Abstract:
A vehicle corner apparatus and method of fabricating a vehicle corner apparatus, utilize a wheel spindle adapted for receiving a self-tapping screw for securing a brake rotor to the wheel spindle. Using a self-tapping screw allows manufacturing and assembly costs to be significantly reduced, in comparison to prior vehicle corners that used a machine screw and a threaded hole in a wheel spindle for securing a rotor to the spindle, and provides greater assurance that the lateral run out of the brake rotor will be maintained at a lower value than can be achieved in prior vehicle corners. The wheel spindle includes a retaining screw hole having a conical web adapted to receive and facilitate installation and increase holding force of the self-tapping screw. The retaining screw hole may also include a counter bore for receipt of a locator pin that is used during subsequent formation of wheel bolt holes in the spindle. The rotor retention screw hole for the self-tapping screw, with or without the counter bore, may be formed by a simple sequence of operations using a pair of coining punches.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates a vehicle corner apparatus, and more particularly to a method and apparatus for retaining a brake rotor in a vehicle corner apparatus. 
     BACKGROUND OF THE INVENTION 
     It is common practice in building vehicles such as cars and trucks to fabricate components and sub-assemblies of major components in locations remote from the site of final assembly of the component or sub-assembly into the vehicle. The remotely fabricated components and sub-assemblies are stored until needed, and shipped to the site of final assembly into the vehicle, as they are needed. 
     One such sub-assembly, known as a “corner” apparatus of a vehicle, typically includes a wheel spindle, and a disk brake rotor attached to the wheel spindle. The corner may also include a number of other components, such as an axle and wheel bearing, a speed sensing apparatus, a disk brake caliper apparatus, and a steering knuckle. 
     It is important that the brake rotor be secured tightly to the wheel spindle, in a predetermined position relative to the wheel spindle, until the corner is assembled into the vehicle, and a wheel is bolted to the wheel spindle, in order to preclude debris from getting between the faying (i.e. mating) surfaces of the rotor and the wheel spindle. Any debris between the faying surfaces will cause lateral run-out of the brake rotor with respect to the wheel spindle that contributes significantly to generating undesirable pulsations of the brakes and vehicle forward motion, during braking. 
     Prior wheel spindles have included a threaded hole for receiving a rotor retaining machine screw that passes through the brake rotor for securing the brake rotor to the wheel spindle in the corner apparatus. Providing the threaded hole requires that sequential drilling and tapping steps be performed during fabrication of the wheel spindle. It is also necessary that extra care and time be taken to ensure that the machine screw properly engages the threads in the threaded hole, when attaching the rotor to the spindle, so that the screw is not cross threaded or the threads damaged. It would be advantageous to eliminate the extra time and cost required for providing the threaded hole and carefully inserting the machine screw into the hole. 
     In prior wheel spindles the threaded hole is typically located with respect to wheel bolt holes in the spindle, for wheel bolts used to secure a wheel to the corner. The wheel bolt holes are in turn typically located in a pattern with respect to a plurality of alignment holes in the spindle. It would be advantageous to eliminate the need for the alignment holes in the spindle. 
     SUMMARY OF THE INVENTION 
     Our invention provides an improved vehicle corner apparatus and method of fabricating a vehicle corner apparatus, through the use of a wheel spindle adapted for receiving a self-tapping screw for securing a brake rotor to the wheel spindle. Using a self-tapping screw allows manufacturing and assembly costs to be significantly reduced, in comparison to prior vehicle corners that used a machine screw and a threaded hole in a wheel spindle for securing a rotor to the spindle. 
     In some forms of our invention, the wheel spindle includes a retaining screw hole having a conical web adapted to receive and facilitate installation and increase holding force of the self-tapping screw. The retaining screw hole may also include a counter bore for receipt of a locator pin that is used during formation of wheel bolt holes in the spindle, to thereby eliminate the need for the plurality of alignment holes used for positioning the wheel bolt holes and a threaded rotor retention screw hole in prior vehicle corner assemblies. 
     In a preferred embodiment of our invention, the rotor retention screw hole for the self-tapping screw, with or without the counter bore, is formed by a simple sequence of operations using a pair of coining punches. 
     Our invention may also take the form of a method for forming a wheel spindle or a vehicle corner apparatus according to our invention. 
     The foregoing and other features and advantages of our invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawing. The detailed description and drawing are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a vehicle corner apparatus, according to our invention; 
         FIG. 2  is a partial cross section of a wheel spindle, according to our invention, of the vehicle corner apparatus of  FIG. 1 ; and 
         FIGS. 3-6  are schematic representations of steps in a method, according to our invention, for forming a spindle and a corner as shown in  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an exemplary embodiment of a corner apparatus  10 , according to our invention, for a vehicle. The corner apparatus  10  includes a wheel spindle  12 , and a brake rotor  14  attached to the spindle  12  by a self-tapping rotor retaining screw  16 . The corner  10  also includes an axle and wheel bearing inside the spindle, a knuckle  18 , a brake caliper apparatus  20 , and a speed sensing apparatus  22  for use in a controlled braking system. The brake caliper apparatus  20  may take a number of forms, including a hydraulic or pneumatic actuated caliper, an electrically actuated caliper, or a hybrid caliper. 
     The wheel spindle  12  defines an axis  24  of the spindle  12 , and includes an annular flange  26  extending perpendicularly to the axis  24 . The annular flange  26  has a rotor receiving surface  28  thereof, adapted for receiving the brake rotor  14 , and includes a rotor retention screw hole  30  in the flange  26 , adapted for receiving the self-tapping screw  16  for retaining the brake rotor  14  against the rotor receiving surface  28  of the annular flange  26 . 
     The brake rotor  14  includes a hole  32  therein for receipt and passage therethrough of the self-taping screw  16 . The hole  32  in the rotor includes a countersink to receive the head of the self-tapping screw  16 , so that the head of the screw  16  lies below a wheel-receiving surface  34  of the rotor  14 . The self-tapping screw  16  passes through the hole  32  in the rotor  14 , and engages the rotor retention screw hole  30  in the wheel spindle  12 , to thereby retain the rotor  14  against the rotor receiving surface  28  of the annular flange  26  of the wheel spindle  12 . 
     As shown in  FIG. 2 , the annular flange  26  of the wheel spindle  12  includes a second surface  36  thereof, separated from the rotor receiving surface  28  by a thickness  38  of the flange  26 . The rotor retention screw hole  30  extends through the thickness  38  of the flange  26 , and defines a screw hole axis  40  extending parallel to the axis  24  of the spindle  12 . 
     The rotor retention screw hole  30  includes web  42  for engaging the self-tapping screw  16 . In the exemplary embodiment depicted in  FIG. 2 , the web  42  is generally conical, and has a first surface  44  thereof converging along the axis  40  of the screw hole  30  in a direction away from the rotor receiving surface  28 , and a second surface  46  thereof separated from the first surface  44  thereof by a thickness  48  of the conical web  42 . The first and second surfaces  44 ,  46  of the conical web  42  are generally smooth and conical shaped, but walls that are curved, or having multiple conical or faceted segments, or having other configurations are also contemplated 
     A portion of the screw hole  30  defines a through-hole  50 , extending along the screw hole axis  40  from the first to the second surfaces  44 ,  46  of the conical web  42 . The through-hole  50  has a diameter and side wall  52  adapted to allow the self-tapping screw  16  to engage the conical web  42 . 
     Those having skill in the art will recognize that the configuration and orientation of the conical web  42  within the retaining screw hole  30  provides a structure that functions in a manner similar to a Bellville washer, to preload an axial strain into the self-tapping screw  16  as the screw  16  is tightened. This preload ensures that the screw  16  will not loosen, or be as readily subject to fatigue failure as the machine screws used in prior corner assemblies having threaded retaining screw holes. The conical web  42  holds the screw  16  so securely in a properly torqued condition, in fact, that no other locking feature is required. 
     As shown in  FIG. 2 , the intersection of the wall  52  of the through hole  50  and the first surface  44  of the conical web  42  may be rounded to provide stress relief and facilitate guiding the self-tapping screw  16  into engagement with the through-hole  50 . The alignment and engagement of the self-tapping screw  16  with the through hole  50  may be further facilitated by tapering the wall  52  of the through-hole outward slightly, at an angle of about 5 degrees from cylindrical, for example, such that the end of the through hole  50  closest to the rotor retaining surface  28  is slightly larger in diameter than the remainder of the through-hole  50 . 
     The conical web  42  may be recessed slightly from the rotor receiving surface  28  of the annular flange  26 , and/or the intersection of the first surface  44  of the conical web  42  with the rotor receiving surface  28  may be rounded, to provide stress relief and facilitate guiding the self-tapping screw  16  into engagement with the through-hole  50 . 
     As shown in  FIG. 2 , the conical web  42  is recessed from both the rotor receiving surface  28  and the second surface  36  of the annular flange  26 . In various embodiments of our invention, it may be desirable to recess the conical web  42  from either or both of the rotor receiving surface  28  and the second surface  36 . 
     In the exemplary embodiment, the conical web  42  is recessed from the second surface  36  of the annular flange  26 , a distance sufficient to form a counter bore  53 . The counter bore  53  has a diameter significantly larger that the through hole  50 , and a generally cylindrical sidewall  54  centered about the screw hole axis  40 . The second surface  46  of the conical web  42  forms a bottom surface of the counter bore  53 , sloping slightly into the annular flange  26  adjacent the wall  54  of the counter bore  53 , in a direction toward the rotor receiving surface  28 . In addition to helping define the second surface  46  of the conical web  42 , the counter bore  53  can be used during subsequent manufacturing operations for indexing the spindle  12  about the spindle axis  24  to properly orient a pattern of wheel bolt holes  56  in the flange  26  with respect to the rotor retention screw hole  30 , so that the wheel bolt holes  56  and the retention screw hole  30  will align with corresponding wheel bolt and retaining screw holes  58 ,  32  in the brake rotor  14 , to thereby allow passage of the wheel bolts  60  and retaining screw  16  through the rotor  14 . 
     While it is possible to form the spindle  12  described above, and in particular the hole  30  for the self-tapping screw  16 , by many manufacturing methods including drilling and boring, we contemplate that a method as described below, with reference to  FIGS. 3-6 , according to our invention, may be preferred. 
       FIGS. 3-6  represent sequentially performed operations for retaining a rotor  14  on a wheel spindle  12 , in a corner apparatus  10  as described above, in relation to the exemplary embodiment shown in  FIGS. 1 and 2 . The method includes fabricating a wheel spindle  12 , defining an axis  24  of the spindle  12 , and including an annular flange  26  extending perpendicularly to the axis  24 . The annular flange  26  is fabricated to include a rotor receiving surface  26  thereof adapted for receiving a brake rotor  14 , and having a rotor retention screw hole  30  in the flange  26  adapted for receiving a self-tapping screw  16  for retaining the brake rotor  14  against the rotor receiving surface  28  of the annular flange  26 . 
     The retaining screw hole  30  is formed by first piercing the annular flange  26  with a pilot hole  62  extending through the thickness  38  of the annular flange  26 , as shown in FIG.  3 . While the pilot hole  62  could be formed by drilling or punching a cylindrical walled hole in the flange  26  by conventional methods, we contemplate that it may be preferred to form a pilot hole  62  having a tapered sidewall by placing the rotor receiving surface  28  of the annular flange  26  against a base die plate  64  having a hole  66  of a die diameter passing through the die plate  64  and centered about the retaining screw hole axis  40 , and punching the pilot hole  62  from the second surface  36  of the annular flange  26  with a punch  68  having an outer diameter smaller than the die diameter. Piercing the annular flange  26  in this manner knocks a tapered slug  70  out of the flange  26 , and leaves a pilot hole  62  having walls that taper outward toward the rotor receiving surface  28  of the flange  26 . 
     As shown in  FIGS. 4 and 5 , the conical web  42  is then formed by a base coining punch  72 , inserted through the hole  66  in the base die  64  into the pilot hole  62 , and a top coining punch  74  that replaces the pilot hole punch  68 . The top coining punch  74  includes a guide hole  76  therein extending into the top coining punch  74  along the axis  40  of the rotor retaining screw hole  30 . The guide hole  76  is adapted for receipt of a locator pin  78  extending from the base coining punch  72 . The locator pin  78  extends from the base coining punch  72  along an axis of the base coining punch  72  coincident with the axis  40  of the rotor retaining screw hole  30 , and is adapted for receipt within the guide hole  76  in the top coining die  78 . 
     The first and second surfaces  44 ,  46 , and the through hole  50  of the conical web  42  are formed in one operation by engaging the locator pin  78  of the base coining punch  72  in the guide hole  76  of the top coining punch  74 , and pressing the base and top coining punches  72 ,  74  into the annular flange  26 , to thereby cause material in the annular flange  26  to be deformed around the top and bottom coining punches  72 ,  74  and an exposed portion of the locator pin  78 . 
     In the exemplary embodiment, the top coining punch  74  has an outer diameter significantly larger than the through hole  50 , centered about the axis  24  of the retaining screw hole  30 , and a distal end having a reverse conical configuration. The top coining punch  74  is pressed into the annular flange  26  to a depth below the second surface  36  of the flange, to form a counter bore  53  in the retaining screw hole  30  having a diameter substantially equal to the outer diameter of the top coining punch  74 , while simultaneously forming the second surface  46  of the conical web  42  and forcing material from the flange  26  to flow around the locator pin  78  to form the through hole  50 . The locator pin  78  may have a slight taper to facilitate material flow and disengagement of the locator pin from the guide hole  76  in the top coining die  74 . 
       FIG. 6  illustrates the manner in which a spindle  12  having a retaining screw hole  30  formed as described above, can facilitate subsequent operations to form wheel bolt holes  56  in the annular flange  26 , by providing a convenient method for indexing the location of the screw hole  30  about the spindle axis  24 , with respect to a desired wheel bolt hole pattern. With the base and top coining punches  72 ,  74  removed, and the rotor retaining surface  28  of the annular flange  26  supported on a machining fixture  82 , a wheel bolt locator pin  80  is inserted into the counter bore  53  in the rotor retaining screw hole  30 , and one or more wheel bolt holes are formed in the annular flange  26  in a pattern located with respect to the wheel bolt locator pin  80 . The wheel bolt holes may be formed by any known method, including operations such as drilling, boring, coining and swaging, or punching. One method that may be particularly advantageous is described in commonly assigned U.S. patent application Ser. No. 09/713,681, titled METHOD AND APPARATUS FOR WHEEL SPINDLES AND THE LIKE WITH IMPROVED LRO and now issued as U.S. Pat. No. 6,408,669. 
     While the embodiments of our invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. We wish to expressly state that the retaining screw hole  30 , as described above, can be formed in many ways other than the method disclosed herein with regard to  FIGS. 3-6 , and that the web  42  may have shapes other than conical, such as one or more convolutions or ridges extending either along or transverse to the axis  40  of the rotor retaining screw hole  30 . Individual elements and aspects of our invention may also be used independently from one another, or in different combinations than are described above and in the drawings with regard to the disclosed embodiments. 
     The scope of the invention is indicated in the appended claims. We intend that all changes or modifications within the meaning and range of equivalents are embraced by the claims.