Abstract:
A knuckle-supported wheelend assembly includes a shaft having a contoured peripheral surface portion proximate to an outboard end featuring a minimum radius and a maximum radius, and a hub mounted on the shaft&#39;s contoured surface portion via a complementary, contoured central bore. The nontapered contoured hub-shaft interface includes a slight twist or jog to reduce backlash and to permit a relative shortening of the length of axial hub-shaft engagement to as little as about 45% of the maximum radius, thereby advantageously reducing scrub radius for a given wheel-tire combination. By eliminating any required taper of the contoured interface, the hub&#39;s inboard face firmly abuts the machined face of the inner race of a knuckle-mounted, shaft-supporting bearing assembly to achieve reduced assembly runout. The hub&#39;s wheel-mounting face and integral annular friction surfaces are each machined with reference to the inboard hub face to ensure a high degree of parallelism.

Description:
FIELD OF INVENTION  
         [0001]    The invention relates to corner modules for motor vehicles that feature a half shaft or stub shaft that is supported for rotation within a bore of a knuckle.  
         BACKGROUND OF THE INVENTION  
         [0002]    The prior art teaches front-end corner modules for motor vehicles in which a knuckle is attached to a vehicle chassis as by several links, such that the knuckle is pivoted relative to the chassis by a steering rod coupling the knuckle to the vehicle&#39;s steering system. Typically, a bearing on the knuckle supports a half shaft or stub shaft for relative rotation. The shaft, in turn, supports a wheelend assembly that typically includes a wheel hub mounted on the shaft, a rotor having a center portion mounted on the wheel hub, and a wheel and tire combination mounted on the wheel hub as by a plurality of lug bolts.  
           [0003]    In order to facilitate repair and replacement of the wheelend&#39;s several components, the wheel hub is typically removably mounted on a splined section of the shaft and axially secured by a nut threadably mounted on the threaded outboard end of the shaft. The splined section of the shaft is typically formed by rolling the spine in the end of the shaft and then heat treating the rolled spline for strength and toughness. A slight helix or twist is often added to the spline along its entire length to minimize backlash upon tightening of the nut to secure the wheel hub on the outboard end of the shaft.  
           [0004]    Unfortunately, the post-rolling heat treatment of the shaft introduces dimensional variations in the splined portion of the shaft. To accommodate tolerance accumulation, the prior art has resorted to use of relatively longer lengths of splined engagement between the wheel hub and the shaft. Such increased axial length of engagement between wheel hub and shaft, in turn, generates a larger scrub radius, for a given wheel-and-tire combination having a fixed offset. Moreover, the tolerance variations in the splined portion of the shaft combine with hub, rotor, and bearing tolerance stack-ups to increase run-out, particularly as to the friction ring of the brake rotor, and to reduced shaft-wheel hub concentricity, thereby limiting possible improvements to vehicle Noise, Vibration and Harshness (NVH) levels.  
           [0005]    Alternatively, U.S. Pat. No. 6,450,585 teaches a wheelend assembly featuring a polygonal shaft-wheel hub interface, wherein the helical spline is replaced by a tapered end portion of the shaft featuring a polygonal outer contour defining a plurality of machined lobes. By using a taper to provide a slightly conical construction of the polygonal outer contour, the &#39;585 patent teaches that a shaft-hub interface is achieved which is free of play in both the axial and radial directions.  
           [0006]    However, as in the case with known splined interfaces, the tapered polygonal shaft-wheel hub interface requires a significantly increased length of axial engagement of the shaft-wheel hub interface, exceeding perhaps 65% or more of the maximum diameter of a given lobe, particularly as the number of lobes is reduced to a number approaching a minimum number of three lobes. This increased length of axial engagement of the shaft-wheel hub interface, in turn, tends to increase scrub radius or kingpin offset for a given wheel-tire combination used with the wheelend assembly, thereby limiting design and packaging flexibility when using such a shaft-hub interface. Moreover, the increased-axial-length, tapered shaft-wheel hub interface requires particularly tight tolerances in order to ensure that the inboard face of the wheel hub can still be suitably biased against the bearing&#39;s inner race by a threaded fastener on the outboard end of the shaft, with an attendant increase in manufacturing costs, in order to avoid an unintended increase in wheel hub runout.  
           [0007]    Accordingly, what is needed is an improved wheelend assembly featuring a shaft-wheel hub interface that overcomes the aforesaid deficiencies of the prior art.  
         SUMMARY OF THE INVENTION  
         [0008]    Under the invention, a wheelend assembly is provided for use in a corner module of a motor vehicle that includes a knuckle having a bore adapted to receive and support the wheelend assembly. The wheelend assembly includes an elongate shaft having a contoured peripheral surface portion proximate to the shaft&#39;s outboard end. The contoured peripheral surface portion of the shaft includes at least three crests when viewed in lateral cross-section, more preferably, an even number of crests to enhance manufacturability. Each crest has a maximum crest diameter that remains substantially constant over a first length of the shaft. In this regard, it is noted that, where the contoured peripheral surface portion has an odd number of crests, the crest will be deemed to have an effective maximum crest diameter equal to twice the maximum crest radius of a given crest.  
           [0009]    The wheelend assembly further includes a bearing assembly supporting the shaft for rotation in the bore of the knuckle, wherein the bearing assembly includes an inner race having a bearing face generally normal to the longitudinal axis of the shaft. The wheelend assembly further includes a wheel hub mounted on the shaft proximate to the shaft&#39;s outboard end. Specifically, the wheel hub includes an outboard wheel-mounting face and an inboard face, the inboard face of the hub directly abutting the bearing face. The wheel hub further includes a central portion with a central bore adapted to matingly receive the contoured peripheral surface portion of the shaft such that the hub rotates with the shaft, with the wheel hub&#39;s central bore engaging the shaft&#39;s contoured peripheral surface portion along a second length of the shaft within the first length of the shaft.  
           [0010]    In accordance with an aspect of the invention, the second length of the shaft, along which the wheel hub&#39;s central bore engages the shaft&#39;s contoured peripheral surface portion, is no greater than about 60% of the maximum crest diameter. More preferably, the second length of the shaft is no greater than about 50% of the maximum crest diameter. And, most preferably, the second length of the shaft is no greater than about 45% of the maximum crest diameter.  
           [0011]    In accordance with another aspect of the invention, each crest defined by the contoured peripheral surface portion of the shaft includes a circumferential jog along a third length of the shaft, within the second length of the shaft engaged by the wheel hub&#39;s central bore. The jog significantly reduces backlash while otherwise permitting the wheel hub to be appropriately biased against the bearing face of the bearing assembly, whereby wheel hub runout is significantly reduced. Preferably, the jog&#39;s third length is no greater than about 30% of the second length of the shaft. A portion of each crest, along the third length of the shaft, preferably defines a line disposed at a predetermined angle with respect to a plane intersecting the longitudinal axis of the shaft. While the invention contemplates a range of suitable angles, the predetermined angle is preferably no greater than about 0.6°.  
           [0012]    Thus, under the invention, a wheelend assembly is provided that advantageously features a shaft-wheel hub interface exhibiting greater concentricity to thereby reduce wheelend vibrations while further providing reduced runout for both the wheel hub and the friction surfaces of the hub&#39;s integrated rotor portion, whereby vehicle NVH levels are significantly improved.  
           [0013]    Further, the significantly-reduced axial dimension of the shaft-wheel hub interface under the invention advantageously provides a reduced scrub radius or kingpin offset for a given wheel-tire combination mounted on the wheel hub, with an attendant increase in design and packaging flexibility.  
           [0014]    Additional features, benefits, and advantages of the invention will become apparent to those skilled in the art to which the invention relates from the subsequent description of several exemplary embodiments and the appended claims, taken in conjunction with the accompanying Drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    In the Drawings, wherein like reference numerals are used to designate like components in each of the several views, and wherein the relative thickness of certain components has been increased for clarity of illustration:  
         [0016]    [0016]FIG. 1 is a longitudinal view, in partial cross-section, of a vehicle&#39;s front-end corner module incorporating an exemplary wheelend assembly in accordance with the invention;  
         [0017]    [0017]FIG. 2 is an elevation of the stub shaft of the exemplary wheelend assembly;  
         [0018]    [0018]FIG. 3 is an end view of the stub shaft showing the contoured peripheral surface portion that defines a generally polygonal shape having six circumferentially-spaced “crests,” with each crest further including a slight circumferential “jog” to reduce backlash in accordance with another aspect of the invention; and  
         [0019]    [0019]FIG. 4 is an end view of the wheel hub, partially broken away to show its integral ventilated friction rings. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    [0020]FIG. 1 shows, in partial longitudinal section, an exemplary front-end corner module  10  for a motor vehicle incorporating a wheelend assembly  12  in accordance with the invention. The illustrated corner module  10  includes a knuckle  14  having a bore  16  within which to receive and support the wheelend assembly  12  for pivoting movement relative to the vehicle&#39;s chassis (not shown). It will be appreciated that, under the invention, the term “knuckle” is intended to broadly encompass any structure by which to support the corner module&#39;s wheelend assembly  12 , including any suitable casting or forging that includes a bore within which to journal a suitable wheelend-supporting shaft. While the wheelend assembly  12  of the illustrated corner module  10  is of the nondriven type, it will be appreciated that myriad aspects of the invention apply equally to driven wheelend assemblies.  
         [0021]    As seen in FIG. 1, the illustrated corner module  10  is a “first generation” or “Gen I” design wherein a cartridge-type bearing assembly  18  is press-fit into the bore  16  of the steering knuckle  14  such that the outer race  20  of the bearing assembly  18  is nonrotatably received and supported within the knuckle bore  16 . However, It will be appreciated that the wheelend assembly  12  of the invention may equally be employed in subsequent corner-module design “generations,” including without limitation, “Gen II,” and “Gen II.5” designs featuring, for example, either a different manner of attaching the bearing assembly  18  to the knuckle  14 , or integration of bearing assembly races with either the knuckle  14  or the bearing-supported wheelend assembly  12 .  
         [0022]    Referring again to FIG. 1, in a manner typical of known “Gen I” designs, the inboard face  24  of the bearing assembly&#39;s inboard outer race  20  is seated against a shoulder  28  defined in the knuckle bore  16 , while a retainer  30  received within a complementary groove  32  of the knuckle bore  16  retains the bearing assembly&#39;s outboard outer race  20 . The exemplary wheelend assembly  12  includes an elongate stub shaft  36  journalled within the bearing assembly&#39;s inboard and outboard inner races  38 , 40 . A radial flange  42  defined on the shaft  36  proximate to the shaft&#39;s inboard end  44  abuts and axially bears against the machined inboard face  46  of the bearing&#39;s inboard inner race  38 .  
         [0023]    In accordance with an aspect of the invention, as best seen in FIGS. 2-4, the shaft  36  includes a contoured peripheral surface portion  48  proximate to its outboard end  50 , by which to transmit torque to a shaft-mounted wheel hub  52 . In the exemplary wheelend assembly  12 , the contoured peripheral surface portion  48  is polygonal when viewed in lateral cross-section, defining six circumferentially-spaced “crests”  54 . Each crest  54  is characterized by a maximum crest diameter D that remains substantially constant over a first length L 1  of the shaft  36 .  
         [0024]    In accordance with an aspect of the invention, the contoured peripheral surface portion  48  is defined on the shaft  36  as by hard-cutting the surface portion  48  after the shaft  36  has been surface-treated. By way of example only, in a constructed embodiment, the contoured peripheral surface portion  48  is machined in the surface-treated shaft using a dual-cutter method as described in European Patent EP 0 907 458 B1. In this manner, the invention achieves a surface finish on the contoured peripheral surface portion  48  of the shaft  36  that significantly exceeds the tolerances of known rolled-then-heat-treated splined surface portions.  
         [0025]    Referring again to FIGS. 1 and 4, the wheel hub  52  of the exemplary wheelend assembly  12  includes a center portion  56  having a central bore  58  adapted to matingly receive the contoured peripheral surface portion  48  of the shaft  36 , such that the mounted hub  52  rotates with the shaft  36  about a shaft axis  60 . In accordance with an aspect of the invention, as illustrated in FIG. 1, the wheel hub&#39;s central bore  58  engages the shaft&#39;s contoured peripheral surface portion  48  along a second length L 2  of the shaft  36 , within the shaft&#39;s first length L 1 . Preferably, the second length L 2  of wheel hub engagement with the contoured peripheral surface portion  48  of the shaft  36  is no greater than about 60% of the maximum crest diameter D. More preferably, the second length L 2  of the shaft  36  is no greater than about 50% of the maximum crest diameter D. And, most preferably, the second length L 2  of the shaft  36  is no greater than about 45% of the maximum crest diameter.  
         [0026]    In accordance with another aspect of the invention, an inboard, axial face  62  of the hub&#39;s center portion  56  directly abuts the machined outboard face  64  of the bearing assembly&#39;s outboard inner race  40 , directly reducing observed wheelend runout. The outboard end  50  of the shaft  36  is threaded to receive a nut  66 , whereby the hub  52  is axially biased towards the shaft&#39;s inboard flange  42  to thereby axially preload the bearing assembly  20  and ensure that the hub&#39;s center portion  56  firmly abuts the bearing assembly&#39;s machined outboard face  64 . The hub&#39;s center portion  56  has an annular mounting face  68  that includes a set of circumferentially-spaced bores adapted to receive wheel-mounting lug bolts  69 , it will be appreciated that the invention is readily adapted to employ other known manners of securing a wheel (not shown) to the mounting face  68  of the hub  52 .  
         [0027]    In accordance with yet another aspect of the invention, as best seen in FIGS. 2 and 3, each crest  54  of the contoured peripheral surface portion  48  of the shaft  36  includes a circumferential jog  66  along a third length L 3  of the shaft, within the second length L 2  of the shaft engaged by the wheel hub&#39;s central bore  58 . The jog  70  significantly reduces backlash while otherwise permitting the wheel hub  52  to be appropriately biased against the bearing assembly&#39;s machined outboard face  64 , whereby wheel hub runout is significantly reduced. Preferably, the jog&#39;s third length L 3  is no greater than about 30% of the second length of the shaft  36 . A portion of each crest  54 , along the third length L 3  of the shaft  36 , preferably defines a line  72  disposed at a predetermined angle a with respect to a plane  74  intersecting the longitudinal axis  60  of the shaft  36 . While the invention contemplates a range of suitable angles, the predetermined angle a is preferably no greater than about 0.6°. It will be appreciated, however, that the invention contemplates the use of “jogs” that generate other shapes when a given crest  54  is viewed in elevation, including one or more arcs (not shown).  
         [0028]    In accordance with another aspect of the invention, the hub  52  includes an integral rotor portion  76  encircling the hub&#39;s center portion  56 . By way of example, as seen in FIGS. 1 and 4, in the exemplary wheelend assembly  10 , the hub  52  is a single, monolithic casting formed, for example, of a nodular or ductile cast iron so as to define both the center portion  56  and the rotor portion  76 . While any suitable material or surface treatment may be used, in the exemplary wheelend  10 , the center portion of the hub  52  is preferably subjected to an austempering heat-treatment after the hub  52  is cast to thereby obtain austempered ductile iron (ADI) in the center portion  56  while leaving the rotor portion  76  as ductile cast iron. In this manner, the center portion  56  is provided an improved strength and fatigue resistance while the rotor portion  76  retains the as-cast characteristics of the material.  
         [0029]    As illustrated in partial breakaway in FIG. 4, the rotor portion  76  of the hub  52  includes a pair of parallel-spaced friction rings  78  separated by a webbing of integrally-formed, radially-extending vanes  80 . However, it will be appreciated that the invention contemplates use of either a single, solid, integrally-formed friction ring, or an assembly that includes friction rings mounted on the hub&#39;s periphery, for example, as taught in U.S. Pat. No. 6,523,651, assigned to the assignee of the present invention, wherein the rotor portion is cast about the hub portion as by insert casting to thereby axially and circumferentially mechanically interlock the rotor portion about the hub portion.  
         [0030]    In accordance with yet another aspect of the invention, and referring again to FIG. 1, upon removal of the hub  52  from the casting mold and after the austempering the hub&#39;s center portion  56 , a first machining stage cuts the hub&#39;s polygonal central bore  58  and then cuts the center portion&#39;s inboard face  62  square to the polygonal central bore  58 . The hub&#39;s center portion  56  is then fixtured with reference to the finished inboard face  62  and central bore  58 , and the inboard and outboard friction surfaces  82  of the hub&#39;s rotor portion  76  are straddle-cut to thereby achieve a high degree of parallelism between the hub&#39;s inboard face  62  and the friction surfaces  82  of the hub&#39;s rotor portion  76 . The hub&#39;s wheel-mounting face  68  is also finished, in parallel to the hub&#39;s inboard face  62 .  
         [0031]    Once the wheel hub  52  is mounted on the shaft  36 , and with the nut  66  tightened to preload the bearing assembly  20  and to bias the inboard face  62  of the hub&#39;s center portion  56  against the outboard face  64  of the bearing assembly&#39;s outboard inner race  34 , the high degree of parallelism between these surfaces with the hub&#39;s wheel-mounting face  68  and the rotor portion&#39;s friction surfaces  82  provides the exemplary wheelend assembly  12  with a significantly reduced runout for both a mounted wheel and the rotor portion  76  of the hub  52 . The reduced runout, in turn, advantageously improves wheelend runout and corner module service life, while further reducing corner module NVH levels.  
         [0032]    While the above description constitutes the preferred embodiment, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the subjoined claims. For example, while the exemplary wheelend assembly is described above in connection with a non-driven front-end corner module, it will be appreciated that the invention is equally applicable to non-driven rear-end corner modules. The invention is further applicable to continuously-driven and selectively-driven front-end and rear-end corner modules, for example, by forming a suitable power-transmitting couple on the inboard end of the stub shaft. Thus, depending upon the location and purpose of the corner module incorporating the exemplary wheelend assembly, the invention contemplates use of a recess or ball cup defined in the inboard end of the shaft, thereby forming a portion of a universal or constant velocity joint by which to “drive” the wheelend assembly with a mating driving shaft.  
         [0033]    Also by way of example only, it will be appreciated that the invention contemplates a non-driven wheelend assembly whose stub shaft extends in the opposite direction, such that the preformed radial flange directly abuts the outboard face of the integrated hub-rotor, and the axial preload is applied via a nut threaded on the inboard end of the shaft, consistent with the approach of a so-called “Gen II.5” prior art design.