Force-balancing mechanisms especially useful for assisted lifting/lowering of aircraft stairs

The disclosed embodiments herein are generally directed toward force-balancing mechanisms for weighted members and/or loads. According to one embodiment, the force-balancing mechanism includes at least one gear rack, at least one spring assembly comprising a spring member operatively connected to the at least one gear rack, a pinion gear intermeshed with the at least one gear rack; and a variable radius cam. Rotation of the cam causes the pinion gear to rotate to thereby in turn linearly drive the at least one gear rack and accumulate spring force of the spring member. The spring member may be a compression or a tension spring. Preferably, the spring member is a compression spring.

FIELD

The embodiments disclosed herein relate generally to force-balancing mechanisms for weighted members and/or loads. In especially preferred embodiments, force-balancing mechanisms are provided that are usefully employed for the force-assisted lifting/lowering of aircraft stairs.

BACKGROUND

Integrated aircraft stairs to allow passengers to board and disembark when the aircraft fuselage door is opened are colloquially known as “airstairs”. Aircraft which include airstairs 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 airstairs as the primary means to allow boarding and disembarking of passenger and aircraft crew members.

In general, most conventional force-balancing mechanisms for airstairs use space-saving torsional bars to accumulate weight energy and power sufficient to provide lift assistance. In this regard, such conventional airstairs will typically employ an actuator/gearbox, which are interconnected by a torsion bar. When the torsion bars are twisted, a large load is accumulated at the ends of the torsion bars which over time results in fatigue failure. When failure occurs, the airstairs may become inoperable resulting in aircraft downtime to allow for repair. As a result, conventional force-balancing mechanisms for airstairs are somewhat problematic due to this continued potential maintenance issue.

What has been needed therefore are space-saving force-balancing mechanisms for loads that are more durable, especially force-balancing mechanisms for loads associated with airstairs for aircraft. It is towards fulfilling such needs for force-balancing mechanisms that the embodiments as disclosed herein are provided.

SUMMARY

The disclosed embodiments herein are generally directed toward force-balancing mechanisms for weighted members and/or loads. According to one embodiment, the force-balancing mechanism comprises at least one gear rack, at least one spring assembly comprising a spring member operatively connected to the at least one gear rack, a pinion gear intermeshed with the at least one gear rack; and a variable radius cam. Rotation of the cam causes the pinion gear to rotate to thereby in turn linearly drive the at least one gear rack and accumulate spring force of the spring member. The spring member may be a compression or a tension spring. Preferably, the spring member is a compression spring.

According to some embodiments the force-balancing mechanism may include a pair of gear racks each intermeshed with the pinion gear, and a pair of spring assemblies. The pair of spring assemblies may be arranged parallel to one another or may be arranged opposite to one another.

The spring assembly may include spaced-apart fixed and moveable end supports between which the spring member is positioned. According to some embodiments, the fixed end support is positioned proximal to the pinion gear and wherein the moveable end support is positioned distal to the pinion gear. A connection rod may be provided to connect the moveable end support to an end of the at least one gear rack. According to other embodiments, the fixed end support is positioned distal to the pinion gear and wherein the moveable end support is positioned proximal to the pinion gear. In such embodiments, the moveable end support may be connected directly to an end of the at least one gear rack.

A flexible actuator cable having one end fixed to a terminal lobe of the cam, and an opposite end for fixed connection to supporting structure (e.g., to aircraft structure supporting an airstair).

The force-balancing mechanism may be usefully employed to force-balance virtually any moveable weighted member or load. In preferred embodiments, the weighted member is an aircraft airstair. Thus, in accordance with other embodiments, the force-balancing mechanism is provided in an aircraft airstair.

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.

DETAILED DESCRIPTION

AccompanyingFIGS. 1A and 1Bare exterior perspective views of a forward section of an aircraft fuselage10equipped with a fuselage opening12and a conventional door14to close the opening12. A foldable airstair18is provided in the opening12and is equipped with a force-balancing mechanism20according to one embodiment of the present invention.

AccompanyingFIGS. 2-3depict the airstair18in greater detail in stowed and deployed conditions, respectively. In this regard, it will be observed that the airstair is provided with respective upper and lower (relative to airstair deployment) airstair sections18-1,18-2, respectively, connected together at hinge point22to allow relative hinged articulation therebetween. An upper end of the upper section18-1includes an attachment bracket24which is connected to a fixed base26for pivotal movements about a generally horizontal pivot axis. The base26is rigidly connected to supporting structure10-1associated with the aircraft fuselage10. A ground-engaging section18-3is pivotally hinged to the lower free end of the lower airstair section18-2at hinge connection25so as to be pivotal between a stowed condition (seeFIG. 2) and a deployed condition (seeFIG. 3). Wheels27are provided with the section18-3so as to engage the ground G when the airstair18is fully deployed. The airstair sections18-1,18-2and18-3are provided with stair treads18-4to allow passengers and crew members to board and disembark when the airstair18is in a deployed condition.

The force-balancing mechanism20employed in the airstair18is depicted in greater detail in accompanyingFIGS. 4A and 4B. In this regard, the force-balancing mechanism20is depicted byFIGS. 4A and 4Bin a common orientation so that the structural positioning of the various components in force-unloaded and force-loaded conditions corresponding to the airstair stowed and deployed conditions, respectively, can be readily discerned. Thus, it will be understood that when in the force-unloaded condition depicted byFIG. 4A, the force-balancing mechanism20will be in a position with the airstair18as depicted byFIG. 2, whereas when in the force-loaded condition depicted byFIG. 4B, the force-balancing mechanism will be in a position with the airstair18as depicted inFIG. 3.

The embodiment of the force-balancing mechanism20depicted inFIGS. 4A and 4Bis generally comprised of a pair of parallel helical compression spring assemblies30,32which include helical compression springs30-1,32-1coupled operatively to rack gears30-2,32-2, respectively. More specifically, each of the springs30-1,32-1is mounted between fixed and moveable end supports30-3a,32-3aand30-3b,32-3b,respectively. The fixed end supports30-3a,32-3aare thus immovably fixed to structure associated with the upper airstair section18-1(a portion of which is shown inFIGS. 4A and 4B), while the movable end supports30-3b,32-3bare fixed to and moveable with the rack gears30-2,32-2, respectively. It will be observed in this regard that the moveable end support30-3bis connected directly to an end of the rack gear30-2whereas the moveable end support32-3bis connected to the rack gear32-2by way of an elongate connection rod33.

The rack gears30-2,32-2are meshed with a pinion gear34which is mounted to the pinion axle36for rotational movement about the axis thereof. A continually variable radius (“nautilus-type”) cam38is also connected to the pinion axle36so as to be rotatable as a unit with the pinion gear34about the axis of the pinion axle36(i.e. as shown by arrow A1inFIG. 2). The profile of the nautilus-type cam38is such that a different radius is presented at successive different degrees of rotation thereof to provide moment arms of varying lengths as the cam38is rotated about the axis of the axle36.

As is perhaps best shown inFIGS. 2 and 3, a flexible actuator cable40is provided with one end pivotally connected to the fixed base26and an opposite end connected to the terminal lobe38-1of cam38. Thus, as the upper airstair section18-1pivots from its stowed position to a deployed condition, the actuator cable40will cause the cam38, and hence the pinion gear36, to rotate in the direction of arrow A1. Rotation of the pinion gear36will in turn cause the rack gears30-2,32-2to move linearly in the direction of arrows A2and A3as shown inFIG. 4Athereby compressing each of the compression springs30-1and32-1, respectively. Thus, as the upper airstair section18-1pivots from its stowed position to a deployed condition, the force-balance mechanism20will translate from its force-unloaded condition as shown inFIG. 4A(i.e., whereby the compression springs30-1,32-1have minimal if any stored compression force) to a force-loaded condition as shown inFIG. 4B(i.e., whereby the compression springs30-1,32-1have substantial or maximum stored compression force). The loaded compression force that is accumulated when the upper airstair section18-1is in its deployed condition may thereby be used to provide force-assisted movement back to the stowed condition from the deployed condition thereof (i.e., when the cam40is rotated in a direction opposite to arrow A1).

AccompanyingFIGS. 5-9depict other embodiments of force-balancing mechanisms according to the invention. In this regard, although not depicted inFIGS. 5-9, the embodiments shown will include a continually variable radius (“nautilus-type”) cam of the type shown, for example by reference numeral38inFIGS. 4A and 4Bwhich is connected to the pinion axle36so as to be rotatable as a unit with the pinion gear34about the axis of the pinion axle36. Thus, such a cam38will similarly be connected to a fixed base structure26via an actuator cable40or like mechanisms as described previously.

The force-balancing mechanism50depicted byFIG. 5is a variant of the dual spring assembly mechanism20described above. Specifically, it will be observed that the mechanism48, like the mechanism20, has dual compression spring assemblies50,52. However, unlike the mechanism20, the mechanism48is arranged so that the compression spring assemblies50,52are opposite to one another. Thus, the spring assemblies52include helical compression springs50-1,52-1coupled operatively to rack gears50-2,52-2, respectively. More specifically, each of the springs50-1,52-1is mounted between fixed and moveable end supports50-3a,52-3aand50-3b,52-3b,respectively. The fixed end supports50-3a,52-3aare thus immovably fixed to structure associated with the upper airstair section18-1(a portion of which is shown inFIG. 5) at a position proximal to the pinion gear36, while the movable end supports50-3b,52-3bare fixed to and moveable with the rack gears50-2,52-2, respectively, at a position distal to the pinion gear36. It will be observed in this regard that the moveable end supports50-3b,52-3bare connected to an end of the rack gears50-2,52-2by way of an elongate connection rod50-4,52-4, respectively.

Rotation of the pinion gear38in the manner described above during pivotal movement of the upper airstair section18-1into the deployed condition thereof will thus linearly drive each of the rack gears50-2and52-2in the direction of arrows A2and A3thereby causing the springs50-1,52-1to be compressed. As such, the force-balancing mechanism48is caused to assume a force-loaded condition so that the accumulated spring force is available to assist when the upper airstair section is moved back into its stowed condition.

FIG. 6depicts a variant of the embodiment shown inFIG. 5whereby similar structural elements are noted by a prime (′) symbol. As shown, the embodiment ofFIG. 6includes fixed position end supports50-3a′,52-3a′ which are distal to the pinion gear38and moveable end supports50-3b′,52-3b′ that are proximal to the pinion gear38(i.e., generally opposite to the embodiment shown byFIG. 5). The moveable end supports50-3b′,52-3b′ are moreover fixed directly to an end of the rack gears50-2′,52-2′ (thereby avoiding the need for the connection rods50-4,52-4of the embodiment shown byFIG. 5). In a similar manner, however, during pivotal movement of the upper airstair section18-1into the deployed condition thereof, each of the rack gears50-2′ and52-2′ will be driven linearly in the direction of arrows A2and A3thereby causing the springs50-1′,52-1′ to be compressed. As such, the force-balancing mechanism48′ is caused to assume a force-loaded condition so that the accumulated spring force is available to assist when the upper airstair section is moved back into its stowed condition.

Single compression spring embodiments of the force-balancing mechanisms are shown inFIGS. 7 and 8and may be used in those instances where lighter duty requirements are needed (i.e., thereby avoiding the weight penalty of a second compression spring and its associated components while yet still providing for sufficient force assistance). More specifically, the force balancing mechanism60as shown inFIG. 7includes a single compression spring60-1mounted between a fixed end support62connected to the upper airstair section18-1at a position proximal to the pinion gear36, and a moveable end support64positioned distal to the pinion gear36. The moveable end support64is connected to the gear rack66by way of a connection rod65. Rotation of the pinion gear36during movement of the upper airstair section18-1from its stowed condition to the deployed condition will therefore effect force-loading in a similar manner to that described above in connection with spring assembly52ofFIG. 5.

The force balancing mechanism60′ as shown inFIG. 8includes a single compression spring60-1′ mounted between a fixed end support62′ connected to the upper airstair section18-1at a position distal to the pinion gear36, and a moveable end support64′ positioned proximal to the pinion gear36. The moveable end support64′ is directly connected to an end of the gear rack66′ (thereby avoiding the need of the connection rod65as shown inFIG. 7). Rotation of the pinion gear36during movement of the upper airstair section18-1from its stowed condition to the deployed condition will therefore effect force-loading in a similar manner to that described above in connection with spring assembly52′ ofFIG. 6.

It will be appreciated that the force-balancing mechanisms in accordance with the various embodiments have been described in connection with an especially preferred end-use application, that is as a force-balancing mechanism for aircraft airstairs. However, the force-balancing mechanisms as described herein could also be suitable used for virtually any purpose where mechanical lift and/or deployment force-assistance is desired for virtually any weighted member, for example, doors, hatches, gantry platforms, overhead stairs and the like. Thus, the use of the force-balancing mechanisms for assisting in the stowage/deployment of airstairs as described herein is understood to be a presently preferred, but non-limiting, embodiment thereof.

Furthermore, it is currently envisioned that compression springs are preferred. However, those skilled in this art could envision modifications which employ tension springs in which case such modifications are entirely within the scope of the embodiments as described herein.