Abstract:
A bearing device for an axle: including a hub wheel; a flange outwardly provided in an outer periphery of the hub wheel in a radial direction; and bolts having serrations provided at their heads. The flange includes through holes formed therein in its circumferential direction such as to pass therethrough in its axial direction, the bolts are attached into the through holes, respectively, in a state where their serrations bite the through holes of the flange, and an annular groove for reducing a biting amount of the serrations of the bolt is formed in an inner peripheral surface of the through hole of the flange.

Description:
BACKGROUND OF THE INVENTION 
   With reference to  FIG. 16 , a disk rotor  5  is fixed to an outer end surface of a flange  10  of a hub wheel  2  by means of a plurality of bolts  12  which are inserted into through holes  11  formed in a circumference of the flange  10 . The disk rotor  5  is fixed to the flange  10  after a bearing device for axle  1  is attached to a drive shaft  4 . Therefore, it is necessary to previously attach the bolts  12  into the through holes  11  of the flange  10 . The bolts  12  are attached into the through holes  11  in non-separable manner so that the bolts  12  do not come out the flange  10  when the bearing device for axle  1  is independently handled. For this reason, the bolt  12  is formed with a serration  13 . The bolt  12  is fitted into the through hole  11  in such a state where the serration  13  bites into a circular inner peripheral surface of the through hole  11 . 
   In this state, a diameter of the through hole  11  is finely increased by its plastic deformation, and an outer end surface of the flange  10  is finely undulated in its circumferential direction and radial direction. As a result, a surface precision of the outer end surface of the flange  10  is lowered. More specifically, an inner diameter of the through hole  11  is expanded by μm unit in the serration  13  of the bolt  12  as shown with arrows in  FIG. 17 , and the surface precision is lowered. The deterioration of the surface precision in the outer end surface of the flange  10  causes the deterioration of adhesion of the disk rotor  5  with respect to the flange  10 , whereby the disk rotor  5  is inclined and its rotation precision is disadvantageously deteriorated. 
   Therefore, it is an object of the present invention to provide a bearing device for axle capable of stabilizing the attachment position of the disk rotor with respect to the hub wheel. 
   SUMMARY OF THE INVENTION 
   The present invention provides a bearing device for axle comprising: a hub wheel; a flange outwardly provided in an outer periphery of the hub wheel in a radial direction; and bolts having serrations provided at their heads, wherein the flange includes a plurality of through holes formed therein in its circumferential direction such as to pass therethrough in its axial direction, the bolts are attached into the through holes, respectively, in a state where their serrations bite the through holes of the flange, and an annular groove for reducing a biting amount of the serration of the bolt is formed in an inner peripheral surface of the through hole of the flange. 
   Depending upon embodiments of the annular groove of the present invention, one annular groove is provided in at least a biting region of the serration in the inner peripheral surface of the through hole, or several annular grooves are independently provided at several locations in the axial direction, or the annular groove is helically continuously formed. In this case, when the bolt is attached into the through hole, the biting amount of the serration of the bolt with respect to the inner peripheral surface of the through hole can be reduced as small as possible and, thus, the flow of the wall portion by the plastic deformation can be suppressed. 
   In one of the embodiments of the present invention, the bolt is attached in a state where the disk rotor of the disk brake apparatus abuts against the outer end surface of the flange directed radially outwardly of the hub wheel, several through holes are provided around the circumference of the flange, the wheel-mounting bolts are fitted into the through holes in a state where the bolts pass through the through hole and serrations provided on the side of the heads of the bolts bite the through holes, and a weak portion is provided around the through hole for permitting a phenomenon in which the through hole is increased in diameter by the plastic deformation when the bolt is mounted into the through hole. 
   The weak portion may has an annular recess which is formed by recessing an outer peripheral portion of the through hole in the flange from an outer side or an inner side of a vehicle concentrically with the through hole, or the weak portion may comprise annular recesses which are formed by recessing an outer diameter side and an inner diameter side of the through hole in the flange from an outer side or an inner side of a vehicle concentrically with the flange. 
   In this case, when the bolt is attached into the through hole, although the flow of the wall portion of the through hole is generated by the plastic deformation by the weak portion around the through hole when the bolt is mounted into the through hole, since the flow of the wall portion is generated in a state where it is absorbed by the weak portion and the flow is less prone to be transferred to the outer end surface of the flange, the outer end surface of the flange becomes less prone to be deformed. 
   The above and other embodiments will be apparent from the following description of the present invention in association with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an enlarged view showing a main portion of a hub wheel in a bearing device for axle according to an embodiment of the present invention; 
       FIG. 2  shows a state before a bolt is attached in  FIG. 1 ; 
       FIG. 3  is an enlarged view showing a main portion of a hub wheel in a bearing device for axle according to another embodiment of the present invention; 
       FIG. 4  shows a state before a bolt is attached in  FIG. 3 ; 
       FIG. 5  is an enlarged view showing a main portion of a hub wheel in a bearing device for axle according to still another embodiment of the present invention; 
       FIG. 6  shows a state before a bolt is attached in  FIG. 5 ; 
       FIG. 7  is an enlarged view showing a main portion of a hub wheel in a bearing device for axle according to yet another embodiment of the present invention; 
       FIG. 8  shows a state before a bolt is attached in  FIG. 7 ; 
       FIG. 9  is a plan view showing an inner end surface of a flange in  FIG. 8 ; 
       FIG. 10  shows a modification of the embodiment shown in  FIG. 9 ; 
       FIG. 11  is an enlarged view showing a main portion of a hub wheel in a bearing device for axle according to yet another embodiment of the present invention; 
       FIG. 12  is an enlarged view showing a main portion of a hub wheel in a bearing device for axle according to yet another embodiment of the present invention; 
       FIG. 13  is an enlarged view showing a main portion of a hub wheel in a bearing device for axle according to yet another embodiment of the present invention; 
       FIG. 14  is an enlarged view showing a main portion of a flange of a hub wheel in a bearing device for axle according to yet another embodiment of the present invention; 
       FIG. 15  is an enlarged view showing a main portion of a flange of a hub wheel in a bearing device for axle according to yet another embodiment of the present invention; 
       FIG. 16  is a vertical sectional view showing a conventional bearing device for axle for a driving wheel; 
       FIG. 17  is an explanatory view for pointing out a conventional problem; and 
       FIG. 18  is a vertical sectional view showing an upper half of a bearing device for axle for a follower wheel to which the present invention can be applied. 
   

   In these figures, the same elements are designated with the same symbols. 
   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to the drawings,  FIG. 1  is an enlarged view showing a main portion of a hub wheel in a bearing device for axle according to an embodiment of the present invention, and  FIG. 2  shows a state before a bolt is attached in  FIG. 1 . Since the entire structure of the bearing device for axle is shown in  FIG. 16 , description thereof will not be repeated. In  FIG. 16 , a reference numeral  1  represents the bearing device for axle of this embodiment, a reference numeral  2  represents a hub wheel, a reference numeral  3  represents a double row angular ball bearing with vertex of contact angles outside of bearing as a rolling bearing, a reference numeral  4  represents a drive shaft, a reference numeral  6  represents a knuckle as a part of a body, a reference numeral  7  represents a brake pad, a reference numeral  10  represents a flange, a reference numeral  11  represents a through hole, a reference numeral  12  represents a bolt, and a reference numeral  13  represents a serration. 
   In order to suppress the outer end surface of the flange  10  from being undulated when the bolt  12  is attached into the through hole  11  of the flange  10  of the hub wheel  2 , this bearing device  1  has the following idea. 
   That is, as shown in the figure, an inner peripheral surface of the through hole  11  of the flange  10  is formed with a plurality of annular grooves  14  adjacently in an axial direction of the through hole  11 . The annular grooves  14  need not be formed over the entire length of the through hole  11 , and may be formed in a region where at least the serration  13  of the bolt  12  bites into the through hole  11 . The number of annular grooves  14  is optionally determined. 
   As shown in  FIG. 2 , a biting margin of the through hole  11  bitten by the serration  13  of the bolt  12  is managed by setting an inner diameter R 1  of a minimum diameter portion of the annular groove  14  of the through hole  11  smaller than an outer diameter R 2  of the serration  13  of the bolt  12 . The biting margin is preferably 0.5 mm or less and more preferably 0.3 mm or less. With this arrangement, the bolt  12  is held such that the bolt  12  does not come out from the through hole  11  and is prevented from rotating. 
   In the above-described embodiment, it is possible to reduce the biting amount of the serration  13  of the bolt  12  with respect to the inner peripheral surface of the through hole  11  when the bolt  12  is attached into the through hole  11 . Therefore, it is possible to reduce the flow of a wall portion around the through hole  11  by the plastic deformation. With this arrangement, it is possible to prevent the flow of the wall portion around the through hole  11  from affecting the outer end surface of the flange  10  and, thus, this advantageously keeps the outer end surface of the flange  10  smooth. 
   Therefore, it is possible to bring the disk rotor  5  into tight contact with the outer end surface of the flange  10  to which the bolt  12  is attached in the non-separable manner, and it is possible to prevent the disk rotor  5  from being inclined unlike the prior art. Therefore, the rotation precision of the disk rotor  5  can be enhanced. 
   As shown in  FIGS. 3 and 4 , for example, the annular groove  14  may be formed helically and continuously in the inner peripheral surface of the through hole  11 . Alternatively, an axial size of the annular groove  14  in a single form may be increased and its sectional shape may be of concave-shape as shown in  FIGS. 5 and 6 . It is preferable that the axial size X of the annular groove  14  and an axial size Y of a region of the serration  13  of the bolt  12  shown in  FIGS. 5 and 6  is in a relation of X≦0.8Y. Any of these cases can obtain the operation and effect similar to that of the above-described embodiment. In the case of examples shown in  FIGS. 5 and 6 , the wall portion around the through hole  11  is slightly flowed when the serration  13  bites at the time of attaching operation of the bolt  12  to the through hole  11 , but this flow of the wall portion is generated in a state where this flow deforms an inner wall of the annular groove  14  and does not affect the outer end surface of the flange  10 . Therefore, this advantageously keeps the outer end surface of the flange  10  smooth. 
   In the above-described embodiment, the biting amount of the serration  13  of the bolt  12  with respect to the inner peripheral surface of the through hole  11  is reduced as small as possible. Alternatively, a weak portion for allowing a phenomenon in which the through hole  11  is increased in diameter by the plastic deformation when the bolt  12  is attached into the through hole  11  maybe provided around the through hole  11 . More specifically, as shown in  FIGS. 7 to 9 , an annular recess  15  which is recessed from an outer side of a vehicle is concentrically formed in an outer peripheral portion of the through hole  11  in the flange  10 . The annular recess  15  functions as the weak portion. As another example of the weak portion, as shown in  FIG. 10 , annular recesses  16   a  and  16   b  which are recessed from the outer side of the vehicle may be formed concentrically with the flange  10  in the outer diameter side and the inner diameter side of the through hole  11  in the flange  10 . The sectional shape in this case is the same as those shown in  FIGS. 7 and 8 . 
   In any of these examples, as the serration  13  bites when the bolt  12  is attached into the through hole  11 , the wall portion is flowed around the through hole  11  and the diameter of the through hole  11  is increased, but since the annular recesses  15 ,  16   a  and  16   b  suppress the flow of the wall portion from spreading to a wide area and absorb such flow, the undulating phenomenon of the outer end surface of the flange  10  can be suppressed, and its smoothness is maintained. In other words, the annular recesses  15 ,  16   a  and  16   b  function as flanges around the outer periphery of the through hole  11  and, thus, the flanges are bent as the wall portion is flowed around the through hole  11 , and the flow is suppressed from spreading toward other portion and is absorbed. Even if the annular recesses  15 ,  16   a  and  16   b  are formed by being recessed from the inner side of the vehicle, such recesses are also included in the present invention. 
   Although various thought is put on the side of the flange  10  in the above-described embodiment, a hole  17  may be formed in the bolt  12  over its entire length as shown in  FIG. 11 , or a bottomed hole  18  may be formed from a head of the bolt  12  to a desired position exceeding the serration  13  as shown in  FIG. 12 . In this case, the bolt  12  becomes weak, as the serration  13  bites when the bolt  12  is attached into the through hole  11  of the flange  10 , not only the wall portion around the through hole  11  is flowed, but also the bolt  12  itself is also reduced in diameter. If the deformation is shared to the outer periphery of the through hole  11  and the bolt  12  in this manner, it is possible to reduce the flow of the wall portion around the through hole  11  of the flange  10 . Therefore, it is possible to prevent the flow of the wall portion from spreading toward the outer end surface of the flange  10 , and the smoothness of the outer end surface of the flange  10  is maintained. 
   Although the hub wheel  2  functions as one inner ring of the double row angular ball bearing with vertex of contact angles outside of bearing  3  as shown in  FIG. 16 , the present invention can also be applied to a structure in which the one inner ring is independent from the hub wheel  2  although not shown in the figure. 
   In the above-described embodiment, the bearing device  1  used for the driving wheel is shown in  FIG. 16 , the present invention can also be applied to a type in which the bearing device for axle  1  is used for a known follower wheel as shown in  FIG. 18 . In the bearing device for axle used for the follower wheel shown in  FIG. 18 , a double row rolling bearing such as the double row angular ball bearing with vertex of contact angles outside of bearing  3  is disposed in the inner periphery of the hub wheel  2 . The hub wheel  2  herein is utilized as an outer ring of the double row angular ball bearing with vertex of contact angles outside of bearing  3 , which comprises two rows of balls  31 , two cages  32  and  33 , and two inner rings  34  and  35 . The features shown in each embodiment is applied to such a case also although not shown in detail. 
     FIGS. 13 ,  14  and  15  show another embodiments.  FIG. 13  corresponds to  FIG. 1 , and shows that the bolt  12  is inserted into the through hole  11  of the flange  10 .  FIGS. 14 and 15  show that the bolt  12  is not inserted and show modifications of the through hole  11 . In the embodiments shown in  FIGS. 13 to 15 , as in  FIGS. 1 to 4 , a helical annular groove  14  shown in  FIGS. 14 and 15  are formed in the inner peripheral surface of the through hole  11 , a first enlarged portion  21  and a second enlarged portion  22  which gradually spread are formed on axially opposite ends of the through hole  11 . The first enlarged portion  21  is provided on an end of the through hole  11  on the side of a bolt seat surface  10   a , and gradually spread toward the bolt seat surface  10   a . The second enlarged portion  22  is provided on an end of the through hole  11  on the side of the outer end surface  10   b  and gradually spread toward the outer end surface  10   b.    
   The inner peripheral surface  11   a  of the through hole  11  located between the first enlarged portion  21  and the second enlarged portion  22  is formed with an annular groove  14 . The annular groove  14  is formed closer to the bolt seat surface  10   a  of the inner peripheral surface  1   a  in the axial direction. When the bolt  12  is inserted into the through hole  11 , the serration  13  of the bolt  12  bites the annular groove  14  formed on the inner peripheral surface  11   a  closer to the bolt seat surface  10   a  and is fixed. The outer peripheral surface of the bolt  12  is not in contact with the first enlarged portion  21  and the second enlarged portion  22  in a state where the bolt  12  is attached into the through hole  11 . 
   An axial region where the serration  13  bites the inner peripheral surface  11   a  is formed closer to the bolt seat surface  10   a  in the axial direction of the through hole  11 . Therefore, the influence of biting of the serration  13  is less prone to be transferred to the outer end surface  10   b , which is advantageous in that the outer end surface  10   b  of the flange  10  is maintained smooth. The flow of wall portion caused by the biting of the serration  13  with respect to the inner peripheral surface  11   a  moves to the annular groove  14 , which suppresses the through hole  11  and its periphery from being deformed, which is advantageous in that the outer end surface  10   b  of the flange  10  is maintained smooth. The flow of wall portion caused by the biting of the serration  13  moves to the first enlarged portion  21  and the second enlarged portion  22  and is absorbed, which is more advantageous in that the outer end surface  10   b  of the flange  10  is maintained smooth. 
   When a width of the second enlarged portion  22  in its axial direction is formed greater than that of the first enlarged portion  21  in its axial direction, this is advantageous in that the outer end surface  10   b  of the flange  10  is maintained smooth. When a width of at least one of the first enlarged portion  21  and the second enlarged portion  22  in its axial direction exceeds 13% of a thickness of the flange  10 , this is advantageous in that the outer end surface  10   b  of the flange  10  is maintained smooth. The first enlarged portion  21  functions as a guiding surface when the bolt  12  is inserted into the through hole  11 , and the bolt  12  can be inserted smoothly. 
   As described above, according to the present invention, the flow amount of the wall portion around the through hole caused by the biting of the serration at the time when the bolt is attached into the through hole of the flange is reduced, the flow of the wall portion is less prone to be transferred to the outer end surface of the flange, and this is advantageous in that the outer end surface is maintained smooth. 
   Further, according to the present invention, the flow of the wall portion around the through hole caused by the biting of the serration at the time when the bolt is attached into the through hole of the flange is not transferred toward the outer end surface of the flange and is absorbed, and this is advantageous in that the outer end surface of the flange is maintained smooth. 
   According to the present invention, since the smoothness of the outer end surface of the flange can be ensured, the disk rotor can be attached to the outer end surface of the flange with an appropriate position without inclination, and rotation precision of the disk rotor can be enhanced.