Rotation device and gear device

Abstract

The invention provides a rotating device and a gear device. A reduction gear according to one embodiment of the present invention is provided with: a housing (2) and a carrier (3); and a main bearing (6) that supports the housing (2) and the carrier (3) so that the housing (2) and the carrier (3) can rotate relative to each other. The main bearing (6) is provided with an outer ring (31), an inner ring (32), and rolling bodies (33). Either the outer ring (31) or the inner ring (32) is insert-cast in at least either the housing (2) or the carrier (3), a protrusion (34) protruding toward the other one of the first ring joining surface (32c) and the first substrate joining surface (40a) is formed on the other one of the first ring joining surface (32c) and the first substrate joining surface (40a), and a recess (40) into which the protrusion (34) is fitted is formed on the other one of the first ring joining surface (32c) and the first substrate joining surface (40a).

Description

Technical Field

[0001] The present invention relates to rotating devices and gear devices. Background Art

[0002] Conventionally, rotating devices and gear devices are known that include two rotating bodies and rolling bearings that enable relative rotation between the two rotating bodies. An example of a rolling bearing is a radial bearing. A radial bearing includes an outer ring, an inner ring, and multiple rolling elements positioned between these outer and inner rings. To simplify and miniaturize the bearing structure in such gear devices, technologies have been disclosed that integrate the outer and inner rings with the rotating body (see, for example, Patent Document 1).

[0003] In this technology, the rotating body (supporting member and disc) is formed from castings such as spheroidal graphite cast iron, while the inner ring (inner lace) is formed from high-carbon chromium bearing steel such as SUJ or carbon steel such as S55C. These dissimilar components are joined, and the inner ring is heat-treated to form the rolling surface of the rolling elements.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 9-14359 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, even if different components are joined as in the conventional technology described above, there is a possibility that the joining will not be complete and the inner ring will fall off the rotating body. Therefore, there is a problem that it is difficult to achieve practical application for simplifying and miniaturizing the bearing structure.

[0009] The present invention provides a rotating device and a gear device capable of reliably simplifying and miniaturizing a bearing structure.

[0010] Solutions for solving problems

[0011] The camming member is a pair of camming members, each of which is connected to the other end of the camming member by a toothed connection, and the camming member is connected to the other end of the camming member by a toothed connection.

[0012] This structure allows the rotating body and the rings of the rolling bearing to be integrated. Even if the connection between the rotating body and the rings is incomplete, the engagement of the protrusions and recesses prevents the rings from falling off the rotating body. This reliably simplifies and miniaturizes the bearing structure.

[0013] In the above structure, it can also be that the rolling bearing is any one of a radial ball bearing and a radial roller bearing, the rotating body joint surface and the ring joint surface are along the axial direction, and another rotating body joint surface extending in a direction intersecting the rotating body joint surface and joined to the ring is formed on the rotating body, and another ring joint surface joined to the other rotating body joint surface is formed on the ring, the convex portion is formed on the ring, and is formed in a manner that gradually protrudes toward the rotating body side as it approaches the other ring joint surface, and the concave portion is formed on the rotating body, and is formed in a manner that gradually deepens as it approaches the other rotating body joint surface.

[0014] In the above structure, the other ring joint surface may be formed in a manner that gradually protrudes toward the other rotating body joint surface as it moves toward the ring joint surface, and the other rotating body joint surface may be formed in a manner that gradually protrudes toward the other ring joint surface as it moves away from the rotating body joint surface.

[0015] In the above structure, the convex portion, the concave portion, the other ring joint surface, and the other rotating body joint surface may be inclined respectively, and the inclination angle of the other ring joint surface and the other rotating body joint surface relative to the radial direction may be larger than the inclination angle of the convex portion and the concave portion relative to the axial direction.

[0016] In the above configuration, the thermal expansion coefficient of the rotating body may be greater than the thermal expansion coefficient of the ring.

[0017] In the above structure, the convex portion may be formed on the entire ring joint surface, and a ring chamfered portion may be formed at the corner on the other ring joint surface side, and the concave portion may be formed on the entire rotating body joint surface, and a rotating body chamfered portion may be formed at the corner on the other rotating body joint surface side.

[0018] In the above configuration, the ring chamfered portion and the rotating body chamfered portion may be formed flat, and the ring chamfered portion and the rotating body chamfered portion may extend in a direction perpendicular to a load action line of the rolling bearing.

[0019] In the above structure, it may also be that the rolling bearing includes any one of a radial ball bearing and a radial roller bearing, and the rotating body joint surface has: an axial rotating body joint surface, which is along the axial direction; and a radial rotating body joint surface, which extends in a direction intersecting the axial rotating body joint surface, and the ring joint surface has: an axial ring joint surface, which is along the axial direction; and a radial ring joint surface, which extends in a direction intersecting the axial ring joint surface, and the convex portion is formed on at least one of the radial rotating body joint surface and the radial ring joint surface, and the concave portion is formed on the other.

[0020] Another form of the rotating device of the present invention comprises: two rotating bodies; and rolling bearings, which support the two rotating bodies so as to rotate freely relative to each other, and the rolling bearings comprise: two rings, which are respectively arranged with the rotating bodies; and a plurality of rolling bodies, which are arranged between the two rings and on the opposite side of the rotating bodies, at least one of the rings is inlaid and cast in at least one of the rotating bodies, and a recess for the ring to be embedded is formed on the rotating body joint surface of the rotating body that is engaged with the ring, and the recess has a step surface for limiting at least any one of the axial movement and radial movement of the ring.

[0021] This structure allows the rotating body and the ring of the rolling bearing to be integrated. Even if the engagement between the rotating body and the ring is incomplete, the ring can be fitted into the recess to prevent it from falling off the rotating body. Furthermore, the stepped surface can restrict the movement of the ring from the recess, thereby ensuring a secure integration of the rotating body and the ring.

[0022] In the above structure, it may also be that the rolling bearing includes any one of a radial ball bearing and a radial roller bearing, and the rotating body joint surface has: an axial rotating body joint surface, which is along the axial direction; and a radial rotating body joint surface, which extends in a direction intersecting the axial rotating body joint surface, and the recess is formed on at least any one of the axial rotating body joint surface and the radial rotating body joint surface, and the recess formed has at least any one of a first step surface formed on the recess of the axial rotating body joint surface and a second step surface formed on the recess of the radial rotating body joint surface, the first step surface limits the axial movement of the ring, and the second step surface limits the radial movement of the ring.

[0023] In the above structure, the first step surface may extend in a direction intersecting the axial rotating body joint surface and contact the axial end surface of the ring, and the second step surface may extend in a direction intersecting the radial rotating body joint surface and contact the radial end surface of the ring.

[0024] In the above configuration, the ring may have a uniform thickness in a cross-sectional shape along the axial direction.

[0025] Another form of the gear device of the present invention comprises: a cylindrical housing having an internal gear; a gear frame arranged on the radial inner side of the housing and supported on the housing in a rotatable manner by means of a rolling bearing; at least one crankshaft supported on the gear frame in a rotatable manner, and an external rotational force is input to the at least one crankshaft; and an external gear meshing with the internal gear, the crankshaft having: a shaft body; and an eccentric portion, which is provided on the shaft body and is eccentric with respect to the rotation axis of the shaft body, the external gear being supported on the eccentric portion in a rotatable manner, and the rolling bearing having : An outer ring, which is arranged in the housing; an inner ring, which is arranged in the gear rack; and a plurality of rolling elements, which are arranged between the outer ring and the inner ring, at least any one of the outer ring and the inner ring is insert-cast in the corresponding housing and any one of the gear rack, at least any one of the insert-cast outer ring and the inner ring has a convex portion formed on the ring joint surface engaged with any one of the housing and the gear rack, and at least any one of the housing and the gear rack has a concave portion for the convex portion to be embedded in the rotating body joint surface engaged with any one of the outer ring and the inner ring.

[0026] This structure allows the outer ring to be integrated with the housing, or the inner ring to be integrated with the carrier. Even if the engagement between the housing and the outer ring, or between the carrier and the inner ring, is incomplete, the protrusions and recesses engage, preventing the outer ring from falling out of the housing. This also prevents the inner ring from falling out of the carrier. Consequently, the bearing structure can be reliably simplified and miniaturized.

[0027] Effects of the Invention

[0028] The above-mentioned rotating device and gear device can reliably simplify and miniaturize the bearing structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a cross-sectional view of a reduction gear transmission according to an embodiment of the present invention.

[0030] Figure 2 yes Figure 1 Enlarged view of Part II.

[0031] Figure 3 These are explanatory diagrams of a method for manufacturing a substrate portion and an inner ring in an embodiment of the present invention.

[0032] Figure 4 It is an enlarged cross-sectional view of a main bearing and a base plate portion in a first modified example of the embodiment of the present invention.

[0033] Figure 5 It is an enlarged cross-sectional view of a main bearing and a base plate portion in a second modified example of the embodiment of the present invention.

[0034] Figure 6 It is an enlarged cross-sectional view of a main bearing and a base plate portion in a third modified example of the embodiment of the present invention.

[0035] Figure 7 It is an enlarged cross-sectional view of a main bearing and a base plate portion in a fourth modified example of the embodiment of the present invention.

[0036] Figure 8 It is an enlarged cross-sectional view of a main bearing and a base plate portion in a fifth modified example of the embodiment of the present invention.

[0037] Description of Reference Numerals

[0038] 1. Speed ​​reduction device (rotating device, gear device); 2. Housing (rotating body); 3. Gear rack (rotating body); 6. Main bearing (rolling bearing); 7. Base plate portion (rotating body); 8. End plate portion (rotating body); 13. Crankshaft; 13a. First eccentric portion (eccentric portion); 13b. Second eccentric portion (eccentric portion); 13c. Shaft body; 15. First external gear (external gear); 16. Second external gear (external gear); 31. Outer ring (ring); 32. Inner ring (ring); 32b. Axial inner end face (axial end face); 32c. First ring joint surface (ring joint surface, axial ring joint surface); 32d. Radial outer end face (radial end face); 32e. Second ring joint surface ( Another ring joint surface, radial ring joint surface); 32f, circular chamfered surface (ring chamfered portion); 32g, plane chamfered surface (ring chamfered portion); 33, rolling element; 34, convex portion; 38, convex portion; 40, concave portion; 40a, first substrate joint surface (rotating body joint surface, axial rotating body joint surface); 40b, second substrate joint surface (another rotating body joint surface, radial rotating body joint surface); 40c, substrate chamfered surface (rotating body chamfered portion); 40d, substrate plane chamfered surface (rotating body chamfered portion); 44a, first step surface; 44b, second step surface; A1, first rotation axis; A2, second rotation axis (rotation axis); L, load action line; θ1, θ2, inclination angle. DETAILED DESCRIPTION

[0039] Next, embodiments of the present invention will be described with reference to the drawings.

[0040] <Reduction gear>

[0041] Figure 1 It is a cross-sectional view of the reduction gear 1 serving as a gear device.

[0042] like Figure 1 As shown, the reduction gear 1 decelerates the rotation of, for example, an electric motor (not shown) and outputs the decelerated output. The reduction gear 1 is an eccentric oscillating type reduction gear. The reduction gear 1 comprises: a cylindrical housing 2; a gear carrier 3 rotatably disposed radially inwardly of the housing 2; and a reduction mechanism 4 coupled to the gear carrier 3. The central axis of the housing 2 coincides with the rotational axis of the gear carrier 3.

[0043] In the following description, these center axes and rotational axes are collectively referred to as the first rotational axis A1. The direction parallel to the first rotational axis A1 is referred to as the axial direction. The direction of rotation of the gear carrier 3 is referred to as the circumferential direction. The radial direction of the housing 2, which is orthogonal to the axial and circumferential directions, is referred to simply as the radial direction.

[0044] <Housing>

[0045] The housing 2 is formed of spheroidal graphite cast iron (ductile iron). For example, FCD450 is used as the spheroidal graphite cast iron. An outer flange portion 2a extending radially outward is integrally formed on the outer peripheral surface of the housing 2. Multiple bolt holes 2b are formed in the outer flange portion 2a. The bolt holes 2b are arranged at equal intervals in the circumferential direction. Bolts (not shown) are inserted into these bolt holes 2b and tightened to, for example, the arm of an industrial robot, thereby securing the reduction gear 1.

[0046] A plurality of pin grooves 2c are formed along the axial direction on the inner circumferential surface 2d of the housing 2. The pin grooves 2c are arranged at equal intervals in the circumferential direction. Internally toothed pins 5 are respectively fitted into the pin grooves 2c. The internally toothed pins 5 function as internal teeth that mesh with the externally toothed gears 15 and 16 of the reduction gear mechanism 4, which will be discussed later.

[0047] Main bearings 6 are provided on both axial sides of the inner peripheral surface 2d of the housing 2. The carrier 3 is rotatably supported by the housing 2 via the main bearings 6. The detailed structure of the main bearings 6 will be described later.

[0048] <Gear rack>

[0049] The carrier 3 includes a disc-shaped base plate portion 7 and an end plate portion 8 that are disposed opposite to each other in the axial direction, and three column portions 9 that are formed to protrude from the base plate portion 7 toward the end plate portion 8 .

[0050] The pillars 9 are arranged at equal intervals in the circumferential direction. An end plate 8 is arranged at the top end 9a of the pillar 9. The end plate 8 is fixed to the pillar 9 by bolts 10. In this state, a space having a certain width in the axial direction is formed between the base plate 7 and the end plate 8.

[0051] A pin 11 is provided at a portion of the column portion 9 radially inward of the bolt 10. The pin 11 positions the end plate portion 8 relative to the base plate portion 7. The pin 11 is fitted into a pin hole 12 provided in the end plate portion 8.

[0052] The base plate 7 and end plate 8 are formed from spheroidal graphite cast iron (ductile iron). For example, FCD450 is used as the spheroidal graphite cast iron. The outer peripheral surfaces of the base plate 7 and the end plate 8 are rotatably supported by the housing 2 via corresponding main bearings 6. Shaft insertion holes 7a and 8a are formed in the radial centers of the base plate 7 and the end plate 8, respectively. The two shaft insertion holes 7a and 8a are coaxially arranged.

[0053] Three crankshaft insertion holes 7b and 8b are formed in the base plate portion 7 and the end plate portion 8, respectively, between circumferentially adjacent column portions 9. The crankshaft insertion holes 7b and 8b are coaxially arranged. Specifically, the center axes A2 of the axially opposing crankshaft insertion holes 7b and 8b are parallel to the first rotation axis A1. A crankshaft bearing 18 is provided in each crankshaft insertion hole 7b and 8b. The crankshaft bearing 18 is, for example, a tapered roller bearing.

[0054] <Reduction Mechanism>

[0055] The reduction mechanism 4 reduces the rotation of the electric motor (not shown) at a predetermined rate, thereby rotating the gear carrier 3. The reduction mechanism 4 includes: three crankshafts 13 inserted into the crankshaft insertion holes 7b and 8b; a transmission spur gear (an example of a gear in the claims) 14 provided at the axial end of each crankshaft 13; and two external gears 15 and 16 (a first external gear 15 and a second external gear 16) provided between the base plate 7 and the end plate 8.

[0056] External teeth 17 are formed on the outer periphery of the transmission spur gear 14. The external teeth 17 mesh with, for example, a motor shaft of an electric motor (not shown).

[0057] The crankshaft 13 is rotatably supported on the gear carrier 3 (base plate 7 and end plate 8) by crankshaft bearings 18. The crankshaft 13 includes a shaft body 13c that rotates about the central axis A2, and a first eccentric portion 13a and a second eccentric portion 13b formed in the axial center of the shaft body 13c. The shaft body 13c is rotatably supported on the gear carrier 3 (base plate 7 and end plate 8) on both axial sides by crankshaft bearings 18.

[0058] The shaft body 13c is coaxially arranged and integrated with the transmission spur gear 14. That is, the crankshaft 13 and the transmission spur gear 14 rotate integrally about the central axis A2. Hereinafter, the central axis A2 will be referred to as the second rotation axis A2 of the crankshaft 13.

[0059] The first eccentric portion 13a and the second eccentric portion 13b are eccentric relative to the second rotation axis A2. The first eccentric portion 13a and the second eccentric portion 13b are arranged axially adjacent to each other between the two crankshaft bearings 18. In other words, the first eccentric portion 13a and the second eccentric portion 13b are arranged axially adjacent to each other between the base plate portion 7 and the end plate portion 8. The first eccentric portion 13a and the second eccentric portion 13b are arranged so that the phase angle is offset by 180 degrees.

[0060] The inner circumferential surfaces of roller bearings 19 are fitted into the eccentric portions 13a and 13b, respectively. The roller bearings 19 are, for example, cylindrical roller bearings. The first external gear 15 and the second external gear 16 are rotatably supported on the crankshafts 13 via the roller bearings 19.

[0061] The first external gear 15 and the second external gear 16 are arranged in the space between the base plate 7 and the end plate 8. Through-holes 15a and 16a are formed in the first external gear 15 and the second external gear 16, respectively, into which the outer circumferential surfaces of roller bearings 19 engage. Consequently, when the first eccentric portion 13a and the second eccentric portion 13b oscillate due to rotation of the crankshaft 13, the first external gear 15 and the second external gear 16 oscillate via the roller bearings 19.

[0062] Openings 15b and 16b are formed in the first external gear 15 and the second external gear 16, respectively, to prevent interference with the column portion 9. Shaft insertion holes 15c and 16c are formed in the radial centers of the first external gear 15 and the second external gear 16, respectively. External teeth 15d and 16d are formed on the outer peripheries of the first external gear 15 and the second external gear 16, respectively. The number of teeth on each of the external teeth 15d and 16d is, for example, one less than the number of internal tooth pins 5 of the housing 2.

[0063] With this structure, as the first and second external gears 15 and 16 oscillate, a portion of the external teeth 15d and 16d of each external gear 15 and 16 meshes with the internal pin 5 of the housing 2. The number of teeth on each external gear 15d and 16d is, for example, one less than the number of teeth on the internal pin 5. Consequently, the meshing points of the external teeth 15d and 16d are offset circumferentially relative to the internal pin 5 (housing 2), causing each external gear 15 and 16 to rotate. This rotation is decelerated relative to the rotation of the crankshaft 13.

[0064] As the external gears 15 and 16 rotate, the crankshafts 13 also rotate around the second rotation axis A2 while revolving around the first rotation axis A1. Each crankshaft 13 is supported on the gear rack 3 (base plate portion 7, end plate portion 8) in a rotatable manner. Therefore, the gear rack 3 rotates as the crankshafts 13 revolve. As a result, the reduction gear 1 reduces the rotation of, for example, an electric motor not shown in the figure and outputs it. Assuming that the gear rack 3 is fixed to the arm of an industrial robot, etc., the reduction gear 1 can reduce the rotation of, for example, an electric motor not shown in the figure and output it from the housing 2.

[0065] Main bearing

[0066] Then, based on Figure 1 、 Figure 2 The detailed structure of the main bearing 6 will be described.

[0067] Figure 2 yes Figure 1 Enlarged view of Part II.

[0068] like Figure 1 、 Figure 2As shown, the main bearing 6 that rotatably supports the base plate 7 and the main bearing 6 that rotatably supports the end plate 8 are arranged symmetrically about a plane extending along the radial direction. Therefore, in the following description, only the main bearing 6 that rotatably supports the base plate 7 will be described, and the description of the main bearing 6 that rotatably supports the end plate 8 will be omitted. In addition, in the following description, the axial center side of the housing 2 (the side facing the internal gear pin 5) may be referred to as the axial inner side, and the axial side opposite the inner side may be referred to as the axial outer side.

[0069] The main bearing 6 is an angular contact ball bearing, a type of radial ball bearing. It comprises an annular outer ring 31, insert-cast in the housing 2; an annular inner ring 32, radially inward of the outer ring 31 and insert-cast in the base plate 7; a plurality of rolling elements 33 disposed between the outer ring 31 and the inner ring 32; and a retainer 37, which retains the rolling elements 33 at equal intervals in the circumferential direction.

[0070] The rolling element 33 is a spherical body. The cage 37 is formed of, for example, resin.

[0071] The outer ring 31 and inner ring 32 are formed from high-carbon chromium bearing steel (SUJ) or carbon steel. For example, S55C is used as carbon steel. However, this is not limiting; high-strength cast iron can also be used to form the outer ring 31 and inner ring 32. For example, FCD700-900 can be used as high-strength cast iron.

[0072] In the following description, a case where the outer ring 31 and the inner ring 32 are formed using S55C will be described.

[0073] The outer ring 31 and the inner ring 32 are slightly different in size, but their shapes are symmetrical about the rolling element 33. Therefore, in the following description, only the inner ring 32 is described, and the description of the outer ring 31 is omitted.

[0074] The inner ring 32 has an L-shaped cross-section along the axial direction. Specifically, the inner ring 32 includes: a rolling surface 32a that contacts the rolling element 33; an axially inner end surface (an example of an axial end surface in the claims) 32b connected to the axially inner end of the rolling surface 32a; a first raceway joint surface (an example of a raceway joint surface or an axial raceway joint surface in the claims) 32c connected to the radially inner end of the axially inner end surface 32b; a radially outer end surface (an example of a radial end surface in the claims) 32d connected to the radially outer end of the rolling surface 32a; a second raceway joint surface (an example of another raceway joint surface or a radial raceway joint surface in the claims) 32e connected to the axially outer end of the radially outer end surface 32d; and a rounded chamfered surface 32f formed at the connection between the first raceway joint surface 32c and the second raceway joint surface 32e.

[0075] The rolling surface 32a is a surface on which the rolling element 33 rolls. The cross-sectional shape of the rolling surface 32a along the axial direction is formed in an arc shape so as to correspond to the surface of the rolling element 33.

[0076] The axially inner end surface 32b extends radially inward from the rolling surface 32a. The axially inner end surface 32b is along the radial direction.

[0077] The first ring engagement surface 32c extends axially outward from the axially inner end surface 32b. A convex portion 34 is formed on the entire axial surface of the first ring engagement surface 32c. The convex portion 34 protrudes radially inward. More specifically, the convex portion 34 is inclined so as to gradually protrude radially inward (toward the substrate portion 7) as it moves from the axially inner end surface 32b toward the axially outer side.

[0078] The radially outer end surface 32d extends outward in the axial direction from the rolling surface 32a. The radially outer end surface 32d is along the axial direction.

[0079] The second ring engagement surface 32e is inclined so as to gradually protrude outward in the axial direction as it moves from the radially outer end surface 32d toward the radially inner side. In other words, the convex portion 38 is also formed on the second ring engagement surface 32e.

[0080] The inclination angle θ2 of the second ring engagement surface 32e with respect to the radial direction is larger than the inclination angle θ1 of the convex portion 34 with respect to the axial direction. More specifically, the inclination angle θ1 is, for example, approximately 1° to 10°, and the inclination angle θ2 is, for example, approximately 5° to 30°.

[0081] The circular chamfered surface 32f connects the axial outer end of the first ring joint surface 32c and the radial inner end of the second ring joint surface 32e. The circular chamfered surface 32f is formed in an arc shape.

[0082] The surface roughness of the first-circle bonding surface 32 c (convex portion 34 ), the second-circle bonding surface 32 e (convex portion 38 ), and the rounded chamfered surface 32 f is, for example, Ra 8.8 μm to 12.5 μm.

[0083] The base plate portion 7, into which the inner ring 32 thus constructed is insert-cast, is formed with a recess 40 for accommodating the inner ring 32. The recess 40 is formed to correspond to the shape of the inner ring 32. Specifically, the recess 40 includes a first base plate-joining surface (an example of a rotating body-joining surface, or an axial rotating body-joining surface, as defined in the claims) 40a overlapping the first ring-joining surface 32c, a second base plate-joining surface (an example of another rotating body-joining surface, or a radial rotating body-joining surface, as defined in the claims) 40b overlapping the second ring-joining surface 32e, and a base plate-chamfered surface 40c overlapping the rounded chamfered surface 32f.

[0084] The first substrate-bonding surface 40a is inclined so that the depth of the recess 40 gradually increases as it moves axially outward, that is, so that the outer diameter of the recess 40 decreases. The second substrate-bonding surface 40b is inclined so that the depth of the recess 40 gradually increases as it moves radially inward, that is, so that it moves axially outward. Due to the second race bonding surface 32e and the second substrate-bonding surface 40b, the second race bonding surface 32e side of the inner race 32 is covered by the substrate portion 7 from the radial outside.

[0085] <Method for manufacturing the base plate and inner ring>

[0086] Then, based on Figure 3 The manufacturing method of the base plate portion 7 and the inner ring 32 will be described. The manufacturing method of the end plate portion 8 and the inner ring 32 and the manufacturing method of the housing 2 and the outer ring 31 are basically the same as the manufacturing method of the base plate portion 7 and the inner ring 32, so the description thereof will be omitted.

[0087] Figure 3 It is an explanatory diagram of a method for manufacturing the base plate portion 7 and the inner ring 32 . Figure 3 The two-dot chain lines in the figure (details will be discussed later) are scales that have been appropriately changed for easier understanding of the description.

[0088] like Figure 3 As shown, first, the base material 35 of the inner ring 32 is placed in a sand mold (not shown). The base material 35 is formed into an annular shape and has a protrusion 34. The base material 35 has a first ring joint surface 32c and a second ring joint surface 32e.

[0089] Next, the molten FCD450 is poured into a sand mold (not shown) to form a rough outline of the substrate portion 7 (at Figure 3 Indicated by two-dot chain lines), and the base material 35 is embedded and cast in the base plate portion 7.

[0090] The melting point of S55C, which is the base material 35, is approximately 1600°C to 1720°C. The melting point of FCD450, which is the base material 7, is approximately 1470°C to 1490°C. Since the melting point of S55C is higher than that of FCD450, the base material 35 does not melt even when the molten FCD450 is poured into the sand mold.

[0091] Next, the substrate 7 is cooled. The thermal expansion coefficient of S55C is 11.7×10 -6 / K. The thermal expansion coefficient of FCD450 is 12×10 -6 / K. Thus, the thermal expansion coefficient of FCD450 is greater than that of S55C. As a result, the substrate portion 7 thermally contracts significantly relative to the base material 35. The second raceway joint surface 32e side of the inner race 32 is covered radially from the outside by the substrate portion 7. Therefore, as the substrate portion 7 thermally contracts, the inner race 32 is pressed radially inward by the substrate portion 7. This prevents radial play of the base material 35 relative to the substrate portion 7 and also prevents rotation of the base material 35 relative to the substrate portion 7.

[0092] A first ring joint surface 32c is formed on the base material 35. A first substrate joint surface 40a is formed on the base plate portion 7. Therefore, the protrusion 34 of the base material 35 is engaged with the recess 40 of the base plate portion 7. Thus, the base material 35 is prevented from moving inward in the axial direction relative to the base plate portion 7. A second substrate joint surface 40b of the base plate portion 7 is formed on the axially outer side of the base material 35. Therefore, the base material 35 is also prevented from moving outward in the axial direction relative to the base plate portion 7. In this way, the protrusion 34, the recess 40, and the second substrate joint surface 40b are used to prevent the base material 35 from moving in the axial direction relative to the base plate portion 7.

[0093] Next, the radially outer side of the base material 35 is machined using, for example, a lathe (not shown) to form the rolling contact surface 32a. This completes the inner ring 32. Furthermore, the outer and inner circumferences and both axial end faces of the base plate 7 are machined to form the base plate 7. The rolling contact surface 32a of the inner ring 32 is then heat treated to harden it. The hardness of the rolling contact surface 32a is, for example, HRC 50-70. The above steps complete the manufacture of the base plate 7 and the inner ring 32.

[0094] In this manner, the inner ring 32 is insert-cast onto the base plate 7. This allows the base plate 7 and inner ring 32 to be integrated. High-carbon chromium bearing steel (SUJ) or carbon steel (S55C) can be used only in areas where the required hardness for the rolling bearing is required. This facilitates finishing of the integrated base plate 7 and inner ring 32.

[0095] A protrusion 34 is formed on the first race engagement surface 32c of the inner race 32. A recess 40, into which the protrusion 34 engages, is formed on the base plate 7. Therefore, even if the engagement between the base plate 7 and the inner race 32 is incomplete due to the joining of dissimilar components, the inner race 32 can be prevented from falling off the base plate 7. Consequently, the bearing structure can be reliably simplified and miniaturized.

[0096] A second ring engagement surface 32e is formed on the inner ring 32. A second substrate engagement surface 40b is formed on the substrate portion 7, overlapping with the second ring engagement surface 32e. The protrusion 34 is inclined so as to gradually protrude radially inward (toward the substrate portion 7) as it approaches the axially outward (the second substrate engagement surface 40b). This configuration improves the rigidity of the protrusion 34 and the recess 40. Axial movement of the inner ring 32 relative to the substrate portion 7 can be reliably prevented. Consequently, the inner ring 32 can be more reliably prevented from falling off the substrate portion 7.

[0097] The second race engagement surface 32e and the second substrate engagement surface 40b are inclined so as to gradually extend axially outward as they move radially inward. Consequently, the second race engagement surface 32e side of the inner race 32 is positioned so that the substrate portion 7 covers the inner race 32 from the radial outside. This prevents radial movement of the inner race 32 relative to the substrate portion 7. Consequently, the inner race 32 can be more reliably prevented from falling off the substrate portion 7.

[0098] The inclination angle θ2 between the second ring joint surface 32e and the second substrate joint surface 40b relative to the radial direction is greater than the inclination angle θ1 between the protrusion 34 and the first substrate joint surface 40a relative to the axial direction. Therefore, the inner ring 32 can be prevented from axial movement relative to the substrate portion 7, while also more reliably preventing radial movement of the inner ring 32 relative to the substrate portion 7.

[0099] The thermal expansion coefficient of the base plate 7 is greater than that of the inner ring 32. Therefore, the base plate 7 experiences greater thermal contraction than the inner ring 32. As a result, after insert-casting the inner ring 32 onto the base plate 7, the base plate 7 can strongly press the inner ring 32 from the radially outer side during thermal contraction. This prevents the inner ring 32 from rotating relative to the base plate 7.

[0100] The inner ring 32 has a rounded chamfered surface 32f. The base plate portion 7 has a base plate chamfered surface 40c. These rounded chamfered surfaces 32f and 40c prevent stress concentration areas from forming on the convex portion 34 and concave portion 40. This further improves the rigidity of the convex portion 34 and concave portion 40, and more reliably prevents the inner ring 32 from falling off the base plate portion 7.

[0101] In order to prevent the inner ring 32 from falling off the base plate portion 7 , it is also effective to roughen the surface roughness of each of the joining surfaces 32 c , 32 e , 40 a , 40 b and the convex portion 34 .

[0102] The above-mentioned functions and effects are also achieved by the end plate portion 8 and the inner ring 32 insert-cast therein, and the housing 2 and the outer ring 31 insert-cast therein.

[0103] The present invention is not limited to the above-described embodiment, and includes embodiments in which various modifications are added to the above-described embodiment without departing from the spirit of the present invention.

[0104] For example, in the above embodiment, a case where the main bearing 6 is employed in the reduction gear 1 is described. However, the present invention is not limited thereto, and the main bearing 6 can be employed in various reduction gears. The main bearing 6 can also be employed in various rotary devices using rolling bearings or gear devices having gears instead of the reduction gear 1.

[0105] In the above embodiment, the reduction gear 1 is described as having three crankshafts 13. The external gears 15 and 16 are described as being oscillatingly rotated by the three crankshafts 13. However, this is not limiting; when configuring the reduction gear 1, it is sufficient to have at least one crankshaft 13. For example, the reduction gear 1 may be configured as a so-called center crankshaft reduction gear having a single crankshaft 13. In this case, the single crankshaft 13 is coaxially arranged with the first rotation axis A1, and the single crankshaft 13 is used to cause the external gears 15 and 16 to oscillate.

[0106] In the above embodiment, the main bearing 6 is described as an angular contact ball bearing, which is a radial ball bearing. However, this is not limiting, and the structure of the main bearing 6 can be employed in various rolling bearings. Rolling bearings, in addition to radial ball bearings, can also refer to radial roller bearings. In other words, the rolling elements 33 are not limited to spheres; they can also be cylindrical rollers. Furthermore, rolling bearings also include thrust bearings.

[0107] In the above embodiment, the housing 2, base plate 7, and end plate 8 are each formed of spherical graphite cast iron. For example, FCD450 is used as the spherical graphite cast iron. The outer ring 31 and inner ring 32 are formed of high-carbon chromium bearing steel or carbon steel. For example, S55C is used as the carbon steel. However, this is not limiting; a variety of materials can be used for the housing 2, base plate 7, end plate 8, outer ring 31, and inner ring 32. When selecting materials, the thermal expansion coefficients of the housing 2, base plate 7, and end plate 8 are preferably greater than those of the outer ring 31 and inner ring 32.

[0108] In the above embodiment, the outer ring 31 is insert-cast in the housing 2, and the inner ring 32 is insert-cast in the base plate 7 and the end plate 8, respectively. However, this is not limiting; either the outer ring 31 or the inner ring 32 may be insert-cast in at least one of the housing 2, the base plate 7, and the end plate 8.

[0109] In the above embodiment, the convex portion 34 is formed on the inner ring 32 and the concave portion 40 is formed on the base plate 7. However, the present invention is not limited thereto, and the convex portion 34 may be formed on the base plate 7 and the concave portion 40 may be formed on the inner ring 32.

[0110] In the above embodiment, the inclination angle θ1 of the projection 34 is described as being approximately 1° to 10°, for example. However, this is not limiting, and the projection 34 may be formed so that the radially inner end of the projection 34 is not located radially inward of the outermost side of the column 9 .

[0111] In the above-mentioned embodiment, the following case is described: a convex portion 34 is formed on the first-circle joint surface 32c, and a convex portion 38 is formed on the second-circle joint surface 32e. A case in which a concave portion 40 is formed on each of the first-circle joint surface 32c and the second-circle joint surface 32e is described. However, this is not limited to this, and it is sufficient that at least the convex portion 34 is formed on the first-circle joint surface 32c, or the convex portion 38 is formed on the second-circle joint surface 32e. The joint surfaces 32c and 32e on which the convex portions 34 and 38 are not formed may also be flat surfaces along the axial or radial direction. It is sufficient that a concave portion 40 is formed on at least one of the first-circle joint surface 32c and the second-circle joint surface 32e, corresponding to the convex portions 34 and 38.

[0112] In the above embodiment, the convex portion 34 is formed over the entire axial direction of the first ring engagement surface 32c. The convex portion 34 is described as being inclined so as to gradually protrude radially inward as it moves from the axially inner end surface 32b toward the axially outer side. However, this is not limiting, and the convex portion 34 and the concave portion 40 may have various shapes.

[0113] For example, the description above describes a case where the convex portion 34 and the concave portion 40 are inclined. However, the convex portion 34 and the concave portion 40 may also be curved. The convex portion 34 and the concave portion 40 may also be formed in a stepped shape. Even in the case of a stepped shape, the convex portion 34 is formed so as to protrude radially inward as it moves axially outward. Furthermore, modifications of the convex portion 34 and the concave portion 40 are described in detail below.

[0114] [First Modification]

[0115] Figure 4 It is an enlarged cross-sectional view of the main bearing 6 and the base plate portion 7 in the first modified example. Figure 4 With the aforementioned Figure 2 In the following modified examples, only the inner ring 32 and the base plate 7 are described. However, the structures of the inner ring 32 and the base plate 7 are applicable to the inner ring 32 and the end plate 8, the housing 2, and the outer ring 31 in the same manner as in the above-mentioned embodiment.

[0116] like Figure 4 As shown, a flat chamfered surface 32g may be formed on the inner ring 32 instead of the round chamfered surface 32f (see the aforementioned Figure 2 ). The flat chamfered surface 32g is formed on the round chamfered surface 32f (see Figure 2 ) is formed in a wide area. The flat chamfered surface 32g is formed flat. The flat chamfered surface 32g is perpendicular to the load action line L of the main bearing 6. A base plate flat chamfered surface 40d is formed in the recessed portion 40 of the base plate portion 7 so as to correspond to the flat chamfered surface 32g.

[0117] This configuration provides the same effects as those of the aforementioned embodiment, and furthermore, the base plate 7 can securely receive the load applied to the main bearing 6. Therefore, deformation of the base plate 7 and the inner ring 32 due to the load applied to the main bearing 6 can be prevented.

[0118] [Second Modification]

[0119] Figure 5 It is an enlarged cross-sectional view of the main bearing 6 and the base plate portion 7 in the second modified example. Figure 5 With the aforementioned Figure 2 Corresponding.

[0120] like Figure 5 As shown, the cross-sectional shape of the convex portion 34 along the axial direction can also be set to a triangular shape. The convex portion 34 is formed in a manner that gradually protrudes radially inward as it moves toward the axial center of the first ring engagement surface 32c. Even in the case of such a configuration, the same effect as that of the aforementioned embodiment can be achieved.

[0121] [Third Modification]

[0122] Figure 6 It is an enlarged cross-sectional view of the main bearing 6 and the base plate portion 7 in the third modified example. Figure 6 With the aforementioned Figure 2 Corresponding.

[0123] like Figure 6 As shown, the cross-sectional shape of the convex portion 34 along the axial direction can also be set to a rectangular shape. Compared with the previous embodiment, the convex portion 34 protrudes radially inward to a greater extent. In addition, the second ring engagement surface 32e of the inner ring 32 is not inclined with respect to the radial direction, but is radially aligned.

[0124] A ring convex-concave portion 36 is formed on the surface of such a convex portion 34 and the entire second ring joint surface 32e. The concave and convex portions of the ring convex-concave portion 36 formed on the mating surface between the convex portion 34 and the first substrate joint surface 40a are arranged alternately in the axial direction. The concave and convex portions of the ring convex-concave portion 36 along the surface of the axial inner end face 32b of the inner ring 32 and the second ring joint surface 32e in the convex portion 34 are arranged alternately in the radial direction. The cross-sectional shape of the concave portion along the axial direction is a triangular shape in which the groove width narrows as it approaches the bottom surface. The cross-sectional shape of the convex portion along the axial direction is a triangular shape that becomes tapered as it approaches the top. The height (depth) H of the ring convex-concave portion 36 is, for example, about 0.1 to 1 mm.

[0125] The recessed portion 40 of the substrate portion 7 is formed into a rectangular shape corresponding to the protrusion 34. Therefore, in addition to the first substrate-jointing surface 40a and the second substrate-jointing surface 40b, the recessed portion 40 also includes a recessed inner side surface 40e that overlaps with the axial inner end surface of the protrusion 34. Substrate protrusions and recesses 41 are formed on these first and second substrate-jointing surfaces 40a, 40b, and recessed inner side surface 40e, corresponding to the ring protrusions and recesses 36. The engagement of these ring protrusions and recesses 36 with the substrate protrusions and recesses 41 reliably prevents the inner ring 32 from falling off the substrate portion 7. Therefore, according to the third modified example, the same effects as those of the aforementioned embodiment can be achieved.

[0126] In the third modified example described above, the concave portions of the ring concave-convex portions 36 have a triangular cross-sectional shape along the axial direction, with the groove width narrowing toward the bottom. The convex portions have a triangular cross-sectional shape along the axial direction, with the cross-sectional shape tapering toward the top. However, this is not limiting, and the concave and convex portions can have any shape. For example, the concave and convex portions can also have a semicircular or rectangular shape instead of a triangular shape.

[0127] [Fourth Modification]

[0128] Figure 7 It is an enlarged cross-sectional view of the main bearing 6 and the base plate portion 7 in the fourth modified example. Figure 7 With the aforementioned Figure 2 Corresponding.

[0129] like Figure 7 As shown, in the fourth modification, the convex portion 34 is not formed on the first-circle engagement surface 32c, and the convex portion 38 is not formed on the second-circle engagement surface 32e.

[0130] On the other hand, a recess 40 is formed in the base plate portion 7, into which the inner ring 32 fits. The recess 40 is formed to correspond to the shape of the inner ring 32. Specifically, the recess 40 has a first base plate joint surface (an example of a rotating body joint surface, an axial rotating body joint surface, in the claims) 40a that overlaps with the first ring joint surface 32c, and a second base plate joint surface (another rotating body joint surface, an example of a radial rotating body joint surface, in the claims) 40b that overlaps with the second ring joint surface 32e.

[0131] A first stepped surface 44a is formed on the first substrate-joining surface 40a of the recess 40, into which the first race-joining surface 32c fits, and contacts the axially inner end surface 32b of the inner race 32. The first stepped surface 44a is perpendicular to the first substrate-joining surface 40a and extends along the radial direction.

[0132] A second stepped surface 44b is formed on the second substrate-joining surface 40b of the recess 40, into which the second race-joining surface 32e fits, and contacts the radially outer end surface 32d of the inner race 32. The second stepped surface 44b is perpendicular to the second substrate-joining surface 40b and extends along the axial direction.

[0133] Therefore, according to the fourth modified example, the first stepped surface 44a can restrict the axial movement of the inner ring 32. The second stepped surface 44b can restrict the radial movement of the inner ring 32. Therefore, in addition to achieving the same effects as the aforementioned embodiment, the base plate portion 7 and the inner ring 32 can be further firmly integrated.

[0134] In the second and third modifications described above, cases where either the convex portion 34 or the convex portion 38 is formed on the inner ring 32 are described. In the fourth modification, a case where the inner ring 32 does not have the convex portions 34 or 38 is described. However, this is not limiting; the second, third, and fourth modifications may be combined. Alternatively, the outer ring 31 may have the convex portions 34 or 38 formed thereon. In this case, the housing 2 may have the concave portion 40 or the stepped surfaces 44a and 44b formed thereon. Alternatively, the inner ring 32 may have the convex portions 34 and 38 formed thereon, and the stepped surfaces 44a and 44b may be formed so as to contact the ends of these convex portions 34 and 38. Alternatively, the convex portion 34 may be formed on at least one of the first ring engagement surface 32c and the second ring engagement surface 32e. The base plate 7 may have the concave portion 40 formed at a location corresponding to the convex portion 34, into which the convex portion 34 engages.

[0135] [Fifth Modification]

[0136] Figure 8 It is an enlarged cross-sectional view of the main bearing 6 and the base plate portion 7 in the fifth modification. Figure 8 With the aforementioned Figure 2 Corresponding.

[0137] like Figure 8 As shown, the difference between the aforementioned 4th variant and the 5th variant is that the inner ring 32 of the 4th variant has a 1st ring joint surface 32c extending in the axial direction, a 2nd ring joint surface 32e extending in the radial direction, and a circular chamfered surface 32f formed at the connection portion of these joint surfaces 32c, 32e. In contrast, the inner ring 32 of the 5th variant does not have the joint surfaces 32c, 32e and the circular chamfered surface 32f.

[0138] More specifically, the inner ring 32 has a ring engagement surface 32h that connects the radially inner end of the axially inner end surface 32b and the axially outer end of the radially outer end surface 32d. Rounded chamfered surfaces 32i are formed at the connection between the axially inner end surface 32b and the ring engagement surface 32h, and at the connection between the radially outer end surface 32d and the ring engagement surface 32h, respectively.

[0139] The cross-sectional shape of the ring engagement surface 32h along the axial direction is formed into an arc shape to correspond to the rolling surface 32a. The center of the arc of the ring engagement surface 32h coincides with the center of the arc of the rolling surface 32a. Therefore, the thickness T of the inner ring 32 along the axial cross-sectional shape is uniform.

[0140] The inner ring 32 thus formed has a uniform thickness T, and can therefore be formed by bending the metal plate by press working. As the metal plate, high carbon chromium bearing steel (SUJ) or carbon steel (S55C) is used.

[0141] Therefore, according to the fifth modification, in addition to achieving the same effects as those of the aforementioned embodiment, the material of the inner ring 32 can be reduced as much as possible, and the manufacture of the inner ring 32 can be facilitated.

[0142] The above-described embodiment and various modifications can be combined as appropriate.

[0143] In the embodiments disclosed in this specification, a component composed of multiple objects may be integrated into one piece, or a component composed of one object may be divided into multiple pieces. Regardless of whether or not the components are integrated, they may be configured in a manner that achieves the purpose of the invention.

Claims

1. A rotating device comprising: two rotating bodies; and Rolling bearings support the two rotating bodies so that they can rotate freely relative to each other. The rolling bearing has: two rings, each of which is aligned with the rotating body; and A plurality of rolling elements are arranged between the two rings and on the side opposite to the rotating body. At least one of the rings is inlaid and cast on at least one of the rotating bodies, A convex portion projecting toward the other is formed on one of a rotating body joint surface of the rotating body that is joined to the ring and a ring joint surface of the ring that is joined to the rotating body. A recessed portion into which the convex portion fits is formed on the other of a rotating body joint surface of the rotating body that is joined to the ring and a ring joint surface of the ring that is joined to the rotating body.

2. The rotating device according to claim 1, wherein: The rolling bearing includes any one of a radial ball bearing and a radial roller bearing, The rotating body joint surface and the ring joint surface are along the axial direction. The rotating body is formed with another rotating body engaging surface extending in a direction intersecting with the rotating body engaging surface and engaging with the ring. The ring is formed with another ring engagement surface that engages with the other rotating body engagement surface, The convex portion is formed on the ring and is formed in a manner that gradually protrudes toward the rotating body as it moves toward the engaging surface of the other ring. The recessed portion is formed in the rotating body and is formed so that its depth gradually increases toward the joint surface of the other rotating body.

3. The rotating device according to claim 2, wherein: The other ring engaging surface is formed in a manner that gradually protrudes toward the other rotating body engaging surface as it approaches the ring engaging surface. The other rotating body joint surface is formed so as to gradually protrude toward the other ring joint surface as it becomes farther away from the rotating body joint surface.

4. The rotating device according to claim 3, wherein: The convex portion, the concave portion, the other ring engagement surface, and the other rotating body engagement surface are inclined respectively. An inclination angle of the other ring engaging surface and the other rotating body engaging surface with respect to a radial direction is larger than an inclination angle of the convex portion and the concave portion with respect to an axial direction.

5. The rotating device according to claim 4, wherein: The thermal expansion coefficient of the rotating body is greater than the thermal expansion coefficient of the ring.

6. The rotating device according to any one of claims 3 to 5, wherein: The convex portion is formed on the entire ring joint surface, and a ring chamfered portion is formed at the corner portion on the other ring joint surface side. The recessed portion is formed on the entire rotating body joint surface, and a rotating body chamfered portion is formed at a corner portion on the other rotating body joint surface side.

7. The rotating device according to claim 6, wherein: The ring chamfered portion and the rotating body chamfered portion are formed flatly. The ring chamfered portion and the rotating body chamfered portion extend in a direction perpendicular to a load action line of the rolling bearing.

8. The rotating device according to claim 1, wherein The rolling bearing includes any one of a radial ball bearing and a radial roller bearing, The rotating body joint surface has: an axial rotating body engaging surface, which is along the axial direction; and a radial rotating body engaging surface extending in a direction intersecting the axial rotating body engaging surface, The ring joint surface has: an axial ring engagement surface, which is along the axial direction; and a radial ring engagement surface extending in a direction intersecting the axial ring engagement surface, The convex portion is formed on at least one of the radial rotating body joint surface and the radial ring joint surface, and the concave portion is formed on the other one.

9. A rotating device comprising: two rotating bodies; and Rolling bearings support the two rotating bodies so that they can rotate freely relative to each other. The rolling bearing has: two rings, each of which is aligned with the rotating body; and A plurality of rolling elements are arranged between the two rings and on the side opposite to the rotating body. At least one of the rings is inlaid and cast on at least one of the rotating bodies, A recessed portion for the ring to fit into is formed on the rotating body joint surface of the rotating body that is engaged with the ring. The recess has a stepped surface that restricts at least one of axial movement and radial movement of the ring.

10. The rotating device according to claim 9, wherein: The rolling bearing includes any one of a radial ball bearing and a radial roller bearing, The rotating body joint surface has: an axial rotating body engaging surface, which is along the axial direction; and a radial rotating body engaging surface extending in a direction intersecting the axial rotating body engaging surface, The recess is formed on at least one of the axial rotating body joint surface and the radial rotating body joint surface. The recessed portion is formed to have at least one of a first step surface formed on the recessed portion of the axial rotating body joint surface and a second step surface formed on the recessed portion of the radial rotating body joint surface. The first step surface limits the axial movement of the ring. The second step surface restricts radial movement of the ring.

11. The rotating device according to claim 10, wherein: The first step surface extends in a direction intersecting the engaging surface of the axial rotating body and contacts the axial end surface of the ring. The second stepped surface extends in a direction intersecting the radial rotating body engaging surface and contacts the radial end surface of the ring.

12. The rotating device according to claim 9 or 10, wherein: The ring includes a case where the thickness is uniform in the cross-sectional shape along the axial direction.

13. A gear device comprising: a cylindrical housing having an internal gear; a gear carrier disposed radially inward of the housing and rotatably supported by the housing via rolling bearings; at least one crankshaft rotatably supported by the gear carrier, to which external rotational force is input; and an external gear meshing with the internal gear, The crankshaft has: the shaft body; and an eccentric portion, which is provided on the shaft body and is eccentric relative to the rotation axis of the shaft body, The external gear is rotatably supported by the eccentric portion. The rolling bearing has: an outer ring disposed on the housing; an inner ring disposed on the gear carrier; and A plurality of rolling elements are arranged between the outer ring and the inner ring, At least one of the outer ring and the inner ring is embedded in and cast into the corresponding housing and the gear rack. At least one of the insert-cast outer ring and the inner ring has a convex portion formed on the ring joint surface that is joined to either the housing or the gear carrier. At least one of the housing and the carrier has a recessed portion, into which the convex portion fits, formed on a rotating body joint surface that is joined to one of the outer ring and the inner ring.

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