Design rules for automotive armatures

　　 Automotive Armature Manufacturer's Statement Single-layer windings are not suitable for large-capacity motors, and small-capacity motors should not be double-layered. The magnetic flux density of the motor core should not be too high or too low. When the frequency and thickness of the silicon steel sheet core material are constant, the iron loss depends on the magnetic flux density. If the magnetic flux density is too high, the iron loss increases, and the motor efficiency decreases. The increased heat from the iron core increases the motor temperature, and the increased excitation power increases the motor power factor, so the magnetic flux density of the core should not be too high. Try to avoid excessive saturation of the magnetization curve. If the magnetic density is too low, it will increase the use of motor materials and increase the cost. The rotor teeth are narrow, the magnetic density is high, and the slot entry wire is large, i.e., the automotive armature slots are large.

　　Automotive Armature Manufacturer's Statement Due to poor air conduction, there are many gaps in the slots, affecting the coils and easily damaging the heat dissipation of the insulation material, accelerating the increase in motor temperature. The slot fill factor of the motor slots cannot be too high or too low. Generally, the slot fill factor for low-speed motors is 75% to 85%, which can effectively prevent the enamelled wire from loosening in the slots. The design of the motor rotor slot shape should use parallel trapezoidal recesses as much as possible, and the edges of the recesses should not have sharp corners. Try to use a circular bottom recess, because the circular slot is filled with aluminum, which is easy to injection mold and the stator chip is easy to insert.

　　The coil current density should not be too large or too small. The motor coil has a certain resistance, and when current passes through the coil, it will cause losses. The winding temperature increases. The motor design should reduce resistance, reduce losses, and improve efficiency. A thicker wire diameter reduces the current density and can reduce resistance, but increases the amount of coil material. Due to the increase in the recess area, the iron core magnetic density increases, thereby increasing the excitation current and iron loss of the motor. When designing the laminated structure, try to design slots with a large area. Generally, induction motors usually take 37A/mm2.

　　The width of the motor slots should not be too large. If the slots are too large, the air gap flux distribution cannot be uniform, the tooth harmonics increase, and the additional losses increase. Usually, the width of the slots is about 3.5 mm. If it is too small, the enamelled wire cannot enter. The number of stator slots should not be too many or too few. Asynchronous motors have a large number of stator slots, a large magnetomotive force, a good electromotive force waveform, small additional losses, and high motor efficiency. The number of slots also increases the contact area between the coil and the core, the coil heating is good, the temperature rise is low, and the performance is good, but the production process is difficult and the cost is high.

　　 Automotive Armature Manufacturer's Statement The critical speed of the rotor should be greater than 1.2 times or less than 0.8 times the rated speed to avoid resonance. Asynchronous motors have a large air gap, large reluctance, and large excitation ampere-turns, which increase the motor excitation current and reduce the motor power factor. A large air gap weakens the harmonic magnetic field, and reduces the extra losses of the motor. Too small an air gap increases extra losses and reduces motor efficiency. Rotor skewing in asynchronous motors weakens the axial harmonic potential phase, thereby reducing additional synchronous torque and additional asynchronous torque, thereby reducing additional losses in the motor, improving efficiency, and reducing noise and vibration.