Patent Publication Number: US-2023160429-A1

Title: Bearing

Description:
FIELD 
     The present disclosure relates to a bearing that uses two types of rollers with different diameters. 
     BACKGROUND 
     A proposed bearing uses two types of rollers with different diameters, thus eliminating a cage that holds rollers. A plurality of larger diameter rollers in Patent Literature 1 are cylindrical rollers arranged between a radially inner ring member and a radially outer ring member, and smaller diameter rollers that are shaft-shaped rollers and are smaller in diameter than the larger diameter rollers are each arranged between the larger diameter rollers. An annular groove in the radially outer ring member allows the smaller diameter rollers to be radially movable. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent Application Laid-open No. 2000-55044 
       
    
     SUMMARY 
     Technical Problem 
     Patent Literature 1 provides no disclosures regarding a radial position and a radial width of the groove in which the smaller diameter rollers are arranged, and the smaller diameter rollers in the groove may move to a space on a radially outer side of center positions of the larger diameter rollers. Therefore, there is a concern about damage to the larger diameter rollers due to increased rolling resistance from contact between the larger diameter rollers. Moreover, the smaller diameter rollers can collide with an inner wall of the groove that is radially outer and thus may be damaged or broken. 
     The present disclosure has been made in view of the above, and an object of the present disclosure is to obtain a bearing that can prevent smaller diameter rollers from moving to a radially outer space beyond the axial centers of larger diameter rollers, thus preventing damage to the smaller diameter and larger diameter rollers and enabling reduction of power loss. 
     Solution to Problem 
     In order to solve the above-stated problems and achieve the object, a bearing according to the present disclosure includes: an inner ring case; an outer ring case disposed around the inner ring case; a plurality of first rollers that roll between an outer periphery of the inner ring case and an inner periphery of the outer ring case; and a plurality of second rollers each of which is disposed between adjacent first rollers. Each of the second rollers: is smaller in diameter than each of the first rollers; and has a longer axial length along a rotation axis than each of the first rollers. The outer ring case includes an annular guide groove housing an end of each of the plurality of second rollers, with the rotation axis of each of the second rollers being perpendicular to a radial direction and a circumferential direction of the bearing. A groove width representing a length of the guide groove along the radial direction of the bearing is greater than a diameter of each of the second rollers. A first radius representing a distance from a bearing axis to an inner wall face of the guide groove that is outer in the radial direction of the bearing is smaller than a distance from the bearing axis to an axial center of each of the first rollers plus a radius of each of the second rollers. 
     Advantageous Effects of Invention 
     According to the present disclosure, the second rollers can be prevented from entering into radially outer space beyond the axial centers of the first rollers. Therefore, damage to the first and second rollers is preventable, and power loss due to contact between the first rollers can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a front view of a bearing according to a first embodiment. 
         FIG.  2    illustrates a cross section of the bearing according to the first embodiment. 
         FIG.  3    is a diagram illustrating a section along line III-III of  FIG.  2   . 
         FIG.  4    is a diagram illustrating a section along line IV-IV of  FIG.  2   . 
         FIG.  5    is a diagram illustrating a section along line V-V of  FIG.  1   . 
         FIG.  6    is a diagram illustrating where radii of parts of the bearing according to the first embodiment are located. 
         FIG.  7    is a diagram illustrating a state in which inner rollers are in contact with rollers during higher speed rotation of the bearing according to the first embodiment. 
         FIG.  8    is a diagram illustrating a roller having another shape. 
         FIG.  9    is a diagram illustrating an inner roller having another shape. 
         FIG.  10    is a sectional view of a bearing according to a second embodiment. 
         FIG.  11    is a sectional view of a bearing according to a third embodiment. 
         FIG.  12    is a diagram used for describing a bearing according to a fourth embodiment. 
         FIG.  13    is a diagram used for describing the bearing according to the fourth embodiment. 
         FIG.  14    is a diagram illustrating a bearing according to a fifth embodiment. 
         FIG.  15    is a diagram illustrating a bearing according to the fifth embodiment. 
         FIG.  16    is a diagram illustrating a bearing according to the fifth embodiment. 
         FIG.  17    is a diagram illustrating a bearing according to the fifth embodiment. 
         FIG.  18    is a diagram illustrating a bearing according to the fifth embodiment. 
         FIG.  19    is a diagram illustrating a bearing according to the fifth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     With reference to the drawings, a detailed description is hereinafter provided of bearings according to embodiments. It is to be noted that these embodiments are not restrictive of the present disclosure. 
     First Embodiment 
     Using  FIGS.  1  to  7   , a description is provided of a bearing according to a first embodiment.  FIG.  1    is a front view of the bearing according to the first embodiment.  FIG.  2    is a cross section of the bearing illustrated in  FIG.  1    taken on a plane perpendicular to a bearing axis O, illustrating a state of lower speed rotation.  FIG.  3    is a diagram illustrating a section along line III-III of  FIG.  2   .  FIG.  4    is a diagram illustrating a section along line IV-IV of  FIG.  2   .  FIG.  5    is a diagram illustrating a section along line V-V of  FIG.  1   .  FIG.  6    is a diagram illustrating where radii of parts are.  FIG.  7    is a cross section of the bearing illustrated in  FIG.  1    taken on a plane perpendicular the bearing axis O, illustrating a state of higher speed rotation. 
     The bearing  100  in  FIGS.  1  to  5    includes: an outer ring case  1 ; an inner ring case  2  disposed at inner side of the outer ring case  1 ; a plurality of rollers  10  as larger diameter rollers, and a plurality of inner rollers  11  that are smaller in diameter than the rollers  10 . Each of the rollers  10  has a radius “a”. Each of the inner rollers  11  has a radius “b”, and a&gt;b. The rollers  10  correspond to first rollers in the claims, and the inner rollers  11  correspond to second rollers in the claims. 
     As illustrated in  FIGS.  2  and  3   , each of the plurality of rollers  10  has a cylindrical shape having, at its center, a rotation axis parallel to the bearing axis O. As illustrated in  FIGS.  2  and  4   , each of the inner rollers  11  has a cylindrical shape having, at its center, a rotation axis parallel to the bearing axis O. An axial length of each inner roller  11  along the rotation axis is longer than an axial length of each roller  10  along the rotation axis. The inner rollers  11  are rod-shaped. Each inner roller  11  is disposed between the adjacent rollers  10 . 
     The outer ring case  1  is annular and includes an internal space for housing the plurality of rollers  10  and the plurality of inner rollers  11 . The inner ring case  2  is also annular. 
     As illustrated in  FIGS.  3  to  5   , the outer ring case  1  includes an annular guide groove  20  that houses some of the plurality of rollers  10 . The guide groove  20  is a recess heading outward in a radial direction of the bearing  100 . An arc  21  in  FIGS.  2  and  6    corresponds to a position of a bottom  20   a  of the guide groove  20  illustrated in  FIG.  3   . As illustrated in  FIG.  6   , the arc  21  has a radius R1 extending from the bearing axis O. An arc  22  corresponds to a position of an outer periphery 2d of the inner ring case  2 . As illustrated in  FIG.  6   , the arc  22  has a radius R2 extending from the bearing axis O. 
     The rollers  10  are in contact with the bottom  20   a  of the guide groove  20  (i.e., the arc  21 ) and the outer periphery 2d of the inner ring case  2  (i.e., the arc  22 ). In other words, the radius R2 plus a diameter 2×a of the roller  10  equals the radius R1. Each roller  10  rotates on its rotation axis with its circumferential face in contact with the arcs  21  and  22 . Each roller  10  also orbits around the bearing axis O with its circumferential face in contact with the arcs  21  and  22 . 
     As illustrated in  FIGS.  3 ,  4 , and  5   , the outer ring case  1  includes a pair of annular guide grooves  30  as second guide grooves housing axial ends  11   a  and  11   b  of each of the plurality of inner rollers  11 . The guide grooves  30  are recesses along the bearing axis O. In  FIGS.  2  and  6   , an arc  31  corresponds to a position of the inner wall faces of the guide grooves  30  of the outer periphery-side. As illustrated in  FIG.  6   , the arc  31  has a radius r1 extending from the bearing axis O. An arc  32  corresponds to a position of the inner wall faces of the guide grooves  30  of the inner periphery-side. As illustrated in  FIG.  6   , the arc  32  has a radius r2 extending from the bearing axis O. The arc  31  is hereinafter referred to as an outer periphery of the guide grooves  30 , and the arc  32  is hereinafter referred to as an inner periphery of the guide grooves  30 . 
     As illustrated in  FIG.  6   , each of the guide grooves  30  has a radial groove width Δr that equals a value radius r1 minus the radius r2. The groove width Δr of each guide groove  30  is greater than a diameter (2×b) of the inner roller  11 . In other words, the radius r2 plus the diameter (2×b) of the inner roller  11  is smaller than the radius r1. For this reason, the inner rollers  11  are radially movable in the guide grooves  30 . 
     A detailed description is provided here of the positions of the outer and inner peripheries  31  and  32  of the guide grooves  30 . The radius r1, being a position of the outer periphery  31  of the guide grooves  30 , is set to a value smaller than a distance r3 (refer to  FIG.  6   ), which is a distance from the bearing axis Oto an axial center O1 of the roller  10 , plus the radius “b” of the inner roller  11 . The distance r3 equals the radius R2 plus the radius “a” of the roller  10 . In other words, the outer periphery  31  of the guide grooves  30  restricts the movement of the inner rollers  11  so that an axial center of the inner roller  11  does not come to a radially outer position compared with the axial center O1 of the roller  10 . This restriction by the outer periphery  31  prevents, unlike the Patent Literature 1, entry of the inner roller  11  into a radially outer space beyond the axial center O1 of the roller  10 . 
     The radius r2, being a position of the inner periphery  32  of the guide grooves  30 , is set to a value smaller than a value of the radius r1 minus the diameter 2×b of the inner roller  11  so as to locate a radially inner position. The r1 is the position of the outer periphery  31  of the guide grooves  30 . Moreover, the radius r2, being the position of the inner periphery  32  of the guide grooves  30 , is set to a value greater than the radius r1 minus a distance “q” (refer to  FIG.  3   ). The distance “q” is a distance between the r1 and 1d which is an external face of the outer ring case  1  closer to the inner ring case  2 . That is, the radius r2 is set to a position outer periphery side than the 1d. 
     As illustrated in  FIGS.  1  and  5   , the outer ring case  1  includes a tapped hole  40  connecting with the guide groove  30 . The inner rollers  11  can be inserted through the tapped hole  40 . After the inner rollers  11  are inserted through the tapped hole  40  during manufacture, a screw  41  is inserted in the tapped hole  40  to close the tapped hole  40 . The tapped hole  40  in  FIG.  5    includes a taper portion into which a head of the screw  41  fits. It is to be noted, however, that the screw  41  has an adjusted length and that a leading end of the screw  41  has an adjusted shape, adjusted surface roughness, and adjusted flatness. This is for the purpose of preventing the inserted screw  41  from forming a step where the screw  41  contacts with the guide groove  30  and interfering with the inner rollers  11 . The tapped hole  40  in  FIG.  1    is provided only in one of sides of the outer ring case  1 ; however, the tapped hole  40  may be formed in each of the sides of the outer ring case  1 . Another alternative is that a plurality of intermittent tapped holes may be formed along a periphery of the outer ring case  1 . With the tapped hole  40 , which is used for the insertion of the inner rollers  11 , and the screw  41  in the outer ring case  1 , the bearing  100  is easy to assemble. 
     A description is provided next of how the bearing  100  operates. As illustrated in  FIG.  7   , when the inner ring case  2  rotates, each roller  10  rotates on its own axis. Each roller  10  also orbits for minimizing rolling resistance with the outer ring case  1 . Each inner roller  11  in contact with the rollers  10  rotates on its own axis in a direction opposite to that of the rollers  10  and orbits in an orbiting direction of each roller  10  having a larger mass. 
     In a nonrotating state or during the lower speed rotation, as illustrated in  FIG.  2   , each inner roller  11  is in contact: with the inner periphery  32  or the outer periphery  31  of the guide grooves  30  in accordance with gravity; and with the roller  10  on each side. On the other hand, during the higher speed rotation, centrifugal force K acts on each inner roller  11 , as illustrated in  FIG.  7   . Here the rollers  10  and the inner rollers  11  operate so as to minimize energy loss, in a state every inner roller  11  is in contact with only the adjacent rollers  10 , and in a state all the inner rollers  11  orbiting equidistantly from the bearing axis O. Thus, during the higher speed rotation, each inner roller  11  rotates on its own axis and orbits while contacting only the adjacent rollers  10  and not contacting with the outer periphery  31  and the inner periphery  32  of the guide grooves  30 . 
     A bearing with an inside diameter of about 70 mm, such as a railroad bearing, rotates at higher speeds as described above for a majority of operating time. For example, when as in the railroad bearing, the inside diameter is 70 mm, the inner ring case  2  has a thickness of 7.75 mm, an outside diameter is 125 mm, and each roller  10  has a diameter of 12 mm and a length of 15 mm, the inner rollers  11  move radially outward at an orbital speed of 15.14 rad/s or more, that is to say, 2.410 rps (144.58 rpm) or more due to the centrifugal force. The inner rollers  11  move at the same orbital speed as the rollers  10 . Therefore, the orbital speed of the inner rollers  11  becomes 144.58 rpm when a motor rotates at a speed of 1076.5 rpm or more. Since a maximum rotation speed of a railroad motor ranges from 3500 rpm to about 4000 rpm and, for Shinkansen bullet trains, 5000 rpm to 6500 rpm, each inner roller  11  is obviously possible to be in a state of contact with only the rollers  10  due to the centrifugal force that acts on each inner roller  11 . 
     While the rollers  10  and the inner rollers  11  are cylindrical in the above description, the rollers  10  may be spherical, as illustrated in  FIG.  8   .  FIG.  8    illustrates a section along line III-III of  FIG.  2   . As illustrated in  FIG.  9   , each inner roller  11  may adopt the shape of a rod having a neck such that a middle part is smaller in diameter than each end of the rod.  FIG.  9    illustrates a section along line IV-IV of  FIG.  2   . 
     According to the first embodiment described above, the outer periphery  31  of the guide grooves  30  restricts the movement of the inner rollers  11  so as to prevent the axial center of each inner roller  11  that radially aligns with the axial center O1 of the roller  10  from coming to the radially outer position. This prevents, unlike Patent Literature 1, each inner roller  11  from entering into the radially outer space beyond the axial center O1 of the roller  10 . Therefore, damage to the rollers  10  and the inner rollers  11  is preventable, and power loss due to contact between the rollers  10  is reduced. With the tapped hole  40 , which is used for the insertion of the inner rollers  11 , in the outer ring case  1 , the bearing  100  is easy to assemble. 
     Second Embodiment 
     Using  FIG.  10   , a description is provided of a configuration of the bearing  100  according to a second embodiment.  FIG.  10    illustrates a section along each of lines III-III and IV-IV of  FIG.  2   . In the second embodiment, only one of the guide grooves  30  is provided to house one of the axial ends  11   a  and  11   b  (refer to  FIG.  4   ) of each of the inner rollers  11 . The configuration is otherwise similar to that of the first embodiment. 
     Third Embodiment 
     Using  FIG.  11   , a description is provided of a configuration of the bearing  100  according to a third embodiment.  FIG.  11    illustrates a section along line V-V of  FIG.  1   . In the third embodiment, not the tapped hole  40  but a hole  42  that is not threaded is formed in the outer ring case  1 . The hole  42  may include a tapered face to facilitate the insertion of the inner rollers  11 . 
     Fourth Embodiment 
     A description in the fourth embodiment is provided of the radius “b” of each inner roller  11  that prevents the rollers  10  from contacting with one another.  FIG.  12    illustrates a state in which the rollers  10  are in contact with each other, with the inner roller  11  contacting the rollers  10 . Let L be a distance between a contact point “g” at which the rollers  10  contact with each other and the bearing axis O. Let R2 be a distance from the bearing axis O to the outer periphery of the inner ring case  2 , with each roller  10  having the radius “a”. The distance L can be determined as follows with the Pythagorean theorem. 
         L =√(( R 2+ a ) 2   −a   2 )
 
     Let H be a distance between the groove width  2  that corresponds to the position indicated by the radius R2 and the inner periphery  32  of the guide groove  30 . A distance U between a center of the inner roller  11  and the contact point g at which the rollers  10  contact each other can be determined using a formula below. 
         U=L —( R 2+ H )— b  
 
     The radius “b” of the inner roller  11  can be determined from a triangle connecting the axial center O1 of the roller  10 , the center of the inner roller  11 , and the contact point g between the rollers  10 . The radius “b” of the inner roller  11  needs to be great compared to the state illustrated in  FIG.  12    and thus satisfies a formula below. 
         b &gt;( L   2 +( R 2+ H ) 2 −2 L ( R 2+ H ))/2( a+L−R 2− H )
 
     A relationship illustrated in  FIG.  13    between the inner roller  11  and the rollers  10  is such that a triangle O1-O2-O formed by three points that are the center O1 of the roller  10 , the center O2 of the inner roller  11 , and the bearing axis O is a right triangle. When an angle at the vertex O of the triangle O1-O2-O is θ1 with the inner rollers  11  being “n” in number, the angle θ1 can be expressed in a formula below. It is to be noted that “n” is an integer greater than or equal to 3. 
       2θ1≤2π≤2θ1×( n+ 1)
 
       wherein 
       θ1=arccos(( b+H+R 2)/( a+R 2))
 
     On the basis of these relations, the radius “b” of the inner roller  11  can take a maximum of b≤(a+R2)cos(π/n)−(H+R2). 
     Based on the above relations, the radius “b” of the inner roller  11  satisfies Formula (1) below. 
       ( L   2 +( R 2+ H ) 2 −2 L ( R 2+ H ))/2( a+L−R 2− H )&lt; b ≤( a+R 2)cos(π/ n )−( H+R 2)  (1)
 
     In the fourth embodiment, a radius (b) range of the inner roller  11  for preventing the rollers  10  from contacting each other is identifiable with Formula (1). Since the contact between the rollers  10  is prevented thus, strength against transient force (impact) is improved. 
     Fifth Embodiment 
     Although a section of each guide groove  30  that faces in a circumferential direction has the shape of a quadrangle in the first embodiment, another shape may be adopted. In  FIG.  14   , the guide groove  30  has a triangular section that faces in the circumferential direction, and the inner roller  11  has triangular ends. In  FIG.  15   , the guide groove  30  has a semicircular section that faces in the circumferential direction, and the inner roller  11  has semicircular ends. In  FIG.  16   , the guide groove  30  has a semielliptical section that faces in the circumferential direction, and the inner roller  11  has semielliptical ends. The section of the guide groove  30  that faces in the circumferential direction and the ends of the inner roller  11  may each have the shape of a combination of a quadrangle, a triangle, a semicircle, and a semiellipse. As illustrated in each of  FIGS.  17  to  19   , the inner periphery  32  of the guide grooves  30  may coincide with the external face  1   d  of the outer ring case  1  that is closer to the inner ring case  2 . In  FIG.  17   , the guide groove  30  has a triangular section that faces in the circumferential direction. In  FIG.  18   , the guide groove  30  has a semicircular section that faces in the circumferential direction. In  FIG.  19   , the guide groove  30  has a semielliptical section that faces in the circumferential direction. In each of  FIGS.  14  to  19   , the respective sections of the left and right guide grooves  30  that face in the circumferential direction have the same shape; however, the left shape and the right shape may be different. 
     Sixth Embodiment 
     An amount of radial movement of the inner roller  11  upon which centrifugal force acts is determined by: the position of the inner periphery  32  of the guide groove  30 ; the position of the outer periphery  31  of the guide groove  30 ; the radius “a” of each roller  10 ; and the radius “b” of each inner roller  11 . It is difficult to strictly determine a relationship among these four dimensions. Therefore, a radial clearance between the guide groove  30  and each inner roller  11  is defined. The radial clearance between the guide groove  30  and each inner roller  11  is set greater than a fit tolerance that is determined from a tolerance class H9 (Japanese Industrial Standard) for respective diameters (2×r1) and (2×r2) of the outer and inner peripheries  31  and  32  of the guide groove  30  that determine the radial groove width Δr of the guide groove  30  and a tolerance class C9 (Japanese Industrial Standard) for the diameter (2×b) of the inner roller  11 . 
     The above configurations illustrated in the embodiments are illustrative of contents of the present disclosure, can be combined with other techniques that are publicly known, and can be partly omitted or changed without departing from the gist of the present disclosure. 
     REFERENCE SIGNS LIST 
     1 outer ring case;  2  inner ring case;  10  roller;  11  inner roller;  20 ,  30  guide groove;  40  tapped hole;  41  screw; O bearing axis.