JP2018042371A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve magnetic characteristics of a magnet and strength of a rotor core while suppressing a shaft press-fitting load to a shaft hole of the rotor core, in a magnet embedded type brushless motor.SOLUTION: A brushless motor 1 has a rotor 3 in which a plurality of rotor magnets 18 each having a circular arc-shaped cross section are buried. The rotor 3 has a shaft 13 and a rotor core 16. The rotor core 16 has a shaft hole 42 to which the shaft 13 is press-fitted and fixed. On an inner peripheral surface 43 of the shaft hole 42, a plurality of protruding parts 46 and a plurality of recessed parts 47 are formed. The protruding parts 46 and the recessed parts 47 are alternately provided on the inner peripheral surface 43 in a circumferential direction. Each protruding part 47 is formed in a substantially trapezoid shape, and arranged at a position opposed to an apex 48 of the rotor magnet 18, where the rotor magnet 18 is the closest to the shaft hole 42.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a brushless motor, and more particularly to a rotor structure of a magnet-embedded brushless motor.

  Conventionally, as a kind of brushless motor, a reluctance motor that generates a rotational force using a magnetic resistance difference between a stator and a rotor is known. In recent years, a magnet-assisted reluctance motor in which a magnet (permanent magnet) is arranged in a rotor has been proposed for the purpose of improving output while using this reluctance motor as a base (Patent Document 1). Such a motor includes a stator including a plurality of phases of windings and a rotor disposed in the stator, and a plurality of magnets are embedded in the rotor. The rotor is composed of a shaft (rotor shaft) that is a rotating shaft and a rotor core in which a magnet is embedded, and the rotor core is press-fitted and fixed in a shaft hole that penetrates the central portion of the rotor core.

  However, in this case, if the shaft is pressed into the rotor core as it is, the inner periphery of the shaft hole of the rotor core and the outer periphery of the shaft are in close contact with each other, so the shaft press-fitting load increases, and the stress causes distortion in the rotor core or the shaft buckles. There is a fear. For this reason, as a method of coupling the rotor core to the shaft in order to reduce the press-fitting load, a knurled (claw-like protrusion) is formed on the outer periphery of the shaft to prevent it from coming off or to prevent rotation, as in Patent Document 2, A technique has been implemented in which the inner periphery of the shaft hole has a concavo-convex structure and the shaft is partially pressed into the surface.

JP 2014-39399 A JP 2010-57274 A

  However, the fixing by the knurling can suppress the press-fitting load, but there is a problem that the center of the rotor core and the center of the shaft easily shake in the radial direction at the time of press-fitting, and it is difficult to keep the axial accuracy of the rotor core high. In addition, although the press-fitting load itself can be suppressed with the method of making the inner periphery of the shaft hole uneven, depending on the position of the recess, the degree of orientation of the magnet may decrease, or the rotor core may be distorted by the press-fitting load or magnet injection molding pressure. There was a problem that occurred.

  An object of the present invention is to improve the magnetic properties of a magnet and the strength of a rotor core while suppressing a shaft press-fitting load on the rotor core in a magnet-embedded brushless motor.

  The brushless motor of the present invention is a brushless motor having a stator having a field coil, and a rotor rotatably disposed in the stator and having a plurality of magnets embedded therein, the rotor being A shaft, and a rotor core fixed to the shaft, the rotor core including a shaft hole into which the shaft is press-fitted and fixed, and the shaft hole has a plurality of shafts held on an inner peripheral surface thereof. And a plurality of concave portions formed between the convex portions, the convex portions and the concave portions are alternately provided along the circumferential direction on the inner peripheral surface, and the convex portions are The magnet is disposed at a position closest to the shaft hole.

  In the present invention, a plurality of convex portions and concave portions are alternately provided along the circumferential direction on the inner peripheral surface of the rotor core shaft hole, and the convex portions are arranged at positions where the magnet is closest to the shaft hole, The shaft is press-fitted and fixed in this shaft hole. As a result, the shaft is less likely to swing in the radial direction during press-fitting as compared with the fixation by the knurled, and the axial accuracy of the rotor core and the shaft is improved. In addition, the unevenness of the inner peripheral surface of the shaft hole allows the load during shaft press-fitting to escape to the recess, reducing the press-fit load, and suppressing distortion of the rotor core and shaft buckling during shaft press-fitting. Furthermore, by arranging the convex portion at the closest portion between the magnet and the shaft hole, the convex portion can secure a larger dimension of the portion that tends to be thin. As a result, the volume of the magnetic body on the back side of the magnet can be increased, the magnetic flux can easily pass, and the magnetization orientation is improved. In addition, when the magnet is injection molded, the molding pressure can be received by the shaft together with the convex portion, and the distortion of the rotor core during the injection molding can be suppressed.

  In the brushless motor, the magnet is formed in a circular arc shape, embedded in the rotor in a state where the convex side portion faces the center side of the rotor, and the convex portion is opposed to the arc apex of the magnet. You may make it arrange | position to a position. Further, in the brushless motor, the magnet has a trapezoidal three-sided cross section, and the upper base portion thereof is embedded in the rotor in a state of being directed toward the center of the rotor. You may make it arrange | position in the position where the said shaft hole is closest to the upper-bottom part.

  Further, the rotor core is formed by laminating a plurality of steel plates having a thickness t, and a distance Lt between the magnet and the inner edge of the convex portion is set to a value that is at least the thickness t (Lt ≧ t). Also good. Thereby, the steel plate for rotor cores can be easily formed by press work. Further, a steel plate portion having a width equal to or greater than the plate thickness t can be secured on the back side of the magnet.

  Furthermore, the convex portion may be formed in a substantially trapezoidal shape, and the width WL of the lower bottom portion on the outer diameter side may be larger than the width WU of the upper bottom portion on the inner diameter side (WL> WU). Thereby, the base angle of a convex part becomes an acute angle (the outer angle of a base angle is an obtuse angle), and press formability improves. Further, by reducing the convex press-fitting surface (upper bottom part), the shaft press-fitting load can be released also in the radial direction, and distortion of the rotor core and shaft buckling during press-fitting of the shaft can be suppressed.

  The brushless motor may be used as a drive source for the electric power steering apparatus. In the brushless motor, since the rotor core and the shaft are coupled with high axial accuracy, rattling due to eccentricity is small, and fluctuations in torque ripple are also suppressed to a low level. For this reason, the feeling of steering can be improved by using the brushless motor in the electric power steering apparatus.

  According to the brushless motor of the present invention, in a brushless motor having a rotor in which a plurality of magnets are embedded, a plurality of protrusions and recesses are provided around the inner peripheral surface of the rotor core into which the rotor shaft is press-fitted. In addition to being alternately provided along the direction, the convex portion is arranged at the position where the magnet is closest to the shaft hole, so that the press-fitting load of the shaft can be reduced and the axial accuracy of the rotor core and the shaft can be improved. It becomes possible. In addition, the convex portion can secure the dimension of the magnetic path of the part that tends to be thin between the magnet and the shaft hole, so that the magnetic flux can easily pass through the back side of the magnet and improve the magnetization orientation. Is possible. Further, when the magnet is injection molded, the molding pressure can be received by the shaft together with the convex portion, and the distortion of the rotor core during the injection molding can be suppressed.

It is explanatory drawing which shows the structure of the brushless motor which is one Embodiment of this invention. It is sectional drawing along the AA line of FIG. It is explanatory drawing which shows the structure of a rotor core. It is the graph which showed the induced voltage waveform at the time of using the rotor of each structure of A and B in FIG. It is explanatory drawing which shows the modification of a rotor magnet shape.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of a brushless motor 1 (hereinafter abbreviated as motor 1) according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along the line AA of FIG. As shown in FIG. 1, the motor 1 is an inner rotor type brushless motor in which a stator (stator) 2 is disposed outside and a rotor (rotor) 3 is disposed inside. The motor 1 is an IPM (Interior Permanent Magnet) type brushless motor in which a magnet is embedded in the rotor 3 and the rotor is rotated by magnet torque and reluctance torque.

  The motor 1 in FIG. 1 is used, for example, as a power source of a column assist type electric power steering apparatus, and is attached to a speed reduction mechanism portion (not shown) provided on a steering shaft. The rotation of the motor 1 is decelerated and transmitted to the steering shaft by the deceleration mechanism, and an operation assisting force is applied to the steering shaft of the automobile. The IPM structure motor has a smaller magnetic friction than the SPM structure motor, and the viscous torque can be kept small. Therefore, the handle has good convergence and is suitable for an electric power steering apparatus.

  The stator 2 includes a bottomed cylindrical housing 4, a stator core 5, a plurality of teeth 5b of the stator core 5, a plurality of field coils 6 (hereinafter abbreviated as coils 6) wound around each tooth 5b, and a bus bar unit. 7. The bus bar unit 7 is attached to the stator core 5 and is electrically connected to the coil 6. The housing 4 is formed in a bottomed cylindrical shape with iron or the like, and also serves as a motor case. A bracket 8 made of synthetic resin is attached to the opening of the housing 4 with a fixing screw 10. A synthetic resin insulator 11 is attached to the stator core 5. Each coil 6 is wound around the outside of the insulator 11. At one end side of the stator core 5, end portions 6 a of the coils 6 are drawn out.

  The stator core 5 is formed by laminating a plurality of steel plate materials (for example, electromagnetic steel plates). As shown in FIG. 2, the outer ring portion 5a of the stator core 5 is formed with a plurality (24 in this case) of teeth 5b extending inward in the radial direction along the circumferential direction. Slots 19 are formed between adjacent teeth 5b. In the motor 1, 24 teeth 5b are provided and have a 24-slot configuration. A coil 6 is accommodated in each slot 19. A bus bar unit 7 that is electrically connected to the coil 6 is attached to one end side of the stator core 5. The stator core 5 is fixed in the housing 4 by means such as press fitting after the bus bar unit 7 is attached.

  The bus bar unit 7 has a structure in which a plurality of copper bus bars 9 are insert-molded in a synthetic resin main body. Each bus bar 9 has a plurality of power feeding terminals 12 protruding in the radial direction. Around the bus bar unit 7, the power supply terminals 12 project radially. When the bus bar unit 7 is attached, each coil end 6 a is welded to the power feeding terminal 12. In the bus bar unit 7, the bus bar 9 is provided in a number corresponding to the number of phases of the motor 1 (in this case, three for the U phase, V phase, W phase and one for connecting each phase). It has been. Each coil end 6a is electrically connected to a power supply terminal 12 corresponding to the phase. On the other hand, a part of the bus bar 9 corresponding to each phase extends in the axial direction from the end face of the bus bar unit 7 to form a bus bar terminal 33 corresponding to the phase.

  A power terminal 31 is also insert-molded in the bracket 8. The power terminal 31 is provided for each of the U, V, and W phases, and one end side 31 a thereof is disposed in the opening 32. The other end 31 b of the power terminal 31 is disposed in the power connector 34. When the bracket 8 is assembled to the housing 4, each bus bar terminal 33 extending in the axial direction from the bus bar unit 7 faces the corresponding power terminal 31 in parallel. In the motor 1, after the bracket 8 is attached to the housing 4, the bus bar terminals 33 and the power terminals 31 are electrically fixed by welding in the openings 32.

  A rotor 3 is concentrically disposed inside the stator 2. The rotor 3 has a shaft 13 that serves as a motor rotation shaft. The shaft 13 is rotatably supported by the housing 4 and the bracket 8 by ball bearings (hereinafter abbreviated as “bearings”) 14a and 14b. The rear bearing 14 a is press-fitted and fixed to a bearing housing portion 4 a formed at the center of the bottom of the housing 4. The front-side bearing 14 b is fixed to the center portion of the bracket 8 by a metal bearing holder 15.

  The shaft 13 is press-fitted and fixed in the shaft hole 42 of the rotor core 16 formed by stacking the rotor core plates 35. As described above, the motor 1 has an IPM configuration, and the rotor core 16 is formed with a plurality of sets of slit groups 17 each having an arcuate (bow-shaped) hole. Each of the slits 17 a to 17 c of the slit group 17 is provided along an arc centered on a virtual point (not shown) set outside the outer periphery of the rotor 3. The slit group 17 is formed in three layers along the radial direction so that the convex side portion thereof faces the center side of the rotor 3. The set of slit groups 17 includes an outermost first slit 17a, an intermediate second slit 17b, and an innermost third slit 17c.

  Each slit group 17 is filled with a bond magnet (bond magnetic material), and a rotor magnet 18 is formed. By filling the bond magnet, an arc-shaped rotor magnet 18 is built in the rotor 3, and the motor 1 becomes a brushless motor having an IPM structure. As the bond magnet, for example, a material obtained by mixing magnetic powder of a rare earth magnet such as a neodymium magnetic material, such as an anisotropic neodymium bond magnetic material, with a synthetic resin such as epoxy is used. The bond magnetic material is formed by filling the slit group 17 by injection molding and performing predetermined magnetization. The injection molding of the rotor magnet 18 is performed after the shaft 13 is press-fitted into the shaft hole 42 of the rotor core 16.

  In the rotor 3, the magnetic pole portion 20 formed of a layered magnet group is formed by the rotor magnet 18 in the slit group 17. The magnetic pole part 20 is arranged with two S poles and N poles alternately (four in total) along the circumferential direction. As a result, the motor 1 has a 4-pole 24-slot (4P24S) structure. The rotor magnets 18 of the magnetic pole portions 20 are arranged in three layers along the radial direction. In the rotor 3, a plurality of d-axes in the direction of the magnetic flux created by the magnetic poles and q-axiss that are magnetically orthogonal to the d-axis are alternately formed in the circumferential direction by the magnetic pole portion 20. In the adjacent magnetic pole portions 20, the areas of the spaces 36 (36a, 36b) formed outside the outermost first slit 17a are different. That is, the distance L between the apex 37 of the first slit 17a (the position closest to the center of the arc convex side portion) and the outer edge 38 of the rotor core 16 is different (La> Lb).

  The rotor core plate 35 is made of an electromagnetic steel plate having a thickness t, and a boss 41 for stacking and fixing is formed so as to protrude along the plate thickness direction. The back surface side of the boss 41 is a fitting recess, and the boss 41 of the adjacent rotor core plate 35 is fitted into the fitting recess, and the plates are laminated and fixed. The boss 41 is provided in the space 36a (bosses 41a) and 36b (41b) of the rotor core 16 and in the vicinity of the shaft hole 42 (boss 41c). The diameter Da of the boss 41a is larger than the diameter Db of the boss 41b (Da> Db). That is, the large boss 41 is disposed in the space 36 having a large distance L. The bosses 41a and 41c have the same dimensions.

  A resolver mounting portion 44 made of a non-magnetic material (for example, made of synthetic resin) is provided integrally with the rotor core 16 at an end portion in the axial direction of the rotor core 16. A resolver 21 serving as a rotation angle detecting means is disposed on the left side of the rotor 3 in FIG. 1, and a rotor (resolver rotor) 22 of the resolver 21 is integrally attached to the left end side of the resolver mounting portion 44. A resolver rotor mounting piece 45 is projected in the axial direction on one end surface side (left end surface side in FIG. 1) of the resolver mounting portion 44, and the resolver rotor 22 is fitted to the resolver rotor mounting piece 45. Installed.

  A stator (resolver stator) 23 of the resolver 21 is fixed in a metal resolver holder 24 by means such as press fitting. The resolver holder 24 is formed in a bottomed cylindrical shape, and is lightly press-fitted (positioned and fixed) to the outer periphery of the end of the rib 26 provided at the center of the bracket 8. The resolver holder 24 is accommodated in a bracket holder 25 made of synthetic resin fixed to the inside of the bracket 8. A metal resolver fixing nut 27 is attached to the bracket holder 25, and the bracket holder 25 and the bracket 8 are fixed by a resolver fixing screw 28 with a flange portion 24a of the resolver holder 24 interposed therebetween. The

  The flange portion 24 a of the resolver holder 24 is attached between the bracket holder 25 and the bracket 8 so as to be slightly movable in the circumferential direction. The resolver holder 24 is fixed to the bracket holder 25 by a resolver fixing screw 28 after the position of the resolver stator 23 is adjusted. At this time, a resolver fixing screw 28 is screwed into the resolver fixing nut 27 from the outside of the bracket 8, and the bearing holder 15 and the resolver holder 24 are fastened together with the bracket 8. Thereby, the resolver holder 24 is fixed to the inside of the bracket 8 in a state where the position in the circumferential direction is adjusted.

  In the motor 1 having such a configuration, the shaft hole 42 of the rotor core 16 has a so-called petal shape in order to ensure the axial accuracy of the rotor core 16 while reducing the load when the shaft 13 is press-fitted into the shaft hole 42 of the rotor core 16. It has become. FIG. 3 is an explanatory diagram showing the configuration of the rotor core 16. As shown in FIG. 3A, in the motor 1 according to the present invention, a plurality of convex portions 46 and concave portions 47 are alternately provided along the circumferential direction on the inner peripheral surface 43 of the shaft hole 42. . The convex portion 46 is formed in a substantially trapezoidal shape, and the width WL on the outer diameter side (lower bottom portion) is larger than the width WU on the inner diameter side (upper bottom portion) (WL> WU). Further, the inner diameter dimension D1 of the convex portion 46 is slightly smaller than the outer diameter dimension D2 of the shaft 13. By forming the convex portion 46 in a substantially trapezoidal shape, the base angle of the convex portion 46 is an acute angle, that is, the outer angle of the base angle that is pulled out by the press (the corner on the concave portion 47 side) becomes an obtuse angle, and press formability is improved.

  Thus, by making the inner periphery of the shaft hole 42 have a concavo-convex structure, the shaft 13 is subjected to partial surface press-fitting, so that the press-fitting load is reduced as compared with the full press-fitting. The concave portion 47 also acts as a gap for releasing the press-fit load, that is, a space that allows the convex portion to be deformed by press-fitting. As a result, the press-fit load can be reduced, and the distortion of the rotor core 16 and the buckling of the shaft 13 during the press-fit of the shaft can be suppressed. In particular, since the convex portion 46 has a substantially trapezoidal shape, the convex portion press-fitting surface (upper bottom side) is reduced, and the shaft press-fitting load can be released also in the radial direction. It becomes possible to effectively reduce the buckling of the shaft 13. Furthermore, unlike the conventional press-fit structure using knurls, the shaft is less likely to shake and the shaft accuracy is improved. As a result, in the electric power steering apparatus using the motor 1, rattling due to rotor eccentricity is reduced and torque ripple fluctuations are also reduced, thereby improving the steering feeling.

  On the other hand, there are a plurality of patterns in the circumferential arrangement of the convex portion 46 and the concave portion 47, and there are two specific ones as shown in FIGS. 3 (a) and 3 (b). That is, the convex portion 46 is disposed at a position facing the apex 48 of the innermost rotor magnet 18 (the position closest to the center of the arc convex side portion and the position where the rotor magnet 18 is closest to the shaft hole 42). (FIG. 3A: A configuration) and the concave portion 47 is arranged (FIG. 3B: B configuration). In the motor 1, among these, the A configuration in which the convex portion 46 is arranged at the position of the apex 48 is adopted, and the rotor core 16 is secured to the shaft 13 while preventing the rotor core 16 from coming off and preventing it from rotating. As described above, the arrangement of the convex portions 46 has a plurality of patterns, and an intermediate configuration between A and B can be considered. Now, two cases A and B will be described.

  In the motor 1 according to the present invention, since the inner peripheral surface 43 of the shaft hole 42 has the A configuration, the convex portion 46 is disposed to face the apex 48 of the rotor magnet 18. More space can be provided on the back side (between the magnet apex 48 and the shaft hole 42). As a result, the volume of the ferromagnetic material existing on the back side of the magnet can be increased, the magnetic flux can easily pass, and the degree of orientation is improved. According to the inventor's measurement, in the case of the B configuration, there are many portions with a low orientation magnetic field in the vicinity of the apex 48, whereas in the A configuration, there are only a few portions with a low orientation magnetic field and the sparseness occurs. It was. In the B configuration, since a gap is formed between the recess 47 and the shaft 13, if the recess 47 is arranged in the vicinity of the magnet, the flow of magnetic flux is hindered during magnetization, and the degree of orientation decreases. It is thought to end

  FIG. 4 is a graph showing an induced voltage waveform when a rotor having each of the A and B configurations is used. As shown in FIG. 4, the induced voltage value of the A configuration is approximately 5% larger than that of the B configuration. When the magnetic flux of the magnet is evaluated by the induced voltage, this indicates that the amount of magnetic flux is larger in the A configuration. As a result, it was found that the A configuration was superior to the B configuration in terms of magnetic characteristics (residual magnetic density) as well as variations in the orientation magnetic field. Accordingly, the motor using the A-configuration rotor has a larger output, and if the output is the same, the A-configuration can reduce the size of the motor itself.

  Moreover, since the convex part 46 is arranged facing the vertex 48, the space | interval between the vertex 48 used as a narrow part and the axial hole 42 becomes large. In the rotor core 16, the distance Lt between the apex 48 and the inner edge portion 46 a of the convex portion 46 is larger than the plate thickness t of the rotor core plate 35. For this reason, the rotor core plate 35 can be easily formed by press working. In this case, in the configuration B, if the distance Lt is increased, the outer diameter of the rotor 3 must be increased accordingly, and the motor is increased in size accordingly. On the other hand, in the A configuration, the dimension of the magnetic path between the third slit 17c and the shaft hole 42 can be secured more than the plate thickness t without increasing the rotor outer diameter, and the motor can be reduced in size and processed. Sexual compatibility is possible.

  Further, when the bond magnetic material is injection-molded into the slit group 17 of the rotor core 16, in the B configuration, the back side of the magnet (between the magnet apex 48 and the shaft hole 42) is thin, and between the shaft 13 There is a gap K in the recess 47. For this reason, when a magnet is injection-molded in the rotor core 16, pressure during molding is applied to the portion of the recess 47, and the rotor core 16 may be deformed by the pressure. On the other hand, in the case of the A configuration, the thickness on the back side of the magnet is large, and the shaft 13 and the convex portion 46 are in contact with each other, so that the shaft 13 is shaped like a wall. For this reason, the molding pressure can be received by the thick convex portion 46 and the shaft 13, and it is difficult to apply a load to the gap K, so that the deformation of the rotor core 16 can be suppressed.

It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.
For example, in the above-described embodiment, the IPM motor using the rotor 3 in which the rotor magnet 18 has an arc shape has been described. However, the shape of the magnet is not limited to the arc shape. For example, as shown in FIG. It is also possible to have a three-sided shape (upper base and two side edges). In this case as well, the rotor magnet 51 is embedded in the rotor 3 with the convex side portion facing the center side of the rotor 3 in the same manner as the rotor magnet 18 shown in FIGS. A convex portion 46 is disposed at a position closest to the shaft hole 42.

  The brushless motor according to the present invention can be widely applied not only to the drive source of the electric power steering apparatus but also to other in-vehicle electric apparatuses, electric products such as hybrid cars, electric cars, and air conditioners. Since the IPM motor such as the brushless motor of the present invention can utilize reluctance torque in addition to the magnet, it can be used as a high-efficiency and high-torque motor not only in the automobile field but also in industrial equipment and home appliances. .

1 Brushless motor 2 Stator
DESCRIPTION OF SYMBOLS 3 Rotor 4 Housing 4a Bearing accommodating part 5 Stator core 5a Outer ring part 5b Teeth 6 Field coil 6a Coil end part 7 Bus bar unit 8 Bracket 9 Bus bar 10 Fixing screw 11 Insulator 12 Feed terminal 13 Shafts 14a, 14b Bearing 15 Bearing holder 16 Rotor core 17 Slit group 17a First slit 17b Second slit 17c Third slit 18 Rotor magnet 19 Slot 20 Magnetic pole portion 21 Resolver 22 Resolver rotor 23 Resolver stator 24 Resolver holder 24a Flange portion 25 Bracket holder 26 Rib 27 Resolver fixing nut 28 Resolver fixing Screw 31 Power terminal 31a One end 31b The other end 32 Opening 33 Bus bar terminal 34 Power connector 35 Rotor core plate G 36 Space 36a, 36b Space 37 First slit apex 38 Outer edge 41 Boss 41a-41c Boss 42 Shaft hole 43 Inner peripheral surface 44 Resolver mounting part 45 Resolver rotor mounting piece 46 Convex part 46a Inner edge part 47 Concave part 48 Magnet apex 51 Rotor magnet 51a Upper bottom part D1 Convex inner diameter D2 Shaft outer diameter K Air gap L Distance Lt between first slit apex and rotor core outer edge Distance between magnet apex and convex inner edge t Rotor core plate thickness WL Under convex part Width of bottom part WU Width of top part of convex part

Claims (6)

A brushless motor having a stator including a field coil, and a rotor that is rotatably arranged in the stator and has a plurality of magnets embedded therein,
The rotor includes a shaft and a rotor core fixed to the shaft,
The rotor core includes a shaft hole in which the shaft is press-fitted and fixed,
The shaft hole includes, on an inner peripheral surface thereof, a plurality of convex portions that hold the shaft, and a plurality of concave portions that are formed between the convex portions, and the convex portions and the concave portions Provided alternately along the circumferential direction on the circumferential surface,
The brushless motor, wherein the convex portion is disposed at a position where the magnet is closest to the shaft hole. The brushless motor according to claim 1,
The magnet is formed in an arc shape in cross section, and is embedded in the rotor in a state where the convex side portion faces the center side of the rotor,
The brushless motor is characterized in that the convex portion is disposed at a position facing the arc apex of the magnet. The brushless motor according to claim 1,
The magnet is formed in a trapezoidal three-sided cross-section, and is embedded in the rotor in a state where the upper bottom portion is directed toward the center of the rotor,
The brushless motor, wherein the convex portion is disposed at a position where the shaft hole is closest to an upper bottom portion of the magnet. The brushless motor according to any one of claims 1 to 3,
The rotor core is formed by laminating a plurality of steel plates having a thickness t.
A brushless motor, wherein a distance Lt between the magnet and the inner edge of the convex portion is at least a value greater than the plate thickness t (Lt ≧ t). In the brushless motor according to any one of claims 1 to 4,
The protrusion is formed in a substantially trapezoidal shape, and the width WL of the lower bottom portion on the outer diameter side is larger than the width WU of the upper bottom portion on the inner diameter side (WL> WU). The brushless motor according to any one of claims 1 to 5,
The brushless motor is used as a drive source of an electric power steering apparatus.

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