ROTOR CORE AND MOTOR INCLUDING THE SAME

A rotor core comprises a rotor stack including a plurality of pole parts, each pole part having a magnet embedded hole having a magnet therein and at least one through hole located between the magnet embedded hole and an outer surface of the each pole part, thereby stably providing high output by increasing output torque and reducing torque ripples, and simplifying the process for stacking and coupling the magnet and the rotor, and reducing manufacturing costs.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No. 10-2023-0056489, filed on Apr. 28, 2023, which is hereby incorporated by reference for all purposes as if fully set forth herein.

BACKGROUND

Field

Some embodiments of the present disclosure generally relate to a rotor core and a motor including the same and, more specifically, a rotor core and a motor including the same, which may stably provide high output by increasing output torque and reducing torque ripples, simplify the process of stacking and coupling a magnet and a rotor, and reduce manufacturing costs.

Description of Related Art

Typically, interior permanent magnet motors (IPMs) are used in electric vehicles and hybrid vehicles because of high efficiency and torque and output density. The IPM has a structure in which magnets are embedded in the rotor and is distinguished from a surface permanent magnet motor (SPM) in which magnets are positioned on the surface of the rotor. As compared with the SPM, the IPM has high output density, making it suitable as the driving motor of the electric vehicle. However, the IPM may generate large torque ripples. Torque ripple is the deviation of the output torque value relative to the average torque value and causes noise vibration, and harshness (NVH) that deteriorates vehicle performance.

There are various attempts to reduce the torque ripples of the IPM, including, e.g., changing the structure of the magnet placement in the rotor core or forming a recess or a hole in the surface or inside of the rotor core. However, most of the conventional attempts are not effective in practice, or are hard to apply in reality due to failure to suggest a specific shape.

Thus, a structure capable of effectively reducing torque ripples through a specific shape is required.

Meanwhile, in general, the rotor core of the motor adopts a stack structure in which electric steel plates, which are thin magnetic bodies, are stacked and fixed to enhance manufacturability. To fix the stacked stacks, mechanical fastening has conventionally been used to embossing or welding the stacks, and chemical fastening which applies an adhesive between the stacks is used. However, the mechanical fastening may deteriorate core magnetism and the permanent magnet due to a change in the shape of the rotor stack, thereby degrading motor performance. The chemical fastening cause to increase manufacturing cost.

As another approach to fix the permanent magnet to the rotor stack, a molding material may be injected after the magnet is inserted, or the magnet is press-fitted into a hole formed in the rotor stack. However, the molding method may have difficulty in adjusting the amount of molding material injected and requires a time for hardening which leads to poor producibility. The press-fitting method may damage the coating on the magnet surface or cause degradation.

Therefore, a need exists for a structure capable of coupling the magnet to the rotor core in a simple and convenient way without deteriorating motor performance.

BRIEF SUMMARY

Conceived in the foregoing background, some embodiments of the present disclosure may relate to a rotor core and a motor including the same, which may stably provide high output by increasing output torque and reducing torque ripples, simplify the process of stacking and coupling a magnet and a rotor, and reduce manufacturing costs.

According to the present embodiments, there may be provided a rotor core, comprising a rotor stack including a plurality of pole parts having a magnet embedding hole where a magnet is embedded and at least one through hole formed between the magnet embedding hole and an outer surface.

According to the present embodiments, there may be provided a rotor core, comprising a rotor stack including a plurality of pole parts having a magnet embedding hole where a magnet is embedded and at least one through hole formed between the magnet embedding hole and an outer surface and a fixing member inserted into the through hole and axially supported by the magnet.

According to the present embodiments, there may be provided a motor comprising a rotor core, comprising a rotor stack including a plurality of pole parts having a magnet embedding hole where a magnet is embedded and at least one through hole formed between the magnet embedding hole and an outer surface or a rotor core, comprising a rotor stack including a plurality of pole parts having a magnet embedding hole where a magnet is embedded and at least one through hole formed between the magnet embedding hole and an outer surface and a fixing member inserted into the through hole and axially supported by the magnet.

According to certain embodiments of the present disclosure, it is possible to stably provide high output by increasing output torque and reducing torque ripples, simplify the process for stacking and coupling a magnet and a rotor, and reduce manufacturing costs.

DETAILED DESCRIPTION

FIG.1is a plan view illustrating a portion of a rotor core and a motor according to an embodiment of the present disclosure.FIG.2is a partial plan view illustrating a rotor core according to an embodiment of the present disclosure.FIG.3is a partial plan view illustrating a rotor core according to an embodiment of the present disclosure.FIG.4is a partial plan view illustrating a portion of a rotor core according to an embodiment of the present disclosure.FIG.5is a partial plan view illustrating a rotor core according to an embodiment of the present disclosure.FIG.6is a partial plan view illustrating a rotor core according to an embodiment of the present disclosure.FIG.7is a partial perspective view illustrating a rotor core according to an embodiment of the present disclosure.FIG.8is a partial exploded perspective view illustrating a rotor core according to an embodiment of the present disclosure.FIG.9is a partial perspective view illustrating a rotor core according to an embodiment of the present disclosure.FIG.10is graphs for illustrating an air gap magnetic flux density of a rotor core according to an embodiment of the present disclosure.FIG.11is graphs for illustrating an average torque and torque ripple of a motor according to an embodiment of the present disclosure.

According to an embodiment of the present disclosure, a rotor core110may include a rotor stack111. The rotor stack111may include a plurality of pole parts120having a magnet embedded hole121where one or more magnet130sare embedded and at least one through hole122formed between the magnet embedded hole121and an outer surface of the pole part120.

Further, according to an embodiment of the present disclosure, there may be provided a motor including the rotor core110. For instance, a motor includes the rotor core110, a stator core101receiving the rotor core110therein, and a rotating shaft fixedly coupled to the rotor core110to rotate along with the rotating core110.

Meanwhile, according to an embodiment of the present disclosure, there may be provided the rotor core110and a motor including the rotor core110, which are described below in detail.

Referring toFIG.1, a motor according to an embodiment of the present disclosure includes a stator core101and a rotor core110. The stator core101includes a plurality of stator teeth102on which a winding103is wound. The stator slots defined by adjacent pair of stator teeth102may be designed and dimensioned to receive the winding103. The structure and shape of the stator core101are generally known, and therefore further detailed description thereof is not given in the present disclosure. The rotor core110according to an embodiment of the present disclosure includes a rotor stack111. A plurality of rotor stacks111are stacked to form the rotor core110(seeFIG.7). The rotor stack111includes a plurality of pole parts120. The plurality of pole parts120are arranged along the circumferential direction, and magnets130are arranged in the magnet embedded holes121formed in the respective pole parts120, with N poles and S poles alternating along the circumferential direction. The rotor core110according to an embodiment of the present disclosure may have, for example, but not limited to, six poles or eight poles. The drawings illustrate only two pole parts120among the plurality of poles and an embodiment of the present disclosure in which one pole part120has a central angle of 45 degrees, although not limited thereto.

Each pole part120has a magnet embedded hole121and at least one through hole122. As shown in the drawings, the magnet embedded hole121may be formed at the radial outer portion of the pole part120, and the magnet130is inserted into the magnet embedded hole121. The rotor core110according to an embodiment of the present disclosure may further include a fixing member170for fixing the magnet130inserted in the magnet embedded hole121. The fixing member170will be described below in detail.

The through hole122is formed between the magnet embedded hole121and the outer surface of the pole part120. For instance, the outer surface of the rotor core110, which is formed as the outer surface of the plurality of pole parts120, may be formed to be coaxial with the central axis of the rotor core110with a constant curvature. Alternatively, as described below in detail, a protrusion401may be formed on the outer surface of the pole part120. The through hole122may be formed between the magnet embedded hole121and the outer surface of the pole part120having a constant curvature or the outer surface of the pole part120formed by the protrusion401.

As the through hole122is formed between the magnet embedded hole121and the outer surface of the pole part120, the output torque of the motor including the rotor core110according to an embodiment of the present disclosure may increase, and torque ripples may be reduced.FIG.10is graphs for illustrating comparison of vertical air gap magnetic flux density B_n in a vertical direction and tangential air gap magnetic flux density B_t between a structure without a through hole (i.e., a conventional rotor core structure) and a structure with a through hole (i.e., a rotor core structure according to an embodiment of the present disclosure). InFIG.10, the torque ripple of the motor is represented as the product of the vertical air gap magnetic flux density B_n and the tangential air gap magnetic flux density B_t.

FIG.10shows that, according to an embodiment of the present disclosure, in both the vertical air gap magnetic flux density B_n and the tangential air gap magnetic flux density B_t, the primary component increases, and the output torque increases in comparison with the conventional rotor core structure without a through hole. In addition, according to an embodiment of the present disclosure, the total harmonic distortion (THD) slightly increases in the vertical air gap magnetic flux density B_n and greatly reduces in the tangential air gap magnetic flux density B_t so that the overall torque ripple reduces in comparing with the conventional rotor core structure without a through hole. The graph ofFIG.10is verified with a finite element method (FEM).

Referring toFIG.2, according to an embodiment of the present disclosure, the through hole122and the magnet embedding hole121may be spaced apart from each other. In other words, as shown inFIG.2, an interval T1may be formed between the through hole122and the magnet embedded hole121. By forming the interval T1between the through hole122and the magnet embedded hole121, it is possible to easily secure rigidity of the rotor stack111and provide ease of punching the through hole122.

For instance, a pair of through holes122may be provided. As shown inFIG.2, a pair of through holes122may be provided between the outer surface of the pole part120and the magnet embedded hole121of the pole part120. Further, according to an embodiment of the present discloser, the pair of through holes122may be formed to be symmetrical with respect to the straight line connecting the center of the rotor core110and the core (or center) of the magnet embedded hole121. The interval T1between the through hole122and the magnet embedded hole121, the diameter of the through hole122, and the interval between the through hole122and the straight dotted line ofFIG.2may be varied to minimize the torque ripple of the motor according to various embodiments the present disclosure.

Referring toFIG.3, according to an embodiment of the present disclosure, the through hole122may be formed to be inscribed, enclosed, or disposed in a circle301in which the magnet130is inscribed, enclosed or disposed. For example, “inscribe” may mean drawing one shape inside another, just touching but not crossing sides. The circle301is coaxial with the rotor stack111. The circle301coaxial with the rotor stack111has a diameter smaller than that of the outer surface of the rotor stack111so that the interval T2between the outer surface of the rotor stack111and the circle301in which the magnet130is inscribed can be constant, stable torque can be output, torque ripple can be reduced, and the rigidity of the rotor core110can be secured.

Referring toFIG.4, according to an embodiment of the present disclosure, a protrusion or protruded portion401convexly protruding from neighboring normals of the outer surface of the pole part120may be formed on the outer surface of the pole part120. In other words, the protrusion401may have a larger curvature than that of the outer surface of the rotor stack111shown inFIGS.2and3, and the through hole122may be formed between the magnet embedding hole121and the outer surface of the protrusion401. An interval T1may be formed between the through hole122and the magnet embedded hole121. According to an embodiment of the present disclosure, the protrusion or protruded portion401may reduce noise in the torque output from the motor and provide stable output.

Referring toFIG.5, according to an embodiment of the present disclosure, the through hole122may be formed to be inscribed, enclosed or disposed in a circle501in which the magnet130is inscribed, enclosed or disposed. For instance, the through hole122has one point of contact with the virtual circle501. The circle501is eccentric with respect to the rotor stack111. In the embodiment shown inFIG.5, a center of the circle501in which the through hole122is inscribed, enclosed or disposed is different from the center of the rotor stack111. The structure of theFIG.5may further reduce torque ripples than the structure ofFIG.3by forming the through hole122to be inscribed, enclosed or disposed in the circle501eccentric with respect to the rotor stack111.

More specifically, according to the embodiment illustrated inFIG.5, the circle501in which the through hole122is inscribed, enclosed, or disposed may be eccentric toward the magnet embedded hole121with respect to the rotor stack111(e.g. upward inFIG.5). In other words, the center O_ε of the circle501in which the through hole122is inscribed, enclosed, or disposed is eccentric with respect to the center O_c of the rotor stack111. For instance, the center O_ε of the virtual circle501is closer to the magnet embedded hole121than the center O_c of the rotor stack111. Accordingly, the circle501in which the through hole122is inscribed, enclosed, or disposed according to the embodiment ofFIG.5has a larger curvature than the circle301in which the through hole122is inscribed, enclosed, or disposed according to the embodiment ofFIG.3, so that torque ripples can further reduced.

Referring toFIG.5, the interval or thickness between the circle501in which the through hole122is inscribed and the outer surface of the protrusion401of the pole part120may be constant. In other words, according to the embodiment ofFIG.5, the through hole122may be formed to be inscribed in the circle501in which the magnet130is inscribed and which is eccentric toward the magnet embedded hole121with respect to the rotor stack111, the protrusion401convexly protruding from neighboring normals of the outer surface of the pole part120may be formed on the outer surface of the pole part120, and the interval between the outer surface of the protrusion401and the circle501may be constant. For example, the outer surface of the protrusion401and the circle501may be parallel to each other. The protrusion401and the circle501in which the through hole122is Inscribed may have a concentric center O_ε which is eccentric with respect to the center O_c of the rotor stack111. And, the interval T3between the outer surface of the protrusion401and the circle501in which the through hole122is inscribed may be constant. In other words, the interval T1between the through hole122and the magnet embedding hole121and the interval T3between the through hole122and the outer surface of the protrusion401each may be constant. Therefore, it is possible to secure the rigidity of the rotor stack111and ease of punching the through hole122and to reduce torque ripples.

Referring toFIG.6, the through hole122may be formed to communicate with, or be connected with, the magnet embedded hole121. In other words, the through hole122may be formed between the magnet embedded hole121and the outer surface of the rotor stack111, and the through hole122may have a portion open toward the magnet embedded hole121to communicate with the magnet embedding hole121. Accordingly, the through hole122and the magnet embedded hole121may be integrated as one single hole structure having combination of a plurality of holes. AlthoughFIG.6illustrates an embodiment in which the protrusion401is formed in the pole part120, the through hole122may be formed to communicate with the magnet embedded hole121even when the protrusion401is not formed in the pole part120. When it is required to secure a sufficient diameter of the through hole122in punching the through hole122between the magnet embedded hole121and the outer surface of the pole part120so as to increase output torque or reduce torque ripples, if the interval between the magnet embedded hole121and the through hole122is too small, the manufacturing process for punching may not be easy, and the rigidity of the rotor stack111may be deteriorated. Thus, it is possible to secure both the ease of the punching and the rigidity of the rotor stack111by forming the through hole122to communicate with, or be connected with, the magnet embedded hole121.

FIG.11illustrates an average torque (Nm) and a torque ripple (%) according to a diameter D_hole of the through hole122according to an embodiment of the present disclosure. In other words, the structure is identical to the conventional structure if the diameter of the through hole122is 0. As shown inFIG.11, when the diameter of the through hole122is about 0.7 mm, the average torque is maximized (i.e. increased by about 3.5%) while the torque ripple is minimized (reduced by about 38%) when the diameter of the through hole122is about 1.3 mm. As such, the diameter of the through hole122for maximizing the average torque may differ from the diameter of the through hole122for minimizing the torque ripple. An appropriate through hole diameter may be set depending on, e.g., the number of rotations, core material, processing limit, or yield safety factor and, if necessary, the through hole122and the magnet embedding hole121may be allowed to communicate with, or be connected to, each other.

Referring toFIG.7, the rotor core110according to an embodiment of the present disclosure may further include a fixing member710that is inserted into the through hole122of the rotor core110. The fixing member710has two opposite ends axially fixed to the magnet130. The fixing member710is inserted into the through hole122and passes through a plurality of rotor stacks111stacked. As the fixing member710inserted in the through hole122is supported by the magnet130on two opposite sides of the fixing member710in the axial direction, the magnet130may be fixed to the magnet embedding hole121. Further, as two opposite ends of the fixing member710are supported by the stacked rotor stacks111as well as by the magnet130, the stacked rotor stacks111may be fixed.

In other words, the fixation of the stacked rotor stacks111and the fixation of the magnet130may simultaneously or mutually be performed or acted by the fixing member710to simplify the coupling process. Further, no physical deformation needs to be applied to the rotor stack111, thereby preventing the deterioration of motor performance. No use of an adhesive leads to cost savings.

Further, according to an embodiment of the present disclosure, the fixing member710may be formed of a non-magnetic body. Therefore, the output torque of the rotor core110and the motor can be increased and the torque ripples can be reduced by the through hole122.

To fixedly couple the stacked rotor core110and magnet130by the fixing member710inserted in the through hole122, the fixing member710may include a load member810and a coupling member or coupler820, which are described below.

In other words, the fixing member710may be press-fitted into the through hole122. In other words, the fixing members710may press-fitted into the through holes122of the rotor stacks111stacked and aligned.

According to an embodiment of the present disclosure, the through hole122may be formed to communicate with, or be connected with, the magnet embedding hole121, and the fixing member710may be supported by the magnet130through a portion where the through hole122and the magnet embedding hole121communicate with, or be connected with, each other. In other words, a portion of the fixing member710may protrude from the through hole122to the magnet embedding hole121through the portion where the through hole122and the magnet embedding hole121communicate, or are connected, and the protruding portion of the fixing member710may be press-fitted into the through hole122while being supported by the magnet130. The magnet130may be fixed to the magnet embedded hole121by the force applied to the magnet130by the fixing member710while being press-fitted, and such a structure is described below in detail.

According to an embodiment of the present disclosure, a rotor core800may include a rotor stack111including a plurality of pole parts120each having a magnet embedded hole121where a magnet130is embedded and at least one through hole122formed between the magnet embedded hole121and an outer surface of the pole part120and a fixing member710inserted into the through hole122and having two opposite ends axially supported by the magnet130.

Further, according to an embodiment of the present disclosure, there may be provided a motor including the rotor core800. In other words, there may be provided a motor including a rotor core800, a stator core receiving the rotor core800therein, and a rotating shaft fixedly coupled to the rotor core800to rotate along with the rotor core110.

Referring toFIG.8, the same features and matters as those in the above-described embodiments, such as the position of the through hole122and the shape of the outer surface of the pole part120are briefly described, and the description will focus primarily on the differences. AlthoughFIG.8illustrates the rotor core800having a protrusion401, the present disclosure is not limited thereto, and the protrusion401may not be provided at the pole part120.

The fixing member710is inserted into the through hole122, and two opposite ends of the fixing member710are axially supported by the magnet130, and the magnet130is fixed with respect to the stacked rotor stacks111. Accordingly, the fixation of the stacked rotor stacks111and the fixation of the magnet130may simultaneously or mutually be performed or acted by the fixing member710to simplify the coupling process. Further, no physical deformation needs to be applied to the rotor stack111, thereby preventing the deterioration of motor performance. No use of an adhesive leads to cost savings.

According to an embodiment of the present disclosure, the fixing member710is formed of a non-magnetic body. Therefore, the output torque of the rotor core800and the motor can be increased and the torque ripples can be reduced by the through hole122.

According to an embodiment of the present disclosure, a pair of through holes122may be provided in one pole part120, and the fixing member710may be inserted into each through hole122.

In other words, the fixing member710may be press-fitted into the through hole122. The stacked rotor stacks111may be fixed by the coupling force provided to the stacked rotor stacks111by the fixing member710while being press-fitted and, as described below, the supporting force provided while two opposite ends of the fixing member710are supported on two axially opposite ends of the stacked rotor stacks111.

According to an embodiment of the present disclosure, the through hole122may be formed to communicate with, or be connected with, the magnet embedded hole121, and the fixing member710may be supported by the magnet130through a portion where the through hole122and the magnet embedded hole121communicate with, or are connected to, each other.

Referring toFIG.9, the magnet130may be fixed in the magnet embedded hole121by the supporting force applied to the magnet130as the fixing member710is inserted into the through hole122. In other words, according to an embodiment of the present disclosure, the through hole122may be formed to communicate with, or be connected with, the magnet embedding hole121, and the fixing member710may be press-fitted into the through hole122while being supported by the magnet130through a portion where the through hole122and the magnet embedded hole121communicate with, or be connected with, each other. The fixing member710may be inserted into the through hole122communicating with, connected to, the magnet embedded hole121and simultaneously supported by the rotor stack111and the magnet130and, as the fixing member710is press-fitted into the through hole122, a fixing force may be provided simultaneously to the magnet130inserted in the magnet embedded hole121and the stacked rotor stacks111. Thus, the coupling process can be simplified. It should be noted that inFIG.9, the portion of the fixing member710protruding through the portion where the through hole122and the magnet embedding hole121communicate is exaggerated for convenience of Illustration and understanding.

Referring back toFIG.8, according to an embodiment of the present disclosure, the fixing member710may include a load member810including a body portion811inserted into the through hole122of the pole part120and a support812having a larger diameter than the body portion811at one end of the body portion811and supported by the magnet130. In other words, the load member810may include the body portion811and the support812, and the body portion811may be inserted or press-fitted into the through hole122of the pole part120. As the body portion811is inserted or press-fitted and fixed in the through hole122of the pole part120, the support812provided at one end of the body portion811is supported by the magnet130. It is illustrated in the drawings that a pair of through holes122are provided at one pole part120, and the load member810is inserted into each through hole122in the same axial direction. Alternatively, the two load members810may be inserted into the through holes122in different directions, the respective supports812of the load members810are supported on two axially opposite ends of the magnet130while axially fixing the magnet130. For instance, one of the supports812of the pair of load members810may be disposed on the upper surface of the pole part120, when the other of the supports812of the pair of load members810may be disposed on the lower surface of the pole part120. Further, the supports812of the load members810inserted into the through hole122in different directions may be supported by the rotor stack111as well as by the magnet130and be fixed to the stacked rotor stacks111.

According to an embodiment of the present disclosure, the fixing member710may further include a coupling member or coupler820supported by the magnet130and coupled to the other end of the body portion811which is an opposite end of the body portion811to an end of the body portion811where the support812is provided. In other words, the support812and the coupling member820may be provided on two opposite ends of the body portion811, respectively, and the support812and the coupling member820may be supported on two axially opposite sides of the magnet130inserted in the magnet embedded hole121, fixing the magnet130. Further, the support812and the coupling member820may be supported by the rotor stack111as well as the magnet130, fixing the stacked rotor stacks111.

According to an embodiment, the coupling member820may be press-fitted over the other end of the body portion811. In other words, after the load member810is inserted or press-fitted into the through hole122of the pole part120, the coupling member820may be press-fitted over the other end of the body portion811.

Therefore, the rotor core and the motor including the same according to some embodiments of the present disclosure described above can stably provide high output by increasing output torque and reducing torque ripples, simplify the process for stacking and coupling the magnet and the rotor, and reduce manufacturing costs.