BACKGROUND OF THE INVENTION
[0001] This invention relates generally to a power transmission belt for a
continuously variable transmission ("CVT"), more particularly to a CVT belt with a fiberloaded
rubber composition, and specifically a rubber composition based on polyolefin
elastomer with both pulp and staple high-modulus fiber.
[0002] A CVT generally has some kind of closed-loop control or feedback
mechanism for automatic and relatively rapid shifting based on the dynamics of the drive
in a system. Often, in a CVT the driver sheave is controlled based on or reacts to a speed
measurement or speed change in order to keep the power source or motor within an
optimum power or speed range, and the driven sheave is controlled based on or reacts to
the torque load. The variable-pitch sheaves may be adjusted by various mechanisms
including mechanical, electro-mechanical, electronic, hydraulic, or the like. Belt-driven
CVTs are widely used in scooters, all-terrain vehicles ("ATV"), snowmobiles,
agricultural equipment, heavy equipment accessory drives, and other vehicles. Generally,
as two pulley halves move axially apart or together to force a change in belt radial
position in a CVT, the belt may be subjected to extreme friction forces as the belt changes
radial position within the sheaves. As two sheave halves move together axially to
increase the pitch line of the belt, the belt is subjected to extreme friction forces and to
high axial or transverse compressive forces. High and variable torque loads result in high
tension forces and high wedging forces which also result in high transverse compressive
forces and frictional forces on the belt. Some applications also use the belt as a clutch,
resulting in additional frictional forces on the contact surfaces of the belt. All these forces
may be very severe in a CVT because of the dynamics of the applications (e.g. frequent,
rapid shifts, with high acceleration loads). As the CVT belt traverses the driver and
driven pulleys, it is also subjected to continual bending or flexing. Rubber CVT belts are
generally used without lubrication in so-called "dry CVT" applications. Thus, the CVT
belt needs to have good longitudinal flexibility, high longitudinal modulus, high abrasion
resistance, and high transverse stiffness. The belt must operate across a wide temperature
range, for a long time.
[0003] Representative of the art is U.S. Pat. No. 6,620,068, which discloses a rawedge
double-cogged V-belt for variable speed drives having curvilinear cogs on the inside
and outside, a layer of spirally wrapped cords made of fibers such as polyester, aramid,
and/or glass fiber. The belt includes compression and tension layers of rubber containing
short fibers aligned laterally for transverse reinforcement. The belt also includes a layer
of reinforcing fabric on the inside and/or outside cog surfaces.
[0004] Also representative of the art is U.S. Pat. No. 4,708,703, which discloses a
CVT belt with aligned upper and lower teeth and grooves, and with longitudinal cords.
The teeth are preferably covered at their tops with transverse stiffening elements to deal
with the problem of buckling and to increase the torque capability.
[0005] U.S. Pat. No. 6,485,386 relates to rigid inserts in a cogged V-belt to increase
transverse stiffness. Herein and in the claims, the term "rubber CVT belt" excludes the
use of such rigid inserts or stiffening elements, as well as the use of external rigid
appendages or clips or blocks.
[0006] Yet, CVT belts need high transverse stiffness due to the aspect ratio and the
high axial forces in use. Various approaches to increasing stiffness have been tried in the
past. The most common approach is to incorporate transversely oriented chopped fibers
into the belt body. This approach has limits.
[0007] U.S. Pat. No. 7,189,785 relates to a blend of HNBR and EPDM or other
ethylene-alpha-olefin elastomer. Extensive data on chopped fiber-loaded elastomers is
included. It teaches that too much (more than 20 parts weight per hundred parts of
elastomer ("phr") leads to processing problems, without benefits regarding heat build up.
[0008] U.S. Pat. No. 8,672,788 relates to a vulcanized rubber CVT belt in the form
of an endless V-belt having a belt body with angled sides, a tensile cord layer of helically
spiraled tensile cord embedded in the belt body, an overcord rubber layer, and an
undercord rubber layer, wherein the tensile cord is a twisted, single-tow bundle of
continuous-filament, carbon fiber. It teaches that the use of 18k carbon cord increased the
transverse stiffness of the CVT belt.
[0009] U.S. Pat. No. 5,610,217 relates to a power transmission belt with a main belt
body portion incorporating an elastomeric composition with an ethylene-alpha-olefin
elastomer reinforced with a filler and a metal salt of an a-b-unsaturated organic acid.
[0010] U.S. Pat. No. 6,616,558 relates to at least one of said elastomeric belt body
portion and said adhesive rubber member exhibits at least one of a complex modulus
measured at 175° C, at 2000.0 cpm and at a strain of 0.09 degrees, of at least 15,000 kPa;
and a tensile modulus, measured at 10% elongation, of at least 250 psi (1.724 MPa).
[0011] U.S. Pat. No. 6,51 1,394 relates to an elastomer composition with an
elastomer blend of low and high molecular weight ethylene-alpha-olefin polymers.
[0012] WIPO Publ. No. WO2010/047029Al relates to a rubber composition for a
flat transmission belt comprising an ethylene-a-olefin elastomer.
[0013] WO2015/045255A1 relates to a cogged V-belt composition with mixture of
short nylon or PET nano-fibers and chopped para-aramid fibers in EPDM elastomer.
[0014] U.S. Pat. No. 6,358,171 to Whitfield discloses use of aramid pulp or staple
fibers in toothed belts.
[0015] It is not known or suggested to use a blend or combination of aramid pulp
fiber and aramid chopped fiber in the main belt-body ethylene-alpha-olefin elastomer
composition of a power transmission belt.
SUMMARY
[0016] The present invention is directed to systems and methods which provide
CVT belts with high transverse stiffness.
[0017] CVT belts need high transverse stiffness due to the aspect ratio and the high
axial forces in use. Thus, the present invention relates to a rubber composition in a CVT
belt. The rubber composition is fiber-loaded with both staple and pulp fibers, preferably
aramid fibers. The elastomer is preferably saturated ethylene-alpha-olefin elastomer.
The composition is calendered to orient the fibers transverse to the belt running direction,
i.e., axially with respect to the axis of the pulleys or sheaves on which the belt runs. The
resulting belt axial or transverse stiffness is in a predetermined range, resulting in
significant performance benefits over conventional CVT belts.
[0018] In some embodiments the invention is directed to an endless rubber CVT
belt having a main belt body having a compression portion, tension portion, an adhesive
layer, and a tensile cord in contact with the adhesion portion and embedded between the
compression portion and the tension portion, angled sides, and a width to thickness ratio
on the order of 2 to 3; wherein at least one of the compression portion, the tension portion
and the adhesion portion comprises an elastomer composition comprising a saturated
ethylene-alpha-olefin elastomer, a staple fiber, and a pulp fiber, or an elastomer, a highmodulus
staple fiber, and a high-modulus pulp fiber; wherein the pulp fiber constitutes
less than 40% (or less than 35%) of the total high-modulus fiber amount.
[0019] The ethylene content of a suitable ethylene-octene elastomer is in the range
of 60.0% to 65.0% by weight, or below 75%, or below 70%, or the melt flow rate of the
ethylene-octene elastomer is less than 5 or less than or equal to 1.0 or 0.5 gm/10 min. or
less,
[0020] The total amount of the staple fiber and pulp fiber may be between 3 and 19
volume percent of the composition or between 1 and 65 phr. One or both fibers may be
aramid fibers.
[0021] In some embodiments the belt exhibits a stiffness on the Dynamic Axial
Stiffness Test of greater than 5.0 kN/mm or greater than 6.0 kN/mm or greater than 7.0
kN/mm, or from about 7 to about 8 kN/mm.
[0022] In some embodiments the belt exhibits a stiffness on the Gates Compression
Test of greater than or equal to 5.0 kN/mm at 90°C or greater than 6.0 kN/mm or 7.0
kN/mm or 8 kN/mm at room temperature, or from about 8 to about 9 kN/mm at room
temperature.
[0023] The foregoing has outlined rather broadly the features and technical
advantages of the present invention in order that the detailed description of the invention
that follows may be better understood. Additional features and advantages of the
invention will be described hereinafter which form the subject of the claims of the
invention. It should be appreciated by those skilled in the art that the conception and
specific embodiment disclosed may be readily utilized as a basis for modifying or
designing other structures for carrying out the same purposes of the present invention. It
should also be realized by those skilled in the art that such equivalent constructions do not
depart from the scope of the invention as set forth in the appended claims. The novel
features which are believed to be characteristic of the invention, both as to its
organization and method of operation, together with further objects and advantages will
be better understood from the following description when considered in connection with
the accompanying figures. It is to be expressly understood, however, that each of the
figures is provided for the purpose of illustration and description only and is not intended
as a definition of the limits of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings, which are incorporated in and form part of the
specification in which like numerals designate like parts, illustrate embodiments of the
present invention and together with the description, serve to explain the principles of the
invention. In the drawings:
[0025] FIG. 1 is a partially fragmented side view of an embodiment of the
invention;
[0026] FIG. 2 is a cross sectional view of the embodiment of FIG. 1 through 2-2;
[0027] FIG. 3 is a partially fragmented perspective view of another embodiment of
the invention;
[0028] FIG. 4 is a graph of elastic modulus versus temperature for three example
compositions;
[0029] FIG. 5 is a diagram of the Load Capability Test rig arrangement;
[0030] FIG. 6 Graphs showing speed loss, belt temperature, and belt slip for four
belt constructions on the Load Capability Test;
[0031] FIG. 7 Graph of power loss on the Load Capability Test for four belt
constructions;
[0032] FIG. 8 is a graph of Gates Compression Test data for a CVT belt sample of
Comp. Belt C tested at 90°C;
[0033] FIG. 9 is a graph of Gates Compression Test data for a CVT belt sample of
Comp. Belt D tested at 90°C; and
[0034] FIG. 10 illustrates sample preparation for the Gates Compression Test.
DETAILED DESCRIPTION
[0035] The problem of improving CVT belt performance can be tied to the
underlying problem of increasing transverse stiffness while improving or at least
maintaining a lot of other properties, such as longitudinal flexibility, crack resistance,
thermal resistance, frictional properties, hysteretic properties, adhesion, tensile strength,
etc.
[0036] It has been known that loading of the rubber composition with short fiber
for the belt body can lead to increased stiffness. Orienting the fiber in the transverse
direction can increase transverse stiffness of the belt while maintaining a higher level of
flexibility in the longitudinal direction (anisotropic modulus). However, the problem of
mixing, dispersing and orienting high modulus fibers into the rubber composition limits
the amount of such fiber that can be practically added. Now it has been discovered that a
proper blend of two different fiber types, and judicious choice of the base elastomer can
have a dramatic effect on a rubber composition modulus and stiffness of the final
compound while still giving improved processing and ultimately improving the resulting
CVT belt performance. By shifting the ratio of pulp to staple fiber, while adopting the
unique properties of the ethylene-alpha-olefin or polyolefin elastomer, one can obtain a
significantly improved level of stiffness in the resulting belt which has in turn resulted in
exceptional durability and load carrying capabilities.
[0037] Thus, the present invention relates to a rubber composition for a CVT belt.
The rubber composition is fiber-loaded with both staple and pulp fibers, preferably
aramid fibers. The elastomer is preferably ethylene-alpha-olefin elastomer. The
composition is calendered or extruded to orient the fibers (longitudinally in a calendered
sheet material), then arranged to be oriented transverse to the belt running direction in the
final belt, i.e., axially with respect to the axis of the pulleys or sheaves on which the belt
runs. The resulting belt axial or transverse stiffness is in a predetermined range, resulting
in significant performance benefits over conventional CVT belts.
[0038] FIG. 3 shows a typical embodiment of the invention in the form of a CVT
belt. Belt 100 has a generally isosceles trapezoidal cross section, with back-, upper-,
outer- or top-side 30 parallel to bottom-, lower-, or inner-side 40. The other two sides,
lateral sides 42 are the pulley contact surfaces which define a V-shape with included
angle a . The belt body includes tensile cord 16 embedded in optional adhesion portion or
adhesion gum layer 116, a tension portion or overcord layer 14, and a compression
portion or undercord layer 12. Adhesion gum layer 116, overcord layer 14, and
undercord layer 12 are generally vulcanized rubber compositions, at least one of which is
of an inventive composition described herein. At least the undercord layer may include
dispersed short fibers oriented in the transverse direction to increase transverse stiffness
of the belt body while maintaining longitudinal flexibility. Tensile cord 16 is the
longitudinal load carrying member. It may be a high modulus, fatigue resistant, twisted
or cabled bundle of fibers, such as polyester, aramid, carbon, PBO or glass fibers or
yarns, and may be treated with an adhesive. In some embodiments, the tensile cord may
be a twisted, single-tow carbon fiber yarn of approximately 12,000 or 18,000 carbon
fibers, as described for example in U.S. Pat. No. 8,672,788, the contents of which are
hereby incorporated herein by reference. The underside or bottom of the belt is often
"notched" or "cogged," i.e., given a wavy profile, to improve the balance of flexibility
and stiffness required from the belt body. The bottom of the belt may be given an
undercord fabric cover (or notch fabric) (not shown) to decrease the formation and
propagation of cracks in the undercord and to increase the transverse stiffness of the belt
body. Likewise the belt back may be given an overcord fabric cover (not shown) for
similar reasons. In one embodiment, no fabric is used.
[0039] FIG. 2 shows another embodiment of the invention in cross section, having
a single rubber composition for the belt body and tensile cords 16 embedded therein. The
overall belt width is called the top width and identified as "TW" in FIG. 2 . The overall
thickness of the belt is identified as "T0" . For wide-range variable-speed drives, such as
the CVT applications mentioned above, special belt cross sections that are relatively wide
and thin, compared to single-speed V-belts, are required. Whereas a typical, conventional
V-belt generally has a top-width of about the same dimension as the thickness, or a ratio
of TW/To from about 1 to about 1.7, a CVT belt according to the invention is typically at
least around twice as wide as it is thick, or having a ratio of TW/T0 of from about 2 to
about 2.5 or even to about 3.0. The width, thickness and V angle determine the range of
speed variation possible, as is known in the art. See for example, Wallace D. Erickson,
ed., "Belt Selection and Application for Engineers," Marcel Dekker, Inc., New York,
(1987), the contents of which are hereby incorporated herein by reference, and especially
chapter six by David E. Roos, "Variable-Speed Drive Design Using V-Belts."
[0040] The CVT belt may have cogs on the inside, backside or both sides as
illustrated in FIG. 1. Referring to FIG. 1, double-cogged CVT belt 10 includes tensile
cord layer 16 sandwiched between overcord layer 14 and undercord layer 12 making up
the main body of the belt. The double-cogged V-belt shown in FIG. 1 also has lower
cogs 18 and upper cogs 20 protruding from the main belt body. Upper cogs 20 include
tip 17, flank 26 and valley or root 22. Likewise lower cogs 18 include tip 19, flank 36
and root 32. The double-cogged V-belt of FIG. 1 is drawn in rack form, i.e., flat and
without curvature of the tensile layer. Representative cog profiles which may be used
include, for example, the profiles disclosed in U.S. Pat. Nos. 8,206,251, 8,333,674, and
8,425,357, the contents of which are hereby incorporated herein by reference.
[0041] FIG. 2 shows a cross section of an embodiment of the invention taken at the
plane 2-2 in FIG. 1 and illustrating an optional relief angle feature of the inventive belt.
The pulley contact faces or side surfaces 42 of the V-belt are cut at an angle a/2 with
respect to the vertical axis of the belt, which should generally coincide with the vertical
axis of a pulley or drive system. Thus, a pair of opposing belt side surfaces 42 describe
an included angle a . Each side surface 42 engages a sheave during operation, with the
sheave angles also substantially equal to a/2. The belt may optionally include an
opposing pair of second side surfaces 44 which are disposed toward the inside surface of
the belt or the lower cog tip 19 and which are cooperating with the first side surfaces 42
by intersecting at a height ht, measured from lower tip 19. Each pair of second side
surfaces 44 describes an included angle g . Angle a may be in the range of approximately
15° to 50° (so about 7° to about 25° per pulley sheave angle). Angle g may be in the
range of approximately 25° to 65°. Namely, g = a + (2 x relief angle). The "relief angle"
may be equal to or greater than approximately 5° and may be defined as (g/2 - a/2).
Although FIG. 1 from which the view of FIG. 2 was taken is of a double-cogged CVT
belt, it should be understood that the section of FIG. 2 is equally representative of a
single-cogged CVT belt or a CVT belt with no cogs.
[0042] Turning to a more detailed description of the rubber compositions in the
CVT belt, the usual definition of "rubber" or "elastomer" is used herein, namely a
material that can be stretched repeatedly to at least about twice its original length and
which will return upon immediate release of the stress to approximately its original
length. Herein, the term "elastomer" or "base elastomer" will be restricted to the
elastomeric polymers used to form the composition, while "rubber" or "rubber
composition" will be used to indicate a composition including the base elastomer and
other compounding ingredients, unless otherwise indicated by the context. Most rubber is
given its final properties by compounding the base elastomer with fillers, process aids,
anti-degradants, curatives, etc., followed by crosslinking or vulcanizing by heating. The
final properties of the fiber-loaded rubber compositions of the present invention may not
necessarily achieve more than twice their original length without breaking, particularly in
the direction of fiber orientation, so this part of the standard definition may be relaxed
herein.
[0043] The compounding principles elucidated herein are believed to be applicable
to a wide variety of elastomers useful in belts, such as polychloroprene (CR), nitrilebutadiene
( BR, HNBR), polyolefin elastomers including copolymers and terpolymers
with unstaturation or those that are fully saturated, natural rubber ( R), and so on.
However, the preferred materials are saturated polyolefin elastomers (POE), such as
ethylene-alpha-olefin copolymer elastomers, including ethylene-propylene, ethylenebutene,
ethylene-pentene, ethylene-octene and so on. By saturated is meant no double
bonds in the main chain or pendant thereto, except possibly in one or both end groups.
The most preferred elastomers are ethylene-octene elastomer (EOM), ethylene-butene
(EBM), and ethylene-propylene elastomers (EPM). In various embodiments, the rubber
composition to be described may be used in at least one of the above mentioned belt
layers, i.e., adhesion gum layer, overcord layer, and undercord layer, or in two or in all
layers. The compositions may include only the base elastomer as the sole elastomer
present, or there may be a blend of the base elastomer with one or more other elastomers.
The base elastomer is always more than 50% of the total of all elastomers present,
preferably more than 70% or 80% or more or about 90% or more, by weight or by
volume.
[0044] Useful ethylene-octene elastomers may be exemplified by the ENGAGE
polyolefin elastomers sold under that trademark by The Dow Chemical Company. The
EOM may have a melt index less than or equal to 5, preferably less than equal to 1, or
most preferably less than or equal to 0.5 grams/10 minutes (2.16 kg @ 190°C) per ASTM
D1238-13. The EOM may have a density (g/cc) between 0.850 and 0.875, preferably
equal to or between 0.855 and 0.870 density, most preferably between 0.860 and 0.870.
The ethylene content may be from 60 to 65 weight percent for EOM.
[0045] Useful ethylene-butene elastomers may be exemplified by the ENGAGE
polyolefin elastomers sold under that trademark by The Dow Chemical Company and the
EXACT copolymers sold under that trademark by ExxonMobil Chemical and the
TAFMER copolymers sold under that trademark by Mitsui Chemicals Group. The EBM
may have a melt index less than or equal to 5, preferably less than equal to 1, or most
preferably less than or equal to 0.5 grams/10 minutes (2.16 kg @ 190°C) per ASTM
D1238-13. The EBM may have a density of equal to or between 0.850 and 0.890, or
from 0.850 to 0.880, or from 0.850 to 0.870. The ethylene content may be from 40 to 60
weight percent for EBM.
[0046] The belt compositions of various embodiments include both staple or
chopped high-modulus fibers, and pulp or fibrillated high-modulus fibers, preferably both
of aramid or aromatic polyamide materials.
[0047] The preferred aramid fibers that may beneficially be used as a reinforcement
of the belt elastomer include meta-aramids, para-aramids, and para-aramid copolymers,
such as those sold under the trademarks KEVLAR and NOMEX by DuPont and
TECHNORA, CONEX, and TWARON by Teijin. The fibers include both fibrillated or
pulped fibers and chopped or staple fiber. For purposes of the present disclosure, the
terms "fibrillated" and "pulp" shall be used interchangeably to indicate this type of fiber,
and the terms, "chopped" or "staple" will be used interchangeably to indicate that type of
fiber. The fibers may optionally be treated as desired based in part on the fiber and
elastomer type to improve their adhesion to the elastomer. An example of a fiber
treatment is any suitable resorcinol formaldehyde latex (RFL).
[0048] The fibers of the staple or chopped variety may be formed of a suitable
aramid or other high-performance fiber and have an aspect ratio or "L/D" (ratio of fiber
length to diameter) preferably equal to 10 or greater. Staple fibers generally have a
uniform cross section over their entire length. The staple fibers may have a length from
about 0 .1 to about 10 mm, or to about 5 mm, preferably from about 1 to about 3 mm. The
staple fibers may have a diameter from about 1 to about 30 microns, preferably from
about 6 to about 20, or about 10 to 15 microns. A mixture of staple fiber types, lengths,
or diameters may be used. Although para-aramid fibers are preferred, the staple fibers
may be of other high-performance or high-modulus polymer materials, such as metaaramid,
polybenzobisoxazole (PBO), polyetheretherketone, vinylon, nylon,
polyacrylonitrile, liquid crystal polymer, or the like.
[0049] The high-modulus fibers of the pulped or fibrillated variety may be
processed where possible for a given fiber type to increase their surface area, formed
preferably of a suitable para-aramid, and may possess a specific surface area of from
about 1m2/g to about 15 m2/g, more preferably of about 3 m2/g to about 12 m2/g, most
preferably from about 7 m2/g to about 11m2/g; or an average fiber length of from about
0 .1mm to about 5.0 mm, more preferably of from about 0.3 mm to about 3.5 mm, and
most preferably of from about 0.5 mm to about 2.0 mm. The pulp fiber may have fibrils
of irregular cross section and shape, but primarily, pulp is characterized by the presence
of many, much smaller diameter fibrils having been split off of or branched from the
original fibers. It may be noted that herein, the term "pulp" has nothing to do with wood,
paper, fruit, fiction or any other common usages from other fields, but is only used here
and in the claims as defined herein.
[0050] The total amount of pulp and staple fiber in the composition may range from
about 1 phr to 65 phr, preferably from about 6 to about 50 phr, or from about 17 to about
35 phr. The amount of aramid pulp or fibrillated fiber used in various embodiments of
the invention may beneficially be from about 0.5 to about 25 parts per hundred weight of
elastomer (phr); is preferably from about 0.9 to about 20 phr, more preferably from about
1.0 to about 15 phr, and is most preferably from about 2.0 to about 10 phr. The amount
of aramid staple fiber used in a preferred embodiment of the invention may beneficially
be from about 0.5 to about 40 parts per hundred weight of elastomer (phr); is preferably
from about 5 to about 35 phr, more preferably from about 10 to about 30 phr, and is most
preferably from about 15 to about 25 phr. The optimum amounts may depend on the
amounts and types of each fiber used, the type of elastomer, and the end result desired.
The range of aramid pulp content is greater than 0, or greater than 5% or 10%, and less
than 100% or 70% or 60% of the total fiber weight. Preferably the aramid pulp weight is
less than 50% or 45% or 40% or 35% of the total fiber weight. With saturated polyolefin
elastomers such as EOM or EBM elastomers, the higher pulp levels are possible, while
for other elastomers such as EPDM or CR, the lower range, less than or equal to 40% or
35% or less of the total fiber, is required.
[0051] More directly related to the end properties is the fiber volume per cent and
the relative amount of pulp as a percent of the total fiber volume. These amounts of pulp
and staple fiber are important for, and may be selected for, the desired end properties of
the composition as well as for the processability thereof, and may depend on other factors
as fiber length and degree of fibrillation and the choice of elastomer. In various
embodiments, for example, those based on 1 to 3 mm length para-aramid fiber for both
staple and pulp portions in polyolefin elastomers, the total fiber volume percent is
advantageously between 3 and 19 volume percent. The total fiber concentration may
advantageously be between 5 and 17 volume percent, or between 7 and 15 volume
percent. The total volume percent of fiber may be from 9 to 13 volume percent. The
range of aramid pulp volume content is greater than 0, or greater than 5% or 10%, and
less than 100% or 70% or 60% of the total fiber volume. Preferably the aramid pulp
volume content is less than 50% of the total fiber volume. More preferably the pulp level
is 40% or less of the total fiber. Most preferably the pulp content is less than 35% of the
total fiber content.
[0052] The other ingredients in the composition may be selected as usual in the art.
One skilled in the relevant art would recognize that the elastomer would preferably be
modified to include additional materials, e.g. plasticizers, anti-degradants, reinforcing
particulate fillers such as carbon black and silica, curatives, coagents, and possibly other
fibers both natural and synthetic such as, cotton, kenaf, hemp, wool, flax, wood fiber,
nylon, polyester, rayon, polyvinyl alcohol, polyvinyl acetate, acrylic, etc. If other highmodulus
staple fibers, of similar length and reinforcing effect as the primary fibers
described above, are included, they should be included in the total fiber content.
[0053] For best wear resistance, the polyolefin elastomer compositions may be
peroxide cured with suitable coagents. The preferred coagents are metal salts of an a-b-
unsaturated organic acid as disclosed in U.S. Pat. No. 5,610,217, the entire contents of
which are hereby incorporated herein by reference. Exemplary metal salts are zinc
diacrylate and zinc dimethacrylate (ZDMA).
[0054] Mixing, calendering, molding, etc.
[0055] The fibers may be added to the elastomer composition via any suitable or
conventional technique, such as by first incorporating fibrillated fibers in a suitable first
elastomer composition to form a fiber-loaded master batch having, for example, a final
fiber content of about 50% by weight, or any other suitable amount; thereafter adding the
fiber loaded master batch to the belt elastomer composition in order to allow for suitable
distribution of the fiber in the belt elastomer composition; and then forming the belt with
the thus fiber loaded elastomer composition via any suitable or conventional technique.
[0056] Examples
[0057] In the following examples, inventive examples are indicated as "Ex." And
comparative examples as "Comp. Ex."
[0058] In a first set of examples, the rubber compositions are shown in volume
percent in Table 1, and in phr in Table 2 . Ex. 1 and Ex. 2 illustrate rubber compositions
based on EOM elastomer with two different ratios of Kevlar pulp to para-aramid (1-mm
chopped Technora) staple fiber. Comp. Ex. 3 is based on EPDM with similar fiber levels
as Ex.2, while Comp. Ex. 4 is based on CR elastomer. Note that the EPDM elastomer is
Vistalon 2504, from Exxon, with a very low Mooney viscosity of about 25, and a broad
molecular weight distribution, and includes about 10 phr of oil, all features intended to
help with dispersing the high fiber loading. The EOM elastomer, on the other hand has a
much higher Mooney viscosity of about 37, (indicating higher molecular weight), and
practically no added oil, yet it was found that the EOM compositions were much easier to
mix, mill and calender than the EPDM recipe.
[0059] Compound testing results are shown in Table 3 .
[0060] Compound rheological properties were evaluated according to ASTM D-
1646 on a Mooney viscometer with small rotor operated at 132°C (270°F) for 30 minutes
(the Mooney Scorch results in Table 3 . Also, Mooney viscosity was evaluated with large
rotor at 125°C. Cure properties were evaluated according to ASTM D-5289 on a
rotorless cure meter at 177°C for 30 minutes and at 200°C for 3 minutes. In Table 3, ML
indicates minimum torque, MH indicates maximum torque, S' is in-phase torque, and S"
is out-of phase torque. Based on MH, Ex. 1 with a preferred pulp level is the stiffest of
these materials.
[0061] Cured compound physical properties were also tested using standard rubber
testing. The tensile test results in the with-grain direction in the low strain region are
particularly interesting. Modulus was determined using common tensile modulus
measurements, in accordance with ASTM D-412 (die C, and using 6"/min. crosshead
speed), and "modulus" (M5 and M10) herein refers to tensile stress at given elongation
(5% and 10% respectively) as defined in ASTM D-1566 and ASTM D-412. Rubber
hardness was tested on standard compression pellets with a durometer according to
ASTM D-2240, using the Shore-A and Shore-D scales, for original and oven-aged
compound samples. Tear results tested according to ASTM D-624, die-C, in two
different directions, with -grain and cross-grain are included for some variables.
[0062] It is apparent from the durometer and tensile properties that these are all
very stiff, hard compositions, pushing the limits of what can be called flexible rubber for
a belt. The with-grain elongation at break (%Eb) at room temperature is only about 15%
for these materials, and the stress at 5% or 10% elongation (M5 and M10, respectively) is
quite high. The with-grain properties are going to be directly related to the transverse
stiffness of the CVT belt. However, the %Eb in the cross-grain direction, the direction
for belt flexibility, is significantly larger. In fact, these compounds were intentionally
selected to maximize transverse stiffness just within the limits of processability and crossgrain
flexibility. The anisotropy ratio (based on either M5 or M10) is another indication
of how well the compound should be able to flex in one direction while being extremely
stiff in the other. While these four compounds have fairly similar anisotropy ratios,
having been compounded to similar modulus or hardness, the inventive examples have
significantly higher cross-grain %Eb, predicting much more flexibility in a belt than the
comparative examples. The cross-grain tensile strength (Tb) of the inventive examples is
also quite a bit higher than the comparative examples, both originally and after heat aging
168 hours at 150°C, attributable to the differences in elastomers. The with-grain tensile
strengths are more comparable, attributable to the similarity in fiber loading and
orientation. It is clear that the two Ex. materials have the highest M5 and M10 at room
temperature (RT) in both grain directions. It is believed this leads directly to the high belt
compression stiffness reported later herein, which in turn leads to outstanding
performance in CVT use.
[0063] It is desirable for the rubber composition for a CVT belt to have a tensile
stress, in the mill direction (with-grain), at a strain of 5% of greater than or equal to1800
psi, greater than or equal to 1900 psi, or greater than or equal to 2000 psi; and for the
EOM compound to have an anisotropic ratio at a tensile strain of 5% of greater than or
equal to 4, or greater than or equal to 4.5, or greater than or equal to 5 . The use of EOM
or EBM with both aramid pulp and aramid staple makes this possible.
[0064] Table 3 includes the results of three abrasion tests for wear resistance, the
so-called DIN test (DIN 53516 or ISO 4649), the PICO abrasion test (ASTM D-2228),
and the Taber abrader test (ASTM D-3389). The DIN and Taber test results are in terms
of volume loss, so lower is better. The PICO test is reported as an index, and a higher
index indicates better resistance to abrasion. It can be seen that the abrasion resistance for
the inventive examples are generally equivalent or sometimes better than the comparative
examples, depending on which test and conditions.
[0065] DeMattia flex crack growth test was according to ASTM D-430 (pierced) at
RT and at 125°C, 0.5" stroke. Both with-grain and cross-grain were slated for test, but
not all results were available for all compounds. At room temperature Ex. 1 is about an
order of magnitude better than Comp. Ex. 3 and 4 .
[0066] Compound dynamic properties were evaluated according to ASTM D-6204
using temperature sweeps on the RPA2000 tester at 6.98% strain after curing the
composition. The compound elastic modulus (G') results are shown in FIG. 4 (Ex. 2 was
not included in this test). It can be seen that the inventive Ex. 1 has a much more
favorable temperature dependent modulus that Comp. Ex. 3 or 4 . Comp. Ex. 4 in
particular shows considerable softening with temperature. The effect on CVT belt
performance is believed to be less "heat fade" where belt performance degrades at higher
operating temperatures.
[0067] Note some observations on processing of the compounds. Comp. Ex. 4,
based on CR elastomer with low Mooney viscosity and broad MW, has oil added to the
composition, but still is quite difficult to process in terms of mixing and calendering
without scorching the rubber. The sensitivity of CR to heat makes dispersing the fiber
while maintaining adequate scorch safety very difficult. The improved heat resistance
and processing of the ethylene elastomers is an advantage over CR. The comparative
EPDM example used a 25 Mooney, broad molecular weight polymer with nearly 10 PHR
of plasticizer to achieve adequate processing, whereas the ethylene-alpha-olefin used a
37 Mooney polymer but required no plasticizer in order to achieve good processing. By
shifting the ratio of pulp to staple fiber, while adopting the unique properties of the
ethylene-alpha-olefin or polyolefin elastomer, the modulus, as indicated by the compound
MH provides a significantly improved level of stiffness in the resulting belt which has
given exceptional durability and load carrying capabilities.
[0068] Speculating further on the reasons for the improved compound performance
observed (but with no intent to thereby limit the scope of the invention), one might infer
from the higher Mooney viscosity of the EOM, a higher molecular weight polymer. Also,
it is generally known that metallocene polymers can have narrower molecular weight
distribution (MWD). Polymers with higher molecular weight and narrower MWD often
give better physical properties.
[0069] To summarize the conclusions from this first series of examples, the choice
of EOM or other saturated polyolefin elastomer as the base elastomer, with a combination
of aramid pulp and staple fiber at high total fiber loading and predetermined ratio of pulp
to total fiber, results in ability to use higher-Mooney elastomer and less oil, giving a more
polymer-rich composition, with better processing characteristics, higher cross-grain
elongation or flexibility and strength at similar or higher with-grain modulus. Later, these
effects will be shown to correlate with dramatic improvements in CVT belt performance.
[0070] TABLE 1.
Composition Comp. Comp.
Ex. 1 Ex. 2
(Volume %) Ex. 3 Ex. 4
EOM (Engage 8180) 63.12% 63.35%
EPDM (Vistalon 2504) 58.02%
CR (Neoprene GW) 53.14%
Para-aramid Pulp 3.35% 5.08% 5.10% 6.15%
Para-Aramid Staple fiber 7.58% 6.44% 6.46% 4.23%
Carbon Black 17.57% 16.94% 16.99% 21.87%
Oil 0.19% 0.18% 5.44% 2.29%
Antioxidant 0.48% 0.46% 0.46% 2.68%
ZnO 0.27% 0.26% 0.26%
Peroxide/coagent cure package 7.43% 7.27% 7.27%
Resin/S-Cure package, etc. 9.64%
Total Volume 100.00% 100.00% 100.00% 100.00°/
Pulp/Total Fiber (vol/vol) 30.6% 44.1% 44.1% 59.3%
[0071] TABLE 2 .
Composition Comp. Comp.
Ex. 1 Ex. 2
(phr) Ex. 3 Ex. 4
EOM (Engage 8180) 100.00 100.00
EPDM (Vistalon 2504) 100.00
CR (Neoprene GW) 100
Para-aramid Pulp 8.70 13.05 14.28 13.5
Para-aramid Staple fiber 19.01 16.53 18.10 9.0
Carbon Black 57.07 54.35 59.52 60
Oil 0.31 0.29 9.43 3.5
Antioxidant 0.92 0.87 0.95 4.3
ZnO 2.76 2.62 2.86
Peroxide/coagent cure package 19.88 19.21 21.
Resin/S-Cure package, etc. 27.50
Total Parts 208.65 206.92 226.14 217.8
Pulp/Total Fiber (wt/wt) 31.4% 44.1% 44.1% 60.1%
[0072] TABLE 3 .
Comp. Comp.
(cont'd) Ex. 1 Ex. 2
Ex. 3 Ex. 4
Moonev Scorch (27 F MU
Initial Vis. 185.39 156.77 156.96 130.58
Minimum Vis.(ML) 98.86 76.04 71.57 75.87
3 Pt Rise (t3) 9.73 11.65 8.56
5 Pt Rise (t5) 12.38 15.24 11.70 7.26
ML(l+4) 89.50 76.64 71.62 76.16
Moonev Viscositv 125°C (MLl+4) MU
ML 141.05 83.87 93.55
ML(l+4) 104.92 93.55
MDR 2000E (3 min.fi¾200°C lb.in
MH 54.98 38.88 51.70 37.88
MH-ML 52.13 36.41 49.41
ML 2.85 2.47 2.29 4.57
Final S 54.87 38.75 51.70 42.45
Final S" 3.06 2.66 4.37 3.61
Scorch2 0.21 0.27 0.23 0.31
T 99 (min) 1.95 1.70 2.31 2.71
Tan Delta final 0.06 0.07 0.08 0.09
MDR 2000E 30 min. (a), 177°C lb.in
MH 64.15 47.46 55.45 32.79
MH-ML 61.08 44.97 53.76
ML 3.07 2.49 2.04 4.39
Final S 63.69 47.12 55.45 37.17
Final S" 2.83 2.40 4.33 5.30
Scorch2 0.44 0.50 0.46 1.27
T 99 (min.) 13.16 13.43 13.89 28.06
Tan Delta final 0.04 0.05 0.08 0.14
Durometer Shore-A 95.81 95.33 92.00
Durometer Shore-D 56.03 53.44 53.33
Specific Gravity 1.17 1.15 1.18 1.41
Original Tensile Pull (a), RT psi.
WITH GRAIN
Comp. Comp.
(cont'd) Ex. 1 Ex. 2
Ex. 3 Ex. 4
% Eb 15.54 14.71 14.63 14.32
M5 2315.57 2184.36 1749.13 1419.61
M10 3427.39 3 116.31 3173.05 2882.15
Tb 3624.92 3084.48 3317.44 3380.58
Break Energy
"C" Tear lb/in kN/m 470
CROSS GRAIN
% Eb 105.94 141.09 72.84 77.30
M5 435.88 399.26 265.00 317.80
M10 683.77 633.56 434.75 515.98
M20 1032.43 957.40 741.46 795.94
M25 1157.92 1067.48 868.83 898.17
M50 1499.06 1368.65 1269.05 1245.33
M100 1252.81 1616.81
Tb 1850.00 1707.97 1425.49 1479.36
Break Energy
"C" Tear lb/in kN/m 246
Anisotropy Ratio at 5%, RT 5.34 5.47 6.60 4.47
Anisotropy Ratio at 10%, RT 4.95 4.92 7.30 5.59
Original Pull (a), 125°C osi.
WITH GRAIN
% Eb 12.06 12.50 9.03
M5 1014.12 1059.16 1261.06
M10 1492.92 1428.77
Tb 1637.76 1443.76 1666.93
Break Energy
"C" Tear lb/in kN/m 151
CROSS GRAIN
% Eb 59.68 55.65 38.53
M5 171.52 155.51 165.65
M10 304.17 262.75 292.91
M20 503.71 402.78 493.38
M25 577.20 451.26 563.75
Comp. Comp.
(cont'd) Ex. 1 Ex. 2
Ex. 3 Ex. 4
M50 797.27 595.01
Tb 836.10 610.09 675.66
Break Energy
"C" Tear lb/in kN/m 101
Anisotropy Ratio at 5%, 125°C 5.91 6.81 7.61
Anisotropy Ratio at 10%, 125°C 4.91 5.44
Oven Aged. 168 hr. 150°C psi. - RT
Durometer Shore-A 96.39 93.00
Durometer Shore-D 57.44 52.67
WITH GRAIN
% Eb 14.74 14.28 11.49
M5 2527.34 2340.17 1800.03
M10 3648.84 3373.09 3832.05
Tb 4385.98 3399.88 4150.52
Break Energy
"C" Tear lb/in kN/m 507
CROSS GRAIN
% Eb 87.08 99.93 38.99
M5 500.76 454.48 489.68
M10 789.96 721.94 808.70
M20 1212.16 1096.60 1255.09
M25 1374.04 1218.12 1401.34
M50 1749.29 1535.91
M100 1944.49 1096.60
Tb 2127.53 1752.69 1647.62
Break Energy
"C" Tear lb/in kN/m 268
Oven Aged. 168 hrs.l50°C osi.
Pulled at 125°C
WITH GRAIN
% Eb 10.06 10.13
M5 1144.21 1240.02
M10 1924.78 1724.41
Comp. Comp.
(cont'd) Ex. 1 Ex. 2
Ex. 3 Ex. 4
Tb 1890.06 1722.67
Break Energy
"C" Tear lb/in 238
CROSS GRAIN
% Eb 52.82 58.39
M5 168.94 178.88
M10 321.81 321.63
M20 544.26 519.49
M25 631.68 586.28
M50 882.77 653.05
Tb 846.56 805.90
Break Energy
"C" Tear lb/in 101
Din Abrasion (cured 35 ¾350°P)
Horizontal Volume Loss (mm3) 130.93 138.40 161.97
Vertical Volume Loss (mm3) 107.87 94.60 101.00
Pico Abrasion Resistance 35 ( ), 350°F
RT Horizontal 111.07 85.60 71.74
RT Vertical 378.71 247.30 287.00 333.77
100°C Horizontal 53.35 39.30
100°C Vertical 97.71 64.80 40.70
Taber Abrader - Volume Loss (mm3)
RT, Cycles (1000), Load Weight (lOOOg), 212.42 268.20 213.60
Suction (70), H-18
RT, Cycles (2000), Load Weight (1000g),
2.66 4.20 4.30 4.22
Suction (0), Round Cast Iron
DeMattia Flex (pierced/0.5" stroke)
[in./Mcycle]
RT cross grain 56 5 11 307
125°C cross grain 5888 5 11 3680
125°C with grain 9200
[kcycle/inch] or [kcycle/2.54 cm]
RT cross grain 53.38 2.54 3.26
125°C cross grain 0.44 2.54 0.76
[0073] In a second series of composition examples, four different polyolefin
elastomers were compared in the same base recipe. The compositions, in phr, are shown
in Table 4 . The total fiber loading was about 28 phr and about 11 volume %. The
amount of pulp was about 31% of the total fiber weight. The main purpose of this series
was to evaluate processability, in terms of dispersion of ingredients in an internal mixer,
handling on a two-roll mill, both of which were repeated three times. The results are
indicated in Table 4 with "+" indicating very good handling and dispersion, "o"
indicating ok or acceptable handling or dispersion, "-" indicating not good handling on
the mill and some undispersed ingredients out of the mixer, and "- -" indicating poor
processability. As indicated, some variables came out crumbly from the mixer, but
generally could be brought together on the mill. The worst case exhibited a scaly surface,
even after milling and three passes in the mixer. Clearly, with all other ingredients being
equal, at these levels of fiber loading, EOM is the best, with EBM acceptable, EPM
difficult but possible to use, and EPDM the most difficult to process.
[0074] TABLE 4 .
Composition Comp.
Ex. 5 Ex. 6 Ex. 7
(phr) Ex. 8
EOM (Engage 8180) 91.3
EBM (Exact 9061) 0 91.3
EPM (VISTALON V706) 0 91.3
EPDM (Nordel 3745) 0 91.3
Carbon Black 57.07 -» -» -»
1-mm para-aramid staple 19.15 -» -» -»
50% para-aramid pulp in
17.4
EPDM masterbatch
Antioxidant 0.92 -» -» -»
ZnO 2.76 -» -» -»
Paraffinic Oil 0.31 -» -» -»
Peroxide cure package 20.36 -» -» -»
Total Parts 209.27 -» -» -»
Pulp/Total Fiber (wt/wt) 31% -» -» -»
1st pass in mixer + + crumbly crumbly
on mill + brittle o -
2d pass in mixer + o crumbly crumbly
on mill + o o o
3d pass in mixer + + - crumbly
on mill + + -scales - -scales
overall processability + o -
[0075] Belt examples and test results:
[0076] In a first comparison, two belt embodiments, Belt A and Belt B are
compared with two commercial CVT belts: Comp. Belt C, which is sold by Gates
Corporation and Comp. Belt D, identified with part number 715000302. These belts all
have pretty much the same dimensions as shown in Table 5, with nominal 31mm top
width, 952 mm length, and 26° V-angle. Comp. Belts C and D are heavier than Belts A
and B due to the CR elastomer density being greater than EOM. Belt B was made with
the same inventive materials as Belt A, but a little bit less rubber in the undercord portion
of the belt, making Belt B a little thinner and lighter. Comp. Belts C and D are
considered examples of highly optimized belts utilizing conventional rubber
compositions.
[0077] These belts were subjected to a number of tests designed to identify
performance differences. These tests include a belt conditioning test lasting about six
hours, followed by a Load Capability Test, Axial Stiffness Test, Bending Loss Test, and
at the end of these tests (about 8 hours total), a Belt Weight Loss Test.
[0078] The Belt Weight Loss Test results are shown in Table 5 . The initial weight
of the inventive belts is approximately 20% lower than the CR belts for the same belt
size. Surprisingly, after the eight hours of performance testing, the wear of the inventive
CVT belts was less than half of the wear of Comp. Belt D. A check of the final belt
dimensions indicates a combination of wear on the sidewalls and permanent reduction in
width from compression (indicated by a small increase in thickness).
[0079] TABLE 5 .
Comp. Comp.
Belt A Belt B
Belt C Belt D
Comp.
Body Composition Ex. 1 Ex. 1 CR
Ex. 4
Tensile cord aramid aramid aramid aramid
Weight (g) 396.29 379.4 474.42 461.50
thickness (mm) 15.20 14.83 15.25 16.79
Pitch length (mm) 952 952 951 951
Belt Weight Loss Test (g) -0.94 -1.04 -1.74 -2.66
Width change (mm) -0.52 -0.51 -0.96 -0.77
Thickness change (mm) 0.07 0.08 0.12 0.07
Comp. Belt D is a representative competitor's premium belt of unknown details, but
believed to be CR elastomer with aramid tensile cord.
[0080] The Load Capability Test is designed to simulate the conditions of the CVT
belt drive with all significant phenomena encountered in the application. This test is
carried out under a controlled, reproducible environment and measuring as many
parameters as is practical, including speed loss, belt slip and belt axial deformation. In
addition belt temperature is measured as it increases due to frictional and hysteretic
energy losses. Test is conducted on an electric dynamometer simulating CVT belt underdrive
conditions. During the test the speed of the driver shaft is constant at 1,500 ± 1 rpm.
Applied torque and hub load are varied. Test parameters are selected in such a way that
some of the tested belts reach the extreme conditions: (1) belt temperature up to about
170 °C; or (2) excessive speed loss (up to 15% caused by belt slip and belt deformation in
the sheaves).
[0081] The Load Capability Test rig arrangement 500 is shown in FIG. 5 . Electric
motor 505 drives the driver pulley 510 on the left, and the CVT belt 100 transfers motion
to the second pulley 520 where the electric generator (not shown) applies a resisting
torque. The generator is mounted on a fixture that can move to the right applying
constant total tension, i.e., hub load H, with position sensor 526. With the distance fixed
between the two halves of the pulleys, the hub load or total tension controls the axial
force applied to the belt in the driver and driven pulleys. To some extent, this simulates
the function of a driven CVT clutch. Spacers inside the pulleys allow changing the belt
pitch diameters, monitored by sensors 522 and 524, and the intended speed ratio. For
these tests the speed ratio is set at approximately 1.6. The actual speed ratio will change
with applied torque and hub load, and it is also influenced by the belt running
temperature, measured with sensor 530.
[0082] The speed loss, s, is defined as percentage of change of the driven pulley
speed, N„, due to a change in the load torque. It is calculated in reference to the driven
pulley speed at zero torque, Nno (no speed loss conditions) according to the following
formulae:
[0083] s % = %
N n o
[0084] The speed loss is obtained by direct measurements of both shaft speeds.
During the test the driver pulley speed is kept constant with precision of about 0 .1%. The
belt slip can also be determined from the speed loss and the measured belt pitch
diameters.
[0085] In the Load Capacity Test, Belts A and B show much better performance
over the Comp. Belts C and D, as seen in FIG. 6 . Specifically, the speed losses are lower
by up to about 50%, depending on the torque level. Belts A and B could be run at higher
torque without reaching the extreme conditions mentioned above. Using Belt A or B, on
the same vehicle would result in a higher maximum achievable speed than with one of the
Comp. Belts. Also, the inventive belt temperatures are lower by up to 30 to 40°C,
depending on power level. Speed loss and belt axial deformation are the main reasons for
the heat generation and increased belt temperature seen in FIG. 6 . To keep belt
temperatures from running away by keeping speed loss at some acceptable level (<4%)
would require limiting the torque range at which the belt can be used for a prolonged
time. Thus, the inventive Belts A and B may be run at higher continuous torques or
loads, relative to the Comp. Belts.
[0086] In the Load Capacity Test, there is speed loss present at any load condition.
As a result, the transfer of power, P, by the CVT drive is associated with a power loss, Ps,
due to the speed loss. It can be expressed by the formulae, Ps = P x s %. The power
loss results are shown in FIG. 7 . The inventive Belts are significantly more efficient than
the Comp. Belts.
[0087] Finally, the Load Capacity Test pushed the belts beyond the torque levels of
FIG. 6 to explore the short term, peak load capacity of the belts. This portion of the test
starts at room temperature and at zero value for the torque. Every one minute the torque
load is increased by 5 Nm until it reaches 145 Nm. The resulting speed loss and belt
temperature at three select torque levels and the belt width change at the maximum torque
are shown in Table 6 . These temperatures do not represent thermal equilibrium since the
test is stopped after 30 minutes. If the test had been continued past that time limit, the
belt temperatures would have been much higher. For the two Comp. Belts, belt
temperatures and slip levels approached the material limits. Clearly, the inventive belts
have much higher peak torque capacity than conventional optimized belts.
[0088] Table 6 includes a comparison of belt width change due to high torque load.
This axial compression of the belt is one of the direct causes of speed loss - change in
belt width results in reduced pitch diameter of the belt in the driver and driven pulleys,
which results in reduced speed ratio and speed loss. The inventive belts exhibit much less
axial compression, a direct result of the increased transverse stiffness characteristics of
the inventive rubber compositions. In addition, the strong performance of the thinner Belt
B suggests the thickness can be advantageously reduced with the improved transverse
properties of these rubber compositions. Thus, a thickness less than 15.0 mm may be
advantageous. The cord position may also advantageously be adjusted to ride closer to
the back surface or roots than to the underside surface or roots, as illustrated in FIG. 10.
[0089] TABLE 6 .
Comp. Comp.
Belt A Belt B
Belt C Belt D
Speed loss at 100 Nm torque (%) 3.1 3.1 5.5 4.2
Speed loss at 120 Nm torque (%) 3.9 4.0 7.7 6.2
Speed loss at 145 Nm torque (%) 5.2 5.7 12.6 11.3
Belt Temperature at 100 Nm torque (°C) 83 79 103 96
Belt Temperature at 120 Nm torque(°C) 96 93 126 118
Belt Temperature at 145 Nm torque (°C) 117 116 171 159
Belt width change at 145 Nm torque (mm) -0.4 -0.7 -1.8 -1.6
[0090] A Dynamic Axial Stiffness Test ("DAST") was run on these four belts to
see the direct influence of the rubber composition on the belt. As discussed above in the
background section, belt change in width caused by belt compression under drive tension
is one of the key characteristics of the belt because it influences the speed loss or speed
ratio and energy loss in the CVT drive resulting in higher temperature and lower
efficiency of the drive. The DAST explores the influence of the belt tension on the
change in belt width. The test rig configuration is the same as used for the Load
Capability Test (FIG. 5).
[0091] Belt axial stiffness is defined for the specific test configuration:
[0093] Change in applied hub load, DH, in the drive results in the change of belt
width, AW. The hub load force is recalculated into the axial (parallel to shaft axis)
direction force component. It represents the pressure between belt and the pulley wall.
Using the fact that the pulley groove angle A = 26 degrees in this test gives the constant
2.17.
[0094] For the purposes of the Dynamic Axial Stiffness Test, the belt is installed
with driver pulley pitch diameter of 95 ± 5 mm, speed ratio of 1.6 ± 0 .1, load torque of 30
Nm, and driver shaft speed of 1500 rpm. The initial hub load is set to H = 3000 ± 100 N,
and the belt is run for about 30 minutes until the belt temperature is above 90°C, but not
greater than 120 °C. Belt radial position is recorded. Then hub load is gradually reduced
to H = 600 N, measuring belt radial position at each step. The reported axial stiffness is
calculated from the belt width difference between 3000N and 600N using the above
formula. The stiffness is the slope of the least squares best fit line through the H versus
A data. The test can be done on belts of any width, in principle, but preferably the belt
width ranges from 25 mm to 35 mm. Likewise, belt length should not affect the test very
much. The test could also be scaled if necessary to evaluate very small or very large
belts. For small belts, the hub load may be reduced, still providing a linear response
region for determining the stiffness. For larger belts, the hub load values or range can be
increased to provide for seating the belt in the pulleys and producing a suitable width
reduction. Thus, hub load should be chosen as appropriate, related to the maximum
application tension in the drive. At similar pitch diameter, belt size should not affect the
transverse stiffness numbers much. However, if small diameter pulleys (or pitch line) is
required for smaller belts, or larger diameter pulleys or pitch line for larger belts, then the
stiffness would have to be adjusted for the difference in wrap distance in order to
compare results with these ATV-size belts. The adjustment could be the equivalent of
determining a modulus value instead of stiffness. More preferable is evaluating belt
transverse stiffness using the compression test described later, at constant sample area and
thickness.
[0095] The summary of the DAST results is shown in Table 7 . Thus, the belt
rubber composition in Belts A and B leads directly to a decrease in width reduction,
which is attributable to an increased axial stiffness of the belt, relative to the comparative
belts. Belts A and B show a dynamic axial stiffness which averages about 75% higher
than Comp. Belts C and D. This in turn leads to the performance improvements
described earlier, namely lower belt running temperature, reduced radial slip, higher load
capacity, and lower speed losses. In an application such as an ATV, this should lead to
better acceleration, higher top speeds, lower belt temperatures, less fade, etc. This also
should reduce the loss of power required to radially slide the belt into and out of the
pulleys at the entrance and exit when belt is transitioning between the spans and inside
the pulleys.
[0096] In light of the results of the Dynamic Axial Stiffness Test and its correlation
with CVT drive performance, it is advantageous that a rubber CVT belt exhibit a Belt
Dynamic Axial Stiffness greater than 5.0 kN/mm or greater than 6.0 kN/mm or greater
than 7.0 kN/mm, or from about 7 to about 8 kN/mm. It should be understood these
numbers are based on the ATV belt sizes and test setup described herein, and may be
transformed on a similar basis for other sizes of belts on other test setups.
[0097] TABLE 7 .
Comp. Comp.
Belt A Belt B
Belt C Belt D
Belt width reduction at H = 3 kN (mm) 0.88 0.90 1.60 1.51
Belt Dynamic Axial Stiffness 1 (kN/mm) 7.4 7.3 4.1 4.3
at 90°C approximately.
[0098] In light of the above results, a simpler axial stiffness test was devised based
on ASTM D575-91 (reapproved in 2012), Test Method A, and called the Gates
Compression Test ("GCT") herein. The ASTM D575 method is used for compression
measurements of elastomeric materials, using standard cylindrical buttons of 28.6 ± 0.1
mm diameter, i.e., about 650 mm2 (1.000 in2) circular cross-sectional area and 12.5 ± 0.5
mm (0.5 in) height. It is impossible to make such a sample from the CVT belts, so a
length of belt is prepared as illustrated in FIG. 10. An initial rough cut piece of belt 110
is provided. The belt width is cut down to 12.5 ± 0.5 mm (0.5 in) with parallel side
surfaces 118 (and the corresponding opposing surface which is not visible). The sample
belt 110 length is trimmed at cut marks 116 and 117, discarding end portions 119 and
120, to give a final test specimen 122 with total side surface 118 area of 650 ± 5 mm2,
which is confirmed using a digital microscope with area measuring capability. Because
of the stiffness of the materials and the relatively small deformations, sandpaper (called
for in the ASTM test) is not used between the flat platens of a compression tester and the
specimen 122.
[0099] The tests are conducted on a dynamic tensile machine using three samples
cut from the same belt, measured separately. Also, the tests are run applying sinusoidal
signal of displacement and recording force at the changing displacement. The test has
been run at three different frequencies 2.5 Hz, 15 Hz and 30 Hz and at two values of
temperature 23°C and 90°C, although other conditions could be used. The frequency
dependence was not very strong, so the 15 Hz results are used. The 90°C temperature
represents typical CVT belt operating range at high loads. The displacement range is
based on the measured typical CVT belt axial deformation (i.e., compression) in the CVT
drive pulleys under the relatively high, close-to-rated-load conditions for the applications,
namely from 0.3 to 0.9 mm.
[0100] FIG. 8 shows an example of the Gates Compression Test ("GCT") data for a
CVT belt sample of Comp. Belt C tested at 90°C. Note that the loading portion (the
lower part of the loop indicated by the arrow) is substantially linear, the slope thereof
providing the axial stiffness of interest. The results can optionally be normalized by the
area and thickness of the sample, but will not be done here since all the samples have the
same dimensions. Some belts show more curvature in the force response, such as the
Comp. Belt D sample shown in FIG. 9 . For all the samples tested, the portion between -
0.6 and -0.9 mm displacement was sufficiently linear for providing a slope or stiffness
value as indicated in FIG. 9 . Thus, compression stiffness is calculated using the linear
section of the curve as illustrated by the arrow between displacement of -0.6 mm and -0.9
mm (the maximum displacement).
[0101] Table 8 shows the test results for a collection of comparative belts found in
the market, as well as the inventive Belt A. The four belts tested on both the GCT and
DAST show a good correlation between the two tests, although the DAST values tend to
be higher than the GCT values at the same temperature of 90°C. The difference could be
the effect of friction force in the radial direction present between belt and sheave in the
DAST. The inventive belt stands out from the pack with the highest stiffness on both
tests. Thus, the GCT stiffness also correlates with CVT drive performance.
[0102] In light of the results of the Gates Compression Test and its correlation with
CVT drive performance, it is advantageous that a rubber CVT belt exhibit a Gates
Compressive Test stiffness greater than or equal to 5.0 kN/mm at 90°C or greater than 6.0
kN/mm or 7.0 kN/mm or 8 kN/mm at room temperature, or from about 8 to about 9
kN/mm at room temperature.
[0103] TABLE 8 .
W GCT/23°C GCT/90°C DAST
Ex. Description
[mm] k [kN/mm] k [kN/mm] k [kN/mm]
Belt A Inventive Belt A 33 8.6 5.0 7.4
Belt B Inventive Belt B 33 - - 7.3
Comp.
Gates CR-aramid cord 33 5.1 3.3 4.1
Belt C
Comp.
MBL BRP 715000302 33 3.7 3.0 4.3
Belt D
Comp.
MBL BRP 715900212 33 1.9 1.5 - Belt E
Comp. Huansong (Blue Label)
33 2.9 1.8 - Belt F 2 113SS-305
Comp. Huansong (Bando)
33 3.1 3.1 -
Belt G 9 11.531.528
Comp. Carlisle JD Ml 68196
3 1 3.2 2.5 - Belt H RSX-182
Comp.
Gates CR-carbon cord 33 4.6 2.9 4.6
Belt I
Comp. Huansong (Red Label)
33 3.7 2.4 -
Belt J 2213SS-220
Comp. Scooter belt
22 4.4 3.7 - Belt K EPDM-carbon cord
Comp. Scooter belt
20 5.8 4.8 - Belt L EPDM-polyester cord
[0104] An additional test for the bending losses of a CVT Belt was carried out on
belts A-D, herein called the Bending Loss Test ("BLT"). This test was able to separate
two sources of loss, bending loss and radial friction loss. The BLT rig for measuring
bending and radial friction losses in CVT Belts was similar in layout to the LCT rig
described in FIG. 5 . The rig allowed for measuring the hub load, shaft speeds and torques
at a chosen temperature, which again was 90°C.
[0105] The measured losses represent torque required to rotate the CVT belt in the
simple drive with two small diameter pulleys with no resistance applied to the driven
shaft. For simplicity, the torque losses measured at relatively low hub load are defined as
belt bending losses, and the difference in torque losses due to an increase in hub load is
defined as the frictional loss due to radial sliding.
[0106] The results from the belt Bending Loss Test are two numbers: bending loss
and radial friction loss. They are calculated as averages from the measured torque losses.
In Table 9 there are test results for four belt constructions, three repeat tests for each
value reported.
[0107] The losses due to bending are about 20% higher for the inventive belts,
which may be reflective of the higher modulus rubber compositions used. At the same
time, the losses to overcome friction in radial sliding in and out of the pulley are
approximately 40% lower, resulting in overall better efficiency on a CVT drive with the
inventive belts.
[0108] TABLE 9 .
Belt A Belt B Comp. Belt C Comp. Belt D
Bending Loss (Ncm) 59, 63, 55 51, 54, 5 1 50, 52, 46 51, 45, 49
Friction Loss (Ncm) 77, 83, 8 1 86, 83, 83 112, 107, 111 122, 113, 107
[0109] In summary, they axial stiffness of inventive Belts A and B is approximately
70% higher than other belts, speed losses are lower at rated torque by 2% to 5%, and the
losses due to bending are about 20% higher while the losses to overcome friction in radial
sliding in and out of the pulley are approximately 40% lower, resulting in overall better
performance on a CVT drive.
[0110] The fiber-loaded rubber compositions described herein may have other
applicability besides CVT belts. Other power transmission belts such as V-belts and
multi-V-ribbed belts, which also benefit from high transverse stiffness could also be
within the scope of the invention. Toothed or synchronous power transmission belts
could also benefit from these compounding concepts, although the orientation effect
therein would best be directed parallel to the belt running direction, at least in the teeth,
which is the direction of maximum load on the teeth.
[0111] Although the present invention and its advantages have been described in
detail, it should be understood that various changes, substitutions, and alterations can be
made herein without departing from the scope of the invention as defined by the
appended claims. Moreover, the scope of the present application is not intended to be
limited to the particular embodiments of the process, machine, manufacture, composition
of matter, means, methods, and steps described in the specification. As one of ordinary
skill in the art will readily appreciate from the disclosure of the present invention,
processes, machines, manufacture, compositions of matter, means, methods, or steps,
presently existing or later to be developed that perform substantially the same function or
achieve substantially the same result as the corresponding embodiments described herein
may be utilized according to the present invention. Accordingly, the appended claims are
intended to include within their scope such processes, machines, manufacture,
compositions of matter, means, methods, or steps. The invention disclosed herein may
suitably be practiced in the absence of any element that is not specifically disclosed
herein.
CLAIMS
What is claimed is:
1. An endless rubber CVT belt comprising a main belt body comprising a
compression portion, tension portion, an adhesion portion, and a tensile cord
in contact with the adhesion portion and embedded between the compression
portion and the tension portion, angled sides, and a width to thickness ratio on
the order of 2; wherein at least one of the compression portion, the tension
portion and the adhesion portion comprises an elastomer composition
comprising a saturated ethylene-alpha-olefin elastomer, a staple fiber, and a
pulp fiber.
2 . The belt of claim 1 wherein the staple fiber is an aramid staple fiber and the
pulp fiber is an aramid pulp fiber.
3 . The belt of claim 2 wherein the aramid staple fiber is para-aramid and the
aramid pulp fiber is para-aramid.
4 . The belt of claim 1 wherein the alpha-olefin of the ethylene-alpha-olefin
elastomer is octene or butene.
5 . The belt of claim 4 wherein the ethylene-alpha-olefin elastomer is ethyleneoctene
elastomer with an ethylene content in the range of below 75% by
weight and a melt flow rate less than 5 gm/10 min. based on ASTM D123 8- 13
with 2.16 kg at 190°C.
6 . The belt of claim 1 wherein the total amount of the aramid staple fiber and
aramid pulp fiber is between 3 and 19 volume percent of the composition and
between 1 and 65 phr.
7 . The belt of claim 4 wherein the ethylene-alpha-olefin elastomer is ethylenebutene
elastomer with an ethylene content in the range of 60.0% to 65.0% by
weight.
8 . The belt of claim 2 wherein the volume of aramid pulp fiber is less than 40%
of the total volume of the staple fiber plus the pulp fiber in the elastomer
composition.
9 . The belt of claim 2 wherein the weight of aramid pulp fiber is less than 40% of
the total weight of the staple fiber plus the pulp fiber in the elastomer
composition.
10. The belt of claim 1 wherein the belt exhibits a stiffness on the Dynamic Axial
Stiffness Test of greater than 5.0 kN/mm.
11. The belt of claim 1 wherein the belt exhibits a stiffness on the Gates
Compression Test of greater than or equal to 5.0 kN/mm at 90°C and greater
than 6.0 kN/mm at room temperature.
12. The belt of claim 1 wherein the overall belt thickness is less than 15 mm.
13. The belt of claim 12 wherein the cord position is closer to the backside than to
the underside of the belt.
14. An endless power transmission belt comprising a main belt body comprising:
a tensile cord embedded in said belt body, and
an elastomer composition comprising an elastomer, a high-modulus
staple fiber, and a high-modulus pulp fiber; wherein the high-modulus pulp
fiber constitutes less than 40% of the total amount of high-modulus staple and
pulp fiber.
15. The power transmission belt of claim 14 in the form of a toothed belt, a Vbelt,
or a multi-V-ribbed belt.
16. The belt of claim 14 wherein the elastomer is an ethylene-alpha-olefin
elastomer, and the total amount of staple fiber and pulp fiber is between 3 and
19 volume percent of the elastomer composition.
17. The belt of claim 14 wherein the elastomer is a saturated ethylene-alpha-olefin
elastomer.
18. The belt of claim 14 wherein the elastomer composition further comprises
other elastomers at less than 50% of the total elastomer present by weight.
19. The belt of claim 14 wherein both the high-modulus staple fiber and highmodulus
pulp fiber are aramid fibers.