New energy vehicle high voltage connector technology, design and trend

In recent years, due to the impact of global economic fluctuations, the North American, European and Japanese connector markets have grown slowly, while emerging markets represented by China have shown a continuous growth momentum, becoming the main driving force for the growth of the global connector market. To this end, the world’s well-known connector companies have transferred their production bases to China, including TE Connectivity, Molex, Delphi, etc., continue to invest and build factories in China. China has become the world’s largest connector production base, especially under the encouragement of government policies. , The steady development of my country’s new energy vehicle industry has driven the sustainable development of automotive connectors.

In recent years, due to the impact of global economic fluctuations, the North American, European and Japanese connector markets have grown slowly, while emerging markets represented by China have shown a continuous growth momentum, becoming the main driving force for the growth of the global connector market. To this end, the world’s well-known connector companies have transferred their production bases to China, including TE Connectivity, Molex, Delphi, etc., continue to invest and build factories in China. China has become the world’s largest connector production base, especially under the encouragement of government policies. , The steady development of my country’s new energy vehicle industry has driven the sustainable development of automotive connectors. After years of technical accumulation, connectors in my country have met the technical level required by high-voltage connectors for new energy vehicles in terms of design capabilities and automated production capabilities. Under the premise that the localization of downstream manufacturers and sufficient technical capabilities, domestic manufacturers have occupied the highest point of high-voltage connectors for new energy vehicles, such as Sichuan Yonggui, AVIC Optoelectronics, Basba and other well-known enterprises. It is hoped that in this new field, corner overtaking will be achieved, and there will be an opportunity to break the monopoly of foreign businessmen in traditional automobile connectors.

1 Technical Analysis of High Voltage Connectors

1.1 Application of High Voltage Connector in Vehicle System

Connectors for new energy vehicles are one of the major categories of connectors. With the development of new energy vehicles in the country in recent years, they are gradually separated from traditional high-voltage, high-current and traditional low-voltage automotive connectors. Compared with traditional high-voltage and high-current connectors, the working conditions of new energy vehicle connectors are more complex and changeable, and the reliability of connectors is higher; compared with traditional low-voltage automotive connectors, due to the increase in voltage level ( At present, the voltage of mainstream systems is higher than 300V DC), which increases the risk of electric shock injury to the human body and requires higher safety requirements for connectors; therefore, the insulation and protection requirements of products are improved compared with traditional low-voltage plug-ins.

The function of the connector for new energy vehicles is mainly to ensure the high-voltage interconnection system of the whole vehicle, that is, to build a bridge where the internal circuit is blocked or isolated so that the current flows. The composition of connectors for new energy vehicles can generally be divided into three parts: auxiliary structures such as shells and seals, insulating parts, and conductive contact pairs. The functions of connection and conduction can be achieved through the plugging and mutual cooperation between the plug sheath and the socket sheath. The high-voltage connector is mainly used in the high-voltage and high-current circuit of new energy vehicles, and acts at the same time as the conductive cable, and transmits the energy of the battery pack to various components in the vehicle system through different electrical circuits, such as battery pack, motor controller, DCDC Body power units such as converters and chargers.

Figure 1 is a layout diagram of the high-voltage connector in the application of the vehicle system.

New energy vehicle high voltage connector technology, design and trend

1.2 Analysis of key items in high-voltage connector design

1.2.1 Temperature rise and derating curve values

Temperature rise is one of the most important design key items in connector design. Abnormal temperature rise will lead to connector ablation due to excessive temperature rise.

The temperature rise of the connector is affected by the following factors:

1. Contact resistance: used for conductive connection, resistance between two contact carriers, such as pinhole-to-insertion contact resistance, pinhole tail and wire crimping resistance, and contact resistance between threaded copper plates and copper plates

2. Physical environment heating: When the connector is in a high temperature environment for a long time, because the materials used in the connector are engineering plastics, metal, rubber, etc., especially engineering plastics require a maximum working temperature of 140 °C, but when the ambient temperature of the product is too high , When the connector reaches thermal equilibrium due to its own contact internal resistance, the ambient temperature is higher than the maximum working temperature allowed by the material. At this time, if the connector is in this environment for a long time, and the internal temperature of the pinhole parts of the connector is heated and the internal temperature cannot be discharged, the internal temperature will continue to rise, and the connector will generate a lot of heat, resulting in ablation of the connector. It can cause the vehicle to burn, which is a very serious problem. Both rubber and metal materials have maximum operating temperature limits that need to be considered when designing.

3. The connection of the plate end: in the case of using bolts in the design, or taking precautions to prevent loosening during the supply; at the same time, when bolting, the torque test must be carried out according to the operating specifications. In the case of screw connection of conductive parts, one of the main failure modes is that the tightening torque is not controlled according to the torque requirements, resulting in abnormal temperature rise and ablation of the connection parts.

4. Derating curve: Now let’s discuss the derating curve. In my understanding, the derating curve is like you choose a product. This product is to be used in a specific environment. According to an attribute value of this product to determine which range of products you choose. The derating curve of high-voltage connectors is to provide customers with a menu, and customers can choose their own suitable dishes according to their own tastes.

The derating curve is the different values ​​corresponding to different currents at different working ambient temperatures. These values ​​are a graph obtained by the plotting method. With this derating graph, the use conditions of the connector can be seen more intuitively.

The following figure is a graphic representation of the temperature rise and derating curves

New energy vehicle high voltage connector technology, design and trend
temperature rise curve

New energy vehicle high voltage connector technology, design and trend
Derating Curve

1.2.2 High Voltage Interlock (HVIL)

For the entire high-voltage interconnection system, in order to ensure the safety of the high-voltage system when it is powered on and off, the concept of high-voltage interlock is introduced in the connection design. A brief description is that when the connector is plugged in and turned on, the high-voltage circuit is first contacted and turned on, and then the high-voltage interlock signal circuit is turned on; when the connector is disconnected, the high-voltage interlock signal is disconnected first, and then the high-voltage circuit is disconnected. Most connector manufacturers put the high-voltage interlock design inside the connector, and some manufacturers put the high-voltage interlock outside the mating cavity through the auxiliary structure design. It is very important to ensure the stability of the high-voltage interlock circuit. If the high-voltage interlock is discontinuous, the possible impact will be very bad. For example, when the car is driving, the signal of the high-voltage interlock circuit is suddenly abnormal, causing the vehicle to suddenly lose power and not operate normally, which will cause traffic accidents.

1.2.3 Locking structure

Understand that the real secondary lock does not have a secondary protective effect, but more effectively protect it. The real meaning of this is that after the primary lock, if the primary lock fails or there is no operation verification in place, the secondary lock is It is very important to ensure that the first lock is protected after the first lock is locked. The most commonly used secondary locking structure combined with a primary lock is the force arm mechanism. Because the primary locking is related to the insertion force, a form similar to the force arm mechanism is required according to the mechanical design concept, so as to achieve both labor-saving and The connector can be easily snapped into place. For the requirements of the lever arm, USCAR has talked about a lot of the ergonomic operability of the lever arm. USCAR also stipulates the force requirements for the relevant primary locks and secondary locks in the case of opposite insertion and non-insertion. In fact, we all think that USCAR is the standard for connectors, but I think the USCAR standard is not only a technical standard, but also guides designers to make the structure reliable in the design process. It can also provide customers with a better product experience. Figure 2 below is a product diagram of a more common locking structure.

New energy vehicle high voltage connector technology, design and trend

New energy vehicle high voltage connector technology, design and trend

1.2.4 Protection class

The protection of the connector is mainly divided into three arrangements:

The first is the board end seal: the board end is the connector socket end which is installed by mechanical connection with four screws. This is a relatively common structure, and there are also some special structures (Figure 3);

New energy vehicle high voltage connector technology, design and trend

The second is the head-to-socket seal: the header-to-socket means that the male end includes the female end or the female end includes the male end, and rubber parts are used for radial and axial protection (Figure 4);

New energy vehicle high voltage connector technology, design and trend

The third is the wire end seal, the protective seal between the wire end connector and the cable (Figure 5).

New energy vehicle high voltage connector technology, design and trend

For high-voltage connectors for electric vehicles, with the development of the market, the performance requirements of OEMs for product protection are also constantly improving. In the early stage of industry development, the protection requirements of IPI67 can already meet the vast majority of customers. However, in the later period, with the failure of the protection of connector products on the market, there are more and more cases of water leakage, insulation failure, and even ablation.

The gradual improvement of protection requirements has become the development trend of electric vehicles. At present, the requirements of IP67 cannot meet the requirements of normal use. Of course, this is not absolute. It also depends on the position of the connector on the vehicle. According to the layout of the high-voltage circuit in the whole vehicle, it will be suspended under the chassis of the car. It is a principle that high-voltage cannot enter the cabin. Therefore, most high-voltage connectors will be located in the chassis near the ground or near the hub. When some When the weather is bad, such as severe weather, heavy rain or some severe cold weather, the water brought by your tires will actually impact these connectors. If you are familiar with the test, there is no IP6K9K in the domestic standard, you will It is found that if the IP67 is used, the impact pressure of the high-pressure water gun is actually not as large as 6k9k. When the car is running at high speed and suddenly wading into the water, the instantaneous water pressure to the connector will be very large, so IP67 is sometimes difficult to meet the actual use requirements. In view of this, the domestic standard QC/T1067 and the foreign standard USCAR divide the connector seal into two grades S1 and S2. For the S2 level, it is clearly stipulated that the applicable occasion is the lower position of the chassis, and 6K and 9K are recommended, so 6K and 9K must be used for future connection protection. If the connector is not arranged in the above position, the design of IP67 can still meet the requirements of the whole vehicle.

1.2.5 Electromagnetic shielding

Electric vehicles have many Electronic devices, the current will generate a magnetic field, and the parts of the vehicle must have the ability to resist interference. In particular, electric vehicles are now used as a carrier, and autonomous driving will be more developed on this basis, so this technical issue is very important. For high-voltage systems, shielded connectors and cables are very important, but we should give priority to system-level layout. This is a prerequisite. If your OBC, the location of your layout, including the system DCDC itself may have some congenital problems, even if the connector is well made, there will be various signal interference problems, so the system type should be considered first, and then the component level should be considered. For the shielding effectiveness of the connector, two methods are generally used. The first way is that on some plastic connectors, there will be a metal shield inside, and the cable shield will be connected to the shield of the metal shell to form an effective 360° shield. The second method, most of the high-voltage and low-current connections will not have secondary connections, but will be connected to the shielding layer of the cable. This method is also commonly used by existing manufacturers, including some well-known domestic ones. The OEM is also considering this method. We call it spring contact (English), which is actually a spring connection.The advantages of this structure are also many, because the size and space will be smaller, and its connection
There will also be more contacts; there are many manufacturers of this structure, mainly represented by companies such as BMW Springs in Switzerland, Basel in the United States, etc. They have many practical and mature application cases in this area. In most cases, for the connection between the wire and the shielding layer, we will use the form of metal inner and outer rings for crimping, placing the shielding layer between the two metal rings, and deforming the shielding layer and the metal ring by cold pressing. Tightly fastened. In addition, we also have a shielding method, which uses a structure similar to the strap spring to replace the spring connection. This structure is often used in military products, and the technology is mature; we have done relevant tests, all of which can meet the design requirements . The structure is applied to the shielding of new energy electric vehicles, which can not only meet the performance requirements, but also is a stamped part, suitable for mass production, and has high cost performance.

1.2.6 Connector material

The material of the connector insulating parts is generally PA66, PBT, ABS, PC, etc. The contact material is generally made of brass, phosphor bronze, beryllium copper, etc., but now the most commonly used materials abroad are copper-nickel-silicon materials. Connector housing materials are generally divided into two materials: plastic and metal.

Regarding how to choose plastic material or metal material, there are generally the following reference points:

1. Lightweight

Due to the demand for lightweight vehicles, especially passenger car manufacturers will try their best to choose plastic connectors on the premise of satisfying product performance to control the weight of the vehicle.

2. The use environment of the product

Because the mechanical strength of metal materials is better than that of plastics. Therefore, in some harsh environments, metal connectors are more suitable. For example, special vehicles, muck trucks, and the electrical connection parts that are not protected when the vehicle is arranged. At this time, the metal connector is slightly better than the plastic connector in terms of environmental impact and mechanical strength.

3. Shielding implementation

For shielded connectors, since the shell of the metal connector itself is used to conduct shielding, it forms a carrier for shielding protection. In general, metal connectors are easier to achieve better shielding effectiveness than plastic connectors, and the shape is more compact.

1.2.7 Connector selection

1.2.7.1 Connector selection process (see the figure below)

New energy vehicle high voltage connector technology, design and trend

1.2.7.2 Interpretation of common technical parameters of connectors

(1) Use position: As the name implies, it is the application position of the connector on different high-voltage electrical appliances of the whole vehicle, and the connector is selected.

New energy vehicle high voltage connector technology, design and trend

(2) Rated voltage: the maximum voltage that electrical equipment (including electricity and power supply equipment) can work stably for a long time.

The rated voltage is proportional to the creepage distance & clearance.

In other words, the higher the rated voltage requirement, the larger, or longer, the connector. Creepage distance & clearance design standard according to GBT 16935.1 (IEC 60664-1),

(3) Rated current: The rated current of electrical equipment refers to the maximum current that is allowed to pass for a long time when the heating does not exceed the allowable temperature for long-term heating under the working conditions of the rated voltage and the reference ambient temperature.

For electric vehicles, P=UI, the rated current is determined according to the power P of the electrical equipment and the output voltage U.

Peak current: The maximum current value generated by the electric vehicle at the moment of rapid acceleration, climbing, and overloading.

The current-carrying cross-sectional area is proportional to the rated current of the connector, in other words, the larger the pin/hole/conductor cross-section, the more current it can pass, and the larger the connector.

(4) HVIL (High Voltage Interlock)

(4.1) Purpose of designing HVIL function

Confirm the integrity of the entire high-voltage system. When the high-voltage system circuit is disconnected or the integrity is damaged, the safety measures of the entire vehicle are activated.

(4.2) Implementation of HVIL function

a. The entire system composition is required, and it must be designed in the system development;
b. It is mainly done through the connector;
c. The HVIL circuit is low-voltage, independent of the power circuit.

(4.3) Principle of connector HVIL function realization

Power and signal terminals should meet:

――When connecting, the power terminal is connected first, and the signal terminal is connected later.

――When disconnected, the signal terminal is disconnected first, and the power terminal is disconnected later.

Special note: The connection of the power terminal indicates good contact, and virtual contact is unacceptable

New energy vehicle high voltage connector technology, design and trend

(5) Shield

Alternating electric field shielding: In order to reduce the coupling interference voltage of the alternating electric field to the sensitive circuit, a metal shielding body with good conductivity can be set between the interference source and the sensitive circuit, and the metal shielding body can be grounded.

The main difference between shielded and unshielded connectors is whether a metal shield with good conductivity is provided.

(6) Protection level

The IP protection level is composed of two numbers. The first marked number indicates the level of the electrical appliance against dust and foreign objects intrusion. The second marked number indicates the degree of airtightness of the electrical appliance against moisture and water intrusion. The larger the number, the better the protection. The higher the level.

(7) Outlet method

It mainly refers to the angle between the cable outlet angle at the tail of the electrical connector plug and the normal direction of the socket mounting surface. According to this, the common ones are 90° (angled) and 180° (straight) outlet electrical connectors.

(8) Socket installation method

In order to meet the needs of OEM designers for different layouts of connectors, the installation methods of electrical connector sockets are subdivided into the following four types:

New energy vehicle high voltage connector technology, design and trend

1.6.2.3 Option Notes

(1) The voltage selection needs to be matched: the rated voltage of the vehicle after the load calculation should be less than or equal to the rated voltage of the connector. If the working voltage of the vehicle exceeds the rated voltage of the connector for a long time, the electrical connector has the risk of creepage and ablation.

(2) The current selection needs to be matched: the rated current of the vehicle after the load calculation should be less than or equal to the rated current of the connector. If the working current of the vehicle exceeds the rated current of the connector for a long time, the electrical connector has the risk of overload and ablation.

New energy vehicle high voltage connector technology, design and trend

(3) Cable selection needs to be matched: vehicle cable selection and matching are divided into cable current carrying matching and cable and connector sealing matching. Regarding cable current carrying, each OEM has special electrical engineers for matching design, which will not be explained here. .

Seal matching: The connector and cable seal rely on the elastic compression of the rubber seal to provide contact pressure between the two, so as to achieve reliable protection performance, such as IP67; according to the calculation, the specific contact pressure is achieved by the specific compression amount of the seal, and so on Introduced, if reliable protection is required, the sealing protection of the connector has specific size requirements for the cable at the beginning of the design;

For the same current-carrying cross-section, the cable can have different outer diameters, such as shielded cable and unshielded cable, national standard cable and LV216 standard cable. When selecting the connector, special attention should be paid to the specifications of the adapter cable to prevent the connector from sealing failure.

(4) The whole vehicle needs flexible wiring: for the whole vehicle wiring, each OEM has requirements for bending radius and slack;

For use cases, it is recommended that after the wiring harness is assembled, the connector terminals themselves will not be stressed. Only when the wiring harness as a whole is subjected to vibration, impact and relative displacement of the vehicle body due to the operation of the vehicle, the purpose of strain relief is achieved through the flexibility of the wiring harness, even if a little strain is transmitted to the connection. Connector terminals, the resulting stress does not exceed the design retention force of the terminal in the connector.

New energy vehicle high voltage connector technology, design and trend

2 Development Trend of High Voltage Connectors

2.1 The role of policy guidance

The formulation of the state’s policy on the new energy electric vehicle industry should be determined according to China’s national conditions. In terms of developing a green transportation system, the national plan proposes to speed up the upgrading of the vehicle and ship structure and promote the use of new energy vehicles. The production and sales of new energy vehicles will reach about 2 million in 2020. Accelerate the use of new energy or clean energy vehicles in new and updated public transport, sanitation, postal, rental, commuter, and light material distribution vehicles in urban built-up areas, and the proportion of use in key areas will reach 80%; New energy or clean energy vehicles are mainly used for adding or replacing work vehicles. Before the end of 2020, all buses in logistics parks, industrial parks, industrial parks, and built-up areas of large-scale separate cities will be replaced with new energy vehicles. Build centralized charging piles and fast charging piles in logistics distribution centers such as logistics parks, industrial parks, industrial parks, large commercial shopping centers, and farmers’ wholesale markets. According to the national policy orientation, OEMs also adjust their internal models according to relevant policies, which determines the development direction of connectors.

2.2 Platformization and customization

There are also many types of electric vehicles, such as passenger cars, logistics vehicles, including custom connectors. The requirements will be different, or some special requirements will be put forward, so there are also unmanned vehicles, Internet of Things vehicles, New energy, etc., we connector manufacturers need to consider, I think this kind of customization (vehicle end and battery end) for the needs of the electric vehicle subdivision industry may be a

A good choice to try, we are now taking the first step. Because in general, these types of cars will be used in different occasions. In fact, they are all a segmented field. Although the volume is not that large, that market belongs to us. We are the top in this market. This is also a Nice choice. The second is platformization. In the future, the battery and the whole vehicle will tend to be platform-based. It is very important to maintain in-depth technical communication with customers to form a platform-based product for both parties. There are many domestic OEMs, and everyone’s platforms are different now, such as batteries. There are many whole package factories, each of which has different module solutions and battery box group solutions. As a connector manufacturer, we need to think about how to make it suitable for platform-based applications.

2.3 Miniaturization and Lightweight

Under the background that the automobile industry is increasingly pursuing energy conservation and environmental protection, the lightweight and miniaturization of automobiles has become a technological trend, and it is also the focus of automobile manufacturers’ technological competition. By controlling the weight of the whole vehicle, it can effectively reduce fuel consumption, reduce exhaust emissions, and improve fuel economy efficiency. In such a large environment as the automotive industry, new energy connectors must be miniaturized and lightweight.

A series of important solutions for the miniaturization and weight reduction of automobiles, including the introduction of smaller-sized high-performance copper alloy wires as signal transmission lines, the introduction of terminal and contact systems that are developing towards miniaturization, and the crimping generated by this miniaturization. Unstable optimization and reliable verification methods; the principle of using high-performance terminals to reduce the size of small-power transmission conductors, and the use of aluminum conductors to replace large-diameter copper conductors that transmit higher power.

3 Conclusion

By analyzing the main technical parameters and selection principles of new energy connectors, as we continue to collect various data feedback, in foreign countries, even the connector manufacturers have set up a lot of vehicle data returns, they will form An alliance, they will continuously improve according to the data to achieve an optimal product.

At the same time, with the domestic connector manufacturers, the actual feedback from OEMs and users is obtained in the actual use process. Even machine manufacturers are constantly simulating whether the connector is stable in the real user environment; including the research and development of our new materials and the overcoming of technical barriers, whether the cost can be commercialized. In the near future, none of these will be problems and will be overcome.

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