U.S. patent application number 09/739165 was filed with the patent office on 2002-06-20 for link chain for a continuously variable transmission.
Invention is credited to Turner, Douglas J..
Application Number | 20020077205 09/739165 |
Document ID | / |
Family ID | 24971110 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020077205 |
Kind Code |
A1 |
Turner, Douglas J. |
June 20, 2002 |
LINK CHAIN FOR A CONTINUOUSLY VARIABLE TRANSMISSION
Abstract
An endless loop transmission chain balances the differences in
moments and stresses on its inner and outer links. The chain is
comprised of a plurality of links that are pivotally connected in
stacks and in overlapping series. The links are fashioned with
holes perpendicular to the link faces, and the links are either
"robust" or "thin". Robust links may be made of material of greater
tensile strength, they may be formed by mating at least two thin
links, and/or they may be made of thicker material. A plurality of
pins serially connects and stacks the links. The pins fit though
the holes in each link perpendicular to the link face. Robust and
thin links are alternated in stacks in a pattern that balances link
tension when the chain is under tension. Fewer links carry the
tension between any set of adjacent pins. When it is used in a
transmission, this chain has at least 10% higher torque-carrying
capacity than the prior art.
Inventors: |
Turner, Douglas J.;
(Rockford, IL) |
Correspondence
Address: |
Stephen Mican, M/S 110-6
Hamilton Sundstrand
4747 Harrison Avenue
PO Box 7002
Rockford
IL
61125-7002
US
|
Family ID: |
24971110 |
Appl. No.: |
09/739165 |
Filed: |
December 18, 2000 |
Current U.S.
Class: |
474/242 |
Current CPC
Class: |
F16G 5/18 20130101 |
Class at
Publication: |
474/242 |
International
Class: |
F16G 001/21 |
Claims
I claim:
1. An endless loop chain having a center axis, comprising: a
plurality of pins; and a plurality of robust links and a plurality
of thin links, each of the robust links and each of the thin links
further comprising two faces parallel to the center axis and having
two spaced holes with axes perpendicular to the two faces, wherein
all of the plurality of both the thin links and the robust links
being pivotally connected in stacks and in overlapping series by
the pins fitted though the holes, wherein the robust links are
distributed evenly throughout the chain in a direction
perpendicular to the center axis of the chain.
2. The endless loop chain of claim 1, wherein each of the robust
links is made of material of greater tensile strength than any of
the plurality of thin links.
3. The endless loop chain of claim 1, wherein each of the robust
links is made by placing at least two of the thin links adjacent
each other.
4. The endless loop chain of claim 1, wherein each of the robust
links is thicker than each of the thin links.
5. The endless loop chain of claim 1, such that, staggered in a
diagonal pattern and stepping from pin to pin across the chain, the
plurality of thin links and the plurality of robust links are
stacked as follows: 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1,
1 where "1" refers to a thin link and "2" refers to a robust
link.
6. The endless loop chain of claim 5, wherein the chain connects at
least two cone pulleys of a transmission, the pulleys including
opposed, variable-spaced cones on shafts, the cones having opposing
faces, and the pin ends frictionally transferring torque between
the opposing faces of the cones.
7. The endless loop chain of claim 6, wherein the transmission is a
continuously variable transmission.
8. The endless loop chain of claim 1, such that, along a line
generally perpendicular to the center axis that zigzags from a
first to a second adjacent pin and back, the plurality of thin
links and the plurality of robust links are stacked as follows: 1,
2, 2, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 2, 2, 1 where "1" refers to a
thin link and "2" refers to a robust link.
9. The endless loop chain of claim 8, wherein the chain connects at
least two cone pulleys of a transmission, the pulleys including
opposed, variable-spaced cones on shafts, the cones having opposing
faces, the pin ends frictionally transferring torque between the
opposing faces of the cones.
10. The endless loop chain of claim 9, wherein the transmission is
a continuously variable transmission.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to a link chain for friction
pulley transmissions, and more particularly to an endless,
flat-link, articulated chain for continuously variable
transmissions of the movable cone type.
BACKGROUND OF THE INVENTION
[0002] Continuously variable transmissions (CVTs), also known as
infinitely variable or step-less transmissions, have long been used
in marine, industrial, and automotive applications. In a CVT,
regardless of the application, the ratio between the rotational
speed of a drive shaft and the rotational speed of a driven shaft
may be continuously varied between two predetermined limits, rather
than in discrete steps.
[0003] In a typical CVT, an endless chain frictionally couples a
pair of pulleys, otherwise known as sheaves. One pulley is
connected to the drive shaft, and the second pulley is connected to
the driven shaft. Links connected by pins comprise the chain. Each
pulley is comprised of two opposed cones, also known as disks,
which are moveable axially towards or away from each other on both
the drive and driven shafts. Generally, one cone is fixed to each
shaft and the second cone moves axially on the same shaft relative
to the fixed cone. Each chain pin may comprise a pair of rockers
that pivot on each other. The two ends of the pin are frictionally
coupled to the opposing surfaces of the cones, which load the pins.
Axial motion of the moveable cone in a drive pulley or a driven
pulley or both places the chain at varying radial positions with
respect to the axis of the pulley. This motion varies the
transmission speed ratio between a drive shaft and a driven
shaft.
[0004] For aerospace electrical power generation, a generator must
typically be driven at a constant speed to enable the generator to
produce constant-frequency electrical power, usually at 400 Hz. A
CVT may be used to drive a generator from the output shaft of a
gearbox driven by a gas turbine engine of an aircraft. The CVT
typically converts the variable engine rotational speed to the
constant speed required to drive the generator. As in any aerospace
application, one of the challenges lies in maximizing the
strength-to-weight ratio of the chain. This helps to maximize the
power-to-weight ratio of the CVT.
[0005] That is, the transmission chain is required to handle the
power demands of the CVT, yet be compact and lightweight. Many
prior art chains used endless articulated patterns of flat links,
with the links connected by pins. These chains carried torque
between the pulleys by means of frictional forces on the ends of
the pins; the links transmitted the tension, or force. The
torque-carrying capacity of a chain multiplied by the pulley speed
equals the power transmitted. However, the link pattern that
optimizes the strength-to-weight ratio of the chain is far from
obvious.
[0006] Many marine and industrial transmission chains are
available. These chains are made from standard materials, are
relatively low in strength-to-weight ratio, and are not designed
for aerospace reliability. In aerospace applications, manufacturers
are willing to use higher-quality materials and optimum designs to
achieve greater reliability and higher strength-to-weight
ratio.
[0007] In some prior art chains, stronger, or robust, links are
used near the outer edges of the chain. As used throughout herein,
the term "robust" refers to a chain link that has the
characteristic of being relatively stronger. Robust links may be
made in one or more of the following three ways: they may be made
of material of greater tensile strength, they may be formed by
mating at least two thin links, and/or they may be made of thicker
material.
[0008] The pattern of robust links repeats every two or three pins
in some designs. In some prior art chains, however, certain links
see excessive loads because they are segregated from other links.
That is, these segregated links do not have sufficient adjacent
links or robust links to carry the tension. This lack of support
causes the segregated links to carry more than their share of the
chain tension, causing higher stress, or tension per unit area, in
the segregated link. In addition, certain pins experience higher
bending, or twisting forces (hereinafter "moments") leading to
higher stresses and premature failure. This will be discussed in
more detail hereinbelow.
[0009] Examples of prior art chains in which certain links
experience excessive loads are found in U.S. Pat. Nos. 4,547,182
and 4,927,404, both to Rattunde. The chains of these patents
attempt to balance the loading of a chain pin to prevent bending
and twisting it. This was tried by placing robust links mostly at
the edges, or mostly near the center. However, the tension
distribution among the links is unequal when strong, or robust,
links are used only at the outer or inner edges of the chain.
DISCLOSURE OF THE INVENTION
[0010] Accordingly, it is an object of this invention to provide a
transmission link chain with improved strength-to-weight ratio.
[0011] Another object is to provide a link chain that balances
stress and moments on the inner and outer links as well as on the
pins.
[0012] Still another object is for fewer links to carry the tension
between any set of pins, but for the chain, when used in a CVT, to
have at least 10% higher torque-carrying capacity (which requires
10% higher tension capacity) than a prior art chain.
[0013] Another object is to provide a link chain with sufficient
reliability for an aerospace CVT.
[0014] A major step in the invention is the recognition that
placing robust links throughout the chain in an evenly distributed
pattern produces a more equally loaded chain.
[0015] According to the invention, an endless loop chain having a
central axis comprises a plurality of pins; the chain also
comprises a plurality of links, each link further comprising two
faces parallel to the center axis, each link fashioned with two
holes perpendicular to the faces, wherein the links are pivotally
connected in stacks and in overlapping series by the pins fitted
though the holes, and wherein robust and thin links are arranged in
the direction perpendicular to the faces, such that robust links
are distributed evenly in the direction perpendicular to the axis
of the chain. In the present invention, the term "robust" refers to
links that may be made in one or more of the following three ways:
they may be made of material of greater tensile strength than
"thin" links, they may be formed by mating at least two thin links,
and/or they may be single links made of thicker material than thin
links. According to one aspect of the invention, a pattern that
balances link stresses and pin moments as nearly equally as
possible uses thin links and robust links that are staggered in a
diagonal pattern, stepping from pin to pin, across the chain as
follows:
[0016] 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 1
[0017] where "1" refers to a thin link and "2" refers to a robust
link.
[0018] According to a second aspect of the invention, a pattern
that balances link stresses and pin moments as nearly equally as
possible uses a chain that is sixteen links wide, such that, along
a line generally perpendicular to the center axis that zigzags from
a first to a second adjacent pin and back, the links are stacked as
follows:
[0019] 1, 2, 21, 1, 2, 1, 1, 1, 1, 2, 1, 1, 2, 2, 1
[0020] where "1" refers to a thin link and "2" refers to a robust
link.
[0021] The invention has utility because it increases the tension
capability of the CVT chain while reducing its weight, thus
increasing the chain's strength-to-weight ratio.
[0022] The above and other objects, features, and advantages of
this invention will become apparent when the following description
is read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a side view of a portion of a CVT including a
chain;
[0024] FIG. 2 is an orthographic projection of a prior-art
three-link chain as used in a CVT similar to FIG. 1, including a
corresponding diagram in which is illustrated the estimated tension
vectors for each link on three chain pins;
[0025] FIG. 3 is an orthographic projection a prior-art alternately
staggered chain as used in a CVT similar to FIG. 1, including a
corresponding diagram in which is illustrated the estimated tension
vectors for each link on two pins;
[0026] FIG. 4 is an isometric view of one embodiment of a chain
according to the present invention, as used in the CVT of FIG.
1;
[0027] FIG. 5 is an orthographic projection of a section of the
chain of FIG. 4, including a corresponding diagram in which is
illustrated the estimated tension vectors for each link on two
chain pins;
[0028] FIG. 6 is an isometric view of a second embodiment of a
chain according to the invention, as used in the CVT of FIG. 1;
and
[0029] FIG. 7 is an orthographic projection of a section of the
chain of FIG. 6, including a corresponding diagram in which is
illustrated the estimated tension vectors for each link on three
chain pins.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Referring to FIG. 1, one embodiment of a CVT 100 is
illustrated, including a pair of friction pulleys 110, 120 coupled
by an endless chain 130. The CVT 100 may incorporate the chain of
the present invention as described in detail hereinafter. Each
pulley, in turn, is comprised of a fixed cone 140, 150 and a
moveable cone 160, 170. The moveable cone moves axially towards or
away from the fixed cone on shafts 180, 190. The motion of the
cones 160, 170, caused by a primary actuator 175 and a secondary
actuator 177, places the chain 130 at varying radial positions on
the pulleys 110, 120. The actuators 175, 177 may be hydraulic,
mechanical, or electromechanical. This changing radial chain
position varies the transmission ratio between the drive shaft 180,
which may for example be the output of a gearbox driven by a jet
engine, and the driven shaft 190, which may e.g. power an electric
generator. Between the two pulleys 110, 120 where the chain is
"clamped" to the pulleys (i.e., in physical connection with the
pulleys), the chain is in an "unclamped space" 195 (i.e., the chain
is not in physical contact with the pulleys). The transmission
ratio varies without steps, continuously, between two predetermined
limits.
[0031] FIG. 2 represents a prior-art transmission chain 200, known
as a three-link arrangement, which is similar to that illustrated
in U.S. Pat. Nos. 4,547,182 and 4,927,404, both to Rattunde. This
chain may be used in a CVT similar in design to the one shown in
FIG. 1. Basically, the chain comprises flat links of varying
strength or thickness (varying robustness) and cylindrical pins. If
the robust links 220 are each comprised of two adjacent thin links
225, for example, this chain is thirty thin links wide. The links,
as shown by the cross-hatching in FIG. 2, are longitudinally
staggered, stepping from pin to pin, along the length of the chain.
The three varieties of cross-hatching show how the pattern of links
repeats. As can be seen in FIG. 2, the pattern of thick and thin
links repeats every three pins 245, 250, 255. Looking closely
reveals that ten thin links 225 (or nine thin and one robust link)
carry the tension between any set of adjacent pins. Robust links
220 are positioned only near the outer edges of the chain. This
structure will be contrasted with the present invention, which is
described in detail hereinbelow.
[0032] To the right of the chain illustration in FIG. 2 is a
diagram 230 of the estimated tension, or force vector, 240 on each
of the robust and thin links 220, 225 along three successive pins
245, 250, 255. The tension vectors 240 may be used to determine
bending and induced moments on the pins 245, 250, 255 when the pins
are unclamped, that is, in the space 195 between pulleys shown in
FIG. 1. Three successive pins 245, 250, 255 are used since, as
mentioned before, the pattern of the chain 200 repeats every three
pins. Since no other external forces act on the chain besides
tension along the chain, the links share equal tension stresses due
to the relationship
.sigma.=E.epsilon. Eq. 1
[0033] where .sigma. is the stress, E is the modulus of elasticity
(which is a constant for all links if the same material is used),
and .epsilon. is the strain (which is constant since all thick and
thin links 220, 225 between adjacent pins stretch together).
Because the tension stress is equal among the links, the tension
load in each link is proportional to its thickness. This comes from
the equation
tension=.sigma.A Eq. 2
[0034] where A is the cross-sectional area of link. To create
free-body diagrams, the tension, or force vector, for each link
220, 225 is assumed to react through the center of the link. With
the length of the vectors 240 defining the magnitude of tension, a
free-body diagram of each pin 245 is calculated and analyzed for
pin bending and induced moments when the chain 200 is unclamped in
the space 195.
[0035] The tension diagram 230 is used to determine pin 245
bending, which tends to flex or bow the pin, and pin moment, which
tends to rotate or twist the pin, as follows: To determine bending,
the pin is analyzed as two halves, split along the center axis 215
of the chain. The moments are summed (each tension at the
corresponding distance) for each pin half about the center axis
215. If the resulting moments are in opposite directions (i.e., the
resulting moment on the left side of the pin 245 has a CW rotation
and the resulting moment on the right side of the pin has a CCW
rotation), the pin tends to flex or bow.
[0036] To determine pin moments, again the pin 245 is analyzed as
two halves, split at the center axis 215. The moments are summed
(each tension at the corresponding distance) for each pin half
about the center axis. If the resulting moments are in opposite
directions (i.e., the resulting moment on the left side of the pin
245 has a CW rotation and the resulting moment on the right side of
the pin has a CCW rotation), and the resulting moments are of equal
magnitude, the pin does not have a twisting moment. In all other
cases, a pin moment is present.
[0037] Referring to FIG. 3, a dual-link, or alternately staggered,
chain 270 is shown that is similar to the chain taught in U.S. Pat.
Nos. 4,547,182 and 4,927,404, both to Rattunde. The width of this
chain is twenty thin links 275, counting the robust links 280 again
as comprising double thin links. As emphasized by the
cross-hatching, the links are staggered like bricks in a wall.
Again, this structure will be contrasted with the present
invention. Robust links 280 are placed in the outer edges and in
the center. To the right of the chain illustration is shown a
diagram 285 of an estimated tension vector 290 for each of the
links along two successive pins 295, 297. Two successive pins are
used because the pattern of the chain repeats every two pins. As
stated before, the tension vectors 290 may be used to determine pin
bending and induced moments on the pin 295 when the chain 270 is
unclamped in the space 195 between the drive and driven pulleys of
a CVT.
[0038] In FIG. 4 is illustrated isometrically a portion of a
staggered, dual-link, chain 300 that is one embodiment of the
present invention. This chain is an improvement on staggered
dual-link chain designs such as the one illustrated in FIG. 3. The
chain 300 is an endless loop chain having a center axis 303. The
chain, typically made of hardened steel, comprises elongated pins
315 and flat links 305, 310. Each pin preferably further comprises
two rockers 320, 325. A weld spot 340 is added to the pins 315 at
each end to prevent them from sliding out. Each pin has two ends
that terminate in pressure reception areas 327, which are angled
surfaces to match the corresponding surfaces of the pulleys 110,
120 and thus reduce wear. Typically, the angle is in the range of
approximately seven to approximately fifteen degrees to the center
axis. Thin links 310 and robust links 305 are connected by the pins
315. In the present invention and as construed throughout,
including the claims, the term "robust" refers to links that may be
made in any one or more of the following three ways: they may be
made of material of greater tensile strength than "thin" links,
they may be formed by mating at least two thin links, or they may
be single links made of thicker material than thin links. Each link
305, 310 comprises two faces 330 parallel to the center axis 303,
and each link 305, 310 is fashioned with two spaced holes 333,
preferably elliptical, having axes perpendicular to the faces 330.
The links 305, 310 are pivotally connected in stacks 335 and in
overlapping series 337 by the pins 315 fitted though the holes 333.
The pins extend past the links so that the ends can connect
frictionally to the pulleys 110, 120.
[0039] Referring to FIG. 5, the chain 300 of FIG. 4 in orthographic
projection, is sixteen links wide, such that, along a line 339
generally perpendicular to the center axis 303 that zigzags from a
first pin to a second adjacent pin and so forth as shown in FIG. 5,
the links 305, 310 are stacked as follows:
[0040] 1, 2, 21, 1, 2, 1, 1, 1, 1, 2, 1, 1, 2, 2, 1
[0041] where "1" refers to a thin link 310 and "2" refers to a
robust link 305 that for simplicity is illustrated as double the
thickness of the thin link, although it need not be limited as
such. Instead, the symbol "2" refers to robust links that, as
stated before, may be made in any one or more of the following
three ways: they may be made of material of greater tensile
strength than the thin links, that may be formed by mating at least
two thin links, and/or they may be single links made of thicker
material than the thin links.
[0042] In accordance with the present invention, the robust links
305 are distributed throughout the chain, as opposed to restricting
their use to the center and near the outer edges as in the prior
art illustrated in FIG. 3. To the right of FIG. 5 is shown a
diagram 336. A force vector 340 is shown for each of the thin and
robust links 310, 305 along two successive pins 350, 355 when the
chain is in the unclamped space 195 between the pulleys 110, 120.
The diagram 336 is used to determine pin 350 bending, which tends
to flex or bow the pin, and pin moment, which tends to rotate or
twist the pin, in the following manner: To determine bending, the
pins are analyzed as two halves, split along the center axis 303 of
the chain 300. The moments are summed (each tension at the
corresponding distance) for each pin half about the center axis
303. If the resulting moments are in opposite directions (i.e., the
resulting moment on the left side of the pin 320 has a CW rotation
and the resulting moment on the right side of the pin has a CCW
rotation), the pin tends to flex or bow.
[0043] To determine pin moments, again the pin 320 is analyzed as
two halves, split at the center axis 303. The moments are summed
(each tension at the corresponding distance) for each pin half
about the center axis 303. If the resulting moments are in opposite
directions (i.e., the resulting moment on the left side of the pin
320 has a CW rotation and the resulting moment on the right side of
the pin has a CCW rotation), and the resulting moments are of equal
magnitude, the pin does not have a twisting moment. In all other
cases, a pin moment is present.
[0044] Using this analysis and as can be seen in FIG. 5, the chain
300 shows relatively small pin bending or pin moment (twisting).
The moment on the pin 320 is comparable to the prior art chain
shown in FIG. 3. Pin bending of the chain 300 is reduced, however,
as compared to the prior art chain 270.
[0045] An isometric view of a portion of a second and preferred
embodiment 370 of the present invention is given in FIG. 6. This
chain, an improvement on a chain such as the one illustrated in
FIG. 2, is a three-link endless loop chain, skewed with a stepped
pattern. "Skewed" means that the links 375, 380 from adjacent pins
385, 390 mesh with or straddle each other. This allows the distance
between pin centers (pitch) to be reduced. The chain, typically
made of hardened steel, is twenty-four thin links 375 wide
(counting robust links 380 again as double width), it has a center
axis 377, and it further comprises a plurality of elongated pins
385. Each pin has two ends terminating in pressure reception areas
387. A weld spot 389 is added to the pin 385 at each end to prevent
it from sliding out. The pin 385 is preferably comprised of two
rockers 391, 393 that pivot on each other.
[0046] The chain further comprises a plurality of thin links 375
and robust links 380, each link further comprising two faces 397
parallel to the center axis 377, each link fashioned with two
spaced holes 399, preferably elliptical, with axes perpendicular to
the faces 397. The links are pivotally connected in stacks 400 and
in overlapping series 402 by the pins 385 fitted though the holes
399. The pins 385 extend past the links 375 so that the ends, which
terminate in pressure reception areas 387, can connect frictionally
to the pulleys 110, 120.
[0047] Looking closely at FIG. 7, an orthographic projection of the
chain 370 of FIG. 6, reveals that only eight thin links 375 (or a
combination of thin and robust links 375, 380, where robust links
count for simplicity as two thin links) carry the tension between
any set of adjacent pins 385, 390. As with FIG. 5, robust links 380
being illustrated for simplicity in FIG. 7 as comprising two thin
links is not be construed as limiting the present invention in any
way. Again, as stated before, robust links may be made in any one
or more of the following three ways: they may be made of material
of greater tensile strength, they may be formed by mating at least
two thin links 375, and/or they may be made of thicker material.
Unlike the prior art of FIG. 2, the robust links 380 in the chain
370 of FIG. 7 are distributed throughout the chain. To the right of
the chain 370 in FIG. 7 is shown an estimated tension diagram 395.
The diagram covers three successive pins 390, 400, 405 when the
chain is in the unclamped space 195 shown in FIG. 1. The tension
vectors can be used as discussed hereinbefore to compute minimal
pin bending and induced moments.
[0048] Modeling the chain 370 of FIGS. 6 and 7 with a finite
element analysis (FEA) program while assuming that the chain is
clamped between the pulleys 110, 120 shows more evenly balanced
loading of the outer links 375 than in the chains disclosed in U.S.
Pat. No. 4,927,404. The chain 370 also produces more evenly
balanced loading of the pins because of the placement of both thin
and robust links 375, 380. A line AB, 407, broken into line
segments A-ab1, then ab1-ab2, and finally ab2-B, can be drawn
across the chain. The line 407 could be drawn as unbroken if a
longer section of chain were illustrated, but then the link
structure would be less apparent. The pattern of the chain 370 in
FIG. 7 is arranged, stepping from pin to pin, diagonally along line
407 across the chain, as follows:
[0049] 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 1
[0050] where "1" refers to a thin link 375 and "2" refers to a
robust link 380. This thin and robust link arrangement avoids
having certain links experience excessive loads because they are
segregated from other links and not supported. This segregation
causes those links to carry more than their share of the chain
tension, causing higher stress in the segregated links.
[0051] One skilled in the art may be familiar with finite element
analysis (FEA). In that process, a structure is approximated by
"finite" elements, such as beams, bars, or plates. The structure is
broken into nodal points. The process then connects these points
with the finite elements (beams, bars, etc.) that best approximate
the actual structure. The process applies loads at the nodal
points. Loads may also be applied on the elements, which then
distribute the loads to the nodal points. Constraints are also
applied to the nodal points to fix the structure being analyzed.
The finite element process then assembles all the data into a
plurality of simultaneous linear equations. Finally, the process
solves for the unknown displacements and then for internal loads
and stresses.
[0052] A portion of the chain 370 illustrated in FIG. 6 was
subjected to stress analysis by a FEA, which is more accurate than
the tension vector method described hereinbefore. The FEA was used
to determine chain tension, which is proportional to
torque-carrying capacity, based on the stresses that the link
material can withstand. The torque-carrying capacity of a chain
multiplied by the pulley speed equals the power transmitted.
[0053] The conclusion is that the stress on a link 375 versus other
links in the chain 370 is more nearly equalized than the stress on
the links of the prior art, such as FIG. 2. The chain 370 has only
eight thin links 375 carrying the tension between any set of
adjacent pins. When it is used in a transmission, this chain has at
least 10% higher torque-carrying capacity than the chain shown in
FIG. 2, which has ten links carrying the tension. Improved link
placement thus results in higher torque-carrying capacity with
fewer links, leading to better load distribution among the
links.
[0054] It may be understood by one with ordinary skill in the art
that this chain may be used on equipment other than continuously
variable transmissions in aircraft. The invention may be used on
land-based transmissions. In fact, it may be used on any rotating
machinery to transfer torque. The invention may be made of
materials other than steel. Furthermore, it may be understood that
this design may be used on relatively smaller as well as larger
equipment.
[0055] All of the foregoing changes are irrelevant. It suffices for
the present invention that an endless loop chain having a central
axis comprises a plurality of elongated pins; the chain also
comprises a plurality of links, each link further comprising two
faces parallel to the center axis, each link fashioned with two
holes perpendicular to the faces, wherein the links are pivotally
connected in stacks and in overlapping series by the pins fitted
though the holes, and wherein thick, robust and thin, ordinary
links are arranged in the direction perpendicular to the faces,
placing robust links throughout the chain in a pattern that
balances link stresses and pin moments as nearly equally as
possible uses ordinary or "thin" links and "robust" links that are
staggered in a diagonal pattern, stepping from pin to pin, across
the chain as follows:
[0056] 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 1
[0057] where "1" refers to a thin link and "2" refers to a robust
link.
* * * * *