JPH04370443A - Internal planetary gear structure - Google Patents

Abstract

PURPOSE:To increase the strength and roundness of each member and to reduce size and weight by introducing a powder injection molding method for manufacture of an internal planetary gear structure. CONSTITUTION:In an internal planetary gear structure, a prototype for a main part is produced by metallic powder injection molding. Sizing and coining are applied on the prototype and surface treatment, such as cementation and nitrification, is further applied thereon. This method ensures size precision, such as roundness, as the advantages, for example, high strength and mass-production possibility of injection molding for metallic powder are maintained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal planetary gear structure suitable for application to a speed reducer or a speed increaser, and particularly to a speed reducer or speed increaser that is small and requires high output.

0002

2. Description of the Related Art Conventionally, a first shaft, an external gear mounted eccentrically on the first shaft, an internal gear with which the external gear internally meshes, and an external gear with which the external gear meshes with the external gear. BACKGROUND ART An internally meshing planetary gear structure is widely known, which includes a second shaft connected through a means for transmitting only the rotational component of the gear.

A conventional example of this structure is shown in FIG. In this conventional example, the above structure is applied to a "reducer" by using the first shaft as an input shaft, the second shaft as an output shaft, and fixing an internal gear.

[0004] An eccentric body 3 is fitted onto the input shaft 1 . An external gear 5 is attached to this eccentric body 3. This external gear 5 is provided with a plurality of inner roller holes 6, into which an inner pin 7 and an inner roller 8 are fitted.

[0005] The outer circumference of the external gear 5 is provided with external teeth such as a trochoidal tooth shape or a circular arc tooth shape. These external teeth are internally meshed with the internal teeth of an internal gear 10 fixed to the casing 12.

The inner pin 7 passing through the external gear 5 is fixed to or fitted into the flange portion 14 of the output shaft 2.

When the input shaft 1 rotates once, the eccentric body 3 rotates once. With one rotation of the eccentric body 3, the external gear 5 also tries to perform rocking rotation around the input shaft 1, but the internal gear 10
Since its rotation is restrained by this, the external gear 5 almost only oscillates while being inscribed in the internal gear 10.

For example, if the number of teeth of the external gear 5 is N and the number of teeth of the internal gear 10 is N+1, the difference in the number of teeth is 1. Therefore, for each rotation of the input shaft 1, the external gear 5 shifts (rotates) by one tooth with respect to the internal gear 10 fixed to the casing 12. This means that one rotation of the input shaft is reduced to -1/N rotation of the external gear.

The oscillating component of the rotation of the external gear 5 is absorbed by the gap between the inner roller hole 6 and the inner pin 7, and only the rotational component is transmitted to the output shaft 2 via the inner pin 7.

As a result, a deceleration of -1/N is finally achieved.

[0011] In this conventional example, the internal gear is fixed,
Although the first shaft is used as the input shaft and the second shaft is used as the output shaft, the reduction gear can also be constructed by fixing the second shaft and using the internal gear as the output shaft. Furthermore, it is also possible to configure a speed increaser by reversing these inputs and outputs.

[0012] By the way, in the speed reducer employing such a conventional internally meshing planetary gear structure, members such as the first shaft, second shaft, internal gear, and external gear have dimensions. The reality is that most of them have been manufactured by machining because high precision is required and appropriate quality is required in terms of surface roughness.

[0013]

[Problems to be Solved by the Invention] However, when manufacturing individual parts by machining in this way, especially when manufacturing small speed reducers, mass production is difficult.
Therefore, there is a problem that it is easy to take time and cost.

Further, processing methods such as pressing and die casting are suitable for mass production, but have the problem that high output cannot be obtained because they are inferior in terms of accuracy and material strength.

[0015] Furthermore, if these parts are manufactured by integral molding of plastic, advantages such as improved assembly, reduced number of parts, and cost reduction can be obtained as a small speed reducer, but they lack strength. It has the disadvantage that high output cannot be expected and continuous operation is difficult because it becomes unusable when the temperature becomes high.

[0016] Furthermore, when these parts are integrally molded using the sintering method, advantages such as low cost and mass production can be obtained for small speed reducers, but sintered products generally have a low density and are It has the disadvantage of being lower in strength than steel.

Therefore, when surface treatments such as carburizing and nitriding are attempted, the interior is carburized and nitrided through the open pores (communicating holes), making surface treatment practically impossible and causing problems in wear resistance. remains.

[0018] In order to overcome this drawback, it is necessary to perform heat treatment after sintering, and the dimensional accuracy deteriorates during the heat treatment.
The reality is that in some cases, machining must be used in combination.

[0019] Also, since sintering is a type of press forming,
The coaxiality is very poor, and therefore machining must be used in combination with gears that require highly accurate coaxiality, such as the above-mentioned planetary gear structure speed reducer, which is the object of the present invention.

Furthermore, since the average particle size of the raw material powder in sintering is relatively large, the surface roughness is poor, and when used as gears, for example, it is expected that some problems will occur in terms of rolling fatigue strength. . If the size of the raw material powder is large, if you try to apply it to a small speed reducer, the tooth profile module will become smaller, resulting in poor tooth profile shape, so the dimensions (
There is also the problem of being limited by modules. Furthermore, since the porous portion has a notch effect, there is also the problem that the bending strength of the protruding portion in particular decreases.

In addition, sintering is two-dimensional forming, it is difficult to form a multi-stage shape due to the press jig, and thin (1.5
It also has drawbacks such as difficulty in manufacturing parts (less than mm) and difficulty in forming long-axis thin-walled products.

[0022] The present invention has been made in view of these conventional problems, and is capable of achieving high output with a small size, reducing cost and mass production, and also enables continuous operation. The purpose is to provide such an internal planetary gear structure.

[0023]

[Means for Solving the Problems] The present invention provides a first shaft, an external gear eccentrically attached to the first shaft, an internal gear with which the external gear internally meshes, and An internal planetary gear structure comprising: a second shaft connected to the external gear via a means for transmitting only an autorotation component of the external gear; the first shaft, the second shaft, the external gear; , the internal gear, and the rotational component transmission means, the original shape is manufactured by metal powder injection molding, and then sizing or coining is performed, and further, nitriding, carburizing, etc. The above object has been achieved by being manufactured by subjecting it to surface treatment.

[0024]

In the present invention, in the internally meshing planetary gear structure, at least a portion of at least one member constituting these is manufactured into its original shape by metal powder injection molding.

[0025] Metal powder injection molding has recently been attracting attention as one of the manufacturing methods next to machining, die casting, powder metallurgy, and lost wax. This metal powder injection molding method uses metal powder (average particle size of about 10 μm).
and an organic binder are kneaded (heated or at room temperature) to homogenize, and then granulated using a pelletizer etc. to form a molding material,
This molding material is injection molded using an injection molding machine.

[0026] A molded article formed by an injection molding machine is generally called a green part (green molded article). The binder is removed (degreased) from the green parts by heating, reduced pressure, pressurization, extraction, and supercritical methods. The degreased body from which the binder has been removed is generally called brown parts. Brown parts are exposed to gas atmosphere (N2, H2, N
H3, vacuum). Sintered bodies are generally called silver parts.

Manufacturing by injection molding of metal powder is optimal for manufacturing small-sized and complex-shaped mass-produced products such as the planetary gear structure that is the object of the present invention, and can produce high-strength, compact and high-output products. However, cost reduction and mass production are also possible. In addition, it can withstand high temperature use and can be operated continuously.

By the way, when actually manufacturing ring-shaped external gears 5 and internal gears 10 using this powder injection molding method, the sintering process involves a fairly large shrinkage, so the accuracy of the gears may be affected. In particular, a problem arose in that the roundness was impaired.

The reasons for this are: (1) These external gears 5 and internal gears 10 are thin ring-shaped parts;
As a result of the sintering process, which causes shrinkage of as much as 0 to 20%, Fig. 5(a)
), the gear pitch circle P tends to be elliptical, and the external gear 5 and internal gear 10 have holes for passing bolts, inner roller holes 6, etc., so injection molding is not possible. It is conceivable that local density differences may sometimes occur, resulting in non-uniform sintering shrinkage and the pitch circle becoming polygonal as shown in FIG. 5(b).

Therefore, if the target member of the present invention is simply manufactured by powder injection molding, it is difficult to ensure the dimensional accuracy such as roundness, verticality, and coaxiality required for the planetary gear structure. A problem arose.

Therefore, in the present invention, these members are first made into their original shapes by powder injection molding, and then subjected to sizing or coining (sizing and coining are effective after powder injection molding) to improve the roundness. After improving dimensional accuracy such as verticality and coaxiality, the material is subjected to nitriding or carburizing treatment to harden the surface and provide sufficient performance in all aspects of strength, precision, and wear resistance. This is how it was done.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows a reduction gear equipped with an internal meshing planetary gear structure to which the present invention is applied. Moreover, FIG. 2 is an exploded perspective view of this reduction gear.

In FIGS. 1 and 2, 21 is an external gear;
2 is an internal gear, 23 is an output shaft (second shaft), 24 is an input shaft (first shaft), 25 is an Oldham ring, 26 is an output shaft cover, 27 is an inner cover, and 28 is a bearing.

The input shaft 24 has an eccentric portion 24a formed therein. Note that there is a hole 2 in the shaft portion 24b of this input shaft 24.
4c is formed and has a so-called hollow structure.

An external gear 21 is attached to the eccentric portion 24a of the input shaft 24 via a bearing 28. Reference numeral 21a is a tooth portion of the external gear 21, 21b is an insertion portion of the bearing 28, and 21c is an Oldham groove portion that engages with the Oldham projection 25b of the Oldham ring 25.

The tooth portion 21a of the external gear 21 meshes with the internal gear 22. Reference numeral 22a in the figure indicates the internal gear 22.
22b is a spigot part, and 22c is a bolt hole for fastening.

The Oldham ring 25 has an Oldham groove 25a.
, Oldham's protrusion 25b. Oldham protrusion 25
b is the Oldham groove portion 2 of the external gear 21 as described above.
1c, and the Oldham groove 25a engages with the Oldham protrusion 23a that is integrally attached to the output shaft 23, absorbing the oscillation component of the external gear 21 by a well-known Oldham mechanism and outputting only the rotational component. The signal is transmitted to the shaft 23.

Note that reference numeral 23b in the figure is a hole provided in the flange of the output shaft 23, 23c is a cover receiving portion, and 23
d indicates the shaft portion, respectively.

When the input shaft 24 rotates once, the eccentric portion 2
4a also rotates once. It is assumed that the external gear 21 performs oscillating rotation around the input shaft 24 due to one rotation of the eccentric portion 24a, but since its rotation is restrained by the internal gear 22, the external gear 21 rotates around the input shaft 24. While being inscribed in 22, it will almost only swing.

For example, if the number of teeth of the external gear 21 is N and the number of teeth of the internal gear 22 is N+1, the difference in the number of teeth is 1. Therefore, every rotation of the input shaft 24 causes the external gear 21 to
is 1 for the internal gear 22 fixed to the casing 30.
It will shift (rotate) by the amount of teeth. This is input shaft 2
This means that one rotation of the external gear 21 is decelerated to -1/N of the rotation of the external gear 21. The oscillating component of the rotation of the external gear 21 is absorbed through the Oldham ring 25, and only the rotational component is transmitted to the output shaft 23. As a result, a deceleration of -1/N is finally achieved.

In this embodiment, in the external gear 21, the tooth portion 21a and the bearing insertion portion 21b are
, and the Oldham groove portion 21c are one-shot molded using the metal powder injection molding described above.

[0043] Also, in the internal gear 22, the tooth portion 2
2a, the spigot part 22b, and the tightening bolt hole part 22c are one-shot molded using metal powder injection molding.

The output shaft 23 also includes an Oldham projection 23a, a flange inner hole 23b, and a cover receiving portion 23c.
, and the shaft portion 23d are molded in one shot using injection molding of metal powder.

Furthermore, in the input shaft 24, the eccentric portion 2
4a, the shaft portion 24b, and the inner diameter hole 24c are formed by one-shot molding using metal powder injection molding.

In the Oldham ring 25, the Oldham groove 25a and the Oldham protrusion 25b are formed by one-shot molding using metal powder injection molding.

[0047] The raw material for injection molding of these metal powders is a relatively soft material that can be sized or coined later. For example, it is preferable to use a Fe-Cr-Mo alloy. However, the present invention does not limit the raw material of the metal powder to this type of alloy.

Next, as shown in FIG. 3, the members whose original shapes have been formed in this way are subjected to coining or sizing, which is a well-known technique such as powder metallurgy, to make these members perfect circles. Improve dimensional accuracy such as degree, verticality, coaxiality, etc.

[0049] Both sizing and coining are processes for making the surface clean and ensuring dimensional accuracy.
Sizing is generally performed by lubrication treatment such as oil impregnation and zinc phosphate film treatment (so-called bonding).

[0050] Furthermore, coining is usually performed cold at a low temperature to reduce the amount of deformation.

Next, the above member is nitrided using, for example, an ion nitriding device to harden the surface. At this time, it is preferable to use an ion nitriding device because the distortion caused by the surface treatment is minimized. Therefore, other surface treatment methods such as nitriding and carburizing may be used as long as they are permissible in terms of dimensional accuracy.

In this way, by manufacturing the important parts of the reducer by a combination of injection molding of metal powder → sizing or coining → surface treatment such as nitriding and carburizing, we can create a reducer that is small but can achieve high output. You will be able to do this.

[0053] Furthermore, if the reduction gear itself can be made smaller, the circumferential speed of the gears can be reduced, and the friction in the meshing portions can also be reduced. Moreover, even though it is small, since the gear parts are made of metal, it is possible to obtain much higher output compared to using plastic, etc. for the gear parts, and continuous operation is possible because it can be used at high temperatures. It is also possible to obtain the effect that

Furthermore, it is possible to reduce noise, improve transmission efficiency, and improve durability.

[0055] In the above embodiment, all the main parts of most of the members were manufactured by the manufacturing process according to the present invention, but in the present invention, it is not always necessary to manufacture all the above parts by this manufacturing process. There's no need.

[0056]

[Effects of the Invention] As explained above, according to the present invention, an internally meshing planetary planet which is small in size yet can achieve high output, enables cost reduction, mass production, and continuous operation. A gear structure can be obtained, and as a result, this structure can be used to manufacture a reduction gear or a speed increaser having the above-mentioned effects as they are, which is an excellent effect.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical sectional view of a reduction gear to which the present invention is applied.

FIG. 2 is a perspective view showing the reducer shown in FIG. 1 exploded into parts.

FIG. 3 is a process diagram showing the manufacturing process of the reduction gear.

FIG. 4 is a sectional view showing a reduction gear employing a conventional internal planetary gear structure.

FIGS. 5(a) and 5(b) are diagrams illustrating the roundness of an internal gear.

[Explanation of symbols]

21...external gear, 22...Internal gear, 23...output shaft, 24...Input shaft, 25...Oldham ring, 26...Output shaft cover, 27...Inner cover, 28...Bearing.

Claims (1)

[Claims] Claims: 1. A first shaft, an external gear mounted eccentrically on the first shaft, an internal gear with which the external gear internally meshes, and the external gear on the external gear. and a second shaft connected through a means for transmitting only the rotational component of the first shaft, the second shaft, the external gear, the internal gear, and the rotational component. At least a part of at least one member of the transmission means is manufactured by producing an original shape by metal powder injection molding, followed by sizing or coining, and further surface treatment such as nitriding or carburizing. Internal planetary gear structure.