Gear system

Abstract

To provide a gear device that can be miniaturized and have high torque. [Solution] The reduction gear 1 of the embodiment comprises a case having an internal tooth pin, and an oscillating gear having external teeth 15d that mesh with the internal tooth pin, and the number of teeth of the external teeth 15d being less than the number of teeth of the internal tooth pin. The position where the uneven shape of the tooth surface 20 on the external tooth 15d reverses is defined as the inflection point Ip, and the point where the surface pressure is maximum on the tooth tip 22t side of the inflection point Ip due to the meshing with the internal tooth pin when the tooth surface 20 is defined as the theoretical tooth profile La is defined as the surface pressure maximum point SPmax, and when the curve along the theoretical tooth profile La is considered to be at the same height, the highest position of the tooth surface 20 on the tooth root 22b side of the inflection point Ip is higher than the height of the tooth surface 20 at the surface pressure maximum point SPmax.

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. The swing gear has external teeth that mesh with the internal teeth of the internal gear.

[0003] Under such a configuration, when the crank shaft rotates by receiving the rotation of the drive source, 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 rotation of the drive source.

[0004] By the way, in recent years, miniaturization and high torque of gear devices have been desired, and various technologies have been proposed. For example, a technology has been disclosed in which, among the external teeth, a contact surface (contact portion) that contacts the internal teeth so as to be substantially pressurized contacts the internal teeth at a pressure angle not exceeding the maximum pressure angle between the maximum pressure angle position on the tooth root (tooth base) side and the maximum pressure angle position on the tooth tip side (see, for example, Patent Document 1). This further sets the maximum pressure angle within a predetermined range. By configuring in this way, it is possible to prevent a decrease in the drive efficiency of the gear device due to an increase in the load and frictional loss applied to the tooth surface of the external teeth, and it is possible to suppress backlash.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Patent No. 3481335 [Overview of the project] [Problems that the invention aims to solve]

[0006] In recent years, there has been a growing demand for further miniaturization and increased torque of gear systems. However, the conventional technologies described above have limitations in terms of miniaturization and torque enhancement of gear systems.

[0007] This invention provides a gear device that can be made even smaller and have higher torque. [Means for solving the problem]

[0008] A gear device according to one aspect of the present invention comprises an internal gear having internal teeth, and an external gear having external teeth that mesh with the internal teeth, wherein the number of teeth of the external teeth is less than the number of teeth of the internal gear, wherein the position where the uneven shape of the tooth surface of the external tooth reverses is defined as the inflection point, and the point where the surface pressure is maximum on the tooth tip side of the inflection point due to the meshing with the internal tooth when the tooth surface of the external tooth is defined as the theoretical tooth profile is defined as the point of maximum surface pressure, and when the curve along the theoretical tooth profile is considered to be at the same height, the highest position of the tooth surface on the tooth root side of the inflection point is higher than the height of the tooth surface at the point of maximum surface pressure.

[0009] This configuration prevents the surface pressure on the entire tooth surface of the external teeth from concentrating in one place. Therefore, the surface pressure can be leveled as much as possible across the entire tooth surface. This reduction in maximum surface pressure on the tooth surface allows for a smaller and higher-torque gear system.

[0010] In the above configuration, the height of the tooth surface at the point of maximum surface pressure is lower than the height of the theoretical tooth profile.

[0011] In the above configuration, the highest point of the tooth surface on the root side of the inflection point is higher than the height of the theoretical tooth profile.

[0012] In the above configuration, the highest point of the tooth surface on the root side of the inflection point is higher than the height of the tooth surface on the tip side of the inflection point.

[0013] In the above configuration, a low surface area is provided on both the tooth root side and the tooth tip side, centered on the point of maximum surface pressure, and the low surface area is within 30% of the total tooth height.

[0014] In the above configuration, the theoretical tooth profile includes an epitrochoidal tooth profile.

[0015] In the above configuration, the tooth surface of the external tooth has a contact surface that contacts the internal tooth so as to be substantially pressurized, a root surface formed on the root side of the contact surface and having a lower height than the theoretical tooth profile, and a tip surface formed on the tip side of the contact surface and having a lower height than the theoretical tooth profile, wherein the highest position of the tooth surface on the root side of the inflection point is higher than the height of the tooth surface at the point of maximum surface pressure, the contact surface contacts the internal tooth at a pressure angle less than or equal to the maximum pressure angle between the maximum pressure angle position on the root side and the maximum pressure angle position on the tip side, and the maximum pressure angle is set in the range of 50° to 80°. [Effects of the Invention]

[0016] The gear mechanism described above can be made even smaller and have higher torque. [Brief explanation of the drawing]

[0017] [Figure 1] This is a cross-sectional view of a speed reducer according to an embodiment of the present invention. [Figure 2] This is a cross-sectional view along the line II-II in Figure 1. [Figure 3] This is a partially enlarged view showing the tooth profile of the external teeth in an embodiment of the present invention. [Figure 4] This figure shows the curve of the theoretical tooth profile La in an embodiment of the present invention. [Figure 5] This is a further enlarged view of a portion of Figure 3. [Figure 6] This is a diagram schematically showing the shape of the contact surface in an embodiment of the present invention. [Figure 7] This is a diagram schematically showing the shapes of the contact surfaces in the first to fourth modified examples of an embodiment of the present invention. [Figure 8] This is a graph showing the change in contact stress accompanying the change in the contact position between the tooth surface and the internal gear pin in an embodiment of the present invention.

Embodiments for Carrying out the Invention

[0018] Next, embodiments of the present invention will be described based on the drawings.

[0019] <Reduction Gear> FIG. 1 is a cross-sectional view of a reduction gear 1 which is a gear device. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 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 connected to, 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> An outer flange portion 2a projecting outward in the radial direction is integrally formed on the outer peripheral surface of the case 2. A plurality of bolt holes 2b are formed in the outer flange portion 2a. The bolt holes 2b are arranged at equal intervals in the circumferential direction. Bolts (not shown) are inserted into these bolt holes 2b, and the reduction gear 1 is fixed by tightening the bolts to, for example, an arm of an industrial robot.

[0021] Multiple pin grooves 2c are formed on the inner circumferential surface of case 2, running axially. The pin grooves 2c are arranged at equal intervals in the circumferential direction. An internal tooth pin 5 is fitted into each pin groove 2c. The internal tooth pin 5 functions as an internal tooth that meshes with the oscillating gears 15 and 16 of the reduction mechanism 4, which will be described later. Main bearings 6 are provided on both the axial sides of the inner circumferential surface of case 2. The carrier 3 is rotatably supported by case 2 via the main bearings 6. The main bearings 6 are, for example, angular contact ball bearings.

[0022] <Career> The carrier 3 comprises a disc-shaped base portion 7 and an end plate portion 8 arranged opposite each other in the axial direction, and three column portions 9 that protrude from the base portion 7 toward the end plate portion 8. Each column portion 9 is arranged at equal intervals in the circumferential direction. An end plate portion 8 is placed on the tip 9a of each 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 base portion 7 and the end plate portion 8. A pin 11 is provided radially inward from the bolt 10 of the column portion 9. 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.

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

[0024] <Deceleration mechanism> The reduction mechanism 4 rotates the carrier 3 at a rotational speed reduced by a constant ratio to the rotational speed of the input shaft 101. The reduction mechanism 4 comprises three crankshafts 13 inserted into each crank insertion hole 7b, 8b, a transmission spur gear 14 provided at the axial end of each crankshaft 13, and two oscillating gears 15, 16 provided between the base plate portion 7 and the end plate portion 8, which oscillate and rotate in conjunction with the rotation of the crankshafts 13.

[0025] External teeth 17 are formed on the outer circumference of the transmission spur gear 14. The external teeth 17 mesh with external teeth 102 formed on the input shaft 101. When these external teeth 17 and 102 mesh, the rotation of the input shaft 101 is transmitted to the transmission spur gear 14, causing the transmission spur gear 14 to rotate.

[0026] The crankshaft 13 is rotatably supported on the carrier 3 (base plate portion 7 and end plate portion 8) via each crank bearing 18. The crankshaft 13 has a shaft body 13c that rotates about a central axis A2, and a first eccentric portion 13a and a second eccentric portion 13b formed in the axial center of the shaft body 13c. Both axial sides of the shaft body 13c are rotatably supported on the carrier 3 (base plate portion 7 and end plate portion 8) via the crank bearings 18.

[0027] The shaft body 13c and the transmission spur gear 14 are arranged coaxially and integrated. That is, the crankshaft 13 and the transmission spur gear 14 rotate together as a single unit around the central axis A2. Hereinafter, the central axis A2 will be referred to as the second rotation axis A2 of the crankshaft 13.

[0028] 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 positioned adjacent to each other in the axial direction between the two crank bearings 18. In other words, the first eccentric portion 13a and the second eccentric portion 13b are positioned adjacent to each other in the axial direction between the base portion 7 and the end plate portion 8. The first eccentric portion 13a and the second eccentric portion 13b are positioned with a phase angle difference of 180°.

[0029] The inner circumferential surfaces of roller bearings 19 are fitted into each of the eccentric portions 13a and 13b. The roller bearings 19 are, for example, cylindrical roller bearings. The first oscillating gear 15 and the second oscillating gear 16 are rotatably supported on each crankshaft 13 via the roller bearings 19.

[0030] The first oscillating gear 15 and the second oscillating gear 16 are positioned in the space between the base plate portion 7 and the end plate portion 8. The first oscillating gear 15 and the second oscillating gear 16 each have through holes 15a and 16a into which the outer circumferential surfaces of the roller bearings 19 are fitted. As a result, when the first eccentric portion 13a and the second eccentric portion 13b oscillate due to the rotation of the crankshaft 13, the first oscillating gear 15 and the second oscillating gear 16 oscillate via the roller bearings 19.

[0031] The first oscillating gear 15 and the second oscillating gear 16 each have openings 15b and 16b, respectively, to avoid interference with the column portion 9. Shaft insertion holes 15c and 16c are formed at the radial center of the first oscillating gear 15 and the second oscillating gear 16. External teeth 15d and 16d are formed on the outer circumference of the first oscillating gear 15 and the outer circumference of the second oscillating gear 16, respectively. The number of teeth on each external tooth 15d and 16d is a predetermined number less than the number of internal tooth pins 5 of the case 2.

[0032] Under this configuration, as the first and second oscillating gears 15 and 16 oscillate, some of the external teeth 15d and 16d of each gear engage with the internal tooth pins 5 of case 2. The number of teeth on each external tooth 15d and 16d is a predetermined number (for example, one) less than the number of internal tooth pins 5. Therefore, each oscillating gear 15 and 16 rotates such that the engagement points of each external tooth 15d and 16d with respect to the internal tooth pins 5 (case 2) are sequentially shifted in the circumferential direction. This rotation is decelerated relative to the rotation of the crankshaft 13.

[0033] As each oscillating gear 15 and 16 rotates, each crankshaft 13 also rotates on its own axis around the second rotation axis A2 while revolving around the first rotation axis A1. Each crankshaft 13 is rotatably supported on the carrier 3 (base plate portion 7, end plate portion 8). Therefore, the carrier 3 rotates in conjunction with the revolution of each crankshaft 13. As a result, the reduction gear 1 reduces the rotation of the input shaft 101 and outputs it from the carrier 3. If the carrier 3 is fixed to the arm of an industrial robot or the like, the reduction gear 1 can reduce the rotation of the input shaft 101 and output it from the case 2.

[0034] <Shape of the external teeth of an oscillating gear> Next, based on Figures 3 to 6, the details of the shapes of the external teeth 15d and 16d of each oscillating gear 15 and 16 will be described. The shapes of the external teeth 15d and 16d are identical. Therefore, in the following explanation, only the external tooth 15d of the first oscillating gear 15 will be described, and the explanation of the external tooth 16d of the second oscillating gear 16 will be omitted.

[0035] Figure 3 is a magnified view of a portion of the tooth profile of external tooth 15d. Figure 4 is a diagram showing the curve of the theoretical tooth profile La. Figure 5 is a further magnified view of a portion of Figure 3. As shown in Figures 3 to 5, the tooth surface 20 of the external tooth 15d is formed with each part displaced by a predetermined dimension relative to the theoretical tooth profile La. This will be explained in detail below.

[0036] First, let's explain the theoretical tooth profile La. The theoretical tooth profile La is formed as a tooth profile curve by the trajectory of a moving circle with a central trajectory of (X0,Y0) shown by the dotted line in Figure 4 and radius rc. More specifically, the theoretical tooth profile La is formed by the reduction ratio from the rotation of the crankshaft 13 to the rotation of the oscillating gears 15 and 16 being -Z I When we set it to +1, let rc be the radius of the internal tooth pin 5, and let Rb be the radius of the pitch circle that passes through the center of the internal tooth pin 5 with the first rotation axis A1 (see Figure 2 for all of these), the tooth profile coordinates (X, Y) of the theoretical tooth profile La satisfy the following equation (1).

[0037]

number

[0038] Therefore, if the difference in the number of teeth between the internal tooth pin 5 and the external tooth 15d is nd, then the number of teeth of the internal tooth pin 5 is nd × Zr, and the number of teeth of the external tooth 15d is nd × Zd. That is, according to the proviso of equation (1), nd = Zd - Zr = 1. The number of teeth of the internal tooth pin 5 is Zr, and the number of teeth of the external tooth 15d is Zd. By changing Φ (one tooth for -180° ≤ Φ ≤ 180°), which indicates the tooth profile phase, from 0° to 180°, the theoretical tooth profile La is formed between the tooth root 22b (corresponding to Φ = 0°) and the tooth tip 22t (corresponding to Φ = 180°) of the external tooth 15d. The difference in the number of teeth nd usually takes the value of 1 or 2.

[0039] Next, we will describe the tooth surface 20 of the external tooth 15d in detail. The tooth surface 20 of the external tooth 15d has a contact surface 20a that contacts the internal tooth pin 5 in such a way that it is substantially pressed against it, a root surface 20b formed on the root side 22b of the contact surface 20a, and a tip surface 20c formed on the tip side 22t of the contact surface 20a. These surfaces 20a to 20c are smoothly connected.

[0040] Here, assuming that the curve along the theoretical tooth profile La is at the same height, the height of the root surface 20b and the height of the tip surface 20c are lower than the height of the theoretical tooth profile La. In other words, the root surface 20b and the tip surface 20c are located inward from the theoretical tooth profile La. In the following explanation, height is defined as being higher or lower than the height of the theoretical tooth profile La. In other words, being higher than the theoretical tooth profile La means being further outward than the theoretical tooth profile La, and being lower than the theoretical tooth profile La means being further inward than the theoretical tooth profile La.

[0041] On the other hand, the contact surface 20a is partially displaced by a predetermined dimension while following the theoretical tooth profile La. Details of the displacement will be described later, but the theoretical tooth profile La is designed to contact the internal tooth pin 5 at a pressure angle less than or equal to the maximum pressure angle between the maximum pressure angle position Pmd on the tooth root 22b side and the maximum pressure angle position Pma on the tooth tip 22t side. This maximum pressure angle is set to a specific value within the range of 50° to 80°, for example, 60°. It is also possible to set different maximum pressure angles on the tooth root 22b side and the tooth tip 22t side, respectively.

[0042] The tooth root surface 20b and tooth tip surface 20c are formed such that their respective heights are lowest relative to the height of the theoretical tooth profile La at the midpoint between adjacent maximum pressure angle positions Pmd or Pma in the circumferential direction. The tooth root surface 20b and tooth tip surface 20c are located on the theoretical tooth profile La at the maximum pressure angle positions Pmd and Pma. The distance △max between the tooth root surface 20b and tooth tip surface 20c at the point where their respective heights are lowest relative to the height of the theoretical tooth profile La is set to be equal to or slightly greater than the sum of the eccentricity tolerances between case 2 and the oscillating gears 15 and 16 (the sum of the combination tolerance on the side where the meshing becomes tighter and the combination tolerance on the side where the meshing becomes looser).

[0043] Next, the displacement of the contact surface 20a will be described in detail based on Figure 6. Figure 6 schematically shows the shape of the contact surface 20a. In Figure 6, the theoretical tooth profile La is shown as a straight line for clarity. Also, each surface 20a to 20c is shown as a range. As shown in Figure 6, the contact surface 20a has an inflection point Ip where the concave-concave shape reverses from a concave shape on the tooth root side 22b to a convex shape on the tooth tip side 22t. That is, the tooth surface 20 on the tooth root side 22b of the inflection point Ip is concave, and the tooth surface 20 on the tooth tip side 22t of the inflection point Ip is convex. On the other hand, the internal tooth pin 5 can be said to have a convex shape all around.

[0044] Under this configuration, when the external tooth 15d and the internal tooth pin 5 mesh, the tooth surface 20 of the external tooth 15d will have uneven contact with the internal tooth pin 5 on the root side 22b of the inflection point Ip, and convex contact with the internal tooth pin 5 on the tip side 22t of the inflection point Ip. Therefore, on the contact surface 20a, the surface pressure is greater at the convex contact points with the internal tooth pin 5 than at the uneven contact points. In other words, when the contact surface 20a is the theoretical tooth profile La, the surface pressure is maximum on the tip side 22t of the inflection point Ip due to the meshing with the internal tooth pin 5. Therefore, when the contact surface 20a is considered to have a theoretical tooth profile La, the point at which the surface pressure (contact stress due to the internal tooth pin 5) is maximized is defined as the point of maximum surface pressure SPmax. The highest point of the contact surface 20a on the tooth root 22b side of the inflection point Ip is made higher than the height of the contact surface 20a at the point of maximum surface pressure SPmax.

[0045] More specifically, the area near the tooth root 22b on the contact surface 20a is located on the theoretical tooth profile La. The height of the contact surface 20a changes at the point where it straddles the tooth root 22b side to the tooth tip 22t side, centered around the inflection point Ip. This change is a gradual decrease in the height of the contact surface 20a from the tooth root 22b side to the tooth tip 22t side, compared to the theoretical tooth profile La. In other words, at the point where it straddles the tooth root 22b side to the tooth tip 22t side, centered around the inflection point Ip, the contact surface 20a is gradually located inward from the tooth root 22b side to the tooth tip 22t side, compared to the theoretical tooth profile La.

[0046] Such changes in the contact surface 20a are made possible by changing the radius rc (see Figure 4) of the moving circle that forms the theoretical tooth profile La. The range Ar over which the height changes is, for example, 30% of the total height of the external tooth 15d. The height of the contact surface 20a at the point of maximum surface pressure SPmax remains constant until the tooth tip surface 20c (maximum pressure angle position Pma). That is, on the contact surface 20a, the highest point on the tooth root 22b side, across the inflection point Ip, is higher than the height on the tooth tip 22t side, across the inflection point Ip. The difference D between the contact surface 20a on the tooth tip 22t side of the inflection point Ip and the theoretical tooth profile La is a maximum of 20 μm (the same applies to each of the following modified examples).

[0047] Thus, the external teeth 15d and 16d described above have the highest point of the contact surface 20a on the tooth root 22b side of the inflection point Ip higher than the height of the contact surface 20a at the point of maximum surface pressure SPmax. This prevents the surface pressure applied to the tooth surface 20 of the external teeth 15d and 16d from concentrating at one point. As a result, the surface pressure can be leveled as much as possible across the entire tooth surface 20. Since the maximum surface pressure applied to the tooth surface 20 can be reduced, the reduction gear 1 can be made smaller and have higher torque.

[0048] More specifically, the height of the contact surface 20a at the point of maximum surface pressure SPmax is lower than the height of the theoretical tooth profile La. In this way, by releasing the point where the surface pressure is maximum in the theoretical tooth profile La from the theoretical tooth profile La, the surface pressure on the contact surface 20a at the point of maximum surface pressure SPmax can be reduced compared to the surface pressure at the point of maximum surface pressure SPmax when the tooth profile is theoretical La. Therefore, the surface pressure can be leveled as much as possible across the entire tooth surface 20.

[0049] At the contact surface 20a, the highest point on the tooth root 22b side, straddling the inflection point Ip, is higher than the height on the tooth tip 22t side, straddling the inflection point Ip. Therefore, the reduction gear 1 can be reliably miniaturized and its torque increased without complicating the shape of the tooth surface 20.

[0050] The external teeth 15d and 16d are configured such that the contact surface 20a of the external teeth contact the internal tooth pin 5 at a pressure angle less than or equal to the maximum pressure angle between the maximum pressure angle position Pmd on the tooth root side 22b and the maximum pressure angle position Pma on the tooth tip side 22t. This maximum pressure angle is set to a specific value within the range of 50° to 80°.

[0051] Therefore, the tips 22t and roots 22b of the external teeth 15d and 16d are not pressed against the internal tooth pin 5, preventing increased surface pressure at the tips 22t and roots 22b, and preventing increased frictional resistance between the internal tooth pin 5 and the external teeth 15d and 16d. Thus, the load capacity of the external teeth 15d and 16d is not reduced at the tips 22t and roots 22b. The load capacity is balanced across the entire tooth profile of the external teeth 15d and 16d, improving the quality of occlusion between the internal tooth pin 5 and the external teeth 15d and 16d. Furthermore, by keeping the pressure angle below the maximum pressure angle set within a predetermined range, both ends of the contact surface 20a can be easily defined, and the tooth profile machining of the oscillating gears 15 and 16 can be facilitated.

[0052] In the above embodiment, the tooth profile coordinates (X, Y) of the theoretical tooth profile La were described as satisfying equation (1). However, the invention is not limited to this, and the theoretical tooth profile La may be an epitrochoidal tooth profile consisting of an epitrochoidal curve. By configuring it in this way, the surface pressure on the tooth surface 20 can be reduced as much as possible.

[0053] In the above embodiment, the height of the contact surface 20a was described as gradually decreasing from the tooth root 22b side to the tooth tip 22t side, centered around the inflection point Ip, and becoming lower than the theoretical tooth profile La. The height of the contact surface 20a at the point of maximum surface pressure SPmax was described as being constant up to the tooth tip surface 20c (maximum pressure angle position Pma). However, it is not limited to this, and the highest point of the contact surface 20a on the tooth root 22b side of the inflection point Ip should be higher than the height of the contact surface 20a at the point of maximum surface pressure SPmax. A detailed explanation follows below.

[0054] [Differentiation] Figure 7 schematically shows the shape of the contact surface 20a in the first to fourth modified examples. To facilitate comparison of each modified example, Figure 7 shows the first to fourth modified examples superimposed on each other. Figure 7 corresponds to the aforementioned Figure 6. As shown in Figure 7, in the first modified example, the height of the contact surface 20a changes on the tooth tip 22t side from the inflection point Ip. This change is a gradual decrease in the height of the contact surface 20a from the tooth root 22b side to the tooth tip 22t side, compared to the theoretical tooth profile La. The height of the contact surface 20a at the point of maximum surface pressure SPmax remains constant until the tooth tip surface 20c (maximum pressure angle position Pma). Even with this configuration, the same effects as those of the embodiment described above are achieved.

[0055] In the second modification, the height of the contact surface 20a is lower than the theoretical tooth profile La only around the point of maximum surface pressure SPmax. More specifically, the height of the contact surface 20a gradually decreases from the root 22b side to the tip 22t side, centered around the inflection point Ip, becoming lower than the theoretical tooth profile La. The height of the contact surface 20a on the tip 22t side of the point of maximum surface pressure SPmax gradually increases towards the tip 22t, eventually becoming the same height as the theoretical tooth profile La. The low surface region Ba, centered around the point of maximum surface pressure SPmax and lower than the theoretical tooth profile La, is within 30% of the total tooth height. This value will be explained in detail below.

[0056] Figure 8 is a graph showing the change in contact stress as the contact position between the tooth surface 20 and the internal tooth pin 5 changes, with the vertical axis representing the contact stress applied to the tooth surfaces 20 of the external teeth 15d and 16d by the internal tooth pin 5, and the horizontal axis representing the distance from the tooth root 22b to the tooth tip 22t of the tooth surface 20. As shown in Figure 8, it can be observed that the change in contact stress is gradual near SPmax, the point of maximum surface pressure where the contact stress is greatest. Therefore, it is effective to form a low surface region Ba including SPmax and its vicinity.

[0057] Here, for example, if the number of internal tooth pins 5 is 20 or more, the distance between two adjacent internal tooth pins 5 in the circumferential direction will be approximately 18°. Converting this value to a ratio of the total tooth height near the point of maximum surface pressure SPmax of the external teeth 15d and 16d, it becomes approximately 15%. From this, the low surface area Ba was set to 15% on the tooth root 22b side and 15% on the tooth tip 22t side, centered on the point of maximum surface pressure SPmax, and the entire low surface area Ba was set to within 30% of the total tooth height. With this configuration, it is only necessary to form an effective shape in specific locations on the external teeth 15d and 16d, and the surface pressure can be easily and reliably leveled as much as possible across the entire tooth surface 20.

[0058] Returning to Figure 7, in the third modified example, the height of the contact surface 20a at the point of maximum surface pressure SPmax is the same as the height of the theoretical tooth profile La. On the other hand, the highest point of the contact surface 20a on the root 22b side of the inflection point Ip is higher than the height of the theoretical tooth profile La. More specifically, the height of the contact surface 20a gradually decreases from the root 22b side to the tip 22t side at the point where it spans from the root 22b side to the tip 22t side around the inflection point Ip, and finally changes to become the same height as the theoretical tooth profile La.

[0059] Even with this configuration, it is possible to prevent the surface pressure applied to the tooth surface 20 of the external teeth 15d and 16d from concentrating in one place. As a result, the surface pressure can be leveled as much as possible across the entire tooth surface 20. Since the maximum surface pressure applied to the tooth surface 20 can be reduced, the reduction gear 1 can be made smaller and have higher torque.

[0060] In the fourth modified example, the overall height of the contact surface 20a gradually decreases as it approaches the tooth tip 22t. The highest point of the contact surface 20a on the tooth root 22b side of the inflection point Ip is the same as the height of the theoretical tooth profile La. Even with this configuration, the same effects as those of the embodiment described above are achieved.

[0061] The present invention is not limited to the embodiments described above, but includes various modifications to the embodiments described above, without departing from the spirit of the invention.

[0062] For example, in the above embodiment, a reduction gear 1 was described as a gear device. However, the above embodiment and its modified configuration can be adopted for various gear devices comprising an internal gear (case 2) having internal teeth (internal tooth pin 5) and an external gear (oscillating gear 15, 16) having external teeth (external teeth 17).

[0063] In the above embodiment, the case in which an internal tooth pin 5 is provided on the inner circumferential surface of case 2 was described. The case in which the internal tooth pin 5 functions as an internal tooth that meshes with the external teeth 15d and 16d of the oscillating gears 15 and 16 was described. However, it is not limited to this, and instead of the internal tooth pin 5, an arc tooth profile that meshes with the external teeth 15d and 16d may be formed on the inner circumferential surface of case 2. In this case, let the radius of the arc tooth profile be rc, and let the radius of the pitch circle passing through the center of the arc tooth profile with respect to the first rotation axis A1 be Rb.

[0064] Among the embodiments disclosed herein, those composed of multiple objects may be integrated, and conversely, those composed of a single object may be divided into multiple objects. Whether or not they are integrated, the invention can be constructed in a way that achieves its objective. [Explanation of Symbols]

[0065] 1…Gear reducer (gear system) 2…Case (internal gear) 5…Inner tooth pin (inner tooth) 15…First oscillating gear (external gear) 16…Second oscillating gear (external gear) 15d,16d…external teeth 20...tooth surface 20a…Contact surface 20b...Bottom surface 20c...tooth tip surface 22b…Tooth bottom 22t...tooth tip Ba…low surface area Ip…Inflection point La...Theoretical tooth shape Pma, Pmd... Maximum pressure angular position SPmax…Maximum surface pressure point

Claims

1. An internal gear having internal teeth, An external gear having external teeth that mesh with the internal teeth, Equipped with, The inflection point is defined as the position where the uneven shape of the tooth surface in the aforementioned external tooth is reversed. When the tooth surface of the external tooth is considered to be the theoretical tooth profile, the point where the surface pressure is greatest on the tip side of the inflection point due to the occlusion with the internal tooth is defined as the point of maximum surface pressure. When we consider the curve along the theoretical tooth profile to be at the same height, The highest point of the tooth surface on the root side of the inflection point is higher than the height of the tooth surface at the point of maximum surface pressure. Gear mechanism.

2. The height of the tooth surface at the point of maximum surface pressure is lower than the height of the theoretical tooth profile. The gear apparatus according to claim 1.

3. The highest point of the tooth surface on the root side of the inflection point is higher than the height of the theoretical tooth profile. The gear apparatus according to claim 1.

4. The highest point of the tooth surface on the root side of the tooth, straddling the inflection point, is higher than the height of the tooth surface on the tip side of the tooth, straddling the inflection point. The gear apparatus according to claim 1.

5. With the point of maximum surface pressure as the center, a low surface region is provided on the tooth root side and the tooth tip side. The aforementioned low surface area is within 30% of the total tooth height. A gear apparatus according to any one of claims 1 to 4.

6. The aforementioned theoretical tooth profile includes an epitrochoidal tooth profile. A gear apparatus according to any one of claims 1 to 4.

7. The tooth surface of the aforementioned external tooth is A contact surface that contacts the internal tooth so as to be substantially pressurized, A tooth root surface formed on the tooth root side of the contact surface and having a lower height than the theoretical tooth profile, A tooth tip surface formed on the tooth tip side of the contact surface and having a lower height than the theoretical tooth profile, It has, In the aforementioned contact surface, the highest point of the tooth surface on the root side of the inflection point is higher than the height of the tooth surface at the point of maximum surface pressure. The contact surface contacts the internal tooth at a pressure angle less than or equal to the maximum pressure angle between the maximum pressure angle position on the root side of the tooth and the maximum pressure angle position on the tip side of the tooth, and the maximum pressure angle is set in the range of 50° to 80°. A gear apparatus according to any one of claims 1 to 4.

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