JP7797253B2 - Electric motor rotor - Google Patents

Description

The present invention relates to a rotor for an electric motor that includes a rotating shaft and a plurality of permanent magnets or secondary conductors arranged axially and circumferentially spaced apart on the outer periphery of the rotating shaft.

Conventionally, a rotor for this type of electric motor is known in which an axially extending reinforcing tube formed by heat curing a prepreg sheet in which a thermosetting resin is impregnated into a fiber base material is tightly attached to the outer periphery of all permanent magnets (see, for example, Patent Document 1).

For such motor rotors, it is necessary to prevent all permanent magnets from scattering outward from the rotating shaft, even under centrifugal force during high-speed rotation. To meet this requirement, the adhesive strength of the reinforcing tube must be increased. Therefore, in the motor rotor described in Patent Document 1, a cylindrical reinforcing tube is fabricated in advance so that the rotating shaft, to which the permanent magnets are attached, can be inserted, and a hollow rotating shaft is used. The motor rotor is then fabricated using a technique known as cold fitting. Specifically, a refrigerant such as liquid nitrogen is circulated through the hollow portion of the rotating shaft, causing the rotating shaft to shrink radially inward. The rotating shaft is then inserted into the reinforcing tube, the refrigerant flow is stopped, and the temperature of the rotating shaft is returned to room temperature, causing the rotating shaft to expand radially outward and return to its original size. The reinforcing tube is then tightly attached to the outer periphery of all permanent magnets.

Japanese Patent Application Laid-Open No. 2017-50925

However, the rotor of the electric motor described in Patent Document 1 is manufactured using a special cold-fitting method, which not only requires specialized tools, but also jigs for manufacturing the cylindrical reinforcing tube from a single piece of prepreg, and a hollow rotating shaft. Therefore, there is considerable room for reexamination in order to turn the rotor of the electric motor described in Patent Document 1 into an inexpensive, general-purpose product.

In light of the above, the present invention aims to provide an electric motor rotor that can be used as an inexpensive, general-purpose product while preventing all permanent magnets or all secondary conductors from scattering outward from the rotating shaft even during high-speed rotation.

In order to solve the above problems, the present invention provides a rotor for an electric motor , which comprises a rotating shaft, a cylindrical core that extends in the axial direction and fits onto the rotating shaft, a pair of core holders that are located at both axial ends of the core and fit onto the rotating shaft to clamp and fix the core, and a plurality of permanent magnets or secondary conductors that are arranged in the axial direction and spaced apart in the circumferential direction between the pair of core holders, wherein the permanent magnets or secondary conductors are embedded in the core, and a reinforcing tube that extends in the axial direction and is formed by heat curing a prepreg sheet in which a fiber base material is impregnated with a thermosetting resin is disposed between the core and the pair of core holders. In this case, the core is closely attached to the outer peripheral surface of the core, and a plurality of grooves extending in the axial direction are formed on the outer peripheral surface of the core, positioned between the embedded locations of each permanent magnet or each secondary conductor, a binder made of a thermosetting resin is inserted into each groove of the core, a prepreg sheet is wrapped around the outer periphery of the core and each binder together with a pair of core holders, and a reinforcing tube extending in the axial direction is formed by heat curing, and this reinforcing tube is bonded to the outer peripheral surface of the core and the outer peripheral surfaces of the pair of core holders, and the reinforcing tube is also bonded to each groove of the core via the heat cured binders.

According to the present invention , the thermosetting resin binder inserted into each groove functions as an anchor. This sufficiently increases the adhesive strength between the core and the pair of core retainers and the reinforcing tube, preventing all permanent magnets or all secondary conductors from scattering outside the core even during high-speed rotation. The resulting motor rotor can then be an inexpensive, general-purpose product.

1A is an axial cross-sectional view showing an outline of a rotor of an electric motor according to a first comparative example of the present invention, and FIG. 1B is an AA cross-sectional view of the same comparative example . FIG. 10 is an axial cross-sectional view showing an outline of a rotor of an electric motor according to a second comparative example of the present invention. 3A is a cross-sectional view taken along line AA, schematically illustrating a process of winding a prepreg when producing the comparative example shown in Fig. 2. FIG. 3B is a cross-sectional view taken along line AA of the comparative example shown in Fig. 2. 1 is a radial cross-sectional view showing an outline of a rotating shaft, a core, and a permanent magnet in an embodiment of a rotor for an electric motor according to the present invention; 5A, 5B, and 5C are radial cross-sectional views each showing a schematic representation of a step in the fabrication of the embodiment shown in FIG. 4; 5B is a schematic axial cross-sectional view showing a rotor precursor after the step shown in FIG. 5B, and FIG. 5C is a schematic axial cross-sectional view showing an embodiment of a rotor for an electric motor according to the present invention after the step shown in FIG.

The first comparative example shown in Figures 1(a) and 1(b) is an example of a rotor for an electric motor classified as an SPM. The electric motor is a motor, and the rotor 1 includes a rotating shaft 2 and a plurality of permanent magnets 3 arranged axially and attached to the outer surface of the rotating shaft 2 at circumferential intervals. The rotating shaft 2 is formed from a metal material containing iron or other magnetic substances. Specifically, each permanent magnet 3 comprises a plurality of magnet pieces 3a, which are constituent units of each permanent magnet 3, arranged in a line axially and attached to the outer surface of the rotating shaft 2 by the magnetic force of the magnet pieces 3a. The number of permanent magnets 3 and their attachment positions on the rotating shaft 2 are not particularly limited, as long as each permanent magnet 3 generates a magnetic field that satisfies the required performance of the motor. Furthermore, the material from which the magnet pieces 3a are made is not particularly limited.

In addition, in the rotor 1, an axially extending reinforcing tube 4 formed by heat-curing a prepreg sheet in which a fiber base material is impregnated with a thermosetting resin is in close contact with the outer circumferential surface of all permanent magnets 3. For the prepreg sheet, the fiber base material can be woven or nonwoven fabrics such as carbon fiber, silicon carbide fiber, Tyranno (SiTiC) fiber, Kevlar fiber, alumina fiber, or boron fiber. The thermosetting resin can be epoxy resin, polyimide resin, or polyether ether ketone resin. It is desirable that the reinforcing tube 4 formed from the prepreg sheet be lightweight and strong enough to prevent all permanent magnets 3 from scattering outward from the rotating shaft 2 even during high-speed rotation. The fiber base material and thermosetting resin are selected taking the above factors into consideration.

Furthermore, the rotor 1 is provided with a pair of magnet retainers 5, 5 located at both axial ends of each permanent magnet 3. These magnet retainers 5 are fitted onto the rotating shaft 2 to clamp and secure all of the permanent magnets 3. Recesses 5a are recessed at multiple locations around the circumferential surface of each magnet retainer 5. Multiple locations around the circumferential surface of the reinforcing tube 4 fit into these recesses 5a, and the reinforcing tube 4 is adhered to the outer surfaces of all of the permanent magnets 3 and the outer surfaces of the pair of magnet retainers 5, 5 that face the permanent magnet 3. Adhesion between all of the permanent magnets 3 and the pair of magnet retainers 5, 5 and the reinforcing tube 4 is achieved when the prepreg sheet, together with the pair of magnet retainers 5, 5, is wrapped around the outer surfaces of all of the permanent magnets 3 and heat-cured to form the reinforcing tube 4. This allows a portion of the thermosetting resin to penetrate into the recesses 5a in each magnet retainer 5 and harden. The multiple circumferential locations of the reinforcing tube 4 that fit into each recess 5a function as anchors, ensuring a sufficiently high adhesive strength between all permanent magnets 3 and the pair of magnet retainers 5, 5 and the reinforcing tube 4 that compares favorably with the adhesive strength achieved by conventional cold fitting.

More specifically, the axial width of the prepreg sheet extends axially outward beyond all of the recesses 5a of each magnet retainer 5. The sheet is pulled out from the original roll and, in the so-called B-stage state, is wrapped around the outer periphery of all of the permanent magnets 3 together with a pair of magnet retainers 5, 5, with a predetermined tension. When attaching the reinforcing tube 4 to all of the permanent magnets 3 and the pair of magnet retainers 5, 5, the precursor, in which the prepreg sheet is wrapped around the outer periphery of all of the permanent magnets 3 together with the pair of magnet retainers 5, 5, is placed inside, for example, a bag or container capable of being decompressed. The decompression causes the prepreg sheet to deform so that it conforms to the inner surface of each recess 5a of each magnet retainer 5 and the outer periphery of each permanent magnet 3. The precursor is then heated to the curing temperature of the thermosetting resin in the prepreg sheet. This heating can be performed continuously while the prepreg sheet remains in the bag or container, or in a batch process in which the prepreg sheet is removed from the bag or container, re-stored in a heat treatment chamber, etc., and heated.

For example, as described above, the motor rotor 1 of the first comparative example manufactured in this manner has a sufficiently high adhesive strength between all of the permanent magnets and the pair of magnet pressers 5, 5 and the reinforcing tube 4, and can prevent all of the permanent magnets 3 from scattering outward from the rotating shaft 2 even during high-speed rotation of the rotor 1. The motor rotor 1 is manufactured by using a pair of magnet pressers 5 that are fitted onto the rotating shaft 2 and have recesses 5a formed in multiple locations on the circumferential surface, and by wrapping the prepreg sheet, which will later become the reinforcing tube 4, around the outer periphery of all of the permanent magnets 3 together with the pair of magnet pressers 5, 5 and heat-curing the prepreg sheet, and therefore the motor rotor 1 can be an inexpensive, general-purpose product.

2 and 3(a) and (b) show the rotor of the electric motor of the second comparative example, which is classified as an IPM. Note that the same components and parts as those of the first comparative example shown in FIGS. 1(a) and 1(b) are designated by the same reference numerals and will not be described again.

The electric motors shown in Figures 2 and 3(a) and (b) are also motors, but the permanent magnets 3 can be replaced with secondary conductors such as windings, in which case the electric motor becomes a generator. The rotor 1 of the motor shown in Figures 2 and 3(a) and (b) includes a cylindrical core 6 fitted onto the rotating shaft 2, and a pair of cylindrical core holders 7, 7 that are fitted onto the rotating shaft 2 and clamp the core 3 at both axial ends.

The motors shown in Figures 2 and 3(a) and (b) are classified as IPM motors, and therefore multiple permanent magnets 3 are embedded in the core 6 at circumferential intervals. In the case of motors classified as IPM, it is desirable to reduce the gap between the rotor 1 and the stator in order to improve rotational performance. In this case, all permanent magnets 3 are embedded near the outer periphery of the core 6.

The outer peripheral surface of each core holder 7 is provided with recesses 7a corresponding to the recesses 5a shown in Figures 1(a) and 1(b) at multiple locations around the circumference. The motor rotor 1 of the second comparative example can also be manufactured in the same manner as the motor rotor 1 shown in Figures 1(a) and 1(b). That is, a prepreg sheet 8, in which a thermosetting resin is impregnated into a fiber substrate, is wrapped around the outer periphery of the core 6 and the pair of core holders 7, and a reinforcing tube 4 extending in the axial direction is formed by heat curing. Furthermore, the reinforcing tube 4 is inserted into each recess 7a of the core holder 7 at multiple locations around the circumference, and the reinforcing tube 4 is bonded to the pair of core holders 7 and the outer peripheral surface of the core 6. Therefore, the multiple circumferential locations of the reinforcing tube 4 inserted into each recess 7a function as anchors, sufficiently increasing the adhesive strength between the core 6 and the pair of core holders 7, 7 and the reinforcing tube 4, preventing all permanent magnets 3 from scattering outside the core 6 even during high-speed rotation. The manufactured motor rotor 1 can be an inexpensive, general-purpose product. The same applies to the generator.

In the rotor 1 of the motor of the second comparative example , including the case of a generator, the recesses 7a recessed in the core holders 7, 7 can also be provided in the core 6. In this case, the recesses are also provided at multiple locations in the circumferential direction of the core 6. The position of each recess thus recessed in the core 6 can be arbitrary in the axial direction of the core 6, and for example, they can be arranged at predetermined intervals in the axial direction. In this case, each recess is formed, for example, by forming notches of a shape corresponding to the radial cross-sectional shape of the recess in the outer peripheral edge portions of multiple electromagnetic steel sheets located at the recessed location of each recess.

Next, an embodiment of a rotor for an electric motor of the present invention , which is classified as an IPM, will be described with reference to Figures 4, 5(a), 5(b), 5(c), and 6. In this embodiment, as in the second comparative example shown in Figures 2 and 3(a) and 3(b), the same components and parts as those in the first comparative example shown in Figures 1(a) and 1(b) are designated by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 4, the rotor 1 of the motor shown in FIGS. 4, 5(a), 5(b), 5(c), and 6 as an electric motor differs from the rotor 1 of the motor shown in FIGS. 2 and 3(a) and 3(b) primarily in the shape and structure of the core 6. Specifically, the core 6 has multiple axially extending grooves 6a located between the axially extending permanent magnets 3 embedded at circumferential intervals. Specifically, each groove 6a has a V-shaped radial cross section and is formed at predetermined intervals around the core 6. The grooves 6a can be formed by cutting out the outer periphery of each electromagnetic steel sheet forming the core 6 in a shape that matches the cross-sectional shape of each groove 6a, forming circumferentially spaced notches, and then stacking the electromagnetic steel sheets in the axial direction so that the notches align.

The permanent magnets 3 extending in the axial direction are embedded in pairs near the outer periphery of the core 6. In each pair, the two permanent magnets 3, 3 are spaced apart so that a gap is formed between them. This arrangement is intended to prevent a decrease in the strength of the core 6 due to the pair of permanent magnets 3, 3 being embedded near the outer periphery.

The motor rotor 1 shown in Figures 4, 5(a), 5(b), 5(c), and 6 also differs from the motor rotor 1 shown in Figures 2 and 3(a) and 3(b) in that a thermosetting resin binder 9 is inserted into each groove 6a. The thermosetting resin used to form the binder 9 is, for example, one that has good affinity with the thermosetting resin of the prepreg sheet 8 wrapped around the outer periphery of the core 6. The same thermosetting resin as the prepreg sheet 8 can be used, and in this case, it is particularly suitable for achieving good affinity.

The binder 9 may be solid or in a B-stage state, similar to the prepreg sheet 8. In either case, it is sufficient that the binder 9 does not fall out of each groove 6a after insertion into the groove 6a. The shape of the solid binder 9 is such that it has a cross-section that closely contacts the side surfaces of each groove 6a. Specific examples include a triangular cross-section. The binder 9 is inserted over the entire axial length of each groove 6a. However, the binder 9 does not necessarily have to be long enough to extend over the entire length of each groove 6a. Multiple short binders 9 can also be inserted into each groove 6a with or without spacing between them. When multiple short binders 9 are inserted with spacing between them, it is desirable to set the spacing so that the melted portions adhere to each other when the prepreg sheet 8 is heated and cured, preventing gaps from forming.

Furthermore, taking into account thermal shrinkage due to heat curing, the binder 9 can be sized so that when inserted into each groove 6a, its outer surface protrudes radially outward from the outer circumferential surface of the core 6. In this case, the protrusion amount can be set based on the thermal shrinkage rate specific to each thermosetting resin.

When manufacturing the motor rotor 1 shown in Figures 4, 5(a), 5(b), 5(c), and 6, a binder 9 is inserted into each groove 6a of the core 6, as shown in Figure 5(a), and a prepreg sheet 8 is wound around the outer periphery of the core 6 and a pair of core holders 7, 7, as shown in Figure 4(b). After winding, the precursor to the rotor 1 has gaps 10 formed between the prepreg sheet 8 and the ends of each core holder 7 facing the core 6 due to the binder 9 protruding radially outward, as shown in Figure 6.

The subsequent processes are similar to those for the rotor 1 of the motor of the comparative example . Then, as shown in Figure 5(c), the gaps 10 shown in Figure 6 disappear due to thermal shrinkage accompanied by melting of the binder 9 during heat curing, and the reinforcing tube 4 extending in the axial direction is formed by the heat curing of the prepreg sheet 8. The reinforcing tube 4 is then bonded to the pair of core holders 7, 7 and the outer peripheral surface of the core 6, and is also bonded to each groove 6a of the core 6 via each heat-cured binder 9. Therefore, even if the permanent magnets 3 are arranged near the outer peripheral surface of the core 6 to improve rotation performance, the strength of the core 6 in the rotor 1 is improved.

Furthermore, instead of the thermosetting resin binder 9 inserted into the groove 6a in the comparative example , which is inserted into the multiple recesses 5a, 7a in the circumferential direction of the reinforcing tube 4, the binder 9 functions as an anchor, sufficiently increasing the adhesive strength between the core 6 and the pair of core holders 7, 7 and the reinforcing tube 4. This makes it possible to prevent all of the permanent magnets 3 from scattering out of the core 6 even during high-speed rotation. As with the comparative example , the rotor 1 of the motor produced can be an inexpensive, general-purpose product. The same applies to generators.

Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited thereto. For example, there are no particular limitations on the shape, size, number, and mounting position of the permanent magnets 3 on the outer circumferential surface of the rotating shaft 2 or the position of embedding them in the core 6, and there are no particular limitations on the number, shape, size, and material of the permanent magnet pieces 3a, which are the constituent units of the permanent magnets 3. There are also no particular limitations on the shape, size, and number of the grooves 6a formed in the core 6. There are also no particular limitations on the type of fiber base material and thermosetting resin that make up the prepreg sheet 8.

1...motor rotor, 2...rotating shaft, 3...permanent magnet, 4...reinforcing tube, 5...magnet holder, 5a, 7a...recess, 6...core, 6a...groove, 7...core holder, 8...prepreg sheet, 9...binder.

Claims (1)

A rotor of an electric motor comprising: a rotating shaft; a cylindrical core extending in the axial direction and fitted onto the rotating shaft; a pair of core holders located at both axial ends of the core and fitted onto the rotating shaft to clamp and fix the core; and a plurality of permanent magnets or secondary conductors arranged axially between the pair of core holders and spaced apart in the circumferential direction,
A permanent magnet or secondary conductor is embedded in the core,
The reinforcing tube is formed by heat curing a prepreg sheet in which a fiber base material is impregnated with a thermosetting resin, and extends in the axial direction. The reinforcing tube is in close contact with the outer peripheral surfaces of the core and a pair of core holders.
A plurality of grooves are formed on the outer peripheral surface of the core, the grooves being positioned between the respective permanent magnets or secondary conductors and extending in the axial direction,
A rotor for an electric motor, characterized in that a thermosetting resin binder is inserted into each groove of the core, a prepreg sheet is wrapped around the core and each binder together with a pair of core holders, and a reinforcing tube extending in the axial direction is formed by heat curing, this reinforcing tube is bonded to the outer surface of the core and the outer surface of the pair of core holders, and the reinforcing tube is also bonded to each groove of the core via each heat-cured binder.