Patent Publication Number: US-2005132684-A1

Title: Wheel for lawnmowers and the like

Description:
BACKGROUND OF THE INVENTION  
      Various types of powered riding lawnmowers have been developed. Such lawnmowers commonly include a deck housing that cover the rotating blades that are used to cut the grass or the like. Such decks are typically movably mounted to the riding mower, and include a housing having a plurality of wheels mounted to the housing to support the deck as it moves across the lawn surface. During use, such wheels encounter objects, and are otherwise subject to substantial wear and tear such that the wheels often need to be replaced in a relatively short period of time.  
     SUMMARY OF THE INVENTION  
      One aspect of the present invention is a wheel assembly including a wheel having a body portion defining opposite sides. The body portion is made of a polymer material, and includes a hub defining a pair of coaxial cylindrical cavities. The cavities have sidewalls defining a first diameter and are open to the opposite sides of the body portion. The hub includes a dividing wall portion between the cylindrical cavities, and the dividing wall portion has an opening therethrough. The wheel assembly further includes first and second bearings positioned in the cavities, and having outer surfaces closely contacting the sidewalls of the cylindrical cavities to thereby retain the bearings in the cylindrical cavities. The first and second bearings preferably include a rolling element.  
      Another aspect of the present invention is a wheel assembly including a wheel having a body portion defining opposite sides. The body portion is made of a polymer material, and the body portion includes an integral hub defining a pair of cavities having sidewalls. The cavities are open to the opposite sides, and the hub includes an integral dividing portion between the cavities. The wheel assembly further includes first and second roller bearings positioned in the cavities.  
      Yet another aspect of the present invention is a method of making a wheel assembly. The method includes providing a mold with a mold cavity in the shape of a wheel. First and second bearings are positioned in the mold cavity, and a pre-fabricated spacer is positioned between the bearings to position the bearings in a spaced apart relationship. A plastic material is injected into the mold cavity around the bearings and the spacer to thereby form the wheel assembly.  
      Yet another aspect to the present invention is a riding lawnmower including a powered main portion configured to support an operator, and a deck assembly operably connected to the main portion. The deck assembly has a housing and at least one powered blade movably mounted on the underside of the housing for cutting grass. The deck includes at least one wheel assembly mounted to the housing via a bracket. The wheel assembly includes a wheel having a body portion including a hub with a pair of spaced apart bearings positioned within the hub. Each bearing includes a rolling element. A pin element is secured to the bracket and extends through the bearing to thereby mount the wheel assembly to the bracket.  
      These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a partially schematic perspective view of a riding lawnmower including a deck with wheel assemblies according to one aspect of the present invention;  
       FIG. 2  is a cross-sectional view of a prior art wheel assembly;  
       FIG. 3  is a perspective view of a wheel assembly according to the present invention;  
       FIG. 4  is a cross-sectional view of the wheel of  FIG. 3  taken along the line IV-IV;  
       FIG. 5  is a perspective view of a spacer;  
       FIG. 6  is a partially schematic elevational view of an injection mold utilized to fabricate the wheel assembly;  
       FIG. 7A  is a cross-sectional view of the mold of  FIG. 6  in the closed position;  
       FIG. 7B  is a cross-sectional view of the mold of  FIG. 7A  in the open position;  
       FIG. 8  is a plan view of the mold of  FIG. 6 ;  
       FIG. 9  is a cross-sectional view of another embodiment of a wheel according to the present invention;  
       FIG. 10  is a perspective view of a two-piece spacer according to another aspect of the present invention;  
       FIG. 11  is a partially schematic elevational view of an injection mold utilized to fabricate the wheel assembly of  FIG. 9 ;  
       FIG. 12  is a cross-sectional view of yet another embodiment of a wheel according to the present invention;  
       FIG. 13  is a perspective view of a two-piece spacer according to yet another aspect of the present invention, wherein the inner spacer is made of metal; and  
       FIG. 14  is a partially schematic elevational view of an injection mold utilized to fabricate the wheel assembly of  FIG. 12 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT  
      For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in  FIG. 1 . However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.  
      With reference to  FIG. 1 , the wheel assembly  1  of the present invention mounts to the housing  2  of a mower deck  3  via a plurality of brackets  4 . The riding mower  5  includes a mounting structure  6  that supports the deck  3  during operation.  
      With further reference to  FIG. 2 , a prior art wheel assembly  10  includes a plastic wheel body  11  mounted to a bracket  4 . An elongated bushing  12  extends through the hub  14  of wheel body  11 , and a bolt  13 , washers  15 ,  16  and nut  17  secure the wheel body  11  to the bracket  4 . The bracket may include a plurality of openings therethrough (not shown) to adjust the height of the wheel assembly  10  to provide for cutting grass to different lengths. In use, the prior art wheel body  11  illustrated in  FIG. 2  tends to distort or wear quickly, such that the central opening through the body  11  becomes non-circular. When the wheel body  11  becomes sufficiently deformed, the wheel body  11  will not rotate, thereby hindering proper operation of the lawnmower.  
      With reference to  FIG. 3 , the wheel assembly  1  of the present invention includes a wheel body  20  made of a plastic material. The wheel body includes a plurality of cavities  21  that reduce the volume of plastic material required to mold the wheel body  20 . The wheel body  20  includes a smoothly curved outer peripheral portion  22  that permits the wheel  1  to slide sideways across the grass surface during mowing. The wheel body  20  includes an integral hub  23  in which bearings  24  and  25  are mounted.  
      With further reference to  FIGS. 4 and 5 , a spacer  26  is positioned between the bearings  24  and  25 . The hub  23  includes cylindrical cavities  27  and  28  that receive the bearings  24  and  25 . The bearings  24  and  25  are commercially available roller bearings having an outer race  29  and an inner race  30 . Inner races  30  include an outer side surface  31  that contacts washers  32  and  33  when the wheel assembly  1  is connected to a bracket  4 . An elongated bolt  34 , lock washer  35 , and nut  36  secure the wheel assembly  1  to the bracket  4 .  
      With reference to  FIG. 5 , the spacer  26  has a generally cylindrical outer surface  37 , and recessed end portions  38  forming an annular lip  39 . As illustrated in  FIG. 4 , the diameter of the cylindrical surface  37  of spacer  26  is somewhat greater than the diameter of the outer races  29  of bearings  24  and  25 . As discussed in more detail below, this arrangement prevents plastic material from entering the bearings  24  and  25  between the outer races and inner races  29  and  30  during fabrication of the wheel assembly. Also, for clarity the spacer  26  is shown as being a separate part in  FIG. 4 . However, during manufacture the spacer  26  melts and fuses to the plastic of the wheel body  20 , thereby forming a substantially one-piece plastic part.  
      With further reference to  FIG. 6 , an injection mold  40  includes mold platens that are movably interconnected by guide rods  43  in a known manner, and plastic injection mold machine  44  feeds melted plastic into the mold  45  via screws  46  in a conventional manner. The mold  45  includes a first mold part or half  47 , and a second mold half or part  48 .  
      With further reference to  FIGS. 7A and 7B , the mold  45  includes a mold cavity  50  formed by cavity halves  50 A and  50 B in the mold parts  47  and  48 , respectively. An elongated support pin  51  extends at least partly into the mold cavity  50 . During fabrication, bearings  24  and  25  are positioned on the support pin with the spacer  25  therebetween prior to injection of the plastic material into the mold cavity  50 . Mold parts  47  and  48  include annular engagement surfaces  52  and  53 , respectively that contact the bearings  24  and  25  when the mold parts  47  and  48  are in the closed position illustrated in  FIG. 7 . In a preferred embodiment, the distance between the surfaces  52  and  53  when the mold is closed is slightly less than the overall length of the bearings  24  and  25  and spacer  26 . When the mold parts  47  and  48  are shifted to the closed position, the spacer  26  is compressed slightly to ensure that the annular lips or surfaces  39  of spacer  26  seal against the outer races  29  of the bearings  24  and  25 , and also to ensure that the engagement surfaces  52  and  53  also engage the peripheral side edges of the outer races of the bearings  24  and  25 . This ensures that the plastic material injected into the mold cavity  50  does not flow around the outer races of the bearings  24  and  25  and enter the bearings themselves.  
      The plastic material is injected into the mold  45  through a screw  54  that is connected to a passageway  55 . As illustrated in  FIG. 8 , passageway  55  connects to a C-shaped passageway  56  that extends around the mold cavity  50 . Gates  57  are in fluid communication with passageway  56 , and inject plastic through opposite peripheral portions of the mold cavity  50  to thereby ensure that the plastic flows through the mold cavity  50  in a uniform manner. The mold assembly  45  also includes a plurality of hot water passages  58 , and ejector pins  59  that are of a conventional design. These conventional components are known to those skilled in the art, and will therefore not be described in more detail herein.  
      During operation, the mold halves  47  and  48  are first separated. An operator then places the bearings  24  and  25  on the support pin  51 , with the spacer  26  positioned between the bearings  24  and  25 . The support pin  51  is preferably horizontally positioned such that the bearings  24 ,  25  and spacer  26  do not slide on pin  51 . The mold halves or parts  47  and  48  are then closed, and molten plastic is injected into the mold cavity  50 . The spacer  26  is preferably made of substantially the same plastic material as the plastic injected into the mold cavity  50 , such that the spacer  26  becomes fused with the other plastic material to form an integral, one piece plastic wheel body portion. Because the plastic flows around the outer surfaces of bearings  24  and  25 , the plastic material contacts the bearings  24  and  25  and thereby retains the bearings  24  and  25  within the wheel assembly  1 .  
      A second embodiment  1 A of a wheel assembly according to the present invention is similar to the wheel  1  of  FIG. 4 , except that a two-piece spacer including a first or outer spacer  60  and a second or inner spacer  61  (see also  FIG. 10 ) is utilized. Also, ball bearings  62 A and  62 B are utilized rather than the roller bearings  24  and  25 . The length of the spacer  61  is selected such that the end surfaces  65  and  66  thereof fit tightly against the inner surfaces  63  and  64  of inner races  67  and  68  of ball bearings  62 A and  62 B when assembled on the elongated support pin  51  (see also  FIG. 11 ) and the mold parts  47  and  48  are closed. The contact between the inner spacer  61  and the inner races  67  and  68  ensures that molten plastic material cannot enter the ball bearings  62 A and  62 B during assembly. Similarly, the end surfaces  71  and  72  contact the outer races  69  and  70  to ensure that molten plastic does not flow into the ball bearings  62 A and  62 B.  
      During assembly, the ball bearings  62 A and  62 B are placed on the elongated support pin  51  with the spacers  60  and  61  positioned between the bearings  62 A and  62 B. The overall dimensions of the mold cavity  50 A are chosen such that the engagement surfaces  52  and  53  contact the ball bearings  62 A and  62 B, respectively, when the mold is closed, and the spacers  60  and  61  are compressed slightly to ensure that the spacers seal against the races of the ball bearings  62 A and  62 B. When the mold is closed, molten plastic is injected into the mold cavity  50  around the ball bearings  62 A and  62 B, and the spacers  60  and  61 . During fabrication, the molten plastic material flows around the outer surfaces  73  and  74  of outer races  69  and  70  to thereby form a tight fit that retains the ball bearings  62 A and  62 B in the wheel body  20 A. For purposes of illustration, the plastic wheel body  20 A and spacer  60  is illustrated as being a separate piece. However, it should be understood that when the molten plastic is injected into the mold cavity  50 , the spacer  60  melts and form a substantially integral one-piece plastic unit with the wheel body. Despite the melting of the spacer  60 , the spacer still provides sufficient sealing against the ball bearings  62 A and  62 B to prevent entry of the molten plastic into the ball bearings. A small amount of clearance is provided between the spacers  60  and  61 , such that inner spacer  61  does not melt or fuse to spacer  60 . In use, inner spacer  61  remains stationary due to the contact with inner races of the ball bearings  62 A and  62 B. After the plastic has solidified, the mold parts  47  and  48  are shifted apart, and the wheel assembly  1 A is removed.  
      Yet another embodiment  1 B or the wheel assembly is illustrated in  FIG. 12 . The wheel assembly  1 B is substantially similar to the wheel assembly  1 A of  FIG. 9 , except that the inner spacer  77  (see also  FIG. 13 ) is made of a metal material and has an inner diameter that is slightly greater than that of the shaft of the bolt  13 . Also, as described in more detail below, during fabrication of the wheel  1 B, cavities for receiving ball bearings  62 A and  62 B are molded into the hub of the polymeric wheel body  20 B, and the ball bearings  62 A and  62 B are press fit into the cavities with the inner surfaces  63  and  64  of the inner races  67  and  68  tightly engaging the ends  78  and  79  of metal inner spacer  77 . The outer diameter of inner spacer  77  is somewhat smaller than the diameter of the opening  75  through the outer spacer  60 , such that the spacer  77  can turn freely with respect to the outer spacer  60 . In operation, the tight fit between the inner spacer  77  and the inner races of the ball bearings  62 A and  62 B causes inner spacer  77  to be fixed relative to the inner races  67  and  68 , such that the inner spacer  77  rotates relative to the polymeric wheel body  20 B. When assembled ( FIG. 12 ) the axial force generated by the bolt  13  and nut  36  is reacted through the inner races of the ball bearings and through the steel or metal inner spacer  77  to prevent crushing of the polymeric portions of the wheel body  1 B.  
      With further reference to  FIG. 14 , during a first method of fabrication, a ball bearing  62 B (not shown in  FIG. 14 ) may be placed on the support rod  51 , and the larger, polymer outer sleeve  60  and inner metal sleeve  77  are also placed on the support rod  51 . A second bearing is then placed on the support rod  51 , with the sleeves  60  and  77  positioned between the two bearings. The first and second mold parts  47  and  48  are then closed, and the mold cavity is filled with molten plastic in a manner that is substantially similar to the method described in more detail above.  
      Alternately, in a second fabrication method first and second “plugs” or cores  80  and  81  are secured within the mold cavity by conventional fasteners or the like (not shown). The plugs  80  and  81  have substantially the same size and shape as the ball bearings  62 A and  62 B. During fabrication utilizing the second method, the inner metal sleeve  77  and outer polymer sleeve  60  are placed on the rod  51 , and the mold parts  47  and  48  are closed. The mold cavity is then filled with molten plastic metal. The plugs  80  and  81  form cavities  82  and  83  adjacent opposite ends of the spacers  60  and  77 . The bearings  62 A and  62 B are then press fit into the cavities  82  and  83  with the inner surfaces  63  and  64  of the bearings tightly abutting the ends  78  and  79  of the inner metal spacer  77 . In a preferred embodiment, the outer diameter of the plugs  80  and  81  is somewhat less than the outer diameter of the bearings  62 A and  62 B, such that a tight press fit is formed when the bearings are installed. As discussed above, the inner diameter of the spacer  60  is somewhat larger than the outer diameter of the spacer  77 , such that the spacer  77  turns freely with respect to the wheel body  1 B formed by the molten metal injected into the mold cavity that melts with and becomes integral with the plastic outer spacer  60 .  
      The wheel assembly of the present invention provides a pair of spaced apart wheel bearings that react moments caused by sideways sliding of the wheel during use. Furthermore, the integral spacers position the bearings during the fabrication process, and also ensures that plastic does not enter the bearings themselves in a manner that would otherwise impede proper operation of the bearings. Still further, the bearings of the present wheel assembly reduce rolling friction, thereby improving the operation of the riding mower.  
      In the foregoing description, it will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed herein. Such modifications are to be considered as included in the following claims, unless these claims by their language expressly state otherwise.