Abstract:
A portable, foldable step ladder in a deployed configuration straddles a tire of a truck, tractor or other heavy vehicle, allowing an operator and mechanic to easily climb toward the engine compartment. A top step rests on the uppermost portion of the tire tread. A middle step and a bottom step are suspended from the top step and, together with their suspensory structure, are foldable into proximity with the bottom surface of the top step. On each side of the top step, a hand rail has a lower portion rotatably connected to the side of the top step near the front thereof. Each hand rail has a transverse portion extending toward the rear of the top step and, attached to the transverse portion, a rear portion extending downward and connected to the sides of the top step near the rear thereof. The hand rail assembly engages the side walls of the tire in hook-like fashion, stabilizing the top step, while the top step supports the hand rail assembly at four points. The hand rail rear portion is removable from the top step, whereupon the top step swings down between the hand rail front portions. The hand rail transverse portions are then rotatable relative to the lower portions, swinging the rear portions into front and rear abutment with the compactly folded step assembly, securing the step assembly.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Provisional Application No. 61/115,900 filed Nov. 18, 2008. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a step ladder for servicing large motor vehicles, more particularly where the step ladder is hand portable, and especially where it is foldable. 
         [0004]    2. General Background and State of the Art 
         [0005]    Tractor trailer operators need to access the engine compartment in all types of weather. Operator steps detachably engaged with a truck&#39;s front wheel and tire include U.S. Pat. Nos. 2,851,312; 3,590,950; 4,800,987; 4,947,961; 5,133,429; 7,168,523; 6,767,023; 6,550,578; 6,044,928; and 4,782,916. All have one or more steps for climbing. All appear to have structure engaging the inner side wall, tread, and outer sidewall of a truck tire. Most appear to be supported entirely by the truck tire or wheel. Some appear to engage the ground for additional support. 
         [0006]    For the most part, the above-identified apparatus appear to lack easily graspable handholds to assist climbing. All but one (U.S. Pat. No. 6,550,578) appear to lack a platform or step positionable at about the level of the tire tread. None of them appear to have a top step or platform positionable directly above the tread. Only some of them appear to fold compactly. 
       INVENTION SUMMARY 
       [0007]    It is among the objects of the present invention to provide a durable, portable, easily manipulated truck tire mountable step ladder which is also foldable and which improves an operator&#39;s ability to climb and carry tools to the engine compartment of a truck tractor or similar vehicle, where the operator needs to safely perform inspections and routine maintenance on a daily basis. 
         [0008]    In accordance with these objects and with others which will be described and which will become apparent, an exemplary embodiment of the tire mountable folding step ladder, for temporary attachment to a tire of a front wheel proximate an engine compartment of a tractor, truck cab, or the like, in accordance with the present invention comprises a tire-mountable step assembly and a tire-mountable hand rail assembly linked to the step assembly. The step assembly and the hand rail assembly cooperate to provide a stable step ladder for climbing over the tire toward the engine compartment of the tractor. 
         [0009]    In an exemplary embodiment, the hand rail assembly has a hand rail traversing the tread portion of the tire when the step ladder is mounted on the tire, providing a hand-hold for a person standing on the step assembly and reaching into the engine compartment of the tractor. 
         [0010]    In an exemplary embodiment, the hand rail is supported at a clearance of at least about 7.5 cm (3 inches) above the top step, assuring that even a thickly gloved hand is able to grasp the hand rail. 
         [0011]    In an exemplary embodiment, the hand rail is supported at the clearance by the hand rail assembly and the hand rail assembly is supported by the step assembly. 
         [0012]    In an exemplary embodiment, the step assembly rests on the tread portion of the tire and the hand rail assembly is substantially fixed relative to the step assembly. 
         [0013]    In an exemplary embodiment, the hand rail assembly stabilizes the step assembly on the tire. 
         [0014]    In an exemplary embodiment has a plurality of steps, at least one of the steps being suspended from another of the steps. 
         [0015]    In an exemplary embodiment, when the step ladder is removed from the tire, the plurality of steps are manipulable into a configuration wherein all of the plurality of steps are parked together in successive top-to-bottom abutting relation. 
         [0016]    In an exemplary embodiment, the step assembly has a top step having side portions, a front, a rear and a tread-engaging bottom surface; and the hand rail assembly has lower portions connected to the side portions of the top step proximate the front portion thereof and extending downward therefrom, a transverse portion extending rearward proximate the side portions of the top step, and a rear portion connected to the side portions of the top step proximate the rear portion thereof and extending downward therefrom. The top step engages the tire tread. The rail assembly engages the inner and outer sidewalls of the tire in hook-like fashion, preventing the top step from sliding off of the tire. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    For a further understanding of the objects and advantages of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawing, in which like parts are given like reference numbers and wherein: 
           [0018]      FIG. 1  is a perspective view of the tractor tire mountable folding step ladder in accordance with the present invention, shown in a mounted relationship with a tractor tire; 
           [0019]      FIG. 2  is a perspective view of the tractor tire mountable folding step ladder in accordance with the present invention; 
           [0020]      FIG. 3  is a partial perspective view of a bottom step and bottom step supports in accordance with the present invention; 
           [0021]      FIG. 4  is a partial perspective view of a middle step and middle step supports in accordance with the present invention; 
           [0022]      FIG. 5  is a partial perspective view of a top step in accordance with the present invention; 
           [0023]      FIG. 6  is an exploded partial perspective of a hand rail assembly in accordance with the present invention; 
           [0024]      FIG. 7  is a partial perspective view of a corner of a top step in accordance with the present invention as seen from beneath; 
           [0025]      FIG. 8  is a perspective view of the step ladder in accordance with the present invention in a folded configuration as seen from the front; 
           [0026]      FIG. 9  is a perspective view of the step ladder in accordance with the present invention in a folded configuration as seen from the rear; 
           [0027]      FIG. 10  is a side elevational view of the step ladder in accordance with the present invention as seen in a folded configuration; and 
           [0028]      FIG. 11  is a top plan view of the step ladder in accordance with the present invention as seen in a folded configuration. 
           [0029]      FIG. 12  is a bottom sectional view of the bottom step. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    The inventors have discovered that for servicing large motor vehicles it is particularly effective to use a durable, portable, easily manipulated truck tire mountable step ladder which is also foldable and which improves a mechanic&#39;s ability to climb and carry tools to the engine compartment of a truck tractor or similar vehicle. 
         [0031]    The present invention will now be described with reference to  FIG. 1 , which illustrates in perspective view a tractor tire  28  supporting a preferred embodiment of the tractor tire mountable folding step ladder  30  in accordance with the present invention, shown generally at  30 , having a foldable step assembly  32  located between two tubular handrail assemblies  34 . The step assembly  32  rests on the tread portion of the tractor tire  28 , engages the tractor tire  28 , and enables a person to climb onto and over the tire  28  and, if desired, into the engine compartment of the tractor. The handrail assemblies  34  engage the sidewalls of the tire  28  and the tractor&#39;s wheel rim, stabilize the step assembly  32  on the tire  28 , provide a hand hold which is safely grasped by the person climbing, and provide for convenient manipulation of the step ladder  30  when deploying or securing the step ladder  30 . 
         [0032]    The STEP ASSEMBLY  32  has a top step  36 , a middle step  38 , and a bottom step  40 . Paired middle step supports  42  suspend the middle step  38  from the top step  36 . Paired bottom step supports  44  suspend the bottom step  40  from the middle step  38 . 
         [0033]    The BOTTOM STEP  40  has a top surface  41 , a bottom surface  43 , a rear edge  51 , a downward extending front portion  47 , and downward extending side portions  49  each having a bottom step support bore  50  (not visible in  FIG. 1 ). 
         [0034]    Each BOTTOM STEP SUPPORT  44  has a lower segment  52  and an upper segment  53 . Each lower segment  52  has a bottom end  54  with an inwardly extending bottom step shoulder bolt  56 ; and also has an upper end  58  with an outwardly extending hinge pin  60 . Each upper segment  53  has a top end  62  (partially obscured by the middle step  3   8 ) and a bottom end  64  with a hinge bore  66  (shown occupied by the hinge pin  60 ). The top end  62  has an outwardly extending common shoulder bolt  63  (one of which is shown projecting through the middle step  38  and the middle step support  42 ). 
         [0035]    The MIDDLE STEP  38  has a top surface  68 , a bottom surface  70 , a downwardly extending front portion  71 , a rear edge  72 , and side portions  74  each having a middle step support bore  76  (obscured by the middle step  38  on one side and by the middle step support  42  on the other side in  FIG. 1 ). 
         [0036]    Each MIDDLE STEP SUPPORT  42  has a bottom end  78  having a bore  80 ; and also has an upper end  82  (obscured by the top step  36  in  FIG. 1 ) having a support-pin-accommodating bore  84  (not visible in  FIG. 1 ). 
         [0037]    The TOP STEP  36  has a top surface  86 , a bottom surface  88 , a downwardly extending front portion  90 , a downwardly extending rear portion  92 , and downwardly extending side portions  94 . Each side portion  94  has an inward-projecting step assembly support pin  96  (not visible in  FIG. 1 ) and a handrail connector bore  97  (not visible in  FIG. 1 ), both located proximate the front portion  90 , and also has a keyhole through bore  98  (not visible in  FIG. 1 ) located proximate the rear portion  92 . 
         [0038]    Each HAND RAIL ASSEMBLY  34  has a hand rail lower portion  46 , a hand rail upper portion  48 , a hand rail transverse portion  50 , and a hand rail rear portion  55 . The hand rail lower portion  46  has bolt-accommodating bore  100  and a rearward-curved bottom end  54  carrying a cap  59 . A top step connecting bolt  102  is shown occupying the bolt-accommodating bore  100 . The hand rail upper portion  48  has a lock pin-accommodating bore  104 , shown occupied by a front lock pin  106 . The hand rail rear portion  55  has a lock pin-accommodating bore  108 , shown occupied by a flanged rear lock pin  110 . A cap  112  is disposed on the hand rail rear portion  55 . 
         [0039]      FIG. 2 , a perspective view of the preferred embodiment of the tractor tire  28  mountable folding step ladder  30  from a different frontal angle, shows the step assembly  32  with top step  36 , middle step  38 , bottom step  40 ; the middle step supports  42  suspending the middle step  38  from the top step  36 ; and the bottom step supports  44  suspending the bottom step  40  from the middle step  38 . 
         [0040]    In  FIG. 2 , the bottom step  40  is again shown with top surface  41 , bottom surface  43 , rear edge  51 , downward extending front portion  47 , and downward extending side portions  49  each having bottom step support bore  67  (not visible in  FIG. 2 ). 
         [0041]    In  FIG. 2 , the bottom step supports  44  are again shown with lower segments  52  and upper segments  53 . Each lower segment  52  has a bottom end  54  with an inwardly extending bottom step shoulder bolt  56 ; and also has an upper end  58  with an outwardly extending hinge pin  60 . Each upper segment  53  has a top end  62  (partially obscured by the middle step  38 ) and a bottom end  64  with a hinge bore  66  (shown occupied by the hinge pin  60 ). The top end  62  has an outwardly extending common shoulder bolt  63  (one of which is shown projecting through the middle step  38  and the middle step support  42 ). 
         [0042]    In  FIG. 2 , the middle step  38  is again shown with top surface  68 , bottom surface  70 , rear edge  72 , and side portions  74  each having a middle step support bore  76  (obscured by the middle step  38  on one side and by the middle step support  42  on the other side in  FIG. 2 ). 
         [0043]    In  FIG. 2 , the middle step supports  42  are again shown with bottom ends  78  each having a bore  80 ; and also having upper ends  82  (obscured by the top step  36 ) each having a bolt-accommodating bore  84  (not visible in  FIG. 2 ). 
         [0044]    In  FIG. 2 , the top step  36  is again shown with top surface  86 , bottom surface  88 , downwardly extending front portion  90 , downwardly extending rear portion  92 , and downwardly extending side portions  94 . Each side portion  94  has an inward-projecting step assembly support pin  96  (not visible in  FIG. 2 ; see  FIG. 7 ) and a handrail connector bore  97  (not visible in  FIG. 2 ), both located proximate the front portion  90 , and also has a keyhole through bore  98  (not visible in  FIG. 2 ) located proximate the rear portion  92 . 
         [0045]    In  FIG. 2 , the hand rail assemblies  34  are again shown with hand rail lower portions  46 , hand rail upper portions  48 , hand rail transverse portions  50 , and hand rail rear portions  55 . The hand rail lower portion  46  has a bolt-accommodating bore  100  and a rearward-curved bottom end  54  carrying a cap  59 . A top step connecting bolt  102  is shown occupying the bolt-accommodating bore  100 . The hand rail upper portion  48  has a lock pin-accommodating bore  104 , shown occupied by a front lock pin  106 . The hand rail rear portion  55  has a lock pin-accommodating bore  108 , shown occupied by a flanged rear lock pin  110 . A cap  112  is disposed on the hand rail rear portion  55 . 
         [0046]      FIG. 3 , a partial perspective view of the preferred embodiment of the tractor tire  28  mountable folding step ladder  30 , shows the bottom step  40  with top surface  41 , bottom surface  43 , rear edge  51 , downward extending front portion  47 , and downward extending side portions  49  each having bottom step support bore  67  (not visible in  FIG. 3 ). 
         [0047]      FIG. 3  also shows the lower segments  52  and upper segments  53 . Each lower segment  52  has a bottom end  54  with an inwardly extending bottom step shoulder bolt  56  (most of which is obscured in  FIGS. 1-3 ); and also has an upper end  58  with an outwardly extending hinge pin  60  (most of which is obscured on the far side, more of which is visible on the near side). Each upper segment  53  has a top end  62  and a bottom end  64  with a hinge bore  66  (shown occupied by the hinge pin  60 ). The top end  62  has an outwardly extending common shoulder bolt  63 . 
         [0048]      FIG. 4 , a partial perspective view of the preferred embodiment of the tractor tire  28  mountable folding step ladder  30 , shows the middle step  38  with top surface  68 , bottom surface  70 , rear edge  72 , and side portions  74  each having a middle step support bore  76  (obscured by the middle step  38  on one side and by the middle step support  42  on the other side). 
         [0049]      FIG. 4  further shows the middle step  38  supports  42  with bottom ends  78  having bores  80 ; the middle step  38  also has upper ends  82  with bolt-accommodating bores  84 . 
         [0050]      FIG. 5 , a partial perspective view of the preferred embodiment of the tractor tire  28  mountable folding step ladder  30 , shows the top step  36  with top surface  86 , bottom surface  88 , downwardly extending front portion  90 , downwardly extending rear portion  92 , and downwardly extending side portions  94 . Each side portion  94  has an inward-projecting step assembly support pin  96  (not visible in  FIG. 5 ) and a handrail connector bore  97 , both located proximate the front portion  90 , and also has a keyhole through bore  98  (not visible in  FIG. 2 ) located proximate the rear portion  92 . This assembly support pin  96  holds the steps in a horizontal configuration. 
         [0051]      FIG. 6 , a partial perspective exploded view of the preferred embodiment of the tractor tire  28  mountable folding step ladder  30 , shows the hand rail lower portion  46 , hand rail upper portion  48 , hand rail transverse portion  50 , and hand rail rear portion  55 . The hand rail lower portion  46  has a bolt-accommodating bore  100  and a rearward-curved bottom end  54  carrying a cap  59 . A top step connecting bolt  102  and its corresponding nut  103  are shown floating proximate the bolt-accommodating bore  100 . The hand rail upper portion  48  has a lock pin-accommodating bore  104 ; the corresponding front lock pin  106  is shown floating in a lateral region of  FIG. 6 . The hand rail rear portion  55  has a lock pin-accommodating bore  108 . The flanged rear lock pin  110  is shown floating in a central region of  FIG. 6 ; the nut  111  is fastened on the end  58  of lock pin  110 . A cap  112  is disposed on the hand rail rear portion  55 . A hand rail internal segment  114 , shown floating between the hand rail lower portion  46  and the hand rail upper portion  48 , has a bolt-accommodating bore  101 , a lock pin-accommodating bore  105 , and a second lock pin-accommodating bore  107  oriented at an angle to the lock-pin-accommodating bore  104 . 
         [0052]      FIG. 7 , a partial perspective view, shows a portion of the top step  36  as viewed from beneath, including the bottom surface  88 , the front portion  90 , and one side portion  94  with hand rail connector bore  97  and inwardly projecting step assembly support pin  96 . The step assembly support pin  96  is provided in the form of a 6.35 mm (0.25 inch) by 9.5 mm (0.375 inch) dowel pin. The primary function of the step assembly support pin  96  is to extend through the bored upper end  82  of the middle step support  42  and thereby to carry loads applied to the middle step  38  and the bottom step  40 . Additionally, because the step assembly support pin  96  is located only a short distance from the downwardly extending front portion  90  of the top step, the middle step support  42  (see, e.g.,  FIG. 2 ) cannot swing more than a few degrees forward of vertical, due to interference with the front portion  90 . 
         [0053]    DIMENSIONS of the step ladder  30  and its components are determined chiefly by the dimensions of the tire  28  of the tractor or other vehicle being serviced. While a typical commercial truck tractor tire  28  has a diameter of about 94 cm (37 inches) and a width of between about 20.3 cm (8 inches) and about 35.6 cm (14 inches), these dimensions vary. Ambulances and local delivery trucks have smaller tires, while military trucks and off-road trucks have larger tires. Therefore, an establishment which typically services a given type of vehicle may prefer the step ladder  30  in specifically ordered dimensions. Accordingly, the most preferred length of the top step side portion  94  and the hand rail transverse portion  50  are determined with reference to the size of tires used on a particular customer&#39;s fleet. 
         [0054]    In an exemplary embodiment of the step ladder  30  in accordance with the present invention, the top step  36  measures about 33 cm (13 inches) front-to-rear and about 40.6 cm (16 inches) wide. The front portion  71  and side portions  94  extend about 4.5 cm (1.75 inches) downward from the top surface  86 . The keyhole bore  98  is located in the side portion  94  about 5 cm (2 inches) forward of the rear portion  92 . The step assembly support pin  96  extends about 0.6 cm (0.24 inch) from the side portion  94 . The middle step  38  measures about 35.6 cm (14 inches) wide and about 17.8 cm (7 inches) front-to-rear and has side portions  74  extending about 4.5 cm (1.75 inches), or slightly less, from the top surface  68 . The bottom step  40  measures about 30.5 cm (12 inches) wide and about 17.8 cm (7 inches) front-to-rear and has side portions  49  extending about 4.5 cm (1.75 inches), or slightly less, from the top surface  41 . The top step  36 , middle step  38  and bottom step  40  have a thickness of about 0.64 cm (0.25 inch). 
         [0055]    The lower segment  52  and upper segment  53  of the bottom step support  44  are about 17.8 cm (7 inches) long, about 3.2 cm (1.25 inches) wide and about 0.64 cm (0.25 inches) thick. The middle step support  42  is about 28 cm (11 inches) long, about 3.2 cm (125 inches) wide and about 0.64 cm (0.25) inches thick. 
         [0056]    The hand rail assembly  34  is formed of tubes having outside diameter about 3.2 cm (1.25 inches), except that the hand rail internal segment  114  has a slightly smaller diameter suitable for fitting within the hand rail upper portion  46  and the hand rail lower portion  48 . The hand rail lower portion  46  is about 51 cm (20 inches) in overall length. The hand rail upper portion  48  extends about 10 cm (4 inches) beyond the hand rail lower portion  46  and curves to join the hand rail transverse portion  50 , which extends about 25.4 cm (10 inches) rearward, curving downward to join the hand rail rear portion  55 , which extends about 28 cm (11 inches) downward. The height of the transverse portion of the hand rail is preferably about 7.5 cm (3 inches) above the top step. 
         [0057]    MATERIALS suitable for the step ladder  30  have high tensile strength and are stiff, hard, not excessively heavy, and relatively impervious to corrosion and abrasion. A preferred embodiment of the step ladder  30  in accordance with the present invention has a top step  36 , middle step  38  and lower step formed of aluminum, preferably 5052 aluminum plate; a bottom step support  44  and middle step support  42  formed of aluminum, and a hand rail assembly  34  formed of aluminum tube. Alternative materials include, but are not limited to, other alloys such as a stainless steel alloy or a non-sparking alloy, polymers such as aramid, and composites based on fibers such as carbon fiber or glass fiber and resins such as epoxy. Coatings such as KEVLAR® material also may be employed. 
         [0058]    Caps  59  and  112  are preferably formed of rubber or any suitable substitute. 
         [0059]    Hardware such as the front lock pin  106 , top step connecting bolt  102 , flanged rear lock pin  110  and the like are preferably formed of aluminum or another compatible material having comparable strength and hardness. The front lock pin  106  is, for example, a CARR LANE® brand lock pin  1 O formed largely of steel alloy and having a ring head (which may be tied to a tether) and a shank equipped with laterally protruding spring-biased ball bearings to hold the shank in place. 
         [0060]    In a preferred embodiment of the step ladder  30  in accordance with the present invention, the top surface  86 , top surface  68 , and top surface  41  are knurled, roughened, hammered, milled, or coated with an abrasive layer or patch to provide improved traction for the operator&#39;s shoe bottom and the bottom surface  88  of the top step  36  is given similar treatment for improved traction upon the tire  28  tread. 
         [0061]    In accordance with the present invention, a description of certain interrelations among parts of the step assembly  32  facilitates understanding the operation of this exemplary embodiment of the tractor tire  28  mountable foldable step ladder  30 . With reference to  FIG. 3  and now also to  FIG. 12 , a bottom sectional view of the bottom step  40 , assembly of the step ladder  30  in accordance with the present invention is accomplished with nuts, washers, cotter pins and the like to hold hardware such as bolts in place. The bottom step  40  is permanently hinged to the bottom end  54  of the lower segment  52  of the bottom step support  44  by a standard 0.25 inch by 0.5 inch shoulder bolt  56 , shown penetrating the bottom end  54  of the lower segment  52 . The bottom step  40  is openable to a limited horizontal, deployed orientation relative to the lower segment  52 , because it is back-stopped against a 6.35 mm (0.25 inch) by 9.5 mm (0.375 inch) dowel pin  116 . 
         [0062]    With particular reference to  FIG. 12 , the bottom step  40  is shown in bottom sectional view having front portion  47 , rear edge  51 , and side portions  49 . Each side portion  49  has a bottom step support bore  67  and an outward-projecting dowel pin  116 . For linkage to the bottom step, the bottom end  54  has a tongue  120  which is penetrated by the bottom step shoulder bolt  56 . Cooperating with the dowel pin  116 , the bottom end  54  has a stop ridge  122 , which because of its location contacts the dowel pin  116  as soon as the bottom step  40  has opened to the deployed orientation relative to the bottom segment  52 . 
         [0063]    With continued reference to  FIG. 3 , the upper end  58  of the lower segment  52  is permanently hinged to the bottom end  64  of the upper segment  53  of the bottom step support  44  by hinge pin  60 , which also may be provided in the form of a bolt or the like. 
         [0064]    The middle step  38 , the bottom end  78  of the middle step support  42 , and the top end  62  of the upper segment  53  of the bottom step support  44  are held together by common shoulder bolt  63 . 
         [0065]    With reference to  FIG. 3 , the downward extending front portion  47  and downward extending side portions  49  stiffen the bottom step  40 . The downward extending side portions  49  also provide structure to form the bottom step support bores  67 , which receive the respective inwardly extending bottom step shoulder bolts  56  of the bottom ends  54  of the lower segments  52  of the bottom step  40  supports  44 . The bottom step  40  is rotatable, relative to the lower segments  52 , from a deployed position substantially perpendicular to the lower segments  52 , to a second position substantially aligned with and nested between the lower segments  52 . This range of rotation is limited because standard 0.25 by 0.5 bottom step shoulder bolt  56  and 0.25 by 0.375 dowel pin  116  are located so that the dowel pin  116  backstops against the stop ridge  122  of the bottom end  54  to prevent the bottom step  40  from drooping when in the deployed orientation relative to the bottom segment  52 . This limited range of rotation prevents the bottom step  40  from opening beyond a substantially horizontal orientation, reducing the likelihood that a person climbing the bottom step  40  would slip off. 
         [0066]    With continued reference to  FIG. 3 , the hinge pin  60  projects outwardly through the hinge bore  66  in the bottom end  64  of upper segment  53  and links the lower segment  52  to the upper segment  53 . The lower segment  52  is rotatable about the hinge pin  60 , relative to the upper segment  53 , from a deployed position extending substantially downward from and collinear with the upper segment  53 , through a range of about 180 degrees, to a folded position substantially adjacent and parallel to the upper segment  53 . 
         [0067]    With reference to  FIG. 3  and  FIG. 4 , the common shoulder bolt  63  extends outwardly from the top end  62  of the upper segment  53  of the bottom step support  44  and projects through the middle step  38  and through the bore  80  in the bottom end  78  of the middle step support  42 , linking the lower step support  44 , the middle step  38  and the middle step support  42 . The upper segment  53  of the bottom step support  44  is rotatable about the common shoulder bolt  63 , relative to the middle step support  42 , over a range of about 180 degrees, from a deployed position projecting substantially downward from and collinear with the middle step support  42  to a folded position substantially adjacent and parallel to the middle step support  42 . As in the case of the bottom step  40  ( FIG. 3 ), this range of rotation is limited by the location of the middle step support bore  76  and (which accommodates a standard 0.25 by 0.5 shoulder bolt  56  in similar manner as for bottom step  40  in  FIG. 3 ) close to a 0.25 inch by 0.375 inch dowel pin  116  (also in similar manner as for bottom step  40  in  FIG. 3 ) to back-stop the middle step  38  in the deployed orientation relative to the middle step support  42 . 
         [0068]    With reference to  FIGS. 2 ,  4  and  7 , the upper end  82  of the middle step support  42  has a support-pin-accommodating bore  84 . The side portion  94  of the top step  36  proximate the front portion  90  thereof has an inwardly projecting step assembly support pin  96  which extends through the support-pin-accommodating bore  84 , linking the middle step support  42  to the top step  36 . The middle step support  42  is rotatable about the step assembly support pin  96 , relative to the top step  36 , from a deployed position projecting substantially downward from and perpendicular to the top step  36 , through a range of about 90 degrees, to a folded position substantially adjacent and parallel to the bottom surface  88  of the top step  36 . This range of rotation is limited by the location of the step assembly support pin  96  close to the downwardly extending front portion  90 , which tends to block the middle step support  42  from swinging forward past an orientation substantially perpendicular to the top step  36 . The rearward swing of the middle step support tends to be limited by the presence of the underlying tractor wheel assembly and the sidewall of the tractor tire  28  ( FIG. 1 ) when the step ladder  30  is in use. 
         [0069]    With reference to  FIG. 2  and  FIG. 5 , the top step-connecting bolt  102  extends through the bolt-accommodating bore  100  in the hand rail lower portion  46  and through the handrail connector bore  97 , linking the side portion  94  of the top step  36  proximate the front portion  90  thereof to the hand rail lower portion  46 . The top step  36  is rotatable, about the top step connecting bolt  102 , through an angular range of at least 90 degrees, from a deployed position substantially horizontal, parallel to the hand rail transverse portion  50  and perpendicular to the hand rail lower portion  46  and the hand rail rear portion  55 , to a folded position substantially vertical and roughly coplanar with the hand rail lower portion  46 . The flanged rear lock pin  110  extends through the lock pin-accommodating bore  108  in the hand rail rear portion  55  and inwardly through the keyhole bore  98  in the side portion  94  of the top step  36 , linking the side portion  94  of the top step  36  proximate the rear portion  92  thereof to the hand rail rear portion  55 . Carrying the weight of the hand rail assembly  34 , the flanged real lock pins  110  settle into and become stably lodged within the keyhole bores  98 . Thus, the two rear lock pins  110  and the two top step connecting bolts  102  cooperate to provide four-point stabilization of the top step  36  relative to the hand rail assembly  34  (identified generally in  FIG. 1 ). 
         [0070]    With reference to  FIG. 2  and  FIG. 6 , the hand rail internal segment  114  is shown floating between the hand rail lower portion  46  and the hand rail upper portion  48  in  FIG. 6 . In the assembled hand rail assembly  34 , best shown in  FIG. 2 , the hand rail internal segment  114  is not visible, being contained within the hand rail upper portion  48  and the hand rail lower portion  46 . The hand rail internal segment  114  fits snugly and extends downward within the hand rail lower portion  46 . The bolt-accommodating bore  101  of the hand rail internal segment  114  is aligned with the bolt-accommodating bore  100  of the hand rail lower portion  46 . The top step  36  connecting bolt  102  extends through the bolt-accommodating bore  100  of the hand rail lower portion  46  and the bolt-accommodating bore  101  of the hand rail internal segment  14 , fixing the hand rail internal segment  114  relative to the hand rail lower portion  46 , in addition to linking the hand rail lower portion  46  to the side portion  94  of the top step  36 . The hand rail internal segment  114  fits snugly and extends upward within the hand rail upper portion  48 . The lock pin-accommodating bore  105  of the hand rail internal segment  114  is aligned with the lock pin-accommodating bore  104  of the hand rail upper portion  48 . The front lock pin  106  extends through the lock pin-accommodating bore  104  of the hand rail upper portion  48  and through the lock pin-accommodating bore  105  of the hand rail internal segment  114 , fixing the hand rail internal segment  114  relative to the hand rail upper portion  48  and thus also relative to the hand rail lower portion  46 . The front lock pin  106  is preferably tethered to the hand rail assembly  34  to avoid loss after removal. 
         [0071]    With reference to  FIG. 1 , the caps  59  on the rearward-curved bottom ends  54  prevent impingement of the rearward-curved bottom ends  54  upon the wheel rim of the tractor or upon persons or equipment while also reducing slippage. The caps  112  on the hand rail rear portions  55  likewise prevent similar impingement. 
         [0072]      FIG. 8 , a perspective view of the preferred embodiment of the tractor tire  28  mountable folding step ladder  30 , shows the step ladder  30 , generally at  30 , in a folded configuration as viewed substantially from the front. Again shown are the top step  36 , middle step  38 , bottom step  40 , the middle step  38  supports  42 , and the bottom step  40  supports  44 . The bottom step  40  is shown with bottom surface  43 , rear edge  51 , front portion  47 , and side portions  49 . The bottom step  40  supports  44  are again shown with lower segments  52  and upper segments  53 . Each lower segment  52  has a bottom end  54  with an inwardly extending bottom step shoulder bolt  56 ; each lower segment  52  also has end  58  with an outwardly extending hinge pin  60 . The middle step  38  is shown with front portion  71  and side portions  74 . The top step  36  is shown with bottom surface  88 , front portion  90 , and side portions  94 . 
         [0073]      FIG. 8  also shows the hand rail lower portions  46  with rearward-curved bottom end  54  carrying a cap  59 ; hand rail upper portions  48 ; hand rail transverse portions  50 ; and hand rail rear portions  55  with caps  112 . Top step-connecting bolts  102  are shown occupying the bolt-accommodating bores  100 . The hand rail upper portion  48  has a lock pin-accommodating bore  104 , shown occupied by a front lock pin  106 . The hand rail rear portion  55  has a lock pin-accommodating bore  108 , shown occupied by a flanged rear lock pin  110 . A cap  112  is disposed on the hand rail rear portion  55 . 
         [0074]      FIG. 9  is a perspective view of the preferred embodiment of the tractor tire  28  mountable folding step ladder  30  in folded configuration, as viewed substantially from the rear. Again shown is the top step  36  having rear portion  92 , side portions  94 , front portion  90  and top surface  86 . Also shown are the rear edge  51  and a small part of the top surface  41  of the bottom step  40 . Hand rail lower portions  46  are shown with rearward-curved bottom ends  54  carrying caps  59 ; also shown are hand rail upper portions  48 ; hand rail transverse portions  50 ; and hand rail rear portions  55  with caps  112 . Top step connecting bolts  102  are shown occupying the bolt-accommodating bores  100 . The hand rail upper portion  48  has a lock pin-accommodating bore  104 , shown occupied by a front lock pin  106 . The hand rail rear portion  55  has a lock pin-accommodating bore  108 , shown occupied by a flanged rear lock pin  110 . A cap  112  is disposed on the hand rail rear portion  55 . 
         [0075]      FIG. 10  is a side elevational view of the preferred embodiment of the tractor tire  28  mountable folding step ladder  30  in folded configuration, showing the top step  36  with rear portion  92 , side portion  94 , front portion  90  and top surface  86 . Hand rail lower portions  46  are shown with rearward-curved bottom ends  54  carrying caps  59 ; also shown are hand rail upper portions  48 ; hand rail transverse portions  50 ; and hand rail rear portions  55  with caps  112 . Top step  36  connecting bolts  102  are shown occupying the bolt-accommodating bores  100 . The hand rail upper portion  48  has a lock pin-accommodating bore  104  (obscured), shown occupied by a front lock pin  106 . The hand rail rear portion  55  has a lock pin-accommodating bore  108 , shown occupied by a flanged rear lock pin  110 . A cap  112  is disposed on the hand rail rear portion  55 . 
         [0076]      FIG. 11  is a top plan view of the preferred embodiment of the tractor tire  28  mountable folding step ladder  30  in folded configuration, showing the top step  36  with side portions  94 , front portion  90  and top surface  86 . Hand rail lower portions  46  are shown with rearward-curved bottom ends  54  carrying caps  59 ; also shown are hand rail upper portions  48 ; hand rail transverse portions  50 ; and hand rail rear portions  55  with caps  112 . The hand rail upper portion  48  has a lock pin-accommodating bore  104  (obscured), shown occupied by a front lock pin  106 . The hand rail rear portion  55  has a lock pin-accommodating bore  108  (obscured), occupied by a flanged rear lock pin  110 . A cap  112  is disposed on the hand rail rear portion  55 . 
         [0077]    With reference to  FIGS. 1 ,  2  and  8 , it is seen that the step ladder  30  in accordance with the present invention is configurable in either a deployed configuration ( FIG. 2 ) or a folded configuration ( FIG. 8 ). In the deployed configuration, the bottom surface  88  and the side portions  94  of the top step  36  rest upon the tread portion of a tractor tire  28  as shown in  FIG. 1 , while the middle step  38  and the bottom step  40  are suspended from the step assembly support pins  96  that project inwardly from the side portions  94  of the top step  36  proximate the front portion  90  thereof. Loads applied to the middle step  38  and the bottom step  40  are thus transferred to the top step  36  proximate the front portion  90  thereof. The hand rail rear portions  55  extend downward behind the tractor tire  28  in a hook-like fashion, engaging the inner side wall of the tractor tire  28 , thereby resisting any applied lateral force that might pull the top step  36  off of the tire  28 . The rearward-curved bottom ends  54  with caps  56  engage the wheel rim of the tractor (not shown in the drawing figures), resisting rotation of the hand rail assembly  34  and top step  36  due to torque resulting from climbing or grasping loads applied to the step assembly  32  or to the hand rail assembly  34 . It will be recalled that in the deployed configuration, the top step  36  is four-point-stabilized relative to the hand rail assembly  34 . The downwardly extending side portions  94  of the top step  36  carry most of the downward load of the top step  36  and, being spaced apart along the circumference of the tire  28 , stabilize the entire step ladder  30  on the tire  28  and resist clockwise or counterclockwise rotation of the step ladder  30  relative to the tire  28  when uneven forces are applied to the hand rail assembly  34  or to the step assembly  32 . 
         [0078]    With continued reference to  FIGS. 1 ,  2  and  8 , transition from the deployed configuration to the folded configuration begins when a user grasps the hand rail transverse portions  50  and lifts the step ladder  30  away from the tire  28 . With the load between the top step  36  and the hand rail rear portion  55  reversed, the flanged rear lock pins  110  are in lifting proximity and alignment with the keyhole bores  98  of the side portions  94  of the top step  36  and are therefore free to be withdrawn from the keyhole bores  98  as soon as the hand rail rear portions  55  can be moved laterally away from the side portions  94  of the top step  36 . The user withdraws the front lock pins  106  from the lock pin-accommodating bores  104  of the hand rail upper portions  48 , freeing the hand rail upper portions  48  to rotate relative to the hand rail internal segments  114  and relative to the hand rail lower portions  46 . The user rotates the hand rail rear portions  55  away from the top step  36 , withdrawing the flanged rear lock pins  110  from the keyhole bores  98 , with the result that the top step  36  is linked to the hand rail assembly  34  only by the top step connecting bolts  102 . The rear portion  92  of the top step  36  falls along an arcuate path toward the hand rail lower portion  46 , whereupon the bottom surface  88  of the top step  36  faces forward. To collapse the bottom step  40 , the user lifts and rotates the front portion  47  of the bottom step  40  to a location between the upper ends  58  of the lower segments  52  of the bottom step  40  supports  44 . The user rotates the bottom ends  64  of the upper segments  53  of the bottom step  40  supports  44  forward and upward until the upper segments  53  abut the bottom surface  70  of the middle step  38 . The user lets the middle step  38  supports  42  fall downward and rearward into proximity with the now-forward-facing bottom surface  88  of the top step  36 , whereupon the top surface  41  of the bottom step  40  is moved against the bottom surface  70  of the middle step  38  and the top surface  68  of the middle step  38  is moved against the bottom surface  88  of the top step  36 , all suspended between and roughly in plane with the hand rail lower portions  46 . The user rotates both of the hand rail upper portions  48  clockwise, or both counterclockwise, relative to the respective hand rail lower portions  46  until one hand rail rear portion  55  abuts the front portion  47  of the bottom step  40 , the front portion  71  of the middle step  38 , and the front portion  90  of the top step  36 , while the other hand rail rear portion  55  abuts the top surface  86  of the top step  36 . As a result, the entire step assembly  32  is retained between the hand rail rear portions  55 . The user reinserts the front lock pins  106  in the lock pin-accommodating bores  104  of the hand rail upper portions  48 , fixing the hand rail upper portions  48  relative to the hand rail internal segments  114  and thus relative to the hand rail lower portions  46 ; however, it is noted that the front lock pins  106  now pass through the second lock pin-accommodating bores  107  (used for storage), which are at an angle relative to the lock pin-accommodating bores  105  (for deployment), in the hand rail internal segment  114 . The angle is predetermined to be appropriate to keep the hand rail rear portions  55  securely abutting the folded step assembly  32 . Alternatively, the user leaves the front lock pins  106  hanging tethered and relies on snugness of fit of the hand rail internal segment  114  within the hand rail upper portion  48  to hold the hand rail rear portions  55  in abutting relation to the folded step assembly  32 . The step ladder  30  is now in the folded configuration. The user conveniently carries the folded step ladder  30  by grasping one of the hand rail transverse portions  50  and secures the folded step ladder  30  in a relatively small space. 
         [0079]    As can be seen from the drawing figures and from the description, each embodiment of the tractor tire  28  mountable folding step ladder  30  in accordance with the present invention solves a problem by addressing the need for a portable, safe and stable platform to mount and access the engine compartment to perform required maintenance and repetitive checks in the normal daily operation of a tractor trailer or other type of vehicle. 
         [0080]    While the specification describes particular embodiments of the present invention, those of ordinary skill can devise variations of the present invention without departing from the inventive concept. For example, more or fewer steps can be employed, the dimensions can be varied considerably to make a narrower or wider ladder to accommodate different size customers or markets. Additional or fewer pins can bolts may be employed in different combinations.