Pressure-augmented kiss seal

Abstract: A kiss seal (42) of C-shaped cross section is provided. The kiss seal (42) includes a first leg (54), a second leg (56), and an arcuate middle portion (46) extending therebetween. The first leg (54) includes a contact surface (24') positioned adjacent a separable flange (28). The second leg (56) is attached to an opposed attachment flange (18) using a face plate (20') and a number of screws (22). The second leg (56) is generally located directly beneath the first leg (54). During sealing use, the arcuate middle portion (46) extends greater-than-180 degrees and is located outboard of one or both flange outboard edges (31). This provides a resultant force vector (58) that acts to enhance sealing. The greater the pressure (P) on the arcuate middle portion (46), the greater the force vector components available to promote sealing.

Description: Field of the Invention The present invention relates to pressure seals, and in particular, to kiss seals used in maintaining an air-tight junction between opposed flange surfaces in an aircraft. Background of the Invention Numerous types of seals have been designed for use on aircraft to seal against gas leakage at junctions formed between connecting ducts, access panels, or the like. These seals are generally termed "kiss" seals because there are located between flanges that are positioned "face-to-face". Conventionally, a kiss seal is secured to one of the flanges and is pressed against the other flange. Pressurized gas inside the duct produces an outward force, against the membrane of the kiss seal. The function of the seal is to prohibit gas leakage at the unsecured flange. A known kiss seal assembly is based on a typical prior art Z-type kiss seal or Z seal. This known kiss seal assembly, an example of which is shown in figures 4A-4C, comprises: a) a first flange having an outboard edge; b) a second flange positioned opposite said first flange and having an outboard edge and c) a kiss seal located between the first and second flanges and comprising a flexible membrane cross-sectionally Z-shaped in its uncompressed state, said flexible membrane having a first leg, a second leg and a middle portion extending therebetween, the first leg being positioned adjacent said first flange, the second leg being attached to said second flange and the upon compression of the seal when moving the first and second flanges together middle portion, extending outboard of at least one of the first and second flange outboard edges. Known kiss seals suffer from a number of design problems, the most significant of which is how to design a kiss seal that will not leak. If leakage is allowed to occur and continue, in many applications the related structure will vibrate and, as a result, cause failure of the seal, the flanges, or both. To form a tight seal between the kiss seal and adjacent flange surfaces, current designs rely primarily on the seal membrane material stiffness to maintain contact with the flanges. Stiff materials require a large amount of force to mate with the flanges, particularly if the seal is large. More flexible materials result in a poor seal. The overall shape of a kiss seal also effects its capacity to form a tight bond. During use, linear portions in the seal planform shape will experience longitudinal twisting. This motion can result in flow leakage. Small openings with circular planforms are therefore most desirable, while large openings with rectangular planforms are cast desirable. In addition, high temperature and high pressure environments, such as within aircraft engines, are further impediments to good seal performance. Engine duct environments often reach temperatures of 150°C (300°F) and pressures of 100 kPa (15 psig). In addition to the above concern, a designer must also consider the range of flange-to-flange distances, called flange gaps, that must be accommodated during use. Each kiss seal has a range of compression heights, called its sealing range, within which the seal will be effective. The design goal is to provide a kiss seal with a sealing range that matches the range of anticipated flange gaps. If the expected flange gap range is wide, the sealing range of the kiss seal must be correspondingly wide. If the flange gap is too wide, leakage will occur. The opposite extreme is called bottoming out. Bottoming out occurs when a kiss seal is compressed beyond its design limits. When a kiss seal bottoms out, the seal buckles and folds over onto itself. In aircraft applications, inflight flange motion and assembly tolerances can be quite large, making it particularly important for kiss seals on aircraft to perform well over a wide range of flange gaps. Therefore, a need exists for a superior kiss seal for use in aircraft applications. The ideal kiss seal should have good sealing capability over a wide range of flange gaps and should require very low compression force to create a seal. The ideal kiss seal should also be able to compress to a small height without bottoming out. The present invention is directed to fulfilling this need. Summary of the Invention In accordance with the present invention, a new and improved kiss seal assembly suitable for use in pressurized ducts and the like is provided. The kiss seal assembly of the invention according to claim 1 comprises: a) a first flange having an outboard edge; b) a second flange positioned opposite said first flange and having an outboard edge and c) a kiss seal located between the first and second flanges and comprising a flexible membrane cross-sectionally C-shaped in its uncompressed state, said flexible membrane having a first leg, a second leg and an arcuate middle portion extending therebetween, the first leg being positioned adjacent said first flange, the second leg being attached to said second flange, and the arcuate middle portion, upon compression of the seal when moving the first and second flanges together, extending outboard of at least one of the first and second flange outboard edges to form a bulbous protrusion. Since the bulbous protrusion extends outwardly from at least one of the flanges vibration-induced wear between the seal and that flange is prevented. The pressure inside of the bulbous protrusion produces a force that counteracts the pressure forces attempting to move the kiss seal away from the unsecured flange. Preferred embodiments of the kiss seal assembly of the invention form the subject matter of the dependent claims. Brief Description of the Drawings The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: Figure 1 is a perspective view of a jet aircraft engine in which kiss seals are used; Figure 2 is a perspective view of the outer cowl of the engine of Figure 1; Figure 3 is a perspective view of a kiss seal suitable for use in the engine cowl shown in figure 2; Figure 4A is a cross-sectional side view of a prior art Z seal assembly with the Z seal in an uncompressed state; Figure 4B is a cross-sectional side view of the Z seal assembly of Figure 4A at a maximum compression height; Figure 4C is a cross-sectional side view of the Z seal assembly of Figure 4A at a minimum compression height; Figure 5A is a cross-sectional side view of a kiss seal assembly formed in accordance with the present invention with the kiss seal in an uncompressed state; Figure 5B is a cross-sectional side view of the kiss seal assembly of Figure 5A at a maximum compression height; Figure 5C is a cross-sectional side view of the kiss seal assembly of Figure 5A at a minimum compression height; and Figure 6 is a cross-sectional side view of a kiss seal assembly formed in accordance with the present invention including flanges that extend outboard by unequal amounts. Detailed Description of the Preferred Embodiment Prior to describing the present invention and in order to better understand the use and benefits of the invention, a brief description of one use of the invention is provided followed by a brief description of a prior art kiss seal assembly. In this regard, figure 1 illustrates a conventional turbofan jet engine 9. Located on opposed sides of the engine 9 are outer cowls 3. The interior of one of the outer cowls 3 is shown in figure 2. Figure 3 is an enlarged perspective view of the kiss seal 1 shown in figure 2. The outer cowls 3 are moved to their closed position shown in figure 1 by being rotated inward about an upper longitudinal hinge lines 5. After being closed, each outer cowl is secured along a lower edge 6 to fasteners located at the bottom of the engine. As shown best in figure 3, a kiss seal 1 is attached to a flange 4 located in the interior surface of an outer cowl 3. As the outer cowl 3 is closed, the unsecured kiss seal surface 7 presses against a flange (not shown) formed in the engine casing. This causes the kiss seal 1 to compress. Pressure P inside of the duct 2 exerts an outward force on the kiss seal 1. The purpose of the kiss seal is to maintain contact between its unsecured surface 7 and the engine flange to prevent duct gases from leaking out of the duct 2 and into the region between the outer cowl 3 and the engine. Existing kiss seals designed for use in aircraft engines of the type shown in figure 1 are not as satisfactory as currently designed. A typical prior art Z-type kiss seal 10 (or "Z seal", for short) is shown in figures 4A-4C. Figure 4A shows the Z seal uncompressed, i.e., prior to when the Z seal contacts the engine flange; figure 4B shows the Z seal 10 partially compressed; and figure 4C shows the Z seal fully compressed. Referring to figures 4A-4C, a typical Z seal 10 includes a fiber-reinforced elastomer membrane 11 having a zig-zag cross-sectional shape. The zig-zag shape includes a diagonal leg 12 that extends between a first leg 14 and a second leg 16. The first and second legs 14, 16 lie generally parallel to and aligned with one another when the Z seal is uncompressed (figure 4A). As noted above and shown in figures 1-3, one of the kiss seal surfaces is clamped or otherwise secured to a flange. This flange is referred to herein as the "attachment flange 18." As shown in figures 4A-4C, the second leg 16 of the Z seal 10 is attached to the attachment flange 18. The attachment is accomplished by securing the second leg 16 between the attachment flange 18 and a face plate 20 using a number of screws 22. As also noted above and shown in figures 1-3, the other surface of the kiss seal contacts a flange that approaches the kiss seal during closure. This flange is referred to herein as the "separable flange 28." The separable flange 28 includes a wear plate 26 on its outer surface that makes contact with the kiss seal. Further, the outer surface of the first leg 14 of the Z seal, i.e., the leg that makes contact with the separable flange 28, is covered with a thin contact material, preferably a thin layer of metal coated with Teflon ™. Referring to figure 4B, during closure, after the wear plate 26 contacts the contact surface 24, the Z seal 10 must be compressed to a certain height before it will provide a seal against leakage during pressure loading. This height is the seal's maximum compression height 30. At heights above this maximum 30, the seal will leak. The value of the maximum compression height for kiss seals in general depends on a number of factors, including membrane stiffness, applied pressure, seal geometry, planform geometry, etc. Still referring to figure 4B, at the Z seal maximum compression height 30, the part of the diagonal leg 12 that is initially nearest the first leg 14 typically folds over onto the first leg 14, while the part of the diagonal leg 12 initially nearest the second leg 16 becomes outwardly arcuate. The tendency to form an arcuate or curved shape is due to the pressure P in the duct. The curved part of the diagonal leg 12 occasionally extends a slight distance outward past the outboard edges 31 of the attachment flange 18. The inventor has discovered that when the forces produced by the duct pressure acting on the diagonal leg 12 during sealing are summed, they produce a Z seal resultant force vector 34 that is directed substantially horizontally outward. The resultant force vector 34 causes a moment M about the outboard seal corner 36 of the first leg 14. This, in turn, causes the first leg 14 to rotate slightly away from the wear plate 26. As viewed in figure 4B, the direction of rotation is counterclockwise. As a result, a slight open wedge 38 is formed between the contact surface 24 and the wear plate 26. When the resultant force vector is resolved into orthogonal and parallel components, the orthogonal force component is approximately zero and the parallel force component is relatively high. (The terms "orthogonal" and "parallel" are relative to the plane of the separable flange 28.) As is apparent from viewing figure 4B, substantially all of the resultant force is resolved into a parallel force. Further, the direction of the force is outward, i.e., away from the duct. The lack of an appreciable orthogonal force reduces the sealing capacity of a Z seal. The inventor has verified, using finite element analysis and lab testing, that even moderate pressure amounts can easily leak past a Z seal of the type shown in Figures 4A-4C. The results of the inventor's investigations show that the sealing capacity of Z seals is only moderately effective within a very small range of compression heights. Referring to figure 4C, a Z seal's absolute minimum compression height 40 is the height at which the Z seal can no longer deform uniformly, and after which the Z seal will buckle or crease. (The term "absolute" refers to the seal itself, without the presence of duct pressure P, since pressure actually helps the seal maintain an unfailed form.) The sealing range within which the Z seal is useful lies between its minimum and maximum compression heights 30, 40. As can be seen from viewing figures 4B and 4C and as confirmed by tests, the Z seal's sealing range is relatively small. Referring to figures 5A-5C, a kiss seal assembly formed in accordance with the present invention comprises a kiss seal 42 (also called herein a "C-type kiss seal" or "C seal" for short) generally including a membrane 44 that begins as cross-sectionally C-shaped and later achieves an outboard bulbous shape during sealing use. By "bulbous" what is meant is that the membrane 44 (as viewed cross-sectionally) defines an arc of greater-than-180 degrees for a near constant radius. As shown in the embodiment of figures 5A-5C, the C-shaped membrane 44 includes a first leg 54, a second leg 56, and an arcuate middle leg 46 extending therebetween and outboard of both flanges 18, 28. The first leg 54 includes an exterior contact surface 24' that faces the separable flange 28 during sealing use. As before, the contact surface 24' may be a thin layer of Teflon -coated metal. The second leg 56 is connected to the attachment flange 18, preferably using a face plate 20' similar to that used with a Z seal. In general, the second leg 56 is aligned with the first leg 54. Figures 5A, 5B and 5C show a kiss seal assembly formed in accordance with the invention with the kiss seal in an uncompressed state, at a maximum compression height, and at a substantially minimal compression height, respectively. In the uncompressed state of figure 5A, the membrane 44 has a definite curve, but is not yet a bulbous protrusion. Referring to figure 5B, just as with a Z seal, a C seal 42 formed in accordance with the invention must be compressed to a certain maximum compression height 30' before effective sealing begins. At heights above the maximum compression height 30', pressure P inside of the duct will push gas between the first leg 54 of the C seal and the separable flange 28. At the maximum compression height, the arcuate middle leg 46 of the membrane 44 begins to take on a bulbous shape by extending in an arc of at least 180 degrees. When the forces acting on a C seal at its maximum compression height 30' are summed, they produce a resultant force vector 58 that lies substantially parallel to the surface of the separable flange 28, i.e., they produce a force vector having a very small orthogonal component, This resultant force vector 58 causes a moment M' about the outboard corner 36' of the separable flange 28. As with the Z seal, this moment M' causes the contact surface 24' of the C seal to rotate slightly away from the wear plate 26. As a result, an open wedge 38' is formed between the contact surface 24' and the wear plate 26. As the C seal is compressed further, the orthogonal component of the resultant force vector 58 increases as shown clearly in figure 5C. Because the attachment flange 18 is approximately as wide as the separable flange 28 and because the flanges are in line with one another as the membrane 44 is compressed, the arcuate middle leg 46 takes on such a bulbous configuration. This shape is in contrast to a Z seal, which does not have a bulbous portion, but instead starts to fold and eventually buckle. The increased orthogonal component of the C seal pushes the first leg 54 toward the wear plate 26. The increased orthogonal component also results in a reduced outward parallel component which in turn reduces the moment M' about the outboard corner 36'. The greater the pressure P on the arcuate middle leg 46, the greater the opposing force vector. This feature can be defined as pressure-augmentation or a self-sealing mechanism, since sealing contact is proportionally related to the applied pressure P. An added benefit of the C seal can be seen in figure 5C. Specifically, the C seal membrane does not fold between the flanges. Therefore, the C seal minimum compression height is the sum of the thicknesses of the upper and lower legs 54, 56 (plus any clamping plates 20') of the C seal membrane. This further increases in the sealing range of a C seal as compared to a Z seal. The moment arm of the C seal moment M' is also reduced which further reduces the value of the C seal moment M'. Figure 6 illustrates a C seal formed in accordance with the invention for use in an environment where the attachment flange 18' extends further outboard than the separable flange 28. In this case, the bulbous protrusion is not uniform with respect to both flanges. However, the resistive characteristics of the resultant vector 58 remains the same (i.e., a larger orthogonal component, a smaller parallel component, and a reduced moment arm.) Preferred embodiments of the present invention have bulbous shapes that extend past the outboard edge 31 of either the separable flange 28 alone (as shown in figure 6) or both the separable flange 28 and the attachment flange 18 (as shown in figure 5C). The bulbous shape may be made to extend past the outboard edge of the attachment flange 18 alone, but this is not a preferred embodiment. During sealing use, contact between the attachment flange 18 and the membrane is acceptable, since the two surfaces are fastened together to prevent vibration-induced wear between the second leg 56 and the attachment flange 18. However, contact between the separable flange 28 and the membrane should be avoided, because vibration-induced wear is likely to occur between these two unsecured surfaces. Therefore, in order to have effective sealing characteristics while maintaining good wear characteristics, the bulbous shape should extend at least beyond the separable flange 28. As will be appreciated from the foregoing, the length to the arcuate middle leg 46 of the membrane 44 of a C-type kiss seal formed in accordance with the invention must be adequate to develop a bulbous protrusion having a greater-than-180 degree arc when in use. This means that the length of the arcuate middle leg, in general, must be at least ½ n times the flange gap distance at the maximum compression height. In addition, since pressure is used as the sealing mechanism rather than material flexure, the seal can be made arbitrarily soft in compression without sacrificing seal performance. This allows for easy door closure, even for very large or oddly-shaped seal planforms.

Claims: A kiss seal assembly comprising: a) a first flange (28) having an outboard edge (31); b) a second flange (18;18') positioned opposite said first flange (28) and having an outboard edge (31;31') and c) a kiss seal located between the first and second flanges (28,18;28,18') and comprising a flexible membrane (44) cross-sectionally C-shaped in its uncompressed state, said flexible membrane (44) having a first leg (54), a second leg (56) and an arcuate middle portion (46) extending therebetween, the first leg (54) being positioned adjacent said first flange (28), the second leg (56) being attached to said second flange (18;18'), and the arcuate middle portion (46), upon compression of the seal when moving the first and second flanges (28,18;28,18') together, extending outboard of at least one of the first and second flange outboard edges (31;31') to form a bulbous protrusion. The kiss seal assembly of claim 1, characterized in that upon compression of the seal, when moving the first and second flanges (28,18;28,18') together, the arcuate middle portion (46) is formed in a bulbous arc of greater than 180 degrees positioned outboard of the outboard edge (31) of said first flange (28). The kiss seal assembly of claim 1 or 2, characterized in that upon compression of the seal, when moving the first and second flanges (28,18;28,18') together, the arcuate middle portion is formed in a bulbous arc of greater than 180 degrees positioned outboard of the outboard edges (31) of both flanges (18,28). The kiss seal assembly of any one of the preceding claims, characterized in that at a maximum compression height (30') the bulbous arcuate middle portion (46) is formed as a semicircle. The kiss seal assembly of any one of claims 1-3, characterized in that at a maximum compression height the arcuate middle portion (46) is formed as a bulbous arc of greater than 180 degrees for a single radius. The kiss seal assembly of claim 4 or 5, characterized in that the arcuate middle portion (46) has a length equal to or greater than ½π times the distance between the first and second flanges (28,18;28,18') when the kiss seal is positioned at its maximum compression height.

Inventors: KOCH WILLIAM J, KOCH, WILLIAM J.
Applicants: BOEING CO, THE BOEING COMPANY
Application year: 1997
Main classification: F16J3
IPC codes: F16J3