JP7629281B2 - Reduction gear - Google Patents

Description

The present invention relates to a reduction gear device.

Patent Document 1 describes a reduction gear device equipped with first and second main bearings interposed between a casing of an output member and first and second flange bodies of a fixed member. These first and second main bearings are equipped with rollers.

JP 2010-159774 A

After examining the technology disclosed in Patent Document 1, the inventors recognized the following problem. The rollers of the main bearing may be provided with a crowning portion. In such cases, peeling may occur on the rolling surface that faces the crowning portion. The technology disclosed in Patent Document 1 does not address this issue, and there is room for improvement.

One aspect of the present invention was made in light of these circumstances, and one of its objectives is to provide a technology that can suppress peeling on the rolling surfaces of the main bearings.

One aspect of the present invention for solving the above-mentioned problems is a reduction gear device including a reduction mechanism having an internal gear and an external gear, an output member to which rotation reduced by the reduction mechanism is transmitted, and a main bearing supporting the output member, the main bearing having a roller. The roller has a middle portion in the roller centerline direction and a crowning portion whose outer diameter gradually decreases from the middle portion toward the end portion in the roller centerline direction. The protruding peak height Rpk of the crowning portion is 0.063 μm or less.

According to one aspect of the present invention, peeling on the rolling surface of the main bearing can be suppressed.

1 is a side cross-sectional view of a reduction gear transmission according to an embodiment. 1 is a front cross-sectional view of a reduction gear transmission according to an embodiment. FIG. 2 is a schematic side view of a roller of the eccentric bearing according to the embodiment. FIG. 4 is a schematic diagram showing the relationship between an inner rolling surface and rollers of an eccentric bearing. 1 is a graph showing roughness curves and load curves used to determine Rpk. 5A and 5B are diagrams showing an example of the shape of a crowning portion of a roller of an eccentric body bearing. FIG. 7A is a schematic diagram for explaining a durability test, and FIG. 7B is a diagram for explaining operations performed in the durability test. FIG. 2 is a schematic side view of a roller of a main bearing according to the embodiment. FIG. 4 is a schematic diagram showing the relationship between the inner rolling surface of the main bearing and the rollers of the main bearing. FIG. 1 is a schematic diagram for explaining an evaluation test.

An example of an embodiment of the present invention will be described below. Identical components will be given the same reference numerals, and duplicate explanations will be omitted. In each drawing, for the sake of convenience of explanation, some components will be omitted as appropriate, and their dimensions will be enlarged or reduced as appropriate. The drawings should be viewed according to the orientation of the reference numerals.

Figure 1 is a side cross-sectional view of a reduction gear 10 according to an embodiment, and Figure 2 is a front cross-sectional view thereof. Figure 2 shows a view in which the rotation phase of the external gear 16 is different from that in Figure 1. The reduction gear 10 is an eccentric oscillating type reduction mechanism that causes one of the internal gear 20 and the external gear 16 to rotate by oscillating the external gear 16 that meshes with the internal gear 20, and outputs the generated rotation component from the output member 50 to the driven device.

The reduction gear 10 mainly comprises an input shaft 12, a crankshaft 14, an external gear 16, an eccentric bearing 18, an internal gear 20, carriers 22, 24, a casing 26, and main bearings 54, 56. Hereinafter, the direction along the central axis CL1 of the internal gear 20 will be referred to as the "axial direction", and the circumferential direction and radial direction of a circle centered on the central axis CL1 will be referred to as the "circumferential direction" and the "radial direction", respectively. First, the overall configuration of the reduction gear 10 of the embodiment will be described, then the eccentric bearing 18 will be described, and then the main bearings 54, 56 will be described.

The input shaft 12 is connected to a drive device (not shown) and is rotated by the rotational power input from the drive device. The drive device may be, for example, a motor, a gear motor, an engine, etc.

The crankshaft 14 is rotated integrally with the input shaft 12. In this embodiment, the crankshaft 14 also serves as the input shaft 12. The reduction gear 10 in this embodiment is a center crank type in which the rotation center line CL2 of the crankshaft 14 is arranged coaxially with the central axis line CL1 of the internal gear 20. The crankshaft 14 includes a shaft body 28 that rotates around the rotation center line CL2 due to the rotation of the input shaft 12, and a plurality of eccentric bodies 30 that can rotate integrally with the shaft body 28.

The eccentric body 30 has its own axis CL3 eccentric to the rotation center line CL2 of the crankshaft 14, and is capable of oscillating the external gear 16. In this embodiment, three eccentric bodies 30 are provided, and the eccentric phases of adjacent eccentric bodies 30 are shifted by 120°. In FIG. 1, the axis of the middle eccentric body 30 among the multiple eccentric bodies 30 is shifted in the depth direction of the paper of this figure from the rotation center line CL2 of the crankshaft 14. The eccentric body 30 in this embodiment is configured as part of the same member as the shaft body 28.

The external gear 16 is provided individually to correspond to each of the multiple eccentric bodies 30. The external gear 16 is provided with a first through hole 34 through which the pin body 32 passes. The first through hole 34 is provided offset from the center of the external gear 16.

The eccentric body bearing 18 is disposed between the eccentric body 30 and the external gear 16. The eccentric body bearing 18 is provided individually corresponding to each of the multiple eccentric bodies 30. The eccentric body bearing 18 is supported by the corresponding eccentric body 30 and supports the external gear 16 corresponding to the eccentric body 30. The external gear 16 is rotatably supported by the corresponding eccentric body 30 via the eccentric body bearing 18. The eccentric body bearing 18 is disposed inside a second through hole 36 that passes through the center of the external gear 16. The eccentric body bearing 18 will be described in detail later.

The internal gear 20 of this embodiment includes an internal gear body 38 that is integrated with the casing 26, and an outer pin 40 that is provided separately from the internal gear body 38 and that constitutes the internal teeth of the internal gear 20. The outer pin 40 is rotatably supported in a pin groove 42 formed on the inner periphery of the internal gear body 38.

The casing 26 is generally cylindrical, with the external gear 16 disposed inside. In this embodiment, the casing 26 also serves as the internal gear body 38.

The carriers 22, 24 include a first carrier 22 (hereinafter, for convenience, referred to as the input side carrier 22) provided on one axial side of the multiple external gears 16, and a second carrier 24 (hereinafter, for convenience, referred to as the non-input side carrier 24) provided on the other axial side of the multiple external gears 16. The carriers 22, 24 rotatably support the crankshaft 14 via the input bearing 44.

The pin body 32 connects the input side carrier 22 and the non-input side carrier 24. A plurality of pin bodies 32 (six in this example) are provided at intervals around the central axis CL1 of the internal gear 20. A roller 46 is fitted around the pin body 32 so as to be rotatable relative to the pin body 32.

The pin body 32 has a main body portion 32a that penetrates the external gear 16, and an end portion 32b that is fitted into a fitting portion formed in one of the input side carrier 22 and the anti-input side carrier 24. In this embodiment, the "one carrier" is the input side carrier 22. The pin body 32 in this embodiment is integrally provided as part of the same member as the other carrier of the input side carrier 22 and the anti-input side carrier 24. In this embodiment, the "other carrier" is the anti-input side carrier 24.

The member that outputs rotational power to a driven device (not shown) (to which rotation reduced by the reduction mechanism is transmitted) is called the output member 50, and the member that is fixed to an external member (not shown) to support the reduction gear 10 is called the fixed member 52. In this embodiment, the output member 50 is the non-input side carrier 24, and the fixed member 52 is the casing 26. It is also possible to use the casing 26 as the output member and the carriers 22, 24 as the fixed members.

The output member 50 is rotatably supported by the fixed member 52 via main bearings 54, 56. The main bearings 54, 56 include a first main bearing 54 (hereinafter also referred to as the input side main bearing 54) disposed between the casing 26 and the input side carrier 22, and a second main bearing 56 (hereinafter also referred to as the non-input side main bearing 56) disposed between the casing 26 and the non-input side carrier 24. The main bearings 54, 56 will be described later.

The operation of the reduction gear 10 described above will now be explained. When rotation is transmitted from the drive unit to the input shaft 12, the crankshaft 14 rotates together with the input shaft 12, and the external gear 16 oscillates due to the eccentric body 30 of the crankshaft 14. At this time, the external gear 16 oscillates so that its axis CL3 rotates around the central axis CL1 of the internal gear 20. When the external gear 16 oscillates, the meshing positions of the external gear 16 and the internal gear 20 are shifted sequentially in the circumferential direction. As a result, each time the input shaft 12 or the crankshaft 14 rotates once, one of the external gear 16 and the internal gear 20 rotates on its own axis by an amount equivalent to the difference in the number of teeth between the external gear 16 and the internal gear 20.

When the non-input side carrier 24 serves as the output member 50 as in this embodiment, the external gear 16 rotates on its axis. On the other hand, when the casing 26 serves as the output member 50, the internal gear 20 rotates on its axis. The output member 50 rotates in synchronization with the rotation component of the external gear 16 or the internal gear 20, outputting the rotation component to the driven device. At this time, the rotation of the input shaft 12 is decelerated at a reduction ratio according to the difference in the number of teeth between the external gear 16 and the internal gear 20, and then output to the driven device.

We now turn to a description of the eccentric bearing 18. The eccentric bearing 18 is a roller bearing and includes a number of rollers 60 and a retainer 62. The retainer 62 maintains the relative positions of the rollers 60 and supports the rollers 60 so that they can rotate freely.

The eccentric bearing 18 has an outer rolling surface 64 that is provided radially outside the roller 60 and on which the roller 60 rolls, and an inner rolling surface 66 that is provided radially inside the roller 60 and on which the roller 60 rolls. The outer rolling surface 64 of this embodiment is not provided on an outer ring dedicated to the eccentric bearing 18, but is provided on the inner circumferential surface of the second through hole 36 of the external gear 16 that faces the roller 60 radially outward. The eccentric bearing 18 of this embodiment does not have an outer ring on which the outer rolling surface 64 is provided. The inner rolling surface 66 of this embodiment is not provided on an inner ring dedicated to the eccentric bearing 18, but is provided on the outer circumferential surface of the eccentric 30 that faces the roller 60 radially inward. The eccentric bearing 18 of this embodiment does not have an inner ring on which the inner rolling surface 66 is provided. The inner rolling surface 66 and the outer rolling surface 64 of this embodiment are provided so as to extend linearly in a cut surface along the axial direction.

The rollers 60 are spaced apart in the circumferential direction. In this embodiment, the rollers 60 are cylindrical rollers, and the rotation center line CL4 of the rollers 60 is parallel to the central axis CL1 of the internal gear 20. Hereinafter, the direction along the rotation center line CL4 of the rollers 60 is referred to as the roller axial direction.

3 is a schematic side view of the roller 60. The roller 60 has an intermediate portion 70 in the roller axial direction, a crowning portion 72 whose outer diameter gradually decreases from the intermediate portion 70 toward the end of the roller axial direction, and a corner portion 74 formed by the outer circumferential surface of the roller 60 and the end surface 60a in the roller axial direction. The crowning portion 72 is hatched in the figure. The intermediate portion 70 of this embodiment constitutes a range including the center of the roller 60 and extends linearly along the rotation center line CL4 of the roller 60. The crowning portion 72 is provided to prevent the edge of the roller 60 from hitting the rolling surfaces 64, 66 when misalignment occurs in the roller 60. The crowning portions 72 of this embodiment are provided individually on both sides of the intermediate portion 70 in the roller axial direction of the roller 60. The corner portions 74 of this embodiment constitute curved chamfered portions.

Next, the peeling suppression technology of the eccentric bearing 18 of this embodiment will be described. Figure 4 is a schematic diagram showing the relationship between the inner rolling surface 66 of the eccentric bearing 18 and the roller 60. Here, a side view of a portion of the roller 60 and a planar development of the inner rolling surface 66 of the eccentric bearing 18 are shown. In this figure, the location where peeling occurs and the rolling location of the roller 60 relative to that location are hatched.

The inventors have found that when the torque input to the reduction gear 10 increases, peeling may occur more easily in the eccentric bearing 18. This peeling tends to occur more easily on the rolling surfaces 64, 66 of the eccentric bearing 18, particularly on the inner rolling surface 66 of the eccentric bearing 18, at the rolling points of the crowning portion 72 of the roller 60.

The inventors have investigated ways to address this issue. As a result, they have found that adjusting the protruding peak height Rpk (hereinafter simply referred to as "Rpk") of the crowning portion 72 of the roller 60 and the dimensionless drop amount Da (described later) of the crowning portion 72 is effective.

Rpk is one of the parameters that indicate the surface roughness of the measurement target surface, and is specified in JIS B6071-2. Figure 5 is a graph showing the roughness curve Cr and the load curve Cl used to calculate Rpk. To calculate Rpk, the roughness curve Cr of the measurement target surface specified in JIS B6071-1 is obtained, and the load curve Cl is calculated from the obtained roughness curve Cr. The level of the intersection of the equivalent straight line Le equivalent to the central part of this load curve Cl with the vertical axis at the horizontal axis 0% position is set as the upper level Lu of the core part, and the level of the intersection of the equivalent straight line Cl with the vertical axis at the horizontal axis 100% position is set as the lower level Ll of the core part. At this time, the part of the roughness curve Cr above the upper level Lu of the core part becomes the protruding peak part 80, and the part below the lower level Ll of the core part becomes the protruding valley part 82.

Rpk is a value indicating the average height of the protruding peaks 80 on the roughness curve Cr. The total cross-sectional area of the protruding peaks 80 on the roughness curve Cr is Sa, and the load length ratio from the 0% position on the horizontal axis to the intersection of the load curve Cl and the straight line L1 at the upper level is Mr1. In this case, Rpk is represented by the height of a right-angled triangle Ta on the load curve Cl, whose base is Mr1 and whose cross-sectional area is equal to Sa.

There are various parameters that represent surface roughness. The inventors have newly discovered that, among these, Rpk is a sensitive indicator of peeling of the eccentric bearing 18. This is believed to be because, among the protruding peaks 80 and protruding valleys 82 in the roughness curve Cr, the height of the protruding peaks 80 has a particular effect on peeling of the eccentric bearing 18. The higher the height of the protruding peaks 80, the greater the surface pressure at the rolling points of the rollers 60 against the rolling surfaces 64, 66 of the eccentric bearing 18, which is believed to make peeling more likely to occur.

Another parameter that represents surface roughness is, for example, the arithmetic mean roughness Ra. This is the average absolute value in the height direction of the roughness curve over the reference length. If this arithmetic mean roughness Ra is used as an index, it will be affected by the shape of the protruding valley portion 82, which is thought to have little effect on peeling of the eccentric bearing 18. For this reason, in this case, peeling of the eccentric bearing 18 cannot be accurately evaluated. In contrast, according to this embodiment, Rpk is used as an index to set the Rpk of the crowning portion 72 of the roller 60. Therefore, compared to using other parameters that are affected by the protruding valley portion 82 of the roughness curve Cr, peeling can be accurately evaluated by eliminating the influence of the protruding valley portion 82, and peeling can be stably suppressed.

Specifically, it is effective to set the Rpk of the crowning portion 72 of the roller 60 to 0.063 μm or less. By satisfying this condition, peeling on the rolling surfaces 64, 66 of the eccentric bearing 18 at the rolling points of the crowning portion 72 of the roller 60 can be suppressed. From this perspective, it is preferable that this Rpk is 0.040 μm or less. These are set based on the results of experimental studies described below. The lower limit of the Rpk of the crowning portion 72 is not particularly limited in relation to peeling. This lower limit is, for example, 0.025 μm in order to process at a realistic cost, given the level of processing technology at the time of filing.

From the same viewpoint as for the crowning portion 72, the Rpk of the middle portion 70 of the roller 60 is preferably 0.063 μm or less. This makes it possible to suppress peeling on the rolling surfaces 64, 66 of the eccentric bearing 18 at the rolling points of the middle portion 70 of the roller 60. The lower limit of the Rpk of the middle portion 70 is not particularly limited in relation to peeling. This lower limit is, for example, 0.013 μm in order to process at a realistic cost, given the level of processing technology at the time of filing.

Such a roller 60 with an Rpk can be obtained, for example, by a polishing process using centerless polishing, barrel polishing, buff polishing, or the like. To obtain a roller 60 with a desired Rpk through this polishing process, the grain size of the abrasive can be adjusted. In this case, the grain size of the abrasive can be changed so that the grain size gradually increases until a predetermined grain size (for example, #1000) is reached.

It is preferable that the Rpk of the intermediate portion 70 of the roller 60 is smaller than the Rpk of the crowning portion 72. The intermediate portion 70 of the roller 60 is easier to polish than the crowning portion 72, and it is easier to make the Rpk smaller than that of the crowning portion 72. Therefore, with the above-mentioned configuration, it is easier to achieve this by matching the Rpk of the crowning portion 72 to the Rpk of the intermediate portion 70.

(Drop amount)
The dimensionless drop amount Da of the crowning portion 72 of the roller 60 is a value that satisfies the following condition. See FIG. 3. The distance from the center 60b of the roller 60 in the roller axial direction to the end face 60a is Lh. The position of Lh×80% from the center 60b of the roller 60 in the roller axial direction is called the evaluation position Pe. In this case, the dimensionless drop amount Da is a value obtained by dividing the drop amount of the crowning portion 72 of the roller 60 at this evaluation position Pe by Lh×80%. The drop amount at the evaluation position Pe here is expressed as the difference between the radius of the intermediate portion 70 and the radius at the evaluation position Pe. The drop amount is made dimensionless in this way in order to evaluate the drop amount of the crowning portion 72 regardless of the length of the roller 60 in the roller axial direction. The evaluation position is set to the position of Lh×80% because the crowning portion 72 is usually provided there, and the drop amount there is considered to affect the peeling of the eccentric bearing 18.

It is effective to set this dimensionless drop amount Da to 0.0026 or more. This is set based on the results of experimental studies described later. By satisfying this condition, peeling on the rolling surfaces 64, 66 of the eccentric bearing 18 at the rolling points of the crowning portion 72 of the roller 60 can be effectively suppressed. In addition, by satisfying this condition, there is also the advantage that edge contact at the end of the roller 60 can be effectively prevented. The upper limit value of the dimensionless drop amount Da is not particularly limited in relation to peeling, but it is preferable to set it to 0.010. If the drop amount of the crowning portion 72 becomes excessive, there is a concern that the surface pressure on the rolling surfaces 64, 66 of the eccentric bearing 18 at the rolling points of the boundary between the crowning portion 72 and the intermediate portion 70 will increase. By setting the dimensionless drop amount Da to the above-mentioned upper limit value or less, such an increase in surface pressure can be avoided.

The inventor conducted a test to set the Rpk and the dimensionless drop amount Da of the crowning portion 72 of the roller 60 as described above. In this test, the eccentric bearing 18 was assembled into the reduction gear 10 under various conditions in which the Rpk and the dimensionless drop amount Da of the roller 60 were changed, and the reduction gear 10 was used as a sample. The diameter of the roller 60 was 6 mm, and the total length Lt in the roller axial direction was 6.5 mm. The Rpk, the dimensionless drop amount Da, and the shape of the crowning portion 72 of the roller 60 are as shown in Table 1 and FIG. 6. The arrow in FIG. 6 indicates the evaluation position Pe. The torque density (described later) of the reduction gear 10 of each sample was 3.1×10 ⁶ N/m ² .

The method for measuring the Rpk of the roller 60 is as follows. First, the stylus of a contact surface roughness measuring instrument is moved on the surface to be measured, the trajectory of the tip of the stylus is measured to obtain a measurement curve, and the roughness curve Cr of the evaluation length Ln is obtained based on the measurement curve. The surface roughness measuring instrument used is the "SURFCOM 2000DX-14" manufactured by Tokyo Seimitsu. The direction of movement of the stylus (measurement direction) is the axial direction of the roller, and the movement speed is 0.3 mm/s. The stylus is made of diamond, and its tip is conical with an apex angle of 60° and a curvature radius of 2 μm. The evaluation length Ln is 1.25 mm, which is 5 times the reference length (0.25 mm), and when the protruding peak height Rpk of the crowning portion 72 is obtained, the crowning portion 72 is included in its entire range. When the protruding peak height Rpk of the intermediate portion 70 is obtained, the evaluation length Ln includes the intermediate portion 70 in its entire range. From the roughness curve Cr obtained in this way, the load curve Cl described above was calculated, and the protruding peak height Rpk was obtained from the load curve Cl.

The above sample reduction gear 10 was subjected to the following durability test. Figure 7 is a diagram for explaining the durability test. As shown in Figure 7 (A), in the durability test, a flywheel 86 was attached to the output member of the reduction gear 10 via an output shaft 84, a weight 88 was attached to the flywheel 86, and under this condition, a rotational force was input to the input shaft 12 of the reduction gear 10 by a drive device 90 (servo motor).

See Figure 7 (B). One cycle is defined as an operation that is performed in the order of acceleration operation → constant speed operation → deceleration operation. One cycle of operation performed by inputting power in the forward rotation direction is called a forward cycle operation, and one cycle of operation performed by inputting power in the reverse rotation direction is called a reverse cycle operation. In the durability test, five forward cycle operations and five reverse cycle operations were alternately repeated until the total number of cycles reached a predetermined reference number.

In this durability test, Jf, Jw, nMax, and ta were adjusted so that the load torque Tf expressed by the following equation (1) became the allowable torque of the reduction gear 10.
Tf=(Jf+Jw)×(nMax/(9.55×ta))... (1)
Tf: Load torque (N×m)
Jf: moment of inertia of the flywheel 86 (kgm ² )
Jw: moment of inertia of the weight 88 (kgm ² )
nMax: Output rotation speed (r/min) output from the output member 50
ta: Acceleration or deceleration time (seconds)

In addition, in this durability test, Wf, Ww, L1, and L2 were adjusted so that the load moment Mf expressed by the following equation (2) became the allowable moment of the reduction gear 10.
Mf=Wf×g×L1+Ww×g×L2... (2)
Mf: Load moment (N x m)
Wf: mass of the flywheel 86 (kg)
Ww: Mass of weight 88 (kg)
L1: Distance (m) from the load point Pa of the input side main bearing 54 to the axial center position of the flywheel 86
L2: Distance (m) from the load point Pa of the input side main bearing 54 to the axial center position of the weight 88

The samples that had undergone the above durability tests were evaluated for the presence or absence of peeling of the eccentric bearing 18 by visually observing the inner rolling surface 66 of the eccentric bearing 18. The results are shown in Table 1. In the peeling item in Table 1, "x" indicates that peeling was observed when the aforementioned reference number was 400,000 times. "○" indicates that no peeling was observed when the reference number was 400,000 times, and slight peeling was observed when the reference number was 800,000 times. "◎" indicates that no peeling was observed when the reference number was 800,000 times, and slight peeling was observed when the reference number was 1,000,000 times. "☆" indicates that no peeling was observed even when the reference number was 1,000,000 times.

As shown in Nos. A and B in Table 1, when the Rpk of the crowning portion 72 of the roller 60 was greater than 0.063 μm, peeling occurred in the eccentric bearing 18. On the other hand, as shown in Nos. C to G, when the Rpk was 0.063 μm or less, peeling of the eccentric bearing 18 was suppressed. Also, as shown in Nos. E to G, when the Rpk of the crowning portion 72 was 0.040 μm or less, peeling was suppressed more. Also, as shown in Nos. D, F, and G, when the dimensionless drop amount Da was 0.0026 or more, peeling was suppressed more than when it was less than 0.0026. Also, as shown in Nos. F and G, when the Rpk of the crowning portion 72 was 0.040 μm or less and the dimensionless drop amount Da was 0.0026 or more, peeling was particularly suppressed.

Next, other improvements to the reduction gear 10 of this embodiment will be described. As mentioned above, when the torque input to the reduction gear 10 is increased, peeling is more likely to occur in the eccentric bearing 18. In this embodiment, the torque density, which will be described next, is used as a parameter related to this torque.

Please refer to Figures 1 and 2. The reduction mechanism 92 constituted by the internal gear 20 and the external gear 16 is regarded as a cylinder. The radius of the pitch circle Cp of the internal gear 20 is the radius R of the cylinder, and the total value of the axial dimension Th of the external gear 16 is the axial dimension Tt of the cylinder. The volume of the cylinder represented by the radius R and the axial dimension Tt of this cylinder (=π x R ² x Tt) is the volume of the reduction mechanism 92. When adjacent external gears 16 are arranged with a gap between them, the gap is not included in the "total value of the axial dimension Th of the external gears 16" here. When there are three external gears 16 as in this embodiment, the total value of the axial dimension Th of the three external gears 16 (Th x 3) is used.

At this time, the torque density mentioned above is the allowable torque of the reduction gear 10 divided by the volume of the reduction mechanism 92. This torque density means the torque applied to the portion per unit volume of the reduction mechanism 92 when the allowable torque is input to the reduction gear 10. The higher the torque density, the higher the allowable torque of the reduction gear 10. The allowable torque here means a predetermined allowable peak torque. More specifically, it means a predetermined allowable value for the peak torque acting on the second carrier 24 when an inertial torque is applied to the rotating object due to the start and stop of the reduction gear 10.

It is effective to set this torque density to 2.9×10 ⁶ N/m ² or more. This is set based on the results of experimental studies. When this condition is satisfied, it is assumed that a large torque that imparts such a torque density is input to the reduction gear 10. When such a large torque is applied, peeling is more likely to occur in the eccentric bearing 18. According to this embodiment, even in such a case, there is an advantage that peeling of the eccentric bearing 18 can be suppressed by satisfying the above-mentioned condition regarding the Rpk of the crowning portion 72 of the roller 60. There is also an advantage that the allowable torque of the reduction gear 10 can be increased while suppressing peeling in this way. The upper limit value of this torque density is not particularly limited. Based on the state of the art at the time of filing, this upper limit value is, for example, 6.0×10 ⁶ N/m ² or less.

To satisfy such torque density conditions, the following methods (1) to (3) are used, for example. When using method (2), for example, heat treatment as described in JP 2016-98860 A may be performed. When using method (3), for example, as described in JP 2016-98860 A, the distance from the central axis CL1 of the internal gear 20 to the axis of the main body 32a of the pin body 32 may be made different from the distance from the central axis CL1 to the axis of the end 32b. This improves the strength of the base of the pin body 32.
(1) Increasing the strength of the materials of the components of the reduction gear 10. (2) Using heat treatment to increase the strength of the components of the reduction gear 10. (3) Increasing the strength of the structure of the reduction gear 10.

Returning to FIG. 1, the main bearings 54 and 56 will be described. The main bearings 54 and 56 are angular roller bearings that can receive radial and thrust loads. The main bearings 54 and 56 include inner rings 51 and 53, outer rings 55 and 57, a number of rollers 75, and a retainer 59.

The rollers 75 are spaced apart in the circumferential direction. In this embodiment, the rollers 75 are cylindrical rollers. As shown in FIG. 1, the rotational center lines CL5 and CL6 of the rollers 75 are inclined with respect to the central axis CL1 to provide a predetermined contact angle. Hereinafter, the direction along the rotational center lines CL5 and CL6 is referred to as the roller center line direction.

The inner rings 51 and 53 are provided radially inward of the rollers 75 and have inner rolling surfaces 67 on which the rollers 75 roll. The outer rings 55 and 57 are provided radially outward of the rollers 75 and have outer rolling surfaces 68 on which the rollers 75 roll. The retainer 59 maintains the relative positions of the rollers 75 and supports the rollers 75 so that they can rotate freely.

In this embodiment, the inner rolling surface 67 is provided on the inner rings 51, 53 dedicated to the main bearings 54, 56. The inner rolling surface 67 may be integrally provided on the outer peripheral surface of the first carrier 22 or the second carrier 24 that faces the roller 75 radially inward, and it is not essential to provide the inner rings 51, 53.

The outer rolling surface 68 in this embodiment is provided on the outer rings 55, 57 dedicated to the main bearings 54, 56. The outer rolling surface 68 may be provided integrally with the inner circumferential surface of the through hole of the casing 26 that faces the roller 75 radially outward, and it is not essential to provide the outer rings 55, 57. The inner rolling surface 67 and the outer rolling surface 68 in this embodiment are provided so as to extend linearly in a cross section along the center line direction of the roller.

Figure 8 is a schematic side view of roller 75. Roller 75 has an intermediate portion 76 in the roller center line direction (CL5/CL6), a crowning portion 77 whose outer diameter gradually decreases from the intermediate portion 76 toward the end in the roller center line direction, and a corner portion 78 formed by the outer circumferential surface of roller 75 and the end surface 75a in the roller center line direction. In the figure, the crowning portion 77 is hatched. In this embodiment, the intermediate portion 76 constitutes a range including the center of roller 75 and extends linearly along the rotation center lines CL5 and CL6 of roller 75. The crowning portion 77 is provided to prevent the edge of roller 75 from hitting the rolling surfaces 67 and 68 when misalignment occurs in roller 75. In this embodiment, the crowning portion 77 is provided individually on both sides of the intermediate portion 76 in the roller center line direction of roller 75. In this embodiment, the corner portion 78 constitutes a curved chamfered portion.

Next, the background that led to the idea of the reduction gear 10 of this embodiment will be explained. Figure 9 is a schematic diagram showing the relationship between the inner rolling surfaces 67 of the main bearings 54, 56 and the rollers 75. Here, a side view of a portion of the rollers 75 and a planar development of the inner rolling surfaces 67 of the main bearings 54, 56 are shown. In this figure, the location where peeling occurs and the location where the rollers 75 roll relative to that location are hatched.

The inventors have found that when the moment acting on the output member of the reduction gear 10 increases, peeling may occur more easily in the main bearings 54, 56. This peeling tends to occur more easily on the rolling surfaces 67, 68 of the main bearings 54, 56, particularly on the inner rolling surfaces 67 of the main bearings 54, 56, at the rolling points of the crowning portions 77 of the rollers 75.

The inventors came up with the idea that the peeling suppression technology of the eccentric bearing 18 described above could be applied to the peeling of the main bearings 54, 56, and investigated countermeasures against peeling of the main bearings 54, 56. As a result, they found that adjusting the protruding peak height Rpk (hereinafter simply referred to as "Rpk") of the crowning portion 77 of the roller 75 was effective.

In the following explanation of peeling of the main bearings 54, 56, explanations that overlap with the peeling suppression technology of the eccentric bearing 18 described above will be omitted, and differences will be mainly explained. Therefore, the explanation of the peeling suppression technology of the eccentric bearing 18 described above also applies to peeling of the main bearings 54, 56 to the extent that there is no contradiction.

Rpk is one of the parameters that indicates the surface roughness of the surface being measured, and the explanation of Rpk regarding peeling of the eccentric bearing 18 described above applies.

According to this embodiment, the Rpk of the crowning portion 77 of the roller 75 is set using the Rpk as an index. This makes it possible to accurately evaluate peeling, and therefore to stably suppress peeling.

Specifically, it is effective to set the Rpk of the crowning portion 77 of the roller 75 to 0.063 μm or less. By satisfying this condition, peeling on the rolling surfaces 67, 68 of the main bearings 54, 56 at the rolling points of the crowning portion 77 of the roller 75 can be suppressed. From this perspective, this Rpk is preferably 0.050 μm or less, and more preferably 0.026 μm or less. These are set based on the results of experimental studies described below. The lower limit of the Rpk of the crowning portion 77 is not particularly limited in relation to peeling. This lower limit is, for example, 0.020 μm in order to process at a realistic cost, given the level of processing technology at the time of filing.

From the same viewpoint as for the crowning portion 77, it is preferable that the Rpk of the intermediate portion 76 of the roller 75 is 0.063 μm or less. This makes it possible to suppress peeling on the rolling surfaces 67, 68 of the main bearings 54, 56 at the rolling points of the intermediate portion 76 of the roller 75. The lower limit of the Rpk of the intermediate portion 76 is not particularly limited in relation to peeling. This lower limit is, for example, 0.020 μm in order to process at a realistic cost, given the level of processing technology at the time of filing.

Such Rpk rollers 75 are obtained by a grinding process similar to that used for the rollers 60 of the eccentric bearing 18.

It is preferable that the Rpk of the intermediate portion 76 of the roller 75 is smaller than the Rpk of the crowning portion 77. The intermediate portion 76 of the roller 75 is easier to polish than the crowning portion 77, and it is easier to make the Rpk smaller than that of the crowning portion 77. Therefore, with the above-mentioned configuration, it is easier to achieve this by matching the Rpk of the crowning portion 77 to the Rpk of the intermediate portion 76.

The inventor conducted a test to set the Rpk of the crowning portion 77 of the roller 75 as described above. In this test, main bearings 54, 56 with various conditions for the Rpk of the roller 75 were assembled into the reduction gear 10, and the reduction gear 10 was used as a sample. The diameter of the roller 75 is 7.5 mm, and the total length Lt in the axial direction of the roller is 9 mm. The Rpk and shape of the crowning portion 77 of the roller 75 are as shown in Table 2.

The method for measuring Rpk of roller 75 is the same as the method for measuring Rpk of roller 60 of eccentric bearing 18. When determining the protruding peak height Rpk of crowning portion 77, the entire range includes crowning portion 77. When determining the protruding peak height Rpk of intermediate portion 76, the evaluation length Ln includes intermediate portion 76 in its entire range.

The following evaluation test was carried out on the above sample reduction gear 10. Figure 10 is a diagram for explaining the evaluation test. As shown in this figure, the evaluation test is carried out on a test unit 10-B, which is made up of only the casing 26, main bearings 54, 56, input side carrier 22, and non-input side carrier 24 of the reduction gear 10. In the evaluation test, with an output shaft 84 attached to the casing 26 or non-input side carrier 24 of unit 10-B, a weight 88 is attached to the tip of the output shaft 84 of unit 10-B to apply a load moment to the output shaft 84, which is then rotated by a drive device 91 (gear motor) for evaluation.

When evaluating the inner ring side in this test, the output shaft 84 is attached to the casing 26, and the drive unit 91 inputs rotation to the casing 26 via an adapter. When evaluating the outer ring side in this test, the output shaft 84 is attached to the non-input side carrier 24, and the drive unit 91 inputs rotation to the non-input side carrier 24 via an adapter. In either case, the drive unit 91 inputs rotation in one direction at a constant speed. Figure 10 shows a case where the output shaft 84 is attached to the non-input side carrier 24 and the outer ring side is evaluated.

The load moment in the evaluation test is determined by the acceleration factor x in the evaluation test, and the load moment Ml is expressed by the following equation (3).
Ml=Mc/((1/x)^(3/10)) ... (3)
(Note that A^B indicates A to the power of B.)
Ml: Load moment (N m)
Mc: Allowable moment (N m)
x: acceleration magnification L3: distance (m) from the application point Pa of the input side main bearing 54 to the axial center position of the weight 88

Inspections in the evaluation test were carried out at intervals of 25% of the cycles, with the target number of cycles being 100%. In these inspections, the rolling surfaces of the inner rings 51, 53, outer rings 55, 57, and rollers 75 of the main bearings 54, 56 were observed. A camera, an optical microscope, and a stylus-type surface roughness and shape measuring instrument were used for these surface observations. In addition to the surface observations, the iron powder concentration and moment stiffness were also evaluated.

The samples that had undergone the above evaluation tests were evaluated for the presence or absence of peeling of the main bearings 54, 56 by visually observing the inner rolling surfaces 67 of the main bearings 54, 56. The results are shown in Table 2. In the peeling section of Table 2, "x" indicates that peeling was observed when the aforementioned reference number was the target number of cycles. "○" indicates that no peeling was observed when the reference number was the target number of cycles, and slight peeling was observed when the reference number was twice the target number of cycles. "◎" indicates that no peeling was observed when the reference number was twice the target number of cycles, and slight peeling was observed when the reference number was 2.5 times the target number of cycles. "☆" indicates that no peeling was observed even when the reference number was 2.5 times the target number of cycles.

As shown in Nos. A and B in Table 2, when the Rpk of the crowning portion 77 of the roller 75 exceeded 0.063 μm, peeling occurred in the main bearings 54 and 56. On the other hand, as shown in Nos. C to E, when the Rpk was 0.063 μm or less, peeling of the main bearings 54 and 56 was suppressed. Also, as shown in No. D, when the Rpk of the crowning portion 77 was 0.050 μm or less, peeling was further suppressed. Also, as shown in No. E, when the Rpk of the crowning portion 77 was 0.026 μm or less, peeling was particularly suppressed.

Explain variations of each component.

The eccentric bearing 18 of this embodiment is not limited to center crank type eccentric oscillating reduction gears, but can also be applied to a distribution type eccentric oscillating reduction gear in which multiple crankshafts 14 are positioned at positions offset from the central axis CL1 of the internal gear 20.

The main bearings 54, 56 of this embodiment are not limited to eccentric oscillating reduction gears, but can be applied to reduction gears having various known reduction mechanisms. Examples of such reduction gears include simple planetary reduction gears and flexible mesh reduction gears.

The number of external gears 16 is not particularly limited and may be one, two, four or more.

Although an example has been described in which the eccentric bearing 18 does not include a dedicated outer ring on which the outer rolling surface 64 is provided, such a dedicated outer ring may be provided. Although an example has been described in which the eccentric bearing 18 does not include a dedicated inner ring on which the inner rolling surface 66 is provided, such a dedicated inner ring may be provided.

The rollers 60 of the eccentric bearing 18 are not limited to cylindrical rollers, but may be tapered rollers, etc. Also, the rollers 75 of the main bearings 54, 56 are not limited to cylindrical rollers, but may be tapered rollers, etc.

The internal teeth of the internal gear 20 may be integrally formed as part of the same member as the internal gear body 38.

The casing 26 may be provided separately from the internal gear body 38.

The eccentric body 30 may be configured separately from the shaft body 28 of the crankshaft 14.

The pin body 32 may be provided separately from the other of the input side carrier 22 and the non-input side carrier 24.

The above describes the embodiments and modifications of the present invention in detail. The above-mentioned embodiments and modifications are merely examples of how the present invention can be put into practice. The contents of the embodiments and modifications do not limit the technical scope of the present invention, and many design modifications, such as changes, additions, and deletions of components, are possible within the scope of the concept of the invention. In the above-mentioned embodiments, the contents in which such design modifications are possible are emphasized by adding the word "embodiment", but design modifications are also permitted even in contents without such notation. Any combination of the above-mentioned components is also valid as an aspect of the present invention. The hatching on the cross sections of the drawings does not limit the material of the objects to which the hatching is applied.

10...reduction gear, 16...external gear, 18...eccentric body bearing, 20...internal gear, 30...eccentric body, 60...rollers, 70...intermediate portion, 72...crowning portion, 54, 56...main bearings, 75...rollers, 76...intermediate portion, 77...crowning portion.

Claims (2)

A reduction gear device comprising: a reduction mechanism having an internal gear and an external gear; an output member to which rotation reduced by the reduction mechanism is transmitted; and a main bearing supporting the output member,
the output member is either a carrier provided on a side of the external gear or a casing integrated with the internal gear,
The main bearing has rollers,
The rollers are disposed between the carrier and the casing,
the roller has an intermediate portion in a roller center line direction, and a crowning portion whose outer diameter gradually decreases from the intermediate portion toward an end portion in the roller center line direction,
A reduction gear transmission, wherein a protruding peak height Rpk of the crowning portion is 0.063 μm or less. The main bearing has a center line of the roller inclined with respect to a center line of the reduced rotation,
The roller has an axial end surface connected to the crowning portion,
2. The reduction gear transmission according to claim 1, wherein the axial end surface does not directly contact an outer ring or an inner ring of the main bearing.

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