U.S. patent number 3,892,459 [Application Number 05/481,590] was granted by the patent office on 1975-07-01 for open barrel terminal and method for terminating an electrical wire therein.
This patent grant is currently assigned to AMP Incorporated. Invention is credited to Larry Eugene Dittmann, Timothy Allen Lemke.
United States Patent |
3,892,459 |
Dittmann , et al. |
July 1, 1975 |
Open barrel terminal and method for terminating an electrical wire
therein
Abstract
The invention relates to a terminal and a method for terminating
an electrical wire therein. The terminal employs a wire barrel
having a asymmetrical pattern of cavities into which the wire is
extruded. The method provides optimum electrical contact through
high level deformation and maximum tensile strength through low
level deformation.
Inventors: |
Dittmann; Larry Eugene
(Harrisburg, PA), Lemke; Timothy Allen (Dillsburg, PA) |
Assignee: |
AMP Incorporated (Harrisburg,
PA)
|
Family
ID: |
23912572 |
Appl.
No.: |
05/481,590 |
Filed: |
June 21, 1974 |
Current U.S.
Class: |
439/442;
174/84C |
Current CPC
Class: |
H01R
4/188 (20130101) |
Current International
Class: |
H01R
4/10 (20060101); H01R 4/18 (20060101); H01r
011/08 () |
Field of
Search: |
;339/95,97-99,223,276
;174/84C,94R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: McGlynn; Joseph H.
Attorney, Agent or Firm: Osborne, Esq.; Allan B.
Claims
What is claimed is:
1. A terminal for receiving an electrical wire therein, which
comprises:
a. a wire barrel having a floor bounded on either side by a
generally vertical sidewall and with the inner surface of the floor
and sidewalls containing a plurality of cavities, the cavities on
the upper portion of the sidewalls being longer in one dimension
than the cavities on the floor and lower portions of the sidewalls.
Description
BACKGROUND OF THE INVENTION
The use of multi-stranded aluminum wire has been retarded because
of the problems of reliably attaching the wire to a terminal at a
reasonable cost. Further, the use of aluminum wire has been impeded
by failures of prior art terminals wherein the failure has been
catastrophic; i.e., sudden, rather than a gradual deterioration
such as experienced with conventional copper conductors and brass,
copper or other like terminals.
One well known problem with aluminum wire is its ability; i.e., the
several individual strands to move or creep under temperature
cycling common to all electrical connections. This phenomenon had
for years prevented the use of conventional crimping technique on
aluminum wire.
Terminals which are attached to electrical conductors through
crimping techniques are either open or closed barrel.
The open barrel terminal is one having a U-shape; i.e., a floor
bounded on two sides by vertical sidewalls. In crimping, the wire
is laid on the floor and the walls are folded or otherwise wrapped
around the wire into an encompassing relation.
A closed barrel terminal is one having a hollow cylinder in which
the conductor is received. The cylinder or portion thereof is
collapsed down onto the wire squeezing such thereinbetween.
With respect to terminating multi-stranded aluminum wire, workers
in the field have been successful in crimping such in closed barrel
terminals wherein perforated liners are employed. These liners,
placed in the hollow cylinder and around the wire, serve to break
up aluminum oxides and further to cause the strands to be squeezed
into the perforations. These actions result in good electrical and
mechanical terminations. One such example of a closed barrel
aluminum termination is disclosed in U.S. application Ser. No.
346,530, filed on Mar. 29, 1973, now abandoned, the disclosure
being incorporated herein by reference.
Contra, aluminum termination in open barrel terminals have not met
with a high degree of acceptability. One reason therefore relates
to the aforementioned creep phenomenon. Another problem, common to
both type of terminals but more conducive in open barrel terminals,
is corrosion, particularly galvanic corrosion.
Accordingly it is an object of the present invention to provide a
terminal and a method of terminating an electrical wire therein
which will cause inter-strand bonding so that the individual
strands cannot move but as a unit and that movement thereof is
prevented by extruding wire into cavities located on the sidewalls
of the terminal.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an open barreled terminal
constructed in accordance with the principles of the present
invention;
FIG. 2 is a view of the asymmetrical pattern of cavities
constructed in accordance with the principles of the present
invention;
FIG. 3 is a cross-sectional view taken normal to the axis of a
prior art terminal;
FIG. 4 is a cross-sectional view taken normal to the axis of the
terminal of FIG. 5;
FIG. 5 is the terminal of FIG. 1 after being crimped onto a
multi-stranded wire in accordance with the principles of the
present invention; and
FIG. 6 is a longitudinal cross-sectional view of the terminal of
FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings wherein like reference numerals
represent corresponding parts in all figures, there is shown in
FIG. 1 an open barrel terminal 10 constructed in accordance with
the present invention. The three prominent elements of terminal 10
are, from front to rear, the tongue 12, wire barrel 14 and
insulation barrel 16. These elements in the preferred embodiment
shown are integral, the terminal being stamped and formed from a
single coplanar sheet of conductive material. However, the novelty
resides in the wire barrel 14 and in the method of crimping it
around a wire. Thus it is to be understood that the presence of
tongue 12 and insulation barrel 16 is not to be taken as limiting
the invention to a terminal possessing all three elements.
Connecting means 12 is the dynamic contact interface of terminal 10
in that it provides a movable; i.e., non-permanent point of
electrical contact between the terminated conducting wire and an
electrical junction such as a motor, control box, generator or the
like (none of which are shown in the drawings). The configuration
of connecting means 12 can take many different shapes as is well
known in the industry. The particular one shown here; i.e., a "ring
tongue," is designed generally to receive a threaded post (not
shown) through hole 18. A nut (not shown) threaded down the post
secures terminal 10 to the post mounting.
The transition or connecting strap 20 between the connecting means
12 and wire barrel 14 may be abrupt or the edges 22 may be curled
as shown to add structural strength to the forwardly extending
connecting means 12. This structural feature is referred to as a
"transitional curl."
Insulation barrel 16 consists of a floor member 24 bounded on
either side by upright sidewalls 26. The dimensions of barrel 16
are such that the sidewalls may be crimped around the outer
insulation jacket 28 of cable 30 as shown in FIG. 5. The beveled
surfaces 32 on the top of each sidewall 26 facilitate the crimping
action as is well known in the art.
The insulation barrel 16 is displaced downwardly with respect to
wire barrel 14. This displacement, generally indicated by reference
numeral 34, accommodates the outer diameter of cable 30 so that the
multi-stranded wire 36 (FIG. 5) will lay in wire barrel 14 without
being bent downwardly as the case would be otherwise.
Wire barrel 14 consists of a floor 38 and opposing sidewalls 40. As
with insulation barrel 16 the sidewalls are beveled to facilitate
crimping.
The floor and inner surfaces of sidewalls 40; i.e., the inner
surface 42 of wire barrel 14, contains a plurality of cavities 44.
Although these cavities are both rectangular and square, the
precise geometry is not critical. However, the general pattern is;
i.e., note that the inside cavities; i.e., those on floor 38 and on
the flanks of the sidewalls, are smaller length and breadthwise,
than those cavities higher up on the sidewalls 40 which are
elongated. As is well known in the art, smaller cavities are
desirable in terminating wire because, for a given inner surface
area, the smaller cavities will provide a larger contact area
between the terminal and wire terminated therein. Prior art
terminals, in attempting to gain all the contact area possible,
punched in small, uniform size cavities throughout the inner
surface of the wire barrel. However, it has been discovered that
the use of small cavities on the sidewalls are self-defeating. As
the sidewalls are crimped, the inner surface area decreases and the
cavities in the fold over region close off before the wire can be
squeezed thereinto. FIG. 3 is a drawing of a prior art terminal.
The terminal herein designated by reference numeral 46, contained a
plurality of cavities 48 which were uniform and small in size,
conforming to prior art practice. As seen in the drawing, as the
wire barrel of terminal 46 was crimped about wire 50, the cavities
in the fold-over region; i.e., upper portions of the sidewalls,
pinched shut before the wire could be compressed thereinto. In
contrast, FIG. 4 is a drawing of a terminal 10 having the cavity
pattern shown in FIG. 2. It is clear that the elongated cavities
remained open to receive wire 36. Both FIGS. 3 and 4 are drawings
from actual photographs of terminals sectioned normal to the
longitudinal axis and across the wire barrel.
FIGS. 4, 5 and 6 illustrate the method and result of crimping wire
barrel 14 around multi-stranded wire 36 as developed by the present
invention.
Two operations are performed simultaneously in terminating wire 36.
After the bared wire is laid in the wire barrel the sidewalls 40
are folded in on the wire by conventional crimping techniques.
FIGS. 4 and 5 illustrates the shape imparted to the top of terminal
10 thereby. At the same time, a die (not shown) strikes the bottom
of the wire barrel sharply and substantially deforms it as shown in
FIGS. 4 and 6, the deformed area being generally designated by
reference numeral 52. The shape of the die is such as to provide
two distinct levels of deformation as clearly shown in FIG. 6 which
is a longitudinal cross-section. The high level deformation is
designated by reference numeral 54 and the low level deformation is
designated by reference numeral 56. FIG. 4 is a normal
cross-sectional view across high deformation level 54. The high
level deformation provides the electrical relation and the low
level deformation provides the mechanical relation between the wire
and wire barrel. There are beneficial and unexpected effects
resulting from the high deformation. With reference primarily to
FIG. 6, an elongation or stretching of wire 36 occurs. The
stretching causes the fracturing of brittle oxide film which
generally is present on the strand's surfaces. The pressure exerted
on the wire from the deformation causes clean metal to be extruded
through the induced fissures in the oxide film. The clean metal is
bonded or cold welded with other extruded clean metal by the
pressure of deformation.
The maximum elongation obviously occurs along the wire's
longitudinal axis. Further, most of the bonding occurs between the
inner strands of wire 36 with little or no bonding occurring at the
interface of the terminal and wire. However, mechanical and
electrical integrity is achieved primarily at the interface with
the extruding into and filling of cavities 44 by the wire.
With respect to the low level deformation 56, the amount of
deformation required to achieve maximum tensile strength is equal
to about a 30 percent reduction in overall cross-sectional area. In
addition to the amount of deformation, tensile strength is enhanced
by subjecting a greater area along the axial plane to the low level
deformation. As FIG. 6 shows, low level deformation 56 is provided
on either axial end of the high level deformation.
With respect to high level deformation 54, the amount of
deformation required to achieve optimum electrical performance is
equal to about a 60 percent reduction in the total cross-sectional
area occupied by a non-deformed wire barrel and wire; provided,
that the ratio of 2 to 1 exists between the cross-sectional area of
the wire barrel and the cross-sectional area of the wire. A 60
percent overall reduction results in reducing the wire by a factor
of about 80 percent which is required to create inter-strand
bonding.
The method used to arrive at the aforementioned 2 to 1 ratio is
simple and straight forward. Knowing the circular cross-sectional
area of a given wire, the width (W) and thickness (T) of the
material to be formed into terminal 10 is computated by solving
these two simultaneous equations:
W = .pi. [1.3(Dw) + T] and
T = 2(CSA)w/W
where:
Dw = wire diameter
(CSA)w = cross-sectional area of the wire
The 1.3 is a multiplier to arrive at the average diameter of the
terminal which, as is well known, must be large enough to permit
wrapping the terminal sidewalls around the wire.
Although the die used to deform terminal 10 is not shown, its shape
can be ascertained from FIGS. 4 and 6. Note that the depression is
generally rectangular with the edges and corners rounded to prevent
stress-cracking of the terminal during deformation. Further,
although not shown, a roughened die has been found to give better
results in deforming the terminal than one having a smooth or
polished face.
Further, with respect to the concept of deforming the wire barrel
14 of terminal 10 with a roughened die, experimental data indicates
that a roughness of 175 microinches gives very good results and is
preferred. However, satisfactory results have been obtained with
dies having a roughness factor ranging from about 32 to about 400
microinches. The method used in roughening the die faces is sand
blasting with ground shot.
The purpose in using a roughened die face is to create a high
degree of friction between the die and wire barrel surface,
particularly along what becomes the sidewalls of the deformed area.
By creating such friction, the thickness of the wall of the wire
barrel being deformed remains uniform or nearly so. By maintaining
a uniform wall thickness, it acts as an extension of the die; i.e.,
very little energy is lost in thinning the walls along the sides of
the die. More energy then is transferred to the wire itself.
Furthermore, more wire barrel material is moved into the wire area
without approaching the stress-cracking level in the material. As
workers in the field can appreciate, the more material moved
inwardly against the wire, the more the wire will be extruded and
more clean metal will result.
As is well known in the art, die faces must be flat or round to
push the wire barrel material rather than to pierce it. In
determining optimum width of a square die face, tests were
conducted. It was found that variations in the amount of wire
elongation occurred with die faces of various widths. Through
additional testing and studies it was determined that a square die
face having a width equal to the thickness of the wire barrel wall
provided the maximum elongation in the center strands of the wires.
Maximum elongation of course means more fresh metal exposed for
bonding. Widths in excess of two thicknesses did not improve the
performance while widths between one and two thicknesses were
inconclusive to establish a more preferred width other than one
thickness. Widths less than one thickness showed definite
deterioration in performance.
It has been observed that the pattern of wire extrusion from the
wire barrel upon high level deformation is parabolic in a plane
parallel to the longitudinal axis with the center strands being
axially extruded the furthest. As noted above, as the wire barrel
is being deformed inwardly, the cavities are being filled by
lateral extrusion of the outermost strands of the wire. Thus,
longitudinal elongation is retarded as far as those strands are
concerned.
In conclusion, the present invention provides a terminal and a
method for terminating wire therein which results in a superior
electrical and mechanical connection. More importantly, the
terminal and method allows the satisfactory termination of stranded
aluminum wire.
The foregoing detailed description has been given for clearness of
understanding only, and no unnecessary limitations should be
understood therefrom, as some modifications will be obvious to
those skilled in the art.
* * * * *