Gear device

Abstract

The invention provides a gear device. A reduction gear according to one embodiment of the present invention is provided with an input shaft and a transmission spur gear each having a plurality of external teeth that mesh with each other. The tooth surface (20) of the external tooth (17) has: a tooth tip surface (20a) on the tooth tip (17a) side; a tooth root surface (20b) on the side of a tooth root (17b); and a connecting surface (20c) which is located between the tooth top surface (20a) and the tooth root surface (20b), is formed in a region including the node (PP), and connects the tooth top surface (20a) and the tooth root surface (20b). The tooth top surface (20a) is formed by a convex surface protruding toward the outer side in the circumferential direction, and the tooth root surface (20b) is formed by a concave surface recessed toward the inner side in the circumferential direction.

Description

Technical Field

[0001] The present invention relates to gear arrangements. Background Art

[0002] Gear devices that reduce the rotation speed of a driving source such as an electric motor and output the reduced speed are used in, for example, industrial robots and machine tools. Among such gear devices, there is, for example, an eccentric oscillating type reduction gear device. The eccentric oscillating type reduction gear device comprises: a housing that is integrated with an internal gear; a gear rack that is arranged radially inwardly of the housing; a plurality of crankshafts that are rotatably supported on the gear rack; and an oscillating gear that oscillates and rotates by utilizing the eccentric portion of the crankshaft and meshes with the internal gear. The gear rack is arranged to be rotatable relative to the housing. A crankshaft gear (eccentric body shaft gear) is mounted on one axial end of the crankshaft.

[0003] Based on such a structure, the input gear connected to the driving source meshes with the crankshaft gear. When the crankshaft gear is rotated by means of the input gear, the crankshaft 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 gear carrier via the crankshaft. As a result, the gear carrier rotates relative to the housing. At this time, the rotation of the gear carrier is reduced in speed relative to the rotation of the input gear.

[0004] However, in recent years, the gear device has been expected to reduce noise, and various technologies have been proposed. For example, there is a technology that uses a plurality of helical gears to form a crankshaft gear and an input gear (for example, see Patent Document 1). By such a structure, the meshing ratio between the crankshaft gear and the input gear is increased, and the gear device is reduced in noise.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2021-139385 Summary of the invention

[0008] Problem that the invention aims to solve

[0009] However, there is a problem that it is difficult to sufficiently reduce noise by simply increasing the meshing ratio as in the above-mentioned prior art. In addition, since the number of parts increases due to the use of a plurality of helical gears, there is a problem of increasing the size and weight of the device.

[0010] The present invention provides a gear device which can reliably reduce noise and prevent increase in size and weight.

[0011] Solutions for solving problems

[0012] A gear device in one form of the present invention comprises two gears each having a plurality of teeth meshing with each other, the tooth surface of each tooth portion comprising: a tooth top surface on the tooth top side; a tooth root surface on the tooth root side; and a connecting surface, which is located between the tooth top surface and the tooth root surface and is formed in an area including a node, connecting the tooth top surface and the tooth root surface, the tooth top surface being formed by a convex surface protruding toward the outer side in the circumferential direction, and the tooth root surface being formed by a concave surface recessed toward the inner side in the circumferential direction.

[0013] By configuring in this way, the teeth of the two gears can be in concave-convex contact with each other. Therefore, the contact area between the teeth can be increased, and the surface pressure when the teeth are meshing with each other can be reduced. As a result, the sound pressure when the gears are meshing with each other can be reduced, and the gear device can be made quieter. When configuring a gear, there is no need to use multiple gears with different tooth shapes, so the gear device can be prevented from being enlarged and heavy.

[0014] In the above configuration, the tooth top 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 curves of the tooth top surface and the tooth root surface.

[0015] In the above structure, the tooth top surface and the tooth root surface may include cycloid curves.

[0016] In the above structure, a modified cycloid curve formed by deforming the cycloid curve may be formed in the area on the tooth top side of the tooth top surface, and the modified cycloid curve is curved in a manner that gradually moves away from the cycloid curve toward the inside of the normal direction of the cycloid curve as it approaches the tooth top.

[0017] In the above structure, the connecting surface may also include an involute curve.

[0018] In the above structure, the tooth surface of each tooth portion may include a tooth bottom surface formed at the root of the tooth root surface, and the tooth bottom surface may include a trochoid curve.

[0019] In the above structure, it can also be that the gear device comprises: a housing having an internal gear; a gear rack supported on the housing in a rotatable manner; at least one crankshaft having: a shaft body supported on the gear rack in a rotatable manner; and an eccentric portion arranged on the shaft body and eccentric with respect to the rotation axis of the shaft body; a swinging external gear supported on the eccentric portion in a rotatable manner and meshing with the internal gear; a spur gear arranged at a position axially outside the crankshaft than the gear rack; and an input gear that transmits rotational force to the spur gear, and the spur gear and the input gear include the two gears.

[0020] Effects of the Invention

[0021] The above-mentioned gear device can reliably reduce noise and prevent increase in size and weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a perspective view of a reduction gear device in an embodiment of the present invention.

[0023] Figure 2 It is a cross-sectional view of a reduction gear transmission in an embodiment of the present invention.

[0024] Figure 3 This is an enlarged view of a state in which the transmission external teeth and the input external teeth are meshed in the embodiment of the present invention, as viewed from the axial direction.

[0025] Figure 4 This is an enlarged view of one of the transmission external teeth in the embodiment of the present invention as viewed from the axial direction.

[0026] Figure 5A It is an explanatory diagram of the equivalent curvature radius R in the embodiment of the present invention, and shows a case where tooth surfaces are in convex-contact with each other.

[0027] Figure 5B It is an explanatory diagram of the equivalent curvature radius R in the embodiment of the present invention, and shows a case where tooth surfaces are in contact with each other as convex surfaces and concave surfaces.

[0028] Figure 6 This is an enlarged view of one of the transmission external teeth in the first modified example of the embodiment of the present invention as viewed from the axial direction.

[0029] Figure 7 It is an explanatory diagram of a modified cycloid curve in a first modified example of the embodiment of the present invention.

[0030] Figure 8 This is an enlarged view of a state in which the transmission external teeth and the input external teeth are meshed with each other in a second modified example of the embodiment of the present invention, as viewed from the axial direction.

[0031] Description of Reference Numerals

[0032] 1. Speed ​​reduction device (gear device); 2. Housing; 3. Gear rack; 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 swing external gear (swing external gear); 16. Second swing external gear (swing external gear); 17. External teeth, transmission external teeth (tooth portion); 17a. Tooth top; 17b. Tooth root; 20. Tooth surface; 20a. Tooth top surface; 20b. Tooth root surface; 20c. Connecting 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, node. DETAILED DESCRIPTION

[0033] Next, embodiments of the present invention will be described based on the drawings.

[0034] <Reduction gear>

[0035] Figure 1 It is a perspective view of the reduction gear 1 as a gear device. Figure 2 It is a cross-sectional view of the reduction gear device 1 .

[0036] like Figure 1 , Figure 2 As shown, the reduction gear 1 reduces the rotation of the input shaft (an example of a gear in the claims) 101 that is rotated by the rotational force of an electric motor (not shown) and outputs the reduced speed. The reduction gear 1 is a so-called eccentric swing type reduction gear. The reduction gear 1 includes: a cylindrical housing 2; a gear frame 3 that is rotatably arranged on the radial inner side of the housing 2; and a reduction mechanism 4 that is connected to the gear frame 3. The central axis of the housing 2 coincides with the rotation axis of the gear frame 3.

[0037] In the following description, the first rotation axis A1 is a common name for these center axes and rotation axes. The direction parallel to the first rotation axis A1 is called the axial direction. The rotation direction of the gear frame 3 is called the circumferential direction. The radial direction of the housing 2 that is orthogonal to the axial direction and the circumferential direction is simply called the radial direction.

[0038] <Housing>

[0039] An outer flange portion 2a extending radially outward is integrally formed on the outer peripheral surface of the housing 2. A plurality of bolt holes 2b for inserting bolts (not shown) are formed on 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 bolts are fastened to, for example, the arm of an industrial robot, thereby fixing the reduction gear 1 to, for example, the arm of an industrial robot.

[0040] A plurality of pin grooves 2c are formed along the axial direction on the inner peripheral surface of the housing 2. The pin grooves 2c are arranged at equal intervals in the circumferential direction. An internal gear pin 5 is inserted into each pin groove 2c. The internal gear pin 5 functions as an internal tooth that meshes with the swing external gears 15 and 16 of the speed reduction mechanism 4 to be described later.

[0041] Main bearings 6 are provided on both sides in the axial direction of the inner peripheral surface of the housing 2. The carrier 3 is rotatably supported by the housing 2 via the main bearings 6. The main bearings 6 are, for example, angular contact ball bearings.

[0042] <Gear rack>

[0043] The gear carrier 3 includes a disc-shaped base plate portion 7 and an end plate portion 8 which are arranged to face each other in the axial direction, and three column portions 9 which are formed to protrude from the base plate portion 7 toward the end plate portion 8 .

[0044] The pillars 9 are arranged at equal intervals in the circumferential direction. The end plate 8 is arranged on the top end 9a of the pillar 9. The end plate 8 is fixed to the pillar 9 by bolts 10. In this state, a space having a certain width in the axial direction is formed between the base plate 7 and the end plate 8.

[0045] A pin 11 is provided at a portion of the column portion 9 that is radially inward of the bolt 10. The pin 11 positions the end plate portion 8 relative to the base plate portion 7. The pin 11 is fitted into a pin hole 12 provided in the end plate portion 8.

[0046] The outer peripheral surface of the base plate portion 7 and the outer peripheral surface of the end plate portion 8 are supported on the housing 2 in a rotatable manner by means of corresponding main bearings 6. Shaft insertion holes 7a and 8a are formed in the radial center of the base plate portion 7 and the radial center of the end plate portion 8, respectively. The two shaft insertion holes 7a and 8a are arranged on the same axis. In the base plate portion 7 and the end plate portion 8, three crankshaft insertion holes 7b and 8b are formed between the column portions 9 adjacent in the circumferential direction, respectively. The crankshaft insertion holes 7b and 8b are arranged on the same axis, respectively. That is, the center axis A2 of the crankshaft insertion holes 7b and 8b opposite to each other in the axial direction is parallel to the first rotation axis A1. Crankshaft bearings 18 are respectively provided in the crankshaft insertion holes 7b and 8b. The crankshaft bearings 18 are, for example, tapered roller bearings.

[0047] <Reduction Mechanism>

[0048] The reduction mechanism 4 rotates the gear frame 3 at a speed reduced by a certain ratio relative to the speed of the input shaft 101. The reduction mechanism 4 includes: three crankshafts 13, which are inserted into the crankshaft insertion holes 7b, 8b; a transmission spur gear (an example of a gear in the claims) 14, which is provided at the axial end of each crankshaft 13; and two swinging external gears 15, 16 (a first swinging external gear 15, a second swinging external gear 16), which are provided between the base plate portion 7 and the end plate portion 8. The three crankshafts 13 are supported on the gear frame 3 (the base plate portion 7 and the end plate portion 8) in a rotatable manner by means of respective crankshaft bearings 18. The two swinging external gears 15, 16 swing and rotate respectively as the crankshafts 13 rotate.

[0049] External teeth (an example of the tooth portion in the claims) 17 are formed on the outer periphery of the transmission spur gear 14. The external teeth 17 mesh with external teeth (an example of the tooth portion in the claims) 102 formed on the input shaft 101. Since these external teeth 17 and 102 mesh, the rotation of the input shaft 101 is transmitted to the transmission spur gear 14. As a result, the transmission spur gear 14 rotates. The detailed shape of each external tooth 17 and 102 will be described later.

[0050] The crankshaft 13 includes a shaft body 13c that rotates about the central axis A2, and a first eccentric portion 13a and a second eccentric portion 13b that are formed at the axial center of the shaft body 13c. Both axial sides of the shaft body 13c are rotatably supported by the gear frame 3 (the base plate portion 7 and the end plate portion 8) by means of crankshaft bearings 18.

[0051] The shaft body 13 c is coaxially arranged and integrated with the transmission spur gear 14 . That is, the crankshaft 13 and the transmission spur gear 14 rotate integrally around the central axis A2 . Hereinafter, the central axis A2 is referred to as the second rotation axis A2 of the crankshaft 13 .

[0052] The first eccentric portion 13a and the second eccentric portion 13b are eccentric with respect to the second rotation axis A2. The first eccentric portion 13a and the second eccentric portion 13b are arranged between the two crankshaft bearings 18 in an axially adjacent manner. In other words, the first eccentric portion 13a and the second eccentric portion 13b are arranged between the base plate portion 7 and the end plate portion 8 in an axially adjacent manner. The first eccentric portion 13a and the second eccentric portion 13b are arranged in a phase angle shifted by 180°.

[0053] The inner peripheral surface of the roller bearing 19 is fitted in each of the eccentric portions 13a and 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 by the crankshafts 13 via the roller bearings 19.

[0054] The first swing external gear 15 and the second swing external gear 16 are arranged in the space between the base plate portion 7 and the end plate portion 8. Through holes 15a and 16a are formed in the first swing external gear 15 and the second swing external gear 16, respectively. The outer peripheral surface of the roller bearing 19 is engaged with the through holes 15a and 16a. Therefore, 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 swing external gear 15 and the second swing external gear 16 swing and rotate with the help of the roller bearing 19.

[0055] Openings 15b and 16b are formed in the first swing external gear 15 and the second swing external gear 16, respectively, for avoiding interference with the column portion 9. Shaft insertion holes 15c and 16c are formed in the radial centers of the first swing external gear 15 and the second swing external gear 16. External teeth 15d and 16d are formed in the outer peripheral portions of the first swing external gear 15 and the second swing external gear 16, respectively. The number of teeth of each external tooth 15d and 16d is less than the number of internal tooth pins 5 of the housing 2, for example, by one.

[0056] Based on such a structure, as the first swing external gear 15 and the second swing external gear 16 swing and rotate, a part of the external teeth 15d and 16d of each swing external gear 15 and 16 meshes with the internal tooth pin 5 of the housing 2. The number of teeth of each external tooth 15d and 16d is less than the number of internal tooth pins 5, for example, by one. Therefore, the meshing parts of each external tooth 15d and 16d are sequentially deviated from the internal tooth pin 5 (housing 2) in the circumferential direction, and each swing external gear 15 and 16 rotates. This rotation is decelerated relative to the rotation of the crankshaft 13.

[0057] As each swinging external gear 15, 16 rotates, each crankshaft 13 also rotates around the second rotation axis A2 as the center and revolves around the first rotation axis A1. Each crankshaft 13 is supported on the gear frame 3 (base plate portion 7, end plate portion 8) in a rotatable manner. Therefore, the gear frame 3 rotates as each crankshaft 13 revolves. As a result, the reduction gear 1 reduces the rotation of the input shaft 101 and outputs it from the gear frame 3. Assuming that the gear frame 3 is fixed to the arm of an industrial robot, etc., the reduction gear 1 can reduce the rotation of the input shaft 101 and output it from the housing 2.

[0058] <Shape of external teeth of transmission spur gear and input shaft>

[0059] Next, based on Figure 3 , Figure 4 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 in detail.

[0060] The shapes of these external teeth 17, 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. The shape of the external teeth 102 of the input shaft 101 is marked with the same reference numerals as the reference numerals of the external teeth 17 of the transmission spur gear 14, and the description is omitted. However, the external teeth 102 of the input shaft 101 will be described as needed (the same applies to the following modified examples). In addition, in the following description, in order to easily distinguish the external teeth 17 of the transmission spur gear 14 and the external teeth 102 of the input shaft 101, the external teeth 17 of the transmission spur gear 14 are referred to as transmission external teeth 17. The external teeth 102 of the input shaft 101 are referred to as input external teeth 102.

[0061] Figure 3 This 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. Figure 4 This is an enlarged view of the transmission external tooth 17 viewed from the axial direction. Figure 3 , Figure 4 In order to make the description easier to understand, the line types of some parts are changed for representation.

[0062] like Figure 3 , Figure 4 As shown, the tooth surface 20 of the transmission external tooth 17 has a tooth top surface 20a on the tooth top 17a side, a tooth root surface 20b on the tooth root 17b side, a connecting surface 20c formed between the tooth top surface 20a and the tooth root surface 20b, and a tooth bottom surface 20d formed at the root of the tooth root surface 20b. The connecting surface 20c connects the tooth top surface 20a and the tooth root surface 20b. The tooth bottom surface 20d spans between the external teeth 17 adjacent in the circumferential direction.

[0063] The tooth top 17a refers to the portion of the transmission external tooth 17 that is radially outward (top end side) from the pitch circle PC. The tooth root 17b refers to the portion of the transmission external tooth 17 that is radially inward (root side) from the pitch circle PC. The tooth surface 20 refers to the side surface that forms the contour of the transmission external tooth 17 when viewed from the axial direction. The connecting surface 20c is formed in the area including the node PP. The node PP refers to the point where the pitch circle PC intersects the side surface of the transmission external tooth 17, and is the point where the transmission external tooth 17 contacts the input external tooth 102.

[0064] The tooth top surface 20a and the tooth root surface 20b are formed by cycloid curves. Thus, the tooth top surface 20a is formed by a convex surface that bulges toward the outer side in the circumferential direction. The tooth root surface 20b is formed by a concave surface that is recessed toward the inner side in the circumferential direction. The connecting surface 20c is formed by an involute curve. Thus, the connecting surface 20c is formed by a convex surface that bulges toward the outer side in the circumferential direction. The tooth bottom surface 20d is formed by a trochoid curve. Thus, the tooth bottom surface 20d is formed by a concave surface that is recessed toward the inner side in the radial direction.

[0065] Based on such a structure, when the external teeth 17 and 102 are meshed, the convex surface and the concave surface are in contact at the respective tooth top surface 20a and the tooth root surface 20b. In addition, when the external teeth 17 and 102 are meshed, the convex surface and the convex surface are in contact at the respective connecting surface 20c. The idea of ​​the shape of the tooth top surface 20a, the tooth root surface 20b and the connecting surface 20c is discussed in detail below.

[0066] First, if the tooth top surface 20a and the tooth root surface 20b are in contact with each other, the surface pressure can be reduced. Compared with the contact between convex surfaces, the contact between convex surfaces and concave surfaces reduces the Hertzian surface pressure by the power of -1 / 2 of the equivalent radius of curvature. That is, when the maximum Hertzian surface pressure is set to Po, the equivalent Young's modulus is set to E, the load is set to F, the length of the contact portion between the external teeth 17 and 102 is set to L, and the equivalent radius of curvature is set to R, the maximum Hertzian surface pressure Po satisfies the following formula (1).

[0067] [Formula 1]

[0068]

[0069] As can be seen from the equation (1), if the equivalent radius of curvature R is larger, the maximum Hertzian surface pressure Po becomes smaller.

[0070] Figure 5A It is an explanatory diagram of the equivalent curvature radius R, showing the state where the tooth surfaces are in convex-contact with each other. Figure 5B It is an explanatory diagram of the equivalent curvature radius R, showing the state where the tooth surfaces are in contact with each other as convex surfaces and concave surfaces.

[0071] like Figure 5A , Figure 5B As shown, for example, the curvature radii of the two tooth surfaces are set to R1 and R2, respectively. The equivalent curvature radius R satisfies the following equation (2).

[0072] [Formula 2]

[0073]

[0074] like Figure 5A As shown in FIG. 1 , when the tooth surfaces are in contact with each other between convex surfaces, the curvature radii R1 and R2 are respectively expressed as positive (+). In contrast, as shown in FIG. Figure 5B As shown in FIG. 1 , when the tooth surfaces are in contact between convex and concave surfaces, the curvature radius R2 of the concave surface is represented by a negative (-). Therefore, it can be seen that the equivalent curvature radius becomes larger in the contact between the convex surface and the concave surface. Therefore, by forming the tooth top surface 20a and the tooth root surface 20b with a cycloid curve, the surface pressure of each external tooth 17, 102 when meshing can be reduced.

[0075] Next, the connection surface 20c is described. In the connection surface 20c, the slip rate is examined. When the slip rates of the external teeth 17, 102 in the involute curve forming the connection surface 20c are set to σ1, σ2, the pitch circle radius of the external teeth 17, 102 is set to r1, r2, the meshing length of the external teeth 17, 102 on the line of action from the meshing point to the pitch circle PC is set to l, and the rotation angle of the external teeth 17, 102 is set to α0, the slip rates σ1, σ2 satisfy the following formula (3).

[0076] [Formula 3]

[0077]

[0078] As can be seen from the equation (3), the sliding rate of the involute curve becomes "0" at the node PP. Therefore, by forming the connection surface 20c by the involute curve, the sliding rate can be minimized.

[0079] However, the formation area of ​​the connection surface 20c is defined by the area where the tooth top surface 20a and the tooth root surface 20b can be connected by the connection surface 20c. This area can be derived, for example, by adjusting the rolling radius created by the pressure angle of the tooth surface 20 and the cycloid curve. For example, the area of ​​the connection surface 20c is in the range of 1 to 20% of the full tooth height. Figure 4 As shown, the full tooth height refers to the difference H1 between the tooth top circle radius Rt and the tooth bottom circle radius Rs.

[0080] In this way, the tooth surface 20 of each of the external teeth 17, 102 described above has a tooth top surface 20a, a tooth root surface 20b, and a connecting surface 20c connecting the tooth top surface 20a and the tooth root surface 20b. The tooth top surface 20a is formed by a convex surface that bulges toward the outer side in the circumferential direction. The tooth root surface 20b is formed by a concave surface that is recessed toward the inner side in the circumferential direction. Therefore, the contact between the tooth top surface 20a of one of the external teeth 17, 102 and the tooth root surface 20b of the other and the contact between the tooth root surface 20b of one of the external teeth 17, 102 and the tooth top surface 20a of the other can be set as 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 are meshed can be reduced. Therefore, the sound pressure when the external teeth 17, 102 are meshed can be reduced, and the speed reducer 1 can be made quieter. When the transmission spur gear 14 and the input shaft 101 are formed separately, there is no need to use a plurality of external teeth having different shapes as in the conventional method, and therefore, it is possible to prevent the reduction gear 1 from being increased in size and weight.

[0081] The tooth top surface 20a and the tooth root surface 20b are formed by the same curve. In contrast, the connection surface 20c is formed by a curve different from the curves of the tooth top surface 20a and the tooth root surface 20b. Therefore, the contact between the tooth top surface 20a of one of the external teeth 17, 102 and the tooth root surface 20b of the other, and the contact between the tooth root surface 20b of one of the external teeth 17, 102 and the tooth top surface 20a of the other can be reliably set as the contact between the convex surface and the concave surface, respectively. By using the connection surface 20c, the tooth top surface 20a and the tooth root surface 20b of each external tooth 17, 102 can be smoothly connected. In other words, the shape of the tooth surface 20 of each external tooth 17, 102 can be reliably realized.

[0082] The tooth top surface 20a and the tooth root surface 20b are formed by a cycloid curve. Therefore, the contact between the tooth top surface 20a of one of the external teeth 17, 102 and the tooth root surface 20b of the other, and the contact between the tooth root surface 20b of one of the external teeth 17, 102 and the tooth top surface 20a of the other can be further reliably set as the contact between the convex surface and the concave surface. In addition, the sliding rate between the external teeth 17, 102 can be reduced. Therefore, the speed reduction device 1 can be further reduced in noise.

[0083] The connection surface 20c is formed by an involute curve. The connection surface 20c is formed in a region including the pitch point PP of each external tooth 17, 102. Therefore, the slip rate can be reduced uniformly over the entire tooth surface 20 of each external tooth 17, 102. Therefore, the speed reduction device 1 can further reduce noise.

[0084] The tooth bottom surface 20d is formed by a trochoid curve. Therefore, 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 further ensure the rigidity of each external tooth 17, 102. Therefore, the speed reducer 1 can be made more low-noise.

[0085] In particular, in the eccentric oscillating type speed reducer 1, by adopting the above-mentioned shape of each external tooth 17, 102, it is possible to effectively reduce noise, and effectively prevent the size and weight from being increased. For example, it is possible to reduce the roaring sound generated from the housing 2 due to the impact transmission generated when the input shaft 101 and the transmission spur gear 14 are meshed.

[0086] In the above embodiment, the tooth surface 20 of each external tooth 17, 102 has a tooth bottom surface 20d and a connecting surface 20c connecting the tooth top surface 20a and the tooth root surface 20b. However, the present invention is not limited to this, and the tooth surface 20 may be formed as shown in the following modified example.

[0087] [First Modification]

[0088] Figure 6 This is an enlarged view of one of the transmission external teeth 17 in the first modification example as viewed from the axial direction.

[0089] like Figure 6 As shown, a modified cycloid curve 21 formed by deforming a cycloid curve may be formed in the region of the tooth tip 22 which is the radially outer end of the tooth tip surface 20a. The modified cycloid curve 21 will be described in detail below.

[0090] Figure 7 It is an explanatory diagram of the modified cycloid curve 21 . Figure 7 Equivalent to Figure 6 Enlarged view of Part VII.

[0091] like Figure 6 , Figure 7 As shown, the modified cycloid curve 21 is a curve that is curved in a manner that gradually moves away from the cycloid curve of the tooth top surface 20a, that is, the theoretical value Ct of the cycloid curve (the cycloid curve in the claims) toward the inner side of the normal direction of the theoretical value as it moves toward the tooth tip 22. The inner side here also refers to the circumferential center side of the transmission external tooth 17.

[0092] More specifically, at the intersection point Pi where the modified cycloid curve 21 intersects the tooth top surface 20a, the modified cycloid curve 21 becomes a tangent to the cycloid curve of the tooth top surface 20a. The modified cycloid curve 21 becomes a tangent to the cycloid curve of the tooth top surface 20a at the intersection point Pi, and is formed with a curvature radius Rc that smoothly connects to the tooth tip 22.

[0093] The modified cycloid curve 21 can be expressed by the following formula (4). That is, when the radius of the rolling circle (hereinafter referred to as the rolling circle) forming the cycloid curve is set to a, the rotation angle of the rolling circle is set to θ, the pressure angle at the involute curve (connection surface 20c) is set to α0, the reference circle diameter is set to r, the function of the correction amount determined by the roll rotation angle is set to R(θ), and the function of the direction (angle) of the correction determined by the roll rotation angle is set to Φ'(θ), the modified cycloid curve 21 satisfies the following formula (4).

[0094] [Formula 4]

[0095]

[0096] Therefore, according to the first modified example, the same effect as the above-mentioned embodiment can be achieved. In addition, the meshing at the tooth tip 22 of each external tooth 17, 102 can be smoother. It is possible to prevent the corners of each external tooth 17, 102 from contacting each other when the meshing (disengagement) of each external tooth 17, 102 is released. Therefore, the surface pressure when each external tooth 17, 102 is meshed can be further reduced, and the speed reduction device 1 can be made quieter.

[0097] [Second Modification]

[0098] Figure 8 This is an enlarged view of the meshing state of the transmission external teeth 17 and the input external teeth 102 in the second modification example as viewed from the axial direction. Figure 8 With the aforementioned Figure 3 Corresponding.

[0099] like Figure 8 As shown, the tooth surface 20 of each external tooth 17, 102 may also be formed by a transition curve. Here, the transition curve refers to a curve in which the radius of curvature gradually changes so that the surface pressure of each external tooth 17, 102 does not increase sharply during the period from the start of meshing to the release of meshing of the tooth surfaces 20 of each external tooth 17, 102. For example, as a transition curve, a corum curve, a cubic parabola, a MacConnel's curve, etc. can be listed.

[0100] Therefore, according to the above-mentioned second modification example, it is possible to achieve the same effects as those of the above-mentioned embodiment.

[0101] The present invention is not limited to the above-described embodiment, and includes embodiments in which various modifications are added to the above-described embodiment within a scope not departing from the gist of the present invention.

[0102] For example, in the above-mentioned embodiment, the case where the tooth top surface 20a and the tooth root surface 20b are formed by a cycloidal curve is described. However, it is not limited to this, and the tooth top surface 20a can be formed by a convex surface that protrudes toward the outer side in the circumferential direction. The tooth root surface 20b can be formed by a concave surface that is recessed toward the inner side in the circumferential direction. The tooth top surface 20a and the tooth root surface 20b may not be the same curve. Even in the case of such a configuration, the contact between the tooth top surface 20a of one of the external teeth 17, 102 and the tooth root surface 20b of the other and the contact between the tooth root surface 20b of one of the external teeth 17, 102 and the tooth top surface 20a of the other can be set as the contact between the convex surface and the concave surface, respectively.

[0103] In the above-mentioned embodiment, the case where the connection surface 20c is formed by an involute curve is described, but the invention is not limited thereto, and any curve that smoothly connects the tooth top surface 20a and the tooth bottom surface 20b may be used.

[0104] In the above-mentioned embodiment, the reduction gear 1 is described as an example of a gear device. The case where the reduction gear 1 is a so-called eccentric oscillating type reduction gear is described. However, it is not limited to this, and the structure of the external teeth 17 and 102 can be adopted in all gear devices having two gears (for example, the transmission spur gear 14 and the input shaft 101) each having a plurality of teeth that mesh with each other (for example, the transmission external teeth 17 and the input external teeth 102).

[0105] In the above-mentioned embodiment, the case where the reduction gear 1 has three crankshafts 13 is described. The case where the three crankshafts 13 are used to make the swing external gears 15 and 16 swing and rotate is described. However, this is not limited to this, and the reduction gear 1 only needs to have at least one crankshaft 13. For example, the reduction gear 1 can also be set as a so-called center crankshaft type reduction gear having one crankshaft 13. In this case, one crankshaft 13 is arranged coaxially with the first rotation axis A1, and one crankshaft 13 is used to make the swing external gears 15 and 16 swing and rotate.

[0106] In the above-mentioned embodiment, in the reduction device 1, the case where the column portion 9 of the gear frame 3 is formed so as to protrude from the base plate portion 7 is described. However, this is not limited to this, and the column portion 9 may not be formed integrally with the base plate portion 7. In this case, the column portion 9 is fixed to the base plate portion 7 using, for example, bolts, in the same manner as the end plate portion 8. The shape of the column portion 9 can be set to be arbitrary, and a space having a certain width in the axial direction can be formed between the base plate portion 7 and the end plate portion 8 using the column portion 9.

[0107] In the embodiments disclosed in this specification, a component composed of multiple objects may be integrated into one, or a component composed of one object may be divided into multiple objects. Regardless of whether the components are integrated or not, they may be configured in a manner that can achieve the purpose of the invention.

Claims

1. A gear device, wherein: The gear device includes two gears each having a plurality of teeth meshing with each other. The tooth surface of each tooth portion has: The tooth top surface on the tooth top side; The root surface of the tooth root side; as well as a connecting surface, which is located between the tooth top surface and the tooth root surface and is formed in a region including a node, connecting the tooth top surface and the tooth root surface, The tooth top surface is formed by a convex surface protruding toward the outer side in the circumferential direction, The tooth root surface is formed by a concave surface that is recessed toward the inner side in the circumferential direction.

2. The gear device according to claim 1, wherein: The tooth top surface and the tooth root surface are formed by the same curve, The connection surface is formed by a curve different from curves of the tooth top surface and the tooth root surface.

3. The gear device according to claim 2, wherein: The tooth top surface and the tooth root surface include cycloid curves.

4. The gear device according to claim 3, wherein: A modified cycloid curve formed by deforming the cycloid curve is formed in a region on the tooth tip side of the tooth tip surface. The modified cycloid curve is curved so as to gradually move away from the cycloid curve toward the inner side in the normal direction of the cycloid curve as it approaches the tooth tip.

5. The gear device according to claim 3, wherein: The connecting surface includes an involute curve.

6. The gear device according to claim 3, wherein: The tooth surface of each tooth portion has a tooth bottom surface formed at the root of the tooth root surface, The tooth bottom surface includes a trochoid curve.

7. The gear device according to any one of claims 1 to 6, wherein: The gear device comprises: a housing having an internal gear; a gear rack rotatably supported on the housing; at least one crankshaft, comprising: a shaft body rotatably supported by the gear carrier; and an eccentric portion provided on the shaft body and eccentric to the rotation axis of the shaft body; a swing external gear rotatably supported by the eccentric portion and meshing with the internal gear; a spur gear disposed on the crankshaft at an axially outer side than the gear carrier; as well as An input gear that transmits rotational force to the spur gear, The spur gear and the input gear comprise the two gears.

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