1. Field of the Invention
The present invention relates to a caged roller assembly capable of providing a large load bearing capacity within a predetermined space, and a planetary gear reduction unit using such caged roller assembly.
2. Description of the Prior Art
A full type roller bearing has been well known as a bearing capable of providing a maximum load bearing capacity within a limited space. However, the full type roller bearing has a problem associated with handling thereof, particularly during assemblage and/or dismantling and also tends to pose a functional problem such as, for example, that associated with roller skewing during use thereof.
To alleviate those problems, various caged roller assembles have hitherto been suggested. The cage used therein to movably retain a plurality of rollers in circumferentially juxtaposed fashion must have two types of retainers for preventing the rollers from separating outwardly and inwardly, respectively.
An example of the cage of the kind discussed above is shown in FIGS. 10A and 10B. The illustrated cage, generally identified by 70, is of a generally ring shape having a width conforming to a longitudinal direction of each rollers 74 and, when cut along the widthwise direction thereof, represents a generally M-shaped section delimited by an intermediate annular wall 71 of a diameter smaller than the pitch circle diameter PAD occupied by the longitudinal axes of the circumferentially juxtaposed rollers 74, first and second side annular walls 72 and 72 one on each side of the intermediate annular wall 71 and having a diameter larger than the pitch circle diameter PAD, and first and second annular collars 73 and 73 each bent radially inwardly from the adjacent outer annular wall 72. The cage 70 has a plurality of roller pockets 75 defined therein so as to be equidistantly spaced from each other in a direction circumferentially of the cage 70 for movably accommodating the respective rollers 74 therein, while leaving a pillar between each neighboring pockets 75.
In this illustrated cage 70, the first and second outer annular walls 72 and 72 jointly serve as a first retainer for preventing the rollers 74 from separating outwardly in a direction axially of the rollers 74 whereas the intermediate annular wall 71 serves as a second retainer for preventing the rollers 74 from separating radially inwardly of the cage 70. More specifically, while each of the roller pockets 75 defined in the cage 70 is delimited by mutually confronting long side edges and mutually confronting end edges, the cage 70 has a plurality of pairs of stop pieces 76, one pair for each pocket 75, protruding into the associated pocket 75 from the long side edge while leaving a space therebetween of a size smaller than the outer diameter of the respective roller 74. Each of the rollers 74 is generally mounted in the associated pocket 75 from inside the cage 70 by causing the corresponding stop pieces 76 to be elastically deformed to pass the roller 74 therebetween into the pocket 75.
If the number of the rollers 74 to be accommodated by the cage 70 within a predetermined space (i.e., the cage 70 having given inner and outer diameters), the width a of the pillar between the neighboring pockets 75 as shown in FIG. 10B has to be reduced. Reduction of the pillar width a brings about not only a limit for machining, but also reduction in physical strength of the cage 70 as a whole. For this reason, there is a need to provide a cage of a structure fundamentally different from the illustrated cage 70.
When it comes to the caged roller assembly that is to be interposed between a planetary gear of a planetary gear reduction unit and a crankshaft, a stringent requirement is imposed on the total surface area of collars of the roller cage. In other words, in the type in which the neighboring crank pins of the crankshaft have respective planetary gears mounted thereon in a juxtaposed fashion, it has been found that as the crank pins undergo an eccentric rotation the collars of the cage tend to frictionally contact respective end faces of the neighboring planetary gears. For this reason, unless each of the collars of the cage have a sufficient surface area, they would interfere with inner peripheries of the neighboring planetary gears.
In order to alleviate the foregoing inconveniences, the assignee of the present invention has suggested, in the Japanese laid-open Patent Publication No. 2000-179544, such a caged roller assembly as shown in FIGS. 11A and 11B. As shown therein, the caged roller assembly disclosed in this Japanese laid-open Patent Publication No. 2000-179544 includes a two-piece cage 81 including generally ring-shaped outer and inner annular members 83 and 84, and a plurality of rollers 82. The outer member 83 includes a ring body 83a of a diameter greater than the pitch circle diameter PAD depicted by respective longitudinal axes of the array of the rollers 82 and first and second annular collars 83b and 83b each bent radially inwardly from opposite ends of the ring body 83a. On the other hand, the inner member 84 is of a generally ring shape having a diameter smaller than the pitch circle diameter PAD depicted by the respective longitudinal axes of the rollers 82. The ring body 83a of the outer member 83 is formed with a plurality of circumferentially equidistantly spaced pockets 85 and the inner member 84 is similarly formed with a corresponding number of circumferentially equidistantly spaced pockets 86. Each of the rollers 82 is movably supported by the outer and inner members 83 and 84 while received in part in the corresponding pocket 85 and in part in the associated pocket 86 with its longitudinal axis aligned in a direction widthwise of each of the outer and inner members 83 and 84. Alternatively, the collars 83b, although they are in one embodiment integral with the outer member 83, may be formed in the inner member 84.
The use of the two-piece cage 81 made up of the outer and inner members 83 and 84 is advantageous in that each of the outer and inner members 83 and 84 can be manufactured to have a plurality of pillars 87 and 88 of a reduced width and, therefore, a relatively large number of rollers 82 can be accommodated within the limited available space. Also, since one of the members, that is, the outer member 8 is provided with the collars 83b, sliding contact with the neighboring component parts does not pose any problem.
However, it has been found that the caged roller assembly disclosed in the above mentioned publication has a problem in assimilability. More specifically, when it comes to assemblage of the caged roller assembly, the rollers 82 are first mounted on the outer member 83 having the collars 83b so as to be received in the associated pockets 85, followed elastically mounting the collarless member, that is, the inner member 84 along the inscribed circle of the array of the rollers 82. (Alternatively, where the collarless member is the outer member, the outer member is elastically mounted along the circumscribed circle of the array of the rollers 82.). It has been found that during this elastic mounting, the collarless member 84 does little deform elastically and, therefore, requiring an increase in number of process steps. In particular, where the collarless member 84 is made of a metallic material, mounting would be hardly achieved unless the dimensional accuracy is precisely controlled.