Patent Description:
In the field of safety, various measures are used to absorb, redirect and/or mitigate the effects of impulse forces on objects of interest. These measures include the use of reinforcements, restraints, padding, crumple zones, break-away panels, shock absorbers, air bags and the like.

However, most of these measures are limited to providing a fixed degree of mitigation or energy absorption. For example, when a particular measure is implemented, it may be effective for acceptably mitigating a given impulse force for one group of cargo or payload, but it may not be as effective for mitigating that same impulse force for other groups (e.g., having different weight). It would be desirable, therefore, to provide a measure for mitigating impulse energy which is not fixed, but which may provide a variable degree of mitigation which depends upon the payload.

<CIT> in accordance with its abstract states a shock absorber for a vehicle making use of plastic deformation. The absorber is mounted between a bumper and the frame of the vehicle to transform impact energy applied to the bumper into deformation energy. The absorber comprises a straight tube that can be plastically deformed. A straight tube is partially enlarged or partially reduced to form different diameter tube portions. These tube portions are connected by step formed between the edge of each one. Thus, a multi-diameter stepped tube is formed. The tubes located at the both ends of this multi-diameter stepped tube are connected to the bumper and the frame of the vehicle respectively.

<CIT> in accordance with its abstract states in order to set up selectively a suitable displacement-load characteristics to absorb an impact energy adapting to the difference of the impact modes, a resistive-portion-comprised shock absorber <NUM> comprising a smaller-diameter tube portion <NUM> and a larger-diameter tube portion <NUM> which are integrally formed by partially reducing or partially enlarging a straight tube that can be plastically deformable, a step portion formed continuously between edge of the each smaller-diameter tube portion and the larger-diameter tube portion by being folded the edge back to the each tube portions, wherein a frictional resistive portion is provided to the smaller-diameter tube portion slidingly inserted into the larger-diameter tube portion, and, a resistive-member-mounted shock absorber <NUM> comprising a smaller-diameter tube portion <NUM> and a larger-diameter tube portion <NUM> which are described above, a step portion <NUM> which is described above, wherein a frictional member is mounted in an interior of the larger-diameter tube portion.

An inversion-formed double-walled tube for use as energy absorber according to independent claim <NUM> and a method of manufacturing an energy absorbing inversion tube assembly for use as energy absorber according to independent claim <NUM> are provided. Optional features are recited in the dependent claims. According to the invention, an inversion-formed double-walled tube for use as energy absorber includes an outer tube having an outer wall thickness, an inner tube disposed inside the outer tube and having an inner wall thickness, and a U-shaped transition portion connecting the inner tube and the outer tube, wherein at least one of the inner and outer wall thicknesses varies along a length of the double-walled tube.

The inner tube and the outer tube may be spaced apart from each other, and the inner tube, the outer tube and the transition portion may be made of aluminum, such as 3003H14 aluminum. The inner and outer wall thicknesses may vary similarly to each other along the length of the double-walled tube, or differently from each other along the length of the double-walled tube, or oppositely from each other along the length of the double-walled tube.

The outer tube may be formed as an external inversion of the inner tube, or the inner tube may be formed as an internal inversion of the outer tube. If the outer tube is formed as an external inversion of the inner tube, then the outer tube and the transition portion may be configured as a plastic deformation zone. On the other hand, if the inner tube is formed as an internal inversion of the outer tube, then the inner tube and the transition portion may be configured as a plastic deformation zone.

The inner and outer tubes may optionally have respective tube lengths that are substantially equivalent to each other. According to the invention the inner tube has a first end adjoining the transition portion and a second end opposite the first end, and the outer tube has a third end adjoining the transition portion and a fourth end opposite the third end. In this arrangement, the inversion-formed double-walled tube may further include an inner fitting attached to the second end of the inner tube, and an outer fitting attached to the fourth end of the outer tube, wherein the inner and outer fittings may be configured for receiving compression and/or tension forces as applied thereto.

The inner fitting may include an axial member connected with the second end of the inner tube and configured to extend inside the inner tube. The inversion-formed double-walled tube may further include an outer sleeve disposed about the outer tube and configured to provide resistance against buckling to the inner and/or outer tube when the inner and outer fittings are subjected to a compressive force. In this configuration, the outer sleeve may have a fifth end attached to the outer fitting and a sixth end attached to the fourth end of the outer tube.

When a compression force above a predetermined compression threshold or a tension force above a predetermined tension threshold is applied to the inner and outer fittings, one of the inner and outer tubes may increase in length and the other of the inner and outer tubes may decrease in length. The inversion-formed double-walled tube may be configured for dissipating impulse energy when a compression or tension impulse force above a respective predetermined compression or tension threshold is applied thereto. More specifically, the inner and outer tubes and the transition portion may be configured for dissipating energy when the compression or tension force above the respective predetermined compression or tension threshold is applied to the inner and outer fittings and the inner and outer tubes change in length.

According to another embodiment, an inversion tube type energy absorber includes: an outer tube having an outer wall thickness and an outer tube length; an inner tube disposed inside the outer tube and having an inner wall thickness and an inner tube length substantially equivalent to the outer tube length; and a transition portion connecting the inner tube and the outer tube and configured as a plastic deformation zone. In this embodiment, at least one of the inner and outer wall thicknesses varies along its respective inner or outer tube length.

The inversion tube type energy absorber may further include: an outer sleeve disposed about the outer tube and having opposed fifth and sixth ends; an inner fitting attached to a second end of the inner tube distal from the transition portion; and an outer fitting attached to the fifth end of the outer sleeve, with the sixth end of the outer sleeve being attached to a fourth end of the outer tube distal from the transition portion. In this configuration, the inner and outer fittings may be configured for receiving compression and/or tension forces as applied thereto and for conveying the compression and/or tension forces to the inner and outer tubes.

According to the invention, a method of manufacturing an energy absorbing inversion tube assembly for use as energy absorber is provided according to claim <NUM>.

The method may further include attaching an inner fitting to a second end of the inner tube distal from the transition portion, and attaching an outer fitting to a fourth end of the outer tube distal from the transition portion, wherein the inner and outer fittings are configured for conveying external compression and/or tension forces to the inner and outer tubes, respectively. Additionally, the method may also include disposing an outer sleeve having opposed fifth and sixth ends about the outer tube, and attaching the fifth end of the outer sleeve to the outer fitting and the sixth end of the outer sleeve to the fourth end of the outer tube.

The above features and advantages, and other features and advantages, of the present invention are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the present teachings, as defined in the appended claims, when taken in connection with the accompanying drawings.

Also disclosed is an inversion tube type energy absorber, comprising: an outer tube having an outer wall thickness and an outer tube length; an inner tube disposed inside the outer tube and having an inner wall thickness and an inner tube length substantially equivalent to the outer tube length; and a transition portion connecting the inner tube and the outer tube and configured as a plastic deformation zone; wherein at least one of the inner and outer wall thicknesses varies along its respective inner or outer tube length.

This inversion tube type energy absorber may further comprise: an outer sleeve disposed about the outer tube and having opposed fifth and sixth ends; an inner fitting attached to a second end of the inner tube distal from the transition portion; and an outer fitting attached to the fifth end of the outer sleeve, with the sixth end of the outer sleeve being attached to a fourth end of the outer tube distal from the transition portion; wherein the inner and outer fittings are configured for receiving compression and/or tension forces as applied thereto and for conveying the compression and/or tension forces to the inner and outer tubes.

Referring now to the drawings, wherein like numerals indicate like parts in the several views, an inversion-formed double-walled tube <NUM> is shown and described herein. Note that in some embodiments, the inversion-formed double-walled tube <NUM> may also be described as an inversion tube type energy absorber <NUM>, an energy absorbing inversion tube assembly <NUM>, or simply as an inversion tube <NUM>.

<FIG> show schematic views illustrating various structural features of the inversion tube <NUM> and its stages of manufacture. For example, <FIG> shows a cross-sectional view of an inversion tube <NUM> before being inverted, which may be referred to as a pre-inversion tube <NUM>. The pre-inversion tube <NUM> is made of metal (e.g., aluminum) and may undergo a process of either "internal inversion" - in which one end of the tube <NUM> is pressed inward and along some length on the inside of the tube <NUM> - or "external inversion" - in which one end of the tube <NUM> is pulled outward and along some length on the outside of the tube <NUM>. In either case, the result of the inversion process is a double-walled tube <NUM> that has an inner tube <NUM> and an outer tube <NUM> along some length of the finished/inverted tube <NUM>.

As illustrated in <FIG>, one end of the pre-inversion tube <NUM> - designated here as a top end <NUM>top-is swaged or spun so as to be completely closed (i.e., a closed end <NUM>C), while the opposing end - designated here as a bottom end <NUM>btm - is left open, and optionally may be outwardly flared (i.e., an open end <NUM>O). The pre-inversion tube <NUM> may be mounted with its open bottom end <NUM>O, <NUM>btm placed over a fixed base <NUM>, with the closed top end <NUM>C, <NUM>top extending upward. A plunger <NUM> may be brought into contact with the top end <NUM>top in preparation for an internal inversion of the tube <NUM>. Note that letters Q, R, S, T, U and V are used in <FIG> and <NUM>-<NUM> to indicate points along the length of the pre-inversion tube <NUM>, starting with point Q near the open bottom end <NUM>O, <NUM>btm, point V at the apex of the rounded/closed top end <NUM>C, <NUM>top, and point S near the middle <NUM>mid of the tube <NUM>. These points Q, R, S, T, U, V are used to show how the inversion tube <NUM> changes in shape as it progresses through the inversion process.

With the pre-inversion tube <NUM> positioned as shown in <FIG>, a compression force FC may be directed downward through the plunger <NUM> as shown. This compression force FC causes the top <NUM>top of the tube <NUM> to collapse inward, and as the plunger <NUM> is pressed further downward it causes the former top <NUM>top of the tube <NUM> to be pressed downward within the interior of the tube <NUM> as well, thus causing an internal inversion <NUM>. If the plunger <NUM> continues to be pressed downward, it may reach the configuration shown in <FIG>, in which the former apex point V is positioned just below the Q points, the U points align laterally with the Q points, the T points align laterally with the R points, and the S points - which were previously at about the middle of the pre-inversion tube <NUM> - are now at the top <NUM> of the resulting double-walled inversion tube <NUM>.

In <FIG>, the double-walled inversion tube <NUM> has an inner tube (or inner tube portion) <NUM> and an outer tube (or outer tube portion) <NUM>, which are joined together at a U-shaped transition portion <NUM> at the S points. The inner tube <NUM> has a first end <NUM> adjoining the transition portion <NUM> and a second end <NUM> opposite the first end <NUM>, and the outer tube <NUM> has a third end <NUM> adjoining the transition portion <NUM> and a fourth end <NUM> opposite the third end <NUM>. The inner tube <NUM> has an inner tube length Li (as measured from the first end <NUM> of the inner tube <NUM> near the transition portion <NUM> and S points, to the second end <NUM> near the U points), and the outer tube <NUM> has an outer tube length Lo (as measured from the third end <NUM> of the outer tube <NUM> near the transition portion <NUM> and S points, to the fourth end <NUM> near the Q points), with the inner and outer tube lengths Li, Lo being about the same length as each other and about the same as the overall double-walled inversion tube length LDW. The former top end <NUM>top which includes points U and V may include a spindle assembly <NUM> or other structure as illustrated in <FIG> which the plunger <NUM> presses upon (and which in turn presses on the former top end <NUM>top). For example, the spindle assembly <NUM> may include a disc <NUM> with an attached downwardly extending stem <NUM>, a frusto-conical guide <NUM>, and an end bolt <NUM> which secures the guide <NUM> to the stem <NUM>. The stem <NUM> may have internal threads to receive the bolt <NUM>, and may optionally have external threads as well. The stem <NUM>, guide <NUM> and bolt <NUM> may be urged by the plunger <NUM> into a central axial cavity <NUM> formed in or through the base <NUM>; thus, the spindle assembly <NUM> may be used to facilitate the internal inversion process. After the internal inversion process is completed, the bolt <NUM> and guide <NUM> may be removed and an appropriate fitting (discussed below) may be attached to the stem <NUM>.

<FIG> show magnified views of the upper and lower locations <NUM>, <NUM> in dashed circles at the top <NUM> and bottom <NUM>, respectively, of the inversion tube <NUM> of <FIG>. In <FIG>, the upper location <NUM> shows (i) the inner wall thickness ti of the inner tube <NUM>, and in particular the inner wall thickness ti1 at the first end <NUM> of the inner tube <NUM>, as well as (ii) the outer wall thickness to of the outer tube <NUM>, and in particular the outer wall thickness to3 at the third end <NUM> of the outer tube <NUM>. Similarly, in <FIG>, the lower location <NUM> shows (i) the inner wall thickness ti of the inner tube <NUM>, and in particular the inner wall thickness ti2 at the second end <NUM> of the inner tube <NUM>, as well as (ii) the outer wall thickness to of the outer tube <NUM>, and in particular the outer wall thickness to4 at the fourth end <NUM> of the outer tube <NUM>. As used herein, reference numerals ti and to without any numerical subscript refer to the wall thicknesses of the inner and outer tubes <NUM>, <NUM>, respectively, in a generalized manner (i.e., anywhere along the length of the respective tube <NUM>, <NUM>), while reference numerals ti1, ti2, to3 and to4 with numerical subscripts refer to the wall thicknesses at specific locations or ends of the tubes <NUM>, <NUM>. Also note that <FIG> shows a generalized wall thickness tpre of the pre-inversion tube <NUM>.

It is noteworthy that conventional approaches to manufacturing inversion tubes (whether internally inverted or externally inverted) utilize a pre-inversion tube which has a uniform wall thickness - i.e., a wall thickness that is constant along the length of the tube. In contrast, the inversion tube <NUM> of the present disclosure intentionally uses a varying wall thickness along some length of the tube <NUM>. This varying wall thickness may be configured so as to absorb compression and/or tension forces at a more controllable, predictable and/or customizable rate than may be accomplished using a conventional inversion tube.

<FIG> show schematic views of a fully inverted inversion tube <NUM> being subjected to various tension and compression loadings. (Note that, as used herein, a "fully inverted" inversion tube <NUM> is one in which the inner tube length Li, the outer tube length Lo, and the length of the overall inverted tube LDW are about the same length of each other. ) Each of these tubes <NUM> may be internally inverted or externally inverted. In <FIG>, an axial member <NUM> extends into and along the full length Li of the inner tube <NUM> and is attached to the inner tube <NUM> at or near the second end <NUM>. In <FIG>, an upwardly directed first force F<NUM> is exerted on the axial member <NUM>, and thus on the second end <NUM> of the inner tube <NUM> as well, while a downwardly directed second force F<NUM> is exerted on the fourth ends <NUM> of the outer tube <NUM>, thus causing a tensile or tension loading or net force FT to be placed on the inversion tube <NUM>. Oppositely, in <FIG>, a downwardly directed first force F<NUM> is exerted on the axial member <NUM>, and thus on the second end <NUM> of the inner tube <NUM> as well, while an upwardly directed second force F<NUM> is exerted on the fourth ends <NUM> of the outer tube <NUM>, thus causing a compressive or compression loading or net force FC to be placed on the inversion tube <NUM>. In <FIG>, no axial member <NUM> is used, and the first force F<NUM> is exerted on the second end <NUM> of the inner tube <NUM> from outside of the inner tube <NUM>. In <FIG>, a downwardly directed first force F<NUM> is exerted on the second end <NUM> of the inner tube <NUM>, while an upwardly directed second force F<NUM> is exerted on the fourth ends <NUM> of the outer tube <NUM>, thus causing a tensile or tension loading or net force FT to be placed on the inversion tube <NUM>. And in <FIG>, an upwardly directed first force F<NUM> is exerted on the second end <NUM> of the inner tube <NUM>, while a downwardly directed second force F<NUM> is exerted on the fourth ends <NUM> of the outer tube <NUM>, thus causing a compressive or compression loading or net force FC to be placed on the inversion tube <NUM>. It should be noted, however, that whether the net loading or net force is considered as "compression" or "tension" depends on the frame of reference used, whether the forces F<NUM>, F<NUM> are "push" forces or "pull" forces, how the elements and linkages transmitting the forces F<NUM>, F<NUM> are arranged, etc..

<FIG> shows a series of schematic views of an inversion tube <NUM> undergoing successive stages of internal inversion, while <FIG> shows an inversion tube <NUM> undergoing external inversion. (Note that, as used herein, reference numeral <NUM> refers to an "internal inversion" and <NUM> refers to an "external inversion", where the use of these reference numerals denotes referring to a resulting manufactured item or physical product. On the other hand, when mention is made herein of an "internal inversion" or an "external inversion" without reference numerals, such mention without reference numerals denotes referring to a manufacturing process, but not to the product manufactured. ) <FIG> begins at view "A" with a pre-inversion tube <NUM> before any inversion has begun. In view "B1", an initially-inverted tube <NUM> is shown, where the apex point V has just been pressed inward. At this point in view "B1", there is substantially no inner tube <NUM> formed yet. However, at view "C1", the inner tube <NUM> begins to form and a double-walled inversion tube <NUM> is created. As the apex point V continues to be pressed inward along the longitudinal axis of the tube <NUM> in views "C1", "D1" and "E1", the overall length LDW of the tube <NUM> continues to decrease, until view "F1" where the inner tube length Li, the outer tube length Lo and the overall inversion tube length LDW are all about the same as each other. Optionally, the apex point V may continue to be pressed inward, such that the inner tube length Li continues to increase and the outer tube length Lo continues to decrease, as shown in view "G1", in which the overall inversion tube length LDW is now longer than it was in view "F1" (and appears to be about the same as the overall length LDW of view "E1").

In a similar manner, <FIG> begins at view "A" with a pre-inversion tube <NUM> before any inversion has begun. In view "B2", an initially-inverted tube <NUM> is shown, where the Q points have just been rolled outward. At this point in view "B2", there is little or no outer tube <NUM> formed yet. However, at view "C2", the outer tube <NUM> begins to form and a double-walled inversion tube <NUM> is created. As the Q, R and other points continue to be rolled outward and along the longitudinal axis of the tube <NUM> in views "C2", "D2" and "E2", the overall length LDW of the tube <NUM> continues to decrease, until view "F2" where the inner tube length Li, the outer tube length Lo and the overall inversion tube length LDW are all about the same as each other. Optionally, the Q, R, S and other points may continue to be rolled outward and along the longitudinal axis of the tube <NUM>, such that the outer tube length Lo continues to increase and the inner tube length Li continues to decrease, as shown in view "G2", in which the overall inversion tube length LDW is now longer than it was in view "F2" (and appears to be about the same as the overall length LDW of view "E2").

Depending upon the intended application for the inversion tube <NUM>, one of the configurations shown in the views of <FIG> may be selected. It may be noted that the configurations shown in view "F1" of <FIG> and in view "F2" of <FIG> appear to be the same, but just upside-down with respect to each other. On one hand that is true, but on the other hand there may be some significant differences between the configurations shown in those two views. First, note that while both configurations appear to begin with the same length and diameter of the pre-inversion tube <NUM> in view "A", the diameters of the inner and outer tubes <NUM>, <NUM> may be different as compared between the two configurations. For example, since the configuration shown in view "F1" of <FIG> is an internal inversion <NUM>, the diameter of the outer tube <NUM> will remain the same as the starting diameter of the pre-inversion tube <NUM>, but the diameter of the inner tube <NUM> will be smaller than the outer and pre-inversion tube diameters. And since the configuration shown in view "F2" of <FIG> is an external inversion <NUM>, the diameter of the inner tube <NUM> will remain the same as the starting diameter of the pre-inversion tube <NUM>, but the diameter of the outer tube <NUM> will be larger than the inner and pre-inversion tube diameters. And second, there is a difference between the "F1" and "F2" configurations in that in the "F1" configuration, the inner tube <NUM> was formed by plastically deforming the original tube wall (as a result of the apex point V being pushed continually inward) with the outer tube <NUM> not being plastically deformed, while in the "F2" configuration, the outer tube <NUM> was formed by plastically deforming the original tube wall (as a result of the Q and other points being rolled continually outward and along the longitudinal axis of the tube) with the inner tube <NUM> not being plastically deformed. The portions of the original pre-inversion tube <NUM> that are subjected to plastic deformation may be referred to as "plastic deformation zones" <NUM>, or collectively as a "plastic deformation zone" <NUM>. These plastic deformation zones <NUM> are denoted in <FIG> by dashed lines and in <FIG> by dash-dot lines. However, given that the fully inverted "F1" and "F2" configurations may be the most commonly selected shape, one may select the pre-inversion tube size and starting dimensions such that the first of the abovementioned differences is negated (i.e., the desired resulting dimensions are achieved), with the second of the abovementioned differences simply offering the designer a choice as to whether it would be more suitable for the plastic deformation to be present in the inner tube <NUM> or the outer tube <NUM> (i.e., depending on the intended application).

For example, <FIG> illustrates one potential application of the double-walled inversion tube/energy absorber assembly <NUM> of the present disclosure. Here, a rear perspective view of an aircraft seat <NUM> equipped with energy absorbing inversion tube assemblies <NUM> is shown. A rigid, generally rectangular frame <NUM> is attached to the back of the seat <NUM>. The frame <NUM> includes two vertical tubes or bars <NUM>, each having a top end <NUM> and a bottom end <NUM>, with a top horizontal tube or bar <NUM> connected to the two top ends <NUM> and a bottom horizontal tube or bar <NUM> connected to the two bottom ends <NUM>. A respective sliding tubular connector <NUM> is slidably connected to each of the two vertical tubes <NUM>, with each tubular connector <NUM> being attached to the lower back of the seat <NUM>. The lower back of the seat <NUM> also includes one or two mounting areas <NUM> (e.g., stanchions), each or both which may also be attached to the tubular connectors <NUM>. Two inversion tubes/energy absorber assemblies <NUM> are arranged on the back of the seat <NUM> such that a top end of each is connected to the top horizontal bar <NUM> (or to a top horizontal bar connector <NUM>) that is connected to the top horizontal bar), and a bottom end of each is connected to the mounting area(s) <NUM>.

In this arrangement, the frame <NUM> may be affixed to the aircraft with some volume of empty space provided underneath the seat <NUM> into which the seat <NUM> may egress in the event of a rough landing, with the inversion tubes <NUM> serving as energy absorbers (similar to so-called shock absorbers). That is, in the event of a landing that provides an impulse force on the seat <NUM> above a predetermined value, the seat <NUM> may glide downward along the vertical tubes <NUM> toward the empty space provided underneath the seat <NUM>, but with the inversion tubes <NUM> effectively absorbing some portion of the impulse energy. With the thickness ti, to of the inner and/or outer tubes <NUM>, <NUM> being varied and profiled as described herein, the seat <NUM>, frame <NUM> and inversion tubes <NUM> may absorb impulse energy in a way that can accommodate a wide range of occupants (e.g., from a <NUM>th percentile female to a <NUM>th percentile male).

<FIG> show various embodiments of an energy-absorbing inversion tube assembly <NUM> according to the present disclosure. Specifically, <FIG> show schematic cross-sectional views of first and second embodiments, respectively, of a fully inverted inversion tube <NUM> configured for tension loading, <FIG> shows a schematic cross-sectional view of an embodiment configured for compression loading, and <FIG> show schematic cross-sectional views of another inversion tube embodiment configured for compression loading, in which <FIG> shows the embodiment without an outer sleeve <NUM> and <FIG> shows the same embodiment with an outer sleeve <NUM>.

<FIG> show two similar but different embodiments that are configured for tension loading. In either embodiment, the inversion-formed double-walled tube <NUM> includes an outer tube <NUM> having an outer wall thickness to, an inner tube <NUM> disposed inside the outer tube <NUM> and having an inner wall thickness ti, and a transition portion <NUM> connecting the inner and outer tubes <NUM>, <NUM>, in which at least one of the inner and outer wall thicknesses ti, to varies along at least some portion of the overall length LDW of the double-walled tube <NUM>. The inner and outer tubes <NUM>, <NUM> may be spaced apart from each other, and the inner tube <NUM>, the outer tube <NUM> and the transition portion <NUM> may be made of aluminum, such as 3003H14 aluminum, or any other suitable material. The inner and outer wall thicknesses ti, to may vary in a way that is similar to each other along the length LDW of the double-walled tube <NUM>, or they may vary differently from each other along the overall tube length LDW (including varying oppositely from each other). For example, (i) both the inner tube thickness ti and the outer tube thickness to may increase in the downward direction <NUM> (i.e., from the top <NUM> of the inversion tube <NUM> to the bottom <NUM>), or (ii) both may decrease in thickness in the downward direction <NUM>, or (iii) one of these two thicknesses ti, to may increase in the downward direction <NUM> while the other of the two thicknesses ti, to decreases, or (iv) one of the thicknesses ti, to may increase or decrease in the downward direction <NUM> while the other remains at a constant thickness. The variation in wall thickness (whether ti or to or both) along the length LDW of the inversion tube <NUM> defines a thickness profile, which may vary linearly or non-linearly (e.g., logarithmically, exponentially, etc.) along the longitudinal axis or overall length LDW of the tube <NUM>.

The outer tube <NUM> may be formed as an external inversion <NUM> of the inner tube <NUM>, or the inner tube <NUM> may be formed as an internal inversion <NUM> of the outer tube <NUM>. If the outer tube <NUM> is formed as an external inversion <NUM> of the inner tube <NUM>, then the outer tube <NUM> and the transition portion <NUM> may be configured as a plastic deformation zone <NUM>. On the other hand, if the inner tube <NUM> is formed as an internal inversion <NUM> of the outer tube <NUM>, then the inner tube <NUM> and the transition portion <NUM> may be configured as a plastic deformation zone <NUM>.

In some configurations, such as those shown in views "F1" and "F2" in <FIG>, and in the embodiments of <FIG>,<FIG>and <NUM>-<NUM>, the inner and outer tubes <NUM>, <NUM> may optionally have respective tube lengths Li, Lo that are substantially equivalent to each other. In such embodiments, these substantially equivalent tube lengths Li, Lo may also be substantially equivalent to the overall length LDW of the inversion tube <NUM> (i.e., Li ≈ Lo ≈ LDW).

In order for the double-walled inversion tube <NUM> to function as an energy absorber, the inner and outer tubes <NUM>, <NUM> may be attached to appropriate fittings <NUM>, <NUM> which can be used to impart compression force or loading FC and/or tension force or loading FT to the inner and outer tubes <NUM>, <NUM>. In practice, there are multiple ways in which the fittings <NUM>, <NUM> may be attached to the inner and outer tubes <NUM>, <NUM>.

In the embodiments shown in <FIG>, the inversion tube <NUM> includes an inner fitting <NUM> attached directly to the second end <NUM> of the inner tube <NUM>, and an outer fitting <NUM> attached directly or indirectly to the fourth end <NUM> of the outer tube <NUM>. In embodiments where the outer fitting <NUM> is attached indirectly to the fourth end <NUM> of the outer tube <NUM> (e.g., <FIG> and <FIG>), an outer sleeve <NUM> may serve as an intermediary therebetween, as described in further detail below. The inner and outer fittings <NUM>, <NUM> are configured for receiving compression and/or tension forces FC, FT that may be applied thereto, which are in turn applied to the respective inner and outer tubes <NUM>, <NUM>. However, the manner in which these fittings <NUM>, <NUM> are attached to the inner and outer tubes <NUM>, <NUM>, and where the fittings <NUM>, <NUM> are disposed with respect to the overall inversion tube assembly <NUM> (i.e., at the top end <NUM> or the bottom end <NUM>), may vary from one specific embodiment to another.

For example, as shown in the embodiment of <FIG>, the inner fitting <NUM> is disposed at the top <NUM> of the inversion tube <NUM> and is connected with the second end <NUM> of the inner tube <NUM>, while the outer fitting <NUM> is disposed at the bottom <NUM> of the inversion tube <NUM> and is connected indirectly with the fourth end <NUM> of the outer tube <NUM> via an outer sleeve <NUM>. The outer sleeve <NUM> is disposed about the outer tube <NUM> (i.e., around and outside the outer tube <NUM>). In this configuration, the outer sleeve <NUM> has a fifth end <NUM> attached to the outer fitting <NUM> and a sixth end <NUM> attached to the fourth end <NUM> of the outer tube <NUM>.

In <FIG>, the inner fitting <NUM> includes a spherical bearing <NUM> which may be attached to an external member (not shown) which may pull upward with a tension force. The inner fitting <NUM> also includes a disc <NUM> disposed inside the inner tube <NUM>, with a stem <NUM> attached to the disc <NUM> and protruding upward through an aperture in the closed end <NUM> of the tube <NUM>. As illustrated here, the stem <NUM> may be externally threaded for engagement with internal threads inside the spherical bearing <NUM>, with an internally threaded locking ring <NUM> being screwed onto the stem <NUM> between the disc <NUM> and the spherical bearing <NUM>.

Additionally in <FIG>, the outer fitting <NUM> includes a spherical bearing <NUM> which is attached to an external member (not shown) which may pull downward with a tension force opposite to the upward tension force acting on the inner fitting <NUM>. An externally threaded stem <NUM> is screwed into internal threads inside the spherical bearing <NUM>, and an internally threaded annular plate <NUM> having a downwardly extending axial boss <NUM> is screwed onto the other end of the stem <NUM>. The annular plate <NUM> has a circumferential flange <NUM> extending downward from the circumferential edge of the plate <NUM>, with fasteners <NUM> (e.g., rivets, welds, etc.) securing the fifth end <NUM> of the outer sleeve <NUM> to the circumferential flange <NUM> of the outer fitting <NUM>.

In <FIG>, the relative locations of the inner and outer fittings <NUM>, <NUM> are opposite that of <FIG>, with the inner fitting <NUM> being disposed at the bottom <NUM> of the inversion tube <NUM> and the outer fitting <NUM> disposed at the top <NUM>. Another difference between the embodiments of <FIG> is that the embodiment of <FIG> includes an axial member <NUM> as part of the inner fitting <NUM>. The axial member <NUM> extends inside the inner tube <NUM> and terminates in a disc <NUM> connected with the closed end <NUM> of the inversion tube <NUM> at the second end <NUM> of the inner tube <NUM> by way of an externally threaded stem <NUM> attached to the disc <NUM> and protruding upward through an aperture in the closed end <NUM> of the tube <NUM> and a locking ring <NUM> being screwed onto the stem <NUM>. And while the embodiment of <FIG> has an outer sleeve <NUM> disposed about the outer tube <NUM> (similar to <FIG>), another difference between the embodiments of <FIG> is that in the embodiment of <FIG>, the outer sleeve <NUM> is not attached to the outer tube <NUM>.

In the embodiment of <FIG>, the inner fitting <NUM> includes structure that is similar to the structure of the outer fitting <NUM> of <FIG>. The inner fitting <NUM> includes a spherical bearing <NUM> which may be attached to an external member (not shown) which may pull downward with a tension force. An externally threaded stem <NUM> is screwed into internal threads inside the spherical bearing <NUM>, and an internally threaded annular plate <NUM> having a downwardly extending axial boss <NUM> may be screwed onto the other end of the stem <NUM>. As shown in <FIG>, the stem <NUM> and the axial member <NUM> may be formed as a single piece; however, they may also be formed and used as two separate pieces. The annular plate <NUM> has a circumferential flange <NUM> extending downward from the circumferential edge of the plate <NUM>, with one end of the outer sleeve <NUM> (e.g., the fifth end <NUM>) extending and fitting snugly along the outer periphery of the circumferential flange <NUM>.

The outer fitting <NUM> of <FIG> includes a spherical bearing <NUM> which may be attached to an external member (not shown) which may pull upward with a tension force opposite to the downward tension force acting on the inner fitting <NUM>. The outer fitting <NUM> also includes an end cap <NUM> attached to the spherical bearing <NUM>, with a circumferential wall <NUM> descending downward from the outer periphery of the end cap <NUM>. The fourth end <NUM> of the outer tube <NUM> is attached to the circumferential wall <NUM> with suitable fasteners <NUM> (e.g., welds, rivets, etc.), and the second end <NUM> of the inner tube <NUM> is attached to the axial member <NUM> (e.g., via the disc <NUM>). The other end of the outer sleeve <NUM> (e.g., the sixth end <NUM>) may abut the circumferential wall <NUM> as shown, or it may optionally extend and fit snugly along the outer periphery of the circumferential wall <NUM>.

<FIG> shows an alternative embodiment which is configured for absorbing a net compression force FC. Here, the relatively short outer tube <NUM> may be formed by an external inversion process, and the structure and arrangement of the inner and outer fittings <NUM>, <NUM> generally match that of the inner and outer fittings <NUM>, <NUM> of <FIG>. The fifth end <NUM> of the outer sleeve <NUM> is attached to the outer fitting <NUM>, and the sixth end <NUM> of the outer sleeve <NUM> is attached to a connection ring <NUM> that wraps around the outside of the inner tube <NUM>. The fourth end <NUM> of the outer tube <NUM> is also attached to the connection ring <NUM>, thus connecting the sixth end <NUM> of the outer sleeve <NUM> and the fourth end <NUM> of the outer tube <NUM> directly or indirectly to each other. (Alternatively, the connection ring <NUM> can be omitted and the fourth and sixth ends <NUM>, <NUM> may be directly attached to each other.

<FIG> show two additional embodiments configured for absorbing a net compression force FC. The connections of the inner and outer fittings <NUM>, <NUM> to the inner and outer tubes <NUM>, <NUM> are the same for these two embodiments, with the only difference being the addition of a two-part outer sleeve <NUM> and sliding collars <NUM> to <FIG>. In both embodiments, the relatively short inner tube <NUM> may be formed using an internal inversion process. In <FIG>, the two-part outer sleeve <NUM> includes a first or inner shell <NUM> which slidably fits within a second or outer shell <NUM>, thus forming a "telescoping" outer sleeve <NUM>. As illustrated in <FIG>, the outer sleeve <NUM> is not attached to either of the inner and outer tubes <NUM>, <NUM>. However, the first or inner shell <NUM> may hug the outer tube <NUM>, and the overall outer sleeve <NUM> may also be supported by the two sliding collars <NUM>. Note that while the lower sliding collar <NUM> appears to be internally threaded and the upper sliding collar <NUM> appears to not be internally threaded, either or both of the sliding collars <NUM> may be threaded or not threaded as desired. The sliding collars <NUM> may also serve as dust caps to prevent foreign matter from entering into the internal structure of the inversion tube assembly <NUM>.

In embodiments that include an outer sleeve <NUM>, the outer sleeve <NUM> may be configured to provide some degree of resistance against buckling to the outer tube <NUM> (and possibly the inner tube <NUM> as well) when the inner and outer fittings <NUM>, <NUM> are subjected to a compressive force FC. The outer sleeve <NUM> may also protect the outer and inner tubes <NUM>, <NUM> from damage during operational use.

When a net compression force or loading FC above a predetermined compression threshold or a net tension force or loading FT above a predetermined tension threshold is applied to the inner and outer fittings <NUM>, <NUM>, one of the inner and outer tubes <NUM>, <NUM> may increase in length and the other of the inner and outer tubes <NUM>, <NUM> may decrease in length. For example, if a net tension loading FT is applied to the fittings <NUM>, <NUM> of the embodiment shown in <FIG>, such that the tension loading FT is higher than the predetermined tension limit or threshold for that embodiment, then the overall length LDW of the inversion tube <NUM> would increase, with the inner tube length Li also increasing in length and the outer tube length Lo decreasing in length. On the other hand, if the same set of tension loading FT and predetermined tension threshold were applied to the embodiment of <FIG>, the change in inner and outer tube lengths Li, Lo would be opposite to that of the <FIG> embodiment. That is, in the embodiment of <FIG>, as the overall length LDW of the inversion tube <NUM> increases, the inner tube length Li would decrease in length, and the outer tube length Lo would increase in length. Thus, the inversion-formed double-walled tube / energy absorbing assembly <NUM> may be configured for absorbing and/or dissipating impulse energy when a compression or tension impulse force FC, FT above a respective predetermined compression or tension threshold is applied to the inversion tube <NUM>. More specifically, the inner and outer tubes <NUM>, <NUM> and the transition portion <NUM> may be configured for dissipating energy (e.g., impulse energy) when a compression or tension force FC, FT above the respective predetermined compression or tension threshold is applied to the inner and outer fittings <NUM>, <NUM>, causing the inner and outer tubes <NUM>, <NUM> to change in length Li, Lo. To achieve this capability for energy absorption and dissipation, the inner and outer tube thicknesses ti, to may be carefully profiled such that one or both of them varies along some length Li, Lo of the respective inner and/or outer tubes <NUM>, <NUM> in a manner that achieves the desired energy absorption and dissipation capability, including providing the desired predetermined compression and/or tension thresholds.

Thus, after a pre-inversion tube <NUM> has been inverted by having one end pressed inward or rolled outward along some length Lpre of the pre-inversion tube <NUM> - thereby creating an internal or external inversion <NUM>, <NUM> having the abovementioned plastic deformation zones <NUM> that have been formed by "rolling up" some portion of the initial walls of the pre-inversion tube <NUM> - the resulting inversion tube <NUM> may be assembled with the inner and outer fittings <NUM>, <NUM> and the optional outer sleeve <NUM> (with appropriate connections made among the inner and outer fittings <NUM>, <NUM>, the ends of the inner and outer tubes <NUM>, <NUM> and the ends of the outer sleeve <NUM>), such that when the inversion tube assembly <NUM> is placed into service and a net compression or tension impulse force FC, FT above the respective predetermined compression or tension threshold is applied to the inversion tube assembly <NUM> via the inner and outer fittings <NUM>, <NUM>, the impulse force will be absorbed and/or dissipated as either (i) the "rolled up" portion of the initial pre-inversion tube walls are "unrolled", or (ii) additional portions of the walls are "rolled up" (depending on the particular configuration of the inversion tube assembly <NUM> being used).

According to another embodiment, an inversion tube type energy absorber <NUM> includes: an outer tube <NUM> having an outer wall thickness to and an outer tube length Lo; an inner tube <NUM> disposed inside the outer tube <NUM> and having an inner wall thickness ti and an inner tube length Li substantially equivalent to the outer tube length Lo; and a transition portion <NUM> connecting the inner tube <NUM> and the outer tube <NUM> and configured as a plastic deformation zone <NUM>. In this embodiment, at least one of the inner and outer wall thicknesses ti, to varies along its respective inner or outer tube length Li, Lo.

In this embodiment, the inversion tube type energy absorber <NUM> may further include: an outer sleeve <NUM> disposed about the outer tube <NUM> and having opposed fifth and sixth ends <NUM>, <NUM>; an inner fitting <NUM> attached to a second end <NUM> of the inner tube <NUM> distal from the transition portion <NUM>; and an outer fitting <NUM> attached to the fifth end <NUM> of the outer sleeve <NUM>, with the sixth end <NUM> of the outer sleeve <NUM> being attached to a fourth end <NUM> of the outer tube <NUM> distal from the transition portion <NUM>. In this configuration, the inner and outer fittings <NUM>, <NUM> may be configured for receiving compression and/or tension forces FC, FT as applied thereto and for conveying the compression and/or tension forces FC, FT to the inner and outer tubes <NUM>, <NUM>, respectively.

According to yet another embodiment, an energy absorbing inversion tube assembly <NUM> includes an inner tube <NUM> disposed within an outer tube <NUM>, the inner and outer tubes <NUM>, <NUM> having respective wall thicknesses ti, to and being connected with each other via a transition portion <NUM>, wherein the wall thickness ti, to of at least one of the inner and outer tubes <NUM>, <NUM> varies along a respective length Li, Lo of the inner or outer tube <NUM>, <NUM>. The energy absorbing inversion tube assembly <NUM> also includes an inner fitting <NUM> attached to a second end <NUM> of the inner tube <NUM> distal from the transition portion <NUM>, and an outer fitting <NUM> attached to a fourth end <NUM> of the outer tube <NUM> distal from the transition portion <NUM>. In the energy absorbing inversion tube assembly <NUM>, the inner and outer fittings <NUM>, <NUM> are configured for conveying external compression and/or tension forces FC, FT to the inner and outer tubes <NUM>, <NUM>, respectively.

The energy absorbing inversion tube assembly <NUM> may further include an outer sleeve <NUM> disposed about the outer tube <NUM> and configured to provide resistance against buckling to the inner and/or outer tube <NUM>, <NUM> when the inner and outer fittings <NUM>, <NUM> are subjected to a compressive force FC. The outer sleeve <NUM> may have a fifth end <NUM> attached to the outer fitting <NUM> and a sixth end <NUM> attached to the fourth end <NUM> of the outer tube <NUM>.

<FIG> shows a flowchart for a method <NUM> of manufacturing an energy absorbing inversion tube assembly <NUM>, which may also be visualized by the progression of views shown in <FIG>, <FIG>. At block <NUM> of <FIG>, a pre-inversion tube <NUM> is provided having opposed first and second ends <NUM><NUM>, <NUM><NUM>, an initial length Lpre and an initial wall thickness tpre which varies along at least a portion of the initial length Lpre. At block <NUM>, an optional step may be performed, in which the first or second end <NUM><NUM>, <NUM><NUM> may be closed, such as by spinning or swaging. More specifically, if the tube <NUM> is to undergo an internal inversion, then the first end <NUM><NUM> may be closed, but if the tube <NUM> is to undergo an external inversion, then the second end <NUM><NUM> may be closed. And at block <NUM>, the first end <NUM><NUM> of the tube <NUM> is inverted toward the second end <NUM><NUM> - either by pressing the closed first end <NUM><NUM> inward toward the open second end <NUM><NUM> to create in internal inversion <NUM>, or by rolling the open first end <NUM><NUM> outward toward the closed second end <NUM><NUM> to create an external inversion <NUM> - thereby forming an inversion tube <NUM> having an inner tube <NUM> disposed within an outer tube <NUM> with the inner and outer tubes <NUM>, <NUM> being connected with each other via a U-shaped transition portion <NUM>, wherein a respective wall thickness ti, to of at least one of the inner and outer tubes <NUM>, <NUM> varies along a respective length Li, Lo of the inner or outer tube <NUM>, <NUM>.

At block <NUM>, an inner fitting <NUM> is attached to a second end <NUM> of the inner tube <NUM> that is distal from the transition portion <NUM> (and also distal from the opposed first end <NUM> of the inner tube <NUM>), and at block <NUM>, an outer fitting <NUM> is attached to a fourth end <NUM> of the outer tube <NUM> that is distal from the transition portion <NUM> (and also distal from the opposed third end <NUM> of the outer tube <NUM>), wherein the inner and outer fittings <NUM>, <NUM> are configured for conveying external compression and/or tension forces FC, FT to the inner and outer tubes <NUM>, <NUM>, respectively. Additionally, the method <NUM> may also include, at block <NUM>, disposing an outer sleeve <NUM> about the outer tube <NUM>, wherein the outer sleeve <NUM> has opposed fifth and sixth ends <NUM>, <NUM>. At block <NUM>, the fifth end <NUM> of the outer sleeve <NUM> may be attached to the outer fitting <NUM>, and at block <NUM>, the sixth end <NUM> of the outer sleeve <NUM> may be attached to the fourth end <NUM> of the outer tube <NUM>.

As discussed above, it is apparent that the double-walled inversion tube/energy absorber assembly <NUM> of the present disclosure - which utilizes a varying and non-constant wall thickness ti, to along some portion of the inner and/or outer tubes <NUM>, <NUM> - solves the technical problem of design limitation, which is presented by the constant wall thickness utilized in conventional inversion tubes. The present inversion tube/energy absorber assembly <NUM> overcomes this technical problem by the technical effect of utilizing the aforementioned varying wall thickness ti, to along one or both of the tubes <NUM>, <NUM>, thereby providing a significant technical advantage over other approaches. In addition to the use of the inversion tube/energy absorber assembly <NUM> for aircraft seat <NUM> applications, many other uses and applications may be contemplated, such as those where conventional shock absorbers have traditionally been used. For each use or application, the designer may determine the appropriate specifications for the pre-inversion tube <NUM> and resulting inversion tube <NUM>, which may include: the material (e.g., 3003H14 aluminum), the method of inversion (i.e., internal or external), starting dimensions of the pre-inversion tube <NUM>, final dimensions of the finished inversion tube <NUM>, and the thickness profile(s) that the inner and/or outer tubes <NUM>, <NUM> should follow.

The above description is intended to be illustrative, and not restrictive. While the dimensions and types of materials described herein are intended to be illustrative, they are by no means limiting and are exemplary embodiments. In the following claims, use of the terms "first", "second", "top", "bottom", "upward", "downward", etc. are used merely as labels, and are not intended to impose numerical or positional requirements on their objects. As used herein, an element or step recited in the singular and preceded by the word "a" or "an" should be understood as not excluding plural of such elements or steps, unless such exclusion is explicitly stated. Additionally, the phrase "at least one of A and B" and the phrase "A and/or B" should each be understood to mean "only A, only B, or both A and B". Moreover, unless explicitly stated to the contrary, embodiments "comprising" or "having" an element or a plurality of elements having a particular property may include additional such elements not having that property. And when broadly descriptive adverbs such as "substantially" and "generally" are used herein to modify an adjective, these adverbs mean "for the most part", "to a significant extent" and/or "to a large degree", and do not necessarily mean "perfectly", "completely", "strictly" or "entirely". Additionally, the word "proximate" may be used herein to describe the location of an object or portion thereof with respect to another object or portion thereof, and/or to describe the positional relationship of two objects or their respective portions thereof with respect to each other, and may mean "near", "adjacent", "close to", "close by", "at" or the like. Relatedly, the word "distal" may be used herein to describe the opposite of "proximate"; e.g., "far (from)", "distantly removed (from)", "spaced apart (from)", "on the other end (of/from)" or the like.

Claim 1:
An inversion-formed double-walled tube (<NUM>) for use as energy absorber, comprising:
an outer tube (<NUM>) having an outer wall thickness (to);
an inner tube (<NUM>) disposed inside the outer tube (<NUM>) and having an inner wall thickness (ti); and
a U-shaped transition portion (<NUM>) connecting the inner tube (<NUM>) and the outer tube (<NUM>),
wherein the inner tube (<NUM>) has a first end (<NUM>) adjoining the transition portion (<NUM>) and a second end (<NUM>) opposite the first end (<NUM>),
wherein the outer tube (<NUM>) has a third end (<NUM>) adjoining the transition portion (<NUM>) and a fourth end (<NUM>) opposite the third end (<NUM>); and
wherein at least one of the inner (ti) and outer wall thicknesses (to) varies along a length (LDW) of the double-walled tube (<NUM>).