Introduction of advantages and disadvantages of flat wire motor, application analysis and prospect of development trend

At present, flat wire motors are more concerned in China, but the application is less, mainly because the new energy market has a short development time, and the main market share is concentrated in the micro passenger car market. Foreign mature flat line motor products are used in new energy vehicles, especially in Japan, European and American enterprises, Toyota and GENERAL Motors have used flat wire motor. Representative examples are the Chevrolet VOLT (Remy Motor) and the Toyota Prius (Denso), which both use oil-cooled solutions. In addition to foreign suppliers such as Remy, Dso and Hitachi, the domestic suppliers with stable shipments are mainly Huayu Electric and Songzheng Motor, and Founder Motor which will be put into production soon.

The drive motor is mainly composed of stator components, rotor assembly, end cover and auxiliary standard parts, and the stator winding includes iron core, copper wire winding, insulation materials, etc.

As the name suggests, the flat wire motor uses the flat copper wire in the stator winding, first make the winding into the shape like a hair card, penetrate into the stator groove, and then weld the end of the hair card at the other end.

Advantages of flat-wire motors

Advantage 1: the same power, smaller volume, less materials, lower cost, or the same volume, the tank full rate increased, increased power density. The round line becomes a flat line. Theoretically, under the premise of constant space, the flat line motor can achieve 70% of the trough full rate, and the filled copper can be increased by 20-30%, producing a stronger magnetic field strength, which is to some extent equivalent to increasing the power by 20-30%.

Advantage 2: better temperature performance. The internal gap becomes less, the contact area between the flat line and the flat line is large, heat dissipation and heat conduction is better; the winding and core groove contact is better, better heat conduction, and the motor is very sensitive to heat dissipation and temperature, heat dissipation is better, performance will improve. Through temperature field simulation, it is concluded that the temperature rise of flat copper wire motor winding with the same design is 10% lower than that of circular copper wire motor.

Advantage 3: lower electromagnetic noise. The flat motor wire has large stress, large rigidity, the armature has better stiffness, and suppresses the armature noise; can take relatively small slot size, effectively reduce the groove torque, and further reduce the electromagnetic noise of the motor.

Advantage 4: short end, save copper, improve efficiency. Traditional round wire motor, due to process problems, its end is generally relatively long, otherwise it is easy to damage the copper wire in the process. For the flat wire motor, because the lines are hard lines, the end can be made a little smaller when processing, and the end size is reduced by 20% compared with the round wire motor, and the space can be further reduced, which can further reduce the volume of the system and achieve miniaturization and lightweight.

Advantage 5: the high efficiency point of the flat line motor is not necessarily much higher than the round line, but the high efficiency area can be further widened.

Disadvantages of flat-wire motors

Disadvantage 1: High-speed skin collection effect. New energy vehicles to do high power density requirements to high speed, before is to do 10,000 or even 12,000, now to the direction of 16,000 or even 20,000. There need to be some good ways to solve it in the process of motor design, which is a bad place.

Disadvantage 2: copper wire requirements are high, round wire motor copper wire domestic manufacturers do more, and the quality can be very good. There are not many manufacturers that can do flat line motor, the requirements are relatively high, and we need to work together to solve the material.

Disadvantage 3: Flat line has many processing processes, the equipment accuracy requirement is high, and the early investment is large, because if its accuracy is not high, the reliability and consistency of the product will be relatively poor. Car companies are also worried about the reliability and stability of quality.

Disadvantage 4: serialization design is difficult, the motor wants to reduce the cost, good is to do it serialization, serialization design is the current flat wire motor is not as good as the round wire motor.

Disadvantage 5: There are too many patent barriers. At present, flat wire motor patents are mainly in European and American and Japanese enterprises. Chinese enterprises have few patents. We have patent layout, but it is not satisfactory.

Disadvantage 6: flat line forming requirements are high and processing difficulty. Because the copper wire has a certain elasticity, so there must be a deformation allowance in the design.

Disadvantage 7: the insulation coating will produce shrinkage deformation after drying. If it is a round line, the contraction will be more uniform, and the flat line is easy to damage, resulting in the actual processing, the yield of the flat line is far lower than the round line.

Production process of flat-wire motor

The main production process of the stator of the card issuing motor, wire forming and paper molding and paper insertion, these two processes are carried out simultaneously. Enter the stator insertion process, and then twist the wire, twist the completion of the welding process. After the welding is completed, the basic stator process of the motor is completed, followed by the coating, and then the performance test and verification. This is the basic process, with a lot of details in the middle.

Production process of flat wire motor: slot paper manufacturing card issuing ring insulation treatment of fixed end ring welding star joint

Application situation of flat wire motor

In the long run, miniaturization, high-speed will be the main development trend of new energy vehicle motor, and miniaturization must require motor power density has greatly improved, from the point of technical requirements, "much starker choices-and graver consequences-in planning" put forward the new energy vehicle drive motor peak power density to reach 4kW / kg, and now this data only reach 3.2-3.3kW/kg.

Flat line winding motor in Chevrolet volt 2, Nissan electric vehicles, Toyota's fourth generation prius foreign manufacturers have been successfully applied, is the inevitable trend of the development of new energy automobile motor development, including byd, saic, Beijing, precision into new energy, makers and motor production enterprises have launched the corresponding research.

Before 2020, the replacement effect of flat line motors on circular motors is still not obvious enough. Thanks to the advantage of small size of flat wire motors, flat wire motors will be prioritized for large-scale application in hybrid models, especially for plug-in models. However, due to domestic policy and market factors, plug-in models accounted for a relatively low proportion. In the field of pure electricity, only SAIC Roewe ERX 5 is equipped with flat wire motor, which is less used.

The development process of the third generation of general flat line motor gives us inspiration

General 1st generation flat wire motor

Chevrolet Voltec, The 4ET50 drive system (Chevrolet Voltec 4ET50-2011) is a dual motor architecture system. The Motor B motor is a flat wire hairpin motor with power 110 kW, torque 370 NM, speed 9500rpm and trough ratio of 12 poles 72 grooves.

The motor adopts the hairpin winding technology of axial plug line, that is to say, the single hairpin winding. This hairpin winding makes the arrangement in the groove very neat, which greatly improves the filling rate of the groove, while the end assembly can be enhanced, and the final effect of these two improvements is to reduce the DC resistance by 30~40%.

Although the hairpin motor can reduce the DC resistance, it is easy to sense the high frequency eddy current electric field on the winding when the frequency is high, producing skin effect.

GM used Voltec model to calculate the motor working point speed statistics, and determined that the motor speed is basically below 6000rpm under urban2 and US06, not more than 8000rpm. That is to say, the low resistance advantage of flat line can be brought into play. From this point of view, the flat wire motor is more suitable for medium and low speed applications.

After the end of the round line winding is painted, it becomes a solid whole. It is difficult for the cooling oil to penetrate into the interior. With the heat of the middle layer conductor, it is easy to form a heat island inside the winding.4ET50 motor adopts the end oil injection cooling technology, because there is a large gap between the end conductors of the flat wire, the nozzle oil directly penetrates into the end of the flat wire winding and takes away the heat of each conductor. The combination of flat line and end oil cooling can greatly improve the heat dissipation capacity and improve the power density.

General 2nd generation flat wire motor

The Spark was released in 2014, and the main drive is a 105 kW motor with a low speed of 4,500 rpm. The combination of technology is: axial insert flat line + double V torque structure + oil injection cooling technology.

The special work on the motor was run by GM's laboratory in Wickham, a suburb of Detroit, and for mass production in Baltimore, Maryland.

The running time of pure electric / extended range hybrid motor is much longer than that of full / plug-in hybrid motor, and the torque and power requirements are also higher. Additional range hybrid generally chooses the power shunt drive structure, with B motor as the main drive motor.

The drive system of the Chevrolet Walker is all propulsion powered by the B motor, so the B motor needs to meet the acceleration and drive requirements. A hairpin permanent magnet B motor and a centralized winding permanent magnet A motor are designed for early products. The choice of concentrated winding is mainly a space limitation.

However, the second generation Volt vehicle architecture drive requirements are split to the A / B motors. The size of the end-B motor was significantly reduced. Due to the low torque requirements of the A motor, a ferrite motor is designed.

In addition, pure electric vehicles are typically used with a single motor drive system, so the drive motor tends to have a large capacity to meet the needs of vehicle acceleration and drive. GM's pure electric Chevrolet Spark motor chose a low-speed IPM and a small deceleration ratio.

If the standard circular line winding is used as the reference control, the circular line resistance is 1.44 times that of the flat line resistance in Voltec, while the circular line resistance is 1.56 times that of the flat line resistance in Spark. That means the resistance of the Spark flat line drops more sharply. In addition to the protocol parameters themselves, this progress also benefits from the maturation of the flatline process.

In Spark motor, the molding and distortion of the hair card are made by CNC precision control + mold molding. In the molding process, not only the servo travel is controlled, but also the real-time feedback loop is closed. Through these technical means, that is, to ensure the accuracy of the winding forming, and can control the stress of the winding group, so that the quality of each turn coil is completely consistent.

General 3rd generation flat wire motor

In 2017, GM released Chevrolet Blot, with peak torque of 360 Nm, peak power of 150kW, peak speed of 8810rpm and peak current of the motor of 400 Arms.

The reducer speed ratio increases, and the motor speed increases by nearly 2 times. When the speed increases, the skin collection effect of the flat line motor conductor increases at high speed, leading to the increase of AC resistance.