Rotor

Abstract

To provide a rotor capable of increasing the nut holding torque compared to conventional rotors when forming slits in the rotor core to reduce the surface pressure or relieve stress between the rotor core and the rotating shaft.SOLUTION: The rotor includes: a rotor core 2; a rotating shaft inserted into the shaft hole 21 of the rotor core 2; and a nut 4 that fastens the rotating shaft to the rotor core 2. The rotor core 2 has slits 23 that are formed for reducing the surface pressure or relieving stress between the rotor core 2 and the rotating shaft on the inner side of the equivalent friction diameter d_w of the bearing surface 41 of the nut 4.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a rotor. [Background technology]

[0002] BACKGROUND ART Conventionally, there are known inventions relating to rotors of embedded magnet type rotating electrical machines in which permanent magnets are embedded in a rotor core (for example, Patent Document 1 listed below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-143128 Summary of the Invention [Problem to be solved by the invention]

[0004] The rotor core constituting the rotor described in Patent Document 1 has multiple stress relief slits on the circumference at a position closer to the rotation axis than the area where multiple pairs of rotor slots are provided circumferentially, which is the same area where tensile stress occurs. This makes it possible to suppress stress concentration at the innermost ends of the rotor slots.

[0005] However, in the rotor described in Patent Document 1, the stress relief slits are located closer to the rotor core's rotational axis, which may cause the stress relief slits to interfere with the seating surface of the nut that fastens the rotor core to the rotational axis. As a result, the contact area between the nut seating surface and the rotor core decreases, reducing the frictional force between them and potentially reducing the nut's holding torque (fixing force).

[0006] The present disclosure provides a rotor that can increase the nut holding torque compared to conventional rotors when a slit is provided in the rotor core to reduce surface pressure or relieve stress between the rotor core and the rotating shaft. [Means for solving the problem]

[0007] One aspect of the present disclosure provides a rotor comprising a rotor core, a rotating shaft inserted into an axial hole of the rotor core, and a nut fastening the rotating shaft to the rotor core, wherein the rotor core has a slit provided on the inner side of the equivalent friction diameter of the seating surface of the nut for reducing surface pressure or alleviating stress between the rotor core and the rotating shaft. [Effects of the Invention]

[0008] According to the above aspects of the present disclosure, when a slit is provided in the rotor core to reduce the surface pressure or relieve stress between the rotor core and the rotating shaft, a rotor can be provided that can increase the nut holding torque compared to conventional rotors. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view illustrating an embodiment of a rotor according to the present disclosure. [Figure 2] 2 is a plan view of a rotor core that constitutes the rotor shown in FIG. 1 and an enlarged view of the vicinity of a shaft hole. [Figure 3] 2 is an explanatory diagram of the relationship between the retaining torque and axial force of the nut of the rotor shown in FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the invention will be described with reference to the drawings.

[0011] 1 is a schematic cross-sectional view showing an embodiment of a rotor according to the present disclosure. The rotor 1 of this embodiment is a rotor with embedded permanent magnets that, together with a stator (not shown), constitutes a motor mounted in an automobile such as a hybrid automobile or an electric automobile. The rotor 1 includes, for example, a rotor core 2, a rotating shaft 3, and a nut 4.

[0012] The rotor core 2 has, for example, a cylindrical shape with a shaft hole 21 provided in the center for inserting the rotating shaft 3. The rotor core 2 is made of, for example, a plurality of electromagnetic steel plates stacked in the axial direction.

[0013] The rotating shaft 3 is, for example, a shaft that is inserted into the axial hole 21 of the rotor core 2 and fixed to the rotor core 2, and rotates around the central axis together with the rotor core 2. The rotating shaft 3 is fixed to the axial hole 21 of the rotor core 2 by, for example, press fitting or interference fitting.

[0014] The nut 4 is fastened to the rotating shaft 3, for example, by screwing an internal thread provided on the inner circumference of the nut 4 into an external thread provided on the outer circumference of the rotating shaft 3, and holds the rotor core 2 between itself and the flange portion 31 of the rotating shaft 3.

[0015] With the nut 4 fastened to the rotating shaft 3, an axial force F acts on both axial end surfaces of the cylindrical rotor core 2 from the seating surface 41 of the nut 4 and the flange portion 31 of the rotating shaft 3 in a direction compressing the rotor core 2 in the axial direction. In addition, a frictional force corresponding to the axial force F acts on a contact surface CF1 between the seating surface 41 of the nut 4 and one end surface of the rotor core 2, and on a contact surface CF2 between the flange portion 31 of the rotating shaft 3 and the other end surface of the rotor core 2.

[0016] 2 is a plan view of one axial end face of rotor core 2 constituting rotor 1 shown in Fig. 1, and an enlarged view of part A near axial hole 21 of rotor core 2. Note that in the enlarged view of part A of rotor core 2 shown in Fig. 2, nuts 4 arranged on the end face of rotor core 2 are shown in a see-through state, and the area corresponding to bearing surface 41 of nut 4 is hatched with dots.

[0017] 2, the rotor core 2 is provided with a plurality of slots 22 for inserting permanent magnets and a plurality of slits 23. The plurality of slits 23 are provided, for example, to reduce the surface pressure when the rotating shaft 3 is press-fitted into the shaft hole 21 of the rotor core 2, or to relieve stress when the rotating shaft 3 is shrink-fitted (interference-fitted) into the shaft hole 21.

[0018] As described above, the rotor 1 of this embodiment includes the rotor core 2, the rotating shaft 3 inserted into the axial hole 21 of the rotor core 2, and the nut 4 that fastens the rotating shaft 3 to the rotor core 2. The rotor core 2 is provided with a slit 23 for reducing the surface pressure or alleviating stress between the rotor core 2 and the rotating shaft 3, on the inner peripheral side of the equivalent friction diameter d_w of the bearing surface 41 of the nut 4.

[0019] With this configuration, the final equivalent friction diameter d_wslit, which takes into consideration the reduction in the contact area between the end face of the rotor core 2 and the seating surface 41 of the nut 4 due to the formation of the slits 23, can be made larger than the original equivalent friction diameter d_w. In this way, the equivalent friction diameter d_wslit in a state where the slits 23 are formed is larger than the original equivalent friction diameter d_w, so that the holding torque T_hold of the nut 4 can be increased compared to a state where the slits 23 are not formed.

[0020] That is, when the axial force F is the same, the friction force between the end face of the rotor core 2 and the seating surface 41 of the nut 4 can be increased when the slits 23 are formed compared to when the slits 23 are not formed. As a result, the rotor 1 of this embodiment can improve the robustness of the fixing force achieved by fastening the nut 4 while enjoying the effect of reducing the surface pressure or stress due to the slits 23.

[0021] The relationship between the holding torque T_hold by the nut 4 and the axial force F will be explained below with reference to Fig. 3. Fig. 3 is an explanatory diagram of the relationship between the holding torque T_hold by the nut 4 of the rotor 1 shown in Fig. 1 and the axial force F. The relationship between the holding torque T_hold and the axial force F can be expressed, for example, by the following equation (1). In the following equation (1), the nut bearing surface friction coefficient μ_wn and the flange surface friction coefficient μ_wf are physical properties and are constant regardless of the presence or absence of the slit 23.

[0022]

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[0023] As described above, in the rotor 1 of this embodiment, by arranging the slits 23 inside the equivalent friction diameter d_w of the nut 4, the equivalent friction diameter d_wslit in the state in which the slits 23 are formed becomes larger than the original equivalent friction diameter d_w. As a result, the holding torque T_hold (fixing force) of the nut 4 increases for the same axial force F.

[0024] 3A and 3B show the assumptions for the calculation and a conceptual diagram of the modeling. The rotor core 2 has multiple slits 23 spaced apart in the circumferential direction. Here, as shown in FIG. 3B, it is assumed that the total length of each slit 23 along the circumferential direction of the rotor core 2 corresponds to half the length of the nut 4. Note that the total length of each slit 23 may be longer than half the length of the rotor core 2.

[0025] According to the formula for friction torque (≒ friction coefficient × surface pressure × area × radius), the holding torque T_slit of the nut 4 is (torque applied to the seating surface 41 of the nut 4) - (torque due to the reduction in contact area at the slit 23), as shown in the following formula (2).

[0026]

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[0027] Furthermore, when a slit 23 is provided in the rotor core 2 (hereinafter referred to as "when a slit is provided"), the contact area S_slit between the end face of the rotor core 2 and the seat surface 41 of the nut 4 can be expressed by the following equation (3).

[0028]

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[0029] On the other hand, from the general formula for fastening design, the relationship between the axial force F and the holding torque T_hold is expressed by the following formula (4).

[0030]

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[0031] The symbols used in each formula are listed in Table 1 below.

[0032] [Table 1]

[0033] Next, the calculation of the equivalent friction diameter d_wslit when there is a slit will be explained. The holding torque T_slit when there is a slit is expressed by the following equation (5).

[0034]

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[0035] In equation (5), the total friction coefficient μ is constant due to its physical properties. In addition, when the surface pressure P_slit due to the axial force F in the case of the slit is considered to be constant regardless of whether the slit 23 is present or not, and the influence of the slit 23 is considered to be minimal, both can be taken outside the integral as shown in the following equation (6).

[0036]

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[0037] If we define the expression in the curly brackets in equation (6) as Aslit and calculate Aslit, we get the following equation (7).

[0038]

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[0039] On the other hand, from the fastening equation, the relationship between the axial force F and the holding torque T_slit is expressed by the following equation (8): Also, the axial force F is the product of the surface pressure P_slit and the contact area S_slit, as shown in the following equation (9).

[0040]

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[0041]

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[0042] Therefore, from equation (6)=equation (8), the following equation (10) is obtained, and by rearranging equation (10), the following equation (11) is obtained.

[0043]

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[0044]

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[0045] Furthermore, by substituting the contact area S_slit of equation (3) and Aslit of equation (7) into the right side of equation (11), the following equation (12) is obtained.

[0046]

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[0047] From the above, by arranging the slits 23 so that the equivalent friction diameter d_wslit in equation (12) is smaller than the equivalent friction diameter d_w, that is, by arranging the slits 23 more inward than the equivalent friction diameter d_w, the equivalent friction diameter d_wslit > the equivalent friction diameter d_w. Therefore, from the above equation (1), which is the basic equation for screw fastening, it can be seen that when the axial force F is the same, the holding torque T_hold (fixing force) of the nut 4 is greater when the rotor core 2 is provided with slits 23 than when the rotor core 2 is not provided with slits 23.

[0048] As described above, according to this embodiment, when slits 23 for reducing the surface pressure or relieving stress between the rotor core 2 and the rotating shaft 3 are provided in the rotor core 2, a rotor 1 can be provided that can increase the holding torque T_hold of the nut 4 compared to conventional rotors.

[0049] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments. Various modifications or substitutions can be applied to the above-described embodiments without departing from the scope of the present invention. [Explanation of symbols]

[0050] 1: rotor, 2: rotor core, 21: shaft hole, 23: slit, 3: rotating shaft, 4: nut, 41: bearing surface, d_w: equivalent friction diameter.

Claims

[Claim 1] A rotor including a rotor core, a rotating shaft inserted into a shaft hole of the rotor core, and a nut fastening the rotating shaft to the rotor core, The rotor core has a slit formed on the inner circumferential side of the equivalent friction diameter of the seating surface of the nut for reducing the surface pressure or alleviating stress between the rotor core and the rotating shaft.

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