Gear device

Abstract

To provide a gear device that can surely reduce noise and also can be prevented from increasing in size and weight.SOLUTION: A speed reduction device comprises an input shaft and a transmission spur gear which have a plurality of external gears meshing with each other, respectively. A tooth flank 20 of an external tooth 17 has an addendum flank 20a on the side of an addendum 17a, a dedendum flank 20b on the side of a dedendum 17b, and a connection face 20c formed in a region including a pitch point PP between the addendum flank 20a and dedendum flank 20b to connect the addendum flank 20a and the dedendum flank 20b together. The addendum flank 20a is formed of a projection surface projecting outward in a circumferential direction, and the dedendum flank 20b is formed of a recessed surface recessed inward in the circumferential direction.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a gear device.

Background Art

[0002] For example, in industrial robots, machine tools, etc., a gear device that decelerates and outputs the rotation of a drive source such as an electric motor is used. Among this type of gear device, there is, for example, an eccentric swing type reduction device. The eccentric swing type reduction device includes a casing in which an internal gear is integrated, a carrier provided inside the casing in the radial direction and rotatably provided with respect to the casing, a plurality of crank shafts rotatably supported by the carrier, and a swing gear that is swing-rotated by an eccentric portion of the crank shaft and meshes with the internal gear. A crank gear (eccentric body shaft gear) is attached to one end in the axial direction of the crank shaft.

[0003] Under such a configuration, an input gear connected to a drive source is meshed with the crank gear. When the crank gear is rotated via the input gear, the crank shaft rotates. As a result, the swing gear swings and rotates while meshing with the internal gear. The rotation of the swing gear is transmitted to the carrier via the crank shaft. Thereby, the carrier is rotated with respect to the casing. At this time, the rotation of the carrier is decelerated compared to the input gear.

[0004] By the way, in recent years, reduction of noise in gear devices has been desired, and various technologies have been proposed. For example, a technology of configuring a crank gear and an input gear using a plurality of helical gears has been disclosed (see, for example, Patent Document 1). By configuring in this way, the meshing rate between the crank gear and the input gear is improved, and an attempt is made to reduce the noise of the gear device.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, there has been a problem that it is difficult to sufficiently reduce the noise simply by improving the meshing ratio as in the above-described conventional technology. In addition, since the number of parts increases by using a plurality of helical gears, there has been a problem that the apparatus becomes large-sized and heavy-weight.

[0007] The present invention provides a gear device that can surely reduce noise and prevent the device from becoming large-sized and heavy-weight.

Means for Solving the Problems

[0008] A gear device according to an aspect of the present invention includes two gears each having a plurality of tooth portions that mesh with each other, and tooth surfaces of each of the tooth portions are formed in a region between a tooth tip surface on the tooth tip side, a tooth root surface on the tooth root side, the tooth tip surface and the tooth root surface, and including a pitch point, and have a connection surface connecting the tooth tip surface and the tooth root surface. The tooth tip surface is formed by a convex surface that protrudes outward in the circumferential direction, and the tooth root surface is formed by a concave surface that is concave inward in the circumferential direction.

[0009] By configuring in this way, the tooth portions of each of the two gears can be brought into concave-convex contact with each other. For this reason, the contact area between the tooth portions can be increased, and the surface pressure when the tooth portions mesh with each other can be reduced. As a result, the sound pressure when the gears mesh with each other can be reduced, and thus the gear device can be reduced in noise. When configuring one gear, it is not necessary to use a plurality of gears having different tooth shapes, so that the gear device can be prevented from becoming large-sized and heavy-weight.

[0010] In the above configuration, the tooth tip surface and the tooth root surface may be formed by the same curve, and the connection surface may be formed by a curve different from the tooth tip surface and the tooth root surface.

[0011] In the above configuration, the tip surface and the root surface of the tooth may include a cycloid curve.

[0012] In the above configuration, a modified cycloid curve obtained by deforming the cycloid curve is formed in a region on the tip side of the tip surface of the tooth, and the modified cycloid curve may curve so as to gradually separate inward in the normal direction of the cycloid curve from the cycloid curve as it goes toward the tooth tip.

[0013] In the above configuration, the connecting surface may include an involute curve.

[0014] In the above configuration, the tooth surface of each tooth portion has a tooth bottom surface formed at the root of the root surface, and the tooth bottom surface may include a trochoid curve.

[0015] In the above configuration, a case having an internal gear, a carrier rotatably supported by the case, a shaft body rotatably supported by the carrier, and at least one crankshaft provided on the shaft body and having an eccentric portion eccentric with respect to the rotation axis of the shaft body, a swing external gear rotatably supported by the eccentric portion and meshed with the internal gear, a spur gear provided axially outside the carrier among the crankshafts, and an input gear for transmitting a rotational force to the spur gear, and the spur gear and the input gear may include the two gears.

Advantages of the Invention

[0016] The above-described gear device can surely reduce noise and prevent enlargement and increase in weight.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0018] Next, embodiments of the present invention will be described with reference to the drawings.

[0019] <Reduction Gear> FIG. 1 is a perspective view of a reduction gear 1 which is a gear device. FIG. 2 is a cross-sectional view of the reduction gear 1. As shown in FIGS. 1 and 2, the reduction gear 1 decelerates and outputs the rotation of an input shaft (an example of a gear in the claims) 101 that rotates by receiving the rotational force of, for example, an electric motor (not shown). The reduction gear 1 is a so-called eccentric swing type reduction gear. The reduction gear 1 includes a cylindrical case 2, a carrier 3 rotatably provided inside the case 2 in the radial direction, and a reduction mechanism 4 connected to the carrier 3. The central axis of the case 2 and the rotation axis of the carrier 3 coincide. In the following description, these common names for the central axis and the rotation axis are referred to as the first rotation axis A1. The direction parallel to the first rotation axis A1 is referred to as the axial direction. The rotation direction of the carrier 3 is referred to as the circumferential direction. The radial direction of the case 2 orthogonal to the axial direction and the circumferential direction is simply referred to as the radial direction.

[0020] <Case> On the outer peripheral surface of the case 2, an outer flange portion 2a that projects radially outward is integrally formed. A plurality of bolt holes 2b into which bolts (not shown) are inserted 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 the bolt holes 2b, and the reduction gear 1 is fixed, for example, by tightening the bolts to an arm of an industrial robot or the like.

[0021] On the inner peripheral surface of the case 2, a plurality of pin grooves 2c extending in the axial direction are formed. The pin grooves 2c are arranged at equal intervals in the circumferential direction. Inner tooth pins 5 are respectively fitted into the pin grooves 2c. The inner tooth pins 5 function as inner teeth that mesh with the oscillating external gear teeth 15 and 16 of the reduction mechanism 4 described later. Main bearings 6 are provided on both axial sides of the inner peripheral surface of the case 2. The carrier 3 is rotatably supported by the case 2 via the main bearings 6. The main bearings 6 are, for example, angular ball bearings.

[0022] <Carrier> The carrier 3 includes a disk-shaped substrate portion 7 and end plate portions 8 that are arranged opposite to each other in the axial direction, and three column portions 9 that project from the substrate portion 7 toward the end plate portions 8. Each column portion 9 is arranged at equal intervals in the circumferential direction. The end plate portion 8 is arranged on the tip 9a of the column portion 9. The end plate portion 8 is fixed to the column portion 9 by bolts 10. In this state, a space having a constant width in the axial direction is formed between the substrate portion 7 and the end plate portion 8. Pins 11 are provided radially inside the bolts 10 of the column portion 9. The pins 11 position the end plate portion 8 with respect to the substrate portion 7. The pins 11 are fitted into pin holes 12 provided in the end plate portion 8.

[0023] The outer peripheral surfaces of the substrate portion 7 and the end plate portion 8 are rotatably supported by the case 2 via the corresponding main bearings 6, respectively. Shaft insertion holes 7a and 8a are formed at the radial centers of the substrate portion 7 and the end plate portion 8, respectively. The two shaft insertion holes 7a and 8a are arranged coaxially. Three crank insertion holes 7b and 8b are formed between the column portions 9 adjacent to each other in the circumferential direction in the substrate portion 7 and the end plate portion 8, respectively. Each of the crank insertion holes 7b and 8b is arranged coaxially. That is, the central axis A2 of the crank insertion holes 7b and 8b facing each other in the axial direction is parallel to the first rotation axis A1. Crank bearings 18 are provided in each of the crank insertion holes 7b and 8b. The crank bearing 18 is, for example, a tapered roller bearing.

[0024] <Reduction mechanism> The reduction mechanism 4 rotates the carrier 3 at a rotational speed reduced at a constant ratio with respect to the rotational speed of the input shaft 101. The reduction mechanism 4 includes three crank shafts 13 inserted into the respective crank insertion holes 7b and 8b and rotatably supported by the carrier 3 (the substrate portion 7 and the end plate portion 8) via the respective crank bearings 18, transmission spur gears (an example of the gear in the claims) 14 provided at the axial end portions of each of the crank shafts 13, and two oscillating external gear gears 15 and 16 (the first oscillating external gear gear 15, the second oscillating external gear gear 16) provided between the substrate portion 7 and the end plate portion 8 and oscillating and rotating as the crank shaft 13 rotates.

[0025] External teeth (an example of the tooth portion in the claims) 17 are formed on the outer peripheral portion of the transmission spur gear 14. The external teeth 17 are meshed with the external teeth (an example of the tooth portion in the claims) 102 formed on the input shaft 101. By meshing these external teeth 17 and 102, the rotation of the input shaft 101 is transmitted to the transmission spur gear 14, and the transmission spur gear 14 is rotated. The detailed shapes of each of the external teeth 17 and 102 will be described later.

[0026] The crankshaft 13 has a shaft body 13c that rotates about the central axis A2, and a first eccentric portion 13a and a second eccentric portion 13b formed at the axial center of the shaft body 13c. Both axial sides of the shaft body 13c are rotatably supported by the carrier 3 (the substrate portion 7 and the end plate portion 8) via the crank bearings 18. The shaft body 13c and the transmission spur gear 14 are coaxially arranged and integrated. That is, the crankshaft 13 and the transmission spur gear 14 rotate integrally about the central axis A2. Hereinafter, the central axis A2 is referred to as the second rotation axis A2 of the crankshaft 13.

[0027] The first eccentric portion 13a and the second eccentric portion 13b are eccentric from the second rotation axis A2. The first eccentric portion 13a and the second eccentric portion 13b are arranged adjacent to each other axially between the two crank bearings 18. In other words, the first eccentric portion 13a and the second eccentric portion 13b are arranged adjacent to each other axially between the substrate portion 7 and the end plate portion 8. The first eccentric portion 13a and the second eccentric portion 13b are arranged with a phase angle shift of 180°. The inner peripheral surface of the roller bearing 19 is fitted to each of the eccentric portions 13a, 13b. The roller bearing 19 is, for example, a cylindrical roller bearing. The first oscillating external gear 15 and the second oscillating external gear 16 are rotatably supported on each crankshaft 13 via the roller bearing 19.

[0028] The first oscillating external gear 15 and the second oscillating external gear 16 are arranged in the space between the substrate portion 7 and the end plate portion 8. Through holes 15a, 16a into which the outer peripheral surface of the roller bearing 19 is fitted are formed in the first oscillating external gear 15 and the second oscillating external gear 16, respectively. Thereby, when the first eccentric portion 13a and the second eccentric portion 13b swing and rotate due to the rotation of the crankshaft 13, the first oscillating external gear 15 and the second oscillating external gear 16 are swung and rotated via the roller bearing 19.

[0029] The first oscillating external gear 15 and the second oscillating external gear 16 are each formed with openings 15b and 16b for avoiding interference with the column portion 9. Shaft insertion holes 15c and 16c are formed at the radial centers of the first oscillating external gear 15 and the second oscillating external gear 16. External teeth 15d and 16d are formed on the outer peripheral portions of the first oscillating external gear 15 and the second oscillating external gear 16, respectively. The number of teeth of each of the external teeth 15d and 16d is, for example, one less than the number of internal teeth pins 5 of the case 2.

[0030] Under such a configuration, as the first oscillating external gear 15 and the second oscillating external gear 16 oscillate and rotate, a part of the external teeth 15d and 16d of each of the oscillating external gears 15 and 16 meshes with the internal teeth pins 5 of the case 2. The number of teeth of each of the external teeth 15d and 16d is, for example, one less than the number of internal teeth pins 5. For this reason, the meshing positions of the external teeth 15d and 16d with respect to the internal teeth pins 5 (case 2) are sequentially shifted in the circumferential direction so that the oscillating external gears 15 and 16 rotate on their own axes. This rotation on their own axes is decelerated with respect to the rotation of the crankshaft 13.

[0031] As each of the oscillating external gears 15 and 16 rotates, each crankshaft 13 revolves around the first rotation axis A1 while rotating on its own axis about the second rotation axis A2. Each crankshaft 13 is rotatably supported by the carrier 3 (substrate portion 7, end plate portion 8). For this reason, the carrier 3 is rotated as each crankshaft 13 revolves. As a result, the speed reduction device 1 reduces the rotation of the input shaft 101 and outputs it from the carrier 3. If the carrier 3 is fixed to an arm or the like of an industrial robot, the speed reduction device 1 can reduce the rotation of the input shaft 101 and output it from the case 2.

[0032] <Shape of External Teeth of Transmission Spur Gear and Shape of External Teeth of Input Shaft> Next, based on FIGS. 3 and 4, details of the shape of the external teeth 17 of the transmission spur gear 14 and the shape of the external teeth 102 of the input shaft 101 will be described. The shapes of these external teeth 17 and 102 are the same. Therefore, in the following description, only the shape of the external teeth 17 of the transmission spur gear 14 will be described. For the shape of the external teeth 102 of the input shaft 101, the same reference numerals as those of the external teeth 17 of the transmission spur gear 14 will be used and the description will be omitted. However, the external teeth 102 of the input shaft 101 will be described as necessary (the same applies to the following modification examples). Further, in the following description, in order to clearly distinguish the external teeth 17 of the transmission spur gear 14 from the external teeth 102 of the input shaft 101, the external teeth 17 of the transmission spur gear 14 will be referred to as transmission external teeth 17. The external teeth 102 of the input shaft 101 will be referred to as input external teeth 102.

[0033] FIG. 3 is an enlarged view of the state in which the transmission external teeth 17 and the input external teeth 102 are meshed, as viewed from the axial direction. FIG. 4 is an enlarged view of one of the transmission external teeth 17, as viewed from the axial direction. In FIGS. 3 and 4, in order to make the description easier to understand, some line types are shown after being changed. As shown in FIGS. 3 and 4, the tooth surface 20 of the transmission external teeth 17 includes a tooth tip surface 20a on the tooth tip 17a side, a tooth root surface 20b on the tooth root 17b side, a connecting surface 20c formed between the tooth tip surface 20a and the tooth root surface 20b and connecting the tooth tip surface 20a and the tooth root surface 20b, and a tooth bottom surface 20d formed at the base of the tooth root surface 20b and straddling between the adjacent external teeth 17 in the circumferential direction.

[0034] The tooth tip 17a shall refer to the radially outer side (tip side) of the pitch circle PC of the transmission external teeth 17. The tooth root 17b shall refer to the radially inner side (base side) of the pitch circle PC of the transmission external teeth 17. The tooth surface 20 shall refer to the side surface forming the outer contour of the transmission external teeth 17 as viewed from the axial direction. The connecting surface 20c is formed in a region including the pitch point PP. The pitch point PP is the point where the pitch circle PC intersects the side surface of the transmission external teeth 17 and is the point where the transmission external teeth 17 and the input external teeth 102 contact each other.

[0035] The tip surface 20a and the root surface 20b are formed by cycloid curves. Therefore, the tip surface 20a is formed by a convex surface that bulges outward in the circumferential direction. The root surface 20b is formed by a concave surface that is concave inward in the circumferential direction. The connecting surface 20c is formed by an involute curve. Therefore, the connecting surface 20c is formed by a convex surface that bulges outward in the circumferential direction. The bottom surface 20d of the tooth is formed by a trochoid curve. Therefore, the bottom surface 20d of the tooth is formed by a concave surface that is concave inward in the radial direction.

[0036] Under such a configuration, when each external tooth 17, 102 meshes, the convex surface and the concave surface come into contact with each other at the respective tip surfaces 20a and root surfaces 20b. Also, when each external tooth 17, 102 meshes, the convex surfaces come into contact with each other at the respective connecting surfaces 20c. Hereinafter, the concept of the shapes of the tip surface 20a, the root surface 20b, and the connecting surface 20c will be described in detail.

[0037] First, when the convex surface and the concave surface come into contact with each other at the tip surface 20a and the root surface 20b, the surface pressure can be reduced. Compared with the contact between convex surfaces, the contact between a convex surface and a concave surface reduces the Hertz surface pressure by -1 / 2 power multiplication of the equivalent curvature radius. That is, when the maximum Hertz surface pressure is Po, the equivalent Young's modulus is E, the load is F, the length of the contact portion between the external teeth 17, 102 is L, and the equivalent curvature radius is R, the maximum Hertz surface pressure Po satisfies the following mathematical formula (1).

[0038]

Equation

[0039] As can be seen from the mathematical formula (1), when the equivalent curvature radius R is large, the maximum Hertz surface pressure Po becomes small.

[0040] FIG. 5 is an explanatory diagram of the equivalent curvature radius R. (a) shows the case where the tooth surfaces are in contact with each other as convex surfaces, and (b) shows the case where the tooth surfaces are in contact with each other as a convex surface and a concave surface. As shown in FIGS. 5(a) and 5(b), for example, let the radius of curvature of two tooth surfaces be R1 and R2 respectively. Here, the equivalent radius of curvature R satisfies the following formula (2).

[0041]

Equation

[0042] As shown in FIG. 5(a), when the tooth surfaces are in contact with convex surfaces, the respective radii of curvature R1 and R2 are each indicated by plus (+), while as shown in FIG. 5(b), when the tooth surfaces are in contact with a convex surface and a concave surface, the radius of curvature R2 of the concave surface is indicated by minus (-). Therefore, it can be seen that the equivalent radius of curvature increases in the contact between the convex surface and the concave surface. Thus, by forming the tooth tip surface 20a and the tooth root surface 20b with cycloid curves, the surface pressure when the respective external teeth 17, 102 mesh can be reduced.

[0043] Next, the connecting surface 20c will be described. Regarding the connecting surface 20c, the slip ratio will be considered. Let the slip ratios of the respective external teeth 17, 102 in the involute curve forming the connecting surface 20c be σ 1 , σ 2 , and let the pitch circle radii of the respective external teeth 17, 102 be r 1 , r 2 . Let the contact length on the line of action from the meshing point between the external teeth 17, 102 to the pitch circle PC be l, and when the rotation angles of the respective external teeth 17, 102 are α 0 , the respective slip ratios σ 1 , σ 2 satisfy the following formula (3).

[0044]

Equation

[0045] As can be seen from formula (3), in the involute curve, the slip ratio becomes "0" at the pitch point PP. Therefore, by forming the connecting surface 20c with an involute curve, the slip ratio can be reduced as much as possible.

[0046] Incidentally, the formation region of the connection surface 20c is limited to a region where the tip surface 20a and the root surface 20b can be connected by the connection surface 20c. This region is derived, for example, by adjusting with the pressure angle of the tooth surface 20 and the rolling circle radius of cycloid curve generation. For example, the region of the connection surface 20c is in the range of 1 to 20% of the whole tooth depth. The whole tooth depth is the difference H1 between the tip circle radius Rt and the root circle radius Rs as shown in FIG. 4.

[0047] Thus, the tooth surfaces 20 of the above-described external teeth 17, 102 each have a tip surface 20a, a root surface 20b, and a connection surface 20c that connects the tip surface 20a and the root surface 20b. The tip surface 20a is formed by a convex surface that protrudes outward in the circumferential direction. The root surface 20b is formed by a concave surface that is concave inward in the circumferential direction. Therefore, the contact between the tip surface 20a of one of the external teeth 17, 102 and the root surface 20b of the other, and the contact between the root surface 20b of one of the external teeth 17, 102 and the tip surface 20a of the other can be made into the contact between the convex surface and the concave surface, respectively. As a result, the contact area between the tooth surfaces 20 can be increased, and the surface pressure when the external teeth 17, 102 mesh can be reduced. Therefore, the sound pressure when the external teeth 17, 102 mesh can be reduced, and thus the reduction gear 1 can be made quieter. When forming the transmission spur gear 14 and the input shaft 101 respectively, it is not necessary to form them using a plurality of external teeth with different shapes as in the prior art, so an increase in size and weight of the reduction gear 1 can be prevented.

[0048] The tip surface 20a and the root surface 20b are formed by the same curve. On the other hand, the connection surface 20c is formed by a curve different from the tip surface 20a and the root surface 20b. Therefore, the contact between the tip surface 20a of one of the external teeth 17, 102 and the root surface 20b of the other, and the contact between the root surface 20b of one of the external teeth 17, 102 and the tip surface 20a of the other can be surely made into the contact between the convex surface and the concave surface. By using the connection surface 20c, the tip surface 20a and the root surface 20b of each external tooth 17, 102 can be smoothly connected. That is, the shape of the tooth surface 20 of each external tooth 17, 102 can be surely realized.

[0049] The tooth tip surface 20a and the tooth root surface 20b are formed by cycloid curves. Therefore, the contact between one tooth tip surface 20a and the other tooth root surface 20b among the external teeth 17, 102, and the contact between one tooth root surface 20b and the other tooth tip surface 20a among the external teeth 17, 102 can be made more surely a convex surface - concave surface contact. Also, the slip rate between the external teeth 17, 102 can be reduced. For this reason, the reduction gear 1 can be further reduced in noise.

[0050] The connecting surface 20c is formed by an involute curve. The connecting surface 20c is formed in a region including the pitch point PP of each external tooth 17, 102. For this reason, the slip rate can be evenly reduced over the entire tooth surface 20 of each external tooth 17, 102. Therefore, the reduction gear 1 can be further reduced in noise. The tooth bottom surface 20d is formed by a trochoid curve. For this reason, the external teeth 17 adjacent to each other in the circumferential direction can be smoothly connected. As a result, it is possible to prevent the formation of a portion where stress is locally applied between the external teeth 17 adjacent to each other in the circumferential direction, and thus the rigidity of each external tooth 17, 102 can be ensured. Therefore, the reduction gear 1 can be further reduced in noise.

[0051] Especially in the eccentric swing type reduction gear 1, by adopting the shapes of the external teeth 17, 102 as described above, it is possible to effectively reduce the noise and effectively prevent the increase in size and weight. For example, the impact generated when the input shaft 101 meshes with the transmission spur gear 14 can be transmitted to reduce the booming noise generated from the case 2.

[0052] In the above - described embodiment, the tooth surface 20 of each external tooth 17, 102 has been described for the case where it has a tooth tip surface 20a, a tooth root surface 20b, a connecting surface 20c formed between the tooth tip surface 20a and the tooth root surface 20b to connect the tooth tip surface 20a and the tooth root surface 20b, and a tooth bottom surface 20d. However, it is not limited to this, and the tooth surface 20 may be formed as shown in the following modification examples.

[0053] [First Modification Example] FIG. 6 is an enlarged view of one of the transmission external teeth 17 in the first modification example as viewed axially. As shown in FIG. 6, a modified cycloid curve 21 obtained by deforming a cycloid curve may be formed in a region of the tooth tip 22 which is the radially outer end of the tooth end surface 20a. The modified cycloid curve 21 will be described in detail below.

[0054] FIG. 7 is an explanatory view of the modified cycloid curve 21. FIG. 7 corresponds to an enlarged view of part VII in FIG. 6. As shown in FIGS. 6 and 7, the modified cycloid curve 21 is a curve that gradually curves inward in the normal direction of the theoretical value from the cycloid curve of the tooth end surface 20a, that is, the theoretical value Ct (cycloid curve in the claims), as it approaches the tooth tip 22. Here, the inner side also refers to the circumferential center side of the transmission external tooth 17.

[0055] More specifically, at the intersection point Pi where the modified cycloid curve 21 intersects the tooth end surface 20a, the modified cycloid curve 21 becomes the tangent of the cycloid curve of the tooth end surface 20a. The modified cycloid curve 21 is formed with a radius of curvature Rc that becomes the tangent of the cycloid curve of the tooth end surface 20a at the intersection point Pi and is smoothly connected to the tooth tip 22.

[0056] The modified cycloid curve 21 can be represented by the following mathematical formula (4). That is, let the radius of the rolling circle (hereinafter simply referred to as the rolling circle) that forms the cycloid curve be a, the rotation angle of the rolling circle be θ, the pressure angle on the involute curve (connection surface 20c) be α0, the reference circle diameter be r, the function of the correction amount determined by the rolling rotation angle be R(θ), and the function of the direction (angle) of the correction determined by the rolling rotation angle be Φ’(θ). Then, the modified cycloid curve 21 satisfies the following mathematical formula (4).

[0057]

Equation

[0058] Therefore, according to the first modification described above, the same effects as those of the aforementioned embodiment can be achieved. In addition to this, the meshing at the tooth tips 22 of each of the external teeth 17, 102 can be made smoother. When the meshing of each of the external teeth 17, 102 is disengaged (separated), it is possible to prevent the corners of each of the external teeth 17, 102 from coming into contact with each other. For this reason, the surface pressure when each of the external teeth 17, 102 meshes can be further reduced, and the reduction gear 1 can be made quieter.

[0059] [Second Modification Example] FIG. 8 is an enlarged view of the state in which the transmission external teeth 17 and the input external teeth 102 in the second modification example are meshed, as viewed from the axial direction. FIG. 8 corresponds to FIG. 3 described above. As shown in FIG. 8, the tooth surfaces 20 of each of the external teeth 17, 102 may be formed as relaxation curves. The relaxation curve referred to here means a curve in which the radius of curvature is gradually changed so that the surface pressure of each of the external teeth 17, 102 does not increase rapidly from the start of meshing to the disengagement of the tooth surfaces 20 of each of the external teeth 17, 102. For example, examples of the relaxation curve include a cycloid curve (Corm curve), a cubic parabola, a McConnell curve, and the like. Therefore, according to the second modification described above, the same effects as those of the aforementioned embodiment can be achieved.

[0060] The present invention is not limited to the above-described embodiment, and includes those obtained by making various modifications to the above-described embodiment without departing from the spirit of the present invention.

[0061] For example, in the above-described embodiment, the case where the tooth tip surface 20a and the tooth root surface 20b are formed as cycloid curves has been described. However, the present invention is not limited to this, and the tooth tip surface 20a may be formed by a convex surface that protrudes outward in the circumferential direction. The tooth root surface 20b may be formed by a concave surface that is concave inward in the circumferential direction. The tooth tip surface 20a and the tooth root surface 20b do not have to be the same curve. Even in such a configuration, the contact between one tooth tip surface 20a and the other tooth root surface 20b among the external teeth 17, 102, and the contact between one tooth root surface 20b and the other tooth tip surface 20a among the external teeth 17, 102 can each be made a contact between a convex surface and a concave surface.

[0062] In the above-described embodiment, the case where the connection surface 20c is formed as an involute curve has been described. However, the present invention is not limited to this, and any curve that smoothly connects the tooth tip surface 20a and the tooth root surface 20b may be used.

[0063] In the above-described embodiment, as an example of the gear device, the reduction gear 1 has been described. The case where the reduction gear 1 is a so-called eccentric swing type reduction gear has been described. However, the present invention is not limited to this, and the above-described configuration of the external teeth 17, 102 can be adopted for a general gear device having two gears (for example, the transmission spur gear 14 and the input shaft 101) each having a plurality of tooth portions (for example, the transmission external teeth 17 and the input external teeth 102) that mesh with each other.

[0064] In the above-described embodiment, the case where the reduction gear 1 includes three crank shafts 13 has been described. The case where the oscillating external tooth gears 15, 16 are oscillated and rotated by the three crank shafts 13 has been described. However, the present invention is not limited to this, and the reduction gear 1 only needs to include at least one crank shaft 13. For example, the reduction gear 1 may be a so-called center crank type reduction gear having one crank shaft 13. In this case, one crank shaft 13 is arranged coaxially on the first rotation axis A1, and the oscillating external tooth gears 15, 16 are oscillated and rotated by one crank shaft 13.

[0065] In the above-described embodiment, in the speed reducer 1, the case where the column portion 9 of the carrier 3 protrudes from the substrate portion 7 has been described. However, the present invention is not limited to this, and the column portion 9 may not be integrally formed with the substrate portion 7. In this case, the column portion 9 is fixed to the substrate portion 7 using, for example, bolts or the like, similar to the end plate portion 8. The shape of the column portion 9 can be arbitrary, and it is sufficient that a space having a constant width in the axial direction is formed between the substrate portion 7 and the end plate portion 8 by the column portion 9.

[0066] Among the embodiments disclosed in this specification, those composed of a plurality of objects may be integrated, and conversely, those composed of a single object may be divided into a plurality of objects. Whether or not they are integrated, they may be configured so as to achieve the object of the invention.

Explanation of Reference Numerals

[0067] 1... Speed reducer (gear device) 2... Case 3... Carrier 13... Crankshaft (shaft) 13a... First eccentric portion (eccentric portion) 13b... Second eccentric portion (eccentric portion) 13c... Shaft body 14... Transmission spur gear (gear, spur gear) 15... First oscillating external gear (oscillating external gear) 16... Second oscillating external gear (oscillating external gear) 17... External teeth, transmission external teeth (tooth portion) 17a... Tooth tip 17b... Tooth root 20... Tooth surface 20a... Tooth tip surface 20b... Tooth root surface 20c... Connection surface 20d... Tooth bottom surface 21... Modified cycloid curve 22... Tooth tip 101... Input shaft (gear, input gear) 102... External teeth, input external teeth (tooth portion) PP... Pitch point

Claims

1. Two gears each having a plurality of teeth that mesh with each other, The tooth surface of each of the teeth is A tooth apex surface on the tooth apex side; A tooth flank on the tooth base side; a connecting surface formed in a region between the addendum surface and the flank surface and including a pitch point, the connecting surface connecting the addendum surface and the flank surface; having The tooth addendum surface is formed by a convex surface that is convex toward the outside in the circumferential direction, The tooth flank is formed by a concave surface that is concave toward the inside in the circumferential direction. Gear mechanism.

2. The tooth addendum surface and the tooth flank surface are formed by the same curve, The connecting surface is formed by a curve different from the addendum surface and the flank surface.

2. The gear arrangement of claim 1.

3. The tooth addendum surface and the tooth flank surface include a cycloid curve.

3. The gear arrangement of claim 2.

4. a modified cycloid curve obtained by modifying the cycloid curve is formed in a region of the tooth tip side of the addendum surface, the modified cycloid curve is curved so as to gradually move away from the cycloid curve toward an inner side in a normal direction of the cycloid curve toward the tooth tip.

4. The gear arrangement of claim 3.

5. The connecting surface includes an involute curve.

4. The gear arrangement of claim 3.

6. Each tooth surface of the tooth portion has a root surface formed at a root of the flank surface, The tooth bottom surface includes a trochoid curve.

4. The gear arrangement of claim 3.

7. A case having an internal gear; a carrier rotatably supported by the case; at least one crankshaft having a shaft body rotatably supported by the carrier and an eccentric portion provided on the shaft body and eccentric with respect to a rotation axis of the shaft body; an oscillating external gear rotatably supported by the eccentric portion and meshing with the internal gear; a spur gear provided on the crankshaft axially outward of the carrier; an input gear that transmits a rotational force to the spur gear; Equipped with The spur gear and the input gear include the two gears, A gear arrangement according to any one of claims 1 to 6.

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