Induction motor

Abstract

This induction motor (1) comprises a stator (2) and a rotor (3). The rotor (3) has a rotor core (3b). When the rotor core (3b) is divided into a central region (3j), two end regions (3k), and two transition regions (3m), the space factor of the central region (3j) is smaller than the space factor of the stator core (2b). The space factor of each end region (3k) is the same as the space factor of the stator core (2b). The space factor of each transition region (3m) is smaller than the space factor of the stator core (2b). The angle (θ1) of a skew (3h) in the central region (3j) is constant. The angle (θ2) of the skew (3h) in each end region (3k) is constant and is different from the angle (θ1) of the skew (3h) in the central region (3j). The angle (θ3) of the skew (3h) in each transition region (3m) changes so as to approximate the angle (θ1) of the skew (3h) in the central region (3j) from each end region (3k) toward the central region (3j).

Description

induction motor

[0001] The present disclosure relates to an induction motor having a rotor.

[0002] An induction motor includes a stator and a rotor disposed on the inner periphery of the stator. The rotor used in an induction motor includes a rotor core, which is a laminate of multiple steel plates, multiple conductors, and two short-circuit rings. The rotor core has multiple slots arranged in a circumferential direction. The rotor core has multiple skews, with each slot inclined relative to the axial direction. Each of the multiple conductors is disposed in each of the multiple slots. Two short-circuit rings are provided at both axial ends of the rotor core and connected to the conductors. In order to drive an induction motor with high motor efficiency, it is desirable to minimize the increase in magnetic resistance.

[0003] Patent Document 1 discloses a technique for improving the motor efficiency of an induction motor by increasing the lamination thickness of the rotor core compared to that of the stator core, thereby reducing the increase in magnetic resistance. In the technique disclosed in Patent Document 1, the number of steel plates in the stator core is the same as the number of steel plates in the rotor core, and the space factor of the rotor core is made smaller than that of the stator core, thereby making the lamination thickness of the rotor core larger than that of the stator core. A known method for making the space factor of the rotor core smaller than that of the stator core is to twist the rotor core after die casting.

[0004] JP 2011-211789 A

[0005] When twisting the rotor core after die-casting to make the space factor of the rotor core smaller than that of the stator core, as in Patent Document 1, it is common to locally twist the axial center portion of the rotor core. When the rotor core is twisted in this way, the skew angle changes in the axial center portion of the rotor core, but the skew angle does not change at both axial ends of the rotor core. As a result, stress concentrates in the conductor between the center portion, where the skew angle has changed due to the twisting, and the both ends, where the skew angle remains unchanged without twisting, resulting in a problem of reduced mechanical strength of the rotor core.

[0006] The present disclosure has been made in consideration of the above, and aims to provide an induction motor that can disperse stress generated in conductors and improve the mechanical strength of the rotor core.

[0007] In order to solve the above-mentioned problems and achieve the object, the induction motor according to the present disclosure includes a stator and a rotor arranged on the inner periphery of the stator with a gap between the stator and the stator. The stator has a stator core which is a laminate of multiple steel plates. The rotor has a rotor core which is a laminate of multiple steel plates and has multiple slots arranged in a circumferential direction, multiple conductors arranged in each of the multiple slots, and short-circuit rings provided at both axial ends of the rotor core and connected to each of the multiple conductors. The space factor of the rotor core is smaller than that of the stator core. The stack thickness of the rotor core is larger than that of the stator core. The rotor core has multiple skews in which each of the multiple slots is inclined with respect to the axial direction. When the rotor core is divided into a central region extending axially at the center of the rotor core in the axial direction, two end regions extending axially and located axially away from the central region, and two transition regions connecting adjacent central and end regions, the space factor of the central region is smaller than the space factor of the stator core. The space factor of each end region is the same as the space factor of the stator core. The space factor of each transition region is smaller than the space factor of the stator core. The skew angle in the central region is constant. The skew angle in each end region is constant and different from the skew angle in the central region. The skew angle in each transition region changes from each end region toward the central region so as to approach the skew angle in the central region.

[0008] The induction motor according to the present disclosure has the advantage of being able to disperse stress generated in the conductors and improve the mechanical strength of the rotor core.

[0009] 10A and 10B are cross-sectional views taken along line XI-XI of FIG. 10A and line XII-XII of FIG. 10A and line XIII-XIII of FIG. 10B;

[0010] An induction motor according to an embodiment will be described in detail below with reference to the drawings.

[0011] First Embodiment. FIG. 1 is a perspective view showing an induction motor 1 according to a first embodiment. FIG. 2 is a plan view showing the induction motor 1 according to the first embodiment. As shown in FIGS. 1 and 2 , the induction motor 1 includes a cylindrical stator 2 and a rotor 3 disposed on the inner periphery of the stator 2 with a gap between the stator 2 and the rotor 3. Although not shown, the induction motor 1 also includes a housing that accommodates the stator 2 and the rotor 3, a shaft provided at the center of the rotor 3, and other components. The induction motor 1 is mounted on a ventilation fan or the like and is driven by a single-phase AC power source (not shown). The rotor 3 is a squirrel-cage rotor. The rotor 3 rotates relative to the stator 2 about a rotation axis AX. Hereinafter, when describing the directions of the components of the induction motor 1, the direction parallel to the rotation axis AX is referred to as the axial direction, the direction perpendicular to the rotation axis AX is referred to as the radial direction, and the direction of rotation about the rotation axis AX is referred to as the circumferential direction.

[0012] As shown in FIG. 1 , the stator 2 has a stator core 2 b. The stator core 2 b is a laminate of multiple steel plates 2 a. The steel plates 2 a constituting the stator core 2 b are magnetic materials consisting of thin, generally annular plates. The multiple steel plates 2 a are stacked without gaps in the axial direction. Note that, in this specification, “laminated without gaps” does not mean that there is no insulating coating of several μm covering the surface of the steel plates, nor that there are no inter-lamination gaps of approximately 10 μm that inevitably occur between adjacent steel plates when the steel plates are stacked using a progressive die. It means that no non-magnetic portion is intentionally sandwiched between the laminates. The non-magnetic portion refers to, for example, a non-magnetic material, such as the inter-lamination gap 3 i described below. The multiple steel plates 2 a are fixed to each other by caulking, welding, adhesive, or the like.

[0013] The stator core 2b has a plurality of teeth 2c arranged in a line in the circumferential direction and a back yoke portion 2d connecting the plurality of teeth 2c at the outer periphery of each tooth 2c. The plurality of teeth 2c are arranged radially around the rotation axis AX. The plurality of teeth 2c are arranged at equal angles in the circumferential direction. A coil (not shown) is wound around each tooth 2c. The coil includes a main coil and an auxiliary coil. A capacitor (not shown) is connected in series to the auxiliary coil. Although not shown, the circuit of the auxiliary coil and capacitor and the circuit of the main coil are connected in parallel to a single-phase AC power supply. The back yoke portion 2d is formed in a cylindrical shape.

[0014] The rotor 3 has a rotor core 3b, a plurality of conductors 3c, and two short-circuit rings 3d. Note that in FIGS. 1 and 2, one of the short-circuit rings 3d is hidden by the rotor core 3b and is in an invisible position. The rotor core 3b is formed in a cylindrical shape. The rotor core 3b is a laminate of a plurality of steel plates 3a. The steel plates 3a constituting the rotor core 3b are magnetic bodies made of thin, annular plates. The plurality of steel plates 3a are laminated in the axial direction. Each of the plurality of steel plates 3a is fixed to one another by caulking, welding, adhesive, or the like. A through-hole 3e is formed in the center of the rotor core 3b, penetrating each steel plate 3a. A shaft (not shown) is inserted into the through-hole 3e.

[0015] FIG. 3 is a plan view showing the rotor 3 according to the first embodiment, illustrating a state in which the short-circuit ring 3d is not provided. FIG. 4 is a side view schematically illustrating the induction motor 1 according to the first embodiment. Note that in FIG. 3, each conductor 3c is hatched with dots to clearly indicate the range of each conductor 3c. In FIG. 4, the stator core 2b is omitted from the right side of the rotation axis AX to more clearly show the difference between the space factor of the stator core 2b and the space factor of the rotor core 3b. As shown in FIG. 3, the rotor core 3b has a plurality of slots 3f arranged in a circumferential direction. The plurality of slots 3f are spaced apart at equal angles in the circumferential direction. The plurality of slots 3f are arranged on the outer periphery of the rotor core 3b. Each slot 3f has a shape in which its circumferential width increases and then decreases as it extends radially outward from the rotation axis AX. As shown in FIG. 4, each slot 3f extends from one axial end to the other axial end of the rotor core 3b.

[0016] 3, the plurality of conductors 3c are arranged in the plurality of slots 3f, respectively. Each conductor 3c is made of a conductive metal material, such as aluminum or an aluminum alloy.

[0017] As shown in Fig. 4, two short-circuit rings 3d are annular members provided at both axial ends of the rotor core 3b and connected to the plurality of conductors 3c, respectively. One short-circuit ring 3d is provided at one axial end of the rotor core 3b. The other short-circuit ring 3d is provided at the other axial end of the rotor core 3b. Each short-circuit ring 3d is made of a conductive metal material. For example, each short-circuit ring 3d is made of aluminum or an aluminum alloy. The short-circuit rings 3d and the conductors 3c are integrally formed by die-casting. Note that the short-circuit rings 3d and the conductors 3c may also be integrally formed by brazing.

[0018] Next, the configurations of the stator core 2b and the rotor core 3b will be described in more detail with reference to FIGS.

[0019] As shown in Fig. 4, in this embodiment, the number of steel plates 2a in the stator core 2b and the number of steel plates 3a in the rotor core 3b are the same. In this embodiment, as an example, a case is illustrated in which the number of steel plates 2a in the stator core 2b and the number of steel plates 3a in the rotor core 3b are both 40. In the stator core 2b, 40 steel plates 2a are stacked with no gaps in the axial direction. In the rotor core 3b, 40 steel plates 3a are stacked in the axial direction. In the rotor core 3b, inter-laminar gaps 3i are formed between some of the steel plates 3a. The space factor of the rotor core 3b is smaller than that of the stator core 2b. The number of steel plates 2a in stator core 2b and the number of steel plates 3a in rotor core 3b are both 40, but because inter-laminar gaps 3i are partially formed in rotor core 3b, the space factor of rotor core 3b is smaller than the space factor of stator core 2b, and stack thickness T2 of rotor core 3b is larger than stack thickness T1 of stator core 2b.

[0020] As shown in Fig. 3, each steel plate 3a constituting the rotor core 3b has a plurality of holes 3g that respectively form a plurality of slots 3f. When viewed along the axial direction, the shapes of the steel plates 3a are the same. As shown in Fig. 4, the positions of the holes 3g in each stacked steel plate 3a are shifted in the circumferential direction. In the rotor core 3b, a plurality of skews 3h are formed in which the holes 3g of each steel plate 3a are connected so as to extend obliquely with respect to the axial direction. In other words, in the rotor core 3b, a plurality of skews 3h are formed in which each of the plurality of slots 3f is inclined with respect to the axial direction.

[0021] The rotor core 3b can be divided into five regions: a central region 3j extending in the axial direction at the center of the rotor core 3b in the axial direction, two end regions 3k extending in the axial direction and provided at positions spaced apart from the central region 3j along the axial direction, and two transition regions 3m connecting adjacent central regions 3j and end regions 3k.

[0022] The space factor of the central region 3j is smaller than that of the stator core 2b. In this embodiment, as an example, a case where the number of steel plates 3a in the central region 3j is 18 is illustrated. In the central region 3j, the 18 steel plates 3a are stacked with inter-laminar gaps 3i between them in the axial direction. The angle θ1 of the skew 3h in the central region 3j is constant over the entire axial length of the central region 3j. In this specification, the phrase "constant skew angle" has the same meaning as when a constant angle of skew is continuously applied using a progressive die, and means that the skew angle is not intentionally changed.

[0023] The space factor of each end region 3k is the same as the space factor of the stator core 2b. In this embodiment, as an example, the case where the number of steel plates 3a in each end region 3k is eight, i.e., the total number of steel plates 3a in the two end regions 3k is 16, is illustrated. In each end region 3k, the eight steel plates 3a are stacked without gaps between them in the axial direction. The angle θ2 of the skew 3h in one end region 3k is the same as the angle θ2 of the skew 3h in the other end region 3k. The angle θ2 of the skew 3h in each end region 3k is constant throughout the entire axial length of each end region 3k and is different from the angle θ1 of the skew 3h in the central region 3j. The angle θ1 of the skew 3h in the central region 3j is smaller than the angle θ2 of the skew 3h in the end region 3k. In order to make the lamination thickness T2 of the rotor core 3b significantly larger than the lamination thickness T1 of the stator core 2b, it is preferable that the angle difference between the angle θ1 of the skew 3h in the central region 3j and the angle θ2 of the skew 3h in the end region 3k be 1.0 degree or more.

[0024] The axial positions of both axial end portions 2 e, 2 f of the stator core 2 b and portions of the two end regions 3 k coincide with each other. The axial positions of one axial end portion 2 e of the stator core 2 b and portions of one end region 3 k coincide with each other. The axial positions of the other axial end portion 2 f of the stator core 2 b and portions of the other end region 3 k coincide with each other.

[0025] The space factor of each transition region 3m is smaller than the space factor of the stator core 2b. In this embodiment, as an example, the number of steel plates 3a in each transition region 3m is three, i.e., the total number of steel plates 3a in the two transition regions 3m is six. In each transition region 3m, three steel plates 3a are stacked axially with inter-lamination gaps 3i. Inter-lamination gaps 3i are also provided between the steel plates 3a located at the boundary between each transition region 3m and the central region 3j, and between the steel plates 3a located at the boundary between each transition region 3m and each edge region 3k. The angle θ3 of the skew 3h in each transition region 3m changes from each edge region 3k toward the central region 3j, approaching the angle θ1 of the skew 3h in the central region 3j. The angle θ3 of the skew 3h in each transition region 3m gradually decreases from each end region 3k toward the central region 3j so as to gently connect the skew 3h in each end region 3k and the skew 3h in the central region 3j.

[0026] Here, the inter-laminar gaps 3i will be described in more detail. The width W of each inter-laminar gap 3i in the central region 3j and the transition region 3m is larger than the thickness of the insulating coating, which is about several μm, covering the surface of the steel sheet 3a and the width of the inter-laminar gap, which is about 10 μm, that inevitably occurs between adjacent steel sheets 3a when the steel sheets 3a are laminated using a progressive die. The width W of each inter-laminar gap 3i in the central region 3j and the transition region 3m is smaller than the thickness of one steel sheet 3a. Although there is some variation, the width W of each inter-laminar gap 3i in the central region 3j and the transition region 3m is in the range of several tens of μm to several hundreds of μm. The rotor core 3b is a laminate in which non-magnetic portions larger than the thickness of one steel sheet 3a are not continuously laminated.

[0027] Here, an example will be described in which the thickness of each of the steel plates 2a, 3a shown in FIG. 4 is 1 mm. Because the total number of steel plates 3a in the central region 3j and the two transition regions 3m is 24, the total thickness of the steel plates 3a in the central region 3j and the two transition regions 3m is 24 mm. Because the total number of steel plates 3a in the two end regions 3k is 16, the total thickness of the steel plates 3a in the two end regions 3k is 16 mm. Hereinafter, the total thickness of the steel plates 3a in the two end regions 3k may also be referred to as the total stack thickness of the two end regions 3k. In the illustrated example, the difference between the stack thickness T1 of the stator core 2b and the stack thickness T2 of the rotor core 3b is 8 mm because there are eight steel plates 3a. The stack thickness T2 of the rotor core 3b is 24 mm + 16 mm + 8 mm = 48 mm. Of this 48 mm lamination thickness T2, excluding 16 mm, which is the total lamination thickness of the two end regions 3k without interlaminar gaps 3i, the lamination thickness is 32 mm. This 32 mm lamination thickness is the sum of the total sheet thickness of the steel plates 3a in the central region 3j and the two transition regions 3m and the total width W of each interlaminar gap 3i. Hereinafter, this lamination thickness may also be referred to as the total lamination thickness of the central region 3j and the two transition regions 3m. Therefore, the total width W of each interlaminar gap 3i is 32 mm - 24 mm = 8 mm. This 8 mm total width W of each interlaminar gap 3i is equal to the difference between the lamination thickness T1 of the stator core 2b and the lamination thickness T2 of the rotor core 3b. In this embodiment, the number of interlaminar gaps 3i is 25. In this embodiment, the average width W of the multiple interlaminar gaps 3i is 8 mm / 25 = 0.32 mm.

[0028] Next, a method for manufacturing the induction motor 1 according to this embodiment will be described with reference to Fig. 4. The method for manufacturing the rotor 3 according to this embodiment includes an assembly step, a die-casting step, a twisting step, and a post-processing step.

[0029] The assembly process is a process of assembling the rotor core 3b by stacking a plurality of stamped steel plates 3a.

[0030] The die-casting process is a process of forming the conductors 3c by casting a conductive metal material into the slots 3f of the assembled rotor core 3b. The die-casting process is carried out by a means commonly used in the technical field of rotor 3 manufacturing.

[0031] The twisting process involves locally twisting the axial center portion of the rotor core 3b, in which the conductors 3c are formed in the slots 3f, while pulling the rotor core 3b in the axial direction. In the twisting process, one axial end portion and the other axial end portion of the outer circumferential surface of the rotor core 3b are rotated in opposite directions around the rotation axis AX. Specifically, the one axial end portion and the other axial end portion of the outer circumferential surface of the rotor core 3b are chucked with jigs (not shown), and the one and the other jigs are rotated in opposite directions around the rotation axis AX. By performing the twisting process, a central region 3j and a transition region 3m, which have a smaller space factor than the stator core 2b, are formed between the two end regions 3k. Note that one jig may be fixed and only the other jig may be rotated around the rotation axis AX, or the other jig may be fixed and only one jig may be rotated around the rotation axis AX. The twisting process may also be performed using another conventionally known method. For example, a hole may be provided at the axial end of the rotor core 3b, and a twisting jig inserted into this hole may be twisted to form a rotor core 3b with a smaller space factor than the stator core 2b.

[0032] The post-processing step is a step of shrink-fitting a shaft onto the twisted rotor core 3 b and turning the rotor core 3 b. The post-processing step is performed by a means commonly used in the technical field of rotor 3 manufacturing.

[0033] The twisting step will now be described in more detail with reference to FIGS. 5 and 6 . FIG. 5 is a diagram illustrating the manufacturing method of the rotor 3 according to the first embodiment, and is a diagram schematically illustrating the state before the rotor core 3b is twisted. FIG. 6 is a diagram illustrating the manufacturing method of the rotor 3 according to the first embodiment, and is a diagram schematically illustrating the state after the rotor core 3b is twisted. FIGS. 5 and 6 are schematic views of half of the entire circumferential length of the rotor core 3b and the short-circuiting ring 3d, i.e., 180 degrees of the rotor core 3b and the short-circuiting ring 3d, unfolded. In FIGS. 5 and 6 , the region of the rotor core 3b excluding the end region 3k is referred to as a twist region 3n. The twist region 3n corresponds to the central region 3j and the transition region 3m formed after the twisting step.

[0034] The dashed-dotted line A in FIG. 5 schematically represents the state of the skew 3h in the twist region 3n before the twisting process. The dashed-two-dotted line B in FIG. 6 schematically represents the state of the skew 3h in the twist region 3n after the twisting process. In FIG. 5 , in order to easily understand the change in the angle of the skew 3h before and after the twisting process, the angle of the skew 3h in the end region 3k before the twisting process is illustrated as different from the angle of the skew 3h in the twist region 3n. Also, in FIG. 6 , in order to easily understand the change in the angle of the skew 3h before and after the twisting process, both the dashed-dotted line A and the dashed-two-dotted line B are shown. Here, the end of the skew 3h in the twist region 3n located at the boundary with the end region 3k on the lower side of the paper is referred to as one axial end 3o, and the end of the skew 3h in the twist region 3n located at the boundary with the end region 3k on the upper side of the paper is referred to as the other axial end 3p.

[0035] As shown in FIG. 6 , when the twisting process is performed, the skew 3 h in the twist region 3 n changes from the state shown by the dashed line A to the state shown by the dashed line B. Specifically, the skew 3 h in the twist region 3 n rotates around one axial end 3 o as a center so as to approach a position along the axial direction. The skew 3 h in the twist region 3 n rotates so that the other axial end 3 p traces an arc 4. That is, when the twisting process is performed, the angle of the skew 3 h in the twist region 3 n relative to the axial direction decreases while the length of the skew 3 h in the extension direction in the twist region 3 n remains unchanged. As a result, the axial length L2 of the skew 3 h in the twist region 3 n after the twisting process becomes longer than the axial length L1 of the skew 3 h in the twist region 3 n before the twisting process.

[0036] This increase in length, i.e., the difference between the axial length L2 and the axial length L1, is the increase L3 in the lamination thickness T2 of the rotor core 3b after the twisting process. As shown in FIGS. 5 and 6 , the number of steel sheets 3a is the same in the twisted region 3n before and after the twisting process. Therefore, the space factor of the twisted region 3n after the twisting process is smaller than that of the twisted region 3n before the twisting process by the increase L3 in the lamination thickness T2 of the rotor core 3b. Meanwhile, the space factor of the end region 3k remains unchanged before and after the twisting process. Therefore, the space factor of the rotor core 3b after the twisting process is smaller than that of the rotor core 3b before the twisting process. This results in the rotor core 3b shown in FIG. 4 . The increase L3 in the lamination thickness T2 of the rotor core 3b is equal to the total width W of the inter-laminar gaps 3i shown in FIG. 4 .

[0037] Next, the effects of the induction motor 1 according to this embodiment will be described.

[0038] First, the effects of the induction motor 1 according to this embodiment will be described in comparison with a comparative example. Fig. 7 is a side view schematically showing an induction motor 1B according to the comparative example. In Fig. 7, the stator core 2b on the right side of the rotation axis AX is not shown. For ease of explanation, the components of the induction motor 1B according to the comparative example will be described using the same reference numerals as those of the induction motor 1 according to this embodiment.

[0039] The common points between induction motor 1 according to this embodiment shown in Fig. 4 and induction motor 1B according to the comparative example shown in Fig. 7 are as follows: In other words, induction motor 1 according to this embodiment and induction motor 1B according to the comparative example have in common that the number of slots in stator 2 is 24, the number of slots in rotor 3 is 34, a single-phase AC power supply of 100V 50Hz is used, the lamination thickness T1 of stator core 2b is 40mm, the number of poles is 4, and the rotation speed is 750 r / min.

[0040] In contrast, the differences between the induction motor 1 according to this embodiment and the induction motor 1B according to the comparative example are as follows: In the rotor 3 according to the comparative example, the lamination thickness T2 of the rotor core 3b is 40 mm, and 40 steel plates 3a are stacked without gaps in the axial direction. In the rotor 3 according to the comparative example, the angle θ4 of the skew 3h is constant over the entire axial length, and the angle θ4 of the skew 3h is an angle equivalent to 2.0 slot pitches. In the rotor 3 according to the comparative example, the space factor of the stator core 2b and the space factor of the rotor core 3b are the same, and the lamination thickness T1 of the stator core 2b and the lamination thickness T2 of the rotor core 3b are the same.

[0041] On the other hand, in the rotor 3 according to this embodiment, the lamination thickness T2 of the rotor core 3b is 44 mm, and 40 steel plates 3a are laminated in the axial direction with partial interlaminar gaps 3i. Furthermore, in the rotor 3 according to this embodiment, the skew angles θ1, θ2, and θ3 are not constant throughout the entire axial length, and the average of the skew angles θ1, θ2, and θ3 is an angle equivalent to approximately 2.2 slot pitches. Specifically, the skew angle θ2 in each end region 3k is an angle equivalent to 3.195 slot pitches, and the skew angle θ1 in the central region 3j is an angle equivalent to 1.500 slot pitches. The skew angle θ3 in each transition region 3m changes from each end region 3k toward the central region 3j, approaching the skew angle θ1 in the central region 3j. Furthermore, in the rotor 3 according to this embodiment, the space factor of the central region 3j and each transition region 3m is smaller than that of the stator core 2b, and the lamination thickness T2 of the rotor core 3b is larger than the lamination thickness T1 of the stator core 2b. Specifically, the total lamination thickness of the two end regions 3k is 20 mm, and the total lamination thickness of the central region 3j and each transition region 3m is 24 mm. The lamination thickness T2 of the rotor core 3b according to this embodiment is 4 mm larger than the lamination thickness T1 of the stator core 2b by the amount of the inter-laminar gap 3i formed in the central region 3j and each transition region 3m. In other words, the lamination thickness T2 of the rotor core 3b according to this embodiment is 4 mm larger than that of the stator core 2b in the central region 3j and the two transition regions 3m. The space factor of 24 mm in the central region 3j and each transition region 3m is 20 mm / 24 mm (= 0.83) smaller than the space factor of the stator core 2b. Here, the dimensions of the lamination thickness T2 of the rotor core 3b, the total lamination thickness of the two end regions 3k, and the total lamination thickness of the central region 3j and the two transition regions 3m are made different from the above-mentioned numerical values.

[0042] FIG. 8 is a graph comparing the performance of the induction motor 1 according to the first embodiment with that of the induction motor 1B according to the comparative example. FIG. 8 shows the input power, output power, and primary copper loss of the induction motor 1 according to the present embodiment and the induction motor 1B according to the comparative example. In FIG. 8, the input power, output power, and primary copper loss of the induction motor 1B according to the comparative example are normalized to 100%. In this embodiment, the space factor of the rotor core 3b shown in FIG. 4 is smaller than that of the stator core 2b, and the lamination thickness T2 of the rotor core 3b is larger than the lamination thickness T1 of the stator core 2b. This reduces magnetic saturation at both axial ends 2e and 2f of the stator core 2b and at both axial ends of the rotor core 3b, thereby reducing the input current and magnetic resistance. As a result, as shown in FIG. 8, the input power and primary copper loss can be reduced compared to the comparative example. Specifically, compared to the comparative example, the input power including all losses is reduced to 98.9%, and the primary copper loss generated in the stator winding is reduced to 95.2%. Furthermore, the output of induction motor 1 according to this embodiment is 100.2%, which is equivalent to that of induction motor 1B according to the comparative example, so that the load on the ventilation fan on which induction motor 1 is mounted does not fluctuate, and motor efficiency can be improved.

[0043] In this embodiment, as shown in Fig. 4, the angle θ1 of the skew 3h in the central region 3j is constant. Also, in this embodiment, the angle θ2 of the skew 3h in each end region 3k is constant and is different from the angle θ1 of the skew 3h in the central region 3j. Also, in this embodiment, the angle θ3 of the skew 3h in each transition region 3m changes so as to approach the angle θ1 of the skew 3h in the central region 3j as it moves from each end region 3k toward the central region 3j. With this configuration, there are no locations in the rotor core 3b where the angles θ1, θ2, and θ3 of the skew 3h change abruptly, allowing stress generated in the conductors 3c to be dispersed. That is, the rotor core 3b has a transition region 3m that gently connects the skew 3h in each end region 3k with the skew 3h in the central region 3j, which can alleviate stress generated in the conductors 3c between the central region 3j, where the angle θ1 of the skew 3h changes due to twisting, and the end regions 3k, where the angle θ2 of the skew 3h does not change due to no twisting, thereby improving the mechanical strength of the rotor core 3b.

[0044] Patent Document 1 discloses a configuration in which short-circuit rings are sandwiched between adjacent steel plates, i.e., a configuration in which short-circuit rings are located at locations other than the axial ends of the rotor core. The configuration disclosed in Patent Document 1 presents the following problems: (1) When manufacturing a rotor in which at least one of the stack thickness of the rotor core and the axial thickness of the short-circuit ring is different, a dedicated die-casting mold is required each time, and replacing the mold takes a lot of time. (2) Because short-circuit rings located at locations other than the axial ends of the rotor core cannot be machined, it is difficult to adjust the input current and torque of an induction motor. (3) Because there is no rotor core, which is a magnetic body, radially facing the stator core at the locations of short-circuit rings located at locations other than the axial ends of the rotor core, local magnetic saturation occurs in the stator core. This problem results in a local increase in magnetic reluctance, which makes it easier for the input current to increase, and an increase in magnetic flux density, which makes it easier for vibration and noise to worsen.

[0045] In this regard, in this embodiment, as shown in Figure 4, there are no short-circuit rings 3d except at the axial ends of the rotor core 3b, so the rotor 3 can be manufactured by performing the twisting process described above after die casting. Therefore, even when manufacturing rotors 3 in which at least one of the laminate thickness T2 of the rotor core 3b and the axial thickness of the short-circuit rings 3d is different, a dedicated die-casting mold is not required each time, and mold replacement is also not required. Therefore, the occurrence of the above problem (1) can be suppressed.

[0046] Furthermore, in this embodiment, since there are no short-circuit rings 3d other than at the axial ends of the rotor core 3b, the short-circuit rings 3d at the axial ends of the rotor core 3b can be cut to reduce the cross-sectional area of ​​the short-circuit rings 3d. Therefore, by increasing the electrical resistance of the short-circuit rings 3d, it becomes easier to adjust the input current and torque of the induction motor 1. This makes it possible to prevent the occurrence of problem (2) above.

[0047] Furthermore, in this embodiment, since there are no short-circuit rings 3d except at the axial ends of the rotor core 3b, the area of ​​the rotor core 3b radially facing the stator core 2b is larger than in the configuration disclosed in Patent Document 1. This makes it possible to suppress local magnetic saturation in the stator core 2b. This makes it possible to suppress local increases in magnetic reluctance and thus suppress increases in input current, and to suppress increases in magnetic flux density and thus suppress deterioration of vibration and noise. Therefore, the occurrence of the problem (3) above can be suppressed.

[0048] In this embodiment, as shown in FIG. 4 , the angle θ1 of the skew 3h in the central region 3j is smaller than the angle θ2 of the skew 3h in the end region 3k. This configuration makes it possible to set the angle θ1 of the skew 3h in the central region 3j the same as the skew angle of a conventionally known rotor core, or to set the average of the angles θ1, θ2, and θ3 of the skew 3h in the central region 3j, end region 3k, and transition region 3m the same as the skew angle of a conventionally known rotor core. That is, in this embodiment, even if the space factor of the rotor core 3b is made smaller than the space factor of the stator core 2b and the lamination thickness T2 of the rotor core 3b is made larger than the lamination thickness T1 of the stator core 2b, the angles θ1, θ2, and θ3 of the skew 3h of the rotor core 3b can be the same as or close to the skew angles of a conventionally known rotor core. This allows the input power of the induction motor 1 to be reduced while maintaining the torque performance, vibration, and noise of the induction motor 1 at the same level as compared with conventionally known rotor cores.

[0049] In this embodiment, as shown in FIG. 4 , the axial positions of the axially opposite end portions 2e, 2f of the stator core 2b and portions of the two end regions 3k coincide with each other. When assembling the stator 2 and the rotor 3 to produce the induction motor 1, axial misalignment between the stator 2 and the rotor 3 may occur due to assembly errors. Even in such cases, in this embodiment, due to the above-described configuration, each of the axially opposite end portions 2e, 2f of the stator core 2b faces a portion of the end region 3k having the same skew angle θ2 in the radial direction. This balances the magnetic reluctance at each of the axially opposite end portions 2e, 2f of the stator core 2b. Therefore, even if axial misalignment between the stator 2 and the rotor 3 occurs due to assembly errors, deterioration of noise and vibration can be suppressed.

[0050] Next, a modification of the first embodiment will be described.

[0051] In this embodiment, the angle of skew 3h in end region 3k before the twisting process is different from the angle of skew 3h in twist region 3n before the twisting process, as shown in Figure 5, but the two angles may be the same. In this way, the steel sheets 3a of rotor core 3b can be stacked while keeping the angle of skew 3h constant in the progressive die that stacks the steel sheets 3a, and there is no need to deliberately change the punching speed, etc., which improves manufacturing efficiency when manufacturing rotor 3.

[0052] 4, the number of steel plates 2a in stator core 2b and the number of steel plates 3a in rotor core 3b are the same, but the number of steel plates 2a in stator core 2b and the number of steel plates 3a in rotor core 3b may be different. That is, as long as it is possible to make the space factor of rotor core 3b smaller than the space factor of stator core 2b and make the lamination thickness T2 of rotor core 3b larger than the lamination thickness T1 of stator core 2b, the number of steel plates 2a in stator core 2b and the number of steel plates 3a in rotor core 3b may be different.

[0053] In this embodiment, as shown in FIG. 4 , the axial positions of the axial ends 2 e, 2 f of the stator core 2 b and portions of the two end regions 3 k coincide with each other, but this is not limited to the illustrated example. For example, the configuration shown in FIG. 9 may be used. FIG. 9 is a side view schematically illustrating an induction motor 1 according to a modified example of the first embodiment. In FIG. 9 , the stator core 2 b is not illustrated to the right of the rotation axis AX. The dashed-dotted line C shown in FIG. 9 is a straight line perpendicular to the axial direction that passes through one axial end 2 e of the stator core 2 b. The dashed-dotted line D shown in FIG. 9 is a straight line perpendicular to the axial direction that passes through the other axial end 2 f of the stator core 2 b. The one axial end 2 e of the stator core 2 b and portions of one end region 3 k coincide with each other in the axial direction. The other axial end 2 f of the stator core 2 b and the other end region 3 k are misaligned in the axial direction. The other axial end 2f of the stator core 2b coincides in position with a part of the other transition region 3m in the axial direction.

[0054] Second Embodiment Next, an induction motor 1A according to a second embodiment will be described with reference to FIGS. 10 to 13. FIG. 10 is a side view schematically illustrating the induction motor 1A according to the second embodiment. FIG. 11 is a cross-sectional view taken along line XI-XI in FIG. 10. FIG. 12 is a cross-sectional view taken along line XII-XII in FIG. 10. FIG. 13 is a cross-sectional view taken along line XIII-XIII in FIG. 10. In FIG. 10, the stator core 2b is omitted from the illustration to the right of the rotation axis AX. In FIGS. 11 to 13, the cross section of the stator 2 is omitted. In FIGS. 11 to 13, each conductor 3c is hatched with dots to clearly indicate the extent of each conductor 3c. This embodiment differs from the first embodiment in that the central region 3j, end region 3k, and transition region 3m all have the same cross-sectional shape. In the second embodiment, parts that overlap with those in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0055] As shown in Figures 10 to 13, the cross-sectional shapes of the central region 3j, the edge region 3k, and the transition region 3m when cut in a direction perpendicular to the axial direction are the same. Note that when the multiple steel plates 3a constituting the central region 3j, the edge region 3k, and the transition region 3m are fixed by crimping, the crimping shape differs between the first steel plate 3a in the stacking order and the second and subsequent steel plates 3a. Therefore, the phrase "same cross-sectional shape" here means that the shapes are the same excluding the crimping shape. The "cross-sectional shape" includes the shapes of the holes 3g constituting the slots 3f, as well as the shapes of the lightening holes, positioning holes, and flux barriers.

[0056] Next, the effects of the induction motor 1A according to this embodiment will be described.

[0057] This embodiment can achieve the same effects as the first embodiment. Furthermore, in this embodiment, as shown in Figures 11 to 13, the central region 3j, the end regions 3k, and the transition region 3m have the same cross-sectional shape when cut in a direction perpendicular to the axial direction. With this configuration, when stacking the steel sheets 3a using a progressive die, it is not necessary to provide a swinging portion in accordance with the angle of the skew 3h, which makes it easier to manufacture the rotor core 3b.

[0058] Another method for twisting the rotor core 3b after die casting to reduce the space factor of the rotor core 3b compared to the space factor of the stator core 2b is, for example, to twist a twisting jig inserted into a hole provided at the axial end of the rotor core 3b. This method requires adjusting the position of the hole to match the angle of the skew 3h when punching the steel plate 3a, which complicates the manufacturing of the rotor core 3b. In contrast, in the present embodiment, the above-described configuration allows the rotor core 3b to be twisted by chucking both axial ends of the outer circumferential surface of the rotor core 3b with a jig, thereby forming the central region 3j and the transition region 3m and easily reducing the space factor of the rotor core 3b. In other words, in this embodiment, there is no need to provide a hole for inserting a twisting jig at the axial end of the rotor core 3b or to adjust the position of the hole to match the angle of the skew 3h when punching the steel plate 3a, which simplifies the manufacturing of the rotor core 3b.

[0059] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0060] 1, 1A, 1B induction motor, 2 stator, 2a, 3a steel plate, 2b stator core, 2c teeth, 2d back yoke, 2e, 2f end, 3 rotor, 3b rotor core, 3c conductor, 3d short ring, 3e through hole, 3f slot, 3g hole, 3h skew, 3i gap between laminations, 3j Central region, 3k end region, 3m transition region, 3n twist region, 3o one end, 3p other end, 4 arc.

Claims

1. A magnetic coil comprising: a stator; and a rotor arranged on an inner circumference of the stator with a gap between it and the stator, wherein the stator has a stator core which is a laminate of a plurality of steel plates, and the rotor has a rotor core which is a laminate of a plurality of steel plates and has a plurality of slots arranged in a line in the circumferential direction, a plurality of conductors arranged in each of the slots, and a short-circuit ring provided at each of both axial ends of the rotor core and connected to each of the plurality of conductors, wherein the space factor of the rotor core is smaller than the space factor of the stator core, the stacking thickness of the rotor core is larger than the stacking thickness of the stator core, and the rotor core has a plurality of skews formed such that each of the plurality of slots is inclined with respect to the axial direction, an induction motor comprising: a central region extending in the axial direction at the center of the rotor core in the axial direction; two end regions extending in the axial direction and located away from the central region along the axial direction; and two transition regions connecting adjacent central and end regions; wherein the space factor of the central region is smaller than the space factor of the stator core; the space factor of each of the end regions is the same as the space factor of the stator core; the space factor of each of the transition regions is smaller than the space factor of the stator core; the angle of skew in the central region is constant; the angle of skew in each of the end regions is constant and different from the angle of skew in the central region; and the angle of skew in each of the transition regions changes so as to approach the angle of skew in the central region as it moves from each of the end regions toward the central region.

2. The induction motor according to claim 1, characterized in that the axial positions of both ends of the stator core and parts of each of the two end regions are aligned in the axial direction.

3. An induction motor as claimed in claim 1 or 2, characterized in that the angle of skew in the central region is smaller than the angle of skew in the end regions.

4. An induction motor as claimed in any one of claims 1 to 3, characterized in that the cross-sectional shapes of the central region, the end regions and the transition region when cut in a direction perpendicular to the axial direction are the same.

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