GB2127626A

GB2127626A - Springs; electrical connectors having electromagnetic interference screens

Info

Publication number: GB2127626A
Application number: GB08310889A
Authority: GB
Inventors: Derek Taylor
Original assignee: Allied Corp
Current assignee: Allied Corp
Priority date: 1982-04-23
Filing date: 1983-04-21
Publication date: 1984-04-11
Also published as: GB2127626B; GB8310889D0

Abstract

A spring structure (fig. 6) includes a coil spring (62) extending round a groove (66) in a cylindrical housing (68), the coil spring (62) being biassed towards the base of the groove by a spring (64) extending round the groove and located within the turns of the coil spring. Such spring structures (42, 44 and 46, 48, fig. 1) provide a circumferential electrical contact between earthed electrical members (20, 24, 26) and, thereby, ensure continuity of radio frequency shielding from a cable screen (22) in contact with member (20). <IMAGE>

Description

SPECIFICATION A spring structure, and an electrical connector with an electromagnetic shielding system This invention relates to a spring structure, and to electrical connectors which include an electromagnetic shielding system.

A conventional electrical connector comprises a first conductive shell member on a first part of the connector, a second conductive shell member on the second part of the connector, and a coupling member around the connector for securing the first and second shell members together. In such an arrangement it is frequently desired to ensure good electrical connection between the first and second shell members completely round the connector. This is to provide radio frequency shielding so that the signals in passing through are not affected by or do not give rise to external electromagnetic fields. It is particularly important that good contact is maintained around the entire periphery of the connector otherwise helical currents can be generated through the shell. The shell will commonly be attached to a sheathing braid on a flexible lead, or a mounting plate on a fixed receptacle.

Conventional radio frequency interference (RFI) shielding systems comprise a grounding strip around the connector which has a large number of resilient fingers. The strip can conveniently be formed by stamping. The strip is secured around one of the shell members and when the connector is in the mated condition the resilient fingers bear against the overlying surface of the other one of the shell members. In this way good continuity of electrical contact is maintained. However, problems can arise: for example with circular environmental connectors which use a key and keyway to ensure correct alignment, as the key and keyway are an impediment to the satisfactory installation of the grounding strip.

This invention can provide improvements in such systems.

In one aspect, the connector of the invention is characterised in that, the primary electromagnetic shielding is provided by resilient contact means around the connector. The contact means takes the form of separate resilient contact members located between the coupling member on the one hand and each of the shell members respectively on the other. In this way it is not required to ensure good uniform electrical contact between the shell members themselves, but rather the RFI shielding path is ensured through the intermediary of the coupling member. If the shell members do have a direct contact path, then the coupling member provides a second interference shielding path around the shell members.

It is known from British Patent Specifications GB-PS 1 542102 and 2057789A to provide for the connection between two conductive cylindrical elements by means of a helically coiled spring which extends around the connector and is partially accommodated in but projects from a groove in one of the elements. However, there are problems associated with supporting and retaining such a spiral coil spring, which place limitations on the size of spring and diameter of wire which can be used. In connectors, the wall thickness of the shells can be such that only very small diameter coil springs can be used, and to ensure individual operation of each coil without it acquiring a permanent set, it is necessary to use small diameter wire. Such small sizes mean that the coil does not remain seated in its groove.

In the preferred embodiment to be described, such a helically coiled spring has a supporting spring around at least substantially all the connector periphery which lies within the turns of the helically coiled spring. This provides the necessary additional support for the helical spring.

Helicaily coiled springs have also been proposed in U.S. Patent US-PS 3739076 in which the spring is forced onto a cable screen by a conical camming surface. This again requires a spring of considerable size and strength.

The invention will now be described by way of example with reference to the drawings, in which: Figure 1 is a sectional view through part of a connector embodying the invention: Figure 2 is a view similar to Figure 1 showing the connector disconnected and omitting certain parts; Figure 3 is a detail showing the spiral or helical spring with its support spring member in its recess; Figure 4 is a front view of the spiral spring with its support spring; Figure 5 is a diagrammatic illustration of one possible position for the spring assembly in two mating elements; Figure 6 is a detail showing the spring of Figure 5 in its groove; Figure 7 illustrates an alternative arrangement to the one shown in Figure 5; Figure 8 is a corresponding view similar to Figure 6 for the arrangement of Figure 7; and Figure 9 illustrates an alternative shape for the spiral spring and the support spring.

Figure 10 is a perspective view of a conventional RFI grounding strip; Figure 11 is a diagrammatic illustration of one possible arrangement of the strip of Figure 10 in two mating elements; Figure 1 2 illustrates an alternative arrangement to that of Figure 1 1; and Figure 13 is a broken-away perspective view of an alternative form of resilient contact member for use in the connector of Figure 1.

The connector shown in Figures 1 and 2 includes a plug 10 and a receptacle 12. The plug 10 has a shell member 22 and a coupling member 24 mounted on the shell member 22.

The receptacle 1 2 includes a shell 26 which is mounted in an aperture in a panel plate or bulkhead 28 where it is secured by a nut 14.

The plug 10 and receptacle 12 have conventional electrical contacts 11, 1 3 which include sockets and pins respectively. The contacts 11, 13 are supported in conventional insulating bodies 15, 16 of the plug 10 and receptacle 1 2 respectively. Conductors 17, 1 8 are terminated at the contacts 11, 13 and are supported and seaied by respective grommets 19, 20.

The receptacle shell 26 carries a grommet nut 30 on screwthreads 36, 38 on the shell 26 and the nut 30 respectively. The nut 30 engages a flange grommet follower 31 which acts upon the grommet 20 so that the grommet 20 forms a seal between the conductor 1 8 and the shell 26 when the nut 30 is tightened.

The connector of Figures 1 and 2 is of the bayonet type. For this purpose the receptacle shell 26 carries bayonet pins 32 which engage in corresponding grooves 34 in the coupling members 24. The coupling member 24, when engaged on the receptacle shell 26, draws the shell member 22 of the plug 10 towards the shell 26 of the receptacle 1 2 and the contacts 11, 1 3 into co-operation by means of an annular washer 33 which is located in a groove in the coupling member 24 and which bears against a shoulder 35 on the shell member 22.

In order to provide electromagnetic shieiding in the.connector the conventional approach would be to include an RFI shielding strip mounted on the innermost portion of the shell member 22.

Such strip is indicated by the reference 40 on Figures 1 and 2. The strip 40 has fingers which engage with the receptacle shell 26, thus ensuring direct RFI shielding connection around the entire periphery of the connector between the shell 22 of the plug 10, and the shell 26 of the receptacle 1 2.

However, in a bayonet type connector, it is found that this conventional RFI shielding system is of poor effectiveness, because the key/keyway system conventionally used to ensure correct polarisation of the shell members makes it difficult to incorporate an effective grounding system to ensure contact completely around the opposed shell members. The key/keyway system indicated at 41,43 in Figure 2 occupies the forward portion of the shell 22 of the plug 10 where the shielding strip is also located.

In accordance with this invention, therefore, an improved FRI shielding system is proposed.

For this purpose the coupling member 24 of the plug 10 carries, an its interior surface near the back end thereof, a recess 42. The coupling member 24 must, of course, extend sufficiently far rearwardly to accommodate the recess 42. in this recess is received a helically coiled or spiral spring 44, sometimes termed a garter spring, which extends around the entire periphery of the connector. The spring 44 is accommodated largeiy in the groove 42 but projects to some extent therefrom. The projecting portion of the spring 44 is engaged by a body 90 forming part of a cable sleeve clamping structure of the connector, the body 90 being screw threaded onto the shell member 22. The body 90 is adapted in the example shown to be connected to the screen 92 of a screened cable 94.For this purpose the screen is pulled over the front of a screen support ring 96 and clamped between the ring 96 and the body 90 by tightening a coupling nut 100. The coupling nut 100 also draws up a cable support clamp member 98 which receives the plastic sleeve 102 of the cable 94.

Thus the body 90 bears against the spring 44 so as to keep the turns of the spring in slight radial or diametric compression between the body 90 and the coupling member 24, thereby ensuring good electrical contact between these two members.

The receptacle shell 26 also includes a groove 46 which accommodates a like spring 48. This spring 48 bears, when the plug 14 is received in the receptacle 12, against the forward end of the coupling member 24 of the plug. In this way good electrical connection is maintained between the coupling member 24 and the receptacle 1 6 with the spring 48 acting as a contact member.

Thus it is seen that the RFI shielding path is maintained from the cable screen 92 to the shell 26 of the receptacle 12 via the intermediary of the coupling member 24. The system does not rely on the shielding strip 40 to maintain good electrical contact around the entire periphery of mating portions of the plug shell 22 and receptacle shell 26. Instead, conductive integrity is maintained around the connector without any RF windows being possible, thereby containing RF emanations and excluding RF interference.

The electrical contact members 44 and 48 used for RFI shielding are positioned well away from the area of shell contact. There is much less danger of these contact members becoming damaged or chewed up thus causing a malfunction of the main connector contacts 11, 13 housed within the shell. This is even more so when the conventoinal grounding strip 40 with its protruding fingers is replaced entirely by a spring or springs of relatively smooth profile, such as the springs 44, 48.

It will be appreciated that an appropriate measured interference is required between the outer surface of the front of the coupling ring 24 and the inner surface of the portion of the shell 26 carrying the grounding spring 48.

The receptacle shell 26 is maintained in electrical contact with the mounting plate 28 by a further helical spring 110 which is held in a groove 1 2 and bears against the plate 28 under the pressure of the nut 14.

The connector shown in Figures 1 and 2 is of the type comprising a plug 10 and a panelmounted receptacle 12. As a modification, the receptacle 1 2 can be of the type in which a nut, similar to the nut 30, is connected to the sheathing braid or screen of a flexible lead. In this modified connector a further spring and groove arrangement of the type described above can be provided between the receptacle shell and the receptacle nut to ensure complete screen-to screen continuity of shielding between the cables of the plug and receptacle.

As illustrated, the connector removes the need for good contact between the opposed shell members 22, 26 by providing instead a shielding path through the coupling member 24. This avoids the need to use a grounding strip 40 but when such a strip is used, a shielding path is provided through the coupling member in addition to the path through the grounding strip 40. In this way, two shielding paths exist, one around the other. The two shielding paths can be separately connected to respective ones of two concentric sheaths of a cable. The use of multiple screening systems and connectors for use therewith is known from, for example, U.S. Patent US-PS 2762025.

Figure 3 is a detail of one of the grooves, say the groove 42 in the interior surface of the coupling member 24, and the associated spiral spring 44. The springs 44, 48 and 110 are preferably similar. It will be seen from Figure 3 that the spiral spring 44 projects to some extent from the groove 42. The spring is provided with a support member 60 which is in the form of a circular or substantially circular spring extending around the coupling member within the turns of the sprial spring 44. The spring 60 is seen more clearly in Figure 4. If it is necessary to form the spiral spring 44 with a gap, then this is arranged to be diametrically opposite to any gap in the spring 60. It will be appreciated that the illustration of Figure 4 is very diagrammatic and is not shown with the correct number of turns on the spiral spring 44.

Figures 5 and 6 show a spiral spring 62 with its support spring 64 in an external groove 66 in a first cylindrical mating element 68 which is received inside a second cylindrical mating element 70. In order to allow the spring 62 to enter the mating element 70, the internal edge of the element 70 is chamfered at its end as shown at 72.

Figures 7 and 8 show the converse arrangement in which a helical spring 76 with its support spring 78 is received in a groove 80 on the internal surface of the outer one 82 of two connector members 82, 84. In this case the outer surface of the inner connector member is chamfered at 86 to allow it to pass into the spring 76 on mating of the connector.

When used in an external groove (Figures 5 and 6) the single-turn C-shaped support spring 64 is biased in a reducing mode, and when in an internal groove (Figures 7 and 8) the spring 78 is biased in an expanding mode, so as always to tend to seat against the base of the groove.

As shown in Figures 5 to 8, the spiral spring is of circular cross-section, as particularly seen in Figures 6 and 8. Figure 9 shows an alternative in which a non-circular helically coiled spring 76 of approximately B-shaped cross-section is used in conjuctionwith a support spring 78 of flat strip form.

The shielding arrangement shown in Figures 3 and 9 including a circular or non-circular spring contains a support spring, can be used in other arrangements where it is desired to maintain electrical contact around the periphery of two cylindrical connector members. It is not restricted to use in the arrangement shown in Figure 1. In particular, it could be used to maintain shielding contact between the shell members themselves of the two parts of a two-part electrical connector, providing the shells were of sufficient thickness to accommodate the coiled spring.

Rather than employing the coiled springs 44 and 48, the shielding connections between the coupling member and the connector shells may be made by means of other suitable resilient contact members. For example, each of the coiled springs 44 and 48 may be replaced by a more conventional grounding strip 1 20 of the type shown in Figure 10.

The grounding strip 1 20 is formed by stamping from a thin sheet of metal, which may, for example, be a copper or nickel based alloy, so that it has a zig-zag configuration. The strip 1 20 is curved to form a closed loop similar to a garter spring and its ends are fastened together by soldering or welding. Along one edge of the strip 120, the vertices of the zig-zag shape are extended to form tabs 122 which are bent so that they extend radially of the loop formed by the strip 120. In use the tabs 1 22 locate in a groove formed in the body on which the strip 1 20 is mounted to prevent axial movement of the strip 120.Each U-shaped portion of the strip 1 20 between a pair of neighbouring tabs 1 22 forms a spring finger 1 24 which is curved along its length so that, for example, as in Figure 10, the finger 124 is displaced at its midpoint towards the centre of the loop formed by the strip 120.

Figures 11 and 12 show how the grounding strip 120 may be positioned in use between two cylindrical mating portions 130 and 132 of a connector. The strip 120 is located on one or other of the portions 130 or 132 by seating the tabs 122 in a small groove 1 34 formed in the surface of the mating portion 130 or 132. The length of the strip 1 20 is chosen to be such that it fits closely around the circumference of the mating portion 130 or 1 32 on which it is mounted. The spring fingers 124 are shaped so that they curve away from the surface of the mating portion 130 and 1 32 on which the strip 120 is mounted and are an interference fit with the other mating portion.Thus, when the two mating portions 130 and 1 32 are fitted together, the spring fingers 124 are trapped between the two portions their natural resilience urging them against the surfaces of both portions to ensure good electrical contact between the two mating portions.

Although the grounding strip 120 shown in Figure 10 can replace the coiled springs 44 and 48, it may in some circumstances be desirable to use both forms of contact member to make the shielding connection between each shell and the coupling member.

Alternatively, a contact ring 1 40 of the type shown in Figure 1 3 can be substituted for either or both of the coiled springs 44 and 48. The contact ring 1 40 comprises a circular spring wire 142 with a silicone rubber jacket 144 to provide the necessary resilience. Over the outside of the jacket 144 is a layer of random or woven wire mesh 146 which is of conducting metal. In use, the ring 140 is located in a groove in exactly the same way as the coiled springs 44 and 48. The rubber jacket 144 enables the ring to be compressed between two mating parts while the mesh layer 146 ensures a good electrical connection. The spring wire 1 42 provides the ring 140 with the rigidity necessary to retain it in place in the groove.

Claims

1. An electrical connector comprising a first conductive shell member (26) on the first part of the connector, a second conductive shell member (22) on the second part of the connector, a coupling member (24) which is retained on the second part of the connector and which extends around the connector for securing the first and second shell members (26, 22) together and resilient contact means around selected portions of the connector for providing electromagnetic shielding, characterised in that the resilient contact means comprises two separate resilient contact members (44, 48; 120; 140) between the coupling member (24) and a member (26, 22) on each of the connector parts respectively whereby a shielding path is provided through the intermediary of the coupling member (24).

2. A connector according to Claim 1, characterised in that the resilient contact means further includes a contact member (40) between the first and second shell members (26, 22).

3. A connector according to Claim 1 or 2, characterised in that at least one of the contact members comprises an annular contact member (44, 48; 140) extending around the connector and accommodated in but projecting from a groove (42, 46) and a support spring (60; 142) around at least substantially all of the connector and engaging the annular contact member (44, 48; 140) to retain it in the groove (42, 46).

4. An electrical connector comprising two circular conductive connector elements (26, 24, 22; 68; 70; 82; 84) on the two posts and means for assuring electrical connection between the said two elements around the connector to provide electromagnetic shielding, characterised in that the said means comprises an annular contact member (44,48; 62; 76; 140) accommodated in but projecting from a groove (42, 112; 66; 80) extending around one of the elements (26, 24; 68; 82) and a support spring (60, 64; 78; 142) around at least substantially all of the connector and engaging the annular contact member (44, 48; 62; 76; 140) to retain it in the groove (42, 112; 66; 80).

5. A connector according to Claim 3 or 4, characterised in that the annular contact member is a helically-coiled spring (44, 48; 62; 76) and in that the support spring (60; 64; 78) lies within the turns of the helically-coiled spring (44,48, 62; 76).

6. A connector according to Claim 5, characterised in that the helically-coiled spring (44, 48; 62; 76) is of non-circular cross-section.

7. A connector according to Claim 4 or 5, characterised in that the support spring (60; 64; 78) is resiiiently biased so as to tend to lie against the base of the groove (42,46; 66; 80).

8. A connector according to Claim 3 or 4, characterised in that the annular contact member comprises an annulus of resilient material (144) having an outer layer (146) of conducting material provided thereon.

9. A connector according to Claim 8, characterised in that the outer conducting layer (146) is of wire mesh.

10. A connector according to Claim 8 or 9, characterised in that the support spring (142) is located within the annulus (144) of resilient material.

11. A connector according to any of Claims 1 to 10, characterised in that at least one of the contact members comprises a ring member (120) having a plurality of resilient fingers (124) projecting therefrom.

12. A spring structure comprising a housing element (26, 24; 68; 70; 82, 84) having a cylindrical surface with a groove (42, 112; 66; 80) extending around said surface, a helicallycoiled spring (44, 48; 62; 76) accommodated in but projecting from said groove (42, 112; 66; 80) characterised in that a support spring (60; 64; 76) extends around at least substantially all of the element (26, 24; 68, 70; 82, 84) and lies within the turns of the helically-coiled spring (44,48; 62; 76).

13. A structure according to Claim 12, characterised in that the support spring (60, 64; 78) is resiliently biased so as to tend to lie against the base of the groove (42, 112; 66; 80).