Patent Publication Number: US-6702398-B2

Title: Hub assembly having minimum runout and process for producing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is division of U.S. patent application Ser. No. 09/329,003, filed Jun. 9, 1999, now U.S. Pat. No. 6,415,508. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     This invention relates in general to hub assemblies, and more particularly to a hub assemblies with surfaces that rotate with essentially no runout and a process for producing the same. 
     Most passenger automobiles and light trucks of current manufacture come equipped with disk brakes, at least at the front wheels of such vehicles. Disk brakes weigh less than drum brakes, which they have to a large measure replaced, are less expensive to manufacture, are easier to service, and provide more effective braking. But disk brakes will produce annoying pulsations, known as “brake judder” if improperly manufactured or maintained. 
     The typical disk brake for a vehicle has a disk which rotates with a road wheel of the vehicle and a caliper which clamps down on the disk when the brakes of the vehicle are applied. Indeed, the caliper has pads which bear against machined surfaces on two sides of the disk, with the friction between the pads and the machined surfaces providing the braking. The machined surfaces must be perfectly flat, and must rotate without runout (wobble), lest brake judder will develop when the brakes are applied. 
     Various arrangements exist for mounting the road wheels—and the brake disks as well—on the suspension systems of the vehicles. In one the road wheel and brake disk for that wheel are bolted to a hub having a spindle which rotates in an antifriction bearing which in turn is fitted to a housing. The housing is attached to a steering knuckle or other component if the vehicle&#39;s suspension system. The disk, being a separate and relatively simple component is easily machined to close tolerances along its critical surfaces. But that surface of the hub against which the brake disk is installed does not lend itself to the same precision. To be sure, it is machined, but the machining occurs before assembly, so the bearing on which the hub rotates and the surface on which it is mounted can all contribute to runout in the surface against which the brake disk is installed. This runout transfers to the brake disk itself. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention resides in a process for providing the rotating hub of a hub assembly with a mounting surface that is essentially free of runout, so that a brake disk installed against that surface will not acquire runout from the hub assembly. The hub has a spindle which rotates on a bearing in a housing, both of which also form part of the hub assembly. At one end of the spindle the hub has a flange provided with a face which is presented away from the housing. That face is machined while the housing is held fast and the hub is rotated on the bearing, and as a consequence the face, which is the mounting surface, rotates with essentially no runout. The invention also resides in a process for assembling a hub assembly and also in the hub assembly itself. 
    
    
     DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the accompanying drawings which form part of the specification and wherein like numerals and letters refer to like parts wherever they occur: 
     FIG. 1 is a sectional view of a hub assembly constructed in accordance with and embodying the present invention, with the hub assembly being fitted to a steering knuckle and having a brake disk and road wheel mounted on it; 
     FIG. 2 is a sectional view of the hub assembly showing the mounting surface of the flange on its hub being machined before threaded studs are fitted to the flange; 
     FIG. 3 is a partial end view of the mounting surface on the flange of the hub; and; 
     FIG. 4 is a sectional view of the hub assembly showing the mounting surface on the flange of its hub being machined while the studs are in the flange. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings (FIG.  1 ), a hub assembly A is mounted on a component C of the suspension system for an automotive vehicle and enables a road wheel W to rotate relative to the component C about an axis X of rotation. Not only does the hub assembly A have the road wheel W attached to it, it also carries a brake disk B which likewise revolves about the axis X. Indeed, the disk B rotates with essentially no runout at its critical friction surfaces, to a large measure this being a consequence of a machining procedure used during the manufacture of the hub assembly A. 
     Considering the hub assembly A first, it includes (FIG. 1) a hub  2 , a housing  4 , and a bearing  6  which enables the hub  2  to rotate relative to the housing  4  about the axis X with relatively little friction. The road wheel W and brake disk B are attached to the hub  2 , while the housing  4  is secured firmly against the component C of the vehicle suspension system. The component C may be a steering knuckle. 
     The hub  2  has (FIG. 1) a flange  10  and a spindle  12  which projects from one face of the flange  10 . Actually spindle  12 , which contains a through bore  14 , emerges from a shoulder  16  located along the inside face of the flange  10  and terminates at an outwardly directed formed end  18  located at its opposite end. Radially beyond the spindle  12  the flange  10  contains threaded studs  20  which project axially from its other face. That face is machined to provide a mounting surface  22  against which the brake disk B fits, and indeed the disk B takes its orientation from the surface  22 . The disk B fits over the studs  20  as does the road wheel W, and lug nuts  24  thread over the studs  20  to secure the brake disk B and road wheel W firmly to the hub  2 . 
     The bearing  6  includes (FIG. 1) an inner race in the form of two cones  26  which fit around the spindle  12  where they are captured between the shoulder  16  and the formed end  18 , there being an interference fit between each cone  26  and the spindle  12 . Each cone  26  has a tapered raceway  28  that is presented outwardly away from the axis X, a thrust rib  30  at the large end of its raceway  28 , and a back face  32 , which is squared off with respect to the axis X, on the end of the thrust rib  30 . The inboard cone  26  is somewhat longer than the outboard cone  26  by reason of having a cylindrical cone extension  34  which projects beyond the small end of its raceway  28 . The inboard cone  26  at its cone extension  34  abuts the small end of the outboard cone  26  along the spindle  12 , that is to say, the two cones  26  abut at their front faces. The back face  32  of the outboard cone  26  abuts the shoulder  16  that lies along the flange  10 . The formed end  18  turns outwardly over and against the back face  32  of the inboard cone  26  and serves to capture the two cones  26  on the spindle  12 . 
     In addition to the cones  26 , the bearing  6  includes (FIG.1) tapered rollers  40 , arranged in two rows, there being a separate row around each cone  26 . Actually, the rollers  40  extend around the raceways  28  for the cones  26 , there being essentially line contact between the tapered side faces of the rollers  40  and the raceways  28 . The large end faces of the rollers  40  bear against the thrust ribs  30 . The rollers  40  of each row are essentially on apex, which means that the envelopes in which their tapered side faces lie have their apices located at a common point along the axis X. Each row of rollers  40  has a cage  42  to maintain the proper spacing between the rollers  40  in that row. 
     The ring-like housing  4  surrounds the spindle  12  as well as the two cones  26  and the two rows of rollers  40  (FIG.  1 ). It forms part of the bearing  6  in that it has tapered raceways  44  which are presented inwardly toward the axis X. Indeed, the housing  4  constitutes the outer race of the bearing  6 . The raceways  44  on the housing  4  taper downwardly toward an intervening surface which separates them. The rollers  40  likewise lie along the raceways  44  of the housing  4 , there being essentially line contact between the raceways  44  and the tapered side faces of the rollers  40 . At their large ends, the raceways  44  open into short end bores  46  in which the thrust ribs  30  of the two cones  26  are located. 
     Generally midway between its ends, the housing  4  has a triangular or rectangular flange  50  which fits against the component C of the suspension system for the vehicle. Here the housing  4  is secured firmly to the suspension system component C with bolts  48  that engage threaded holes  52  located in the lobes of the flange  50 . 
     The end bores  46  in the housing  4  contain closures  54  which fit around the thrust ribs  30  on the cones  26  to establish fluid barriers at the ends of the housing  4 . 
     These barriers isolate the rollers  40  and the raceways  28  and  44  from road contaminants, such as water, ice-melting salts and dirt. U.S. Pat. Nos. 5,022,659 and 5,816,711 disclose suitable closures. 
     The formed end  18  unitizes the hub assembly A. But the hub  2  does not always have the formed end  18 . Initially, the spindle  12  of the hub  2  extends from the shoulder  16  all the way to its end as a cylindrical surface. The two cones  26  with their complement of rollers  40  and the housing  4  captured between the rollers  40  of the two rows are installed over the cylindrical surface of the spindle  12  and advanced until the back face  32  of the outboard cone  26  comes against the shoulder  16  at the other end of the spindle  12 . A portion of the spindle  12  projects beyond the back face  32  of the inboard cone  26 . This portion is deformed into the formed end  18 . PCT application GB 98/01823 (International Publication No. WO98/58762), discloses a rotary forming process for upsetting the initially extended end of the spindle  12  and converting that end into the formed end  18  which captures the cones  26  on the spindle  12  and in effect unitizes the entire hub assembly A. 
     Other means may secure the two cones  26  on the spindle  12  as well. For example, the end of the spindle  12  may have threads and a nut engaged with those threads and turned down against the back face  32  of the inboard cone  26 . Also, the end of the spindle  12  may have a groove and a snap ring fitted to the groove. 
     When the hub assembly A is so unitized, its bearing  6  exists in a condition of slight preload. Actually the spacing between the inner raceways  34  on the cones  26  determines the setting of the bearing  6 , and that spacing depends on the length of the cone extension  34  for the inboard cone  26 , inasmuch as the rotary forming procedure which produces the formed end  18  drives the inboard cone  26  toward the outboard cone  26  with enough force to cause the cone extension  34  on the former to abut the small end of the latter. Since the bearing  6  is set to a condition of preload and interference fits exist between its cones  26  and the spindle  12 , the hub A rotates within the housing  4  without any radial or axial free motion. As a consequence, the axis X remains stable. 
     Only after the hub assembly A is unitized with its bearing  6  set in preload, is the outboard face of the flange  10  for the hub  2  machined to provide the mounting surface  22 . But the machining occurs before the threaded studs  20  are installed in the flange  10 . Indeed, before the machining and likewise before the installation of the bearing  6  and housing  4  on the hub  4 , the flange  10  of the hub  4  is provided with holes  56  for receiving the studs  20  and a shallow annular relief  58  at the holes  56  (FIGS.  2  and  3 ). The relief  58  opens away from the housing  4  and extends circumferentially along the flange  10  without interruption. The holes  56  open into the relief  58 . 
     To machine the outboard face of the flange  10  in order to produce the machined mounting surface  22 , the housing  4  is inserted into and clamped within a stationary chuck  64  so that the housing  4  remains in a fixed position (FIG.  2 ). Next, the hub  2  is engaged with a rotary drive  66 . The engagement may occur within the bore  14  of spindle  12  and from either end of the bore  14  (access from one end shown in full lines in FIG. 2, access from the other end shown in interrupted lines). This type of engagement is particularly suitable when the bore  14  contains a spline as it will if the hub  2  is to be coupled to the drive train of the vehicle so that the road wheel W actually propels the vehicle. On the other hand, the drive  66  may include a dog  68  (shown in interrupted lines in FIG. 2) which engages the flange  10  at one of its holes  56 , all without obstructing the outboard face of the flange  10 . The rotary drive  66  turns the hub  4 , causing it to rotate about the axis X. The axis X remains stable because the chuck  64  firmly grips the housing  4  and the bearing  6  operates in preload. With the hub  4  rotating, a cutting or facing tool  70  is advanced generally radially across the outboard face of the flange  10 . The facing tool  70  removes metal from the flange  10 , both radially outwardly and radially inwardly from the relief  58 , and produces the machined mounting surface  22 . That surface  22  is slightly conical and concave, it projecting farthest at the periphery of the flange  10 . A rotating grinding wheel may be run over the machined surface  22  to improve its finish and precision. 
     The mounting surface  22  on the flange  10  fixes the orientation of the brake disk B with respect to the axis X. In this regard the brake disk B contains (FIG. 1) holes  74  which are arranged in the pattern of the studs  20  and are only slightly larger than the threaded shanks of the studs  20 , so that the brake disk B fits over the studs  20 . Indeed, the disk B in the region of its holes  74  has a machined reference surface  76  which is planar. The machined reference surface  76  of the disk B initially abuts the machined mounting surface  22  on the flange  10  of the hub  4  at the periphery of the mounting surface  22  owing to the concavity of the surface  22 . But the nuts  24 , when turned down, draw the reference surface  76  of the disk B against the mounting surface  22 , and insure that the reference surface  76  seats firmly against the mounting surface  22  at the periphery of the latter. The disk B also has two machined friction surfaces  78  that lie outwardly from the reference surface  76 . The friction surfaces  78  occupy planes that are generally perpendicular to the axis X. All three surfaces  76  and  78  are machined with precision. 
     The brake disk B is relatively small and its reference surface  76  and friction surfaces  78  can be machined with relative ease and with considerable precision. The lug nuts  24  secure the brake disk B firmly to the hub  2  of the hub assembly A with the reference surface  76  of the brake disk B firmly abutting the mounting surface  22  on the flange  10  of the hub  4 . As a consequence, the brake disk B rotates relative to the housing  4  with essentially no runout at the friction surfaces  78 . 
     The outboard face of the flange  10  on the hub  2  may also be machined while the threaded studs  20  are in the flange  10  (FIG.  4 ). This requires two facing tools  80  and  82 , the former being located radially outside of the shallow relief  58  and the latter being located within the relief  58 . The tool  80  moves inwardly from the periphery of the flange  10  and produces that region of the machined mounting surface  22  that lies radially outwardly from the relief  58 . The tool  82  moves inwardly from the shallow relief  58  and produces that region of the machined mounting surface  22  that lies radially inwardly from the shallow relief  58 . 
     This invention is intended to cover all changes and modifications of the example of the invention herein chosen for purposes of the disclosure which do not constitute departures from the spirit and scope of the invention.