Second, the structural characteristics of the axial magnetic field motor
1. The disadvantages of axial magnetic field motors
The magnetic field of the axial magnetic field motor is axial, and the stator and rotor are placed in equal position in the motor. Both the stator and the rotor are disc-shaped, so they are also called disc motors. The stator core is generally formed by double-sided insulated cold-rolled silicon steel sheet strips. On the silicon steel strip, a groove of exactly the same size is punched out at a certain distance, under the condition that the corresponding slots are aligned one by one. The stator core with the lower wire groove on the end face is formed by winding. The stator winding effective conductors are radially distributed in space. The rotor is a high magnetic energy permanent magnet, which is fixed on the disc core. The core machining of the axial motor stator is the key to motor manufacturing.
In actual production, due to various deficiencies in the blanking process and the unique structure of the stator core itself, the thickness of the silicon steel sheet is extremely thin, 0.5 to 1.0 mm, and thus the following problems occur more or less in the automatic forming of the circumference: The silicon steel sheets on both sides of the aligned slots are "bell-shaped" open; in the winding forming, in the case of insufficient rigidity of the winding machine, compaction is often caused; and the pre-perforated grooves are difficult to align. problem.
2. Armature core based on soft magnetic composite material (sMc)
Due to the magnetic circuit geometry, the axial magnetic field motor is difficult to manufacture the core by the lamination technology. The two methods can solve the problem of the laminated core: one is to use a solid body for processing or to use a printed core; the other is to use a coreless or Approximate magnetic circuit structure without iron core. The feasibility of these two methods is based on the acquisition of new materials: three-dimensional shaping by soft magnetic powder composites or directly through the pressing process to manufacture the stator core; high-performance hydromagnets and good thermal properties Plastic materials with mechanical properties to reduce or eliminate the use of ferromagnetic materials. At present, plastic materials are rarely used as structural members of motors due to cost. It is only used in plastic axial field motors that require light weight and high efficiency.
In order to overcome the difficulty in manufacturing laminated cores, the stator core is machined from SMC solid cylinders. A lot of slots are opened in the solid cylinder to secure the armature winding
group. The winding is fabricated into a concentrated winding which shortens the end connection of the phase winding and reduces the winding resistance, thereby reducing copper losses. Third, the characteristics of SMC materials
SMC used in axial magnetic field motors: The material is pressed from soft magnetic particles covered with an insulating film on the surface. The high-purity iron powder having good magnetic properties is mixed with the resin, and after treatment, a substance having high density and high strength and excellent compressibility is produced. The iron powder and lubricant mixture is first extruded, and during the extrusion process, stress is generated between the powders, which can be released by heat-treating the assembly at a sufficiently high temperature. The iron particles are electrically insulated from each other to ensure that SM (the material has a high electrical resistivity. The electrical resistivity, mechanical properties and magnetic properties of the SMC material depend on the size, density, thickness of the insulation, extrusion process and Heat treatment cycle. The characteristics of the sMc material can therefore be adjusted to suit the specific requirements of certain applications.
In general, the saturation magnetic density and relative magnetic permeability of SMC materials are lower than those of silicon steel sheets, as shown in Figure 2. The reason for the low magnetic permeability is that the magnetic flux in the SMC component must constantly pass through the non-magnetic insulation between the iron particles. The sMc material is used in motors because of its high electrical resistivity, which produces eddy current losses that are lower than those of silicon steel sheet materials. However, motors with SMC: materials have higher hysteresis losses. The total iron loss produced by the SMC material and the silicon steel sheet is shown in Figure 3. Another reason for the high loss of SMC is that the insulation between the iron particles on the surface of the sMc core is damaged, so that the eddy current loss on the surface is excessive. Therefore, the SMc stator core should be well pressed.
