Internally meshing planetary gear structure of the flexible gear type

Abstract: An internally meshing planetary gear structure of the flexible gear type is intended to achieve the lightening, miniaturization and high load capacity by increasing the meshing points of the gear even if the difference in the teeth number between the external gear and the internal gear is two or more. The difference in the teeth number between each of the external gears and the internal gear is set to be N (N: integer being two or more), the tooth profile of the external gear is constructed on the basis of the innermost enveloping curve of N epitrochoid parallel curves which are superposed to be shifted in phase from each other, and the tooth profile of the internal gear is constructed on the basis of the innermost enveloping curve of N trochoid internally enveloping curves which mesh with the above epitrochoid parallel curves and which are superposed to be shifted from each other by the same phase as in the external gear.

Description: The present invention relates to an internally meshing planetary gear structure of the flexible gear type, that is, the so-called wave gear structure for a small sized reduction or speed up gear. As a flexible meshing type planetary gear structure, there has been known such a technique as described in Japanese Patent Laid-open No. sho 63-130949. Hereinafter, this technique will be explained. Fig. 6 is a sectional view showing the structure according to the prior art; and Fig. 7 is a sectional view taken along the line VII- VII of Fig. 6. In general, this structure is called as a wave gear structure. An external spline 22A is provided on an input rotating shaft 21. It is connected to an internal spline 22B provided on an eccentric body 23 as a wave generator. An eccentric body bearing 24 is provided around the outer periphery of the eccentric body 23. An external gear 28 is provided around the outer periphery of the eccentric body bearing 24. The external gear 28 is constituted of a flange portion 29, annular portion 30 and an external teeth portion 31. The external teeth portion 31 is positioned around the outer periphery of an outer ring 27 of the eccentric body bearing 24. In the above, the outer ring 27, annular portion 30 and the external teeth portion 31 are able to be flexibly deformed. External teeth 31A provided around the external teeth portion 31 are constituted of a trochoid tooth profile or the like. The external teeth 31A mesh with internal teeth 33A constituted of pins rotatably supported by the internal gear 32. The external teeth 31A is smaller in the teeth number than the internal teeth (pins) of the internal gear 32 by two pieces. The configuration of the external teeth 31A is so constructed that two of the epitrochoid curves in which the radius ratio between the rolling circle and the base circle is an integer are superposed to be shifted in phase from each other, and the innermost one of the superposed curves is taken as the tooth profile curve. This configuration is disclosed in Japanese Patent Publication No. 1208548. The rotation is transmitted from the input rotating shaft 21 to the wave generator (eccentric body 23). The eccentric body 23 deforms the external teeth portion 31 of the external gear 28 through the eccentric gear bearing 24. As the external teeth portion 31 is deformed by the projecting portions of the eccentric body 23, the external teeth 31A mesh with the internal teeth (pins) 33. Accordingly, the external teeth portion 31 is shifted in phase by the difference in the teeth number between the external teeth 31A and the pins 33A during one rotation of the eccentric body 23. By such shifting, the external gear 28 is rotated, which is transmitted to the output shaft 34. Specifically, in this example, the teeth number of the external teeth 31A is 100, and the teeth number of the internal teeth (pins) 33A is 102. Consequently, the difference in the teeth number is 2, so that the reduction ratio is (-2/100= -1/50). Here, the internal gear 32 is fixed. However, as for the external gear 28 and the internal gear 32, if one is fixed, the other relatively becomes the output side. Also, if the output shaft is taken as the input side, the input rotating shaft becomes the output shaft for taking out the increased output. In the prior art gear device as explained above, the internal teeth (pins) 33A constituting the circular arc tooth profile portion of the internal gear mesh with the external teeth 31A of the external gear 28 having the trochoid tooth profile or the like. Accordingly, the internal gear 32 is contacted with the external gear 28 at one contact point. As a result, in the internal gear 32 constituted of the circular arc tooth profile having the same radius, the allowable load is almost determined depending on the restriction of the surface pressure applied to the tooth surface. This has a limitation to the miniaturization of the wave gear device and the enhancement of the load capacity. In a planetary reduction gear using a circular arc tooth profile (external pins) as the internal gear tooth profile and a torochoid teeth profile as the external gear tooth profile (this is well known as the trademark registration "CYCLO" reduction gear according to the present applicant), as described above, the above problem (limitation in the load applied to the tooth surface) has been solved by the improvement of the tooth profile as shown in Japanese Patent Publication No. sho 63-4056. Namely, as described above with reference to Fig.8 showing the meshing state of the above tooth profile , in this planetary reduction gear, the epitrochoid parallel curve (see Fig. 9 ) is used as the external gear tooth profile 9 and a trochoid internally enveloping line (see Fig. 10 ) is used as the internal gear tooth profile 11. This makes it possible to increase the meshing points between the external gear and the internal gear at two points, and hence to achieve the improvement of the load applied on the tooth surface. More specifically, in this technique, as shown in Fig. 8 , the tooth profile of the external teeth 9 of the external gears is constituted of an epitrochoid parallel curve. On the other hand, the tooth profile of the internal teeth 11 of the internal gear 10 is constituted of a trochoid internally enveloping line composed of circular arc tooth profile portions P and P at both ends and a tooth profile portion Q at the intermediate portion (this portion is mated to the tooth profile of the external teeth which is constituted of the epitrochoid parallel curve). In the gear structure of the above prior art, the improvement of the tooth profiles makes possible the contact at two points. Therefore, it is possible to reduce the surface pressure applied to the tooth surface, resulting in the miniaturization of the device and in the enhancement of the load capacity. However, even using the above tooth profiles, there is a limitation to the enhancement of the load ability on the tooth surface yet. Thus, the higher load ability on the tooth surface has been required to further achieve the miniaturization and lightening of the reduction gear. Accordingly, it may be considered that the above problem is solved by applying the above tooth profiles to the above wave gear device. However, in the above planetary reduction gear, the difference in the teeth number between the external gear and the internal gear is one. On the other hand, in the wave gear device, the difference in the teeth number must be an integer being two or more. Namely, in the wave gear device, it is preferred that the difference in the teeth number is the integer magnification of the number of the projecting portions of the eccentric body 23 as the wave generator. Since the number of the projecting portions of the eccentric body is two or more for balancing the load, so that the difference in the teeth number becomes an integer being 2 or more. Therefore, the above tooth profiles cannot be directly applied to the wave gear device as they are. The object of the present invention is to provide an internally meshing planetary gear structure of the flexible gear type, wherein the internal teeth and the external teeth are constructed on the basis of the tooth profiles used in the prior art internally meshing planetary reduction gear, thereby realizing the lightweight, compact and high performance reduction or speed up gear. According to the present invention, there is provided an internally meshing planetary gear structure of the flexible gear type as defined in claim 1. Therefore, in the case of obtaining the same reduction ratio as in the case that the difference in the teeth number is one, it is possible to increase the teeth number of the internal gear and the external gear by the magnification of N as compared with the prior art in addition to two points meshing. This makes it possible to increase the meshing teeth number in the area effective for the load transmission, and to reduce the meshing in the area not effective for the power transmission and being larger in sliding. Therefore, it is possible to reduce the surface pressure at the contact point and to reduce the loss in the power transmission. Incidentally, in the technique as shown in Japanese Patent Publication No. sho 63-4056 described above, the difference in the teeth number is one. It is difficult to apply this technique to the case that the difference in the teeth number N is two or more as it is. In this regard, according to the the present invention, by use of the above construction, the external gear can be contacted with the internal gear at two points in the area effective for the load transmission even if the difference in the teeth number N is two or more. Since the tooth profile as described in Japanese Patent Publication No. sho 63-4056 can be applied to the wave gear device having a difference in the number of teeth of two or more, as a result, the external teeth of the external gear can be contacted (meshed) with the internal teeth of the internal gear at the multi-points in the area effective for the load transmission. In addition, when the phase-shifting amounts of the epitrochoid parallel curves in N pieces according to the external gear, and the trochoid internally enveloping lines in N pieces according to the internal gear are respectively set to be 1/N of one tooth, it is possible to keep the strength and the other characteristics at the same level for all the teeth. The above and other features and advantages of the present invention will become more apparent from the following description of the invention taken in conjunction with the accompanying drawings, wherein like reference characters designate the same or similar parts, and wherein: Fig. 1 is a sectional view showing the main part of an embodiment of the present invention, which is taken from a location equivalent to the section taken along the line VII-VII of Fig. 6; Fig. 2 is an enlarged view of the tooth profile (formed by superposing epitrochoid parallel curves) of each external gear in the embodiment; Fig. 3 is an enlarged view of the tooth profile (formed by superposing the trochoid internally enveloping lines) of internal teeth of an internal gear in the embodiment; Fig.4 is a partially enlarged view of a meshing portion between the external gear and the internal gear of the embodiment; Fig. 5 is a view of a meshing portion where the rotational phase is slightly shifted from the condition of Fig. 4 ; Fig. 6 is a sectional view showing the whole construction of an example of a flexible meshing type gear meshing structure common to the embodiment of the present invention and the prior art; Fig. 7 is a sectional view taken along the line VII-VII of Fig. 6; Fig. 8 is a view of a meshing portion between the external gear and the internal gear according to the the prior art; Fig. 9 is an enlarged view of the tooth profile (formed by superposing epitrochoid parallel curves) of external teeth of each external gear according to the prior art planetary reduction gear (difference in teeth number: 1); and Fig. 10 is an enlarged view of the tooth profile (formed by superposing the trochoid internally enveloping lines) of internal teeth of an internal gear of the prior art planetary reduction gear (difference in teeth number: 1). Hereinafter, one embodiment will be explained with reference to the accompanying drawings. The gear meshing structure of the embodiment has the same construction as that shown in Fig. 6 & 7, except that the tooth profile of external teeth (indicated at numeral 131A) and the tooth profile of internal teeth (indicated at numeral 133A) are different from those in the prior art. Accordingly, there will be mainly explained the tooth profiles of the external teeth 131A and internal teeth 133A, wherein only the numerals are displaced. Fig. 1 is a sectional view of the main part of an flexibly meshing type gear meshing structure according to the present invention, which is taken from a location equivalent to the section taken along the line VII-VII of Fig. 6. As shown in Fig.2, the tooth profile of the external teeth 131A of the external gears is constituted of the innermost curve of two epitrochoid parallel curves superposed to be shifted in phase from each other by 1/2 of one tooth. Also, the tooth profile of the internal teeth 133A of the internal gear 32 is constituted of the innermost curve of two trochoid internally enveloping lines which are superposed to be shifted in phase from each other by 1/2 of one tooth as shown in Fig. 3. The internal teeth 133A are not formed of pins but formed integrally with the main body material of the internal gear 32. Here, the term "innermost" means the "center side" of the external gear 28 or the internal gear 32. In the above, the basic superposed curves for the tooth profiles of the external teeth 131A and the internal teeth 133A are the tooth profile curves of the external teeth and the internal teeth as shown in Japanese Patent Publication No. sho 63-4056 (see Figs. 9 and 10). Specifically, the epitrochoid parallel curve is taken as the basic curve for the external teeth 131A. On the other hand, the internally enveloping line, which is formed by the external teeth composed of the epitrochoid parallel curve in the case where the teeth number between the external teeth and the internal teeth is 1, is taken as the basic curve for the internal teeth 133A. The reason why two of the above curves are superposed to be shifted in phase from each other by 1/2 of one tooth is that the difference in the teeth number between the external teeth and the internal teeth is two. If the difference in the teeth number is 3, the innermost curve of three curves superposed to be shifted in phase from each other by 1/3 of one tooth is taken as the tooth profile curve. In the case that the difference in the teeth number is three or more, similarly, the tooth profile curve is obtained by superposing the curves in the same number as the difference N in the teeth number. In addition, in the case where the difference in the teeth number is two, the shifting of two curves is not necessarily to be 1/2 of one tooth; however, in such a case, the shifting amounts must be the same for the external gear and for the internal gear. Also, in the case that the tooth profile is actually formed, the modification of the teeth may be made. For example, the teeth edges or teeth roots of the external teeth 131A and the internal teeth 133A are suitably rounded. By constructing the external teeth 131A and the internal teeth 133A as described above, the external teeth 131A of the external gear 28 and the internal teeth 133A of the internal gear 32 are contacted with each other at two points in the area effective for the load transmission, just as the gear of the device described in Japanese Patent Publication No. sho 63-4056. Figs. 4 and 5 show meshing states between the external teeth 131A and the internal teeth 133A when the eccentric body 23 is rotated, in the gear meshing structure of this embodiment. According to the flexible meshing type gear meshing structure of the present invention, since the meshing points between the external teeth of the external gear and the internal teeth of the internal gear are increased as compared with the prior art structure, it is possible to improve the load ability of the gear. Therefore, it is possible to obtain the lightweight, compact and high performance reduction or speed up gear.

Claims: An internally meshing planetary gear structure of the flexible gear type comprising: a rigid internal gear (32); a flexible external gear (28) externally meshing with the internal gear (32); and a wave generator (23) for flexibly deforming the external gear (28); wherein the difference in the teeth number between the external gear (28) and the internal gear (32) is set to be N which is an integer being two or more; characterized in that the tooth profile of the external gear (28) is constructed on the basis of the enveloping curve nearest to the center of the external gear (28) which is defined by superposition of N epitrochoid parallel curves which are shifted in phase relative to each other; and the tooth profile of the internal gear (32) is constructed on the basis of the enveloping curve nearest to the center of the internal gear (32) which is defined by N trochoid internally enveloping curves which mesh with the above epitrochoid parallel curves and which are superposed to be shifted from each other by the same phase as on the external gear (28). An internally flexible meshing planetary gear structure according to claim 1, wherein said phase-shifting amounts of the N epitrochoid parallel curves onto the external gear (28), and of the N trochoid internally enveloping curves on the internal gear (32) are respectively set to be 1/N of one tooth.

Inventors: HIRAO AKIRA, ISHIDA TOSHIHIRO, OGURA YUZO, HIRAO, AKIRA, ISHIDA, TOSHIHIRO, OGURA, YUZO
Applicants: SUMITOMO HEAVY INDUSTRIES, SUMITOMO HEAVY INDUSTRIES, LTD.
Application year: 1993
Main classification: F16H1
IPC codes: F16H55