Abstract:
A tapered roller wheel bearing assembly may include: a hub provided with a hub flange for mounting a wheel formed radial outwardly at an end portion thereof and a hub raceway formed at a side portion close to the hub flange; an outer ring enclosing the hub and provided with an outer raceway corresponding to the hub raceway on an interior circumference thereof; and a tapered roller disposed between the hub raceway and the outer raceway and allowing a relative rotation of the hub and the outer ring, wherein a flange base is formed between the hub flange and the hub raceway and a first undercut for grinding the hub raceway is formed at the flange base, and wherein a second undercut for dispersing stress concentrated on the first undercut is further formed at the flange base.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2013-0032179 filed in the Korean Intellectual Property Office on Mar. 26, 2013, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to a tapered roller wheel bearing assembly. More particularly, the present invention relates to a tapered roller wheel bearing assembly having a second undercut for dispersing stress concentrated on a first undercut formed at a flange base portion. 
         [0004]    (b) Description of the Related Art 
         [0005]    Generally, a bearing is disposed between a rotating element and a non-rotating element so as to smooth rotation of the rotating element. Various types of bearings such as a ball bearing, a tapered roller bearing, needle bearing, and so on are currently used. 
         [0006]    A wheel bearing is one type of such bearings, and rotatably connects a wheel that is the rotating element to a vehicle body that is non-rotating element. The wheel bearing includes an inner ring (and/or a hub) connected to one of a wheel or a vehicle body, an outer ring connected to the other of the wheel or the vehicle body, and rolling elements disposed between the outer ring and the inner ring. 
         [0007]    Balls or tapered rollers are used as the rolling elements of the wheel bearing. Wheel bearings using balls are applied to small vehicles, and wheel bearings using tapered rollers are applied to large vehicles such as buses, trucks and so on. 
         [0008]    A conventional tapered roller wheel bearing assembly is illustrated in  FIG. 1  to  FIG. 3 . 
         [0009]    As shown in  FIG. 1  to  FIG. 3 , the conventional tapered roller wheel bearing assembly  10  includes a hub  20 , an inner ring  60 , an outer ring  30 , and first and second tapered rollers  40  and  50 . 
         [0010]    A hub flange  23  for mounting a wheel is formed at a side portion of the hub  20  and a stepped portion  26  is formed on the other side portion of the hub  20 . In addition, a hub raceway  25  is formed on an exterior circumference of the hub  20  between the hub flange  23  and the stepped portion  26 , and a flange base  24  is formed at a connecting portion of the hub raceway  25  and the hub flange  23 . Typically, a cross-section of the flange base  24  is formed in a curved fashion. A bolt hole  29  is formed at a radial outer portion of the hub flange  23  and a bolt is inserted in the bolt hole  29  such that the wheel is mounted on the hub flange  23 . In addition, a pilot  22  for supporting the wheel is protruded from a side surface of the hub  20  in an axial direction. 
         [0011]    The inner ring  60  is press-fitted onto the stepped portion  26  and an inner raceway  62  is formed on an exterior circumference of the inner ring  60 . After the inner ring  60  is press-fitted onto the stepped portion  26 , an end portion  27  of the hub  20  is bent radially outwardly so as to catch the inner ring  60 . Thereby, preload is applied to the first and second tapered rollers  40  and  50 . 
         [0012]    The outer ring  30  is spaced radially outwardly from the hub  20  and the inner ring  60  and encloses the hub  20  and the inner ring  60 . First and second outer raceways  32  and  34  corresponding to the hub raceway  25  and the inner raceway  62  are formed on an interior circumference of the outer ring  30 . 
         [0013]    A plurality of first tapered rollers  40  is mounted between the hub raceway  25  and the first outer raceway  32  in a state of being mounted in a first retainer  42 , and a plurality of second tapered rollers  50  is mounted between the inner raceway  62  and the second outer raceway  34  in a state of being mounted in a second retainer  52 . 
         [0014]    Meanwhile, in a case that the first and second tapered rollers  40  and  50  are mounted on the hub  20  and the inner ring  60 , the hub raceway  25  and protruded portions positioned at both end portions of the hub raceway  25 , the inner raceway  62 , and protruded portions positioned at both end portions of the inner raceway  25  that may contact with the first and second tapered rollers  40  and  50  should be machined precisely. Generally, although edges of the tapered rollers are arched, raceways are not machined in an arched fashion but are machined in a straight fashion due to characteristics of machining. In addition, since machined surfaces of each raceway and machined surfaces of protruded portions positioned at the both end portions of each raceway form angles, an edge portion at which the machined surfaces are joined is difficult to be machined. To solve such problems, an undercut is formed at the edge portion at which the machined surfaces are joined. That is, a groove is formed in advance circumferentially at the edge portion at which the machined surfaces are joined for ease of machining. 
         [0015]    However, if the undercut is formed for ease of machining, the wheel bearing assembly becomes weak against impact. Particularly, if instant impact or strong impact is applied through the hub flange  23 , as shown in  FIG. 4 , stress is concentrated on the undercut  28  formed at the flange base  24  and crack may occur around the undercut  28  or the hub  20  may be damaged due to concentration of stress. Since the undercut  28  should be formed for ease of machining, means for dispersing stress that may be concentrated on the undercut  28  is necessary. 
         [0016]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0017]    The present invention has been made in an effort to provide a tapered roller wheel bearing assembly having advantages of dispersing stress by forming an additional undercut near an undercut for machining a hub raceway. 
         [0018]    A tapered roller wheel bearing assembly according to an exemplary embodiment of the present invention may include: a hub provided with a hub flange for mounting a wheel formed radial outwardly at an end portion thereof, a stepped portion formed at an exterior circumference of the other end portion thereof, and a hub raceway formed at an exterior circumference between the hub flange and the stepped portion; an inner ring press-fitted on the stepped portion of the hub and provided with an inner raceway formed at an exterior circumference thereof; an outer ring enclosing the hub and the inner ring and provided with first and second outer raceways corresponding to the hub raceway and the inner raceway and formed at an interior circumference thereof; a first tapered roller disposed between the hub raceway and the first outer raceway and allowing a relative rotation of the hub or the inner ring and the outer ring; and a second tapered roller disposed between the inner raceway and the second outer raceway and allowing the relative rotation of the hub or the inner ring and the outer ring, wherein a flange base is formed between the hub flange and the hub raceway and a first undercut for grinding the hub raceway is formed at the flange base, and wherein a second undercut for dispersing stress concentrated on the first undercut is further formed at the flange base. 
         [0019]    The second undercut may be formed at a radial outside of the first undercut and spaced apart from the first undercut by a predetermined distance. 
         [0020]    Size of the second undercut may be larger than that of the first undercut. 
         [0021]    A pilot for supporting the wheel may be protruded in an axial direction at a side surface of the hub and the second undercut may be formed at the same radial position as the pilot substantially. 
         [0022]    A first sealing member for preventing inflow of foreign material may be mounted between the hub flange and an end of the outer ring, and a second sealing member for preventing inflow of foreign material may be mounted between an interior circumference of the other end portion of the outer ring and an exterior circumference of the inner ring. 
         [0023]    The second undercut may be positioned at a radial inside from the first sealing member. 
         [0024]    A tapered roller wheel bearing assembly according to another exemplary embodiment of the present invention may include: a hub provided with a hub flange for mounting a wheel formed radial outwardly at an end portion thereof and a hub raceway formed at a side portion close to the hub flange; an outer ring enclosing the hub and provided with an outer raceway corresponding to the hub raceway on an interior circumference thereof; and a tapered roller disposed between the hub raceway and the outer raceway and allowing a relative rotation of the hub and the outer ring, wherein a flange base is formed between the hub flange and the hub raceway and a first undercut for grinding the hub raceway is formed at the flange base, and wherein a second undercut for dispersing stress concentrated on the first undercut is further formed at the flange base. 
         [0025]    The second undercut may be formed at a radial outside of the first undercut and spaced apart from the first undercut by a predetermined distance. 
         [0026]    Size of the second undercut may be larger than that of the first undercut. 
         [0027]    A pilot for supporting the wheel may be protruded in an axial direction at a side surface of the hub and the second undercut may be formed at the same radial position as the pilot substantially. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a cross-sectional view of a conventional tapered roller wheel bearing assembly. 
           [0029]      FIG. 2  is a cross-sectional view of a hub used in a conventional tapered roller wheel bearing assembly. 
           [0030]      FIG. 3  is a partial perspective view of a hub used in a conventional tapered roller wheel bearing assembly. 
           [0031]      FIG. 4  illustrates stress distribution when impact is applied to a hub used in a conventional tapered roller wheel bearing assembly. 
           [0032]      FIG. 5  is a cross-sectional view of a tapered roller wheel bearing assembly according to an exemplary embodiment of the present invention. 
           [0033]      FIG. 6  is a cross-sectional view of a hub used in a tapered roller wheel bearing assembly according to an exemplary embodiment of the present invention. 
           [0034]      FIG. 7  is a partial perspective view of a hub used in a tapered roller wheel bearing assembly according to an exemplary embodiment of the present invention. 
           [0035]      FIG. 8  illustrates stress distribution when impact is applied to a hub used in a tapered roller wheel bearing assembly according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0036]    An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
         [0037]      FIG. 5  is a cross-sectional view of a tapered roller wheel bearing assembly according to an exemplary embodiment of the present invention,  FIG. 6  is a cross-sectional view of a hub used in a tapered roller wheel bearing assembly according to an exemplary embodiment of the present invention, and  FIG. 7  is a partial perspective view of a hub used in a tapered roller wheel bearing assembly according to an exemplary embodiment of the present invention. 
         [0038]    A tapered roller wheel bearing assembly  100  illustrated in  FIG. 5  to  FIG. 7 , for better comprehension and ease of description, exemplifies any one tapered roller wheel bearing assembly among various tapered roller wheel bearing assemblies. Therefore, it is to be understood that spirit of the present invention is not limited to the tapered roller wheel bearing assembly  100  exemplified in this specification but is applied to various tapered roller wheel bearing assemblies. It is further to be understood that the spirit of the present invention can be applied to any bearing including a rotating ring (a ring that can be rotatable), a non-rotating ring (a ring that cannot be rotatable), and a plurality of tapered rollers interposed between the rotating ring and the non-rotating ring. In addition, the tapered roller wheel bearing assembly illustrated in  FIG. 5  to  FIG. 7  is a tapered roller wheel bearing assembly for a driving wheel. Since a tapered roller wheel bearing assembly for a driven wheel is similar to the tapered roller wheel bearing assembly for the driving wheel, however, it is to be understood that the spirit of the present invention is not limited to the tapered roller wheel bearing assembly for the driving wheel but is applied to the tapered roller wheel bearing assembly for the driven wheel. 
         [0039]    In addition, for ease of description,  FIG. 5  to  FIG. 7  exemplify that the spirit of the present invention is applied to a ‘3 rd -generation tapered roller wheel bearing’, but is not limited thereto. That is, the spirit of the present invention can be applied to tapered roller wheel bearings of all the generations. 
         [0040]    Meanwhile, for ease of description, a region close to a wheel (not shown) is called an outboard and a region far from the wheel is called an inboard in all the constituent elements included in the tapered roller wheel bearing assembly. 
         [0041]    As shown in  FIG. 5  to  FIG. 7 , the tapered roller wheel bearing assembly  100  according to an exemplary embodiment of the present invention includes a hub  110 , an inner ring  130 , an outer ring  160 , and first and second tapered rollers  140  and  150 . It is shown in this specification, but is not limited to, that two rows  2  tapered rollers are used. The number of rows of the tapered rollers may be suitably chosen by a person of an ordinary skill in the art. Typically, the first and second tapered rollers  140  and  150  may be formed by fitting a plurality of tapered rollers into first and second retainers  142  and  152  made of resin material. 
         [0042]    The hub  110  has a cylindrical shape and the wheel of a vehicle is coupled to an outboard end portion of the hub  110 . For this purpose, a hub flange  114  extending radially outwardly and a pilot  112  protruding to an outboard side along a rotation axis are formed at the outboard end portion of the hub  110 . A bolt hole is bored at the hub flange  114  such that the wheel of the vehicle is coupled to the hub  110  through coupling means such as a bolt, and the pilot  112  guides and supports the wheel when the wheel is coupled to the hub  110 . In addition, a stepped portion  116  is formed on an inboard end portion of the hub  110 , and an end portion  118  is extended from the stepped portion  116 . The end portion  118  is extended straightly to the rotation axis direction before orbital forming, but is deformed plastically in a radial outward direction after the orbital forming. A hub raceway  120  is formed on an exterior circumference between the stepped portion  116  of the hub  110  and the hub flange  114 , and a flange base  122  is formed between the hub flange  114  and the hub raceway  120 . 
         [0043]    The inner ring  130  is press-fitted on the stepped portion  116  of the hub  110 , and an inner raceway  132  is formed on an exterior circumference of the inner ring  130 . The inner ring  130  is mounted on the hub  110  through orbital forming of the end portion  118  of the hub  110 . In this process, preload may be applied to the first and second tapered rollers  140  and  150 . It is exemplified in this specification that the inner ring  130  is mounted on the hub  110  through the orbital forming, but the inner ring  130  may be mounted on the hub  110  by a bolt. 
         [0044]    The outer ring  160  is positioned radially outwardly from the hub  110  and encloses the hub  110  and the inner ring  130 . First and second outer raceways  162  and  164  corresponding to the hub raceway  120  and the inner raceway  132  are formed on an interior circumference of the outer ring  160 , and a part of exterior circumference of the outer ring  160  protrudes radially outwardly to form a flange. A bolt hole (not shown) is bored at the flange such that the outer ring  160  is coupled to a vehicle body (for example, a knuckle) through coupling means such as a bolt. 
         [0045]    The first tapered roller  140  is disposed between the hub raceway  120  and the first outer raceway  162 . The second tapered roller  150  is disposed between the inner raceway  132  and the second outer raceway  164 . The first and second tapered rollers  140  and  150  allow relative rotation of the hub  110  and the inner ring  130 , and the outer ring  160 . 
         [0046]    In addition, a first sealing member  170  is mounted between the hub flange  114  and an outboard end of the outer ring  160  so as to prevent inflow of foreign material such as dust and moisture, and a second sealing member  172  is mounted between an inboard end of the outer ring  160  and the exterior circumference of the inner ring  130  so as to prevent inflow of foreign material such as dust and moisture. The first and second sealing members  170  and  172  may be sealing members of the same type or different type. 
         [0047]    Meanwhile, it is exemplified in this specification that the tapered roller wheel bearing assembly  100  includes the hub  110  connected to the wheel and rotating and the outer ring  160  connected and fixed to the vehicle body, but the tapered roller wheel bearing assembly is not limited thereto. That is, the hub  110  may be connected to the vehicle body and the outer ring  160  is connected to the wheel and rotates. 
         [0048]    In addition, the tapered roller wheel bearing assembly  100  according to the exemplary embodiment of the present invention uses the tapered rollers  140  and  150  as rolling elements. Therefore, an undercut for machining the raceways is necessary. For these purposes, a first undercut  124  is formed on the flange base  122  connected to the hub raceway  120 . That is, a side edge of the first tapered roller  140  is inserted in the first undercut  124 . However, if external impact is applied to the hub flange  114 , stress is concentrated on the first undercut  124 . Therefore, crack may occur or the tapered roller wheel bearing assembly  100  may be damaged. Therefore, a second undercut  126  is formed near the first undercut  124  so as to disperse stress according to the exemplary embodiment of the present invention. The second undercut  126  is formed on the flange base  122  and is spaced apart from the first undercut  124  radially outwardly by a predetermined distance. If the second undercut  126  is formed far from the first undercut  124 , stress cannot be dispersed. In contrast, if the second undercut  126  is formed very close to the first undercut  124 , the first and second undercuts  124  and  126  are operated as one groove and stress may be concentrated thereon. Therefore, a distance between the first undercut  124  and the second undercut  126  is very important to achieve spirit of the present invention, and may be set depending on size of the tapered roller wheel bearing assembly  100  as a suitable value by a person of an ordinary skill in the art. For example, the distance between the first undercut  124  and the second undercut  126  may be, but is not limited to, about 0.3 cm-2 cm. 
         [0049]    In addition, size of the second undercut  126  may be larger than that of the first undercut  124  in order to heighten stress dispersion effect. Herein, the size of the undercut may be depth or radius of the undercut. Further, the second undercut  126  may be formed at the same radial position as the pilot  112 , and may be formed at a radial inner position than the first sealing member  170 . 
         [0050]    The second undercut  126  disperses stress concentrated on the first undercut  124 . 
         [0051]    A cross-sectional shape of the second undercut  126  has a smooth curved line. 
         [0052]      FIG. 8  illustrates stress distribution when impact is applied to a hub used in a tapered roller wheel bearing assembly according to an exemplary embodiment of the present invention. 
         [0053]    Since the second undercut  126  is positioned near the first undercut  124 , as shown in  FIG. 8 , stress concentrated on the first undercut  124  is disposed to the first and second undercuts  124  and  126 . If maximum stress applied to the first and second undercuts  124  and  126  is calculated, maximum stress applied to the first undercut  124  is larger than that applied to the second undercut  126 . However, the maximum stress applied to the first undercut  124  is reduced by more than 10%, compared with a conventional taper bearing. That is, since part of stress concentrated on the first undercut  124  is absorbed by the second undercut  126 , strength of stress concentrated on the first undercut  124  is reduced. Therefore, possibilities of crack occurrence around the first undercut  124  may be lowered and possibilities of breakdown of the tapered roller wheel bearing assembly  100  may also be lowered. Resultantly, the tapered roller wheel bearing assembly  100  may endure stronger impact. 
         [0054]    As described above, stress may be dispersed by forming an additional undercut near an undercut for machining a hub raceway according to an exemplary embodiment of the present invention. Therefore, the tapered roller wheel bearing assembly may endure stronger impact. 
         [0055]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.