Why is tinned copper wire, aluminum wire and aluminum bar the development trend of wire harness materials for new energy vehicles in the future?

According to public data, China's annual sales of new energy vehicles have increased from 75,000 a decade ago to 9.5 million, accounting for more than 60% of the global total, with a compound annual growth rate of 71%. At present, the domestic new energy automobile industry is entering a period of accelerated development, and the achievements in the fields of new energy vehicles and power batteries are also becoming rapidly popular. Consumers' preference for new energy vehicles not only stems from environmental awareness and the pursuit of low-carbon travel methods, but also because of the pursuit of more efficient energy conversion forms. Compared with traditional fuel vehicles, new energy vehicles have advantages in environmental protection and intelligence, but the biggest advantage is energy conversion efficiency.

The energy conversion efficiency of the combustion engine is usually between 20% and 30%, and the rest of the energy is lost in the form of waste heat energy. The energy conversion efficiency of new energy vehicles can reach 80%-90%, whether it is pure electricity or plug-in hybrid, the energy conversion efficiency is much higher than that of fuel vehicles. As more efficient power units in new energy vehicles gradually replace inefficient power units, energy efficiency will be further improved. The rise of new energy vehicles not only represents the green transformation of transportation mode, but also indicates the direction of efficient use of energy in the future.

According to the research of domestic and foreign scholars, the energy conversion efficiency of new energy vehicles is also affected by factors such as battery performance and motor efficiency, body weight and energy conversion loss during charging and discharging. These losses directly limit further improvements in energy conversion efficiency.

Judging from the current technological development trend, optimizing the material and connection mode of conductive lines of new energy vehicles is the best way to improve the energy conversion efficiency.

Traditional automobile wire has always been made of copper as conductor material. However, copper wire also has some defects: for example, it is easy to produce patina formed by oxidation. It will not only make the appearance of the wire worse, but more importantly, its conductive performance is far less than that of pure copper. Therefore, it will significantly increase the resistance in the circuit and reduce the transmission efficiency of the current, which may affect the performance and safety of new energy vehicles.

In order to solve the problem of easy oxidation of copper wire, the common solution is to use tinned copper wire. The tin layer can effectively prevent copper from coming into contact with oxygen and water in the air, thereby slowing down the oxidation process of copper, and the tinned copper wire has good electrical conductivity and mechanical properties, which determine its application value in the field of new energy vehicles.

However, due to the low melting point of the tin layer, the local high temperature may cause the tin layer to melt and affect the welding effect when welding tinned copper wire by ultrasonic wire harness welding. Therefore, in the process of ultrasonic welding of tinned copper wire, how to accurately control the welding temperature and time is a very difficult technical difficulty to overcome.

And the production cost of tinned copper wire is relatively high. This limits its wide application in the field of new energy vehicles to a certain extent. It is currently only used in high-end new energy vehicles. China needs to import a large amount of copper every year, and the price of copper has continued to rise in recent years. The scarcity of copper resources and the rising price make the cost of automobile wire high.

Can we improve energy conversion efficiency and reduce production costs at the same time? In the industry, aluminum wire is regarded as a viable alternative to copper wire, and major new energy automobile manufacturers have tried to use aluminum wire to replace copper wire, because aluminum wire has the following advantages in new energy vehicles:

1. Good electrical conductivity:

Aluminum has a resistivity of 2.65×10-8 Ω·m, while copper has a resistivity of 1.72×10-8Ω·m. Although the resistivity of aluminum is higher than that of copper, the resistance requirements of the vehicle circuit can be met by increasing the wire diameter of the aluminum wire (about 1.3 times).

2. Lightweight:

Aluminum has a density of 2.7g/cm³, while copper has a density of 8.96g/cm³. The density of aluminum is only one-third that of copper, so it only needs to increase the cross-sectional area of aluminum wires by about 30% to achieve weight loss.

3. Cost effectiveness:

Due to the imbalance of copper and aluminum mineral resources and mining costs in China, the price of copper wire is much higher than that of aluminum wire. By using aluminum wire instead of copper wire, we can reduce the production cost of new energy vehicles and make them more competitive in the market.

In the field of automotive wiring harnesses, cost and weight are also one of the key reasons for the development of automotive wiring harnesses to lightweight. The use of aluminum wire instead of traditional copper wire does have the advantage of reducing cost and weight. However, there are also some technical difficulties in the application of aluminum wires, such as:

1. Connection reliability:

The metal oxidation, electrochemical corrosion and other problems that may occur in the traditional crimping of aluminum wire and copper wire will lead to the loosening of connection points or the increase of resistance, which will affect the performance of the entire wire.

2. Creep effect:

Creep is the slow deformation of metal materials under the action of external forces for a long time. Due to the difference of thermal expansion coefficient of copper and aluminum, aluminum wire is more prone to creep. Under certain conditions, the creep rate of aluminum wire can be as high as 25 times that of copper wire, which has a significant effect on the fatigue resistance and service life of aluminum wire.

3. Wire volume increase:

The conductivity of aluminum wires is weak, in order to meet the electrical conductivity requirements of automotive wires, it is necessary to increase the cross-sectional area of aluminum wires, which will increase the volume of wires to a certain extent, and bring greater challenges to the connection.

In order to improve the conductive efficiency of the aluminum wire, the original monofilm structure is replaced by a conductive aluminum bar, which solves the problem of weak conductive ability. The conductive aluminum bar adopts a flat design to reduce the occupied space. In addition, the conductive aluminum bank can be arranged close to the bottom of the car, reducing the chassis bulge caused by the wire, making the body more beautiful. At the same time, because the aluminum bar has a certain rigidity, the power wire can be automatically assembled when it is processed and installed to the body, which solves the problem that the automatic production and assembly cannot be realized due to the softness of the wire. In addition, the rigid structure also avoids the use of guard plates in the conductor direction definition, thus reducing the cost of the conductor.

The design of the conductive aluminum bar needs to be closely fitted with the body design, and the processing of the aluminum bar wire should be completed in the wiring harness factory. When the parts are finished processing, the aluminum wire should have been assembled. Because the aluminum wire has a certain rigidity, it can be processed by automatic bending and forming equipment or automatic manipulator. High degree of automation, accurate size control, and can be customized production of different models.

New energy vehicles have significant advantages in environmental protection, intelligence and efficient energy conversion, and are gradually replacing traditional fuel vehicles. However, we must also face up to some limitations of new energy vehicles themselves, and these challenges need to be solved gradually. The selection and connection method of conductive circuit materials is one of the key issues to achieve lightweight and improve energy conversion efficiency, which is of great significance to promote the further development of new energy vehicles.