JP7472599B2 - Planetary reducer - Google Patents

Description

The present invention relates to a planetary reducer.

A planetary reduction gear has been known that has a sun gear, a plurality of planetary gears arranged around the sun gear, and an internal gear surrounding the plurality of planetary gears. A conventional planetary reduction gear is described in, for example, Japanese Utility Model Application Laid-Open Publication No. 54-8074.
Japanese Utility Model Application Publication No. 54-8074

The planetary gear of a planetary reduction gear is supported via a bearing on a carrier pin that extends parallel to the central axis. Conventionally, needle bearings have often been used as the bearings that support this planetary gear. However, when needle bearings are used, the planetary gear is placed directly on the outer circumferential surface of the carrier pin via multiple rollers. Therefore, with needle bearings, it is not possible to position the end face of the planetary gear and the carrier in the axial direction so that they are not in contact with each other, and contact between the end face of the planetary gear and the carrier creates a large rotational resistance.

For this reason, conventional planetary reducers are equipped with washers that come into contact with the end faces of the planetary gears in addition to the needle bearings to reduce rotational resistance. However, this type of structure cannot completely eliminate rotational resistance, and requires the placement of high-precision washers with low friction in the circumferential direction.

In addition, when needle bearings are used, the entire inner circumferential surface of the planetary gear comes into contact with the rollers of the needle bearing. For this reason, the entire inner circumferential surface of the planetary gear needs to be machined with high precision.

The object of the present invention is to provide a structure that can reduce the number of parts of a planetary reducer, reduce the axial dimension of the planetary reducer, and reduce the area of the inner circumferential surface of the planetary gear that requires high-precision machining.

The present invention is a planetary reducer that reduces the speed of rotation from a first rotational speed to a second rotational speed lower than the first rotational speed, and includes a sun gear that rotates at the same rotational speed around a central axis, a plurality of planetary gears that mesh with the sun gear on the radial outside of the sun gear, a plurality of carrier pins that support the plurality of planetary gears, a carrier that fixes the plurality of carrier pins with a circumferential gap, a pair of bearings that support the planetary gears rotatably relative to the carrier pins, and an annular internal gear that meshes with the planetary gears on the radial outside of the plurality of planetary gears, and the pair of bearings each have an inner ring fixed to the carrier pin, an outer ring fixed to the planetary gear, and a plurality of spheres interposed between the inner ring and the outer ring, and the outer ring has a flange portion that protrudes in a direction away from the carrier pin, and the inner peripheral portion of the planetary gear is fixed to the outer ring between the pair of flange portions.

According to the present invention, the planetary gear can be positioned in the axial direction by a pair of flanges provided on the outer ring of the bearing, making it possible to keep the axial end faces of the planetary gear out of contact. This makes it possible to eliminate the rotational resistance caused by the contact of the end faces of the planetary gear. This makes it unnecessary to use parts to reduce the rotational resistance. As a result, the number of parts in the planetary reducer can be reduced, and the axial dimensions of the planetary reducer can be reduced.

In addition, according to the present invention, the inner circumference of the planetary gear is fixed to the outer ring of the bearing between a pair of flanges. Therefore, of the entire inner circumference of the planetary gear, only the portion between the pair of flanges requires high dimensional accuracy for fixing. This makes it easier to machine the inner circumference of the planetary gear.

FIG. 1 is a vertical cross-sectional view of a planetary reduction gear. FIG. 2 is a cross-sectional view of the sun gear, the planetary gears, and the first internal gear taken along line AA in FIG. FIG. 3 is a partial vertical cross-sectional view of the planetary gear and bearing. FIG. 4 is a partial vertical cross-sectional view of a planetary gear and a bearing according to a first modified example. FIG. 5 is a vertical sectional view of a planetary reduction gear according to a second modified example.

Below, exemplary embodiments of the present invention will be described with reference to the drawings. In this application, the direction parallel to the central axis of the sun gear is referred to as the "axial direction", the direction perpendicular to the central axis is referred to as the "radial direction", and the direction along the arc centered on the central axis is referred to as the "circumferential direction". However, the above "parallel direction" also includes directions that are approximately parallel. Furthermore, the above "orthogonal direction" also includes directions that are approximately orthogonal.

In the following explanation, the right side in FIG. 1 is referred to as the "input side," and the left side in FIG. 1 is referred to as the "output side."

<1. Planetary reduction gear according to one embodiment>
1 is a vertical cross-sectional view of a planetary reduction gear 1 according to an embodiment of the present invention. This planetary reduction gear 1 is a device that reduces rotational motion of a first rotation speed input from a motor to rotational motion of a second rotation speed lower than the first rotation speed and outputs the reduced rotational motion. The planetary reduction gear 1 is used, for example, by being incorporated into a joint of a robot together with a motor. However, the planetary reduction gear 1 may also be used in other devices such as an assisted suit or an unmanned transport vehicle.

As shown in FIG. 1, the planetary reducer 1 of this embodiment includes one sun gear 10, multiple planetary gears 20, a planetary support portion 30, a first internal gear 40, a second internal gear 50, and an output shaft 60.

The sun gear 10 is a gear arranged along the central axis 91. The sun gear 10 is connected to a motor, which is a drive source, via an input shaft 11. The input shaft 11 is rotatably supported via a bearing in a casing (not shown). The sun gear 10 and the input shaft 11 rotate around the central axis 91 at a first rotation speed before deceleration by the driving force input from the motor. A plurality of external teeth 12 are provided on the outer circumferential surface of the sun gear 10. The plurality of external teeth 12 are provided at a constant angular pitch around the central axis 91. Each external tooth 12 protrudes radially outward on the outer circumferential surface of the sun gear 10.

The planetary gear 20 is a gear arranged radially outside the sun gear 10. FIG. 2 is a cross-sectional view of the sun gear 10, the multiple planetary gears 20, and the first internal gear 40 taken along line A-A in FIG. 1. However, in FIG. 2, hatching indicating the cross section and the illustration of the teeth of each gear are omitted to avoid cluttering the drawing. As shown in FIG. 2, in this embodiment, three planetary gears 20 are arranged at equal intervals around the sun gear 10. However, the number of planetary gears 20 in the planetary reducer 1 may be one or two, or may be four or more.

Each planetary gear 20 has a pin hole 23 in the center. A carrier pin 32, which will be described later, is inserted into the pin hole 23. Each planetary gear 20 is supported by the carrier pin 32 so that it can rotate around a planetary shaft 92 that is parallel to the central axis 91.

As shown in FIG. 1, the planetary gear 20 has a first planetary gear 21 and a second planetary gear 22. The first planetary gear 21 and the second planetary gear 22 are separate members and fixed to each other. The first planetary gear 21 is an annular gear that meshes with the sun gear 10. The first planetary gear 21 has a plurality of first gear teeth 211 on its outer circumferential surface. The plurality of first gear teeth 211 are provided at a constant angular pitch centered on the planet shaft 92. Each of the first gear teeth 211 protrudes outward from the outer circumferential surface of the first planetary gear 21. The first gear teeth 211 mesh with the external teeth 12 of the sun gear 10 described above.

The second planetary gear 22 is a gear with a smaller diameter than the first planetary gear 21. The second planetary gear 22 has a plurality of second gear teeth 221 on its outer circumferential surface. The plurality of second gear teeth 221 are arranged at a constant angular pitch centered on the planetary shaft 92. Each of the second gear teeth 221 protrudes outward on the outer circumferential surface of the second planetary gear 22. The plurality of second gear teeth 221 are located closer to the output side than the plurality of first gear teeth 211. In addition, the number of first gear teeth 211 that the first planetary gear 21 has is different from the number of second gear teeth 221 that the second planetary gear 22 has.

The planetary support 30 is a unit that supports multiple planetary gears 20. As shown in FIG. 1, the planetary support 30 has a cage-shaped carrier 31 and multiple carrier pins 32. The carrier 31 is an annular member centered on a central axis 91. The carrier 31 is supported so as to be rotatable around the central axis 91. The carrier 31 has multiple window portions 33. The window portions 33 are holes that penetrate the carrier 31 in the radial direction. The multiple window portions 33 are provided at equal intervals around the central axis 91. The multiple carrier pins 32 are fixed to the carrier 31 with intervals in the circumferential direction. Each carrier pin 32 extends axially along the planetary axis 92 at the window portion 33.

The planetary gear 20 is disposed within the window portion 33 of the carrier 31. The planetary gear 20 is rotatably supported on the carrier pin 32 via a pair of bearings 34. Ball bearings are used for the bearings 34. The planetary gear 20 can revolve around the central axis 91 together with the carrier 31 while rotating around the planetary shaft 92.

The first internal gear 40 is an annular gear that meshes with the first planetary gear 21 on the radial outside of the multiple planetary gears 20. The first internal gear 40 is arranged coaxially with the central axis 91. The first internal gear 40 is fixed to a casing (not shown). Therefore, even when the planetary reduction gear 1 is driven, the first internal gear 40 is kept stationary. The first internal gear 40 has multiple first internal teeth 41. The multiple first internal teeth 41 are arranged at a constant angular pitch centered on the central axis 91. Each first internal tooth 41 protrudes radially inward on the inner peripheral surface of the first internal gear 40. The first gear teeth 211 of the first planetary gear 21 described above mesh with the first internal teeth 41 of the first internal gear 40.

The second internal gear 50 is an annular gear that meshes with the second planetary gear 22 on the radially outer side of the multiple planetary gears 20. The second internal gear 50 is located on the output side of the first internal gear 40. The second internal gear 50 is also arranged coaxially with the central axis 91. The second internal gear 50 is rotatably supported via a bearing in a casing (not shown). A bearing 35 is also interposed between the carrier 31 and the second internal gear 50. Therefore, the carrier 31 and the second internal gear 50 can rotate at different rotation speeds.

The second internal gear 50 has a plurality of second internal teeth 51. The second internal teeth 51 are arranged at a constant angular pitch around the central axis 91. Each second internal tooth 51 protrudes radially inward on the inner circumferential surface of the second internal gear 50. The second gear teeth 221 of the second planetary gear 22 described above mesh with the second internal teeth 51 of the second internal gear 50. The number of first internal teeth 41 of the first internal gear 40 is different from the number of second internal teeth 51 of the second internal gear 50.

The output shaft 60 is a shaft that is disposed along the central axis 91. The output shaft 60 is located on the output side of the carrier 31. In this embodiment, the second internal gear 50 and the output shaft 60 are formed from a single member. However, the second internal gear 50 and the output shaft 60 may be separate members.

When the sun gear 10 rotates at the first rotation speed, the planetary gears 20 rotate about the planetary shaft 92 due to meshing with the sun gear 10. Furthermore, the planetary gears 20 revolve around the sun gear 10 along the first internal gear 40 due to meshing with the first internal gear 40. That is, the multiple planetary gears 20 revolve around the central shaft 91 while rotating about the planetary shaft 92. At this time, the rotation speed of the planetary gears 20 revolving around the central shaft 91 is an intermediate rotation speed that is lower than the first rotation speed.

As described above, the number of first internal teeth 41 of the first internal gear 40 is different from the number of second internal teeth 51 of the second internal gear 50. Therefore, as the planetary gear 20 revolves, the second internal gear 50 rotates at a rotation speed corresponding to the difference in the number of teeth relative to the first internal gear 40. The rotation speed of this second internal gear 50 becomes a second rotation speed that is even lower than the intermediate rotation speed. As a result, the second internal gear 50 and the output shaft 60 rotate at the second rotation speed around the central axis 91. Therefore, a rotational motion of the second rotation speed after deceleration can be extracted from the output shaft 60.

<2. Planetary gears and bearings>
Next, a more detailed description will be given of the structure of the planetary gear 20 and the pair of bearings 34 that support the planetary gear 20. FIG.

As shown in FIG. 3, the second planetary gear 22 has a gear portion 222 having the above-mentioned multiple second gear teeth 221, and an insertion portion 223 located on the input side of the gear portion 222. The insertion portion 223 is inserted into the inside of the first planetary gear 21. At that time, the spline 224 provided on the outer peripheral surface of the insertion portion 223 fits into the first spline 212 provided on the inner peripheral surface of the first planetary gear 21. This fixes the first planetary gear 21 and the second planetary gear 22.

In this embodiment, the inner circumferential surface of the second planetary gear 22 is the inner circumferential surface of the planetary gear 20. The second planetary gear 22 has a protrusion 225 on its inner circumferential surface. The protrusion 225 is an annular protrusion that protrudes toward the planetary shaft 92. As a result, the inner circumferential surface of the second planetary gear 22 has a first inner circumferential surface 226 and a pair of second inner circumferential surfaces 227. The first inner circumferential surface 226 is the inner circumferential surface of the protrusion 225. The axial length of the first inner circumferential surface 226 is shorter than the axial length of the planetary gear 20. One of the pair of second inner circumferential surfaces 227 is located on the input side of the protrusion 225. The other of the pair of second inner circumferential surfaces 227 is located on the output side of the protrusion 225. That is, the first inner circumferential surface 226 is located between the pair of second inner circumferential surfaces 227 in the axial direction. Additionally, the diameter of the first inner circumferential surface 226 is smaller than the diameter of the pair of second inner circumferential surfaces 227.

As shown in FIG. 3, each of the pair of bearings 34 has an annular inner ring 71, an annular outer ring 72, and a number of spheres 73. The inner ring 71 is fixed to the carrier pin 32. The outer ring 72 is located outside the inner ring 71 and is fixed to the second planetary gear 22. The multiple spheres 73 are interposed between the inner ring 71 and the outer ring 72.

The outer ring 72 has an annular flange portion 721. The flange portion 721 protrudes from the outer peripheral surface of the outer ring 72 in a direction away from the carrier pin 32. In the following, the flange portion 721 of the input side bearing 34 of the pair of bearings 34 is referred to as the "first flange portion 721a", and the flange portion 721 of the output side bearing 34 is referred to as the "second flange portion 721b". The first flange portion 721a protrudes outward from the input side end of the outer ring 72 of the input side bearing 34. The second flange portion 721b protrudes outward from the output side end of the outer ring 72 of the output side bearing 34.

The protrusion 225 of the second planetary gear 22 is located between the first flange portion 721a and the second flange portion 721b. The first inner peripheral surface 226, which is the inner peripheral surface of the protrusion 225, is fixed to the outer ring 72. This fixes the planetary gear 20 to the outer ring 72. For example, shrink fitting is used as a method for fixing the first inner peripheral surface 226 to the outer ring 72. However, other fixing methods such as press fitting or adhesives may be used instead of shrink fitting.

The input end face of the protrusion 225 contacts the output side face of the first flange portion 721a. The output end face of the protrusion 225 contacts the input side face of the second flange portion 721b. This positions the planetary gear 20 in the axial direction with respect to the pair of bearings 34.

In this manner, in the structure of this embodiment, the planetary gear 20 is positioned in the axial direction by the flange portions 721 of the pair of bearings 34. This makes it possible to eliminate the rotational resistance caused by the contact of the end faces of the planetary gear 20 by making the axial end faces of the planetary gear 20 non-contact. Therefore, there is no need to provide a member for reducing the rotational resistance. This allows the number of parts in the planetary reducer 1 to be reduced. In addition, the axial dimension of the planetary reducer 1 can be reduced.

The inner circumference of the planetary gear 20 is fixed to the outer ring 72 of the bearing 34 between a pair of flanges 721. Therefore, of the entire inner circumference of the planetary gear 20, only the first inner circumference 226 located between the pair of flanges 721 requires high dimensional accuracy for fixing. This makes it easier to machine the inner circumference of the planetary gear 20.

The flange portion 721 and the second inner peripheral surface 227 of the planetary gear 20 face each other. A gap 74 exists between the flange portion 721 and the second inner peripheral surface 227 of the planetary gear 20. In other words, among the inner peripheral surfaces of the planetary gear 20, the pair of second inner peripheral surfaces 227 do not contact the outer ring 72 of the bearing 34. Therefore, high dimensional accuracy is not required for the second inner peripheral surfaces 227. This makes it easier to machine the planetary gear 20.

In addition, in the structure of this embodiment, the first flange portion 721a is located closer to the output side than the input side end face of the planetary gear 20. Also, the second flange portion 721b is located closer to the input side than the output side end face of the planetary gear 20. That is, in the axial direction, the pair of flange portions 721 are contained between both axial end faces of the planetary gear 20. Therefore, in addition to the axial dimension of the planetary gear 20, there is no need to ensure an axial dimension for arranging the pair of flange portions 721. Therefore, the overall axial length of the planetary reducer 1 can be reduced.

As shown in FIG. 3, the planetary reducer 1 of this embodiment is provided with a pair of annular washers 75. One of the pair of washers 75 is interposed in the axial gap between the input side end face of the inner ring 71 of the input side bearing 34 and a part of the carrier 31. The other of the pair of washers 75 is interposed in the axial gap between the output side end face of the inner ring 71 of the output side bearing 34 and a part of the carrier 31. In this way, an axial gap of the thickness of the washer 75 can be secured between the bearing 34 and the carrier 31. This allows the axial end faces of the planetary gear 20 and the carrier 31 to be kept in a non-contact state. As a result, sliding friction between the planetary gear 20 and the carrier 31 can be eliminated.

Of the surfaces constituting the window portion 33 of the carrier 31, the surfaces other than the surface that contacts the washer 75 are non-contact surfaces. Therefore, when manufacturing the carrier 31, it is sufficient to process only the surface that contacts the washer 75 among the surfaces constituting the window portion 33 with high dimensional accuracy. This makes it easier to manufacture the carrier 31.

3. Modifications
Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. Various modified examples will be described below, focusing on the differences from the above embodiment.

<3-1. First modified example>
4 is a partial vertical cross-sectional view of the planetary gear 20 and the bearing 34 of the planetary reducer 1 according to the first modified example. The planetary reducer 1 of the first modified example includes an annular shim 76 in addition to the pair of washers 75 described above.

The shim 76 is interposed in the axial gap between the inner ring 71 of one of the pair of bearings 34 and a part of the carrier 31. When manufacturing the planetary reducer 1, the axial position of the inner ring 71 relative to the carrier 31 is adjusted by selecting the number or thickness of the shims 76. This allows the bearing 34 to be preloaded in the axial direction. As a result, the gap between the inner ring 71 and the sphere 73, and between the sphere 73 and the outer ring 72, can be reduced. This allows the backlash of the rotational motion after deceleration to be reduced.

In addition, instead of the shim 76, a preload may be applied to the inner ring 71 of the bearing 34 using an elastic member such as a wave washer.

<3-2. Second modified example>
5 is a vertical cross-sectional view of a planetary reduction gear 1 according to a second modified example. The planetary reduction gear 1 according to the second modified example does not include a second internal gear 50. Furthermore, the planetary gear 20 does not have second gear teeth 221. The carrier 31 and the output shaft 60 are formed from a single member. In this planetary reduction gear 1, the intermediate rotation speed, which is the rotation speed of the carrier 31, is taken out of the output shaft 60 as the second rotation speed after reduction.

In the planetary reduction gear 1 of this modified example, the planetary gear 20 is also positioned in the axial direction by flange portions 721 provided on a pair of bearings 34. The inner peripheral portion of the planetary gear 20 is fixed to the outer ring 72 of the bearing 34 between the pair of flange portions 721. As a result, as in the above embodiment, it is possible to obtain the effects of reducing the number of parts of the planetary reduction gear 1, reducing the axial dimension, and making it easier to machine the inner peripheral portion of the planetary gear 20.

<3-3. Other Modifications>
The detailed shape of the planetary reducer may differ from the shapes shown in the drawings of the present application. Furthermore, the elements appearing in the above-described embodiment and modified examples may be appropriately combined to the extent that no contradiction occurs.

This invention can be used in planetary reducers.

LIST OF SYMBOLS 1 Planetary reducer 10 Sun gear 11 Input shaft 12 External teeth 20 Planetary gear 21 First planetary gear 22 Second planetary gear 23 Pin hole 30 Planetary support portion 31 Carrier 32 Carrier pin 33 Window portion 34 Bearing 35 Bearing 40 First internal gear 41 First internal teeth 50 Second internal gear 51 Second internal teeth 60 Output shaft 71 Inner ring 72 Outer ring 73 Sphere 74 Gap 75 Washer 76 Shim 91 Central shaft 92 Planetary shaft 211 First gear teeth 212 First spline 221 Second gear teeth 222 Gear portion 223 Insertion portion 224 Spline 225 Protrusion 226 First inner circumferential surface 227 Second inner circumferential surface 721 Flange portion 721a First flange portion 721b Second flange portion

Claims (6)

A planetary reducer that reduces a rotational motion of a first rotation speed to a rotational motion of a second rotation speed lower than the first rotation speed,
a sun gear rotating at the first rotational speed about a central axis;
a plurality of planetary gears that mesh with the sun gear on the radially outer side of the sun gear;
A plurality of carrier pins supporting the plurality of planetary gears;
a carrier that fixes the plurality of carrier pins at intervals in a circumferential direction;
a pair of bearings that rotatably support the planetary gear relative to the carrier pin;
an annular internal gear that meshes with the planetary gears on the radially outer side of the planetary gears;
Equipped with
Each of the pair of bearings is
An inner ring fixed to the carrier pin;
An outer ring fixed to the planetary gear;
A plurality of spheres interposed between the inner ring and the outer ring;
having
The outer ring is
A flange portion protruding in a direction away from the carrier pin,
An inner circumferential portion of the planetary gear is fixed to the outer ring between the pair of flange portions,
an axial length of the inner peripheral portion of the planetary gear is shorter than an axial length of the planetary gear,
The planetary gear is
a first inner circumferential surface fixed to the outer ring between the pair of flange portions;
a pair of second inner circumferential surfaces facing the pair of flange portions;
having
a gap exists between the flange portion and the second inner circumferential surface . 2. The planetary reducer according to claim 1 ,
The planetary reduction gear further comprises a washer interposed in an axial gap between a portion of the carrier and the inner ring. 3. The planetary reducer according to claim 1 or 2 ,
The planetary reduction gear further comprises a washer and a shim interposed in an axial gap between a portion of the carrier and the inner ring. A planetary reducer according to any one of claims 1 to 3 ,
The planetary gear is
a first planetary gear having a plurality of first gear teeth;
a second planetary gear having a plurality of second gear teeth and a smaller diameter than the first planetary gear;
having
The internal gear is
a first internal gear having an annular shape that meshes with the first planetary gear;
a second internal gear having an annular shape that meshes with the second planetary gear;
having
A planetary reduction gear, wherein the second internal gear rotates at a second rotational speed after reduction relative to the first internal gear. A planetary reducer according to any one of claims 1 to 4 ,
The internal gear is fixed to a casing of the planetary reduction gear,
The carrier rotates at a second rotational speed after reduction in speed. A planetary reducer according to any one of claims 1 to 5 ,
The carrier is a cage-type carrier having a plurality of windows in which the planetary gears are arranged.

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