Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to an improved dielectric
molded plastic self-locking strain relief flexure relief bushing.
The demand for effective safe electrical appliances has
created a need for strain relief bushings which easily lock
into wall apertures and absorb strain at the bushing. Bushings
of this sort æe in use today by the multimillions of units.
Another important problem encountered in the use of wire,
cord, eable and similar items having flexibility, which may
generally be referred to hereinafter as "cable", particularly
as used in electrical appliances, has been wear and breakage
due to flexure stress and/or abrasion of cable, particularly
near an aperture from which cable extend. Past solutions to
flexure stress combined with strain relief have been surpris-
ingly complicated. They include expensive springs extending
from plugs such as in the typical plug of a toaster or an iron,
flared extensions from an opening to limit movement and flexure
of cable, flexible rubber sheaths in lieu o~ springs on cable
extending from electric plugs, and many more.
As effective as strain relief bushings have been, para-
doxically, flexure stress has been a prime source of theirfailure. Cable, properly held by a conventional molded self-
locking plastic strain relief bushing has traditionally failed
after normal use due to flexure stress at the active face of the
bushing. For instance, the cable held only by a strain relief
bushing in a vacuum cleaner is still subject to flexure and
failure at the strain relief bushing after prolonged use due
to stress~
Combination strain relief bushings with flexure relief
to solve the combined problem of strain relief and flexure stress
relief have been expensive, complicated or impracticable.
Com~ination solutions such as engaging a spring in a strain
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relief bushing still bear the cost of assembly and the cost
of the spring. Solutions such as found in U. S. Patent No.
2,72~,736 in a strain relief bushing with an integral molded
plastic spring for flexure relief still bear the cost of a
large amount of plastic and complicated dies, molds and the
difficulty of molding. Almost twenty years after U. S. Patent
No. 2,724,736, a simpler, less expensive solution to combined
flexure and strain relief was found in U. S. Patent No.
3,749,818.
Even U. S. Patent No. 3,749,818 was found to require
complicated molds. The webbing used for flexure relief itself
has been found subject to some flexure stress and the protrusion
for flexure relief was subject to damage from bumping into
objects while in use.
Expedients such as the abandoned invention disclosed in
Fig. 5 of U. S. Patent No. 3,749,818 were gropings of the prior
art toward simplicity and effectiveness in providing combined
strain relief and flexure relief in a strain relief bushing by
using extending fingers to alter the bending anble of cable.
The fingers of Fig. 5, while promoting benefit, were not effect-
ive enough to prevent wear and effective stress relief.
According to the present invention, a molded plastic
dielectric strain relief bushing, self lockable in an aperture,
is combined with an effective stress relief in the form of an
integral regularly flared portion at an active face of the
strain relief bushing~
The present invention extends the use life of cable
against flexure stress at an active face of a conventional
prior art self-locking strain relief bushing whether such bush-
ing is in separated sections, or a one-piece bushing of sections
joined by webbing or straps.
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The strain relief-flexure relief bushing of the present
invention now offers an additional stress relief in what was
formerly only a strain relief bushing with only simple addi- ;
tional construc~ion.
The strain relief-fle~ure relief bushing of the present
invention substitutes for often conductive flared metal fittings
of the past which often had to be screw set and which may or
may not have included strain relief characteristics and for the
nonconductive stress reliefs which required cable to have sec-
ondary strain relief ~acilities.
Although such novel feature or features believed to be
characteristic of the invention are pointed out in the claims,
the invention and the manner in which it may be carried out may
be further understood b~ reference to the description follow-
ing and the accompanying drawings.
Fig. 1 is a plan view of a stress relief-flexure relief
bushing of the present invention.
Fig. 2 is a front elevation of Fig. 1.
Fig. 3 is a side elevation section of a bushing of
Figs. 1 and 2 engaged in an aperture.
Fig. 4 is a side elevation of a bushing of Figs. 1 - 3
engaged with cable in an aperture.
Fig. 5 is a plan view of another embodiment of the
stress relief-flexure relief bushing of the present invention.
Fig. 7 is a plan view of another embodiment of the
stress relief-flexure relief bushing of the present invention.
Figs. 6 and 8 are details of exemplary bushing
locking means for locking bushings in an aperture.
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Referring now to the figures in greater detail, where
like reference numbers denote likeparts in the various figures.
A preferred embodiment of the strain relief-flexure
relief bushing 10 of the present invention is shown in Figs. 1
- 4. The strain relief-flexure relief bushing 10 includes a
shank 11 and a gripblock 12 joined by a strap 13. The shank 11
and gripblock 12 in effect, functions as a unitary bushing
shank. On the face of the shank 11 is a distended portion 14
which may look flared, having an opening 15. A cable 16, as
shown in Fig. 4, extends through the opening 15 and is engage- -
able in the shank 11 held by the gripblock 12 locked in an
aperture 17 in a wall 18. The bushing 10 is self locking, en-
gaging the wall in the slots 19, 20 in the gripblock 12 and
shank 11, respectively. The opening 15 has an inside diameter
A as indicated by the arrows A in Figs. 2 and 3 and a maximum
outside diameter B as indicated by the arrows B in Figs. 2 and
3. The lip 21 is on a plane with the outside diameter B. The
length L from the co~mencement of the regular distension of
the distended portion 14 to the outside diameter is indicated
by the arrow L in Fig. 3.
In Fig. 5, one variant preferred embodiment shows a
bushing 30 having a shank 31, a gripblock 32, which function
together as a unitary shank joined by a strap 33 or webbing,
with a distended portion 34 extending from the gripblock 32.
The bushing in closed position is indicated in phantom.
The bushing 50 as shown in Fig. 7 is another preferred
variant of the present invention. The bushing 50 includes a
sha~k 51, a gripblock 52. A distended portion 53 extends from
the shank 51. The shank Sl and gripblock 52 are linked by a
strap 55. Aperture grasping fingers 56 extend from the shank
51 for self locking the bushing 50 into an aperture. --"
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In Figs. 6and8, variant self-lock shank camming fingers
61, 62 are shown engaging an aperture 17in wall l~.
In use, a cable 16 is extended through the opening 15 of
the distended portion 14 as shown in Figs. 1 - 4. With the
gripblock 12 engaged, the bushing 10 may be pushed into the
aperture 17. The wall 18 of the aperture 17 cams against the
ca~ning surfaces 22, 23, enforcing a strain relief grip on the
cable 16. Until the bushing 10 is ultimately locked in the
wall 18, engaged in the slots 19, 20, maintaining a strain relief
grip on said cable 16.
The cable 16 in normal free movement i5 protected against
flexure stress since it cannot bend sharply from the point of
exit from the bushing 10 at inside diameter A to the outside
diameter B of the distended portion 14. The flexure of the
cable 16 at the inside diameter A is relieved by lim~ing the
bending of the cable 16 between the inside diameter A and the
outside diameter B. The lip 21, while of greater diameter than
the outside diameter B, being on a plane with the outside
diameter B, has little or no effect on reducing the flexure
stress at the inside diameter A.
The regularity of the flaring of the distended portion
14 provides a smooth non-abrasive surface to further protect
cable 16.
Where at a minimum, thecutside diameter B of the dis-
tended portion 14 is 1.5 larger than the inside diameter A
with a regular distention D as indicated at arrow D in Fig. 3
and where the distance L between the inner diameter A and
outside diameter B is no less than .25 of the inner diameter A,
flexure tests on cable in an appliance with a strain relief-
flexure relief bushing 10 of the present inven~ion for use instandard 120-volt 60-cycle current have shown that such electric
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cable can be flexed over 50,000 cycles at an angle of 180 on a
cable length of two to three feet without the cable showing
unusual wear or abrasion where such cable extends from such dis-
tended portion 14 of a strain relief-flexure relief bushing 10
of the present invention.
Larger dimensions of L and B of course extend the flexure
stress life of cable.
The bushings 30, 50 of Figs. 5 and 7 are variants em-
ploying distending portions 34, 53 constructed as set forth above.
The bushing 50 as shown in Fig. 7 has fingers 56 illus-
trative of variant wall 18 graspinq means. The cam fingers61,
62 of Figs. 6 and 8 are illustrative of further typical wall 18
grasping means on a bushing 10, 30, 50 of the present invention.
The terms and expressions which are employed are used
as terms of description; it is recognized, though, that various
modifications are possible.
It is also understood the following claims are intended
to cover all of the generic and specific features of the in
vention which, as a matter of language, might fall therebetween.
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