Method for manufacturing a speed reducer and gear unit

Abstract

Compared to speed reducers equipped with gear units having cycloidal tooth profiles, this invention provides a speed reducer equipped with a gear unit that does not become larger even when the reduction ratio is increased. [Solution] A speed reducer comprising a gear unit that reduces the rotation of an input shaft and transmits it to an output shaft, wherein the gear unit comprises an inner gear that rotates eccentrically with respect to the input shaft and an outer gear in which the inner gear is housed, the outer gear and the inner gear are sintered bodies, the tooth profiles of the outer gear and the inner gear are tooth profiles with a tooth height greater than that of a cycloidal tooth profile, and the outer gear is connected to the output shaft.

Description

Technical Field

[0001] The present disclosure relates to a speed reducer and a method for manufacturing a gear unit.

Background Art

[0002] Patent Document 1 and Patent Document 2 disclose a gear unit provided in a speed reducer. This gear unit includes an internal gear and an external gear that meshes with the internal gear. The internal gear is an annular gear having internal teeth extending toward the rotation axis of the internal gear, and is also called an outer gear. The external gear is a gear having external teeth extending in a direction away from the rotation axis of the external gear, and is also called an inner gear. The inner gear rotates while being eccentric with respect to the outer gear.

[0003] In Patent Document 1, the tooth profiles of the inner gear and the outer gear are formed by a trochoid curve. In Patent Document 2, a cycloid tooth profile formed by a cycloid curve composed of an epicycloid curve and a hypocycloid curve is used. The diameters of the circles for drawing the epicycloid curve and the hypocycloid curve are the same. In the following description, the cycloid curve composed of the epicycloid curve and the hypocycloid curve disclosed in Patent Document 2 is simply referred to as a cycloid curve. In the cycloid tooth profile formed by this cycloid curve, it is possible to increase the number of teeth compared to the tooth profile using the trochoid curve. In the gear unit of Patent Document 2, by making the eccentricity between the outer gear and the inner gear larger than the theoretical value, the load acting on the tooth surfaces where the outer gear and the inner gear mesh is reduced. The theoretical value is a numerical value obtained by calculation from the number of teeth of the inner gear, the number of teeth of the outer gear, and the diameter of the pitch circle of the inner gear. If the eccentricity is the theoretical value, the inner gear and the outer gear can be meshed without causing rotation failure.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] There is a need to miniaturize gear reducers. To increase the reduction ratio, it is necessary to increase the number of teeth on the inner and outer gears. When the number of teeth on the inner and outer gears increases, the outer diameter of the inner and outer gears also increases. In particular, the technology in Patent Document 2 has an eccentricity between the inner and outer gears that is greater than the theoretical value, and in addition to the increase in the diameter of the outer gear due to the increase in the number of teeth, the increase in the eccentricity also leads to an increase in the diameter of the outer gear, making it impossible to avoid making the gear reducer larger.

[0006] One of the objectives of this disclosure is to provide a gear reducer equipped with a gear unit that does not become larger even when the reduction ratio is increased, compared to a gear reducer equipped with a gear unit having a cycloidal tooth profile. [Means for solving the problem]

[0007] The reduction gear of the present disclosure is a reduction gear comprising a gear unit that reduces the rotation of an input shaft and transmits it to an output shaft, wherein the gear unit comprises an inner gear that rotates eccentrically with respect to the input shaft, and an outer gear in which the inner gear is housed. The outer gear and the inner gear are sintered bodies, and the tooth profiles of the outer gear and the inner gear are tooth profiles with a tooth height greater than that of a cycloidal tooth profile. The outer gear is connected to the output shaft. [Effects of the Invention]

[0008] The gearbox of this disclosure does not become larger even when the reduction ratio is increased, compared to a gearbox equipped with a gear unit having a cycloidal tooth profile. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic perspective view of the gearbox described in Embodiment 1. [Figure 2] Figure 2 is an exploded perspective view of the gearbox shown in Figure 1. [Figure 3] Figure 3 is a cross-sectional view taken along line III-III in Figure 1. [Figure 4] Figure 4 is a cross-sectional view of the gearbox shown in Figure 1, taken along the line IV-IV in Figure 3. [Figure 5] Figure 5 is a cross-sectional view of the gearbox shown in Figure 1, obtained by cutting it along the VV section in Figure 3. [Figure 6] Figure 6 is an enlarged view of the area enclosed by the dotted rectangle in Figure 4. [Figure 7] Figure 7 is a comparison diagram showing the size of the gear unit shown in Figure 5 and the gear unit having a tooth profile formed by a cycloid curve. [Figure 8] Figure 8 is an explanatory diagram illustrating the design procedure for the inner and outer gears shown in Figure 6. [Figure 9] Figure 9 is an explanatory diagram illustrating the procedure for changing the reduction ratio of a gearbox. [Modes for carrying out the invention]

[0010] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0011] <1> The reduction gear of the present disclosure is a reduction gear comprising a gear unit that reduces the rotation of an input shaft and transmits it to an output shaft, wherein the gear unit comprises an inner gear that rotates eccentrically with respect to the input shaft, and an outer gear in which the inner gear is housed. The outer gear and the inner gear are sintered bodies, and the tooth profiles of the outer gear and the inner gear are tooth profiles with a tooth height greater than that of a cycloidal tooth profile. The outer gear is connected to the output shaft.

[0012] Tooth profiles with tooth thickness and eccentricity larger than those of a cycloid tooth profile are, for example, a Geocloid (registered trademark) tooth profile, a Paracloid (registered trademark) EX tooth profile, or a Megafloid (registered trademark) tooth profile.

[0013] The inner gear includes a plurality of outer teeth extending in a direction away from the central axis of the inner gear, and inner tooth grooves formed between two adjacent outer teeth. The outer gear includes a plurality of inner teeth extending in a direction toward the central axis of the outer gear, and a plurality of outer tooth grooves formed between two adjacent inner teeth.

[0014] In a gear having a tooth profile with a tooth thickness larger than that of a cycloid tooth profile, the number of teeth can be increased without increasing the outermost diameter of the gear. Therefore, in the gear unit provided in the reducer of the present disclosure, the reduction ratio can be increased without increasing the outermost diameter of the outer gear.

[0015] In a sintered gear having a tooth profile with a tooth width larger than that of a cycloid tooth profile, it is necessary to correct distortions such as roundness generated in the sintering process by sizing. Here, if the sizing allowance in the direction along the tooth thickness (thickness) is large, the dimensional accuracy of the tooth thickness deteriorates due to variations in the springback amount, and the meshing between the inner gear and the outer gear deteriorates. As one method of solving this problem, it is conceivable to increase the sizing allowance in the direction along the tooth depth (depth) and decrease the sizing allowance in the direction along the tooth thickness. Considering these points, in the speed reducer of the present disclosure, as shown in the manufacturing method of the gear unit described later, the inner gear and the outer gear are designed such that the tip clearance is larger than the tooth flank clearance. The tooth flank clearance is the clearance between the outer teeth and the inner teeth adjacent in the direction along the pitch circle of the inner gear. The tip clearance is the clearance between the tip of the outer tooth and the outer tooth groove in the direction away from the central axis of the inner gear, and the clearance between the inner tooth groove and the tip of the inner tooth. As described above, in the sintered gear, since it is easy to improve the dimensional accuracy of the tooth thickness by sizing, even if the tooth flank clearance at the time of designing the inner gear and the outer gear is small, the tooth flanks of the inner gear and the outer gear can be meshed with high dimensional accuracy. On the other hand, by designing the inner gear and the outer gear such that the tip clearance is increased, even if the springback amount of the tooth width during sizing is large, it is difficult for the tip to contact the tooth bottom. In the inner gear and the outer gear manufactured based on such a design, operations such as polishing for fine adjustment of dimensions can be omitted. When operations such as polishing are omitted, the productivity of the speed reducer including the inner gear and the outer gear is improved.

[0016] <2>In the speed reducer according to <1> above, the tooth flanks and tips of the inner gear and the outer gear may not have polishing marks.

[0017] Polishing marks are machining marks formed on a workpiece through the polishing process. The absence of polishing marks on the tooth surface and tooth tip means that the inner gear and outer gear were obtained without undergoing polishing. Inner gears and outer gears that do not require polishing are highly productive. Therefore, a gearbox including inner gears and outer gears is also highly productive.

[0018] Here, sizing marks are formed on the inner and outer gears. Sizing marks are abrasion marks formed by friction between the sizing mold and the gear. Sizing marks are clearly distinguishable from polishing marks.

[0019] <3> the above <1> or <2> In the speed reducer described above, the sintered body is formed of an iron alloy mainly composed of iron, and the iron alloy may contain at least one alloying element selected from copper, nickel, tin, chromium, molybdenum, manganese, and carbon.

[0020] The inner and outer gears formed from the above iron alloy exhibit superior mechanical strength.

[0021] <4> the above <3> In the gearbox described herein, the density of the sintered body is 6.6 g / cm³. 3 It may be greater than or equal to (grams per cubic centimeter).

[0022] Density is 6.6 g / cm³ 3 The sintered iron alloy described above exhibits excellent mechanical strength.

[0023] <5> the above <1> from <4> A reduction gear as described in any of the above, further comprising a housing, wherein the inner gear includes a first inner gear and a second inner gear having a smaller diameter than the first inner gear, and the outer gear may include a first outer gear that meshes with the first inner gear and a second outer gear that meshes with the second inner gear. The first inner gear and the second inner gear are coaxially integrated. The first outer gear is fixed to the housing so as not to rotate with the rotation of the first inner gear. The second outer gear is housed in the housing so as to be rotatable with the rotation of the second inner gear.

[0024] In the reduction gear having the above configuration, the first stage of reduction is performed by the first inner gear and the first outer gear, and the second stage of reduction is performed by the second inner gear, which is integrated with the first inner gear, and the second outer gear. Therefore, the reduction ratio of the above reduction gear is very high. Furthermore, the above reduction gear is compact due to its structure in which the first inner gear and the second inner gear are integrated.

[0025] <6> The present disclosure is a method for manufacturing a gear unit comprising an inner gear and an outer gear in which the inner gear is housed, and which reduces the rotation of an input shaft in a reduction gear and transmits it to an output shaft, comprising: step A for manufacturing a plain inner gear and a pre-outer gear made of powder molded bodies; step B for sintering the plain inner gear and the pre-outer gear; and step C for sizing the sintered plain inner gear and the sintered pre-outer gear, respectively, to manufacture the inner gear and the outer gear. In step A, the plain inner gear and the pre-outer gear are manufactured to satisfy the following conditions I and II. Condition I: The tooth profiles of the pre-outer gear and the pre-outer gear are tooth profiles with a greater tooth height than cycloidal tooth profiles. Condition II: When the center of the tooth thickness of the pre-outer gear coincides with the center of the tooth groove width of the pre-outer gear, the tooth tip clearance is greater than the tooth surface clearance.

[0026] The method for manufacturing a gear unit according to the present disclosure makes it possible to manufacture a gear unit for a speed reducer according to the present disclosure.

[0027] <7> the above <6> In the method for manufacturing a gear unit as described above, the design of the tooth profiles of the planar gear and the pre-outer gear in step A may include: step A1 of designing a reference inner gear that satisfies condition I based on the reduction ratio of the inner gear and the outer gear, the outer diameter of the outer gear, and the inner diameter of the inner gear; step A2 of designing a reference outer gear that meshes with the reference inner gear based on the eccentricity of the inner gear with respect to the reference inner gear and the outer gear; and step A3 of modifying the shape of at least one of the reference inner gear and the reference outer gear to create a designed inner gear and a designed outer gear that satisfies condition II. In step A, the planar gear and the pre-outer gear are manufactured based on the designed inner gear and the designed outer gear.

[0028] Step A in the manufacturing method of the gear unit includes the design of the tooth profiles of the pre-outer gear and the pre-inner gear. The procedure for designing the tooth profiles is as follows: First, the number of teeth of the inner gear and outer gear is determined from the desired reduction ratio. The number of teeth of the outer gear is the number of teeth of the inner gear plus 1. Next, the external dimensions of the gear unit, i.e., the outer diameter of the outer gear, are determined, as is the inner diameter of the inner gear, i.e., the inner diameter of the inner through-hole in the inner gear where the input shaft is located. Based on this information, a reference inner gear with a tooth profile that is taller than the cycloidal tooth profile is designed. Furthermore, the eccentricity of the inner gear relative to the outer gear is determined. The eccentricity is a theoretical value that can be calculated, for example, from the number of teeth of the inner gear and outer gear and the outer diameter of the outer gear. The eccentricity may be changed from the theoretical value as needed. Once the shape and eccentricity of the reference inner gear are determined, a reference outer gear corresponding to that reference inner gear is designed. In a gear reducer, the tooth profile of the reference outer gear is usually uniquely determined once the eccentricity, the shape of the reference inner gear, and the outer diameter of the reference outer gear are determined. In a combination of a reference inner gear and a reference outer gear, the tooth surface clearance and the tooth tip clearance are approximately the same when the center of the tooth thickness of the reference inner gear and the center of the tooth groove width of the reference outer gear coincide. In the manufacturing method of the gear unit of this disclosure, a design inner gear and a design outer gear are created by modifying the shape of at least one of the reference inner gear and the reference outer gear so that the tooth tip clearance is greater than the tooth surface clearance. Based on this design inner gear and design outer gear, a pre-inner gear and a pre-outer gear are manufactured by powder compaction.

[0029] the above <7> As described above, by designing a large tooth tip clearance, even if springback occurs during sizing, it is possible to manufacture a gear unit that meshes accurately without the tooth tips and roots of the inner and outer gears coming into contact.

[0030] <8> the above <7> In the method for manufacturing a gear unit as described above, the tooth surface clearance in step A3 is 10 μm or more and 20 μm or less, and the tooth tip clearance may be 50 μm or more.

[0031] If the tooth surface clearance during design is 10 μm or more, a gear unit that meshes smoothly can be manufactured even if springback occurs during sizing. If the tooth surface clearance is 20 μm or less, backlash is reduced, and a gear unit with inner and outer gears that mesh with high precision can be manufactured.

[0032] If the tooth tip clearance is 50 μm or more, contact between the tooth tip and tooth root in the gear unit can be prevented. The tooth root refers to the bottom of the inner tooth groove or the bottom of the outer tooth groove.

[0033] [Details of the embodiments of this disclosure] Specific examples of the gearboxes of this disclosure will be described below with reference to the drawings. Identical reference numerals in the drawings indicate the same or corresponding parts. The dimensions of the components shown in each drawing are for illustrative purposes only and do not necessarily represent actual dimensions. The present invention is not limited to these examples and is intended to be included in the claims, with all modifications within the meaning and scope equivalent to the claims being included.

[0034] <Embodiment 1> ≪Overall Structure≫ The reduction gear 1 shown in Figure 1 includes a gear unit 2 that reduces the rotation of the input shaft 10 and transmits it to the output shaft. In this example, the output shaft is not shown. The shape and configuration of the output shaft will be briefly described in the description of the gear unit 2.

[0035] The gearbox 1 in this example can be applied, for example, to the joints or drive units of a robot, the drive units of a conveying device, and the drive units of opening and closing devices such as shutters. The higher the reduction ratio of the gearbox 1, the easier it is to improve the precision of the operation of the drive unit and the easier it is to increase the torque of the drive unit.

[0036] ≪Gear Unit≫ As shown in the exploded perspective view of Figure 2, the gear unit 2 in this example comprises an inner gear 3 and an outer gear 4, and reduces the rotation of the input shaft 10 in two stages. This gear unit 2 further comprises an eccentric cam 5, a housing 6, and an oil seal 7. One of the features of the reducer 1 in this example is the tooth profile of the inner gear 3 and outer gear 4 in the gear unit 2. The tooth profile will be explained in a later section.

[0037] The inner gear 3 in this example is a two-stage gear including a first inner gear 31 and a second inner gear 32. The first inner gear 31 and the second inner gear 32 are integrated coaxially. That is, the first inner gear 31 and the second inner gear 32 have a common inner rotation axis 3s (see Figure 3). The first inner gear 31 and the second inner gear 32 each have a plurality of external teeth 3T that extend radially from the inner rotation axis 3s, perpendicular to the inner rotation axis 3s, and an inner tooth groove 3G formed between two adjacent external teeth 3T, 3T.

[0038] The second inner gear 32 has a smaller diameter than the first inner gear 31. In this example, the first inner gear 31 has 25 external teeth (3T). The second inner gear 32 has 20 external teeth (3T). The first inner gear 31 is involved in the first stage of deceleration, and the second inner gear 32 is involved in the second stage of deceleration.

[0039] The tooth profile of the external tooth 3T of InnaGear 3 is a tooth profile with greater tooth height and eccentricity than a cycloid tooth profile. Examples of such tooth profiles with greater tooth height include the Geocloid® tooth profile, the Paracoid® EX tooth profile, or the Megafloyd® tooth profile. In this example, the tooth profile of the external tooth 3T is the Geocloid® tooth profile.

[0040] The inner gear 3 rotates eccentrically with respect to the input shaft 10 (Figure 1). The component that causes the inner gear 3 to rotate eccentrically with respect to the input shaft 10 is the eccentric cam 5. The eccentric cam 5 comprises a base portion 51, a cam portion 52, and a counterweight 53. As shown in Figure 3, the eccentric cam 5 has a cam through-hole 5h that penetrates the base portion 51 and the cam portion 52. The input shaft 10 is fitted into the cam through-hole 5h. A groove portion 5g is formed in the cam through-hole 5h, extending in the direction along the cam through-hole 5h, and the rib portion 10r of the input shaft 10 is fitted into this groove portion 5g. Due to the engagement between the rib portion 10r and the groove portion 5g, the eccentric cam 5 rotates at the same speed as the input shaft 10 without slipping. The counterweight 53 cancels out the reaction of the eccentric rotation of the inner gear 3.

[0041] The base portion 51, which is part of the eccentric cam 5, has a first central axis 51c that passes through the center of the outer diameter of the base portion 51. The first central axis 51c coincides with the shaft rotation axis 10s of the input shaft 10. A first bearing 11 is positioned on the outer circumference of the base portion 51. The first bearing 11 is a radial bearing. The first bearing 11 is fitted into the first housing hole 41h of the first outer gear 41, which will be described later. Therefore, the eccentric cam 5, including the base portion 51, is rotatably supported relative to the first outer gear 41.

[0042] The second central axis 52c, which passes through the center of the outer diameter of the cam portion 52, is positioned eccentrically from the shaft rotation axis 10s of the input shaft 10. A second bearing 12 is positioned on the outer circumference of this cam portion 52. The second bearing 12 is a radial bearing. The second bearing 12 is fitted into the inner through hole 3h of the inner gear 3. The inner through hole 3h has a large diameter portion and a small diameter portion, with a step formed between the large diameter portion and the small diameter portion. The second bearing 12 is fitted into the large diameter portion of the inner through hole 3h and is secured by the step. The inner rotation axis 3s of the first inner gear 31 is positioned coaxially with the second central axis 52c of the cam portion 52.

[0043] As shown in Figure 4, when the input shaft 10 rotates, the second central axis 52c of the cam portion 52 revolves around the shaft rotation axis 10s, and the cam portion 52 rotates with the second central axis 52c as its center of rotation. As the second central axis 52c revolves, the inner rotation axis 3s of the inner gear 3, which is located on the outer circumference of the cam portion 52, also revolves around the shaft rotation axis 10s. Here, since the second bearing 12 is located between the cam portion 52 and the inner gear 3, the rotation of the cam portion 52 is not transmitted to the inner gear 3. The inner gear 3 rotates by meshing with the first outer gear 41, which will be described later, in accordance with the eccentric behavior of the inner rotation axis 3s, that is, its orbital behavior of revolving around the shaft rotation axis 10s.

[0044] The outer gear 4 in this example includes a first outer gear 41 and a second outer gear 42 that are independent of each other, as shown in Figure 2. The first outer gear 41 and the second outer gear 42 are cylindrical members. The cylindrical first outer gear 41 has an outer central axis 41c (Figure 4). As will be described later, the first outer gear 41 does not rotate around the outer central axis 41c. The cylindrical second outer gear 42 has an outer rotation axis 42s. The second outer gear 42 rotates around the outer rotation axis 42s. The first outer gear 41 includes internal teeth 4T that are perpendicular to the outer central axis 41c and extend in a centripetal direction toward the outer central axis 41c, and outer tooth grooves 4G formed between two adjacent internal teeth 4T. Similarly, the second outer gear 42 comprises internal teeth 4T that are perpendicular to the outer rotation axis 42s and extend in a centripetal direction toward the outer rotation axis 42s, and outer tooth grooves 4G formed between two adjacent internal teeth 4T. The outer central axis 41c of the first outer gear 41 and the outer rotation axis 42s of the second outer gear 42 are arranged coaxially.

[0045] The first outer gear 41 is configured to be non-rotatable. The first outer gear 41 is fixed, for example, to the installation location of the reduction gear 1. As shown in Figure 3, the first inner gear 31 is arranged inside the first outer gear 41. As shown in Figure 4, the external teeth 3T of the first inner gear 31 mesh with the outer tooth groove 4G of the first outer gear 41, and the internal teeth 4T of the first outer gear 41 mesh with the internal tooth groove 3G of the first inner gear 31. The number of internal teeth 4T is the number of external teeth 3T plus 1. In this example, the number of internal teeth 4T of the first outer gear 41 is 26.

[0046] As shown in Figure 3, the first outer gear 41 in this example comprises a first gear portion 41A on which internal teeth 4T are formed, and a first cylindrical portion 41B integrated coaxially with the first gear portion 41A. The first outer gear 41 has a first storage hole 41h that penetrates the first outer gear 41 along the outer central axis 41c. The first storage hole 41h comprises a large diameter portion, a medium diameter portion, and a small diameter portion, which are arranged in order from the first gear portion 41A toward the first cylindrical portion 41B. The large diameter portion is positioned corresponding to the first gear portion 41A, and a plurality of internal teeth 4T are arranged on the inner circumferential surface of the large diameter portion. The first inner gear 31 is positioned in this large diameter portion. The first inner gear 31 is fixed against the step between the large diameter portion and the medium diameter portion. The medium diameter portion has an inner diameter smaller than the envelope connecting the tooth tips of the plurality of internal teeth 4T. The counterweight 53 of the eccentric cam 5 is positioned in the medium diameter portion. The small-diameter section has a smaller inner diameter than the medium-diameter section. The first bearing 11 is positioned in the small-diameter section. As a result, the input shaft 10 is rotatably supported at the position of the small-diameter section. A step is further formed in the small-diameter section, and the first bearing 11 is held against this step. This holding prevents the eccentric cam 5 from coming off the first outer gear 41 and keeps it in place on the first outer gear 41.

[0047] The outer central axis 41c of the first outer gear 41 is coaxial with the shaft rotation axis 10s of the input shaft 10. Inside the first outer gear 41, the inner rotation axis 3s of the first inner gear 31 revolves around the shaft rotation axis 10s by the eccentric cam 5. At this time, the first inner gear 31 meshes with the first outer gear 41 while changing its contact position with the first outer gear 41 in the direction of rotation of the input shaft 10. Due to this meshing, the first inner gear 31 rotates in the opposite direction to the rotation of the input shaft 10. The rotational speed of the first inner gear 31 becomes slower than the rotational speed of the input shaft 10. As a result, the rotation of the input shaft 10 is reduced and transmitted to the first inner gear 31. This transmission of rotation is the first stage of reduction.

[0048] As shown in Figures 3 and 5, the second outer gear 42 is rotatably supported within a housing 6 connected to the first outer gear 41. In this example, the housing 6 is a cylindrical member. The first outer gear 41 is connected to the housing 6 by a screw 6B. The outer diameter of the housing 6 is slightly smaller than the outer diameter of the first outer gear 41. The housing 6 has a substantially cylindrical housing hole 6h that houses the second outer gear 42. The second outer gear 42 is positioned inside the housing hole 6h. A step is formed in the housing hole 6h, and the flange 42F of the second outer gear 42 is fitted against this step. The inner diameter of the housing hole 6h is larger than that of the second inner gear 32 and is approximately the same as the outer diameter of the first inner gear 31. The second outer gear 42, positioned inside the housing hole 6h, is configured to be rotatable relative to the first outer gear 41. The outer rotation axis 42s of the second outer gear 42 is coaxial with the shaft rotation axis 10s.

[0049] A second inner gear 32 is positioned inside the second outer gear 42. In the reduction gear 1, the number of teeth of the second inner gear 32 is always less than the number of teeth of the first inner gear 31. As shown in Figure 5, the external teeth 3T of the second inner gear 32 mesh with the outer tooth groove 4G of the second outer gear 42, and the internal teeth 4T of the second outer gear 42 mesh with the internal tooth groove 3G of the second inner gear 32. The number of internal teeth 4T is the number of external teeth 3T plus 1. In this example, the number of internal teeth 4T of the second outer gear 42 is 21.

[0050] As shown in Figure 3, the second outer gear 42 in this example comprises a second gear portion 42A on which internal teeth 4T are formed, and a second cylindrical portion 42B integrated coaxially with the second gear portion 42A. The second outer gear 42 has a second housing hole 42h that penetrates the second outer gear 42 along the outer rotation axis 42s. The second housing hole 42h comprises a large-diameter portion and a small-diameter portion arranged sequentially in the direction from the second gear portion 42A toward the second cylindrical portion 42B. The large-diameter portion is positioned corresponding to the second gear portion 42A, and multiple internal teeth 4T are arranged on the inner circumferential surface of the large-diameter portion. The second inner gear 32 is positioned in this large-diameter portion. The end face of the second inner gear 32 is abutted against the step between the large-diameter portion and the small-diameter portion.

[0051] Multiple mounting holes 42eh are formed on the end face 42e of the second cylindrical portion 42B. The end face 42e is the face opposite to the face facing the first outer gear 41. The multiple mounting holes 42eh are arranged to surround the second storage hole 42h, as shown in Figure 1. An output shaft 19, shown by a dashed line, is mounted in the mounting holes 42eh. The output shaft 19 comprises a shaft portion and a disc portion located at the tip of the shaft portion. Through holes are formed in the disc portion at positions corresponding to the mounting holes 42eh. The output shaft 19 is connected to the second outer gear 42 by passing a screw (not shown) through these through holes and mounting holes 42eh and screwing the disc portion to the end face 42e of the second cylindrical portion 42B.

[0052] As shown in Figure 3, the second inner gear 32, located inside the second outer gear 42, is integrated coaxially with the first inner gear 31 and therefore behaves the same as the first inner gear 31. That is, the inner rotation axis 3s of the second inner gear 32 revolves around the shaft rotation axis 10s, and the second inner gear 32 rotates in the opposite direction to the input shaft 10. At that time, as shown in Figure 5, the second inner gear 32 meshes with the second outer gear 42 while changing the position of contact with the second outer gear 42 in the direction of rotation of the second inner gear 32. Since the second outer gear 42 is configured to be rotatable, the second outer gear 42 rotates when the second inner gear 32 meshes with the second outer gear 42. Because the second outer gear 42 has more teeth than the second inner gear 32, the second outer gear 42 rotates in the same direction as the second inner gear 32 at a slower rotational speed. In other words, the rotation of the second inner gear 32 is reduced and transmitted to the second outer gear 42. This transmission is the second stage of reduction.

[0053] Let's discuss the reduction ratio in the reduction gear 1 of this example. The reduction ratio R satisfies equation (1) below, where Z1 is the number of teeth of the first inner gear 31 and Z2 is the number of teeth of the second inner gear 32. As already mentioned, the number of teeth of the first outer gear 41 is the number of teeth of the first inner gear 31 plus 1, and the number of teeth of the second outer gear 42 is the number of teeth of the second inner gear 32 plus 1, so the variables related to the number of teeth of the first outer gear 41 and the second outer gear 42 are not included in equation (1) below.

[0054]

number

[0055] In this example, the number of teeth Z1 of the first inner gear 31 is 25, and the number of teeth Z2 of the second inner gear 32 is 20, so the reduction ratio R is 1 / 105. The larger the denominator in equation (1), the higher the reduction ratio R, and the smaller the denominator, the lower the reduction ratio R. As is clear from equation (1), the reduction ratio R can be increased by reducing the number of teeth Z1 of the first inner gear 31 or increasing the number of teeth Z2 of the second inner gear 32. For example, if the number of teeth Z1 of the first inner gear 31 is changed to 24 while keeping the number of teeth Z2 of the second inner gear 32 the same, the reduction ratio R becomes 1 / 126. On the other hand, the reduction ratio R can be decreased by increasing the number of teeth Z1 of the first inner gear 31 or decreasing the number of teeth Z2 of the second inner gear 32. For example, if you keep the number of teeth Z1 of the first inner gear 31 the same and change the number of teeth Z2 of the second inner gear 32 to 17, the reduction ratio R will be approximately 1 / 56.3.

[0056] The inner gear 3 and outer gear 4 described above are sintered bodies. Sintered bodies are obtained by sintering a compacted body. Compacted bodies are obtained by pressure molding raw material powder containing metal powder. The metal powder is, for example, pure iron powder or iron alloy powder with iron as the main component. Here, "iron alloy with iron as the main component" means that when the mass of the iron alloy is taken as 100% by mass, it contains more than 50% by mass, 80% or more by mass, or 90% or more by mass of iron element. The iron alloy may also contain at least one alloying element selected from copper, nickel, tin, chromium, molybdenum, manganese, and carbon. The above alloying elements contribute to improving the mechanical properties of the iron-based sintered body. The content of copper, nickel, chromium, manganese, and molybdenum is, for example, 0.5% by mass or more and 5.0% by mass or less in total, or 1.0% by mass or more and 3.0% by mass or less. The carbon content is, for example, 0.2% by mass or more and 2.0% by mass or 0.4% by mass or more and 1.0% by mass. The composition of the sintered body can be determined, for example, by X-ray spectroscopy.

[0057] The inner gear 3 and outer gear 4 in this example are sintered iron alloys. The iron alloys in this example are, for example, D-40 or D-60 manufactured by Sumitomo Electric Industries Sintered Alloys Co., Ltd. D-40 is an iron alloy containing 2.0 mass% copper and 0.8 mass% carbon. D-60 is an iron alloy containing 4.0 mass% nickel, 0.5 mass% molybdenum, 1.5 mass% copper and 0.5 mass% carbon.

[0058] The density of the sintered body is, for example, 6.6 g / cm³. 3 That concludes the explanation. Such sintered bodies have excellent mechanical strength. The density of the sintered body is 6.8 g / cm³. 3 The above is also acceptable. The density of D-40 is approximately 6.8 g / cm³. 3 Therefore, the density of D-60 is approximately 6.9 g / cm³. 3 The density can be calculated based on the composition determined by X-ray spectroscopy.

[0059] As shown in Figures 2 and 3, the gear unit 2 in this example further includes an oil seal 7. The oil seal 7 seals the inner surface of the housing hole 6h and the outer surface of the second outer gear 42. As a result, the grease applied to the inside of the gear unit 2 can be retained inside the gear unit 2. A detailed description of the configuration of the oil seal 7 is omitted.

[0060] The reduction gear 1, equipped with the gear unit 2 described above, can reduce the rotation of the input shaft 10 in two stages and transmit it to the output shaft. Therefore, the reduction ratio of the reduction gear 1 is very high. Furthermore, the reduction gear 1 in this example is compact due to its structure, which includes an integrated first inner gear 31 and a second inner gear 32.

[0061] ≪Inner gear and outer gear tooth profiles≫ As already mentioned, the tooth profile of the outer gear 4, which has a tooth profile created by the inner gear 3 and the envelope of the trajectory of the tooth profile curve group of the inner gear 3, is a tooth profile with a greater tooth height than a cycloidal tooth profile. Tooth height is the length from the root circle to the tip of the tooth. The method for creating the outer gear 4 is described in detail in Japanese Patent Publication No. 5765655, of which the present applicant is the right holder. Examples of tooth profiles with a greater tooth height than a cycloidal tooth profile are geocloidal tooth profiles, paracoid EX tooth profiles, or megafloyd tooth profiles. The design method for geocloidal tooth profiles is described in detail in Japanese Patent Publication No. 5561287, of which the present applicant is the right holder. The design method for megafloyd tooth profiles is described in detail in Japanese Patent Publication No. 4557514, of which the present applicant is the right holder. The design method for paracoid EX tooth profiles is described in detail in Japanese Patent Publication No. 5252557. The technologies described in the above four patent documents relate to internal gear pumps.

[0062] Whether the tooth profile of inner gear 3 and outer gear 4 is greater in height than the cycloidal tooth profile can be evaluated by whether the eccentricity 'e' of inner gear 3 relative to outer gear 4 satisfies the following equation (2). 'Z1' is the number of teeth of inner gear 3, as already mentioned. 'D1' is the diameter of the root circle of inner gear 3.

[0063]

number

[0064] The right-hand side of equation (2) above represents the theoretical value of the eccentricity of the cycloidal tooth profile. In other words, the eccentricity of a normal cycloidal tooth profile is the same as the value obtained from the right-hand side. That is, if the eccentricity 'e' of the configuration in this example is greater than the theoretical value of the eccentricity of a cycloidal tooth profile obtained from the right-hand side, then the tooth profiles of the inner gear 3 and outer gear 4 can be evaluated as having a greater tooth height than a cycloidal tooth profile.

[0065] The details of the meshing between the inner gear 3 and the outer gear 4 will be explained based on Figure 6. Figure 6 shows a state in which the center of the tooth thickness of the outer tooth 3T of the inner gear 3 coincides with the center of the width of the outer tooth groove 4G of the outer gear 4. The tooth thickness of the outer tooth 3T is the length of the outer tooth 3T along the rotational direction of the inner gear 3. The width of the outer tooth groove 4G is the distance between two adjacent inner teeth 4T. However, when the reduction gear 1 is operating, the inner gear 3 and the outer gear 4 will not be in the state shown in Figure 6. When the reduction gear 1 is operating, the outer tooth 3T of the inner gear 3 contacts the inner tooth 4T of the outer gear 4 in the rotational direction of the inner gear 3, so the center of the tooth thickness of the inner tooth 4T and the center of the width of the inner tooth groove 3G do not coincide.

[0066] Between the inner gear 3 and the outer gear 4, a tooth surface clearance 2f and a tooth tip clearance 2t are formed. The tooth surface clearance 2f is the gap between adjacent outer teeth 3T and inner teeth 4T in the direction along the pitch circle 3p of the inner gear 3. There are two tooth surface clearances 2f, one on each side of the outer tooth 3T, and the two tooth surface clearances 2f are of the same size. The pitch circle 3p, shown by the dashed line, is a circle with its center at the inner rotation axis 3s of the inner gear 3, and its radius is the straight line connecting its center to the point where the outer tooth 3T contacts the inner tooth 4T when the gear unit 2 rotates. On the other hand, the tooth tip clearance 2t is the gap between the tooth tip of the outer tooth 3T of the inner gear 3 and the outer tooth groove 4G, or the gap between the tooth tip of the inner tooth 4T of the outer gear 4 and the inner tooth groove 3G. The two tooth tip clearances 2t are of the same size. The tip of the external tooth 3T is the part of the external tooth 3T that is furthest from the inner rotation axis 3s. The tip of the internal tooth 4T is the part of the internal tooth 4T that is closest to the outer central axis 41c and the outer rotation axis 42s.

[0067] In gears with a tooth profile that is taller than a cycloidal tooth profile, the number of teeth can be increased without increasing the outermost diameter of the gear. Therefore, in the gear unit 2 provided in the reduction gear 1 of this disclosure, the reduction ratio can be increased without increasing the outermost diameter of the outer gear 4. Figure 7 is a drawing comparing the size of the gear unit 2 of this example with the size of an existing gear unit 100 having a cycloidal tooth profile. In Figure 7, the existing gear unit 100 is shown by a dashed line. The number of teeth of the first inner gear 31 and the first outer gear 41 provided in the gear unit 2 is the same as the number of teeth of the existing inner gear 103 and the existing outer gear 104 provided in the existing gear unit 100. Also, the eccentricity of the first inner gear 31 and the existing inner gear 103 are both 0.9 mm. In this case, the outer diameter of the first outer gear 41 was 44.3 mm, while the outer diameter of the existing outer gear 104 was 49 mm.

[0068] In sintered inner gear 3 and outer gear 4, which have tooth profiles with tooth heights greater than cycloidal tooth profiles, when dimensional correction is performed by sizing, the amount of springback in the direction along the tooth height tends to be large, making it difficult to improve the dimensional accuracy of the tooth height. On the other hand, the amount of springback in the direction along the tooth thickness tends to be small, making it easy to improve the dimensional accuracy of the tooth thickness by sizing. Considering these points, in the reduction gear 1 of this example, the inner gear 3 and outer gear 4 are designed so that the tooth tip clearance 2t is larger than the tooth surface clearance 2f, as shown in the manufacturing method of the gear unit 2 described later. As mentioned above, in sintered gears, it is easy to improve the dimensional accuracy of the tooth thickness by sizing, so even if the tooth surface clearance 2f of the inner gear 3 and outer gear 4 is small during design, the tooth surface of the inner gear 3 and the tooth surface of the outer gear 4 can mesh with good dimensional accuracy. On the other hand, by designing the inner gear 3 and outer gear 4 to increase the tooth tip clearance 2t, even if the amount of springback in tooth height during sizing is large, the tooth tips are less likely to come into contact with the tooth roots.

[0069] In the inner gear 3 and outer gear 4 manufactured based on the design described above, processes such as grinding to fine-tune the dimensions can be omitted. The tooth surfaces and tips of the inner gear 3 and outer gear 4 in this example do not have grinding marks. The absence of grinding marks means that the inner gear 3 and outer gear 4 were obtained without undergoing grinding work. Therefore, a gearbox equipped with inner gear 3 and outer gear 4 without grinding marks offers superior productivity.

[0070] ≪Method of manufacturing a gear unit≫ The gear unit 2 described above is manufactured by the following processes A through C. Process A: A process for manufacturing a pre-outer gear and a pre-under gear, which are made from compacted powder molded bodies. Process B: A process for sintering the pre-outer gear and the pre-outer gear. Process C: The sintered plain gear and pre-outer gear are sized to produce the inner gear 3 and outer gear 4.

[0071] [Process A] In process A, the pre-outer gear and pre-outer gear are manufactured to satisfy the following conditions I and II. Condition I: The tooth profiles of the pre-outer gear and the pre-na gear are tooth profiles with greater tooth height than the cycloidal tooth profile. Condition II: When the center of the tooth thickness of the pre-outer gear coincides with the center of the tooth groove width of the pre-outer gear, the tooth tip clearance 2t is greater than the tooth surface clearance 2f.

[0072] Plane gears and pre-outer gears that satisfy the above conditions I and II are designed based on the following design philosophy, for example. First, the number of teeth of inner gear 3 and outer gear 4 is determined from the desired reduction ratio. The reduction ratio is arbitrarily determined according to the application of the reducer 1.

[0073] The outer diameter of the outer gear 4 is determined. This outer diameter can also be arbitrarily determined according to the space in which the reduction gear 1 is positioned. Of course, if the outer diameter is too small, it will not be possible to design an inner gear 3 and outer gear 4 with a number of teeth that satisfies the desired reduction ratio. Therefore, although the outer diameter of the outer gear 4 can be arbitrarily determined, there is a lower limit to the outer diameter depending on the number of teeth.

[0074] The inner diameter of the inner gear 3 is determined. The inner diameter of the inner gear 3 is the inner diameter of the inner through hole 3h in which the input shaft 10 and the second bearing 12 are positioned. The inner diameter of the inner gear 3 is approximately equal to the outer diameter of the second bearing 12. The outer diameter of the input shaft 10 and the outer diameter of the second bearing 12 are arbitrary values ​​determined to satisfy the required strength and durability according to the application of the reduction gear 1.

[0075] The eccentricity of the inner gear 3 relative to the outer gear 4 is determined. The eccentricity e can be calculated, for example, from the tooth tip diameter and tooth root diameter of the inner gear 3 in the design tooth profile before any adjustments are made to the tooth tip clearance, etc., which are within the constraints of the outer diameter of the inner gear 3 and the outer gear 4 determined as described above, using the following formula. e = (Inner gear tip diameter - Inner gear root diameter) / 4 The eccentricity may be changed as needed, within the constraints of the outer diameter of the outer gear 4.

[0076] Once the reduction ratio, the outer diameter of the outer gear 4, and the inner diameter of the inner gear 3 are determined, step A1 is performed to design a reference inner gear that satisfies condition I based on these values. In this example, a reference inner gear with a geocloid® tooth profile was designed as the tooth profile that satisfies condition I. The design procedure will be explained with reference to Figure 8. For the sake of clarity, the tooth profile shown in Figure 8 is depicted as having a higher tooth height than the tooth profile shown in Figure 6. Also, in Figure 8, the tooth surface clearance 2f and tooth tip clearance 2t are shown to be considerably larger than they actually are.

[0077] As shown by the dashed line in Figure 8, process A2 is carried out to design the reference outer gear 9 that meshes with the reference inner gear 8, based on the reference inner gear 8 and the eccentricity. In the reducer 1, once the eccentricity, the shape of the reference inner gear 8, and the outer diameter of the reference outer gear 9 are determined, the tooth profile of the reference outer gear 9 is uniquely determined. In the combination of the reference inner gear 8 and the reference outer gear 9, the tooth surface clearance 2f and the tooth tip clearance 2t are approximately the same when the center of the tooth thickness of the reference inner gear 8 and the center of the tooth groove width of the reference outer gear 9 coincide.

[0078] In this example, step A3 is performed to modify the shape of the reference outer gear 9 so that the tooth tip clearance 2t is larger, and to create a designed inner gear 80 and a designed outer gear 90 whose tooth tip clearance 2t is larger than the tooth surface clearance 2f. Figure 8 shows an example in which only the shape of the reference outer gear 9 is modified and the shape of the reference inner gear 8 is not changed. Specifically, the tooth groove of the reference outer gear 9 is deepened and the tooth height is reduced to create the designed outer gear 90 shown by the solid line. The shape of the designed inner gear 80 is the same as the shape of the reference inner gear 8.

[0079] Unlike this example, the shape of the reference inner gear 8 may be modified, or the shapes of both the reference inner gear 8 and the reference outer gear 9 may be modified.

[0080] The tooth surface clearance 2f between the designed inner gear 80 and the designed outer gear 90 is, for example, 10 μm or more and 20 μm or less. If the tooth surface clearance 2f at the time of design is 10 μm or more, even if springback occurs during sizing, a gear unit 2 can be manufactured in which the inner gear 3 and outer gear 4 mesh smoothly without contact. If the tooth surface clearance 2f is 20 μm or less, backlash is reduced, and a gear unit 2 can be manufactured with an inner gear 3 and outer gear 4 that mesh with high precision.

[0081] The tooth tip clearance 2t in the designed inner gear 80 and the designed outer gear 90 is, for example, 50 μm or more. If the tooth tip clearance 2t at the time of design is 50 μm or more, contact between the tooth tip and tooth root in the gear unit 2 can be prevented. The tooth root refers to the bottom of the inner tooth groove or the bottom of the outer tooth groove.

[0082] Based on the design inner gear 80 described above, a mold for powder compaction of the plain inner gear is manufactured, and based on the design outer gear 90, a mold for powder compaction of the pre-outer gear is manufactured. Using these molds, the plain inner gear and pre-outer gear are manufactured by powder compaction. The metal powder used to form the plain inner gear and pre-outer gear is, for example, an iron alloy. The composition of the iron alloy is, for example, D-60 manufactured by Sumitomo Electric Industries, Ltd.

[0083] [Process B] The pre-outer gear and pre-coated gear are sintered under a heated atmosphere. The heated atmosphere is an inert atmosphere such as nitrogen. The temperature of the heated atmosphere, i.e., the sintering temperature, is, for example, 1140°C.

[0084] [Process C] The plain gear and the pre-outer gear are sized. Sizing is carried out, for example, according to the method for manufacturing a ring-shaped sintered body described in the applicant's patent publication No. 6961895. A sizing mold is used in this method for manufacturing a ring-shaped sintered body. The sizing mold comprises a die, a core rod, an upper punch, and a lower punch. The die has a sizing hole. The core rod is positioned in the center of the sizing hole. The upper punch pushes the ring-shaped sintered body from above into the annular space between the die and the core rod. The lower punch supports the ring-shaped sintered body being pushed into the annular space from below. The inner circumference of the sizing hole has an approach portion having a slope that gradually decreases in diameter toward the bottom, and an outer diameter sizing portion that is connected to the lower end of the approach portion and extends parallel to the axis of the core rod. The outer circumference of the core rod has an approach portion that gradually increases in diameter toward the bottom, and an inner diameter sizing portion that is connected to the lower end of the approach portion and extends parallel to the axis of the core rod. The inner gear 3 and outer gear 4 of this example are manufactured by sizing the plain inner gear and pre-outer gear using the sizing mold described above. Sizing marks are formed on the tooth surfaces and tooth tips of the inner gear 3 and outer gear 4. The sizing marks are abrasion marks that extend in a direction along the thickness of the inner gear 3 and outer gear 4.

[0085] As already mentioned, in sintered inner gears 3 and outer gears 4 with tooth profiles that are taller than cycloidal tooth profiles, the springback of the outer teeth 3T and inner teeth 4T along the tooth height tends to be large when sizing is performed to correct dimensions. In this example, since the inner gear 3 and outer gear 4 are designed so that the tooth tip clearance 2t is larger than the tooth surface clearance 2f, even if the springback of the outer teeth 3T and inner teeth 4T along the tooth height is large, the outer tooth 3T will not come into contact with the tooth root of the outer tooth groove 4G, nor will the inner tooth 4T come into contact with the tooth root of the inner tooth groove 3G.

[0086] On the other hand, with inner gear 3 and outer gear 4, when dimensional correction is performed by sizing, the springback of the outer tooth 3T and inner tooth 4T along the tooth thickness tends to be small. Therefore, even without designing inner gear 3 and outer gear 4 to have a large tooth surface clearance 2f, the tooth surfaces of inner gear 3 and outer gear 4 can be meshed with precision.

[0087] Inner gear 3 and outer gear 4 manufactured based on the design philosophy described above, the grinding process required for fine-tuning dimensions can be omitted. Tooth profiles with a height greater than that of a cycloidal tooth profile are more complex in shape and difficult to grind with high precision. By omitting this cumbersome grinding process, the gear unit 2, which includes the inner gear 3 and outer gear 4, can be manufactured with high productivity. Furthermore, the productivity of the reducer 1, which includes this gear unit 2, is also improved.

[0088] Geocroid tooth profiles are relatively easy to modify in shape. Therefore, with geocroid tooth profiles, the tooth width can be reduced without increasing the tooth height. Consequently, in gears employing geocroid tooth profiles, the number of teeth can be changed without significantly altering the gear dimensions. Due to these characteristics, in gear unit 2 employing geocroid tooth profiles, it is easy to change the number of teeth of inner gear 3 and outer gear 4 without increasing the outer diameter and eccentricity of outer gear 4, or decreasing the inner diameter of inner gear 3. This point is explained with reference to Figure 9.

[0089] Figure 9 is a front view of the inner gear 3, as seen from the side where the second inner gear 32 is located. In Figure 9, three virtual circles with the same center as the center of the inner through hole 3h of the inner gear 3 are shown by dashed lines. Of the three virtual circles, the first virtual circle as seen from the center of the inner through hole 3h is the root circle 321 of the second inner gear 32. The root circle 321 is a circle that connects all the roots of the second inner gear 32 and is coaxial with the inner through hole 3h. The second virtual circle as seen from the center of the inner through hole 3h is the tip circle 329 of the second inner gear 32. The tip circle 329 is a circle that connects all the tips of the second inner gear 32 and is coaxial with the inner through hole 3h. The third virtual circle as seen from the center of the inner through hole 3h is the root circle 311 of the first inner gear 31. The root circle 311 is a circle that connects all the roots of the first inner gear 31 and is coaxial with the inner through-hole 3h.

[0090] If the wall thickness T1 of the first inner gear 31, which is the difference between the radius of the root circle 311 and the radius of the tip circle 329, is too thin, the strength of the punch used to form the first inner gear 31 will decrease. Similarly, if the wall thickness T2 of the second inner gear 32, which is the difference between the radius of the inner through hole 3h and the radius of the root circle 321, is too thin, the strength of the punch used to form the second inner gear 32 will decrease. Therefore, wall thicknesses T1 and T2 must be greater than or equal to the specified values.

[0091] As already explained with reference to equation (1), to increase the reduction ratio R, it is necessary to either decrease the number of teeth Z1 of the first inner gear 31 or increase the number of teeth Z2 of the second inner gear 32. Decreasing Z1 reduces the root circle 311, and increasing the number of teeth Z2 increases the tip circle 329. In other words, increasing the reduction ratio R reduces the wall thickness T1. In a geocloid tooth profile, which has a high degree of freedom in the shape of each tooth, the reduction in wall thickness T1 can be made smaller than in a cycloid tooth profile. Therefore, a geocloid tooth profile has room to achieve a higher reduction ratio R than a cycloid tooth profile. If it were to attempt to achieve the same high reduction ratio as a geocloid tooth profile using a cycloid tooth profile, it may be necessary to increase the outer diameter of the first inner gear 31 in order to make the wall thickness T1 greater than a predetermined value. Increasing the outer diameter of the first inner gear 31 leads to an increase in the outer diameter of the outer gear 4.

[0092] As already explained with reference to equation (1), to lower the reduction ratio R, it is necessary to increase the number of teeth Z1 of the first inner gear 31 or decrease the number of teeth Z2 of the second inner gear 32. If Z2 is reduced to lower the reduction ratio R, the wall thickness T2 decreases. In a geocloid tooth profile, which has a high degree of freedom in the shape of each tooth, the reduction in wall thickness T2 can be made smaller than in a cycloid tooth profile. Therefore, a geocloid tooth profile has room to lower the reduction ratio R than a cycloid tooth profile. If it is attempted to achieve the same reduction ratio as a geocloid tooth profile using a cycloid tooth profile, it may be necessary to reduce the inner diameter of the inner through-hole 3h in order to make the wall thickness T2 above a predetermined value. A reduction in the inner diameter of the inner through-hole 3h leads to a reduction in the strength of the input shaft 10.

[0093] <Embodiment 2> The gear unit 2 may be a single-stage reduction gear unit 2. For example, the gear unit 2 can be composed of the second inner gear 32 and the second outer gear 42 shown in Figure 3. In that case, if the cam portion 52 of the eccentric cam 5 is located inside the second inner gear 32, the second inner gear 32 and the second outer gear 42 can perform a single-stage reduction. [Explanation of symbols]

[0094] 1 Reducer 10 Input shaft, 10s Shaft rotation axis, 10r Rib section 11 First bearing, 12 Second bearing 19 Output shaft 2 Gear Units 2f tooth surface clearance, 2t tooth tip clearance 3 Inner Gear 3h inner through hole, 3p pitch circle, 3s inner rotation axis 3G inner tooth groove, 3T outer tooth 31 First inner gear, 311 Base circle 32 Second inner gear, 321 Base circle, 329 Tip circle 4 Outerwear 4G outer tooth groove, 4T inner tooth 41 First Outer Gear 41c Outer central axis, 41h First storage hole 41A First gear section, 41B First cylindrical section 42 Second Outer Gear 42e end face, 42eh mounting hole, 42h second storage hole, 42s outer rotating shaft 42A Second gear section, 42B Second cylindrical section, 42F Flange section 5. Eccentric cam 5h cam through hole, 5g groove 51 Base section, 51c First central axis 52 Cam section, 52c Second central shaft 53 Counterweight 6 Housing 6B screw, 6h housing hole 7 Oil seal 8 Standard inner gear 80 Design Inner Gear 9 Standard outer gear 90 Design Outer Gear 100 Existing Gear Units 103 Existing inner gear, 104 Existing outer gear T1, T2 thickness

Claims

1. A reduction gear comprising a gear unit that reduces the rotation of an input shaft and transmits it to an output shaft, The gear unit comprises an inner gear that rotates eccentrically with respect to the input shaft, and an outer gear in which the inner gear is housed. The outer gear and the inner gear are sintered bodies. The tooth profiles of the outer gear and the inner gear are tooth profiles with a greater tooth height than cycloidal tooth profiles. The outer gear is connected to the output shaft. reducer.

2. The gearbox according to claim 1, wherein the tooth surfaces and tooth tips of the inner gear and the outer gear do not have polishing marks.

3. The aforementioned sintered body is formed from an iron alloy with iron as the main component, The gearbox according to claim 1 or claim 2, wherein the iron alloy contains at least one alloying element selected from copper, nickel, tin, chromium, molybdenum, manganese, and carbon.

4. The density of the sintered body is 6.6 g / cm³. ３ The gearbox according to claim 3.

5. Furthermore, it is equipped with a housing, The inner gear includes a first inner gear and a second inner gear having a smaller diameter than the first inner gear. The outer gear includes a first outer gear that meshes with the first inner gear and a second outer gear that meshes with the second inner gear. The first inner gear and the second inner gear are integrated coaxially. The first outer gear is fixed to the housing so as not to rotate in conjunction with the rotation of the first inner gear. The reduction gear according to claim 1 or claim 2, wherein the second outer gear is housed in the housing so as to be rotatable in conjunction with the rotation of the second inner gear.

6. A method for manufacturing a gear unit comprising an inner gear and an outer gear in which the inner gear is housed, which reduces the rotation of an input shaft in a reduction gear and transmits it to an output shaft, Step A involves manufacturing a pre-outer gear and a pre-under gear made from compacted powder. Step B involves sintering the plain gear and the pre-outer gear, The process includes step C, which involves sizing the sintered plain inner gear and the sintered pre-outer gear to produce the inner gear and the outer gear, In step A, Condition I: The tooth profiles of the plain gear and the pre-outer gear are tooth profiles with a greater tooth height than the cycloidal tooth profile, In a state where the center of the tooth thickness of the pre-outer gear coincides with the center of the tooth groove width of the pre-outer gear, condition II is when the tooth tip clearance is greater than the tooth surface clearance. The plain gear and the pre-outer gear are manufactured to satisfy the following conditions: A method for manufacturing a gear unit.

7. The design of the tooth profiles of the pre-outer gear and the pre-outer gear in step A is as follows: Step A1 involves designing a reference inner gear that satisfies condition I based on the reduction ratio between the inner gear and the outer gear, the outer diameter of the outer gear, and the inner diameter of the inner gear. Step A2 involves designing a reference outer gear that meshes with the reference inner gear based on the eccentricity of the inner gear relative to the reference inner gear and the outer gear, Step A3 involves modifying the shape of at least one of the reference inner gear and the reference outer gear to create a design inner gear and a design outer gear that satisfy condition II. The method for manufacturing a gear unit according to claim 6, wherein in step A, the pre-inner gear and the pre-outer gear are manufactured based on the designed inner gear and the designed outer gear.

8. The method for manufacturing a gear unit according to claim 7, wherein the tooth surface clearance in step A3 is 10 μm or more and 20 μm or less, and the tooth tip clearance is 50 μm or more.

Images