Abstract:
A protective structure for a vehicle having an opening on an upper surface is provided. One embodiment of the invention has at least a partial enclosure around an area defined laterally by the vehicle opening with an overhead and side protective capability. An embodiment of the invention has an overhead cover that is formed to substantially enclose a top area of the enclosure and having multiple panels that may be locked into place or opened by an occupant for exit through a top area of the enclosure. Biasing devices may be provided to bias the panels toward an open position and thereby facilitate occupant egress. The multiple panels in this embodiment extend upwardly and inwardly from a section of the enclosure&#39;s side walls. Ballistic windows are provided on the protective structure such that an occupant can view laterally and vertically through the enclosure and overhead cover. A shield or protective plate can be mounted on one side of the enclosure.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 12/844,899, filed Jul. 28, 2010 now U.S. Pat. No. 8,146,480, which is a continuation of U.S. patent application Ser. No. 11/998,977, filed Nov. 10, 2007 now U.S. Pat. No. 7,823,498, the disclosures of which are expressly incorporated by reference herein. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the United States Government for any governmental purpose without payment of any royalties thereon. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to protective structures. In particular, the invention relates to protective structures used for protection against projectiles. 
     BACKGROUND OF THE INVENTION 
     The invention relates to protective structures. There is a significant need for the invention as there are no protective structures available or known which provide the features and benefits of the invention. 
     SUMMARY OF THE INVENTION 
     The invention relates to protective structures. The invention relates to protective structures adapted to protect against projective weapons or fragments that in one embodiment is mounted to a vehicle to enclose at least part of an area that a weapons or apparatus operator occupies. Embodiments of the invention have an upper portion which has protective overhead segments that can be locked and positioned such that an occupant of the protective structure have overhead protection as well as the ability to exit from the protective structure by positioning the segments to permit exit or entry from the top area of the protective structure. In certain illustrative embodiments, biasing devices are provided to bias segments toward open positions and thereby facilitate occupant egress. The structure may include a latching mechanism for at least two of the overhead protective segments which are adapted to withstand an impact from projectiles or fragments from bomb blasts. The protective structure has ballistic window placed around the structure, including the overhead protective segments which permit viewing through the windows and protection against expected projectiles or fragments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
         FIG. 1  is a side view of a vehicle with an embodiment of the invention mounted thereon; 
         FIG. 2  is a top view of the vehicle of  FIG. 1  without the an embodiment of the invention mounted thereon; 
         FIG. 3  is a perspective view of one embodiment of a vehicle protective structure; 
         FIGS. 4A ,  4 B,  4 C  4 D and  4 E are top, front, curb side, driver side and rear views, respectively, of the structure of  FIG. 3 , without the shield; 
         FIGS. 5A and 5B  are perspective and top views, respectively, of an embodiment of a first portion of a vehicle protective structure; 
         FIGS. 6A , B, C, D, E and F are perspective, top, sectional, curb side, rear and driver side views of an embodiment of a second portion of a vehicle protective structure.  FIG. 6C  is a sectional view along the line  6 C- 6 C of  FIG. 6E ; 
         FIGS. 7A and 7B  are perspective views of one type of ballistic windows; 
         FIGS. 8A , B, C, D, E, F, and G are perspective, top, bottom, curb side, front, driver side, and rear views, respectively, of an embodiment of an third portion of a vehicle protective structure; 
         FIG. 9  is an enlarged view of a portion of  FIG. 8C ; 
         FIGS. 10A ,  10 B, and  10 C are front, top and curb side views, respectively, of  FIG. 3 ; 
         FIG. 11  is a perspective view of an illustrative third portion of a vehicle protective structure; 
         FIG. 12  is an enlarged view of a portion of  FIG. 11 , showing an illustrative biasing device; 
         FIG. 13A  is a top perspective view, in partial section, of the third portion of  FIG. 11 , showing the driver side and curb side doors in closed positions; 
         FIG. 13B  is an enlarged view of a portion of  FIG. 13A , showing details of the door locking device; 
         FIG. 14A  is a top perspective view, in partial section, of the third portion similar to  FIG. 13A , showing the curb side door in a first open position; 
         FIG. 14B  is an enlarged view of a portion of  FIG. 14A , showing details of the door locking device; 
         FIG. 15A  is a top perspective view, in partial section, of the third portion similar to  FIG. 13A , showing the curb side door in a second open position; 
         FIG. 15B  is an enlarged view of a portion of  FIG. 15A , showing details of the door locking device; 
         FIG. 16A  is a top perspective view, in partial section, of the third portion similar to  FIG. 13A , showing the curb side door in a third or fully open position; 
         FIG. 16B  is an enlarged view of a portion of  FIG. 16A , showing details of the door locking device; 
         FIG. 17  is a diagram illustrating spring torque as a function of door displacement; and 
         FIG. 18  is a bottom perspective view of the third portion of  FIG. 11 , showing the movable top frame in a closed position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a side view of a vehicle  10  with one embodiment of a vehicle protective structure  12  mounted thereon.  FIG. 2  is a top view of the vehicle  10  of  FIG. 1  without the structure  12  mounted thereon. Structure  12  includes a first (lower) portion  14 , a second (intermediate or wall) portion  16  and a third (upper) portion  18 . The first portion  14  is fixed to a turret (traversal portion)  22  ( FIG. 2 ) on an upper section  15  of the vehicle  10  and disposed around an opening  24  ( FIG. 2 ). More particularly, the upper section  15  defines a plane  17  through which the opening  24  extends. The turret  22  is configured for rotation about a rotational axis  19  extending through the opening  24  substantially perpendicular to the plane  17 . The second portion  16  is fixed to the first portion  14  and includes a plurality of windows disposed substantially vertically around the opening  24 . As further detailed herein, the second portion  16  at least partially encloses a perimeter of a space extending generally above the opening  24 . 
     Windows used in these embodiments of the invention are ballistic windows. Ballistic windows are components that are capable of stopping bullets or projectiles, including bomb or explosive fragments, fired at it and can be made of impact resistant materials including materials known as bullet-resistant glass or ballistic windows. The term “bullet” is meant to be used broadly in this case referring to ballistic or high velocity projectiles or weapons, including fragmentary devices and explosives or explosively formed projectiles, which are fired at or in the direction of the window(s) in question. Bullet-resistant glass is frequently constructed using a strong but transparent material such as polycarbonate thermoplastic or by using layers of laminated glass. One desired result is a material with an appearance and light-transmitting behavior of standard glass but offers varying degrees of protection from projectile weapons depending on the weight, configuration and weight requirements or limitations. A polycarbonate layer, including products such as Cyrolon®, Lexan® and Tuffak®, is sometimes sandwiched between layers of regular glass. The use of plastic in the laminate provides impact-resistance, such as physical assault with a hammer, an axe, etc. The plastic provides little in the way of bullet-resistance. The glass, which is much harder than plastic, flattens the bullet and thereby prevents penetration. Ballistic windows, ballistic glass, impact resistant glass or bullet-resistant glass can be 70-75 mm (2.8-3.0 in) thick, but could be more or less depending on the threat or weapons the windows are designed to defeat. Bullet-resistant glass includes glass constructed of laminated glass layers built from glass sheets bonded together with polyvinyl butyral or polyurethane. The glass can include one-way bullet-resistant glass as well as newer types of bullet-resistant glass or transparent materials such as aluminum oxynitride used as the outside “strike plate” layer. 
     The third portion  18  is fixed to the second portion  16  and extends upwardly and inwardly from the second portion  16  over the opening  24 . The third portion  18  includes a plurality of windows. A shield  28  may be disposed in front of the first, second and third portions  14 ,  16 ,  18 . In the case of armed conflict, foreign internal defensive operations or riot control engagements, structure  12  can protect a weapons operator or gunner  26  ( FIG. 1 ) who operates a weapon, illustratively a gun  20  or other device such as a water cannon, high intensity laser or other anti-personnel or non-lethal personnel weapon system. The gunner or protective structure occupant  26  is located in the opening  24 . However, structure  12  can protect individuals other than a gunner  26 , for example, an observer. Structure  12  can also be used to protect or mount a sensor system or other items of equipment requiring protection and impact resistant windows standing alone or in combination with a weapons system or other anti-personnel or riot control system. 
       FIG. 3  is a perspective view of the vehicle protective structure  12  without the vehicle  10 .  FIGS. 4A ,  4 B,  4 C  4 D and  4 E are top, front, curb side, driver side and rear views, respectively, of the structure  12  of  FIG. 3 , without the shield  28 . As best seen in  FIGS. 3 and 4A , the first, second and third portions  14 ,  16 ,  18  define a front opening  42 . The gun  20  ( FIG. 1 ) is disposed in the front opening  42  and the shield  28  ( FIG. 3 ) is mounted adjacent the front opening  42 . 
     In the embodiment shown in  FIGS. 4A-4E , second portion  16  includes windows  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144 . Window  130  is the front curb side window; window  132  is the second curb side window; window  134  is the rear curb side window; window  136  is the right rear window; window  138  is the left rear window; window  140  is the rear driver side window, window  142  is the second driver side window; and window  144  is the front driver side window. 
     The windows  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144  of the second portion  16  are substantially planar (not curved) and may be rectangular in shape. Second portion  16  may have eight windows as shown, but more or fewer windows may be used. 
     The eight windows  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144  may be the same size and, additionally, may be the same type of window (i.e., interchangeable) as the windows  36  in the doors of the vehicle  10  of  FIG. 1 . “Same type” of window means the windows have substantially the same size and shape and are interchangeable without any modifications. One or more of the windows  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142  and  144  may be hinged. In  FIGS. 4A-4E , the front driver side and curb side windows  144 ,  130  are shown mounted with hinges  40 A to the second portion  16 . Hinges  40 A allow windows  144 ,  130  to rotate outward and rearward. 
     Third portion  18  may have seven windows  146 ,  148 ,  150 ,  152 ,  154 ,  156 ,  158  as shown, but more or fewer windows may be used. Window  146  is the front curb side window; window  148  is the rear curb side window; window  150  is the right rear window; window  152  is the left rear window; window  154  is the rear driver side window; window  156  is the front driver side window; and window  158  is the top window. Windows  146 ,  148 ,  150 ,  152 ,  154 ,  156  and  158  may be substantially planar. 
     The windows  148 ,  158 ,  154  may be the same type of window (i.e., interchangeable) as the windows  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144  of the second portion  16  and the windows  36  of the vehicle doors. Windows  148 ,  158  and  154  may be rectangular. Windows  146 ,  150 ,  152 ,  156  may be trapezoidal in shape and be the same type of window (i.e., interchangeable) as the window  38  in the door of vehicle  10  ( FIG. 1 ). Top window  158  ( FIG. 4A ) may be mounted with a hinge  40 B so that window  158  may rotate upwardly and rearwardly. 
     Front and rear driver side windows  156 ,  154  ( FIG. 4C ) may be mounted to the second portion  16  as a single unit using hinge  40 C. Thus, front and rear driver side windows  156 ,  154  may rotate outwardly and downwardly as a single unit. Front and rear curb side windows  146 ,  148  ( FIG. 4D ) may be similarly mounted using a hinge  40 C to thereby rotate outwardly and downwardly as a single unit. The front driver and curb side windows  156 ,  146  may be the same type of window as window  38  in the door of vehicle  10  ( FIG. 1 ), that is, substantially trapezoidal. The rear driver and curb side windows  154 ,  148  may be the same type of window as window  36  in the door of vehicle  10  ( FIG. 1 ), that is, substantially rectangular. 
     Third portion  18  may include right rear and left rear windows  150 ,  152 . The two rear windows  150 ,  152  may be the same type of window as window  38  in the door of vehicle  10  ( FIG. 1 ), that is, substantially trapezoidal. 
       FIGS. 5A and 5B  are perspective and top views, respectively, of one embodiment of a first portion  14  of the vehicle protective structure  12 . The bolt holes  44  in the first portion  14  form a pattern that may be the same pattern as the bolt hole pattern in both the second portion  16  ( FIG. 6B ) and the third portion  18  ( FIG. 8C ). First portion  14  includes a pair of mounting brackets  46  and a rear bolt weldment  48  for fixing the first portion  14  to a vehicle, such as vehicle  10 . 
       FIGS. 6A , B, C, D, E and F are perspective, top, sectional, curb side, rear and driver side views of an embodiment of a second portion  16  of a vehicle protective structure  12 .  FIG. 6C  is a sectional view along the line  6 C- 6 C of  FIG. 6E . The windows  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144  of the second portion  16  are not shown in  FIGS. 6A-6F . However, the window openings in second portion  16  for windows  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142  and  144  are labeled with the corresponding window reference numeral for clarity. 
     Referring to  FIGS. 6A and 6F , the front driver side window  144 , the second driver side window  142 , and the rear driver side window  140  are mounted to a first side frame  160 . Referring to  FIGS. 6A and 6D , the front curb side window  130 , the second curb side window  132 , and the rear curb side window  134  are mounted to a second side frame  162 . The rear windows  136  and  138  are mounted to an end frame  164 , wherein the end frame  164  is connected between the first side frame  160  and the second side frame  162 . 
     The gun  20  ( FIG. 1 ) fits in front opening  42  ( FIGS. 6A , B, C). Front opening  42  provides for about 60 degrees of horizontal gun rotation, that is, about 30 degrees each side of the center position. Thus, the first, second and third portions  14 ,  16 ,  18  provide about 300 degrees of protective to the gunner. The pattern of the bolt holes  50  ( FIG. 6B ) may be the same as the pattern of the bolt holes  44  in the first portion  14  ( FIG. 5A ) and the pattern of the bolt holes  52  in the third portion  18  ( FIG. 8C ). 
       FIG. 7A  shows a rectangular ballistic window  36  (see also  FIG. 1 ) that includes a frame  56  and a flange  58 . Windows  36  may be used for windows  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144  of the second portion  16 . Flange  58  may be bolted to second portion  16  so that each window is positioned in a corresponding window opening. The front driver side and front curb side windows  144 ,  130  (see also  FIGS. 4D and 4C ), rather than being bolted to the second portion  16 , may be mounted on a hinge  40 A. A manually operated opening and closing device  60  ( FIG. 6B ) (details not shown) may be provided for rotating the front driver side and front curb side windows  144 ,  130  outwardly. In certain embodiments, each opening and closing device  60  may include a latching device for securing the window  144 ,  130  in a desired (e.g., closed) position, and a biasing device for biasing the window  144 ,  130  toward an open position. 
       FIGS. 8A , B, C, D, E, F, and G are perspective, top, bottom, curb side, front, driver side, and rear views, respectively, of an embodiment of a third portion  18  of a vehicle protective structure  12 . The windows  146 ,  148 ,  150 ,  152 ,  154 ,  156 ,  158  of the third portion  18  are not shown in  FIGS. 8A-8G . However, the window openings in third portion  18  for windows  146 ,  148 ,  150 ,  152 ,  154 ,  156 ,  158  are labeled with the corresponding window reference numeral for clarity. Ballistic window  36  of  FIG. 7A  may be used for windows  148 ,  158 ,  154 .  FIG. 7B  shows a ballistic window  38  (see also  FIG. 1 ) having a frame  34  and a flange  32 . Ballistic window  38  may be used for windows  150 ,  152 ,  156 . Flange  32  may be bolted to third portion  18  so that each window is positioned in a corresponding window opening. 
     Referring to  FIGS. 8F and 8D , the front and rear driver side windows  156 ,  154  and the front and rear curb side windows  146 ,  148  are fixed to respective frames  66 ,  64 ,  70 ,  68 . Frame  64  is fixed to a hinge  40 C, and frame  66  is fixed to frame  64  to define a first movable frame  166 , such that windows  156 ,  154  may be rotated outwardly and downwardly as a single unit. Similarly, frame  68  is fixed to a hinge  40 C, and frame  70  is fixed to frame  68  to define a second movable frame  168 , such that windows  146 ,  148  may be rotated outwardly and downwardly. Movable frames  166  and  168  are slanted (extend upwardly and inwardly from the second portion  16 ) toward the opening  24  to reduce the potential for blockage by the vehicle during an accident (e.g., rollover). Additionally, movable frames  166  and  168  may each be operably coupled to a biasing device (e.g., spring) for biasing the frame  166 ,  168  toward an open position to facilitate quick egress by a vehicle occupant. 
     Referring to  FIG. 8B , frame  72  for window  158  may be fixed to third portion  18  with a hinge  40  such that window  158  may be rotated upwardly and rearwardly. To secure top window  158 , driver side windows  156 ,  154  and curb side windows  146 ,  148  in a closed position, flanges or bosses  74  ( FIG. 9 ) are fixed to frames  72 ,  68  and  64 . Frame  72  has two bosses  74  and frames  68 ,  64  have one boss each. Each boss  74  includes an opening therein for receiving a quick release pin  76 . Thus, the opening in boss  74  of frame  68  is aligned with the opening in one of the bosses  74  of frame  72  and pin  76  is inserted therein. Similarly, the opening in boss  74  of frame  64  is aligned with the opening in the other of the bosses  74  of frame  72  and pin  76  is inserted therein. To rotate the top window  158  and the side windows  156 ,  154  and  146 ,  148 , the quick release pins  76  are removed from the openings in the bosses  74 . Pins  76  may be attached to lanyards to prevent misplacing them. 
     Referring to  FIG. 8A , upper opening  78  in third portion  18  may be closed with an elastic net  80  shown in  FIG. 10B . 
     Referring to  FIG. 8C , the pattern of the bolt holes  52  ( FIG. 8C ) may be the same as the pattern of the bolt holes  44  in the first portion  14  ( FIG. 5A ) and the pattern of the bolt holes  50  in the second portion  16  ( FIG. 6B ). In one embodiment, the second portion  16  is fixed to the first portion  14  using threaded fasteners all having the same size head and the third portion  18  is fixed to the second portion  16  using threaded fasteners all having the same size head as the fasteners used to fix the second portion  16  to the first portion  14 . In some embodiments of the invention, the second portion  16  is not used and the third portion  18  is fixed directly to the first portion  14 . In other embodiments of the invention, the second portion  16  is fixed to the first portion  14  and the third portion  18  is not included. 
     Third portion  18  may include one or more handles  30  ( FIGS. 4A and 4B ). 
       FIGS. 10A ,  10 B, and  10 C are front, top and curb side views, respectively, of  FIG. 3 . Shield  28  may be fixed to a pintle (not shown) that is used to mount the gun  20  ( FIG. 1 ). Shield  28  includes a front portion  92  and right and left side portions  84 ,  86  that extend rearwardly from the front portion  92 . Front portion  92  includes at least one ballistic window  82  and an elongated opening or slot  88  for receiving the barrel  21  of gun  20  ( FIG. 1 ). The transverse extent “h” ( FIG. 10B ) of the shield  28  is greater than the transverse extent “m” of the front opening  42 . Front portion  92  may include a top plate  90  that extends above the opening  88 . 
     Projectile resistant armor (e.g., steel) and ballistic glass may be used to fabricate vehicle protective structure  12 . 
     With reference to  FIG. 11 , a further illustrative third portion  218  is shown for use with vehicle  10 . The third portion  218  may be operably coupled to the vehicle  10  with or without second portion  16  and/or first portion  14  in a manner similar to that detailed above with respect to third portion  18 . A turret (traversal portion)  22  may be operably coupled to the third portion  218  to rotate the third portion  218  about the axis  19  of vehicle opening  24 . 
     The third portion  218  illustratively includes a plurality of ballistic windows including a front curb side window  220 , a rear curb side window  222 , a rear window  224 , a rear driver side window  226 , a front driver side window  228 , and a top window  230 . Illustratively, the windows  220 ,  222 ,  224 ,  226 ,  228 , and  230  are all substantially planar. Additionally, the windows  220 ,  222 ,  224 ,  226 ,  228 , and  230  all illustratively have the ballistic characteristics of windows  146 ,  148 ,  150 ,  152 ,  154 ,  156 , and  158  of third portion  18  as further detailed above. 
     The third portion  218  illustratively includes a first or driver side frame  232  configured to support the rear driver side window  226 , and a second or curb side frame  234  configured to support the rear curb side window  222 . An end frame  236  extends between the first and second side frames  232  and  234  and is configured to support the rear window  224 . A first or driver side movable frame (door)  238  is pivotally coupled to the first side frame  232  through a hinge  240 A. Similarly, a second or curb side movable frame (door)  242  is pivotably coupled to the second side frame  234  through a hinge  240 B. A receiving space  244  is defined between the side frames  232  and  234  and extends along a longitudinal axis  245  above the vehicle opening  24 . 
     The hinge  240 A illustratively provides for pivoting movement of the first door  238  relative to the first side frame  232  (as shown by arc α in  FIG. 11 ) between a closed position and a plurality of open positions. More particularly, the first door  238  is illustratively configured to move in a counterclockwise direction successively from the closed position ( FIG. 13A ) (inward from the first side frame  232  toward the longitudinal axis  245  of the receiving space  244 ), to a first open position (outward from the first side frame  232  away from longitudinal axis  245  of the receiving space  244 ), to a second open position, and to a third or fully open position. Similarly, the second door  242  is illustratively supported by the hinge  240 B for pivoting movement relative to the second side frame  234  (as shown by arc α in  FIG. 11 ) between a closed position and a plurality of open positions. More particularly, the second door  242  is illustratively supported for movement in a clockwise direction from the closed position ( FIG. 13A ) (inward from the second side frame toward the longitudinal axis  245  of the receiving space  244 ), to a first open position ( FIG. 14A ) (outward from the second side frame  232  away from the longitudinal axis  245  of the receiving space  244 ), to a second open position ( FIG. 15A ), and to a third or fully open position ( FIG. 16A ). 
     A protective cover  247  may be supported by an upper portion of each door  238  and  242 . Each cover  247  is illustratively formed of armored plate and meets along a vertical plane parallel to the axis  245 . 
     With reference to  FIG. 12 , each hinge  240  illustratively includes a pivot pin or rod  246  supported for rotation between upper and lower supports or bosses  247 A and  247 B. Each boss  247  is secured to respective frame  232 ,  234  and may support a bearing  248  receiving the pivot rod  246 . Swing arms  249 A,  249 B couple upper and lower portions of the pivot rod  246  to respective door  238 ,  242 . 
     A first biasing device  250 A is operably coupled to the hinge  240 A of the first door  238  and is configured to bias the first door  238  from the closed position toward the first open position. Similarly, a second biasing device  250 B is operably coupled to the hinge  240 B of the second door  242  and is configured to bias the second door  242  from the closed position toward the first open position. With further reference to  FIG. 12 , each biasing device  250  illustratively comprises a torsion spring  252  received over the pivot rod  246  of respective hinge  240 , and operably coupled intermediate the door  238 ,  242  and respective frame  232 ,  234 . 
     The torsion spring  252  is configured to operate in different modes depending upon the relative position of the door  238 ,  242  relative to the side frame  232 ,  234 . While reference in the following description may be directed to the second door  242  and associated biasing device  250 B, it should be understood that the first door  238  and associated biasing device  250 A operate in a similar manner (except for pivoting in an opposite direction (i.e., counterclockwise direction as opposed to clockwise direction from the closed position)). 
     With further reference to  FIG. 12 , the torsion spring  252  illustratively includes a plurality of active coils  254  extending between retaining tabs  256  and  258  supported at opposing ends. The upper tab  256  is received within a retainer  260  coupled to frame  232 ,  234 , while the lower tab  258  is coupled to respective door  238 ,  242  by a fastener  262  received within swing arm  249 B. The fastener  262  and/or swing arm  249 B may be removed to facilitate replacement of the spring  252 . 
     The torsion spring  252  is designed to permit the door  238 ,  242  to open automatically (i.e., “pop open”), even when the vehicle  10  is supported on its opposing side. In other words, the torque generated by the spring  252  is sufficient to move the door  238 ,  242 , without manual force being applied by the operator, from its closed position to its first open position. In the illustrated embodiment, the spring  252  is configured to provide a spring torque having a value of “+A,” wherein “+A” is equal to 900 lb.-in. when the door  238 ,  242  is in the closed position. 
     With reference to  FIGS. 13A and 13B , a first door locking device  270 A is operably coupled to the first door  238  and is configured to secure the first door  238  in a selected one of the closed, first open, second open, and third open positions. Similarly, a second door locking device  270 B is operably coupled to the second door  242  and is configured to selectively secure the second door  242  in a selected one of the plurality of positions. Illustratively, each door locking device  270  comprises a rotatable index member  272  operably coupled to the door  238 ,  242  and configured to rotate about the pivot rod  246  of hinge  240 . A plurality of circumferentially spaced recesses  274 A,  274 B,  274 C,  274 D are formed within the outer periphery  276  of the index member  272  and are associated with the rotational positions of the door  238 ,  242 . A pin  278  is configured to be releasably received within a selected one of the recesses  274  of the index member  272  to lock the door  238 ,  242  in the desired position. The pin  278  may be spring biased toward the index member  272  and released by the operation of a pull handle  280 . 
     In certain illustrative embodiments, the pull handle  280  may require combined twisting and pulling motions to release the pin  278 . In certain other illustrative embodiments, an explosive may be used to forcibly uncouple the pin  278  (e.g., through fragmentation of the pin  278 ), in the case of emergency egress. Fragmentation of the pin  278  helps prevent potential jamming of the locking device  270  and door  238 ,  242  in a closed position due to vehicle impact. 
     With reference now to  FIGS. 13A-17 , operation of the doors  238 ,  242  will be further detailed. While in the following description the operation of the second door  242  will be used for illustrative purposes, it should be appreciated that the first door  238  operates in a similar manner (except for pivoting in an opposite direction (i.e., counterclockwise direction as opposed to clockwise direction from the closed position)). 
     In  FIGS. 13A and 13B , the curb side door  242  is shown in a closed position. In this position, the pin  278  of locking device  270 B is secured within a first recess  274 A of index member  272  to prevent movement of the door  242 . The dimensions and relative positioning of the pin  278  within the recess  274 A is configured to prevent inadvertent or undesired opening of the door  242  due to an impact or an explosive blast. As illustrated in  FIG. 17 , the torsion spring  252  of the biasing device  250 B in the closed position provides a clockwise torque (having a value of “+A” due to the deflection of the torsion spring  252  in a counter-clockwise direction from its relaxed position (illustratively 135 degrees from the second open position as further detailed herein). Upon releasing the pin  278  of the locking device  270 , the “+A” torque provided by the torsion spring  252  will cause the door  242  to swing open without further operator assistance. As such, a spring load mode is defined intermediate the closed position of  FIGS. 13A and 13B  and the first open position of  FIGS. 14A and 14B . 
     With reference to  FIGS. 14A and 14B , the curb side door  242  is shown in a first open position, illustratively 60° counter-clockwise from the closed position. In this position, the pin  278  of locking device  270 B is secured within a second recess  274 B of the index member  272  to prevent movement of the door  242 . As shown in  FIG. 17 , the torsion spring  252  of the biasing device  250 B in the first open position provides a reduced clockwise torque (having a value of “+B”) compared to that in the closed position. More particularly, intermediate the first open position and the second open position of the door  242 , the spring  252  defines a spring assist mode. In the spring assist mode, the spring  252  provides torque to assist the operator in moving the door  242 , but not sufficient torque to move the door  242  without additional external force from the operator. 
       FIGS. 15A and 15B  illustrate the curb side door  242  in a second open position, illustratively 135° counter-clockwise from the closed position. In this position, the pin  278  of locking device  270 B is secured within a third recess  274 C of the index member  272  to prevent movement of the door  242 . As illustrated in  FIG. 17 , the torsion spring  252  of the biasing device  250 B in the second open position is in a relaxed state (i.e., provides no torque to the door  242 ). 
       FIGS. 16A and 16B  illustrate a third or fully open position. In this position, the pin  278  of locking device  270 B is secured within a fourth recess  274 D of the index member  272  to prevent movement of the door  242 . As shown in  FIG. 17 , the torsion spring  252  of the biasing device  250 B in the third open position provides a reduced counter-clockwise torque (having a value of “−C”) compared to that in the closed position. More particularly, intermediate the second open position and the third open position of the door  242 , the spring  252  defines a spring resist mode. In the spring resist mode, the spring  252  provides counter-clockwise torque to resist the operator from moving the door  242  in a clockwise direction from the second open position toward the third open position. 
       FIGS. 11 and 17  illustrate a top frame  282  supporting the top window  230 . The top frame  282  is supported for sliding movement within a plane substantially parallel to plane  17  (e.g., substantially horizontal) between a closed position, an intermediate position, and a fully opened position. A pair of linear slides  284  facilitates sliding movement of the top frame  282 . Each linear slide  284  illustratively includes a stationary rail  286  and a carriage  288  operably coupled to the rail  286  for linear movement therealong. Each stationary rail  286  is fixed to one of the side frames  232 ,  234 , while the carriages  288  are fixed to the top frame  282 . Bearing members, such as ball bearings (not shown) may be positioned intermediate the stationary rail  286  and the carriage  288  to facilitate relative movement therebetween. 
     A locking device  290  is operably coupled to the linear slide  284  and is configured to secure the top frame  282  in a selected one of the closed, intermediate, and fully opened positions. The locking device  290  illustratively includes a spring biased pin (not shown) configured to engage recesses in one of the carriages  288  of the linear slide  284 . A pull handle  292  may be coupled to the pin for releasing the pin from the selected recess in the linear slide  284 . 
     While the invention has been described with reference to certain preferred embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.