Eccentric oscillation gear device

Abstract

Eccentric oscillation gear device (1), comprising: a crankshaft (10) formed with an eccentric portion (10a); a crankshaft bearing (12a, 12b) rotatably supporting the crankshaft (10); an oscillation gear (14) having a tooth portion (14a) and an insertion hole (14c) into which the eccentric portion (10a) is inserted; an outer cylinder (2) having internal teeth (3) that mesh with the tooth portion (14a) of the oscillation gear (14); and a carrier (4) to which the crankshaft bearing (12a, 12b) is mounted and which is designed to generate a relative difference in rotational speed between the carrier (4) and the outer cylinder (2) by means of an oscillating movement of the oscillating gear (14) together with a rotation of the eccentric section (10a), wherein the carrier (4) is formed with: a central through hole (4d, 7a); a mounting portion (4e, 7b) arranged at a position radially offset from the central through hole (4d, 7a) and to which the crankshaft bearing (12a, 12b) is mounted; and an oil groove (25) in which a lubricating oil can be stored, wherein the oil groove (25) is provided in a surface of the carrier (4) oriented towards the oscillation gear (14) at a position between the central through-hole (4d, 7a) and the mounting portion (4e, 7b), wherein the carrier (4) comprises a base plate section (4a), the mounting section (4e, 7b) comprises a base plate-side mounting point (4e) formed in the base plate section (4a), the oil groove (25) comprises a base plate-side groove (27) formed in a surface of the base plate portion (4a) oriented toward the oscillation gear (14), the base plate-side groove (27) comprises a bottom wall (27a) and a pair of side walls (27b), and a radially outer edge of the bottom wall (27a) and the side walls (27b) is connected to the mounting recess (4e), and a radially inner edge of the bottom wall (27a) and the side walls (27b) is connected to the central through hole (4d).

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to an eccentric oscillation gear device.2. BackgroundHeretofore, there has been known an eccentric oscillation gear device for reducing a rotational speed between two corresponding elements at a given speed reduction ratio, as disclosed in JP 2011-141017 A. This eccentric oscillation gear device includes an outer cylinder fixable to one of the corresponding members and a carrier disposed inside the outer cylinder and fixable to the other corresponding member. A crankshaft bearing is attached to a central portion of the carrier, and a crankshaft is arranged to pass through the central portion and simultaneously be supported by the crankshaft bearing. The carrier is configured to be relatively rotated with respect to the outer cylinder according to an oscillation rotation of an oscillation gear attached to an eccentric portion of the crankshaft. The carrier has a groove formed in an oscillating gear oriented surface thereof at a position between adjacent ones of a plurality of rotational motion synchronizing members extending in a radial direction thereof. This makes it possible to move grease in the radial direction over the groove.As stated above, in the carrier of the eccentric oscillation gear device disclosed in JP 2011-141017 A, a groove that allows grease to reach a location requiring lubrication is formed at a position between adjacent rotational movement synchronizing members extending in the radial direction. However, in this structure, the following problem occurs. During the drive of the transmission device, the grease is liable to flow from a radially outer edge to the inside of the carrier by the action of a centrifugal force generated by rotation of the carrier. This makes it difficult to lubricate the crankshaft bearing.Document DE 11 2013 004 516 T5 describes an eccentric rotary gear device comprising a plurality of crankshafts each formed with an eccentric portion, a plurality of crankshaft bearings rotatably supporting the corresponding crankshaft, a rotary gear having a tooth portion and an insertion hole into which the eccentric portion is inserted. The eccentric rotary gear device further includes an outer cylinder having internal teeth that mesh with the tooth portion of the rotary gear, and a carrier to which the plurality of crankshaft bearings are attached and configured to generate a relative rotational speed difference between the carrier and the outer cylinder by a rotational movement of the rotary gear together with a rotation of the eccentric portion. The plurality of crankshaft bearings are arranged at intervals in a circumferential direction of the carrier. The carrier includes a plurality of mounting portions corresponding to the plurality of crankshaft bearings and configured to mount the respective crankshaft bearings thereto, and a plurality of oil grooves capable of retaining lubricating oil therein. Each of the plurality of oil grooves is disposed along a peripheral edge corresponding to the plurality of mounting portions in a surface of the carrier facing the rotary gear, and the eccentric rotary gear device further includes a connection groove formed to establish an alternate connection between the oil grooves.US 2011 / 0 015 024 A1 describes a transmission device with an outer cylinder which is fastened to a first counter piece and a crankshaft in the interior of the outer cylinder. An external gear is fixed to an eccentric part of the crankshaft and engages with the internal gear of the external cylinder. A carrier is fastened to a second counter piece. By the tilting rotation of the external gear, the carrier is rotated coaxially with the external cylinder. A cylindrical body is inserted into an axial through bore of the carrier. The carrier has a first portion at an end of the cylindrical body and a second portion at an axially intermediate portion of the cylindrical body. The other end of the cylindrical body extends in the direction of a corresponding counter piece and protrudes axially beyond the second section. The outer diameter of the remaining portions of the cylindrical body does not exceed the outermost diameter of the portion to which the first and second portions are attached.SUMMARY OF THE INVENTIONAn object of the present invention is to make lubrication of the crankshaft bearing possible.According to an aspect of the present invention, there is provided an eccentric oscillation gear device including: a crankshaft formed with an eccentric portion; a crankshaft bearing rotatably supporting the crankshaft; an oscillation gear having a tooth portion and an insertion hole into which the eccentric portion is inserted; an outer cylinder having inner teeth that mesh with the tooth portion of the oscillation gear; and a carrier to which the crankshaft bearing is attached and configured to generate a relative difference in rotational speed between the carrier and the outer cylinder by means of an oscillation motion of the oscillation gear together with a rotation of the eccentric portion. The bracket is formed with: a central through hole; a mounting portion disposed at a position radially offset from the central through hole and to which the crankshaft bearing is attached; and an oil groove in which a lubricating oil can be stored. The oil groove is provided in a surface of the carrier oriented toward the oscillation gear at a position between the central through hole and the mounting portion. The carrier includes a base plate portion. The mounting portion includes a base plate side mounting location formed in the base plate portion. The oil groove includes a base plate-side groove formed in a surface of the base plate portion in alignment with the oscillation gear. The base plate-side groove includes a bottom wall and a pair of side walls. A radially outer edge of the bottom wall and the side walls is connected to the mounting recess. A radially inner edge of the bottom wall and the side walls is connected to the central through holeBrief Description of the DrawingsFIG. 1 is a sectional view showing an overall structure of an eccentric oscillation gear device according to an embodiment of the present invention. FIG. 2 is a front view illustrating a support base as viewed from the end plate portion side. FIG. 3 is a front view illustrating the end plate portion as viewed from the support base side.Detailed Description of the Preferred Embodiments of the InventionReferring now to the drawings, the present invention will be described in detail based on an embodiment.An eccentric oscillation gear device (hereinafter, simply referred to as a "gear device") according to an embodiment of the present invention is applicable, for example, as a speed reducer in rotating portions such as a rotating body and an arm joint of a robot, or rotating portions of various machine tools.As shown in FIG. 1, the transmission device 1 according to this embodiment is configured to rotate an unillustrated input shaft to thereby rotate a crankshaft 10, and to oscillatingly rotate oscillation gears 14, 16 in interlocking relation to eccentric portions 10 a, 10 bof the crankshaft 10, to thereby obtain an output rotational speed that is decreased with respect to an input rotational speed. This makes it possible to generate relative rotation between a base (a corresponding member) and a rotating body (another corresponding member) of a robot.As shown in FIGS. 1 to 3, the transmission device 1 includes an outer cylinder 2, a carrier 4, a plurality of (three in the illustrated embodiment) crankshafts 10, first and second oscillating gears 14, 16, and a plurality of (three in the illustrated embodiment) transmission gears 20.The outer cylinder 2 defines an outer surface of the gear device 1 and has an approximately circular cylinder shape. The outer cylinder 2 has a large number of pin grooves 2b formed in an inner peripheral surface thereof. Each of the pin grooves 2 bis formed to extend in an axial direction of the outer cylinder 2 and have a semi-circular shape in a cross section perpendicular to the axial direction. The pin grooves 2b are arranged side by side in the inner peripheral surface of the outer cylinder 2 at circumferentially uniform intervals.The outer cylinder 2 includes a large number of internal teeth pins 3. Each of the internal teeth pins 3 is attached to a respective one of the pin grooves 2b. Specifically, each of the internal teeth pins 3 is fitted into a corresponding one of the pin grooves 2 band positioned in a position where it extends in the axial direction of the outer cylinder 2. Thereby, a large number of internal tooth pins 3 are arranged side by side along the circumferential direction of the outer cylinder 2 in uniform portions. The aforementioned first external teeth 14 aof the first oscillation gear 14 and the aforementioned second external teeth 16 aof the second oscillation gear 16 mesh with the internal teeth pins 3.The outer cylinder 2 is provided with a flange. The flange is formed with an insertion hole 2c, thereby allowing a fastening device (in the illustrated embodiment, a bolt for fixing the outer cylinder 2 to a base of a robot, for example) to be inserted through.The carrier 4 is accommodated in the outer cylinder 2 in an axial relationship to the outer cylinder 2. The carrier 4 is adapted to be relatively rotated with respect to the outer cylinder 2 about the same axis. More specifically, the carrier 4 is disposed radially inside the outer cylinder 2 and in this state is supported relatively rotatably with respect to the outer cylinder 2 by a pair of main bearings 6 provided in an axially spaced relationship with each other.The support 4 includes a support base 5 and an end plate portion 7. the support base 5 includes a base plate portion 4 aand a plurality of (three in the illustrated embodiment) shaft portions 4 c.The base plate portion 4a is disposed inside the outer cylinder 2 at a position adjacent to one of the axially opposite ends of the outer cylinder 2. The base plate portion 4a has a cross-sectionally circular central through hole 4d provided in a radially central portion thereof. As shown in FIG. 2, the base plate portion 4a has a plurality of (three in the illustrated embodiment) mounting recesses 4e provided around the central through hole 4d at circumferentially uniform intervals. Each of the mounting recesses 4e constitutes a mounting location by which a base plate-side bearing 12a of the foregoing crankshaft bearing is allowed to be mounted thereon (base plate-side mounting location). Each of the mounting recesses 4e is formed in a concave shape having an opening oriented toward the first oscillation gear 14.The base plate portion 4 ais formed with a fastening hole 4 gthrough which a fastening device (a bolt for fixing the bracket 4 to, for example, a rotating body of a robot in the illustrated embodiment) is allowed to be fastened thereto.The end plate portion 7 is formed separately from the base plate portion 4a and is disposed within the outer cylinder 2 at a position adjacent to the other end of the outer cylinder 2 in an axially spaced relationship to the base plate portion 4a. That is, the end plate portion 7 is disposed on a side opposite to the base end portion 4 awith respect to the first and second oscillation gears 14, 16.The end plate portion 7 has a cross-sectionally circular central through hole 7a provided in a radially central portion thereof. The central through hole 7 aof the end plate portion 7 and the central through hole 4 dof the base plate portion 4 aform a central through hole of the bracket 4 which is formed penetratingly in a radially central region of the bracket 4 extending in a rotational axis of the bracket 4.As shown in FIG. 3, the end plate portion 7 has a plurality of (three in the illustrated embodiment) mounting holes 7 bprovided around the central through hole 7 aat positions corresponding to the plurality of mounting recesses 4 e. Each of the mounting holes 7b constitutes a mounting location by which an end plate-side bearing 12b of the foregoing crankshaft bearing is allowed to be mounted thereon (end plate-side mounting location). Each of the mounting holes 7b is formed in the shape of a through hole having an opening oriented toward the second oscillation gear 16. That is, the bracket 4 has a mounting portion by which the aforementioned crankshaft bearing is allowed to be mounted thereon, the mounting portion including the mounting recess 4 eformed in the base plate portion 4 a(base plate side mounting location) and the mounting hole 7 bformed in the end plate portion 7 (end plate side mounting location).Each of the three shaft portions 4 cis provided in an integral relationship with the base plate portion 4 aand linearly extends from one (axially inner surface) of opposite main surfaces of the base plate portion 4 atoward the end plate portion 7. Each of the shaft portions 4 cis fixed to the end plate portion 7 by a bolt 9 (see FIG. 1 ). Specifically, the end plate portion 7 is formed with a plurality of (three in the illustrated embodiment) bolt insertion holes 7 c, and each of the shaft portions 4 c(the support base 5) is formed with fastening holes 4 fat positions corresponding to the bolt insertion holes 7 c, extending axially away from a distal edge surface thereof. Then, the bolt 9 is inserted into each of the bolt insertion holes 7 cof the end plate portion 7 from a side opposite to the support base 5. The bolt 9 is screwed to a corresponding one of the fastening holes 4 fof the shaft portions 4 c. In this way, the base end portion, the shaft portions 4 c, and the end plate portion 7 are integrated.Positioning of the end plate portion with respect to the support base 5 is performed by a positioning pin 11. The positioning pin 11 is inserted into a through hole 7d penetrating the end plate portion 7 and then into a corresponding pin hole 4h opened at the distal edge surfaces of the shaft portions 4c.An input shaft (omitted from illustration) is provided and functions as an input member to which a driving force of a non-illustrated driving motor is input. The input shaft may be inserted into the central through hole 7 aof the end plate portion 7 and the central through hole 4 dof the base plate portion 4 a. The input shaft is disposed such that an axis thereof is coincident with the axis of the carrier 4, that is, rotatable about the axis of the carrier 4. The input shaft includes an input gear (omitted from illustration) provided on an outer circumferential surface of one end thereof.The three crankshafts 10 are arranged inside the outer cylinder 2 and around the input shaft at equal intervals (see FIG. 2 ). That is, each of the crankshafts 10 is disposed at a position offset from the radially central portion of the carrier 4.Each of the crankshafts 10 is rotatably supported with respect to the carrier 4 by a crankshaft bearing (see FIG. 1 ). The crankshaft bearing includes a base plate side bearing 12a attached to the mounting recess 4e and an end plate side bearing 12b attached to the mounting hole 7b. Specifically, the base plate-side bearing 12 ais attached to a first of axially opposite ends of each of the crankshafts 10 and mounted in a corresponding one of the mounting recesses 4 eprovided in the base plate portion 4 a. That is, the mounting recess 4 eis provided in a number of plural corresponding to the number (three) of the base plate side bearing 12 a(crankshaft bearing). On the other hand, the end plate side bearing 12 bis attached to the other, second end of each of the crankshafts 10 and is mounted to a corresponding one of the mounting holes 7 bprovided in the end plate portion 7. That is, the mounting hole 7 bis provided in a number of plural corresponding to the number (three) of the end plate side bearing 12 b(crankshaft bearing). In this manner, each of the crankshafts 10 is rotatably supported with respect to the base plate portion 4 aand the end plate portion 7.Each of the crankshafts 10 has a shaft body 10c and first and second eccentric portions 10a, 10b integrally formed on the shaft body 10c. The first eccentric portion 10a and the second eccentric portion 10b are disposed between portions of the crankshaft supported by the bearings 12a, 12b in axially laterally juxtaposed relationship. Each of the first and second eccentric portions 10 a, 10 bis formed in a columnar shape and is disposed to protrude radially outward from the shaft body 10 cin eccentric relation to an axis of the shaft body 10 c. The first and second eccentric portions 10a, 10b are arranged eccentrically with respect to the axis of the shaft body 10c by given eccentric amounts such that there is a phase difference of a given angle therebetween.Each of the crankshafts 10 is provided with a fitting portion 10 dat the end thereof, that is, at a location axially outward from a portion thereof attached to a corresponding one of the mounting holes 7 bof the end plate portion 7. The transmission gears 20 are fitted into the fitting portions 10 dof the crankshafts 10 with reference. Each of the transmission gears 20 has external teeth 20 athat mesh with the input gear of the unillustrated input shaft such that rotation of the input shaft can be transmitted to a corresponding crankshaft 10. That is, each of the transmission gears 20 is configured to be integrally rotated with a corresponding one of the crankshafts 10 about the same rotational axis as that of the crankshaft 10.A closed space is defined inside the outer cylinder so as to be surrounded by respective opposed inner surfaces of the end plate portion 7 and the base plate portion 4a and an inner peripheral surface of the outer cylinder.The first oscillating gear 14 is installed in the closed space inside the outer cylinder 2 and simultaneously attached to the first eccentric portion 10a of each of the crankshafts 10 through a first rolling bearing 18a. Therefore, when each of the crankshafts 10 is rotated, the first eccentric portion 10a is eccentrically rotated, the first oscillation gear 14 is oscillatory rotated in interlocking relation to the eccentric rotation and simultaneously meshes with the internal gear pins 3.The first oscillation gear 14 has a dimension slightly smaller than an inner diameter of the outer cylinder 2. The first oscillating gear 14 includes first external teeth 14 a; a through hole 14 bformed in a radially central portion thereof; a plurality of (three in the illustrated embodiment) first eccentric portion insertion holes 14 c; and a plurality of (three in the illustrated embodiment) shaft portion insertion holes 14 d. The first external teeth 14a have a waveform which continues smoothly over the entire circumference of the first oscillation gear 14. The number of the first external teeth 14 ais slightly smaller than the number of the internal pins 3.The through hole 14 bis provided in the radially central portion of the first oscillation gear 14. The input shaft (omitted from illustration) may be inserted through the through hole 14 bwith a clearance.The plurality of first eccentric portion insertion holes 14 care provided around the through hole 14 bof the first oscillation gear 14 at circumferentially uniform intervals. Each of the first eccentric portions 10 aof the crankshafts 10 is inserted through a respective one of the first eccentric portion insertion holes 14 cwith the first rolling bearing 18 abeing interposed therebetween.The plurality of shaft portion insertion holes 14 dis provided around the central through hole 14 bof the first oscillation gear 14 at circumferentially uniform intervals. Each of the shaft portion insertion holes 14 dis disposed at a position between circumferentially adjacent ones of the first eccentric portion insertion holes 14 c. Each of the shaft portions 4 cis inserted through a respective one of the shaft portion insertion holes 14 dwith a clearance.The second oscillating gear 16 is installed in the closed space inside the outer cylinder 2 and simultaneously attached to the second eccentric portion 10 bof each of the crankshafts 10 through a second rolling bearing 18 b. The first oscillation gear 14 and the second oscillation gear 16 are provided in a relationship axially laterally adjacent to each other in accordance with the arrangement of the first eccentric portion 10a and the second eccentric portion 10b. Therefore, when each of the crankshafts 10 is rotated and the second eccentric portion 10 bis eccentrically rotated, the second oscillation gear 16 is oscillatory rotated in interlocking relation to the eccentric rotation while meshing with the internal teeth pins 3.The second oscillation gear 16 has a dimension slightly smaller than the inner diameter of the outer cylinder 2, and members having the same structure as those of the first oscillation gear 14. Specifically, the second oscillation gear 16 includes second external teeth 16 a; a through hole 16 b; a plurality of (three in the illustrated embodiment) second eccentric portion insertion holes 16 c; and a plurality of (three in the illustrated embodiment) shaft portion insertion holes 16 d. Each of these members has the same configuration as that of a corresponding one of the first external tooth 14 a, the through hole 14 b, the plurality of first eccentric portion insertion holes 14 c, and the plurality of shaft portion insertion holes 14 d. Each of the second eccentric portions 10 bof the crankshafts 10 is inserted through a respective one of the Zweitexzenterbschnittseinführlöcher 16 cwith the second rolling bearing 18 bbeing interposed therebetween.The carrier 4 is formed with an oil groove 25 in which a lubricating oil can be stored. The oil groove 25 is provided in a number of plural ones corresponding to the number of the crankshafts 10 (or the mounting recesses 4e or the mounting holes 7b). Each of the oil grooves 25 includes a base plate-side groove 27 formed in a surface of the base plate portion 4 aaligned to the first oscillation gear 14, and an end plate-side groove 29 formed in a surface of the end plate portion 7 inaligned to the second oscillation gear 16.In particular, since the mounting recess 4 eis provided in a number of plural (three in the illustrated embodiment) spaced positions around the central through hole 4 d, the base plate-side groove 27 is also provided in a number of plural (three in the illustrated embodiment) spaced positions around the central through hole 4 d.The base plate side groove 27 is located between the central through hole 4 dand the mounting recess 4 e, thereby allowing the base plate side bearing 12 ato be mounted thereto (base plate side mounting location). Specifically, the base plate-side groove 27 is formed in the axially inner surface of the base plate portion 4 a(surface of the base plate portion 4 aaligned to the first oscillation gear 14) as a groove that communicates between the central through hole 4 dand the mounting recess 4 e. The base plate-side groove 27 has a bottom wall 27 aapproximately parallel to the axially inner surface of the base plate portion 4 a(surface of the base plate portion 4 aaligned to the first oscillation gear 14), and a pair of side walls 27 buplevating axially from circumferentially opposite edges of the bottom wall 27 a, that is, the base plate-side groove 27 is formed to be concave (concaved) axially outward from the axially inner surface of the base plate portion 4 a. Further, a radially outer edge of each of the bottom wall 27 aand the side walls 27 bis connected to the mounting recess 4 e, and a radially inner edge of each of the bottom wall 27 aand the side walls 27 bis connected to the central through hole 4 d. Therefore, lubricating oil can be stored also in the axially inner surface of the base plate portion 4 aat a position adjacent to the base plate side bearing 12 awith being fitted into the mounting recess 4 e. A gap is formed between the first oscillation gear 14 and the surface of the base plate portion 4a in alignment with the first oscillation gear 14. Thus, through this gap, the lubricating oil can reach a meshing area between the inner teeth pins 3 and the first outer teeth 14 aand the adjacent main bearing 6 in addition to the inside of the base plate-side groove 27.Similarly, because the mounting hole 7 bis provided in a number of plural (three in the illustrated embodiment) spaced positions around the central through hole 7 a, the end plate-side groove 29 is also provided in a number of plural (three in the illustrated embodiment) spaced positions around the central through hole 7 a.The end plate side groove 29 is located between the central through hole 7 aand the mounting hole 7 b, thereby allowing the end plate side bearing 12 bto be mounted thereto (end plate side mounting location). Specifically, the end plate-side groove 29 is formed in an axially inner surface of the end plate portion 7 (surface of the end plate portion 7 facing the second oscillation gear 16) as a groove that connects between the central through hole 7 aand the mounting hole 7 b. The end plate-side groove 29 has a bottom wall 29 aapproximately parallel to the axially inner surface of the end plate portion 7, and a pair of side walls 29 buplevating axially from circumferentially opposite edges of the bottom wall 29 a, that is, the end plate-side groove 29 is formed to be concave (concaved) axially outward from the axially inner surface of the end plate portion 7. Further, a radially outer edge of each of the bottom wall 29 aand the side walls 29 bis connected to the mounting hole 7 b, and a radially inner edge of each of the bottom wall 29 aand the side walls 29 bis connected to the central through hole 7 a. Therefore, lubricating oil can be stored also in the axially inner surface of the end plate portion 7 at a position adjacent to the end plate side bearing 12 bintegrated in the mounting hole 7 b. A gap is formed between the second oscillation gear 16 and the surface of the end plate portion 7 oriented toward the second oscillation gear 16. Thus, through this gap, lubricating oil can reach a meshing area between the inner teeth pins 3 and the second outer teeth 16 aand the adjacent main bearing 6 in addition to the inside of the end plate-side groove 29.As explained above, in this embodiment, the oil groove in which lubricating oil can be stored is formed on the side of the central through hole 4d, 7a (on the side of the radially central portion) with respect to the mounting portion (mounting recess 4e, mounting hole 7b), thereby allowing the crankshaft bearing (base plate side bearing 12a, end plate side bearing 12b) to be mounted thereon. By doing so, it becomes possible to prevent a situation in which, when a centrifugal force is generated by rotation of the carrier 4, oil flows out radially outward from the mounting portion (mounting recess 4 e, mounting hole 7 b) via the oil groove. Moreover, the oil groove 25 is located between the central through hole 4 d, 7 aand the mounting portion (mounting recess 4 e, mounting hole 7 b), whereby it becomes possible to facilitate the flow of the oil from the central through hole 4 d, 7 ainto the oil groove 25. This makes it possible to maintain lubrication of the crankshaft bearing (base plate-side bearing 12 a, end plate-side bearing 12 b). Further, the oil groove 25 is formed in the surface of the carrier 4 in alignment with the oscillating gear 14, 16 so that it becomes possible to counteract the increase in time and labor in the process of forming the oil groove 25.In this embodiment, the mounting recess 4e is formed in a concave shape with an opening oriented toward the first oscillation gear 14, and the base plate-side groove 27 is formed so as to allow the bottom wall 27a thereof to be connected to the mounting recess 4e. Further, the mounting hole 7 bis formed in a through hole shape having an opening oriented to the second oscillation gear 16, and the end plate-side groove 29 is formed so as to allow the bottom wall 29 athereof to be connected to the mounting hole 7 b. Therefore, the lubricating oil is stored in the oil groove 25 and is simultaneously stored in the mounting portion (mounting recess 4 e, mounting hole 7 b) formed in a cavity or a through hole shape for connection with the oil groove 25. This makes it possible to improve lubricity for the crankshaft bearing (base plate-side bearing 12 a, end plate-side bearing 12 b).In this embodiment, the bearings (base plate-side bearing 12 aand end plate-side bearing 12 b) for supporting the crankshaft 10 are disposed on axially opposite sides, respectively, with respect to the first and second oscillating gears 14, 16 such that the base plate-side bearing 12 aand the end plate-side bearing 12 bare relatively lubricated by lubricating oil stored in the base plate-side groove 27 and lubricating oil stored in the end plate-side groove 29. This makes it possible to support the crankshaft 10 at positions on longitudinally opposite sides thereof, thereby ensuring lubrication of the two bearings 12 a, 12 b.In this embodiment, the crankshaft 10 is provided in a number of plural, thereby making it possible to drive the first and second oscillating gears 14, 16 using the crankshafts 10 each reduced in diameter and ensure lubrication of each of the crankshaft bearings.Note that the present invention is not limited to the above-described embodiment, but various changes and modifications may be made thereto without departing from the spirit and scope as set forth in the appended claims. Although the transmission device according to the above-described embodiment is configured to be provided with, for example, two oscillating gears 14, 16, the present invention is not limited thereto. In one example, the transmission device may also be configured to be provided with only one oscillating gear or three or more oscillating gears.The above-described embodiment has been described based on an example in which the outer cylinder 2 is fixed to the base and the carrier 4 is relatively rotated with respect to the outer cylinder 2. Alternatively, the carrier 4 may also be fixed to a stationary member such as a base, and the outer cylinder 2 may be relatively rotatable with respect to the carrier 2.Although the transmission device according to the present embodiment is configured such that the crankshaft bearing includes the base plate-side bearing 12 aand the end plate-side bearing 12 b, the present invention is not limited thereto. Further, the transmission device may be configured to be provided with only one of the base plate-side bearing 12 aand the end plate-side bearing 12 b. In this case, the transmission device may be configured such that the oil groove 25 is provided in only one of the base plate portion 4 aand the end plate portion 7 provided with the bearing 12 a, 12 b.The above-described embodiment will be explained below. (1) In the above-described embodiment, a bracket is formed with an oil groove in which a lubricating oil can be stored and which is formed on a side of a central through hole with respect to a mounting portion to allow a crankshaft bearing to be mounted thereon. This makes it possible to prevent a situation in which, when a centrifugal force is generated by rotation of the carrier, oil flows radially outward from the mounting portion via the oil groove. Moreover, the oil groove is located between the central through hole and the mounting portion, thereby making it possible to promote the flow of oil from the central through hole into the oil groove by a centrifugal force. This makes it possible to maintain lubrication of the crankshaft bearing. Moreover, the oil groove is formed in a surface of the carrier oriented toward an oscillating gear, thereby making it possible to counteract the increase in time and effort in the process of forming the oil groove. (2) The bracket may include a base plate portion and an end plate portion formed separately from the base plate portion and disposed on a side opposite to the base plate portion with respect to the oscillation gear. The mounting portion may include a base plate side mounting location formed in the base plate portion and an end plate side mounting location formed in the end plate portion. The crankshaft bearing may include a base plate side bearing disposed at the base plate side mounting location and an end plate side bearing disposed at the end plate side mounting location. In this case, the oil groove preferably includes a base plate-side groove formed in a surface of the base plate portion oriented toward the oscillation gear, and an end plate-side groove formed in a surface of the end plate portion oriented toward the oscillation gear.In the embodiment having this feature, the bearings supporting the crankshaft are disposed on respectively axially opposite sides with respect to the oscillating gear, such that the two bearings, i.e., the base plate-side bearing and the end plate-side bearing, are respectively lubricated by a lubricating oil stored in the base plate-side groove and a lubricating oil stored in the end plate-side groove. This makes it possible to support the crankshaft at positions on longitudinally opposite sides thereof while ensuring lubrication of the two bearings.(3) The crankshaft bearing may be a plurality of crankshaft bearings arranged at intervals in a circumferential direction of the carrier. The mounting portion may include a plurality of mounting portions each provided corresponding to a respective one of the plurality of crankshaft bearings. In this case, it is preferable that the oil groove is a plurality of oil grooves each provided corresponding to each of the plurality of mounting portions.In the embodiment having this feature, the crankshaft is provided in a number of plural, thereby making it possible to drive the oscillating gear using the crankshafts each reduced in diameter and ensure lubrication of each of the crankshaft bearings.As described above, the transmission device according to the above-described embodiment can lubricate the crankshaft bearing.

Claims

An eccentric oscillation gear device (1) comprising: a crankshaft (10) formed with an eccentric portion (10a); a crankshaft bearing (12a, 12b) rotatably supporting the crankshaft (10); an oscillation gear (14) having a tooth portion (14a) and an insertion hole (14c) into which the eccentric portion (10a) is inserted; an outer cylinder (2) having inner teeth (3) meshing with the tooth portion (14a) of the oscillation gear (14); and a carrier (4) to which the crankshaft bearing (12a, 12b) is attached and which is configured to generate a relative difference in rotational speed between the carrier (4) and the outer cylinder (2) by means of an oscillatory movement of the oscillatory gear (14) together with a rotation of the eccentric portion (10a), wherein the carrier (4) is formed with: a central through hole (4d, 7a); a mounting portion (4e, 7b) which is arranged at a position radially offset from the central through hole (4d, 7a) and to which the crankshaft bearing (12a, 12b) is attached; and an oil groove (25) in which a lubricating oil can be stored, wherein the oil groove (25) is provided in a surface of the carrier (4) oriented toward the oscillation gear (14) at a position between the central through hole (4d, 7a) and the mounting portion (4e, 7b), the carrier (4) comprising a base plate portion (4a), the mounting portion (4e, 7b) comprising a base plate side mounting location (4e) formed in the base plate portion (4a), the oil groove (25) comprising a base plate side groove (27) formed in a surface of the base plate portion (4a) oriented toward the oscillation gear (14), the base plate side groove (27) comprising a bottom wall (27a) and a pair of side walls (27b), and a radially outer edge of the bottom wall (27a) and the side walls (27b) is connected to the mounting recess (4e), and a radially inner edge of the bottom wall (27a) and the side walls (27b) is connected to the central through hole (4d).The eccentric oscillation gear device (1) according to claim 1, wherein: the carrier (4) comprises an end plate portion (7) formed separately from the base plate portion (4a) and disposed on a side opposite to the base plate portion (4a) with respect to the oscillation gear (14); the mounting portion (4e, 7b) comprises an end plate-side mounting location (7b) formed in the end plate portion (7); the crankshaft bearing (12a, 12b) comprises a base plate-side bearing (12a) attached to the base plate-side mounting location (4e) and an end plate-side bearing (12b) attached to the end plate-side mounting location (7b); and the oil groove (25) includes an end plate side groove (29) formed in a surface of the end plate portion (7) oriented toward the oscillation gear (14).The eccentric oscillation transmission device (1) according to claim 1 or 2, wherein: the crankshaft bearing (12a, 12b) is a plurality of crankshaft bearings (12a, 12b) arranged at intervals in a circumferential direction of the carrier (4); the mounting portion (4e, 7b) is a plurality of mounting portions (4e, 7b) each provided corresponding to a respective one of the plurality of crankshaft bearings (12a, 12b); and the oil groove (25) is a plurality of oil grooves (25) each provided corresponding to a respective one of the plurality of mounting portions (4e, 7b).

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