The present disclosure relates to a locknut assembly.

In particular the disclosure is concerned with a locknut assembly comprising a nut and a compression washer.

Locknut assemblies are used to prevent the loosening of nuts and bolts due to vibration and relative movement of the parts to which they are attached. Different ways of preventing the loosening of the nut and bolt include having a resin liner in the thread of the nut and/or bolt, locking wire or pins, or the provision of an extra locking nut adjacent the main clamping nut.

Whilst all of these known alternatives provide satisfactory locknut capability in most situations, they each have their disadvantages. For example, a resin liner on a nut and bolt assembly has a limited number of uses, sometimes limited to one use only.

Locking wire and pins are time consuming and inconvenient to deploy. The use of a secondary nut to tighten the main nut introduces an extra operation for a fitter and also increases the total count part and weight of the assembly.

Hence, a locknut assembly which is simple to deploy and comprises a minimum number of parts, is highly desirable.

Summary

Accordingly there is provided a locknut assembly comprising a nut and a compression washer, the nut being provided with : a head portion; and a retention portion extending from the head portion to a free end distal to the head portion; wherein a threaded bore is provided through the centre of the head portion and retention portion; the head portion, retention portion and threaded bore all being coaxial with respect to a common central axis; the retention portion having a frusto conical outer bearing surface which has a first diameter adjacent the head portion and a second diameter at the distal end, the first diameter being greater than the second diameter; the compression washer comprising : a ring member having an inner bearing surface having a region of minimum diameter which is less than the first diameter, and greater than the second diameter, such that when the compression washer is pushed along the outer bearing surface of the retention portion toward the head portion, the inner bearing surface exerts a radially inward compression force on the retention portion.

The free end of the retention portion may comprise a shoulder which extends radially outwards. The shoulder may have a region of maximum diameter, with a lead in region and lead out region to either side of the region of maximum diameter.

The retention portion may comprise at least one slot which extends through the retention portion, and extends from the free end at least part of the way to the head portion to thereby form resilient fingers which extend from the head portion to the free end. The retention portion may comprise at least four equi-spaced slots and four equi- spaced fingers.

The inner bearing surface of the compression washer may have a leading edge and a trailing edge, the diameter of inner bearing surface decreasing from the leading edge to the region of minimum diameter at a location part way along the inner bearing surface, and then increasing towards the trailing edge. The diameter of the leading edge may be substantially the same as the diameter at the trailing edge.

The region of minimum diameter of the compression washer may have a diameter less than the region of maximum diameter of the shoulder of the retention portion.

The compression washer may be located on the retention portion. The compression washer may be located on the retention portion between the head portion and the shoulder on the retention portion. Accordingly there is provided a method of assembly of a locknut, the locknut comprising a nut and a compression washer, the nut being provided with a head portion; and a retention portion extending from the head portion to a free end distal to the head portion, the free end provided with a shoulder which extends radially outwards, the shoulder being profiled with a lead in region and a lead out region to either side of a region of maximum diameter; the head portion and retention portion being coaxial with respect to a common central axis; the compression washer comprising : a ring member having an inner bearing surface having a region of minimum diameter which is less than the region of maximum diameter of the shoulder; the method of assembly comprising the steps of : orientating the compression washer with its leading edge adjacent the free end of the retaining portion; and urging the region of minimum diameter of the inner bearing surface of the compression washer past the retaining shoulder.

Hence there is provided a locknut assembly which comprises only two parts, which is simple to assemble, and which acts to grip a bolt to which it is attached to thereby increase frictional contact between the retaining portion and the bolt which, in use, will extends the locknut.

Brief Description of the Drawings

Examples of the present disclosure will now be described with reference to the accompanying drawings, in which:

Figure 1 shows an isometric view of a locknut assembly according to the present disclosure;

Figure 2 shows a cross-sectional view of the locknut assembly of Figure 1 assembled to clamp two articles together;

Figure 3 shows a side view of the nut; Figure 4 shows an isometric view of the locknut assembly; and

Figure 5 shows a cross-sectional view of the locknut assembly as shown in Figure 4.

Detailed Description

Figure 1 shows a locknut assembly 10 according to the present disclosure. In the example shown the locknut assembly 10 is fitted to a bolt 12. A cross-sectional view of this is shown in Figure 2 with the bolt 12 and locknut assembly 10 deployed to bond a first sheet 14 and a second sheet 16 together. Other views of the parts of the locknut assembly 10 are shown in Figures 3 to 5.

The locknut assembly 10 comprises a nut 18 and a compression washer 20. As shown in Figure 3, the nut 18 is provided with a head portion 22 and a retention portion 24. The head portion 22 is shown as being hexagonal, although may be of any appropriate or conventional shape. The retention portion 24 extends from the head portion 22 to a free end 26 distal to the head portion 22. A threaded bore 28 is provided through the centre of the head portion 22 and retention portion 24, although for clarity the threaded bore 28 is shown as a plane surface in Figures 4, 5. The head portion 22, retention portion 24 and threaded bore 28 are all coaxial with respect to a common central axis 30. The retention portion 24 has a frusto-conical (i.e. a truncated cone) outer bearing surface 32 which has a first diameter 34 adjacent the head portion 22, and a second diameter 36 at the distal free end 26, the first diameter 34 being larger than the second diameter 36.

The compression washer 20 is a ring member having an inner bearing surface 42, where the inner bearing surface 42 has a region of minimum diameter 44. The minimum diameter 44 of the compression washer 20 is less than the first diameter 34, and greater than the second diameter 36 of the retaining portion 24. The free end 26 of the retention portion 24 comprises a shoulder 46 which extends radially outwards. The shoulder 46 is profiled with a lead-in region 48 and a lead-out region 50. The lead-in region 48 and lead-out region 50 are to either side of a region of maximum diameter 52 of the shoulder 46.

The retention portion 24 comprises at least one slot 54 which extends through the retention portion 24, and extends from the free end 26 at least part of the way to the head portion 22. This forms resilient fingers 56 which extend from the head portion 22 to the free end 26. In the example shown in Figures 1 to 5 there are four spaced slots 54, and hence four spaced fingers 56, which are equi-spaced around the circumference of the retention portion 24. In alternative examples, there may be provided two, three or more than four equally spaced slots 54 and fingers 56.

The inner bearing surface 42 of the compression washer 20 has a leading edge 60 and a trailing edge 62. The diameter of the inner bearing surface 42 decreases from the leading edge 60 to the region of minimum diameter 44 at a location part way along the inner bearing surface 42, and then increases in diameter towards the trailing edge 62. In the example shown, the diameter of the leading edge 60 of the inner bearing surface 42 of the compression washer 20 is substantially the same as the diameter at the trailing edge 62. However, in other examples, not shown, the diameter of the inner bearing surface 42 at the leading edge 60 may be different to that of the diameter of the inner bearing surface 42 at the trailing edge 62 of the compression washer 20.

The region of minimum diameter 44 of the compression washer 20 has a diameter less than the region of maximum diameter 52 of the shoulder 46 of the retention portion 24.

To assemble the locknut assembly 10 the compression washer 20 is orientated with its leading edge 60 adjacent the free end 26 of the retention portion 24. The washer and nut are then urged together such that the region of minimum diameter 44 of the inner bearing surface 42 of the compression washer 20 is urged past the retaining shoulder 46. This locates the compression washer 20 on the retention portion 24. Once the region of minimum diameter 44 of the inner bearing surface of the compression washer is pushed passed the shoulder 46, the compression washer 20 is retained on the retention portion 24 between the head portion 22 and the shoulder 46 on the retention portion 24.

In operation, a bolt 12 of an appropriate size to fit the threaded bore 28 is used in conjunction with the locknut assembly 10. The bolt 12 may be of a conventional type, and does not form part of the device of the present disclosure. In the example shown in Figure 2, a bolt 12 is first passed through two sheets 14, 16 to be clamped together, and then entered into the threaded portion 28 of the retention portion 24. The locknut 10 with the compression washer 20 is wound down the thread 28 of the bolt 12 until the trailing edge 62 of the compression washer 20 makes contact with the surface of sheet 14. As the head portion 22 (i.e. nut 18) is further tightened it is urged towards the sheets 14, 16. However the compression washer 20 is held in position between the head portion 22 and sheet 14. Hence, as the nut 18 is rotated, the compression washer 20 is pushed along the outer bearing surface 32 of the retention portion 24 towards the head portion 22. In doing so, the inner bearing surface 42, and in particular the region of minimum diameter 44 of the inner bearing surface 42 of the compression washer 22, exerts a radially inward compression force on the retention portion 24. The fingers 56 of the retention portion 24 are then bent towards the bolt 12 by the radially inward compression force to effectively clamp the fingers 56 onto the bolt 12, thus increasing the frictional contact between them. The nut 18 may be tightened against the sheet 14 on the bolt 12 by a predetermined torque to achieve a desired radially inward

compression force. The retention portion 24 is hence rigidly fixed to the bolt 12.

Provided the nut 18 is tightened up to a sufficient torque, this arrangement will resist loosening rotation due to vibration and relative motion of the sheets 14, 16.

To remove the locknut assembly 10, the fitter slackens the nut 18. As the nut 18 moves relative to the compression washer 20 along the bolt 12, the radially inward

compression force on the fingers 56 is relieved, allowing the fingers 56 to unclamp the bolt 12. As the nut 18 is further unwound, the shoulder 46 catches the compression washer 20 and moves it away from the sheet article 14. Hence a fitter is required to handle only a single assembly of parts when fitting the locknut 10, and required to tighten up only one nut. This simplifies assembly of structures where a locknut is required. Since the fingers 56 are resilient, the locknut assembly 10 of the present disclosure may be used many times.

Although the locknut 10 of the present disclosure may be employed in any number of applications, it has particular efficacy in high vibration applications such as on railway tracks, rotating machinery (for example, circular saws, wind turbines) and high vibration environments (for example automotive and aerospace applications).

Although preferred embodiment(s) of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made without departing from the scope of the invention as defined in the claims.