FLEXIBLE SHAFT COUPLING

Abstract

A flexible shaft coupling has a first gear (45) and a second gear (43) that meshes with the first gear (45). The first gear (45) has a first tooth surface (46s), the second gear (43) has a second tooth surface (44s), and at least one of the first tooth surface (46s) or the second tooth surface (44s) is convex when viewed in the direction of tooth travel.

Description

Technical area

[0001] The present disclosure relates to a flexible shaft coupling. Technical background

[0002] A railway vehicle has electric motors mounted on a bogie to transmit power to the wheel axles. During the running of the railway vehicle, the bogie vibrates due to disturbances, which may potentially cause misalignment between the drive shafts of the electric motors and the axles. To compensate for such misalignment between the drive shafts and the axles and to transmit power from the electric motors to the axles, flexible shaft couplings are arranged between the drive shafts of the electric motors and the axles. For example, Patent Literature 1 describes a gear flex coupling that absorbs relative displacements during steering of a parallel-cardan steering bogie. The gear flex coupling in Patent Literature 1 has gears with an involute profile. Citation listPatent literature

[0003] Patent Literature 1: Unexamined Japanese Patent Application Publication No. 2019-011773 Brief description of the inventionTechnical problem

[0004] To accommodate larger relative displacements using external and internal gears with an involute profile, the contact areas between these gears must be smaller, resulting in higher contact loads.

[0005] Under these circumstances, it is an object of the present disclosure to reduce the contact stress in a flexible shaft coupling. Solution to the problem

[0006] To achieve the above-mentioned objective, a flexible shaft coupling according to one aspect of the present disclosure includes a first gear and a second gear meshing with the first gear. The first gear has a first tooth surface, the second gear has a second tooth surface, and at least one of the first tooth surface and the second tooth surface is curved outwardly when viewed in the tooth direction. Advantageous effects of the invention

[0007] In the flexible shaft coupling according to the above-mentioned aspect of the present disclosure, at least one of the first tooth surface of the first gear or the second tooth surface of the second gear is curved outward when viewed in the tooth direction. This reduces the contact stress in the flexible shaft coupling. Short description of the drawings Fig. 1 is a plan view of a bogie in a rail vehicle with a flexible shaft coupling according to Embodiment 1; Fig. 2 is a perspective view of the flexible shaft coupling according to Embodiment 1; Fig. 3 is a schematic diagram of the flexible shaft coupling according to Embodiment 1, showing the internal structure; Fig. 4 is a partial perspective view of an external gear in Embodiment 1; Fig. 5 is a schematic diagram of an external gear of the external gear and an internal tooth of an internal gear in Embodiment 1, showing the positional relationship between the teeth; Fig. 6 is a schematic diagram of the external tooth of the external gear and the internal tooth of the internal gear in Embodiment 1, showing the positional relationship between the teeth; Fig. 7 is a schematic cross-sectional view of the internal tooth of the internal gear and the external tooth of the external gear in Embodiment 1; Fig. 8 is a schematic cross-sectional view of the internal tooth of the internal gear and the external tooth of the external gear in Embodiment 1; Fig. 9 is a schematic cross-sectional view of an internal tooth of an internal gear and an external tooth of an external gear in Modification 1 of Embodiment 1; Fig. 10 is a schematic cross-sectional view of an internal tooth of an internal gear and an external tooth of an external gear in Modification 2 of Embodiment 1; Fig. 11 is a schematic cross-sectional view of an internal tooth of an internal gear in Embodiment 2; Fig. 12 is a view of the inner tooth in Fig. 11, which shows an internal tooth pitch point and an adjacent area enlarged; Fig. 13 is a schematic cross-sectional view of an external tooth of an external gear in Embodiment 2; Fig. 14 is a schematic cross-sectional view of the external tooth of the external gear in Embodiment 2; and Fig. 15 is a schematic cross-sectional view of the internal tooth of the internal gear and the external tooth of the external gear in Embodiment 2 Description of Embodiments.

[0008] A flexible shaft coupling according to one or more embodiments of the present disclosure will be described with reference to the drawings. Components that are identical or corresponding to one another are provided with the same reference numerals in the drawings. Embodiment 1

[0009] As in Fig. 1, a rail vehicle comprises a bogie 1 having a bogie frame 11 supporting the vehicle body of the rail vehicle, wheel units 2 enabling the rail vehicle to travel, electric motors 3 generating power to rotate the wheel units 2, flexible shaft couplings 4 receiving power from the electric motors 3, transmission devices 5 transmitting power from the flexible shaft couplings 4 to the wheel units 2, and suspensions 6 limiting the oscillating movements of the transmission devices 5. The wheel units 2, the electric motors 3, the flexible shaft couplings 4, the transmission devices 5, and the suspensions 6 are mounted on the bogie 1.

[0010] Each wheel unit 2 has wheels 21 in contact with a running surface and an axle 22 supporting the wheels 21. The axle 22 is supported by the bogie frame 11 with an axial spring.

[0011] Each electric motor 3 is attached to the bogie frame 11. The electric motor 3 receives alternating current (AC) with customized parameters such as current and frequency. Receiving alternating current, the electric motor 3 rotates to generate power. The electric motor 3 has a drive shaft 31 that transmits the generated power to the outside. The drive shaft 31 is connected to the flexible shaft coupling 4 to transmit the power from the electric motor 3 to the flexible shaft coupling 4. In the example below, the vertical direction is referred to as the Z-axis. The direction parallel to a central axis AX of the drive shaft 31 of the electric motor 3, which extends horizontally when the rail vehicle is stopped horizontally, is referred to as the X-axis. The direction perpendicular to the Z-axis and the X-axis is referred to as the Y-axis.

[0012] The flexible shaft coupling 4 is located between the electric motor 3 and the transmission device 5. The flexible shaft coupling 4 transmits the power from the electric motor 3 to the transmission device 5.

[0013] The transmission device 5 is supported by the bogie frame 11 with the suspension 6. The transmission device 5 has an output shaft 51 connected to the flexible shaft coupling 4 for receiving power from the flexible shaft coupling 4. The transmission device 5 comprises, for example, a reduction gear with multiple gears having different numbers of teeth. The transmission device 5 receives power via the output shaft 51 and transmits the power to the axle 22 to rotate the axle 22 and the wheels 21. This enables the rail vehicle to travel.

[0014] While the rail vehicle is moving, the wheel unit 2, the transmission device 5, or other components are displaced, for example, by disturbing vibrations from the road surface. This can cause a misalignment between the output shaft 51 of the transmission device 5 and the drive shaft 31 of the electric motor 3.

[0015] The flexible shaft coupling 4, which transmits power from the electric motor 3 to the transmission device 5, is flexible and can compensate for a misalignment between the output shaft 51 and the input shaft 31.

[0016] The structure of the flexible shaft coupling 4 is described with reference to the Fig. 2 and Fig. 3 described. Fig. 2 is a perspective view of the flexible shaft coupling 4. Fig. 2 shows the flexible shaft coupling 4 partly in section. Fig. 3 is a schematic cross-sectional view of the flexible shaft coupling 4 along the central axis AX of the drive shaft 31.

[0017] The flexible shaft coupling 4 has an outer tube unit 41 and an inner tube unit 42 within the outer tube unit 41.

[0018] The outer tube unit 41 includes a first outer sleeve 411 located adjacent to the input shaft 31 and a second outer sleeve 412 located adjacent to the output shaft 51. The first outer sleeve 411 and the second outer sleeve 412 are secured together with fasteners such as bolts.

[0019] As in Fig. As shown in Figure 3, both the first outer sleeve 411 and the second outer sleeve 412 have an annular internal gear 43 along their inner surface. The internal gear 43 is an example of a second gear. The internal gear 43 has internal teeth 44 that protrude into the outer tube unit 41.

[0020] The inner tube unit 42 includes a first inner sleeve 421 into which the input shaft 31 is fitted, and a second inner sleeve 422 into which the output shaft 51 is fitted. Both the first inner sleeve 421 and the second inner sleeve 422 are open at both ends.

[0021] Both the first inner sleeve 421 and the second inner sleeve 422 have an annular external gear 45 along their outer surface. The external gear 45 is an example of a first gear. The external gear 45 has external teeth 46 that protrude outward from the inner tube unit 42.

[0022] The external gear 45 on the first inner sleeve 421 meshes with the internal gear 43 on the first outer sleeve 411. The external gear 45 on the second inner sleeve 422 meshes with the internal gear 43 on the second outer sleeve 412.

[0023] In the above structure, when the drive shaft 31 of the electric motor 3 rotates, the external gear 45 on the first inner sleeve 421 mounted on the drive shaft 31 rotates integrally with the drive shaft 31. The rotation of the first inner sleeve 421 causes the rotation of the first outer sleeve 411, and the external gear 45 on the first inner sleeve 421 meshes with the internal gear 43 on the first outer sleeve 411.

[0024] The first outer sleeve 411 is connected to the second outer sleeve 412 by means of fastening elements. The second outer sleeve 412 thus rotates integrally with the first outer sleeve 411. The internal gear 43 on the second outer sleeve 412 meshes with the external gear 45 on the second inner sleeve 422. The second inner sleeve 422 thus rotates while the second outer sleeve 412 rotates.

[0025] When the second inner sleeve 422 rotates, the output shaft 51 fitted into the second inner sleeve 422 rotates integrally with the second inner sleeve 422. In the above structure, the power is transmitted from the electric motor 3 to the transmission device 5 via the flexible shaft coupling 4, as shown in Fig. 1 described.

[0026] To compensate for misalignment during travel of the rail vehicle, the inner tube unit 42 in the flexible shaft coupling 4 is tilted relative to the outer tube unit 41. More specifically, the central axis of the inner tube unit 42 is tilted relative to the central axis of the outer tube unit 41. The tilt of the inner tube unit 42 relative to the outer tube unit 41 is hereinafter referred to as a displaced state. The flexible shaft coupling 4 accommodates a predetermined range of angles of this tilt. The tilt of the flexible shaft coupling 4 by the maximum permissible angle is hereinafter referred to as the maximum displaced state.

[0027] In the flexible shaft coupling 4, each internal tooth 44 and each external gear 46 have different profiles to suppress a reduction in the contact area between the internal tooth 44 and the external gear 46 in the shifted state.

[0028] The structure of the internal tooth 44 and the external gear 46 will be described in detail below with reference to Fig. 4 to 7.

[0029] Fig. Figure 4 is a partial perspective view of the external gear 45 on the second inner sleeve 422, taken with respect to Fig. 3. As described in Fig. As shown in Figure 4, each external gear 46 has the shape of an isosceles trapezoid when viewed in the tooth direction. The external gear 46 is thicker at a tooth root 46b than at a tooth tip 46t. The external gear 46 is curved, or more precisely, the surface of the tooth tip 46t and a tooth surface 46s each curve in the center.

[0030] Fig. 5 and Fig. 6 each schematically shows the positional relationship between the external gear 46 of the external gear 45 on the first inner sleeve 421 and the internal tooth 44 of the internal gear 43 on the first outer sleeve 411 in the maximum displaced state, in which the central axis of the inner tube unit 42, more precisely, the central axis of the first inner sleeve 421, is inclined by the maximum allowable angle with respect to the central axis of the outer tube unit 41. In this state, the end of the first inner sleeve 421 in the negative X-axis direction is Fig. 3 in the positive Z-axis direction, and the end of the first inner sleeve 421 in the positive X-axis direction in Fig. 3 is shifted in the negative Z-axis direction. Fig. 5 is a diagram viewed in the negative Z-axis direction showing the external gear 46 and the internal gear 44 located at the top in the vertical direction. Fig. Figure 6 is a diagram viewed in the positive Y-axis direction showing the external gear 46 and the internal gear 44 located at the end in the negative Y-axis direction. Fig. 5 and Fig. 6 the external gear 45 rotates upwards.

[0031] In Fig. 5, the external gear 46 is closer to the internal tooth 44 in the central region of the external gear 46 in the tooth direction, i.e., in the X-axis direction. This positional relationship also applies to the external gear 46 and the internal tooth 44 located in the lower region in the vertical direction. In a non-displaced state in which the central axis of the inner tube unit 42 is not inclined with respect to the central axis of the outer tube unit 41, the external gears 46 and the internal teeth 44 are all in the same positional relationship as in Fig. 5. More specifically, each external gear 46 is closer to the corresponding internal tooth 44 in the tooth direction in the middle region of the external gear 46.

[0032] In the maximally displaced state, as in Fig. 6, the external gear 46, which is located at the end in the negative Y-axis direction, is in contact with the internal tooth 44 at a point near the end of the external gear 46 in the tooth running direction.

[0033] Fig. Figure 7 is a schematic cross-sectional view of the internal gear 44 and the external gear 46, taken with respect to Fig. 6. More specifically, Fig. 7 a cross section of the external gear 46 perpendicular to the tooth running direction, including the central region of the external gear 46 in the tooth running direction in the non-displaced state. Fig. Figure 8 is a schematic cross-sectional view of the internal gear 44 and the external gear 46, taken with respect to Fig. 6 were described. Fig. Figure 8 shows a cross-section of the external gear 46 perpendicular to the tooth direction, including a contact point between the external gear 46 and the internal tooth 44 near the end of the external gear 46 in the tooth direction. The cross-sections are not shown hatched below.

[0034] The pitch circle of each gear is represented below by a dash-dotted line. For clarity, the pitch circles are linear in the enlarged views. The pitch circle of the external gear 45 is referred to as the external gear pitch circle Cp1. The pitch circle of the internal gear 43 is referred to as the internal tooth pitch circle Cp2. A point on the external gear pitch circle Cp1 of the external gear 46, i.e., a pitch circle point of the external gear 46, is referred to as the external gear pitch circle point 46c. A point on the internal tooth pitch circle Cp2 of the internal tooth 44, i.e., a pitch circle point of the internal tooth 44, is referred to as the internal tooth pitch circle point 44c. The flexible shaft coupling 4 has a backlash between the internal tooth 44 of the internal gear 43 and the external gear 46 of the external gear 45 to allow for, for example, misalignment or mechanical tolerance.The external gear 46 and the internal tooth 44 each have a non-involute profile that differs from an involute profile created with an involute function.

[0035] As in the Fig. 7 and Fig. As shown in Figure 8, the tooth surface 46s of the external gear 46 is in the shape of a straight line when viewed in the tooth direction. In other words, the tooth surface 46s of the external gear 46 has a straight line shape in a cross section perpendicular to the tooth direction. The tooth surface 46s of the external gear 46 is hereinafter referred to as the external gear surface 46s. The external gear surface 46s is an example of a first tooth surface of the first gear.

[0036] The internal tooth 44 has a profile that differs from the profile of the external gear 46. The internal tooth 44 has a tooth surface 44s that is curved outward, or more precisely, in the shape of an arc when viewed in the tooth extension direction. More specifically, the tooth surface 44s of the internal tooth 44, in a cross-section perpendicular to the tooth extension direction, has the shape of an arc that protrudes toward the external gear 46. The tooth surface 44s of the internal tooth 44 is hereinafter referred to as the internal tooth surface 44s. The internal tooth surface 44s is an example of a second tooth surface of the second gear.

[0037] More specifically, the inner tooth surface 44s has the shape of a circular segment, whose tangent T passes through the inner tooth pitch circle point 44c when viewed in the tooth direction. The tangent T is represented below by a two-dot chain line.

[0038] The tangent T is parallel to the adjacent external gear surface 46s of the external gear 46, that is, parallel to the external gear surface 46s facing the internal tooth surface 44s and touched by the tangent T. In other words, the internal tooth surface 44s has the shape of an arc with a tangent that is parallel to the external gear surface 46s when viewed in the tooth direction.

[0039] The inner tooth surface 44s is closest to the outer gear surface 46s at the inner tooth pitch circle point 44c and gradually moves away from the outer gear surface 46s from the inner tooth pitch circle point 44c toward a tooth root 44b and a tooth tip 44t of the inner tooth 44.

[0040] The inner tooth surface 44s of the inner tooth 44 is curved outward in a cross-section perpendicular to the tooth running direction and is closest to the opposing outer gear surface 46s at the inner tooth pitch circle point 44c. More specifically, the inner tooth surface 44s has the shape of an arc in the cross-section with a tangent T passing through the inner tooth pitch circle point 44c and parallel to the outer gear surface 46s of the outer gear 46. In other words, the tangent T passes through the inner tooth pitch circle point 44c and is parallel to a straight line corresponding to the outer gear surface 46s of the outer gear 46 in a cross-section perpendicular to the tooth running direction. This prevents contact between an edge 44e of the tooth tip 44t and the outer gear 46 in the maximum displaced state, as shown in Fig. 8. This thus suppresses a reduction in the contact area between the inner tooth surface 44s and the outer gear surface 46s and reduces the contact stress between the inner tooth 44 and the outer gear 46.

[0041] The internal tooth surface 44s of the internal gear 43 has an arc shape when viewed in the tooth direction, as described above. With this structure, when the contact stress between the internal tooth 44 and the external gear 46 is higher, the internal tooth surface 44s and the external gear surface 46s come into contact with a larger contact area between these surfaces, and the internal tooth 44 undergoes elastic deformation. This structure can thus suppress the contact stress between the internal tooth 44 and the external gear 46 compared to the case where the internal tooth surface 44s of the internal gear 43 has a shape other than an arc shape when viewed in the tooth direction.

[0042] In the present embodiment, the contact load at a contact position between the internal tooth 44 and the external gear 46 can be adjusted by adjusting the relative radii of curvature of the internal tooth 44 and the external gear 46 at the contact position. Specifically, the internal tooth 44 and the external gear 46 can have larger relative radii of curvature to reduce the contact load at the contact position.

[0043] The reduced contact load can reduce extreme pressure and thus reduce frictional heat. This can eliminate vibrations of the meshing internal gear 43 and external gear 45, which in turn reduces vibration and noise.

[0044] By suppressing a reduction in the contact area, the flexible shaft coupling 4 can accommodate a larger displacement. This increases the design flexibility of the peripheral devices.

[0045] By suppressing the contact load, the flexible shaft coupling 4 has less wear and thus a longer service life.

[0046] The shapes of the internal gear surface 44s and the external gear surface 46s can be adjusted according to the inclination angle to be accommodated by the flexible shaft coupling 4.

[0047] The inner tooth surface 44s of the inner tooth 44 and the outer gear surface 46s of the outer gear 46 are both in the shape of a straight line or outwardly curved, rather than being inwardly curved, when viewed in the tooth direction. At least one of the inner tooth surface 44s of the inner tooth 44 or the outer gear surface 46s of the outer gear 46 is outwardly curved when viewed in the tooth direction. For example, at least one of the inner tooth surface 44s of the inner tooth 44 or the outer gear surface 46s of the outer gear 46 may have any outwardly curved shape that is not an arc shape when viewed in the tooth direction.More specifically, in a cross-section perpendicular to the tooth running direction, the inner tooth surface 44s may simply be closest to the outer gear surface 46s at the inner tooth pitch circle point 44c, or the outer gear surface 46s may simply be closest to the inner tooth surface 44s at the outer gear pitch circle point 46c.

[0048] As in Fig. As shown in Figure 9, the inner tooth surface 44s of the inner tooth 44 may have a straight line shape when viewed in the tooth direction, and the outer gear surface 46s of the outer gear 46 may be curved outward when viewed in the tooth direction. The outer gear surface 46s of the outer gear 46 preferably has an arc shape that curves toward the inner tooth surface 44s of the inner tooth 44 when viewed in the tooth direction.

[0049] In the embodiment as in Fig. 10, the internal tooth surface 44s and the external gear surface 46s may both be curved outwardly from each other. More specifically, in a cross section perpendicular to the tooth extension direction, the internal tooth surface 44s may have the shape of an arc that curves toward the opposite external gear surface 46s, and the external gear surface 46s may have the shape of an arc that curves toward the opposite internal tooth surface 44s. When the internal tooth surface 44s and the external gear surface 46s both have the shape of arcs in a cross section perpendicular to the tooth extension direction, the radii of curvature of these arcs may be the same or different. In a cross section perpendicular to the tooth extension direction, the arcs of the internal tooth surface 44s and the external gear surface 46s may have the radii of curvature adjusted according to the contact load to be absorbed.

[0050] In the embodiment described above, the internal tooth surface 44s is closest to the external gear surface 46s at the internal tooth pitch circle point 44c. However, the internal tooth 44 may also have any other structure that prevents contact between the edge 44e and the external gear 46. For example, the internal tooth surface 44s may be closest to the external gear surface 46s near the internal tooth pitch circle point 44c. In other words, the tangent T may pass through a point near the internal tooth pitch circle point 44c on the internal tooth surface 44s, rather than through the internal tooth pitch circle point 44c.

[0051] The tangent T may be parallel to the external gear surface 46s facing the internal tooth surface 44s and contacted by the tangent T in a displaced state in which the inclination angle is smaller than in the maximum displaced state.

[0052] The direction in which the inner tube unit 42 is displaced is not limited to the direction in the above example. In one example, the end of the first inner sleeve 421 may be displaced in the negative X-axis direction in Fig. 3 in the negative Z-axis direction, and the end of the first inner sleeve 421 in the positive X-axis direction in Fig. 3 may be shifted in the positive Z-axis direction.

[0053] In the embodiments described above, the shapes of the internal tooth 44 on the first outer sleeve 411 and the external gear 46 on the first inner sleeve 421 were determined with respect to Fig. 4 to 8. The information relating to Fig. The shapes of the internal tooth 44 and the external gear 46 described in Figures 4 to 8 can also be applied to the internal tooth 44 on the second outer sleeve 412 and the external gear 46 on the second inner sleeve 422. Embodiment 2

[0054] A flexible shaft coupling 4 according to embodiment 2 is described with reference to Fig. 11 to 14. The basic structure and basic operation of the flexible shaft coupling 4 according to Embodiment 2 are the same as or similar to the basic structure and basic operation of the flexible shaft coupling 4 according to Embodiment 1. However, unlike Embodiment 1, the internal tooth 44 of the internal gear 43 and the external gear 46 of the external gear 45 have different contact angles to more reliably prevent contact between the edge 44e of the internal tooth surface 44s and the external gear surface 46s. Embodiment 2 will be described focusing on the differences from Embodiment 1. A perpendicular to the pitch circle of each gear is represented below by a two-dot chain line.

[0055] Fig. 11 is a view of the internal tooth 44 of the internal gear 43. Fig. 12 is a view of the inner tooth 44 in Fig. 11, which shows the inner tooth pitch circle point 44c and an adjacent area enlarged.

[0056] As in the Fig. 11 and Fig. As shown in Figure 12, the internal tooth 44 has a contact angle α1 formed by the tangent T at the internal tooth pitch circle point 44c and a perpendicular P1 to the internal tooth pitch circle Cp2. The contact angle α1 of the internal tooth 44 is hereinafter referred to as the internal tooth contact angle α1.

[0057] Fig. 13 and Fig. 14 are each a representation of the external gear 46 of the external gear 45. As in Fig. As shown in Figure 13, the external gear 46 has a contact angle α2 formed by the external gear surface 46s and a perpendicular P2 to the external gear pitch circle Cp1 at the external gear pitch circle point 46c on the external gear pitch circle Cp1. The contact angle α2 of the external gear 46 is hereinafter referred to as the external gear contact angle α2.

[0058] As in the Fig. 13 and Fig. For example, as shown in Figure 14, the external gear pressure angle α2 of the external gear 46 decreases with the rotation of the external gear 45. In the drawings, the external gear 46 rotates clockwise.

[0059] In the present embodiment, the external gear pressure angle α2 of the external gear 46 decreases with the rotation of the external gear 45, and therefore, the external gear pressure angle α2 of the external gear 46 is preset to a value greater than the value of the internal tooth pressure angle α1 of the internal tooth 44. The external gear pressure angle α2 is set by the designer to the value achieved, for example, by adding the external gear pressure angle α2, which decreases with the rotation of the external gear 46, to the internal tooth pressure angle α1 of the internal tooth 44. The tangent to the internal tooth surface 44s at the point of contact with the external gear surface 46s is thus parallel to the external gear surface 46s when the external gear 46 is inclined to decrease the external gear pressure angle α2, as shown in Fig. 15. This prevents contact between the edge 44e of the inner tooth surface 44s and the outer gear surface 46s.

[0060] The present disclosure is not limited to the embodiments described above and may be implemented in other embodiments with appropriate modifications.

[0061] For example, in the embodiments of the present disclosure, the external gear pressure angle α2 of the external gear 46 is set larger than the internal tooth pressure angle α1 of the internal tooth 44 to prevent contact between the edge 44e of the internal tooth 44 and the external gear surface 46s. Instead, the radius of curvature of the arc of the internal tooth surface 44s can be further reduced. This prevents contact between the edge 44e of the internal tooth 44 and the external gear surface 46s.

[0062] In the embodiments of the present disclosure, the external gear 45 rotates clockwise. However, the external gear 45 may also rotate counterclockwise. In this case, the drawings described in Embodiments 1 and 2 are modified according to the rotation direction of the external gear 45. For example, the inclinations of the right and left sides of the external gear 46 in Fig. 14 and Fig. 15 swapped.

[0063] The flexible shaft coupling 4 can also be used for structures other than rail vehicles that transmit power from the input shaft of an electric motor to an output shaft.

[0064] The foregoing describes some example embodiments for illustrative purposes. Although specific embodiments have been presented in the above discussion, those skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be considered in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the appended claims and the full scope of equivalents of those claims. List of reference symbols 1 bogie 2 wheel unit 3 electric motor 4 Flexible shaft coupling 5 Gear device 6 Suspension 11 bogie frame 21 wheels 22 Axis 31 Drive shaft 41 Outer pipe unit 42 Inner pipe unit 43 Internal gear 44 inner tooth 44b Tooth base 44c Internal tooth pitch circle point (pitch circle point of the internal tooth) 44th edge 44s inner tooth surface (tooth surface of the inner tooth) 44t tooth tip 45 External gear 46 Outer tooth 46b Tooth base 46c External tooth pitch circle point (pitch circle point of the external tooth) 46s Outer tooth surface (tooth surface of the outer tooth) 46t tooth tip 51 Output shaft 411 First outer sleeve 412 Second outer sleeve 421 First inner sleeve 422 Second inner sleeve AX central axis Cp1 external tooth pitch circle (pitch circle of the external tooth) Cp2 internal tooth pitch circle (pitch circle of the internal tooth) α1 internal tooth pressure angle (pressure angle of the internal tooth) α2 External tooth pressure angle (pressure angle of the external tooth) P1, P2 Vertical T Tangent

Claims

[1] Flexible shaft coupling, comprising: a first gear; and a second gear meshing with the first gear, the first gear having a first tooth surface, the second gear having a second tooth surface, and at least one of the first tooth surface or the second tooth surface being curved outwardly when viewed in the tooth direction. [2] A flexible shaft coupling according to claim 1, wherein at least one of the first tooth surface or the second tooth surface has an arc shape when viewed in the tooth direction. [3] A flexible shaft coupling according to claim 1 or 2, wherein the first tooth surface has a straight line shape when viewed in the tooth direction, and the second tooth surface has an arc shape having a tangent parallel to the straight line when viewed in the tooth direction. [4] Flexible shaft coupling according to claim 3, wherein the tangent passes through a point on a pitch circle of the second gear and is parallel to the straight line. [5] Flexible shaft coupling according to one of claims 1 to 4, wherein the first tooth surface and the second tooth surface have different pressure angles. [6] Flexible shaft coupling according to one of claims 1 to 5, wherein the first tooth surface has a larger pressure angle than the pressure angle of the second tooth surface. [7] Flexible shaft coupling according to one of claims 1 to 6, wherein the first gear is an external gear and the second gear is an internal gear.

Images