Motor, washing machine employing same, and method for manufacturing electronic steel sheet for rotor

Abstract

A washing machine disclosed herein is provided with a motor for rotating a drum. The motor is provided with a stator, a rotor, and a plurality of permanent magnets supported by the rotor. The rotor is provided with a plurality of stacked electronic steel sheets. Each of the plurality of electronic steel sheets includes a hub part, a plurality of spoke parts arranged spaced at intervals in the circumferential direction along the circumference of the hub part, and a plurality of bridge parts connecting the plurality of spoke parts and the hub part. In at least one of the plurality of electronic steel sheets, the bridge part has a thin-walled portion that has a convex shape in the direction opposite to the direction of deflection due to punching and is thinner than the hub part and the spoke part.

Description

Motor, washing machine employing the same, and method of manufacturing electrical steel sheet for rotor

[0001] The present disclosure relates to a motor, a washing machine employing the same, and a method for manufacturing an electrical steel sheet for a rotor.

[0002] An electric motor comprises a rotor and a stator. The rotor is equipped with multiple permanent magnets. The rotor rotates through electromagnetic interaction with the stator. Electric motors are used as rotational driving sources for various electrical and electronic products.

[0003] Japanese Patent Publication No. 2010-220388 describes a rotor of a permanent magnet motor. The disclosed rotor comprises a plurality of permanent magnets and a laminated iron core that supports the plurality of permanent magnets. The laminated iron core is formed by laminating magnetic plates. A rotational shaft hole into which a rotational shaft is inserted is provided in the center of the magnetic plate. A plurality of permanent magnets are arranged in a cylindrical shape so that different magnetic poles are adjacent near the outer circumference of the magnetic plate. A thin-walled portion is provided in the magnetic plate between the rotational shaft hole and the permanent magnets.

[0004] Japanese Published Patent No. 2016-007136 describes a permanent magnet embedded type motor having a stator having a stator core with a winding wound thereon, and a rotor rotatably disposed with a gap between it and the inner surface of the stator core. The rotor has a rotor core formed by laminating steel plates having a plurality of magnet embedding holes, and a plurality of permanent magnets housed in each of the plurality of magnet embedding holes. In the steel plates, a bridge portion is formed by the circumferential ends of the magnet embedding holes and the outer circumference of the steel plates, and two adjacent bridge portions are connected to each other by a thin-walled connecting portion.

[0005] International Publication No. 2013 / 053479 discloses a rotor laminate package comprising a plurality of flat rotor laminates for rotary electric machinery, particularly for brushless synchronous motors. The rotor laminate has a hub having a hub axis and at least two spokes arranged circumferentially around the hub axis. A pair of first rotor laminates is rotated 180° relative to the same pair of second rotor laminates and aligned around the hub axis. By doing so, the thickness of the rotor laminate in the hub region of the formed rotor laminate is reduced by at least 40% to 60%, and preferably by at least 50%, compared to the thickness of the rotor laminate in the spoke region.

[0006] A motor according to one aspect of the present disclosure comprises a stator, a rotor facing the stator with an air gap between them, and a shaft fixed to the rotor. The rotor comprises a laminate having a shaft hole in the center into which a shaft is inserted, and a plurality of permanent magnets supported by the laminate. The laminate comprises a plurality of laminated electrical steel sheets. Each of the plurality of electrical steel sheets comprises a hub portion having a hole formed corresponding to the shaft hole, a plurality of spoke portions spaced apart from one another in a circumferential direction along the circumference of the hub portion and having a plurality of permanent magnets arranged in the spaces between them, and a plurality of bridge portions connecting the plurality of spoke portions and the hub portion. In at least one of the plurality of electrical steel sheets, the bridge portion has a thin-walled portion having a convex shape opposite to the direction of deflection caused by punching and having a thickness thinner than that of the hub portion and the spoke portions.

[0007] A washing machine according to one aspect of the present disclosure comprises a housing, a water-retaining tub elastically supported inside the housing, a drum rotatably installed inside the tub and receiving laundry, and the aforementioned motor for rotating the drum.

[0008] A method for manufacturing an electrical steel sheet for a rotor according to one aspect of the present disclosure comprises the steps of: press-cutting a metal sheet to form an electrical steel sheet intermediate having a hub portion with a hole formed in the center, a plurality of spoke portions, a plurality of spoke portions spaced apart from each other in a circumferential direction along the periphery of the hub portion, and a plurality of flat bridge portions connecting the plurality of spoke portions and the hub portion; and thinning the plurality of bridge portions into a convex shape in the opposite direction of the punching direction.

[0009] FIG. 1 is a schematic diagram of a washing machine according to one embodiment of the present disclosure.

[0010] Figure 2 is a schematic plan view of a conventional electrical steel sheet for a rotor.

[0011] Figure 3 is a plan view of a conventional rotor equipped with the electrical steel sheet shown in Figure 2.

[0012] Figure 4 is a diagram showing the problems of a motor using the rotor shown in Figure 3.

[0013] Figure 5 is a drawing showing the state of the electrical steel sheet after cutting press processing.

[0014] Figure 6 is a drawing showing the state of an electrical steel sheet when it is thinned by compression processing.

[0015] Figure 7 is a drawing showing the state of an electrical steel sheet after a cutting process that removes a horizontally extended area.

[0016] Figure 8 shows an example of a method for forming a concave-shaped thin-walled portion using a press device.

[0017] Figure 9 is a drawing showing an example of a method for forming a convex-shaped thin-walled portion using a press device.

[0018] FIG. 10 is a schematic perspective view of a rotor according to one embodiment of the present disclosure.

[0019] FIG. 11 is a schematic perspective view of an electrical steel sheet applied to a rotor shown in FIG. 10.

[0020] FIG. 12 is a partial cross-sectional view of a laminate of a rotor according to one embodiment of the present disclosure illustrated in FIG. 10.

[0021] FIG. 13 is a partial cross-sectional view of a laminate of a rotor according to one embodiment of the present disclosure.

[0022] The various embodiments of this document and the terms used therein are not intended to limit the technical features described in this document to specific embodiments, and should be understood to include various modifications, equivalents, or substitutions of said embodiments.

[0023] In relation to the description of the drawings, similar reference numerals may be used for similar or related components.

[0024] The singular form of the noun corresponding to the item may include one or multiple items, unless the relevant context clearly indicates otherwise.

[0025] In this document, each of the phrases such as "A or B", "at least one of A and B", "at least one of A or B", "A, B or C", "at least one of A, B and C", and "at least one of A, B, or C" may include any one of the items listed together in the corresponding phrase, or all possible combinations thereof.

[0026] For example, the phrase “at least one of A, B, and C” may include one of A, B, C, A and B, A and C, B and C, and A and B and C.

[0027] The term "and / or" includes a combination of multiple related described components or any of the multiple related described components.

[0028] Terms such as "first," "second," or "first" or "second" may be used simply to distinguish a component from another corresponding component and do not limit the components in other aspects (e.g., importance or order).

[0029] Where any (e.g., 1st) component is referred to as "coupled" or "connected" to another (e.g., 2nd) component, with or without the terms "functionally" or "communicationly," it means that said any component may be connected to said other component directly (e.g., via a wire), wirelessly, or through a third component.

[0030] Terms such as "include" or "have" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in this document, and do not preclude the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0031] When it is said that a component is "connected," "combined," "supported," or "in contact" with another component, this includes not only cases where the components are directly connected, combined, supported, or in contact, but also cases where they are indirectly connected, combined, supported, or in contact through a third component.

[0032] When it is said that a component is located "on" another component, this includes not only cases where one component is in contact with the other, but also cases where another component exists between the two components.

[0033] A clothing processing device is a concept that encompasses a device for washing clothing (objects to be washed), a device for drying clothing (objects to be dried), and a device capable of performing both washing and drying of clothing. In the term 'clothing processing device,' 'clothing' refers to objects to be processed (objects to be washed or objects to be dried) and does not refer only to literal clothing. A washing machine is an example of a clothing processing device, and washing machines according to various embodiments can perform washing, rinsing, spin-drying, and drying processes.

[0034] Washing machines according to various embodiments may include a top-loading washing machine in which a laundry inlet for loading or unloading laundry is provided to face upward, or a front-loading washing machine in which a laundry inlet is provided to face forward. Washing machines according to various embodiments may include washing machines with loading methods other than top-loading washing machines and front-loading washing machines.

[0035] In the case of a top-loading washing machine, laundry can be washed using a water flow generated by a rotating body such as a pulsator. In the case of a front-loading washing machine, laundry can be washed by rotating the drum to repeatedly raise and lower the laundry. A front-loading washing machine may include a washing machine capable of drying laundry contained inside the drum. The washing machine capable of drying may include a hot air supply device for supplying high-temperature air into the drum and a condensation device for removing moisture from the air discharged from the drum. As an example, the washing machine capable of drying may include a heat pump device. Washing machines according to various embodiments may include washing machines with washing methods other than those described above.

[0036] A washing machine according to various embodiments may include a housing that accommodates various components inside. The housing may be provided in the form of a box with a laundry input opening formed on one side.

[0037] The washing machine may include a door for opening and closing a laundry input. The door may be rotatably mounted to the housing by means of a hinge. At least a portion of the door may be made transparent or translucent so that the interior of the housing is visible.

[0038] The washing machine may include a tub provided inside the housing to store water. The tub is provided in a roughly cylindrical shape with a tub opening formed on one side, and may be positioned inside the housing such that the tub opening corresponds to the laundry inlet.

[0039] The tub can be connected to the housing by a damper. The damper can absorb vibrations generated during the rotation of the drum and attenuate vibrations transmitted to the housing.

[0040] The washing machine may include a drum designed to accommodate laundry.

[0041] The drum may be positioned inside the tub such that a drum opening provided on one side corresponds to a laundry inlet and a tub opening. Laundry may pass through the laundry inlet, the tub opening, and the drum opening in sequence to be received inside the drum or withdrawn from the drum.

[0042] The drum can rotate inside the tub and perform respective actions according to the washing, rinsing, and / or spin-drying cycles. A number of holes are formed in the cylindrical wall of the drum so that water stored in the tub can flow into the interior of the drum or out of the exterior of the drum.

[0043] The washing machine may include a drive unit configured to rotate the drum. The drive unit may include a drive motor and a rotating shaft for transmitting the driving force generated by the drive motor to the drum. The rotating shaft may pass through the tub and be connected to the drum.

[0044] The drive unit can rotate the drum in the forward or reverse direction to perform each operation according to the washing, rinsing, and / or spin-drying, or drying cycles.

[0045] The washing machine may include a water supply device configured to supply water to the tub. The water supply device may include a water supply pipe and a water supply valve provided in the water supply pipe. The water supply pipe may be connected to an external water source. The water supply pipe may extend from the external water source to a detergent dispenser and / or the tub. Water may be supplied to the tub through the detergent dispenser. Water may be supplied to the tub without passing through the detergent dispenser.

[0046] The water supply valve can open or close the water supply pipe in response to an electrical signal from the control unit. The water supply valve can allow or block the supply of water from an external water source to the tub. The water supply valve may include, for example, a solenoid valve that opens and closes in response to an electrical signal.

[0047] The washing machine may include a detergent dispenser configured to supply detergent to the tub. The detergent dispenser may include a manual detergent dispenser in which the user must add the detergent to be used for each wash cycle, and an automatic detergent dispenser that stores a large amount of detergent and automatically dispenses a predetermined amount during a wash cycle. The detergent dispenser may include a detergent container for storing detergent. The detergent dispenser may be configured to supply detergent into the tub during the water supply process. Water supplied through the water supply pipe may be mixed with the detergent by passing through the detergent dispenser. The water mixed with the detergent may be supplied into the tub. The term "detergent" is used as a collective term for pre-wash detergent, main wash detergent, fabric softener, bleach, etc., and the detergent container may be divided into a pre-wash detergent storage area, a main wash detergent storage area, a fabric softener storage area, and a bleach storage area.

[0048] The washing machine may include a drainage device configured to discharge water contained in a tub to the outside. The drainage device may include a drain pipe extending from the bottom of the tub to the outside of the housing, a drain valve provided in the drain pipe to open and close the drain pipe, and a pump provided on the drain pipe. The pump may pump water from the drain pipe to the outside of the housing.

[0049] The washing machine may include a control panel disposed on one side of the housing. The control panel may provide a user interface for the user to interact with the washing machine. The user interface may include at least one input interface and at least one output interface.

[0050] At least one input interface can convert sensory information received from a user into an electrical signal.

[0051] At least one input interface may include a power button, an operation button, a course selection dial (or course selection button), and a wash / rinse / spin setting button. At least one input interface may include, for example, a tact switch, a push switch, a slide switch, a toggle switch, a micro switch, a touch switch, a touchpad, a touchscreen, a jog dial, and / or a microphone.

[0052] At least one output interface can visually or audibly convey information related to the operation of the washing machine to the user.

[0053] For example, at least one output interface can convey information to the user regarding the washing course, the washing machine's operating time, and washing settings, rinse settings, and spin settings. Information regarding the operation of the washing machine may be output via a screen, indicator, voice, etc. At least one output interface may include, for example, a Liquid Crystal Display (LCD) panel, a Light Emitting Diode (LED) panel, a speaker, etc.

[0054] The washing machine may include a communication module for communicating with an external device via wired and / or wireless means.

[0055] The communication module may include at least one of a short-range communication module or a long-range communication module.

[0056] The communication module can transmit data to external devices (e.g., servers, user devices, and / or home appliances) or receive data from external devices. For example, the communication module can establish communication with servers and / or user devices and / or home appliances and transmit and receive various types of data.

[0057] To this end, the communication module may support the establishment of a direct (e.g., wired) communication channel or a wireless communication channel between external devices, and the performance of communication through the established communication channel. According to one embodiment, the communication module may include a wireless communication module (e.g., a cellular communication module, a short-range wireless communication module, or a GNSS (global navigation satellite system) communication module) or a wired communication module (e.g., a LAN (local area network) communication module, or a power line communication module). The corresponding communication module among these communication modules may communicate with an external device through a first network (e.g., a short-range communication network such as Bluetooth, WiFi (wireless fidelity) direct, or IrDA (infrared data association)) or a second network (e.g., a legacy cellular network, a 5G network, a next-generation communication network, the Internet, or a long-range communication network such as a computer network (e.g., a LAN or WAN). These various types of communication modules may be integrated into a single component (e.g., a single chip) or implemented as multiple separate components (e.g., multiple chips).

[0058] A short-range wireless communication module may include, but is not limited to, Bluetooth communication modules, BLE (Bluetooth Low Energy) communication modules, Near Field Communication modules, WLAN (Wi-Fi) communication modules, Zigbee communication modules, infrared (IrDA, infrared Data Association) communication modules, WFD (Wi-Fi Direct) communication modules, UWB (ultrawideband) communication modules, Ant+ communication modules, microwave (uWave) communication modules, etc.

[0059] The remote communication module may include a communication module that performs various types of remote communication and may include a mobile communication unit. The mobile communication unit transmits and receives wireless signals with at least one of a base station, an external terminal, and a server on a mobile communication network.

[0060] In one embodiment, the communication module can communicate with external devices, such as a server, a user device, or other home appliances, through a nearby access point (AP). The access point (AP) can connect a local area network (LAN) to which the washing machine or user device is connected to a wide area network (WAN) to which the server is connected. The washing machine or user device can be connected to the server through the wide area network (WAN). The control unit can control various components of the washing machine (e.g., drive motor, water supply valve). The control unit can control various components of the washing machine to perform at least one operation, including water supply, washing, rinsing, and / or spin-drying, according to user input. For example, the control unit can control the drive motor to adjust the rotation speed of the drum or control the water supply valve of the water supply device to supply water to the tub.

[0061] The control unit may include hardware such as a CPU or memory, and software such as a control program. For example, the control unit may include an algorithm for controlling the operation of components within the washing machine, at least one memory for storing data in the form of a program, and at least one processor for performing the aforementioned operation using data stored in at least one memory. The memory and the processor may each be implemented as separate chips. The processor may include one or more processor chips or one or more processing cores. The memory may include one or more memory chips or one or more memory blocks. Additionally, the memory and the processor may be implemented as a single chip.

[0062] A drive motor that rotates a drum comprises a stator and a rotor positioned on the inner side of the stator at a distance from the stator. The rotor comprises a laminate in which a plurality of electrical steel sheets are stacked. The laminate comprises a hub portion and a plurality of spoke portions arranged spaced apart from each other in a circumferential direction centered on the hub portion. A plurality of permanent magnets are disposed in the gaps between the spoke portions. In a rotor of this type, leakage of magnetic flux inward in the radial direction may occur from the spoke portions. Consequently, the magnetic flux outward in the radial direction from the spoke portions decreases, which may degrade the performance of the motor. To suppress such performance deterioration, the portion of the electrical steel sheet connecting the spoke portion to the hub portion can be thinned. However, during the process of thinning the portion connecting the spoke portion to the hub portion, warping of the electrical steel sheet may occur, and the manufacturing cost may increase due to an increase in processing steps.

[0063] The present disclosure aims to provide a motor capable of suppressing performance deterioration caused by magnetic flux leakage through partial thinning of the electrical steel sheet without increasing processing steps or causing warping of the electrical steel sheet. The present disclosure aims to provide a washing machine employing the aforementioned motor. The present disclosure aims to provide a method for manufacturing an electrical steel sheet for a rotor. However, the technical problems to be solved by the present disclosure are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present disclosure belongs from the description below.

[0064] Hereinafter, embodiments of a motor according to the present disclosure, a washing machine employing the same, and a method for manufacturing an electrical steel sheet for a rotor will be described with reference to the attached drawings. However, the following description is merely illustrative.

[0065] FIG. 1 is a schematic diagram of a washing machine (1) according to one embodiment of the present disclosure. The washing machine (1) shown in FIG. 1 is a so-called drum-type washing machine. The washing machine (1) of the present embodiment is an fully automatic washing machine capable of automatically performing a series of processes including washing, rinsing, and spin-drying. The washing machine (1) of the present embodiment may also be a washing machine capable of drying. Referring to FIG. 1, the washing machine (1) may be equipped with a housing (2), a tub (3), a drum (4), and a driving motor (5) that rotates the drum (4).

[0066] The housing (2) is a box-shaped container formed by panels, frames, etc., and forms the outer perimeter of the washing machine (1). A circular opening (not shown) may be provided on the front of the housing (2) for loading and unloading laundry. The opening (not shown) may be opened and closed by a door (6).

[0067] A tub (3) is housed inside a housing (2). The tub (3) may be a cylindrical water-retaining container having a tub opening (3a) on one side and a bottom on the opposite side of the tub opening (3a). The tub (3) is positioned so that the tub opening (3a) faces an inlet provided on the front of the housing (2). The tub (3) is supported by the housing (2) via an elastic member. For example, a plurality of dampers (not shown) may be installed on the lower inner side of the housing (2), and the tub (3) may be supported by the plurality of dampers. Additionally, a plurality of coil springs (not shown) may be installed on the upper inner side of the housing (2), and the tub (3) may be suspended from the plurality of coil springs.

[0068] On the upper part of the housing (2), that is, on the upper part of the tub (3), a water supply pipe (7a) for receiving washing water from the outside and a detergent container (7b) for mixing detergent into the washing water supplied through the water supply pipe (7a) may be installed. On the lower part of the housing (2), a drain pump (8a) and a drain hose (8b) for discharging washing water to the outside of the housing (2) after washing is finished may be installed.

[0069] The drum (4) may be a cylindrical container with a bottom having a diameter slightly smaller than that of the tub (3). The drum (4) is received so as to be rotatable inside the tub (3). A drum opening (4a) is provided on one side of the drum (4), namely on the side opposite the bottom, opposite the tub opening (3a). Laundry can be received inside the drum (4) through the input port, the tub opening (3a), and the drum opening (4a) provided in the housing (2). A plurality of spin-drying holes are formed along the entire circumference of the side of the drum (4).

[0070] The drum (4) is positioned so that it is inclined upward toward the front of the housing (2), and the tub (3) is also positioned so that it is inclined upward at the same angle as the drum (4). On the inner surface of the drum (4), a plurality of lifters (4b) are arranged at a predetermined distance from each other. The lifters (4b) lift the laundry along with the washing water upward by the rotation of the drum (4) and then drop it from a predetermined height. As the drum (4) rotates, the laundry and washing water repeatedly rise and fall, thereby washing the laundry.

[0071] The drum (4) is made rotatable within the tub (3) by the shaft (4c), which is fixed at the center of the bottom, being supported by the bottom of the tub (3). The rear end of the shaft (4c) is fixed to a pulley (4d). The pulley (4d) is connected to a motor (5) installed at the bottom of the housing (2) by a belt (4e). The rotational force of the motor (5) is transmitted to the shaft (4c) through the belt (4e) and the pulley (4d).

[0072] The motor (5) includes a rotor (5a) and a stator (5b). A shaft (30) is inserted into the rotor (5a) so that the rotor (5a) and the shaft (4c) can rotate together. The stator (5b) is positioned to surround the rotor (5a) with an air gap interposed therebetween. The rotor (5a) is rotated by the magnetic force generated by current flowing through the winding coils of the stator (5b).

[0073] FIG. 2 is a schematic plan view of a conventional electrical steel sheet (10A) for a rotor. As illustrated, the electrical steel sheet (10A) comprises a hub portion (11), a plurality of spoke portions (12), and a plurality of bridge portions (13A). The hub portion (11) is a ring-shaped member provided on the inner side of the rotor. A motor shaft is inserted into a hole (14) on the inner side of the hub portion (11). The plurality of spoke portions (12) are fan-shaped members spaced apart from each other to surround the hub portion (11). The plurality of bridge portions (13A) are parts connecting the hub portion (11) and the plurality of spoke portions (12). The width of the plurality of bridge portions (13A) is extremely narrow compared to the outer width of the plurality of spoke portions (12). The bridge portions (13A) are flat. That is, the electrical steel sheet (10A) has a uniform thickness overall.

[0074] FIG. 3 is a plan view of a conventional rotor (5aA) having an electrical steel sheet (10A) as shown in FIG. 2. The rotor (5aA) has a laminate (20A) and a permanent magnet (40). The laminate (20A) is formed by laminating a plurality of electrical steel sheets (10A). The laminate (20A) has a hub laminate (21), a plurality of spoke laminates (22), and a plurality of bridge laminates (23A). The hub laminate (21) is a portion in which the hub portions (11) of the plurality of electrical steel sheets (10A) are laminated. The plurality of spoke laminates (22) is a portion in which the plurality of spoke portions (12) of the plurality of electrical steel sheets (10A) are laminated. The plurality of bridge laminates (23A) is a portion in which the plurality of bridge portions (13A) of the plurality of electrical steel sheets (10A) are laminated. A shaft not shown is inserted into the shaft hole (24) in the central part of the hub laminate (21). Permanent magnets (40) are placed between two adjacent spoke laminates (22) among a plurality of spoke laminates (22). The permanent magnets (40) are arranged so that their circumferentially opposite faces have the same magnetic pole. In this case, magnetic flux of the same magnetic pole as the magnetic poles of the opposing faces of the two permanent magnets (40) flows in the magnetic poles of the spoke laminate (22) between the two adjacent permanent magnets (40).

[0075] FIG. 4 is a diagram showing the problems of a motor using the rotor (5aA) illustrated in FIG. 3. Referring to FIG. 4, magnetic flux flows in this motor as indicated by arrow F1. That is, magnetic flux flows from the rotor (5aA) to the stator (5bA) and then returns from the stator (5bA) to the rotor (5aA). Accordingly, the rotor (5aA) rotates. In this motor, as indicated by arrow F2, a portion of the magnetic flux may flow inward in the radial direction of the rotor (5aA), that is, from the spoke laminate (22) to the hub laminate (21). This leakage of magnetic flux causes a deterioration in the performance of the motor. Since the leakage of magnetic flux inward in the radial direction occurs through the bridge section (bridge laminate), the present disclosure thins the bridge section (bridge laminate) to magnetically saturate the magnetic flux flowing inward in the radial direction of the rotor, making it difficult for the magnetic flux to flow. Thinning of the bridge portion (bridge laminate) can be implemented by various methods.

[0076] Electrical steel sheet (10A) can be manufactured by cutting and press processing a metal sheet. FIG. 5 is a drawing showing the state of the electrical steel sheet (10A) after cutting and press processing. Referring to FIG. 5, sagging (139) occurs in the cutting direction on the cut surface of the bridge portion (13A) of the electrical steel sheet (10A). Cutting and press processing is performed by placing the steel sheet on a die and punching it with a punch having a shape that corresponds to the outer shape of the electrical steel sheet (10A). Therefore, the direction of the sagging (139) is the punching direction of the punch, and is the downward direction in FIG. 5. Sagging also occurs on the cut surface of the hub portion (11) or spoke portion (12) of the electrical steel sheet (10A), but this is omitted in FIG. 5.

[0077] Thinning can be performed, for example, by compressing the bridge portion of an electrical steel sheet. FIG. 6 is a drawing showing the state of an electrical steel sheet (10B) when thinning is performed by compression processing. Referring to FIG. 6, for example, the bridge portion (13A) of the electrical steel sheet (10A) shown in FIG. 5 is compressed using a press device. Then, as the upper surface of the bridge portion (13A) is pressed downward, an electrical steel sheet (10B) having a bridge portion (13B) with reduced thickness is formed. That is, the upper surface of the bridge portion (13B) is concave relative to the upper surface of another part of the electrical steel sheet (10B), and the lower surface of the bridge portion (13B) is the same surface as the lower surface of another part of the electrical steel sheet (10B). In this case, as the bridge portion (13B) with reduced thickness is formed, the width of the bridge portion (13B) is expanded by an amount corresponding to the reduction in thickness. In FIG. 6, the dotted line represents the edge in the width direction of the bridge portion (13A) before compression processing, and the solid line represents the edge in the width direction of the bridge portion (13B) after compression processing. Therefore, an additional cutting process is required to remove the expanded area (135) after compression processing, that is, the area between the solid line and the dotted line. FIG. 7 is a drawing showing the state of the electrical steel sheet (10B) after the cutting process to remove the horizontally expanded area (135).

[0078] In one embodiment, the thinning of the bridge portion can be performed by deforming the bridge portion into a concave or convex shape. Deforming it into a concave shape means deforming it so that it is immersed relative to the upper surface of the electrical steel sheet and protrudes downward relative to the lower surface. Conversely, deforming it into a convex shape means deforming it so that it protrudes upward relative to the upper surface of the electrical steel sheet and is concave relative to the lower surface. Then, the material corresponding to the reduction in thickness of the bridge portion is used to make the bridge portion concave or convex, so that an increase in the width of the bridge portion does not occur. Therefore, the cutting process to remove the aforementioned expansion area (135) may become unnecessary.

[0079] First, the case of thinning the bridge portion into a concave shape will be explained. FIG. 8 shows an example of a method for forming a thin portion with a concave shape using a press device. Referring to FIG. 8, a concave portion (821) is provided in a die (82). An electrical steel sheet (10A) is placed on the die (82), and a stripper (83) is lowered to press the electrical steel sheet (10A) toward the die (82). A punch (81) is lowered to press the bridge portion (13A) of the electrical steel sheet (10A) into the concave portion (821) of the die (82) to thin the bridge portion (13A) into a concave shape. At this time, the direction of bending in the concave portion (821) of the electrical steel sheet (10A) indicated by arrow C11 and the direction of bending outside the concave portion (821) of the electrical steel sheet (10A) indicated by arrow C12 are the same. Therefore, the electrical steel sheet (10A) is significantly deformed. When a plurality of electrical steel sheets (10A) that have completed the process of forming a concave-shaped thin-walled section are laminated and caulked, the residual stress of the plurality of electrical steel sheets (10A) increases and the iron loss increases, which may lead to a deterioration in the performance of the motor.

[0080] Next, a case in which the bridge portion is thinned into a convex shape is described. FIG. 9 is a drawing showing an example of a method for forming a thin portion with a convex shape using a press device. Referring to FIG. 9, a convex portion (921) is provided in the die (92). A concave portion (912) having a shape complementary to the convex portion (921) is provided in the punch (91). An electrical steel sheet (10A) is placed on the die (82), and the stripper (93) is lowered to press the electrical steel sheet (10A) toward the die (92). Then, the punch (91) is lowered to press the bridge portion (13A) of the electrical steel sheet (10A) between the concave portion (912) of the punch (91) and the convex portion (921) of the die (92) to thin the bridge portion (13A) into a convex shape. At this time, the direction of bending of the convex portion (921) of the electrical steel sheet (10A) indicated by arrow C21 and the direction of bending other than the convex portion (921) of the electrical steel sheet (10A) indicated by arrow C22 are opposite to each other. In other words, the direction of deflection (139) (see FIG. 5) during the cutting press processing of the electrical steel sheet (10A), that is, the punching direction, and the direction in which the bridge portion (13A) of the electrical steel sheet (10A) becomes convexly thin are opposite to each other. Therefore, the deformation of the electrical steel sheet (10A) is relatively smaller compared to the process shown in FIG. 8.

[0081] Taking these points into consideration, a rotor (5a) according to one embodiment of the present disclosure employs an electrical steel sheet having a bridge portion thinned into a convex shape. FIG. 10 is a schematic perspective view of a rotor (5a) according to one embodiment of the present disclosure. FIG. 11 is a schematic perspective view of an electrical steel sheet (10) applied to the rotor (5a) shown in FIG. 10. Referring to FIG. 10, the rotor (5a) may have a laminate (20) and a permanent magnet (40). The laminate (20) is formed by stacking a plurality of electrical steel sheets (10) shown in FIG. 11. Referring to FIG. 11, the electrical steel sheet (10) may have a hub portion (11), a plurality of spoke portions (12), and a plurality of bridge portions (13).

[0082] The hub portion (11) is a ring-shaped member located on the inner side, i.e., the central part, of the rotor (5a). A hole (14) is provided in the central part of the hub portion (11). A plurality of spoke portions (12) are arranged at equal intervals to surround the hub portion (11) on the outer side of the rotor (5a). Each of the plurality of spoke portions (12) may be, for example, in a fan shape. Each of the plurality of spoke portions (12) is provided with a rim (121) having an outer circumference. The rim (121) may have the shape of an arc segment. When the rims (121) of the plurality of spoke portions (12) are combined, they form a broken arc. Although eight spoke portions (12) are shown in FIG. 11, they are not limited thereto. The electrical steel sheet (10) may have fewer than 8 spoke sections (12) and may have 9 or more spoke sections (12). Multiple spoke sections (12) are spaced apart from each other at equal intervals, thereby forming a space in which a permanent magnet (40) is placed between two adjacent spoke sections (12). The bridge section (13) is a part that connects the hub section (11) and the spoke section (12). The width of the bridge section (13) is extremely narrow compared to the width of the outer side of the spoke section (12). In FIG. 11, the bridge section (13) has a convex shape in the opposite direction to the direction of the sagging caused by punching (Fig. 8: 139) by the method shown in FIG. 9. In addition, the bridge section (13) is thinned so that it has a thin thickness compared to other parts of the electrical steel sheet (10).

[0083] A laminate (20) illustrated in FIG. 10 is formed by stacking a plurality of electrical steel sheets (10). The laminate (20) may comprise a hub laminate (21), a plurality of spoke laminates (22), and a plurality of bridge laminates (23). The hub laminate (21) is a portion where the hub portions (11) of the plurality of electrical steel sheets (10) are stacked, and an axle hole (24) is formed by holes (14) in the center of the hub laminate (21). The plurality of spoke laminates (22) is a portion where the plurality of spoke portions (12) of each of the plurality of electrical steel sheets (10) are stacked. The plurality of spoke laminates (22) are arranged at equal intervals in the circumferential direction to surround the hub laminate (21). The plurality of bridge laminates (23) is a portion where the plurality of bridge portions (13) of the plurality of electrical steel sheets (10) are stacked. A plurality of spoke laminates (22) are connected to a hub laminate (21) by a plurality of bridge laminates (23).

[0084] The shaft (30) of the motor (5) shown in FIG. 1 is positioned along the central axis of the laminate (20). For example, the shaft (30) is inserted into an axle hole (24) provided in the center of the hub laminate (21).

[0085] A plurality of permanent magnets (40) are arranged inside a laminate (20). The plurality of permanent magnets (40) are arranged circumferentially spaced apart from each other inside the laminate (20) with a spoke laminate (22) in between. For example, the plurality of permanent magnets (40) are arranged radially in the arrangement spaces between the plurality of spoke laminates (22). The plurality of permanent magnets (40) are arranged such that the mutually opposing faces (circumferential faces) of two adjacent permanent magnets (40) have the same magnetic pole. For example, each of the plurality of permanent magnets (40) has a circumferentially arranged N pole and S pole, and two adjacent permanent magnets (40) are arranged such that their N poles face each other or their S poles face each other. Magnetic flux of the same magnetic pole as the magnetic poles of the opposing faces of the two permanent magnets (40) flows through the magnetic poles of the spoke laminate (22) between the two adjacent permanent magnets (40). When current is supplied to the windings of the stator (Fig. 1: 5a), a magnetic field is formed. As the magnetic flux of each pole of a plurality of spoke laminates (22) repels and attracts the magnetic field of the stator (5b), the rotor (5a) rotates relative to the stator (5b). This rotor (5a) is also called a spoke rotor.

[0086] As illustrated in FIG. 11, the bridge portion (13) of the electrical steel sheet (10) according to the present embodiment has a convex shape in the opposite direction to the direction of the sagging caused by stamping (Fig. 5: 139). Accordingly, in FIG. 10, the bridge laminate (23) also has a convex shape in the opposite direction to the direction of the sagging caused by stamping (Fig. 5: 139) overall.

[0087] FIG. 12 is a partial cross-sectional view of a laminate (20) of a rotor (5a) according to one embodiment of the present disclosure illustrated in FIG. 10. At least one of the plurality of electrical steel sheets (10) forming the laminate (20) has a convexly thinned bridge portion (13). The bridge portions (13) of all the plurality of electrical steel sheets (10) forming the laminate (20) of the present embodiment are thinned in a convex shape. That is, the bridge portion (13) has a thin portion (131) with a thickness thinner than the hub portion (11) and the spoke portion (12). If the electrical steel sheet (10) having the thinned bridge portion (13) is referred to as the first electrical steel sheet (10-1), then in the present embodiment, all of the plurality of electrical steel sheets (10) are the first electrical steel sheet (10-1).

[0088] The thickness of the portion other than the thin-walled portion (131) of the electrical steel sheet (10) is denoted as t1. In other words, the thickness of the bridge portion (13) before thinning is t1. For example, the thickness of the bridge portion (13) before thinning may be the same as the thickness of the hub portion (11) and the spoke portion (12). The thickness of the thin-walled portion (131) of the electrical steel sheet (10) is denoted as t2. That is, the thickness of the bridge portion (13) after thinning is denoted as t2. The magnetic flux density passing through the electrical steel sheet (10) is denoted as Φ. For example, the magnetic flux density passing through the bridge portion (13) is denoted as Φ. The saturation magnetic flux density of the material of the electrical steel sheet (10) is denoted as Bs. For example, the saturation magnetic flux density of the material of the bridge portion (13) is denoted as Bs. The thickness (t2) is determined to satisfy the following equation (1).

[0089] Φ>Bsⅹt² / t1 -----Equation(1)

[0090] According to this, the certainty of magnetic flux saturation occurring in the bridge section (13) is increased. As a result, leakage magnetic flux flowing from the spoke section (12) through the bridge section (13) toward the inner diameter of the rotor (5a) can be reduced, and the motor (5) can be made to have higher torque. In addition, as described above, the thinning of the bridge section (13) can be achieved by press forming without the addition of a process to remove the expanded area (135) described in FIGS. 6 and 7. Therefore, it is possible to increase the performance of the motor (5) while minimizing the increase in material and process costs. In addition, by connecting a plurality of spoke portions (12) and a hub portion (11) with a plurality of thin-walled bridge portions (13), the strength of the rotor (5a) can be increased without reducing the performance of the motor (5). Furthermore, the rotor (5a) according to one embodiment of the present disclosure can rotate at a rotational speed of approximately 500 rpm to 20,000 rpm in a drum-type washing machine (1) as shown in FIG. 1. Specifically, the rotor (5a) can rotate at 400 rpm to 700 rpm during washing and at 14,000 rpm to 20,000 rpm during spin drying. This rotational speed of the rotor (5a) is the rotational speed assuming that the power of the motor (5) equipped with the rotor (5a) is transmitted to the rotation shaft (Fig. 1:4c) (see FIG. 1) of the drum (Fig. 1:4) by means of a pulley (Fig. 1:4d).

[0091] An example of a method for manufacturing an electrical steel sheet (10) for a rotor (5a) is briefly described. An example of a method for manufacturing an electrical steel sheet (10) may include the step of forming an electrical steel sheet intermediate (10A) by press cutting a metal sheet to form a hub portion (11) having a hole (14) formed in the center, a plurality of spoke portions (12) arranged spaced apart from each other in a circumferential direction along the circumference of the hub portion, and a flat bridge portion (13A) connecting the plurality of spoke portions and the hub portion, and the step of thinning the bridge portion (13A) into a convex shape in the opposite direction of the punching direction. Since the electrical steel sheet (10A) shown in FIG. 2 is identical to the intermediate in the process of forming the electrical steel sheet (10), the electrical steel sheet intermediate is indicated by attaching reference numeral 10A.

[0092] To thin the bridge portion (13A), an electrical steel intermediate (10A) is placed on a die (92) provided with a convex portion (921) that is convex in the opposite direction of the punching direction, so that the bridge portion (13A) and the convex portion (921) are aligned. Next, a stripper (93) is lowered to press the electrical steel intermediate (10A) toward the die (92). Next, a punch (91) provided with a concave portion (912) having a shape complementary to the convex portion (921) is lowered to press the bridge portion (13A) of the electrical steel intermediate (10A) between the concave portion (912) of the punch (91) and the convex portion (921) of the die (92), thereby thinning the bridge portion (13A) into a convex shape. Accordingly, it can be manufactured on an electrical steel sheet (10) having a thinned bridge portion (13) as shown in FIGS. 11 and 12.

[0093] In FIG. 10 and FIG. 12, a first electrical steel sheet (10-1) having a bridge portion (13) in which the entire plurality of electrical steel sheets (10) are thinned is shown, but the present disclosure is not limited thereto.

[0094] FIG. 13 is a partial cross-sectional view of a laminate (20) of a rotor (5a) according to one embodiment of the present disclosure. Referring to FIG. 13, a plurality of electrical steel sheets (10) may include a plurality of first electrical steel sheets (10-1) and a plurality of second electrical steel sheets (10-2) having a flat second bridge portion (13-2) having a thickness equal to that of the spoke portion (12) and the hub portion (11). The second bridge portion (13-2) has a flat region (132) corresponding to the thin portion (131) of the first electrical steel sheet (10-1). That is, the second electrical steel sheet (10-2) is flat with a uniform thickness overall. The second electrical steel sheet (10-2) may be the same as the electrical steel sheet (10A) shown in FIG. 2. The laminate (20) includes a first laminate (20-1) in which a plurality of first electrical steel sheets (10-1) are laminated, and a second laminate (20-2) in which a plurality of second electrical steel sheets (10-2) are laminated. The first laminate (20-1) can be laminated on the flat second laminate (20-2). According to the rotor (5a) having the first laminate (20-1) in this manner, the deterioration of motor performance due to leakage of magnetic flux in the radial direction can be suppressed.

[0095] A washing machine according to one aspect of the present disclosure comprises: a housing; a tub capable of storing water elastically supported inside the housing; a drum rotatably installed inside the tub and receiving laundry; and a motor that rotates the drum, comprising a stator, a rotor opposite to the stator with an air gap between them, and a shaft fixed to the rotor. The rotor comprises: a laminate comprising a plurality of laminated electrical steel sheets and having a shaft hole in the center into which the shaft is inserted; and a plurality of permanent magnets supported by the laminate. Each of the plurality of electrical steel sheets comprises a hub portion having a hole formed corresponding to the shaft hole, a plurality of spoke portions spaced apart from one another in a circumferential direction along the circumference of the hub portion, wherein the plurality of permanent magnets are arranged in the spaced intervals, and a plurality of bridge portions connecting the plurality of spoke portions and the hub portion. In at least one of the plurality of electrical steel sheets, the bridge portion has a thin-walled portion having a convex shape opposite to the direction of deflection caused by punching and having a thickness thinner than the hub portion and the spoke portions.

[0096] A motor according to one aspect of the present disclosure comprises: a stator; a rotor facing the stator with an air gap between them; and a shaft fixed to the rotor. The rotor comprises a laminate comprising a plurality of laminated electrical steel sheets and having a shaft hole in the center into which the shaft is inserted; and a plurality of permanent magnets supported by the laminate. Each of the plurality of electrical steel sheets comprises a hub portion having a hole formed corresponding to the shaft hole, a plurality of spoke portions spaced apart from one another in a circumferential direction along the circumference of the hub portion, wherein the plurality of permanent magnets are disposed in the spaced portions, and a plurality of bridge portions connecting the plurality of spoke portions and the hub portion. In at least one of the plurality of electrical steel sheets, the bridge portion has a thin-walled portion having a convex shape opposite to the direction of deflection caused by punching, and is thinner than the hub portion and the spoke portions.

[0097] In one embodiment, the plurality of bridge portions in all of the plurality of electrical steel sheets (10) may have the thin portions.

[0098] In one embodiment, the plurality of electrical steel sheets may include a plurality of first electrical steel sheets having a plurality of bridge portions having a thin-walled portion; and a plurality of second electrical steel sheets having a plurality of second bridge portions having a thickness equal to that of the spoke portion and the hub portion.

[0099] In one embodiment, the laminate may include a first laminate in which a plurality of the first electrical steel sheets are laminated, and a second laminate in which a plurality of the second electrical steel sheets are laminated.

[0100] In one embodiment, the first laminate may be laminated on the second laminate.

[0101] In one embodiment, if the magnetic flux density passing through the electrical steel sheet is Φ, the saturated magnetic flux density of the material of the electrical steel sheet is Bs, the thickness of the portion of the electrical steel sheet other than the thin-walled portion is t1, and the thickness of the thin-walled portion of the electrical steel sheet is t2, then Φ > Bs × t2 / t1 can be satisfied.

[0102] As one embodiment, the motor may be driven at a rotational speed of 400 to 20,000 rpm.

[0103] A method for manufacturing an electrical steel sheet for a rotor according to one aspect of the present disclosure comprises: a step of press-cutting a metal sheet to form an electrical steel sheet intermediate having a hub portion having a hole formed in the center, a plurality of spoke portions spaced apart from each other in a circumferential direction along the circumference of the hub portion, and a plurality of flat bridge portions connecting the plurality of spoke portions and the hub portion; and a step of thinning the plurality of bridge portions into a convex shape in the opposite direction to the punching direction.

[0104] In one embodiment, the thinning step may include: placing the electrical steel sheet intermediate on a die having a convex portion in the opposite direction of the stamping direction so that the bridge portion and the convex portion are aligned; lowering a stripper to press the electrical steel sheet intermediate toward the die; and lowering a punch having a concave portion having a shape complementary to the convex portion to press the bridge portion between the concave portion and the convex portion, thereby thinning the bridge portion into a convex shape.

[0105] According to the present disclosure, the bridge portion of the electrical steel sheet for a motor rotor can be thinned without increasing the processing steps or causing outward bending in the radial direction. By doing so, the deterioration of motor performance caused by leakage of magnetic flux inward in the radial direction of the rotor can be suppressed.

[0106] However, the technical effects intended to be achieved in this document are not limited to those mentioned above, and other technical effects not mentioned will be clearly understood by those skilled in the art to which this disclosure belongs from the description in this document.

[0107] As described above, although the electrical steel sheets for motors, washing machines, and rotors of the present disclosure have been explained by limited embodiments and drawings, the present disclosure is not limited to the above embodiments and various modifications are possible within the scope without departing from the spirit thereof.

Claims

1. Housing (2); A water-retaining tub (3) elastically supported inside the above housing (2); A drum (4) that is rotatably installed inside the above tub and accommodates laundry; A motor (5) for rotating the drum, comprising a stator (5b), a rotor (5a) facing the stator with an air gap between them, and a shaft (30) fixed to the rotor; The above rotor is, A laminate (20) comprising a plurality of laminated electrical steel plates (10) and having an axial hole (24) in the center into which the shaft is inserted; It includes a plurality of permanent magnets (40) supported on the above-mentioned laminate, Each of the above plurality of electrical steel sheets (10) is, It includes a hub portion (11) having a hole (14) corresponding to the shaft hole (24), a plurality of spoke portions (12) spaced apart from each other in a circumferential direction along the circumference of the hub portion and having a plurality of permanent magnets arranged in the said spacing, and a plurality of bridge portions (13) connecting the plurality of spoke portions and the hub portion. A washing machine having, in at least one of the plurality of electrical steel sheets (10), the bridge portion (13) has a convex shape opposite to the direction of the deflection (139) caused by stamping and has a thin-walled portion (131) that is thinner than the hub portion and the spoke portion.

2. In Paragraph 1, A washing machine in which the bridge portion (13) in all of the above plurality of electrical steel sheets (10) has the thin portion (131).

3. In Paragraph 1, The above plurality of electrical steel sheets (10) are, A plurality of first electrical steel sheets (10-1) having a plurality of bridge portions (13) having a plurality of thin-walled portions (131); A washing machine comprising a plurality of second electrical steel plates (10-2) having a plurality of second bridge portions (13-2) having a thickness identical to that of the spoke portion and the hub portion.

4. In Paragraph 3, The above laminate comprises a washing machine including a first laminate (20-1) in which a plurality of the first electrical steel plates (10-1) are laminated, and a second laminate (20-2) in which a plurality of the second electrical steel plates (10-2) are laminated.

5. In Paragraph 4, The first laminate is a washing machine laminated on the second laminate.

6. In any one of paragraphs 1 through 5, A washing machine satisfying Φ > Bs × t2 / t1, where Φ is the magnetic flux density passing through the electrical steel sheet, Bs is the saturation magnetic flux density of the material of the electrical steel sheet, t1 is the thickness of the portion of the electrical steel sheet other than the thin-walled portion, and t2 is the thickness of the thin-walled portion of the electrical steel sheet.

7. In any one of paragraphs 1 through 6, The above motor is a washing machine having a rotational speed of 400 to 20,000 rpm.

8. Stator (5b); A rotor (5a) facing the stator with an air gap in between; It includes a shaft (30) fixed to the rotor above, The above rotor is, A laminate (20) comprising a plurality of laminated electrical steel plates (10) and having an axial hole (24) in the center into which the shaft is inserted; It includes a plurality of permanent magnets (40) supported on the above-mentioned laminate, Each of the above plurality of electrical steel sheets (10) is, It includes a hub portion (11) having a hole (14) corresponding to the shaft hole (24), a plurality of spoke portions (12) spaced apart from each other in a circumferential direction along the circumference of the hub portion and having a plurality of permanent magnets arranged in the said spacing, and a plurality of bridge portions (13) connecting the plurality of spoke portions and the hub portion. A motor having, in at least one of the plurality of electrical steel sheets (10), the bridge portion (13) has a convex shape opposite to the direction of deflection (139) caused by stamping and has a thin-walled portion (131) that is thinner than the hub portion and the spoke portion.

9. In Paragraph 8, The bridge portion (13) of all of the plurality of electrical steel sheets (10) is a motor having the thin-walled portion (131).

10. In Paragraph 8, The above plurality of electrical steel sheets (10) are, A plurality of first electrical steel sheets (10-1) having a plurality of bridge portions (13) having a plurality of thin-walled portions (131); A motor comprising a plurality of second electrical steel plates (10-2) having a plurality of second bridge portions (13-2) having a thickness identical to that of the spoke portion and the hub portion.

11. In Paragraph 10, The above-mentioned laminate is a motor comprising a first laminate (20-1) in which a plurality of the first electrical steel sheets (10-1) are laminated, and a second laminate (20-2) in which a plurality of the second electrical steel sheets (10-2) are laminated.

12. In Paragraph 11, The first laminate is a motor laminated on the second laminate.

13. In any one of paragraphs 8 through 12, A motor satisfying Φ > Bs × t2 / t1, where Φ is the magnetic flux density passing through the electrical steel sheet, Bs is the saturation magnetic flux density of the material of the electrical steel sheet, t1 is the thickness of the portion of the electrical steel sheet other than the thin-walled portion, and t2 is the thickness of the thin-walled portion of the electrical steel sheet.

14. A method for manufacturing electrical steel sheets for rotors, A step of forming an electrical steel sheet intermediate (10A) by press cutting a metal sheet to form a hub portion (11) having a hole (14) formed in the center, a plurality of spoke portions (12) spaced apart from each other in a circumferential direction along the circumference of the hub portion, and a plurality of flat bridge portions (13A) connecting the plurality of spoke portions and the hub portion; A method for manufacturing an electrical steel sheet for a rotor, comprising the step of thinning the plurality of bridge portions (13A) into a convex shape in the opposite direction of the stamping direction.

15. In Paragraph 14, The above-mentioned thinning step is, A step of placing the electrical steel sheet intermediate on a die (92) having a convex portion (921) provided in the opposite direction of the stamping direction so that the bridge portion and the convex portion are aligned; A step of lowering the stripper to press the electrical steel sheet intermediate toward the die side; A method for manufacturing an electrical steel sheet for a rotor, comprising the step of lowering a punch (91) provided with a concave portion (912) having a shape complementary to the convex portion, thereby pressing the bridge portion between the concave portion and the convex portion to thin the bridge portion into a convex shape.

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