Introduction to the advantages and disadvantages of flat wire motors, application analysis and development trend prospects

 At present, flat wire motors are more concerned in China, but their applications are relatively small , mainly because the development time of the new energy market is relatively short, and the main market share is concentrated in the mini-passenger vehicle market.

       There are already mature flat wire motor products used in new energy vehicles abroad, especially Japanese and European and American companies, Toyota and GM have adopted flat wire motors.

       The most representative ones are Chevrolet VOLT (Remy Motor) and Toyota Prius (Japan Denso), both of which use oil cooling solutions.

       In addition to foreign suppliers such as Remy, Denso, and Hitachi, domestic suppliers with stable shipments mainly include Huayu Electric, Songzheng Electric, and Founder Electric, which is about to be put into production.

       The drive motor is mainly composed of stator components, rotor components, end covers and auxiliary standard parts, and the stator windings also include iron cores, copper wire windings, insulating materials, etc.

       As the name suggests, the flat wire motor uses flat copper wire in the stator winding. First, the winding is shaped like a hairpin, penetrated into the stator slot, and then the end of the hairpin is welded at the other end.

▲Segmented hairpin winding

▲Continuous hairpin winding

Advantages of flat wire motors

Advantage 1: The same power, smaller volume, less material, lower cost, or the same volume, the slot full rate is increased, and the power density is increased. The round wire becomes a flat wire. In theory, under the premise of the same space, the flat wire motor can achieve a 70% slot full rate, and the filled copper can be increased by 20-30% to generate a stronger magnetic field strength. In a way that equates to a 20-30% increase in power.

Advantage 2: Better temperature performance. The internal gap is reduced, the contact area between the flat wire and the flat wire is large, and the heat dissipation and heat conduction are better; the contact between the winding and the core slot is better, and the heat conduction is better; and the motor is very sensitive to heat dissipation and temperature, and the heat dissipation Better, performance will improve. Some people have simulated the temperature field and found that the temperature rise of the flat copper wire motor with the same design is 10% lower than that of the round copper wire motor.

Advantage 3: Lower electromagnetic noise. The wire of the flat wire motor has relatively large stress and high rigidity, and the armature has better rigidity, which 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 .

Advantage 4: The end is short, saving copper and improving efficiency. For traditional round wire motors, due to process problems, the ends of the motors are generally left relatively long, otherwise the copper wire will be easily damaged during the process. For flat wire motors, because the wires are all hard wires, the ends can be made smaller during processing . Compared with the round wire motors, the end size is reduced by 20%, and the space is further reduced, which can reduce the volume of the system. Further reduction, miniaturization and light weight are realized.

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

Disadvantages of flat wire motors

Disadvantage 1: High-speed skin effect. The high power density of new energy vehicles requires a high speed. In the past, it was 10,000 or even 12,000 rpm, but now it is done in the direction of 16,000 or even 20,000. There needs to be some good ways to solve it in the process of motor design, which is a bad place.

Disadvantage 2: The copper wire requirements are high. There are many domestic manufacturers of round wire motor copper wires, and the quality can be very good. There are not many manufacturers that can make flat wire motors better, and the requirements are relatively high, and everyone needs to work together to solve the materials.

Disadvantage 3: The flat wire has many processing procedures, high equipment precision requirements, and large initial investment, because if its precision 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: Serialized design is difficult. In order to reduce the cost of the motor, it is best to serialize it. The serialized design is the place where the current flat wire motor is inferior to the round wire motor.

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

Disadvantage 6: The flat wire forming requirements are high and the processing is difficult. Because copper wire has a certain elasticity, it is necessary to leave a deformation allowance in the design.

Disadvantage 7: The insulating coating will shrink and deform after drying. If it is a round wire, the shrinkage will be more uniform, while the flat wire is prone to damage, resulting in a much lower yield rate of the flat wire in actual processing. .

Flat wire motor production process

       The main production process of the hairpin motor stator is wire forming, paper forming and paper insertion. These two processes are carried out simultaneously. Enter the wire insertion process of the stator, then twist the wire, and then perform the welding process after the twisting is completed. After the welding is completed, the basic process of the stator of the motor is completed, followed by coating, and then performance testing and verification. This is the basic flow with lots of details in between.

       Flat wire motor production process: slot paper → manufacturing hairpin → hairpin threading → end ring shaping → end ring welding → star point → insulation treatment at welding

Application of flat wire motor

       In the long run, miniaturization and high speed will be the main development trends of new energy vehicle motors, and miniaturization will inevitably require a substantial increase in motor power density. From the perspective of technical requirements, the "Thirteenth Five-Year Plan" proposes new energy vehicles. The peak power density of the drive motor should reach 4kW/kg, and the current data only reaches 3.2-3.3kW/kg.

       Flat wire winding motors have been successfully applied in foreign manufacturers such as Chevrolet volt2, Nissan electric vehicles, Toyota's fourth-generation Prius, etc. It is an inevitable trend in the development of my country's next-generation new energy vehicle motors. Currently, BYD, SAIC, BAIC, and Jingjin New Energy are in Internal OEMs and motor manufacturers have carried out corresponding research.

       Before 2020, the replacement of flat wire motors to circular motors is still not obvious enough. Thanks to the advantages of the small size of the flat wire motor, the flat wire motor will be preferentially applied in large-scale hybrid vehicles, especially plug-in vehicles. However, due to policy and market factors in China, the proportion of plug-in models is relatively low. In the pure electric field, only one model of SAIC Roewe ERX5 is equipped with a flat wire motor, which is rarely used.

Further reading:

01 Features of flat wire motor

• higher efficiency

1. Compared with the traditional round wire motor, the hair-pin motor can increase the slot full rate by 20%~30% (the copper occupies more per unit cross-sectional area), which can effectively reduce the winding resistance and thus reduce the copper loss;
2. The thicker the wire and the smaller the resistance, the smaller the energy lost due to heat on the wire;
3. The length of the end of the flat wire motor is 5~10mm shorter than that of the round wire motor, which effectively reduces the copper consumption of the end winding and further improves the motor efficiency;

• higher power density

1. As mentioned above, the slot full rate of the flat wire motor is higher, so under the same volume, the effective stator winding area of the flat wire motor is larger, so that the flat wire motor can output higher power and torque under the same loss;
   
   

• better heat dissipation

1. The flat wire of the flat wire motor has a more regular shape, fits closely in the stator slot, and has better contact with the teeth and yoke of the stator core, reducing the thermal resistance in the slot, and the heat conduction efficiency is higher;

• NVH performance is better

1. The motor using the flat wire structure will have better stiffness due to the better stiffness of the windings;
2. The flat wire winding is inserted through the end of the iron core, and there is no need to insert the wire from the slot. In the electromagnetic design, a smaller slot design can be selected to effectively reduce the cogging torque pulsation;

02Flat  wire motor processing technology

The overall process flow is as follows:

2.1 Paper Insertion Process

Process content: paper forming, paper cutting, paper insertion

Slot paper forming process: cold forming, hot forming

Paper shape: O, C, B, S

At present, the most popular drive motor is O-type, and double C-type is also useful (see the figure below). B-type and S-type can improve the insulation performance of the product, but it will reduce the full rate of pure copper slots and increase the difficulty of manufacturing, especially With 6-layer or 8-layer lines, the difficulty increases significantly and the manufacturing stability is worse.

The Type B design is currently patented.

 

2.2 PIN coil forming

Process content: straightening, removing patent leather, cutting, forming

Patent skin removal process: mechanical patent skin removal, laser patent skin removal

PIN forming process: stamping forming, spring machine technology forming

 

At present, stamping forming is the most popular process, so how to reduce the damage to the copper wire during the forming process has become a very important issue.

2.3 PIN pre-insertion

Pre-inserting the PIN into the profiling tooling makes it difficult to automatically insert cross-layer wires, and the difficulty of automatic insertion of 6-layer and 8-layer wires will also be greatly improved.

2.4 PIN overall insertion

Insert all the PINs pre-inserted into the profiling tool into the iron core, and press into the corresponding design size.

2.5 Flaring

Purpose of flaring:

1. Open the distance of each circle of solder joints to ensure the normal progress of the torsion and the creepage distance of the solder joints inside and outside the same groove;

2. The consistency of size after flaring is the basis to ensure the smooth progress of subsequent twisting

2.6 Turning the head

key point:

1. After twisting the head, the 2 wires that need to be welded are flush;

2. The copper wire cannot be damaged after twisting the head;

3. The slot paper cannot be damaged after turning the head.

2.7 Cut flat

Which form to use for cutting and leveling is a question worthy of study. At present, most domestic equipments have obvious step difference on the end face of copper wire after cutting and leveling.

2.8 Welding

 

As far as welding is concerned, welding itself is not difficult, but it is difficult to fast clamp and detect.

At present, the two most popular welding processes for flat wire motors are TIG welding and laser welding. Of course, there are also companies experimenting with CMT cold welding or other welding methods.

No matter what welding process is used, how to judge the quality of so many solder joints in such a small space is currently a difficult topic.

2.9 Coating and dipping

1. There are currently two main types of coating materials: powder and liquid. At present, these two materials are controlled by foreign companies.

The selection of materials determines the different process sequence:
when selecting powder materials, the process sequence is to apply first and then dip paint;
| select liquid materials, the process sequence is to dip paint first and then coat;
the specific process requirements shall be carried out according to the requirements of materials .

2. There are many kinds of dipping techniques, including traditional dipping, vacuum dipping, vacuum pressure dipping, drip dipping, etc., as well as the latest EUV dipping, which has a lot to do with the selection of paint materials. The paint process is also different and needs to be tested and verified. At present, drip dipping may be used more.

2.10 Copper nose soldering

Copper nose welding is currently mostly used for resistance welding, which can be welded with solder (brazing material, etc.) or without solder.

With the increasing market requirements for motor technology trends, the general trend of flat wire drive motors is coming:

The first stage: From 2018 to 2020, the penetration rate in the field of new energy passenger vehicles will reach 50%. Market space : Assuming that in 2020, the flat wire will achieve 50% penetration in the annual sales of new energy passenger vehicle drive motors in China. According to 2020 The annual sales volume of 1.6 million new energy passenger vehicles is estimated to be 800,000 sets of flat wire motors in China. Assuming a unit price of 3,500 yuan, the market size is close to 3 billion yuan. Calculated based on a 10% net profit rate, it corresponds to an industry net profit of 300 million yuan.

The second stage: From 2021 to 2022, the penetration rate in the field of new energy passenger vehicles will reach 90%. Market space: Assuming that in 2022, the flat wire will achieve 90% penetration in the annual sales of passenger vehicle drive motors. According to 3.2 million in 2022 It is estimated that the sales volume of new energy passenger vehicles requires 2.88 million units. Assuming that the unit price is 3,000 yuan, the market size is close to 9 billion yuan. Calculated at a net profit rate of 10%, it corresponds to an industry net profit of 900 million yuan.

The third stage: After 2023, the market share of new energy passenger vehicles will be close to 100%, and at the same time, it will gradually penetrate into the field of logistics vehicles and passenger vehicles. The market size continues to grow.