Abstract:
A folding staircase for use in a door opening having a threshold. The folding staircase has a pair of stringers that have an upper end and a lower end that is adapted for contacting a ground surface. The stringers are spanned by at least one tread. A hinge is connected to a floor near the door opening and a threshold plate pivotally connected thereto is movable between a use position and a stowed position. The staircase may be provided with a lifting mechanism that biases the staircase and threshold plate toward their stowed positions. The lifting device provides a variable force that provides more rotational force when the staircase would require a user to bear more of its weight and less force when less of the weight of the staircase would be borne by a user.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Folding staircases for recreational vehicles (RVs) are necessary for easily entering and exiting the RV. Typically, RVs which can be towable units or motorhomes are well above the ground upon which they rest. Previous staircases to facilitate movement to and from RVs have been unwieldy for various reasons. In some cases, steps that fold out of RVs do not span from the RV to the ground, but remain suspended above the ground. These types of steps therefore fail to provide a sturdy and consistent path to the ground because they remain somewhat independently held above the adjacent ground, which may or may not have a slope. Other steps include multiple linkages and moving parts and only unfold with great effort on the part of a user. There is a need for RV steps that require little effort of their user and provide a steady consistent path to the ground upon which the RV rests. 
       SUMMARY OF THE INVENTION 
       [0002]    The present invention is a folding staircase that is adapted for use in a door opening. The door opening is in a wall that has an inner wall surface that is located within an indoor space and an outer wall surface that is located in an outdoor space. The door opening receives a door that separates the indoor space from the outdoor space. 
         [0003]    The folding staircase has a pair of stringers that are spanned by at last one tread. Each of the stringers has an upper edge and a lower edge, an upper end and a lower end. The lower end is adapted for contacting a ground surface. The upper end is for abutting the outer wall surface. A hinge is adapted for being mounted to a floor within the indoor space and is spaced from the threshold. A threshold plate is connected to the hinge. The threshold plate is pivotable between a use and a stowed position. The threshold plate has a first ramped portion that is adapted to reach a distance that is at least the height that the threshold is above the floor. This enables the threshold plate to span over the threshold in its use position. The first ramped portion continues into a spanning portion that is adapted for directly overlying the threshold and spanning between the inner wall surface and the outer wall surface when the threshold plate is in its use position. The spanning portion continues into an offsetting portion that is substantially parallel to the outer wall surface and adjacent to the threshold when the threshold plate is in its use position. The threshold plate aligns the upper end of the stringers adjacent to the outer wall surface when the threshold plate is in its use position. 
         [0004]    In another aspect of the invention, the staircase may be provided with a lifting mechanism that assists moving the staircase from its use to its stowed position. The lifting mechanism provides a biasing rotational force upon the threshold plate and staircase toward the stowed position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is side view of the staircase with a sectional view through the door frame and floor with the staircase and threshold plate in the use position; 
           [0006]      FIG. 2  is a side view with a sectional view through the door frame and floor with the staircase in  FIG. 1  and threshold plate in the stowed position; 
           [0007]      FIG. 3  is a front view of the staircase shown in  FIGS. 1 and 2  in its stowed position; 
           [0008]      FIG. 4  is a sectional view taken about the line  4 - 4  in  FIG. 3 ; 
           [0009]      FIG. 5  is a magnified view of area  5  in in  FIG. 1 ; 
           [0010]      FIG. 6  is a perspective view of the staircase shown in  FIGS. 1-5  in its use position showing the area adjacent to the threshold; 
           [0011]      FIG. 7  is a perspective view of a staircase with a lifting device as seen from the indoor space with the staircase in its use position; 
           [0012]      FIG. 8  is a perspective view of the staircase shown in  FIG. 7 , with the staircase in its use position; 
           [0013]      FIG. 9  is a perspective view of the staircase in  FIGS. 7 and 8  with the staircase between its use and stowed position; 
           [0014]      FIG. 10  is a perspective view of the staircase in  FIGS. 7-9  in the stowed position; 
           [0015]      FIG. 11  is an exploded perspective view of the staircase shown in  FIGS. 7-10 ; 
           [0016]      FIG. 12  is a side view of the staircase shown in  FIG. 8  in the use position; 
           [0017]      FIG. 13  is a side view of the staircase shown in  FIG. 9  positioned between its use and stowed position; and 
           [0018]      FIG. 14  is a side view of the staircase shown in  FIG. 10  in its stowed position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    The folding staircase  10  of the present invention is shown in  FIG. 1 . The folding staircase  10  is for use in a door opening  16  within a wall  18  that has an inner wall surface  20  that is located within an indoor space  22  and an outer wall surface  24  that is located in an outdoor space  26 . The door opening  16  includes a door frame  17  having a threshold  27  and vertical door jambs  30  that span from the outer wall surface  24  to the inner wall surface  20  within the door opening  16 . The jambs  30  are the vertical portions of the door frame  17  lining the door opening  16  and are best shown in  FIG. 5  and have metal door stops  31  that are extensions from the jambs  30  extending along the vertical sides of the door opening  16 . Within the indoor space  22  a floor  35  defines the lowermost portion of the indoor space  22  and the threshold  27  rises above the floor  35 . 
         [0020]    The folding staircase  10  has a pair of stringers  38  that are spaced parallel to each other and are spanned by treads  40 . The treads  40  may be affixed mechanically to their respective stringers  38  or welded to the stringers  38  and in the staircase  10  shown in  FIG. 5 , the treads  40  are bolted to the stringers  38 . Each of the stringers  38  has an upper edge  44  and a lower edge  46 . The stringers  38  each have a lower end  48  that includes a pivotal foot  50  that is pivotally affixed to an adjustable leg  52 . In some instances having a pivotal foot  50  near the lower end is not necessary. The stringers  38  have an upper end  54  that is adapted for abutting the outer wall surface  24 . Adjacent to the upper end  54  is a truncated upper surface  56  that is perpendicular to the upper end  54  of the stringers  38 . The upper end  54  is designed to be held adjacent to and abutting the outer wall surface  24 , but not touching it. This is shown in  FIG. 1 . 
         [0021]    A hinge  60  is connected near the upper end  54  of the stringers  38  and to the floor  35 . The hinge  60  includes a floor mounting portion  64  and a threshold plate  66  that pivots about a pivot axis  67  with respect to the floor mounting portion  64 . The floor mounting portion  64  is adapted to be mounted to the floor  35  as shown in  FIG. 1 . The threshold plate  66  has a first ramped portion  68  that is adapted to reach upwardly to the distance the threshold  27  rises above the floor  35 . The first ramped portion  68  continues into a spanning portion  70  that is adapted to directly overlie the threshold  27  as shown in  FIGS. 1 and 6 . The spanning portion  70  has an upper surface  72  and a lower surface  74 . The lower surface  74  may be spaced above the threshold  27  by a predetermined amount. This spacing above the threshold  27  is shown in  FIG. 5 . The spanning portion  70  continues into an offsetting portion  78  that extends downwardly from the spanning portion  70 . The offsetting portion  78  is adapted to be parallel to the outer wall surface  24  and when the threshold plate  66  is in the position shown in  FIG. 1 . The offsetting portion  78  continues into a mounting portion  80  that is perpendicular to it. The mounting portion  80  is mounted adjacent to the truncated upper surface  56  of the stringers  38 . This may be accomplished by mechanical fasteners  82  such as bolts or rivets driven through lateral tabs  84  extending from the mounting portion  80 . 
         [0022]    The hinge  60  and staircase  10  have a use position that corresponds to the position shown in  FIGS. 1 and 6 , and a stowed position shown in  FIGS. 2 and 7 . In the use position, the stringers  38  are located below the threshold  27 . When the staircase  10  is in its stowed position it is positioned so the staircase  10  fits completely within the lateral boundaries of the door opening  16 . In the stowed position, the lower edge  46  of the stringers  38  are located completely with the indoor space  22  and are inside the door jambs  30 . In this position, the center of gravity  88  for the staircase  10  is located inward of the pivot axis  67 . As such, the staircase  10  is biased inward. The stringers  38  have locking mechanisms  90  that are located near their lower edges  46 . The locking mechanisms  90  have locking pins  92  that are biased outward with a spring and a stop bracket  93 . Each locking pin  92  has an extended position shown in  FIG. 5  and a retracted position in which the locking pin  92  is retracted within the locking mechanism  90 . The locking pins  92  have an inclined surface that is adapted to strike the door stop  31  when the staircase  10  is moved from its use position to its stowed position and this pushes the locking pins  92  inward to clear the door stops  31 . Once the locking pins  92  pass the door stops  31  they extend behind it as shown in  FIG. 5  to lock the staircase  10  in place. The locking pins  92  may be retraced by twisting a handle  96  that pulls on release linkages  97 , which retract the pins  92 . When the staircase  10  is in its stowed position it is biased to rest upon the stop brackets  93  that prevent the staircase  10  from falling inward. 
         [0023]    The folding staircase  10  may also be assisted through the use of a lifting device  98  that reduces the force necessary to move the staircase  10  from its use position to its stowed position. The lifting device  98  is shown in  FIG. 7  as viewed from the indoor space. The lifting device  98  has a cover  100  that is shown removed in  FIG. 8 . In the embodiment shown in  FIGS. 6-11 , a threshold plate  102  has a first hinge flange  105  and a second hinge flange  106 . The first and second hinge flanges  105 ,  106  are positioned such that they extend beyond the door jambs  30  and obstruct no portion of the door opening  16 . The hinge flanges  105 ,  106  define the ends of the threshold plate  102 . The threshold plate  102  pivots about pivot axis  104  that acts as a hinge for the threshold plate  102  and the pivot axis  104  is defined by the central axis of two bolts  108  extending through the hinge flanges  105 ,  106  of the threshold plate  102 . The bolts  108  also extend through corresponding opposing first and second hinge flanges  118  and  122  on first and second mounting brackets  110 ,  112  that are affixed within the indoor space  22 . The first mounting bracket  110  is shown on the left side in  FIG. 8  and the second mounting bracket  112  is shown on the right side. The mounting brackets  110 ,  112  have corresponding wall mounting flanges  120  and  121 . The first wall mounting flange  120  is perpendicular to the first hinge flange  118  on the first mounting bracket  110 . The second wall mounting flange  121  is perpendicular to the second hinge flange  122  on the second mounting bracket  112 . Each mounting bracket  110 ,  112  has a floor flange  123 ,  125  that is for fastening the mounting brackets  110 ,  112  to the floor  35 . On the first mounting bracket  110 , the first wall mounting flange  120 , first hinge flange  105  and first floor flange  123  are all perpendicular with respect to each other and are all joined to form a rigid corner  127 . On the second mounting bracket  112 , the second wall mounting flange  121 , second hinge flange  122  and second floor flange  125  are all perpendicular with respect to each other and are joined to form a rigid corner  129 . As such, the mounting brackets  110 ,  112  are extremely rigid yet light weight. Each mounting flange  110 ,  112  has an inner edge  131 ,  132  and an outer edge  133 ,  135  respectively. Each hinge flange  118 ,  122  extends from the outer edge  133 ,  135  of its corresponding wall mounting flange  120 ,  121 . As such, the mating hinge flanges  105 ,  106  of the threshold plate  102  are maintained offset from the door jambs  30  because the inner edges  131  and  132  are typically aligned with or slightly inset from the edges of the door opening  16 . In other words, the inner edges  131 ,  132  are slightly inset or aligned with the door jambs  30 . The hinge flanges  105 ,  106  of the threshold plate  102  are located between the inner edges  131 ,  132  and outer edges  133 ,  135  of the wall mounting flanges  120 ,  121 . The threshold plate  102  spans across the threshold  27  to the outdoor space  26  and is joined to the stringers  38  near the upper ends  54  of the stringers  38 . The pivot axis  104  extends through both hinge flanges  105 ,  106  so that the threshold plate  102  can pivot with respect to the door frame  17  and the pivot axis  104  is fixed with respect to the door frame  17 . The hinge flanges  105 ,  106  of the threshold plate  102  pivotally ride within the hinge flanges  118 ,  122  on the mounting brackets  110 ,  112  which restrains the threshold plate  102  from axial movement while allowing it to pivot about the pivot axis  104 . 
         [0024]    A pair of gas springs  126  are connected between the second hinge flange  122  of the second mounting bracket  112  and the second hinge flange  106  of the threshold plate  102 . The gas springs  126  straddle the hinge flange  122  on the second mounting bracket  112  and the hinge flange  106  on the threshold plate  102 . The gas springs  126  exert a force in a direction that extends their length. The gas springs  126  have a first end  128  pivotally connected at pivot point  130  located on the second hinge flange  122  of the second mounting bracket  112 . This pivotally fixes the first end  128  and pivot point  130  with respect to the door opening  16 . The gas springs  126  have a second end  134  pivotally connected at pivot point  136  on second hinge flange  106  of the threshold plate  102 . Pivot point  136  is pivotally fixed with respect to the second hinge flange  106  on the threshold plate  102 . Thus, the second end  134  and pivot point  136  move with respect to the door opening  16  as the threshold plate  102  pivots. The gas springs  126  work well for providing lifting assistance in the present invention because they have a relatively flat force curve when compared to other springs such as coil springs. Because the gas springs  126  straddle the hinge flanges  122  and  106 , they do not exert a bending force on the flanges  122 ,  106  to which they are connected. Each spring  126  exerts a force along its line of action  140  that acts through the pivot points  130 ,  136 .  FIG. 12  shows the staircase  10  in its use position in which the pivotal feet  50  contact the ground. In the use position, the line of action  140  of the gas springs  126  is relatively near the pivot axis  104  of the threshold plate  102 . The distance of the line of action  140  from the pivot axis  104  is shown as D 1  in  FIG. 12 . When the line of action  140  is relatively near the pivot axis  104 , the gas springs  126  do not exert a relatively strong moment on the staircase  10  via the threshold plate  102 , and thus, the assistance to the user is relatively light. In the use position, the center of gravity  88  is relatively near the outer wall surface  24  and a large amount of assistance is not needed because a user does not bear a large portion of the weight of the staircase  10 . As the staircase  10  is moved between the use and stowed position to a position where the staircase  10  is approximately perpendicular to the outer wall surface  24 , the center of gravity  88  is at its farthest from the outer wall surface  24  and a user of the staircase  10  will bear a large portion of the weight to of the staircase  10 . This position is shown in  FIG. 13 . In this position, the line of action  140  is relatively far from the pivot axis  104  of the threshold plate  102  and this provides a relatively high amount of assistance because the springs  126  generate a relatively large moment about the pivot axis  104  that urges the staircase  10  towards its stowed position. Hence the springs  126  are able to generate a large amount of assistance when a user of the staircase  10  would bear the most weight during lifting it. The distance between the line of action  140  and the pivot axis  104  when the staircase  10  is between its use and stowed positions is shown as D 2  in  FIG. 13 . Distance D 2  is the largest distance that the line of action  140  is from the pivot axis  104  and coincides with the position of the staircase  10  when the center of gravity  88  is farthest from the wall  18 . Thus, the line of action  140  moves farther from the pivot axis  104  as the staircase  10  is rotated from its use position toward its stowed position for a portion of the pivotal movement. As the staircase  10  is further lifted towards its stowed position, again the line of action  140  moves relatively nearer the pivot axis  104 . The relationship between the line of action  140  and the pivot axis  104  in the stowed position is shown as D 3  in  FIG. 14 . As such, relatively little biasing rotative force is provided near the stowed position because assistance is not needed. As shown in  FIG. 2 , the center of gravity  88  will be inside the door frame  17 , and in the case of the staircase  10  shown in  FIGS. 6-11 , the center of gravity  88  will be farther from the inner wall surface  20  than the pivot axis  104  of the threshold plate  102 . As such, the staircase  10  will be biased inwardly under its own weight to rest on its stop brackets  93  as shown in  FIG. 4 . When the staircase  10  rests on its stop brackets  93 , the gas springs  126  are designed to exert no biasing force. As such, in the event the gas springs  126  need to be changed, they may be easily removed without any need to compress the gas springs  126  to facilitate their removal. 
         [0025]    The folding staircase  10  and lifting device are designed so that no part of the lifting device is within the door opening  16 . In other words, no parts of the mounting brackets  110 ,  112  and the parts affixed thereto protrude within the space between the door jambs  30 . This can be seen in  FIGS. 6 and 7 . Thus, the path through the door opening  16  is unobstructed by any parts of the staircase  10 . 
         [0026]    In the use position of the staircase  10 , the threshold plate  102  extending to its inner edge  142  covers the mounting flanges  123 ,  125  and the cover  100  covers the lifting device  98  as shown in  FIG. 7 . Laterally, the threshold plate  102  covers the floor mounting flanges  123 ,  125  of the mounting brackets  110 ,  112  because the hinge flanges  105 ,  106  of the threshold plate  102  pivotally ride along the insides of the hinge flanges  118 ,  122  of the mounting brackets  110 ,  112 . Thus, most of the mounting hardware and working parts associated with lifting the staircase  10  remain hidden with respect to a user of the staircase  10 . When a user of the staircase  10  shown in  FIGS. 6-11  is ready to store the staircase  10 , he will lift up near the lower end  48  of the staircase. As the staircase  10  is lifted, the gas springs  126  provide more assistance as the line of action  140  shifts from its relatively near position to the pivot axis  104  shown in  FIG. 8  to its relatively far position shown in  FIG. 9 . The user of the staircase  10  will receive the most assistance when the staircase  10  is in the position shown in  FIGS. 9 and 13 . As such, the user of the staircase  10  will need to exert a relatively low and nearly constant force as the staircase  10  is moved from its use position to its stowed position. 
         [0027]    The invention is not limited to the description above but may be modified within the scope of the following claims below.