Abstract:
A ball joint comprises a ball stud having a stud portion at a middle thereof, a ball portion and a screw portion at opposite sides of the stud portion, and a seat surface portion facing the screw portion between the respective portions, and a bearing member into which the ball portion is slidably fitted so as to universally pivotably-support the ball stud, so that the stud portion is inserted through a mounting member, and a nut is screwed with the screw portion projected from the mounting member, and the seat surface portion abuts and is fastened to the mounting member by fastening the nut to the mounting member. The seat surface portion abutting the mounting member is subjected to a co-rotation preventing process which prevents the ball stud from co-rotating along with the nut when the nut is fastened.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a ball joint used, for example, at a connection portion of a vehicle stabilizer.  
           [0003]    2. Description of the Related Art  
           [0004]    Thus type of ball joint is, as disclosed in Japanese Patent Application Laid-Open (JP-A) No. 8-284948, constructed so that a ball portion at one end portion of a ball stud is slidably fitted together with a ball seat and the ball stud is universally pivotably-supported. Furthermore, in order to fix it to a mounting member, the distal end side of the ball stud, at which a screw portion is formed, is passed through the mounting member, and a nut is screwed into the screw portion and fastened. The mounting member is thereby sandwiched by the seat surface portion formed at the ball stud and the nut, and is fastened.  
           [0005]    When the nut is fastened and the ball stud is fixed to the mounting member, because the ball stud freely rotates with respect to the ball seat, if the rotation torque of the nut exceeds the frictional resistance of the seat surface portion for the mounting member, co-rotation in which the ball stud co-rotates along with the nut occurs, and fastening cannot be carried out. In a conventional art, a hexagonal head wrench is fitted with a hexagonal socket formed at the distal end surface of the ball stud, and due to the ball stud being regulated, fastening of the nut is possible. However, the fastening work is troublesome and this is unsatisfactory arises. Thus, in the above-described publication, it is proposed that a co-rotation preventing plate, whose area is greater than that of the seat surface, is sandwiched between the seat surface and the mounting member, and the co-rotation is prevented by increasing the frictional resistance with respect to the mounting member by the co-rotation preventing plate.  
           [0006]    However, if the co-rotation preventing plate is used, an increase in the number of parts and the troublesomeness of assembly work in accordance therewith are brought about. Furthermore, it is supposed that there are cases in which, in accordance with the state of the degree of surface roughness of the abutting surfaces of the mounting member and the co-rotation preventing plate, the increase in frictional resistance is slight, and co-rotation cannot be reliably prevented.  
         SUMMARY OF THE INVENTION  
         [0007]    Thus, an object of the present invention is to provide a ball joint which, without leading to an increase in the number of parts and the accompanying troublesomeness of assembly work, can reliably prevent co-rotation of a ball stud.  
           [0008]    The present invention provides a ball joint comprising: a ball stud having a stud portion at a middle thereof, a ball portion and a screw portion at opposite sides of the stud portion, and a seat surface portion facing the screw portion between the respective portions; and a bearing member into which the ball portion is slidably fitted so as to universally pivotably-support the ball stud, so that the stud portion is inserted through a mounting member, and a nut is screwed with the screw portion projected from the mounting member, and the seat surface portion abuts and is fastened to the mounting member by fastening the nut to the mounting member. The seat surface portion abutting the mounting member is subjected to a co-rotation preventing process which prevents the ball stud from co-rotating along with the nut when the nut is fastened.  
           [0009]    In accordance with the ball joint of the present invention, because a co-rotation preventing process is applied to the seat surface portion of the ball stud, the co-rotation preventing process works on the mounting member when the nut is fastened, and the ball stud is prevented from co-rotating along with the nut. Accordingly, without leading to an increase in the number of parts and the accompanying troublesomeness of assembly work, the co-rotation of a ball stud can be reliably prevented.  
           [0010]    A specific example of the co-rotation preventing process relating to the present invention is the forming of projections biting into the mounting member in a fastened state. In this case, when the nut is fastened and the seat surface portion is fastened to the mounting member, the projections bite into the mounting member, and the co-rotation of the ball stud is prevented. The projections are preferably a sharp shape easily biting into the mounting member, and when painting is carried out on the mounting member, the co-rotation can be sufficiently prevented in a state in which the projections bite into the paint layer. With respect to the height of the projections, if it is too low, the co-rotation preventing effect is weak, and if it is too high, although co-rotation is prevented, looseness occurs. Therefore, a suitable height is required. For example, when a nut whose stipulated value of screw torque is 40 to 60 N • m is used, a height of the projection corresponding to this screw torque is suitably 0.03 to 0.12 mm.  
           [0011]    Furthermore, another specific example of the co-rotation preventing process is a surface-roughening process increasing the frictional resistance with respect to the mounting member. The surface-roughening process is for increasing the degree of surface roughness, and with respect to the degree of surface roughness, for example, if co-rotation arises when the degree of surface roughness Ra is about 0.5 to 1.5, by carrying out a surface-roughening process such that Ra is 2.0 or more, the co-rotation can be prevented. As a method of a surface-roughening process, shot peening or the like may be suitably adopted. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a longitudinal sectional view showing a ball joint relating to an embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is a side view of a ball stud structuring the ball joint relating to the embodiment of the present invention;  
         [0014]    [0014]FIG. 3 is a sectional view taken along line III-III in FIG. 2;  
         [0015]    [0015]FIG. 4A is a plan view of one portion of a seat surface portion of a ball stud on which a projection relating to the embodiment of the present invention is formed, and FIG. 4B is a side view of one portion of the seat surface portion thereof;  
         [0016]    [0016]FIG. 5 is a transverse sectional view of a ball stud showing another embodiment of the present invention;  
         [0017]    [0017]FIG. 6 is a graph showing the relationship between the height of the projection and a co-rotation generated torque relating to the embodiment of the present invention; and  
         [0018]    [0018]FIG. 7 is a graph showing the relationship of a degree of surface roughness and a co-rotation generated torque relating to the embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1 through FIGS. 4A and 4B.  
         [0020]    [0020]FIG. 1 shows a ball joint used for a connection portion of a vehicle stabilizer. A ball joint  1  relating to the embodiment is formed such that a ball stud  10  and a pivotably-supporting member  20  universally pivotably-supporting the ball stud  10  are a main body, and is fixed to a plate-shaped mounting member  40 .  
         [0021]    As shown in FIG. 2, at the ball stud  10 , a ball portion  12  is formed at one end portion of a cylindrical stud portion  11 , and a collar portion  13  is formed at intermediate portion in the axial direction of the stud portion  11 , and furthermore, a screw portion  14  is formed at the distal end side from the collar portion  13  of the stud portion  11 , that is, on the peripheral surface of the opposite side of the ball portion  12 . The pivotably-supporting member  20  is structured from a ball seat  21  and a housing  22  in which the ball seat  21  is press-fit and accommodated. As shown in FIG. 1, the ball seat  21  is a cylindrical shape having a bottom and having a collar portion  21   a  at the upper end rim, and a spherical seat  21   b  is formed at the inside thereof. The ball seat  21  is molded from a hard resin such as polyacetal, polybutylene terephthalate, or the like. The housing  22  also is a of cylindrical shape having a bottom and having a collar portion  22   a  at the upper end rim. One end of a support bar  23  extending in the radial direction of the housing  22  is fixed to the outer peripheral wall of the housing  22 .  
         [0022]    As shown in FIG. 1, the ball portion  12  of the ball stud  10  is slidably fitted together with the spherical seat  21   b  of the ball seat  21 . In this way, the ball stud  10  is pivotably-supported universally, that is, so as to freely rotate in an oscillating manner and so as to freely rotate axially, around the ball portion  12  with respect to the ball seat  21 . Reference numeral  30  in FIG. 1 is an umbrella-shaped dust cover. The dust cover  30  is fixed by the end rim at the large diameter side thereof being sandwiched between the collar portion  21   a  of the ball seat  21  and the collar portion  22   a  of the housing  22 , and the end rim at the small diameter side thereof is anchored to the collar portion  13  of the ball stud  10 . The interior of the ball seat  21  is thereby covered.  
         [0023]    As shown in FIG. 1, the ball joint  1  is fastened by sandwiching the mounting member  40  by the collar portion  13  of the ball stud  10  and a nut  50  by passing the distal end portion of the ball stud  10  on which the screw portion  14  is formed through a through hole  40   a  formed in the mounting member  40  and by screwing the nut  50  with the screw portion  14  so that the ball joint is fastened to the mounting member  40 . In this fixed state, a ring-shaped seat surface portion  13   a  of the collar portion  13  facing the screw portion  14  abuts the mounting member  40 . As shown in FIG. 2, a plurality of projections  15  preventing the ball stud  10  from co-rotating at the time of fastening the nut  50  are formed at the seat surface portion  13   a.    
         [0024]    As shown in FIG. 3, the plurality of projections  15  (there are 6 projections in this case) are formed at uniform intervals along the outer peripheral rim of the seat surface portion  13   a,  and are arranged radially on the whole. As shown in FIGS. 4A and 4B, the projection  15  is a triangular pyramid shape whose plane view is a longitudinally elongated isosceles triangle shape and whose side view is a right-angled triangle shape. When the projection is made to be the tallest and is viewed in plan view, the short base portion is along the circumference of the seat surface portion  13   a,  and the distal end extends toward the axial center of the seat surface portion  13   a.  With respect to the dimensions of the projection  15 , for example, when the screw portion  14  of the ball stud  10  is M 10 , the ball portion  12  has a diameter of 16 mm, and the outside diameter of the seat surface portion  13   a  is 16.5 mm, the height of the projection  15  is about 0.03 to 0.12 mm, and the length thereof is about 2 mm.  
         [0025]    In accordance with the above described ball joint  1 , as shown in FIG. 1, if the nut  50  is fastened in order to fix to the mounting member  40 , the plurality of projections  15  formed at the seat surface portion  13   a  of the collar portion  13  of the ball stud  10  bite into the mounting member  40 , and in accordance therewith, the co-rotation of the ball stud  10  is prevented. When paint is applied to the mounting member  40 , the co-rotation is sufficiently prevented in a state in which the projections  15  bite into the paint layer. In the present embodiment, without using a new member to prevent co-rotation, prevention of co-rotation can be achieved by forming the projections  15  at the seat surface portion  13   a  of the collar portion  13 . Accordingly, the co-rotation of the ball stud  10  can be reliably prevented without leading to an increase in the number of parts and the accompanying troublesomeness of assembly work.  
         [0026]    Next, another embodiment of the present invention will be described with reference to FIG. 5.  
         [0027]    In the present embodiment, as shown in FIG. 5, instead of forming the above-described projections  15  at the seat surface portion  13   a  of the collar portion  13 , a surface-roughening process  16  is applied to the seat surface portion  13   a  by a method such as shot peening or the like, and the degree of surface roughness is increased. In this way, if the seat surface portion  13   a  is subjected to a surface-roughening process, the frictional resistance of the seat surface portion  13   a  with respect to the mounting member  40  increases, and the co-rotation of the ball stud  10  at the time of fastening the nut  50  is prevented. It should be noted that, with respect to the degree of surface roughness of the seat surface portion  13   a,  for example, if co-rotation occurs when the degree of surface roughness Ra is about 0.5 to 1.5, co-rotation can be reliably prevented by surface-roughening processing so that the Ra is 2.0 or more.  
       EXAMPLES  
       [0028]    Next, examples of the present invention will be described.  
         [0029]    [1] Forming of projections  
         [0030]    The projections of the shape and the arrangement shown in FIG. 3 and FIGS. 4A and 4B were formed, while changing the height in a range of 0.01 to 0.16 mm, at a seat surface portion of a collar portion of a ball stud which is the same as the ball stud  10  shown in FIG. 2 and whose material was steel equivalent to S30C to S45C. The projections were formed by forging at the same time as the molding of the ball stud. As shown in FIG. 1, these ball studs were fastened to a mounting member by nuts, and the screw torque when co-rotation arose at the ball stud was investigated. It should be noted that the screw portion with which the nut was screwed was M 10 , and an electrophoretic coating of a cationic resin was applied at a thickness of 20±10 μm to the surface of the mounting member into which the projections bit.  
         [0031]    [0031]FIG. 6 shows the relationship between the height of the projection and co-rotation generating torque. A specified value of the screw torque of an M 10  screw portion is 40 to 60 N • m, and it is known that it suffices to ensure about 0.03 mm as the height of the projection at which co-rotation does not arise even if the specified value of the screw torque is 60 N • m which is the upper limit. Furthermore, for safety, even if the screw torque is two times 60 N • m, that is, 120 N • m, the height of the projection at which co-rotation does not arise is about 0.12 mm. However, because there is a concern that if the height of the project is greater than that, the nut will loosen, the height of the projection in this case is appropriately 0.03 to 0.12 mm.  
         [0032]    [2] Surface-roughening process  
         [0033]    Instead of forming the projections, the seat surface portion of a collar portion of a steel ball stud (the screw portion was M 12 ), which was the same as the ball stud  10  shown in FIG. 2, was subjected to surface-roughening processing while varying the degree of surface roughness Ra in a range from about 0 to 5.0. These ball studs were fastened to the mounting member by nuts in the same way as described above, and the screw torque when co-rotation arose at the ball stud was investigated.  
         [0034]    [0034]FIG. 7 shows the relationship between the degree of surface roughness and co-rotation generating torque. The specified value of the screw torque of the screw portion of M 12  is 80 to 100 N • m. It can be understood that, as a degree of surface roughness at which co-rotation does not arise in accordance therewith, it suffices to ensure an Ra of 2.0 or more.