Abstract:
A wheelchair lift ( 20 ) for a vehicle is disclosed. The wheelchair lift includes a lift platform ( 22 ) coupled to a support structure ( 32 ) by an attachment assembly ( 74 ). The lift platform is reciprocal between a stowed position and an extended position, wherein the lift platform is coplanar with a first plane. The wheelchair lift also includes a redundant support assembly ( 80 ) in communication with the lift platform to provide secondary support of the lift platform when the lift platform is in the extended position and to maintain the lift platform in a second plane substantially parallel to the first plane if a portion of the attachment assembly fails.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/413,513, filed on Sep. 25, 2002, the disclosure of which is hereby expressly incorporated by reference, and priority from the filing date of which is hereby claimed under 35 U.S.C. § 119(e). 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to lifts for mobility impaired persons, and more particularly, to redundant support systems for passenger lifts.  
         BACKGROUND OF THE INVENTION  
         [0003]    The Americans with Disabilities Act (ADA) requires the removal of physical obstacles to those who are physically challenged. Included within the scope of the ADA are motor vehicles, such as trains and buses. Specifically, new, used or remanufactured buses shall comply with the applicable provisions of the statute. One such provision requires that deployed platforms, when occupied, shall prevent the platform from dropping an occupant in the event of a single failure of any load-carrying component. Thus, to comply with the ADA, redundant systems need to be included on passenger lifts.  
           [0004]    Currently, there are a wide variety of passenger lifts available for motor vehicles. One such lift is adapted to be mounted within an entryway of a motor vehicle. Such a lift includes a reciprocating lift platform mounted within the vehicle and selectively actuatable between at least a raised and a lowered position. The lift platform consists of an inboard platform and an outboard platform. The outboard platform is hingedly attached to the outboard edge of the inboard platform by two sets of horizontally oriented pin assemblies. The pin assemblies are located on opposite sides of the lift platform. The inboard edge of the inboard platform is hingedly attached to two vertical support columns located at the entrance of the passenger vehicle by a second set of two horizontally oriented pin assemblies. The vertical support columns may be selectively raised and lowered to convey the attached lift platform between the raised and lowered positions.  
           [0005]    The pin assemblies allow the lift platform to be rotatably transfigured from a stowed position to an extended position. In the extended position, the upper planar surface of the inboard platform is oriented parallel with and above the ground. The outboard platform is rotated on the pin assemblies outward from the inboard platform until the outboard platform is coplanar with the inboard platform. Once in the extended position as described, the lift platform is lowered to the ground or sidewalk so that a mobility impaired individual may board the lift platform. Once in the raised position, the lift platform is level with the floor of the motor vehicle. The mobility-impaired passenger is then free to deboard the lift platform and enter the passenger compartment of the vehicle.  
           [0006]    The lift platform is then-rotatably transfigured into the stowed position. This is done by rotating the outboard platform until the upper surface of the outboard platform is parallel with and opposing the upper surface of the inboard platform. The inboard platform and outboard platform are further rotated as a unit into a vertical stowed position, nested between and parallel with the vertical support columns.  
           [0007]    Although such a lift is effective at accommodating mobility impaired passengers, such as those in a wheelchair, and providing access into and out of a motor vehicle, it is not without its problems. One such problem associated with currently available passenger lifts, such as the one described above, involves the connection interfaces between the inboard platform and the vertical support columns, and the inboard platform and the outboard platform, respectively. Specifically, if a catastrophic failure occurs at one of the pin assemblies, the inboard platform or outboard platform could canter to one side, separate from one another, or drop, potentially injuring the lift user or others in proximity to the lift. Such a passenger lift is not only dangerous, it also fails to comply with the ADA regarding single failure of any load-carrying component.  
           [0008]    For at least the foregoing reason, there exists a need for a passenger lift that includes redundant support systems in the event of a failure at one of the pin assemblies, wherein the redundant support systems comply with the ADA requirements.  
         SUMMARY OF THE INVENTION  
         [0009]    In accordance with the present invention, one embodiment of a passenger lift for conveying a passenger between a first elevation and a second elevation is disclosed. The passenger lift includes a lift platform coupled to a support structure by an attachment assembly. The lift platform is reciprocal between a stowed position and an extended position, wherein the lift platform is coplanar with a first plane. The passenger lift also includes a redundant support assembly in communication with the lift platform to provide secondary support of the lift platform when the lift platform is in the extended position and to maintain the lift platform in a second plane substantially parallel to the first plane if a portion of the attachment assembly fails.  
           [0010]    In accordance with the present invention, a second embodiment of a passenger lift for conveying a passenger between a first elevation and a second elevation is disclosed. The passenger lift includes a lift platform coupled to a support structure by an attachment assembly. The lift platform is reciprocal between a stowed position and an extended position, wherein the lift platform is in a first plane. The passenger lift also includes a first limit stop and a second limit stop. If a portion of the attachment assembly fails, the lift platform engages the first and second limit stops, thereby maintaining the lift platform in a second plane substantially parallel to the first plane.  
           [0011]    In accordance with the present invention, a third embodiment of a passenger lift for conveying a passenger between a first elevation and a second elevation is disclosed. The passenger lift includes a first platform coupled to a support structure by an attachment assembly. The first platform is reciprocal between a stowed position and an extended position, wherein the first platform is in a first plane. The passenger lift also includes a second platform coupled to the first platform by the attachment assembly. The second platform is reciprocal between a stowed position and an extended position, wherein the second platform is substantially in the first plane. The passenger lift further includes a first redundant support assembly in communication with the first platform to provide secondary support of the first platform when the first platform is in the extended position and to maintain the first platform in a second plane substantially parallel to the first plane if a portion of the attachment assembly fails. The passenger lift still further includes a second redundant support assembly in communication with the second platform to provide secondary support of the second platform when the second platform is in the extended position and to maintain the second platform substantially in the second plane if a portion of the attachment assembly fails. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0013]    [0013]FIG. 1 is a perspective view of one embodiment of a stowable passenger lift assembly formed in accordance with the present invention;  
         [0014]    [0014]FIG. 2 is a partial cross-section view of the stowable passenger lift assembly shown in FIG. 1, wherein the stowable passenger lift assembly is in a semi-extended position;  
         [0015]    [0015]FIG. 3 is a side elevational view of the stowable passenger lift assembly of FIG. 2 reciprocating from an extended position to a fully stowed position;  
         [0016]    [0016]FIG. 4 is an exploded view of the pivot connection between the folding outboard platform and the inboard platform of the stowable passenger lift assembly of FIG. 1; and  
         [0017]    [0017]FIG. 5 is a horizontal cross sectional view of the pivot connection of FIG. 4, when the stowable passenger lift assembly is in the extended position. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    The present invention will now be described with reference to the accompanying drawings where like numerals correspond to like elements. FIGS.  1 - 5  illustrate one embodiment of a stowable passenger lift assembly having a redundant support assembly formed in accordance with the present invention. For purposes of this detailed description, the redundant support assembly will be subdivided into a first and a second redundant support system. For clarity, the vehicle to which the passenger lift assembly may be installed within has not been illustrated. Although the first and second redundant support systems are discussed in relation to their use with a passenger lift assembly mounted in a motor vehicle, it is apparent to those skilled in the art that this is done for illustrative purposes and should not be construed as limiting the scope of the invention. For example, it is apparent to those skilled in the art that the first and second redundant support systems are equally applicable to any type of lift, including cargo lifts, and passenger lifts mounted in locations other than in a vehicle, such as a stairway. Additionally, although illustrative terms such as vertical and horizontal are used herein, they are descriptive in nature and should not be construed as limiting.  
         [0019]    The present invention is directed to a first redundant support system located at the connection interface between the inboard platform and the mounting structure of a stowable passenger lift assembly. The present invention is further directed to a second redundant support system located at the connection interface between the outboard platform and the inboard platform of a stowable passenger lift assembly. In the event of a failure at one of the connections between the inboard platform and either the mounting structure or the outboard platform, the first redundant support system constrains movement of the inboard platform with respect to the mounting structure, while the second redundant support system constrains movement of the outboard platform with respect to the inboard platform, respectively. Accordingly, the first and second redundant support systems provide a continued connection between the mounting structure and the inboard platform, and the inboard platform and the outboard platform, respectively, thereby providing a safety feature for the passenger lift assembly which also complies with ADA requirements.  
         [0020]    One illustrative embodiment of a stowable passenger lift assembly, generally designated  20 , incorporating the redundant support systems of the present invention is shown in FIG. 1. Generally described, the stowable passenger lift assembly  20  (hereinafter “lift assembly  20 ”) includes a lift platform  22  for supporting a passenger. The lift platform  22  is formed by an inboard platform  24  pivotally attached at one end to a folding outboard platform  28  by pin assemblies  118 . The lift platform  22  is pivotally attached to a mounting structure  32  by pin assemblies  74  at the opposite end of the inboard platform  24 . The pin assemblies  74  and  118  are collectively referred to as an attachment assembly. Although the attachment assembly of the illustrated embodiment is described as formed from pin assemblies, it should be apparent to those skilled in the art that the attachment assembly may be formed from other connecting members than those depicted. For instance, the attachment assembly may include connecting members that permit motion other than pivotal movement, such as translational movement. The lift assembly  20  includes other components, not shown for ease of illustration but well known in the art, such as a reciprocating assembly for lifting the platform between a lowered and a raised position and reciprocating the lift platform  22  between a stowed and an extended position.  
         [0021]    The lift assembly  20  is adapted to be slidably mounted to a frame structure of a vehicle (not shown), such as the doorframe of the entryway of a bus, by the mounting structure  32 . In partial operation, the lift platform  22  reciprocates between the stowed and extended positions, as shown partially in phantom in FIG. 3. In the stowed position, the folding outboard platform  28  is juxtaposed against the inboard platform  24 , with the folding outboard platform  28  and the inboard platform  24  disposed in a vertical orientation. In the extended position, the folding outboard platform  28  and the inboard platform  24  extend horizontally outward from the mounting structure  32  and are substantially coplanar.  
         [0022]    Referring now to FIG. 2, the inboard platform  24  of the lift platform  22  will now be described. For ease of illustration, FIG. 2 is a partial cross-sectional view of the lift assembly  20  in a semi-extended position. FIG. 2 illustrates only one side of the lift assembly  20 ; however, the other side of the lift assembly  20  is identical in construction and operation. The inboard platform  24  includes a rigid floor structure  40  for supporting a mobility-impaired passenger. In the embodiment shown, the floor structure  40  is formed by upper and lower generally planar floor panels  42  and  44 , preferably of a metallic material, such as steel, interconnected by planar end walls  48  and  50  (end wall  50  is best shown in FIG. 3) positioned at the inboard and outboard ends  52  and  54  of the inboard platform  24 , respectively. For clarity in the description, the terms “inboard” and “outboard” are used herein to convey relative positions of portions of the lift assembly  20  when mounted within a vehicle, and therefore should not be construed as limiting the scope of the present invention.  
         [0023]    The end walls  48  and  50  of the inboard platform  24  are positioned in a plane substantially orthogonal to the upper and lower panels  42  and  44 , as best shown in FIG. 3. The end wall  48  includes a planar support surface  56  and the end wall  50  includes a planar restraining surface  58 . Referring to FIGS. 2 and 3, the inboard platform  24  further includes side curbs  60 , which extend upwardly from each side of the upper panel  42 . The side curbs  60  begin at about the outboard edge of the inboard platform  24  and extend longitudinally to a position past the inboard end wall  48 , thereby forming side curb extensions  62 . The side curb extensions  62  include apertures, which are adapted for receiving journal members, such as pivot pins  72 . Each side curb  60  enhances the structural strength of the inboard platform  24  and provides a bumper for the sides of the inboard platform  24 , thereby increasing the safety of the lift assembly  20 . As will be described in more detail below, the inboard platform  24  is pivotally attached to the mounting structure  32  at the inboard end  52  of the side curbs  60 , and pivotally attached to the outboard platform  28  at the outboard end  54  of the side curbs  60 .  
         [0024]    Referring now to FIGS. 1 and 2, the mounting structure  32  of the present invention will now be described in detail. The mounting structure  32  is preferably constructed of a metallic material, such as steel, and includes two spaced apart, vertically disposed support columns  66  interconnected by a horizontally disposed base  68 . The distance between the support columns  66  is suitable for receiving the inboard platform  24  therebetween, as best shown in FIG. 1. Referring now to FIG. 2, the base  68  of the illustrative embodiment is substantially rectangular in cross-section and includes an outboard-facing restraining surface  70  adapted to act as a limit stop and abut against the support surface of the inboard platform  24  when the lift assembly  20  is in the extended position. The vertical columns  66  are adapted to be selectively raised and lowered by a reciprocating assembly (not shown). Since the reciprocating assembly is not part of the present invention, it will not be described in detail.  
         [0025]    The vertical support columns  66  include apertures (hidden in FIG. 2) disposed a suitable distance above the top surface of the base  68  for receiving journal members, such as pivot pins  72 . Any conventional pivot pin may be used, and thus it will not be described in any more detail. As assembled, the pivot pins  72  extend through the support column apertures and the corresponding apertures in the inboard ends  52  of side curbs  60 , thereby forming the pin assemblies  74 . Thus, the pin assemblies  74  pivotally attach the inboard platform  24  to the mounting structure  32 . As such, the pivot pins  72  define a horizontal pivot axis of the inboard platform  24  with respect to the mounting structure  32 .  
         [0026]    In accordance with one aspect of the present invention, the lift assembly  20  further includes a first redundant support system for providing a safety feature positioned at the connection interface (i.e. pin assemblies  74 ) between the inboard platform  24  and mounting structure  32 . Referring now to FIGS. 2 and 3, the first redundant support system  80  includes a redundant support member  82  fixedly secured to each of the vertical support columns  66  above and slightly inboard of the pivot pins  72 . As best shown in FIG. 2, the redundant support member  82  may be, for example, a cylindrical pin having a flat head. To cooperate with the redundant support members  82 , the side curbs extensions  62  include an outboard limit recess  84  and an inboard recess  86  that defines a support arm  88 . Each recess  84  and  86  is sized and configured to receive the redundant support members  82  when the inboard platform  24  is oriented in the stowed position and the extended position, respectively, the redundant support member  82  acting as a limit stop. The support arm  88  extends substantially orthogonal from the upper panel  42 , and is adapted to contact the redundant support member  82  in the extended position. Thus, in this embodiment, the redundant support member  82 , the recesses  84  and  86 , and the support arm  88  form the first redundant support system  80 .  
         [0027]    Referring now to the operation between the inboard platform  24  and the mounting structure  32 , attention is directed to FIG. 3. FIG. 3 is a side elevational view of the lift assembly  20  reciprocating from an extended position to a fully stowed position. In normal operation, the inboard platform  24  pivots about pivot pins  72  from the vertical stowed position to the horizontal extended position. In the stowed position, the upper surface of the outboard platform  28  is parallel with and opposes the upper surface of the inboard platform  24 , the inboard platform  24  and outboard platform  28  are nested between and substantially parallel with the vertical support columns  66 , and the redundant support member  82  is received by the limit recess  84  (see FIG. 2). Upon rotation from the vertical position to the extended position, the inboard platform  24  continues to rotate until the support surface  56  of the inboard platform  24  contacts, and thus, is restrained by restraining surface  70  (see FIG. 2) of the base  68 . In the extended position, the upper planar surface of the inboard platform  24  is oriented in a substantially horizontal position, the redundant support member  82  is received by the recess  86  (see FIG. 2), and the support arm  88  abuts against the inboard side of the redundant member  82 .  
         [0028]    When the lift assembly  20  is in the extended position and the lift platform  22  is supporting a passenger, the load applied thereto by the passenger is supported by the restraining surface  70  of the mounting structure  32  in conjunction with the pivot pins  72 . However, the redundant support members  82  are in a no-load condition in the extended position when the pin assemblies  74  are functioning properly. As such, the rotational and translational movement of the lift platform  22  is constrained by the contact between the support surface  56  and the restraining surface  70 , and the pivot pins  72 .  
         [0029]    Referring back to FIGS. 1 and 2, the folding outboard platform  28  of the lift platform  22  will now be described in detail. As shown best in FIG. 2, the outboard platform  28  is similarly constructed to the inboard platform  24  and includes upper and lower generally planar panels  100  and  102  interconnected by end walls  104  and  106  (end wall  106  is shown in FIG. 1) positioned at the inboard end  108  and outboard end (not shown) of the folding outboard platform  28 , respectively. Referring now to FIG. 3, the end wall  104  lies in a plane substantially orthogonal to the upper and lower panels  100  and  102 , and includes a planar support surface  110  that is adapted to abut against the restraining surface  58  of the inboard platform  24  in the extended position, the restraining surface  58  acting as a limit stop.  
         [0030]    As best shown in FIG. 2, the outboard platform  28  further includes side curbs  112  that extend upwardly from each side of the upper panel  100  and extend longitudinally along its length to a position past the inboard end wall  104 , thereby forming side curb extensions  114 . The side curb extensions  114  include apertures through which the folding outboard platform  28  is pivotally attached by journal members, such as pivot pins  116 , to the outboard end  54  of the inboard platform  24 . Any conventional pivot pin may be used, and thus it will not be described in any more detail. As assembled, the pivot pins  116  extend through inboard platform apertures and the corresponding outboard platform apertures at the inboard end  108  of side curbs  112 , thereby forming the pin assemblies  118 . The pin assemblies  118  pivotally attach the inboard platform  24  to the folding outboard platform  28 . As such, the pivot pins  116  define a horizontal pivot axis of the folding outboard platform  28  with respect to the inboard platform  24 .  
         [0031]    In accordance with another aspect of the present invention, the lift assembly  20  further includes a second redundant support system for providing a safety feature positioned at the connection interface (i.e. pin assemblies  118 ) between the folding outboard platform  28  and the inboard platform  24 . Referring now to FIGS. 4 and 5, the second redundant support system  120  includes metallic bushings  124  fixedly secured the outboard apertures of the inboard platform side curbs  60 . The bushings  124  include a cylindrical bore  126  (see FIG. 5) for receiving the pivot pins  116 , and a semi-circular inward extending flange  130 . As shown in FIG. 4, the open end of the flange  130  faces the inboard end of the inboard platform  24 . Alternatively, the inward extending flange  130  may, for example, extend circumferentially to form a completely circular flange. In either case, the flange  130  includes an inner safety surface  132  for constraining the movement of the folding outboard platform  28  in the event of a failure of pivot pins  116 , the inner safety surface  132  acting as a limit stop.  
         [0032]    Referring now to FIGS. 4 and 5, the redundant support system  120  further includes a cylindrical boss  140  that extends on both sides of the outboard platform side curbs  112 . The boss  140  defines a cylindrical, longitudinally extending bore  142  sized to receive a sleeve bearing  144 , which in turn, includes a bore sized for receiving the pivot pin  116  in rotational engagement. The redundant support system  120  may omit the sleeve bearing  144 , if desired. The outward extending portion  148  of the boss  140  defines an abutment surface  150  along its outer surface. The outer diameter of the portion  148  of boss  140  is sized to seat within the flange  130  so that the abutment surface  150  contacts the safety surface  132  of the flange  130  when assembled.  
         [0033]    Referring now to the operation between the inboard platform  24  and the folding outboard platform  28  of the lift platform, attention is directed again to FIG. 3. In normal operation, the outboard platform  28  pivots about pivot pins  116  from a folded position, wherein the upper surface of the outboard platform  28  is parallel with and opposes the upper surface of the inboard platform  24  in the horizontal orientation, to the extended position, wherein the upper surface of the outboard platform  28  is substantially coplanar with the upper surface of the inboard platform  24 . Upon rotation from the folded position to the extended position, the outboard platform  28  continues to rotate until the support surface  110  of the outboard platform  28  contacts, and thus, is restrained by restraining surface  58  of the inboard platform  24 . In the extended position, the inboard and outboard platform assemblies  24  and  28  form a substantially horizontal lift platform for supporting a passenger between the raised and lowered position.  
         [0034]    When the lift assembly  20  is in the extended position and the lift platform  22  is supporting a passenger, the passenger applies a load thereto. A portion of the load applied thereto is supported by the restraining surface  58  of the inboard platform  24  in conjunction with the pivot pins  116  on its outboard end. Additionally, the passenger load is supported by restraining surface  70  of the mounting structure  32  in conjunction with the pivot pins  72 , as was described above. However, the inner safety surfaces  132  are in a no-load condition in the extended position when the pin assemblies  118  are functioning properly. As such, the rotational and translational movement of the outboard platform  28  is constrained by the contact between the support surface  110  and the restraining surface  58 , and the pivot pins  116 .  
         [0035]    With reference to FIGS.  1 - 5 , one example of the operation of the lift assembly  20  incorporating the first and second redundant support systems  80  and  120  will now be described in detail. The lift assembly  20  begins in the stowed position. In the stowed position, the upper surface of the outboard platform  28  is parallel with and opposes the upper surface of the inboard platform  24 , the inboard platform  24  and outboard platform  28  are nested between and substantially parallel with the vertical support columns  32 , and the redundant support members  82  are received by the limit recesses  84 . When the inboard platform  24  is rotated to the extended position, the inboard platform  24  rotates about a horizontal axis defined by pivot pins  72 . Rotation continues until the support surface  56  of the inboard platform  24  contacts the restraining surface  70  of the mounting structure  32 . In this position, the upper planar surface of the inboard platform  24  is oriented in a substantially horizontal position and will be maintained in a substantially horizontal position throughout the remaining deployment of the lift platform  22  due to the contact between the support surface  56  and the restraining surface  70 . Moreover, the redundant support members  82  are received by the inboard recesses  86 , and the support arms  88  rest against the redundant support members  82 , preferably in a substantially no-load configuration. It should be apparent that the phrase “substantially horizontal position” includes the normal operating range of a lift assembly within the scope of this disclosure. At this stage, the outboard platform  28  has yet to be extended and remains folded, resting upon the inboard platform  24 .  
         [0036]    In continuing the deployment of the lift assembly  20 , the outboard platform  28  is rotated about pivot pins  116 , outward from the inboard platform  24  until the support surface  110  of the outboard platform  28  contacts the restraining surface  58  of the inboard platform  24 , limiting further rotation of the outboard platform  28 . In the extended position, the outboard platform is supported by the restraining surface  58  of the inboard  24 , and the pivot pins  116 . Once in the extended position as described, the lift platform  22  formed by the inboard and outboard platforms  24  and  28  may be lowered by a reciprocating assembly (not shown) to a position below the floor of the vehicle, until the outward edge (not shown) of the outboard platform  28  contacts the ground, curb or the like. In this position, a passenger may traverse onto the lift platform  22 .  
         [0037]    Once the passenger is supported by the lift platform  22 , the drive assembly (not shown) may then be actuated to raise the vertical support columns  32 , and thereby raise the lift platform  22 . Once in the, raised position, the lift platform  22  is level with the floor of the passenger vehicle (not shown). The passenger is then free to deboard the lift platform  22  into the passenger compartment of the vehicle.  
         [0038]    In the event of a failure of one of the pivot pins  72  while the passenger is on the lift platform  22 , the movement of the lift platform  22  is constrained and maintained horizontally by the first redundant support system  80 . Preferably, in the event of a failure of one of the pivot pins  72 , the first redundant support system  80  aids in maintaining the lift, platform at substantially the same elevation of the lift platform prior to the failure of the pivot pin  72 , and substantially parallel with the position of the lift platform just prior to the failure of the pivot pin  72 .  
         [0039]    For the purposes of the detailed description, substantially the same elevation means that a separation distance separating the lift platform prior to the failure of the pivot pin  72  and after the failure of the pivot pin  72  is of a degree that would not reasonably lead to an injury of an occupant of the lift. Similarly, for the purposes of this detailed description, substantially parallel means that a separation angle present between the inclination of the lift platform prior to the failure of the pivot pin  72  and the inclination of the lift platform after the failure of the pivot pin  72  is of a degree that would not reasonably lead to injury to an occupant of the lift platform, such as by causing a wheelchair to roll with sufficient force to overrun the retaining curbs or other such restraints, or cause an impact injury to the user, or that would cause an unreasonable loss of balance to a standing user of the lift.  
         [0040]    The first redundant support system  80  maintains the horizontal orientation of the lift platform  22  in the event of a failure of one of the pivot pins  72  through the redundant support member  82 . More specifically, the support arm  88  of the side curb  60  (on the side of the failed pin) engages the redundant support member  82 , inhibiting further about the restraining surface  70  and/or translation of the inboard platform  24  in a direction outboard of the vehicle. Accordingly, the load previously supported by the failed pin is supported by the redundant support member  82  while maintaining the inboard platform  24  in a horizontal position. Thus, the first redundant support system  80  acts as a redundant support structure, whereby in the event of a failure of one of the load bearing pivot pins  72 , the load associated with the failed pivot pin is transferred to and supported by the redundant support member  82 .  
         [0041]    Additionally, in the event of a failure of one of the pivot pins  116  while the passenger is on the lift platform  22 , the movement of the outboard platform  28  is constrained and maintained at substantially the same elevation and substantially parallel with the position of the lift platform just prior to the failure of the pivot pin  116  by the second redundant support system  120 . Specifically, the abutment surface  150  of boss  140  (on the side of the failed pin) engages with and is restrained by the safety surface  132  of the flange  130 , inhibiting further rotation about the restraining surface  58  and/or translation of the outboard platform  28  in a direction outboard of the vehicle. Accordingly, the load previously supported by the failed pin is supported by the flange  130  while maintaining the outboard platform  28  in a horizontal position. Thus, the second redundant support system  120  acts as a redundant support structure, whereby in the event of a failure of one of the load bearing pivot pins  116 , the load associated with the failed pivot pin is transferred to and supported by the flange  130 .  
         [0042]    Once the passenger has entered the vehicle, the lift assembly  20  is then rotatably transfigured into the stowed position. This is accomplished by rotating the outboard platform  28  about pivot pins  116 , until the upper surface of the outboard platform  28  is parallel with and opposes the upper surface of the inboard platform  24 . The inboard platform  24  and outboard platform  28  are then rotated about the pivot pins  72  until the outboard limit recesses  84  contacts the redundant support member  82 . In this position, the inboard platform  24  and outboard platform  28  are secured by means well know in the art, such as by latches, in their stowed position, nested between and substantially parallel with the vertical support columns  66 .  
         [0043]    While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.  
         [0044]    The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: