An inscribed meshing planetary gear construction

Abstract: In an inscribed meshing planetary gear construction provided with a carrier pin (a carrier member) 116, rigidity and stability are improved and its entire length is shortened, resulting in that in particular, the connection between an input shaft 101 and an eccentric body 103 can be improved so as to reduce the number of component parts and the number of assembling steps. In order to realize this object, a flange part 114 of an output shaft 102, a carrier pin 116 and a support ring 117 are supported at both ends by a pair of bearings 115a and 115b, and then a reduction gear mechanism is disposed between bearings 115a and 115b. The input shaft 101 is formed with a D-cut part of cross section by cutting a part of its outer circumference in parallel with its axial direction. This cut part is utilized so as to set a circumferential position (a stop of rotation) between the input shaft 101 and an eccentric body 103. A carrier pin 116 has a pipe-like spacer 125 at its central part, the axial position of the flange part 114, the carrier pin 116 and the support ring 117 is set through a spacer 125.

Description: This invention relates to an inscribed meshing planetary gear construction according to the precharacterizing portion of claim 1 as it is preferably applied to a speed increasing gear or a reduction gear, more particularly, a small-sized speed increasing gear or a reduction gear in which a high output torque is required. In the prior art, it is widely known to provide a speed increasing gear or a reduction gear employing an inscribed meshing planetary gear construction comprising a first shaft, an external-tooth gear mounted (assembled) on the first shaft through a eccentric body in a state where the external-tooth gear can be rotated eccentric around the first shaft, an internal-tooth gear with which the external-tooth gear is inscribed and meshed, and a second shaft connected to the external-tooth gear through means for transmitting only the rotation component of the external-tooth gear. An example of the prior art of this construction is shown in Figs. 8 and 9. This prior art is constructed such that said first shaft is applied as an input shaft, said second shaft is applied as an output shaft and at the same time said construction is applied to a reduction gear by fixing the internal-tooth gear. Eccentric bodies 3a, 3b are fitted to the input shaft 1 with a predetermined phase difference (180° in this example). The eccentric bodies 3a, 3b are integrated into one body. Two external-tooth gears 5a, 5b are placed on to each of these eccentric bodies 3a, 3b through eccentric bearings 4a, 4b. A plurality of inner roller holes 6 are provided in the external-tooth gears 5a, 5b and then an inner pin 7 and an inner roller 8 are fitted in these roller holes. A main object of providing two external-tooth gears (in plural rows) is to increase a transmittance capacity, maintain a strength and keep a rotational balance. External teeth 9 such as trochoidal teeth or circular teeth etc. are provided at outer circumferences of said external-tooth gears 5a, 5b. The outer teeth 9 are inscribed and meshed with the internal-tooth gear 10 fixed to a casing 12. The internal teeth of the internal-tooth gear 10 are constructed such that an outer pin 11 is loosely fitted to an inner pin hole 13 and held to be easily rotatable. An inner pin 7 passing through said external-tooth gears 5a, 5b is tightly fitted to or fixed to a flange part 14 of the output shaft 2. When the input shaft 1 is rotated once, the eccentric bodies 3a, 3b is also rotated once. The external-tooth gears 5a, 5b are apt to oscillatebly rotate around the input shaft 1 through this one revolution of the eccentric bodies 3a and 3b. However, since the rotation is restricted by the internal-tooth gear 10, the external-tooth gears 5a, 5b almost merely perform oscillation while being inscribed with the internal-tooth gear 10. Now, it is assumed that the number of teeth of the external-tooth gears 5a, 5b is N and the number of teeth of the internal-tooth gear 10 is N+1, then the difference between the numbers of teeth is 1. Consequently, the external-tooth gears 5a, 5b are displaced by one tooth relative to the internal-tooth gear 10 fixed to the casing 12 every time the input shaft 1 is rotated. This means that one revolution of the input shaft 1 is decelerated to a revolution of -1/N of the internal-tooth gear. Oscillation component of the external-tooth gears 5a, 5b is absorbed by clearances between the inner roller holes 6 and the inner pins 7 and then only the rotational component is transmitted to the output shaft 2 through the inner pins 7. In this case, the inner roller holes 6a, 6b and the inner pins 7 (inner rollers 8) form an "isokinetic inscribed meshing mechanism". As a result, finally, a reduction of reduction ratio -1/N can be accomplished. In the example of this prior art, the internal-tooth gear of the inscribed meshing planetary gear construction is fixed, the first shaft is an input shaft and the second shaft is an output shaft. However, a reduction gear can also be constructed by fixing the second shaft and applying the first shaft as an input shaft and the internal-tooth gear as an output shaft. Furthermore, a speed increasing gear can also be constructed by reversing these inputs and outputs. As described above, the inner pin 7 has a function to form an circular tooth acting as one of elements of said isokinetic inscribed meshing mechanism constructed with the inner roller holes 6a, 6b, and also has another function acting as a carrier member for transmitting a rotational force of a rotation of external-tooth gears 5a, 5b to the output shaft 2. In particular, in order to keep a superior former function, it was essential to provide the inner rollers 8 capable of being freely rotated around the outer circumference of the inner pins 7. The inner roller 8 shows a problem of expensive cost due to the fact that the material must be hard and both outer and inner circumferences thereof must be coaxially and accurately machined (processed or manufactured). In view of this fact, an idea has been proposed that the function which forms a circular tooth of one of the elements of the isokinetic inscribed meshing mechanism and another function which acts as a carrier member for transmitting a rotational force of the external-tooth gears 5a, 5b to the output shaft 2 are separated, and even if the inner roller 8 is eliminated, it has a similar performance to that of having the inner roller 8. It is an object of the present invention to create an inscribed meshing planetary gear construction of increased fatigue strength which may be produced at reduced manufacturing costs and which may be assembled in a time saving manner. According to the present invention, this object has been performed by an inscribed meshing planetary gear construction according to claim 1. Within such an inscribed meshing planetary gear construction, a part of an outer circumference of the first shaft is cut in parallel with its axial direction to form a cut part having the cross sectional shape of about D-shape, and this cut part is utilized to define a positioning in the circumferential direction of each of the first shaft and the eccentric body. In this case, an inner diameter of the bearing of the first shaft facing to the second shaft may be set to be slightly smaller than an outer diameter of the first shaft, and then a filling material is enclosed at a slight remained cut part. According to a preferred embodiment, a carrier member passes through the external-tooth gear and is disposed so that the external-tooth gear is held by the annular support ring and the flange part of the second shaft, and further both the support ring and the flanger part are supported at both ends at a casing through a pair of bearings. As a result, rigidity of the reduction gear mechanism, in particular, rigidity and stability in respect of the radial direction can be improved. Due to employment of this construction, it becomes possible to make an inner diameter of the bearing of the second shaft smaller, and a part of an outer circumference can be cut in parallel with an axial direction of the first shaft to enable D-shaped cut part. By forming the same shape hole including the cut part in the eccentric body, a position setting in the circumferential direction (stopping of rotation) can be obtained. Since the structure for preventing the rotation can be employed, the cut part line between the first shaft and the eccentric body are changed from an acute angle (prior art) to an obtuse angle so that a concentration of stress hardly occurs. Also, since a key which restricts a minimum thickness of the eccentric body is not present, it becomes possible to increase a diameter of the first shaft and at the same time it becomes possible to decrease an outer diameter of the eccentric body. Therefore, the load capacity can be increased or a more small sized eccentric body can be used in response to the application. In the prior art, since the machining of key-way in the first shaft had to be cut by an end mill whereby a machining efficiency was quite inferior and a mass productivity was poor. However, in the case where a D-shaped cut part is formed, after many input shafts are arranged, and then the cut part is formed by a broach machining whereby the machining efficiency can be remarkably improved and the mass productivity is further improved. As a result, a further cost-reduction can be attained. Also, the number of component parts can be naturally decreased in correspondence with no presence of key, so that the number of assembling operations can be reduced. Although there is no special problem even if an inner diameter of the bearing of the first shaft facing to the second shaft is completely smaller diameter than that of a flat surface of the cut part due to said both supporting structures, it may be slightly lower set than that of an outer diameter of the first shaft (to a degree in which the cut part is slightly remained) and a filling material may be filled in the cut part slightly remained. With such an arrangement, it becomes possible to present a reduction in strength of the bearing at the second shaft from increasing. As a filling material, either resin or solder or the like can be applied. The above and other objects, 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 a reduction gear to which an inscribed meshing planetary gear construction is applied according to a first embodiment of the present invention; Fig. 2 is a sectional view taken along a line II-II of Fig. 1; Fig. 3 is a sectional view showing a reduction gear to which an inscribed meshing planetary gear construction is applied according to a second embodiment of the present invention; Fig. 4 is a sectional view taken along a line VI-VI of Fig. 3; Fig. 5 is a front elevational view and a top plan view of an input shaft; Fig. 6 is a sectional view showing a relation between an input shaft and an eccentric body; Fig. 7 is a sectional view showing a relation among an input shaft, an eccentric body and a bearing at an output shaft side; Fig. 8 is a sectional view showing a basic reduction gear to which the prior art inscribed meshing planetary gear construction is applied; Fig. 9 is a sectional view taken along a line XV-XV of Fig. 8. Referring now to the drawings, some preferred embodiments of the present invention will be described in detail. Fig. 1 is a sectional view showing a reduction gear to which an inscribed meshing planetary gear construction of the present first invention is applied, and Fig. 2 is a sectional view taken along a line II-II of Fig. 1. In the following description, the same or similar parts as or to those of the construction of the well-known example already described are denoted by the same latter two-digit numbers. One end of each of carrier pins (carrier members) 116 which is separated from the flange part 114 is fitted (press fitted) to the flange part 114 of the output shaft 102. The support ring 117 is fitted (press fitted) to the other end of the carrier pin 116, and then "a carrier" is constructed by the support ring 117 and the carrier pin 116. The flange part 114, the carrier pins 116 and the support ring 117 are supported at both ends at the casing 112 by the pair of bearings 115a and 115b. The pipe-like spacer 125 is fitted (press fitted) at a central part of the carrier pin 116. Accordingly, even if there is a slight difference in a fitting depth of the carrier pin 116 into the support ring 117 or into the flange part 114, a distance between the support ring 117 and the flange part 114 is always kept constant under a function of this spacer 125 without failing, and further the same distance can be assured at portions of all (4) carrier pins 116. The external-tooth gears 105a and 105b are formed with carrier pin holes (through-holes) 120 through which the carrier pins 116 are passed. Size of each of the carrier pin holes 120 is set in such a manner that the carrier pins 116 are not contacted with the external-tooth gears 105a and 105b even if the external-tooth gears 105a and 105b are oscillated. The inner pins 107 are press fitted to the support ring 117 and the flange part 114. Accordingly, their free rotation can not be performed. However, due to the facts that 1) since each of the inner pins is a simple column-like shape, a mirror surface finishing can be easily (at a low cost) with a hard raw material; 2) since a reduction gear mechanism is held by the pair of bearings 115a and 115b, an entire rigidity can be quite improved and inner pins 107 can be supported under a quite stable state; and 3) since a construction in which the inner pins 107 and the carrier pins 116 are separated, a radial load applied from the output shaft or the like is received by the carrier pins 116, no strong radial load is applied to the inner pins 107, so that they can be supported in a more stable condition; even if the inner rollers are practically eliminated and the inner pins 107 can not rotate, there is no problem at all. However, the inner pins 107 is not necessary to be press fitted, it may be freely fitted. Action of this preferred embodiment will be described as follows. It is quite similar action to that of the prior art well-known example that the external-tooth gears 105a and 105b are oscillatably rotated together with a rotation of the input shaft 101, and the rotation of input shaft 101 becomes a reduced rotation (rotational) of the external-tooth gears 105a and 105b according to an engagement (meshing) between the outer pins 111 corresponding to the inner teeth of the internal-tooth gear 110 and the external-tooth gears 105a and 105b . Rotation of the external-tooth gears 105a and 105b is absorbed at their oscillating components by clearances between the inner pin holes 119 and the inner pins 107, and only a rotational component is transmitted to the flange part 114 of the output shaft 102 and the support ring 117 through the inner pins 107. The rotational force transmitted to the support ring 117 is transmitted to the output shaft 102 through the carrier pin 116. Since the external radial load acting against the output shaft 102 is received at both ends by the bearing 115a, and by the bearing 115b through the carrier pins 116 and the support ring 117, the external radial load does not influence against the inner pins 107. According to this preferred embodiment, since the reduction gear mechanism is supported at both ends by a pair of bearings 115a and 115b, it may provide some effects that a quite high rigidity can be attained, a connection among the flange part 114, the carrier pins 116 and the support ring 117 can be performed quite simply and at a high accuracy, the inner rollers in the inner pins 107 may also be eliminated to attain a low cost. Next, Fig. 3 is a sectional view showing a reduction gear to which an inscribed meshing planetary gear construction of the present invention is applied, and Fig. 4 is a sectional view taken along a line VI-VI of Fig. 3. One end of each of carrier pins (carrier members) 316 which is separated from the flange part 314 is fitted (press fitted) to the flange part 314 of the output shaft 302. The support ring 317 is fitted (press fitted) to the other end of the carrier pin 316, and then "the carrier" is constructed by the support ring 317 and the carrier pin 316. The flange part 314, the carrier pins 316 and the support ring 317 are supported at both ends at the casing 312 by the pair of bearings 315a and 315b. The pipe-like spacer 325 is fitted (press fitted) at a central part of the carrier pin 316. Accordingly, even if there is a slight difference in a fitting depth of the carrier pin 316 into the support ring 317 or into the flange part 314, a distance between the support ring 317 and the flange part 314 is always kept constant under a function of this spacer 325 without failing, and further the same distance can be assured at portions of all (4) carrier pins 316. As shown in Figs. 5 and 6, a part of an outer circumference of the input shaft 301 is cut in parallel with an axial direction, and then a cut part 340 having a about D-shaped form of cross section is made. The eccentric body 303 is provided with holes 341 having the same shape as that of a cross sectional shape of the input shaft 301 including a shape of the cut part 340, and then a position of setting in an axial direction (a stopper of rotation) between the input shaft 301 and the eccentric body 303 is defined under the fitting of the holes 341 (Fig. 6). A relation between an eccentric direction of the eccentric body 303 and a position of the cut part, it may be defined in reference to a strength and a common utilization (in particular, in the case where many external-tooth gears are employed in a reduction gear). An inner diameter of a bearing 335 of the input shaft 301 at the output shaft side is formed slightly smaller than an outer diameter of the input shaft 301 and then a filling material 336 such as resin or solder or the like is enclosed in the remained cut part (a part hatched in Fig. 7). This aims at keeping an inner diameter of the bearing 335 at the output shaft side as large as possible and aims at an avoidance of reduction of strength under a presence of the cut part as well as aims at a restriction of immersion of dusts or iron powder into this part. The inner pins 307 are press fitted to the support ring 317 and the flange part 314. Accordingly, their free rotation can not be performed. However, due to the facts that 1) each of the inner pins is a simple column-like shape, and a mirror surface finishing can be easily (at a low cost) with a hard raw material; 2) a reduction gear mechanism is held by the pair of bearings 315a and 315b so as to support it at both ends, and then an entire rigidity can be quite improved and inner pins 307 can be supported under a quite stable state; and 3) a construction in which the inner pins 307 and the carrier pins 316 are separated, a radial load applied from the output shaft or the like is received by the carrier pins 316, no strong radial load is applied to the inner pins 307, so that they can be supported in a more stable condition; even if the inner rollers are practically eliminated and the inner pins 307 can not rotate, there is no problem at all. However, the inner pins 307 are not necessary to be press fitted, but may be freely fitted. Action of this preferred embodiment will be described as follows. First it is quite similar action to that of the described example that the external-tooth gear 305 is oscillatably rotated together with a rotation of the input shaft 301, and the rotation of input shaft 301 becomes a reduced rotation of the external-tooth gears 305 according to an engagement (meshing) between the outer pins 311 corresponding to the inner teeth of the internal-tooth gear 310 and the external-tooth gear 305a. Next, rotation of the external-tooth gear 305 is absorbed at their oscillating components by clearances between the inner pin holes 319 and the inner pins 307, and only a rotational component is transmitted to the flange part 314 of the output shaft 302 and the support ring 317 through the inner pins 307. The rotational force transmitted to the support ring 317 is transmitted to the output shaft 302 through the carrier pin 316. Since the external radial load acting against the output shaft 302 is received at both ends by the bearing 315a, and by the bearing 315b through the carrier pins 316 and the support ring 317, the external radial load may not influence against the inner pins 307. This action is quite the same as those of the aforesaid present first and second inventions. In addition, since vibration of the flange part 314 and the support ring 317 in the radial direction is almost eliminated, external radial load acting against the input shaft 301 is also decreased, resulting in that a load in strength around bearings 335 and 336 of the input shaft 301, in particular, around a bearing 335 at the output shaft side is reduced and then the input shaft 301 at this part can be made a small diameter, that is, the bearing 335 can be made small. As a result, it became possible to employ the technique that a part of an outer circumference of the input shaft 301 is cut in parallel with its axial direction. This cut part is utilized to set a circumferential position between the input shaft 301 and the eccentric body 303. Advantage provided by the position setting structure has already been described in detail. The present invention can be necessarily applied to the system having two external-tooth gears. Actually, the present third invention is applied to the preferred first and second embodiments of the present invention. It should be noted that the circumferential position between the input shaft and the eccentric body is set by the structure having a D-shaped cross section. While the invention has been described with reference to specific embodiments, their descriptions are illustrative and are not to be constructed as limiting the scope of the invention. Various modifications and changes may occur to those skilled in the art without departing from the scope of the invention as defind by the appended claims.

Claims: An inscribed meshing planetary gear construction which comprises; a first shaft (101;301), an eccentric body 103a,103b;303) provided on the first shaft (101;301), an external-tooth gear (105a,105b;305) placed on an eccentric axis on the first shaft (101;301) through the eccentric body (103a,103b;303), an internal-tooth gear (110;310) with which the external-tooth gear (105a,105b;305) is inscribed and meshed, a second shaft connected to the external-tooth gear (105a,105b;305) through means for transmitting only a rotational component of the external-tooth gear (105a,105b;305), and a casing (112;312), said means for transmitting the rotational component comprising inner pins (107;307) acting as an isokinetic inscribed meshing mechanism in respect to inner pin holes (119;319) disposed in the external-tooth gear (105a,105b;305), an annular support ring (117;317) for receiving a rotation corresponding to the rotational component of the external-tooth gear (105a,105b;305) through the inner pins (107;307), and a carrier member (116;316) projected from a flange part (114;314) formed in the second shaft (102;302), connected and fixed to the support ring (117;317), wherein said annular support ring (117;317) and said flange part (114;314) of the second shaft (102;302) are arranged in such a manner as to hold the external-tooth gear (105a,105b;305) therebetween, both said support ring (117;317) and said flange part (114;314) are supported at both ends to said casing (112;312) through a pair of bearings (115a,115b;315), characterized in that a part of an outer circumference of said first shaft (101;301) is cut in parallel with its axial direction to form a cut part (140;340) having its cross sectional shape of D-shape, and said cut part (140;340) is utilized to define a positioning in the circumferential direction between each of said first shaft (101;301) and said eccentric body (103a,103b;303). An inscribed meshing planetary gear construction according to claim 1, characterized in that said first shaft (301) is supported by a pair of bearings (335, 336), one of the bearing (335) is faced to said second shaft (302), an inner diameter of said bearing (335) facing to the second shaft (302) is set to be slightly smaller than an outer diameter of the first shaft (301) and a filling material (336) is enclosed at a slight remained cut part between said first shaft (301) and said bearing (335) facing to said second shaft (302).

Inventors: EGAWA MASANORI, ISHIGAKI ATSUSHI, KONISHI TOSHIYUKI, MINEGISHI KIYOJI, TAKAHASHI ATSUSHI, TANAKA HIDEYOSHI, TANIGAWA MASAYUKI, EGAWA, MASANORI, ISHIGAKI, ATSUSHI, KONISHI, TOSHIYUKI, MINEGISHI, KIYOJI, TAKAHASHI,ATSUSHI, TANAKA, HIDEYOSHI, TANIGAWA, MASAYUKI
Applicants: SUMITOMO HEAVY INDUSTRIES, SUMITOMO HEAVY INDUSTRIES, LTD.
Application year: 1992
Main classification: F16H1
IPC codes: F16H1