Attachment bolt for positive locking

Abstract

A fastening bolt has a threaded screw (11) with a terminal portion (18) whose diameter (19) is less than that of the threaded portion, and an end surface (21) of said terminal portion has a transverse opening groove (22). The fastening bolt also has a nut (30) comprising a threaded body (32) and an unthreaded crown (34) drilled with at least two holes (35) diametrically opposite to one another and a rod (23), able to fit in the groove of the screw and in the two lateral holes of the nut to lock the bolt. The body of the nut comprises a driving portion (38), as well as a cylindrical portion (39) less thick than the driving portion, and the cylindrical portion (39) of the nut has an elliptical deformation that was previously a circular shape.

Claims

1. Fastening bolt comprising: a screw, said screw comprising a head, a threaded portion disposed along a first axis, and a terminal portion, said terminal portion being adjacent along the first axis to the threaded portion, said terminal portion having a diameter less than a minimum diameter of the threaded portion, said terminal portion having an end face with a transverse opening groove in the end face; a nut comprising a front bearing surface, a threaded body disposed along a second axis comprising a threaded portion, and the nut further including an unthreaded crown, adjacent to the threaded body along the second axis, on a side of the nut opposite the bearing surface, said crown having at least two lateral holes, diametrically opposite one another; a rod, able to fit in the groove of the screw and in the two lateral holes of the nut; said bolt being characterized in that: the nut has an elliptical deformation of the threaded portion previously in a circular shape having an outer diameter, the ratio between the outer diameter of the threaded portion before deformation and a nominal diameter of the nut is between 1.30 and 1.35 inclusive; and the ratio between the height of the threaded portion and the nominal diameter of the nut is greater than or equal to 0.65.

2. A fastening bolt according to claim 1, such that the threaded body of the nut comprises a driving portion close to the front bearing surface, an outer lateral surface of said driving portion being able to mate with an assembly tool.

3. A fastening bolt according to claim 2, such that the threaded portion is disposed between the driving portion and the unthreaded crown.

4. A fastening bolt according to claim 1, such that a smaller outer diameter of the elliptically deformed threaded portion is less than a minimum outer diameter of the driving portion.

5. A fastening bolt according to claim 1, such that the nut comes from a method comprising an elliptical deformation of the threaded portion and the unthreaded crown previously in a circular shape.

6. A fastening bolt according to claim 5, such that a minimum inner diameter of the unthreaded elliptical crown is greater than a diameter of the terminal portion of the screw.

7. A fastening bolt according to claim 1, such that the threaded body of the nut comprises a driving portion and that a length of the driving portion along the second axis is less than or equal to one-third the total length of the threaded body along said axis.

8. A fastening bolt according to claim 1, such that the nut is made of steel and the screw is made of a titanium alloy.

9. A fastening bolt according to claim 1, such that the nut and the screw are made of a titanium alloy.

Description

(1) The invention will be better understood when reading the following description and examining the accompanying figures. These are provided for information purposes only and are not exhaustive concerning the invention. The figures illustrate the following:

BRIEF DESCRIPTION OF THE DRAWINGS

(2) FIG. 1: An exploded view of a fastening bolt according to one embodiment of the invention;

(3) FIG. 2: A cross-section view of a nut member of FIG. 1 after elliptical deformation;

(4) FIG. 3: A cross-section view of a nut member of FIG. 1 before elliptical deformation;

(5) FIG. 4: A top plan view of a nut member of FIG. 1 after elliptical deformation.

DETAILED DESCRIPTION

(6) FIG. 1 shows a side of a fastening bolt according to one embodiment of the invention, in an unassembled form.

(7) The bolt 10 comprises a screw 11, disposed along a first axis 12. The screw 11 comprises a head 13, said head 13 possessing a bearing surface 14 able to come into contact with a structure to be assembled. The head 13 further possess a lateral driving surface 15, able to mate with an assembling tool. In the example of FIG. 1, the surface 15 has a shape called “bi-hexagonal” or “twelve-toothed.”

(8) The head 13 is extended along the axis 12 by a cylindrical shaft 16. The shaft 16 is itself extended by a threaded portion 17. One end of the screw 11 opposite the head is formed by a terminal portion 18, which extends the threaded portion 17 along the axis 12. The terminal portion 18 has a smooth lateral surface, whose diameter 19 is less than a minimum diameter 20 of the threaded portion 17. “Minimum diameter” refers to the root diameter of the threaded portion 17.

(9) One end face 21 of said terminal portion comprises a transverse opening groove 22. This groove is able to accommodate a rod 23 when the bolt 10 is assembled.

(10) As is visible in FIG. 1, the groove 22 has a slotted cross-section, but alternative shapes are possible.

(11) Furthermore, the bolt 10 comprises a nut 30, disposed along a second axis 31. When the bolt 10 is assembled, the first axis 12 and the second axis 31 are identical.

(12) The nut 30 comprises a head 32, of which one end along axis 31 supports a front bearing surface 33 able to come into contact with a structure to be assembled. Another end of the body 32 is extended by a crown 34, said crown being pierced by at least two lateral holes 35, diametrically opposite one another. The holes 35 are able to accommodate a rod 23 when the bolt 10 is assembled.

(13) FIG. 2 depicts a cross-section view of the nut 30, along a cross-section plane A-A, passing through the axis 31 and perpendicular to FIG. 1.

(14) A thread 36 is formed on the inner surface of the body 32. The thread 36 is able to cooperate with the threaded portion 17 of the screw 11 when installing the nut on the screw.

(15) The crown 34 atop the body 32 is not threaded, and an inner diameter 37 of said crown is preferentially greater than a root diameter of the thread 36.

(16) The threaded body 32 of the nut comprises a driving portion 38 close to the bearing surface 33. An outer lateral surface of said portion 38 is able to mate with a tool assembling the nut onto the screw. In the example in FIGS. 1 and 2, the driving portion 38 has a “bi-hexagonal” or “twelve-toothed” shape.

(17) The body 32 further comprises a chimney 39, located between the driving portion 38 and the crown 34.

(18) The chimney 39 is preferentially chosen to be of low thickness. More preferentially, a smaller outer diameter 40 of the chimney is less than an minimum outer diameter 41 of the driving portion 38.

(19) A total height 42 of the threaded body 32 along the axis 31 between the bearing surface 33 and an end of the threading 36 is equal to a height 43 of the driving portion 38 plus a height 44 of the chimney 39.

(20) Furthermore, the chimney 39, and potentially the crown 34, have an oval or elliptical shape. More specifically, the outer diameter 40 of the chimney, and potentially that of the crown, as can be seen in FIG. 2, are slightly less than the outer diameter 45 of the crown 34, as can be seen in FIG. 1.

(21) The diameter 40 represents the smallest diameter of the ellipse formed by an outer edge of the crown 34 and the diameter 45 represents the largest diameter of said ellipse.

(22) This elliptical shape is created during the manufacturing of the nut 30, from the nut 130 depicted in FIG. 3. The chimney 139 and the crown 134 of the nut 130 have a circular cross-section.

(23) The elliptical deformation of the nut 130 is created in a known manner, by pinching or flattening the chimney 139 and potentially the crown 134, before a heat treatment. A similar method is, for example, described in the document EP2452082.

(24) Preferentially, the elliptical deformation is carried out at the midpoint of the chimney 139, meaning at an equal distance from the driving portion and the crown 134.

(25) The elliptical shape of the thread of the chimney 39 ensures the immobilization of the nut 30 on the screw 11, by locking, when the bolt 10 is assembled. The bolt 10 therefore has dual anti-loosening safety: Both the locking effect and the rod 23 holding system.

(26) In a known manner, it is desirable for the small diameter 40 of the ellipse to be narrow enough to ensure the locking function, but without the deformation exceeding the elastic limit of the material forming the nut. Thus, when the screw is introduced into the nut 30 for the first time, the nut will elastically, and not plastically, deform.

(27) Preferentially, the inner diameter 37 of the crown 34, which corresponds to the smallest diameter of the ellipse, is greater than the diameter 19 of the terminal portion of the screw 11. Thus, there is no risk that the edges of the groove 22 will become enmeshed in the holes 35 when the nut 30 is installed on the screw 11.

(28) Relative to the total height 42, along the axis 31, of the threaded body 32, the chimney 39 is higher than the chimneys of the nuts of the prior art, such as the slotted nut of document FR2955632.

(29) Furthermore, the outer diameter 140 of the chimney 139 before deformation and a nominal diameter 46 of the nut have a ratio between 1.30 and 1.35 inclusive. The ratio between the diameter 140 and the diameter 46 is, for example, equal to 1.33.

(30) Additionally, the ratio between the height 44 of the threaded chimney 39 and the nominal diameter 46 of the nut is greater than or equal to 0.65.

(31) “Nominal diameter of the nut” refers to a value indicating the size of the nut, e.g. 6 mm or ¼ inch. The nominal diameter corresponds to a minimum root diameter of the nut according to the AS8879 standard. In the context of the present invention, that minimum diameter is measured in the driving portion, which does not undergo any deformation during manufacturing.

(32) These height and diameter characteristics of the chimney 39 advantageously give that chimney an elasticity that enables it to deform circularly when the nut is assembled on the screw, then returns to its elliptical shape when disassembled. The bolt 10 therefore has a stable behavior over many installation cycles.

(33) According to another preferential form of the invention, the height 43 of the driving portion 38 is less than or equal to one-third the total height 42 of the threaded body. Thus, the driving height is enough to allow the tightness torque to change without making the nut heavier.

(34) The bolt 10 of FIG. 1 has particularly been compared to bolts of the prior art, with the nut being locked by elliptical deformation as in document FR2955632.

(35) The bolts have been subjected to assembly/disassembly tests according to the NFL22-500 standard: Maximum screwing torque: 6.6 N.Math.m; tightness torque: 43 N.Math.m; minimum unscrewing torque: 1.16 N.Math.m. The tests were conducted on an automatic measurement instrument, at 10 rpm.

(36) In bolts of the prior art, after five assembly/disassembly cycles, the small diameter of the ellipse of the elliptical deformation of the nut substantially increased, and no longer provides a sufficient locking function. The nut plastically deforms when installed on the screw.

(37) On the other hand, steel nuts 30 maintain their elliptical shape without a plastic deformation of the small ellipse diameter after fifty assembly/disassembly cycles on screws 11 made of titanium alloy TA6V, coated and lubricated, for example with the HI-KOTE® NC coating distributed by the company Hi-Shear Corp and cetyl alcohol. The smallest inner diameter 37 of the ellipse was measured for ten new nuts 30, as well as ten nuts 30 that have undergone assembly/disassembly cycles. The results are listed in table 1 below:

(38) TABLE-US-00001 TABLE 1 Small diameter (mm) 1 2 3 4 5 6 7 8 9 10 Average New nut 12.9 12.9 12.8 12.9 13.0 13.0 13.0 12.9 12.9 13.0 12.93 Nut after 50 12.9 13.0 13.1 12.9 12.9 13.0 13.0 12.8 12.9 12.9 12.94 cycles

(39) The results above show that the dimensions of the ellipse formed by the chimney 39 and the crown 34 barely vary at all after fifty installation/removal cycles on one screw 11.

(40) Compared to the nuts of the prior art, the height and diameter of the chimney 39 therefore make it possible to increase the elasticity of said nut, such that the elastic deformation limit is not exceeded when the nut is installed on the screw. The elliptical shape is thereby preserved, which ensures a stability of the screw/nut locking torque during repeated installation/removal cycles.

(41) Equivalent tests were conducted on nuts 30 and screws 11 made of TA6V titanium alloy, each of said parts being coated appropriately. An appropriate coating is, for example, a solid lubricant film like MoS2 or a dyed corrosion-resistant coating like HI-KOTE® or Kalgard® FA. The results show that the TA6V titanium alloy nuts withstand at least fifteen installation/removal cycles on TA6V titanium alloy screws.