Patent Publication Number: US-2021172476-A1

Title: Radial roller bearing cage

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2019-221413 filed on Dec. 6, 2019, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to a radial roller bearing cage made of resin. 
     2. Description of Related Art 
     In related art, some planetary gear devices used for transmissions of vehicles (e.g., automobiles) are configured such that a plurality of planetary gears is disposed between an external gear and an internal gear, and each of the planetary gears is rotatably supported by a radial roller bearing. The radial roller bearing includes a plurality of rollers and a cage configured to hold the rollers such that the rollers are rollable. Roller bearings used in planetary gear devices support rotation of planetary gears while the roller bearings receive centrifugal force caused by revolution of the planetary gears. Accordingly, in order to secure strength, cages made of metal have been widely used. However, due to request for weight reduction and cost reduction, there have been made attempts to employ cages made of resin (e.g., see Japanese Unexamined Patent Application Publication No. 2006-77801 (JP 2006-77801 A)). 
     A cage described in JP 2006-77801 A is configured such that two rib portions constituted by annular bodies facing each other at an interval in the axial direction of the cage and a plurality of bars arranged at predetermined intervals in the circumferential direction of the cage are integrally formed by use of a resin material. In each of the two rib portions, an annular core is embedded for improvement in strength. The annular core is made of a strength material higher in strength than the resin material. The core is made of a resin material combined with a metallic material such as rolled steel or reinforced fiber such as glass fiber. 
     SUMMARY 
     In the cage described in JP 2006-77801 A, the core is embedded in each of the two rib portions, and therefore, man-hours at the time of manufacturing and weight increase. Although weight reduction and cost reduction are achieved in comparison with a metal cage, further weight reduction and further cost reduction have been requested. In consideration of the aforementioned circumstances, the inventor of the disclosure started to develop a resin cage having improved strength and found that the strength of the cage can be increased particularly by dispersing stress of annular bodies. Thus, the disclosure has been accomplished. That is, the disclosure provides a radial roller bearing cage made of resin and having improved strength. 
     One aspect of the disclosure relates to a radial roller bearing cage including a pair of annular bodies and a plurality of bars by which the annular bodies are axially connected to each other. The annular bodies and the bars are integrally formed by resin molding. A plurality of pockets separated from each other by the bars is provided between the annular bodies. A projection projecting radially inwardly is provided in at least one of parts of at least one of the annular bodies, the parts axially facing the pockets, respectively. 
     With the aspect of the disclosure, it is possible to improve the strength of the radial roller bearing cage made of resin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is an exploded perspective view illustrating a planetary gear device using a radial roller bearing including a cage according to an embodiment of the disclosure; 
         FIG. 2A  is a sectional view illustrating a section of the roller bearing together with portions near the roller bearing; 
         FIG. 2B  is a sectional view taken along a line II-II in  FIG. 2A ; 
         FIG. 3A  is a side view of the radial roller bearing; 
         FIG. 3B  is a front view illustrating an axial end face of the radial roller bearing; 
         FIG. 4  is a sectional view of the cage taken along a line IV-IV in  FIG. 3A ; 
         FIG. 5  is a perspective view illustrating one axial end of the cage; 
         FIG. 6  is a developed view schematically illustrating an inner peripheral surface of the cage, which is developed into a planar shape; 
         FIG. 7  is a stress distribution chart illustrating stress distribution caused in the cage of the radial roller bearing according to the embodiment; and 
         FIG. 8  is a stress distribution chart illustrating stress distribution caused in a cage of a radial roller bearing according to a comparative example. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiment 
     An embodiment of the disclosure will be described below with reference to  FIGS. 1 to 7 . Note that the embodiment described below shows a specific example of the disclosure. The technical scope of the disclosure is not limited to such a specific example. 
     Overall Configuration of Planetary Gear Device 
       FIG. 1  is an exploded perspective view illustrating a planetary gear device using a radial roller bearing including a cage according to an embodiment of the disclosure.  FIG. 2A  is a sectional view illustrating a section of the roller bearing together with portions near the roller bearing, and  FIG. 2B  is a sectional view taken along a line II-II in  FIG. 2A . 
     A planetary gear device  1  includes a sun gear  11  having external teeth  111  on its outer peripheral surface; an internal gear  12  having internal teeth  121  on its inner peripheral surface; a plurality of (three in the present embodiment) planetary gears  13  disposed between the sun gear  11  and the internal gear  12 ; a carrier  14  including a plurality of (three) support shafts  141  configured to support the planetary gears  13 , respectively; radial roller bearings  10  (see  FIGS. 2A, 2B ) each disposed between a corresponding one of the planetary gears  13  and a corroding one of the support shafts  141 ; and a plurality of washers  15  disposed such that each of the washers  15  faces a corresponding one of axial end faces  13   a ,  13   b  of the planetary gears  13 . The planetary gear  13  includes external teeth  131  meshing with the external teeth  111  of the sun gear  11  and the internal teeth  121  of the internal gear  12 . 
     The sun gear  11 , the internal gear  12 , and the carrier  14  are supported to be coaxially rotatable relative to each other around a rotation axis O. Further, the planetary gears  13  rotate about respective rotation axes O 1  to O 3  around the support shafts  141 . The planetary gears  13  revolve around the rotation axis O and rotate around the respective rotation axes O 1  to O 3 . In  FIGS. 2A, 2B , one planetary gear  13  rotating around the rotation axis O 1  is illustrated. Hereinafter, a direction parallel to the rotation axis O 1  is referred to as an axial direction, and a direction perpendicular to the rotation axis O 1  is referred to as a radial direction. 
     A shaft  110  is fixed to a central part of the sun gear  11  in a relatively non-rotatable manner. The planetary gear  13  is configured such that the support shaft  141  is inserted through a shaft hole  130  extending through a central part of the planetary gear  13 , and the radial roller bearing  10  is disposed between an inner peripheral surface  130   a  of the shaft hole  130  and an outer peripheral surface  141   a  of the support shaft  141 . The radial roller bearing  10  includes a cage  2  made of resin and a plurality of (nine in the present embodiment) rollers  3  made of metal. The rollers  3  are formed in a columnar shape and roll on the inner peripheral surface  130   a  of the shaft hole  130  of the planetary gear  13  and the outer peripheral surface  141   a  of the support shaft  141  along with rotation of the planetary gear  13 . 
     The carrier  14  supports the planetary gears  13  via the radial roller bearings  10  such that the planetary gears  13  can rotate and revolve. Further, the carrier  14  includes first and second disk portions  142 ,  143  configured such that the planetary gears  13  are disposed between the first and second disk portions  142 ,  143  in the axial direction, an outer wall portion  144  configured to bridge respective end parts, on the outer peripheral side, of the first and second disk portions  142 ,  143 , and a fitting tube  145  fixed to an end part, on the inner peripheral side, of the first disk portion  142 . 
     A spline portion  145   a  to which a shaft (not shown) is fitted in a relatively non-rotatable manner is formed on the inner periphery of the fitting tube  145 . An opening  144   a  is formed on the outer wall portion  144  such that part of the planetary gear  13  projects from the opening  144   a . The external teeth  131  of the planetary gear  13  thus projecting from the opening  144   a  mesh with the internal teeth  121  of the internal gear  12 . The washers  15  are each disposed between a corresponding one of the first and second disk portions  142 ,  143  and a corresponding one of the axial end faces  13   a ,  13   b  of the planetary gears  13 . 
     As illustrated in  FIG. 2A , both end parts of the support shaft  141  are respectively press-fitted into fitting holes  142   a ,  143   a  formed in the first and second disk portions  142 ,  143 . The support shaft  141  has a cylindrical shape having a cavity  140  formed in its central part. An oil hole  141   b  communicating with the cavity  140  is opened on the outer peripheral surface  141   a . Lubricant flowing into the cavity  140  is supplied to the radial roller bearing  10  from the oil hole  141   b.    
     With reference to  FIGS. 3A to 6 , a configuration of the radial roller bearing  10  will described in detail.  FIG. 3A  is a side view of the radial roller bearing  10 , and  FIG. 3B  is a front view illustrating an axial end face of the radial roller bearing  10 .  FIG. 4  is a sectional view of the cage  2  taken along a line IV-IV in  FIG. 3A .  FIG. 5  is a perspective view illustrating one axial end of the cage  2 .  FIG. 6  is a developed view schematically illustrating an inner peripheral surface of the cage  2 , which is developed into a planar shape. 
     The cage  2  includes a pair of annular bodies  21  having a ring shape, and a plurality of bars  22  provided between the annular bodies  21 . The annular bodies  21  are connected to each other in the axial direction by the bars  22  (i.e., the annular bodies  21  are axially connected to each other by the bars  22 ). The annular bodies  21  and the bars  22  are integrally formed by resin molding. In other words, the annular bodies  21  and the bars  22  are made of resin, and are integral with each other. As a resin material for the annular bodies  21  and the bars  22 , nylon-66 obtained by adding a predetermined amount of a reinforced fiber material such as glass fiber or carbon fiber, polyphenylene sulfide (PPS) resin, or polybutylene terephthalate (PBT) resin can be appropriately used, for example. 
     A plurality of pockets  20  separated from each other by the bars  22  is provided between the annular bodies  21 . The number of the bars  22  and the number of the pockets  20  are the same as the number of the rollers  3  included in the radial roller bearing  10 , and in the present embodiment, nine bars  22  are provided at regular intervals along the circumferential direction of the annular bodies  21 . Each of the pockets  20  is defined into a rectangular shape by two bars  22  adjacent to each other and the annular bodies  21 . The annular bodies  21  have the same shape and the same size. 
     The rollers  3  are restrained from moving away from the pockets  20  by inner-peripheral-side and outer-peripheral-side projections  223 ,  224  (see  FIG. 4 ) provided in the bars  22 .  FIG. 4  illustrates one roller  3  in a virtual line (an alternate long and two short dashes line). The distance between two bars  22  adjacent to each other is larger than the diameter of the roller  3  at the central part of the pocket  20  in the radial direction, and when the roller  3  is to be accommodated in the pocket  20 , the bars  22  are elastically deformed. 
     On an outer peripheral surface  22   a  of each of the bars  22  in the cage  2 , an oil groove  221  where lubricant flows is formed to extend in the axial direction. Further, on an inner peripheral surface  22   b  of each of the bars  22  in the cage  2 , an oil groove  222  where lubricant flows is formed to extend in the axial direction. The oil groove  222  formed on the inner peripheral side of the bar  22  is formed in a linear shape within a range that reaches both axial end faces  2   a ,  2   b  of the cage  2 , the range including respective inner peripheral surfaces  21   a  of the annular bodies  21 . 
     The cage  2  is made of a single resin material. The cage  2  is formed by injection molding in which melted resin is injected into a metal mold. In  FIG. 6 , the flow of the melted resin when the cage  2  is formed by injection molding is indicated by a plurality of arrows, and a part corresponding to a gate through which the melted resin is injected is surrounded by a broken line and indicated by a reference sign G. In the present embodiment, the cage  2  is molded by injecting the melted resin into the cavity of the metal mold from three places at the same time. 
     As illustrated in  FIG. 6 , the melted resin injected from each of the gates G at the three places is divided into two directions and flows in the cavity. Then, the flows of the melted resin join each other at a plurality of places. In a meeting point at which the flows of the melted resin join each other (i.e., meet each other), a weld indicated by a reference sign W is formed (i.e., a weld W is generated). Here, the weld is a joint-shaped part that is inevitably formed when the flows of the melted resin hit and join each other, and the weld is a part having a strength lower than other parts. In the present embodiment, three welds W are formed in each of the annular bodies  21 . In each of the annular bodies  21 , a part where the weld W is formed is a part facing the pocket  20  in the axial direction. 
     When the carrier  14  rotates along with the rotation of the sun gear  11  or the internal gear  12 , the cage  2  rotates around the support shaft  141  while the cage  2  receives centrifugal force caused by the revolution of the planetary gear  13 . Therefore, the annular bodies  21  elastically deform into a substantially elliptical shape due to the centrifugal force, and thus, stress is caused therein. Particularly, when the stress concentrates on a part where the weld W is formed, breakage starting from the weld W easily occurs. 
     In view of this, in the disclosure, in order to improve strength by reducing stress concentration, a projection  211  projecting inwardly in the radial direction is provided in at least one of parts of at least one of the annular bodies  21 , the parts respectively facing the pockets  20  in the axial direction. The projection  211  is provided at least at a position where the weld W is generated at the time of resin molding. In the present embodiment, the projections  211  are provided in parts of both of the annular bodies  21 , the parts respectively facing both sides of all the pockets  20  in the axial direction. 
     As illustrated in  FIG. 3B  in an enlarged manner, the projection  211  has a curved shape projecting inwardly in the radial direction. In  FIG. 3B , an extension line L 1  extending from the inner peripheral surface  21   a  of the annular body  21  is illustrated as an alternate long and two short dashes line that overlaps with a part where the projection  211  is formed. Further, in  FIG. 3B , a straight line L 2  that connects both circumferential ends  211   b  corresponding to distal ends of the lower part of the projection  211  is illustrated as an alternate long and short dash line. 
     Each of the three welds W reaches an apex  211   a  having the highest projection height in the projection  211 . That is, the weld W is formed over the whole projection  211  in its height direction (the radial direction). Here, the projection height indicates a distance from the extension line L 1  in the radial direction of the cage  2 . The apex  211   a  projects inwardly in the radial direction beyond the straight line L 2 , and a part of the roller  3  projects further inwardly in the radial direction beyond the apex  211   a.    
     Note that, in the present embodiment, the circumferential width (the distance between both circumferential ends  211   b ) of the projection  211  is smaller than the opening width of the pocket  20  on the inner peripheral surface  22   b , and the whole projection  211  is provided in the part facing the pocket  20  in the axial direction. However, the structure of the projection  211  is not limited to this structure, and a part of the projection  211  may be provided in a part facing the bar  22  in the axial direction. That is, both circumferential ends  211   b  of the projection  211  may be present at positions aligning with the bars  22  in the axial direction. 
       FIG. 7  is a stress distribution chart illustrating, by gray scale, stress distribution caused in the cage  2  when the radial roller bearing  10  according to the present embodiment is provided in the planetary gear device  1  and the planetary gear  13  revolves together with the carrier  14 .  FIG. 8  is a stress distribution chart illustrating, by gray scale, stress distribution when a radial roller bearing  10 A according to a comparative example is used instead of the radial roller bearing  10 . The radial roller bearing  10 A according to the comparative example is configured similarly to the radial roller bearing  10  according to the present embodiment except that the cage  2  is not provided with the projections  211 . Therefore, in  FIG. 8 , constituents of the radial roller bearing  10 A are denoted by the same reference signs as those denoting their corresponding constituents of the radial roller bearing  10 , and redundant descriptions are omitted. 
     In  FIGS. 7, 8 , the magnitude of stress is shown by depth of color. A part with deeper color has larger stress, and a part with lighter color has smaller stress. Note that, in  FIGS. 7, 8 , the relationship (scale) between the depth of color and magnitude of stress is the same. 
     As illustrated in  FIG. 8 , in the radial roller bearing  10 A according to the comparative example, a part with large stress occurs in a central part, in the circumferential direction of the annular body  21 , of a part facing one side of the pocket  20  in the axial direction such that the part with large stress extends along the radial direction. Since the weld W is formed in the part with large stress, breakage or the like easily occurs in the part where the weld W is formed. 
     In the meantime, in the radial roller bearing  10  according to the present embodiment, stress is dispersed in comparison with the radial roller bearing  10 A according to the comparative example, and stress is greatly reduced in the part where the weld W is formed. Thus, breakage starting from the weld W can hardly occur, and thus, the strength of the cage  2  improves. Further, in the present embodiment, the projections  211  are provided in the parts respectively facing both sides of all the pockets  20  in the axial direction, the parts including the parts where the welds W are formed. Accordingly, stress concentration is reduced in the entire annular body  21  in the circumferential direction, and this also improves the strength of the cage  2 . 
     The disclosure has been described based on the embodiment and its modification, but the embodiment and modification described above do not limit the disclosure. 
     Further, the disclosure can be carried out by appropriately modifying the embodiment by omitting some configurations or adding or replacing configurations within a range that does not depart from the scope of the disclosure.