JP7327115B2 - Rotor manufacturing method - Google Patents

Description

This technology relates to a method of manufacturing a rotor used in an electric motor or the like.

Conventionally, as a method of manufacturing a rotor used in an electric motor mounted on a vehicle such as an electric vehicle, for example, a method of fixing a rotor shaft to the inner peripheral surface of a rotor core by hydroforming is known (Patent Document 1). In this manufacturing method, a tubular rotor shaft is arranged on the inner periphery of a rotor core formed by laminating electromagnetic steel sheets. The rotor shaft is fixed to the mold of the hydroforming machine with both ends exposed to the outside of the rotor core. Then, the rotor shaft is fixed to the rotor core by a hydroforming method in which a portion of the rotor shaft corresponding to the rotor core is expanded by injecting liquid into the inner portion of the rotor shaft to increase the internal pressure. For the rotor shaft, medium carbon steel (for example, S45C) having a carbon content of 0.3% or more with high material strength is used in order to ensure the strength of the torque transmission portion.

JP-A-2001-268858

However, in the rotor manufacturing method described in Patent Document 1, medium carbon steel is used for the rotor shaft, so the deformability of the rotor shaft is low. For this reason, when the hydroforming method is used for expansion, a large pressurizing force is required, which may lead to an increase in the size of the hydroforming molding machine and the molding die. Moreover, since the deformability of the rotor shaft is low, there is a risk that cracks will occur when the rotor shaft is expanded by the hydroforming method.

Furthermore, since the rotor shaft has low deformability and high hardness, when the rotor shaft is expanded by hydroforming, the outer surface of the rotor shaft does not easily bite into gaps (shear marks) in the electromagnetic steel sheets of the rotor core. It was difficult to ensure a sufficient contact area between the rotor and the rotor core. Also, since the rotor shaft is made of medium carbon steel, it has a lower thermal conductivity than low carbon steel. For this reason, the contact area between the outer surface of the rotor shaft and the rotor core is small, and the thermal conductivity of the rotor shaft is low, so the cooling effect of the rotor core is small. I had to suppress it. In addition, since the outer surface of the rotor shaft does not easily bite into the gap between the magnetic steel sheets of the rotor core, the frictional force between the rotor shaft and the rotor core cannot be increased, making it difficult to secure torque transmission force.

Therefore, it is an object of the present invention to provide a rotor manufacturing method capable of improving the torque transmission force and the cooling effect of the rotor core.

This rotor manufacturing method is a manufacturing method of a rotor having a tubular rotor shaft and a tubular rotor core fixed to a rotor core mounting surface formed on an outer peripheral portion of the rotor shaft, wherein the rotor shaft is , a surface modification step in which a metal having a carbon content of less than 0.3% is used as a base material and the surface is modified by penetrating solute atoms from the surface of the rotor shaft; and after performing the surface modification step, a cutting step of scraping off the surface-modified layer to form the rotor core mounting surface; and a fixing step of fixing the surface and the rotor core.

According to this rotor manufacturing method, the torque transmission force and the cooling effect of the rotor core can be improved.

Sectional drawing which shows the rotor which concerns on 1st Embodiment. 4 is a flowchart showing a rotor manufacturing method according to the first embodiment; 1A and 1B are schematic cross-sectional views along the rotor manufacturing method according to the first embodiment, in which (a) is after press molding, (b) is after carburizing, (c) is after cutting, (d) is after quenching, (e) shows the state after the rotor core is fixed. 3A and 3B are enlarged cross-sectional views showing a fixing portion between a rotor shaft and a rotor core according to the first embodiment, where (a) is before hydroforming and (b) is after hydroforming; 6 is a flow chart showing a method for manufacturing a rotor according to the second embodiment; 7A and 7B are schematic cross-sectional views along the rotor manufacturing method according to the second embodiment, in which (a) is after press molding, (b) is after carburizing, (c) is after cutting, and (d) is fixing of the rotor core. After that, (e) is the state after quenching.

<First embodiment>
A first embodiment of a method for manufacturing a rotor according to the present disclosure will be described below with reference to FIGS. 1 to 4. FIG. In this embodiment, the axial direction Z or the direction of the rotation axis means the direction along the rotation axis C of the rotor 1, as shown in FIG.

[Structure of Rotor]
First, the configuration of the rotor 1 will be described with reference to FIG. The rotor 1 constitutes an electric motor by being combined with a stator (not shown). As shown in FIG. 1 , the rotor 1 has a rotor core 2 and a rotor shaft 3 . The rotor core 2 is formed by laminating a plurality of electromagnetic steel sheets 20 having holes 20a along the axial direction Z. As shown in FIG. The electromagnetic steel sheet 20 is made of, for example, a silicon steel sheet. The rotor core 2 is formed in a cylindrical shape whose center axis coincides with the rotation axis C. As shown in FIG. In addition, an inner peripheral surface 21 and an outer peripheral surface 22 of the rotor core 2 are formed in a substantially planar shape along the axial direction Z, respectively.

The rotor shaft 3 is formed in a substantially cylindrical shape whose center line coincides with the rotation axis C. As shown in FIG. The rotor shaft 3 is made of low carbon steel, for example. Low carbon steel here means carbon steel with a carbon content of less than 0.3%. In this embodiment, the rotor shaft 3 is made of S20C carbon steel with a carbon content of 0.2%.

The rotor shaft 3 has a rotor core mounting surface 30 formed on the outer periphery, a fitting portion 31 for fitting the bearing 4, and splines 32 and recesses 33 formed on the inner periphery. . The rotor core mounting surface 30 is arranged substantially in the center of the outer peripheral surface in the axial direction Z, and is fixed to the inner peripheral surface 21 of the rotor core 2 . The fitting portions 31 are arranged at both ends in the axial direction Z, and the bearings 4 can be fitted to the outer peripheral surfaces thereof. The spline 32, which is an example of the engaging portion, is formed at one end in the axial direction Z on the inner peripheral portion, and has an uneven shape that protrudes or dents in the radial direction with the axial direction Z as its longitudinal direction. It can be engaged with the illustrated output shaft to transmit driving force. In the figure, cross-hatched parts are hardened by quenching. A space inside the inner peripheral surface 34 of the substantially cylindrical rotor shaft 3 is defined as an internal space 35 .

The recessed portion 33 is arranged substantially in the center of the inner peripheral portion in the axial direction Z, and positioned on the inner peripheral side of the rotor core mounting surface 30 . The recessed portion 33 is formed in a shape that is recessed radially outward compared to both end portions in the axial direction Z in the inner peripheral portion. The recesses 33 have the function of temporarily retaining cooling fluid (ATF: Automatic Transmission Fluid) flowing axially inside the rotor shaft 3 when the rotor 1 is in use. As a result, the rotor core 2 is cooled via the rotor shaft 3 by the cooling liquid positioned in the recess 33 when the rotor 1 is in use.

[Manufacturing method of rotor]
Next, a method for manufacturing the rotor 1 according to this embodiment will be described along the flowchart shown in FIG. First, the rotor core 2 is formed (step S1). Here, a plurality of annular magnetic steel plates 20 having holes 20a are punched out from a band-shaped magnetic steel plate in a progressive press machine (not shown), and the plurality of magnetic steel plates 20 are laminated along the direction of the rotation axis. By doing so, a cylindrical rotor core 2 is formed.

Next, as shown in FIG. 3A, a cylindrical steel material 3a made of carbon steel (for example, S20C) having a carbon content of 0.2% is press-formed to form a rotor shaft 3. is obtained (step S2, press step). In this press molding, a press molding machine (not shown) is used to form a mounting portion 30a in which a rotor core mounting surface 30 (see FIG. 3D) is formed on the outer peripheral portion of the rotor shaft 3 by a cutting process described later; A fitting portion 31, a spline 32 on the inner peripheral portion, and a concave portion 33 are formed. The mounting portion 30a is arranged substantially in the center in the axial direction Z, the fitting portions 31 are arranged at both ends in the axial direction Z, and the spline 32 is formed at one end in the axial direction Z on the inner peripheral portion. At this time, the carbon content of the surface of the cast material is 0.2%, and the surface hardness is about HV150, for example.

Next, as shown in FIG. 3(b), the cast material of the rotor shaft 3 is carburized to modify the surface of the cast material (step S3, surface modification step). By this carburizing treatment, carbon penetrates (dissolves) as solute atoms from the surface of the cast material of the rotor shaft 3, and the surface is modified in the penetrated thickness (layer). The penetration depth of carbon is, for example, about 0.8 mm at maximum from the surface, and is 0.7 mm in this embodiment. As a carburizing method here, for example, vacuum carburizing using a carburizing gas in a high-temperature, reduced-pressure environment is applied. The method of carburizing treatment is not limited to vacuum carburizing, and an appropriate method such as gas carburizing using carburizing gas in an environment without reduced pressure can be applied. Also, here, only carburizing is performed and then gradual cooling is performed, and quenching is not performed immediately thereafter. In this case, the carbon content of the surface of the casting is, for example, 0.6%, the surface hardness is increased to, for example, about HV300, and the structure of the casting is, for example, a pearlite structure containing proeutectoid ferrite.

Next, as shown in FIG. 3C, the hardened carburized layer 30b of the attachment portion 30a of the rotor shaft 3 is scraped off to form the rotor core attachment surface 30 (step S4, cutting step). Here, cutting is performed up to a depth of 1 mm from the surface. The carburized layer 30b may be scraped off by a processing method other than cutting. Since the penetration depth of carbon is 0.7 mm from the surface, the carburized layer 30b is entirely scraped off. Moreover, since hardening is not performed after carburizing in step S3, the surface hardness is not too hard, and cutting work can be easily performed. As the carburized layer 30b hardened by the surface modification is scraped off, the rotor core mounting surface 30 is exposed to the base material, so the carbon content of the rotor core mounting surface 30 is 0.2%, and the surface hardness is about HV150, for example. Become.

Here, in the present embodiment, the depth of the carburized layer 30b formed by the carburizing process is set to 0.7 mm, and the cutting depth in the cutting step is set to 1 mm, but the depth is not limited to this. In other words, the carburized layer 30b should be entirely scraped off, and for this purpose, the penetration depth of carbon should be shallower than the depth of cutting. For example, the depth of the carburized layer 30b may be 0.4 mm, and the cutting depth in the cutting process may be 0.5 mm. Since the cutting depth may vary depending on the cutting position depending on the dimensions of the cast material, the depth of the carburized layer 30b and the cutting depth are set so that the carburized layer 30b is completely removed at all cutting positions. make it

Next, as shown in FIG. 3D, both ends of the rotor shaft 3 in the axial direction Z are hardened (step S5). In this embodiment, a fitting portion hardening step of hardening the fitting portion 31 by quenching and a spline hardening step of hardening the spline 32 by quenching are performed. In the figure, the portions hardened by quenching are indicated by cross hatching. Quenching improves the surface hardness of the fitting portion 31 and the splines 32 to, for example, about HV800. After that, the surface of the fitting portion 31 is polished (step S6, polishing step).

Next, as shown in FIG. 3(e), the rotor core 2 formed in step S1 is fixed to the rotor core mounting surface 30 (step S7, fixing step). In this embodiment, the fixing process is performed after the fitting part hardening process and the spline hardening process are performed. In the fixing step, the rotor core mounting surface 30 and the rotor core 2 are fixed such that the rotor core mounting surface 30 and the inner peripheral surface 21 of the rotor core 2 are pressed against each other in the radial direction. In the fixing step, the rotor core 2 and the rotor shaft 3 are positioned so that the inner peripheral surface 21 of the rotor core 2 and the rotor core mounting surface 30 face each other, and the internal space 35 inside the inner peripheral surface 34 of the rotor shaft 3 is pressurized. As a result, the outer shape of the rotor core mounting surface 30 is enlarged and fixed. In this embodiment, in the fixing step, the inner peripheral surface 21 of the rotor core 2 is positioned so as to face the rotor core mounting surface 30 , and the inner peripheral portion of the rotor shaft 3 is pressed to move the rotor core mounting surface 30 to the inner peripheral surface of the rotor core 2 . It is fixed by a hydroforming method that bites into the surface 21 .

Here, the rotor shaft 3 and the rotor core 2 are attached to a hydroforming machine (not shown). Then, the rotor shaft 3 and the rotor core 2 are positioned and held so that the rotor core mounting surface 30 radially faces the inner peripheral surface 21 of the rotor core 2 with a gap G therebetween (see FIG. 4A). Then, a hydroforming machine injects a high-pressure liquid (for example, several hundred MPa) into the inner portion of the rotor shaft 3 to pressurize the inside of the rotor shaft 3 . When the rotor core mounting surface 30 is plastically deformed by pressurization so as to expand radially outward, it abuts against and pushes the inner peripheral surface 21 of the rotor core 2, and the rotor core 2 elastically expands radially outward. transform. At this time, as shown in FIG. 4(b), the gap G between the rotor core mounting surface 30 and the rotor core 2 disappears and they are in close contact. At this time, the rotor core mounting surface 30 expands by the hydroforming method and bites into the shear marks 20b between the electromagnetic steel plates 20 on the inner peripheral surface 21 of the rotor core 2, thereby fixing the rotor shaft 3 and the rotor core 2. can.

After that, the liquid inside the rotor shaft 3 is removed, and the rotor core 2 shrinks radially inward and returns to the shape before being elastically deformed and expanded. The plastically deformed rotor core mounting surface 30 is pressed against the rotor core 2 that has contracted inward in the radial direction (an interference fit state). This keeps the rotor shaft 3 fixed to the rotor core 2 . The rotor core 2 and rotor shaft 3 are removed from the hydroforming machine to complete the rotor 1 . After that, the rotor shaft 3 is fitted with the bearing 4 (see FIG. 1), and the stator is arranged radially outside the rotor 1, thereby manufacturing the motor.

As described above, according to the rotor manufacturing method of the present embodiment, the carburized layer 30b is hardened by surface modification without carburizing and quenching the rotor shaft 3 having a carbon content of 0.2%. is scraped away to form a rotor core mounting surface 30, which is fixed to the rotor core 2 by a hydroforming method. Since the carbon content of the rotor core mounting surface 30 is as low as 0.2%, the plastic deformability is high, and since the base material is exposed on the rotor core mounting surface 30, the rotor shaft 3 can be deformed by hydroforming. While suppressing the occurrence of cracks, the shear marks 20b between the magnetic steel sheets 20 on the inner peripheral surface 21 of the rotor core 2 are embedded and maintained. On the other hand, if medium carbon steel such as S45C is used for the rotor shaft, the plastic deformability is low, and cracks may occur in the rotor shaft. It is rarely done.

Therefore, according to the present embodiment, compared to the case of using medium carbon steel, the plastic deformability of the rotor shaft 3 is improved, crack generation is suppressed, and the real contact area between the rotor core 2 and the rotor shaft 3 is reduced. can be improved. By improving the real contact area between the rotor core 2 and the rotor shaft 3, the thermal conductivity between the rotor core 2 and the rotor shaft 3 can be improved, the cooling effect of the rotor core 2 can be improved, and the iron loss of the motor can be reduced. can be planned. Further, by improving the real contact area between the rotor core 2 and the rotor shaft 3, the frictional force between the rotor core 2 and the rotor shaft 3 can be improved both in the axial direction and the rotational direction, and the torque transmission force can be improved. can.

Further, according to the rotor manufacturing method of the present embodiment, the rotor shaft 3 is made of low carbon steel with a carbon content of 0.2%. Therefore, compared to the case of using medium carbon steel, the thermal conductivity of the rotor shaft 3 can be improved, so the cooling efficiency of the rotor core 2 can be improved, and the thermal demagnetization of the magnets used in the rotor core 2 can be reduced. It is possible to reduce the cost by reducing the rare earth elements in the magnet. In addition, since the rigidity of the rotor shaft 3 can be reduced compared to the case of using medium carbon steel, the cold workability can be improved, the die life can be extended, and the machinability can be improved. Cutting tool cost can be reduced.

In the present embodiment described above, the case where the rotor shaft 3 is made of S20C, which is carbon steel with a carbon content of 0.2%, has been described, but the present invention is not limited to this. The rotor shaft 3 may be made of a metal having a carbon content of less than 0.3% as a base material, and in addition to low-carbon steel and ultra-low-carbon steel, pure iron and low-carbon alloy steel may also be used. When the carbon content is less than 0.3%, the plastic deformability of the rotor shaft 3 and the cooling efficiency of the rotor core 2 can be improved compared to medium carbon steel. The carbon content is more preferably 0.2% or less, most preferably 0.2%.

Further, in the present embodiment, the case where the carburizing process is performed as the surface modification process of the cast material of the rotor shaft 3 has been described, but the present invention is not limited to this. For example, as the surface modification process of the cast material of the rotor shaft 3, nitriding treatment for infiltrating nitrogen as solute atoms from the surface, carbonitriding treatment for infiltrating carbon and nitrogen, boron treatment for infiltrating boron, etc. You may apply the processing method which penetrates the solute atom of .

Further, in the present embodiment, the depth of the carburized layer 30b formed by the carburizing process is set to 0.7 mm, and the cutting depth in the cutting process is set to 1 mm, but the depth is not limited to this. In other words, the carburized layer 30b should be entirely scraped off, and for this purpose, the penetration depth of carbon should be shallower than the depth of cutting. For example, the depth of the carburized layer 30b may be 0.4 mm, and the cutting depth in the cutting process may be 0.5 mm. Since the cutting depth may vary depending on the cutting position depending on the dimensions of the cast material, the depth of the carburized layer 30b and the cutting depth are set so that the carburized layer 30b is completely removed at all cutting positions. make it

Moreover, in the present embodiment, the case where quenching is applied to both the fitting portion hardening step of the fitting portion 31 and the spline hardening step of the spline 32 has been described, but the present invention is not limited to this. For example, shot peening or coating may be applied.

Moreover, in the present embodiment, the case where the hydroforming method is applied as the fixing process for fixing the rotor core 2 to the rotor core mounting surface 30 has been described, but the present invention is not limited to this. For example, shrink fitting may be applied in which the rotor shaft 3 is inserted into the place where the rotor core 2 is heated and expanded, and then fixed by cooling. In this case, expansion of the rotor shaft 3 becomes unnecessary, so the possibility of the rotor shaft 3 cracking due to expansion can be suppressed.

<Second embodiment>
Next, a second embodiment of the present disclosure will be described in detail with reference to FIGS. 5 and 6. FIG. In the present embodiment, the fixing step is performed after the cutting step and before the fitting portion hardening step and the spline hardening step are performed. The configuration is different from that of the first embodiment, which is performed after the spline hardening process is performed. However, since other configurations are the same as those of the first embodiment, the same reference numerals are used and detailed description thereof is omitted.

A method for manufacturing the rotor 1 according to this embodiment will be described along the flowchart shown in FIG. Steps S1 to S4 (see FIGS. 6A to 6C) are the same as those in the first embodiment, so description thereof will be omitted.

As shown in FIG. 6(c), the hardened carburized layer 30b of the mounting portion 30a is scraped off to form the rotor core mounting surface 30, and then the rotor core mounting surface is formed as shown in FIG. 6(d). 30, the rotor core 2 formed in step S1 is fixed (step S10, fixing step). In this embodiment, the fixing step is performed after the cutting step and before the fitting portion hardening step and the spline hardening step. In the fixing step, the inner peripheral surface 21 of the rotor core 2 is positioned so as to face the rotor core mounting surface 30 , and the inner peripheral portion of the rotor shaft 3 is pressed to cause the rotor core mounting surface 30 to bite into the inner peripheral surface 21 of the rotor core 2 . Fix by hydroforming method. The hydroforming method is the same as in the first embodiment, so detailed description is omitted.

After the rotor core 2 and the rotor shaft 3 are removed from the hydroforming machine, both ends of the rotor shaft 3 in the axial direction Z are hardened as shown in FIG. 6(e) (step S11). In this embodiment, a fitting portion hardening step of hardening the fitting portion 31 by quenching and a spline hardening step of hardening the spline 32 by quenching are performed. In the figure, the portions hardened by quenching are indicated by cross hatching. Quenching improves the surface hardness of the fitting portion 31 and the splines 32 to, for example, about HV800.

In this embodiment, the rotor core 2 is fixed during quenching. Therefore, if water is used as a coolant for rapid cooling after quenching, the water may adhere to the rotor core 2, which is not preferable. Therefore, in this embodiment, it is preferable to apply a method that does not use water as a coolant for quenching. That is, a refrigerant such as oil or gas other than water is used, or cooling is performed without using a refrigerant. As such hardening, it is preferable to apply laser hardening, for example.

After that, the surface of the fitting portion 31 is polished (step S12, polishing step), and the rotor 1 is completed. After that, the rotor shaft 3 is fitted with the bearing 4 (see FIG. 1), and the stator is arranged radially outside the rotor 1, thereby manufacturing the motor.

As described above, according to the rotor manufacturing method of the present embodiment, the carburized layer 30b is hardened by surface modification without carburizing and quenching the rotor shaft 3 having a carbon content of 0.2%. is scraped away to form a rotor core mounting surface 30, which is fixed to the rotor core 2 by a hydroforming method. Therefore, as in the first embodiment, by increasing the real contact area between the rotor core 2 and the rotor shaft 3 while suppressing the occurrence of cracks in the rotor shaft 3, It is possible to improve the thermal conductivity, improve the cooling effect of the motor, and reduce the iron loss of the motor. Further, by improving the real contact area between the rotor core 2 and the rotor shaft 3, the frictional force between the rotor core 2 and the rotor shaft 3 can be improved both in the axial direction and the rotational direction, and the torque transmission force can be improved. can.

Further, according to the rotor manufacturing method of the present embodiment, the execution timing of the fixing step is before the fitting portion hardening step and the spline hardening step are performed, and before the fitting portion 31 and the splines 32 are hardened. , it is possible to further reduce the possibility of cracks occurring in the rotor shaft 3 even if the hydroforming method is performed.

In addition, according to the rotor manufacturing method of the present embodiment, since the fitting part 31 and the spline 32 are quenched by a method that does not use water as a coolant, water does not adhere to the rotor core 2 during cooling after quenching. It can be difficult.

In the above-described first embodiment, the fixing step is performed after the cutting step and after the fitting portion hardening step and the spline hardening step are performed. Although the case where the steps are performed after the steps are performed and before the fitting portion hardening step and the spline hardening step are performed has been described, the present invention is not limited thereto. For example, the fixing step may be performed after performing the cutting step and the fitting portion hardening step and before performing the spline hardening step, or after performing the cutting step and the spline hardening step and It may be performed before the fitting portion hardening process is performed.

<Summary of each embodiment>
The first and second embodiments described above have at least the following configurations. The manufacturing method of the rotor (1) of the first and second embodiments includes a tubular rotor shaft (3) and a rotor core mounting surface (30) formed on the outer periphery of the rotor shaft (3). A rotor (1) having a cylindrical rotor core (2), wherein the rotor shaft (3) is made of a metal having a carbon content of less than 0.3% as a base material, and the rotor shaft ( a surface modification step of modifying the surface by allowing solute atoms to penetrate from the surface of 3); ), and after performing the cutting step, the rotor core mounting surface (30 ) and a fixing step of fixing the rotor core (2).

With this configuration, the deformability of the rotor shaft (3) can be improved, so the real contact area between the rotor core (2) and the rotor shaft (3) can be increased while suppressing the occurrence of cracks in the rotor shaft (3). be able to. As a result, the heat conductivity between the rotor core (2) and the rotor shaft (3) can be improved, the cooling effect of the rotor core (2) can be improved, and the iron loss of the motor can be reduced. The torque transmission force can be improved by increasing the frictional force between (2) and the rotor shaft (3) both in the axial direction and in the rotational direction. That is, the torque transmission force and the cooling effect of the rotor core (2) can be improved.

Further, in the method of manufacturing the rotor (1) of the first and second embodiments, in the fixing step, the rotor core mounting surface (30) is plastically deformed so that the rotor core mounting surface (30) is fixed to the rotor core ( 2) is fixed by biting into the inner peripheral surface (21). With this configuration, the frictional force between the rotor core (2) and the rotor shaft (3) can be further increased in both the axial direction and the rotational direction, thereby further improving the torque transmission force. Further, the thermal conductivity between the rotor core (2) and the rotor shaft (3) can be further improved to further improve the cooling effect of the rotor core (2) and reduce iron loss of the motor.

Further, in the method of manufacturing the rotor (1) of the first and second embodiments, in the fixing step, the inner peripheral surface (21) of the rotor core (2) and the rotor core attachment surface (30) are arranged to face each other. By positioning the rotor core (2) and the rotor shaft (3) at the position of the rotor core (2) and the rotor shaft (3) and pressurizing the space (35) inside the inner peripheral surface (34) of the rotor shaft (3), the rotor core mounting surface (30) Enlarge the outer shape of the and fix it.

According to this configuration, by performing the fixing step, the space (35) inside the inner peripheral surface (34) of the rotor shaft (3) is pressurized to expand the outer shape of the rotor core mounting surface (30), thereby increasing the rotor core. The mounting surface (30) and the inner peripheral surface (21) of the rotor core (2) are brought into pressure contact in the radial direction. Therefore, the real contact area between the rotor core (2) and the rotor shaft (3) can be improved. As a result, the heat conductivity between the rotor core (2) and the rotor shaft (3) can be improved, the cooling effect of the rotor core (2) can be improved, and the iron loss of the motor can be reduced. The torque transmission force can be improved by increasing the frictional force between (2) and the rotor shaft (3) both in the axial direction and in the rotational direction.

Further, in the method of manufacturing the rotor (1) of the first and second embodiments, in the fixing step, the rotor core (2) is fixed to the rotor core mounting surface (30) by shrink fitting. According to this configuration, it is possible to prevent the rotor shaft (3) from cracking due to expansion.

Further, in the method of manufacturing the rotor (1) of the first and second embodiments, a fitting part hardening process is performed to harden a fitting part (31) for fitting the bearing (4) to the rotor shaft (3). Have a process. According to this configuration, the wear resistance of the bearing (4) fitted by press fitting can be enhanced.

Further, in the manufacturing method of the rotor (1) of the first and second embodiments, the fitting portion (31) is hardened by quenching in the fitting portion hardening step. According to this configuration, curing can be effectively achieved by a simple method.

Further, in the rotor (1) manufacturing method of the first embodiment, the fixing step is performed after the fitting portion hardening step is performed. According to this configuration, hardening can be performed by an inexpensive and easy technique such as induction hardening.

Further, in the rotor (1) manufacturing method of the second embodiment, the fixing step is performed after the cutting step and before the fitting portion hardening step. According to this configuration, the rotor shaft (3) and the rotor core (2) are fixed before the fitting portion (31) is hardened. can further reduce the possibility of cracking.

Reference Signs List 1 Rotor 2 Rotor core 3 Rotor shaft 4 Bearing 21 Inner peripheral surface of rotor core 30 Rotor core mounting surface 30b Carburized layer (surface-modified layer)
31... Fitting portion 34... Inner peripheral surface of rotor shaft 35... Internal space (space inside inner peripheral surface of rotor shaft)

Claims (8)

A method for manufacturing a rotor having a tubular rotor shaft and a tubular rotor core fixed to a rotor core mounting surface formed on the outer periphery of the rotor shaft, comprising:
The rotor shaft is made of a metal having a carbon content of less than 0.3% as a base material,
a surface modification step of infiltrating solute atoms from the surface of the rotor shaft to modify the surface;
a cutting step of scraping off the surface-modified layer to form the rotor core mounting surface after the surface modification step;
a fixing step of fixing the rotor core mounting surface and the rotor core so that the rotor core mounting surface and the inner peripheral surface of the rotor core are in pressure contact with each other in the radial direction after the cutting step. 2. The method of manufacturing a rotor according to claim 1, wherein, in said fixing step, said rotor core mounting surface is fixed by biting into the inner peripheral surface of said rotor core by plastically deforming said rotor core mounting surface. In the fixing step, the rotor core and the rotor shaft are positioned so that the inner peripheral surface of the rotor core and the rotor core mounting surface face each other, and the space inside the inner peripheral surface of the rotor shaft is pressurized. 3. The method of manufacturing a rotor according to claim 1, wherein the fixing is performed by enlarging the outer shape of the rotor core mounting surface. 3. The method of manufacturing a rotor according to claim 1, wherein in the fixing step, the rotor core is fixed to the rotor core mounting surface by shrink fitting. 5. The rotor manufacturing method according to claim 1, further comprising a fitting portion hardening step of hardening a fitting portion for fitting the bearing to the rotor shaft. 6. The rotor manufacturing method according to claim 5, wherein the fitting portion is hardened by quenching in the fitting portion hardening step. 7. The rotor manufacturing method according to claim 5, wherein the fixing step is performed after the fitting portion hardening step is performed. 7. The rotor manufacturing method according to claim 5, wherein the fixing step is performed after performing the cutting step and before performing the fitting portion hardening step.

Images