JP4720632B2 - Brushless motor - Google Patents

Description

  The present invention relates to an inner rotor type brushless motor formed by arranging a plurality of permanent magnets on the outer peripheral surface of a rotor core.

  Conventionally, as shown in FIG. 6, a rotor 1 in which a plurality of permanent magnets 4 are arranged in the circumferential direction on the outer peripheral edge of the rotor core 3, and the rotor 1 is driven to rotate while surrounding the outer periphery of the rotor 1. An inner rotor type brushless motor is known which includes a stator 2 that generates a magnetic field (see, for example, Patent Document 1).

In the brushless motor, when the rotor 1 has a large diameter, the moment of inertia increases, resulting in a decrease in responsiveness. In order to prevent this increase in the moment of inertia, it is conceivable to provide a hole in the rotor core 3. However, since the rotor core 3 forms part of the magnetic circuit, the moment of inertia is simply provided by providing a hole. However, there is a problem that the strength of the magnetic field also decreases and the motor characteristics deteriorate.
JP 2005-176451

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a brushless motor capable of reducing the moment of inertia of the rotor without affecting the motor characteristics.

In order to solve the above problems, the present invention is achieved by arranging a plurality of permanent magnets 4 in the circumferential direction on the outer peripheral edge of the rotor core 3 and press-fitting and fixing the rotor shaft 5 in the central through hole of the rotor core 3. And a stator 2 that surrounds the outer periphery of the rotor 1 and generates a magnetic field for driving the rotor 1, and each permanent magnet 4 has a cross section perpendicular to the axis O of the rotor core 3. A tangent line T passing through the circumferential center point B of the inner peripheral edge of the rotor core 3 is drawn, and the axis O of the rotor iron core 3 passes through between the permanent magnet 4 depicting the tangent line T and another permanent magnet 4 adjacent thereto. When the arc L (or circle) A passing through the circumferential center B of the permanent magnet 4 is drawn around the intersection C of the tangent line T and the straight line L, the permanent magnet 4 is drawn. Outside each arc A and the rotor In a position corresponding to one-to-one inside each permanent magnet 4 in the area S to be the interior of the heart 3, to form pores 10 for inertia moment suppressed, are arrayed in the circumferential direction of the region S The portion excluding the plurality of holes 10 is a fixed frame portion 11 for fixing the rotor shaft 5 and the rotor core 3 .

  In the brushless motor of the present invention, the region S drawn as described above is a portion where the magnetic flux density in the rotor core 3 is very sparse, and therefore the portion that hardly functions as a yoke. Focusing on this point, a hole 10 for suppressing the moment of inertia is formed in the region S. Thereby, it is possible to reduce the moment of inertia of the rotor 1 without affecting the motor characteristics, and to improve the response.

  In the present invention, there is an effect that the moment of inertia of the rotor can be reduced without affecting the motor characteristics.

Hereinafter, the present invention will be described based on embodiments shown in the accompanying drawings. 1 to 3 show an example of a brushless motor according to an embodiment of the present invention. The brushless motor of this example is an inner rotor type brushless motor having the same basic configuration as the conventional one shown in FIG. 6, and the rotor core 3 is formed in a cylindrical shape (annular cross section) using a magnetic material. In addition, a cylindrical rotor shaft 5 is press-fitted and fixed in the central through hole of the rotor core 3. A plurality of tile-shaped permanent magnets 4 (four in this example) curved with a curvature along the outer peripheral surface are bonded to the outer peripheral surface having a circular cross-section of the rotor core 3, thereby reducing the outer peripheral surface. It covers the whole thing.
It is. The permanent magnets 4 are arranged on the circumference at equal intervals (a slight gap) in the circumferential direction of the rotor core 3 so that the permanent magnets 4 adjacent in the circumferential direction have different polarities. Provided.

  The rotor 1 composed of the rotor core 3, the permanent magnet 4, and the rotor shaft 5 has a rotor shaft in a substantially cylindrical case 7 via a pair of bearings 6 that support both axial ends of the rotor shaft 5. 5 is accommodated so as to be rotatable around an axis O. A stator 2 is mounted on the inner peripheral surface of the case 7 so as to surround the outer periphery of the rotor 1 with a predetermined interval. The stator 2 has a main body formed in a cylindrical shape surrounding the rotor 1 using a magnetic material, and a plurality (six in this example) of magnetic pole teeth 8 from the inner peripheral surface of the main body. A groove portion 9 is formed between the magnetic pole tooth portions 8 adjacent to each other in the circumferential direction so as to be spaced apart at equal intervals in the circumferential direction. A coil (not shown) is wound around each magnetic pole tooth portion 8, and each adjacent groove portion 9 is set as a storage position of the coil. By appropriately controlling the energization of the coil, a magnetic field for rotating the rotor 1 around its axis is generated in the stator 2.

  The structure of the hole 10 which is a characteristic part of the present invention will be described in detail below. The hole 10 is a hollow portion provided inside the rotor core 3 having a cylindrical shape penetrating both ends, and corresponds to the inside of each permanent magnet 4 arranged in the circumferential direction in a one-to-one correspondence. By forming four locations for convenience, it plays the role of reducing the moment of inertia of the entire rotor core 3.

  The hole 10 is formed so as to be in a region S indicated by hatching in FIG. 1 in a cross section perpendicular to the axis O of the rotor iron core 3. In order to derive this region S, in each permanent magnet 4 which has an outwardly convex sectional fan shape and whose inner peripheral edge is bonded to the outer peripheral edge of the rotor core 3, first, the inner peripheral edge (main In the example, a tangent line T passing through the circumferential center point B of the rotor iron core 3) is drawn. In FIG. 1, a tangent line T is drawn with respect to the upper right permanent magnet 4.

  Next, the rotor core 3 passes through the center of the gap provided between the permanent magnet 4 depicting the tangent line T and another permanent magnet 4 adjacent to the permanent magnet 4 (lower right in FIG. 1). A straight line L extending from the axis O is drawn. Then, an arc A passing through the circumferential center point B of the inner periphery of the permanent magnet 4 describing the tangent line T is drawn with the intersection C of the tangent line T and the straight line L as the center. This arc A has a radius R from the central intersection C to the center B in the circumferential direction.

  When the arcs A are drawn between the permanent magnets 4 arranged in a plurality of rows and the other permanent magnets 4 adjacent thereto, the arcs A are outside the arcs A and inside the rotor core 3. This region becomes the region S for forming the holes 10.

  In this example, the outer peripheral edge of the rotor core 3 has a circular shape in a cross section orthogonal to the axis O, and the inner peripheral edge of the permanent magnet 4 has an arc shape that perfectly follows the outer peripheral edge of the rotor core 3. Therefore, in a pair of adjacent permanent magnets 4, arcs A drawn toward the other with the circumferential center point B as the center coincide with each other. Therefore, an arc A passing through the circumferential center point B on both sides is drawn for each combination of permanent magnets 4 with the intersection C of the tangent line T passing through the circumferential center point B between a pair of adjacent permanent magnets 4 as the center. In this case, the region inside the rotor core 3 surrounded by the four arcs A drawn for convenience is the region S.

  If the holes 10 are formed so as to occupy substantially the entire area S, the moment of inertia of the rotor core 3 can be effectively reduced without substantially affecting the strength of the magnetic field. Is as follows.

  FIG. 4 (a) shows the magnetic flux density distribution that occurs when the rotor core 3 is not provided with the air holes 10 (that is, the conventional case shown in FIG. 6), and FIG. 4 (b) shows the rotor core. 3 shows a magnetic flux density distribution generated when the holes 10 are provided. The thin lines in the figure are magnetic flux lines, and these magnetic flux density distributions and magnetic flux lines are obtained by electromagnetic field analysis. If the magnetic flux density is blue, it indicates a sparse state, and the magnetic flux density becomes denser as it approaches green, yellow, and red. If the gap between the magnetic flux lines is wide, the magnetic flux density is sparse, and if the magnetic flux density is concentrated, the magnetic flux density is dense.

  As can be seen from FIG. 4, the magnetic flux lines generated from the circumferential half of the permanent magnet 4 (for example, the left half of the upper right permanent magnet 4 in the figure) are the other permanent adjacent to the side close to the circumferential half. The magnet 4 passes through the rotor core 3 so as to draw an arc toward the circumferential half on the near side (the right half of the permanent magnet 4 at the upper left in the figure). And outside these arc-shaped magnetic field lines, the magnetic flux density is very sparse. Since the portion where the magnetic flux density is very sparse in the rotor core 3 hardly exhibits the effect as a yoke, in the present invention, paying attention to this point, substantially the entire area S is substantially entirely removed. The holes 10 are formed so as to occupy. Note that the arc A having a radius R drawn to form the region S approximates the magnetic field lines starting from the circumferential center of the permanent magnet 4 and ending at the circumferential center of another adjacent permanent magnet 4. .

  In FIG. 5, the generated torque when the hole 10 is not formed (that is, the conventional case shown in FIG. 6 or FIG. 4A) is indicated by “◇”, and the hole 10 is large in the region S. The generated torque in the case where the portion is formed so as to occupy the portion (that is, in the case of this example shown in FIGS. 1 to 3 and FIG. 4B) is indicated by “*”, but also from the comparison in this graph As is apparent, the presence or absence of the air holes 10 hardly affects the motor characteristics of the brushless motor. On the other hand, the moment of inertia of the rotor core 3 is reliably reduced by the presence of the holes 10.

  Theoretically, the moment of inertia can be reduced most if the entire area S is the holes 10, but in consideration of actual mass productivity, the rotor shaft 5 and the rotor core as shown in the figure. 3 is preferably provided in the region S, and the portion excluding the fixed frame portion 11 in the region S is preferably the hole 10.

  In this example, a plurality of permanent magnets 4 are arranged on the outer peripheral edge of the rotor core 3 by adhering the permanent magnets 4 to the outer surface having a circular cross section of the rotor core 3 as described above. However, the present invention is not limited to this. For example, the permanent magnets 4 may be embedded in the rotor core 3 so as to be arranged on the outer peripheral edge of the rotor core 3.

It is explanatory drawing of an example brushless motor in embodiment of this invention. The external appearance of a brushless motor same as the above is shown, (a) is a perspective view, (b) is a side view. The internal structure of a brushless motor same as the above is shown, (a) is a front sectional view, and (b) is a side sectional view. It is the figure which analyzed the electromagnetic field which generate | occur | produces in a brushless motor, and expressed the density of magnetic flux density in the color, (a) shows the case where a hole is not provided, (b) shows the case where a hole is provided. It is the graph which made the generated torque of a brushless motor compare with the presence or absence of a hole. It is explanatory drawing of the conventional brushless motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotor 2 Stator 3 Rotor core 4 Permanent magnet 10 Air hole A Circular arc B Center point in the circumferential direction C Intersection L Straight line O Shaft center S area T Tangential line

Claims (1)

A rotor in which a plurality of permanent magnets are arranged in the circumferential direction on the outer peripheral edge of the rotor core and the rotor shaft is press-fitted and fixed in a through hole in the center of the rotor core, and a magnetic field for driving the rotor while surrounding the rotor A brushless motor comprising a stator that generates a tangent line, and in a cross section perpendicular to the axis of the rotor iron core, a tangent line passing through a central point in the circumferential direction of the inner peripheral edge of each permanent magnet, A straight line extending from the axis of the rotor iron core is drawn so as to pass between the other permanent magnets adjacent to the permanent magnet, and passes through the center point in the circumferential direction of the permanent magnet around the point where the tangent line and the straight line intersect. when drawing an arc, a position corresponding to the one-to-one inside each permanent magnet in the region to be the interior of the outer and and and rotor iron core of each arc drawn about the permanent magnets, the holes for the inertia moment suppressed Formed, the brushless motor, wherein a portion excluding the plurality of holes are arrayed in the circumferential direction, and a fixed frame part for fixing the rotor shaft and the rotor iron core of the above areas.