Flat wire motors generally adopt 4 or 8 layers of flat wire structure, and each process can be produced fully automatically by proprietary equipment. The product consistency is good and the production efficiency is high. However, the requirement for equipment specificity is high. And the economic type is not suitable for small batch production of prototypes.
Flat wire motor windings in the stator slot arrangement, slot full rate, pure copper slot full rate of 70%, improve the motor torque output capacity and heat dissipation capacity; magnet double V structure rotor, the high utilization rate of magnets, improve the motor torque and power capacity; flat wire motor stator PIN foot end using laser welding, full and round welding joints, high welding strength, high welding efficiency, good consistency of welding joints.
A flat wire motor has the structural features of small size, lightweight, and high power density. The flat wire motor stator core designed by Founder has a 220mm outer diameter, 8 conductors per slot, C-type insulating paper, planetary connection for winding, 4-way parallel connection, center point connected by sink ring, compact structure, and high reliability.
The flat wire motor has high output performance. Founder The flat wire motor has a peak performance of 350Nm/170kW and continuous performance of 150Nm/65kW.
The maximum efficiency of the motor is 97.5% and the average NEDC efficiency is >94%.
Advantages of flat wire motors
1. has a high slot full rate. Usually can reach more than 70% of the slot full rate. Improving the slot full rate can effectively enhance the power density of the motor. And improves the heat dissipation in the stator slot.
2. has a stronger heat dissipation capacity. In addition to the flat wire at a low speed due to the AC resistance decline in heat generation. Compared to the round wire stator, reduce the thermal resistance in the slot, so that better heat transfer.
3. with stronger power torque capability. Flat wire motor lower heat generation and better heat dissipation capacity, electromagnetic design to properly enhance the thermal load of the stator winding, give more space to the rotor, to ensure that the flat wire stator temperature is similar to the round wire stator increases the rotor outer diameter to enhance the peak output capacity of the motor.
4. flat wire winding motor compared to the round wire winding motor. More efficiency advantages at low speed, more suitable for China’s urban road conditions for the vehicle needs.
A. Industry development drivers, the five advantages of flat wire motors
Advantage 1: High energy conversion efficiency brings battery cost savings.
Flat-wire motors can significantly improve conversion efficiency and reduce battery costs. According to SAIC Green Channel’s evaluation, the conversion efficiency of flat-wire motors is 1.12% higher than that of traditional round-wire motors under WLTC conditions. The difference between the two efficiency values is 2% in the full range average. In urban conditions (low speed and high torque), there is a 10% difference between the two efficiency values.
Lower copper consumption results in higher conversion efficiency for flat-wire motors than for round-wire.
Of the energy lost by the motor, 65% comes from copper consumption, 20% from iron consumption, 10% from wind friction loss, and 5% from stray loss. The copper consumption comes from the resistive heating of the current through the copper wire Q=I2R. When the slot full rate is higher, the copper wire required for the same power motor is shorter. Thus reducing the internal resistance, reducing the heat generation, and reducing copper consumption.
Theoretically, the slot fill rate of round wire is generally around 40%, while flat wire can be increased to 70%. Due to the circular cross-section of round wire, irregular gaps between wires are inevitable. While flat wire has smaller gaps and higher slot fill rates.
The high-efficiency range of flat-wire motors is much higher than that of round-wire motors. The general requirement for the high-efficiency range of round wire motors is that the percentage of the range with efficiency >85% should not be less than 85%. We call it “double 85”. The efficiency range for flat-wire motors is not less than 90% of the efficiency range > 90%. We call it “double 90”. The efficiency of the motor is related to the speed and torque. And the frequent start-stop conditions in the city are low speed and high torque conditions. It is the low-efficiency range of the round wire motor, while the conversion efficiency of the flat wire motor is higher in this condition.
Advantage 2: Good heat dissipation, improve high-temperature dynamics.
Flat-wire motors have good heat dissipation performance, reducing the temperature rise by 10% compared to round-wire motors. Due to the closer contact of flat wire compared to round wire, the heat dissipation is improved and it is found that the thermal conductivity between windings at a high slot fill rate is 150% of a low slot fill rate. The windings are anisotropic in terms of thermal conductivity, with the axial thermal conductivity being 100 times higher than the radial direction. Better acceleration performance can be achieved for the whole vehicle under lower temperature rise conditions.
Advantage 3: High power density, stronger power of the whole car.
According to the evaluation of SAIC Green Core Channel, the full rate of the flat wire motor slot has increased. As the copper wire filling volume increases by 20-30% in the same volume, we expect the output power to increase by 20-30%. It makes the whole vehicle more powerful.
Advantage 4: low electromagnetic noise, the whole car is quieter.
The stress of flat wire motor wire is larger and more rigid, and the armature has better rigidity. has a suppressive effect on armature noise. A relatively small slot size can be taken to effectively reduce the slot torque and further reduce the electromagnetic noise of the motor.
Advantage 5: Small size brings high integration efficiency and meets the development trend of all-in-one electric drive.
Due to the higher slot fill rate of flat wire, we expect the volume of the same power motor to decrease by 30% due to less copper wire usage and the corresponding stator. In addition, the flat wire motor is a more advanced winding method to bring a more easily cut motor end, compared with the round wire motor to reduce 15-20% of the end size, space to further reduce the motor miniaturization and lightweight.
B. We are solving barriers to flat wire motor applications one by one
Flat wire has many advantages that are incomparable to traditional windings, but at the same time flat wire motors also have some disadvantages. But in general, there is no shortcoming. With the development of technology and the gradual increase in penetration, we are going to solve the barriers to the application of flat wire motors one by one.
Application barrier 1: “skin effect” and “proximity effect” are obvious, AC impedance increases, and conversion efficiency decreases at high speed.
Skin effect refers to the phenomenon when there is AC current or alternating electromagnetic field in a conductor. The current inside the conductor is not uniformly distributed. And the current is concentrated in the “skin” part of the conductor. The proximity effect refers to the conductors close to each other, when there is an alternating current, each conductor is in the magnetic field generated by its own current. But also in the magnetic field generated by the current in other conductors. It makes the current distribution in each conductor will be affected by the neighboring conductors and uneven phenomenon. The “skin effect” and “neighboring effect” will increase the AC impedance. It will increase the AC impedance and reduce the conversion efficiency at high speed.
The “skin effect” does not affect the rapid increase in the penetration of flat wire motors, but engineers have also had improvement options:
1) increasing the aspect ratio of flat wire to indirectly increase the specific surface area of flat wire;
2) reducing the size of the conductor to indirectly increase the specific surface area of flat wire. But this will also reduce the full rate of the slot, we need to evaluate it.
3) using a multi-speed gear
4) 3D printing of copper wire, which allows for arbitrary variations in conductor size and cross-section, giving great freedom in winding design, which results in an electrically separated structure within the conductor, said electrically separated structure being used to limit the eddy current path so that the current density is “forced” In addition to the arbitrary connection geometry that can be achieved with the help of 3D printing, which does not require the traditional soldering process of winding joints, this solution cannot be mass produced in the short term.
Application barrier 2: non-standardization.
Different car companies have different design solutions, and the stator is the core of the motor design. After setting the stator size, the wire shape and size of the wire change at any point. It requires custom-made expensive tooling molds, low compatibility, and high difficulty of serialization.
Application Barrier 3: Flat wire motor production line investment is 2-5 times that of round wire.
Flat wire motors require high product consistency and technical difficulty. It requires investment in high-precision automated servo equipment, welding equipment, HairPin wire forming equipment, and tooling. We have confirmed the trend of electrification of automobiles and flat-wire motors. And flat-wire motors are gradually becoming the darling of capital.
Application Barrier 4: High demand for flat wire, high cost of flat wire and technical difficulty.
The processing of flat wire has become more difficult:
1) Switching from a round to a rectangular shape results in a more complex copper wire production process.
2) Coating is more difficult.
It is very difficult to coat the R corner of the flat wire, and it is difficult to ensure the uniformity of the insulation layer here. The insulation coating will shrink after drying, and the flat wire is non-uniformly shrunken and easily deformed, which requires improvement to make the coating thickness at the R corner thicker.
3) After the flat wire is bent into a hairpin, the stress is concentrated at the R corner.
It will easily lead to the breakage of the coating layer.
4) The industry requires flat wire with high precision, a large cross-sectional area, and a small number of turns.
Single wire inconsistency on the overall performance of the impact significantly increased, the consistency of the flat wire requirements are high, complex processing costs make the flat wire cost more, but also makes the flat wire processing companies enjoy a higher technical premium.
5) The enameled wire used in new energy vehicles is directly related to the stability of the vehicle’s operation, the quality control process, research and development, and process design capabilities of the electromagnetic wire manufacturers put forward high requirements.
It requires reasonable design and strict control of multiple control points such as drawing and coating speed, coordination of drawing and coating, drawing die configuration, tension control, coating die configuration, baking temperature, insulating paint viscosity, and working environment.
The biggest cost of flat wire is the raw material, oxygen-free copper rod. And the processing cost is not a high value in motors. A stable supply of qualified products is the key to cooperation with car companies. With the main cost being raw materials, there is not much incentive for car companies to seek suppliers with lower processing fees.
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