Note: Descriptions are shown in the official language in which they were submitted.
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AN ELECTRICAL CONNECTOR ASSEMBLY
INCLUDING MEANS FOR GROUNDING AND
TERMINATING A COAXIAL CABLE
This invention relates to an electrical connector
assembly including means for grounding and ~erminating a
free end of ~ coaxial cable, the coaxial cable being of
the type including a dielectric separating a central
conductor from a conductive braid and including an
insulator jacket surrounding ~he shield conductor.
U.SO Patent 3,373,243 issuing March 12, 1968 to
Janowiak for "An Electrical Multi-Conductor Cable Con-
necting Assembly," U.S. Patent 3,634~815 issuing January
11, 1971 to Stevens for "A Connector Assembly Adapted For
Use With A Coaxial Cable," assigned to the assignee of
the instant application, and U.S. Patent 3,074,045
issuing January 15, 1963 to Overholser for a "Cable
Connector and Method of Assembly" provided a conductive
frusto-conical ferrule for terminating the free end of a
coaxial cable and grounding the cable braid to the
connector shell. Although not appreciated earlier, the
manner in which and the force by which a connector
assembly grips and/or clamps the coaxial cable may be
responsible for an electrical open circui~ developing
between the braid shield and the connector shell. During
tempera~ure cycling, the insulator jacket has been found
to flow and/or relax and the conductive ferrule axially
backing off from abutting contact with the connector
shell, thereby leading to the open circuit. Clearance
fitting of the ferrule in the shell provides an
inadequate conductive path for shielding and provision of
a resilient or rubber-like seal member between the shell
and ferrule prevents shielding altogether.
Accordingly, a more desirable electrical connector
assembly for use with a coaxial cable would reliably
maintain closed circuit relationship be~ween the
conductive braid of the cable and the connector shell.
An object of the instant invention is to provide an
electrical connector assembly for terminating a coaxial
cable which offers good radio frequency interference
shielding performance coupled with ease of assembly.
Another object of the instant invention is to
provide a coaxial electrical termination having redundant
means for shielding against radio frequency interference.
Still another object is to provide an improved
termination requiring only a minimum of redesign of an
existing termination.
Briefly stated, the foregoing and other objects are
accomplished by a conductive cylindrical shell having an
interior cavity receiving a conductive ferrule, a collar
and the free end of a coaxial cable, the shell having
internal thread adjacent the entry to its cavity engaging
external thread on the collar, the collar and ferrule
being disposed about the cable end with the insert being
wedged between the braid shield and the dielectric and
the collar being disposed against the jacket.
A ground arrangement for grounding the braid shield
2~ to the connector shell includes the interior wall of the
shell having internal thread and an interior end wall,
and the ferrule having a stepped annular shoulder
defining spaced end faces and circumferential faces, one
of the circumferential faces being provided with external
thread, the external thread being adapted to threadably
interengage with the internal thread whereby the end
wall may be axially, threadably, drawn together in~o
abutment with one of the end faces and be disposed in
metal-to-metal contact, both the engaged thread and the
end face being abutted with the end wall providing a
redundant electrical path between the braid and connector
shell.
One way of carrying out the invention is described
in detail below with reference to the drawings which
illustrate the specific embodiment of this invention; in
which:
FIG~RE 1 is a view, in cross section; of a prior art
electrical connector assembled to a coaxial cable.
FIGURE 2 is a view, in cross-section, of an elec-
trical connector assembled to a coaxial cable.
Referring to FIGURE 1, a prior art plug electrical
connector 10 is shown terminating the free end of a
coaxial cable 30. The coaxial ~able 30 is of the type
which comprises a central conductor 32, a dielectric 34,
an outer conductor or braid shield 36 and an external
rubber insulator jacket 38, each being coaxial one with
the other.
The plug electrical connector 10 comprises a hollow
cylindrical shell 12 of electrically conductive material;
a tubular collar 20 having external thread 28 and a
radial flange 22 extending outwardly therefrom; and a
tubular ferrule 40, ~he ferrule and the collar being
coaxially received in the shell so as to be generally
concentric with central conductor 32 with each
cooperating to clamp about the cable. The connector
shell 12 has a primary axis, an external end face 14~ and
an interior cavity which includes a generally cylindrical
interior wall that terminates at an end wall 16
transvérse to its primary axis, the interior cavity
receiving ferrule 40 and collar 20 and the interior wall
including internal thread 18 therearo~nd.
Collar 20 includes a tubular sleeve 26 which has
successively increasing internal diameter sections 26a,
26b, and 26c which define shoulders whose edges trace an
imaginary cone and bite against the jacket 38.
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. Ferrule 40 is of electrically conductive material
and includes a frusto-conical, wedge-shaped body 42, an
annular flange 48 having an end face 46 and an internal
bore 44 extending axially therethrough, the diameter of
internal bore 44 being slightly greater than the external
diameter of dielectric 34.
Ferrule 40 and collar 20 are disposed about the free
end of the cable with ferrule body 42 being wedged
between dielectric 34 and outer conductor 36 and collar
20 being driven into engagement with the cable jacket,
the body applying an outward radial pressure to both the
braid shield 36 and the rubber jacket 38 and the
shoulders defined by diameter sections 26a, 26b and 26c
axially engaging cable jacket 38.
Radio frequency interference protection must come as
a result of metal-to-metal contact between end face 46 of
ferrule 40 and end wall 16 of shell 12, the metal contact
providing a continuous electrical circuit path between
plug shell 12 and braid shield 36. Temperature effects
on jacket 38 could allow axial back-off of the ferrule
from metal-to-metal contactO
In accord with this invention~ FIGURE 2 shows
improved RFI shielding connection between plug connector
10 and coaxial cable 30. Shell 12 includes end wall 16
and internal thread 18. Ferrule 40 includes adjacent its
end face 46 a stepped annular shoulder 52 spacing an end
face 46' therefrom and defining, respectively, a first
circumferential face around annular shoulder 52 and a
second circumferential face around annular flange 48, the
circumferential face around flange 48 including external
thread 54 and the circumferential face around shoulder 52
being without external thread. The end faces 46, 46' of
ferrule 40 and end wall 16 of shell 12 are disposed,
respectively, in a plane perpendicular and inclined to
the primary axis of the connector and end wall 16 is
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adap~ed to abut end face 46 when assembled into the
shell. The in~ernal thread lB is adapted to engage with
the external thread 54 and the external thread 28 on
collar 16.
The internal/external thread provide thread surfaces
which contact to increase frictional forces resisting any
rotation of the ferrule leading to axial back-off from
metal-to-metal contact. In this regard, tight abutment
of end wall 16 with the end face 46 also enhances
frictional forces tending to resist rotation.
The wedge-shaped frusto-conical body 42 includes
helical cam surfaces 58, such as thread, about its
exterior surface to threadably engage with shield braid
36 when the wedge-shaped body is axially, rotatably,
inserted between the dielectric and outer cond~ctor
braid. Such cam surfaces cooperate to resist external
axial pull forces which may act on the cable. The
annular shoulder 52 would be hexagonal in cross-section
to assist the threadable assembly of ferrule 40 into the
braid 36.
As a result o~ assembly of ferrule 40 into connector
shell 12, the end wall 16 is abutting the end face 46 to
provide a first ground path and the internal/external
thread 18, 54 are engaging to provide a second ground
25 path. The sense of all threads 18, 54 and 58 wouldr
preferably, be the same so that when ferrule 40 is
threaded either into braid shield 36 or into shell 12 or
when the collar 16 is threadably inserted into the shell,
all thread engagements are further tightened.
For assembly, the cable 30 is trimmed to provide a
square-cut free end for termination. Collar 20 is then
slipped over the cable and positioned axially rearward of
the square-cut end and ferrule 40 is threadably inserted
between the braid shield 36 and dielectric 34. A contact
pin 60 is passed over a bare projecting end of central
conductor 32 and soldered thereto. Following this, shell
12 is joined ~o the cable passing over ferrule 40.
Collar 20 is screwed into the sleeve 12 and its end face
24 brought into engagement with the end face 14 and the
S jacket 38.
