Patent Abstract:
A cover assembly is provided for a wheel hub, which includes a coupler and a cap. The coupler has a forward segment with a coupler forward opening and a coupler rearward segment with a coupler rearward opening. The cap has a cap opening, a cap barrel, and a cap end plate. The coupler rearward segment is configured for connection to a wheel hub, while the cap is configured for connection to the coupler forward segment and for selectively removable coverage of the coupler forward opening. The cap barrel has a first threaded surface and the coupler forward segment has a second threaded surface, which are selectively engagable to enable threadable connection of the cap to the coupler forward segment. The coupler rearward segment has a smooth engagement surface capable of press fitting connection to the wheel hub.

Full Description:
TECHNICAL FIELD 
   The present invention relates generally to a hub-spindle assembly for a wheel and associated axle, and more particularly to a hub-spindle assembly having a hub filled with a liquid lubricant, wherein the hub is fitted with a cover assembly to retain the liquid lubricant therein. 
   BACKGROUND OF THE INVENTION 
   A hub-spindle assembly for a rotatable wheel and associated stationary axle typically includes a hub, a spindle and a plurality of wheel bearings. The hub is a mount for the rotatable wheel and encloses a rotation chamber, which houses the wheel bearings. The spindle extends from the end of the axle and is received into the rotation chamber. The hub and wheel rotate about the spindle during rotational operation of the wheel. The wheel bearings are positioned between the spindle and hub within the rotation chamber to provide a friction-reduced rotation surface. The rotation chamber also contains a viscous lubricant to lubricate the wheel bearings. 
   A chamber opening is formed in the front of the hub to access the rotation chamber. It is often desirable to access the rotation chamber during maintenance of the hub, for example, when inspecting, servicing, or replacing the lubricant or wheel bearings within the rotation chamber. A bearing cap is typically provided over the chamber opening during rotational operation of the wheel to seal the rotation chamber from the external environment and specifically to prevent the intrusion of contaminants into the rotation chamber, such as grit or moisture. Such contaminants can damage or accelerate wear of the wheel bearings, thereby diminishing the life of the wheel bearings and necessitating frequent replacement, or in some cases causing failure of the hub-spindle assembly with potentially catastrophic results. 
   The above-described hub-spindle assembly is conventional to virtually all types of conveyances employing wheels and axles, including motor vehicles and trailers. In addition, petroleum-based grease lubricants are the most common type of lubricants used in such hub-spindle assemblies. Despite the widespread use of grease lubricants, however, it is generally known that liquid lubricants are more effective lubricating agents than grease lubricants in hub-spindle assemblies. Liquid lubricants exhibit improved heat transfer properties relative to grease lubricants, thereby more effectively transferring heat away from the wheel bearings of the hub-spindle assembly during operation. In addition, commercial-grade liquid lubricants usually contain a lower level of particulates than commercial-grade grease lubricants. Consequently, a hub-spindle assembly lubricated with a liquid lubricant advantageously tends to exhibit a slower rate of wear than one lubricated with a grease lubricant under equivalent operating conditions. 
   Grease lubricants are used in hub-spindle assembly applications although liquid lubricants have superior performance characteristics because liquid lubricant-containing hubs are operationally more problematic than grease lubricant-containing hubs. The bearing cap for a grease lubricant-containing hub is typically retained in place over the chamber opening during operation of the wheel by press fitting the smooth-edged bearing cap onto the correspondingly smooth-edged circular chamber opening. The bearing cap cannot be press fitted onto the chamber opening too tightly since it is periodically necessary to remove the bearing cap for wheel maintenance purposes, such as servicing the lubricant. The press-fitted bearing cap is removed from the chamber opening by manually prying the bearing cap away from the chamber opening with a screw driver, chisel, pry bar, or the like when it is necessary to access the interior of the rotation chamber. However, the press-fitted bearing cap is usually formed from a more lightweight material, which is not as sturdy as the heavier material from which the hub is formed. Thus, the bearing cap is not press fitted too tightly onto the chamber opening to prevent damage to the bearing cap during placement or removal. 
   Press-fitted bearing caps are not readily adaptable to liquid lubricant applications because the less viscous liquid lubricants are more prone to leakage past press-fitted bearing caps than the more viscous grease lubricants. As noted above, the need to periodically manually remove the press-fitted bearing cap from the hub often results in an incomplete seal between the press-fitted bearing cap and hub, which is not fluid-tight. Press-fitted bearing caps are also susceptible to water intrusion either during inactivity or during rotational operation of the wheel. Although liquid lubricants and grease lubricants are both petroleum-based, liquid lubricants are much less effective than grease lubricants when contaminated with water. Water forms emulsions with liquid lubricants, whereas water does not readily mix with grease lubricants because of the lower viscosity of liquid lubricants relative to grease lubricants. As a result, grease lubricants retain their effectiveness to a greater degree in the presence of water than liquid lubricants which quickly break down. 
   Hubs which are specifically designed for liquid lubricant applications typically have threads on the chamber opening, which are coupled with corresponding threads on the bearing cap. Threadably-coupled bearing caps and hubs are much less susceptible to liquid lubricant leakage and water intrusion than press-fitted bearing caps and hubs. Nevertheless, many conventional hubs are still designed for press-fitted bearing caps. Such hubs lack threads on the chamber opening to accommodate threads on the bearing cap so that only press-fitted bearing caps and grease lubricants can be used with the hubs. Consequently, the advantages of liquid lubricants go unrealized for these hubs. 
   If it becomes necessary or desirable to use liquid lubricants in a conventional hub lacking a threaded chamber opening, it is usually necessary to replace the entire unthreaded hub with a new threaded hub. This procedure is both time consuming and costly. Accordingly, it is an object of the present invention to provide means for practically and economically converting a grease lubricant-containing hub to a liquid lubricant-containing hub. More particularly, it is an object of the present invention to provide a cover assembly for an unthreaded chamber opening of a hub, which effectively retains a liquid lubricant in the rotation chamber of the hub. It is another object of the present invention to provide a cover assembly for a chamber opening of a hub, which is resistant to intrusion of water or other contaminants into the rotation chamber of the hub. It is a further object of the present invention to provide a cover assembly for a chamber opening of a hub, which enables visual inspection of a liquid lubricant within the rotation chamber of the hub without removal of the cover assembly. It is still a further object of the present invention to provide a cover assembly for a chamber opening of a hub, which readily enables the addition of a liquid lubricant into the rotation chamber of the hub without removal of the cover assembly. It is yet a further object of the present invention to provide a cover assembly for a chamber opening of a hub, which provides ready access to the rotation chamber of the hub for servicing the wheel bearings therein. It is another object of the present invention to provide a cover assembly for a chamber opening of a hub, which is sufficiently sturdy to withstand the rigors of everyday operation. These objects and others are accomplished in accordance with the invention described hereafter. 
   SUMMARY OF THE INVENTION 
   The present invention is a cover assembly for a wheel hub. The cover assembly comprises a coupler and a cap. The coupler has a forward segment with a coupler forward opening and a coupler rearward segment with a coupler rearward opening. The cap has a cap opening, a cap barrel, and a cap end plate. The coupler rearward segment is configured for connection to a wheel hub, while the cap is configured for connection to the coupler forward segment and for selectively removable coverage of the coupler forward opening. 
   In accordance with one embodiment, the cap barrel has a first threaded surface and the coupler forward segment has a second threaded surface. The first and second threaded surfaces are selectively engagable to enable threadable connection of the cap to the coupler forward segment. The cap barrel may be received into the coupler forward segment or alternatively the coupler forward segment may be received into the cap barrel. In a preferred embodiment, the coupler forward segment is received into the cap barrel with the first threaded surface being an internal surface of the cap barrel and the second threaded surface being an external surface of the coupler forward segment. 
   The coupler rearward segment preferably has a smooth engagement surface capable of press fitting connection to the wheel hub with the coupler rearward segment being receivable into the wheel hub. In accordance with a more specific embodiment, the cap end plate has a cap opening and a selectively removable cap plug is positioned in the cap opening. In accordance with another more specific embodiment, the coupler forward segment and the coupler rearward segment are separated by a flange having a beveled edge. 
   The above-recited coupler is preferably an element of a hub-spindle assembly for a rotatable wheel. In addition to the coupler, the hub-spindle assembly further comprises a wheel hub and a wheel bearing. The wheel hub has a hub chamber and a hub forward opening. The wheel bearing is positioned in the hub chamber. 
   The cap barrel has a first threaded surface and the coupler forward segment has a second threaded surface. The first and second threaded surfaces are selectively engagable to enable threadable connection of the cap to the coupler forward segment with the coupler forward segment preferably being received into the cap barrel. The coupler rearward segment has a smooth engagement surface for press fitting into the hub chamber via the hub forward opening. 
   The present invention is additionally a method for covering an unthreaded forward opening of a hub chamber of a wheel hub with a threaded cap. The method comprises press fitting a coupler rearward segment of a coupler having a coupler rearward opening into an unthreaded forward opening of a hub chamber of a wheel hub. A threaded cap is provided having a cap opening, a cap barrel with a first threaded surface, and a cap end plate. The first threaded surface of the cap barrel is threadably connected to a second threaded surface of a coupler forward segment. The coupler has a coupler forward opening with the cap selectively removably covering the coupler forward opening and correspondingly covering the unthreaded forward opening of the hub chamber. The coupler rearward segment has a smooth engagement surface press fitted into the unthreaded forward opening. 
   The present invention will be further understood from the drawings and the following detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a hub-spindle assembly and an associated cover assembly of the present invention. 
       FIG. 2  is an elevational view in partial cross-section of the hub-spindle assembly and cover assembly of  FIG. 1  taken along line  2 — 2 . 
       FIG. 3  is an exploded perspective view of the cover assembly of  FIG. 1 . 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a hub-spindle assembly is shown and generally designated  10 . The hub-spindle assembly  10  comprises a hub  12  and a spindle  14 , which are similar to those disclosed in U.S. Pat. No. 5,551,530, incorporated herein by reference. The spindle  14  is a shaft having an end rearwardly extending away from the hub  12  to engage an axle (not shown), which supports the spindle  14 . The hub  12  is constructed in the typical manner of a conventional grease lubricant-containing hub. In particular, the hub  12  has a substantially tubular configuration with an open interior to receive a forwardly-extending end of the spindle  14  via the hub rear  16  as described below. The hub  12  functions as a mount for a wheel (not shown) and the spindle  14  functions as an axis of rotation for the hub  12  and the wheel mounted thereon. 
   A cover assembly  18  engages the hub front  20 . The cover assembly  18  comprises a coupler  22  and a bearing cap  24 . The coupler  22  likewise has a tubular configuration as described below. The bearing cap  24  fits over the open front end (shown in  FIGS. 2 and 3 ) of the coupler  22 . The bearing cap  24  has a cylindrical configuration, which includes a cap barrel  26  and a cap end plate  28 . The cap barrel  26  has a cap rearward end  30  and a cap forward end  32 . The cap rearward end  30  is open and the cap forward end  32  is covered by the cap end plate  28 . The cap barrel  26  and cap end plate  28  are preferably integrally constructed as a unitary structure from a rigid, strong material having transparent properties, such as a light-weight, transparent plastic, and more particularly a molded polycarbonate plastic. The term “transparent” as used herein refers to materials that are substantially clear or translucent, to the extent a liquid lubricant is visible therethrough. The hub  12 , spindle  14 , and coupler  22  are preferably fabricated from strong, heavy-weight, durable metals such as cast iron or steel. 
   A cap opening  34  is formed in the cap end plate  28  and a cap plug  36  resides in the cap opening  34 . The cap plug  36  is removably retained in the cap opening  34 , preferably by press fitting, to form a fluid-tight seal at the interface between the cap opening  34  and the cap plug  36 . The cap plug  36  is preferably fabricated from a somewhat flexible elastomeric material, such as a stiffened synthetic rubber, and has a relatively small pressure vent port  38  extending therethrough. 
   Further details of the hub-spindle assembly  10  and cover assembly  18  are shown and described hereafter with reference to  FIGS. 2 and 3 . Elements of  FIGS. 2 and 3 , which are common to  FIG. 1 , are identified by the same reference characters. As disclosed above, the hub  12  has a tubular configuration, which defines a rotation chamber  40  (alternately termed a hub chamber), a hub rearward opening  42 , and a hub forward opening  44 . The hub chamber  40  extends between the hub rear  16  and hub front  20  and is bounded by a hub interior wall  46 . The hub rearward opening  42  is positioned at the hub rear  16 , while the hub forward opening  44  is positioned at the hub front  20 . For purposes of the present description, the terms “rear” or “rearward” are used to define a relative position more proximal to the axle and the terms “front” or “forward” are used to define a relative position more distal from the axle. 
   The hub chamber  40  houses a threaded forward end  48  of the spindle  14 , which extends through the hub rearward opening  42 , into the hub chamber  40 , and partially out the hub chamber  40  via the hub forward opening  44  without engaging the hub interior wall  46 . The hub chamber  40  further houses a rearward wheel bearing  50 , which is positioned between the hub  12  and spindle  14  proximal to the hub rearward opening  42 . The hub chamber  40  similarly houses a forward wheel bearing  52 , which is positioned between the hub  12  and spindle  14  proximal to the hub forward opening  44 . The rearward and forward wheel bearings  50 ,  52  are conventional bearings, which engage the hub interior wall  46  and the spindle forward end  48  to provide a friction-reduced rotation surface between the hub  12  and spindle  14  as the hub  12  rotates about the spindle  14 . A spindle nut  54  is threadably coupled with the spindle forward end  48  to maintain the positional relationship between the hub  12 , spindle  14 , and wheel bearings  50 ,  52  within the hub chamber  40 . 
   The hub rearward opening  42  has a circular perimeter of a fixed inside diameter. The inside diameter of the hub rearward opening  42  is substantially greater than the outside diameter of the spindle  14  adjacent the hub rearward opening  42  to provide a rearward annulus  56  between the hub  12  and spindle  14 . The rearward annulus  56  is plugged by a fluid-tight rearward seal  58  positioned in the rearward annulus  56 . The rearward seal  58  has a toroidal configuration, which conforms to the contours of the hub rearward opening  42  and the spindle  14 . The rearward seal  58  is preferably fabricated from an elastomeric material, which prevents fluid leakage into or out of the hub chamber  40  via the hub rearward opening  42 . 
   The hub forward opening  44  likewise has a circular perimeter of a fixed inside diameter, which is substantially greater than the outside diameter of the spindle forward end  48  adjacent the hub forward opening  44  and is also substantially greater than the outside diameter of the spindle nut  54 . Both the spindle forward end  48  and spindle nut  54  extend forward out of the hub chamber  40  via the hub forward opening  44  without engaging the hub interior wall  46  or the perimeter of the hub forward opening  44 . The hub forward opening  44  has an inside face  60  with a relatively smooth unthreaded surface. 
   The coupler  22  has a tubular configuration, which defines a coupler chamber  62 , a coupler rearward opening  64 , and a coupler forward opening  66 . The coupler chamber  62  is open at both ends, extending between the coupler rearward opening  64  and the coupling forward opening  66 . The coupler chamber  62  has a uniform inside diameter, which is essentially equal to the inside diameters of the coupler rearward opening  64  and coupler forward opening  66 , respectively. The inside diameter of the coupler forward opening  66  is substantially greater than the outside diameter of the spindle forward end  48  adjacent the coupler forward opening  66  and is also substantially greater than the outside diameter of the spindle nut  54 . Both the spindle forward end  48  and spindle nut  54  extend into the coupler chamber  62  via the coupler rearward opening  64  without engaging the coupler interior wall  68  or the perimeter of the coupler forward opening  66 . 
   The coupler  22  has a coupler exterior wall  70 , which is encircled by a coupler flange  72  approximately midway between the coupler rearward opening  64  and the coupler forward opening  66 . The coupler flange  72  segments the coupler exterior wall  70  into a coupler rearward segment  74  and a coupler forward segment  76 . The coupler forward segment  76  is provided with male threads  78  on its surface and has a fixed outside diameter. In contrast, the coupler rearward segment  74  has a relatively smooth unthreaded surface and a fixed outside diameter, which is approximately equal to the inside diameter of the hub forward opening  44 . The approximately equal diameters of the coupler rearward segment  74  and hub forward opening  44  enable fluid-tight fixable coupling of the coupler  22  with the hub  12  by press fitting the coupler rearward segment  74  into the hub forward opening  44  until the rearward edge  79  of the coupler flange  72  engages the perimeter the hub forward opening  44 . The rearward edge  79  is preferably beveled to facilitate removal of the coupler rearward segment  74  from the hub forward opening  44 , if desired. 
   The materials of the hub  12  and coupler  22  are of sufficient strength that a substantial force can be employed by mechanical means to press fit the coupler rearward segment  74  into the hub forward opening  44 , thereby ensuring a fluid-tight seal between the coupler rearward segment  74  and hub forward opening  44  without damaging the hub  12  or coupler  22 . Furthermore, there is no operational need for periodic removal of the coupler  22  from the hub  12  once the coupler  22  has been press fitted into the hub  12  for servicing the lubricant contained within the hub chamber  40 . Accordingly, the desirability of a looser fit between the coupler  22  and hub  12  to facilitate removal is obviated in contrast to the requirements of prior art press-fitted bearing caps and hubs. 
   As disclosed above, the bearing cap  24  is open at the cap rearward end  30 , having a cap rearward opening  80 , which exposes a cap interior  82 . A continuous cap lip  84  encircles the entire perimeter of the cap rearward opening  80 . The cap interior  82  is enclosed on the sides by the cap barrel  26  and on the cap forward end  32  by the cap end plate  28 . More particularly, the cap interior  82  is bounded on the sides by a cap interior side wall  86  and on the cap forward end  32  by a cap interior end wall  88 . The cap interior side wall  86  is provided with female threads  90  on its surface and has a fixed inside diameter, which is approximately equal to the outside diameter of the coupler forward segment  76 . The female threads  90  of the bearing cap  24  align with the male threads  78  of the coupler  22 , enabling fluid-tight threadable coupling of the bearing cap  24  over the coupler forward opening  66  and coupler forward segment  76 . The bearing cap  24  and coupler  22  are sized such that the spindle forward end  48  and spindle nut  54 , which extend into the coupler chamber  62 , do not interfere with fluid-tight threadable coupling of the bearing cap  24  and coupler  22 . 
   Fluid-tight threadable coupling is preferably effected by tightly screwing the female threads  90  down onto the male threads  78  until the cap lip  84  engages the forward face of the coupler flange  72 . An O-ring  92  is optionally positioned around the coupler forward segment  76  against the forward face of the coupler flange  72  to enhance the integrity of the fluid-tight seal at the threads  78 ,  90 . 
   As disclosed above, the cap plug  36  is preferably press fitted into the cap opening  34 . A ridge  94  are provided on the rearward end of the cap plug  36  to facilitate retention of the cap plug  36  in the cap opening  34 . The cap plug  36  is selectively removable from the cap opening  34  as desired, and preferably during maintenance of the hub-spindle assembly  10  to add a liquid lubricant to the hub chamber  40  via the cap opening  34 . Removing only the cap plug  36  rather than the entire bearing cap  24  to add fresh liquid lubricant to the hub chamber  40  substantially prevents the liquid lubricant already in the hub chamber  40  from escaping via the coupler forward opening  66 . Removal of the cap plug  36  is effected by manually prying the cap plug  36  out of the cap opening  34 , while replacement of the cap plug  36  is effected by manually press fitting the cap plug  36  back into the cap opening  34 . 
   In contrast, if one desires to drain the liquid lubricant from the hub chamber  40 , it is preferable to completely remove the bearing cap  24  from the coupler forward opening  66 . Removal of the bearing cap  24  is effected simply by manually unscrewing the bearing cap  24  and draining the liquid lubricant from the hub chamber  40  via the coupler forward opening  66 . Replacement of the bearing cap  24  over the forward opening  66  is effected simply by manually screwing the bearing cap  24  back on. 
   The pressure vent port  38  forwardly tapers from a wide mouth to a pin hole where the pressure vent port  38  opens into the external environment. The pressure vent port  38  permits hot expanded air to exit the hub chamber  40  during normal operation of the hub-spindle assembly  10 . At the same time, the pressure vent port  38  essentially prevents significant leakage of liquid lubricant from the hub chamber  40  via the pressure vent port  38  during normal operation. 
   When the hub-spindle assembly  10  and cover assembly  18  are cooperatively coupled in the manner disclosed above, the hub chamber  40  and coupler chamber  62  in combination define a substantially continuous lubricant chamber  40 ,  62 . The lubricant chamber  40 ,  62  has a void volume defined by the portion of the lubricant chamber  40 ,  62 , which is unoccupied by any impermeable structural components, such as the spindle  14 , rearward and forward wheel bearings  50 ,  52 , and spindle nut  54 . The lubricant chamber  40 ,  62  is maintained in selective fluid isolation from the external environment of the hub-spindle assembly  10  for purposes of retaining a liquid lubricant therein by positioning the selectively removable bearing cap  24  over the coupler forward opening  66  and positioning the hub rearward seal  58  in the hub rearward opening  42 . 
   The lubricant chamber  40 ,  62  is specifically adapted for retaining a liquid lubricant therein to lubricate the hub-spindle assembly  10 . In a preferred practice, it is only necessary to fill a portion of the void volume of the lubricant chamber  40 ,  62  with a selected liquid lubricant to effectively lubricate the hub-spindle assembly  10  during operation. A liquid lubricant is generally defined herein as a lubricant which flows under the force of gravity at ambient temperature, whereas a grease lubricant does not flow under the force of gravity at ambient temperature. A preferred liquid lubricant is a conventional petroleum-based lubricant such as a grade SAE 50/95 gear and bearing oil. 
   It is apparent that the cover assembly of the present invention has particular utility to retrofit applications, wherein an existing grease lubricant-containing hub is converted to a liquid lubricant-containing hub. However, the cover assembly of the present invention is not limited to retrofit applications, but also has utility for original equipment and replacement equipment applications, if desired. Furthermore, the cover assembly of the present invention is not limited to liquid lubricant applications, but also has utility for grease lubricant applications, if desired. 
   While the forgoing preferred embodiments of the invention have been described and shown, it is understood that alternatives and modifications, such as those suggested and others, may be made thereto and fall within the scope of the invention. 
   GLOSSARY OF DRAWING TERMS 
   Attny Docket No. 016P0301 
   
       
       10 hub-spindle assembly 
       12 hub 
       14 spindle 
       16 hub rear ( 12 ) 
       18 cover assembly 
       20 hub front ( 12 ) 
       22 coupler 
       24 bearing cap 
       26 cap barrel ( 24 ) 
       28 cap end plate ( 24 ) 
       30 cap rearward end ( 26 ) 
       32 cap forward end ( 26 ) 
       34 cap opening ( 24 ) 
       36 cap plug 
       38 vent port ( 36 ) 
       40 hub chamber ( 12 ) 
       42 hub rearward opening ( 12 ) 
       44 hub forward opening ( 12 ) 
       46 hub inferior wall ( 40 ) 
       48 spindle forward end ( 14 ) 
       50 rearward wheel bearing 
       52 forward wheel bearing 
       54 spindle nut 
       56 hub rearward annulus ( 42 ) 
       58 hub rearward seal ( 56 ) 
       60 inside face ( 44 ) 
       62 coupler chamber ( 22 ) 
       64 coupler rearward opening ( 22 ) 
       66 coupler forward opening ( 22 ) 
       68 coupler interior wall ( 22 ) 
       70 coupler exterior wall 
       72 coupler flange 
       74 coupler rearward segment 
       76 coupler forward segment 
       78 male threads ( 76 ) 
       79 rearward edge ( 72 ) 
       80 rearward opening 
       82 cap interior 
       84 cap tip 
       86 cap interior side wall 
       88 cap interior end wall 
       90 female threads ( 86 ) 
       92 O-ring 
       94 ridge ( 36 )

Technology Classification (CPC): 1