Abstract:
A counterbalance mechanism for counterbalancing weight of a bottom-hinged door (such as a clamshell-type airstair door of an aircraft) includes an operator handle, a hoist rod pivotally connected at one end to the operator handle and at an opposite end thereof to the door near a bottom region thereof. A force accumulator assembly is provided which includes a force biasing member which accumulates and dissipates a bias force when opening and closing the door, respectively, to provide mechanical counterbalance to the weight of the door. A bellcrank assembly operatively connects the operator handle to the force accumulator. In such a manner, weight counterbalancing of the door is achieved.

Description:
FIELD 
     The embodiments disclosed herein relate generally to counterbalance mechanisms for bottom-hinged doors, especially bottom-hinged clamshell-type aircraft fuselage doors (e.g., airstair doors). 
     BACKGROUND 
     Bottom-hinged, clamshell-type aircraft fuselage doors that integrally include steps to allow passengers to board and disembark when the door is opened are colloquially known as “airstair” doors. Aircraft provided with airstair doors can thus provide service to many less populated airport environments since a fixed-based gantry platform to allow passengers to board and disembark is not necessarily required. For these reasons, many regional transport and general aviation aircraft are equipped with airstair fuselage doors. 
     Since aircraft fuselage doors are bottom hinged, some form of weight counterbalance mechanism is typically required to assist an operator (typically on-board personnel) to open and close the door. Various mechanisms based on hydraulic, electric or spring actuation concepts are therefore known and used in aircraft designs. In the case of hydraulic actuation, for example, systems are known which possess substantial load capacities and relatively simplistic operational modes, including automated push-button door opening and closing. Similar automated operations based on electric motor actuation systems are also known whereby an electrical actuator or motor performs the door movement. However, there are actuation cycle limitations imposed on both hydraulic and electric actuation concepts due to the necessary recharge of hydraulic accumulators and/or on-board batteries that are required for proper operation. In addition, there are substantial space penalties associated with the incorporation of hydraulic and electric door actuation mechanisms that may preclude their being used on certain types of aircraft designs. 
     U.S. Pat. No. 5,704,569 to Daniels (the entire content of which is expressly incorporated hereinto by reference) describes a mechanical counterbalance mechanism for upwardly and inwardly operated aircraft cargo doors. The counterbalance mechanism as disclosed therein includes a guide tube having a rod that extends outwardly therefrom and compression springs which oppose the outward movement of the rod. A linkage system includes a bellcrank and a push rod which connects the guide tube to the cargo door to assert a counterbalancing force during door opening and closing. 
     While the counterbalance mechanism as described in the Daniels &#39;569 patent is suitable for upwardly and inwardly operated cargo doors, it is not conveniently adapted for use with cargo airstair doors. Therefore, there exists continued need for a counterbalancing mechanism that may be employed for bottom-hinged clamshell-type aircraft airstair doors. It is therefore towards providing solutions to such a need that the embodiments of the present invention are directed. 
     SUMMARY 
     The disclosed embodiments herein are directed toward counterbalance mechanisms which, in some embodiments, are especially adapted for counterbalancing bottom-hinged clamshell-type aircraft doors, e.g., airstair doors. 
     According to some disclosed embodiments, counterbalance mechanism for counterbalancing weight of a bottom-hinged door (such as a clamshell-type airstair door of an aircraft) includes an operator handle, a hoist rod pivotally connected at one end to the operator handle and at an opposite end thereof to the door near a bottom region thereof. A force accumulator assembly is provided which includes a force biasing member which accumulates and dissipates a bias force when opening and closing the door, respectively, to provide mechanical counterbalance to the weight of the door. A bellcrank assembly operatively interconnects the operator handle to the force accumulator as an inverse parallelogram linkage. In such a manner, rotational movement of the operator handle in one of counterclockwise and clockwise directions is applied to one end of the bellcrank assembly and is translated into opposite rotational directions of the other end of the bellcrank assembly so as to load and unload spring force on a force biasing member associated with a force accumulator. 
     In some embodiments, the bellcrank assembly will include first, second and third bellcranks, with the first and second bellcranks operatively connected by a linkage arm. Thus, rotational movement of the operator handle in one rotational direction will be transferred to the first bellcrank of the bellcrank assembly and translated into an opposite rotational movement of second and third bellcranks of the bellcrank assembly to thereby cause respective loading or unloading of biasing force of the force biasing member. As such, weight counterbalancing of the door is achieved. 
     According to some embodiments, the biasing member comprises a compression spring. If employed, the compression spring may be mounted between lower and upper spring caps. 
     The force accumulator in certain embodiments may comprise a piston assembly, with a compression spring coaxially surrounding the piston assembly. 
     The bellcrank assembly according to some embodiments may comprise a fixed-position lower bearing block having a lower bearing shaft, wherein an end of each of the operator handle and the first bellcrank is fixed to the lower bearing shaft so the operator handle and the first bellcrank rotate as a unit with one another and with the lower bearing shaft. According to other embodiments, the bellcrank assembly may additionally or alternatively comprise a fixed position upper bearing block having an upper bearing shaft, wherein respective ends of the second and third bellcranks are fixed to the upper bearing shaft so the second and third bellcranks rotate as a unit with one another and with the lower bearing shaft. 
     Aircraft having bottom-hinged clamshell-type airstair doors may be retrofitted by installing a counterbalance mechanism according to the embodiments disclosed herein and thereafter operatively interconnecting the counterbalance mechanism with the door. 
     These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof. 
    
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
       The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative embodiments in conjunction with the drawings of which: 
         FIGS. 1A and 1B  are exterior perspective views of a forward aircraft fuselage showing the airstair door in closed and opened positions, respectively; 
         FIG. 2  is an interior perspective view of an airstair door equipped with a counterbalance mechanism according to an embodiment of the invention in a closed position; 
         FIG. 3  is an enlarged interior perspective view of the counterbalance mechanism in a condition when the airstair door is in a closed position; 
         FIG. 4  is an interior perspective view of an airstair door equipped with a counterbalance mechanism according to an embodiment of the invention in an opened position; and 
         FIG. 5  is an enlarged interior perspective view of the counterbalance mechanism in a condition when the airstair door is in a opened position. 
     
    
    
     DETAILED DESCRIPTION 
     Accompanying  FIGS. 1A and 1B  are exterior perspective views of a forward section of an aircraft fuselage  10  equipped with a bottom-hinged, clamshell-type airstair door  12  shown in closed and opened positions, respectively. As is conventional, the airstair door  12  is equipped with a hinge assembly  14  located at the lower end  12   a  of the door. A series of steps  12   c  are provided between the lower end  12   a  and the upper end  12   b  of the door  12  which allow passengers and crew to board and disembark from the aircraft fuselage  10  when the door  12  is in its opened position (i.e., when the door  12  is pivoted in the direction of the arrow A D  in  FIG. 1A  so the upper end  12   b  of the door  12  is near the ground as depicted in  FIG. 1B ). 
     According to embodiments of the present invention, the airstair door  12  is operatively connected to a counterbalance mechanism  20  as will be described in greater detail with reference to accompanying  FIGS. 2-5 . In this regard, the counterbalance mechanism  20  is depicted in  FIGS. 2-3  with the door  12  in a closed position (i.e., as shown in  FIG. 1A ), while the counterbalance mechanism  20  is depicted in  FIGS. 4-5  with the door  12  in an opened position (i.e., as shown in  FIG. 1B ). 
     The counterbalance mechanism  20  includes an operator handle  22  which operatively connects the counterbalance mechanism  20  to the lower end  12   a  of the door  12  by a hoist rod  24 . In this regard, the hoist rod  24  is pivotally connected at its upper end  24   a  to a connection boss  22   a  of the operator handle  22  located between the handle knob  22   b  at the free end  22   c  of the handle  22  and its opposite fixed end  22   d  thereby establishing an upper hoist rod pivot axis  24 - 1 . The opposite lower end  24   b  of the hoist rod  24  is similarly pivotally connected to the lower end  12   a  of the door  12  to thereby establish a lower hoist rod pivot axis  24 - 2 . 
     A lower bearing block  26  is fixed to the aircraft fuselage frame  10   a  adjacent the doorway entrance  11  (see  FIG. 1B ) and includes a lower bearing block shaft  28  which defines and rotates about a shaft axis  28 - 1 . One end  28   a  of the bearing shaft  28  is fixed to the lower end  22   d  of the handle  22  while the opposite end  28   b  of the bearing shaft  28  is fixed to an end  30   a  of a first bellcrank  30 . The opposite end  30   b  of bellcrank  20  is pivotally connected to one end  40   a  of a link arm  40  so as to be pivotal about a pivot axis  40 - 1 . The opposite end  40   b  of the link arm  40  is pivotally connected to an end  50   a  of a second bellcrank  50  so as to be pivotal about pivot axis  40 - 2 . 
     An upper bearing block  60  is fixed to aircraft fuselage frame  10   a  and includes an upper bearing block shaft  62  which defines and rotates about axis  60 - 1 . The opposite end  50   b  of second bellcrank  50  and an end  70   a  of third bellcrank  70  are fixed to shaft  62  so each of bellcranks  60  and  70  rotate as an integral unit with the shaft  62  about the axis  60 - 1 . The first, second and third bellcranks  30 ,  50  and  70 , respectively, and their associated shafts  28  and  62  are thus connected by the linkage arm  40  to establish an inverse parallelogram linkage mechanism between the operator handle  22  and a force accumulator assembly  80  as will be described in greater detail below. 
     The force accumulator assembly  80  includes a piston assembly  82  having a piston rod  84 . A lower end  82   a  of the piston  82  is pivotally connected to the aircraft fuselage frame  10   a  while an opposite end  82   b  of the piston rod  84  is pivotally connected to end  70   b  of the third bellcrank  70 . The end  82   a  of the piston  82  is thus pivotal about the axis  80 - 1  while the end  82   b  of the piston rod  84  is pivotal about the axis  70 - 1 . A compression spring  86  coaxially surrounds the piston  82  and piston rod  84  and is captured between lower and upper end caps  86   a ,  86   b , respectively. 
     In use during a door opening cycle with the door  12  initially in the closed position as shown in  FIGS. 1A ,  2  and  3 , an operator inside the fuselage  10  may operate the interior door release handle  16  or ground crew outside the aircraft may operate the exterior door release handle  18  so as to release the door and allow it to be pivoted about hinge  14  (arrow A D  in  FIG. 1A ) to its opened position (see  FIG. 1B ). Once the door  12  has been released, the operator inside the fuselage  10  will then apply a generally downward counterclockwise force (as viewed from the right in  FIGS. 2 and 3 ) on the handle  22  which will urge the door  12  to pivot about the hinge  14  by virtue of the hoist rod  24  being connected between the handle  22  and the door  12 . This counterclockwise movement of the handle  22  will be translated into concurrent counterclockwise movement of the first bellcrank  30  about the axis  28 - 1  due to the fixed connection of the handle  22  and bellcrank  30  to bearing shaft  28  at their respective ends  22   d  and  30   a.    
     The counterclockwise pivotal movement of the bellcrank  30  will in turn cause the second and third bellcranks  50 ,  70 , respectively to pivot as a unit with the bearing shaft  62  in a clockwise direction about the shaft axis  60 - 1  (as viewed from the right of  FIGS. 2 and 3 ) by virtue of the operative connection between the bellcranks  30  and  50  provide by link arm  40  (i.e., since the structures collectively form an inverse parallelogram linkage mechanism). The clockwise movement of the third bellcrank  70  will thus retract the piston arm  84  of the accumulator  80  against the force of the compression spring  86 . Thus, as the door  12  pivots about the axis  14 - 1  (see  FIG. 2 ) in the direction of arrow A D  (see  FIG. 1A ), its weight and the force of gravity will be counterbalanced by the continual loading of spring force provided by the compression spring  86  thereby providing a continual mechanical counterbalance against such door weight. 
     The closure cycle of the door  12  when in the opened position as shown in  FIGS. 1B ,  4  and  5  is reverse to that described above. That is, with particular reference to  FIGS. 4 and 5 , an operator will manually apply a generally upward clockwise rotational force (as viewed from the right of  FIGS. 4 and 5 ) to the handle  22  thereby provide a lifting force to the door by virtue of the hoist rod  24  being connected to the door  12 . This movement of the handle  22  will in turn cause the bearing shaft  28  and the first bellcrank  30  to rotate in a clockwise direction thereby urging the bellcranks  50  and  70  to rotate as a unit with the shaft  62  in a counterclockwise direction by virtue of the link arm  40  being connected pivotally between the bellcranks  30  and  50  (i.e., since the structures collectively form an inverse parallelogram linkage mechanism). The counterclockwise movement of the third bellcrank  70  will thus cause the piston rod  84  to extend thereby unloading or dissipating the spring force that had previously been accumulated or loaded by the compression spring  86  during the door opening cycle of operation. The spring force of the compression spring  86  will thus provide force assistance as a mechanical counterbalance during the pivotal movement of the door  12  from its closed position to its open position (i.e., in a direction opposite to arrow A D  in  FIG. 1A ). 
     Those skilled in this art will appreciate that various equivalent modifications and/or alterations may be made to the embodiment described above. For example, a tension spring or other similar biasing mechanisms may be employed instead of the compression spring  86  described previously, in which case the structures could be modified to accumulate the biasing force of such devices to yield similar and substantially equivalent functional effects to those described previously. 
     Therefore, while the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.