Rotor part for attachment to the shaft of a rotating electric motor, rotor with rotor part, and method for producing a rotating electric motor and a rotor

Abstract

A rotor part 300 includes a tubular sleeve 301 having a first end surface and a second end surface, a number of magnet segments 311 arranged circumferentially on a radially outer side of the sleeve 301, and a tubular part 321 configured to radially cover the magnet segments 311 from the outside so that the magnet segments 311 are held between the tubular part 321 and the sleeve 301. The sleeve 301 has an inner circumferential surface including a tapered surface that gradually widens radially outward in a direction from the first end surface to the second end surface.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe invention relates to a rotor part fixed to a shaft of a rotating electric machine, a rotor including the rotor part, and a method of manufacturing the rotating electric machine and the rotor.2. Description of the Prior ArtWhen an electric motor using permanent magnets in the rotor rotates at a high speed, the electric motor must be strengthened to resist the centrifugal force generated at high speeds in view of the strength of the permanent magnets and the mounting structure of the magnets. Generally, as the reinforcing structure for covering the permanent magnets, a sleeve made of, for example, carbon fiber or titanium is used. For example, JP H11-89 142 A discloses a high speed synchronous motor provided with ring-shaped magnets and having its outer periphery reinforced by carbon fiber reinforced plastic (CFRP).The ring-shaped magnets disclosed in JP H11-89 142A are subject to restrictions on enlargement due to manufacturing restrictions, whereby it is difficult to provide a larger electric motor that provides a higher torque. When the ring-shaped magnets are fitted on a magnetic ring and fastened to a shaft with a strong press fit to prevent disengagement at high speeds, the ring-shaped magnets may be broken by the expansion of the magnetic ring due to the strong press fit.If, on the other hand, the press fit is selected such that the ring-shaped magnets do not break, the press fit for the magnets and the magnetic ring is too weak. This allows the magnets and the magnetic ring to slip, and causes insufficient torque in the high speed range or high speed failure.In addition, in the above-mentioned method disclosed in JP H11-89 142A, the rotor member is fixed to the shaft with a so-called "oil pressure composition". The use of this method requires a complicated and bulky manufacturing apparatus with complex and difficult operations. This creates the problem of reduced efficiency of production. In addition, for the oil pressure composition, a hole is required in the magnetic ring (rotor sleeve) in order to guide oil pressure from the outside between the magnetic ring and the shaft. In high speed operation, a stress concentration is generated near the hole, and the maximum stress prevents the highest possible speed from being reached. Further, the hole must be exactly balanced, arranged and formed with respect to a balanced wave. This increases the manufacturing cost.In JP H11-89 142 A, it is stated that the oil hole is removed by machining after the fixing of the rotor part and the shaft by oil pressure assembly in order to avoid stress concentration. However, this processing after completion of the runner is a risky procedure beyond the extension of a simple operation. It is necessary to observe the magnetic attraction of the permanent magnets during machining and possible chemical damage to the rotor body itself caused by cutting fluid. Therefore, such a process has a problem of causing high cost.In addition, JP H11-89 142 A states that the sleeve is expected to exert a seating force on the shaft even when the rotational speed at the outer periphery of the rotor part is 250 m / s or more. It is intended that the rotor part rotates stably at the maximum speed and without loosening the rotor part, i.e. slipping. However, an electric motor used for, for example, the main shaft of a machine tool is subject to the important requirement that not only does the rotor part not slip, but also that as large a cutting torque as possible is generated. The constitution disclosed in JP H11-89 142A does not meet the requirement that when the cutting load torque is applied at the maximum rotation speed, the rotor member does not slip on its attachment. Although a similar problem occurs between the magnets and the magnetic ring, JP H11-89 142A does not mention any countermeasures therefor. Since at the maximum speed only the fitting force of the sleeve with respect to the shaft remains, there is a problem that the magnets and the sleeve slide in the rotational direction under increased load.US 5 170 085 A is directed to a rotor for a rotary machine, wherein each permanent magnet has an arc-shaped cross section and is disposed on an outer periphery of an iron core member, and wherein a non-magnetic metal tube is pressure-applied across the outer peripheries of the arc-shaped magnets. The arc-shaped magnets each have a tapered end portion, the taper of each magnet being small at its central portion and becoming larger toward the opposite sides in the width direction of the arc-shaped magnet. DE 88 03 915 U1 discloses an electric motor in which the laminated rotor core is fastened by stowage. DE 43 41 514 A1 relates to a laminated rotor core equipped with permanent magnets, which consists of a plurality of circumferentially separated sheet metal segments and in which the permanent magnets are arranged on the inner periphery of the sheet metal segments extending in the circumferential direction and / or extending radially between the sheet metal segments, JP 2000-23 399 A and JP H03-212 136 A each disclose a rotor, wherein permanent magnets are fastened with a conical fit. FR 592 705 A describes a circuit breaker for a magnetic fuse with a magnetic flywheel, for explosion engines, having the characteristic that it is arranged outside the flywheel. From GB 377 757 A a dynamo is known, wherein the magnets are held on the rotor by means of a press fit cover. FR 855 887 A relates to steering of motor bicycles and DE 15 75 148 A relates to a conical fastening member.In view of the described difficulties, the invention is intended to provide a rotor part and a rotor of an electric machine in which manufacturing efficiency is improved, magnets are prevented from being damaged during the manufacturing process, the torque and output of a rotating electric machine are increased, and the torque is transmitted to a rotating shaft without failure.SUMMARY OF THE INVENTIONA rotor part according to a first aspect of the invention is press-fitted to the shaft of a rotating electric machine. The rotor part includes: a tubular sleeve having a first end on a first side in the axial direction and a second end on a second side in the axial direction; a plurality of magnet segments arranged radially outside of the sleeve in the circumferential direction; and a tubular part covering the plurality of magnet segments from outside in the radial direction to hold the magnet segments between the tubular part and the sleeve. In order to enable press-fitting, the sleeve has an inner circumferential surface including a tapered surface continuously expanding radially outward in the extending direction from the first end to the second end. The inner circumferential surface of the sleeve does not include a portion where the radius of the inner circumferential surface decreases in the direction from the first to the second end. The magnet segments may be separated in the circumferential direction, and may or may not be separated in the axial direction of the shaft a plurality of times.Preferably, the tapered surface of the sleeve is a single linearly tapered surface or comprises a plurality of linearly tapered surfaces connected together and inclined at different angles from a rotational axis, respectively. The sleeve has a thick side that is smaller in diameter due to the tapered structure. The thick side preferably has an end section in order that a pressing tool can build up sufficient pressure during the production of a press fit. The end portion of the sleeve is thus thick. This allows an increased press-fitting force to be applied to the end portion during the press-fitting. The end portion of the sleeve preferably has a taper angle of 0° so that the end portion has a constant inner diameter.In a preferred form, the inner circumferential surface of the sleeve has a cylindrical surface with a constant radius and extends over a certain range from the first end to the second end. The tapered surface includes a linearly tapered surface extending from the cylindrical surface toward the second end. A gap is preferably formed at least partially between the sleeve and the magnet segments. In addition, the sleeve has an outer edge which is preferably cylindrical, and each magnet segment has an inner circumferential surface which is preferably circular arc-shaped. The radius of curvature of the inner circumferential surface of the magnet segment is greater than the radius of the outer circumferential surface of the sleeve.The tapered surface preferably extends from the first end to the second end. The tapered surface is preferably a linearly tapered surface. In this case, the preferable taper ratio of the straight tapered surface is 1 / 200 to 1 / 30, and it is preferable that the sleeve has no holes having openings on the inner peripheral surface.A movement preventing structure is preferably provided between the sleeve and the magnet segments to prevent relative movement between the sleeve and the magnet segments. The tubular member is preferably made of a material having high specific strength (tensile strength per unit density) and includes carbon fiber, glass fiber, non-magnetic metal, aramid fiber, silicon carbide fiber, boron fiber, titanium alloy fiber, ultra high molecular weight polyethylene, or polybutylene terephthalate fiber. Such a fiber reinforced plastic (FRP) is also preferable as the material for the tubular member, wherein carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, boron fiber, titanium alloy fiber, ultra high molecular weight polyethylene or polybutylene terephthalate fiber is used. A composite material of any combination of these materials is also preferred. The tubular member may contain nonmagnetic metal.A rotor according to another aspect of the invention includes a shaft having an outer circumferential surface that expands radially outward in the extending direction from a first side in the axial direction to a second side in the axial direction, and the described rotor part in which the sleeve is fixed to the shaft on the radially outer side such that the second end of the sleeve is located on the second side in the axial direction of the shaft with respect to the first end of the sleeve. Since no oil pressure composition is required for this arrangement, no oil holes are required in the sleeve. It is thus possible to avoid stress concentrations in the vicinity of the holes and advantageously provide an increased maximum rotational speed.The sleeve is deformed to expand radially outward by the shaft when the rotor member is fixed to the shaft so that the outer circumferential surface of the sleeve and the inner circumferential surfaces of the magnet segments contact each other under pressure. "Contact under pressure" means that relative movement of members is prevented by a pressing force between their surfaces. However, relative movement of these elements may be permitted when the compressive force is removed. The prevention of the relative movement may or may not continue when the compressive force is removed.Substantially the entire portion (e.g., greater than 90 percent) of the inner circumferential surface of the sleeve and the outer circumferential surface of the shaft contact the surfaces over the axial distance the tubular member is mounted. This arrangement provides a wider area of contact (e.g., a range greater than 90 percent) between the inner circumferential surface of the sleeve and the outer circumferential surface of the shaft to reduce the compressive force between the surfaces. As a result, a press fit between the surfaces can be produced more easily. For ease of disassembly, there may be a very small groove for supplying lubricating oil to the contacting surfaces. In such an arrangement, the same value of at least over 90 percent can be applied to the area where the surfaces contact and are secured together. Preferably, the sleeve deforms beyond its elastic deformation range. A rotating electric machine of another aspect of the invention includes the described rotor.In an in-use rotary electric machine including the rotor part fixed to the shaft, the tubular part preferably has a pressing in which the fixing torque between the sleeve and the shaft and between the magnet segments and the sleeve exceeds the maximum torque of the rotary electric machine at the allowable rotational speed.For any concentration of applied stress, the maximum speed of the rotor is limited by its limit stress. Therefore, an arrangement which produces stress concentrations is preferably not used. Thus, the hole connecting the outer circumferential surface of the rotor and the radially inner surface of the rotating sleeve disclosed in JP H11-891 42A is preferably not provided. The omission of the hole avoids stress concentrations and can further increase the rotational speed.A method of manufacturing a rotor part to be press-fitted to a shaft according to another aspect of the invention includes the step of: arranging a plurality of magnet segments in the circumferential direction on an outer circumferential surface of the tubular sleeve having a first end on a first side in the axial direction, a second end on a second side in the axial direction, and an inner circumferential surface including a tapered surface continuously expanding radially outward in the extending direction from the first end to the second end; and arranging a tubular part to cover the plurality of magnet segments from the outside in the radial direction. The step of disposing the tubular member may comprise directly winding a material of the tubular member around the outer circumferential surface of the magnet segments.A method for manufacturing a rotor of a rotating electric machine including the rotating part manufactured by the described method includes the step of: providing a shaft having an outer circumferential surface in a region to which the rotor part is fastened, the outer circumferential surface expanding radially outward in the extending direction from a first side in the axial direction to a second side in the axial direction; and fastening the rotor part radially outward to the shaft by an interference fit.The step of press-fitting the rotor part includes: fitting the sleeve to the shaft from the first side in the axial direction so that the second end of the sleeve is disposed on the second side in the axial direction opposite to the first end; press-fitting the sleeve to the shaft by pushing the first end of the sleeve to the second side in the axial direction; and causing the sleeve to expand radially outward by the force press-fitting, thereby press-fitting the sleeve at a predetermined fitting position.The rotor part preferably contains at least partially a gap between the sleeve and the magnet segments. In the step of fixing the rotor part by press-fitting, the outer circumferential surface of the sleeve and the inner circumferential surfaces of the magnet segments are brought into face-to-face contact with each other over almost the entire surface by expanding the sleeve radially outward to fill the gap.The outer circumferential surface of the sleeve is preferably cylindrical, and the inner circumferential surface of each magnet segment is in the shape of a circular arc. Here, the inner circumferential surface of the magnet segment has a radius of curvature that is larger than the radius of the outer circumferential surface of the sleeve. In the fixing step of the rotor part by press-fitting, the outer circumferential surface of the sleeve and the inner circumferential surfaces of the magnet segments are brought into face-to-face contact with each other by expanding the sleeve radially outward.BRIEF DESCRIPTION OF THE DRAWINGSThe described objects, advantages and features of the invention and other objects, advantages and features will become apparent from the description of the following preferred embodiments with reference to the drawings.It shows: FIG. 1 is a sectional view of an electric motor according to an embodiment of the present invention; FIG. 2 is a sectional view of a shaft in FIG. 1 ; FIG. 3 is a sectional view of a rotor part in FIG. 1 ; FIG. 4 is an outer view of the rotor part in FIG. 1 as viewed from the axial direction; FIG. 5 is a sectional view of a sleeve in FIG. 3 ; FIG. 6 is a perspective view of one of the magnet segments in FIG. 3 ; FIG. 7 is a perspective view of a tubular member in FIG. 3 ; FIG. 8 is a graph showing the centrifugal forces acting on the shaft, the sleeve and the magnet segments, the fastening torque between the shaft and the sleeve and the fastening torque between the sleeve and the magnet segments, respectively, depending on the rotational speed of the electric motor; FIG. 9 shows the equilibrium of the forces between the tubular part, the magnet segments and the sleeve during standstill of the electric motor; FIG. 10 shows the equilibrium of the forces between the tubular part, the magnet segments and the sleeve during the rotation of the electric motor; FIG. 11 is a flow chart showing a manufacturing method of the rotor part and the rotor according to an embodiment of the present invention; FIG. 12 is a flow chart showing a manufacturing method of the rotor part and the rotor according to another embodiment of the present invention; FIG. 13 shows the step of arranging the magnet segments on the sleeve; FIG. 14 shows the assembled rotor part; FIG. 15 is a partially enlarged view of FIG. 14 ; FIG. 16 is a sectional view illustrating a fixing step of the rotor part to the shaft; FIG. 17 is a partially enlarged sectional view of FIG. 16 ; FIG. 18 is a sectional view of the rotor part fixed to the shaft; FIG. 19 shows the change of state of the rotor part in a step in which the rotor part is fastened to the shaft; FIG. 20 is an enlarged view of the rotor part of another embodiment; FIG. 21 is an enlarged view of the rotor part of still another embodiment; FIG. 22 is an enlarged view of the rotor part of still another embodiment; FIG. 23 shows the rotor part of yet another embodiment; and FIG. 24 shows the rotor part of yet another embodiment.DETAILED DESCRIPTIONHereinafter, an embodiment of the invention will be described in detail with reference to the drawings. First, the arrangement of an electric motor 100 of an embodiment of the invention will be described with reference to FIG. 1. Note that in the following description, the direction along the central axis of the shaft of the electric motor 100 is referred to as an axial direction. The left side in the drawing in FIG. 1 is referred to as an axial front side, and the right side is referred to as an axial rear side. It should also be noted that the axial front side and the axial rear side have been selected in the following description for the purpose of easily and conveniently illustrating the invention and are not intended to restrict the directions, for example front side and rear side, of the electric motor.The electric motor 100 includes a housing 102 defining an interior space 101, a stator 110 statically disposed in the interior space 101 of the housing 102, and a rotor 400 rotatably disposed on the radially inner side of the stator 110. The stator 110 includes a stator core 103 and a coil 104 wound on the stator core 103. The stator core 103 is composed of laminated thin plates which are, for example, electromagnetic plates.A power line (not shown) electrically connected to the coil 104 is routed away from the stator 110. The power line is connected to a power source (not shown) located outside the electric motor 100 via a through hole disposed in the housing 102.The rotor 400 includes a shaft 200 extending axially in the inner space 101 and a rotor part 300 fixedly attached to the outer side of the shaft 200 in the radial direction.The shaft 200 of this embodiment will be described below with reference to FIG. 2. The shaft 200 is in the form of a tube having a central axis O 1 and a central hole 201 concentric with the central axis O 1. Since the motor is provided as a built-in motor for a main shaft of a machine tool, the shaft 200 is provided with the center hole 201 in this embodiment. However, the shaft 200 of the invention may be constructed differently. The shaft 200 may be made of solid material and may not have the center hole 201.The central axis O 1 of the shaft 200 is a rotational axis of the electric motor 100. The shaft 200 is rotatably supported in the housing 102 at its axial front side via a bearing (not shown) installed in the front side wall of the housing 102. Similarly, the shaft 200 is rotatably supported in the housing 102 at its axial rear side via a bearing (not shown) installed in the rear side wall of the housing 102.The shaft 200 has a tapered outer circumferential surface 202 that expands radially outward from the axial rear side toward the axial front side as viewed from the axial rear side. The shaft 200 has an axial front side portion 203 and a step 204 which is an example of a stopper that is easy to manufacture. The tapered outer circumferential surface 202 extends continuously from the axially rearward end 205 to the axially forward end 206. A cylindrical outer circumferential surface 207 extending linearly in the axial direction is located at the axial rear side of the axial rear end 205 of the tapered outer circumferential surface 202.The tapered outer circumferential surface 202 may preferably include a linearly tapered surface, i.e., a conical surface. With such an arrangement, the radius of the tapered outer circumferential surface 202 increases linearly and gradually from the axially rearward end 205 to the axially forward end 206. The tapered outer circumferential surface 202 may preferably include a linearly tapered surface having a taper ratio of 1 / 200 to 1 / 30.A stopper member 203 and the step 204 serving as a stopper are given as a design example of easy assembly in manufacturing. The stopper member 203 has a cylindrical outer peripheral surface extending in the axial direction and protruding radially beyond the tapered outer peripheral surface 202 to form the step 204 between the surface 202 and the axial front end 206.The rotor part 300 of the embodiment will now be described with reference to FIGS. 3 to 7. The rotor part 300 includes a tubular sleeve 301, a plurality of magnet segments 311 arranged outside the sleeve 301 in the circumferential direction in the radial direction, and a tubular part 321 covering the magnet segments 311 from the outside as viewed in the radial direction. For manufacturing and shaping reasons, the magnet segments 311 may be divided into multiple pieces. FIG. 3 shows two axially separated pieces.The sleeve 301, see FIG. 5, is made of a tubular member having the central axis O 2 and has a first end 302 on its axial rear side (i.e., the axially first side), a second end 303 on the axial front side (i.e., the axially second side), and a cylindrical outer circumferential surface 304. The sleeve 301 has a protrusion part 305 that protrudes radially outward from the outer circumferential surface 304. The protrusion part 305 serves as a design example for more easy axial arrangement of the magnets during the manufacturing process.The sleeve 301 may be made of magnetic metal, for example, SS 400 or S 45C. The sleeve 301 has a thickness which is preferably thin for easily establishing the press-fit of the sleeve 301 on the shaft 200. The sleeve 301 may have a thickness of 1 mm to 2 mm at its thinnest portion. The press-fitting of the sleeve 301 to the shaft 200 will be described later.In this embodiment, the sleeve 301 has a tapered inner circumferential surface 306 (i.e., a tapered surface) that continuously expands radially outward from the first end 302 toward the second end 303. The tapered inner circumferential surface 306 continuously extends from the first end 302 to the second end 303, and does not include a portion where its radius decreases in the direction from the first end 302 to the second end 303 (i.e., in the axial forward direction). In other words, the tapered inner circumferential surface 306 has a radius that increases continuously in the axially forward direction between the first end 302 and the second end 303 over the entire length.The tapered inner circumferential surface 306 may preferably be a linearly tapered surface. In this case, the radius of the tapered inner circumferential surface 306 linearly increases from a radius R 3 of the tapered inner circumferential surface 306 at the first end 302 to a radius R 4 of the tapered inner circumferential surface 306 at the second end 303 in a direction from the first end 302 to the second end 303. The radius R 4 is larger than the radius R 3, i.e. R 4 >R 3. The tapered inner circumferential surface 306 may preferably be a linearly tapered surface having a taper ratio of, for example, 1 / 200 to 1 / 30.The range of this numerical value will be described later.The amount of taper of the tapered inner circumferential surface 306 is set to correspond to the amount of taper of the tapered outer circumferential surface 202 of the shaft 200. More specifically, when the tapered outer circumferential surface 202 of the shaft 200 and the tapered inner circumferential surface 306 of the sleeve 301 are given the same rectilinear taper, the outer circumferential surface 202 and the inner 306 are made to have the same taper ratio (for example, 1 / 100).In the assembled electric motor 100 in FIG. 1, the sleeve 301 is press-fitted on the tapered outer circumferential surface 202 of the shaft 200 such that the central axis line O 1 of the shaft 200 is aligned with the central axis line O 2 of the sleeve 301. In this arrangement, the second end 303 of the sleeve 301 contacts the step 204 of the stopper member 203 serving as a stopper and provided for easy assembly. The radius R 4 of the tapered inner circumferential surface 306 at the second end 303 is substantially equal to the radius of the axial front end 206 of the tapered outer circumferential surface 202.In addition, the tapered inner circumferential surface 306 of the sleeve 301 and the tapered outer circumferential surface 202 of the shaft 200 closely contact each other and have a high surface pressure, so that the sleeve 301 is pressed outward in the radial direction by the shaft 200. The assembled arrangement of the sleeve 301 and the shaft 200 will be described later.The magnet segments 311, see FIG. 6, are made of a circular arc-shaped magnetic piece having an inner radius with a predetermined radius of curvature. Specifically, the magnet segment 311 has a front axial surface 312, a rear axial surface 313, a first circumferential end surface 314, a second circumferential end surface 315, a radially inner surface 316, and a radially outer surface 317. The inner surface 316 of the magnet segment 311 is circular arc-shaped. The outer surface 317 may include a curved or planar surface or a combination of a curved surface and a planar surface.In the embodiment shown in FIG. 6, the surfaces 312, 313, 314 and 315 can be seen clearly. These surfaces may actually be curved surfaces or very small surfaces running between a tapered surface and a curved surface, and they are sometimes difficult to see due to the design of the magnetic circuit or the specification of the electric motor. Moreover, all surfaces are defined by edges which are actually chamfered and formed into a curved shape. Thus, in some cases the surfaces are not determined by the lines of the drawing.The inner surface 316 is circular arc-shaped with a predetermined radius of curvature and extends in the axial direction so as to connect a radially inner side edge of the axial front side surface 312 to the radially inner side edge of the axial rear side surface 313. The outer surface 317 may have a circumferentially smooth curved line forming, for example, a circular arc surface or another curved surface. The radius of curvature of the inner surface 316 will be described later.The tubular member 321, as shown in FIG. 7, is made of a tubular material extending in the axial direction. Specifically, the tubular part 321 has an axial front surface 322, an axial rear surface 323, a pipe inner surface 324, and a pipe outer surface 325. In the embodiment shown in FIG. 7, the end faces 322 and 323 can be clearly seen. These end surfaces are sometimes only ambiguous due to the material or structure of the tubular member and the manufacturing process.The tubular part 321 has a strength with respect to a deforming force acting outward in the radial direction. In other words, the tubular part 321 has a substantially invariable radius (diameter). In addition, the tubular member 321 is preferably made of a non-magnetic material because it is desired to prevent reduced performance due to heat generation or leakage magnetic flux. The tubular member 321 is preferably low in density so as to generate less centrifugal force upon rotation.The tubular member 321 is preferably made of a material having high specific strength (tensile strength per unit density) and includes carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, boron fiber, titanium alloy fiber, ultra high molecular weight polyethylene, or polybutylene terephthalate fiber. In addition, FRP (Fiber Reinforced Plastic) is also preferable as a material for the tubular member 321, wherein FRP comprises carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, boron fiber, titanium alloy fiber, ultra high molecular weight polyethylene, or polybutylene terephthalate fiber. A composite material of any combination of these materials is also preferred. In addition, the tubular member 321 may be made of austenitic stainless or non-magnetic metal including titanium alloys.In the embodiments shown in FIGS. 3 and 4, the assembled rotor part 300 comprises a total of eight magnet segments 311. More specifically, two magnet segments 311 are disposed axially adjacent to each other at a circumferential position A in FIG. 4, and form a pair. Similarly, two magnet segments 311 are disposed axially adjacent to each other at circumferential positions B, C, and D in FIG. 4, and each form a pair.Thus, the rotor part 300 of the embodiment includes four pairs of magnet segments 311 circumferentially arranged on the outer circumferential surface 304 of the sleeve 301 at substantially equal intervals. The magnet segments 311 on the axial rear side are arranged in the axial direction by a structure, for example, a protruding part 305 formed on the sleeve 301.The tubular member 321 is attached to cover and surround all the magnet segments 311 in four circumferential pairs (eight magnets in total) from the outer side in the radial direction of the segments 311. In the assembled electric motor 100 in FIG. 1, as described, the sleeve 301 is pressed radially outward by the shaft 200. This press-fitting force causes the sleeve 301 to deform radially outward. As a result, each magnet segment 311 is also pressed outward in the radial direction.As described, the tubular part 321 has a strength against deformation in the radially outward direction. Therefore, upon receiving the pressure that the magnet segments 311 exert, the tubular part 321 causes a reaction force that presses the magnet segments 311 back inward in the radial direction.This arrangement allows the magnet segments 311 to be held firmly between the sleeve 301 and the tubular member 321. This arrangement thus prevents relative movement of the magnet segments 311 against the sleeve 301 and the tubular member 321 even when the rotor member 300 is operated at high speed when the electric motor 100 is operated.This mechanism will be described in detail with reference to Figs. 8 to 10. FIG. 8 shows: the centrifugal forces acting on each member; the fastening torque between the sleeve 301 and the shaft 200; and the fastening torque between the sleeve 301 and the magnet segments 311, each depending on the rotational speed of the electric motor 100. The two fastening torques drop with increasing rotational speed. The "fastening torque" is obtained by multiplying a frictional force in the circumferential direction between the contact surfaces of two parts by the radial distance between the rotational axis and the contact surfaces (i.e., radius of the contact surface). A larger fastening torque indicates difficulties with relative circumferential movement (difficulty with slipping) of one part with respect to the other part.In FIG. 8, line 10 shows the fastening torque between the shaft 200 and the sleeve 301, and line 12 shows the fastening torque between the sleeve 301 and the magnet segments 311. Lines 14, 16, and 18 in FIG. 8 show the centrifugal forces of the magnet segments 311, the sleeve 301, and the tubular part 321. Line 20 shows the maximum torque of the electric motor 100.As shown in FIG. 8, the fastening torque 10 and 12 is considerably higher than the maximum torque 20 of the motor 100 at standstill (i.e., at zero speed), and it decreases as the speed of the motor 100 increases and gradually reaches the maximum torque 20.The maximum torque 20 of the electric motor 100 falls from approximately 10000 min-1, here in an example engine having a maximum power output of 90 kW. When the rotation speed increases at a constant torque, the output increases steadily according to the expression (output of the electric motor= torque×rotation speed). However, this is not realistic because of the limited power supply from the driving source. In the design of electric motors for high speeds and high torque, the torque is therefore adapted to drop from a certain speed so that instead the power output remains constant. Therefore, the torque decreases from about 10000 min-1 in this example.FIGS. 9 and 10 show the force equilibrium during standstill and during rotation. For purposes of clarity of drawing and description, Figures 9 and 10 show the principal force relationship between magnet segment 34 and sleeve 36.FIG. 9 shows the equilibrium of forces between the tubular part 32, the magnet segment 34 and the sleeve 36 during a standstill of the electric motor. The arrow 30 in FIG. 9 denotes a force that the magnet segment 34 exerts on the sleeve 36. Arrow 26 indicates a reaction force that sleeve 36 exerts on magnet segment 34. The arrow 28 indicates a friction force between the sleeve 36 and the magnet segment 34. The arrow 24 in FIG. 9 denotes a force that the tubular part 32 exerts on the magnet segment 34 (i.e., the compressive holding force of the tubular part 32). The arrow 22 indicates a reaction force that the magnet segment 34 exerts on the tubular part 32.For convenience of drawing and explanation, only the relationship between the magnet segment 34 and the sleeve 36 will be explained. However, one skilled in the art will readily appreciate that the force relationship between the sleeve 36 and the shaft 37 may be explained in a similar manner, except that the force that the magnet segment 34 exerts on the sleeve 36 and the force by the press fit of the sleeve 36 must be added to a force that the sleeve 36 exerts on the shaft 37.FIG. 10 shows the balance of forces between the tubular member 32, the magnet segment 34, and the sleeve 36 during rotation of the electric motor. Arrow 52 in FIG. 10 denotes a force that the magnet segment 34 exerts on the sleeve 36. Arrow 42 indicates a reaction force that sleeve 36 exerts on magnet segment 34. Arrow 48 denotes a frictional force between the sleeve 36 and the magnet segment 34. arrow 46 denotes a force that the tubular member 32 exerts on the magnet segment 34 (i.e., the compressive holding force of the tubular member 32). Arrow 54 denotes a reaction force exerted by the sleeve 36 via the magnet segment 34 on the tubular part 32. Arrow 38 denotes a total force applied to tubular member 32. A dashed arrow 40 denotes a centrifugal force acting on the magnet segment 34. A dashed arrow 44 indicates a centrifugal force acting on the tubular member 32.The compressive holding force 46 that the tubular member 32 exerts during rotation, see FIG. 10, has a value obtained by subtracting the centrifugal force 44 acting on the tubular member 32 during rotation from the compressive holding force 24 at standstill, see FIG. 9. The tubular member 32 is therefore preferably made of a material containing carbon fiber as a main component. The low mass tubular member 32 provides a less decreased compressive holding force 24 due to centrifugal force, whereby an increased force holds the magnet segment and the sleeve, and the rotational speed can be further increased.The force 52 shown in FIG. 10 is less than the force 30 shown in FIGS. 9 and 10 due to the centrifugal force 40 of the magnet segment 34 and the centrifugal force 44 of the tubular member 32; this reduces the force 42 and thus the frictional force 48 between the sleeve 36 and the magnet segment 34; thus, the fastening torque between the sleeve 36 and the magnet segment 34 is reduced when the electric motor 100 is rotating.For simplicity of the drawing and description, only the force relationship between the magnet segment 34 and the sleeve 36 has been explained. However, one skilled in the art will readily appreciate that the force relationship between the sleeve 36 and the shaft 37 may be explained in a similar manner, except that the force due to the press fit of the sleeve 36 and the force that the magnet segment 34 exerts on the sleeve 36 must be added to a force that the sleeve 36 exerts on the shaft 37, and the centrifugal force that acts on the sleeve 36 must be taken into account. Thus, the fastening torque between the sleeve 36 and the shaft 37 is also reduced when the electric motor 100 rotates.The compressive holding force 46 of the tubular member 32 must be maintained at maximum engine speed and the circumferential attachment torque between the sleeve 36 and the magnet segment 34 and between the sleeve 36 and the shaft 37 given by the compressive holding force 46 must exceed the maximum torque of the engine at each speed and at any time. A distance of more than a factor of five from the maximum torque of the motor is preferred.Therefore, for the rotor part 300 of this embodiment, the press-fit of the tubular part 321 is adjusted so that the fastening torque between the sleeve 301 and the shaft 200 exceeds the maximum torque of the rotary electric machine 100, and that the fastening torque between the magnet segments 311 and the sleeve 301 exceeds the maximum torque of the electric motor 100, throughout the operation range of the rotary electric machine 100.In an arrangement as in FIG. 8, the fastening torque 10 between the shaft 200 and the sleeve 301 and the fastening torque 12 between the sleeve 301 and the magnet segment 311 exceed the maximum torque 20 of the electric motor 100 at each rotational speed of the electric motor 100. This prevents relative movement between the shaft 200 and the sleeve 301 and between the sleeve 301 and the magnet segment 311 during operation of the electric motor 100.The operation of the electric motor 100 will now be described with reference to FIGS. 1 to 7. By flowing a current from a power source outside the electric motor 100 into a coil 104 via a power line, the stator 110 generates a rotating magnetic field around the central axis O 1. The rotating magnetic field generated by the stator 110 generates an electromagnetic force to the magnet segments 311 of the rotor part 300 in the circumferential direction. Therefore, the rotor part 300 rotates together with the shaft 200.A manufacturing method of the rotor part 300 according to an embodiment of the invention will now be described with reference to FIGS. 11 to 19. The manufacturing method S 10 for the rotor part 300 includes steps S 1 to S 5. In step S 1, the sleeve 301 is provided. For example, the inner and outer peripheral surfaces of a tubular material are machined to form the tapered inner peripheral surface 306 and the tapered outer peripheral surface 304. In addition, for example, the protrusion part 305 is formed as needed to facilitate assembly. The radius R 4' of the tapered inner circumferential surface 306 at the second end 303 of the sleeve 301 provided in step S 1 is smaller than the radius R 4 in the assembled electric motor 100 (see FIG. 17 ). Similarly, the radius R 3' of the tapered inner circumferential surface 306 at the first end 302 of the sleeve 301 provided in step S 1 is smaller than the radius R 3 in the assembled electric motor 100.In step S 2, the magnet segments 311 are provided. Specifically, eight magnet segments 311, each having a substantially circular arc-shaped configuration, and an inner surface 316 having a predetermined radius of curvature, are provided. In step S 3, the tubular part 321 is provided. The material of the tubular part 321 preferably has high specific strength (tensile strength per unit density) and includes carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, boron fiber, titanium alloy fiber, ultra high molecular weight polyethylene, or polybutylene terephthalate fiber. In addition, any FRP (Fiber Reinforced Plastic) containing the above materials, austenitic stainless materials or titanium, nonmagnetic metal such as titanium alloys is preferred, and a composite material thereof is also preferred.Steps S 1 to S 3 may be performed simultaneously or in any order. Steps S 1 to S 3 may be performed at respective manufacturing locations, or at least two of steps S 1 to S 3 may be performed at the same manufacturing location.In step S 4, a total of eight magnet segments 311 are arranged on the outer circumferential surface 304 of the sleeve 301. The step S 4 will be described below with reference to FIG. 13. First, two magnet segments 311 provided in step S 2 are disposed adjacent to each other in the axial direction at the circumferential position A to form a pair, and are mounted on the outer circumferential surface 304 of the sleeve 301. Similarly, two magnet segments 311 are disposed adjacently in the axial direction at the circumferential positions B, C, and D, respectively, to form a pair, and are mounted on the outer circumferential surface 304 of the sleeve 301.The pair of magnet segments 311A at the circumferential position A has a strong magnetic field, thereby giving a south pole on the inner surface 316 side and a north pole on the outer surface 317 side. On the other hand, the pair of magnet segments 311B have a magnetic field at the circumferential position B such that a north pole is formed on the inner surface 316 side and a south pole is formed on the outer surface 317 side.The pair of magnet segments 311C at the circumferential position C has a magnetic field such that a south pole is formed on the inner surface 316 side and a north pole is formed on the outer surface 317 side. Similarly, the pair of magnet segments 311D have a magnetic field at the circumferential position D such that a north pole results on the side of the inner surface 316 and a south pole results on the side of the outer surface 317.In summary, in this embodiment, the magnet segment pairs 311A to 311D are arranged in the circumferential direction such that their south poles and north poles alternate in the circumferential direction. In this embodiment, it is preferable that the magnet segments 311 are magnetized before step S 4. This allows the magnet segment pairs 311 to be maintained in a common magnetic field generated by the magnet segments 311, thereby making the arranging operation of the magnet segments 311 on the outer circumferential surface 304 of the sleeve 301 easy.In step S 5, the tubular member 321 is attached to cover the magnet segments 311 from the outside in the radial direction. Specifically, the tubular part 321 provided in step S 3 is attached outside the magnet segments 311 in the radial direction such that the inner surface 324 of the tubular part 321 faces the outer surfaces 317 in the radial direction of the magnet segments 311. In this state, the tubular part 321 and the magnet segments 311 may have a clearance fit or a weak press fit. As the press-fit, a weak press is sufficient to prevent the tubular part 321 from falling off.In FIG. 12, another embodiment of the manufacturing method for the rotor part 300 is explained. In place of step S3 in FIG. 11, in step S5, the tubular part 321 may be directly arranged on the magnet segments 311 by winding a material of the tubular part 321 around the outer periphery of the magnet segments 311 (step S3'). For example, material in the form of a strip, a belt, or an arc may be used to cover the outer periphery of the magnet segments 311, so as to form a certain thickness of a winding layer formed by a number of turns of the material in the rotational direction around the outer periphery of the magnet segments 311.In this embodiment, the radius of the inner circumferential surfaces 316 of the magnet segments 311 is set larger than the outer circumferential surface 304 of the sleeve 301. More specifically, see FIG. 15, R 7 is greater than R 8( R 7 >R 8), where R7 is the radius of curvature of the inner surface 316 of the magnet segments 311, and R8 is the radius of the outer circumferential surface 304 of the sleeve 301.Such an arrangement provides a gap 330 between the inner surfaces 316 of the magnet segments 311 and the outer circumferential surface 304 of the sleeve 301 at the circumferential end portions of the inner surfaces 316 of the magnet segments 311. The gap 330 has a function to be described later.If the outer periphery of the magnet segments 311 is non-circular, the tubular part 321 may be deformed along the outer periphery of the magnet segments 311 when press-fitted to make a surface contact between the outer surface of the segment 311 and the inner surface of the tubular part 321 connecting the two parts.When the tubular member 321 is placed on the radially outer side of the magnet segments 311, the rotor member 300 can be provided as an integrated member in which the magnet segments 311 are held between the sleeve 301 and the tubular member 321.The rotor part 300 shown in FIG. 14 is produced in steps S 1 to S 5. Since the rotor part 300 is prefabricated as an integrated part, the rotor part 300 can be easily transported. In the field of built-in electric motors, for example, such a rotor part assembly is sometimes manufactured and sold as a single product. The rotor part 300 of the embodiment has a conventional structure and is easy to handle. This is advantageous in this technical field from a distribution point of view.Next, the manufacturing method of the rotor according to an embodiment of the invention will be further described with reference to FIG. 11. The method S 20 for producing the rotor comprises the steps S 6 to S 8. In step S 6, the shaft 200 from FIG. 2 is provided. The tapered outer circumferential surface 202 is formed by, for example, machining the outer circumferential surface of a tubular member. Before or after the above procedure, the cylindrical outer peripheral surface 207 and the stopper member 203 may be formed as needed.In step S 7, the rotor part 300 provided in step S 5 is placed on from the axial rear side of the shaft 200. Step S 7 will now be described with reference to FIGS. 16 and 17. First, the sleeve 301 of the rotor part 300 is fitted onto the axial rear side of the shaft 200 provided in step S 6 from the second end 303 side.The shaft 200 is held so that an end surface (not illustrated) of an axially second side (front side) of the shaft is pressed toward an axially first side (rear side), and the end 302 of the sleeve 301 of the rotor part 300 is pressed toward the axially front side. In other words, the rotor part 300 is pushed in the axial forward direction as indicated by the arrow E in FIG. 16.This causes the front end of the tapered inner circumferential surface 306 of the sleeve 301 to contact the tapered outer circumferential surface 202 of the shaft 200 at a contact point P. This state is shown in Fig. 16. It is preferred, see FIG. 17, that the radius of the tapered outer circumferential surface 202 at the point P is equal to the radius R 4' of the tapered inner circumferential surface 306 of the second end 303 of the sleeve 301 provided in step S 1.In step S 8, the rotor part 300 is further moved over the shaft 200 with pressure in the axial forward direction. More specifically, the rotor part 300 is pressed in the axially forward direction to a certain position, e.g., the position where the second end 303 of the sleeve 301 contacts the step 204 of the stopper part 203, see FIG. 17.The sleeve 301 extends radially outward by a difference δ between the radius R 1 and the radius R 4' as it moves axially a distance x from the contact point P forward toward the step 204. Thereby, the rotor part 300 is press-fitted to the rotor shaft 200 in this state with a press φ2δ. Note that the sleeve 301 is deformed beyond its elastic deformation range preferably in this state.The sleeve 301 expands radially outward by the pressing force applied thereto until the sleeve 301 reaches the predetermined attachment position. This causes the magnet segments 311 to move outward in the radial direction. By this movement, the tubular member 321 receives an outward force and therefore also expands radially outward. Thus, the tubular part 321 builds up an elastic compressive force that holds the magnet segments 311 and the sleeve 301 between the tapered outer circumferential surface 202 of the shaft 200 and the tubular part 321 by generating pressing forces (surface pressing forces) between the contacting surfaces. The pressing forces hold the magnet segments 311 against circumferential movement on the outer circumferential surface 304 of the sleeve 301, and the inner circumferential surface 306 of the sleeve 301 on the tapered outer circumferential surface 202 of the shaft 200.Note that the inner circumferential surface 306 of the sleeve 301 is preferably brought into surface contact with the tapered outer circumferential surface 202 of the shaft 200, almost in the entire region (more than 90 percent) between the axial front surface 322 of the tubular part 321 and the rear surface 323.Particular dimensions of the shaft 200 and the sleeve 301 are presented below as an example. The taper ratio of both the tapered outer circumferential surface 202 of the shaft 200 and the tapered inner circumferential surface 306 of the sleeve 301 is set to 1 / 100. The thickness of the sleeve 301 at its second end 303 is set to 1 mm. The axial length of the sleeve 301, i.e., the distance between the first end 302 and the second end 303, is set to 100 mm.This results in a thickness of the sleeve 301 at its first end 302 of 1.5 mm. When the diameter of the outer circumferential surface 304 of the sleeve 301 is set to φ80 mm (i.e., the radius is 40 mm), a diameter of the tapered inner circumferential surface 306 of the second end 303 is φ78 mm (i.e., R4=39 mm). The diameter of the tapered inner circumferential surface 306 at the first end 302 is φ77 mm (i.e., R3=38.5 mm).When the outer diameter of the axial end 206 of the shaft 200 is set to φ78.5 mm (i.e., R1=39.25 mm), the outer diameter of the tapered outer circumferential surface 202 of the shaft 200 is φ77.5 mm (i.e., the radius is 38.75 mm) at a position 100 mm rearward from the axial front end 206.In this case, when the sleeve 301 is press-fitted on the shaft 200 with the second end 303 of the sleeve 301 contacting the step 204 of the shaft 200, the sleeve 301 and the shaft 200 are press-fitted with each other by an over-measurement of φ0.5 mm.Upon completion of step S 8, the rotor part 300 is press-fitted to the shaft 200, thereby producing the rotor 400 in FIG. 18. Thus, the step S 7 and the step S 8 together form a step S 9 in which the rotor part 300 is press-fitted to the shaft 200 from the outside in the radial direction.As described, in this embodiment, the magnet segments 311 are arranged in the circumferential direction, and the radius of curvature R 7 of the inner circumferential surface 316 of each magnet segment 311 is set larger than the radius of curvature R 8 of the outer circumferential surface 304 of the sleeve 301. This prevents breakage of the magnets when manufacturing the rotor 400.FIG. 19 shows the prevention of breakage of the magnets, which will be described below. Portion (a) in FIG. 19 corresponds to FIG. 15 and illustrates the rotor part 300 before press-fitting to the shaft 200. Portion (b) in FIG. 19 corresponds to FIG. 4 and illustrates the rotor part 300 after press-fitting is made on the shaft 200.As described, the gap 330 is formed between the inner circumferential surfaces 316 of the magnet segments 311 and the outer circumferential surface 304 of the sleeve 301 before press-fitting the rotor part 300 onto the shaft 200. If the press-fit of the rotor part 300 onto the shaft 200 is produced in step S 8, the rotor part 300 expands radially outwards by the named difference δ.As explained in section (b) in FIG. 19, the sleeve 301 expands radially outward and fills the gap 330. This produces a surface contact between the outer circumferential surface 304 of the sleeve 301 and the inner circumferential surfaces 316 of the magnet segments 311. The gap 330 is formed by the difference between the radius of curvature R 7 of the inner circumferential surfaces 316 of the magnet segments 311 and the radius R 8 of the outer circumferential surface 304 of the sleeve 301. The size of the gap 330 is determined by the extension of the sleeve 301 in step S8.According to the described arrangement, the gap 330 serves as a "clearance" that allows the sleeve 301 to expand and prevents an excessive force from being applied from the sleeve 301 to the magnet segments 311 in step S 8. This prevents breakage in the magnet segments 311.In this embodiment, the magnet segments 311 are composed of four pairs arranged separately in the circumferential direction, and they are not connected in the form of a ring. Such an arrangement can successfully prevent damage to the magnet segments 311 when a force is applied to the magnet segments 311, compared to ring-shaped magnets in step S 8. By adjusting the size and number of magnet segments 311 used, application of segments 311 to a large electric motor can be easily made.In this embodiment, as described, the sleeve 301 expands radially outward and fills the gap 330, thereby allowing surface contact between the outer circumferential surface 304 and the inner circumferential surfaces 316 of the magnet segments 311 in step S 8. This arrangement allows the outer peripheral surface 304 of the sleeve 301 and the inner peripheral surfaces 316 of the magnet segments 311 to closely and firmly abut each other, and the pressing force in the rotor 400 to be uniformly distributed throughout them when the assembly is completed. Such a structure increases the frictional force (fastening torque) between the outer circumferential surface 304 of the sleeve 301 and the inner circumferential surfaces 316 of the magnet segments 311, thereby effectively preventing relative movement of the magnet segments 311 against the sleeve 301 during operation of the electric motor 100.Moreover, in this embodiment, the tapered surfaces 202 and 306 are used to expand the sleeve 301 to press-fit the rotor part 300 on the shaft 200 in step S8. Such an arrangement enables uniform and highly precise expansion of the sleeve 301 in order to stably hold the magnet segments 311 between the sleeve 301 and the tubular member 321. Thereby, the rotor 400 becomes a fixed structure, and the rotor 400 can be used in a motor for a product that is operated at high speed.In this embodiment, the process of press-fitting the rotor part 300 to the shaft 200 requires only a press machine that presses the rotor part 300 in an axial direction. No other complicated machines are required, thereby increasing productivity and decreasing manufacturing cost.According to this embodiment, a so-called "thermal insertion method" in which the rotor part 300 and a part of the shaft 200 are heated for press-fitting may not be used. As a result, high-temperature demagnetization of the magnets due to the heating is avoided.Since a "thermal insertion method" is not used in this embodiment, the rotor member 300 can be firmly fixed to the shaft 200 although a material having a small linear expansion coefficient such as carbon fiber, titanium or glass fiber is used.According to the embodiment, by appropriately adjusting the extent (taper ratio, inclination angle against the axial direction) of the tapered surfaces 202 and 306, it becomes possible to easily and independently set a pressure between the sleeve 301 and the tubular part 321. This allows the rotor part 300 to be applied to electric motors of different types and sizes.Note that the tapered outer circumferential surface 202 and the tapered inner circumferential surface 306 are preferably provided with a taper ratio in the range of 1 / 1000 to 1 / 30. This value range is described below. When the sleeve 301 is press-fitted on the shaft 200 with the taper ratio at the upper limit (1 / 30), an elastic compressive force is applied from the sleeve 301 radially inward to the shaft 200. Immediately after the establishment of the press-fit of the sleeve 301 on the shaft 200, the elastic compressive force causes the sleeve 301 to move away from the shaft 200 along the tapered outer circumferential surface 202.Consequently, the inventor of the invention has found from the results of studies that a taper ratio larger than 1 / 30 (for example, 1 / 10, 1 / 5) would cause the following adverse difficulties. When the press-fit of the sleeve 301 is generated on the shaft 200, the force of the sleeve 301 which pulls away from the shaft 200 tends to exceed the frictional force between the sleeve 301 and the shaft 200. This would result in the sleeve 301 dropping off the shaft 200.With a taper ratio larger than 1 / 30, a rather large force is required for press-fitting the sleeve 301 to the shaft 200, which requires a larger manufacturing machine. From this viewpoint, it is preferable to set the taper ratio to a maximum value of 1 / 30.As for the minimum value (1 / 1000) of the taper ratio, if the taper ratio is smaller than 1 / 1000, a longer axial distance (the aforementioned distance x) is necessary to obtain a predetermined allowance (ø0.5 mm in the aforementioned example) when press-fitting between the sleeve 301 and the shaft 200. This deteriorates an effective operation. In addition, a taper ratio smaller than 1 / 1000 may result in machining errors in the actual machining operation. From this viewpoint, the minimum value of the taper ratio is preferably 1 / 1000. From the above viewpoint, the minimum value of the taper ratio is more preferably 1 / 200 in view of the actual manufacturing cost. This minimum value allows turning and cutting operations.In another embodiment of the invention, a movement preventing structure may be provided between the sleeve 301 and the magnet segments 311 to prevent relative movement between the sleeve 301 and the magnet segments 311. This structure will now be described with reference to Figs. 20 to 22. Reference numerals that do not differ from the described embodiment are again used for comparable parts that will not be explained any more.First, a rotor part 500 of another embodiment of the invention will be described with reference to FIG. 20. The portion (a) in FIG. 20 corresponds to the portion (a) in FIG. 19 and shows a rotor part 500 to be press-fitted on the shaft 200. The portion (b) in FIG. 20 corresponds to the portion (b) in FIG. 19 and shows the rotor part 500 press-fitted on the shaft 200.The rotor part 500 of this embodiment includes a movement preventing structure 501 on the outer circumferential surface 304 of the sleeve 301. The movement preventing structure 501 has a function of preventing relative movement of the sleeve 301 against the magnet segments 311, and is configured to increase the coefficient of friction between the sleeve 301 and the magnet segments 311. The movement preventing structure 501 may include, for example, a high friction resin coating layer, an adhesive resin layer, a layer prepared by sandblasting, a coating layer containing material for improving the friction coefficient, and a layer in which the friction coefficient has been improved by a chemical surface treatment.The movement preventing structure 501 may be composed of a protrusion extending radially from the outer circumferential surface 304 of the sleeve 301. In this case, the magnet segment 311 may include, on the inner circumferential surface 316, an engaging portion that receives the protrusion. When the movement preventing structure 501 is made of a coat layer, its thickness is preferably between 0.01 and 0.1 mm.When the movement preventing structure 501 is the protrusion extending radially from the outer circumferential surface 304 of the sleeve 301, the height of the protrusion is preferably 0.5 mm or more and 1 / 3 or less than the thickness of the magnet segments 311. The providing operation of the movement preventing structure 501 of the sleeve 301 may be performed in step S 1 together with the cutting operation of the outer circumferential surface 304 of the sleeve 301, or may be performed in step S 4 before arranging the magnet segments 311 on the sleeve 301.As shown in the portion (b) in FIG. 20, when the sleeve 301 is expanded radially outward by an interference amount against the shaft 200 to fill the gap 330, the outer circumferential surface 304 of the sleeve 301 and the inner circumferential surfaces 316 of the magnet segments 311 together make a surface-to-surface contact via the movement preventing structure 501. The provision of the gap 330 prevents fractures in the magnet segments 311 due to the expansion of the sleeve 301 in the radial direction.The surface contact between the outer circumferential surface 304 of the sleeve 301 and the inner circumferential surfaces 316 of the magnet segments 311 effectively prevents a relative movement of the magnet segments 311 against the sleeve 301 and the tubular part 321 at high rotational speeds of the rotor part 500 during operation of the electric motor 100.The rotor part 510 of another embodiment of the invention will now be described with reference to FIG. 21. The portion (a) in FIG. 21 corresponds to the portion (a) in FIG. 19 and shows a rotor part 510 to be press-fitted on the shaft 200. The portion (b) in FIG. 21 corresponds to the portion (b) in FIG. 19 and shows the rotor part 510 press-fitted on the shaft 200.The rotor part 510 of this embodiment includes a movement preventing structure 511 on the inner circumferential surface 316 of the associated magnet segment 311. The movement preventing structure 511 is similarly configured to increase the friction coefficient between the sleeve 301 and the magnet segment 311. The movement preventing structure 511 may be composed of a protrusion extending radially from the inner circumferential surface 316 of the magnet segment 311.As shown in the portion (b) in FIG. 21, when the sleeve 301 is expanded radially outward to fill the gap 330, the outer circumferential surface 304 of the sleeve 301 and the inner circumferential surfaces 316 of the magnet segments 311 together make surface contact via the movement preventing structure 511. Such an arrangement effectively prevents relative movement of the magnet segment 311 against the sleeve 301 and the tubular member 321 at high speeds of the rotor member 510 during operation of the electric motor 100.The providing operation of the movement preventing structure 511 on the inner circumferential surface 316 of the magnet segment 311 may be performed in step S 2 together with the manufacturing of the magnet segments 311, or may be performed in step S 4 before the arranging of the magnet segments 311 on the sleeve 301.The rotor part 520 of still another embodiment of the invention will be described with reference to FIG. 22. The portion (a) in FIG. 22 corresponds to the portion (a) in FIG. 19 and shows a rotor part 520 to be press-fitted on the shaft 200. The portion (b) in FIG. 22 corresponds to the portion (b) in FIG. 19 and shows the rotor part 520 press-fitted on the shaft 200.The movement preventing structure 521 in the rotor part 520 of this embodiment is independently formed and inserted between the sleeve 301 and the associated magnet segment 311. The movement preventing structure 521 has a considerable coefficient of friction against the sleeve 301 and the magnet segment 311. The movement preventing structure 521 may be, for example, a friction sheet having a processed surface that increases the friction coefficient, an adhesive sheet having adhesive on the surface, or a rubber blanket made of, for example, NBR or silicone having adhesiveness. The movement preventing structure 521 preferably has a thickness of 0.03 to 0.1 mm.As illustrated in section (b) in FIG. 22, the expansion of the sleeve 301 in the radial direction outward fills the gap 330, thereby creating a surface-to-surface contact between the outer circumferential surface 304 of the sleeve 301 and the inner circumferential surface 316 of the magnet segment 311 via the movement preventing structure 521. With this arrangement, at high speeds of the rotor part 520, the magnet segments 311 do not move against the sleeve 301 and the tubular part 321 during operation of the electric motor 100.The above embodiment is described as having circular arc-shaped magnet segments having a certain radius of curvature. The magnet segments can, however, also be shaped differently. Such an arrangement will be described with reference to Fig. 23.Fig. 23 shows a rotor part 600 of still another embodiment of the invention. The portion (a) of FIG. 23 shows an outer view of the rotor part 600 as viewed from the axial direction, and the portion (b) of FIG. 23 shows a partially enlarged view of the portion (a).The rotor part 600 includes a sleeve 601, a plurality of magnet segments 611 arranged radially outside the sleeve 601, and a tubular part 321 that covers the magnet segments 611 radially from the outside.The sleeve 601 of this embodiment includes concave inwardly directed depressions 602 in the outer circumferential surface 604. The recesses 602 extend axially from one axial end of the sleeve 601 to the other axial end of the sleeve and are each defined by a substantially planar bottom surface and circumferential end surfaces that protrude from the respective circumferential ends of the bottom surface. The depressions 602 are distributed over the circumference of the outer circumferential surface 604 at uniform intervals. Between two adjacent recesses 602, there is a convex protrusion 603 that protrudes outward in the radial direction from the bottom surface of the recesses 602.The magnet segments 611 each include an inner circumferential surface 616 on their radially inner side and an outer circumferential surface 617 on their radially outer side. In this embodiment, the outer circumferential surface 617 of the magnet segment 611 has a curved surface as in the above embodiment. In contrast, the inner circumferential surface 616 of the magnet segment 611 is substantially planar.In the assembled rotor part 600, see FIG. 23, the magnet segments 611 are located in the corresponding recesses 602 formed in the sleeve 601 to allow surface contact between the inner circumferential surfaces 616 of the magnet segments 611 and the bottom surfaces of the recesses 602. The circumferential projections 603 on both sides of the respective recess 602 prevent the magnet segments 611 from moving in the circumferential direction.Each recess 602 may have axial end surfaces protruding from the two axial ends of the bottom surface of the recess 602. In this case, the axial ends of the recess 602 prevent the magnet segments 611 from moving in the axial direction.In this embodiment, the arranging operation of the magnet segments 611 on the radially outer side of the sleeve 601 is easier in step S 4. In addition, it is possible to prevent relative movement of the magnet segments 611 with respect to the sleeve 601 during operation of an electric motor in which the rotor part 600 is used.Referring to FIG. 24, a rotor part 700 of still another embodiment of the invention will be described. As in the previous embodiment, the same reference numerals are used for comparable elements, which will not be described again. The rotor part 700 includes a tubular sleeve 701, a plurality of magnet segments 311 arranged outside the sleeve 301 in the radial direction, and a tubular part 321 covering the magnet segments 311 from the outside in the radial direction.The sleeve 701 is made of a tubular member having a central axis line O 2 and includes a first end 702 on the axial rear side (i.e., the first axial side), a second end 703 on the axial front side (i.e., the second axial side), and a cylindrical outer circumferential surface 704 extending in the axial direction. The sleeve 701 has a protrusion 705 that protrudes outward in the radial direction from the outer circumferential surface 704 (cylindrical surface) at the axially rear end of the sleeve. The protrusion 705 is an example of easily arranging the magnets in the axial direction during the manufacturing process.The sleeve 701 includes a cylindrical surface 704 extending radially forward from the first end 702, a tapered inner circumferential surface 705, and a tapered inner circumferential surface 706 both continuously expanding radially outward in the axially forward direction. The radius of the cylindrical surface 704 is constant in the direction from the first end 702 to the second end 703.The first tapered inner circumferential surface 705 is a conical surface that extends from an axially front end edge 704A of the cylindrical surface 704 and has a first inclination angle θ 1 against the axis O 2. The second tapered inner circumferential surface 706 is a conical surface extending from an axially front end edge 705A of the first tapered inner circumferential surface 705 to the axially front end of the second end 703 and having a second inclination angle θ 2 against the axis O 2. The first angle θ 1 is set smaller than the second angle θ 2.As described, in the invention, permanent magnet segments are used which are not annular but are divided at least in the circumferential direction. In securing the sleeve to the shaft, the tapered surfaces are used to expand the sleeve for an interference fit on the shaft. This allows the sleeve and the tubular part to be given a pressure which is greater than in the case of thermal insertion. This allows a durable attachment of the magnet segments and the sleeve to the shaft. Since the magnet segments are divided in the circumferential direction, the magnet segments do not break even under severe pressing, thereby firmly holding the magnet segments between the sleeve and the tubular member. This further reinforces the structure of the rotor part. Thereby, a rotor part for a rotating electric machine to be operated at higher speed can be provided.In addition, the fixing operation of the sleeve to the shaft can be simplified, and complicated manufacturing machines are unnecessary. This results in improved manufacturing efficiency and reduced manufacturing cost.Since the magnet segments are divided in the circumferential direction, breakages in the magnet segments are effectively suppressed by the expansion of the sleeve in the radial direction in the fastening operation of the sleeve to the shaft. Therefore, even when the rotor part is fixed with a large pressure, no breakage occurs in the magnets. Thus, the rotor part can be operated at a higher speed compared to any conventional rotor parts.The circumferentially divided magnet segments allow easy production of the magnet segments and the use of relatively large magnet segments. By using large magnet segments, it is possible to produce rotating electric machines with higher torque, which are not obtained with ring-shaped magnets. Thus, a rotating electric machine of the invention can rotate with higher torque and higher speed, and a rotating electric machine with increased power output can be provided.Although eight magnet segments are arranged in the circumferential direction in the described embodiment, any number of magnet segments may be used under the boundary condition that two or more magnet segments are arranged in the circumferential direction. In addition, a gap may be located between two adjacent magnet segments, or they may contact each other.The tapered outer circumferential surface of the shaft and the tapered inner circumferential surface of the sleeve may include, in addition to the linearly tapered surface, a tapered surface whose radius of curvature varies in the axial direction, like an exponential function tapered surface.In the described embodiment, the tubular member is press-fitted to the radial outside of the magnet segments 311 (step S 5). However, a material in the form of a strip, a belt, an arc, or a thread may be applied to the radially outer side of the magnet segments 311 to assemble the rotor part 300.In the above embodiments, the invention is described as applied to an electric motor. However, the invention can be suitably applied to any rotary electric machine including a generator.The invention has been described with embodiments, but it is not intended to limit the scope of the invention as set forth in the claims. Furthermore, not all combinations of the features described in the embodiments are intended to be required for the features or methods of the invention. Moreover, one skilled in the art is readily able to modify or revision the described embodiments. It is clear from the claims that any embodiments with such modifications or variations are included in the technical scope of the invention.It is preferable that an execution procedure in each process including the movements, processes, steps and stages in the apparatuses, systems, programs and methods described in the claims, the description and the drawings do not specify "before" and "before", and therefore, they can be executed in any desired order as long as no preceding output is used in a subsequent process. For convenience, the terms "first" and "next" may be used in any claim, description, and acts in the drawings without specifying any order of execution.EXAMPLES:A first example of the invention discloses a rotor part (300) to be fixedly press-fitted to the shaft (200) of a rotating electric machine (100), the rotor part (300) comprising:a tubular sleeve (301) having a first end (302) on a first side in the axial direction and a second end (303) on a second side in the axial direction;a plurality of magnet segments (311) circumferentially disposed radially outward of the sleeve (301); anda tubular member (321) covering the plurality of magnet segments (311) from the outside in the radial direction to hold the magnet segments (311) between the tubular member (321) and the sleeve (301),wherein:the sleeve (301) has an inner circumferential surface including a tapered surface (306) continuously expanding radially outward in the extending direction from the first end (302) to the second end (303),the inner circumferential surface of the sleeve (301) does not include a portion where the radius of the inner circumferential surface decreases in the direction from the first end (302) to the second end (303).A second example of the invention includes the rotor part of Example 1, wherein the tapered surface (306) of the sleeve (301) is a linearly tapered surface, or includes a plurality of linearly tapered surfaces connected to each other and inclined to a rotation axis at different angles, respectively.A third example of the invention includes the rotor part according to Example 1 or 2, wherein the inner circumferential surface of the sleeve (701) has a cylindrical surface (704) having a constant radius and extending from the first end (702) toward the second end (703), the tapered surface including a linearly tapered surface extending from the cylindrical surface (704) toward the second end (703).A fourth example of the invention includes the rotor part according to Example 2 or 3, wherein the linearly tapered surface has a taper ratio of 1 / 200 to 1 / 30.A fifth example of the invention includes the rotor part according to any one of Examples 1 to 4, wherein the sleeve (301) does not include a hole having an opening on the inner circumferential surface of the sleeve (301).A sixth example of the invention comprises the rotor part according to any one of examples 1 to 5, wherein a gap (330) is formed at least partially between the sleeve (301) and the magnet segments (311).A seventh example of the invention comprises the rotor part of any one of Examples 1 to 6, wherein:the outer circumferential surface of the sleeve (301) is cylindrical,and the inner circumferential surface (316) of each magnet segment (311) is circular arc-shaped and has a radius of curvature which is larger than the radius of curvature of the outer circumferential surface (304) of the sleeve (301).An eighth example of the invention includes the rotor part according to any one of Examples 1 to 7, further including a movement preventing structure (501) to prevent relative movement between the sleeve (301) and the magnet segments (311).A ninth example of the invention includes the rotor part according to any one of Examples 1 to 8, wherein the tubular part (321) includes:carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, boron fiber, titanium alloy fiber, ultra high molecular weight polyethylene or polybutylene terephthalate fiber;fiber-reinforced plastic containing carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, boron fiber, titanium alloy fiber, ultra high molecular weight polyethylene, or polybutylene terephthalate fiber;or nonmagnetic metal.According to a tenth example of the invention, there is provided a rotor (400) comprising:a shaft (200) having an outer circumferential surface (202) that expands radially outward in the extending direction from a first axial direction side to a second axial direction side; andthe rotor part (300) according to any one of claims 1 to 9, wherein the rotor part (300) is fixed to the shaft (200) on a radially outer side of the shaft (200) such that the second end (303) of the sleeve (301) is disposed on the second side in the axial direction of the shaft (200) with respect to the first end (302) of the sleeve (301),wherein the sleeve (301) is deformed to expand radially outward by the shaft (200) when the rotor part (300) is fixed to the shaft (200), so that the outer circumferential surface (304) of the sleeve (301) and the inner circumferential surfaces (316) of the magnet segments (311) contact each other under pressure.An eleventh example of the invention includes the rotor according to Example 10, wherein the inner circumferential surface of the sleeve (301) and the outer circumferential surface (202) of the shaft (200) contact with almost all surfaces over which the tubular member (321) is fitted.A twelfth example of the invention comprises the mover of Example 10 or 11, wherein the sleeve (301) deforms beyond its elastic deformation range.According to a thirteenth example of the invention, there is provided a rotary electric machine (100) including the rotor (400) according to any one of Examples 10 to 12.A fourteenth example of the invention includes the rotating electric machine of Example 13, wherein the tubular member (321) has a pressing in which the fastening torque between the sleeve (301) and the shaft (200) exceeds the maximum torque of the rotating electric machine (100) at the allowable rotation speed, and the fastening torque between the magnet segments (311) and the sleeve (301) exceeds the maximum torque of the rotating electric machine (100) at the allowable rotation speed.According to another example of the invention, there is provided a method of manufacturing a rotor part (300) to be press-fitted to a shaft (200), comprising:arranging a plurality of magnet segments (311) in the circumferential direction on an outer circumferential surface (304) of the tubular sleeve (301) having a first end (302) on a first side in the axial direction, a second end (303) on a second side in the axial direction, and an inner circumferential surface including a tapered surface (306) continuously expanding radially outward in the extending direction from the first end (302) to the second end (303); andarranging a tubular member (321) for covering the plurality of magnet segments (311) from the outside in the radial direction.A sixteenth example of the invention includes the method of example 15, wherein the step of disposing the tubular portion (321) includes directly winding a material of the tubular portion (321) around the outer circumferential surface of the magnet segments (311).A seventeenth example of the invention comprises the method of manufacturing a rotor (400) for a rotating electric machine (100) including the rotor part (300) manufactured by the method according to example 15 or 16, comprising:providing a shaft (200) having an outer circumferential surface (202) in a region to which the rotor part (300) is fixed, the outer circumferential surface (202) expanding radially outward in the extending direction from a first side in the axial direction to a second side in the axial direction; andfixing the rotor part (300) to the outside of the shaft (200) in the radial direction by means of a press fit, whereinthe step of fastening the rotor part (300) with a press fit comprises:attaching the sleeve (301) to the shaft (200) from the first axial direction side so that the second end (303) of the sleeve (301) is disposed on the second axial direction side of the shaft (200) opposite to the first end (302);attaching the sleeve (301) to the shaft (200) with an interference fit by pushing the first end (302) of the sleeve (301) to the second side in the axial direction; andcausing the sleeve (301) to expand radially outward in an interference fit manner by the force of the sleeve (301), thereby the sleeve (301) being press fitly attached at a predetermined attachment position.An eighteenth example of the invention includes the method of Example 17, wherein the rotor part (300) includes at least one piece of a gap (330) between the sleeve (301) and the magnet segments (311), wherein in the attaching step of the rotor part (300), the outer circumferential surface (304) of the sleeve (301) and the inner circumferential surfaces (316) of the magnet segments (311) are brought into face-to-face contact with each other over almost the entire face by expanding the sleeve (301) radially outward to fill the gap (330).A nineteenth example of the invention includes the method of Example 18, wherein the outer circumferential surface (304) of the sleeve (301) is cylindrical, and the inner circumferential surface (316) of each magnet segment (311) is in the shape of a circular arc and has a radius of curvature larger than the radius of the outer circumferential surface (304) of the sleeve (301), wherein in the attaching step of the rotor part (300), by press-fitting, the outer circumferential surface (304) of the sleeve (301) and the inner circumferential surfaces (316) of the magnet segments (311) are brought into surface-to-surface contact with each other by expanding the sleeve (301) radially outward.

Claims

A rotor part (700) to be fixedly press-fitted to the shaft (200) of a rotating electric machine (100), the rotor part (700) comprising: a tubular sleeve (701) having a first end (702) on a first side in the axial direction and a second end (703) on a second side in the axial direction; a plurality of magnet segments (311) arranged in circumferential alignment radially outside the sleeve (301); a tubular part (321) configured to cover the magnet segments (311) from outside in the radial direction to hold the magnet segments (311) between the tubular part (321) and the sleeve (701), the sleeve (701) having an inner circumferential surface (704, 705, 706) comprising: a cylindrical surface (704) having a constant radius, wherein the cylindrical surface (704) is provided in an axial portion of the sleeve (701) which extends from the first end (702) in a direction toward the second end (703) and extends to an end edge (704a) on the axially second side of the cylindrical surface (704), a tapered surface (705, 706) which is connected to the end edge (704a) on the axially second side of the cylindrical surface (704) and which extends from the end edge (704)) on the axially second side of the cylindrical surface (704) to the second end (703), the tapered surface (705, 706) continuously expanding radially outward in the extending direction toward the second end (703), the tapered surface (705, 705, 706) comprises: a first linear tapered surface (705) extending in an axial section from the end edge (704a) on the axially second side of the cylindrical surface (704) in a direction toward the second end (703) and extending to an end edge (705a) on the axially second side of the first linear tapered surface (705); and a second linear tapered surface (706) extending from the end edge (705a) on the axially second side of the first linear tapered surface (705) to the second end (703), wherein the second linear tapered surface (706) has a different expansion ratio than the first linear tapered surface (705).

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