GB2028948A - Improvements in or Relating to Self-locking Nuts - Google Patents

Abstract

A self-locking nut has a body 10 with an internally threaded bore 13, a passage 16 extending inwardly from an outer face 11 of the nut, and a locking element 18 located therein, which projects from the outer face of the nut, but is restrained from leaving the passage. After tightening the nut, the locking element 18 can be urged inwardly, deeper into the passage 16 to deform the material of the nut body in the region of the inner end of the passage 16, thereby to engage firmly the threads of the nut with those of an element on which the nut is threaded. The locking element may be a hardened steel ball, or bar or rod. The nut may have only one flat as shown, or may be hexagonal, and may be provided with a plurality of passages and associated locking elements. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Self-locking Nuts This invention relates to self-locking nuts, by which term is meant an internally threaded member in the form of a nut and having means adapted to increase the resistance to loosening following the tightening of the nut on a correspondingly-threaded element.

There have been innumerable proposals for increasing the resistance to loosening of a nut once tightened on to an externally threaded element. The simplest proposals comprise using a specially-formed washer between the nut and a surface against which the nut is tightened, such as a "shake-proof" washer or a Grover spring washer. A more secure arrangement is to employ a tab-washer which has to be bent against a flat of the nut once tightened. Yet another possibility is to employ two nuts; following tightening of the first nut, the second nut is run down the threads of the second element and tightened on to the first nut. Both of the last two arrangements are relatively secure, but nevertheless are inconvenient to use, require more assembly time than a simple nut and are relatively costly.

In an attempt to overcome the disadvantages of the above-mentioned prior arrangements, there have been proposals for self-locking nuts, which once threaded on to a threaded element and tightened against a surface, require a relatively high torque to be released. For example, there have been several proposals for nuts partially split thereacross in a generally radial plane so that on tightening the nut against the surface, the part thereof nearer the surface moves axially of the threaded element by a lesser amount than the other part of the nut during the final stage of tightening, thereby relatively moving the two parts and deforming the nut. This tends to bind the nut on to the thread of the threaded element, and a suitable design of the two parts can produce an effect similar to that of using separate nuts.

Other proposals for self-locking nuts include fitting various forms of inserts, such as one or more plugs or a ring, into the body of the nut and made of a plastics material so that the insert engages the threads of the externally threaded element when the nut is used. Such a nut with a plastics material insert has the considerable disadvantage that as soon as the plastics material engages the element threads, a much-increased torque is required to turn the nut, irrespective of whether or not the nut has yet engaged the surface against which it is to be tightened.

Consequently, the tightening of such a nut to a predetermined torque is virtually impossible, even if an allowance is made for the resistance to turning imparted by the plastics material insert, for this resistance will depend upon factors such as temperature and the rather low manufacturing tolerances of fitting the insert. A further disadvantage of such a nut is that the efficiency of the self-locking action decreases the further the nut is moved along a threaded element, and thus each time the nut is used.

It is a principal aim of this invention to provide a self-locking nut which, once tightened, may be set to provide a self-locking action but which nevertheless does not require an increased torque until the self-locking action is operative.

According to this invention, there is provided a self-locking nut, comprising a body having an internally-threaded bore and a passage extending inwardly from an outer circumferential face towards the threaded bore, and a rigid locking element located in the passage, the locking element being of such a length that when engaging the radially inner end of the passage the radially outer end of the element projects beyond the adjacent outer circumferential face of the body, the locking element being restrained from leaving the passage, and being disposed so that following tightening of the nut on an externally threaded element, an inwardly-directed force applied to the locking element deforms the material of the nut body in the region of the inner end of the passage so as firmly to engage the threads on the threaded element.

It will be appreciated that with the self-locking nut of this invention, the torque required to tighten the nut is not affected by the means providing the self-locking action, until such time as the locking element has been forced radially inwardly to deform the material of the body of the nut. Thus, a nut of this invention may be tightened on a threaded element precisely to a predetermined torque, and then the locking element forced inwardly, whereafter loosening of the nut requires a greatly increased torque owing to the deformation of the material of the nut body radially inwardly on to the threads of the threaded element.

The body of the nut of this invention may take a wide variety of forms, depending upon the intended use of the nut. For example, the body may be in the form of a conventional hexagonal nut, and the passage may be bored radially inwardly from one flat thereof. Tightening may then be effected by means of a conventional open-ended spanner, except that the spanner is used to engage only those flats of the nut not including the passage. Once fully tightened, the spanner is then engaged with the flat of the nut having the passage and protruding locking element; on applying torque thereto, the spanner will tend to force the locking element inwardly.

Such an arrangement of course requires the locking element to protrude only to a very small extent beyond the adjacent flat, for otherwise the spanner could not be engaged therewith.

However, the flat from which the passage extends may be relieved to allow the locking element to protrude further therefrom, but the nut would then not be in the form of a true regular hexagon.

For a hexagonal nut, the flat diametrically opposed to that having the locking element may also be provided with a corresponding locking eiement, so that on driving both locking elements radially inwardly, an even greater resistance to turning is generated. Alternatively, the region of the nut diametrically opposed to the locking element may be of rounded form, so as to allow an open-ended spanner to roll therearound when engaged with the flat from which the locking element projects; in this way, an increased force directed inwardly may be applied to the locking element when the spanner is operated.

Another possibility for tightening a hexagonal nut of this invention is to use a box (or plug) spanner having on one inner face thereof an axially-extending recess in which the projecting portion of the locking element can be accommodated. If the walls defining the inner end of the recess are tapered to blend with the general walls of the spanner, once the nut has been tightened, the spanner may be driven axially further on to the nut by means of a blow applied to the opposite end of the spanner, which action drives the locking element inwardly of the nut as the protruding part of the locking element rides up the tapered walls at the end of the recess.

Alternatively, once tightened the spanner could be removed from the nut and a different face engaged with the flat from which the locking element protrudes. A blow on the end of the spanner will then drive the locking element to move inwardly to allow the spanner fully to engage the nut.

Another possible form for the body is to be generally cylindrical but with a single driving flat thereon. Such a form of nut intended primarily for a vehicle wheel fastening is described and claimed in British Patent Specification No.

1,271,223, and is used with a rotatable sleeve therearound to prevent removal other than with a correspondingly-formed key. Further to increase security, the nuts described in that prior Specification may have one or more rivets let into the cylindrical surface so the or each rivet head upstands from the surface; by coding the positions of the rivets a great number of individual combinations can be obtained each operable only by a unique tool. The nut element of the prior Specification No. 1,271,223, can be replaced by a nut arranged according to this invention, with the or each rivet substituted by a corresponding number of passages each having a locking element.So long as such a nut is operated by the correct tool, no force will be imparted on the or each locking element, but if an incorrect tool is ,forced on to the nut, or even some other device in an attempt to remove the nut, the locking elements will be driven radially inwardly to deform the body of the nut and thus to increase the resistance to turning of the nut. Security is thus improved even more, because once the locking elements have been moved inwardly, it is even more difficult to remove the nut from a stud on which it has been threaded.

Yet another possible form for the body of the nut is purely cylindrical, with no flat or other face being provided thereon for engagement by a driving tool. For such a body, the or each locking element can be arranged to project beyond the nut body circumference to an extent sufficient for engagement by a driving tool, so that the or each locking element itself is used to impart torque to the body of the nut. Advantageously, the projecting portion of the or each locking element is of part-spherical shape, and the driving tool has a cylindrical bore for receiving the body of the nut, with one or more recesses being provided in the bore for receiving the projecting portion of the or each locking element.For such an arrangement, the nut may be threaded along a threaded element, by means of the interengagement between the walls of the tool defining the or each recess and the or each projecting locking element portion, until the nut is tightened against a surface. Then, as the nut starts to require an increased torque to be turned, by virtue of the part spherical form of the projecting portion of the or each locking element, an inwardly-directed force is generated on the or each locking element as the tool is turned further, untii eventually a sufficient force is generated to move the or each locking element inwardly, thereby deforming the material of the body of the nut. Eventually, the tool may turn freely around the outside of the nut body, and the nut is locked on to the threaded element.Such an arrangement is useful when a permanent fastening is required with antivibration properties; clearly, because the or each locking element has been moved inwardly, it would be most difficult to remove the nut, since there are no driving faces thereon.

In order to allow an effective locking action, the force which must be applied to a locking element of a nut in this invention should not be excessively high, and it is therefore preferred for the passage to extend substantially to the locus of the major diameter of the thread formed in the bore of the nut body. Preferably, the passage is formed with a conventional metal drill bit and thus the passage has a conical portion at the blind end thereof; for such a passage, the apex of the conical portion should lie substantially on the pitch circle of the major diameter of the thread.

Conveniently, the or each locking element is in the form of a sphere, such as a hardened steel ball. The diameter of such a ball (and of the passage in which the ball is located) can be selected taking into account the major diameter of the thread within the nut body, the radial length of the passage to the outer circumferential face through which the passage opens, and the required amount of projection of the locking 4 element beyond the adjacent outer circumferential face.

By way of example only, certain specific embodiments of this invention will now be described, reference being made to the accompanying drawings, in which: Figure 1 is a plan view of a first embodiment self-locking nut of this invention; Figure 2 is a side view of the nut of Figure 1, with the locking element in a first position; Figure 3 is a side view of the nut of Figure 1 but with the locking element in a second position; Figure 4 is an end view of a driving tool for the nut of Figures 1 to 3; Figure 5 is a plan view of a second embodiment of nut of this invention; Figure 6 is a plan view of a power-operated tool for locking a nut of this invention; and Figure 7 is a sectional view of a third embodiment of nut of this invention.

Referring to Figures 1 to 3, there is shown a first embodiment of self-locking nut arranged in accordance with this invention and comprising a nut body 10 having a generally cylindrical outer surface 11 but formed with a single driving flat 12. The body 10 has a bore 13 concentric with the axis of the cylindrical outer surface 11, which bore is internally threaded and the major diameter of the thread is shown at 14. A passage 1 6 of circular-section is drilled radially into the nut body from the cylindrical outer surface thereof, the passage 1 6 being blind and having a generally conical form at its radially inner end. The conical form is cut by a metal drill appropriately ground at its tip, and the apex 1 7 of the conical form lies substantially on the major diameter 14 of the thread in the nut body.Located in the passage 1 6 is a hardened steel ball 18, the diameter of the ball being substantially that of the passage. the cylindrical outer surface 11 of the nut body is peened inwardly of the passage at 19 so as to prevent withdrawal of the ball.

The amount a by which the ball 18 projects from the cylindrical outer surface 11 of the nut is arranged to be substantially equal to the height of the conical form at the radially inner end of the passage 1 6. The amount a can be adjusted by an appropriate selection of ball diameter (and consequently passage diameter), taking into account the radial nut body wall thickness from the major diameter 14 of the thread to the cylindrical outer surface.

Figure 4 shows a tool adapted for driving the nut of Figures 1 to 3. The tool has a body 20 formed with a bore 21 of a diameter suitable for receiving snugly the body 10 of the nut. The wall of the tool is thickened locally to define an internal flat 23 for engaging the driving flat 12 of the nut. A recess 24 extends from the free end of the tool parallei to the axis thereof at an appropriate angular disposition relative to the flat 23 for receiving the projecting portion of the ball 18.

During tightening of the nut of Figures 1 to 3 with the tool of Figure 4, no force is imparted to the ball 18. Once the nut has been torqued to the required value, the tool is removed, and another wool similar to that of Figure 4 but not provided with the recess 24 is offered up to the nut. That other tool is then driven axially, for example by means of a hammer blow, and this forces the ball 1 8 radially inwardly, deforming the material of the nut body as shown in Figure 3, in the region of the blind inner end of the passage 1 6.

It will be appreciated that two or more passages 1 6 can be provided, to increase the locking action. Moreover, the relative disposition of the or each passage can be coded with respect to the driving flat 12, so that the nut is drivable only by means of a tool having appropriately disposed recesses. Once the nut has been tightened with such a tool, the or each ball 16 need not be driven radially inwardly, to allow easy removal by the proper tool. If however, a tool not having the correct disposition of recesses is used in an attempt to remove the nut, the or each ball 16 need not be driven radially inwardly, to allow easy removal by the proper tool.If however a tool not having the correct disposition of recesses is used in an attempt to remove the nut, the or each ball will be driven inwardly as the tool is pressed over the nut body, thereby locking the nut. Once the correct tool is used again, the or each ball may move radially outwardly, so that the material of the nut body may re-form in the region of the apex 1 7 of the passage 1 6, at least to an extent sufficient to release the nut to allow removal thereof. Such an arrangement is especially advantageous for vehicle road wheel nuts, such as have been described in British Patent Specification No. 1,271,223.

Figure 5 shows a second embodiment of selflocking nut of this invention, the principle of operation of which is identical with that of the nut of Figures 1 to 3. The nut of Figure 5 however is of hexagonal cross-section and is provided with two co-axial passages 25 extending inwardly from diametricaily-opposed flats 26 and 27 of the nut body 28. This nut may be driven by a conventional open-ended spanner, provided the spanner is not engaged with the flats 26 and 27.

To lock the nut, the spanner can be engaged with those flats, or a separate tool such as a conventional box (or plug) spanner used in the manner as described above for locking the nut of Figures 1 to 3.

The nut may instead be locked by means of a power operated tool such as is shown in Figure 6.

This tool comprises a pair of first-order levers 30 and 31 both pivoted on a bar 32. Ends 33 and 34 of the levers are adapted for engaging the opposed flats 26 and 27 of a nut to be locked, and between the opposite ends of the levers there is disposed an air-operated piston actuator 35.

After a nut has been tightened, the ends 33 and 34 are fitted over the projecting balls 36 and 37 and air is supplied to the actuator 35 to drive the balls inwardly, thereby locking the nut.

The actuator 35 can be replaced by a manually operated mechanism -for instance, an expander having left- and right-handed threads disposed between the levers 30 and 31. To obtain sufficient force between the ends 33 and 34, the mechanical advantage should appropriately be selected.

Figure 7 shows a cross-section through a third embodiment of nut having a plurality of passages 40 each fitted with a locking element (not shown). As can be seen, each passage is drilled at an appropriate axial position relative to the threaded bore of the nut so that the apex of each passage lies substantially on the major diameter of the thread and aligned with the peak thereof.

It will be appreciated that the locking elements need not be balls, as described above. For example, for a relatively thick-walled nut, a bar or rod-like locking element could instead be used.

Alternatively, two or more axially-aligned balls could be used in a relatively long passage.

Claims (13)

Claims

1. A self-locking nut comprising a body having an internally-threaded bore and a passage extending inwardly from an outer circumferential face towards the threaded bore, and a rigid locking element located in the passage, the locking element being of such a length that when engaging the radially inner end of the passage the radially outer end of the element projects beyond the adjacent outer circumferential face of the body, the locking element being restrained from leaving the passage and being disposed so that following tightening of the nut on an externally threaded element, an inwardly-directed force applied to the locking element deforms the material of the nut body in the region of the inner end of the passage so as firmly to engage the threads of the body on to the threads of the threaded element.

2. A self-locking nut as claimed in claim 1, wherein the body is of hexagonal overall crosssectional shape, the passage being bored radially inwardly from one flat thereof.

3. A self-locking nut as claimed in claim 2, wherein the body is provided with a second passage and locking element, extending inwardly of the body from a flat thereof opposed to that having the first-mentioned locking element.

4. A self-locking nut as claimed in claim 1 or claim 2, wherein the region of the nut diametrically opposed to the locking element is of rounded form, thereby to allow an open-ended spanner to roll therearound when also engaged with the flat from which the locking element projects.

5. A self-locking nut as claimed in claim 1, wherein the body is generally cylindrical but with a single driving flat thereon, the locking element protruding from the cylindrical face thereof.

6. A self-iocking nut as claimed in claim 5, wherein there is a plurality of projections upstanding from the cylindrical face of the body in a predetermined coded relationship with respect to the single driving flat, at least one of the projections being a locking element located in a passage to allow deformation of the inner end of the passage.

7. A self-locking nut as claimed in claim 6, wherein there is a rotatable sleeve located on the body to surround the cylindrical surface thereof.

8. A self-locking nut as claimed in claim 1, wherein the body is of circular cross-sectional shape, and has at least one locking element projecting from the cylindrical surface thereof which locking element projects to an extent sufficient for engagement by a tool to allow torque to be imparted to the body of the nut.

9. A self-locking nut as claimed in claim 8, wherein the projecting portion of the locking element is of part-spherical shape.

10. A self-locking nut as claimed in any of the preceding claims, wherein the passage extends inwardly of the nut body substantially to the locus of the major diameter of the thread formed in the bore of the nut body.

11. A self-locking nut as claimed in any of the preceding claims, wherein the inner blind end of the passage has a conical form with the apex of the conical form lying substantially on the pitch circle of the major diameter of the thread in the body.

12. A self-locking nut as claimed in any of the preceding claims, wherein the locking element is spherical.

13. A shelf-locking nut substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 3 or in Figures 5 to 7 of the accompanying drawings.