gear drive

Abstract

Gear drive (100) comprising: an internal gear link having an internal gear (10) formed on an inner circumferential surface, an external gear (28) configured to rotate eccentrically relative to the internal gear (10) while engaging with the internal gear (10), wherein: a plurality of recesses (9) extend along an axis (12) of the gear drive (100) and are provided at equal intervals in a circumferential direction of the internal gear link in an inner circumferential surface of the internal gear link, the internal gear (10) is formed by inserting cylindrical links (8) into the recesses (9), and the length of the cylindrical links (8) in a circumferential direction that makes contact with the recesses (9) is shorter at the end portions of the cylindrical links (9) on at least one side in an axial direction of the gear drive (100) than at the middle portions of the cylindrical links. (8) in the axial direction,wherein an inclined part (9a), which forms a ring in the circumferential direction, is provided in the inner circumferential surface of the inner gear member at a position facing the end parts of the cylindrical members (8) on at least one side in the axial direction.

Description

TECHNICAL FIELDA technique for a gear transmission is provided.PRIOR ARTThere is known a gear transmission having a configuration in which an external gear eccentrically rotates relative to an internal gear while engaging with the internal gear. In this type of gear transmission, the internal gear can be formed by forming a recess in an inner circumferential surface of an internal gear member and inserting a cylindrical member into the recess. Japanese Patent Application Publication No. 2006-46596 discloses a gear transmission in which an internal gear is formed by forming a plurality of recesses in an inner circumferential surface of a housing (internal gear member) and inserting pins (cylindrical members) into the recesses.JP 2001-232 516 A, JP 2009-293 650 A, JP 2013-92 179 A and DE 10 2014 016 928 A1, the latter being a post-published document, each show gear drives having an internal gear member and an external gear configured to rotate eccentrically relative to the internal gear.SUMMARY OF THE INVENTIONThe cylindrical members inserted into the above-mentioned recesses correspond to the internal teeth of the internal gear. The cylindrical members rotate within the recesses while engaging the external gear. These recesses are formed in an inner circumferential surface of a housing. In an internal gear having such a configuration, lubricant present between the recesses and the cylindrical members can leak out of the recesses when the cylindrical members rotate. Therefore, oil films in the recesses may leak and friction between a surface of the recesses and the cylindrical members may become larger. Further, oil films may leak on surfaces of the cylindrical members, and friction between the cylindrical members and the external gear may become larger. This can reduce the service life of the gear drive. Here, a technique for solving the above problem and realizing a gear transmission having a long life is disclosed.PROBLEM SOLUTIONThe technique herein is directed to a gear transmission including an internal gear member having an internal gear formed on an inner periphery of the internal gear member and an external gear configured to rotate relative to the internal gear while engaging the internal gear. In this gear transmission, a plurality of recesses are provided on an inner circumferential surface of the internal gear member. The plurality of recesses extend in the inner circumferential surface of the internal gear member along an axis of the pinion gear. Further, the plurality of recesses are provided at equal intervals in a circumferential direction of the internal gear member in the inner circumferential surface of the internal gear member. The internal gear is formed by inserting cylindrical members into the recesses. In the gear transmission herein, the length of the cylindrical members in a circumferential direction making contact with the recesses is shorter at end portions of the cylindrical members on at least one side in an axial direction of the gear transmission than at middle portions of the cylindrical members in the axial direction.The cylindrical members inserted into the recesses correspond to the internal teeth of the internal gear. In the following description, the recesses formed in the inner circumferential surface of the internal gear member may be referred to as "insertion recesses". In the above-mentioned gear transmission, the contact area in each insertion groove is smaller at the end parts than at the central part of the corresponding cylindrical member on at least one side in the axial direction. In other words, the area exposed from the insertion groove is larger at the end part than at the central part of the cylindrical member in the axial direction. Therefore, the end portions of the cylindrical members have a larger area making contact with a lubricant on the outside of the insertion recesses. The lubricant making contact with the end portions of the cylindrical members travels along an outer circumferential surface of the cylindrical members and moves toward the central portion of the cylindrical members. It becomes easier to supply the lubricant between the insertion grooves and the cylindrical members, and the oil film can be prevented from leaking in the insertion grooves and on the cylindrical members.Further, "the external gear eccentrically rotates relative to the internal gear" is intended to mean not only a configuration in which the external gear eccentrically extends relative to an axis of the pinion gear, but also a configuration in which the internal gear eccentrically rotates relative to the axis of the pinion gear. That is, "the external gear eccentrically rotates relative to the internal gear" means that the internal gear or the external gear eccentrically rotates relative to the axis of the pinion gear, and the internal gear and the external gear eccentrically rotate relative to each other. Further, "the end portions of the cylindrical members on at least one side in the axial direction" is to be understood as meaning both a configuration having one end portion in the axial direction and a configuration having the two end portions in the axial direction. Also, "the length of the cylindrical members in the circumferential direction making contact with the recess is short" is intended to mean a configuration in which the end portions of the cylindrical members in the axial direction make no contact with the insertion recess at all. That is, "the length of the cylindrical members in the circumferential direction making contact with the recess is short" is also understood to mean a configuration in which a clearance is provided between the inner circumferential surface of the internal gear member and the cylindrical members.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a cross-sectional view of a gear transmission of a first embodiment. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1. FIG. 3 is an enlarged partial cross-sectional view of an internal gear member (an enlarged view of a part in FIG. 1 ). FIG. 4 is a schematic view explaining features of the first embodiment. FIG. 5 is a schematic view explaining features of a second embodiment. FIG. 6 is a schematic view explaining features of a third embodiment. FIG. 7 is a schematic view explaining features of a fourth embodiment.DESCRIPTION OF EMBODIMENTSSeveral technical features of the gear transmission of the present invention will be explained below. The points explained below can also each be technically useful per se.The gear train may include an internal gear and an external gear. The internal gear and the external gear may rotate eccentrically relative to each other while being meshed with each other. The external gear may rotate eccentrically while engaging the internal gear. Alternatively, the internal gear may rotate eccentrically while engaging the external gear. The internal gear may be formed on an inner circumferential surface of an annular internal gear member. The internal gear may be formed by a plurality of recesses (insertion recesses) formed in the inner circumferential surface of the internal gear member and cylindrical members inserted into the insertion recesses. When the external gear eccentrically rotates, a carrier holding the external gear may be provided. The carrier may be supported by the internal gear member via a pair of bearings (main bearings).In the eccentrically rotating external gear type, the internal gear member may also function as a housing of the gear transmission. That is, the internal gear may be formed on an inner periphery of the housing. In this case, a carrier, a crankshaft, and an external gear may be disposed in the housing. The crankshaft may be rotatably supported by the carrier. The crankshaft may include an eccentric body. The external gear may mesh with the eccentric body of the crankshaft and rotate eccentrically with the rotation of the crankshaft. The internal gear may mesh with the external gear and may have a number of teeth different from the number of teeth of the external gear.The cylindrical members inserted into the insertion recesses may function as the teeth of the internal gear. In this case, the inner circumferential surface between adjacent insertion recesses in the inner circumferential surface of the internal gear member may function as tooth recesses of the internal gear. In a cross section perpendicular to the axis of the gear drive, the shape of each insertion recess may be circular arc-shaped. The plurality of insertion recesses may extend along the axis of the gear transmission. In this case, the insertion recesses may be provided at equal intervals in the circumferential direction of the internal gear member. In the case of circular arc-shaped insertion recesses, the center of a virtual circle including a surface of the insertion recess is coaxial with the rotation axis of the cylindrical member, and the diameter of the virtual circle and the diameter of the cylindrical member are substantially equal. The cylindrical members can rotate in the insertion recesses and function as a plain bearing between the external gears and the insertion recesses.As compared with the center parts in the axial direction, the end parts of the cylindrical members in the axial direction may have a shorter circumferential length in contact with the insertion groove. That is, a larger area may be exposed from the insertion groove at the end parts than at the center part of the cylindrical members in the axial direction. One of the end parts in the axial direction may have a larger area exposed from the insertion groove than the central part. Alternatively, both end portions in the axial direction may have a larger area exposed from the insertion recess than the central portion. Further, the end portions of the cylindrical members in the axial direction may be separated from the inner circumferential surface of the internal gear members (insertion recesses) along the entire circumference in the circumferential direction. Movement of the cylindrical members in the axial direction can be restricted by running the main bearings.An inclined part forming a ring in the circumferential direction of the internal gear member is provided in the inner circumferential surface of the internal gear member at a position facing the end part of the cylindrical members on at least one side in the axial direction. Because the inclined part is provided, the thickness of the side walls defining the insertion groove can be thinner at the end part than at the middle part of the insertion grooves in the radial direction of the pinion gear. When the pinion gear is viewed in a plan view (from an axial direction of the pinion gear), an end part (an outer edge) of a large-diameter side of the inclined part may be disposed outside the insertion groove in the radial direction of the pinion gear. In this case, the end part of the insertion groove may be disposed at the inclined part in the axial direction of the pinion gear. In other words, the cylindrical members may be disposed on the inclined parts when the arrangement is viewed from the axial direction of the pinion gear.The large diameter side of the inclined part may be disposed outside a small diameter side of the inclined part in the axial direction of the pinion gear. That is, at the part where each inclined part is provided, the thickness of the internal gear member in the radial direction of the pinion gear gradually becomes larger in the axial direction of the pinion gear from the end parts toward the central part of the internal gear member. Further, the inclined parts may be locally provided at the end parts of the insertion recesses in the axial direction of the gear. In this case, the inclined parts may be provided at equal intervals in the circumferential direction without forming a ring around the circumferential direction of the internal gear member.At a position facing an end part of the cylindrical members in the axial direction, the depth of the insertion recesses may be deeper than at a position facing the middle part of the cylindrical members in the axial direction. In other words, in the axial direction of the gear transmission, an insertion groove making contact with the cylindrical member (first insertion groove) and an insertion groove making no contact with the cylindrical member (second insertion groove) may be sequentially provided, and the second insertion grooves may be provided at a position facing the axial direction end parts of the cylindrical members. The center of a first virtual circle including a surface of the first insertion groove and the center of a second virtual circle including a surface of the second insertion groove may be arranged coaxially. The diameter of the second virtual circle may be larger than the diameter of the first virtual circle.EMBODIMENTSFirst EmbodimentNext, the basic configuration of a pinion gear 100 will be described with reference to FIGS. 1 and 2. FIG. 1 shows a longitudinal cross-sectional view of the pinion gear 100 (a cross-sectional view along an axis 12 of the pinion gear 100). FIG. 2 is a cross-sectional view of the pinion gear 100 (a cross-sectional view taken along a line perpendicular to the axis 12 of the pinion gear 100). The pinion gear 100 includes an internal gear 10, a carrier 4, a crankshaft 14, and external gears 28. The internal pins 8 have a cylindrical shape and are inserted into insertion recesses 9 formed on an inner circumferential surface 7 of the housing 6. The housing 6 is an example of an internal gear member, and the internal pins 8 are an example of cylindrical members.The carrier 4 is rotatably supported by the housing 6 via a pair of bearings (hereinafter also referred to as main bearing 22). The main bearings 22 restrict movement of the carrier 4 in the axial direction and in the radial direction relative to the housing 6. In the gear train 100, angular contact ball bearings are used as the main bearings 22. Outer races 24 of the main bearings 22 cover axial direction end surfaces of the inner pins 8. Movement of the internal pins 8 in the axial direction is restricted by the outer races 24.The carrier 4 comprises a first plate 4 aand a second plate 4 c. The first plate 4 aincludes a columnar portion 4 b. The columnar portion 4 bextends from the first plate 4 ato the second plate 4 cand is fixed to the second plate 4 cby a screw 34. The bolt 34 extends through the second plate 4c and is fixed to a bolt groove 34a in the columnar portion 4b. An oil seal 18 is disposed between the housing 6 and the first plate 4 a. Further, positioning pins (not shown) for fixing the position in the circumferential direction are inserted into the columnar portion 4 band the second plate 4 c. Pin holes 36 provided in the columnar portion 4b are shown in FIG. 2. And also in the second plate 4c, pin holes (not shown) are provided. The positioning pins extend through the pin holes of the second plate 4c and are inserted into the pin holes 36.The crankshaft 14 is rotatably supported on the carrier 4 by a pair of bearings 20. The pair of bearings 20 restrict movement of the crankshaft 14 in the axial direction and in the radial direction relative to the carrier 4. In the gear transmission 100, tapered roller bearings are used as the pair of bearings 20. The crankshaft 14 includes an input gear 32 and two eccentric bodies 30, and the eccentric bodies 30 are disposed between the pair of bearings 22. The eccentric bodies 30 mesh with the external gears 28 via cylindrical roller bearings 26. The external gears 28 are supported by the carrier 4 via the crankshaft 14. Further, the input gear 32 is disposed outside the pair of bearings 20.In the gear transmission 100, the torque of a motor is transmitted to the input gear 32. When the torque of the motor is transmitted to the input gear 32, the eccentric bodies 30 eccentrically rotate with the rotation of the crankshaft 14. The external gears 28 rotate eccentrically about the axis 12, and the two eccentric bodies 30 are symmetrically eccentric. Consequently, the two external gears 28 rotate eccentrically about the axis 12 while being symmetrically eccentric with respect to the axis 12. The number of teeth of the external gears 28 is different from the number of teeth of the internal gear 10 (the number of internal pins 8) (see FIG. 2 ). Thus, when the external gears 28 eccentrically rotate, the carrier 4 holding the external gears 28 rotates relative to the housing 6 in accordance with the difference between the number of teeth of the external gears 28 and the internal gear 10.Features of the housing 6 will be described below with reference to FIGS. 2 to 4. Furthermore, FIG. 4 schematically shows the features of the housing 6, wherein not exactly the actual size is shown. Further, the internal pins 8 and the external gears 28 are shown by a two-dot chain line in FIG. 3, and the internal pins 8 are shown by a broken line in FIG. 4. The inner circumferential surface 7 of a central part 6 aof the housing 6 protrudes further toward the axis 12 than the end parts 6 b. In other words, the inner diameter of the middle part 6a is smaller than the inner diameter of the end parts 6b. A flat part 11 is provided at both ends of the middle part 6a (at both ends in the direction of the axis 12). The position of the outer races 24 of the main bearings 22 is fixed by the flat parts 11 (see also FIG. 1 ). The flat portions 11 regulate movement of the main bearings 22 in the direction of the axis 12, thereby adjusting the preload of the carrier 4 relative to the housing 6. The flat parts 11 can also be referred to as running support units. The insertion recesses 9 and the inclined parts 9a are provided in the middle part 6a. As shown in FIG. 2, each inclined part 9 aconstitutes a ring around the circumferential direction of the housing 6 on opposite sides in the direction of the axis 12, and an outer periphery of each inclined part 9 ais disposed on an outer side of the insertion recesses 9 in the radial direction of the pinion gear 100 (in the direction perpendicular to the axis 12). That is, an end part (an outer edge) of a large-diameter side of the inclined part 9 ais disposed outside the bottom of the insertion recesses 9.As described above, movement of the internal pins 8 in the direction of the axis 12 is restricted by the external races 24. As shown in FIG. 3, the internal teeth pins 8 extend to substantially the same position as the flat parts 11. Further, the external gears 28 are configured to make contact with the entirety of the internal pins 8 in the direction of the axis 12. Therefore, parts of the tooth surface of the external gears 28 (a part of the tooth surface in the direction of the axis 12) face the inclined parts 9 ain the radial direction (the direction perpendicular to the axis 12). As shown in FIG. 4, the end portions of the insertion recesses 9 are disposed at the inclined portions 9a. That is, the insertion recesses 9 do not extend to the flat parts 11. Therefore, the end portions of the internal pins 8 protrude from the insertion recesses 9. In other words, the end parts of the internal teeth pins 8 do not make contact with the inner circumferential surface 7 of the housing 6. The end parts of the internal teeth pins 8 are separated from the inner circumferential surface 7 of the housing 6 along the entire circumference in the circumferential direction. Since the end portions of the internal teeth pins 8 are exposed from the insertion recesses 9, they easily make contact with a lubricant. Further, the depth of the insertion recesses 9 is deeper at the inclined parts 9a than at other parts. Therefore, a clearance is provided in the inclined parts 9a between the insertion recesses 9 and the internal teeth pins 8. A lubricant is easily held in this space. And, as is clear from FIGS. 3 and 4, the thickness in the radial direction of the side walls (of the housing 6) defining the insertion recesses 9 is thinner at the end parts than at the middle parts of the insertion recesses 9.A simple description of the manufacturing process for the housing 6 will be given below. Manufacturing steps for an inner part of the housing 6 will be described. First, the both sides of the inner circumferential surface of the housing 6 are leveled, and the inner diameter of the both end portions 6b of the housing 6 is made larger than the central portion 6a. Thereby, the flat parts 11 are formed at the axial direction end parts of the middle part 6 a. Then, corners of the central part 6 a(end parts of the flat parts 11 that are radially closer to the axis 12) are planarized to provide rings in the circumferential direction of the housing 6 (see also FIG. 1 ). The corners of both sides of the central portion 6a in the case 6 are leveled. Thereby, inclined parts 9 aare formed in the middle part 6 aat the opposite ends in the direction of the axis 12. Then, the central part 6a is leveled to form the insertion recesses 9 along the axis 12. At this time, the tool for forming the insertion recesses 9 initially makes contact with the inclined parts 9a. That is, the tool for forming the insertion recesses 9 makes a planarization inside the large-diameter-side end parts of the inclined parts 9 a(on the axis 12 side).Advantages of the gear drive 100 will be described below. As described above, the internal pins 8 configure the internal gear 10 and are inserted into the insertion recesses 9. At the central parts of the internal teeth pins 8, the surfaces of the internal teeth pins 8 make contact with the insertion recesses 9, and do not easily make contact with the lubricant at outer parts of the corresponding insertion recesses 9. However, in the gear transmission 100, since the end parts of the internal teeth pins 8 do not make contact with the inner circumferential surface 7 of the housing 6 (the insertion recesses 9), the end parts of the internal teeth pins 8 can make contact with the lubricant at the outer parts of the insertion recesses 9. Further, the lubricant can be held in the space between the insertion recesses 9 and the internal teeth pins 8 at the position where the inclined parts 9a are formed. Therefore, the lubricant can travel along the outer periphery of the internal teeth pins 8 and can move from the end parts to the middle parts of the internal teeth pins 8. As a result, leakage of the oil film between the internal pins 8 and the insertion recesses 9 can be prevented. Further, leakage of the oil film between the internal pins 8 and the external gears 28 can also be prevented. That is, by providing the inclined parts 9 a, friction between the internal teeth pins 8 and the insertion recesses 9 and / or between the internal teeth pins 8 and the external gears 28 can be reduced.The internal pins 8 must be inserted into the insertion recesses 9 along the direction in which the insertion recesses 9 extend (direction of the axis 12). For example, when the inclined parts 9 aare not provided, the internal pins 8 must be inserted into the insertion recesses 9 while the internal pins 8 are held parallel to the axis 12. As described above, the internal teeth pins 8 function as slide bearings for the insertion recesses 9. That is, there is almost no clearance between the internal pins 8 and the insertion recesses 9. The insertion of the internal pins 8 into the insertion recesses 9 with almost no clearance while the internal pins 8 are held parallel to the axis 12 is a complicated operation. In the gear transmission 100, because the inclined part 9 ais provided at least on the insertion side, the internal pins 8 can be inserted along the inclined parts 9 awhen the internal pins 8 are inserted into the insertion recesses 9. That is, it is not necessary to keep the internal pins 8 parallel to the axis 12 when the internal pins 8 are inserted into the insertion recesses. The manufacturing process of the pinion gear 100 (the step of inserting the internal pins 8 into the insertion recesses 9) can be simplified.As described above, when the insertion recesses 9 are formed in the inner circumferential surface 7 of the housing 6, the tool for forming the insertion recesses 9 initially makes contact with the inclined part 9 aon a side in the direction of the axis 12. Since the tool initially makes contact with the inclined part 9 a, occurrence of burrs in the end parts of the insertion recesses 9 can be suppressed as compared with the case where the insertion recesses are formed in a housing without the inclined parts 9 a. Because the inclined parts 9 aare provided, the burr removing step after the insertion recesses 9 are formed can be simplified. That is, the manufacturing process for the pinion gear 100 (the burr removing step) can be simplified.And, since the tool makes contact with the inclined part 9 awhen the insertion recesses 9 are formed, the load applied to the tool for forming the insertion recesses 9 can be reduced. Therefore, the rotational speed and / or the moving speed of the tool can be reduced, and the processing time of the insertion recesses 9 can be shortened. Further, the pinion gear 100 has an extra step of forming the inclined parts 9a as compared with the conventional pinion gear not provided with inclined parts. However, because the inclined parts 9 aform a ring along the inner circumferential surface 7 of the housing 6, the inclined parts 9 acan be formed in one step per side. The manufacturing time can be reduced remarkably as compared with performing the step of removing the burrs occurring in each insertion groove 9.Second EmbodimentFIG. 5 shows a part of a gear transmission of a second embodiment. In particular, the shape of a housing 206 is different from that of the housing 6 of the gear transmission 100. The other configurations are substantially the same as those of the pinion gear 100. In addition, components that are the same as those of the pinion gear 100 are denoted by the same reference numerals or reference numerals having the same two lower digits, and repeated description of these components is omitted here. FIG. 5 shows a part corresponding to FIG. 4 from which the gear drive 100 has been described.As shown in FIG. 5, large-diameter-side end portions of inclined portions 209 aare formed radially inward of bases of the insertion recesses 209. In other words, the diameter of the large-diameter-side end portions of the inclined portions 209 ais smaller than that of the inclined portion 9 a. In the case 206, the area of the flat parts 211 is larger than that of the case 6, and therefore, the contact area of the outer races 24 of the bearings 22 (see also FIG. 1 ) and the case 206 is larger, and the bearings 22 can be held more reliably. And, in the case 206, when the insertion recesses 209 are formed in the inner circumferential surface, the tool initially makes contact with the flat parts 211 and the inclined parts 209 a.Further, in the case 206, the areas making contact with the insertion grooves 209 are smaller at the end parts than at the middle parts of the internal teeth pins 8, and therefore, the end parts of the internal teeth pins 8 easily make contact with the lubricant at the outer parts of the insertion grooves 209. The lubricant adhering to the end parts of the internal teeth pins 8 moves to the central part of the internal teeth pins 8, and oil film leakage between the internal teeth pins 8 and the insertion recesses 9 and / or between the internal teeth pins 8 and the external gears 28 can be prevented (see also FIG. 2 ).Third EmbodimentFIG. 6 shows a part of a gear transmission of a third embodiment not according to the invention. In particular, the shape of a housing 306 is different from that of the housing 6 of the gear transmission 100. The other configurations are substantially the same as those of the pinion gear 100. Components that are the same as those of the pinion gear 100 have the same reference numerals or reference numerals with the same two lower digits, and a repeated description of these components is omitted here. FIG. 6 shows a part corresponding to FIG. 4 from which the gear 100 has been described.As shown in FIG. 6, the housing 306 does not include inclined parts. Two insertion recesses (first insertion recesses 309, second insertion recesses 309a) having different diameters are provided in the housing 306. The center of a first virtual circle including the surface of the first insertion groove 309 and the center of a second virtual circle including the surface of the second insertion groove 309 aare arranged coaxially. Further, the diameter of the second virtual circle is larger than the diameter of the first virtual circle. That is, the second insertion recesses 309 aare deeper than the first insertion recesses 309. The first insertion recesses 309 face the center parts of the internal teeth pins 8 in the axial direction, and the second insertion recesses 309 a face the end parts of the internal teeth pins 8 in the axial direction. The first insertion recesses 309 and the second insertion recesses 309 aare connected to each other. The internal pins 8 make contact with a surface of the first insertion recesses 309 and make no contact with a surface of the second insertion recesses 309 a. Therefore, no clearance is provided between the internal teeth pins 8 and the housing 306 at the end part side of the internal teeth pins 8. A lubricant is held between the second insertion grooves 309 aand the internal teeth pins 8, and this lubricant can move toward the central part of the internal teeth pins 8 (the part inserted into the first insertion grooves 309).Further, the flat parts 311 of the housing 306 have larger areas than those of the housing 6, and therefore, the contact areas of the outer races 24 of the bearings 22 and the housing 306 can be enlarged. Further, in the case 306, the internal teeth pins 8 are inserted into the first insertion recesses 309 via the second insertion recesses 309 a. Because the diameter of the second insertion recesses 309 ais larger than the diameter of the internal teeth pins 8, the operation of inserting the internal teeth pins 8 can be performed more easily than a configuration in which the internal teeth pins 8 are directly inserted into the first insertion recesses 309 without a large clearance.Fourth EmbodimentFIG. 7 shows a part of a gear transmission of a fourth embodiment not according to the invention. Specifically, the shape of a housing 406 is different from that of the housing 6 of the pinion gear 100. The other configurations are substantially the same as those of the pinion gear 100. Components that are the same as those of the pinion gear 100 are denoted by the same reference numerals or by reference numerals having the same two lower digits, and repeated description of these components is omitted here. FIG. 7 shows a part corresponding to FIG. 4 from which the gear 100 has been described.Similar to the housing 306, the housing 406 does not include any sloped portions. In the case 406, the diameter of the second insertion recesses 409a becomes smaller as it approaches the first insertion recesses 409. In other words, the housing 406 includes a plurality of inclined parts (second insertion recesses) 409 ain the circumferential direction of the housing 406. Therefore, it is easy to insert the internal gear pins 8 into the first insertion recesses 409, and a reservoir for the lubricant can also be maintained at the end portions of the internal gears 8. Further, a large area of a holding unit 411 can be secured. Moreover, since the tool for forming the first insertion recesses 409 initially makes contact with the inclined parts (second insertion recesses 409 a), the deburring process can be simplified.Although specific examples of the present invention have been described in detail, these examples are merely illustrative and do not limit the scope of the invention in any way. The technique defined in the claims also includes various changes and modifications to the specific examples described herein. The technical elements explained in the present specification or the drawings provide technical utility individually or in various combinations. The present invention is not limited to the combinations described herein. The examples explained in the present specification and the drawings satisfy several purposes, each of which provides technical utility for the present invention.List of Reference Numerals6 Housing 7 Inner peripheral surface of internal gear member 8 Cylindrical member 9 Recess 10 Internal gear 28 External gear 100 Gear train

Claims

A pinion gear (100) comprising: an internal gear member having an internal gear (10) formed on an inner circumferential surface; an external gear (28) configured to eccentrically rotate relative to the internal gear (10) while engaging the internal gear (10); wherein: a plurality of recesses (9) extend along an axis (12) of the pinion gear (100) and are provided at equal intervals in a circumferential direction of the internal gear member in an inner circumferential surface of the internal gear member; the internal gear (10) is formed by inserting cylindrical members (8) into the recesses (9); and the length of the cylindrical members (8) in a circumferential direction making contact with the recesses (9), An inclined part (9a) forming a ring in the circumferential direction is provided in the inner circumferential surface of the internal gear member at a position facing the end parts of the cylindrical members (8) on the at least one side in the axial direction at the end parts of the cylindrical members (9) on at least one side in an axial direction of the pinion gear (100) is shorter than at middle parts of the cylindrical members (8) in the axial direction.The gear transmission (100) according to claim 1, wherein: when viewed from the axial direction, an end part on a large diameter side of the inclined part (9a) is disposed outside the recesses (9).The gear transmission (100) according to claim 1 or 2, wherein: the depth of the recesses (9) is deeper at a position facing the end parts of the cylindrical members (8) in the axial direction than at a position facing the middle parts of the cylindrical members (8) in the axial direction.

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