CVT belt

Abstract

The invention relates to a CVT belt having a body 2 extending over the entire section of the belt and comprising a cord 3 comprising carbon fibers or PBO fibers and having a central axis I along its length. The body is made from a single compound including a nitrile group-containing copolymer rubber as a primary elastomer. The belt has a top tooth profile (4), an axis A orthogonal to the central axis and extending at a point where the thickness of the belt is highest, a cross section defined by a cross-sectional plane orthogonal to the central axis I and taken at the axis A. The cross-section has a trapezoidal shape, a top side (7) defining a top width, a bottom side (8) defining a bottom width, and two lateral sides (9, 10).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the priority of Italian Patent Application No. 102022000006695 filed on April 5, 2022, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to a continuously variable transmission belt or CVT belt. Background Art

[0004] A belt for a continuously variable transmission or variable speed drive is a belt used in a closed loop control system with a feedback mechanism for automatic and relatively fast gear changes.

[0005] Typically, in a continuously variable transmission, the driver pulley responds to speed measurements or speed changes to keep the power source within the optimum power or speed range, while the driven pulley responds to torque loads. Belt-driven CVTs are widely used in scooters, all-terrain vehicles, snowmobiles, and even cars.

[0006] When the two half pulleys are moved axially apart or together to forcibly change the belt radial position, the belt may be subject to high friction forces because the belt changes radial position within the pulleys. When the two half pulleys are moved axially together to increase the pitch line of the belt, the belt is subject to high friction forces and high axial or lateral compression forces. High variable torque loads result in high tension and high wedging forces, which also result in high lateral compression forces on the belt.

[0007] All of these forces can be very severe in a CVT due to dynamic applications (e.g., frequent, rapid gear changes with high acceleration loads).Because the CVT belt spans across the drive and driven pulleys, it is subject to constant bending or flexing.

[0008] Rubber CVT belts are used without lubrication in so-called "dry CVT" applications.

[0009] CVT belts must be designed to have good longitudinal flexibility, high longitudinal modulus, high wear resistance and high transverse stiffness. The belts must be able to operate over a wide temperature range for long periods of time.

[0010] Power transmission belts generally include a body made of an elastomeric material into which are embedded a plurality of longitudinal linear durable inserts, also known as ropes or "cords".

[0011] Each component of the power transmission belt contributes to increasing performance in terms of mechanical resistance, in order to reduce the risk of failure (eg breakage) of the power transmission belt and to increase the specific transmittable power.

[0012] In particular, the rope helps to ensure the mechanical properties required of the power transmission belt and plays a vital role in determining the modulus of the power transmission belt and in particular ensuring long-term stable performance. The rope is generally obtained by winding a high modulus fiber multiple times.

[0013] Because CVT belts are subject to high loads, the cords are typically made with high modulus fibers.

[0014] The rope is usually treated with a suitable material to increase the compatibility of the fibers with the host compound surrounding the rope. The host compound is able to connect the various elements mentioned above and ensure that they contribute in a synergistic way to the final performance of the power transmission belt.

[0015] From EP 2 480 802 it is known to make a CVT belt having an above-cord layer, a below-cord layer and a bonding layer surrounding the cords, the bonding layer being interposed between the below-cord layer and the above-cord layer.

[0016] The different layers usually have different compositions and are made of vulcanized rubber with various additives. The above-the-cord and below-the-cord layers usually include fibers, while the bonding layer usually does not. Other reinforcement layers may also be added to the belt.

[0017] Both the lower side and the upper side are preferably ribbed or toothed and may be covered by a fabric and / or other coating. The covering fabric has the purpose of increasing the wear resistance, thereby protecting the working surface of the power transmission belt.

[0018] Finally, the bulk compound allows the various elements described above to be joined and ensures that the various elements forming the power transmission belt itself contribute synergistically to the ultimate performance of the CVT belt.

[0019] In recent engines with significantly improved performance, the CVT belt is subjected to higher temperatures, which cause the materials forming the various components to age more quickly, and the CVT belt must have better mechanical properties in order to have a longer average service life.

[0020] In particular, new applications place greater demands on the belt's compressibility (also referred to as the belt's lateral stiffness) in response to the demands of the belt during use.

[0021] If the belt is less compressible, it will deflect less and wear less.

[0022] Although various approaches have been used to alter the compressibility of the belt, no significant improvement has resulted. Summary of the invention

[0023] A first object of the invention is to obtain a CVT belt, in particular a single-sided or double-sided toothed belt, having excellent mechanical characteristics, which is resistant to high temperatures and therefore has a longer service life.

[0024] According to the invention, this object is achieved by a CVT belt according to claim 1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to better understand the present invention, it will now be described with reference to the accompanying drawings, in which:

[0026] - Figure 1 is a schematic side view of a CVT belt according to the present invention, with a portion extracted to view the embedded cord;

[0027] - Figure 2 is along Figure 1 A schematic cross-sectional view of a CVT belt taken along the A or H axis;

[0028] - Figure 3 is a graph reporting the results of duration testing of examples of inventive belts and comparative belts;

[0029] - Figure 4 is a schematic diagram of a transmission system including a CVT belt for testing durability disclosed in an example;

[0030] - Figure 5 is a schematic diagram of a test apparatus for measuring the compressibility or stiffness of a belt;

[0031] - Figure 6 is a schematic diagram of a testing machine for stiffness testing, in which two samples are inserted; and

[0032] - Figure 7 is a graph of compressibility / stiffness performed on belts according to the invention and comparative belts. DETAILED DESCRIPTION

[0033] Figure 1 A CVT belt is shown, indicated as a whole by reference numeral 1. The CVT belt 1 comprises a body 2 made of elastomeric material, in which a plurality of longitudinal filamentary resistant inserts 3 (also referred to as cords) are embedded. In a first embodiment, the body 2 has a first toothing or top toothing 4 on a first or top side, optionally covered by a first or top covering fabric 4b, and a second toothing or bottom toothing 5 on a second or bottom side, optionally covered by a second or bottom covering fabric 5b.

[0034] In an alternative embodiment, the belt has only a top toothing, while the bottom surface has no teeth and is therefore flat.

[0035] Hereinafter, the expression "the elastomeric material essentially consists of..." means that the elastomeric material may include a small percentage of other polymers or copolymers which may be added to the elastomeric material without changing the chemical-physical properties of the mixture and thus without departing from the scope of the present invention.

[0036] Hereinafter, it should be understood that "additive for elastomeric materials" means a certain material which is added to the elastomeric material to change its chemical and physical properties.

[0037] The CVT belt includes a single-layer body.

[0038] By single layer it is meant that it has the same composition over the entire extension of the strip from top to bottom, so it does not distinguish between a bonding layer, a layer below the cords or a layer above the cords, since these layers are indistinguishable and cannot be separated from one another.

[0039] Preferably, the body is made of a compound comprising one elastomeric material as main elastomer, optionally in combination with other elastomeric materials and additives.

[0040] “Main elastomer” means the elastomer present in excess of 50% by weight in the compounds constituting the body, calculated on the total weight of all elastomers in the body, thus excluding all other non-elastomeric components of the power transmission belt, such as cords or fabrics.

[0041] The main body is entirely formed of a single rubber composition, thus forming a single layer and comprising an HNBR elastomer, i.e., a nitrile-containing copolymer rubber comprising acrylonitrile units (a), monomer units (b) of an α,β-ethylenically unsaturated nitrile monomer other than acrylonitrile, and conjugated diene monomer units (c).

[0042] Therefore, there is no difference between the rubber composition near the top side or the bottom side and the rubber composition surrounding the cord 3 .

[0043] More preferably, the HNBR has an iodine value of 120 or less, and even more preferably has an iodine value of 80 or less.

[0044] Preferably, the content of the sum of the acrylonitrile units (a) and the monomer units (b) of the α, β-ethylenically unsaturated nitrile monomers other than acrylonitrile is 1 to 50% by weight in the total monomer units, and the content ratio of the acrylonitrile units (a) to the monomer units (b) of the α, β-ethylenically unsaturated nitrile monomers other than acrylonitrile is 10:90 to 90:10 in terms of the weight ratio of "content of acrylonitrile units (a):content of monomer units (b) of the α, β-ethylenically unsaturated nitrile monomers other than acrylonitrile".

[0045] In the nitrile group-containing copolymer rubber of the present invention, it is preferred that the total content of the acrylonitrile unit (a) and the monomer units (b) of an α,β-ethylenically unsaturated nitrile monomer other than acrylonitrile is 10 to 45% by weight in the total monomer units.

[0046] In the nitrile-containing copolymer rubber of the present invention, it is preferred that the content ratio of the acrylonitrile unit (a) to the monomer unit (b) of the α, β-ethylenically unsaturated nitrile monomer other than acrylonitrile is 20:80 to 80:20 in terms of the weight ratio of "content of acrylonitrile unit (a):content of monomer unit (b) of the α, β-ethylenically unsaturated nitrile monomer other than acrylonitrile".

[0047] In the nitrile-containing copolymer rubber of the present invention, it is preferred that the content ratio of the acrylonitrile unit (a) to the monomer unit (b) of the α, β-ethylenically unsaturated nitrile monomer other than acrylonitrile is 25:75 to 75:25 in terms of the weight ratio of "content of acrylonitrile unit (a):content of monomer unit (b) of the α, β-ethylenically unsaturated nitrile monomer other than acrylonitrile".

[0048] In the nitrile group-containing copolymer rubber, it is preferred that the content of the conjugated diene monomer unit (c) is 10 to 90% by weight.

[0049] Preferably, the above-mentioned rubber composition includes a nitrile group-containing copolymer rubber blended with a cross-linking agent, and in the belt, the rubber composition is cross-linked.

[0050] In the context of the present invention, the term "nitrile group-containing copolymer rubber" refers to a copolymer containing at least acrylonitrile units, α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile, and conjugated at least one diene monomer unit.

[0051] The term "copolymer" encompasses polymers having more than one monomer unit. In one embodiment of the invention, the copolymer is preferably derived from, for example, the three monomer types (a), (b) and (c) described above, and is therefore a terpolymer. The term "copolymer" also encompasses, for example, a further tetrapolymer, which is derived from the three monomer types (a), (b) and (c) described above and a further monomer unit (d).

[0052] The α,β-ethylenically unsaturated nitrile used to form the α,β-ethylenically unsaturated nitrile unit (a) can be any known α,β-ethylenically unsaturated nitrile. It is preferably an α,β-ethylenically unsaturated nitrile monomer having 2 to 5 carbon atoms, because the carbon atoms other than the cyano group are preferably also represented as (C2-C5)-α,β-ethylenically unsaturated nitrile, such as α-haloacrylonitrile, for example α-chloroacrylonitrile and α-bromoacrylonitrile; α-alkylacrylonitrile, for example methacrylonitrile, ethacrylonitrile; or a mixture of two or more α,β-ethylenically unsaturated nitriles. Methacrylonitrile, ethacrylonitrile or a mixture thereof is particularly preferred. Methacrylonitrile is very particularly preferred.

[0053] The amount of components a) acrylonitrile and b) α,β-ethylenically unsaturated nitrile units is generally in the range of 1 to 50% by weight, preferably 10 to 45% by weight, more preferably 15 to 42% by weight, still more preferably 20 to 40% by weight, particularly preferably 26 to 36% by weight, based on 100% by weight of the total amount of all monomer units.

[0054] In certain embodiments, preferably, except acrylonitrile unit (a), α except acrylonitrile, monomer unit (b) of β-ethylenically unsaturated nitrile monomer and conjugated diene monomer unit (c), nitrile-containing copolymer rubber according to the present invention also comprises carboxyl-containing monomer unit (d). By also comprising carboxyl-containing monomer unit (d), carboxyl can be introduced into nitrile-containing copolymer rubber of the present invention.

[0055] The carboxyl-containing monomers constituting the carboxyl-containing monomer units (d) are not particularly limited, as long as they are monomers having one or more unsubstituted (free) carboxyl groups that are not esterified. Examples thereof include α, β-ethylenically unsaturated monocarboxylic acid monomers, α, β-ethylenically unsaturated polycarboxylic acid monomers, α, β-ethylenically unsaturated dicarboxylic acid monoester monomers, etc. Carboxyl-containing monomers also include monomers having carboxyl groups that form carboxylate. In addition, the anhydrides of α, β-ethylenically unsaturated polycarboxylic acids can be used as carboxyl-containing monomers, since the anhydride groups thereof break after copolymerization to form carboxyl groups.

[0056] Furthermore, the nitrile group-containing copolymer rubber according to the present invention may contain an α, β-ethylenically unsaturated monocarboxylic acid ester monomer (e) in addition to the acrylonitrile unit (a), the monomer unit (b) of an α, β-ethylenically unsaturated nitrile monomer other than acrylonitrile, the conjugated diene monomer unit (c) and the carboxyl group-containing monomer unit (d) contained as required.

[0057] The α,β-ethylenically unsaturated monocarboxylic acid ester monomer constituting the α,β-ethylenically unsaturated monocarboxylic acid ester monomer (e) is not particularly limited. Examples thereof include α,β-ethylenically unsaturated monocarboxylic acid alkyl ester monomers, α,β-ethylenically unsaturated monocarboxylic acid alkoxyalkyl ester monomers, α,β-ethylenically unsaturated monocarboxylic acid aminoalkyl ester monomers, α,β-ethylenically unsaturated monocarboxylic acid hydroxyalkyl ester monomers, α,β-ethylenically unsaturated monocarboxylic acid fluoroalkyl ester monomers, etc.

[0058] The rubber composition of the present invention comprises the above-mentioned nitrile group-containing copolymer rubber of the present invention and a cross-linking agent.

[0059] The crosslinking agent is not particularly limited, and for example, a sulfur-based crosslinking agent, an organic peroxide crosslinking agent, a polyamine-based crosslinking agent, etc. can be used.

[0060] The content of the crosslinking agent in the rubber composition of the present invention is not particularly limited, but is preferably 0.1 to 20 parts by weight, more preferably 0.2 to 15 parts by weight, and still more preferably 0.5 to 10 parts by weight, relative to 100 parts by weight of the nitrile group-containing copolymer rubber. By setting the content of the crosslinking agent within the above range, the mechanical properties of the resulting crosslinked rubber can be made better.

[0061] Furthermore, in order to improve the mechanical properties of the obtained crosslinked rubber, the main body preferably contains a filler. The filler is any filler commonly used in the rubber field, and any of an organic filler and an inorganic filler can be used, but from the viewpoint of efficient compounding, an inorganic filler is preferred.

[0062] The inorganic filler may be any inorganic filler commonly used in rubber, such as carbon black, silica, clay, aluminum oxide, aluminum hydroxide, magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide, magnesium oxide aluminum, titanium oxide, kaolin, pyrophyllite, bentonite, talc, attapulgite, calcium magnesium silicate, aluminum silicate, magnesium silicate, calcium silicate, crystalline aluminosilicate, etc. Among them, carbon black, silica and clay are preferably used, and silica and clay are more preferably used. The inorganic filler may be used alone in a single type or in combination of multiple types.

[0063] The carbon black may be any carbon black commonly used for compounding in rubber, such as furnace black, acetylene black, thermal black, channel black, graphite, and the like.

[0064] As for silicon dioxide, it is not particularly limited, but may be natural silicon dioxide such as quartz powder, silica powder, etc.; synthetic silicon dioxide such as silicic anhydride (such as silica gel, aerosol, etc.), hydrated silicic acid, etc., among which synthetic silicon dioxide is preferred.

[0065] The clay is not particularly limited as long as the clay is a natural mineral including hydrated aluminosilicate as a main component, but may be montmorillonite, pyrophyllite, kaolinite, halloysite, sericite, or the like.

[0066] As for the inorganic filler, there can be used an inorganic filler obtained by subjecting it to coupling treatment with a silane coupling agent, an aluminum coupling agent, a titanium coupling agent, etc., or subjecting it to surface modification treatment with a higher fatty acid or its metal salt, a derivative of a higher fatty acid such as its esters, amides, etc., a surfactant, etc. At this time, as for the inorganic filler, an inorganic filler previously subjected to surface modification treatment can be used, or when preparing the rubber composition, the inorganic filler can be subjected to surface modification treatment by blending a surface modifier such as a coupling treatment agent used together with the inorganic filler.

[0067] Further, the rubber composition may include, in addition to the above components, compounding agents commonly used in the rubber field, such as metal oxides (such as zinc oxide, magnesium oxide, etc.), α,β-ethylenically unsaturated carboxylic acid metal salts (such as zinc methacrylate, zinc acrylate, etc.), plasticizers, co-crosslinking agents, crosslinking aids, crosslinking retarders, anti-aging agents, antioxidants, light stabilizers, anti-scorching agents (such as primary amines, etc.), activators (such as diethylene glycol, etc.), processing aids, slip agents, adhesives, lubricants, flame retardants, mildew inhibitors, acid acceptors, antistatic agents, pigments, foaming agents, etc. The amount of these compounding agents is not particularly limited, and as long as the compounding amount is within the range that does not impair the purpose and effect of the present invention, the compounding agent can be compounded in an amount according to the purpose of compounding.

[0068] Moreover, within the scope that the effect of the present invention is not hindered, the rubber composition of the present invention may also include rubber other than the above-mentioned nitrile-containing copolymer rubber. Such rubber other than the nitrile-containing copolymer rubber of the present invention includes acrylic rubber, ethylene-acrylic acid copolymer rubber, fluorine rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-diene terpolymer rubber, epichlorohydrin rubber, polyurethane rubber, chloroprene rubber, silicone rubber, fluorosilicone rubber, chlorosulfonated polyethylene rubber, natural rubber, polyisoprene rubber, etc. When mixing rubber other than the nitrile-containing copolymer rubber of the present invention, the amount thereof is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, and still more preferably 10 parts by weight or less, relative to 100 parts by weight of the nitrile-containing copolymer rubber of the present invention.

[0069] The rubber composition of the present invention is prepared by mixing the above ingredients preferably in a non-aqueous system. The preparation method of the rubber composition of the present invention is not particularly limited, but can be generally prepared by the following method: kneading the ingredients other than the cross-linking agent and the heat-unstable ingredients (co-cross-linking agent, etc.) by a mixer such as a Banbury mixer, an internal mixer, a kneading machine, etc. to perform primary kneading, then transferring the mixture to an open mill, etc., and adding the cross-linking agent and the heat-unstable ingredients, etc. to perform secondary kneading.

[0070] Advantageously, fillers are added in an amount ranging between 0 and 80 phr, more advantageously about 40 phr. Advantageously, light-colored reinforcing fillers (such as talc, calcium carbonate, silica and silicates) are added in an amount ranging between 0 and 80 phr, advantageously about 40 phr. Silanes may also be used advantageously in an amount ranging between 0 and 5 phr.

[0071] Advantageously, zinc oxide and magnesium oxide are added in amounts ranging between 0 and 15 phr.

[0072] Advantageously, ester plasticizers such as trimellitate or ethyl ester or glycol ether ester (eg, ADK classifier 700 or ADK classifier 735) are added in an amount advantageously ranging between 0 phr and 20 phr.

[0073] Advantageously, pre-vulcanization aids such as triallyl cyanurate and organic or inorganic methacrylates (such as metal salts) are advantageously added in an amount ranging between 0 and 20 phr, or organic peroxides such as cumene peroxide are advantageously added in an amount ranging between 0 and 15 phr, for example.

[0074] Advantageously, the mixture in the elastomeric material also comprises reinforcing fibers, more advantageously in an amount comprised between 1%wt and 20%wt, preferably between 5%wt and 15%, alternatively between 2phr and 40phr, preferably between 5phr and 30phr, even more advantageously 20phr. Advantageously, the length of the reinforcing fibers is comprised between 0.1mm and 10mm, more preferably between 1mm and 6mm.

[0075] The use of fibers can further improve the mechanical properties of the mixture constituting the body.

[0076] The fibers are therefore present throughout the body including the area surrounding the cord, which allows ensuring a higher rigidity.

[0077] Preferably, the fibers are chopped fibers.

[0078] Advantageously, the reinforcing fibers comprise aromatic polyamide, more advantageously aromatic polyamide, for example, which may advantageously be used Fibers, which can be adhered to the mixture by RFL-based treatment. For example, the grid used can have a matrix of VP-SBR, a copolymer of vinyl pyridine and styrene butadiene.

[0079] Aramid fibers have proven to be particularly effective, such as, for example, Teijn fibers having a length of 3 mm. fiber.

[0080] The rope 3 is preferably constituted by a coil of a continuous filamentary resistant element or "rope" wound into a helix.

[0081] The rope 3 preferably comprises carbon fibers or PBO.

[0082] Alternatively, the rope may also be of the so-called “hybrid” type, ie made from at least one first material and one second material.

[0083] The use of a cord 3 made of two different materials in the form of fibres or filaments enables the resistant insert 3 itself to adhere better to the mixture constituting the body of the CVT belt 1 .

[0084] The cord 3 is preferably treated with a water-based treatment known as reactive impregnation, but may also be treated with a similar treatment or with RFL, ie a composition based on latex, resorcinol and formaldehyde.

[0085] In the case where the rope 3 comprises two fiber materials, the first material and the second material are preferably selected from the group consisting of glass fibers, aramid fibers, polyester fibers, carbon fibers, PBO fibers, polyamide fibers, polyketone (POK) fibers, PEEK fibers, polyvinyl acetate (PVA) fibers, liquid crystal polymer (LPC) fibers and PEN fibers.

[0086] The first material preferably has a lower modulus than the second material and is preferably wrapped around the second material.

[0087] Preferably, in a cross section, the second material occupies a surface comprised between 15% and 75% relative to the total surface of the cross section itself. Still more preferably, the second material occupies a surface comprised between 45% and 55% relative to the total surface.

[0088] Even more advantageously, in cross section, the fibers of the two materials occupy a similar surface in order to balance the positive properties of both as much as possible to obtain the best performance on the belt.

[0089] The first material is preferably glass fiber and the second material is preferably carbon fiber.

[0090] Preferably, the fibers of the first material are wrapped around the fibers of the second material to at least partially coat the fibers of the first material from the outside, even more preferably to completely coat the fibers of the second material.

[0091] Preferably, the rope 3 according to the invention exhibits a twist of the Lang's Twist type, ie with two twists in the same direction, and in this respect said embodiment has proven to be particularly effective.

[0092] The number of filaments forming the resistant insert, as well as the number of elementary filaments or the denier of the insert or the entire embodiment, may vary without departing from the invention.

[0093] The number of yarns formed from fibers of the first material is preferably between 3 and 18, preferably between 8 and 15, in order to obtain optimal properties.

[0094] The number of yarns formed from fibers of the second material is preferably between 1 and 5, more preferably between 1 and 3, even more preferably 1.

[0095] The first material is preferably a low modulus fiber, more preferably a fiber selected in the group consisting of glass, aramid, PA, PET.

[0096] The second material is preferably a high modulus fiber, more preferably a fiber selected from the group consisting of carbon and PBO, even more preferably carbon.

[0097] A merely indicative example of a resistant insert 3 comprises 12 glass yarns completely surrounding 1 carbon yarn.

[0098] To form the resistant insert 3, the glass filaments are preferably treated with a water-based treatment known as reactive impregnation, but other treatments may also be used as RFL-based treatments.

[0099] The filaments are then twisted together for the first time to form a yarn. The yarn is then wound around a carbon fiber yarn.

[0100] In this way, the yarn forms an insert, preferably with a size between 0.7 mm and 1.4 mm, in particular 1.15 mm.

[0101] An example of such a configuration is known by the abbreviation 22tex 3*12, 400Tex*1.

[0102] The first twisting operation to which the filaments are subjected to twist formation consists of a plurality of twists in the first direction S (clockwise direction).

[0103] The second twisting operation to which the twist ring carbon fibers are subjected when they are rewound consists of twisting and is carried out in the same direction S so as to form a rope referred to as S.

[0104] These cords therefore exhibit a lay of the Langbach lay type, ie they have two lays in the same direction.

[0105] The twisting experienced by the filaments of the carbon fiber forming twist is all in the same first direction S.

[0106] Using the same method and the same procedure, the rope 3 is twisted twice in a direction opposite to the first direction, namely in a direction called Z (counterclockwise), to form the rope Z.

[0107] In order to form the belt according to the invention, the ropes S and Z are preferably deposited simultaneously on the mold, whose helical pitch is, for example, between 1.5 mm and 5 mm, advantageously between 2.0 mm and 3.5 mm, more advantageously between 2.1 mm and 2.6 mm, for example 2.56 mm, whereby this measurement should be understood as the distance between the center points of two ropes with the same twist.

[0108] The rope 3 has a central axis I along its length, such as Figure 1 and Figure 2 shown.

[0109] The toothing 4 is preferably covered by a first covering fabric and the second toothing 5 is preferably covered by a second covering fabric, which is preferably made of one or more layers and can be obtained using different weaving techniques, for example a weaving technique known as 2×2 twill.

[0110] The first covering fabric of the first tooth shape or the top tooth shape preferably comprises an aliphatic or aromatic polyamide, more preferably an aliphatic polyamide, even more preferably is made of polyamide yarn, such as polyamide 6 or polyamide 66.

[0111] Preferably, the second covering fabric (if present) of the second tooth shape 5 has a composite structure consisting of weft and warp threads, wherein the weft is composed of a thread formed of an elastic thread as a core and one, two or more composite threads wound on the elastic thread. Each composite thread preferably includes a thread of high heat resistance and high mechanical resistance and at least one coated thread wound on the thread of high heat resistance and high mechanical resistance. Preferably, each composite thread includes a thread of high heat resistance and high mechanical resistance and a pair of coated threads wound on the thread of high heat resistance and high mechanical resistance. The elastic thread is preferably made of polyurethane. The thread of high heat resistance and high mechanical resistance is preferably made of para-aromatic polyamide.

[0112] like Figure 1 and Figure 2 As shown, the belt has an axis A which is orthogonal to said central axis I and which extends at the point where the thickness of the belt is greatest.

[0113] The cross section defined by a cross-sectional plane orthogonal to the central axis I and taken at the axis A has a Figure 2 The maximum thickness (or height) H of the belt is defined as the distance between the top side and the bottom side. In other words, the axis A is taken from the point where the distance between the top side and the bottom side is the largest, such as Figure 1 and Figure 2 shown.

[0114] The belt has a top side defining a top width 7 , a bottom side 8 defining a bottom width, and two lateral sides 9 , 10 .

[0115] The top side 7 corresponds to the wider base of the trapezoid. The bottom side 8 corresponds to the smaller base of the trapezoid; therefore, the top width 7 is greater than the bottom width 8.

[0116] The two lateral sides 9 and 10 define an angle α with the top side, such as Figure 1 The public.

[0117] The angle α is preferably comprised between 24° and 30°, preferably between 26° and 28°.

[0118] Figure 2 The edge defined by the intersection of the top side and the lateral side, indicated at 12, is beveled, or chamfered, or corner-cut or rounded.

[0119] This improved geometry of the edges allows reducing the friction on the pulleys, thus reducing wear and improving the duration of the belt.

[0120] Furthermore, the belt has better compressibility or lateral stiffness than known belts and is able to resist external disturbances without undergoing any changes over a longer time span.

[0121] Preferably, the following reported conditions are used. Figure 5 The lateral stiffness measured by a testing machine is preferably higher than 7000 N / mm, even more preferably higher than 8000 N / mm after at least 200 seconds of testing. Figure 7 shown.

[0122] The thickness of the strip, or the height H defined as the distance between the top side and the bottom side, is preferably between 4 mm and 25 mm, more preferably between 8 mm and 20 mm, for example 16.6 mm.

[0123] The distance Hp between the top side and the central axis I of the rope is preferably between 1 mm and 12 mm, more preferably between 1 mm and 9 mm, for example 6 mm.

[0124] The ratio between the thickness or height H of the strip and Hp is preferably comprised between 0.1 and 0.6, more preferably between 0.1 and 0.4.

[0125] The projected top width WP is defined as the distance between the two intersection points of the extensions of the top side and the lateral sides, and is comprised between 10 mm and 50 mm, even more preferably between 15 mm and 45 mm.

[0126] The bottom width is preferably comprised between 12 mm and 42 mm. More preferably, the bottom width is comprised between 20 mm and 40 mm.

[0127] The CVT belt may have different lengths, but the length is preferably between 300 mm and 1500 mm, more preferably between 900 mm and 1300 mm, for example 1100 mm.

[0128] By examining the properties of a CVT belt made in accordance with the present invention, the advantages that can be achieved are apparent.

[0129] It has been experimentally verified that the CVT belt according to the invention ensures significantly improved high temperature resistance while maintaining excellent mechanical properties, in particular high lateral stiffness.

[0130] Although some embodiments have been disclosed by way of example of the present invention, it will be apparent to those skilled in the art that the types of fibers and the materials forming them as well as the materials of the host compound and other components of the power transmission belt may be modified without departing from the scope of the present invention.

[0131] In the following, "parts" are parts by weight unless otherwise specified. The testing or evaluation methods of physical properties and characteristics are as follows.

[0132] Example 1 and Comparative Examples 2-3:

[0133] According to the CVT belt of the present invention (such as Figure 1 The production process of (as shown) is as follows:

[0134] The body consisted of a HNBR compound loaded with 10% of aramid fibers having a length of 3 mm.

[0135] The rope is a hybrid rope made of glass yarn surrounding a single carbon yarn, with the configuration of 22tex3*12, 400Tex*1 as described above.

[0136] Treat the rope with the aqueous solution.

[0137] The top fabric covering the top teeth is made of nylon 66 yarn.

[0138] The bottom fabric of the bottom tooth shape is made of composite yarn, in which the weft thread is composed of a thread formed of a PU elastic thread as a core and two or more composite threads wound on an elastic thread formed of PA and nylon 66.

[0139] The effective length of the belt is 1109.3, the angle α is 26, and the total thickness is 16.6 mm at the height H. The distance Hp between the center point of the rope and the top side is 6 mm.

[0140] Therefore, the ratio between H / Hp is 0.3614.

[0141] The projected top width is 38.6mm and the bottom width is 32mm.

[0142] The top teeth have a pitch of 9.4 mm and the bottom pitch is 11.2 mm. The body is made of a single composition from top to bottom.

[0143] The edges between the top side 7 and the lateral sides 9, 10 are beveled.

[0144] The belt according to the invention was compared with belt 2 and belt 3 .

[0145] The part number for band 2 is BANDO PN: WBB1202 and the part number for band 3 is MITSUBOSHIPN: 280 652. The part number identifies the band geometry and material.

[0146] use Figure 4 The system shown is testing the durability of 3 belts on a test bench. The system described above replicates an all-terrain vehicle known as the CAN-AM Maverick turbo.

[0147] Table 1 discloses the test conditions:

[0148] Table 1

[0149]

[0150]

[0151] The test was stopped at the point of tape breakage or when the temperature of the tape at the top surface exceeded 90°C.

[0152] from Figure 3 As can be seen from the graph of FIG. 1 , the line for the CVT belt of the present invention is higher than the line for the comparative belt, thereby showing improved torque durability over a longer span of hours.

[0153] Example 4 and Comparative Example 5:

[0154] exist Figure 5 The testing machine shown performs a compression test, also known as a stiffness test.

[0155] like Figure 6 As shown in the schematic diagram, two belts are placed back to back and measured simultaneously to obtain parallel results. The tests are performed on an MTS 810 servo-hydraulic test system by applying an average load of 500N and a dynamic load of ±100N at a frequency of 10Hz.

[0156] The results over time are collected and shown in Figure 7 In the graph of , the results obtained with the belt of the present invention are compared with the results obtained with the Mitsubishi belt of Example 3 used above.

[0157] If the angle α of the belt changes, Figure 5 The angle of 13.5° will change because the testing machine must follow the contour of the tape exactly. The length of the tape sample is 80 mm and the length of the surface of the testing machine where the sample lies is di 60 mm.

[0158] From the test results it can be seen that the stiffness measured on the belts of the invention is always better than the comparison belts and this is expected to result in lower wear and therefore longer lasting performance.

[0159] In particular, the stiffness consistently exceeds 7000 N / mm over a long time span.

Claims

1. A CVT belt (1) having a body (2) extending over the entire cross section of the belt and including a cord (3), the cord (3) comprising carbon fibers or PBO fibers and having a central axis I along its length, the body being made of a single compound comprising a nitrile-containing copolymer rubber as a main elastomer, the nitrile-containing copolymer rubber comprising acrylonitrile units (a), monomer units of α,β-ethylenically unsaturated nitrile monomers other than acrylonitrile (b), and conjugated diene monomer units (c), and having an iodine value of 120 or less, and the belt having: oTop tooth profile (4), o an axis A orthogonal to the central axis and extending at the point where the thickness of the strip is greatest, o a cross section defined by a cross-sectional plane orthogonal to said central axis I and taken at said axis A, said cross section having a trapezoidal shape and a top side (7) defining a top width, a bottom side (8) defining a bottom width and two lateral sides (9, 10), o the top width is greater than the bottom width, o the two lateral sides form an angle α with the top side, o The projected top width Wp is defined as the distance between the two intersection points of the extensions of the top side and the lateral side, It is characterized in that - the edges (11, 12) defined by the intersection of the top side and the lateral side are beveled, chamfered, corner-cut or rounded, - the distance Hp between the top side and the central axis I of the rope is comprised between 1 mm and 6 mm, - The ratio between the height H of the strip, defined as the distance between the top side and the bottom side, and the Hp is comprised between 0.1 and 0.

6.

2. The CVT belt (1) according to claim 1, characterized in that This comprises a ratio between said thickness and said Hp between 0.1 and 0.

4.

3. The CVT belt (1) according to claim 1 or 2, characterized in that: The CVT belt comprises a top tooth profile (4) on the top side and a bottom tooth profile (5) on the bottom side.

4. CVT belt (1) according to any one of the preceding claims, characterized in that The top toothing (4) and the bottom toothing (5) have different pitches.

5. CVT belt (1) according to any one of the preceding claims, characterized in that The top toothing (4) has a pitch between 5 mm and 15 mm.

6. The CVT belt (1) according to any one of claims 3 to 5, characterized in that The bottom toothing (5) has a pitch between 5 mm and 12 mm.

7. CVT belt (1) according to any one of the preceding claims, characterized in that The projected top width Wp is comprised between 15 mm and 45 mm.

8. CVT belt (1) according to any one of the preceding claims, characterized in that The bottom width is comprised between 12 mm and 42 mm.

9. CVT belt (1) according to any one of the preceding claims, characterized in that The angle α is comprised between 24° and 30°.

10. CVT belt (1) according to any one of the preceding claims, characterized in that The top tooth profile (4) and the bottom tooth profile (5) are covered by fabric.

11. CVT belt (1) according to any one of the preceding claims, characterized in that The body (2) comprises fibers evenly distributed in the body from the top side to the bottom side.

12. The CVT belt (1) according to claim 11, characterized in that Said fibres are present in a percentage ranging from 1% to 20%wt by weight of the total weight of said body.

13. CVT belt (1) according to any one of the preceding claims, characterized in that The fibers are chopped fibers.

14. CVT belt (1) according to any one of the preceding claims, characterized in that The fibers are made of aliphatic polyamide or aromatic polyamide.

15. A CVT belt according to any one of the preceding claims, characterised in that When measured at a load of 500 N by applying a dynamic load of ±100 N at a frequency of 10 Hz using the testing machine of FIG. 5 , the stiffness is higher than 7000 N / mm.

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