Note: Descriptions are shown in the official language in which they were submitted.
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Docket Number B01-037PCT
Title
Power Transmission Belt
Field of the Invention
The invention relates to power transmission belts,
more particularly to power transmission belts having a
tensile cord having both Z twist and an S twist sections.
Background of the Invention
Power transmission belts generally comprise an
elastomeric body and an embedded tensile cord. The tensile
cord may comprise a single strand or a yarn. In the case
of yarn, the yarn strand may comprise an S twist or a Z
twist. The tensile cord in the belt would then comprise
either an S twist yarn or a Z twist yarn. The S and Z
notation refers to the "handedness" of the yarn and is
characterized by the diagonal form of the ply having a
diagonal analogous to an "S" or "Z" letter, see Fig. 8A and
8B.
In certain belts, the tensile member cord comprises
two separate cords, each having opposite twist
construction. In particular, a cord having a "Z" twist
construction is located adjacent to a cord having an "S"
twist construction. The use of adjacent cords having
opposite twists is to address the problem caused by
tracking force. Tracking force is the force caused by the
torque of the cord twist as load is applied to the belt.
Tracking force will cause a belt to be noisy and to wear
prematurely due to excessive heating. In the prior art
tracking force is reduced by having separate cords, each
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having opposing twist directions, running adjacent to each
other through a belt body.
The cords may be applied by one of two methods. First,
a cord having a first twist, say a Z twist, is applied with
spacing for the second cord having an opposite or S twist.
The second method is to spiral both Z twist and S twist
cords on the belt build at the same time using separate
spools, creels and application rollers.
Representative of the yarn art is US 4,402,178 (1995)
to Negishi et al. which discloses a multifilament textured
yarn having alternating twists thereon.
Also representative of the yarn art is US 3,434,275
(1969) to Backer et al. which discloses strands having S
and Z twists that are joined by bonding, fusing, or
entanglement.
The prior art with respect to belts requires two
separate cords having opposing twists to control tracking
force. This requires means for handling and applying two
cords during belt construction, resulting in decreased
efficiency and increased cost.
What is needed is a power transmission belt having a
single tensile cord with discrete alternating Z twist and S
twist sections. What is needed is a power transmission
belt having a tensile cord with both Z twist and S twist
sections randomly distributed along a length of the belt.
What is needed is a power transmission belt having a
tensile cord with both Z twist and S twist sections
randomly distributed across a width of the belt. What is
needed is a power transmission belt having a single tensile
cord with alternating Z twist and S twist sections that
neutralize a tracking force. The present invention meets
these needs.
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Summary of the Invention
A feature of the invention is to provide a power
transmission belt having a single tensile cord with
discrete alternating Z twist and S twist sections.
Another feature of the invention is to provide a power
transmission belt having a tensile cord with both Z twist
and S twist sections randomly distributed along a. length of
the belt.
Another feature of the invention is to provide a power
transmission belt having a tensile cord with both Z twist
and S twist sections randomly distributed across a width of
the belt.
Another feature of the invention is to provide a power
transmission belt having a single tensile cord with
alternating Z twist and S twist sections.
Other aspects of the invention will be pointed out or
made obvious by the following description of the invention
and the accompanying drawings.
The invention comprises a multi-ribbed belt having a
tensile cord. The tensile cord having areas of alternate
twist along a length of a single cord. In particular, an S
twist section is separated from a Z twist section by a
node, thereby creating alternate S twist and Z twist
sections along a length of a tensile cord. As a result, the
inventive belt comprises a belt having a tensile cord
having a random distribution of S twist sections and Z
twist sections along a length of the belt as well as across
a width of the belt. This significantly reduces tracking
force while using only a single cord in belt construction.
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Brief Description of the Drawings
Fig. 1 is a plan view of a tensile cord.
Fig . 2 is a detail of a node .
Fig. 3 is a belt cross-section at line 3-3 in Fig. 6.
Fig. 4 is a belt cross-section at line 4-4 in Fig. 6.
Fig. 5 is a cross-section view of a prior art belt having
separate S twist and Z twist cords.
Fig 6. is a perspective view of the inventive belt.
Fig. 7 is a plan view of an alternate tensile cord.
Fig. 8A and 8B are representations of an S twist and a Z
twist.
Detailed Description of the Preferred Embodiment
Fig. 1 is a plan view of a tensile cord. This form of
yarn twist includes separate Z twist and S twist sections
in a single tensile cord. Each Z twist section is separated
from an S twist section by a node, thereby creating
alternate S twist and Z twist sections in a tensile cord.
Cord 10 may comprise any tensile cord material known in the
art including nylon, polyester, aramid, rayon, PEN,
fiberglass and carbon fiber.
Cord 10 comprises alternate twist plied yarn comprised
of alternating sections of S twist and Z twist, such as
section 5 and section 6 respectively. The S and Z twist
sections are not coextensive, being separated by reversal
nodes or bonds 3. The distance between reversal nodes is
the twist length measured in turns per inch. A twist
length for the Z twist is L1. A twist length for the S
twist is L2.
In Fig. 1, the distance C represents one cycle from a
first S twist section to the next S twist section. L1
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represents the first partial cycle of Z twist and L2
represents the second partial cycle of S twist.
Each S twist section and Z twist section may have
equal lengths or may be of unequal lengths, each giving a
favorable result, i.e.:
L1 = L2
or
L1 ~ L2
Fig. 2 is a detail of a node. One turn of the S twist
section is 11a. One turn of the Z twist is 11b. Each
strand having an S twist is depicted by 12 and 12a. Node 3
is formed by the process described in US Patent No.
5,829,241 and US Patent No. 4,873,821 among others,
incorporated herein by reference. The yarn singles strands
are unwound and passed through holes in a baffle board and
then through tensioners before entering a torque jet. The
yarns are twisted into an S twist or Z twist before exiting
the torque jet. They may then ply together into a plied
yarn strand that passes through a booster torque jet. The
booster torque jet may be used to assist the torque jet in
generating singles twist so slightly higher ply twisting is
achievable. The yarn is then passed through another torque
jet that imparts an opposite twist at each node, thereby
creating an alternate S twist and Z twist along a length of
a tensile cord. In the preferred embodiment, the plied
yarn strand does not pass through a bonder at each node,
instead relying solely on the entanglement and overplying
caused by the torque jet and booster jet at each node 3.
The inventive belt is not limited to using cord produced by
the method described herein. Other methods known in the art
are available to produce a tensile cord having discrete,
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alternate S twist and Z twist sections. Each cord having
this characteristic will produce a satisfactory result in
the inventive belt.
Fig. 3 is a belt cross-section at line 3-3 in Fig. 6.
The inventive belt comprises elastomeric body 100.
Elastomeric body 100 may comprise any material known in the
power transmission belt art, including EPDM, SBR, CR, HNBR,
BR, and NBR. The inventive belt comprises a mufti-ribbed
profile 101. The belt may also comprise any profile known
in the art, including a v-belt or toothed profile. The
tensile cord having the alternating S twist 103 and Z twist
103 is embedded in elastomeric body 100.
During fabrication, the tensile cord is applied to the
belt body in a continuous fashion such as in a helical
wrap. For example, the cord is wound upon the belt
layers) on a build mandrel as is known in the art.
Unlike the prior art, the inventive belt requires only
a single tensile cord spool comprising both S twist and Z
twist sections as described herein. The prior art requires
a separate S twist cord and a separate Z twist cord applied
simultaneously to fabricate a low tracking force belt. In
the inventive belt, since the S twist sections and Z twist
sections are randomly distributed along a length of a
single tensile cord, the S twist and Z twist sections are
randomly distributed along a length of the belt as well as
across a width of the belt. The random distribution of S
twist and Z twist sections significantly reduces or
neutralizes a belt tracking force without the need for
separate S twist and Z twist tensile cords.
A belt tracking force is caused by the action of a
tensile cord when the belt is under a tensile load. The
twist of the tensile cord will cause the belt to track, or
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move to one side of a belt centerline during operation.
Tracking can cause excessive noise, heating and wear,
leading to premature failure. Reducing or neutralizing the
tracking force causes a commensurate reduction in noise and
wear caused by the belt tracking properly in a pulley.
This, in turn, results in increased belt life by reducing
heat and fatigue.
Further, using a single tensile cord feedstock having
alternate twists instead of two separate feedstocks, each
having a different twist, simplifies the belt fabrication
process thereby reducing the cost of each belt.
An illustration of the random distribution if S twist
and Z twist sections in the belt is shown in Fig. 4, a belt
cross-section at line 4-4 in Fig. 6. Fig. 4 represents a
cross-section of the belt taken across a location different
than that represented in Fig. 3. The S twist sections 102
and Z twist sections 103 have a distribution that differs
from the distribution in Fig. 3 because of the random
nature of the location of each S twist section and Z twist
section in the tensile cord in the belt.
Fig. 5 is a cross-section view of a prior art belt
having separate S twist and Z twist cords. The belt has a
mufti-ribbed profile 101. S twist cords 102 and Z twist
cords 103 are shown in an alternating arrangement where
each S twist cord is flanked by Z'twist cords, and vice
versa.
Fig 6. is a perspective view of the inventive belt. S
twist sections 102 and Z twist sections 103 are shown
embedded in the elastomeric body 100.
Fig. 7 is a plan view of an alternate tensile cord. A
base yarn is twisted into a three strand, each strand
having an S twist and having a predetermined number of
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turns per inch. Each strand having an S twist is
individually depicted by 12 and 12a and 12b. The three
separate S twist yarns are then twisted with a cord having
an overall Z twist at a predetermined number of turns per
inch. This embodiment results in tensile cord that is
homogeneous along a length. Although a certain number of
strands are identified in this description for each S
twist, the number is exemplary and not offered to limit the
number of strands that could comprise a tensile cord.
Further each separate strand may comprise a Z twist and the
overall cord may have an S twist with the same result in
the inventive belt.
Fig. 8A and 8B are representations of an S twist and a
Z twist.
Although a single form of the invention has been
described herein, it will be obvious to those skilled in
the art that variations may be made in the construction and
relation of parts without departing from the spirit and
scope of the invention described herein.
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