Abstract:
The rotor of a braking apparatus is fitted onto a cylindrical positioning portion  19   a,  and in this condition, fixed to the hub  8   a  using bolts which are threaded into the screw holes  11   a  in the rotating flange  10   a,  and tightened. As the hub  8   a  rotates, the runout in the radial direction of the outer peripheral surface  20   a  of the cylindrical positioning portion  19   a  is controlled up to 15 μm, to suppress the runout of the vehicle wheel. With this construction, running performance such as riding comfort and diving stability is improved.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is a continuation of International Application No. PCT/JP03/00727, which was filed on Jan. 27, 2003. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     This invention relates to an improvement of a bearing unit for wheel that supports an automobile wheel such that it can rotate freely with respect to a suspension apparatus. More particularly, this invention is directed to a construction in which the rotating braking member is attached to a rotating flange formed around the outer peripheral surface of the hub, such that the bolts are inserted through the holes in the rotating member for braking and into screw holes that are formed in the rotating flange for screw-fixing.  
       BACKGROUND  
       [0003]     With construction as shown in  FIG. 3 , for example, the wheel rim  1  of an automobile wheel and the rotor  2  of a disc-brake for brake apparatus are supported by the knuckle  3  of the suspension apparatus such that they can rotate freely. In other words, the outer race  6  of the bearing unit  5  for wheel, which is the object of this invention, is fastened to the circular support-hole section  4  formed on the knuckle  3  using a plurality of bolts  7 .  
         [0004]     On the other hand, the wheel rim  1  and rotor  2  are attached and fastened to the hub  8  of the bearing unit  5  for wheel by a plurality of bolts  9 . In order to do this, a rotating flange  10  is formed on the portion of the outer peripheral surface on the outer end section of the hub  8  that protrudes from the outer race  6 . (Here, the “outer” in the axial direction is the outside in the width direction when the bearing unit is assembled into the automobile, and is the left side in the drawings; and the “inner” in the axial direction is the center side in the width direction and is the right side in the drawings. This is the same for all the drawings of this disclosure.), and screw holes  11  are formed at a plurality of locations (generally 4 to 6 locations) that are evenly spaced around in the circumferential direction of a single circumference near the outer peripheral edge of the rotating flange  10 . Also, through holes  12 ,  13  are formed in both the wheel rim  1  and rotor  2  in the portion near the inner peripheral edge that corresponds to the screw holes  11 . When attaching and fastening the wheel rim  1  and rotor  2  to the hub  8 , the bolts  9  are inserted through both of the through holes  12 ,  13  from the outer side toward the inner side, then screwed into the screw holes  11  and tightened.  
         [0005]     Moreover, a plurality of rows of outer-race tracks  14   a,    14   b  are formed around the inner peripheral surface of the outer race  6 , and a stationary flange  15  is formed around the outer peripheral surface of the outer race  6 . This outer race  6  is fastened to the knuckle  3  by connecting the stationary flange  15  to the knuckle  3  using bolts  7 . On the other hand, the hub  8  comprises a hub body  16  and an inner race  17  that is combined with the hub body  16 . The rotating flange  10  is formed on part of the outer peripheral surface of the hub body  16  in the section that protrudes from the opening on the outer end of the outer race  6 . Also, a cylindrical positioning portion  19  is formed on the surface of the outer end of the hub body  16 . The outer peripheral surface  20  of this cylindrical positioning portion  19  is concentric with the hub body  16 .  
         [0006]     The wheel rim  1  and rotor  2  having their inner peripheral edge sections fitted onto this cylindrical positioning portion  19 , are attached to and fastened to the surface on one side of the rotating flange  10  (the outer surface in the example shown in the figure) using the bolts  9 . In this state, the wheel rim  1 , rotor  2  and hub  8  are all concentric with each other. Moreover, with the rows of outer-race tracks  14   a,    14   b,  the outer-race track  14   a  is located on the outer side while the outer-race track  14   b  is located on the inner side, and a first inner-race track  21  is formed directly around the outer surface in the middle section of the hub body  16  in the section that faces the outer-race track  14   a  on the outer side. Furthermore, a small diameter stepped section  22  is formed around the outer peripheral surface of the inner end section of the hub body  16 , and an inner race  17  is fastened onto the small-diameter stepped section  22  to form the hub  8 . A second inner-race track  23  is formed around the outer peripheral surface of this inner race  17  to face the outer-race track  14   b  on the inner side.  
         [0007]     There is a plurality of rolling bodies, or balls  24 ,  24  located between each of the outer-race tracks  14   a,    14   b  and first and second inner-race tracks  21 ,  23 , and they are held by retainers  25 ,  25  such that they can roll freely. With this construction, a double-row angular ball bearing in a back-to-back combination is constructed, to support the hub  8  inside the outer race  6  such that it rotates freely, and to support radial loads and thrust loads. There are seal rings  26   a,    26   b  located between the inner peripheral surface on both ends of the outer race  6  and the outer peripheral surface around the middle section of the hub body  16  and the outer peripheral surface around the inner end of the inner race  17 , so that they seal off the internal space, where the balls  24 ,  24  are located, from the outside. Furthermore, the example shown in the figures is directed to a bearing unit  5  for the driven wheels of an automobile (rear wheels in the case of a FR and RR automobile, the front wheels in the case of a FF automobile and all of the wheels in the case of a 4WD automobile), so a spline hole  27  is formed in the center of the hub body  16 . A constant velocity joint  28  having a spline shaft  29  is provided, and the spline shaft  29  of the constant-velocity joint  28  is inserted into this spline hole  27 .  
         [0008]     As shown in  FIG. 3 , when the bearing unit  5  for vehicle wheel described above is in use, the outer race  6  is fastened to the knuckle  3 , and the wheel rim  1  and the rotor  2  with tire (not shown in the figure) mounted to the wheel rim  1  are fastened to the rotating flange  10  of the hub body  16 . When doing this, as described above, the wheel rim  1 , rotor  2  and hub  8  become concentric with each other by fitting the inner peripheral edges of the wheel rim  1  and rotor  2  onto the cylindrical positioning portion  19 . Also, of these, the rotor  2  is combined with a support and caliper (not shown in the figure) fixed to the knuckle  3 , to form a disc brake for braking. When braking, a pair of pads located on both sides of the rotor  2  presses against the both side surfaces of the rotor  2 .  
         [0009]     In the construction described above, in order to prevent the rotor  2  from whirling (the outer peripheral edge of the rotor  2  runs out in the radial direction as the rotor  2  turns) when moving, the geometric center of the rotor  2  must coincide with the center of rotation of the hub  8 . On the other hand, in the case of a so-called third-generation bearing unit for vehicle wheel where the first inner-race track  21  is formed directly around the outer peripheral surface of the middle section of the hub  8 , as shown in  FIG. 3 , a stepped shape is formed between the middle section in the axial direction of the hub body  16  where the first inner-race track  21  is formed, and the small-diameter stepped section  22  around which the inner race  17  having the second inner-race track  23  is fitted for fixing. In the case of this construction, as the parallelism and concentricity of the first and second inner-race tracks  21 ,  23  becomes poor, it becomes easy for the geometric center and the center of rotation of the hub  8  to come out of alignment. When these centers come out of alignment, it becomes easy for the outer peripheral surface  20  around the cylindrical positioning portion  19  formed on the outer end surface of the hub  8  to whirl with runout in the radial direction as the hub  8  rotates.  
         [0010]     When the outer peripheral surface  20  around the cylindrical positioning portion  19  whirls because of this reason, the rotor  2  that is fitted around this cylindrical positioning portion  19  begins to whirl with runout in the radial direction. As a result, even though the wheel balance is secured with respect to the vehicle wheel, the rotating balance when actually moving becomes poor, and driving performance when traveling at high speed, which is based on comfort and driving stability, becomes poor. Particularly, in the structure where the work of attaching and fastening the rotor  2  to the rotating flange  10  is performed by screwing in and tightening bolts  9  in the screw holes  11  formed in the rotating flange  10 , it becomes easy for the rotor  2  to be affected by whirling of the outer peripheral surface  20  around the cylindrical positioning portion  19 .  
         [0011]     The bearing unit for vehicle wheel according to the present invention is invented, taking such background into consideration, to suppress runout in the radial direction of the rotor  2  or rotating member for braking such as brake drum based on the rotation of the hub  8 .  
       SUMMARY OF THE INVENTION  
       [0012]     The bearing unit for vehicle wheel of this invention is for supporting a vehicle wheel and rotating member for braking on the suspension apparatus such that it can rotate freely, and it comprises: a non-rotating outer race, a hub that rotates on the radially inside of the outer race, and a plurality of rolling elements.  
         [0013]     The outer race has two rows of outer-race tracks formed around its inner peripheral surface, and when in operation, it is supported by the suspension so as not to rotate.  
         [0014]     Also, the hub comprises a combination of a hub body and one inner race.  
         [0015]     The hub body comprises: a rotating flange that is formed around the outer peripheral surface on the outer end of the hub body, in order to support the vehicle wheel and rotating member for braking, and has screw holes for fastening the vehicle wheel and rotating member for braking; a first inner-race track that is formed directly around the outer peripheral surface in the middle section of the hub body to face the outer-race track on the outer side of the two outer-race tracks; and a cylindrical positioning portion that is provided on the outer end surface of the hub body, and around which the inner peripheral edge of the rotating member for braking is fitted.  
         [0016]     Moreover, the inner race has a second inner-race track formed around its outer peripheral surface so as to face the outer-race track on the inner side of the two outer-race tracks, and the inner race is fitted around the inner end section of the hub body.  
         [0017]     Furthermore, a plurality of the rolling elements are located between each of the outer-race tracks and inner-race tracks such that they can roll freely.  
         [0018]     Particularly, in the case of the bearing unit for vehicle wheel of this invention, as the hub rotates, the runout is only 15 μm or less in the radial direction at least in the part of the outer peripheral surface of the cylindrical positioning portion onto which the rotating member for braking is fitted. The cylindrical positioning portion is located on the outer end of the hub.  
         [0019]     In the case of the bearing unit for vehicle wheel of this invention constructed as described above, the geometric center of the rotating member for braking that is fitted around the cylindrical positioning portion coincides with the center of rotation of the hub, so as to suppress whirling of the rotating member for braking, so that it is possible to improve the driving performance of the automobile, mainly based on riding comfort and driving stability.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a cross-sectional drawing of a first example of the embodiment of the invention.  
         [0021]      FIG. 2  is a cross-sectional drawing of a second example of the embodiment of the invention.  
         [0022]      FIG. 3  is a cross-sectional drawing showing an example of the installation of the bearing unit for vehicle wheel to which this invention is applied. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]      FIG. 1  shows a first example of the embodiment of the invention. In the bearing unit  5   a  for vehicle wheel according to this example, there is a stationary flange  15  formed around the outer peripheral surface in the middle section of the outer race  6  for attaching and securing the outer race  6  to a knuckle  3  (see  FIG. 3 ). Also, there are two rows of outer-race tracks  14   a,    14   b  formed around the inner peripheral surface of the outer race  6 . Moreover, with respect to the hub  8   a,  a first inner-race track  21  and a second inner-race track  23  are formed around the outer peripheral surfaces of the hub body  16   a  and the inner race  17 , such that they respectively face the outer-race tracks  14   a,    14   b.    
         [0024]     In other words, a first inner-race track  21  is formed directly around the outer peripheral surface in the middle section of the hub body  16   a,  and an inner race  17  is fitted around a small-diameter stepped section  22  that is formed around the section near the inner end of the hub body  16   a,  and a second inner-race track  23  is formed around the outer peripheral surface of the inner race  17 . Also, in order to prevent the inner race  17  from coming apart from the small-diameter stepped section  22 , a crimped section  30  is formed around the inner end of the hub body  16   a.  That is, after the inner race  17  has been fitted onto the small-diameter stepped section  22 , the section on the inner end of the hub body  16   a  that protrudes from the inner end surface of the inner race  17  is plastically deformed outward in the radial direction to form a crimped section  30 , and this crimped section  30  holds the inner end surface of the inner race  17 . With this construction, the inner race  17  is securely fastened around the inner end section of the hub body  16   a  to form the hub  8   a.    
         [0025]     Moreover, a rotating flange  10   a  for attaching to the wheel rim  1  and the rotor  2  or drum, which is the rotating body of the brake (see  FIG. 3 ), is formed around the outer peripheral surface near the outer end of the hub body  16   a,  in the section that protrudes from the opening on the outer end of the outer race  6 . Screw holes  11   a  are formed at a plurality of locations around this rotating flange  10   a  in the circumferential direction on the circumference the center of which is located on the rotating center of the hub body  16   a.  These screw holes  11   a  are for screwing in the bolts  9  (see  FIG. 3 ) that fasten the wheel rim  1  and rotor  2 .  
         [0026]     Also, there is a cylindrical positioning portion  19   a  formed on the outer end surface of the hub body  16   a,  in order that the wheel rim  1  and rotor  2  are fitted around and supported by the cylindrical positioning portion  19   a  such that the cylindrical positioning portion  19   a  is concentric with the hub body  16   a.  In this example, of the outer peripheral surface  20   a  around the cylindrical positioning portion  19   a,  provided on the based end section (inner end section) is a large-diameter section  31  around which the inner peripheral edge section of the rotor  2  is fitted, and provided from the middle section to the tip end section (outer end section) is a small-diameter section  32  around which the inner peripheral edge section of the wheel rim  1  is fitted. The large-diameter section  31  and the small-diameter section  33  are concentric with each other, and are connected by a stepped section  33 .  
         [0027]     Moreover, there is a plurality of balls  24 ,  24  located between each of the outer-race tracks  14   a,    14   b  and first and second inner-race tracks  21 ,  23 , and they are held by retainers  25 ,  25  such that they can roll freely. There is a pair of sealing rings  26   a,    26   b  located between the inner peripheral surface on both end sections of the outer race  6  and the outer peripheral surface around the middle section of the hub body  16   a  and the outer peripheral surface around the inner end section of the inner race  17 , so as to cutoff the internal space  34 , where the balls  24 ,  24  are located, from the outside and to prevent the grease filled inside this internal space  34  from leaking, as well as to prevent foreign matter from getting inside this internal space  34 .  
         [0028]     The outer peripheral surface  20   a  (large-diameter section  31  and small-diameter section  32 ) around the cylindrical positioning portion  19   a  of the bearing unit  5   a  for vehicle wheel described above runs out in the radial direction as the hub  8   a  rotates on the inner diameter side of the outer race  6 . In the case of the bearing unit  5   a  for vehicle wheel of this invention, this runout is kept to 15 μm or less. In other words, when the outer race  6  is secured and the probe of a displacement sensor is in contact with the outer peripheral surface  20   a  and the hub  8   a  is allowed to rotate, the precision in dimensions and shape of the outer peripheral surface  20   a  with respect to the center of rotation of the hub  8   a  is provided such that the runout of the values measured by the displacement sensor (difference between the maximum value and minimum value) is 15 μm or less. In this invention, it is acceptable if the runout of at least the small-diameter section  32  of the outer peripheral surface  20   a,  is kept to 15 μm or less (the runout of just the small-diameter section  32  is controlled to be 15 μm or less), however, it is preferred that in addition to the small-diameter section  32 , that the runout of the large-diameter section  31  also be kept to 15 μm or less.  
         [0029]     In addition to improving the precision of the shape and dimensions of all of the components of the bearing unit  5   a  for vehicle wheel, the work of securing the precision of the outer peripheral surface  20   a  in this way can be performed by finishing the outer peripheral surface  20  of the cylindrical positioning portion  19   a  after assembling the bearing unit  5   a  for vehicle wheel. Of these, the work of performing a finishing process after assembly is performed by turning, grinding, or micro-finishing the outer peripheral surface  20   a  to finish the outer peripheral surface  20   a  into a cylindrical surface that is concentric with the center of rotation of the hub  8   a.  In this case, before performing turning, grinding or micro-finishing of the outer peripheral surface  20   a  of the cylindrical positioning portion  19   a,  all of the components of the bearing unit  5   a  for vehicle wheel except for the outer peripheral surface  20   a  of the cylindrical positioning portion  19   a  are processed to a specified shape and dimension. Also, the outer peripheral surface  20   a  of the cylindrical positioning portion  19   a  is processed to a rough shape and dimensions. Next, the components of the bearing unit  5   a  for vehicle wheel are assembled to the state as shown in  FIG. 1 . After that, the hub  8   a  is rotated with the outer race  6  fixed, and the turning, grinding or micro-finishing of the outer peripheral surface  20   a  is performed.  
         [0030]     In any case, in the bearing unit  5   a  for vehicle wheel of this example, the amount of whirling of the outer peripheral surface  20   a  (especially the small-diameter section  31 ) of the cylindrical positioning portion  19   a,  which is formed on the outer end surface of the hub body  16   a  and around which the rotor  2  (see  FIG. 3 ) is fitted, is kept to 15 μm or less, so it is possible to suppress whirling of the rotor  2  during operation, and thus it is possible to improve the driving performance of the automobile such as riding comfort and driving stability.  
         [0031]     In other words, according to experimentation performed by the inventors, as shown in the Table below, when the amount of whirling is 20 μm or more, the driving performance of the automobile such as riding comfort and driving stability was never good, however, when the amount of whirling was kept to 15 μm or less, the driving performance became good.  
                           TABLE 1                                   Whirling Amount (μm)   Evaluation                           50   x           30   x           20   x           15   ∘           10   ∘                      
 
         [0032]     Next,  FIG. 2  shows a second example of the embodiment of the invention. In the case of the bearing unit  5   b  for vehicle wheel in this example, an inner ring  17  is fitted on the small-diameter step portion  22  at the inner end of the hub body  16   b  of the hub  8   b,  and the inner end of the inner ring  17  is projected inward of the inner end surface of the hub body  16   b.  In the state when it is installed in the vehicle, the inner end surface of the inner ring  17  is abutted with the outer end surface of the constant velocity joint  28  ( FIG. 3 ) so as to prevent the inner ring  17  from coming out of the hub body  16   b.  The other construction and function are similar to those of the case of the first example, and so redundant explanation is omitted. Incidentally, the present invention is not limited to the bearing unit for driven wheel as shown, and can be applied to the bearing unit for non-driven wheel.  
         [0033]     The bearing unit for vehicle wheel according to this invention, is constructed and functions as described above, and makes it possible to improve driving performance such as comfort and stability when driving at high speed.