GB1563359A

GB1563359A - Strain relief bushings

Info

Publication number: GB1563359A
Application number: GB5267376A
Authority: GB
Original assignee: Tucker Fasteners Ltd
Current assignee: Tucker Fasteners Ltd
Priority date: 1975-12-17
Filing date: 1976-12-16
Publication date: 1980-03-26
Also published as: AT366521B; NL7613675A; JPS5945842B2; SE435756B; ES454850A1; DE2556878C3; CH606892A5; FR2335973A1; FR2335973B1; DK145166C; AU505950B2; NL184249B; DE2556878B2; SE7613846L; DK566876A; DE2556878A1; DK145166B; JPS5279166A; ATA929676A; NL184249C

Description

(54) IMPROVEMENTS IN OR RELATING TO STRAIN RELIEF BUSHINGS (71) We, TUCKER FASTENERS LIMITED, a British Company of Walsall Road, Birmingham, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is concerned with improvements in or relating to strain relief bushings.

It is a common practice, where an electric cable or fluid hose has to pass through a hole in a metal panel, to provide in the hole a plastics bushing which is arranged to grip the cable or hose firmly so that tension applied to the cable or hose at one side of the panel will not be transmitted to the other. It is known also to make the hole in the panel other than round, and for the bushing to have a complementary external cross-section so that torque applied to the cable or hose at one side of the panel will likewise not be transmitted to the other.

A strain relief bushing is known which can be inserted in a non-circular hole in a panel to permit a cable or hose to be threaded through it and the cable or hose then gripped by a ratchet-like tooth hinged in an aperture at one side of the bushing and bearing on a flexible finger which is caused to press against and grip the cable or hose. A shortcoming of this arrangement is that the grip of the bushing on the cable or hose cannot be released as readily as may be desirable.

It is one of the various objects of the present invention to provide an improved strain relief bushing which overcomes the foregoing shortcomings and which can readily be inserted in a hole in a panel and securely retained therein, permittitig a cable or hose to be subsequently threaded through it, and which thereafter can be locked to grip the cable or hose firmly and yet readily released if desired.

There is hereinafter described in detail to illustrate the invention by way of example a strain relief bushing comprising a hollow body which has a shank of non-circular external cross section for insertion into a complemen- tarily shaped hole in a panel and has an enlarged head to engage the panel at one side and retaining means to engage the panel at the other side. This illustrative bushing also comprises a locking member arranged to be brought into gripping engagement with a cable or hose threaded through the bushing, the locking member being rotatably mounted in the body, and having two diametrically opposed fingers which, by engagement with the wall of a non-circular bore of the body, are forced, upon rotation of the locking member through part of a revolution, into said gripping engagement on opposite sides of the cable or hose.

Each of the flanges of the locking member of the illustrative bushing has a longitudinal ridge which seats in one of two longitudinal grooves in the inside wall of the body when in gripping engagement with the cable or hose to prevent accidental release of the grip. Such grip, however, can be released to permit ad justment or removal of the cable or hose upon further rotation of the locking member in the same direction.

The locking member of the illustrative bushing projects from the end of the shank of the body of the bushing opposite the head, but it is there confined within the cross-sectional area of the shank so that the bushing can be inserted in the hole in the panel with the locking member already assembled in the body. Smoothly curved enlarged mouths of co-axial bores in the body and locking members avoid the need to reinforce the cable or hole at the locality of exit from the bushing, whichever way round the bushing may have been assembled in the panel. Flats on the projecting portion of the locking member, for example to afford an hexagonal periphery, may be provided to permit rotation of the member by a spanner.

The illustrative strain relief bushing can readilv be inserted in a hole in a panel from one side and securely retained there, permitting a cable or hose to be subsequently threaded through it and thereafter gripped and released by rotation of the locking member.

The invention provides a strain relief bush ing comprising a hollow body which has a shank of non-circular external cross-section for insertion into a complemantarily shaped hole in a panel and has an enlarged head to engage the panel at one side and retaining means to engage the panel at the other side, the body having a non-circular bore therethrough, and the bushing also comprising a locking member, with a bore through it for a cable, rotatably mounted in said bore of the body and having at least one movable finger which, by engagement with the wall of said non-circular bore, is forced, upon rotation of the locking member through part of a revolution, into gripping engagement with a cable threaded through the locking member.

There now follows a detailed description, to be read with reference to the accompanying drawings, of the illustrative bushing aforementioned. It will be realised that this illustrative bushing has been selected for description by way of example and not of limitation of the invention.

In the accompanying drawings: Figure 1 is a view in perspective of the illustrative bushing showing two parts thereof before asembly together; Figure 2 is a view, with parts broken away, of the bushing of Figure 1, with the two parts of the illustrative bushing assembled in a hole in a panel, (a cable gripped by the bushing being omitted for the sake of clarity); and Figure 3 is a view in section on the line IIIIII of Figure 2.

The illustrative strain relief bushing consists of a body 12 and a locking member 14 (Figure 1) both preferably, but not necessarily, made by injection moulding of a suitable thermoplastic material, for example nylon (e.g. that sold under the Registered Trade Mark ZYTEL).

The body 12 of the illustrative bushing comprises a shank 16 the outer periphery of which presents two parallel faces joined by arcs of a circle so that when the shank is inserted in a hole 18 in a panel M (Figure 2) of similar outline, the body 12 will not rotate. At one end of the shank is an enlarged head 20, an annular flange 22 of which abuts one side of the panel.

The body 12 is hollow, having a bore 24 through it, part 24' of which, extending from the end opposite the head 20, is defined by four symmetrically disposed walls. One opposing pair of walls 26, 26' form parts of a cylinder but are closer together than the cylinder's diameter. The other opposing pair of walls 28, 28' form parts of a cylinder of smaller radius and having a common axis. The result is a bore of substantially oval crosssection. The oposing walls 26, 26' constitute more than half of the periphery of the bore 24, and have centrally disposed longitudinal grooves 30 for a locking purpose as later described.

At its head end, the bore 24 of the body 12 of the illustrative bushing is circular in crosssection and flares arcuately to provide a smoothly curved enlarged mouth 24", the minimum diameter of which is less than the minimum transverse dimension of the part 24'.

Between the mouth 24" and the part 24' is a transverse slot 32 which opens into the head 20 from one side (the same side as the wall 28) and provides a retaining shoulder 34 (for a purpose which will appear hereinafter) which extends right round the part 24 of the bore.

Each of the walls 28, 28' of the shank 16 of the body 12 has a rectangular opening 36 in each of which are accommodated two resilient retainers 38, 40, integral with the edge of the opening farthest from the head 20.

Preferably, as shown, the retainer 38 has one ratchet tooth, and the retainer 40 has two; they project beyond the outer wall of the shank 16 so that one pair of teeth (i.e. one at each side of the shank) can engage the opposite side of the panel M from the head, the three pairs of teeth enabling the body to be readily inserted into and retained in panels of different thicknesses. Alternatively, other means of retaining the body in the hole may be provided instead of the particular configuration of retainers shown.

The locking member 14 of the illustrative bushing has a hollow shank 46 and an hexagonal head 48; the shape of the head is determined by the means it is intended to use to rotate it, and may be varied accordingly.

A bore 50, which extends right through the locking member, is substantially cylindrical in a relaxed condition of the member and opens at the head end in a smoothly curved enlarged mouth 52 similar to the mouth 24" of the bods 12.

The shank 46 is constituted in part by two fingers 54 hinged at longitudinally disposed necks 56 where the material of the shank is of reduced thickness by virtue of longitudinal grooves in the outer wall of the shank, the fingers being accommodated in rectangular openings in the wall so that they can flex about the necks 56. The fingers 54 are symmetrically disposed about the axis of the locking member, and each increases in thickness from the neck 56, its outer wall projecting from the otherwise cylindrical wall of the shank. The diameter of the cylindrical part of the outer wall of the shank is slightly less than the distance between the central portions of the walls 26, 26' of the body, and the outer edges of the fingers 54, in the relaxed condition of the locking member, are not quite as far apart as the central portions of the walls 28, 28', so that the locking member can be inserted without difficulty into the bore 24 of the body when orientated with the outer edges of the fingers aligned with the middle of the walls 28, 28'. When thus inserted, two outwardly directed lugs 60 at the end of the shank 46 opposite the head 48 come into register with the slot 32, the lugs yielding sufficiently for them to pass through the bore 24 and clicking into overlapping engagement with the retaining shoulder 34 to prevent inadvertent separation of the body and locking member. The head 48 of the locking member is wholly within the periphery of the shank 16 of the body so that the bushing can be inserted in the panel M after assembly of its two parts.

Thus assembled and inserted in a complementarily shaped hole in the panel M, the ilustrative bushing is ready to receive a cable C (Figure 3). The mouths 24", 52 at both ends of the bushing enable it to be inserted into the panel from whichever side is most convenient, the bell-shaped mouths eliminating the need for reinforcement of the cable where it emerges from the bushing.

After threading the cable C through the illustrative bushing and adjusting it lengthwise, the locking member 14 may be rotated clockwise (viewing Figure 3) through 90" to bring it into the position, relative to the body, indicated in Figure 3. (The locking member is shown in the same position in Figure 2, but the cable is omitted for the sake of clarity).

In thus rotating the locking member, conveniently by means of a spanner engaging the head 48, the fingers 54 are forced inwardly towards one another by the walls 26, 26' until longitudinal ridges 62 become seated in the grooves 30 of the body. At such time, the fingers firmly grip the cable by pressing against it from opposite sides. The locking members resist any attempt to release the cable by reverse rotation, but the cable can be released by rotation of the locking member through a further 90" clockwise with the aid of a spanner, whereupon the fingers recover their relaxed positions and permit the cable to be withdrawn.

Alternatively, if desired, the cable can be threaded through the illustrative bushing first, and then the bushing inserted in the hole in the panel, before or after rotating the locking member to grip the cable.

WHAT WE CLAIM IS:- 1. A strain relief bushing comprising a hollow body which has a shank of non-circular external cross-section for insertion into a complementarily shaped hole in a panel and has an enlarged head to engage the panel at one side and retaining means to engage the panel at the other side, the body having a non-circular bore therethrough, and the bushing also comprising a locking member, with a bore through it for a cable, rotably mounted in said bore of the body and having at least one movable finger which, by engagement with the wall of said non-circular bore, is forced, upon rotation of the locking member through part of a revolution, into gripping engagement with a cable tEreaded~through the locking chamber.

2. A bushing according to claim 1 the locking member of which has two symmetrically disposed fingers movable from relaxed positions in which a cable can be threaded between the fingers into gripping positions upon rotation of the locking member through 90".

3, A bushing according to claim 2 said fingers of which form part of a shank of the locking member which, with the fingers in their relaxed position, has a cross-section with maximum and minimum dimensions slightly less than those of a substantially oval crosssection of said bore in the body.

4. A bushing according to claim 3 said fingers of which have longitudinal ridges arranged, when the fingers assume their gripping positions, to engage grooves in the body to prevent inadvertent release.

5. A bushing according to claim 1 the body and locking member of which are moulded as separate parts from plastics material and assembled by inserting the locking member in said bore of the body.

6. A bushing according to claim 5 comprising lugs on the locking member which engage a retaining shoulder provided by a slot in the head of the body to prevent inadvertent separation of the two parts.

7. A bushing according to claim 6 the locking member of which projects from one end of the body and is wholly within the crosssectional area of the shank of the body so that the bodv and locking member can be assembled together before inserting the bushing into a hole in a panel 8. A bushing according to claim 7 the head of the locking member of which is provided with flats to facilitate rotation by means of a spanner.

9. A bushing according to claim 1 in which said bores of the body and locking member are co-axial and have smoothly curved enlarged mouths, one at one end of the bushing, the other at the other, so that the cable will not need reinforcing whichever way round the bushing may have been assembled in the panel.

10. A strain relief bushing substantially as hereinbefore described with reference to the accompanying drawings.

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

Claims

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

46 opposite the head 48 come into register with the slot 32, the lugs yielding sufficiently for them to pass through the bore 24 and clicking into overlapping engagement with the retaining shoulder 34 to prevent inadvertent separation of the body and locking member. The head 48 of the locking member is wholly within the periphery of the shank 16 of the body so that the bushing can be inserted in the panel M after assembly of its two parts.

Thus assembled and inserted in a complementarily shaped hole in the panel M, the ilustrative bushing is ready to receive a cable C (Figure 3). The mouths 24", 52 at both ends of the bushing enable it to be inserted into the panel from whichever side is most convenient, the bell-shaped mouths eliminating the need for reinforcement of the cable where it emerges from the bushing.

After threading the cable C through the illustrative bushing and adjusting it lengthwise, the locking member 14 may be rotated clockwise (viewing Figure 3) through 90" to bring it into the position, relative to the body, indicated in Figure 3. (The locking member is shown in the same position in Figure 2, but the cable is omitted for the sake of clarity).

In thus rotating the locking member, conveniently by means of a spanner engaging the head 48, the fingers 54 are forced inwardly towards one another by the walls 26, 26' until longitudinal ridges 62 become seated in the grooves 30 of the body. At such time, the fingers firmly grip the cable by pressing against it from opposite sides. The locking members resist any attempt to release the cable by reverse rotation, but the cable can be released by rotation of the locking member through a further 90" clockwise with the aid of a spanner, whereupon the fingers recover their relaxed positions and permit the cable to be withdrawn.

Alternatively, if desired, the cable can be threaded through the illustrative bushing first, and then the bushing inserted in the hole in the panel, before or after rotating the locking member to grip the cable.

WHAT WE CLAIM IS:- 1. A strain relief bushing comprising a hollow body which has a shank of non-circular external cross-section for insertion into a complementarily shaped hole in a panel and has an enlarged head to engage the panel at one side and retaining means to engage the panel at the other side, the body having a non-circular bore therethrough, and the bushing also comprising a locking member, with a bore through it for a cable, rotably mounted in said bore of the body and having at least one movable finger which, by engagement with the wall of said non-circular bore, is forced, upon rotation of the locking member through part of a revolution, into gripping engagement with a cable tEreaded~through the locking chamber.
2. A bushing according to claim 1 the locking member of which has two symmetrically disposed fingers movable from relaxed positions in which a cable can be threaded between the fingers into gripping positions upon rotation of the locking member through 90".
3, A bushing according to claim 2 said fingers of which form part of a shank of the locking member which, with the fingers in their relaxed position, has a cross-section with maximum and minimum dimensions slightly less than those of a substantially oval crosssection of said bore in the body.
4. A bushing according to claim 3 said fingers of which have longitudinal ridges arranged, when the fingers assume their gripping positions, to engage grooves in the body to prevent inadvertent release.
5. A bushing according to claim 1 the body and locking member of which are moulded as separate parts from plastics material and assembled by inserting the locking member in said bore of the body.
6. A bushing according to claim 5 comprising lugs on the locking member which engage a retaining shoulder provided by a slot in the head of the body to prevent inadvertent separation of the two parts.
7. A bushing according to claim 6 the locking member of which projects from one end of the body and is wholly within the crosssectional area of the shank of the body so that the bodv and locking member can be assembled together before inserting the bushing into a hole in a panel
8. A bushing according to claim 7 the head of the locking member of which is provided with flats to facilitate rotation by means of a spanner.
9. A bushing according to claim 1 in which said bores of the body and locking member are co-axial and have smoothly curved enlarged mouths, one at one end of the bushing, the other at the other, so that the cable will not need reinforcing whichever way round the bushing may have been assembled in the panel.
10. A strain relief bushing substantially as hereinbefore described with reference to the accompanying drawings.