Fitting and associated grommet for supporting a conduit penetrating a panel

A fitting and an associated grommet are provided for supporting a conduit penetrating a panel and limiting energy transfer between the conduit and panel. The fitting may include a grommet having annular first and second sections spaced apart from one another and an annular wall extending between the first and second sections such that the wall and first and second sections define a bore. A plurality of ribs protrude from the annular wall, the ribs being distributed circumferentially around the annular wall and spanning between the first and second sections. A tubular liner extends through the bore of the grommet and contacts the first and second sections. The plurality of ribs extend into the bore, and at least some of the ribs contact the liner.

FIELD OF THE INVENTION

Embodiments of the present invention are generally directed to fittings and associated grommets for supporting a conduit penetrating a panel, and, more particularly, to fittings and grommets for limiting thermal and/or noise propagation therethrough.

BACKGROUND OF THE INVENTION

Traditionally, commercial airplanes were constructed with fuselage structures composed mainly of aluminum. These airplanes were often designed such that multiple tubes carrying hydraulic fluid were required to penetrate the fuselage at different points. Often, fittings were included at these penetration points to facilitate passage of the tubes through the fuselage and to provide for proper attachment of the hydraulic tubes to the fuselage structure in a way that restrained tube movement and prevented damage to both the tube and structure. In addition, in cases where the fuselage was pressurized, these fittings were designed to minimize the leakage through the penetration hole of the tube. Finally, the fitting served the additional purpose of facilitating aircraft assembly and servicing by acting as a connector for tubes being connected from outside the fuselage, thereby allowing external portions of the tubes to be connected and disconnected without significant disruption of the fuselage structure.

In more recent times, commercial airplanes in increasing numbers are being designed and constructed with composite fuselage and wing structures, meaning these structures incorporate components of metal and components composed of other materials. Some of the most common non-metallic materials to be used in aircraft construction are polymer-based materials. These materials are relatively inexpensive and lightweight while at the same time providing sufficient strength for many applications, and as such, designers are making significant use of those materials.

While polymer-based materials offer several advantages in aircraft construction, they also create several challenges. Presently, titanium hydraulic system tubes are used to transport hydraulic fluid through polymer-based thermoset composite fuselages. At certain instances, the fluid in these tubes may have operating temperatures high as 275° F. Using standard fittings designed for aluminum fuselages, the penetration of these tubes through the fuselage skin can lead to localized areas near the penetration hole with temperatures elevated to a point where thermoset composite material aging and degradation is a concern. As such, a need in the art for a new fitting that allows tube penetration through a thermoset composite fuselage while avoiding excessive localized heating.

Another challenge presented by the use of polymer-based materials in aircraft construction is the unwanted transmission of vibrational energy. Hydraulic system components, such as motors, pumps, and actuators, tend to vibrate as they operate. These vibrations may be transmitted along the hydraulic tubes leading to and away from the hydraulic components. When the hydraulic tubes pass through and come in contact with the fuselage, some of the vibrational energy may be transmitted to the fuselage. Additionally, because the hydraulic tubes are carrying a fluid, some of the energy associated with the movement of the fluid may be also transmitted to the fuselage. This vibrational energy may cause the fuselage to vibrate and produce noise in the fuselage. In the past, the damping capacity of the aluminum plane structures was sufficient to maintain the vibration-induced fuselage noise at an acceptable level. However, the capacity of composite fuselage structures to dampen mechanical vibrations is less than that of the aluminum structures, mainly due to the characteristics of the materials used in the composite fuselages. Hence, there is a need in the art for a new fitting that will dampen vibrations being transmitted from hydraulic tubes to composite fuselages through which the tubes are penetrating.

SUMMARY OF THE INVENTION

Embodiments of the present invention address at least some of the needs described above while providing still additional advantages. In this regard, a fitting and an associated grommet are provided that effectively limit heat transfer from a conduit that passes through or is other wise attached to the fitting to the surrounding structure. Additionally, a fitting and associated grommet are provided that dampen vibrations from a conduit that passes through or is otherwise attached to the fitting to the surrounding structure.

In one embodiment, a fitting is provided for supporting a conduit penetrating a panel and limiting energy transfer between the conduit and panel. The fitting may include a grommet having annular first and second sections spaced apart from one another and an annular wall extending between the first and second sections such that the wall and first and second sections define a bore. A plurality of ribs protrude from the annular wall. The ribs are distributed circumferentially around the annular wall and span between the first and second sections. A tubular liner extends through the bore of the grommet and contacts the first and second sections. The plurality of ribs extends into the bore, and at least some of the ribs contact the liner.

In another embodiment, an air vehicle is provided that includes a fuselage having a fuselage panel with at least one conduit extending through the fuselage panel and a fitting, such as described above, that is disposed between the fuselage panel and the conduit. A grommet, such as that employed by the aforementioned fitting, is also provided by another aspect of the present invention. As a result of the construction of the grommet and the resulting fitting, the grommet and the resulting fitting may limit thermal transfer and/or vibrations to the surrounding structure, such as the fuselage of an aircraft.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1 and 2, fragmentary views are provided of an air vehicle100, such as an airplane, constructed in accordance with an embodiment of the present invention. The air vehicle100has a fuselage102defined by and constructed of a fuselage panel104. The fuselage panel may be formed of various materials, and in one embodiment the fuselage panel through which the conduit passes may be comprised of composite materials, such as carbon fiber reinforced plastic. A conduit106extends from inside the fuselage102, through the fuselage panel104, to outside the air vehicle. A fitting110is disposed between the fuselage panel104and conduit106, the fitting110acting to support the conduit106.

Referring toFIGS. 3 and 4, therein is shown the fitting110ofFIG. 1, but now without the fuselage panel for the purpose of clarity. Fitting110includes isolator assembly130. Referring toFIGS. 4-7, the isolator assembly includes a pair of bushings132and a grommet134. The grommet134has annular first and second end sections136, with an annular wall138extending between the end sections136. The end sections136and wall138together define a bore140that extends through the grommet. The wall138is typically disposed between the inner and outer perimeters of the end sections136, such that the inner dimensions of each end section is smaller than the inner dimensions of the wall, and the outer dimensions of each end section is greater than the outer dimensions of the wall. A plurality of ribs142protrude from the wall138, the ribs142being distributed circumferentially around the wall138. Typically, the ribs are spaced evenly about the wall, although unequal spacing and/or different rib shapes may be employed if desired. In one example, a cylindrical wall includes 12 ribs spaced every 30 degrees about the circumference of the wall. Each rib142spans the distance between the end sections136and protrudes from the wall138enough to extend into the bore140.

The bushings132may have narrower liner sections144that extend into the bore140defined by the grommet134from opposing directions. The liner sections144mate within the bore140such that the liner sections144form a more or less continuous tubular liner. The bushings132may also have wider portions146that extend from each end of the bore140and abut the first and second end sections136. The bushings132are generally tubular, such that when the bushings132mate, they define a lumen150. The lumen150serves to accommodate a conduit, as discussed below. The wider portions of the bushings may include a lip151that surrounds an end section of the grommet and discourages lateral movement of the grommet.

Bushings132may be comprised of thermoplastic material, such as polyetheretherketone (PEEK), polyamide, or polyimide, which allows the bushings to insulate the threaded pipe. In some embodiments, the bushings are constructed of material or materials with low thermal conductivity and high heat resistance. This allows the bushings to act as intermediaries between any higher temperature bodies and parts, such as a fuselage wall, that are intended to be shielded from elevated temperatures.

Referring toFIG. 8, when the liner sections144of bushings132extend into bore140, some, if not all, of the liner sections144come in contact with ribs142. As such, a series of pockets148are formed circumferentially around the isolator assembly130, each pocket148being defined by adjacent ribs142, the end sections136of the grommet134, the annular wall138, and the liner section144of the bushing132.

Referring again toFIGS. 3 and 4, in addition to the isolator assembly, a fitting can include a conduit, such as threaded pipe112having an abutment114. Threaded pipe112is accommodated in the lumen150of the liner formed by the bushings132. The threaded pipe112could be part of and serve as the conduit106(FIG. 2), could attach to other structures such that the pipe112and other structures together form conduit106, or could further accommodate another conduit therein. A hex nut120is screwed onto the threaded pipe112, thereby containing the isolator assembly between the abutment and nut. In one embodiment, the threaded pipe and nut are made of titanium. The threaded pipe112may extend through titanium exterior washers116, interior washers118, which are also contained by nut and abutment. In one embodiment, the exterior washers are made of titanium and the interior washers are made of a structural composite material rated for use at elevated temperatures.

Referring toFIGS. 2 and 9, fitting110is assembled with fuselage panel104such that panel104is accommodated between the first and second end sections136of the grommet134. Components of fitting110are then distributed somewhat symmetrically on either side of panel104. In one embodiment, bushings132extend from opposing ends of grommet134, and interior and exterior washers116,118sit in series with the grommet134and bushings132. Threaded pipe112extends through the washers116,118and the lumen150defined by the bushings132, such that abutment114contacts an exterior washer118on one side of panel104and threaded pipe112extends beyond the exterior washer118on the opposing side of panel104. Nut120is screwed onto threaded pipe112, and as nut120is screwed down threaded pipe112and contacts exterior washer118, the washers116,118, isolator fitting130, and panel104are all compressed between abutment114and nut120. In this way, the first and second end sections136are compressed against opposing sides of the fuselage panel104, thereby substantially preventing gas from passing between the fitting110and said fuselage panel104. The first and second end sections136may include raised features152configured to enhance the seal with panel104. Bushings may be constructed of a material that also has a high load carrying capacity to help in maintaining the integrity of the bushings as nut120is screwed onto threaded pipe112and isolator fitting130is compressed.

In its assembled state, fitting110, through placement of the grommet134between the conduit106and the fuselage panel104, serves to at least partially isolate the fuselage panel104from both the thermal and mechanical (e.g., vibrational) energy being transmitted along the conduit106. The grommet may include a thin annular wall that is easily deformed. For example, a grommet constructed of ethylene propylene diene monomer rubber may have a wall thickness of 0.20 in. As such, significant deformations of the grommet by the conduit are required to produce non-negligible forces on the panel. Further, the grommet contacts the bushings only at the ribs, and as such, the amount of thermal energy transferred via conduction from the conduit through the bushing to the grommet is reduced. In the areas between the ribs, the grommet and bushing create a series of pockets that trap air and serve to insulate the conduit contained inside the bushing.

In one embodiment, grommet is made of an elastomeric material. Due to the relatively low elastic modulus of this material, its ability to dissipate mechanical energy internally, and its low thermal conductivity, use of an elastomeric material enhances the ability of the grommet to provide mechanical and thermal insulation between the conduit and panel. In a particular embodiment, the grommet is composed of an elastomeric material that is resistant to attack by hydraulic fluid, such as ethylene propylene diene monomer.

Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. For example, while the previous embodiments have pertained to an air vehicle, embodiments of the present invention are applicable to any system in which a panel is penetrated by a body transmitting heat or vibrations, and specifically can be applied to other types of vehicles or structures. Also, in some embodiments, the sections of the grommet that border the annular wall are not end sections, but rather some other sections adjacent to neither or only one end of the grommet. In some embodiments, the ribs of the grommet contact the fuselage panel, thereby establishing a series of air pockets between the grommet and panel that further insulate the panel. In yet other embodiments, the grommet and/or fitting are not round or cylindrical, as shown, but instead are other shapes in cross section (e.g., a square annulus, a triangular annulus, or an irregular annulus), or are only partially annular. Finally, in other embodiments, the components making up the fitting are not distributed symmetrically on either side of the fuselage panel when the fitting and panel are assembled, but are arranged in one of a variety of ways that suit the application.