stable contact at multiple points; the leaf spring type jack is composed of a brass car part and a crown spring stamping part. , product consistency and low cost. Figure 3 shows Amphenol's patented RADSOK jack structure, which uses a hyperbolic crown spring technology that increases the contact area by 65% and has a highly wear-resistant silver plated surface.
The jack of the wire spring type contact member is a wire spring hole, and the structure of the jack hole and the structure of the leaf spring type jack are similar, except that the wire spring type jack is composed of a spring wire, and the wire spring type jack has excellent performance, but the process is complicated. The cost is also higher. After comparing the contact forms of the above contacts, the high-voltage and high-current connector of the electric passenger vehicle adopts a high-current leaf spring type contact. At the same time, in order to improve contact reliability and current carrying capacity, as well as to meet other requirements of high current contact parts, the high current leaf spring type contact member adopts a two-stage leaf spring type jack of double reed. Finally, through the calculation of the contact resistance of the large current contact, the design of the structure and the modification of the sample design, the large current contact was successfully designed.
2.2.2 High pressure performance design
In order to meet the design requirements of high-voltage connectors for electric passenger cars, various parts of the high-voltage connector must have sufficient dielectric strength through structural design and material selection to ensure high-pressure resistance. The high-voltage performance design of high-voltage connectors for electric passenger vehicles mainly includes creepage distance, interface air gap and insulation materials.
Creepage distance means that when the working voltage is too large, the instantaneous overvoltage will cause the current to release the arc outward along the gap between the insulation, damaging the device and even the operator. This insulation gap is the creepage distance, and the working voltage of the arc determines the climb. Electrical distance. In the design of the high-voltage connector structure, the creepage distance should be increased as much as possible. Considering that the connector medium withstand voltage is above 400V, after careful calculation and verification, the creepage distance of the connector is designed to be 24mm or more, which can fully satisfy the high voltage. Connector 600V usage requirements.
In order to improve the high-pressure resistance of the connector, when the connector is inserted, the interface portion should be fitted with no air gap. The interface of the connector mainly includes the plug connector of the plug connector and the socket connector, the connector contact and the connection portion of the wire. These parts require full filling of the medium and no air to reliably ensure that the connector is not broken down. In order to prevent the existence of the interface air gap, the following measures were taken in the design of the high voltage connector:
a. A soft insulating material is used at the mating interface to ensure that the air gap is filled while the plug is in place.
b. The insulation outside the contact of the jack is molded, and the gap outside the contact is filled.
c. The mating surface of the plug and the socket adopts a tapered structure.
d. After the contact piece is connected to the cable, part of the cable insulation extends into the connector housing insulation.
In order to improve the high-pressure resistance of the connector, the high-voltage connector of the electric passenger car adopts PPA with good insulation performance, high breakdown voltage, high insulation strength, good stability under high temperature and high pressure, arc resistance, leakage resistance and low hygroscopicity. (Polyphthalamide) plastic.
2.2.3 overall structural design
The structure of the final designed high-voltage connector for electric passenger cars is shown in Figure 4. The structure of the high voltage connector is an inner conductor, an insulating layer, a shielding layer, and an outer casing from the inside to the outside.
2.3 Overall design of high voltage wiring harness
2.3.1 Shielding performance design
In order to meet the basic requirements of reliable electrical connection, the designed high-voltage harness has excellent electromagnetic shielding performance, and the shielding performance design of the high-voltage harness is developed. The shielding performance design of the high-voltage harness mainly includes the shielding performance design of the high-voltage cable itself, the shielding performance design of the combination of the high-voltage cable and the high-voltage connector, the shielding performance design of the high-voltage connector itself, and the shielding performance design at the high-voltage connector insertion interface. In order to improve the shielding performance of the high-voltage cable itself, the high-voltage cable adopts a shielding structure, and this should be noted if the cable is a combination of a signal line and a power line. In order to improve the shielding performance of the junction of the high-voltage cable and the high-voltage connector, the reliability of the contact between the two is ensured, especially in the case where the connection is not loosened under strong dynamic conditions, and the inner conductor of the high-voltage cable and the high-voltage connector After the connection, the cable braid is in contact with the shield layer, and a separate shield metal woven mesh is placed at the joint of the cable braid and the connector to enhance the shielding effect. In order to improve the shielding performance of the high voltage connector itself, the connector is designed with a metal casing. In order to improve the shielding performance at the connector interface of the connector, a shield spring structure is adopted to ensure reliable contact between the plug and the socket housing; the inner conductor of the connector head is lower than the interface of the housing to prevent the inner conductor from contacting the finger or other The metal has a certain protective effect and increases safety; after the plugging, the socket connector and the plug connector are reliably in contact with each other, so that the mating surface is shielded from the outside.
2.3.2 Mechanical protection and dustproof and waterproof design
Due to the large diameter of the high-voltage cable of the electric passenger car, a special wiring direction is required, that is, the high-voltage harness of the electric passenger car is arranged outside the vehicle, so the high-voltage harness of the electric passenger car must be mechanically protected and dustproof and waterproof. In order to improve the mechanical protection and dustproof and waterproof performance of the high-voltage harness, protective measures such as sealing rings are adopted between the connectors and the connector connecting cables to prevent moisture and dust from entering, thereby ensuring the sealing environment of the connector. Avoid the risk of short circuits between contacts and prevent moisture from entering, avoiding sparks and other safety issues.
2.3.3 Service life design
When the electric passenger car is driving on the road, it will be affected by factors such as the unevenness of the road surface and the speed of the vehicle, which will cause high vibration, which will cause friction and wear between the high-voltage harness and the contact parts and other harnesses, as well as the fatigue wear of the high-voltage harness itself. . In order to improve the service life and quality of the high-voltage harness, the connection between the high-voltage cable and the high-voltage connector should be strengthened, the connection between the high-voltage connectors should be locked, and the wiring scheme should be optimized. The high-voltage harness material should be selected from wear-resistant materials and wires. Anti-fatigue copper strands are used. In addition, the connection between the high-voltage connectors is the weak point of the high-voltage harness itself. In order to improve the service life of the high-voltage harness and meet the requirements of the high-voltage electrical system, the number of plug-ins and the connection quality of the high-voltage connector must be ensured.
2.3.4 Overall structural design
The structure of the final designed high-voltage harness for electric passenger cars is shown in Figure 5.

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3 performance test of high voltage harness
In order to verify the structural rationality, contact area, contact resistance, and vibration resistance of high-voltage harness designed by high-voltage and high-current contact technology, whether high-reliability, long-life and high-current performance requirements are met, high-voltage harness samples in electric passenger vehicles After the development, the relevant performance tests were carried out according to the corresponding design requirements. The test results are shown in Table 1. It can be seen that the performance of the high-voltage harness of the electric passenger vehicle satisfies the standard requirements, and the contact structure, the connector structure and the design of the entire high-voltage harness have certain rationality.
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4 conclusion
This paper briefly introduces the functional use of high-voltage harness for electric passenger cars and the development at home and abroad. Starting from the characteristics, requirements and environment of electric passenger vehicles, the performance requirements and design points of high-voltage harness for electric passenger vehicles (high voltage resistance, high current resistance, environmental resistance, shielding, safety and reliability, etc.) are analyzed. The main design of the cable, the main design of the connector and its contact parts are discussed in detail, and the overall scheme of the wiring harness is given. Finally, the test situation of the developed sample is introduced. From the use requirements and test results, it can be concluded that the developed high-voltage harness can meet the requirements of electric passenger vehicles. With the development of the electric vehicle industry, the high-voltage harness will be further developed, can withstand higher voltages, more current, and will be used in a variety of different models, but also in terms of functions, such as having its own testability, The current, temperature and other changes of the harness can be monitored in real time.