Flexible spring electrical contact for an electrical connector

A female electrical contact including at least one axial elongate flexible spring offset from the axis (A) of the contact and elastically deformable in a transverse direction. The flexible spring (6) comprises a tail (5) engaged in a support (2, 4); a contact portion (7); an intermediate portion (8) located between the tail portion (5) and the front contact portion (7), and having longitudinal curvature of large radius without any folding so as to enable it to bend elastically in a transverse direction; and a portion (10) having a reduced moment of inertia located between the intermediate portion and the front contact portion, thereby making the spring suitable for distributing bending stresses over the entire length of the intermediate portion and facilitating progressive and continuous elastic bending thereof the three portions (5, 7, 8) and having predetermined transverse curvature imparting desired stiffness thereto; an abutment surface (2a) being located at the rear of the spring to keep its deformation within its elastic limits.

FIELD OF THE INVENTION 
The present invention relates to female type contacts for an electrical 
connector, each contact having at least one elongate flexible spring 
extending substantially axially and spaced apart from the axis of the 
contact, the spring being elastically deformable in a transverse direction 
when an associated male type contact is inserted or extracted. 
More particularly, but not exclusively, the invention relates to contacts 
for connectors that are intended for space applications, which contacts, 
given the special characteristics of to the space environment (vacuum, 
weightlessness, large temperature differences, impossibility of corrective 
maintenance), must satisfy requirements of high reliability, long useful 
like, and as great a reduction as possible in the forces required for 
insertion and extraction. 
BACKGROUND OF THE INVENTION 
Various "split-tube" contacts of the above-specified type are known in 
which the tube structure makes it difficult to control the 
insertion/extraction force, in particular because of excessive tolerance 
ranges. It is therefore necessary to sort contacts so as to eliminate 
those which are out-of-range. 
In addition, presently manufactured flexible spring contacts do not provide 
a sufficient safety margin. This drawback is a direct result of the 
structure and the method of manufacture used for the flexible springs 
currently in use. The contact end of a spring is obtained by folding a 
metal part that was initially rectilinear in the longitudinal direction. 
When the contact end is subjected to radial resilient forces during 
insertion/extraction operations, it pivots relative to the fixing portion 
via a fold that acts as a hinge. As a result, stresses are concentrated 
and the metal is subjected to considerable stress at the fold, which means 
that its safety factor is insufficient for certain applications, such as 
space applications. 
Furthermore, in a flexible spring contact organized in that way, only the 
contact end is displaceable and it alone determines the force bearing 
against the pin of the male contact with which it is required to 
co-operate (the bearing force being determined in particular by its length 
and its slope), thereby determining the insertion/extraction force. The 
remainder of the spring is not involved in determining said force, and as 
a result, when considered overall, the spring is too rigid for it to be 
possible to obtain an insertion/extra ction force that is as small as 
could be desired for making it easy to operate connectors having a large 
or a very large number of contacts. 
SUMMARY OF THE INVENTION 
It is a particular object of the invention to remedy the above-described 
drawbacks of present flexible spring electrical contacts so as to enable 
them to be more satisfactory as regards reliability, useful life, and 
magnitude of insertion/extraction force, in particular for special 
applications such as use in the space environment. 
To this end, the present invention provides a female type electrical 
contact for an electrical connector, the contact including at least one 
elongate flexible spring extending substantially axially with an offset 
from the axis of the contact, and being elastically deformable 
transversely, 
essentially characterized in that said flexible spring comprises: 
a tail portion engaged in a support; 
a front contact portion designed to bear against a male type contact when 
inserted in said female contact; 
an intermediate portion situated between the tail portion and the front 
portion of the contact, which intermediate portion is curved 
longitudinally towards the axis of the contact with curvature of large 
radius and without any fold, and is suitable for bending elastically in 
the transverse direction when a male type contact is inserted; and 
a portion having a reduced moment of inertia situated between the 
intermediate portion and the front portion, thereby obtaining a reduction 
in resistance to bending suitable for distributing stresses over the 
entire length of the intermediate portion and encouraging continuous and 
progressive elastic bending of the intermediate portion when the flexible 
spring co-operates with a male type contact; 
at least one of the intermediate portion, the portion having a reduced 
moment of inertia, and the front portion having a predetermined transverse 
curvature imparting desired stiffness thereto; 
and the contact further comprises an abutment surface situated behind the 
flexible spring (relative to the axis of the contact) to limit transverse 
deformation of the spring and to keep it within its elastic deformation 
limits. 
Advantageously, in a simple embodiment of the flexible spring, the portion 
having a reduced moment of inertia is narrower than the intermediate 
portion and the front portion on either side thereof. Still for the same 
purpose, the thickness of the flexible spring may be substantially 
constant throughout all of its portions; it is then possible, at least in 
some embodiments, for the flexible spring overall to be obtained from a 
sheet of metal. 
Still for the purpose of simplifying manufacture of the spring-blade 
cutouts, it is advantageous for the transverse curvature of the flexible 
spring to be substantially constant, at least over the entire length of 
the intermediate portion, the portion having a reduced moment of inertia, 
and the front portion. This transverse curvature can then be obtained by a 
conventional technique of curving the spring already cut out in a sheet of 
metal. 
When made in accordance with the invention, each spring is capable of being 
highly adapted to elastic deformation without there being a concentration 
of stress in any particular region, this being achieved by eliminating the 
fold that is present in the flexible spring of prior art contacts. 
The elastic deformation limit can be extended by using beryllium-copper 
that is completely or partially treated to the core, and this remains 
possible within acceptable cost constraints with springs being produced 
from a cutout and curved thin strip of beryllium-copper regardless of 
which technological solution (individual springs or groups of springs) is 
adopted. 
Because of these dispositions that spread stresses over the entire surface 
of the part avoiding the stress concentrations that are usually 
encountered, a remarkable safety factor of more than 2 is achieved, 
between the range of normal use and the limiting deformation where 
deformation becomes permanent. 
By appropriate scaling, the same shape can be applied to a wide range of 
contact sizes. 
In a preferred embodiment which should give satisfaction over a large 
number of applications, the contact further comprises: 
an outer rigid tubular body inside which the above-mentioned flexible 
spring is received, the portion of the inside surface of the tubular body 
situated behind the flexible spring constituting the above-mentioned 
abutment surface; and 
an internal plug situated in the rear portion of the tubular body with the 
tail portion of the flexible spring being engaged between the plug and the 
tubular body. 
In practice, the tubular body and the inside plug can be secured to each 
other by crimping, thereby clamping the tail portions of the springs 
between them. 
Various structures associated with various manufacturing processes can be 
envisaged. Thus, in a first possible implementation, use is made of blade 
cutouts made in unitary form that have their tail portions engaged between 
the tubular body and the inside plug and the widths of their respective 
tail portions are such that they surround the inside plug and come into 
lateral abutment against one another. Alternatively, the flexible springs 
may be connected together at a single component part and their tail 
portions combined in the form of a tubular sleeve which is engaged between 
the tubular body and the inside plug. In either case, provision may be 
made for the tail portion to have at least one radial projection extending 
inwards and engaged in a housing in the inside plug so as to hold the 
spring axially.

DESCRIPTION OF PREFERRED EMBODIMENTS 
With reference initially to FIGS. 1 to 5, the female type contact 1 
comprises, for example, an outer tubular body or tube 2 which is open at 
both ends, one of its ends being designed to receive a male contact, e.g., 
of the pin type (whose lateral outline is represented schematically by 
chain-dotted lines referenced by the letter M), and having an edge that 
curves inwards to form a guiding lip 3. 
At its rear end, the tube 2 receives a solid plug 4 whose own rear end is 
shaped in any appropriate manner (not shown) enabling it to be connected 
to an electric cable. 
The tail portions 5 of a plurality (in this case three) flexible springs 6 
that are uniformly spaced apart circumferentially are engaged between the 
outer tube 2 and the plug 4. 
As can be seen better in FIG. 2, each spring 6 is in the form of an 
elongate metal spring blade made of beryllium-copper for example, and at 
least locally treated to its core. The spring has a front contact portion 
7 and a rear tail portion 5 which are connected together by an 
intermediate portion 8 of continuous large-radius curvature towards the 
axis A of the contact and without folding. 
In order to enable the spring to have sufficient stiffness given its 
relatively small thickness, it is curved transversely along its entire 
length. Its radius of transverse curvature is the same, at least over the 
entire length of above-mentioned portions 7 and 8. 
In order to increase the longitudinal flexibility of the metal spring and 
to obtain stress distribution along the entire length of its intermediate 
portion 8, thereby making it highly suitable for elastic bending when 
subjected to transverse forces, a portion having a reduced moment of 
inertia is provided at 10 between the front portion of the contact 7 and 
its intermediate portion 8, this portion being achieved in this case by 
reducing the width of the metal spring. The region of reduced width 10 is 
disposed between the portions 7 and 8 that are of progressively increasing 
width. 
Finally, when seen from above (FIG. 2) the flexible spring has an outline 
of varying width which, in combination with its transverse curvature, 
gives rise to a member of longitudinally varying stiffness and of 
controlled longitudinal flexibility. 
The cross-sections of the various portions of the contact 1 are shown in 
FIGS. 4 and 5, namely: in FIG. 4 the cross-section of the contact portion 
of the springs on line IV--IV of FIG. 1; in FIG. 5 the cross-section of 
the tail portion 5 of the springs on line V--V of FIG. 1; and finally, in 
FIG. 3, an end view of the contact 3 on line III--III of FIG. 1. 
During a connection operation, inserting the pin M of a male contact in the 
female sleeve 1 causes the contact front portions 7 of the springs 6 to be 
raised transversely as shown in FIG. 1. The wall 2a of the tubular body 2 
serves as an abutment limiting the transverse deflection of the spring 6. 
The controlled deformation in the various areas of each spring makes it 
possible, while maintaining good-quality electrical contact with the male 
pin, to reduce the force with which the contact portion 7 bears against 
the pin, thereby reducing the wear of these members. 
Above all, such a shape makes it possible to work with the metal well below 
its elastic deformation limit (e.g., in a deformation range corresponding 
approximately to half the value of such limit, i.e., with a safety factor 
of 2), and it is thus certain that the metal will never be caused to work 
in its plastic deformation region. 
In addition, a flexible spring designed in this way can be made of a highly 
resilient material such as core-treated beryllium-copper, using a 
manufacturing process that is simpler than that required of unitary female 
contacts. In this case, as shown in FIG. 2, each spring is cut out as a 
single flat piece from a metal sheet, after which it is curved 
transversely and longitudinally. Thereafter it is core-treated overall 
The tail portions 5 of the springs 6 are of a width such that when 
installed in the tubular body, they contact one another laterally and 
jointly cover the plug 4 completely, as can be seen in FIG. 5. This 
ensures that the springs 6 are locked laterally in appropriate positions. 
Furthermore, each spring 6 may have a radial projection 11 at or near the 
free end of its tail 5. The projection extends inwards and is engaged in a 
recess (e.g., an annular groove 12) formed in the plug 4. The springs 6 
are thus retained axially. 
FIG. 6 shows an embodiment in which the tail portions 5' are integral with 
one another and form a tubular sleeve which is fitted inside the outer 
tube 12, being engaged between the outer tube and the plug 4. All of the 
springs 6' and the tubular sleeve 5' are connected together, thus forming 
a single piece 13. 
The piece 13 may be made in various different ways, e.g., by machining 
individual springs 6' in a length of tube, or more simply and more 
cheaply, by cutting out a metal blank as shown in FIG. 6 while flat and 
then in rolling it to form the transverse curvature of the springs 6' and 
of the sleeve 5'. Cutouts formed in the base of the metal blank enable the 
radial projections 11 for providing axial retention to be formed. 
It will be understood that an electrical contact according to the invention 
can be made with an arbitrary number of flexible springs using the 
dispositions set forth above. The flexible springs are then angularly 
distributed in a uniform manner so that the male contact is guided axially 
by the springs or spring portions that face one another. 
However, if the contact has only one flexible spring, certain special 
features need to be provided as described below with reference to FIGS. 7 
to 10, for the purpose of ensuring proper guidance for the associated male 
contact. 
The contact 14 shown in FIG. 7 is made, in general, in the same way as the 
contact 1 of FIG. 1 (and the same numerical references are retained for 
designating items that are identical), that the contact 14 has only one 
flexible spring 6. 
To compensate the transverse force exerted by the contact portion 7 on the 
associated male contact pin M to guide it during insertion/extraction, a 
guidance and thrust piece 15 is provided facing the flexible spring 6 and 
optionally shaped approximately like a contact spring, except insofar as 
it is not designed to flex transversely. The guidance and thrust piece 15 
has a tail portion 5 designed to be engaged between the tubular body 2 and 
the plug 4 in the same manner as a flexible contact spring 6 or 6' as 
described above. It is curved transversely, but it does not have a region 
of reduced second moment of area. It may advantageously be wider than a 
flexible spring so as to facilitate guiding the male pin M, as can be seen 
clearly in FIG. 10 which shows the respective positions of the contact 
pieces 6 and 15 against a pin M engaged in the contact. FIG. 9 shows the 
same contact when the pin is absent. 
The single flexible spring 6 and the guidance and thrust piece 15 may be 
constituted two by independent members in the manner described above, each 
being individually engaged and retained between the tube 2 and the plug 4, 
or alternatively they may be in the form of a one-piece member obtained by 
cutting out a metal blank 16 while flat, as shown in FIG. 8, and then 
rolling and curving such blank. The one-piece member 16 is then installed 
like the member 13 in FIG. 6.