Abstract:
This invention relates to an improved vehicle wheel hub and bearing unit assembly and method for producing the same wherein an outer brake rotor mounting surface of the wheel hub and bearing assembly is subjected to a microfinishing process. The method for producing the vehicle wheel hub and bearing assembly comprises the steps of: (a) providing a vehicle wheel hub including an inboard end, an outboard end, and a main body having a radially outwardly extending flange, the flange having an outer surface which defines an outer brake rotor mounting surface of the vehicle wheel hub; (b) providing a bearing unit to rotatably support the vehicle wheel hub relative thereto; (c) assembling the bearing unit onto the vehicle wheel hub to produce a vehicle wheel hub and bearing unit assembly which defines a longitudinal axis; (d) preloading the bearing unit; (e) providing a microfinishing assembly having a microfinishing wheel; (f) supporting the vehicle wheel hub and bearing assembly on the microfinishing fixture; and (g) operating the microfinishing fixture whereby the microfinishing wheel engages the outer brake rotor mounting surface of the vehicle wheel hub and bearing unit assembly to produce a finished vehicle wheel hub and bearing assembly, the outer brake rotor mounting surface of the finished vehicle wheel and bearing unit assembly being microfinished relative to the longitudinal axis of the vehicle wheel hub and bearing unit assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/095,364, filed Aug. 5, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to vehicle brakes and in particular to an improved vehicle wheel hub and bearing unit assembly and method for producing the same. 
     A conventional vehicle wheel hub and bearing unit assembly associated with a driven front wheel of a vehicle includes a wheel hub and a bearing unit assembly. The wheel hub includes a generally stepped main body having an opened inboard end, an opened outboard end, and a generally axially extending main body. The main body of the wheel hub includes internal splines for receiving mating external splines provided on an axle for rotatably connecting the wheel hub to the axle for rotation therewith. The main body of the wheel hub also includes a generally radially outwardly extending flange having a plurality of circumferentially spaced apart stud receiving holes formed therein. The stud receiving holes receive wheel studs and nuts for securing a brake rotor of a disc brake assembly and a vehicle wheel to the flange of the wheel hub for rotation therewith. Alternatively, the stud receiving holes in the wheel hub flange can be threaded and receive threaded bolts for securing the brake rotor and/or the vehicle wheel to the flange of the wheel hub for rotation therewith. 
     The vehicle wheel hub is also provided with a bearing seat for receiving the associated bearing unit. The bearing unit includes an inner race and an outer race. The outer race of the bearing unit includes a generally radially outwardly extending flange having a plurality of circumferentially spaced apart stud receiving holes formed therein. The stud receiving holes of the bearing unit flange receive studs and nuts for securing the outer race to a steering knuckle of a vehicle so as to rotatably support the wheel hub relative thereto. 
     When used with a preassembled cartridge type of bearing unit, a fully machined wheel hub and a fully machined brake rotor are assembled and installed on a vehicle in the following manner. First, the cartridge bearing unit is installed about the bearing seat of the wheel hub in a press-fit relationship therewith. The cartridge bearing unit can either be a pregreased sealed-for-life cartridge bearing, or of the type having a pair of bearing elements, either ball bearings or tapered roller bearings, disposed between an inner bearing race or cup and an outer bearing race or cup. 
     Once the bearing unit is installed about the wheel hub, a nut is threaded onto the end of the wheel hub and tightened to pre-load the bearing unit assembly to predetermined specifications. Next, the assembled wheel hub and bearing assembly is secured to the steering knuckle for rotation relative thereto. Following this, a brake rotor of a disc brake assembly and a vehicle wheel are secured to the flange of the wheel hub for rotation therewith. Next, the disc brake assembly, which includes a brake caliper slidably supported on a pair of pins, the pair of brake pads, and a hydraulically actuable piston, is secured via an anchor plate to a fixed part of a vehicle. 
     When fully assembled on the vehicle, a pair of opposed friction plates of the brake rotor are disposed adjacent the brake pads of the disc brake assembly and separated from engagement therewith by a predetermined normal brake running clearance when the piston is not actuated. During operation, when the piston of the disc brake assembly is actuated, the brake shoes take up the normal running clearance and frictionally engage the friction plates. 
     In order to provide the normal brake running clearance, the brake rotor needs to be manufactured to tight specifications. In particular, the brake friction plate surfaces need to be oriented in a perpendicular relationship relative to the axis of the rotor, and in a parallel relationship relative to one another. If these tight specifications are not maintained in the friction plate surfaces, excessive lateral or axial runout or excessive thickness variations in the friction plate surfaces of the rotor can occur which can lead to undesirable results. For example, premature or uneven wear of the brake pads can occur which can cause undesirable noise, vibration, or brake shudder. 
     As discussed above, the brake rotor is secured to the wheel hub. In particular, an inner brake rotor mounting surface of the brake rotor is disposed adjacent an outer brake rotor mounting surface of the wheel hub when the brake rotor is secured to the wheel hub. Typically, the outer brake rotor mounting surface of the wheel hub is machined by a conventional lathe machining process. Thus, when fully assembled on the vehicle, the total “stack up” axial runout of the friction plate surfaces of the brake rotor is the sum of the axial runout of the friction plate surfaces of the brake rotor, the axial runout of the associated outer brake rotor mounting surface of the wheel hub, the axial runout of the associated vehicle wheel hub bearing unit, and any deflection caused by the “clamping” of the associated vehicle wheel. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved vehicle wheel hub and bearing unit assembly and method for producing the same wherein an outer brake rotor mounting surface of the wheel hub and bearing assembly is subjected to a microfinishing machining process. The method for producing the vehicle wheel hub and bearing assembly comprises the steps of: (a) providing a vehicle wheel hub including an inboard end, an outboard end, and a main body having a radially outwardly extending flange, the flange having an outer surface which defines an outer brake rotor mounting surface of the vehicle wheel hub; (b) providing a bearing unit to rotatably support the vehicle wheel hub relative thereto; (c) assembling the bearing unit onto the vehicle wheel hub to produce a vehicle wheel hub and bearing unit assembly which defines a longitudinal axis; (d) preloading the bearing unit; (e) providing a microfinishing assembly having a microfinishing wheel; (f) supporting the vehicle wheel hub and bearing assembly on the microfinishing fixture; and (g) operating the microfinishing fixture whereby the microfinishing wheel engages the outer brake rotor mounting surface of the vehicle wheel hub and bearing unit assembly to produce a finished vehicle wheel hub and bearing assembly, the outer brake rotor mounting surface of the finished vehicle wheel and bearing unit assembly being microfinished relative to the longitudinal axis of the vehicle wheel hub and bearing unit assembly. As a result, the vehicle wheel hub and bearing unit assembly of this invention includes an outer brake rotor mounting surface which is of a near gage quality surface. 
     Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a first embodiment of a vehicle wheel hub and bearing unit assembly in accordance with this invention. 
     FIG. 2 is a schematic diagram of a microfinishing machine for producing the vehicle wheel hub and bearing unit assembly in accordance with this invention. 
     FIG. 3 is a block diagram illustrating a sequence of steps for producing a vehicle wheel hub and bearing unit assembly in accordance with the present invention. 
     FIG. 4 is a sectional view of the vehicle wheel hub and bearing unit assembly illustrated in FIG. 1 including a brake rotor secured thereto. 
     FIG. 5 is a partial sectional view illustrating the first microfinishing process of FIG. 2 for producing the first embodiment of a vehicle wheel hub and bearing unit assembly in accordance with this invention. 
     FIG. 6 is a partial sectional view illustrating a second microfinishing process for producing a second embodiment of a vehicle wheel hub and bearing unit assembly in accordance with this invention. 
     FIG. 7 is a partial sectional view illustrating a third microfinishing process for producing a third embodiment of a vehicle wheel hub and bearing unit assembly in accordance with this invention. 
     FIG. 8 is a partial sectional view illustrating a fourth microfinishing process for producing a fourth embodiment of a vehicle wheel hub and bearing unit assembly in accordance with this invention. 
     FIG. 9 is a partial sectional view illustrating a sixth microfinishing process for producing a fifth embodiment of a vehicle wheel hub and bearing unit assembly in accordance with this invention. 
     FIG. 10 is a partial sectional view illustrating a seventh microfinishing process for producing a sixth embodiment of a vehicle wheel hub and bearing unit assembly in accordance with this invention. 
     FIG. 11 is a sectional view illustrating a second embodiment of a vehicle wheel hub and bearing unit assembly in accordance with this invention. 
     FIG. 12 is a sectional view of a portion of the flange of a portion of a third embodiment a vehicle wheel hub and bearing unit assembly in accordance with this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, there is illustrated in FIG. 1 a first embodiment of a vehicle wheel hub and bearing unit assembly, indicated generally at  10 , produced in accordance with this invention. As shown therein, the vehicle wheel hub and bearing unit assembly  10  defines a longitudinal axis X and includes a vehicle wheel hub  12  and a bearing unit  14 . The vehicle wheel hub  12  can be forged, cast, or otherwise formed. 
     The vehicle wheel hub  12  includes a generally stepped main body having an opened inboard end  16 , an opened outboard end  18 , and a generally axially extending main body  20  having a generally radially outwardly extending flange  22 . The flange  22  extends generally perpendicular to the longitudinal axis X of the vehicle wheel hub and bearing unit assembly  10 . The vehicle wheel hub  12  is provided with a bearing seat  24  for receiving the bearing unit  14 . The bearing seat  24  includes a generally axially extending bearing seat surface  24 A and a generally radially extending bearing seat surface  24 B. As will be discussed below, in accordance with the present invention, the flange  22  of the vehicle wheel hub  12  includes an outer surface  22 B which defines an outer brake rotor mounting surface  22 B which is finish machined by a microfinishing or microgrinding process in order to produce the vehicle wheel hub and bearing unit assembly  10  of this invention. As used herein, the term microfinishing or microgrinding means a process which exerts a relatively low force onto the part and which is operative to change the associated surface geometry of such part. As will be discussed below, in accordance with the present invention the metal removed from the outer brake rotor mounting surface  22 B of the flange  22  of the wheel hub  12  during the microfinishing process is approximately in the range from about 5 microns to about 200 microns. 
     The flange  22  of the vehicle wheel hub  12  has a plurality of circumferentially spaced lug bolt receiving holes  22 A formed therein (only two of such lug bolt receiving holes  22 A are illustrated in FIG.  1 ). As will be discussed below, a lug bolt  26  (shown in FIG.  4 ), is disposed in each of the lug bolt receiving holes  22 A to secure a disc brake rotor  60  (shown in FIG.  4 ), and a vehicle wheel (not shown) to the vehicle wheel hub  12  for rotation therewith. In some cases, the outboard end  18  of the vehicle wheel hub  12  is adapted to receive a dust cover (not shown) to prevent dirt, mud, water, and other debris from entering into the interior of the vehicle wheel hub  12  through the opened outboard end  18 . 
     Also, as shown in this embodiment, the outer brake rotor mounting surface  22 B of the flange  22  of the wheel hub  12  defines a generally flat surface. Alternatively, the profile of the surface of the outer brake rotor mounting surface  22 B can be other than illustrated. For example, the outer brake rotor mounting surface  22 B can have a non-flat surface profile which can include for instance, a generally tapered, convex, spherical, curved, or concave profile. FIG. 12 illustrates an example of a tapered profile, shown exaggerated for clarity and discussion purposes. As shown therein, a flange  22 ′ of a wheel hub  12 ′ includes an outer brake rotor mounting surface  22 B′ having a generally tapered profile which is tapered radially inwardly from a point D 1  to a point D 2  along the surface of the flange  22 ′ by a predetermined distance Y. The distance Y is the axial distance defined between the point D 1  and the point D 2  on the outer surface of the flange  22 ′ of the wheel hub  12 ′. 
     The illustrated bearing unit  14  is a pregreased, sealed-for life, one-piece cartridge style bearing pack assembly and includes an outwardly extending flange  28 . The flange  28  has a plurality of circumferentially spaced mounting bolt receiving holes  28 A formed therein (only one of such mounting bolt receiving holes  28 A is illustrated in FIG.  1 ). A mounting bolt (not shown) is disposed in each of the mounting bolt receiving holes  28 A to secure the bearing unit  14  to a non-rotatable component of the vehicle, such as the steering knuckle (not shown), so as to rotatably support the vehicle wheel hub  12  relative thereto. Alternatively, the bearing unit  14  can be other than illustrated if desired. For example, the bearing unit  14  can be of the type having a pair of bearing elements, either ball bearings or tapered roller bearings, disposed between an inner bearing race or cup and an outer bearing race or cup. 
     The vehicle wheel hub and bearing assembly  10  further includes a spanner nut  30  which is installed on a threaded portion of the vehicle wheel hub  12  adjacent the opened inboard end  16  thereof. When installed, the spanner nut  30  is operative to secure the bearing unit  14  on the vehicle wheel hub  12  and to preload the bearing unit  14 . To accomplish this, the spanner nut  30  is provided with internal threads  30 A. The internal threads  30 A of the spanner nut  30  mate with external threads  12 A provided on the vehicle wheel hub  12  adjacent the inboard end  16  thereof. As is known, the spanner nut  30  is tightened against the inboard end surface  14 A of the bearing unit  14  to a predetermined torque in order to exert a predetermined clamp load on the bearing unit  14 . 
     Turning now to FIGS. 2 and 3, the method and apparatus for producing the first embodiment of the vehicle wheel hub and bearing unit assembly  10  of this invention will be discussed. Initially, in step  100 , the bearing unit  14  is pressed onto the bearing surface  24  of the vehicle wheel hub  12  and advanced (to the right in FIG. 1) until an outboard end surface  15 A of an inner race  15  of the bearing unit  14  engages the bearing seat surface  24 B of the wheel hub  12 . Next, in step optional  102 , the spanner nut  30  is installed on the threaded end of the vehicle wheel hub  12  and tightened against an inboard end surface  15 B of the inner race  15  of the bearing unit  14  so as to exert a predetermined clamp load on the bearing unit  14 . Alternatively, the bearing unit  14  can be preloaded in a manner other than illustrated. For example, the bearing unit  14  can be preloaded using a bolt  110  and a nut  112  as illustrated in FIG. 11; using an “in-process” half-shaft (not shown) and a nut (not shown) which are used in the assembling of the vehicle and are not used just to produce the wheel hub and bearing assembly  10 ′ of this invention; or any other suitable method which is effective to secure the wheel hub  12  and the bearing unit  14  together and to preload the bearing unit  12 . 
     Following this, in step  104 , the vehicle wheel hub and bearing unit assembly  10  is subjected to a microfinishing process. To accomplish this, the assembled vehicle wheel hub and bearing unit assembly  10  is supported on a suitable fixture, such as the fixture  40  shown in FIG. 3, and is subjected to a microfinishing operation. The illustrated fixture  40  includes a motor  42 , a flexible torque drive  44 , an expandable mandrel  46 , an upper clamp member  48 A a lower clamp member  48 B, and a mircofinishing assembly  50 . 
     In the illustrated embodiment, the flexible torque drive member  44  is effective to rotate the vehicle wheel hub  12  relative to the bearing unit  14  so as to minimize the external forces exerted on the wheel hub  12  and/or the bearing unit  14  which can deflect or load the wheel hub  12  and/or the bearing unit  14  and thereby affect the axial runout thereof. The expanding mandrel  46  is effective to operatively connect the flexible torque drive member  44  to the wheel hub  12 . Alternatively, the fixture  40  can be other than illustrated if desired. However, the particular fixture  40  that is used is preferably selected so as minimize the external forces exerted on the wheel hub  12  and/or the bearing unit  14  which can deflect or load the wheel hub  12  and/or the bearing unit  14  and which can affect the axial runout thereof. For example, the fixture could include a wheel hub which is rotated using a drive nut (not shown) which drives off of the bearing retention nut; or a friction drive wheel member (not shown) which is located anywhere on the wheel hub. 
     Once the vehicle wheel hub and bearing unit assembly  10  is supported on fixture  40 , the motor  42  is actuated and the mandrel  46  is operative to rotate the vehicle wheel hub  12  relative to the bearing unit  14  in a first direction as indicated by arrow R 1  in FIG.  3 . Preferably, at the same time, the microfinishing assembly  50  is actuated whereby a microfinishing wheel  52  engages the outer brake rotor mounting surface  22 B of the vehicle wheel hub  12  so as to microfinish machine the outer brake rotor mounting surface  22 B and thereby produce the vehicle wheel hub and bearing assembly  10  of this invention. The microfinishing wheel  52  is rotated in a second opposite direction as indicated by arrow R 2  in FIG.  3 . Since the vehicle wheel hub  12  is rotated in a first direction and the microfinishing wheel  52  is rotated in a second opposite direction during step  104 , the outer brake rotor mounting surface  22 B is machined relative to the longitudinal axis of rotation X of the vehicle wheel hub and bearing assembly  10 . Alternatively, the direction R 1  of rotation of the vehicle wheel hub  12  and/or the direction R 2  of rotation of the microfinishing wheel  52  can be other than illustrated if desired. 
     As best shown in FIG. 5, during step  104  an outer surface  52 A of the microfinishing wheel  52  engages substantially the entire outer brake rotor mounting surface  22 B of the wheel hub  12 . Also, preferably, during step  104 , a lubricating oil (shown at  54  in FIG. 2) is supplied to the outer brake rotor mounting surface  22 B which is subjected to the microfinishing process to assist the microfinishing process. Alternatively, as will be discussed below, the profile and/or the area of the outer brake rotor mounting surface  22 B can be other than illustrated, and/or the wheel hub  12  can have the associated lug bolts  26  installed therein during the microfinishing process if so desired. 
     FIG. 6 illustrates a second machining process for producing a second embodiment of a vehicle wheel hub and bearing unit assembly  110  in accordance with this invention. As shown therein, an outer brake rotor mounting surface  122 B of a flange  122  of a wheel hub  112  is subjected to a microfinishing process by a pair of spaced apart microfinishing assemblies  114  and  116  when lug bolts  118  (only one lug bolt  118  shown in FIG. 6) are installed in the associated lug bolt receiving holes  122 A of the wheel hub  112 . 
     As discussed above, during the microfinishing process, the wheel hub  112  is rotated in a first direction and the microfinishing assemblies  114  and  116  are rotated in a second opposite direction, as indicated by arrows R 3  and R 4 . Thus, in this embodiment having the lug bolts  118  installed therein, only a portion of the entire brake outer brake rotor mounting surface  122 B of the wheel hub  112  is microfinished machined. Also, as shown in FIG. 6, each of the lug bolt receiving holes  122 A is provided with a slightly recessed or countersunk portion  122 C adjacent the outer brake rotor mounting surface  122 B of the wheel hub  112 . Alternatively, the direction of rotation of the vehicle wheel hub  112  and/or the direction of rotation R 3  and R 4  of one or both of the microfinishing assemblies  114  and  116 , respectively, can be other than illustrated if desired. 
     FIG. 7 illustrates a third microfinishing process for producing a third embodiment of a vehicle wheel hub and bearing unit assembly  130  in accordance with this invention. As shown therein, an outer brake rotor mounting surface  132 B of a flange  132  of a wheel hub  134  is subjected to a microfinishing process by a single microfinishing assembly  146  without any lug bolts (not shown) installed in the associated lug bolt receiving holes  134 A of the wheel hub  134 . 
     As discussed above, during the microfinishing process, the wheel hub  134  is rotated in a first direction and the microfinishing assembly  134  is rotated in a second opposite direction, as indicated by arrow R 5 . Alternatively, the direction of rotation of the vehicle wheel hub  134  and/or the direction R 5  of rotation of the microfinishing assembly  146  can be other than illustrated if desired. Thus, in this embodiment, substantially the entire outer brake rotor mounting surface  132 B of the wheel hub  132  is microfinished without any lug bolts installed therein. Also, as shown in FIG. 7, each of the lug bolt receiving holes  134 A is provided with a slightly recessed or countersunk portion  134 C adjacent the outer brake rotor mounting surface  132 B of the wheel hub  132 . 
     FIG. 8 illustrates a fourth microfinishing process for producing a fourth embodiment of a vehicle wheel hub and bearing unit assembly  140  in accordance with this invention. As shown therein, a wheel hub  142  includes a stepped flange  144  having an outer raised flange  146  which defines an outer brake rotor mounting surface  146 B. In this embodiment, the outer brake mounting surface  146 B of the raised flange  146  of the wheel hub  142  is subjected to a microfinishing process by a single microfinishing assembly  148  without any lug bolts (not shown) installed in the associated lug bolt receiving holes  150  of the wheel hub  142 . 
     As discussed above, during the microfinishing process, the wheel hub  142  is rotated in a first direction and the microfinishing assembly  148  is rotated in a second opposite direction, as indicated by arrow R 6 . Alternatively, the direction of rotation of the vehicle wheel hub  142  and/or the direction R 6  of rotation of the microfinishing assembly  148  can be other than illustrated if desired. Thus, in this embodiment, substantially the entire outer brake rotor mounting surface  146 B of only the raised flange  146  of the stepped flange  144  of the wheel hub  142  is microfinished without any lug bolts installed therein. 
     FIG. 9 illustrates a fifth machining process for producing a fifth embodiment of a vehicle wheel hub and bearing unit assembly  160  in accordance with this invention. As shown therein, a wheel hub  162  includes a stepped flange  164  having an outer raised flange  166  which defines an outer brake rotor mounting surface  166 B. In this embodiment, the outer brake rotor mounting surface  166 B of the raised flange  166  of the wheel hub  162  is subjected to a microfinishing process by a single microfinishing assembly  168  when lug bolts  170  (only one lug bolt  170  illustrated in FIG. 9) are installed in the associated lug bolt receiving holes  172  of the wheel hub  162 . 
     As discussed above, during the microfinishing process, the wheel hub  162  is rotated in a first direction and the microfinishing assembly  168  is rotated in a second opposite direction, as indicated by arrow R 7 . Alternatively, the direction of rotation of the vehicle wheel hub  162  and/or the direction R 7  of rotation of the microfinishing assembly  168  can be other than illustrated if desired. Thus, in this embodiment, substantially the entire outer brake rotor mounting surface  166 B of only the raised flange  166  of the stepped flange  164  of the wheel hub  162  is microfinished when the lug bolts  170  are installed therein. Also, as shown in FIG. 9, each of the lug bolt receiving holes  172  is provided with a slightly recessed or countersunk portion  172 A adjacent the outer surface of the stepped flange  164  of the wheel hub  162 . 
     FIG. 10 illustrates a sixth microfinishing process for producing a sixth embodiment of a vehicle wheel hub and bearing unit assembly  180  in accordance with this invention. As shown therein, a wheel hub  182  includes a stepped flange  184  having a outer recessed flange  186  which defines an outer brake rotor mounting surface  186 B. In this embodiment, the outer brake mounting surface  186 B of the raised flange  186  of the wheel hub  182  is subjected to a microfinishing process by a single microfinishing assembly  188  when lug bolts  190  (only one lug bolt  190  illustrated in FIG. 10) are installed in the associated lug bolt receiving holes  192  of the wheel hub  182 . 
     As discussed above, during the microfinishing process, the wheel hub  182  is rotated in a first direction and the microfinishing assembly  188  is rotated in a second opposite direction, as indicated by arrow R 8 . Alternatively, the direction of rotation of the vehicle wheel hub  182  and/or the direction R 8  of rotation of the microfinishing assembly  188  can be other than illustrated if desired. Thus, in this embodiment, substantially the entire outer brake rotor mounting surface  186 B of only the recessed flange  186  of the stepped flange  184  of the wheel hub  182  is microfinished when the lug bolts  190  are installed therein. 
     One advantage of this invention is that the microfinishing finish machining operation utilizes a low pressure grinding or machining wheel which exerts minimal pressure onto the associated outer brake rotor mounting surface  22 B,  122 B,  132 B,  146 B,  166 B, and  186 B of the respective vehicle wheel hub  12 ,  112 ,  134 ,  142 ,  162 , and  182 . As a result, the axial runout along the microfinished surface of the outer brake rotor mounting surface of the vehicle wheel hub and bearing unit assembly of this invention is reduced compared to that of a conventional non-microfinished finish machined prior art vehicle wheel hub. For example, using the microfinishing process of the present invention can result in an axial runout along the outer brake rotor mounting surface of the vehicle wheel hub and bearing assembly of this invention which is consistently around 10 microns or smaller, and usually around 6 microns or smaller. As discussed above, a prior art wheel hub machined by a conventional lathe machining process can produce an axial runout therein can be as great as about 50 microns. As a result, as shown in FIG. 4, when a disc brake rotor  60  is mounted to the vehicle wheel hub and bearing unit assembly  10 , the resulting total stack up axial runout of the outer surfaces  62 A and  64 A of the brake plates  62  and  64 , respectively, is also reduced. In addition, the reduced axial runout of the vehicle wheel hub and bearing unit assembly of this invention simplifies the initial mounting and service mounting of the associated disc brake rotor since special attention to the particular orientation of the brake rotor with respect to the vehicle wheel hub and bearing unit assembly is not necessary. 
     Another advantage of this invention is that the use of the flexible torque drive is effective to minimize the external forces exerted on the wheel hub and/or the bearing unit which can deflect or load the wheel hub and/or the bearing unit and thereby affect the axial runout thereof. Also, depending upon the particular construction and application, the vehicle wheel hub and bearing unit assembly of this invention may be produced with a reduction in the number of manufacturing steps compared to that to produce the prior art vehicle wheel hub and bearing unit assembly. 
     Although this invention has been illustrated and described in connection with the particular vehicle wheel hub and bearing assembly disclosed herein, the invention can be used in connection with other vehicle wheel hubs and/or other bearing units. For example, the vehicle wheel hub can have a different structure than that illustrated in the drawings; the vehicle wheel hub could not have a spanner nut installed thereof, the vehicle wheel hub and bearing assembly can be used on a driven front/rear wheel end assembly; on a non-driven front/rear wheel end assembly, on a selectively driven two/four wheel driven wheel end assembly; and on a full time four wheel driven wheel end assembly. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been described and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.