The hairpin is used in the copper winding of the permanent magnet synchronous motor. Take the permanent magnet synchronous motor used in most new energy vehicles as an example.

The motor structure includes stator assembly, rotor assembly, base, end cover and other auxiliary standard parts. The stator assembly contains the stator core, copper wire windings, lead wires and insulating materials, and is generally fixed to the motor housing. Copper wire windings are divided into traditional round wire windings and new hairpin windings. The rotor assembly includes rotor cores, permanent magnets, rotating shafts, bearings and other components, and is connected to the output rotating shaft to drive gears to drive the vehicle.

The development of motor has always been centered on the needs of the entire vehicle, and the hairpin motor has the technical advantage of rolling over the traditional round wire motor. New energy vehicles are currently in a period of rapid development, product quality is rapidly improving, and consumers have higher and higher requirements for vehicle performance. The main requirements of the whole vehicle for the electric drive system include: high efficiency, high power density, excellent NVH, high integration and low cost; the flat hairpin motor crushes the traditional round wire motor in these 5 technical indicators.   

The cross-sectional area of the motor winding wire is quadrilateral, which is obviously different from the traditional round wire motor. In the manufacturing process of the stator assembly of the hairpin motor, the windings need to be made into a hairpin shape and inserted into the stator. Therefore, this kind of hairpin motor is also called a hairpin motor.

The penetration rate of the hairpin motor has increased rapidly. In 2021, Tesla's replacement of domestic hairpin motor will drive a significant increase in the penetration rate, and the trend of hairpin motor has been determined.

Many potentially explosive models use hairpin motor, and the penetration rate is expected to rapidly increase to 95% in 2025. At the Shanghai Auto Show in 2021, hairpin motor shined brightly, and many high-end models were equipped with hairpin motors. BYD’s DMI models and e++ platforms are all flat-wire motors. Star models such as Volkswagen MEB, Nio ET7, Zhiji L7, and Jikrypton 001 all use flat-wire motors.

It is estimated that 23.67 million new energy vehicles will be sold globally in 2025. According to the "New Energy Vehicle Industry Development Plan (2021-2035)", the goal is to achieve a sales penetration rate of about 20% of new energy vehicles by 2025, and pure electric vehicles will become the mainstream of new sales vehicles by 2035; according to new energy vehicles in recent years On this basis, we estimate that China’s new energy vehicle sales will reach 8.96 million (penetration rate 30%) in 2025, and global sales will be 23.67 million.

The hairpin motor winding has a hundred times the market space in the future. According to calculations, the penetration rate of flat hairpin motors in 2020 is about 10%, the penetration rate of superimposed new energy vehicles is about 5.4%, and the comprehensive penetration rate of hairpin motor is less than 1%. In the future, new energy vehicles will replace traditional fuel vehicles, hairpin motor will replace traditional round wire motors, and hairpin motor will have a hundred times the market space.

The driving force for the development of the new energy industry, the four advantages of hairpin motor:

1. High energy conversion efficiency brings battery cost savings. Hairpin motors can greatly improve conversion efficiency and reduce battery costs. According to the evaluation of SAIC Green Core Channel, the conversion efficiency of the hairpin motor is 1.12% higher than that of the traditional round wire motor in the WLTC working condition; on the global average, the efficiency difference between the two is 2%; in the urban working condition (low speed and high torque), There is a 10% difference in efficiency between the two. According to a typical A-class car with a range of 500km (equipped with a 60kwh battery pack and a 150kw motor), under WLTC operating conditions, the battery cost with hairpin motors can be saved by 672 CNY, and under urban conditions, the battery cost can be saved by 6000 CNY.

Taking NIO as an example, the gross profit of bicycles in 2021Q1 is 8417 CNY, and the net profit of bicycles is only 2239 CNY. In the case that the cost of new energy vehicles and power batteries is still high, how to reduce costs is the eternal pursuit of car companies, and improving the efficiency of motors is one of the effective ways to reduce costs.

The reduction in copper consumption brings about a higher conversion efficiency of hairpin motors than round wires. Of the energy consumed by the motor, 65% comes from copper consumption, 20% comes from iron consumption, 10% comes from wind friction losses, and 5% comes from stray losses. The copper loss comes from the resistance heating Q=I2R when the current flows through the copper wire. When the slot full rate is higher, the copper wire required by the same power motor is shorter, and the internal resistance is reduced, the heat generation is reduced, and the copper consumption is reduced.

Generally speaking, the slot full rate of round wires is generally around 40%, while that of hairpin can be increased to 70%. Since the cross section of the round wire is circular, it is inevitable that there will be irregular gaps between the wires, while the gap between the hairpin is smaller and the slot full rate is higher.

2. Good heat dissipation, improve high-temperature dynamics. The hairpin motor has good heat dissipation performance, and the temperature rise is 10% lower than that of the round wire motor. Due to the tighter contact between the hairpin and the round wire, the heat dissipation is improved. Research has found that the thermal conductivity between the windings at a high slot fill rate is 150% of the low slot fill rate. The winding has anisotropy in thermal conductivity, and the axial thermal conductivity is 100 times that of the radial direction. Under the condition of lower temperature rise, the whole vehicle can achieve better acceleration performance.

3. High power density, more powerful vehicle power. The power of the motor is positively correlated with the copper content. According to the evaluation of SAIC Green Core Channel, the slot full rate of the hairpin motor has been increased. The copper wire filling volume under the same volume has increased by 20-30%, and the output power is expected to increase by 20-30%. Strong. At the national policy level, high motor power density is advocated. According to the “13th Five-Year Plan”, the power density of new energy passenger car motors should meet 4.0kw/kg, which is higher than the current round-line motor's level of about 3.5kw/kg. At the moment when the power density of round wire motors enters a difficult mode, the development of hairpin motor is an inevitable way. According to the announcement of Morn Electric, the power density of the current leading company's hairpin motor is about 4.5kw/kg.

4. The electromagnetic noise is low, and the whole vehicle is quieter. The stress of the hairpin motor wire is relatively large, the rigidity is relatively large, the armature has better rigidity, and has a suppressing effect on the armature noise; a relatively small notch size can be used to effectively reduce the cogging torque and further reduce the electromagnetic noise of the motor.

Application problems include 5 points:

1. The requirements for hairpin wire are high, the cost of hairpin wire is high, and the technology is difficult. The processing of the hairpin wire becomes more difficult.

2. Switching from a circular shape to a rectangular shape has resulted in a more complicated copper wire production process.

3. The coating difficulty increases. The paint film coating at the R corner of the flat wire is very difficult, and it is difficult to ensure the uniformity of the insulating layer here; the insulating coating will shrink after drying, and the flat wire shrinks unevenly and is easy to deform. Need to be improved to make the coating thickness at the R corner thicker.

4. After the flat wire is bent into a hairpin, the stress at the R corner is concentrated, which will easily cause damage to the coating.

5. High precision requirements for hairpin wire, large cross-sectional area, fewer turns, and inconsistent single wires have a significant impact on the overall performance, high requirements for uniformity of hairpin wire, and complex processing costs make the hairpin wire more expensive, Which also enables hairpin motor processing companies to enjoy a higher technological premium.

The enameled wire used in new energy vehicles is directly related to the stability of the whole vehicle. It places high requirements on the quality control process, research and development and process design capabilities of magnet wire manufacturers. Coordination, reasonable design and strict control of multiple control points such as drawing die configuration, tension control, painting die configuration, baking temperature, insulating paint viscosity, and working environment.

The biggest cost of the hairpin wire is the raw material oxygen-free copper rod, and the value of the processing fee in the motor is not high. Stable supply of qualified products is the key to cooperation with car companies. With raw materials as the main cost, car companies are not motivated to seek suppliers with lower processing fees.

Honest Automation is China's leading new energy vehicle drive motor equipment solution provider. We have a complete set of drive motor assembly production lines, hairpin motor stator assembly production line.