GB1593055A - Self-locking nut - Google Patents

Description

(54) A SELF-LOCKING NUT (71) I, GIULIO MONTICELLI, an Italian Citizen, of Via Savona, 134, Milan, Italy, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a self-locking nut assembly for substantially reducing the risk of nut loosening by shocks, vibrations and the like, to which a nut is ordinarily subjected during use.

The commonest method of nut locking is to interpose a spring washer between the nut and a bearing plane such as a screw, in which case the nut locking depends upon the elastic reaction of the washer in an axial direction tending to hold together the threads on the nut and screw (or other equivalent member on which said nut is screwed down). It is also known to the special metal fittings shaped to engage with one side of the nut and tending to avoid unscrewing of the nut. It has also been proposed to make self-locking nuts with nylon inserts, or to differently shape the nut thread.

All of the prior art systems suffer from the basic disadvantage of not providing correct nut locking under all types of operating conditions, or of having undue production costs and problems.

Specification No. 372 209 describes a two-part self-locking nut device which comprises (a) a nut having a head (2) adapted to be tightened, e.g. hexagonal in shape, a conical neck portion (referenced as 1) which has a maximum diameter less than that of the head, the nut being slit (3) throughout its height, and being evidently internally threaded to fit on a threaded screw (9), and (b) a circular ring ("socket" 4) which is adapted to engage the neck portion of the nut with a clearance (7) below the head of the nut; the ring is resilient and constructed so as to maintain a substantially constant pressure between the piece (5) into which the screw (9) fits and the split nut. As the nut is tightened the ring tends to be crushed and it tightly surrounds the conical part of the nut. The pressure on the ring depends on the angle of the conical part of the nut.

In this device, it is not possible to know precisely the driving torque of the nut, since it is not known what is the torque absorbed by deformation of the ring. Also, there is a maximum height of the device-probably 16 mm-since a height of about 7mm is needed for the ring 4 to be adequately shaped to engage the neck of the nut.

I have devised an improved locking nut device of the aforesaid type, which is more compact in axial height and which has a known torque for the ring deformation.

According to the invention, I provide a two-part self-locking nut adapted to receive a male threaded member, comprising (a) a nut having a body having a polygonal outer surface, a circular neck portion extending downwardly from said body having a diameter less than the distance between opposite faces of the polygonal body whereby an annular offset is formed where the neck portion meets the body, an axial internally threaded hole extending through the body and the neck portion, a longitudinal slot being formed through the body and the neck portion to connect with the axial hole, and (b) a resilient ring, of thickness slightly greater than the neck length, engaging the neck portion of the nut so as to reduce the size of the threaded hole (to thereby provide locking friction between the threads on the nut and male threaded member), the perimeter of the inner edge of the opening in the resilient ring being larger than the outer perimeter of the circular neck, said resilient ring having a noncircular internal surface that contacts said circular neck at spaced regions on said circular neck to thereby promote resilient deformation of said resilient ring, the interference between the circular neck and the inner edge of the resilient ring being in the range of 0.2 to 0.5%.

The principle of the device according to the invention consists in forming a longitudinal slit in the nut body to impart thereto elasticity in a radial direction and taking advantage of such elasticity to radially restrict or narrow the nut to provide a self-locking effect against the threading of a screw or equivalent member on which the nut is screwed down.

By suitably calculating the interference between the nut neck and the inner surface of the resilient contraction ring, and imparting a suitable radial elasticiaty to the latter, self-locking of the nut can be modified or adjusted, and any tolerances in the thread diameters can be compensated for as well. The contraction ring also performs the function of limiting the sector vibrations in highly strcssed mechanisms.

The invention will be hereinafter described with reference to the figures of the accompanying drawings, in which: Figure 1 is a plan view of a first embodiment of a self-locking nut according to the invention Figure 2 is a cross-section taken along line 2-2 of Figure l; Figure 3 is a plan view of the particular embodiment of contraction ring shown in Figure 1; Figures 4 and 5 are plan and sectional views; respectively, showing a second embodiment of contraction ring; and Figures 6 and 7 show the use of the nut shown in Figures 1 and 2.

Referring to Figures 1 and 2, the nut portion comprises a body 2 having a hexagonal outer surface 4 beneath which is a circular neck 6 of smaller diameter than the distance between opposite facets of the surface 4; the nut has an axial hole 8 which is internally threaded at 10, and a slit 12 extending from top to bottom of the nut and from the hole 8 to the exterior. The nut ithus has radial elasticity and is inwardly deformable with closing up of the slit 12.

Around the neck 6 is a resilient circular ring 14 of an inner perimeter larger than that of the circumference of the neck portion 6 of the nut, and which engages the neck 6 so as to resiliently deform the nut and decrcase the size of the axial hole 8.

The ring alone is shown in Figures 4--5 where the contraction ring 14 has two recesses 18. Another embodiment is shown in Figure 3, which is a plan view of a contraction ring 14' having a squared opening 16.

In Figure 3 the ring 14' has an opening of square shape with rounded corners, in which the spacing between the two opposing sides iis smaller than the outer perimeter of neck 9. The quadrangular shape of the opening 16 in contraction ring 14' causes a reduction in the radial width of the ring at the radiused angles of the opening; this confers on the ring a degree of radial elasticity allowing elastic yielding of the ring for compensating any tolerances in the thread diameters, after the nut sectors have been locked against the screw.

The contraction ring shown in Figure 3 contacts the neck 6 of the nut only at the central zones lof the straight lengths of its inner opening, but this involves a stress concentration which at times it would be desirable to reduce.

For that purpose, the contraction ring may be shaped as shown in Figure 4 and 5.

while maintaining the inner development of the opening profile larger than the peripheral development of nut neck 6. This ring 14 is provided with a circular opening 16 of a diameter less than that of neck 6. In order to impart spring properties to ring 14, the inner profile of opening 15 is locally interrupted or broken away, by opposing recesses 18, reducing the radial width of the ring, imparting the desired elasticity to the latter, and an inner development larger than the peripheral development of the neck.

The recesses 18 are shown as a semicircular shape, although they could be of any suitable shape.

The interference between the ring 14 and nut neck is in the range of 0.2 to 0.5% of the threading major diameter. It is preferable to select lower rates for threadings of higher diameter, for example an interference in the range of 0.2 to 0.4% for threadings of a diameter larger than 16mm, and on the other hand a higher interference for threadings of lower diameter, for example in the range of 0.3 to 0.5% for threadings of a diameter lower than 16 mm.

The use of the nut of Figures 1 and 2 is shown in Figures 6 and 7. There is shown a screw 20, the end of which passes through a hole in a piece 22 having a bearing or abutting surface 24, on which contraction ring 14 rests, while the nut 2 is partially screwed down on screw 20 and not yet contacting said contraction ring 14 (Figure 6).

As soon as nut neck 6 comes in contact with the ring 14, due to the initial action of opposed sloping surfaces 26 and 28, the nut 2 is forced to become radially restricted or narrowed against the threading of screw 20.

Forces screwing of nut 2 will cause the neck 6 to fully penetrate into ring 14, whereby (Figure 7) the nut is completely locked on the screw 20. Since the nut is caused to radially and elastically deflect against the threading of screw 20, the nut 1 can be readily unscrewed and then reused, after removal of the nut from its associated ring 14.

It will be seen in Figures 6 and 7 that the thickness of ring 14 is only slightly larger than the length of neck 6 of the nut, so that no appreciable overall size is added to that of the nut, as otherwise occurs with the use of conventional washers interposed between the nut and a corresponding bearing surface.

WHAT I CLAIM IS: 1. A two-part self-locking nut adapted to receive a male threaded member, comprising (a) a nut having a body having a polygonal outer surface, a circular neck portion extending downwardly from said body and having a diameter less than the distance between opposite faces of the polygonal body whereby an annular offset lis formed where the neck portion meets the body, an axial internally threaded hole extending through the body and the neck portion, a longitudinal slot being formed through the body and neck portion to connect with the axial hole, and (b) a resilient ring, of thickness slightly greater than the neck length, engaging the neck portion of the nut so as to reduce the size of the threaded hole (to thereby provide locking friction between the threads on the nut and male threaded member), the perimeter of the inner edge of the opening in the resilient ring being larger that the outer perimeter of the circular neck, said resilient ring having a non-circular internal surface that contacts said circular neck at spaced regions on said circular neck thereby to promote resilient deformation of said resilient ring, the interference between the circular neck and the inner edge of the resilient ring being in the range of 0.2 to 0.5%.

2. A two-part nut as claimed in Claim 1, wherein the resilient ring has a circular opening with opposed recesses therein.

3. A two-part nut as claimed in Claim 1, wherein the resilient ring has an opening in the shape of a square having rounded corners.

4. A two-part nut as claimed in any preceding claim , wherein the resilient ring and the free end of the neck portion of the nut have opposed sloping surfaces.

5. A two-part self-locking nut, substantially as hereinbefore described with reference to the accompany drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. between the nut and a corresponding bearing surface. WHAT I CLAIM IS:

1. A two-part self-locking nut adapted to receive a male threaded member, comprising (a) a nut having a body having a polygonal outer surface, a circular neck portion extending downwardly from said body and having a diameter less than the distance between opposite faces of the polygonal body whereby an annular offset lis formed where the neck portion meets the body, an axial internally threaded hole extending through the body and the neck portion, a longitudinal slot being formed through the body and neck portion to connect with the axial hole, and (b) a resilient ring, of thickness slightly greater than the neck length, engaging the neck portion of the nut so as to reduce the size of the threaded hole (to thereby provide locking friction between the threads on the nut and male threaded member), the perimeter of the inner edge of the opening in the resilient ring being larger that the outer perimeter of the circular neck, said resilient ring having a non-circular internal surface that contacts said circular neck at spaced regions on said circular neck thereby to promote resilient deformation of said resilient ring, the interference between the circular neck and the inner edge of the resilient ring being in the range of 0.2 to 0.5%.

2. A two-part nut as claimed in Claim 1, wherein the resilient ring has a circular opening with opposed recesses therein.

3. A two-part nut as claimed in Claim 1, wherein the resilient ring has an opening in the shape of a square having rounded corners.

4. A two-part nut as claimed in any preceding claim , wherein the resilient ring and the free end of the neck portion of the nut have opposed sloping surfaces.

5. A two-part self-locking nut, substantially as hereinbefore described with reference to the accompany drawings.