Speed reducer

Abstract

To provide a speed reducer capable of forming a recess part so as to be adjacent to a portion into which a gear is fitted.SOLUTION: In a speed reducer 5, a side part 50a of a first gear 50 and a side part 51a of a second gear 51, which are fitted to each other in a radial direction, forms a recess part 62.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a speed reducer.

Background Art

[0002] Patent Document 1 discloses a speed reducer. A recess is provided in this speed reducer so as to accumulate a lubricant.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a speed reducer, it is desirable that a lubricant remains in a portion where gears are engaged with each other.

[0005] Therefore, one of the problems of the present invention is to provide a speed reducer capable of forming a recess adjacent to a portion where gears are engaged.

Means for Solving the Problems

[0006] In the speed reducer according to one aspect of the present invention, a recess is formed in side portions of a first gear and a second gear that are engaged with each other in the radial direction.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view schematically showing the structure of a rotating machine 1 according to a specific example. FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1. FIG. 2 is a cross-section along a virtual plane including the rotation axis x. This rotating machine 1 is a rotating machine having a motor and a speed reducer for reducing the rotation of the motor, and is incorporated in, for example, an electric assist bicycle. The rotating machine 1 includes a housing 2. The housing 2 generally has, for example, an approximately cylindrical shape as a whole. The housing 2 is fixed to, for example, the frame of a bicycle. Note that the bicycle includes all types of bicycles such as road bicycles, cross bicycles, mountain bicycles, and city bicycles.

[0009] A crankshaft 3 is rotatably supported in the housing 2 around the rotation axis x. In this example, the rotation axis x coincides with the central axis of the housing 2. The crankshaft 3 has one end 3a on one side S1 in the direction along the rotation axis x (hereinafter referred to as the "rotation axis direction"), and the other end 3b on the other side S2 opposite to the one side S1. Both the one end 3a and the other end 3b project from the housing 2 in the rotation axis direction. Crank arms (not shown) extending in a direction orthogonal to the rotation axis x are attached to the one end 3a and the other end 3b, respectively. A pedal (not shown) is attached to the tip of the crank arm. A chain ring (not shown) is further attached to the crank arm attached to the one end 3a.

[0010] The housing 2 has a housing (hereinafter referred to as the "motor housing") 20 that houses the motor 4, a housing (hereinafter referred to as the "gear housing") 21 that houses the speed reducer 5 according to an embodiment of the present invention, and a cover (hereinafter referred to as the "gear cover") 22. The motor housing 20, the gear housing 21, and the gear cover 22 are coupled to each other by fastening components 23 such as bolts extending in the rotation axis direction. The space between the motor housing 20 and the gear housing 21 is sealed by an annular member (hereinafter referred to as the "gasket") 24. The space between the gear housing 21 and the gear cover 22 is sealed by an annular member (hereinafter referred to as the "gasket") 25. The housing 2 is formed of, for example, a metal material or a resin material. From the viewpoint of thermal conductivity, the motor housing 20 and the gear housing 21 are preferably formed of a metal material. The gaskets 24 and 25 are formed of a metal material or a resin material having elasticity or resilience.

[0011] The motor housing 20 has a cylindrical outer portion (hereinafter referred to as the "outer peripheral portion") 20a centered on the rotation axis x, a cylindrical inner portion (hereinafter referred to as the "inner peripheral portion") 20b centered on the rotation axis x, and a wall 20c connecting the outer peripheral portion 20a and the inner peripheral portion 20b. In this example, the wall 20c connects the ends of the outer peripheral portion 20a and the inner peripheral portion 20b on the other side S2. The outer peripheral portion 20a surrounds the motor 4 from the outer peripheral side in the radial direction orthogonal to the rotation axis x. The inner peripheral portion 20b is disposed inside the motor 4. The inner peripheral surface of the inner peripheral portion 20b faces the outer peripheral surface of the crankshaft 3. In this example, the wall 20c extends along a virtual plane orthogonal to the rotation axis x. That is, the wall 20c faces the motor 4 in the rotation axis direction and forms a bottom.

[0012] A bearing 10 is disposed between the inner peripheral end of the wall 20c and the outer peripheral surface of the crankshaft 3. The bearing 10 is a bearing having rolling elements, for example, a ball bearing. In this way, the motor housing 20 supports the crankshaft 3 so as to be relatively rotatable via the bearing 10 at the inner peripheral end of the wall 20c. The housing 2 further has an annular end cover 26. The end cover 26 covers the other end side S2 of the bearing 10 along the rotational axis direction. The end cover 26 is fixed to the wall 20c by fastening components 27 such as screws, for example. The other end 3b of the crankshaft 3 projects from the housing 2 to the other end side S2 through a hole (through hole) of the end cover 26 formed along the rotational axis x.

[0013] Figure 3 is a cross-sectional view taken along line 3-3 of Figure 2. Referring to Figures 2 and 3 together, the motor 4 has a stator 40 and a rotor 41 that is relatively rotatable with respect to the stator 40. The stator 40 has a magnetic body (hereinafter referred to as "yoke"), that is, a stator core 42, a coil 43, and an insulator 44. The stator core 42 is formed from a laminate in which a plurality of annular silicon steel sheets or electromagnetic steel sheets are laminated in the rotational axis direction. The stator core 42 is fixed to the inner peripheral surface of the outer peripheral portion 20a of the motor housing 20. The stator core 42 has a plurality of teeth 42a arranged circumferentially around the rotational axis x. The coil 43 is wound around each tooth 42a. The insulator 44 insulates the stator core 42 and the coil 43.

[0014] The stator 40 is covered with a predetermined member 45 (see FIG. 2). The predetermined member 45 is formed of, for example, a resin material having heat conductivity. A substrate (hereinafter referred to as "printed circuit board") 46 is fixed to the other end side S2 of the predetermined member 45. The printed circuit board 46 is provided with a plurality of electronic components such as wiring for electrically connecting the coil, a temperature sensor for detecting temperature, and a magnetic sensor. This printed circuit board 46 is electrically connected to, for example, the outer peripheral surface of the rotating device 1 or another substrate provided outside. Further, the printed circuit board 46 may be composed of a printed circuit board and a plurality of bus bars, and the printed circuit board and the plurality of bus bars may be electrically connected. A sensor (not shown) for detecting the torque acting on the crankshaft 3 is incorporated in the rotating device 1. A control circuit capable of determining the current value of the current supplied to the coil 43 based on the detected value of the torque from this sensor is mounted on the printed circuit board 46. Current is supplied to the coil 43 from, for example, a battery (not shown) mounted on a bicycle. Thus, the control circuit can control the rotational speed of the motor 4 according to the value of the torque of the crankshaft 3.

[0015] The rotor 41 has a magnet 47 and a magnetic body (hereinafter referred to as "yoke") 48. The yoke 48 is formed of, for example, a magnetic material. A plurality of magnets 47 arranged in the circumferential direction are supported by the yoke 48. The magnet 47 faces the outer peripheral surface of the pole portion (hereinafter referred to as "tooth") 42a of the stator core 42 with a predetermined magnetic gap. When current is supplied to the coil 43, the rotor 41 can rotate relative to the stator 40 about the rotation axis x due to the magnetic interaction between the coil 43 and the magnet 47. Note that the yoke 48 may be, for example, a cylindrical member centered on the rotation axis x, the magnet 47 may be a single cylindrical permanent magnet, or a plurality of permanent magnets may be connected to each other in the circumferential direction to form a cylindrical shape.

[0016] The rotor 41 is attached to the motor shaft 49. The motor shaft 49 has a cylindrical main body 49a centered on the rotation axis x and a flange 49b that extends annularly in the radial direction from the outer peripheral surface of the main body 49a. The outer peripheral surface of the main body 49a is defined by a cylindrical surface centered on the rotation axis x, while the outer peripheral surface of the flange 49b is defined by a cylindrical surface having a central axis eccentric from the rotation axis x. The rotor 41 is fixed to the outer peripheral surface of the main body 49a, for example, by press-fitting. The motor shaft 49 is supported so as to be relatively rotatable via a bearing 11 on the outer peripheral surface of the inner peripheral portion 20b of the motor housing 20 adjacent to the end portion on the other end side S2. The bearing 11 is a bearing having rolling elements, for example, a ball bearing. In the rotational axis direction, the inner peripheral surface of the main body 49a faces the outer peripheral surface of the crankshaft 3. In the gear housing 21, a speed reducer 5 described later is connected to the end portion on the one end side S1 of the motor shaft 49.

[0017] The gear housing 21 has a cylindrical outer portion (hereinafter referred to as the "outer peripheral portion") 21a centered on the rotation axis x. A plate 28 is fixed to the inner peripheral surface of the outer peripheral portion 21a adjacent to the end portion on the other end side S2 of the outer peripheral portion 21a. In this example, the plate 28 is directly fixed to the outer peripheral portion 21a, but it may be indirectly fixed via other members. The gear cover 22 has a cylindrical outer portion (hereinafter referred to as the "outer peripheral portion") 22a centered on the rotation axis x and a cylindrical inner portion (hereinafter referred to as the "inner peripheral portion") 22b that is inside the outer peripheral portion 22a and has a smaller diameter and is centered on the rotation axis x. The speed reducer 5 is housed in the gear housing 21 and the gear cover 22. The speed reducer 5 is arranged side by side with the motor 4 in the rotational axis direction. The plate 28 is formed in an annular shape that extends across between the motor 4 and the speed reducer 5. That is, the speed reducer 5 is arranged on the opposite side of the motor 4 with the plate 28 interposed therebetween in the rotational axis direction.

[0018] FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2. Referring to FIGS. 2 and 4 together, the speed reducer 5 constitutes a cycloid speed reducer as an example. The speed reducer 5 includes a first gear 50 formed on the outer peripheral portion 21a of the gear housing 21, a second gear 51 disposed on the inner peripheral side of the first gear 50 and fitted to the first gear 50, and a third gear 52 disposed on the further inner peripheral side of the first gear 50 and fitted to the second gear 51. The first gear 50 is a fixed gear. The second gear 51 is a ring gear used as a planetary gear. The third gear 52 is supported on the outer peripheral surface of the flange 49b of the motor shaft 49 via a bearing 12. The bearing 12 is a bearing having rolling elements, for example, a ball bearing. As is apparent from FIG. 2, the bearing 12 and the third gear 52 are arranged side by side in the rotational axis direction. The third gear 52 is supported on the outer peripheral surface of the main body 49a of the motor shaft 49 via a bearing 13. The bearing 13 is a bearing having rolling elements, for example, a ball bearing.

[0019] As shown in FIG. 4, a plurality of teeth 53 arranged in the circumferential direction are formed on the side portion, i.e., the inner peripheral portion 50a, of the first gear 50. A plurality of teeth 54 arranged in the circumferential direction are formed on the side portion, i.e., the outer peripheral portion 51a, of the second gear 51. The outer peripheral portion 51a is surrounded by the first gear 50. A plurality of teeth 55 arranged in the circumferential direction are formed on the side portion, i.e., the inner peripheral portion 51b, of the second gear 51. A plurality of teeth 56 arranged in the circumferential direction are formed on the side portion, i.e., the outer peripheral portion 52a, of the third gear 52. As described above, since the outer peripheral surface of the flange 49b is a cylindrical surface having a central axis eccentric from the rotational axis x, the central axis x1 of the second gear 51 is eccentric from the rotational axis x. On the other hand, the central axes of the first gear 50 and the third gear 52 coincide with the rotational axis x. Thus, while the central axis x1 of the second gear 51 rotates around the rotational axis x, the second gear 51 rotates eccentrically with respect to the first gear 50 and the third gear 52.

[0020] In this example, the number of teeth 53 of the first gear 50 is greater than the number of teeth 54 on the outer peripheral portion 51a of the second gear 51. The number of teeth 54 on the outer peripheral portion 51a of the second gear 51 is greater than the number of teeth 55 on the inner peripheral portion 51b of the second gear 51. Similarly, the number of teeth 55 on the inner peripheral portion 51b of the second gear 51 is greater than the number of teeth 56 on the outer peripheral portion 52a of the third gear 52. When the motor shaft 49 rotates around the rotation axis x, due to its eccentricity and the difference in the number of teeth, a part of the teeth 54 of the second gear 51 meshes with a part of the teeth 53 of the first gear 50. At the same time, on the side opposite to the meshing with the first gear 50 across the rotation axis x, a part of the teeth 55 of the second gear 51 meshes with a part of the teeth 56 of the third gear 52. As a result, the second gear 51 rotates in a direction opposite to the rotation direction of the motor shaft 49. At this time, the third gear 52 rotates in the same rotation direction as the rotation direction of the second gear 51. Thus, the rotation speed of the motor shaft 49 is reduced at a predetermined reduction ratio.

[0021] Returning to FIG. 2, the third gear 52 has a cylindrical main body 52b centered on the rotation axis x and a cylindrical protruding portion 52c centered on the rotation axis x protruding from the main body 52b to one end side S1. The main body 52b has teeth 56 on the outer peripheral portion 52a and is supported by the motor shaft 49 via a bearing 13 on the inner peripheral surface. The protruding portion 52c is supported on the outer peripheral surface of the output shaft 58 via a one-way clutch 57 on its inner peripheral surface, while being supported on the inner peripheral surface of the outer peripheral portion 22a of the gear cover 22 via a bearing 14 on its outer peripheral surface. The bearing 14 is a bearing having rolling elements, for example, a needle bearing. The output shaft 58 is formed in a cylindrical shape around the rotation axis x. The output shaft 58 is arranged side by side with the motor shaft 49 in the rotation axis direction.

[0022] The output shaft 58 is supported on the inner peripheral surface of the inner peripheral portion 22b of the gear cover 22 via the bearing 15 on its outer peripheral surface, while being supported on the outer peripheral surface of the crankshaft 3 via the bearing 16 on its inner peripheral surface. The bearings 15 and 16 are bearings having rolling elements, for example, ball bearings. The inner peripheral surface of the output shaft 58 and the outer peripheral surface of the crankshaft 3 facing each other are connected via a one-way clutch 59. Note that at least a part of the one-way clutches 57 and 59 is covered with a fluid, that is, a lubricant (not shown).

[0023] The one-way clutches 57 and 59 can transmit the rotational force of the third gear 52 to the output shaft 58 in one direction around the rotation axis x (that is, rotate the third gear 52 and the output shaft 58 in the same direction), while being configured to allow relative rotation between the third gear 52 and the output shaft 58 in the other direction around the rotation axis x. The end of the other end side S2 of the output shaft 58 faces the motor shaft 49, while the end of the one end side S1 of the output shaft 58 is disposed outside the gear cover 22. The end of the one end side S1 of the output shaft 58 is connected to a chain ring fixed to the crank arm on the one end side S1. In this way, the rotational force generated by the motor 4 is decelerated by the speed reducer 5 at a predetermined reduction ratio and transmitted from the output shaft 58 to the chain ring.

[0024] FIG. 5 is a perspective view showing a state in which the gear cover 22 and the bearing 14 are removed from the rotating device 1. FIG. 6 is a partial cross-sectional perspective view taken along line 6-6 of FIG. 4. Referring to FIGS. 5 and 6 together, a curved surface 60 continuous in the circumferential direction is formed at the end of the one end side S1 of the inner peripheral portion 50a of the first gear 50. The curved surface 60 is formed, for example, on a cylindrical surface around the rotation axis x. In the inner peripheral portion 50a, the teeth 53 and the curved surface 60 are arranged side by side in the rotation axis direction. In this example, the curved surface 60 extending in the rotation axis direction intersects the surface (hereinafter referred to as the "end face") 53a of the tooth 53 extending in the radial direction. The end face 53a is formed along a virtual plane orthogonal to the rotation axis x in this example. On the other hand, in the radial direction, the end of the tooth 53 is disposed on the side of the second gear 51 with respect to the curved surface 60.

[0025] A curved surface 61 that is continuous in the circumferential direction is formed at an end portion on one end side S1 of the outer peripheral portion 51a of the second gear 51. The curved surface 61 is defined by, for example, a cylindrical surface around the rotation axis x. In the outer peripheral portion 51a, the teeth 54 and the curved surface 61 are arranged side by side in the rotation axis direction. In this example, the curved surface 61 is adjacent to the surface (hereinafter referred to as the "end face") 54a of the tooth 54 in the radial direction. The curved surface 61 is arranged on the side opposite to the curved surface 60 of the first gear 50 in the radial direction. The end face 54a extending in the radial direction intersects the curved surface 61 extending in the rotation axis direction. The end face 54a is defined along a virtual plane orthogonal to the rotation axis x in this example. The end face 54a extends along, for example, the same virtual plane as the end face 53a. On the other hand, in the radial direction, the end portion of the tooth 54 is arranged on the first gear 50 side with respect to the curved surface 61.

[0026] A recess 62 is formed by the curved surface 60 and the end face 53a of the first gear 50 and the curved surface 61 and the end face 54a of the second gear 51. The recess 62 is a recess that is recessed toward the other end side S2. That is, the recess 62 is formed by the inner peripheral portion 50a of the first gear 50 and the outer peripheral portion 51a of the second gear 51 that fit together in the radial direction. This recess 62 forms a region (a housing portion for the lubricant W) where the lubricant W accumulates. At least a part of the region including the meshing portion of the teeth 53 of the first gear 50 and the teeth 54 of the second gear 51 is covered with the lubricant W. Even if the lubricant W leaks from between the first gear 50 and the second gear 51 or between the second gear 51 and the third gear 52 due to the eccentric rotation of the second gear 51, the recess 62 can store the lubricant W inside. The lubricant W accumulated in the recess 62 in this way is drawn back between the first gear 50 and the second gear 51 or between the second gear 51 and the second gear 52 again.

[0027] An example of the usage mode of the rotating device 1 as described above will be explained. When a user of a bicycle incorporating the rotating device 1 pedals to rotate the crank arm, the crankshaft 3 rotates around the rotation axis x. In this example, when viewed from one side S1, the crankshaft 3 rotates clockwise. When the torque sensor detects an increase in the torque acting on the crankshaft 3 that is equal to or greater than a predetermined threshold value, the control circuit of the printed circuit board 46, which is electrically connected from an external power source via another substrate, supplies current to the coil 43 of the motor 4. Due to the magnetic interaction between the coil 43 and the magnet 47, the rotor 41 rotates relative to the stator 40 around the rotation axis x. The rotational force generated by this rotation is transmitted from the motor shaft 49 to the speed reducer 5. The rotor 41 and the motor shaft 49 rotate counterclockwise when viewed from one side S1.

[0028] In the speed reducer 5, the rotational speed is decreased by the engagement of the first gear 50, the second gear 51, and the third gear 52, and the rotational force is transmitted from the second gear 52 to the output shaft 58. Note that due to the function of the speed reducer 5, the rotation direction of the motor shaft 49 is opposite to the rotation direction of the output shaft 58. That is, when viewed from one side S1, the output shaft 58 rotates clockwise. The rotational force with a decreased rotational speed is transmitted from the output shaft 58 to the chain ring and the crankshaft 3. As a result, the rotational force of the motor 4 assists the rotation of the crank arm of the bicycle while increasing its torque. In this way, the user of the bicycle can easily pedal even in a situation where the torque is large due to the rotational force of the motor 4.

[0029] In such a rotating device 1, an inner peripheral portion 50a of a first gear 50 and an outer peripheral portion 51a of a second gear 51 that fit into each other in the radial direction form a recess 62. The recess 62 is formed, for example, at an end portion on one end side S1 of the first gear 50 and the second gear 51 in the rotation axis direction. As a result, when the teeth 53 of the first gear 50 and the teeth 54 of the second gear 51 mesh with each other, the lubricant W that leaks out in the rotation axis direction from between them can stay in the recess 62. In this way, it is possible to prevent the lubricant W from leaking from between the first gear 50 and the second gear 51 to other spaces. As a result, by surely reducing the wear of the first gear 50 and the second gear 51, it is possible to realize a longer service life of the speed reducer 5.

[0030] In the speed reducer 5 of the rotating device 1 as described above, the recess 62 is formed continuously in the circumferential direction around the rotation axis x, but may be partially formed in a partial region in the circumferential direction. Further, the recess 62 is formed by the first gear 50 and the second gear 51 that fit into each other in the radial direction. For example, additional recesses may be formed by the second gear 51 and the third gear 52 that similarly fit into each other in the radial direction. This additional recess may also be formed continuously in the circumferential direction around the rotation axis x, or may be partially formed in a partial region in the circumferential direction. When an additional recess is formed, a cylindrical wall portion may be formed between the recess 62 and the additional recess. Further, the formation of the recess 62 may be omitted, and only the additional recess may be provided.

[0031] Furthermore, in the speed reducer 5, the end face 53a of the tooth 53 of the first gear 50 that forms the recess 62 and the end face 54a of the tooth 54 of the second gear 51 are defined along the same virtual plane, but may be defined along different virtual planes. That is, the distance from the end portion of the first gear 50 on one side S1 in the rotation axis direction to the end face 53a and the distance from the end portion of the second gear 51 on the same one side S1 to the end face 54a may be different from each other. Further, the recess 62 is formed by the curved surface 60 and the end face 53a of the first gear 50 and the curved surface 61 and the end face 54a of the second gear 51, but may be formed by the curved surface 60 and the end face 53a of the first gear 50 and the tooth 54 of the second gear 51, or by the tooth 53 of the first gear 50 and the curved surface 61 and the end face 53a of the second gear 51.

[0032] Note that the speed reducer 5 according to an embodiment of the present invention is incorporated into the rotating device 1 attached to an electric assist bicycle. However, the speed reducer 5 may be used for other applications such as industrial robots and machine tools instead of the electric assist bicycle. Also, the above-described speed reducer 5 is configured as a cycloid speed reducer as an example, but may be other types of speed reducers such as a harmonic gear speed reducer.

[0033] The embodiments described above are for facilitating the understanding of the present invention and are not for limiting and interpreting the present invention. Also, the above-described embodiments do not limit the objects to which the present invention is applied, and the present invention can include any object as its application target. Each component included in the above embodiments, as well as its arrangement, material, conditions, shape, size, etc. are not limited to those illustrated and can be changed as appropriate. For example, the present invention includes differences that occur in the implementation such as manufacturing tolerances. Also, components shown in different embodiments can be partially substituted or combined with each other within a technically non-contradictory range. Also, each configuration can be selectively combined as appropriate so as to achieve at least part of the above-described problems and effects.

Description of Reference Numerals

[0034] 1 Rotating machine, 10 Bearings, 11 Bearings, 12 Bearings, 13 Bearings, 14 Bearings, 15 Bearings, 16 Bearings, 2 Housing, 20 Motor housing, 20a Outer part (outer peripheral part), 20b Inner part (inner peripheral part), 20c Wall, 21 Gear housing, 21a Outer part (outer peripheral part), 22 Gear cover, 22a Outer part (outer peripheral part), 22b Inner part (inner peripheral part), 23 Fastening parts, 24 Annular member (gasket), 25 Annular member (gasket), 26 End cover, 27 Fastening parts, 28 Plate, 3 Crankshaft, 3a One end, 3b The other end, 4 Motor, 40 Stator, 41 Rotor, 42 Magnetic body (stator core), 42a Magnetic pole part (teeth), 43 Coil, 44 Insulator, 45 Predetermined member, 46 Substrate (printed circuit board), 47 Magnet, 48 Magnetic body (yoke), 49 Motor shaft (rotating shaft), 5 Reducer, 50 First gear, 50a Inner peripheral part (side part), 51 Second gear, 51a Outer peripheral part (side part), 51b Inner peripheral part (side part), 52 Third gear, 52a Outer peripheral part (side part), 53 Teeth, 53a Surface (end face), 54 Teeth, 54a Surface (end face), 55 Teeth, 56 Teeth, 57 One-way clutch, 58 Output shaft, 59 One-way clutch, 60 Curved surface, 61 Curved surface, S1 One side, S2 The other side, W Lubricant, x Axis of rotation, x1 Central axis

Claims

1. A speed reducer in which side portions of a first gear and a second gear that fit together in the radial direction form recesses.

2. The side portion of the first gear includes a circumferentially continuous curved surface and a plurality of teeth arranged in the circumferential direction. The side portion of the second gear includes a circumferentially continuous curved surface and a plurality of teeth arranged in the circumferential direction. The speed reducer according to claim 1, wherein the curved surface of the first gear and the curved surface of the second gear face each other in the radial direction.

3. In the radial direction, the ends of the plurality of teeth of the first gear are on the second gear side with respect to the curved surface of the first gear. The speed reducer according to claim 2, wherein in the radial direction, the ends of the plurality of teeth of the second gear are on the first gear side with respect to the curved surface of the second gear.

4. The speed reducer according to any one of claims 1 to 3, wherein fluid accumulates in the recess.

5. In the radial direction, the curved surface of the first gear and the plurality of teeth are arranged side by side. The speed reducer according to any one of claims 1 to 4, wherein in the radial direction, the curved surface of the second gear and the plurality of teeth are arranged side by side.

6. In the radial direction, a third gear that fits onto the second gear is provided. The side portion of the first gear is an inner peripheral portion that surrounds the second gear. The side portion of the second gear is an outer peripheral portion that is surrounded by the first gear. In the radial direction, the outer peripheral portion of the third gear and the inner peripheral portion of the second gear fit together. The speed reducer according to any one of claims 1 to 5, wherein the second gear rotates eccentrically with respect to the first gear and the third gear.

7. The speed reducer according to any one of claims 1 to 6, wherein the first gear is a fixed gear.

8. Comprising a rotating shaft. The speed reducer according to claim 7, wherein the third gear is supported by the rotating shaft.

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