Rotor of an electric motor and method for its manufacture

Abstract

Rotor (10) of an electric motor, comprising: a cylindrical rotor core (14) having an axis (O) and provided with a through-opening (14a); a plurality of magnets (16) arranged radially outwardly on the rotor core (14); a tubular cover tube (18, 18') surrounding the plurality of magnets (16); and a filling material (20) filled into a gap between the rotor core (14) and the cover tube (18, 18'), wherein the rotor core (14) a plurality of projections (22) projecting radially outward from an outer peripheral surface (26) of the rotor core (14), the plurality of projections (22) extending in an axial direction (O) from a first end surface (28) of the rotor core (14) in one direction of the axial direction (O) to a second end surface (30) of the rotor core (14) in the other direction of the axial direction (O); and a cutout (24) formed to be recessed radially inward from a radially outer end surface (32) of at least one of the projections (22) and having a bottom surface (38) located radially inward from an outer peripheral surface (26) of the rotor core (14) has, wherein the plurality of projections (22) are arranged so as to be lined up in a circumferential direction of the rotor core (14), wherein each of the plurality of magnets (16) is arranged between two projections (22) adjacent to each other in the circumferential direction, wherein the cutout (24) extends from the first end surface (28) to the second end surface (30), and wherein a cross-sectional area of ​​the cutout (24) becomes smaller during its axially forward extension from the axially rear end surface (28) of the rotor core (14).

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The invention relates to a rotor of an electric motor and a method for producing the rotor of the electric motor. 2. Description of the state of the art

[0002] Known rotors have a plurality of magnets arranged radially outwardly on the rotor core, a cylindrical cover tube surrounding the plurality of magnets, and a resin filled in a gap between the cover tube and the rotor core (for example, Japanese Patent Laid-Open No. JP 2013-169103 A).

[0003] When manufacturing the above rotors, resin is generally injected into a gap between a rotor core and a cover tube. Such a gap is narrow, and it is difficult to position a gate of the injection molding machine at the gap. Furthermore, a cover tube is sometimes locally deformed due to the injection pressure of the resin injected into the gap.

[0004] JP 2010 - 206 939 A describes a rotor 10 with a rotor core, a plurality of magnets provided around the rotor core and arranged in the circumferential direction of the rotor core, and a rotor cover attached to the periphery of the plurality of magnets. DE 10 2013 002 354 A1 describes a rotor of an electric motor having a rotor core, a plurality of magnets spaced apart from one another on an outer circumferential surface of the rotor core, and a cylindrical protective tube enclosing the magnets. DE 10 2013 101 956 A1 describes a rotor for an electric machine having a magnet carrier, a plurality of magnets arranged on the magnet carrier, and a rotor core arranged between a shaft and the magnet carrier, wherein the rotor core is made of plastic.US 2012 / 0 187 792 A1 describes a motor comprising a rotor with a rotating shaft, a magnetic body rotatable together with the rotating shaft, first and second permanent magnets secured to an outer periphery or an inner periphery of the magnetic body, a stator comprising an iron core arranged around the rotor, and a coil for exciting the iron core. DE 10 2004 030 063 A1 describes an electric rotating field machine with a stationary stator and a rotatably mounted rotor, wherein at least one permanent magnet element is provided for generating the excitation flux and at least one electric excitation coil, wherein the permanent magnet element is secured to the rotor of the rotating field machine.JP 2007-318 942 A describes an apparatus for manufacturing a magnet-embedded rotor, wherein a permanent magnet is fitted into a plurality of holes of a laminated iron core formed by laminating plate-shaped magnetic elements, and wherein a pure material is filled through a filling hole. DE 10 2004 027 036 A1 describes a synchronous motor having a rotor to which magnets are secured by clamping elements, the clamping elements consisting of webs arranged on the rotor and between the magnets. JP 2010-136 514 A describes a rotor yoke formed by laminating three types of rotor cores obtained by press-working a magnetic thin plate to a prescribed dimension. DE 10 2010 053 364 A1 describes a permanent magnet motor having a rotor and a stator pole piece, wherein an air gap is formed between the rotor and the stator pole piece.It is an object of the invention to propose a further rotor and a method for its production. This object is achieved by a rotor according to the invention as defined in claim 1 and a method according to the invention as defined in claim 7. SUMMARY OF THE INVENTION

[0005] According to one aspect of the invention, a rotor of an electric motor comprises a rotor core, a plurality of magnets arranged radially outwardly on the rotor core, a cover tube surrounding the plurality of magnets, and a filling material filled in a gap between the rotor core and the cover tube.

[0006] The rotor core has a plurality of projections projecting radially outward from an outer peripheral surface of the rotor core, the plurality of projections extending in an axial direction from a first end surface of the rotor core in one direction of the axial direction to a second end surface of the rotor core in the other direction of the axial direction, and a cutout formed to be recessed radially inward from a radially outer end surface of at least one of the projections.

[0007] The plurality of protrusions are arranged in a row along the circumferential direction of the rotor core. Each magnet is arranged between two protrusions adjacent to each other in the circumferential direction. The cutout extends from the first end surface to the second end surface. The filler material may be a resin. The cutout may extend from the first end surface to the second end surface.

[0008] According to another aspect of the invention, a method for manufacturing a rotor of an electric motor comprises providing a rotor core having a cutout formed to be recessed radially inward from an outer peripheral surface of the rotor core, the cutout extending in an axial direction from a first end surface of the rotor core in one direction of the axial direction to a second end surface of the rotor core in the other direction of the axial direction.

[0009] The method further comprises arranging a plurality of magnets radially outwardly of the rotor core such that the cutout is located at a position between two of the magnets that are adjacent to each other in a circumferential direction of the rotor core, arranging a cover tube to surround the plurality of magnets, and injecting a filler material into the cutout and filling a gap between the rotor core and the cover tube with the filler material. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above and other objects, features and advantages of the invention will become clear from the description of the following embodiments with reference to the accompanying drawings, in which Fig. 1 is a sectional side view of a rotor according to one embodiment; Fig. 2 a sectional view of the Fig. 1 shown rotor along II-II in Fig. 1 is; Fig. 3 an enlarged view of area III in Fig. 2 is; Fig. 4 is a flow diagram of a method of manufacturing a rotor according to one embodiment; Fig. 5 a view of a step S3 in Fig. 4 manufactured structure; Fig. 6 a state at the end of step S4 in Fig. 4 shows; Fig. 7 shows a state at the end of step S5 in Fig. 4 shows; Fig. 8 shows a positional relationship between a cutout and a gate in the circumferential direction in the Fig. 7 shows the state shown; Fig. 9 shows a state at the end of step S6 in Fig. 4 shows; Fig. 10 is a view of a rotor according to another embodiment; and Fig. 11 is a view of a rotor according to yet another embodiment. DETAILED DESCRIPTION

[0011] Embodiments of the invention will be described in detail below based on the drawings. First, with reference to Fig. 1 to 3, a rotor 10 according to one embodiment will be described. Note that in the following description, an axial direction corresponds to a direction along a rotational axis O of a rotor, a radial direction corresponds to a direction of the radius of a circle centered on the axis O, and the circumferential direction corresponds to a circumferential direction of the circle. Furthermore, the direction indicated by arrow A in the figures is referred to as forward in the axial direction (or axially forward) for convenience.

[0012] The rotor 10 is rotatably mounted on a radially inner side of a stator (not shown) of an electric motor and, together with the stator, forms the electric motor. The rotor 10 includes a rotating shaft 12, a rotor core 14, a plurality of magnets 16, a cover tube 18, and a filler material 20. The rotating shaft 12 is a columnar member extending in the axial direction.

[0013] The rotor core 14 is a cylindrical member fixedly disposed radially outwardly of the rotating shaft 12. The rotor core 14 consists of a plurality of magnetic steel sheets stacked in the axial direction and is arranged to be centered around the axis O. The rotor core 14 is formed with a through hole 14a into which the rotating shaft 12 is inserted.

[0014] The rotor core 14 includes a plurality of protrusions 22 and a plurality of cutouts 24. Each of the protrusions 22 protrudes radially outward from an outer peripheral surface 26 of the rotor core 14 and extends in the axial direction from a first end surface 28 of the rotor core 14 in the axially rearward direction to a second end surface 30 of the rotor core in the axially forward direction. In this embodiment, a total of eight protrusions 22 are formed so as to be lined up at approximately equal intervals in the circumferential direction.

[0015] As in Fig. As shown in Figure 3, each projection portion 22 includes a pair of opposing side surfaces 40 and 42 and a radially outer end surface 32. The side surfaces 40 and 42 are substantially planar surfaces that extend radially outward from the outer peripheral surface 26 and extend in the axial direction. The end surface 32 extends between the side surfaces 40 and 42 and extends in the axial direction.

[0016] Each cutout 24 is formed on the rotor core 14 so as to be recessed radially inward from the radially outer end surface 32 of the projection part 22. As shown in Fig. 3, each cutout 24 is defined by a pair of facing side surfaces 34 and 36 and a bottom surface 38 extending between the side surfaces 34 and 36.

[0017] The side surfaces 34 and 36 are substantially flat surfaces arranged to be circumferentially spaced apart by a predetermined distance and extending in the axial direction so as to be substantially parallel to each other. The bottom surface 38 is a substantially flat surface located radially inward from the outer peripheral surface 26 and extending in the axial direction.

[0018] Therefore, an outer peripheral surface 44 of the rotor core 14 is defined by the outer peripheral surface 26, the side surfaces 34, 36, 40 and 42, the bottom surface 38 and the end surface 32.

[0019] Each of the magnets 16 is an elongated magnetic element (e.g., neodymium or ferrite) extending in the axial direction and is arranged between two of the projections 22 adjacent to each other in the circumferential direction so as to be fixed to the outer peripheral surface 26 of the rotor core 14. In this embodiment, a total of eight magnets 16 are arranged so as to be lined up in the circumferential direction at substantially equal intervals.

[0020] The cover tube 18 is a tubular member that radially surrounds the plurality of magnets 16. The cover tube 18 is made of non-magnetic materials such as stainless steel and is arranged to be centered around the axis O.

[0021] The filler material 20 is filled into a gap between the rotor core 14 and the cover tube 18. More specifically, the filler material 20 is filled into a gap between each magnet 16 and the cover tube 18, a gap between each protrusion 22 and the cover tube 18, and the interior of each cutout 24. For example, the filler material 20 is a resin.

[0022] Next, with reference to Fig. 4 to 8, a method for manufacturing the rotor 10 will be described. In step S1, a manufacturer produces the rotor core 14.

[0023] In particular, the manufacturer punches several electromagnetic steel plates by pressing and stacks the punched electromagnetic steel plates in the axial direction, thereby Fig. 1 and Fig. 2 shown rotor core 14 is manufactured.

[0024] In step S2, the manufacturer arranges the plurality of magnets 16 radially outwardly of the rotor core 14 manufactured in step S1. Specifically, the manufacturer arranges each magnet 16 at a position between two of the protrusions 22 that are adjacent to each other in the circumferential direction, that is, on the outer peripheral surface 26 of the rotor core 14.

[0025] In this embodiment, the manufacturer can easily position the magnets 16 on the outer peripheral surface 26 without bonding the magnets to the outer peripheral surface 26 of the rotor core 14, for example, by means of an adhesive, since the projections 22 of the rotor core 14 can prevent displacement of the magnets 16 in the circumferential direction.

[0026] In step S3, the manufacturer arranges a cover tube 18' to surround the plurality of magnets 16. Specifically, the manufacturer prepares the cover tube 18' ( Fig. 5). The cover tube 18' is a cylindrical element that has a smaller diameter than that of the Fig. 1 and Fig. 2 and has the same axial length as the cover tube 18.

[0027] Then, the manufacturer places the cover tube 18' over the magnets 16 fixed to the outer circumferential surface 26 of the rotor core 14 in such a way that it surrounds the magnets 16 from the outside radially. This state is shown in Fig. 5. Through this step S3, an assembly 50 comprising the rotor core 14, the magnets 16, and the cover tube 18' is manufactured. In this assembly 50, the inner peripheral surface of the cover tube 18' is in contact with the outer surfaces of the magnets 16.

[0028] In step S4, the manufacturer places the structure 50 produced in step S3 into a first mold 102 of an injection molding machine 100. The injection molding machine 100 according to an embodiment will be described below with reference to Fig. 6 are described.

[0029] The injection molding machine 100 includes the first mold 102, a second mold 104, a filler material supply unit 106, a connecting line 107, and a heated runner 108. The first mold 102 is designed with a round recess 110.

[0030] The second mold 104 is configured to be movable toward and away from the first mold 102. The second mold 104 has a pressure-exerting surface 104a facing the first mold 102. The filler material supply unit 106 supplies the filler material into the connecting pipe 107, where the filler material is heated to liquefy it. The filler material supplied into the connecting pipe 107 flows through the connecting pipe 107 and flows into the heated runner 108.

[0031] The heated runner 108 has a heating device (not shown) and supplies the filler material, which has flowed in a liquefied state from the connecting line 107. A plurality of gates 112 are formed at the exits of the heated runner 108.

[0032] Each gate 112 opens to the outside of the pressure application surface 104a of the second mold 104. The filler material that has flowed into the heated runner 108 flows through the heated runner 108 to be injected from the gate 112.

[0033] The sprues 112 are arranged so that they are arranged at substantially equal intervals in the circumferential direction. The positions of these sprues 112 correspond to the positions of the cutouts 24 formed on the rotor core 14 in the circumferential direction.

[0034] For example, the heated runner 108 is provided with a total of eight sprues 112, the positions of which in the circumferential direction correspond to those of a total of eight cutouts 24

[0035] In this step S4, the manufacturer places the structure 50 produced in step S3 into the cavity 110 of the first mold 102 so that it is concentric with the cavity 110. This state is shown in Fig. 6. In the state shown in Fig. 6, the axially forward end surface 30 of the rotor core 14 is in contact with a bottom surface 114 defining the cavity 110.

[0036] At step S5, the injection molding machine 100 moves the second mold 104 toward the first mold 102 so that the cavity 110 of the first mold 102 is closed by the pressure surface 104a of the second mold 104 (this operation is the so-called “mold closing process”).

[0037] This condition is in Fig. 7. In the state shown in Fig. As shown in Figure 7, the axially rearward end surface 28 of the rotor core 14 is in surface contact with the pressure application surface 104a. Furthermore, the cover tube 18' is spaced radially inwardly from a side surface 116 defining the cavity 110.

[0038] Furthermore, the sprues 112 are arranged such that they each face the cutouts 24 formed on the rotor core 14. Fig. Fig. 8 shows the positional relationship in the circumferential direction between a cutout 24 and a gate 112 in the Fig. 7 shown state schematically.

[0039] As in Fig. As shown in Figure 8, at the end of step S5, the gates 112 are positioned relative to the cutouts 24 such that they face and open toward the respective cutouts 24. In this embodiment, each gate 112 is arranged at a position closer to the bottom surface 38 than to the radially outer end surface 32 of each projection portion 22.

[0040] At step S6, the injection molding machine 100 injects the filler material (e.g., a resin) into the cutouts 24. Specifically, the injection molding machine 100 drives the filler material supply unit 106 to supply the filler material into the heated runner 108 to inject the filler material from the gates 112 into the cutouts 24.

[0041] The filler material injected into the cutouts 24 flows through the cutouts 24 and enters the gap between the cover tube 18' and the rotor core 14. Due to the pressure of the injected filler material, the cover tube 18' expands radially outward, so that it comes into contact with the side surface 116 of the cavity 110. As a result, the above-mentioned cover tube 18 is formed.

[0042] Further, the filler material injected from the gates 112 is filled between each magnet 16 and the cover tube 18, between each projection portion 22 and the cover tube 18, and into the interior of each cutout 24. As a result, the above-mentioned filler material 20 is formed.

[0043] This condition is in Fig. 9. Through this step S6, a structure 52 comprising the rotor core 14, the magnets 16, the cover tube 18, and the filler material 20 is manufactured.

[0044] In step S7, the manufacturer fixes the rotary shaft 12. Specifically, the manufacturer prepares the rotary shaft 12 and inserts it into the through hole 14a of the rotor core 14 of the assembly manufactured in step S6 so that it is fixed there.

[0045] For example, the rotary shaft 12 is fixed by a shrink fit in the through hole 14a of the rotor core 14. Through this step S7, the Fig. 1, the rotor 10 shown is manufactured.

[0046] As mentioned above, in this embodiment, the rotor core 14 is designed with cutouts 24, into which the filler material is then injected in step S6. This design allows the cover tube 18' to be expanded evenly in step S6.

[0047] This effect will be described below. For comparison, assume that no cutout 24 is formed. In this case, at step S6, each gate 112 may be arranged at the gap between the radially outer end surface 32 of each projection portion 22 and the inner surface of the cover tube 18'.

[0048] In this case the sprues are 112 compared to the one in Fig. 8. Therefore, when the gates 112 are arranged closer to the cover tube 18' and the filler material is injected, the cover tube 18' may be deformed more by the injection pressure of the filler material in the area near the gates 112, which may cause the cover tube 18' to be deformed unevenly.

[0049] In contrast, according to this embodiment, by forming the cutouts 24, it is possible to arrange the sprues 112 so that they are spaced radially inwardly from the cover tube 18', as in Fig. 8 is shown.

[0050] This allows the injection pressure of the filler material applied to the cover tube 18' in the area closer to the gates 112 when the filler material is injected from the gates 112 at step S6 to be reduced. As a result, it is possible to prevent the cover tube 18' from being unevenly deformed by the injection pressure.

[0051] In addition, when no cutout 24 is formed, it is necessary to position each gate 112 at the extremely narrow gap between the cover tube 18' and the radially outer end surface 32 of each projection part 22 at step S6.

[0052] In contrast, according to this embodiment, the sprues 112 can be positioned much more easily with respect to the cutouts 24, each of which has a comparatively larger dimension in the radial direction. This can improve the efficiency of the process.

[0053] Furthermore, in this embodiment, the cutouts 24 are formed such that the bottom surface 38 of each cutout 24 is positioned radially further inward than the outer peripheral surface 26 of the rotor core 14. According to this configuration, since the gates 112 can be arranged at a greater distance from the cover tube 18' at step S6, it is possible to more effectively prevent the cover tube 18' from being unevenly deformed.

[0054] It should be noted that various variations are possible for the cutout 24. As an example, the side surfaces 34 and 36 defining the cutout 24 may be formed by conical surfaces inclined with respect to the axis O such that the side surfaces 34 and 36 approach each other in their axially forward extension from the axially rearward end surface 28 of the rotor core 14.

[0055] Furthermore, the bottom surface 38 defining the cutout 24 may be formed by a conical surface inclined such that the bottom surface 38 extends radially outward while extending axially forward from the axially rear end surface 28 of the rotor core 14.

[0056] In these variations, the cross-sectional area of ​​the cutout 24 gradually decreases as it extends axially forward from the axially rear end surface 28 of the rotor core 14. Since, in these variations, the injection pressure of the filler material at a position near the axially rear end surface 28 of the rotor core 14 can be reduced at step S6, it is possible to prevent the cover tube 18' from being unevenly deformed.

[0057] Furthermore, the cutouts 24 may be formed to extend axially forward from the axially rear end surface 28 of the rotor core and terminate at a position located rearward in the axial direction from the axially front end surface 30 of the rotor core 14. Furthermore, the bottom surface 38 of the cutout 24 may be an arcuate surface that is recessed radially inward from the axial direction.

[0058] Furthermore, the method for manufacturing the rotor according to the invention is also applicable to a method for manufacturing a rotor that does not have projections 22. An example of such a rotor is shown in Fig. 10 shown.

[0059] It should be noted that in the Fig. In the rotor 60 shown in Figure 10, elements similar to those of the above-mentioned rotor 10 are designated by the same reference numerals. The rotor 60 includes the rotating shaft 12, a rotor core 62, the plurality of magnets 16, the cover tube 18, and a filler material 64.

[0060] The rotor core 14 has a cylindrical outer peripheral surface 66 and a plurality of cutouts 68 recessed radially inward from the outer peripheral surface 66. Each of the cutouts 68 is arranged between two magnets 16 that are adjacent to each other in the circumferential direction of the rotor core 62.

[0061] Next, with reference to Fig. 4 a process for producing the Fig. 10. In step S1, the manufacturer sets the rotor 60 shown in Fig. 10 shows the rotor core 62.

[0062] In step S2, the manufacturer arranges the plurality of magnets 16 radially outward on the rotor core 62 so that they are lined up at substantially equal intervals in the circumferential direction. For example, the manufacturer fixes the plurality of magnets 16 to the outer circumferential surface 66 of the rotor core 62 using an adhesive or the like.

[0063] In step S3, the manufacturer arranges the cover tube 18' to surround the plurality of magnets 16. This produces an assembly including the rotor core 62, the magnets 16, and the cover tube 18'.

[0064] In step S4, the manufacturer inserts the structure manufactured in step S3 into the cavity 110 of the first mold 102 of the above-mentioned injection molding machine 100 so that it is concentric with the cavity 110.

[0065] At step S5, the injection molding machine 100 moves the second mold 104 toward the first mold 102 and closes the cavity 110 of the first mold 102 through the pressure-applying surface 104a of the second mold 104 (i.e., the "mold closing process"). At this time, the gates 112 are arranged to face the respective cutouts 68 of the rotor core 62.

[0066] In step S6, the injection molding machine 100 injects a filler material (e.g., a resin) into the cutouts 68. As a result, the cover tube 18A expands radially outward due to the pressure of the injected filler material, and the cover tube 18 and the filler material 64 shown in Figure 110 are formed. Through this step S6, a structure including the rotor core 62, the magnets 16, the cover tube 18, and the filler material 64 is manufactured.

[0067] In step S7, the manufacturer fixes the rotary shaft 12. Specifically, the manufacturer inserts the rotary shaft 12 into the through hole 69 of the rotor core 62 of the assembly manufactured in step S6 so that it is fixed there. Through this step S6, the Fig. 10 shown rotor 60 was manufactured.

[0068] In this embodiment, the sprues 112 can be positioned to be spaced radially inward from the cover tube 18' by forming the cutouts 68 similarly to the above embodiment.

[0069] Thereby, the injection pressure applied to the cover tube 18' in a region close to the gates 112 when the filler material is injected from the gates 112 at step S6 can be reduced, and as a result, the cover tube 18' can be prevented from being unevenly deformed.

[0070] It should be noted that the number of cutouts can be 24 or 68, one or “N” (“N” is an integer greater than one but less than the number of magnets, 16).

[0071] The number of gates 112 can be one or "M" ("M" is an integer greater than one but less than the number of cutouts, 24 or 68). In this case, a gate 112 is arranged to face a cutout 24 or 68.

[0072] Furthermore, in step S6, the filling material may be filled into a gap between the rotor core 14 and the cover tube 18' without expanding the cover tube 18'. In this case, the Fig. 11, the rotor 70 shown is manufactured.

[0073] The rotor 70 includes the assembly 50, a filler material 72 filled into the gap between the cover tube 18' and the rotor core 14 of the assembly 50, and the rotating shaft 12 inserted into the through hole 14a of the rotor core 14 of the assembly 50. In this rotor 70, the outer surfaces of the magnets 16 are in surface contact with the inner peripheral surface of the cover tube 18'.

[0074] Further, instead of the above steps S2 and S3, the manufacturer may first arrange the cover tube 18' to surround the rotor core 14, and then press-fit the plurality of magnets 16 between the outer peripheral surface 26 of the rotor core 14 and the cover tube 18' to manufacture the assembly 50.

[0075] Furthermore, in the above-mentioned step S3, the manufacturer can Fig. 1 and then arrange it so that it surrounds the magnets 16, which have been fixed to the outer peripheral surface 26 of the rotor core 14, from the radial outside.

[0076] In this case, a gap is formed between the outer surface of the magnets 16 and the inner peripheral surface of the cover tube 18. Subsequently, in step S6, the filling material 20 can be filled into the gap between the rotor core 14 and the cover tube 18 without expanding the cover tube 18 in order to Fig. 1 to produce the rotor 10 shown.

[0077] The invention has been described based on the embodiments of the invention, but the above embodiments do not limit the invention according to the claims. Although embodiments that combine features currently described in the embodiments may be included within the technical scope of the invention, not all combinations of elements described in the embodiments are essential as "means for solving the problems" of the invention. Furthermore, it is obvious to those skilled in the art that various changes and modifications can be added to the above embodiments.

[0078] It should be noted that with regard to the execution order of processing in the acts, operations, steps, processes, and stages of the apparatus, system, program, and method in the claims, the description, and the drawings, the processing may be performed in any order unless "before" or "before" is specifically described, and unless the result of the previous processing is used in the subsequent processing. In the sequence of the activities of the claims, the description, and the drawings, it is not always necessary for the processing to be performed in this order, although "first," "then," "subsequently," or the like may be used for convenience.

Claims

[1] Rotor (10) of an electric motor, comprising: a cylindrical rotor core (14) having an axis (O) and provided with a through-opening (14a); a plurality of magnets (16) arranged radially outwardly on the rotor core (14); a tubular cover tube (18, 18') surrounding the plurality of magnets (16); and a filling material (20) filled into a gap between the rotor core (14) and the cover tube (18, 18'), wherein the rotor core (14) a plurality of projections (22) projecting radially outward from an outer peripheral surface (26) of the rotor core (14), the plurality of projections (22) extending in an axial direction (O) from a first end surface (28) of the rotor core (14) in one direction of the axial direction (O) to a second end surface (30) of the rotor core (14) in the other direction of the axial direction (O); and a cutout (24) formed to be recessed radially inward from a radially outer end surface (32) of at least one of the projections (22) and having a bottom surface (38) located radially inward from an outer peripheral surface (26) of the rotor core (14) has, wherein the plurality of projections (22) are arranged so as to be lined up in a circumferential direction of the rotor core (14), wherein each of the plurality of magnets (16) is arranged between two projections (22) adjacent to each other in the circumferential direction, wherein the cutout (24) extends from the first end surface (28) to the second end surface (30), and wherein a cross-sectional area of ​​the cutout (24) becomes smaller during its axially forward extension from the axially rear end surface (28) of the rotor core (14). [2] The rotor (10) of claim 1, wherein the cutout (24) extends from the first end surface (28) to the second end surface (30). [3] The rotor (10) of claim 1, wherein the cutout (24) extends axially forward from the axially rear end surface (28) of the rotor core (14) and terminates at a position axially rearward of the axially front end surface (30) of the rotor core (14). [4] Rotor (10) according to one of claims 1 to 3, wherein side surfaces (34, 36) of the cutout (24) are formed by conical surfaces which are inclined with respect to the axis (O) such that the side surfaces (34, 36) approach each other in their axially forward direction from the axially rear end surface (28) of the rotor core (14). [5] A rotor (10) according to any one of claims 1 to 4, wherein the bottom surface (38) of the cutout (24) is formed by a conical surface which is inclined such that the bottom surface (38) extends radially outwardly while extending axially forwardly from the axially rear end surface (28) of the rotor core (14). [6] Rotor (10) according to one of claims 1 to 5, wherein the bottom surface (38) of the cutout (24) is an arcuate surface which is recessed radially inwardly as viewed from the axial direction. [7] Method for producing a rotor (10) of an electric motor according to one of the preceding claims 1 to 6, comprising: Providing a rotor core (14); arranging a plurality of magnets (16) radially outwardly on the rotor core (14) such that the cutout (24) is located at a position between two of the magnets (16) which are adjacent to one another in a circumferential direction of the rotor core (14); arranging a cover tube (18) to surround the plurality of magnets (16); arranging a sprue (112) of an injection molding machine (100) for injecting a filler so that it faces an interior of the cutout (24); and Injecting the filler (20) through the sprue (112) into the interior of the cutout (24) by the injection molding machine (100), and filling a gap between the rotor core (14) and the cover tube (18) with the filler (20), wherein the cover tube (18) is designed to expand radially outward due to a pressure of the injected filler (20), wherein, when the sprue (112) is arranged to face the interior of the cutout (24), the sprue (112) is arranged at a position closer to a bottom surface (38) of the cutout (24) than to the radially outer surface (32) of the at least one projection (22). [8] The method according to claim 7, wherein the injection molding machine (100) comprises: a first mold (102) formed with a cavity; and a second mold (104) adapted to be movable in directions toward and away from the first mold (102) and having a pressure-applying surface (104a) on which the gate (112) is formed, the method comprising: Placing an assembly of the rotor core (14), a plurality of magnets (16) and the cover tube (18) in the cavity (110) such that the second end surface (30) of the rotor core (14) contacts the bottom surface (114) of the cavity (110); and Moving the second mold (104) toward the first mold (102) to contact the pressure application surface (104a) with the first end surface (28) of the rotor core (14) while the sprue (112) is arranged to face the interior of the cutout (24), and closing the cavity (110) by the pressure application surface (104a). [9] The method according to claim 7 or 8, wherein the magnets (16) are positioned on the outer peripheral surface (26) without adhering the magnets (16) to the outer peripheral surface (26) of the rotor core (14). [10] A method according to any one of claims 7 to 9, wherein the method further comprises: instead of the first two process steps, first arranging a cover tube (18') so as to surround the rotor core (14), and then press-fitting the plurality of magnets (16) between the outer peripheral surface (26) of the rotor core (14) and the cover tube (18').

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