Abstract:
A nut rotation prevention structure is provided with a shaft member, a nut, and a rotation prevention member. A wheel hub is supported by the shaft member. The nut is engaged through threads with a first portion of the shaft member, the first portion protruding from the wheel hub. The rotation prevention member is mounted to a second portion of the shaft member and prevents the rotation of the nut, the second portion protruding from the nut. A key groove is formed in the second portion. The rotation prevention member has a tube-shaped section and a connection section. A portion of the shaft member, the portion having the key groove formed therein, is inserted in the tube-shaped section. The connection section connects the tube-shaped member to the nut. The tube-shaped section is affixed to the key groove by staking.

Description:
CROSS TO RELATED APPLICATIONS 
     This application is a national stage application under 35 U.S.C. 371 and claims the benefit of PCT Application No. PCT/JP2012/071438 filed 24 Aug. 2012, which designated the United States, which PCT Application claimed the benefit of Japanese Patent Application No. 2011-196204 filed on Sep. 8, 2011, the disclosure of each of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a nut rotation restriction structure applied to, for example, a nut used to couple a wheel hub to a shaft member, such as a knuckle spindle or an axle housing. 
     BACKGROUND ART 
     In the prior art, a wheel hub is coupled to a knuckle spindle by a nut and supported to be rotatable by the knuckle spindle in a front axle portion of a vehicle.  FIG. 5  is a cross-sectional view showing a coupling structure in which a wheel hub is coupled to a knuckle spindle by a nut. 
     Bearings  11  and  12 , which are arranged in a wheel hub  10 , support the wheel hub  10  to be rotatable on a knuckle spindle  14  of a knuckle  13 . The knuckle spindle  14  includes a projection  14   a  that projects from the wheel hub  10 . Male threads (not shown) are formed on an outer surface of the projection  14   a . A nut  15  is fastened to the projection  14   a  with a predetermined tightening torque so that a proper pre-load is applied to the bearings  11  and  12 . 
     A wheel  16  and a brake drum  17  are fixed to the wheel hub  10  by a plurality of wheel bolts  18  and wheel nuts  19 . In regard to such a structure coupling the wheel hub  10  to the knuckle spindle  14 , patent document 1 discloses a technique for further fixing a lock plate to the nut  15 .  FIG. 6  is an exploded perspective view showing in perspective the structure of each element of the nut rotation restriction structure described in patent document 1. 
     As shown in  FIG. 6 , in the nut rotation restriction structure described in patent document 1, the knuckle spindle  14  that extends in the axial direction A includes a key groove  14   b , which has an opening in a distal end surface  14   c  of the knuckle spindle  14  and extends in the axial direction A. Three female threaded portions  20  are arranged in an end surface  15   a  of the nut  15  in the circumferential direction at 120° intervals. A disk-shaped lock plate  25  includes a central portion with an insertion receptacle  26  fitted to the knuckle spindle  14 . An engagement piece  27 , which is engaged with the key groove  14   b  of the knuckle spindle  14 , extends toward the center from the inner rim of the lock plate  25 . Further, the lock plate  25  includes eighteen bolt holes  28  arranged at 20° intervals in the circumferential direction so that three of the eighteen bolt holes  28  would be opposed to the female threaded portions  20  of the nut  15  when the engagement piece  27  is engaged with the key groove  14   b.    
     When the wheel hub  10  is loosely coupled to the knuckle spindle  14 , the nut  15  is fastened to the knuckle spindle  14  with a predetermined tightening torque that applies a proper pre-load to the bearings  11  and  12 . Then, the engagement piece  27  is engaged with the key groove  14   b , and the knuckle spindle  14  is fitted in the insertion receptacle  26  of the lock plate  25 . Further, bolts  29  are fastened through the bolt holes  28  to the female threaded portions  20  to fix the lock plate  25  to the nut  15 . 
     In such a structure, the engagement of the key groove  14   b  of the knuckle spindle  14  with the engagement piece  27  of the lock plate  25  fixed to the nut  15  restricts rotation of the nut  15 . In addition, the bolt holes  28  of the lock plate  25  are arranged at narrower intervals than the female threaded portions  20  of the nut  15 . This facilitates the alignment of the female threaded portions  20  with the bolt holes  28 . 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Laid-Open Utility Model Publication No. 05-83451 
     SUMMARY OF THE INVENTION 
     In the rotation restriction structure described above, the lock plate  25  includes the bolt holes  28  that are formed based on the engagement piece  27 , which is engaged with the key groove  14   b  of the knuckle spindle  14 . Further, the rotation amount of the nut  15  corresponds to the predetermined tightening torque and varies accordingly. Thus, when fixing the lock plate  25  to the nut  15 , the female threaded portions  20  of the nut  15  need to be aligned with the bolt holes  28  of the lock plate  25 . 
     In this case, the engagement piece  27  of the lock plate  25  is engaged with the key groove  14   b  in patent document 1. Thus, the rotation amount of the nut  15  has to be adjusted. The rotation amount adjustment consequently changes the pre-load applied to the bearings  11  and  12 . This may deteriorate the bearing performance, for example, the duration of the bearings  11  and  12  may be shortened and the generated heat may be increased. Moreover, to improve the assembling efficiency of the front axle, unit type bearings that include common inner and outer races for the two bearings  11  and  12  are nowadays used. In the unit type bearing, the range for the proper pre-load is extremely narrow. Thus, adjustment of the rotation amount of the nut  15  may drastically deteriorate the bearing performance. This problem is not limited to the front axle and also applies to the rear axle. 
     It is an object of the present invention to provide a rotation restriction structure that allows for a nut to be tightened with a predetermined tightening torque, while also restricting rotation of the tightened nut. 
     To achieve the above object, one aspect of the present invention is a nut rotation restriction structure including a shaft member, a nut, and a rotation restriction member. The shaft member supports a wheel hub. The nut is fastened to a first portion of the shaft member. The first portion projects from the wheel hub. The rotation restriction member is coupled to a second portion of the shaft member. The second portion projects from the nut, and the rotation restriction member restricts rotation of the nut. The second portion includes a key groove. The rotation restriction member includes a sleeve and a coupling portion. A portion of the shaft member where the key groove is formed is inserted into the sleeve. The coupling portion couples the sleeve to the nut. The sleeve is swaged and fixed to the key groove. 
     In the above structure, the sleeve of the rotation restriction member is swaged to the key groove to restrict rotation of the nut. In this case, the rotation restriction member is movable in the axial direction of the shaft member and the circumferential direction of the shaft member until the sleeve is swaged to the key groove. That is, the rotation restriction member coupled to the nut is movable, together with the nut, in the axial direction of the shaft member until the sleeve is swaged to the key groove. Thus, after setting the tightening position of the nut, the rotation restriction member may be fixed to the shaft member in correspondence with the position of the nut. As a result, there is no need to adjust the rotation amount of the nut when fixing the rotation restriction member to the shaft member. This allows for the rotation of the nut when tightened by a predetermined tightening torque to be restricted. 
     Preferably, the coupling portion is fixed by a bolt fastened to the nut. 
     In the above structure, the rotation restriction member is fixed to the nut by tightening the bolt. This allows for the rotation restriction member to be separated from the nut by removing the bolt from the nut. Thus, the rotation restriction member may be exchanged by disengaging the swaged portion of the sleeve from the key groove. 
     Preferably, the second portion of the shaft member is accommodated in the sleeve of the rotation restriction member. 
     In the above structure, the rotation restriction member covers the portion of the shaft member projecting from the nut (second portion). Thus, mechanical external force directed toward such a portion acts on the rotation restriction member. In this manner, the rotation restriction member protects the shaft member from mechanical external force. 
     Preferably, the nut has a polygonal cylindrical form. The coupling portion includes a fitting recess portion, into which the nut is fitted. An outer surface of the nut is engaged with an inner surface of the fitting recess portion to couple the coupling portion to the nut. 
     In the above structure, the nut is in planar contact with the coupling portion. Thus, in comparison with when the nut is in point contact with the coupling portion, the rotation force of the nut acting on the coupled locations is spread. This allows for the nut and the coupling portion to be held coupled to each other in a further stable manner even when vibration or the like of the shaft member causes the rotation force of the nut to act on the coupled locations of the nut and the coupling portion. 
     Preferably, the shaft member includes a third portion that projects from the sleeve. The key groove extends beyond the sleeve. The key groove includes an end located in the third portion in an axial direction of the shaft member. A portion of the key groove extending beyond the sleeve has a length in the axial direction of the shaft member that is less than a depth of the fitting recess portion. 
     In the above structure, even when the rotation restriction member moves in the axial direction and the swaged portion comes into contact with the end of the key groove, the nut remains fitted in the fitting recess portion. This limits separation of the rotation restriction member and the nut. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view showing a nut rotation restriction structure according to a first embodiment of the present invention. 
         FIG. 2  is a perspective view showing a coupling portion of a rotation restriction member of  FIG. 1  coupled to a nut. 
         FIG. 3  is a schematic perspective view showing a nut rotation restriction structure according to a second embodiment of the present invention. 
         FIG. 4  is a perspective view showing a coupling portion of the rotation restriction member of  FIG. 3  coupled to a nut. 
         FIG. 5  is a cross-sectional diagram of a prior art example showing the cross-sectional structure around a wheel hub in a front axle. 
         FIG. 6  is a diagram illustrating a basic structure of a nut rotation restriction structure described in patent document 1. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A first embodiment of a nut rotation restriction structure according to the present invention will now be described with reference to  FIGS. 1 and 2 . In the first embodiment, members that are the same as those shown in  FIGS. 5 and 6  are denoted by the same reference characters and will not be described in detail. 
     As shown in  FIG. 1 , in the first embodiment, a knuckle spindle  14 , which serves as a shaft member rotatably supporting the wheel hub  10 , includes a projection  14   a,  which serves as a first portion projecting from the wheel hub  10 . Male threads (not shown) are formed on an outer surface of the projection  14   a . The knuckle spindle  14  includes a key groove  14   b  that has an opening in a distal end surface  14   c  and extends in the axial direction A. 
     A nut  15 , which is fastened to the male threads of the knuckle spindle  14 , is a so-called hexagonal nut and includes three female threaded portions  20  that are arranged in an end surface  15   a  in the circumferential direction at 120° intervals. 
     A rotation restriction member  30 , which restricts rotation of the nut  15 , includes a sleeve  31 , into which the knuckle spindle  14  is inserted, and a circular flange  32 , which is formed integrally with one end of the sleeve  31 . The sleeve  31  has a size allowing for the sleeve  31  to rotate about the axial direction A when the knuckle spindle  14  is inserted. The length of the sleeve  31  in the axial direction A is greater than the length of the projection  14   a  projecting from the nut  15  (length of second portion). 
     The flange  32 , which serves as a coupling portion, includes three through holes  33  arranged in the circumferential direction at 120° intervals and respectively corresponding to the female threaded portions  20  of the nut  15 . Bolts  29  are fastened to the female threaded portions  20  of the nut  15  through the through holes  33  of the flange  32  at positions where the through holes  33  are opposed to the female threaded portions  20 . This fixes the rotation restriction member  30  to the nut  15 . A sheet of SPCC (cold rolled steel sheet) having a thickness of 1.6 mm is pressed and shaped to integrally form the sleeve  31  and the flange  32  in order to obtain the rotation restriction member  30 . 
     The procedures for coupling the rotation restriction member  30  will now be described with reference to  FIG. 2 . First, when the flange  32  is held near the nut  15 , the knuckle spindle  14  is inserted into the sleeve  31 . Then, the rotation restriction member  30  is rotated about the axial direction A while the knuckle spindle  14  is inserted in the sleeve  31  to align the through holes  33  of the flange  32  with the female threaded portions  20  of the nut  15 . Subsequently, the bolts  29  are fastened to the female threaded portions  20  of the nut  15  through the through holes  33  of the flange  32  to fix the rotation restriction member  30  to the nut  15 . 
     Then, as shown in  FIG. 2 , for example, a tool such as a chisel or a hammer is used on the rotation restriction member  30 , which is fixed to the nut  15 , to swage a swaged portion  35 , which is a portion of the sleeve  31  facing the key groove  14   b , to the key groove  14   b . More specifically, after fixing the rotation restriction member  30  to the nut  15 , the swaged portion  35  is swaged to the key groove  14   b  of the knuckle spindle  14 . The swaged portion  35  of the sleeve  31  that is swaged is engaged with the key groove  14   b  so that the rotation restriction member  30  restricts rotation of the nut  15 . 
     The operation of the nut rotation restriction structure in the first embodiment will now be described. As described above, before swaging the swaged portion  35  of the sleeve  31  to the key groove  14   b , the rotation restriction member  30  is rotated to align the through holes  33  and the female threaded portions  20  and fix the rotation restriction member  30  to the nut  15 . Thus, when fixing the rotation restriction member  30  to the nut  15 , there is no need to adjust the rotation amount of the nut  15  that has been tightened with the predetermined tightening torque. 
     Further, the rotation restriction member  30  is fixed to the nut  15  by the bolts  29 . This restricts movement of the rotation restriction member  30  away from the nut  15  in the axial direction A. 
     The sleeve  31  is formed so that the length in the axial direction A is greater than the length of the projection  14   a , which projects from the nut  15 . Thus, when the rotation restriction member  30  is coupled to the nut  15 , the sleeve  31  covers the outer surface of the projection  14   a . This allows for the side surface of the knuckle spindle  14  to be protected from mechanical external force. 
     A nut in which the female threaded portions is coated with a resistance material formed from, for example, a resin has been applied as a nut of which rotation is restricted after being tightened. When this nut is tightened, the resistance material is deformed. The deformation increases the rotation resistance of the nut and restricts rotation of the nut. Further, the sleeve  31  described above may be formed integrally with the nut  15 . 
     Rotation of these nuts is restricted when tightened by a predetermined torque. However, the rotation restriction always partially deforms the nut. Deformation of the nut, regardless of whether it is partial, drastically lowers the mechanical reliability of the nut. Thus, once the nut is removed from the knuckle spindle  14 , the nut should not be used again. In other words, when the nut has to be removed from the knuckle spindle  14 , for example, to perform an inspection on the vehicle, a new nut has to be prepared. 
     The nut fastened to the knuckle spindle  14  is relatively large and expensive. Thus, when the nut needs to be exchanged whenever removed from knuckle spindle, a heavy burden would be imposed on the vehicle owner. 
     In this regard, with the above-described structure, partial deformation of the nut  15  does not occur when coupling the nut  15  to the knuckle spindle  14 . Thus, the nut  15  may be used again. Although the rotation restriction member  30  needs to be exchanged whenever removed from the nut  15 , the rotation restriction member  30  is less expensive compared to the nut  15 . This reduces the burden on the vehicle owner. 
     The nut rotation restriction structure of the first embodiment has the advantages listed below. 
     (1) In the first embodiment, when the rotation restriction member  30  is fixed to the nut  15 , the rotation amount of the nut  15  does not have to be adjusted after being tightened with the predetermined tightening torque. Thus, the rotation of the nut may be restricted when tightened with a predetermined tightening torque. 
     (2) In the first embodiment, the rotation restriction member  30  is fixed to the nut  15  with the bolts  29 . This restricts movement of the rotation restriction member  30  in the axial direction A away from the nut  15 . 
     (3) In the first embodiment, when the rotation restriction member  30  is coupled to the nut  15 , the sleeve  31  covers the outer surface of the projection  14   a . Thus, the outer surface of the knuckle spindle  14  is protected from mechanical external force. 
     (4) In the first embodiment, removal of the nut  15  from the knuckle spindle  14  requires the rotation restriction member  30 , which is inexpensive, to be exchanged. However, the nut  15 , which is expensive, may be used again. This reduces the burden on the vehicle owner. 
     Second Embodiment 
     A second embodiment of a nut rotation restriction structure according to the present embodiment will now be described with reference to  FIGS. 3 and 4 . In the second embodiment, members that are the same as those shown in  FIGS. 5 and 6  are denoted by the same reference characters and will not be described in detail. Further, in the second embodiment, the method for coupling the rotation restriction member to the nut differs from the first embodiment. The different parts will be described in detail. 
     As shown in  FIG. 3 , in the second embodiment, the knuckle spindle  14  includes a closed portion  14   d  forming one end of the key groove  14   b  and located toward the basal end from the distal end surface  14   c . The nut  15 , which is a hexagonal nut, includes a flat end surface  15   a , which serves as a contact surface. 
     A rotation restriction member  40  includes a sleeve  41 , into which the knuckle spindle  14  is inserted, and a coupling portion  42 , which is formed integrally with the basal end of the sleeve  41  and has the form of a polygonal prism. The side of the coupling portion  42  opposite to the sleeve  41  forms a fitting recess portion  43  into which the nut  15  is fitted. The fitting recess portion  43  has the form of a polygonal prism and includes a star-shaped polygonal bottom surface that is based on a regular dodecagon. The profile of the coupling portion  42  also has the form of a star-shaped polygonal prism conforming to the form of the fitting recess portion  43 . The nut  15  is fitted to the fitting recess portion  43  so that the engagement of the outer surface of the nut  15  with the inner surface of the fitting recess portion  43  couples the coupling portion  42  and the nut  15 . 
     The knuckle spindle  14  of the second embodiment is formed so that the distal end surface  14   c  is located toward the front of the sleeve  41  of the rotation restriction member  40  in the axial direction A when the nut  15  is fitted to the rotation restriction member  40 . In this manner, the knuckle spindle  14  of the second embodiment includes a portion projecting from the sleeve  41  (third portion). The key groove  14   b  of the knuckle spindle  14  is closed at the opening in the distal end surface  14   c  by the closed portion  14   d  so that the length of a portion of the key groove  14   b  extending out of the sleeve  41  in the axial direction A is less than the depth of the fitting recess portion  43 . 
     The procedures for coupling the rotation restriction member  40  will now be described with reference to  FIG. 4 . First, when the coupling portion  42  is held near the nut  15 , the knuckle spindle  14  is inserted into the sleeve  41 . Then, the rotation restriction member  40  is rotated about the axial direction A while the knuckle spindle  14  is inserted in the sleeve  41  and positioned relative to the nut  15  to fit the nut  15  to the fitting recess portion  43 . When the nut  15  is fitted to the fitting recess portion  43 , the rotation restriction member  40  is coupled to the nut  15 . 
     Then, as shown in  FIG. 4 , for example, a tool such as a chisel or a hammer is used on the rotation restriction member  40  coupled to the nut  15  to swage a swaged portion  45 , which is the portion of the sleeve  41  facing the key groove  14   b , to the key groove  14   b . More specifically, with the rotation restriction member  40 , after fitting the nut  15  to the fitting recess portion  43 , the swaged portion  45  of the sleeve  41  is swaged to the key groove  14   b  of the knuckle spindle  14 . The swaged portion  45  of the sleeve  41  that is swaged is engaged with the key groove  14   b  so that the rotation restriction member  40  restricts rotation of the nut  15 . 
     The operation of the nut rotation restriction structure in the second embodiment will now be described. As described above, before swaging a portion of the sleeve  41  to the key groove  14   b  of the knuckle spindle  14 , the rotation restriction member  40  is coupled to the nut  15 . Thus, when coupling the rotation restriction member  40  to the nut  15 , there is no need to adjust the rotation amount of the nut  15 , which has been tightened with the predetermined tightening torque. Further, the key groove  14   b  is formed so that when the nut  15  is fitted in the rotation restriction member  40 , the length from the distal end of the sleeve  41  in the axial direction A is less than the depth of the fitting recess portion  43 . As a result, even when the rotation restriction member  40  moves in the axial direction A, the swaged portion  45  of the swaged sleeve  41  comes into contact with the closed portion  14   d . This limits separation of the nut  15  from the fitting recess portion  43 . 
     As described above, the nut rotation restriction structure of the second embodiment has the advantages listed below in addition to advantages (1) and (4) of the first embodiment. 
     (5) The nut  15  is fitted into the fitting recess portion  43  to couple the rotation restriction member  40  and the nut  15 . Thus, bolt fastening or the like does not have to be performed to couple the rotation restriction member  40  and the nut  15 . This improves efficiency when coupling the rotation restriction member  40 . 
     (6) The outer surface of the nut  15  is in planar contact with the inner surface of the fitting recess portion  43 . Thus, in comparison with when the outer surface of the nut  15  is in point contact with the inner surface of the fitting recess portion  43 , the coupled locations spread the rotation force of the nut  15  acting on the coupling portion  42 . This allows for the nut  15  and the coupling portion  42  to be held coupled to each other in a further stable manner. 
     (7) The key groove  14   b  is formed so that the length of a portion extending out of the sleeve  41  in the axial direction A is less than the depth of the fitting recess portion  43  when the nut  15  is fitted in the rotation restriction member  40 . As a result, even when the closed position  14   d  restricts movement of the rotation restriction member  40  in the axial direction A, the nut  15  remains fitted in the fitting recess portion  43 . This prevents coupling between the nut  15  and the rotation restriction member  40  from being released. 
     (8) The profile of the coupling portion  42  has the form of a star-shaped polygonal prism conforming to the form of the fitting recess portion  43 . Thus, the profile may be used to position the nut  15  relative to the rotation restriction member  40 . 
     The above embodiments may be modified as described below. 
     In the knuckle spindle  14  of the second embodiment, the closed portion  14   d  may be omitted. However, it is preferable that the fitting of the nut  15  into the fitting recess portion  43  rigidly couple the rotation restriction member  40  and the nut  15  so that the rotation restriction member  40  is not moved in the axial direction A by vibration when the vehicle travels. 
     In the first and second embodiments, the nut  15  only needs to have a polygonal cylindrical form and does not have to be a hexagonal nut. For example, the nut  15  may be an octagonal nut. In the second embodiment, it is preferable that the profile of the coupling portion  42  be changed in accordance with the form of the nut. 
     In the first embodiment, the length of the sleeve  31  of the rotation restriction member  30  in the axial direction A may be less than the length of the projection portion  14   a  that projects from the nut  15 . 
     In the first embodiment, the rotation restriction member is coupled to the nut  15  by fastening bolts. Further, in the second embodiment, the rotation restriction member  40  is coupled to the nut  15  by fitting the nut  15  into the fitting recess portion  43 . However, the coupling method of the rotation restriction member and the nut is not limited in such manners as long as the rotation restriction member rotates together with the nut.