Patent Publication Number: US-2005116529-A1

Title: Shopping cart wheel

Description:
BACKGROUND OF THE INVENTION  
      1. Technical Field  
      The present invention relates to wheels for shopping carts and, more particularly, to an improved shopping cart wheel, including a wheel hub supporting a wheel thereon and having a central axial opening, an first precision bearing unit having a rotating cylindrical central hub, an outer toroidal bearing jacket surrounding the central hub and a plurality of ball bearings rotatably mounted within the bearing jacket for rotatably supporting the central hub there between, an second precision bearing unit similar to the first precision bearing unit, the first and second precision bearing units mounted within the central axial opening of the wheel hub generally contacting one another to provide increased weight capacity and greater side load withstanding capability.  
      2. Description of the Prior Art  
      When the average consumer visits a grocery store to purchase groceries, little thought is given to the shopping cart into which the groceries are placed prior to purchase. However, unless the shopping cart functions correctly for the shopper, the entire shopping experience is made much more difficult and it is even likely that the consumer will cease to shop at the particular store where the inconvenience was encountered. Therefore, there is a need to make shopping carts as reliable and maintenance free as possible to increase consumer satisfaction with the shopping experience and decrease maintenance costs to the grocery store.  
      Of all of the elements of the shopping cart, it is the shopping cart wheels which undergo the most stress and strain during the lifespan of the shopping cart and, in fact, it is the shopping cart wheels which force the retirement of many shopping carts from active duty. Particularly with the proliferation of discount stores such as Sam&#39;s Club® and other such wholesale outlets, the amount and weight of groceries being purchased is increasing, thus resulting in additional strain and stress being placed on the shopping cart wheels. Also, due to the high-pressure washing systems used to clean shopping carts, the wheels, and particularly the wheel bearings, are often denuded of lubricant which can decrease the lifespan of the shopping cart wheel. Finally, shopping cart wheels are exposed to a great deal of side stress due to the sliding of the wheels sideways on the floor surface during cornering of the shopping cart, which further increases the stress loads placed on the wheels and wheel bearings of the shopping cart wheel. There is therefore a need for an improved shopping cart wheel which will better withstand the increased weight demands and increased side forces applied to the wheels to increase the lifespan of the wheel and decrease maintenance costs to the grocery store.  
      Various wheels have been proposed in the prior art, such as Hicks, U.S. Pat. No. 5,690,395 and Kern et al., U.S. Pat. No. 5,871,286, each of which attempt to address and solve the problems of increased weight demands and increased wear on the wheels, but do not fully solve either of the problems for various reasons which are inherent in their designs. Consequently, there is still a need for an improved shopping cart wheel which will address and solve the problems not solved by those wheels found in the prior art.  
      Therefore, an object of the present invention is to provide an improved shopping cart wheel.  
      Another object of the present invention is to provide an improved shopping cart wheel which includes two precision bearing units mounted in the central axial opening of the wheel to greatly improve the weight capacity and side load capacity of the wheel.  
      Another object of the present invention is to provide an improved shopping cart wheel in which the first and second precision bearing units are each mounted adjacent opposite ends of the central axial opening of the wheel hub with the central hubs of each of the precision bearing units contacting one another to greatly increase the structural strength of the shopping cart wheel.  
      Another object of the present invention is to provide an improved shopping cart wheel which is superior to those wheels found in the prior art, yet also is relatively economical in construction to permit its widespread use.  
      Finally, an object of the present invention is to provide an improved shopping cart wheel which is relatively simple and inexpensive in construction and is safe, efficient, and durable in use.  
     SUMMARY OF THE INVENTION  
      The present invention provides an improved shopping cart wheel which includes a wheel hub supporting a wheel thereon and having a central axial opening having inner and outer sides. Mounted within the central axial opening adjacent one end thereof is a first precision bearing unit having a rotating cylindrical central hub, an outer toroidal bearing jacket surrounding the central hub and a plurality of ball bearings rotatably mounted within the outer toroidal bearing jacket and rotatably supporting the rotating central hub therebetween, and mounted within the central axial opening adjacent the opposite end thereof is an second precision bearing unit having a rotating cylindrical central hub, an outer toroidal bearing jacket surrounding the central hub and a plurality of ball bearings rotatably mounted within the outer toroidal bearing jacket and rotatably supporting the rotating central hub therebetween. The central hub of the first precision bearing unit is generally contacting the central hub of the second precision bearing unit within the central axial opening in generally coaxial alignment such that the improved shopping cart wheel will withstand greater side load forces and have increased weight-carrying capacity.  
      The improved shopping cart wheel as thus described provides several advantages not found in the prior art. For example, the use of the precision bearings will greatly decrease the maintenance needs of the wheel thus increasing the lifespan of the wheel and reducing the maintenance costs for operation of the wheel and hence the cart on which the wheel is mounted. Also, the design and construction of the wheel is such that the cost per unit is kept affordable, which permits the wheel of the present invention to be used in a greater number of situations. Finally, because the improved shopping cart wheel of the present invention provides greater capacity to withstand side load forces without failing and further includes increased weight-carrying capacity, it is superior to those wheels found in the prior art. It is thus seen that the improved shopping cart wheel of the present invention provides a substantial improvement over those devices found in the prior art.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of the improved shopping cart wheel of the present invention mounted on a shopping cart;  
       FIG. 2  is a detail perspective view of the improved shopping cart wheel of the present invention; and  
       FIG. 3  is a front sectional elevational view of the improved shopping cart wheel showing the precision bearings within the central axial opening of the wheel hub.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The improved shopping cart wheel  10  of the present invention is shown best in  FIGS. 1, 2  and  3  as including a wheel hub  12  on which is circumferentially mounted a wheel  50  which, in the preferred embodiment, would be constructed of metal, plastic such as polyurethane or a rubber compound, depending on the intended use of the shopping cart wheel. In the preferred embodiment, the wheel hub  12  would be molded from a high-impact plastic such as polypropylene and further includes a central axial opening  14  which, in the preferred embodiment, is generally cylindrical in shape extending perpendicularly through the wheel hub  12  in coaxial alignment with the rotational axis of the wheel hub  12 .  
      Mounted within central axial opening  14  are a pair of precision bearing units, a first precision bearing unit  16  mounted adjacent one side of central axial opening  14  and a second precision bearing unit  26  mounted adjacent the opposite side of central axial opening  14 , as shown best in  FIGS. 2 and 3 . As each of the first and second precision bearing units  16  and  26  are preferably identical, the following description of first precision bearing unit  16  should be understood to apply equally to second precision bearing unit  26 . First precision bearing unit  16  preferably includes a rotating cylindrical central hub  18  which is rotatably mounted within an outer generally toroidal bearing jacket  20 , as shown best in  FIGS. 2 and 3 . The bearing jacket  20  is preferably generally square U-shaped in cross section to provide a channel in which rotatably reside a plurality of ball bearings  22  which rotatably support the central hub  18  therebetween. It is further preferred that the ball bearings  22  be Teflon-coated or the like to minimize friction and also reduce the need for lubrication for the ball bearings  22 . In the preferred embodiment, the central hub  18  would have a diameter of approximately one centimeter and a length of approximately two centimeters, and the diameter of bearing jacket  20  would be approximately two centimeters, although the specific dimensions of the bearing unit elements is not critical to the present invention so long as the functionality of the bearing unit is maintained. For example, it may be preferable to include a larger bearing unit  16  in the case of use of a larger wheel hub  12  to decrease friction and increase the lifespan of the shopping cart wheel  10 .  
      It should be noted that, in the preferred embodiment, central axial opening  14  of wheel hub  12  would include a step configuration wherein the outer ends of central axial opening  14  have a greater diameter than the inner connecting section of central axial opening  14 . The primary purpose for this is to insure that the first and second precision bearing units  16  and  26  fit snugly and securely into the central axial opening  14  to minimize as much as possible wobble motion of the shopping cart wheel  10  when it is mounted on the shopping cart  60 . Of course, it should also be noted that the exact dimensions of the central axial opening  14  may be modified or changed to accommodate various shaped bearing units  16  and  26  merely by modifying the mold from which the wheel hub  12  is produced.  
      The shopping cart wheel  10  of the present invention is shown as being mounted on a shopping cart  60  by a swivel bracket  62  through which a mounting pin  64  is extended, as shown best in  FIGS. 1 and 3 . The mounting pin  64  extends through the central hubs  18  of first and second precision bearing units  16  and  26  such that the improved shopping cart wheel  10  is rotatably mounted on the mounting pin  64  on swivel bracket  62 . Of course, many other types of mounting brackets and systems may be used in connection with the improved shopping cart wheel  10  of the present invention, any of which would be understood by one skilled in the art.  
      It is the unique combination of the first and second precision bearing units  16  and  26  mounted within the central axial opening  14  of wheel hub  12  that render the present invention superior to those wheels found in the prior art. For example, the dual precision bearings permit the shopping cart wheel  10  to support an increased amount of weight over those wheels found in the prior art and, furthermore, because the precision bearings  16  and  26  are mounted adjacent the opposite sides of the central axial opening  14  of wheel hub  12 , improved resistance to side load conditions which tend to damage shopping cart wheels is obtained. Also, the bearing units  16  and  26  are sealed, which means that the incursion of foreign objects into the bearing units  16  and  26  is generally prevented. Finally, because of the relatively simple construction of the shopping cart wheel  10  of the present invention, the cost for construction of the shopping cart wheel is greatly reduced, thus permitting its use in many different situations where such an improved wheel would not otherwise be available for use.  
      It should be noted that it is contemplated to include a plastic cover (not shown) to be mounted on each of the opposite sides of the wheel hub  12  completely covering and enclosing the first and second precision bearing units  16  and  26  to protect them and generally prevent the incursion of contaminants which will degrade the performance of the bearing units, although the exact size and shape of the plastic cover will be determined on a case-by-case basis depending on the structure and format of the wheel itself. Also, it is further contemplated to include a cylindrical steel spanner  30  which extends between and connects the central hubs  18  of first and second precision bearing units  16  and  26  for additional structural strength of the improved shopping cart wheel  10 , and although the inclusion of such a steel spanner unit is not critical to the present invention, it is desirable.  
      It is to be understood that numerous additions, substitutions, and modifications may be made to the improved shopping cart wheel  10  of the present invention which fall within the intended broad scope of the appended claims. For example, the precise size, shape, and construction materials used in connection with the wheel  10  are not critical so long as the functional features described herein are maintained. Furthermore, the precise nature of the first and second precision bearing units  16  and  26  is only somewhat critical to the present invention so long as the units are precision bearing units having the functional characteristics of a precision bearing in order to insure proper functionality of the improved shopping cart wheel  10  of the present invention. Finally, although the present invention has been described for use in connection with shopping carts, it should be noted that the wheel may be used with other types of carts, any of which would be understood by those skilled in the art.  
      There has therefore been shown and described an improved shopping cart wheel  10  which accomplishes at least all of its intended objectives.