What is a flat wire motor? What are its advantages?
As the name suggests, a flat wire motor uses flat copper wire in its stator winding. The winding is first made into a hairpin-like shape, then inserted into the stator slot, and finally the ends of the hairpin are soldered together at the other end.
Advantages of flat wire motors
Advantage 1: For the same power output, smaller size, less material, and lower cost; or for the same volume, increased slot fill factor and higher power density. Theoretically, by changing from round to flat wire, a flat wire motor can achieve a 70% slot fill factor while maintaining the same space. The amount of copper filled can increase by 20-30%, generating a stronger magnetic field, which is equivalent to increasing power by 20-30% to some extent.
Advantage 2: Better temperature performance. Fewer internal gaps result in a larger contact area between the flat wires, leading to better heat dissipation and conduction; better contact between the windings and the core slots also improves heat transfer. Since motors are highly sensitive to heat dissipation and temperature, improved heat dissipation enhances performance. Temperature field simulations have shown that, for the same design, the temperature rise of a flat copper wire motor winding is 10% lower than that of a round copper wire motor.
Advantage 3: Lower electromagnetic noise. Flat wire motor conductors have higher stress and rigidity, resulting in better armature stiffness and suppressing armature noise; smaller slot sizes can be used, effectively reducing cogging torque and further lowering motor electromagnetic noise.
Advantage 4: Shorter ends save copper and improve efficiency. Traditional round wire motors, due to manufacturing limitations, generally have relatively long ends; otherwise, the copper wires are easily damaged during processing. For flat wire motors, because the wires are all hard wires, the ends can be made smaller during processing, reducing the end size by 20% compared to round wire motors. This further reduces space requirements, allowing for a smaller system size and achieving miniaturization and weight reduction.
Advantage 5: The highest efficiency point of a flat wire motor may not be much higher than that of a round wire motor, but the high efficiency range can be further expanded.
Types of flat wire motors
The winding types of flat wire motors mainly include I-pin, Hair-pin, X-pin, and S-winding.
I-Pin
The I-Pin winding is I-shaped, inserted directly, and then soldered to both sides. This eliminates the need for single-slot assembly, further reducing the space required for winding assembly. The disadvantages are a more complex soldering process and larger end dimensions.
Hairpin
Hair-pins are shaped like hairpins. They are first shaped, then inserted, and then soldered on one side. It is the most widely used form of flat wire winding.
X-pin
The X-pin winding is mainly optimized at the soldering end.
Compared to X-pin, hair-pin has a lower end height, which can further reduce the size of the motor, which is beneficial for the layout of the axial space of the vehicle and increases power density. The manufacturing process is relatively simple compared to wave winding. The investment in upgrading the current hair-pin production line is relatively low. The product performance and investment significantly surpass wave winding, and it is about to become a new trend in hairpin motors.
S-winding
The S-winding is S-shaped, and after forming, the two ends do not need to be welded. It also has a smaller end space, resulting in better NVH performance, reduced torque pulsation, smoother operation, and better performance cooling.
