Electrical couplings and components

A grounding contact member for electrically connecting cooperating metal shells in a coupling comprises a metal band divided along both edges into several spring contact fingers that are bent inwardly into two U-shape portions. The contact member is located in an annular recess around the inside of a coupling ring with the fingers at one end engaging the metal shell on which the coupling ring is mounted and the fingers at the other end engaging the other metal shell to which the coupling ring is connected.

BACKGROUND OF THE INVENTION 
The present invention relates to electrical couplings and components of 
couplings. The invention is more particularly concerned with couplings 
having grounding fingers that establish electrical connection between 
parts. 
Electrical couplings, such as those between electrical cable clamps to 
electrical connectors or the like, often have an outer metal shell in 
several parts that are retained with one another by means of a coupling 
ring. The coupling ring is rotatably mounted on one part of the coupling 
and is internally threaded, so that it can be screwed onto the cooperating 
other part of the coupling to draw parts into mating engagement. The metal 
shell of the coupling usually provides a part of a ground path for an 
assembly in which the coupling is connected. While there is electrical 
connection between the parts of the coupling via the interfacing accessory 
teeth on the electrical connector and cable clamp, this in many 
assemblies, provide only a poor electrical connection or high resistance 
conductivity because of sloppy engagement between interfacing accessory 
teeth and also compounded by the presence of contaminants such as dirt or 
grimes or rust or poor assembly. 
The present invention provides an improved, reliable and consistent 
electrical continuity between an electrical connector and its cable clamp 
or "backshell" by use of spring contact grounding fingers secured on one 
part of the coupling (such as by welding or solder), the fingers being 
arranged to make a sliding electrical contact with the other part of the 
coupling when the two are coupled together. The grounding fingers ensure a 
solid electrical continuity and maintain this continuity even if the two 
parts of the coupling are not fully mated. 
It can be understood that the present invention also provide an improved, 
reliable and consistent electrical continuity between an electrical 
connector and its coupling part such as a bracket or panel or structure in 
the aircraft. The grounding fingers ensures a solid electrical continuity 
and maintain this continuity even if the connector mounting screws were 
insufficient in having the two parts of the coupling fully mated. This 
present invention grounding fingers is an improvement to the straight wave 
springs described in application Ser. No. 08/986,378. 
BRIEF SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a spring contact 
grounding fingers which solves the problems of the prior art. 
It is another object of the present invention to provide an electrical 
coupling comprising: a first metal member of circular section; a second 
rotatable member mounted on a part of the first member, an annular recess 
formed around on inner surface of the second member or an outer surface of 
the first member; and an electrical contact member located in the annular 
recess, the contact member having a plurality of spring contact fingers 
extending axially of the coupling, the contact member being arranged to 
engage the outer surface of the first member and the inner surface of the 
second member such that the contact member makes electrical contact with 
at least the first member. 
The contact fingers are preferably bent inwardly of the contact member. The 
contact member may include an annular band encircling the first member and 
integral with the fingers, the fingers projecting from the opposite edges 
of the band. The spring contact grounding may be of beryllium copper. The 
first member may be a first shell and the second member a coupling ring, 
the annular recess being formed around the inner surface of the coupling 
ring. The annular band of the contact member is axially installed on the 
first shell thus the other end of the contact member is arranged for 
contact with an outer surface of a second shell. The contact member may be 
entirely enclosed within the coupling ring. 
It is a further object of the present invention to provide an electrical 
coupling comprising: a first metal shell of circular section; a coupling 
ring mounted on a part of the first shell, the coupling ring being 
arranged to engage a surface of a part of a second shell; an annular 
recess formed around an inner surface of the coupling ring; and the 
contact member having a plurality of spring contact fingers extending 
axially of the coupling and (for this description but not limited to) bent 
inwardly into first and second resilient U-shape portions at opposite 
ends, the contact member being arranged to engage the outer surface of the 
first shell and an outer surface of the second shell such that the contact 
member makes a low impedance connection between the two shells. 
Yet another object of the present invention to provide an electrical 
coupling comprising: a first member of circular section; a second 
rotatable member mounted on a part of the first member; an annular recess 
formed around an outer surface of the first member; and an electrical 
contact member located in the annular recess, the contact member having a 
plurality of contact fingers extending axially of the coupling and bent 
inwardly into first and second resilient U-shaped portions at opposite 
ends of each finger, the fingers at both ends of the contact member 
engaging the recess in the first member and an outer surface of the 
contact member engaging the inner surface of the second member such that 
the contact member makes electrical and low impedance connection between 
the first and second members. 
A still further object of the present invention to provide a contact member 
for making electrical and low impedance connection between different parts 
of a coupling assembly, the contact member comprising: a circular band of 
resilient metal having fingers along opposite edges of the band, the 
fingers being bent inwardly to form resilient U-shape portions such that 
the contact member can be retained in an annular recess in the coupling 
with the fingers along opposite edges establishing low impedance 
connection between different parts. 
It is also an object of the present invention to provide a contact member 
for making electrical and low impedance connection between different parts 
of a coupling, the contact member comprising: a circular band of resilient 
metal, a plurality of contact fingers along opposite edges of the band, 
the fingers being bent inwardly to form resilient U-shape portions such 
that the contact member can be retained in an annular recess in one of the 
parts of the coupling with the fingers making electrical contact with the 
one part and with an outer surface of the contact member contacting an 
inner surface of the other part such that the contact member establishes a 
solid and consistent electrical connection between the two parts.

DETAILED DESCRIPTION OF THE INVENTION 
The electrical coupling comprises a forward part in the form of an 
electrical connector 1 and a rear part in the form of a cable clamp or 
backshell 2 that is, in use, secured to the rear of the electrical 
connector 1. 
The electrical connector I shown for this description is a Plug that has a 
first outer metal shell 10 supporting a coupling ring 11 at its forward 
end by means of which the coupling is secured via a retaining ring (not 
shown). Inside the shell 10 an electrically insulated grommet 12 supports 
plurality of electrical contacts 13, which may be either sockets or pins, 
the contacts being connected to respective wires 14 extending rearwardly. 
The grommet 12 projects a short distance beyond the rear end of the shell 
10. On its outer surface, the shell 10 has a screw thread 15 spaced from 
the rear end by a smooth, annular contact region 16. A series of 
triangular teeth 17 (designated as MS3155 accessory teeth) extends around 
the rear end of the shell 10. 
The cable clamp or backshell 2 has a second outer metal shell 20 shown in 
FIG. 2 with a slightly smaller external diameter than that of the first 
shell 10 in the electrical connector 1. The shell 20 is similarly provided 
with MS3155 accessory teeth 27 at its forward end shaped to lock into the 
teeth 17 on the shell of connector 1. The shell 20 is hollow with a bore 
21 extending along its length through which extend the wires 14. At its 
forward end, the bore has a tapered portion 22 adapted to envelope the 
projecting rear end of the grommet 12 when the two parts are secured 
together. A backshell coupling ring 23 is rotatably mounted on the shell 
20 and project from its forward end. On its surface at its forward end, 
the ring 23 has a thread 25 shaped to engage the external thread 15 on the 
shell 10 of the connector 1. Just rearwardly of the thread 25, the ring 23 
has an internal annular recess 26 of rectangular section. The recess 26 
extends rearwardly approximately with the base of the teeth 27 so that the 
forward end of the teeth 27 project about half way along the length of the 
recess. 
The backshell 2 also includes an electrical grounding contact member 30 
clipped within the coupling ring 23. The contact member 30 is a strip or 
band of conductive, spring metal, such as beryllium copper, about 0.005 in 
thick, and is cut with a series of slots 31 and 32 along opposite edges to 
divide the strip into two series of spring fingers 33 and 33'. The contact 
member 30 is bent into a circular shape and opposite ends joined together. 
The spring fingers 33 and 33' extend axially of the assembly and are bent 
at their free ends into two substantially U-shape resilient portions 34 
and 34'. The fingers 33 and 33' are separated from one another by a 
straight intermediate portion 36 provided by the central part of the 
contact strip. The resilient portions 34 and 34' each have a straight 
inclined ramp 37 and 37' directed centrally of the contact strip and bent 
upwardly at its free end into a contact region 38 and 38' of curved 
profile. The left hand ramp 37 forms a flared opening to the contact 
member 30. The contact member 30 is located within the recess 26 around 
the coupling ring 23, with the straight intermediate portion located on 
the floor of the recess. In this position, the free end of the right hand 
resilient portion 34' contacts an annular contact region 28 around the 
outer surface of the shell 20 at its left hand end, in the region of the 
teeth 27, and is compressed slightly radially outwardly, so that a solid 
electrical contact is established between the shell 20 and contact member 
30. 
The backshell 2 is brought up to the rear of the connector I and the thread 
25 on the backshell coupling ring 23 is engaged with the thread 15 on the 
shell 10 of the connector 1. The coupling ring 23 is rotated about the 
backshell 2 to draw the two parts of the coupling further into engagement. 
As the rear of the connector I enters the flared, rear end of the 
grounding contact member 30, the contact region 38 makes sliding 
electrical contact with the contact region 16 at the rear end of the shell 
10, the external diameter of the shell 10 being slightly greater than the 
internal diameter of the contact member 30 in its contact region 38. 
Rotation of the coupling ring 23 does not cause rotation of the grounding 
contact member 30 because this is not attached to the coupling ring 23 by 
welding or otherwise. When the coupling ring is rotated to its full extent 
the teeth 17 are in engagement with teeth 27 and the spring fingers 33 and 
33' establish an effective electrical interconnection between the two 
shells 10 and 20, independently of the coupling ring 23. 
The grounding contact member 30 has the advantage that it can be preformed 
into a circular shape before assembly into the coupling, which enables a 
close control to be maintained on the finished dimensions. The contact 
member 30 is easily clipped into the recess 26 in the coupling ring 23 and 
the ring 23 subsequently pushed rearwardly onto the shell 20 of the 
backshell 2. As this happens, the rear resilient portion 34' is deformed 
and is urged into electrical contact with the outside shell 20. Because 
the contact member 30 is assembled before the coupling ring 23 it enables 
quality and electrical testing of the assembled contact member 30 to be 
carried out more readily. The simple shape of the spring fingers 33 and 
33' makes them easy to manufacture. The resilience of the contact member 
30 also helps reduce the effects of vibration on the coupling by damping 
out the vibration, even if the coupling ring should become loose. The 
contact member 30 also helps to maintain electrical continuity between the 
two shells 10 and 20 even if the coupling ring 23 should become loose. It 
can be seen, therefore, that the electrical continuity through the 
coupling has a very high integrity. This is very important in that it 
ensures that the electrical screening of any system including the coupling 
is maintained. This gives the system a high immunity to electrical 
magnetic interference (EMI) and lightning strikes. 
It will be appreciated that the grounding contact member 30 could be use to 
ensure a good electrical path between other parts of a coupling or between 
parts of two mating couplings For example, as shown in FIG. 5, the contact 
member 30 is used to make electrical connection between an inner member 50 
and an outer rotatable member 51. In the arrangement illustrated, the 
contact member 30 is located in a recess 26 around the outer surface of 
the inner member 50 with its intermediate portion 36 facing outwardly to 
engage the inner surface of the outer member 51. Alternatively, the 
contact member 30 could be located in a recess around the inner surface of 
the outer member 51.