Eddy current reduction gear

Abstract

The eddy current speed reducer (100) comprises a rotor (10) and a stator (20). The rotor (10) comprises a hub (12), a rotor body (11) and spokes (13). The spokes (13) have neutral axes (N1, N2). The neutral axis (N1) is the neutral axis when the spokes (13) are bent in the circumferential direction of the rotor body (11). The neutral axis (N1) is located forward of the center line (C1) of the spokes (13) in the circumferential direction in the rotation direction (R) of the rotor (10). The neutral axis (N2) is the neutral axis when the spokes (13) are bent in the axial direction of the rotor body (11). The neutral axis (N2) is located closer to the rotor body (11) than the center line (C2) of the spokes (13) in the axial direction.

Description

Technical Field

[0001] The present disclosure relates to an eddy current type speed reduction device. Background Art

[0002] Eddy current reduction gears have been used as auxiliary brakes for large vehicles such as trucks and buses. For example, as disclosed in Patent Document 1, an eddy current reduction gear comprises a rotor fixed to the vehicle's rotating shaft and a stator fixed to the vehicle's non-rotating portion. The rotor includes a hub mounted on the rotating shaft and a rotor body, which is a cylindrical conductor. One axial end of the rotor body is connected to the hub via a plurality of spokes. The stator holds a plurality of magnets arranged circumferentially on the inside of the rotor body.

[0003] The rotor of an eddy-current speed reducer rotates along with the vehicle's rotating shaft, subjecting it to air resistance. Patent Document 2 addresses the cross-sectional shape of the spokes connecting the rotor body to the wheel hub to reduce this air resistance. More specifically, Patent Document 2 describes a spoke cross-sectional shape in which the axial length of the rotor body is significantly smaller than its circumferential length. According to Patent Document 2, this cross-sectional shape flattens at least a portion of the spoke, thereby reducing air resistance during rotor rotation.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-78425

[0007] Patent Document 2: Japanese Patent Application No. 2013-521749 Summary of the Invention

[0008] Problems that the invention will solve

[0009] When the eddy current reduction gear is engaged (braking), the rotor body, a conductor, rotates within the magnetic field generated by the array of magnets, generating eddy currents within the rotor body. The interaction between these eddy currents and the magnetic field generates a braking force in the rotor body that is directed opposite to the direction of rotation. At this point, a bending load in the circumferential direction of the rotor body is applied to each spoke fixed to the rotor body. In other words, the braking force in the opposite direction of rotation acts on the rotor body, applying a bending load in the opposite direction of rotation to each spoke. This causes each spoke to bend, with the front portion in the direction of rotation extending and the rear portion contracting.

[0010] On the other hand, when the eddy current reduction gear is disengaged (non-braking state), the rotor body is not subject to a magnetic field, and no braking force is generated. Therefore, the spokes are not subjected to circumferential bending loads from the rotor body. Repeated switching between the braking and non-braking states repeatedly applies circumferential bending loads to the spokes.

[0011] Furthermore, when the eddy current reduction gear is in a braking state, Joule heat is generated in the rotor body through which the eddy current flows, causing the rotor body to heat up. Consequently, the rotor body thermally expands and expands in diameter. At this time, deformation is restricted at one axial end of the rotor body due to the spokes being fixed thereto. On the other hand, the other axial end of the rotor body is free from spokes and can deform freely. Consequently, the diameter of the end on the opposite side of the rotor body is larger than the diameter of the end on the spoke side. As a result, each spoke is subjected to an axial bending load in the rotor body. Each spoke bends, with the portion on the rotor body side extending and the portion on the opposite side contracting.

[0012] When the eddy-current reduction gear is switched from a braking state to a non-braking state, the rotor body's temperature decreases, causing it to contract and return to its original shape. Consequently, the spokes are no longer subjected to axial bending loads from the rotor body. Repeated switching between the braking and non-braking states repeatedly applies axial bending loads to the spokes.

[0013] In this manner, the spokes are repeatedly subjected to bending loads in both the circumferential and axial directions of the rotor body. However, conventional eddy current reduction gears, such as those exemplified in Patent Documents 1 and 2, do not specifically consider the circumferential and axial bending loads acting on the spokes. From the perspective of the durability of eddy current reduction gears, it is desirable to suppress fatigue damage to the spokes by considering both the circumferential and axial bending loads acting on the spokes.

[0014] An object of the present disclosure is to improve the durability of an eddy current reduction gear by suppressing fatigue damage to a spoke.

[0015] Means for solving problems

[0016] The eddy current reduction gear disclosed herein comprises a rotor and a stator. The rotor includes a hub, a rotor body, and spokes. The hub is mounted on a rotating shaft. The rotor body has a cylindrical shape. The spokes extend from the hub toward the rotor body and are fixed to one axial end of the rotor body. The rotor rotates together with the rotating shaft. The stator is arranged on the inner side or the outer side of the rotor body. The spokes have a first neutral axis and a second neutral axis. The first neutral axis is the neutral axis when the spokes are bent along the circumferential direction of the rotor body. The first neutral axis is located forward of the center line of the spokes in the circumferential direction in the direction of rotation of the rotor. The second neutral axis is the neutral axis when the spokes are bent along the axial direction of the rotor body. The second neutral axis is located closer to the rotor body than the center line of the spokes in the axial direction.

[0017] Effects of the Invention

[0018] According to the present disclosure, fatigue damage of the spoke can be suppressed, thereby improving the durability of the eddy current speed reducer. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a cross-sectional view showing a schematic configuration of an eddy current speed reducer according to an embodiment.

[0020] Figure 2 This is another cross-sectional view schematically showing the configuration of the eddy current speed reducer according to the embodiment.

[0021] Figure 3 Viewed from the spoke side Figure 1 as well as Figure 2 A diagram of a rotor included in an eddy current reduction gear is shown.

[0022] Figure 4A This is an example that can be used as Figure 3 The cross-sectional shape of the rotor spokes is shown in the figure.

[0023] Figure 4B This is an example that can be used as Figure 3 The cross-sectional shape of the rotor spokes is shown in the figure.

[0024] Figure 4C This is an example that can be used as Figure 3 The cross-sectional shape of the rotor spokes is shown in the figure.

[0025] Figure 4D This is an example that can be used as Figure 3 The cross-sectional shape of the rotor spokes is shown in the figure.

[0026] Figure 4E This is an example that can be used as Figure 3 The cross-sectional shape of the rotor spokes is shown in the figure.

[0027] Figure 4F This is an example that can be used as Figure 3 The cross-sectional shape of the rotor spokes is shown in the figure.

[0028] Figure 5 Is used to illustrate Figure 1 as well as Figure 2 Schematic diagram of the braking state of the eddy current reduction gear shown.

[0029] Figure 6 Is used to illustrate Figure 1 as well as Figure 2 Schematic diagram of the non-braking state of the eddy current reduction gear shown.

[0030] Figure 7A This is a diagram illustrating the cross-sectional shape of a conventional spoke.

[0031] Figure 7B This is a diagram illustrating the cross-sectional shape of a conventional spoke.

[0032] Figure 7C This is a diagram illustrating the cross-sectional shape of a conventional spoke.

[0033] Figure 8 This is a schematic diagram for explaining the circumferential bending load applied to the spokes in the rotor of the eddy current speed reducer.

[0034] Figure 9 This is a schematic diagram for explaining the axial bending load applied to the spokes in the rotor of the eddy current speed reducer. DETAILED DESCRIPTION

[0035] As described above, when the eddy current speed reducer is in the braking state, the spokes connecting the rotor body and the hub are subjected to bending loads in the circumferential and axial directions of the rotor body. Figure 8 as well as Figure 9 This is a schematic diagram for explaining the bending load applied to the spokes in the rotor of the eddy current speed reducer.

[0036] like Figure 8 As shown in FIG. 1 , in the rotor 90 of the eddy current reduction gear, when a braking force F in the direction opposite to the rotational direction R is generated on the rotor body 91, a bending load P1 in the circumferential direction of the rotor body 91 is applied to the spokes 93 connecting the rotor body 91 to the hub 92. The bending load P1 causes the spokes 93 to bend in the direction opposite to the rotational direction R. Therefore, a tensile stress σ is generated in the front portion of the spokes 93 in the rotational direction R of the rotor body 91. t1 , compressive stress σ is generated in the rear part c1 .

[0037] On the other hand, Figure 9 As shown by the two-dot chain line in the middle, when the rotor body 91 thermally expands and the end portion of the rotor body 91 opposite to the spoke 93 expands relatively in diameter, a bending load P2 in the axial direction of the rotor body 91 is applied to the spoke 93. Due to the bending load P2, the spoke 93 bends in the axial direction toward the side opposite to the rotor body 91. Therefore, a tensile stress σ is generated in the portion of the spoke 93 on the rotor body 91 side. t2 , a compressive stress σ is generated in the portion on the side opposite to the rotor body 91 c2 If the eddy current speed reducer is switched from the braking state to the non-braking state, the bending loads P1, P2 and the stress σ t1 , σ t2 , σ c1 , σ c2 be removed.

[0038] In this way, in the spoke, only tensile stress is repeatedly generated in a certain portion, and only compressive stress is repeatedly generated in other portions. In other words, the spoke is subjected to fatigue load under so-called pulsation conditions.

[0039] When a material is subjected to a fatigue load under pulsating conditions, the fatigue life of the material is shortened when the fatigue load is tensile stress compared to when the fatigue load is compressive stress, even if the absolute values ​​of the stresses are the same. For example, in areas of the material where only tensile stress is repeatedly generated, cracks are more likely to form and grow. In contrast, in areas where only compressive stress is repeatedly generated, cracks are less likely to form and grow. Therefore, the present inventors focused on tensile stress and developed spoke shapes that could reduce tensile stress even when compressive stress is increased.

[0040] When a rod-shaped component such as a spoke bends, tensile stress is generated within the component in areas that stretch due to the bending, and compressive stress is generated in areas that contract due to the bending. A neutral plane exists between these areas, where there is no stretching. The intersection of this neutral plane and a cross-section of the component perpendicular to it is called the neutral axis. The greater the distance from the neutral axis, the greater the stress generated when the component bends. Therefore, when the spoke bends circumferentially around the rotor body due to the braking force generated by the rotor body, the farther the spoke moves forward from the neutral axis of the circumferential bending in the direction of rotation of the rotor, the greater the tensile stress, and the farther it moves rearward from the neutral axis of the circumferential bending, the greater the compressive stress. To reduce the maximum tensile stress, the distance from the neutral axis of the circumferential bending to the surface of the spoke forward in the direction of rotation can be shortened.

[0041] When the spoke bends in the axial direction of the rotor body due to thermal expansion of the rotor body, the spoke experiences greater tensile stress as it moves toward the rotor body from the neutral axis of axial bending, and greater compressive stress as it moves away from the rotor body. To reduce the maximum tensile stress, the distance from the neutral axis of axial bending to the surface of the spoke facing the rotor body can be shortened.

[0042] Based on the above findings, the present inventors have completed the eddy current reduction gear according to the embodiment.

[0043] The eddy current reduction gear of the embodiment includes a rotor and a stator. The rotor includes a hub, a rotor body, and spokes. The hub is mounted on a rotating shaft. The rotor body has a cylindrical shape. The spokes extend from the hub toward the rotor body and are fixed to one axial end of the rotor body. The rotor rotates together with the rotating shaft. The stator is arranged on the inner side or the outer side of the rotor body. The spokes have a first neutral axis and a second neutral axis. The first neutral axis is the neutral axis when the spokes are bent along the circumferential direction of the rotor body. The first neutral axis is located forward of the center line of the spokes in the circumferential direction in the direction of rotation of the rotor. The second neutral axis is the neutral axis when the spokes are bent along the axial direction of the rotor body. The second neutral axis is located closer to the rotor body than the center line of the spokes in the axial direction (first configuration).

[0044] In the rotor of the eddy-current speed reducer of the first configuration, the spokes have a first neutral axis that serves as the neutral axis when bending in the circumferential direction of the rotor body. This first neutral axis is positioned forward of the centerline of the spokes in the circumferential direction of the rotor body in the rotor's rotational direction. Therefore, the distance from the first neutral axis to the front surface of the spoke in the rotational direction is smaller than when the first neutral axis is aligned with the circumferential centerline. This reduces the maximum tensile stress generated in the spokes when a circumferential bending load is applied to the spokes due to the braking force generated by the rotor body.

[0045] The spokes also have a second neutral axis, serving as their neutral axis when bent in the axial direction of the rotor body. This second neutral axis is located closer to the rotor body than the spoke's centerline in the axial direction of the rotor body. Therefore, the axial distance from the second neutral axis to the rotor body-side surface of the spoke is smaller than when the second neutral axis coincides with the axial centerline. This reduces the maximum tensile stress generated in the spokes when axial bending loads due to thermal expansion of the rotor body are applied.

[0046] Thus, according to the first configuration, when using an eddy current reduction gear, it is possible to simultaneously reduce the tensile stress generated in the spokes when the spokes bend circumferentially around the rotor body, and the tensile stress generated in the spokes when the spokes bend axially around the rotor body. This can suppress fatigue damage to the spokes and extend their fatigue life. Consequently, the durability of the eddy current reduction gear can be improved.

[0047] Eddy current reduction gears are required to be smaller and lighter for reasons such as improving vehicle loadability and fuel efficiency. To achieve this, the spokes must also be smaller. The first configuration reduces fatigue damage to the spokes, allowing for smaller spokes. This allows for a smaller and lighter eddy current reduction gear.

[0048] Eddy current reduction gears require high braking force to overcome insufficient braking performance, for example, in heavily laden vehicles. In eddy current reduction gears with high braking force, the higher braking force and the resulting greater heat generation increase the bending load on the spokes, making them susceptible to fatigue damage. However, according to the first configuration, when bending loads are applied to the rotor body in the circumferential and axial directions, the tensile stress generated in the spokes is reduced, thereby suppressing fatigue damage to the spokes. Therefore, the eddy current reduction gear of the first configuration is capable of handling higher braking forces.

[0049] In the eddy current speed reducer of the embodiment, it is preferable that the surface of the spoke on the rotor main body side is a plane perpendicular to the axial direction of the rotor main body (second configuration).

[0050] According to the second configuration, the surface of the spoke on the rotor body side is a plane substantially perpendicular to the axial direction of the rotor body. In other words, the surface of the spoke on the rotor body side is essentially a flat surface with no protrusions or projections. This allows the spoke to be positioned closer to the stator, located inside or outside the rotor body. As a result, the eddy current reduction gear can be reduced in size in the axial direction.

[0051] It is preferable that the spoke has a cross section in which the length in the axial direction of the rotor body decreases as it goes rearward in the rotation direction of the rotor (third configuration).

[0052] According to the third configuration, the cross section of the spoke is formed so that its axial length decreases as it moves rearward in the direction of rotation of the rotor. This reduces the chance of airflow flowing rearward in the direction of rotation along the spoke surface being separated during rotor rotation, thereby reducing air resistance on the spoke.

[0053] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In each figure, the same or corresponding components are denoted by the same reference numerals, and the same description will not be repeated.

[0054] [Structure of eddy current reduction gear]

[0055] Figure 1 This is a longitudinal cross-sectional view showing the schematic structure of the eddy current reduction gear 100 of the present embodiment. The reduction gear 100 is used as an auxiliary brake for vehicles such as trucks and buses. The longitudinal cross-section refers to a cross-section when cut with a plane including the axis X of the rotating shaft 200 of the vehicle using the reduction gear 100. The rotating shaft 200 is, for example, a transmission shaft or a drive shaft. Hereinafter, the direction in which the axis X extends is referred to as the axial direction, and the circumferential direction and radial direction of the ring or cylinder centered on the axis X are referred to as the circumferential direction and radial direction.

[0056] Reference Figure 1 The reduction gear 100 includes a rotor 10 and a stator 20. The rotor 10 rotates along with a rotating shaft 200 of the vehicle around an axis X. The stator 20 is fixed to a non-rotating portion of the vehicle such as a transmission cover so as not to rotate along with the rotating shaft 200.

[0057] The rotor 10 includes a rotor body 11, a hub 12, and a plurality of spokes 13. The rotor body 11 is substantially cylindrical, centered around the axis X of the rotating shaft 200. The rotor body 11 is made of a ferromagnetic material, such as carbon steel, low-alloy steel, or cast steel. More specifically, the rotor body 11 is made of, for example, chromium-molybdenum steel or low-alloy cast steel. Alternatively, the rotor body 11 may be made of steel containing, by weight, 0.05-0.15% C, 0.10-0.40% Si, 0.5-1.0% Mn, 0.05% or less P, 0.50% or less Ni, 0.2-1.0% Mo, 0.01-0.03% Nb, 0.03-0.07% V, 0.0005-0.003% B, 0.02-0.09% Sol / Al, and 0.01% or less N, with the remainder consisting essentially of Fe. The material constituting the rotor body 11 preferably has high heat resistance. The inner peripheral surface of the rotor body 11 may be covered with a copper plating layer having high electrical conductivity. A plurality of cooling fins 14 are provided on the outer peripheral surface of the rotor body 11.

[0058] The hub 12 is radially positioned inward of the rotor body 11. It is offset axially from the rotor body 11. The hub 12 has a generally annular plate shape centered on the axis X of the rotating shaft 200. The hub 12 is attached to the rotating shaft 200 via a support member 30. The hub 12 is made of, for example, steel, typically cast iron.

[0059] Multiple spokes 13 are radially arranged around the hub 12. Each spoke 13 extends radially from the hub 12 toward the rotor body 11. Each spoke 13 connects the rotor body 11 to the hub 12, which is mounted on the rotating shaft 200. Therefore, the rotor body 11 rotates about the axis X together with the rotating shaft 200, the hub 12, and the spokes 13. While not particularly limited, approximately eight to ten spokes 13 are provided between the rotor body 11 and the hub 12.

[0060] The radially outer end portion 131 of each spoke 13 is fixed to one axial end portion of the rotor body 11. The radially inner end portion 132 of each spoke 13 is inserted into the recess 121 provided on the outer peripheral surface of the hub 12. The end portion 132 is not fixed to the hub 12. Figure 1 In the illustrated example, the surface 133 of the spoke 13 on the rotor body 11 side is a plane substantially perpendicular to the axial direction.

[0061] The spokes 13 are made of a ferromagnetic material, such as carbon steel or cast steel. More specifically, they are made of, for example, chromium-molybdenum steel or low-alloy cast steel. The material of the spokes 13 is preferably high in strength. The material of the spokes 13 may be different from or the same as that of the rotor body 11.

[0062] The stator 20 is arranged radially inside the rotor body 11 . The stator 20 includes a stator case 21 , a magnet holding member 22 , a plurality of permanent magnets 23 , and a plurality of pole pieces 24 .

[0063] The stator housing 21 includes a housing body 211 and a body retaining member 212. The housing body 211 is formed into a generally annular plate centered on the axis X. The housing body 211 faces the surface 133 of the spoke 13. The surface of the housing body 211 facing the spoke 13 is preferably a plane substantially parallel to the surface 133 of the spoke 13. The housing body 211 is fixed to the body retaining member 212.

[0064] The main body retaining member 212 includes a side portion 212a facing the housing body 211 and a bottom portion 212b protruding from the side portion 212a toward the housing body 211. The bottom portion 212b is attached to a non-rotating portion of the vehicle via a support portion 212c. The housing body 211, the side portion 212a, and the bottom portion 212b of the main body retaining member 212 form a housing space within the stator 20. Within this housing space are the magnet retaining member 22, a plurality of permanent magnets 23, and a plurality of pole pieces 24.

[0065] The magnet holding member 22 has a cylindrical shape centered on the axis X. The magnet holding member 22 is disposed substantially coaxially with the rotor body 11. The magnet holding member 22 is made of a ferromagnetic material such as carbon steel or cast steel.

[0066] The magnet holding member 22 is mounted so as to be slidable in the circumferential direction relative to the stator housing 21, for example, via an annular sliding plate (not shown). The magnet holding member 22 is connected to a drive device (not shown) such as a cylinder or electric actuator via a connecting rod mechanism (not shown). The drive device rotates the magnet holding member 22 about the rotating axis 200 and moves circumferentially relative to the stator housing 21. Rotating the magnet holding member 22 about the rotating axis 200 switches the reduction gear 100 between a braking state and a non-braking state.

[0067] Figure 2 This is a partial cross-sectional view of the reduction gear 100 cut along a plane perpendicular to the axis X of the rotating shaft 200. Figure 2 In FIG, the stator housing 21 is omitted.

[0068] like Figure 2 As shown, the magnet holding member 22 holds a plurality of permanent magnets 23 on its outer circumferential surface. These permanent magnets 23 are arranged circumferentially at predetermined intervals. Each permanent magnet 23 is fixed to the outer circumferential surface of the magnet holding member 22, for example, using an adhesive. The permanent magnets 23 are, for example, neodymium magnets, ferrite magnets, or samarium cobalt magnets.

[0069] Each permanent magnet 23 has a pair of magnetic poles (a north pole and a south pole). The magnetic poles of each permanent magnet 23 are oriented radially and are opposite in orientation to the magnetic poles of the adjacent permanent magnets 23. That is, each permanent magnet 23 has a north pole or south pole on the radially inner side and an opposite south pole or north pole on the radially outer side.

[0070] The pole pieces 24 are made of a ferromagnetic material such as carbon steel or cast steel. They are circumferentially arranged at predetermined intervals between the rotor body 11 and the permanent magnets 23. In this embodiment, the number of pole pieces 24 is equal to the number of permanent magnets 23.

[0071] [Detailed structure of the rotor]

[0072] Below, refer to Figure 3 as well as Figures 4A to 4F , the structure of the rotor 10 will be described in more detail.

[0073] Figure 3 1 is a diagram showing a portion of the rotor 10 viewed from the spoke 13 side. Figure 3 The spokes 13 extend radially between the rotor body 11 and the hub 12. Of the radial ends 131 and 132 of the spokes 13, the outer end 131 is fixed to the end surface of the cylindrical rotor body 11, for example, by welding. The inner end 132 is inserted into the recess 121 of the hub 12 so that the spokes 13 can move radially relative to the hub 12.

[0074] The spoke 13 has a uniform cross-section along its entire radial length or substantially its entire length. At least the portion 134 of the spoke 13 that is exposed from the hub 12 and not fixed to the rotor body 11 has a uniform cross-section. The cross-section of the spoke 13 refers to the cross-section of the spoke 13 extending in the radial direction, taken along a plane perpendicular to the radial direction. That is, Figure 3 Section IV-IV in FIG. 1 is a cross section of the spoke 13 .

[0075] Figures 4A to 4F The diagram illustrates shapes that can be adopted as the cross-sectional shape of the spoke 13 used in the rotor 10 . Figures 4A to 4F The spokes 13A to 13F shown have different cross-sectional shapes. For example, one of the spokes 13A to 13F is applicable to the spoke 13 .

[0076] Reference Figures 4A to 4F The dashed lines labeled C1 represent the circumferential centerlines (centers of the circumferential widths) of the spokes 13A-13F, and the dashed lines labeled C2 represent the axial centerlines (centers of the axial widths) of the spokes 13A-13F. The dashed lines labeled N1 represent the neutral axes of the spokes 13A-13F when bent circumferentially. The intersection of the neutral plane and the cross section of each spoke 13A-13F, where neither tensile nor compressive stress is generated when bent circumferentially, is the neutral axis N1. The dashed lines labeled N2 represent the neutral axes of the spokes 13A-13F when bent axially. The intersection of the neutral plane and the cross section of each spoke 13A-13F, where neither tensile nor compressive stress is generated when bent axially, is the neutral axis N2.

[0077] For all spokes 13A-13F, the neutral axis N1, when circumferentially curved, is located forward of the circumferential centerline C1 in the rotational direction R. Specifically, for each spoke 13A-13F, the distance Df from the neutral axis N1 to the front end in the rotational direction R is smaller than the distance Dr from the neutral axis N1 to the rear end in the rotational direction R. The center of gravity of the spokes 13A-13F is located forward of the centerline C1 in the rotational direction R. Each cross-section of the spokes 13A-13F is asymmetrical with respect to the centerline C1.

[0078] Furthermore, for all spokes 13A to 13F, the neutral axis N2, when bent in the axial direction, is located closer to the rotor body 11 than the axial centerline C2. Specifically, for each spoke 13A to 13F, the distance Dp from the neutral axis N2 to the end on the rotor body 11 side is shorter than the distance Dd from the neutral axis N2 to the end on the side opposite the rotor body 11. The center of gravity of each spoke 13A to 13F is located axially closer to the rotor body 11 than the centerline C2. Each cross-section of each spoke 13A to 13F is asymmetrical with respect to the centerline C2. Each cross-section of each spoke 13A to 13F is asymmetrical about any straight line.

[0079] Each of the spokes 13A, 13B, and 13D-13F has a cross-section whose axial length substantially decreases as it moves rearward in the rotational direction R. Furthermore, in each cross-section of the spokes 13A, 13B, and 13D-13F, the circumferential length substantially decreases as it moves axially away from the rotor body 11. In other words, the spokes 13A, 13B, and 13D-13F have a shape that tapers as a whole or substantially as a whole toward the rear in the rotational direction R and tapers axially toward the side opposite the rotor body 11.

[0080] The cross-sections of spokes 13A to 13C are divided by multiple straight lines, each with an angle between them. Meanwhile, in the cross-sections of spokes 13D and 13E, the straight lines are connected by curved lines. In spoke 13F, the cross-section is defined solely by curved lines. In other words, spokes 13D to 13F have a cross-sectional shape without angles.

[0081] In the spokes 13A to 13E, the surfaces 133 on the rotor body 11 side are entirely linear when viewed in cross section. Specifically, the surfaces 133 on the rotor body 11 side of the spokes 13A to 13E are planes substantially perpendicular to the axial direction. In contrast, the surface 133 on the rotor body 11 side of the spoke 13F is curved when viewed in cross section.

[0082] [Operation of the eddy current reduction gear]

[0083] The following mainly refers to Figure 5 as well as Figure 6 , the operation of the reduction gear 100 will be described. Figure 5 as well as Figure 6 These are schematic diagrams for explaining the braking state and the non-braking state of the deceleration device 100 , respectively.

[0084] (Braking status)

[0085] First, refer to Figure 5When the reduction gear 100 is in a braking state, each permanent magnet 23 is arranged directly below the pole piece 24. Therefore, the magnetic flux from each permanent magnet 23 passes through the pole piece 24 and reaches the rotor body 11 that rotates together with the rotating shaft 200. As a result, eddy currents are generated on the inner circumferential surface of the rotor body 11. Through the interaction between the eddy currents and the magnetic field generated by the permanent magnets 23, a braking force in the opposite direction to the rotation direction R is generated in the rotor body 11. In addition, along with the generation of eddy currents, Joule heat is generated in the rotor body 11, and the temperature of the rotor body 11 rises. As a result, thermal expansion of the rotor body 11 occurs.

[0086] When a braking force in the direction opposite to the rotational direction R is generated in the rotor body 11 , a bending load in the direction opposite to the rotational direction R (circumferential bending load) is applied to the radially outer end portion 131 of the spoke 13 fixed to the rotor body 11 .

[0087] When the rotor body 11 is thermally expanded, the end portion of the rotor body 11 on the side not restrained by the spokes 13, out of the two axial ends of the rotor body 11, is deformed more radially outward than the end portion on the spoke 13 side. Figure 5 As a result, a bending load (axial bending load) pressing the radially outer end 131 of the spoke 13 toward the side opposite to the rotor body 11 is applied.

[0088] The spoke 13 is subjected to a circumferential bending load, which causes a bending deformation that is convex toward the front side in the rotation direction R. As a result, the spoke 13 is convex toward the front side in the rotation direction R. Figures 4A to 4F ) as the boundary, tensile stress is generated in the front part in the rotation direction R, and compressive stress is generated in the rear part. In addition, due to the axial bending load, the spoke 13 is deformed so as to be convex in the axial direction toward the rotor body 11. Therefore, in the spoke 13, the neutral axis N2 ( Figures 4A to 4F ) is a boundary, tensile stress is generated in the portion on the rotor body 11 side, and compressive stress is generated in the portion on the side opposite to the rotor body 11.

[0089] (Non-braking state)

[0090] Reference Figure 6When the reduction gear 100 switches from the braking state to the non-braking state, the magnet holding component 22 rotates, and each permanent magnet 23 is arranged so as to span adjacent pole pieces 24. In the non-braking state, a magnetic circuit is formed between the magnet holding component 22, the permanent magnet 23, and the pole pieces 24, and the magnetic flux from the permanent magnet 23 does not reach the rotor body 11. Therefore, the braking force on the rotor body 11 is released. In addition, the rotor body 11, which once expanded thermally, gradually cools and returns to its original cylindrical shape. As a result, the circumferential and axial bending loads on the spokes 13, as well as the tensile and compressive stresses in the spokes 13, are eliminated.

[0091] [Effect]

[0092] In the eddy-current speed reducer 100 of this embodiment, each spoke 13 connecting the rotor body 11 to the hub 12 has a neutral axis N1 when bent in the circumferential direction. When the rotor body 11 generates a braking force and a circumferential bending load acts on the spokes 13, tensile stress is generated in the front portion in the rotational direction R, and compressive stress is generated in the rear portion, with respect to the neutral axis N1. The absolute values ​​of these stresses increase with increasing distance from the neutral axis N1.

[0093] In this embodiment, the neutral axis N1 is positioned forward of the circumferential centerline C1 of the spoke 13 in the rotational direction R. Therefore, in the spoke 13, the distance Df from the neutral axis N1 to the front end in the rotational direction R is smaller than the distance Dr from the neutral axis N1 to the rear end in the rotational direction R. This reduces the maximum value of the tensile stress when the spoke 13 is subjected to a circumferential bending load.

[0094] In this embodiment, each spoke 13 also has a neutral axis N2 when bent in the axial direction. When an axial bending load is applied to the spoke 13 due to thermal expansion of the rotor body 11, tensile stress is generated in the spoke 13 on the rotor body 11 side, and compressive stress is generated in the spoke 13 on the side opposite to the rotor body 11, with the neutral axis N2 as the boundary. The absolute values ​​of these stresses increase with increasing distance from the neutral axis N2.

[0095] In this embodiment, the neutral axis N2 is located closer to the rotor body 11 than the center line C2 of the spoke 13. Therefore, in the axial direction, the distance Dp from the neutral axis N2 to the end on the rotor body 11 side is shorter than the distance Dd from the neutral axis N2 to the end on the side opposite to the rotor body 11. This reduces the maximum tensile stress when the spoke 13 is subjected to an axial bending load.

[0096] In this embodiment, when the spokes 13 are subjected to circumferential and axial bending loads, the maximum value of the tensile stress generated in the spokes 13 decreases, while the maximum value of the compressive stress increases. However, compared to repeated tensile stress, repeated compressive stress is less likely to cause fatigue damage to the spokes 13. Therefore, by reducing the maximum value of the tensile stress generated in the spokes 13, even if the maximum value of the compressive stress increases instead, fatigue damage to the spokes 13 can be suppressed.

[0097] For reference, in Figures 7A to 7C The cross-sectional shape of a conventional spoke is shown in FIG. Figure 7A as well as Figure 7B In the spokes 93A and 93B shown, the neutral axis N1 of circumferential bending coincides with the centerline C1. Therefore, in the spokes 93A and 93B, the distance Df from the neutral axis N1 to the front end in the rotational direction R is equal to the distance Dr from the neutral axis N1 to the rear end in the rotational direction R. In this case, the maximum tensile stress and the maximum compressive stress generated when the spokes 93A and 93B bend circumferentially are equal. In other words, the cross-sectional shape of the spokes 93A and 93B does not reduce the tensile stress generated by the circumferential bending load.

[0098] exist Figure 7C In the illustrated spoke 93C, the neutral axis N2 of axial bending coincides with the centerline C2. Therefore, in spoke 93C, the axial distance Dp from the neutral axis N2 to the end on the rotor body side is equal to the axial distance Dd from the neutral axis N2 to the end on the side opposite the rotor body. In this case, the maximum tensile stress and the maximum compressive stress generated when spoke 93C bends in the axial direction are equal. In other words, the cross-sectional shape of spoke 93C does not reduce the tensile stress generated by axial bending loads.

[0099] Compared to conventional spokes, the spokes 13 in this embodiment take into account both circumferential and axial bending loads, adopting a cross-sectional shape that reduces both the tensile stress caused by circumferential bending and the tensile stress caused by axial bending. This effectively suppresses fatigue damage in the spokes 13 and extends their fatigue life. Consequently, the durability of the eddy current reduction gear 100 including the spokes 13 is enhanced.

[0100] According to this embodiment, fatigue damage to the spokes 13 can be suppressed by simply focusing on the cross-sectional shape of the spokes 13, without increasing the cross-sectional area or weight of the spokes 13. This reduces fatigue damage to the spokes 13, allowing for miniaturization of each spoke 13 or reduction in the number of spokes 13 provided in the eddy current reduction gear 100. This reduces the size and weight of the eddy current reduction gear 100, improving its vehicle mountability. Furthermore, the fuel efficiency of a vehicle equipped with the eddy current reduction gear 100 can be improved.

[0101] In this embodiment, the spokes 13 have a cross-sectional shape that is less susceptible to fatigue damage even when circumferential and axial bending loads are repeatedly applied due to the braking force generated by the rotor body 11 and the thermal expansion of the rotor body 11. This allows the eddy current reduction gear 100 using the spokes 13 to achieve higher braking force.

[0102] In this embodiment, Figures 4A to 4E The surfaces 133 of the illustrated spokes 13A to 13E on the rotor body 11 side are substantially perpendicular to the axial direction. This allows the spokes 13 to be positioned close to the stator 20 disposed inside the rotor body 11, reducing the axial dimension of the eddy current speed reducer 100.

[0103] In this embodiment, Figure 4A 、 Figure 4B as well as Figures 4D to 4F The illustrated spokes 13A, 13B, and 13D-13F each have a cross-section whose axial length decreases as it moves rearward in the rotational direction R. In this manner, during the rotation of the rotor 10, airflow flowing rearward in the rotational direction R over the surfaces of the spokes 13A, 13B, and 13D-13F is less likely to separate from these surfaces. This reduces the air resistance of the rotor 10.

[0104] In particular, the spokes 13D to 13F have a cross-sectional shape without corners, thereby further reducing the air resistance of the rotor 10 .

[0105] Although the embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present disclosure.

[0106] In the above embodiment, the surfaces 133 of the spokes 13A to 13E facing the rotor body 11 are substantially flat. However, the shape of the surfaces 133 of the spokes 13 is not limited to this. The surfaces 133 of the spokes 13 may be, for example, convex surfaces toward the rotor body 11 or concave surfaces facing in the opposite direction.

[0107] In the above embodiment, the stator 20 is arranged radially inside the rotor main body 11. However, the stator 20 may be arranged radially outside the rotor main body 11.

[0108] In the above embodiment, a rotor 10 including spokes 13 is used in a permanent magnet eddy current reduction gear 100. However, the rotor 10 can also be used in an electromagnet eddy current reduction gear. That is, in the reduction gear 100, an electromagnet can be provided instead of the magnet holding member 22, permanent magnets 23, and pole pieces 24. When the cross-sectional shape of the spokes 13 in the above embodiment is adopted, the structure of the stator 20 is not particularly limited.

[0109] Description of Reference Numerals

[0110] 100: Eddy current reduction device

[0111] 10: Rotor

[0112] 11: Rotor body

[0113] 12: Wheel Hub

[0114] 13, 13A~13F: spokes

[0115] 20: stator

[0116] 200: Rotation axis

[0117] N1, N2: Neutral axis

[0118] C1, C2: center lines

Claims

1. A reduction gear, which is an eddy current reduction gear, characterized in that: have: a rotor including a hub mounted on a rotating shaft, a cylindrical rotor body, and a spoke extending from the hub toward the rotor body and fixed to one axial end of the rotor body, wherein the rotor rotates together with the rotating shaft; and a stator, which is arranged on the inner side or the outer side of the rotor body, The spokes have: a first neutral axis, which is a neutral axis when the spokes are bent in the circumferential direction of the rotor body and is located forward of a center line of the spokes in the circumferential direction in the rotational direction of the rotor; as well as A second neutral axis is a neutral axis when the spokes are bent in the axial direction, and is located closer to the rotor body than the center line of the spokes in the axial direction. The first neutral axis is the intersection of the neutral plane and the cross section of the spoke where no tensile stress or compressive stress is generated when the spoke is subjected to circumferential bending. The second neutral axis is the intersection of the neutral plane and the cross section of the spoke where no tensile stress or compressive stress is generated when the spoke is subjected to axial bending. In the spoke, a distance from the first neutral axis to the front end in the rotation direction is smaller than a distance from the first neutral axis to the rear end in the rotation direction. In the spoke, a distance from the second neutral axis to an end portion on the rotor main body side is smaller than a distance from the second neutral axis to an end portion on the opposite side to the rotor main body.

2. The reduction gear according to claim 1, characterized in that: A surface of the spoke on the rotor main body side is a plane perpendicular to the axial direction.

3. The reduction gear according to claim 1 or 2, characterized in that: The spokes have a cross-section whose axial length decreases toward the rear in the rotational direction.

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