Abstract:
A bearing apparatus for a vehicle driving wheel has a pre-loading mechanism formed in the serration fitted portion between the stem portion of the outer joint member and the wheel hub. A fastening member combines the wheel hub and the outer joint member. A releasing member, adapted to be arranged on the wheel hub, enables removal of the fastening mechanism.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to Japanese Patent Application No. 2002-227447 filed Aug. 5, 2002, which application is herein expressly incorporated by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a bearing apparatus for rotatably supporting a driving wheel of a vehicle. 
   BACKGROUND OF THE INVENTION 
   A power transmission apparatus transmits power from the vehicle engine to the vehicle wheels. The apparatus enables radial, axial and moment displacements caused by the bound of wheels and the turning of the vehicle during travel. The apparatus includes a drive shaft  100  arranged between the engine and the driving wheel. One end of the drive shaft  100  is connected to a differential gear  102  via a slidable constant velocity universal joint  101 . The other end of the drive shaft is connected to a wheel  105  via a bearing apparatus  104  which includes a fixed type constant velocity universal joint  103 , as shown in  FIG. 13 . 
   A prior art bearing apparatus  104  for a vehicle driving wheel is shown in  FIG. 11 . The apparatus  104  includes a wheel hub  106  for mounting the wheel  105 , a double row rolling bearing  107  for rotatably support the wheel hub  106  and a fixed type constant velocity universal joint  103 . The universal joint  103  is adapted to be connected to the wheel hub  106  to transmits the power to the wheel hub. 
   It is known that torsion is created in the drive shaft  100  by a large torque from the engine, via the slidable constant velocity universal joint  101 , at a low engine speed, such as during starting movement of a vehicle. As a result, torsion is also created on an inner ring  109  of the double row rolling bearing  107  which supports the driving shaft  100 . A stick-slip noise is generated at the abutting surfaces between the outer joint member  108  and the inner ring  109  due to radical slip therebetween when a large amount of torsion exist in the driving shaft  100 . 
   A bearing apparatus for a vehicle driving wheel is known for example from Japanese Laid open publication No. 5404/1999. The bearing apparatus has a wheel hub  110  on which the inner ring  109  is fitted. The inner wheel  109  is axially secured by a caulked portion  111  formed on the inner end portion of the wheel hub  110 . The wheel hub  110  and the outer joint member  108  are united by a nut  113 . The outer joint member  108  is fitted in the wheel hub  110  via the serration  112 . The shoulder of the outer joint member  108  is abutted to the inner end surface of the caulked portion  111 . 
   Accordingly, the pre-load of the double row rolling bearing  107  can be easily controlled and maintained without strongly fastening the nut  113  as in a conventional manner and also without strictly controlling the fastening torque. In addition, the wheel hub  110  and the outer joint member  108  can be united by lightly tightening the nut  113 . Therefore it is possible to prevent generation of the stick-slip noise at the abutting surfaces between the inner ring  109  and the outer joint member  108  although the torsion would be caused on the outer joint member  108 . However, in such a bearing apparatus for a driving wheel, noise generation or loosening of the nut  113  is sometimes caused during rapid acceleration and deceleration times when circumferential backlash occurs in the fitted portion of the serration  112 . In order to resolve this problem, a helix angle is provided in the serration  112  of the outer joint member  108 . The serration  112  is press fit into the serration  114  of the wheel hub  110  to eliminate the circumferential backlash in the fitted portion. In such a construction, a problem exists in that a machine, such as a press or the like, is required to assemble or disassemble the wheel hub  110  and the outer joint member  108 . This reduces the working efficiency. 
   While this structure can maintain the pre-load of the rolling bearing  107  lightly tightened to the nut  113 , another problem is created. A small gap is created at the abutted portion between the wheel hub  110  and the outer joint member  108 . This lowers the sealing performance. If rain water penetrates into the bearing, the serration fitted portion will be rigidly seized by rust, which also reduces the working efficiency. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a bearing apparatus for a vehicle driving wheel which has high reliability and an excellent maintenance ability. Thus, a high working efficiency exist in assembling and disassembling the bearing apparatus. 
   To achieve the objects of the present invention, a bearing apparatus for a vehicle driving wheel is provided with a double row rolling bearing. A wheel hub is integrally formed with a wheel mounting flange at one end of the double row rolling bearing. A cylindrical stepped portion of smaller diameter axially extends from the other end of the wheel hub. An inner ring is fitted on the stepped portion of smaller diameter of the wheel hub. The inner ring is secured on the wheel hub through a caulked portion formed by plastically deforming the end of the stepped portion radially outwardly. An outer joint member has a shoulder adapted to be abutted to the end surface of the caulked portion. A stem portion axially extends from the shoulder. The outer joint member is inserted in the wheel hub, via a serration fitted portion, to attain a detachable engagement with the wheel hub. The bearing apparatus further comprises a pre-loading mechanism formed in the serration fitted portion between the stem portion of the outer joint member and the wheel hub. A fastening mechanism combines the wheel hub and the outer joint member. A releasing mechanism is adapted to be arranged on the wheel hub to remove the fastening mechanism. 
   According to the provision of the pre-loading mechanism formed in the serration fitted portion between the stem portion of the outer joint member and the wheel hub, it is possible to eliminate circumferential backlash and prevent noise generation at rapid acceleration and deceleration times of the vehicle as well as the loosening of the bolt due to the circumferential backlash. In addition it is possible to easily disassemble the bearing apparatus although the serration of the stem portion and the wheel hub is fitted in the pre-load condition. This is due to the provision of the releasing mechanism adapted to be arranged on the wheel hub to remove the fastening mechanism. 
   According to the present invention, the serration fitted portion is pre-loaded by providing a helix angle on the serration of the stem portion of the outer joint member. The helix angle has a predetermined angle relative to the axis of the stem portion. This structure provides the pre-load in the serration fitted portion in order to prevent circumferential backlash. This, in turn, prevents noise generation at rapid acceleration and deceleration times of vehicle as well as the loosening of the bolt due to the circumferential backlash. In addition, it is possible to improve sealing performance by preventing fretting abrasion at the caulked portion and the shoulder of the outer joint member. 
   According to the present invention, the outer end surface of the wheel hub is formed with an internal thread. The wheel hub and the outer joint member are united by a plate. The plate has a circular aperture formed at a position corresponding to the internal thread. A central aperture is formed with an internal thread. The plate abuts the outer end surface of the wheel hub. A securing bolt is screwed into an internal thread formed in the shaft of the outer joint member through the central aperture of the plate. This structure makes it possible to reduce the weight of the bearing apparatus as well as to easily disassemble the bearing apparatus. This improves the working efficiency in assembling and disassembling the bearing apparatus even though the serration of the stem portion and the wheel hub is fitted in the pre-load condition. 
   According to the present invention, the releasing mechanism includes a releasing jig formed with an external thread. An internal thread, which engages the external thread of the releasing jig, is formed on a pilot portion of the wheel hub. Accordingly, it is possible to separate the wheel hub and only mount the releasing jig on the wheel hub by screwing the bolt into the internal thread formed in the center of the releasing jig. Thus, it is possible to improve the working efficiency of assembly and disassembly of the bearing apparatus even though the serration of the stem portion and the wheel hub is fitted in the pre-load condition. 
   According to the present invention, the outer end portion of the wheel hub is formed with an annular recess with a tapered internal circumferential surface. The annular recess receives a fastening member formed with a serration on its inner circumferential surface. The diameter of the fastening member is reduced by screwing a securing bolt into an internal thread formed in the stem portion of the outer joint member. Since the fastening member applies the pre-load at the serration fitted portion, it is possible to unite and to pre-load the stem portion and the wheel hub without providing the pre-loading mechanism between the serration fitted portion. 
   According to the present invention, the fastening member is a split ring formed with slits arranged along its circumference. Alternatively, the fastening member is formed as a plurality of circumferentially separated parts. This structure reduces the diameter of the fastening member. 
   More particularly, according to the present invention, a plurality of slits are formed on either the inner or outer circumferential surface of the fastening member. This structure reduces the diameter of the fastening member and thus also improves the working efficiency during assembly and disassembly of the bearing apparatus. 
   According to the present invention, an elastic ring is fitted in an annular space formed between the end surface of the inner ring and the shoulder of the outer joint member. One end of a pulsar ring is arranged on the shoulder of the outer joint member engaging the elastic ring. This structure prevents the plastic ring from falling off as well as remarkably improving the sealing performance between the end surface of the inner ring and the shoulder of the outer joint member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a longitudinal section view showing a first embodiment of the bearing apparatus for a driving wheel of the present invention; 
       FIG. 2  is a cross section view showing a releasing jig of the present; 
       FIG. 3  is an enlarged partial cross section view of  FIG. 1  of the bearing apparatus for a driving wheel of the present invention; 
       FIG. 4  is a longitudinal section view of the bearing apparatus for a driving wheel of the present invention of the first embodiment for explaining a method of disassembling; 
       FIG. 5  is a longitudinal section view showing a second embodiment of the bearing apparatus for a driving wheel of the present invention; 
       FIG. 6  is a longitudinal section view of the bearing apparatus for a driving wheel of the present invention of the second embodiment for explaining a method of disassembling; 
       FIG. 7(   a ) is a front elevation view showing an another releasing jig of the present, and  FIG. 7(   b ) is a cross section view; 
       FIG. 8  is a longitudinal section view showing a third embodiment of the bearing apparatus for a driving wheel of the present invention; 
       FIG. 9(   a ) is a front elevation view showing one embodiment of the fastening member of the present invention, and  FIG. 9(   b ) is a cross section view thereof; 
       FIGS. 10(   a ), ( b ) and ( c ) are front elevation views showing other embodiments of the fastening members; 
       FIG. 11  is a longitudinal section view showing a bearing apparatus for a driving wheel of the prior art; 
       FIG. 12  is a longitudinal section view showing another bearing apparatus for a driving wheel of the prior art; 
       FIG. 13  is a longitudinal section view showing one example of power transmission apparatus into which a bearing apparatus for a driving wheel is incorporated. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be hereinafter described with reference to the accompanied drawings.  FIG. 1  is a longitudinal section view showing a first embodiment of a bearing apparatus for a vehicle driving wheel of the present invention. 
   The apparatus has a wheel hub  1 , a double row rolling bearing  2  and an constant velocity universal joint  3  which are assembled as a unit. In the description below, the term “outboard side” of the apparatus denotes a side which is positioned outside of the vehicle body. The term “inboard side” of the apparatus denotes a side which is positioned inside of the body when the apparatus is mounted on the vehicle body. 
   The wheel hub  1  is formed integrally with a wheel mounting flange  4  at the outboard side of the wheel hub  1  on which a wheel (not shown) is mounted. The wheel hub  1  has an inner raceway surface  1   a  at the outboard side of the double row rolling bearing  2 . A cylindrical stepped portion  1   b  of smaller diameter axially extends from the inner raceway surface  1   a . The outer circumferential surface of the wheel hub  1 , from the inner raceway surface  1   a  to the cylindrical stepped portion  1   b , is formed with a hardened layer having a surface hardness of HRC 54˜64. It is preferable to use a high frequency induction heating as a heat treatment which can easily carry out a local heating and setting of the depth of a hardened layer. The end of the stepped portion is not hardened and has a surface hardness less than HRC 25 to enable the end to be plastically deformed to form caulked portion  6 . 
   The stepped portion  1   b  of small diameter of the wheel hub  1  is press fit with an inner ring  7  to form a so-called “third generation” structure. The inner ring  7  is immovably secured in an axial direction. The outer circumferential surface of the inner ring  7  is formed with inner raceway surface  7   a  at the inboard side of the double row rolling bearing  2  to form a double row inner raceway surface of the bearing  2 . 
   The double row rolling bearing  2  has an outer member  8 , inner member  9  and a double row rolling elements  10  and  10 . The outer member  8  is integrally formed on its outer circumferential surface with a body mounting flange  8   a . On its bore surface, the outer member  8  has a double row outer raceway surfaces  8   b  and  8   b . On the other hand, the inner member  9  has the wheel hub  1  and the inner ring  7 . The double row rolling elements  10  and  10  are contained between the outer raceway surfaces  8   b  and  8   b  and the inner raceway surfaces  1   a  and  7   a . The rolling elements  10  are freely rotatably held by cages  11  and  11 . Seals  12  and  13  are arranged at the ends of the bearing  2  to prevent leakage of grease contained within the bearing  2  as well as ingress of rain water or dusts. The illustrated ball rolling elements  10  and  10  may be replaced for example by conical rolling elements. 
   The constant velocity universal joint  3  has an outer joint member  14 , a joint inner ring  15 , a cage  16  and torque transmitting balls  17 . The outer joint member  14  has a cup-shaped mouth portion  14   a , a shoulder  14   b  that forms the bottom of the mouth portion  14   a , and a stem portion  18  which axially extends from the shoulder  14   b . The outer circumferential surface of the stem portion  18  is formed with a serration (or a spline)  18   a . An external thread  18   b  is formed on the inner circumferential surface of the stem portion  18 . The serration  18   a  of the stem portion  18  is formed with a helix angle of a predetermined angle relative to the axis of the stem portion  18 . 
   The serration  18   a  of the stem portion  18  is fitted into the serration  5  of the wheel hub  1  by inserting the stem portion  18  into the wheel hub  1  until the shoulder  14   b  of the outer joint member  14  abuts the inner end surface of the caulked portion  6 . Thus a pre-load is caused at the fitted portion of the serrations of the wheel hub  1  and the stem portion  18  in order to eliminate circumferential backlash. Finally the wheel hub  1  and the outer joint member  14  are axially united by screwing a securing bolt  20  into the internal thread  18   b  via a plate  19  abutting onto the outer end surface  1   c  of the wheel hub  1 . In this case, the stem  18  can be easily fitted into the serration  5  of the wheel hub  1  if the fitted length is less than ½˜⅓ the whole length of the serration  18   a  of the stem portion  18 . Accordingly, the stem portion  18  of the outer joint member  14  can be inserted into the wheel hub  1  by fastening the bolt  20 . 
   Alternatively, the serration  18   a  of the stem portion  18 , with the helix angle, in order to apply the pre-load to the fitted portion with the serration  5  of the wheel hub, it is possible to appropriately set the tooth thickness of the serrations  18   a  and  5  of the stem portion  18  and the wheel hub  1 , respectively, to apply the pre-load at their fitted portions. 
   One embodiment of the releasing jig  19 ′ used for disassembling the bearing apparatus to repair it is formed as a plate shaped configuration as shown in  FIG. 2 . The jig  19 ′ has an internal thread  19   a  to engage the securing bolt  20  at the center. The jig  19 ′ also has a plurality of circular apertures  19   b  near its periphery. Internal threads Id are formed on the outer end surface of the wheel hub  1  at positions corresponding to those of the circular apertures  19   b  of the releasing jig  19 ′. 
   An elastic ring  21  is inserted around the caulked portion  6  of the wheel hub  1  in an annular space formed between the inner ring  7  and the shoulder  14   b . The elastic ring  21  is pressed down by a pulsar ring  22  for ABS (Anti-lock Brake System) press fit onto the outer circumferential surface of the shoulder  14   b  to prevent the elastic ring  21  from coming out of the annular space. The pulsar ring  22  is formed by press forming a steel plate and is formed with a plurality of irregularities  22   a  to detect the rotation speed using an oppositely arranged sensor. The pulsar ring may be integrally heat bonded to the elastic ring or may be inserted into an annular recess  21   a  formed in the elastic ring  21 ′ as shown in  FIG. 3 . 
   According to this embodiment, the rolling bearing adopts a so-called “self-retain structure” in which the inside gap of the rolling bearing  2  is a negative gap to improve the rigidity of the bearing. The inner ring  7  is axially secured by the caulked portion to maintain the negative gap. Accordingly, this structure makes it possible, not only to sub-unitize the bearing portion, but to easily incorporate a bearing portion to a vehicle because it is unnecessary to control the pre-load by setting the fastening torque. In addition it is possible to prevent loosening of bolt  20  because of the application of the pre-load at the serrations  5  and  18   a  to eliminate the circumferential backlash. Also, it is possible to prevent ingress of rain water or dusts through a gap between the caulked portion  6  and the shoulder  14   b . Furthermore, it is possible to remarkably improve the sealing performance between the caulked portion  6  and the shoulder  14   b  because of the presence of the elastic ring  21  inserted in the annular space formed between the inner ring  7  and the shoulder  14   b.    
   A method for disassembling the bearing apparatus of the first embodiment will be described with reference to  FIG. 4 . First, the bolt  20  and the plate  19  fastened onto the outer end surface  1   c  of the wheel hub  1  are removed. The bolt  23  is screwed into the stem portion  18  of the outer joint member  14  in order to plug the internal threaded aperture  18   b . Any member may be used in place of the bolt  23  so as to plug the aperture  18   b . The releasing jig  19 ′ is abutted onto the outer end surface  1   c  of the wheel hub  1  and aligning the circular aperture  19   b  with the internal thread  1   d  formed on the outer end surface  1   c . The bolt  24  is screwed into the internal thread  1   d  so as to secure the releasing jig  19 ′ on the outer end surface  1   c . Finally, the securing bolt  20  is screwed into the internal thread  19   a  of the releasing jig  19 ′. Continuing the screwing operation, the tip end of the bolt  20  abuts on the head of bolt  23  and thus the outer joint member  14  will be gradually pushed out from the wheel hub  1 . Thus, according to the bearing apparatus of the present invention, it is possible to reduce its weight and to assure its reliability compared with the bearing apparatus of the prior art. In addition it is possible to easily assemble and disassemble the bearing apparatus and thus to improve the maintenance working efficiency. 
     FIG. 5  is a longitudinal section view showing a second embodiment of the bearing apparatus for a driving wheel of the present invention. The only difference between this embodiment and the first embodiment is in the structure of the stem portion of the outer joint member and therefore like numerals are used to designate like structure also in  FIG. 5 . 
   The stem portion  26  of the outer joint member  25  in the constant velocity universal joint  3 ′ is formed with a serration (or spline)  26   a  at the circumferential surface. A threaded portion  26   b  is formed at the end. Similarly to the first embodiment, the helix angle is applied to the serration  26   a  inclined at a predetermined angle relative to the axis of the stem portion  26 . In order to apply the pre-load to the fitted portion of the serrations  5  and  26   a  and thus eliminate circumferential backlash, the stem portion  26  is fitted into the wheel hub  1 ′ with the serration  26   a  of the stem portion  26  press fit into the serration  5  of the wheel hub  1 ′ until the shoulder  14   b  abuts the inner end surface of the caulked portion  6  of the wheel hub  1 ′. Finally the wheel  1 ′ and the outer joint member  25  are axially united by screwing the securing nut  27  into the threaded portion  26   b  of the stem portion  26 . A numeral  27   a  denotes a caulked portion to engage notched portions formed at the tip end of the stem portion  26  to form a detent of the securing nut  27 . 
   A method for disassembling the bearing apparatus of the second embodiment will be described with reference to  FIG. 6 . First, the securing nut  27  fastened onto the outer end surface  1   c  of the wheel hub  1 ′ is removed. The caulked portion  27   a  of the securing nut  27  is deformed. A releasing jig  28  is inserted within a pilot portion le of the wheel hub  1 ′. The inner circumferential surface is formed with an internal thread  29  and the outer circumferential surface of the releasing jig  28  is formed with an external thread  28   a  to engage with the internal thread  29 .  FIG. 7(   a ) is a front elevation view of the releasing jig  28 .  FIG. 7(   b ) is a cross section view. The releasing jig  28  has a generally cup-shaped configuration and is formed with a flat chamfered surface  28   b  on its bottom and a internal thread  28   c  at its center. 
   The bolt  30  is screwed into the internal thread  28   c  of the releasing jig  28 . The tip end of the bolt  30  abuts the stem portion  26 . Thus, the outer joint member  25  is pushed out from the wheel hub  1 ′ so as to secure the releasing jig  19 ′ on the outer end surface  1   c.    
     FIG. 8  is a longitudinal section view showing a third embodiment of the bearing apparatus for a driving wheel of the present invention. The only difference between this embodiment and the first embodiment is in the structure of the stem portion of the outer joint member. Thus, like numerals are used to designate like structure in  FIG. 8 . 
   The stem portion  26  of the outer joint member  25  is formed with a serration (or spline)  26   a  at the circumferential surface. A threaded portion  26   b  is at the end. On the other hand, the outer end portion of the wheel hub  31  is formed with an annular recess  33  to receive a fastening member  32 . The inner circumferential surface of the annular recess  33  is formed with a tapered surface  33   a . The tapered surface has a taper angle larger than the wedge angle. The outer circumferential surface of the fastening member  32  is also formed with a tapered surface  32   a  corresponding to the tapered surface  33   a . As shown in  FIG. 9 , the fastening member  32  is a split-ring having one slit on its circumference. The fastening member  32  has a serration  32   c  formed on its inner circumferential surface. The serration  32   c  engage a serration  26   a  of the stem portion  26 . 
   As shown in  FIG. 8 , the securing nut  27  is screwed on the threaded portion  26   b  formed on the end portion of the stem portion  26 . The fastening member  32  is moved axially inward and thus reduces its diameter by the tapered surface  33   a  of the wheel hub  31 . Thus the serration  32   c  of the fastening member  32  is strongly fastened onto the serration  26   a  of the stem portion  26  to apply the pre-load to the fitted portion of the serrations  32   c  and  26   a . Accordingly, circumferential backlash at the fitted portion can be eliminated. 
   The power from the constant velocity universal joint  3 ′ is transmitted to the serration  32   c  of the fastener  32 , via the serration  26   a  of the outer joint member  25 , and then to the wheel hub  31 , via the friction between the tapered surfaces  32   a  and  33   a . If the power is large enough to overcome the friction, it can be transmitted to the wheel hub  31 , via the serrations  26   a  and  5 . In disassembling the bearing apparatus, the fastening member  32  can be easily removed from the wheel hub  31  by only removing the securing nut  27 . This is due to the tapered surfaces  32   a  and  33   a  of the fastening member  32  and the wheel hub  31  being formed to have a tapered angle larger than the wedge angle. 
   The fastening member  32  may be formed in many other configuration for example as shown in  FIG. 10 . It is of course that each of these fastening members has a tapered surface similar to that shown in  FIG. 9 . 
   A fastening member  34  shown in  FIG. 10(   a ) has a two-piece structure in which a serration  34   a  and a plurality of slits  34   b  are formed on its inner circumferential surface. A fastening member  35  shown in  FIG. 10(   b ) is also a two-piece structure with serration  35   a  formed on its inner circumferential surface and a plurality of slits  35   b  formed on its outer circumferential surface. A fastening member  36  shown in  FIG. 10(   c ) is a simple two-piece structure with only a serration  36   a  formed on its inner circumferential surface. Other structure for example that separate into more than three pieces may be adopted. 
   As described above, since it is possible to obtain the pre-loaded fitted condition between the serration  26   a  of the stem portion  26  and the serration  32   c  of the fastening member  32  by fastening the securing nut  27  and reducing the diameter of the fastening member  32 , it is possible to dispense with the helix angle on the serration  26   a  of the stem or to make the helix angle small. This further improves the working efficiency in the assembling or disassembling operation. 
   It is intended that the present invention is construed as including all alternations and modifications insofar as they come within the scope of the appended claims or their equivalent.