The stator of the brushed permanent magnet DC motor is equipped with a fixed main pole and brush, and the rotor is equipped with armature windings and commutators. The power of DC power supply enters armature winding through brush and commutator, which generates armature current. The magnetic field generated by armature current interacts with the main magnetic field to produce electromagnetic torque, which makes the motor rotate to drive the load. Due to the existence of brush and commutator, brush motor has complex structure, poor reliability, many faults, large maintenance workload, short life, and commutation sparks are prone to electromagnetic interference. There are magnets in the fixed part of the permanent magnet DC motor with brushes, which is called the main pole, and brushes in the fixed part. The rotating part has an annular core and windings wound on the annular core.
Types of Brush Permanent Magnet DC Motor
Brushless permanent magnet DC motors can be roughly classified into the following three categories:
1) Brush disc winding motor. Brush disc winding motor is bonded to a cylinder block with rare earth material. The winding made of enameled copper wire is placed in the cylinder block to form a rotor. The motor phase is adjusted by mechanical commutator. Mechanical commutator adjusts voltage phase by friction between fixed carbon brush and rotating copper commutation surface. The brush of this motor has been wearing away in use, and the life of the motor can hardly exceed 2000 hours. At the same time, because of the high speed of the motor, two-stage gear deceleration must be adopted, which brings two problems. One is the noise, the other is the loss of efficiency. After deceleration, the rated efficiency of the motor can only reach 68%-72%. However, the capacity of batteries used in electric bicycles is limited, generally 36V/12Ah capacity. If the motor efficiency is not high, it will increase the power consumption and affect the mileage.
2) Brush-printed winding motor. Brush-printed winding motor uses printed copper foil as winding, which reduces the weight of the motor. Because this kind of motor is all produced on the automatic production line, the technology has reliable guarantee, so that the life of the motor can be increased to 3000 hours, the noise can be greatly reduced, and the efficiency can be increased to 72%-76%. But this kind of motor has "buzz" high frequency noise, the efficiency is still not ideal after gear deceleration, the use of brush commutator makes the motor life can not be further improved.
3) Brush-pressed winding motor. By pressing the wound copper wire into a new type of winding, the efficiency of the motor can be increased to 74%-78%. At present, this kind of motor is still used by many electric bicycle manufacturers, but its efficiency, noise and life defects still need to be improved.