Patent Publication Number: US-2005117969-A1

Title: Anti-slip step for a motor vehicle and a method of forming the same

Description:
BACKGROUND OF THE INVENTION  
      The present invention generally relates to steps and more particularly to steps for heavy duty motor vehicles, such as industrial trucks, to facilitate the ingress and egress of operators to and from cabs of the trucks.  
      Truck steps are conventionally constructed from metal plates having planar support surfaces. Grip structures are typically formed in the support surface to prevent slippage, especially when the step is wet or covered with ice. Drainage holes may also be formed in the metal plate to allow water to drain from the support surface. The grip structures are disposed around openings in the plate and usually have curved side walls defining continuous top rims. While grip structures of this construction will improve the grip of a step, the continuous nature of the top rims can still render the top rims and, thus, the step quite slippery when the step is wet or covered with ice. In order to address this deficiency of conventional grip structures, other grip structures have been developed. Such grip structures are disclosed in U.S. Pat. No. 3,181,440 to Mullaney et al. and U.S. Pat. No. 4,343,119 to Bahnfleth.  
      The rosette of the Bahnfleth patent includes a plurality of spaced-apart extensions having arcuate edges. The extensions slope inwardly to provide the rosette with a relatively narrow cross-shaped opening. Although contact portions of the rosette edges are discontinuous in a plane of contact, these contact portions are small. Moreover, the slope of the extensions present major surfaces that are located just below the contact portions. These major surfaces can become slippery when the rosette is wet or covered with ice. Moreover, the narrowness of the opening in the rosette can make the rosette susceptible to clogging with dirt or ice.  
      The grip structures of the Mullaney et al. patent comprise cylindrical flanges that extend upright from a metal tread plate  14 . Top portions of the flanges are gulleted to provide a number of fairly deep truncated gripping edges. In order to increase the height of the flanges and permit the flanges to extend upright, the flanges are thinned. With the foregoing high-profile construction, the flanges may trap footwear and cause injury if they are not properly spaced apart. For this reason, the Mullaney et al. patent discloses that the flanges must be spaced closely together. Such close spacing, however, may not always be desirable.  
      Based on the foregoing, there is a need in the art for an improved anti-slip step having low profile grip structures. The present invention is directed to such an anti-slip step.  
     SUMMARY OF THE INVENTION  
      In accordance with the present invention, an anti-slip step for a motor vehicle is provided. The step includes a tread plate with a top surface and a bottom surface. A plurality of grip structures extend upwardly from the top surface of the tread plate. Each of the grip structures at least partially defines a hole extending through the tread plate. Each of the grip structures includes a base having a continuous, curved side wall that is joined to the tread plate. A plurality of spaced-apart tabs are joined to the base and extend upwardly therefrom. A plurality of drain structures extend downwardly from the bottom surface of the tread plate. Each of the drain structures at least partially defines a drain hole extending through the tread plate.  
      In accordance with another feature of the present invention each of the grip structures has a height (H) and the side wall of the base is joined to the tread plate so as to form a radius of curvature (RC) between the base and the top surface of the tread plate, wherein the ratio of the radius of curvature (RC) to the height (H) of the grip structure is greater than 0.5.  
      Also provided in accordance with the present invention is a method of forming an anti-slip step. Pursuant to the method, a tread plate is provided having top and bottom surfaces. A plurality of holes are formed in the tread plate. For at least one of the holes, a boundary region of the tread plate disposed around the hole is bent so as to extend out of the plane of the top surface and thereby form a first structure at least partially defining a first opening. For at least another one of the holes, a boundary region disposed around the hole is bent so as to extend out of the plane of the top surface and thereby form a second structure at least partially defining a second opening, wherein the second structure extends a farther distance from the tread plate than the first structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:  
       FIG. 1  is a perspective view of a step;  
       FIG. 2  is an elevational view of a grip structure in a tread plate of the step;  
       FIG. 3  is an elevational view of a drain structure in the tread plate of the step;  
       FIG. 4 . is a vertical sectional view of the grip structure;  
       FIG. 5  is a vertical sectional view of the drain structure;  
       FIG. 6  is a plan view of a hole in the tread plate from which the grip structure is formed; and  
       FIG. 7  is a plan view of a hole in the tread plate from which the drain structure is formed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      It should be noted that in the detailed description that follows, identical components have the same reference numerals, regardless of whether they are shown in different embodiments of the present invention. It should also be noted that in order to clearly and concisely disclose the present invention, the drawings may not necessarily be to scale and certain features of the invention may be shown in somewhat schematic form.  
      Referring now to  FIG. 1 , there is shown a portion of a step  10  embodied in accordance with the present invention. The step  10  is adapted for installation on a motor vehicle, especially an industrial truck having an elevated cab, such as a dump truck or a tractor for pulling a semitrailer. The step  10  includes a support structure  12  that is preferably composed of a metal, such as aluminum. The support structure  12  includes a tread plate  14 , a pair of opposing end flanges  16 , front flange  18  and a rear flange (not shown). The tread plate  14  is rectangular and includes top and bottom surfaces  22 ,  24 . The end flanges  16  are joined at bends to opposing end portions of the tread plate  14 , respectively, and extend downwardly therefrom. Although not shown, the end flanges  16  may have holes formed therein for receiving screws, bolts or other elongated fasteners that may be used to secure the step  10  between side supports of a stair. The front flange  18  and the rear flange are joined at bends to opposing side portions of the tread plate  14 , respectively, and extend downwardly therefrom. Each of the front flange  18  and the rear flange has an L-shaped cross-section and includes a downwardly-extending first member  26  joined at a bend to an inwardly-extending second member  28  so as form an interior ledge. In each of the front flange  18  and the rear flange, the first and second members  26 ,  28  are preferably disposed at least substantially perpendicular to each other. The second members  28  of the front and rear flanges  18 ,  20  are preferably disposed at least substantially parallel to the tread plate  14 . The support structure  12  is preferably formed from a single metal plate by appropriately cutting out the corners of the single plate and appropriately bending front, rear and end portions of the single plate to form the end flanges  16 , the front flange  18  and the rear flange, respectively.  
      A plurality of grip structures  32  and drain structures  34  extend from the tread plate  14  and at least partially define a plurality of grip openings  36  and drain openings  38  in the tread plate  14 , respectively. The grip structures  32  extend upwardly from the top surface  22  of the tread plate  14 , while the drain structures  34  extend downwardly from the bottom surface  24  of the tread plate  14 . The grip structures  32  provide non-continuous gripping to footwear brought into contact with the tread plate  14 , while the drain structures  34  facilitate the drainage of water from the top surface  22  of the tread plate  14  so as to prevent the pooling of water thereon.  
      Preferably, the grip structures  32  and the drain structures  34  are arranged such that the tread plate  14  has alternating longitudinally-extending rows of grip structures  32  and drain structures  34 . In the specific version of the invention disclosed in  FIG. 1 , there is a longitudinal middle row of drain structures  34  disposed between longitudinal front and rear rows of the grip structures  32 . It should be appreciated, however, that the present invention is not limited to this particular arrangement of the grip structures  32  and the drain structures  34 .  
      Referring now to  FIGS. 2 and 4 , each of the grip structures  32  comprises a curved base  40  that is joined to the top surface  22  of the tread plate  14 . The base  40  preferably comprises a continuous curved side wall. More preferably, the base  40  comprises a frusto-conical side wall. A plurality of tabs  42  are joined to the base  40  and extend upwardly therefrom. The base  40  and each of the tabs  42  have at least substantially the same thickness as the thickness of the tread plate  14 . Preferably, each of the tabs  42  has a substantially angular shape, with a pair of non-parallel sides  42   a  extending downwardly and outwardly from opposing ends of a free top end  42   b . Bottom portions of the tabs are  42  integrally joined to top portions of the base  40 . The tabs  42  at least partially define the grip opening  36 , which has a diameter “D1”, as is best shown in  FIG. 4 . The tabs  42  are spaced apart around the periphery or circumference of the base  40  so as to cooperate with the base  40  to form a plurality of alternating ridges and valleys, wherein the ridges are comprised of the top ends  42   b  of the tabs  42  and the valleys are comprised of top end portions  40   a  of the base  40 . The sides  42   a  of the tabs  42  are joined to the top end portions  40   a  of the base  40  at bends. Both the top ends  42   b  of the tabs  42  and the top end portions  40   a  of the base  40  are slightly arcuate in the horizontal direction. Outer and inner edges of both the top ends  42   b  of the tabs  42  and the top end portions  40   a  of the base  40  are preferably uniform in height along their lengths. In addition, the top ends  42   b  of the tabs  42  are substantially horizontally disposed. The top end portions  40   a  of the base  40 , however, slope slightly inward. The top ends  42   b  of the tabs  42  are disposed a height “H” above the top surface  22  of the tread plate  14 , i.e., each grip structure  32  has a height “H”. Preferably, the top end portions  40   a  of the base  40  have at least substantially the same arcuate length as the top ends  42   b  of the tabs  42 .  
      In each grip structure  32 , the base is joined to the top surface of the tread plate  14  so as to form a radius of curvature RC 1  between the base and the top surface, wherein the ratio of the radius of curvature RC 1  to the height H 1  of the grip structure (i.e., RC 1 /H) is greater than 0.5, more preferably greater than 0.75, still more preferably greater than 1. In addition, each grip structure is constructed such that the ratio of the height H of the grip structure to the diameter D 1  of the grip opening of the grip structure (i.e., H/D 1 ) is less than 0.75, more preferably less than 0.5, still more preferably less than 0.3. Furthermore, the ratio of the height H of each grip structure  32  to the thickness “T” of the tread plate  14  (i.e., H/T) is preferably less than 3, more preferably less than 2. With the IS foregoing structure, the grip structures  32  have low profiles that do not require the grip structures  32  to be disposed closely together.  
      Referring now to  FIGS. 3 and 5 , each of the drain structures  34  comprises a plurality of tabs  46  joined to the bottom surface  24  of the tread plate  14  and extending downwardly therefrom. The tabs  46  have at least substantially the same thickness as the thickness of the tread plate  14 . Preferably, each of the tabs  46  has a substantially angular shape, with a pair of non-parallel sides  46   a  extending upwardly and outwardly from opposing ends of a free bottom end  46   b . Top portions of the tabs  46  are integrally joined to the bottom surface  24  of the tread plate  14 . The tabs  46  at least partially define the drain opening  38 , which has a diameter “D2”, as best shown in  FIG. 5 . The bottom ends  46   b  of the tabs  46  are disposed a distance or depth “Dp” below the bottom surface  24  of the tread plate  14 , i.e., each drain structure  34  has a depth “Dp”.  
      In each drain structure  34 , each tab  46  is joined to the bottom surface  24  of the tread plate  14  so as to form a radius of curvature RC 2  between the tab  46  and the bottom surface  24 , wherein the ratio of the radius of curvature RC 2  to the depth Dp of the drain structure  34  (i.e., RC 2 /Dp) is greater than 1, more preferably greater than 2, still more preferably greater than 3. Preferably, the radius of curvature RC 2  of the drain structures  34  is at least substantially the same as the radius of curvature RC 1  of the grip structures  32 .  
      The diameter D 2  of the drain openings  38  of the drain structures  34  is preferably at least substantially the same as the diameter D 1  of the grip openings  36  of the grip structures  32 . The depth Dp of the drain structures  34 , however, is preferably less than the height H of the grip structures  32 . Still more preferably, the ratio of the depth Dp of the drain structures  34  to the height H of the grip structures  32  (Dp/H) is less than 1, more preferably less than 0.75, still more preferably less than 0.5.  
      In lieu of having the construction described above, the drain structures  34  may have the same structure (with the same dimensions) as the grip structures  32  (except for extending downwardly from the bottom surface  24 ), wherein the tabs  46  are joined to bases joined to the bottom surface  24 .  
      Preferably, each of the grip structures  32  and each of the drain structures  34  is formed using a punching operation and an embossing operation, wherein in the punching operation, a hole is formed in the tread plate  14 , and in the embossing operation, a boundary region of the tread plate  14  around the hole is pushed away from the tread plate  14  so as to extend out of the plane of the tread plate  14 , i.e., so as to extend out of the plane of the top surface  22  or the bottom surface  24 , as the case may be. The holes for forming the drain structures  34  are similar to the holes for forming the grip structures  32 , except the holes for forming the drain structures  34  are about 13% larger than the holes for the grip structures  32  and except for the difference noted below. In another embodiment of the present invention, all of the holes for the grip structures  32  and the drain structures  34  have the same size and configuration.  
      One of the holes for the grip structures  32 , designated with the reference numeral  50 , is shown in  FIG. 6 . The hole  50  is generally star-shaped and is defined by a plurality of interior edges of the tread plate  14  that define tabs  52  that will become the tabs  42  for the grip structure  32 . The interior edges of the tread plate  14  include radially-inward first edges  54  and radially-outward second edges  56 , which respectively correspond to the top ends  42   b  of the tabs  42  and the top end portions  40   a  of the bases  40 . Each of the first and second edges  54 ,  56  has a slight outward bend (about 8 degrees) to permit the top ends  42   b  of the tabs  42  and the top end portions  40   a  of the base  40  to be smoothly formed when the boundary region (designated by the reference numeral  58 ) of the tread plate  14  around the hole  50  is pushed outward. The boundary region  58  has an outer perimeter  60  shown by a circular dashed line.  
      One of the holes for the drain structures  34 , designated with the reference numeral  62 , is shown in  FIG. 7 . The hole  62  is also generally star-shaped and is defined by a plurality of interior edges of the tread plate  14  that define tabs  64  that will become the tabs  46  for the drain structure  34 . The interior edges of the tread plate  14  include radially-inward first edges  66  (which respectively correspond to the bottom ends  46   b  of the tabs  46 ) and radially-outward second edges  68 . Each of the first and second edges  66 ,  68  has a slight outward bend (about 10 degrees) to permit the bottom ends  46   b  of the tabs  46  to be smoothly formed when the boundary region (designated by the reference numeral  70 ) of the tread plate  14  around the hole  62  is pushed outward. The boundary region  70  has an outer perimeter  72  shown by a circular dashed line.  
      Once the holes  50 ,  62  are formed in the tread plate  14 , the boundary regions  58 ,  70  of the tread plate  14  around the holes  50 ,  62  are contacted by embossing dies on a press and pushed upwardly or downwardly (depending on the arrangement of the press and the support structure  12 ) to form the grip structures  32  and the drain structures  34 . With regard to the hole  50  for a grip structure  32 , the boundary region  58  extends radially outward from the second edges  56  to form an annular portion between the second edges  56  and the outer perimeter  60  of the boundary region  58 . With regard to the hole  62  for a drain structure  34 , the boundary region  70  has a radius about equal to the distance of the second edges  68  from the center of the hole  62 . The boundary regions  58  for the holes  50  are determined by the radii of the dies for the grip structures  32 , and the boundary regions  70  for the holes  62  are determined by the radii of the dies for the drain structures  34 . The dies for the grip structures  32  have larger radii than the dies for the drain structures  34 .  
      When the dies for the drain structures  34  are aligned with the holes  62  and pressed against the tread plate  14 , the dies for the drain structures  34  only contact the tabs  64  and bend them to form the tabs  46  for the drain structures  34 , whereas when the dies for the grip structures  32  are aligned with the holes  50  and pressed against the tread plate  14 , the dies for the grip structures  32  contact the annular portions of the tread plate  14  disposed radially outward from the second edges  56  and bend them to form the bases  40  for the grip structures  32 .  
      From the foregoing description, it should be appreciated that the step  10  of the present invention is simple to produce, has improved anti-slip features and facilitates the drainage of water from the step  10 . The low profile of the grip structures  32  permits the grip structures  32  to be more spread out without increasing the risk of trapping footwear.  
      While the step  10  is especially adapted for use on an industrial truck having an elevated cab, the step  10  can also be used in other applications, such as on ships, locomotives and on fixed structures, such as elevated industrial walkways.  
      While the invention has been shown and described with respect to particular embodiments thereof, those embodiments are for the purpose of illustration rather than limitation, and other variations and modifications of the specific embodiments herein described will be apparent to those skilled in the art, all within the intended spirit and scope of the invention. Accordingly, the invention is not to be limited in scope and effect to the specific embodiments herein described, nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.