JOINING SYSTEM

Abstract

Joining system, between a first front element (1) and a second rear element (2), comprising a through hole (3), the joining system comprising: - a threaded bolt (4) to pass through the through hole (3) of the first element (1) and the second element (2), - a stem (5) configured to be located concentrically to the threaded bolt (4) in at least the front longitudinal area (4.2) of the threaded bolt (4) and to move together with said threaded bolt (4), the stem (5) comprising an outer face (5.1) comprising at least a tapered longitudinal section (5.3), - a housing (7) attached to the second rear element (2) and comprising a conical inner face (7.1) for housing the stem (5), and - a fastening element (6) configured for threading the rear longitudinal area (4.1) of the threaded bolt (4) for fixing the joining system.

Description

JOINING SYSTEM FIELD OF INVENTION The invention relates to the technical field of joining systems between structural elements. More specifically, it relates to panel joints in the aeronautical sector. STATE OF THE ART There are multiple known joining systems between two structures that have an opening for the introduction of a joining system element. For example, bolted structural connections are well-known. These connections have the drawback that they require the elements to be joined to be in a precise, aligned position, as this type of connection does not allow for misalignment. Similarly, these connections do not allow for load control during assembly and disassembly. Furthermore, disassembly can sometimes be complicated because it requires access to both sides of the connection, which is not always possible or easy. Clearance-fit joints are also known. These joints still have the disadvantage of not being able to absorb misalignments between the elements being joined, and it is not possible to control the load transmitted by the joint system during assembly and disassembly. Additionally, this joint system can result in a loose bolt fit and has low load transfer due to the clearance itself. Quick-release fasteners are also common. This type of joint does allow for some compensation for misalignment between the elements being joined. However, this type of joint also has the disadvantage of providing a loose bolt fit and having low load transfer capacity. They also require perpendicular installation since the threaded portion is perpendicular to the joint and cannot be tilted. Tapered shank fasteners are also known. This type of fastener can accommodate small misalignments, although it requires that the holes in the elements to be joined be tapered. Also well-known are the door fastening systems used in the aeronautical sector, such as door latches. These systems have the drawback of not being able to withstand structural loads and are often complex. Door hooks are also common, but they are heavy, primarily due to their complexity. Furthermore, this type of fastening can only withstand axial loads. SUMMARY OF THE INVENTION The invention therefore addresses the need for joining elements, more specifically the joining of structural elements such as large panels. The objective of the invention is for the joining system to facilitate assembly and disassembly and to accommodate misalignments between the elements being joined. These misalignments may be due to dissimilar deformations of the elements themselves. More specifically, the system that is the subject of the invention allows the union between at least a first front element and a second rear element, each of the elements comprising a through hole. The front element is understood to be the one that is in front and the rear element is understood to be the one that is behind according to the direction of introduction of the joining system. The system that is the subject of the invention comprises: - A threaded bolt comprising a longitudinal shaft and configured to pass through the through hole of the first element and the second element. The threaded bolt comprises a front longitudinal section and a rear longitudinal section. - A stem configured to be located concentrically to the threaded bolt in at least the forward longitudinal portion of the threaded bolt. The stem is configured to move with the threaded bolt. The stem also comprises a curved outer face, i.e., its external surface, comprising at least one tapered longitudinal portion directed toward the rear longitudinal portion of the threaded bolt. Directed indicates that its diameter decreases toward the rear longitudinal portion of the threaded bolt. - A housing configured to be attached to the second rear element. The housing comprises a conical inner face, i.e., a conical internal surface, for housing the stem in the assembled position of the joining system. - A fastening element configured for threading the rear longitudinal area of ​​the threaded bolt for fixing the joining system when mounted on at least the first element and the second element. The threaded bolt, along with the fastener, is responsible for transferring axial loads. The threaded bolt also creates the force required for assembly by rotating within the fastener, which could be, for example, a nut. The connecting element is the other component that holds the system in place and transfers axial loads. The connecting element reacts to the installation force exerted by the threaded bolt. The stem, in turn, transfers the shear load. During assembly of the joining system, the tapered section of the stem aligns the elements to be joined as it advances along with the threaded bolt. The housing provides the necessary space for the tapered section of the stem to pass through the through holes of the elements to be joined and transfers the axial loads. Furthermore, the conical area of ​​the housing allows for alignment by partially corresponding to the external truncated conical shape of the stem. The claimed invention has the following advantages: - Correcting significant mismatches between through holes, for example, drill holes, of the elements to be joined. - The gradual transfer of load, due, for example, to structural weight, between the joined elements during assembly and disassembly. This gradual transfer is achieved with controlled tightening. As the tapered piece is inserted into the through-holes of the parts to be joined, the joint is gradually loaded as the bolt and stem advance. Therefore, the alignment of the through-holes occurs gradually as the joint is tightened / loosened by the tapered piece. - Its use for multiple assembly and disassembly cycles. - The reduction in assembly time required for the pre-positioning of the elements to be joined. The invention saves time and tooling since otherwise it is necessary to precisely align the holes of the parts to be joined beforehand. - Reduced weight compared to, for example, door opening and closing elements such as hinges, latches, etc. - Easy assembly and disassembly, as it is not necessary to access both sides of the joining system, since the invention allows access from the front, eliminating the need to access the rear. - Easy inspection, maintenance, and repair. - Use in combination with other complementary solutions. DESCRIPTION OF THE FIGURES To complete the description and provide a better understanding of the invention, a set of drawings is provided. These drawings form an integral part of the description and illustrate embodiments of the invention. The drawings comprise the following figures. Figure 1 shows a first example of the realization of a longitudinal section of a first element and a second element to be joined and of a joining system in the assembled position. Figures 2A-2E show a longitudinal section of a first element and a second element to be joined, and a second example of an embodiment of a joining system according to the invention. Figure 2 shows an assembly sequence for said embodiment of the joining system. Figure 3 shows a longitudinal section of a third example of an embodiment of a first element and a second element to be joined and of a joining system in the assembled position. Figure 4 shows a perspective view of the corresponding embodiment example in Figure 3. DETAILED DESCRIPTION OF THE INVENTION The figures show several examples of the implementation of the joining system of the invention. The first element (1) is represented as being located in a front position and the second element (2) as being located in a rear position. Both elements (1, 2) comprise a through hole (3). The first and second elements (1, 2) can be made of any material, for example, metallic, composite material, CFRP, etc. The represented joining system comprises: - The threaded bolt (4) passing through the through hole (3) of the first element (1) and the second element (2). The threaded bolt (4) comprises a rear longitudinal zone (4.1) and a front longitudinal zone (4.2). - The stem (5) configured to be located concentrically to the threaded bolt (4) in at least the front longitudinal area (4.2) of the threaded bolt (4). The stem (5) comprises an outer face (5.1) comprising at least one tapered longitudinal section (5.3) pointing towards the rear longitudinal area (4.1) of the threaded bolt (4). - The housing (7) attached to the second rear element (2). The housing (7) comprises a conical inner face (7.1) where the stem (5) is housed in its mounted position. - The fastening element (6) threaded to the rear longitudinal area (4.1) of the threaded bolt (4) for fixing the joining system. The housing (7) is attached to the second rear element (2) by any joining means, for example, riveting, adhesive bonding, etc. In one embodiment, the stem (5) is attached to the threaded bolt (4). This connection can be made, for example, by means of a pin or a ring. This connection facilitates the disassembly of the joining system. In another embodiment, the stem (5) and the threaded bolt (4) form a single piece. This reduces the number of parts in the fastening system and facilitates its disassembly. In one embodiment, the single piece could consist of a solid stem (5), without an axial through-hole, terminating at its rear in a threaded cylinder, i.e., the rear longitudinal section (4.1) of the threaded bolt (4) that is capable of engaging with the fastening element (6). In one embodiment, the fastening element (6) can be a nut. In one embodiment, the clamping element (6) comprises a spherical float. This allows the stem (5) to be tilted during the initial assembly stages and permits assembly even when the holes in the first element (1) and the second element (2) are not aligned. This movement is shown in Figure 2, where the third and fourth images of the assembly sequence allow the threaded bolt (4) to be tilted. The clamping element (6) allows the threaded bolt (4) to be tilted while also allowing it to be tightened. Centering is then achieved using the male-female conical surfaces. Centering occurs by advancing the male conical portion over the through holes (3) of the elements (1, 2) to be joined. The female conical piece acts as a housing, and its conical shape helps the threaded bolt (4) advance towards the fastening element (6). Furthermore, the fastening element (6) shown in figure 3 comprises a curved front part (6.1) that contributes to this spherical mobility. In the embodiment shown in the figures, the joining system could comprise a bushing attached to the inner face (7.1) of the housing (7) to prevent wear of said inner face (7.1). This bushing is not shown in the figures. In one embodiment, shown in the figures, the clamping element (6) is configured to be located after the front end of the housing (7). Thus, the housing (7) and the clamping element (6) are configured such that the housing (7) is located longitudinally between the clamping element (6) and the second rear element (2). It is, therefore, an element independent of the housing (7). Figure 2 shows a second example of the embodiment of the joining system of the invention and also the assembly sequence of said embodiment. The fastening element (6) forms a single piece with the housing (7). This embodiment has the advantage of preventing the fastening element (6) from falling into an inaccessible area, for example, of an aircraft, and thus improves the safety and ease of assembly of the joining system. More specifically, in the embodiment shown, the fastening element (6) is located at the rear end of the housing (7). More specifically, it corresponds to a nut embedded in the front end of the housing (7). As discussed above, Figure 2 describes the assembly sequence of the joining system. In the first image, the first front element (1) and the second rear element (2) are misaligned; that is, their respective through-holes (3) are not on the same longitudinal axis. The sequence shown shows that the housing (7) is attached to the second rear element (2). The threaded bolt (4) and stem (5) are inserted into the free space created by the two through-holes (3) from the front. In the second image, the rear end of the threaded bolt (4) contacts the fastening element (6) and begins to be threaded into it (6). In the embodiment shown, the distance between the rear end of the threaded bolt (4) and the rear end of the stem (5) is greater than the length of the housing (7). Thus, the length of the threaded bolt (4) is such that it engages with the thread of the fastener (6) when the rear end of the stem (5) is still outside the through holes (3) of the elements to be joined (1, 2). This allows the threading to control the longitudinal displacement of the stem (5) and therefore the axial force exerted by it on the elements to be joined (1, 2). The third image depicts the sliding and deformation between the components of the joining system of the invention. The joining system allows for an inclination between the threaded bolt (4) and the housing (7), as previously described. In the fourth image, it can be seen how the stem (5) pushes the second rear element (2) whose through hole (3) aligns with the through hole (3) of the first front element (1). The last image shows the final configuration of the joining system in its mounted position. In both embodiments, the conical inner face (7.1) of the housing (7) comprises a complementary shape to the outer face (5.1) of the stem (5), so that both elements are perfectly fitted once the joining system is assembled. In the embodiments shown, the stem (5) and the threaded bolt (4) are flush on their back side. During alignment, high pressure can be applied to the edges of the through-holes (3) of the elements (1, 2) to be joined. To prevent material wear, the joining system may include bushings (8), for example, made of carbide, located in these through-holes (3) as shown, for example, in Figure 3. Figures 3 and 4 illustrate an exemplary embodiment in which the fastening system comprises a retaining sleeve (9) connected to the fastening element (6), for example, a nut. The retaining sleeve (9) comprises means for: - prevent the rotation of said fastening element (6) around the longitudinal axis of the threaded bolt (4), and - limit the displacement along the longitudinal axis of the threaded bolt (4) of said fastening element (6). Thus, the retaining sleeve (9) limits the fastening element (6) both in its rotation around the threaded bolt (4) and in its longitudinal displacement relative to said threaded bolt (4). The retaining sleeve (9) acts, in a way, as a housing for the fastening element (6). This arrangement has advantages, for example, when disassembling the fastening system, which would be done from the front. During disassembly, the threaded bolt (4) moves longitudinally towards the front of the fastening system and, at a certain point, loses contact with the fastening element (6). The retaining sleeve (9) then houses the fastening element (6), preventing it from falling and becoming lodged in an inaccessible area, such as that of an aircraft. According to the embodiment shown in the figures, the retaining bushing (9) comprises a first surface (9.3) intended to be positioned perpendicular to the longitudinal axis of the threaded bolt (4). This first surface (9.3) comprises a first hole for housing the fastening element (6). In one embodiment, this first hole is shaped to complement the fastening element (6). In this way, the retaining bushing (9) prevents the fastening element (6) from rotating about the longitudinal axis of the threaded bolt (4). In the embodiment shown, the retaining bushing (9) also comprises at least a second surface (9.2) intended to be positioned parallel to the longitudinal axis of the threaded bolt (4). This second surface (9.2) partially covers the fastening element (6) and the rear portion of the housing (7) longitudinally. The second surface (9.2) is attached to the first surface (9.3). In the embodiment shown, the retaining bushing (9) comprises four second surfaces (9.2) as can be seen in Figure 4. It could alternatively comprise a single continuous second surface (9.2) surrounding the threaded bolt (4). The second surface (9.2) comprises at least one second hole (9.1) for the insertion of a through-bolt connecting the retaining bushing (9) to the housing (7). A screw, the tip of which would be located in the housing (7), can be inserted into this second hole (9.1). In this way, the retaining bushing (9) is secured to the housing (7), preventing longitudinal displacement and rotation between the two elements. In the embodiment shown in the figures, the housing (7) further comprises a hollow (7.2) facing the second holes (9.1) of the retaining sleeve (9) for insertion of the screw mentioned above. In the embodiment shown in Figures 3 and 4, there is a clearance (not shown) between the fastening element (6) and the retaining sleeve (9). This clearance allows for spherical rotation of the fastening element (6), i.e., around the two axes orthogonal to the longitudinal axis. As mentioned previously, this allows the threaded bolt (4) and the stem (5) to be tilted during the initial assembly stages, permitting assembly even when the holes in the first element (1) and the second element (2) are not aligned. The spherical rotation of the fastening element (6) allows the threaded bolt (4) and the fastening element (6) to be joined even while the threaded bolt (4) is still tilted. Finally, in the embodiment shown in Figures 3 and 4, the fastening element (6) comprises a front section with a larger radial dimension than the rear section located in correspondence with the hole in the first surface (9.3). Specifically, the curved front portion (6.1) has a larger transverse dimension than said hole. This helps the fastening element (6) to be retained in the retaining sleeve (9) once it is separated from the threaded bolt (4). It also provides a contact surface between the fastening element (6) and the housing (7) adapted for the case where the threaded bolt (4) and the fastening element (6) are inclined.

Claims

1. - Joining system, between at least a first front element (1) and a second rear element (2), each of the elements (1, 2) comprising a through hole (3), the joining system being characterized in that it comprises: - a threaded bolt (4) comprising a longitudinal axis and configured to pass through the through hole (3) of the first element (1) and the second element (2) and comprising a rear longitudinal zone (4.1) and a front longitudinal zone (4.2), - a stem (5) configured to be located concentrically to the threaded bolt (4) in at least the front longitudinal zone (4.2) of the threaded bolt (4) and to move together with said threaded bolt (4), the stem (5) comprising an outer face (5.1) comprising at least a tapered longitudinal section (5.3) pointing towards the rear longitudinal zone (4).1) of the threaded bolt (4), - a housing (7) configured to be attached to the second rear element (2) and comprising a conical inner face (7.1) for housing the stem (5) in the mounted position of the joining system, and - a fastening element (6) configured for threading the rear longitudinal area (4.1) of the threaded bolt (4) for securing the joining system when mounted on at least the first element (1) and the second element (2).

2. Joining system according to claim 1, characterized in that the stem (5) is attached to the threaded bolt (4).

3. Joining system according to claim 1, characterized in that the stem (5) and the threaded bolt (4) form a single piece.

4. Joining system according to any one of the preceding claims, characterized in that the conical inner face (7.1) of the housing (7) comprises a shape complementary to the outer face (5.1) of the stem (5). 5.- A joining system according to any one of the preceding claims, characterized in that the fastening element (6) and the housing (7) form a single piece.

6. A joining system according to claim 5, characterized in that the fastening element (6) is located at a rear end of the housing (7).

7. A joining system according to any one of the preceding claims 1 to 4, characterized in that the housing (7) and the fastening element (6) are configured such that the housing (7) is located longitudinally between the fastening element (6) and the second rear element (2).

8. A joining system according to any one of the preceding claims, characterized in that the fastening element (6) is a nut.

9. A joining system according to claims 6 and 8, characterized in that the nut is embedded in the housing (7). 10.- A fastening system according to any one of the preceding claims, characterized in that the fastening element (6) comprises a spherical float.

11. A fastening system according to claim 10, characterized in that the fastening element (6) comprises a curved front portion (6.1).

12. A fastening system according to any one of the preceding claims, characterized in that the distance between the rear end of the threaded bolt (4) and the rear end of the stem (5) is greater than the length of the housing (7). 13.- A fastening system according to any one of the preceding claims, characterized in that it comprises a retaining bushing (9) in connection with the fastening element (6), the retaining bushing (9) comprising means for: - preventing rotation of the fastening element (6) about the longitudinal axis of the threaded bolt (4), and - limiting the displacement of the fastening element (6) about the longitudinal axis of the threaded bolt (4).

14. A fastening system according to claim 13, characterized in that the retaining bushing (9) comprises a first surface (9.3) intended to be located in a mounting position perpendicular to the longitudinal axis of the threaded bolt (4) and comprising a first hole for housing the fastening element (6).

15. A fastening system according to claim 14, characterized in that the retaining bushing (9) comprises at least a second surface (9.2) intended to be located in a mounting position parallel to the longitudinal axis of the threaded bolt (4) so ​​that it partially covers longitudinally the fastening element (6) and the rear of the housing (7), the second surface (9.2) comprising at least a second hole (9.1) for the insertion of a through-hole joining the retaining bushing (9) to the housing (7).

Images