Planetary gear mechanism and power transmission unit

Abstract

A planetary gear mechanism 10 has a sun gear 11, a plurality of planetary gears 12, a carrier 13 supporting the plurality of planetary gears 12, and a pair of thrust bearings 14 for supporting axial forces in the planetary gears 13. Each planetary gear 13 has a planetary shaft part 23 where a first gear 21 and a second gear 22 are juxtaposed in the axial direction and positioned on the outer periphery. The carrier 13 has a support shaft 26 for supporting the planetary gears 12, and a pair of disk parts 27. The planetary shaft part 23 has a bearing raceway surface 25 on an end face 24 in the axial direction thereof. The thrust bearings 14 have a plurality of balls 31 disposed between the bearing raceway surface 25 and a lateral surface 28 of the disk parts 27, and a cage 32 holding the plurality of balls 31.

Description

Planetary gear mechanism and power transmission unit

[0001] The present invention relates to a planetary gear mechanism and a power transmission unit.

[0002] Patent Document 1 discloses a planetary gear mechanism. The planetary gear mechanism includes a ring gear, a sun gear, a plurality of planetary gears disposed between the ring gear and the sun gear, and a carrier that supports the plurality of planetary gears. The planetary gear mechanism is used as a reducer.

[0003] Japanese Patent Application Laid-Open No. 2021-63521

[0004] Figure 7 is a cross-sectional view showing a planetary gear portion of a conventional planetary gear mechanism 100. A carrier 90 has a support shaft 89 and a pair of disk portions 88 located on both axial sides of the support shaft 89 to support a planetary gear 91. The planetary gear mechanism 100 has a pair of thrust bearings 92 for supporting the axial force of the planetary gear 91, and a radial bearing 93 for supporting the radial force of the planetary gear 91. The planetary gear 91 shown in Figure 7 is a stepped pinion gear having a large-diameter gear 98 and a small-diameter gear 99.

[0005] The thrust bearing 92 has a plurality of needle rollers 94 and annular plate-shaped first and second raceways 95 and 96 with which the needle rollers 94 roll. The first raceway 95 is attached to the side surface of the disk portion 88 of the carrier 90. The second raceway 96 is attached to the end of the shaft portion 911 of the planetary gear 91.

[0006] To save energy, it is necessary to reduce the rotational resistance in the planetary gear mechanism 100. Furthermore, to reduce the weight of equipment that incorporates the planetary gear mechanism 100, it is necessary to reduce the size of the planetary gear mechanism 100. Therefore, an object of the present invention is to provide a planetary gear mechanism that is capable of reducing rotational resistance and making it possible to reduce the axial dimension, and a power transmission unit that has such a planetary gear mechanism.

[0007] The planetary gear mechanism of the present invention comprises a sun gear, a plurality of planetary gears arranged between a ring gear and the sun gear, a carrier supporting the plurality of planetary gears, and a pair of thrust bearings for supporting the axial force of the planetary gears, wherein the planetary gears have a first gear that meshes with the sun gear, a second gear that meshes with the ring gear, and a planetary shaft portion on the outer periphery where the first gear and the second gear are lined up in the axial direction, the carrier has a support shaft for supporting the planetary gears and a pair of disc portions located on both axial sides of the support shaft, the planetary shaft portion has a bearing raceway surface on its axial end face, and the thrust bearing has a plurality of balls arranged between the bearing raceway surface and the side of the disc portion, and a cage that holds the plurality of balls.

[0008] The present invention is a power transmission unit for transmitting the power of a motor to an axle, comprising: a planetary gear mechanism to which the rotational force of the motor is input; and a differential gear mechanism that receives the rotational force of the carrier of the planetary gear mechanism as an input and outputs power to the axle.

[0009] FIG. 1 is a configuration diagram showing an electric drive unit. FIG. 2 is a cross-sectional view showing a planetary gear portion of a planetary gear mechanism. FIG. 3 is an enlarged cross-sectional view showing an end of a planetary shaft portion shown in FIG. 2. FIG. 4 is a view of a cage viewed along the bearing axial direction. FIG. 5 is a cross-sectional view showing a modified example of a second bearing raceway surface. FIG. 6 is a view showing a modified example of a disengagement prevention portion. FIG. 7 is a cross-sectional view showing a planetary gear portion of a conventional planetary gear mechanism.

[0010] <Outline of Embodiments of the Present Invention> The following is a description of outlines of embodiments of the present invention. (1) A planetary gear mechanism according to an embodiment of the present invention includes a sun gear, a plurality of planet gears arranged between a ring gear and the sun gear, a carrier supporting the plurality of planet gears, and a pair of thrust bearings for supporting an axial force of the planet gears, the planet gears include a first gear meshing with the sun gear, a second gear meshing with the ring gear, and a planet shaft portion on an outer periphery of which the first gear and the second gear are aligned in the axial direction, the carrier includes a support shaft for supporting the planet gears and a pair of disk portions located on both axial sides of the support shaft, the planet shaft portion has a bearing raceway surface on an end face in the axial direction, and the thrust bearing includes a plurality of balls arranged between the bearing raceway surface and a side surface of the disk portion, and a cage for holding the plurality of balls.

[0011] The planetary gear has a planetary shaft portion, whose axial end face has a bearing raceway surface with which balls roll and contact, and the balls roll and contact the side surface of the disk portion of the carrier. Therefore, the thrust bearing that supports the axial force of the planetary gear does not require a raceway member with rolling elements that roll and contact, as in the past. As a result, it is possible to reduce the axial dimension of the planetary gear mechanism. Because the thrust bearing has balls as rolling elements, it is possible to reduce rotational resistance compared to when the rolling elements are rollers.

[0012] (2) In the planetary gear mechanism of (1), the planetary shaft portion has a fall-off prevention portion that prevents the balls from falling off in the bearing axial direction by contacting a part of the balls from the side opposite the bearing raceway surface in the bearing axial direction. The fall-off prevention portion provides a unit in which the planet gears having the planetary shaft portion and the thrust bearing are integrated, making it easier to assemble the planetary gear mechanism.

[0013] (3) In the planetary gear mechanism of (2), the anti-disengagement portion has a protruding portion that protrudes axially from a portion radially inward of the bearing raceway surface, and a contact portion that is continuous with the protruding portion and has an outer diameter larger than the diameter of the inscribed circle of the plurality of balls. The contact portion comes into contact with a portion of the ball from the side opposite the bearing raceway surface in the axial direction of the bearing, thereby preventing the ball from disengaging in the axial direction of the bearing.

[0014] (4) Or, in the planetary gear mechanism of (2), the dropout prevention portion has a protruding portion that protrudes in the axial direction from a portion radially outward of the bearing raceway surface, and a contact portion that is continuous with the protruding portion and has an inner diameter smaller than the diameter of the circumscribing circle of the plurality of balls. The contact portion comes into contact with a portion of the ball from the side opposite the bearing raceway surface in the bearing axial direction, thereby preventing the ball from dropping out in the bearing axial direction.

[0015] (5) In the planetary gear mechanism of (3), the cage has an annular portion located radially outward of the plurality of balls in the bearing direction, and a plurality of column portions extending radially inward from the annular portion, and pockets for accommodating the balls are located radially inward of the annular portion between adjacent column portions in the bearing circumferential direction, and the pockets open radially inward. With this configuration, the plurality of balls can be arranged along the bearing raceway surface, and then the cage can be attached to the plurality of balls, or the plurality of balls held by the cage can be attached to the bearing raceway surface. This facilitates assembly of the planetary gear and thrust bearing.

[0016] (6) In the planetary gear mechanism of any one of (1) to (5), the side surface of the disk portion has a second bearing raceway surface with which the balls roll, and the second bearing raceway surface is a groove surface that continues in the circumferential direction of the bearing. Compared to a case in which the side surface of the disk portion is flat and part of the flat surface becomes the bearing raceway surface and comes into contact with the balls, the balls come into contact with the groove surface of the disk portion (second bearing raceway surface), making it possible to reduce the surface pressure of the contact.

[0017] (7) Or, in the planetary gear mechanism of any one of (1) to (5), the side surface of the disk portion has a second bearing raceway surface with which the balls roll and come into contact, and the second bearing raceway surface is a flat annular plane that is continuous with the flat surface portion of the disk portion that does not come into contact with the balls. In this case, the disk portion of the carrier does not need to have a recessed groove that is continuous in the bearing circumferential direction.

[0018] (8) A power transmission unit according to an embodiment of the present invention is a power transmission unit for transmitting power from a motor to an axle, and includes any one of the planetary gear mechanisms described in (1) to (7) above, to which the rotational force of the motor is input, and a differential gear mechanism that receives the rotational force of the carrier of the planetary gear mechanism as an input and outputs power to the axle. Since the axial dimension of the planetary gear mechanism is reduced, the axial dimension of the power transmission unit can also be reduced.

[0019] <Details of the embodiment of the present invention> [Power transmission unit] Fig. 1 is a configuration diagram showing an electric drive unit. The electric drive unit 5 shown in Fig. 1 is mounted on an electric vehicle. The electric drive unit 5 has an electric motor 6 and a power transmission unit 50 for transmitting the power of the electric motor 6 to an axle 9. The power transmission unit 50 has a planetary gear mechanism 10, which is a speed reducer, and a differential gear mechanism 8. The electric drive unit 5 has a case 51 that houses the motor 6, the planetary gear mechanism 10, and the differential gear mechanism 8. The case 51 integrates the electric motor 6, the planetary gear mechanism 10, and the differential gear mechanism 8.

[0020] The electric motor 6 has a stator 61, a rotor 62, and an output shaft 63 that rotates integrally with the rotor 62. The rotational force of the output shaft 63 is input to a sun gear 11 of a planetary gear mechanism 10. The planetary gear mechanism 10 reduces the rotational speed of the output shaft 63 of the electric motor 6. The configuration of the planetary gear mechanism 10 will be described later. The differential gear mechanism 8 receives the rotational force of a carrier 13 of the planetary gear mechanism 10 as an input and outputs power to an axle 9. The differential gear mechanism 8 is a device that absorbs the rotational difference between the left and right wheels that occurs when the vehicle turns and transmits power to the left and right wheels. The differential gear mechanism 8 includes multiple bevel gears and has a conventionally known configuration, so a detailed description thereof will be omitted.

[0021] The electric drive unit 5 shown in Fig. 1 has a ring gear 52 that is integral with a case 51. The ring gear 52 has an annular shape and has internal teeth 53 on its inner periphery. A portion of the planetary gear 12 of the planetary gear mechanism 10 meshes with the ring gear 52. The ring gear 52 may be included in the planetary gear mechanism 10.

[0022] [Planetary Gear Mechanism 10] The planetary gear mechanism 10 has a sun gear 11 having external teeth 17, a plurality of (for example, four) planetary gears 12, and a carrier 13. The ring gear 52, sun gear 11, and carrier 13 are arranged coaxially around a single rotation axis C0 of the planetary gear mechanism 10. The plurality of planetary gears 12 are arranged at equal intervals between the ring gear 52 and the sun gear 11. The carrier 13 supports the plurality of planetary gears 12.

[0023] The carrier 13 has support shafts 26 in the same number as the planetary gears 12. The planetary gears 12 rotate around the support shafts 26, centering on a central axis C1 of the planetary gears 12. The central axis C1 is parallel to the rotation axis C0 of the planetary gear mechanism 10. The planetary gears 12 revolve around the rotation axis C0 and rotate around the central axis C1.

[0024] 2 is a cross-sectional view showing a planetary gear portion of the planetary gear mechanism 10, showing a cross section along a plane including the central axis C1. The planetary gear mechanism 10 has a pair of thrust bearings 14 and a radial bearing 15. The thrust bearing 14 and the radial bearing 15 are bearings for supporting the planetary gear 12 so that it can rotate relative to a support shaft 26 of the carrier 13. As will be described later, the planetary shaft portion 23 of the planetary gear 12 has a cylindrical shape. The planetary shaft portion 23 rotates (spins) around the central axis C1 while being supported by the thrust bearing 14 and the radial bearing 15.

[0025] The directions in the planetary gear portion supported by the thrust bearing 14 and the radial bearing 15 are defined below. The direction along the central axis C1 and the direction parallel to the central axis C1 are defined as the "bearing axial direction." The direction perpendicular to the central axis C1 is defined as the "bearing radial direction." The direction along the circle centered on the central axis C1 is defined as the "bearing circumferential direction."

[0026] The planetary gear 12 has a first gear 21 that meshes with the external teeth 17 of the sun gear 11 (see FIG. 1 ), a second gear 22 that meshes with the internal teeth 53 of the ring gear 52, and a cylindrical planetary shaft portion 23. The first gear 21 has a larger outer diameter (diameter) than the second gear 22, so that the first gear 21 is a large-diameter gear and the second gear 22 is a small-diameter gear. The first gear 21 and the second gear 22 are aligned in the axial direction (bearing axis direction) and located on the outer periphery of the planetary shaft portion 23. The planetary gear 12 of this embodiment is a stepped pinion gear having the large-diameter first gear 21 and the small-diameter second gear 22.

[0027] Figure 3 is an enlarged cross-sectional view of the end of the planetary shaft portion 23 shown in Figure 2. The planetary shaft portion 23 has a first bearing raceway surface 25 on its axial end face 24. Balls 31 of the thrust bearing 14 are in rolling contact with the first bearing raceway surface 25. In the cross-section shown in Figure 3, the first bearing raceway surface 25 has a concave arc shape. The radius of the concave arc is slightly larger than the radius of the balls 31. The first bearing raceway surface 25 is a concave groove surface that continues in the circumferential direction of the bearing.

[0028] 1 and 2, the carrier 13 has a plurality of support shafts 26 for supporting a plurality of planetary gears 12 (planetary shaft portions 23), and a pair of disk portions 27. The disk portions 27 are located on both axial sides of the support shafts 26. The plurality of support shafts 26 and the pair of disk portions 27 are integral with each other. The planetary gears 12, the pair of thrust bearings 14, and the radial bearing 15 are disposed between the pair of disk portions 27.

[0029] The thrust bearing 14 is a bearing for supporting the axial force of the planetary gear 12. As shown in Fig. 3, the thrust bearing 14 has a plurality of balls 31 and a cage 32 that holds the plurality of balls 31. The plurality of balls 31 are arranged between the first bearing raceway surface 25 and the side surface 28 of the disk portion 27.

[0030] Figure 4 is a view of the cage 32 as viewed along the bearing axial direction. In Figures 3 and 4, the cage 32 has an annular portion 33 and multiple pillar portions 34. The annular portion 33 is a portion located radially outward from the multiple balls 31 in the bearing radial direction. The pillar portions 34 are portions extending radially inward from the annular portion 33 in the bearing radial direction. Pockets 35 that accommodate the balls 31 are located radially inward of the annular portion 33 and between two pillar portions 34 that are adjacent in the bearing circumferential direction. The pockets 35 open radially inward in the bearing radial direction.

[0031] As shown in Figure 3, the side surface 28 of the disc portion 27 of the carrier 13 has a second bearing raceway surface 36 with which the balls 31 roll and make contact. The side surface 28 of the disc portion 27 has a portion 29 (hereinafter referred to as the "flat surface portion 29") that is a flat surface that does not come into contact with the balls 31. The flat surface portion 29 is a flat surface that is perpendicular to the bearing axial direction. In the embodiment shown in Figure 3, the second bearing raceway surface 36 is a flat annular plane that is continuous with the flat surface portion 29. In other words, the balls 31 roll and make contact with the flat surface of the side surface 28 of the disc portion 27. For this reason, the disc portion 27 does not need a recessed groove that continues in the circumferential direction of the bearing.

[0032] Figure 5 is a cross-sectional view showing a modified example of the second bearing raceway surface 36. In the modified example shown in Figure 5, the side surface 28 of the disc portion 27 has a second bearing raceway surface 36 with which the balls 31 roll, and this second bearing raceway surface 36 is a surface of a concave groove that continues in the circumferential direction of the bearing. In other words, the second bearing raceway surface 36 has a concave arc shape in the cross section shown in Figure 5. The radius of this concave arc is slightly larger than the radius of the balls 31.

[0033] In the embodiment shown in Fig. 3, the side surface 28 of the disk portion 27 is flat, and part of this flat surface forms the second bearing raceway surface 36, and the balls 31 roll and contact the second bearing raceway surface 36. In the modified embodiment shown in Fig. 5, compared to the embodiment shown in Fig. 3, the balls 31 come into contact with the surface of the recessed groove (second bearing raceway surface 36), making it possible to reduce the surface pressure of that contact.

[0034] The radial bearing 15 (see FIG. 2) is a bearing for supporting the radial force of the planetary gear 12. The radial bearing 15 has a plurality of rollers (needle rollers) 38 and a cylindrical cage 39 that holds the plurality of rollers 38. The outer peripheral surface 261 of the support shaft 26 of the carrier 13 is the raceway surface with which the rollers 38 roll and make contact, and the inner peripheral surface 231 of the planetary shaft portion 23 of the planetary gear 12 is the raceway surface with which the rollers 38 roll and make contact. In the embodiment shown in FIG. 2, the radial bearing 15 is composed of two rows of needle rollers with a cage.

[0035] When assembling the planetary gear mechanism 10, the unit in which the planet gear 12 and thrust bearing 14 are integrated is attached to the carrier 13. Therefore, as shown in Fig. 3 (Fig. 5), the planet shaft portion 23 of the planet gear 12 has a drop-off prevention portion 41 that prevents the balls 31 from dropping off from the planet gear 12. The drop-off prevention portion 41 comes into contact with a part of the balls 31 from the side opposite the first bearing raceway surface 25 in the bearing axial direction, thereby preventing the balls 31 from dropping off outside the bearing axial direction (to the right in Figs. 3 and 5).

[0036] The fall-off prevention portion 41 is provided at the end of the planetary shaft portion 23 and has a protruding portion 46 and a contact portion 47. The protruding portion 46 is a ring-shaped portion that protrudes axially from a portion 45 that is radially inward of the first bearing raceway surface 25. The contact portion 47 is continuous with the protruding portion 46 and has an outer diameter D2 that is larger than the diameter D1 of the inscribed circle K1 of the plurality of balls 31.

[0037] The contact portion 47 comes into contact with a portion of the ball 31 from the side opposite the first bearing raceway surface 25 in the bearing axial direction. The plurality of balls 31 are held by the cage 32 in a manner that limits radial displacement. This makes it possible to prevent the balls 31 from falling off outside the bearing axial direction (to the right in the cases of FIGS. 3 and 5 ) before the unit in which the planetary gear 12 and thrust bearing 14 are integrated is assembled to the carrier 13. Such a falling-off prevention portion 41 makes it easier to assemble the planetary gear mechanism 10.

[0038] 3, as described above, the cage 32 has an annular portion 33 located radially outward of the plurality of balls 31 in the bearing direction, and a plurality of pillar portions 34 extending radially inward in the bearing direction from the annular portion 33. Pockets 35 that accommodate the balls 31 open radially inward in the bearing direction.

[0039] In order to integrate the planetary gear 12 and the thrust bearing 14, it is possible to arrange the plurality of balls 31 along the first bearing raceway surface 25, and then attach the cage 32 to the plurality of balls 31 by elastically deforming the cage 32. Alternatively, the plurality of balls 31 held by the cage 32 can be attached to the first bearing raceway surface 25. As described above, the planetary gear 12 and the thrust bearing 14 can be easily assembled.

[0040] Figure 6 is a diagram showing a modified example of the fall-off prevention portion 41. The fall-off prevention portion 41 shown in Figure 6 has a protruding portion 46 and a contact portion 47. The protruding portion 46 is a ring-shaped portion that protrudes in the axial direction from a portion 48 that is radially outward of the first bearing raceway surface 25. The contact portion 47 is continuous with the protruding portion 46 and is a ring-shaped portion that has an inner diameter D4 that is smaller than the diameter D3 of the circumscribing circle K2 of the multiple balls 31.

[0041] The contact portion 47 comes into contact with a portion of the ball 31 from the side opposite the first bearing raceway surface 25 in the bearing axial direction. The plurality of balls 31 are held by the cage 32 in a manner that limits radial displacement. This provides a configuration that prevents the balls 31 from falling out of the bearing axial direction (to the right in the case of FIG. 6 ) before the unit in which the planetary gear 12 and thrust bearing 14 are integrated is assembled to the carrier 13. Such a falling-out prevention portion 41 makes it easy to assemble the planetary gear mechanism 10.

[0042] 6, the cage 32 has an annular portion 33 located radially inward of the plurality of balls 31, and a plurality of pillar portions 34 extending radially outward from the annular portion 33. A pocket 35 that accommodates the balls 31 is located radially outward of the annular portion 33 and between two pillar portions 34 that are adjacent in the circumferential direction of the bearing. The pocket 35 opens radially outward from the bearing.

[0043] In order to integrate the planetary gear 12 and the thrust bearing 14, it is possible to arrange the plurality of balls 31 along the first bearing raceway surface 25, and then attach the cage 32 to the plurality of balls 31 by elastically deforming the cage 32. Alternatively, the plurality of balls 31 held by the cage 32 can be attached to the first bearing raceway surface 25. As described above, the planetary gear 12 and the thrust bearing 14 can be easily assembled.

[0044] In the embodiment shown in Fig. 6, the side surface 28 of the disk portion 27 of the carrier 13 has a second bearing raceway surface 36 with which the balls 31 roll, and the second bearing raceway surface 36 is a grooved surface that continues in the circumferential direction of the bearing. Although not shown, similar to the embodiment shown in Fig. 3, the second bearing raceway surface 36 may be a flat annular plane that is continuous with the flat surface portion 29. In other words, the balls 31 may be configured to roll on the flat surface of the side surface 28 of the disk portion 27.

[0045] [Planetary Gear Mechanism 10 and Power Transmission Unit 50 of the Present Embodiment] As described above, the planetary gear mechanism 10 of the present embodiment (see FIG. 1 ) includes the sun gear 11, a plurality of planet gears 12 arranged between the ring gear 52 and the sun gear 11, a carrier 13 that supports the plurality of planet gears 12, and a pair of thrust bearings 14 that support the axial force of the planet gears 12. The planet gear 12 includes a first gear 21 that meshes with the sun gear 11, a second gear 22 that meshes with the ring gear 52, and a planet shaft portion 23. The first gear 21 and the second gear 22 are aligned in the axial direction and located on the outer periphery of the planet shaft portion 23.

[0046] The carrier 13 has a support shaft 26 for supporting the planet gear 12 (planetary shaft portion 23), and a pair of disk portions 27 located on both axial sides of the support shaft 26. The planetary shaft portion 23 has a first bearing raceway surface 25 on an axial end face 24 thereof. The thrust bearing 14 has a plurality of balls 31 arranged between the first bearing raceway surface 25 and a side surface 28 of the disk portion 27, and a cage 32 that holds the plurality of balls 31.

[0047] The power transmission unit 50 (FIG. 1) has the planetary gear mechanism 10 having the above-described configuration. The power transmission unit 50 has the planetary gear mechanism 10 in which the rotational force of the electric motor 6 is input to the sun gear 11, and the differential gear mechanism 8 in which the rotational force of the carrier 13 of the planetary gear mechanism 10 is input and which outputs power to the axle 9.

[0048] In the planetary gear mechanism 10, the planet shaft portion 23 of the planet gear 12 has, at its axial end face 24, a first bearing raceway surface 25 with which balls 31 roll and contact, and the balls 31 roll and contact a side surface 28 of a disk portion 27 of the carrier 13. Therefore, the thrust bearing 14 that supports the axial force of the planet gear 12 does not require a first raceway ring 95 and a second raceway ring 96 as in the conventional case (see FIG. 7 ). As a result, it is possible to reduce the axial dimension of the planetary gear mechanism 10.

[0049] Since the axial dimension of the planetary gear mechanism 10 is reduced, the axial dimension of the power transmission unit 50 is also reduced. This makes it possible to reduce the weight of the planetary gear mechanism 10, and the weight of the power transmission unit 50 including the planetary gear mechanism 10 is also reduced.

[0050] In this embodiment, the thrust bearing 14 has balls 31 as rolling elements. This reduces rotational resistance compared to when the rolling elements are conventional needle rollers 94 (see FIG. 7 ). As a result, the power transmission unit 50 having the planetary gear mechanism 10 can save energy.

[0051] [Others] The planetary gear mechanism 10 of this embodiment is not only applicable to the power transmission unit 50 for transmitting the power of the electric motor 6 to the axle 9, but can also be applied to other devices. Each part of the planetary gear mechanism 10 may have a form other than that shown in the drawings. For example, the radial bearing 15 may have a form other than that shown in the drawings.

[0052] The above-described embodiments are illustrative in all respects and are not limiting. The scope of the present invention is defined by the claims rather than the above-described embodiments, and includes all modifications within the scope equivalent to the configurations described in the claims.

[0053] DESCRIPTION OF SYMBOLS 6 Motor 8 Differential gear mechanism 9 Axle 10 Planetary gear mechanism 11 Sun gear 12 Planet gear 13 Carrier 14 Thrust bearing 21 First gear 22 Second gear 23 Planet shaft portion 24 End face 25 First bearing raceway surface 26 Support shaft 27 Disk portion 28 Side surface 29 Flat surface portion 31 Ball 32 Cage 33 Annular portion 34 Column portion 35 Pocket 36 Second bearing raceway surface 41 Fall-off prevention portion 45 Inner portion 46 Protrusion 47 Contact portion 48 Outer portion 50 Power transmission unit D1 Diameter D2 Outer diameter D3 Diameter D4 Inner diameter K1 Inscribed circle K2 Circumscribed circle

Claims

Sun gear and a plurality of planetary gears disposed between a ring gear and the sun gear; a carrier supporting the plurality of planetary gears; a pair of thrust bearings for supporting the axial force of the planetary gear; and the planetary gear includes a first gear that meshes with the sun gear, a second gear that meshes with the ring gear, and a planetary shaft portion where the first gear and the second gear are aligned in the axial direction and located on the outer periphery, the carrier has a support shaft for supporting the planetary gear and a pair of disk portions located on both axial sides of the support shaft, The planetary shaft portion has a bearing raceway surface on an end surface in the axial direction thereof, The thrust bearing includes a plurality of balls arranged between the bearing raceway surface and a side surface of the disk portion, and a cage that holds the plurality of balls. Planetary gear mechanism. 　 the planetary shaft portion has a drop-out prevention portion that prevents the balls from dropping out in the bearing axial direction by contacting a part of the balls from the side opposite to the bearing raceway surface in the bearing axial direction; 2. The planetary gear mechanism according to claim 1. 　 The fall-off prevention portion has a protruding portion that protrudes in the axial direction from a portion that is radially inward of the bearing raceway surface, and a contact portion that is continuous with the protruding portion and has an outer diameter that is larger than the diameter of the inscribed circle of the plurality of balls.

3. The planetary gear mechanism according to claim 2. 　 The fall-off prevention portion has a protruding portion that protrudes in the axial direction from a portion that is radially outward of the bearing raceway surface, and a contact portion that is continuous with the protruding portion and has an inner diameter that is smaller than the diameter of a circumscribing circle of the plurality of balls.

3. The planetary gear mechanism according to claim 2. 　 the cage has an annular portion located outward in the bearing radial direction of the plurality of balls, and a plurality of pillar portions extending inward in the bearing radial direction from the annular portion, a pocket for accommodating the ball is provided between adjacent column portions in the circumferential direction of the bearing and inside the annular portion in the radial direction of the bearing, The pocket opens radially inward in the bearing.

4. The planetary gear mechanism according to claim 3. 　 the side surface of the disk portion has a second bearing raceway surface with which the balls roll and come into contact, 3. The planetary gear mechanism according to claim 1, wherein the second bearing raceway surface is a surface of a recessed groove that is continuous in the circumferential direction of the bearing. 　 the side surface of the disk portion has a second bearing raceway surface with which the balls roll and come into contact, 3. The planetary gear mechanism according to claim 1, wherein the second bearing raceway surface is a flat annular plane that is continuous with a flat surface portion of the disk portion that is not in contact with the balls. 　 A power transmission unit for transmitting power from a motor to an axle, a planetary gear mechanism according to claim 1 to which a rotational force of the motor is input; and a differential gear mechanism that receives a rotational force of the carrier of the planetary gear mechanism as an input and outputs power to the axle. Power transmission unit.

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