This invention relates to a connector or fastener and in particular to connectors and fasteners which are adapted to control the degree of axial loading of the parts at the connection or fastening. It is often desired to tighten a threaded fastener or connection to provide a predetermined interface loading, and this loading is generally expressed as the torque which is necessary to achieve the desired degree of loading. One difficulty associated with this method of achieving a predetermined loading is that it does not take into account the possibility of contamination or damage on either of the mating threads, such that simply producing relative movement of the mating threads may account for a substantial portion of the applied torque, resulting in loading below the desired value. Similar problems may also arise where different connector materials or plated surfaces are encountered, resulting in a wide spread of interface loads for a given torque value.

Conventionally, tightening a connection to a desired loading is achieved by means of a torque wrench or similar tool, or by means of a self-torque connection which typically allows an outer torque ring, engageable with a tightening tool, to slip at a predetermined torque value. This invention has particular application in cable connectors for use in connecting cables to provide a

predetermined interface loading. At present, such cables are typically connected by providing a coupling nut rotatably mounted on and axially connected to the end of one cable for engaging an external thread carried on the end of the other cable. The nut is tightened to bring the respective mating faces of the cables together. To avoid overloading the connector a torque wrench may be utilised or the nut may be replaced with or supplemented by a self- torque connection. However, as described above, damaged or dirty threads may result in a connection in which the interface loading obtained is lower than one would expect for a predetermined applied torque.

It is among the objects of the present invention to provide a connector which obviates or mitigates the above- mentioned disadvantages .

According to the present invention there is provided a connector or fastener for use in connecting first and second parts, the connector including a coupling assembly for mounting on the first part, said assembly comprising a member carrying a first thread for engaging a corresponding second thread carried by the second part; a drive assembly normally rotatably coupled to the threaded member and having a driven member adapted for rotation by a tightening means; and coupling means operatively associated with the threaded member and a portion of the drive assembly for maintaining the rotational coupling of the threaded member relative to the drive assembly by maintaining the relative axial positioning thereof, rotation of the driven member

advancing the threaded member along the second thread until the mating faces of the first and second parts are brought together and said portion of the drive assembly is restrained against further axial movement by the first part, further rotation of the driven member with advancement of the threaded member only being possible until the axial loading on the first and second parts, corresponding to the force acting between said portion of the drive assembly and the first part, reaches a predetermined value and the coupling means disengages to permit rotation of said driven member independently of the threaded member.

The coupling assembly may be axially coupled to the first part when the parts to be joined are, for example, cable connections. Alternatively, the coupling assembly may simply abut a surface of the first part. Also, the second thread may be defined by the second part or may be defined by a separate member mounted on the second member.

The present invention has particular application in connecting first and second parts having respective first and second mating faces which are to be brought together and loaded to a predetermined degree, such as so-called TNC cable connections. An operator may hand-tighten the connection by rotating the driven member to advance the threaded member up the thread on the second part. This movement continues until the mating faces of the parts are brought together. A degree of further hand-tightening is possible, without significant thread slippage, to provide

axial loading of the faces, but only until the loading at the faces equals the coupling force applied by the coupling means. Additional hand-tightening advances the threaded member further up the second thread, and results in axial movement of the threaded member relative to the first part. This decouples the driven member and threaded member and permits rotation of the driven member with no corresponding movement of the threaded member. Before the faces are brought together, the coupling may be such that the torque which may be applied to the threaded member via the driven member is greater than the torque which would normally be required to produce the desired degree of axial loading on the contacting faces. Thus, the connector may continue to allow tightening even when the threads of the parts are dirty or damaged. Further, and more importantly, the connector allows connections to be accurately made at a desired interface loading, rather than the torque which would, for a selected set of conditions, be equivalent to such a loading: at the point when the faces meet it is the resulting axial loading at the abutting faces which determines whether the coupling means will permit independent rotation of the driven member.

Said portion of the drive assembly may be in the form of a drive member for rotatably coupling the driven member and the threaded member. The coupling assembly may further comprise respective drive portions of the driven and threaded members and a drive portion of the drive member for coupling with the threaded member, the coupling means

acting to clamp the drive portion of the threaded member between the drive portions of the driven member and the drive member. Most preferably, low friction material is provided between the drive portions of the driven member and threaded member, and high friction material is provided between the drive portions of the drive member and threaded member. Preferably also, the coupling means includes a spring or spring assembly which may be located between opposing surfaces of the driven member and the drive member.

In an alternative embodiment, the driven member and the threaded member may be coupled directly to one another, and compressible friction material may be provided between the mating faces thereof. Preferably, the coupling means, in the form of a spring or spring assembly, is located between opposing surfaces of the threaded member and said portion of the drive assembly, said portion being axially coupled to the driven member.

This and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 illustrates a connector assembly in accordance with a first embodiment of the present invention; Figure 2 illustrates a connector assembly in accordance with a second embodiment of the present invention; and

Figure 3 illustrates a fastener assembly in accordance

with a third embodiment of the present invention.

Reference is first made to Figure 1 of the drawings in which the illustrated assembly 10 is shown being utilised to connect first and second parts in the form of a cable 12 and a female cable connector 14. The cable connector 14 is provided with a female connector portion 16 which carries an external thread 18. A male connector portion 20 is provided on the end of the cable 12 and defines an end face 22 which lands on a shoulder 24 defined by a step in the female portion 16. A nitrile rubber gasket 26 provides a seal between the portions 16, 20.

The connector 10 is mounted on the male portion 20 and includes a coupling assembly 11 having a driven member, in the form of a spring housing 28, which has an knurled outer surface for hand tightening. A slip member 30 is normally coupled with the spring housing 28 and carries an internal thread 32 for engaging the thread 18 carried by the female portion 16. Also located within the spring housing 28 is a drive member 34 which is held axially relative to the male end portion 20 by a retaining ring 36. The drive member 34 includes a radially outwardly extending annular drive portion 38 and a cylindrical portion 39 which extends along the male end portion 20. One face of the drive portion 38 serves to retain a set of wave springs 40, a retaining plate 42 located over the cylindrical portion 39 engaging the other end of the springs 40. The retaining plate 42 is itself held within the spring housing 28 by a spring retaining ring 44, accommodated in an annular groove

46 formed on the inside surface of the housing 28.

The wave springs 40 are pre-compressed such that the springs 40 tend to bias the spring housing 28 rearwardly

(in the direction of arrow A) and clamp a radially extending drive portion 31 of the threaded slip member 30 between a radially inwardly extending drive portion 29 of the housing 28 and the drive portion 38 of the drive member

34. There is low friction material in the form of a PTFE slip ring 48 provided between the engaging surfaces of the housing 28 and the slip member 30 and a compressible friction material 50, such as nitrile rubber bonded cork, between the slip member 30 and the drive member 34.

In use, the slip member 30, drive member 34, wave springs 40 and spring retaining plate 42 are assembled into the spring housing 28 and retained in position by the retaining ring 44. This sub-assembly 11 is then fitted to the male connector portion 20 and held in position by the retaining ring 36. The springs 40 are pre-loaded to a value of 374N (84 lbf) , which is the desired axial loading at the connector interfaces 22, 24 (the recommended torque figure for typical TNC connectors is 16.27 Nm (12 inlb) which equates to an axial load at the connector interfaces of 374N (84 lbf) ) .

To form the connection between the cable 12 and the connector 14, the male connector portion 20 is located in the female connector portion 16 and the spring housing 28 rotated such that the threaded slip member 30 advances forwards over the thread 18, "pulling" the spring assembly

28 forwardly, drive to the slip member 30 being transferred via the retaining ring 44, plate 42, spring assembly 40, drive member 34 and friction material 50. This continues until the faces 22, 24 meet, at which point further forward motion of the drive member 34 is prevented by the retaining ring 36. Further tightening, with only limited thread slippage, is only possible up to the point where the interface loading reaches 374N (84 lbf) . Above this loading, the "pull" of the advancing slip member 30 on the spring housing 28 exceeds 374N, causing compression of the wave springs 40 and forward movement of the slip member 30 and spring housing 28 relative to the drive member 34. Such movement increases the spacing between the drive portion of the drive member 34 and the drive portion of the spring housing 28, allowing the compressible friction material 50 to expand. As a result of this drive is no longer transferred to the slip member 30 via the drive member 34. Accordingly, slippage may now occur between the spring housing 28 and the slip member 30, and thus the spring housing 28 may be rotated indefinitely with no corresponding rotation of the slip member 30. The connector assembly is now mated at the correct interface loading.

Sufficient frictional force is available for demating the threads, since the torque required for demating threads is always lower than that for mating.

During mating of the threads, and prior to the faces 22, 24 coming into contact, the inherent frictional forces

required to allow slippage greatly exceed 16.27 Nm (12 inlb) thereby allowing the cable 12 to be mated to a connector 14 which has dirty or damaged threads: the inherent frictional forces within the assembly 11 are only effective while there is no relative axial movement of the spring assembly 28 and the drive member 34, and as soon as such movement occurs the frictional forces are rapidly reduced to a level which permits rotation of the spring assembly 28 independently of the slip member 30. Reference is now made to Figure 2 of the drawings which shows an alternative assembly 110. The majority of the components of the assemblies 10, 110 are similar, such that similar reference numbers, prefixed with a "1", will be used to indicate the corresponding components of the second assembly 110.

The rate of the spring 140 in this embodiment is 623N

(140 lbf) and this uprated spring pre-load necessitates provision of a drive link between the spring housing 128 and the drive member 134; the accumulated frictional forces within the spring housing 128, which in the first described assembly 10 maintained drive contact between the housing 28 and drive member 34, are insufficient to provide the drive necessary to overcome the uprated spring pre-load and compress the wave springs 140. Accordingly, a drive pin 160 is provided to rotatably key the spring housing 128 to the drive member 134 and remove any dependence on frictional forces.

It will be noted that the slip ring 48 has been

omitted, replaced by a low friction coating on the spring housing drive portion 129 and an O-ring 162 located in an annular slot 164 in the drive portion 129. The low friction coating may be provided by plating the drive portion 129 with CORP AN 311 (Molybdenum) , which also provides corrosion resistance.

Further, the spring retaining plate 142 is provided with bonded seals 166, 168 on its inner and outer diameters. The seals 166, 168 and the O-ring 162 together protect the interior of the spring housing 128 against contamination.

The assembly 110 operates in a similar manner to the assembly 10 described above.

Reference is now made to Figure 3 of the drawings, which illustrates a bolt-type fastener 200 in accordance with a third embodiment of the present invention. The fastener 200 is illustrated connecting first and second parts, in the form of first and second plates 202, 204.

The fastener 200 includes a coupling assembly 206 which extends above the first plate 202, the assembly 206 including a pin-like member 208 having a flattened upper end 209 and a threaded lower end 210. In use, the member 208 extends through aligned bores 212, 213 in the plates 202, 204 and engages a thread 214 defined by the second bore 213. The coupling assembly 206 further comprises a drive assembly 216 normally coupled to the member 208 and including a driven member in the form of a cap 218 for location over the upper end of the member 208. The cap 218

defines an upper wall 220 which is normally coupled to the upper surface of the flattened end of the member 208 via a layer of a compressible friction material 222. The cap side wall 223 extends down around the upper end of the member 208 and defines an annular slot to locate a ring 224 for retaining a further portion of the drive assembly 216 in the form of a load ring 226.

Coupling means in the form of pre-compressed wave springs 228 is located between the load ring 226 and the lower face of the member upper end 209. The springs 228 thus normally bias the cap 218 into coupling engagement with the member upper end 209.

In use, to tighten the fastener 200, the cap 218 is rotated clockwise (assuming a right hand thread) such that the member 208 will travel down through the threaded plate 204 until the load ring 226 abuts the upper surface of the clearance hole plate 202. Further rotation of the cap 218 will result in further downward travel of the member 208 which will in turn cause the wave springs 228 to compress, resulting in loss of drive friction between the cap 218, the friction material 222, and the upper end of the member 208. A compressive load determined by the designed pre¬ load of the wave springs 228 will now exist between the plates 202, 204. If located in a countersunk bore, the fastener 200 may be positioned such that upper surface of the cap 218 is flush with the surrounding surface, drive to the cap 218 being provided by a suitable rotating tool provided with a

high friction surface for engaging the relatively large surface area provided by the cap 218.

The fastener 200 may also be particularly useful in applications where the fastener is subject to vibration. It will be clear to those of skill in the art that the above-described connector and fastener assemblies provide simple and convenient means for forming connections having a desired interface loading and avoid the disadvantages associated with existing arrangements in which thread condition may have a significant effect on the interface loading that is achieved by applying a particular torque to the connector.

It will also be clear to those of skill in the art that the above-described embodiments are merely exemplary of the present invention, for example: the connectors and fasteners of the present invention may be used in a wide variety of connector or threaded fastener applications where either access for conventional torquing devices is limited or where it is desired to provide a predetermined axial loading, or both.