Clearance floating anchor nut

A floating anchor nut configured to receive a bolt is described. The floating anchor nut comprises a plate having a bolt aperture and retention features for retaining a nut. The floating anchor nut additionally comprises the nut that itself comprises an internally threaded body and a flange extending from an outer surface of the body, the nut being retained through interaction of the flange with the retention features, the retention features allow limited parallel displacement with respect to a plane of the plate. The flange is positioned along the body so that at least a portion of the body is counter-sunk into the bolt aperture of the plate.

FOREIGN PRIORITY

This application claims priority to European Patent Application No. 17193348.4 filed Sep. 26, 2017, the entire contents of which is incorporated herein by reference.

FIELD

The present disclosure relates to a floating anchor nut and to a fastener assembly comprising the floating anchor nut with improved blindside clearance.

BACKGROUND

Floating anchor nuts are often used with bolts in fastening situations where access to the nut is impaired. In particular, they can be useful to clamp two components together with a pre-set tensile loading while accounting for some misalignment in the components due to manufacturer's tolerances.

Floating anchor nuts are used in the production of aircrafts, particularly in gas turbine engines, where it is not uncommon to find many hundreds of floating anchor nuts being used.

The currently available floating anchor nuts can be difficult to use in situations where there is limited blindside clearance. In worse case scenarios, the bolt can impinge part of a component lying behind the floating anchor nut.

SUMMARY

According to a first aspect, the present disclosure can be seen to provide a floating anchor nut which is configured to receive a bolt. The floating anchor nut comprises: a plate and a nut. The plate has a bolt aperture and retention features for retaining the nut. The nut comprises an internally threaded body and a flange extending from an outer surface of the body. The nut is retained through interaction of the flange with the retention features, the retention features allow for limited parallel displacement with respect to a plane of the plate. The flange is positioned along the body so that at least a portion of the body is counter-sunk into the bolt aperture of the plate.

In addition to the features described above, the body of the nut may be generally cylindrical and the bolt aperture may be a circular aperture having a diameter larger than the diameter of the body. The nut may be displaceable within an annular region of clearance in the bolt aperture. Optionally the body may project through the bolt aperture to protrude through the plane of the plate.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the flange may be positioned at a distal end of the body such that the body of the nut has a single portion extending between the flange and a proximal end of the body.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the flange is provided partway along the body such that a distal end portion of the body protrudes from one side of the flange and a proximal end portion of the body protrudes from the other side of the flange. The flange may be provided less than halfway along the length of the body from the distal end. For example, the flange may be provided around a third of the way along the length of the body from the distal end.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the internal thread of the body in the distal end portion may be deformed. For example, the internal thread of the body in the distal end portion may be ovalised.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the plate may have a first retention feature and a second retention feature arranged on opposite sides of the bolt aperture that interact with the flange.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the plate may have a first opening and a second opening each configured to receive a fastener. The first opening may have a first lip and the second opening may have second lip. Alternatively or additionally, the flange may have a first recess and a second recess, the first recess being configured to provide room for a fastener received in the first opening and/or the first lip and the second recess being configured to provide room for a fastener received in the second opening and/or the second lip.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the flange may extend circumferentially around the outer surface of the body.

According to a second aspect, the present disclosure can be seen to provide a fastener assembly comprising a bolt having a threaded shaft and a floating anchor nut in accordance with any one of the foregoing statements.

According to a third aspect, the present disclosure can be seen to provide an assembly comprising a first component, a second component, the floating anchor nut accordance with any one of the foregoing statements and a bolt having a threaded shaft. The first component has a first hole extending therethrough. The second component is arranged adjacent to the first component and has a second hole extending therethrough. The first and second components are arranged such the first hole is adjacent to and aligned with the second hole. The plate of the floating anchor nut is fastened to the second component such that the bolt aperture is aligned with the second hole. A portion of the body of the nut extends through the bolt aperture. The threaded shaft of the bolt extends through the first and second holes and is received in the internally threaded body, whereby the first component and the second component are fastened together.

In addition to one or more features described above, or as an alternative to any of the foregoing embodiments, the second component may include a counter-bore (48) aligned with the second hole. The plate may be fastened to the second component such that the bolt aperture is aligned with the counter-bore. A portion of the body of the nut may then protrude through the bolt aperture to be accommodated in the counter-bore.

In addition to one or more features described above, or as an alternative to any of the foregoing embodiments, the threaded shaft may extend through the body and may protrude by at least two full thread pitches beyond the body.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the assembly may be an air cooled oil cooler assembly of a gas turbine engine.

According to a fourth aspect, the present disclosure can be seen to provide a gas turbine engine comprising the floating anchor nut in accordance with any one of the foregoing statements relating to the first aspect, a fastener assembly in accordance with any of the foregoing statements relating to the second aspect, or an assembly in accordance with any of the foregoing statements relating to the third aspect.

According to a fifth aspect, the present disclosure can be seen to provide a method of joining a first component having a first hole extending therethrough to a second component having a second hole extending therethrough. The method comprises the steps of attaching the floating anchor nut in accordance with any one of the foregoing statements relating to the first aspect to the second component by fastening the plate to the second component, wherein a portion of the body of the nut extends through the bolt aperture, aligning the first component with the second component passing a threaded shaft of a bolt through the first hole, through the second hole and into engagement with a proximal end of the nut, and tightening the bolt to a predetermined tensile load to fasten the first component to the second component.

In addition to one or more features described above, or as an alternative to any of the foregoing embodiments, the method may include providing a counter-bore in the second component aligned with the second hole. The attaching of the floating anchor nut may comprise fastening the plate to the second component so that the portion of the body of the nut protrudes through the bolt aperture to be partially accommodated in the counter-bore. The threaded shaft of the bolt may be brought into engagement with a proximal end of the nut within the counter-bore.

In addition to one or more features described above, or as an alternative to any of the foregoing embodiments, the method may include drilling the second component to provide the counter-bore. The method may also include drilling the first and/or second component to provide the first and/or second hole. The first and second holes may be through-holes linking one side of the component to the other; whereas the counter-bore may be a blind hole of wider diameter than the second hole and extending only partway through the second component, for example, between 10 to 50% of the way through the second component. The diameter of the counter-bore might be the same as or less than the diameter of the bolt aperture. Equally, the diameter of the counter-bore might be larger than the diameter of the bolt aperture.

DETAILED DESCRIPTION

A prior art floating anchor nut is depicted in the exploded view ofFIG. 5.

The floating anchor nut101comprises a plate103and a nut111, the plate103defining an X-Y plane for the movement of the nut111. The nut111is retained by retention features107,109that engage a flange115extending from an outer surface117of the nut111. The nut111comprises an internally threaded, generally cylindrical body113, the flange115extending from the end of the body113closest to the plate103. The flange115and retention features107,109cooperate to retain the nut111with respect to the plate103, such that limited displacement of the nut111is allowed in a Z direction perpendicular to an X-Y plane of the plate103, whilst limited displacement of the nut111is also allowed in an X-Y plane, i.e., parallel to the plane of the plate103. Owing to this limited displacement of the nut111, the nut111is said to “float”.

The body113of the nut111has a bore which is provided with an internal thread for receiving a bolt102. The engagement of the flange115with the retention features107,109or other features restricts the rotation of the nut111so that a bolt102can be screwed into the threaded bore when the floating anchor nut101is positioned on a blindside of a component.

The resulting fastener assembly1100, comprising the floating anchor nut111and bolt102, is usually intended to be used with a recommended tensile pre-load, under which, two components can be clamped together by the fastener assembly and when subject to vibrations during normal use, should not come undone.

FIG. 6shows the known fastener assembly1100, in use, fastening together a first and second component140,144, e.g., such as casings and/or housings of a gas turbine engine. During manufacture of the second component144or shortly before being fastened to the first component140, the floating anchor nut101is secured to a blindside of a second component144to provide a threaded hole for the bolt102to engage.

As shown, the bolt102can be passed through a first hole142in a first component140, through a second hole146in a second component144and into a threaded bore of the floating anchor nut101. The thread of the bolt102engages with the thread in the body113, enabling the first component140and second component144to be fastened together.

With this arrangement, should there be any misalignment within the normal manufacturing tolerances of the first and second components140,144, e.g., causing the first hole142and the second hole146to be misaligned with one another, then the nut111can “float” within the retention features107,109of the plate103to accommodate for such misalignment while allowing the threads of the nut111and bolt102to engage squarely.

To meet the usual installation recommendations and achieve the prescribed tensile loading, the bolt102should engage the whole length of the nut's thread with at least two full thread pitches at the tip of the bolt shaft104protruding from the body113. Additional bolt length might be specified to allow for manufacturing tolerances in other parts. Another consideration when selecting the fastener assembly is that the bolts102may only be available in certain lengths, e.g., 2.5, 5 or 10 mm length intervals for metric bolt sizes.

Sufficient clearance should be allowed for to accommodate the height of the floating anchor nut101and the portion of the bolt102that protrudes therefrom. In constrained environments, e.g., as often found in gas turbine engines, where space and access can be limited, it is not always possible to provide adequate clearance to rule out contact between the tip of the bolt shaft104and neighbouring components.

Moreover, manufacturer's tolerances for each component as well as restrictions due to set bolt sizes all need to be factored in when designing how the components are to be fastened together. These considerations can stack up, occasionally resulting in fouling and/or damage to a neighbouring component on a blindside of the assembly; for instance the tip of the bolt102may end up engaging a component150on the blindside of the assembly during installation. The danger then is that such damage may go unnoticed and ultimately may be the source of corrosion or a crack that could result in the component failing.

One option to avoid the possibility of fouling in such areas where there is limited space is to use a shorter bolt. However, because bolts102are usually available only in set lengths (e.g., of approximately 2.5 or 5 mm intervals for metric bolts102), this may mean that the requirement for two full thread pitches to be present beyond the floating anchor nut101cannot always be satisfied, or at least cannot be guaranteed, taking into account other manufacturing tolerances of the other parts, e.g., the thickness of the components in the region where the bolt102passes though. This may reduce the potential reliability of the fastener assembly.

An exemplary fastening assembly100comprising a floating anchor nut1in accordance with the present disclosure will now be described with reference toFIGS. 1 to 3B.

FIG. 1shows a floating anchor nut1in an exploded view comprising a plate3and a nut11. This same floating anchor nut can be seen inFIGS. 2A and 2B. The plate3extends in an X-Y plane, as with the prior art nut111(i.e., the X-Y plane corresponds to the flat surface of the plate3which abuts the nut11). It comprises a centrally arranged bolt aperture5and a pair of retention features7,9arranged either side to retain the nut11as will be explained below. One difference to note here, however, is that the bolt aperture5is larger than the bolt aperture105found in a traditional floating anchor nut.

In the depicted embodiment, the plate3may further comprise a first opening27having a lip31and a second opening29having a lip33. The first opening27and the second opening29are arranged to receive a first fastener and second fastener respectively (not shown) for securing the plate3to a component, for example, on a blindside of a component, in this case a second component44(seeFIG. 4). Other arrangements, such as plain apertures or slots, etc., may be used together with fasteners for securing the plate3to the component44.

As before, the nut11comprises an internally threaded, generally cylindrical body13as well as a flange15extending from an outer surface17of the body13.

An internal thread within a bore of the body13is configured to receive a similarly threaded shaft4of an intended bolt2, in much the same way as the prior art. The abutment of the flange15against the retention features7,9and the lips31,33, serves to ground or limit any rotation of the nut11with respect to the plate3. Thus the nut11remains (rotationally) generally locked in position within the plate3for the bolt2to be screwed into without the installer having access to the nut11.

As shown inFIGS. 1, 2A and 3A, the flange15may extend in a continuous manner circumferentially around the body13of the nut11. However, a flange15that extends only partially around the outer surface17, or a segmented flange15extending from the outer surface17of the body13could be used to the same effect.

There is a difference in the axial position of the flange15compared to the prior art floating anchor nut101, which will be explained further below.

The nut11is retained with respect to the plate3via interaction of the flange15with the retention features7,9and the underlying surface of the plate3. The retention features7,9allow the nut11to “float” with respect to the plate3while maintaining its capture (i.e., they allow limited displacement of the nut in the X, Y and Z directions, as before).

In the embodiment depicted inFIGS. 1-3B, there are two retention features; a first retention feature7disposed at a lower side of the plate3and a second retention feature9disposed at an upper side of the plate3. It is, however, envisioned that the plate3can comprise any number of retention features provided that they can retain or capture the nut11suitably.

The retention features7,9and other points of contact are positioned so as to allow limited movement of the nut11in the X-Y directions.

For example, the flange15has a first region19corresponding to the first retention feature7and a second region21corresponding to the second retention feature9. The width of the nut11in the Y direction provided by the extremities of the first region19and the second region21is smaller than the separation between the first and second retention features7,9, to allow a limited amount of movement in the Y direction.

The flange15further comprises a first recess35and a second recess37provided on opposite sides of the body13. The first recess35provides room for the first lip31and/or the first fastener inserted in the first opening27, and the second recess37provides room for the second lip33and/or the second fastener inserted in the second opening29. The width of the nut11in the X direction between the first and second recesses35,37is smaller than the separation between the first and second openings27,29, to allow a limited amount of movement in the X direction.

Thus the first and second regions19,21and the first and second recesses35,37allow the nut11to “float” in the in the X, Y directions, i.e., in a plane parallel to that of the plate3, before parts start to engage.

The amount of X-Y displacement that the nut can undergo may be up to a few millimetres in any direction in the plane of the plate3, or smaller, e.g., ±1 mm. For example, the permitted movement may be between 0.5 and 2 mm in any direction of the X-Y plane, e.g., greater than 0.7 mm or 0.9 mm, and/or less than 1.75 mm or 1.5 mm

The interaction of the retention features7,9with the flange15also allows for limited displacement of the nut11perpendicular to the plane of the plate3, i.e. in a Z direction. As above, the retention features7,9and other points of contact may be positioned so as to allow limited movement of the nut11in the Z direction.

The amount of Z displacement that the nut can undergo may be up to a millimetre or so perpendicular to the plane of the plate3, or smaller, e.g., ±0.5 mm. For example, the permitted movement may be between 0.1 and 1 mm perpendicular to the plane of the plate.

Whilst the embodiments of the floating anchor nut depicted in the Figures allow for some displacement of the nut11in the Z direction, in other embodiments, not shown herein, the interaction of the retention features7,9with the flange15may be a closer fit.

As mentioned above, the position of the flange15with respect to the body13is different to known floating anchor nuts: it is positioned along the body away from a proximal end26as opposed to at the proximal end26(the proximal end26being the end of the nut11which is closest to the head of the bolt2).

Thus the body13of the nut11may have a generally cylindrical form which is divided into two portions by the flange15: a first, distal end portion23on a first side of the flange15and a second, proximal end portion25on a second side of the flange15that is engaged first by the bolt2. Alternatively, the flange15may be positioned at a distal end24such that the body13of the nut11has a single portion extending between the flange15and the proximal end26.

As shown in the embodiment ofFIGS. 1-2B, the flange15may be provided approximately a third of the way along the length of the body13from the distal end24. The flange could also be provided in a variety of other positions along the body including midway along, though a position partway along, for example, less than halfway along the body13from the distal end24, can have advantages.

The amount of displacement of the nut11in the Z direction relative to plate3allowed for by the retention features7,9is small enough to ensure that the proximal end26of the body13of the nut11extends through the bolt aperture5in the plate3as can be seen best inFIG. 2B. The diameter of the bolt aperture5is therefore larger than the diameter of the prior art plates103. The diameter of the bolt aperture5now corresponds to the outer surface17of the body13with an allowance for the permitted movement of the nut11in the X-Y direction, as shown inFIGS. 2B and 3B.

This difference in diameters between the body13and the bolt aperture5may be greater than or equal to the difference in separations between the first and second openings27,29and the first and second recesses35,37. The difference in diameters may also be greater than or equal to the difference in separation between the first and second retention features7,9and the first and second regions19,21. As such, the nut11can still “float” in the X-Y direction parallel to the plane of the plate3, whilst also allowing the nut11to “float” in the Z direction.

The bolt aperture5in the embodiment ofFIGS. 1-3Bis depicted as a circular aperture, as a hole of this shape is easy to form from known manufacturing methods, such as drilling. However, provided that the bolt aperture5has an area that is large enough to ensure that the nut11is maintained in the bolt aperture5in a manner that allows it to float, then the bolt aperture can conceivably take any shape, for instance the aperture might be a regular polygon.

Through the re-positioning of the flange15, the body13and, hence, the internal thread of the nut11is counter-sunk with respect to the plate3. 25% or more, e.g., 50% or more, of the nut11may be housed within the second component44. In this way, a bolt2engaging the nut11can still engage the same length of thread while needing to protrude by a smaller extent from the surface of the plate3.

An exemplary use of the floating anchor nut1and bolt3can be seen inFIG. 4.

FIG. 4shows an assembly, for instance an air cooled oil cooler assembly in a gas turbine engine, comprising a first component40having a first hole42and a second component44having a second hole46. A counter-bore48(the purpose of which will be described further below) is provided on the blindside of the second component44aligned with the second hole46. In the assembly, the first component40is positioned adjacent to the second component44, with the first hole42being adjacent and generally aligned with the second hole46, and the counter-bore48being on the blindside, spaced from the first hole42.

The first and second components40,44of the assembly are fastened together by a fastener assembly100comprising a bolt2and the floating anchor nut1as described above. The floating anchor nut1is fastened to the second component44with a first fastener (not shown) extending through the first opening27and a second fastener (not shown) extending through the second opening29and into the second component44. The floating anchor nut1may be attached to the rear surface of the second component44during the component manufacture stage. The counter-bore48may be formed in the second component44, e.g., by drilling or pre-forming in a casting, prior to the attachment of the floating anchor nut1.

The proximal end portion25of the body13, extending through the bolt aperture5, is accommodated by the counter-bore48. Thus the proximal end26and a portion of the body13extending beyond the plate3is housed in the second component44, within the counter-bore48.

Thus the method may comprise the steps of drilling a counter-bore48in the second component44of larger diameter than a through-hole for the bolt2, and attaching the plate3to the second component44with a portion of the nut11protruding into the counter-bore48.

The shaft4of the bolt2extends through the first hole42in the first component40, through the second hole46in the second component44and into the internally threaded body13that is partially countersunk into the second component44. The engagement of the threads for the full length of the body13ensures that the bolt2can transfer the necessary tensile loadings to the floating anchor nut1. The tip of the threaded shaft4of the bolt2can also extend beyond the distal end24of the body13by at least two full thread pitches. This helps to ensure that the intended tensile loadings can be used reliably. It further ensures that the completion of fastening can be inspected by eye, where there is sight-access to this region. Any misalignment in the holes of the components40,44can be taken up through the permitted “floating” of the nut11within the plate3.

Accordingly, the interaction of the bolt2and the floating anchor nut1can provide a secure fastener assembly extending between the first component40and the second component44to clamp them together.

Whilst not depicted in the Figures, the body13may be deformed slightly at the distal end24, for example, by ovalising, such that the internal thread of the nut11pinches slightly against regions of the bolt2and/or may also be out of its normal alignment. This subtle deformation in the thread helps to prevent the bolt2from working loose when subject to vibrations. Other systems could also be employed to restrict the nut and bolt working loose, for example, an adhesive, a polymer collar, or other such measure.

In the assembly100ofFIG. 4, as in the prior art assembly1100ofFIG. 6, the floating anchor nut1ensures that the first component40and the second component44are fastened together securely even when there is a slight misalignment due to the usual engineering tolerances. The limited parallel displacement of the nut11allows the nut to slightly alter its position in a direction parallel to the plate3to accommodate any such misalignment. Thus the bolt2can always be received squarely in the nut11regardless of possible misalignment in the components40,44.

The fastener assembly100also provides improved blindside clearance over known assemblies1100. As can be seen inFIG. 4, because the flange15is provided along the body13of the nut11away from the distal end24, a portion of the body13near the proximal end26extends through the bolt aperture5. Thus, the proximal end26of the nut11is counter-sunk into the second component44, and in particular is accommodated within the counter-bore48. As such, less of the nut11extends from the outer surface of the plate3. Hence, a shorter bolt2may be used which extends a smaller distance from the surface of the second component44while maintaining the same length of threaded contact.

In the scenario where the fastener assembly100is located close to another component50, for instance a fluid tank50, e.g., an air cooled oil cooler, the separation between the tank50and the tip of the bolt2can be increased by using a shorter bolt as a result of the flange15being disposed partway along the body13. Therefore, the risk of a bolt2causing damage to or fouling the tank50(or other components in other scenarios) is decreased compared with the prior art fastener assembly1100.

Greater clearance can be achieved by positioning the flange15closer to, or at, the distal end24of the body13. However, a balance must be struck between the desired clearance and the amount of material that must be removed from the second component44to form a counter-bore48large enough to accommodate the portion of the body13extending through the bolt aperture5. Should too much material be removed from the second component44then the integrity of the fastening between the two components40,44may be weakened beyond usefulness.

The use of a floating anchor nut1according to the present disclosure allows for the weight of the fastener assembly100to be reduced compared with assemblies known in the prior art. As the nut11is at least partially counter-sunk within the second component44, a shorter bolt2can be used while still achieving the same amount of threaded engagement. On a metric arrangement, this might mean a bolt2which is 2.5 mm or 5 mm shorter is used (e.g., by moving the flange15a distance of 2.5 mm or 5 mm or so along the body13of the nut11away from the proximal end26). Other savings in weight can be gained through removal of material in the second component44to provide the counter-bore48. In addition, a bigger bolt aperture5is provided in the plate3to accommodate the nut11, thus less material is used in the plate3too compared with the plate103of the assembly1100. By itself this might amount to just a few tens of grams in the weight of the fastener assembly100; however in a gas turbine engine many hundreds of these floating anchor nuts will be in use, and accordingly there is a potential for a significant amount of weight to be saved. Whilst the apparatus of the disclosure has been shown and described with reference to embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.