Patent Description:
The present invention concerns a power transmission belt and, in particular, a belt for use in power transmission systems in motor vehicles and relative transmission system.

The present invention is used preferably for transmission of movement in a transmission assembly of a motor vehicle comprising an engine.

The transmission of movement in motor vehicles is performed preferably using synchronous power transmission belts, also called toothed belts.

In motor vehicles, power transmission belts, also known as multi-groove or poly-V belts, are also used to drive accessories of an engine. An accessory transmission generally comprises a drive pulley connected to a crankshaft of an internal combustion engine of the motor vehicle, at least a second and a third pulley connected for example to an alternator and to an accessory, for example a hydraulic pump, and a transmission belt to connect the pulleys to one another.

Said belts generally comprise a body made of elastomeric material, preferably EPDM for the poly-V belts and HNBR for the toothed belts, a plurality of filiform resistant inserts embedded longitudinally in the body, and a coupling portion integrally connected to the body and comprising a plurality of teeth transverse to the movement direction of the belts in use in the case of toothed belts, or ribs along the direction of movement of the poly-V belt.

Today's engines require the transmission members and in particular the transmission belts to have an increasingly long average working life despite having to operate at high temperatures and with much greater mechanical stress.

In order to prolong the average working life of the transmission belt by reducing its abrasion, it is common practice to provide a layer of material more resistant to abrasion such as, for example, a fabric, a non-woven fabric or a thermoplastic material that covers the ribs at least partially.

However, said solution does not fully solve the problems of ensuring long life.

Furthermore, whether a fabric or a continuous layer of thermoplastic material is used as covering material, both tend to be very stressed and "stretched" at the grooves and ribs during the vulcanization stage. This means that the covering material is weakened at the very points where the stress is greatest during use.

To solve this problem both the fabrics used in the toothed belts and those used in the poly-V belts generally comprise a plurality of threads, including at least one elastic thread which allows the entire fabric to be elastic so that the fabric adheres better to the working surface of the belt, namely to the surface which engages on the pulleys during use, as illustrated for example in the patent <CIT>.

It should furthermore be noted that the above-mentioned covering fabrics entail greater friction between the contact surface of the belt and the pulley. Said greater friction, in addition to further increasing the possibility of breakage, also increases the noise level of the belt during operation.

Alternative technical solutions have therefore been tried in order to obtain simultaneously a high resistance to wear, low noise level, in particular low noise level also in damp conditions, and improved adhesion of the fabric on the body.

The elastic material generally used as elastic thread in the fabrics used in the transmission belts is polyurethane, as illustrated in the same patent described above.

Polyurethane provides adequate elasticity and at the same time does not negatively affect belt performance.

During the manufacturing process of the toothed belts and, in particular, during the vulcanization process, the polyurethane thread generally melts and therefore creates a series of empty spaces in the structure.

These empty spaces inside the belt structure are potentially starting or trigger points for defects that emerge during use of the belt such as cracks, fissures and similar discontinuities that lead to breakages and therefore shorten the life of the belt.

None of the solutions currently on the market simultaneously solve all the problems of the belts and in particular the search is ongoing for a transmission belt with controlled friction, low noise level and at the same time good adhesion, without the problems due to the use of polyurethane.

Due to these problems, the search continues for more performing transmission belts that meet the increasingly stringent specifications established by car manufacturers.

<CIT> discloses an endless power transmission belt made primarily of an elastomeric material and having a load-carrying section, a ribbed section adjacent the load-carrying section with the ribbed section having a plurality of ribs and the ribs being defined by a plurality of alternating projections and recesses, and a knit cover fabric bonded against the ribs and defining the inside surface of the belt with the knit fabric affording extensibility in a plurality of directions to assure the belt is particularly adapted to be operated in associated sheaves with minimum stresses being imposed thereon due to the cover fabric.

The object of the present invention is to provide a toothed or poly-V transmission belt that solves the above-mentioned problems and which, in particular, avoids the discontinuities underlying the defects encountered during use of the belt and at the same time has optimal performance.

The above-mentioned object is achieved by a belt according to claim <NUM>.

The expression "main elastomer" means that it is present in the compound forming the body of the belt by over <NUM>% by weight calculated on the total weight of all the elastomers in the compound, therefore excluding all the other non-elastomeric components of the belt.

The expression "first elastomeric material consists essentially of" means that in addition to all the usual additives, it is possible to add to the compound small percentages of other polymers or copolymers without negatively affecting the chemical compatibility between the body compound and the other elements forming the toothed belt and therefore without departing from the scope of the present invention.

By "elastolefin" we mean a fibrous polymer material composed for at least <NUM>% by weight of partially cross-linked macromolecules, therefore they have low crystallinity and can be spun, in which the macromolecules are composed of ethylene and at least one other olefin. Said fibers are for example XLA like those described in the article "<NPL>. Said fibers are elastic, namely when elongated even by <NUM>% they rapidly return to their original length.

With reference to <FIG>, the number <NUM> indicates a poly-V belt comprising a body <NUM> comprising a first elastomeric material, a plurality of filiform resistant inserts <NUM> embedded longitudinally in the body, also called "cords" below, and a coupling portion <NUM> integrally connected to the body and comprising a plurality, of ribs, in the following also called "V-shaped ribs" <NUM> positioned side by side and alternating with V-shaped grooves <NUM> that form the work surface <NUM>. The belt <NUM> furthermore has a back <NUM> defined by the surface opposite the work surface.

Preferably the body <NUM> is made of a compound comprising one or more elastomeric materials and numerous additives. The elastomeric material(s) are indicated overall for convenience below as "first elastomeric material".

The body <NUM> of the belt advantageously comprises as main elastomer within the first elastomeric material an elastomer selected from the group formed of natural rubber (NR), polychloroprene (CR), acrylonitrile butadiene rubber (NBR) and relative hydrogenated elastomers known as hydrogenated acrylonitrile butadiene rubber (HNBR) or zinc salts of hydrogenated acrylonitrile butadiene rubber grafted with unsaturated carboxylic acid esters, polyisoprene, styrene-butadiene rubbers, ethylene-alpha-olefin elastomers, EPDM, polyurethane, fluoroelastomers, ethylene acrylic elastomers (AEM), bromobutyl, chlorosulfonated polyethylene (CSM) or alkyl-chlorosulfonate, chlorinated polyethylene, epoxidized natural rubber, SBR, NBR carboxylates, HNBR carboxylates, ACM and mixtures of these compounds.

The body <NUM> preferably comprises as first or further elastomeric material at least one copolymer of polyolefin or a rubber containing units of acrylonitrile.

More preferably the first elastomeric material comprises an elastomer selected from the group formed of EPM (ethylene-propylene monomer), EPDM (ethylene-propylene-diene monomer), NBR (acrylonitrile butadiene rubber), HNBR (hydrogenated acrylonitrile butadiene rubber), ZnHNBR (acrylonitrile butadiene rubber with zinc salts), XHNBR (peroxide-vulcanized hydrogenated acrylonitrile butadiene rubber).

In particular, of the rubbers containing units of acrylonitrile, the preferred ones are NBR, HNBR and modified HNBR, for example HNBR modified with zinc salt or ZnHBR or XHNBR. In particular, of the polyolefin copolymers, EPDM is preferred.

Even more preferably the body <NUM> comprises EPDM.

Even more preferably it consists essentially of EPDM.

In particular the embodiment is preferred in which the body comprises more than <NUM>% by weight with respect to the total weight of elastomer, more preferably more than <NUM>% of EPDM.

Alternatively the embodiment in which the body consists essentially of EPDM is also preferred.

The compound of the body can comprise, in addition to the elastomeric materials, conventional additives such as, for example, reinforcing agents, fillers, pigments, stearic acid, accelerators, vulcanization agents, antioxidants, activators, initiators, plasticizers, waxes, prevulcanization inhibitors, antidegradants, process oils and similar.

On the work surface, namely above the ribs, a covering material is generally arranged, preferably a fabric <NUM>, more preferably selected from the group consisting of woven fabric or non-woven fabric or knitted fabric.

Preferably the fabric <NUM> is treated with an elastomeric material. Preferably the fabric <NUM> is a knitted fabric.

The knitted fabric has proved to be particularly preferred when it has a warp-knitted or jersey construction.

The weight of the fabric <NUM> preferably ranges from <NUM> to <NUM>/m<NUM>, more preferably from <NUM> to <NUM>/m<NUM>, for example <NUM>/m<NUM>.

The fabric <NUM> is formed of at least one primary non-elastic thread and a secondary elastic thread, but can also comprise further threads or combine one or more secondary elastic threads with several primary non-elastic threads.

As materials for the primary thread, the polymer materials commonly used in technical fabrics can be advantageously used such as, for example, aliphatic or aromatic polyamides, polyesters, and also natural-based fabrics such as cotton, if necessary also in complex structures or mixed with several threads of chemical type wound over one another.

The use of a fabric comprising primary polyamide threads, preferably an aliphatic polyamide such as nylon <NUM>/<NUM>, is particularly preferred.

Preferably both in warp and weft a fabric with dtex between <NUM> and <NUM> dtex, more preferably between <NUM> and <NUM> dtex, is used.

Preferably the elongation is greater than <NUM>% at <NUM> N in both directions and greater than <NUM>% at <NUM> N. The sample is raw. It is tested on dynamometer as a sample of a <NUM> wide fabric with distance of <NUM> between the two dynamometer clamps. The traction is applied at a speed of <NUM>/min.

In a preferred embodiment, also the back <NUM> of the belt <NUM> is provided with a covering material, more preferably a fabric.

On the back <NUM> a fabric <NUM> is generally arranged preferably selected from the group consisting of woven fabric or non-woven fabric or knitted fabric.

The knitted fabric is particularly preferred when it has a warp-knitted or jersey construction.

According to a preferred aspect of the present invention the fabric <NUM> of the work surface or the fabric <NUM> of the back <NUM> comprise at least one elastolefin thread.

Alternatively it is also possible to combine an elastolefin thread with one or more further elastic threads of different material.

The transmission belt of the present invention is formed preferably according to the well-known molding process.

It has been noted that unlike the case when the fabric comprises a single polyurethane thread, after the belt vulcanization step the elastolefin surprisingly has a different behavior, preventing the formation of empty spaces and defects typical of the use of polyurethane.

In a different embodiment of the invention in <FIG> a toothed belt is indicated overall by the number <NUM>. The belt <NUM> comprises a body <NUM>. In the body <NUM> a plurality of longitudinal filiform resistant inserts <NUM> are embedded, also alternatively called "cords".

The belt further comprises a toothing <NUM> composed of a plurality of teeth <NUM> which in use form the work surface <NUM>, namely the surface that engages on a corresponding pulley of the transmission system.

The toothed belt further comprises a back <NUM> opposite the work surface <NUM>.

Preferably the body <NUM> comprises a first elastomeric compound comprising a first main elastomeric material.

Advantageously the pitch of the belt is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, for example <NUM> ideal for applications on vehicles.

The body <NUM> of the toothed belt advantageously comprises a first elastomeric material selected from the group consisting of natural rubber (NR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR) and relative hydrogenated elastomers known as hydrogenated acrylonitrile butadiene rubber (HNBR) or zinc salts of hydrogenated acrylonitrile butadiene rubber grafted with unsaturated carboxylic acid esters, polyisoprene, styrene-butadiene rubbers, ethylene-alpha-olefin elastomers, EPDM, polyurethane, fluoroelastomers, ethylene acrylic elastomers (AEM), bromobutyl, chlorosulfonated polyethylene (CSM) or alkyl-chlorosulfonate, chlorinated polyethylene, epoxidized natural rubber, SBR, NBR carboxylates, HNBR carboxylates, ACM and mixtures of these compounds.

Advantageously the first elastomeric material is present in the body compound as "main elastomer", namely it is present in the body compound in over <NUM>% by weight calculated on the total weight of all the elastomers in the compound, therefore excluding all the other non-elastomeric components of the belt.

The body <NUM> preferably comprises as first or as further elastomeric material at least one copolymer of polyolefin or a rubber containing units of acrylonitrile.

More advantageously, the copolymer(s) used as body compounds are nitrile rubbers, advantageously they are acrylonitrile butadiene rubbers, known under the acronym NBR. Even more advantageously, they are hydrogenated acrylonitrile butadiene rubbers, or HNBR, or also XHNBR, namely carboxylated hydrogenated acrylonitrile butadiene rubbers.

For example, fully saturated HNBRs, which have a double bond residual percentage of <NUM>% at the most, can be used, but alternatively HNBRs with a lower degree of saturation such as, for example, partially saturated HNBRs having a saturation degree of <NUM>% or <NUM>%, can also be used.

Even more advantageously, in combination with a first elastomeric material, also an elastomeric material formed of a mixture of one or more copolymers is used, obtained from a diene monomer and a monomer containing nitrile groups where an acid or a salt of an unsaturated carboxylic acid are added to one or more of said copolymers. More advantageously the unsaturated carboxylic acid is methacrylic or acrylic acid and said salt is a zinc salt of the methacrylic or acrylic acid. Even more advantageously, a zinc salt of the methacrylic acid is used. Even more advantageously, the zinc salt of the methacrylic acid is added in a quantity ranging from <NUM> to <NUM> phr.

For example, the elastomers sold by Zeon under the following names are advantageously used: ZSC <NUM>, ZSC <NUM>, ZSC <NUM>, ZSC <NUM>, ZSC <NUM>, ZSC 2295R and ZSC <NUM>.

In particular it is possible to partially or entirely substitute the HNBRs previously cited, namely the ZETPOL and/or THERBAN, with a ZSC which comprises an unsaturated carboxylic acid and zinc oxide and/or with THERBAN ART which comprises an unsaturated carboxylic acid salt.

Mixed compounds of polyolefins and rubbers containing units of acrylonitrile, more preferably compounds containing a copolymer of ethylene with NBR or HNBR or the above-mentioned modified HNBRs, are also preferred. For example rubbers containing EPDM (ethylene propylene diene monomer) or EPM (ethylene propylene monomer) can be added to polymers containing units of acrylonitrile in a quantity preferably ranging from <NUM> to <NUM>%.

In addition to the elastomeric materials, the body compound can comprise conventional additives such as, for example, reinforcement agents, fillers, pigments, stearic acid, accelerators, vulcanization agents, antioxidants, activators, initiators, plasticizers, waxes, prevulcanization inhibitors, antidegradants, process oils and similar.

The cords <NUM> are formed of a plurality of threads or strands or yarns and each thread is formed of a plurality of filaments. Preferably the cords <NUM> are made of at least one material selected from the group consisting of glass fibers, aramid fibers, carbon fibers, PBO fibers, even more preferably they have at least outer filaments made of glass, since this material has proved to be particularly critical when it has to be used at low temperatures.

Alternatively the cords can be made of two different materials. Even more preferably at least the outer surface of the cords is made of glass fibers.

Advantageously the work surface of the transmission belt <NUM> is covered by a covering <NUM>. The covering <NUM> is selected more advantageously from the group consisting of woven fabric, knitted fabric, or non-woven fabric.

The covering fabric <NUM> of the toothing <NUM> or the optional covering fabric of the back <NUM> can consist of one or more layers and can be obtained by means of different weaving techniques, for example, by means of the weaving technique known as 2x2 twill.

The covering fabric <NUM>, <NUM> has a structure composed of a weft and a warp.

More advantageously if a woven fabric is used, the covering <NUM>, <NUM> comprises threads which extend substantially in the longitudinal direction of the toothed belt. Generally said longitudinal threads are the weft threads.

Advantageously the weft threads comprise at least an elastic thread and at least a thread with high thermal and mechanical resistance such as, for example, aliphatic polyamide, aromatic or aramid polyamide, PET, polyesters, and also natural-based fabrics such as cotton, if necessary also in complex or mixed structures with several threads of chemical type wound on one another.

The elastic thread serves to facilitate the extension of the fabric so as to follow the profile of the teeth during the vulcanization phase.

Even more advantageously the weft threads comprise an elastic thread and at least one first and one second thread, more preferably the first and the second thread are polyamides, even more preferably they are made of an aliphatic polyamide such as the polyamide <NUM>, <NUM> and an aromatic polyamide such as, for example, a poly-para-aramid, as for example illustrated in the patent <CIT>.

In a preferred embodiment both threads wound around the thread or the elastic threads are made of polyaramid.

In a particularly preferred embodiment of the invention, a transmission belt <NUM> in which the work surface is covered by a fabric in which a first thread of polyaramid fibers is wound around an elastic thread in a first direction S and a second thread of polyaramid fibers is wound in the opposite direction Z around the first thread proved particularly resistant in oil.

According to an aspect of the present invention, the elastic thread comprises fibers of an elastolefin that allows the elasticity of the fabric during formation of the tooth. More preferably there is one elastic thread and it is made entirely of elastolefin. Optionally it is also possible to use several elastic threads including at least one made of elastolefin.

It has been noted that the use of elastolefin as a base for the elastic thread not only allows the fabric to extend correctly during the vulcanization phase to form the work surface, but also avoids the discontinuities that occur when using polyurethane threads.

Advantageously the weft threads comprise para-polyaramid fibers.

For example the weft threads can be formed by winding around a polyurethane thread a pair of para-polyaramid threads, for example Technora threads.

Advantageously the warp threads comprise meta-polyaramid fibers.

The use of meta-polyaramid threads has proved particularly advantageous since it has surprisingly been found that it is able to maintain optimal tension values also at high temperatures and in oil mixed with petrol. In particular Conex threads, even more preferably in configuration <NUM>/<NUM>, have proved to be particularly advantageous.

Advantageously fabrics are used that have weft threads composed of an elastolefin thread on which two poly para-aramid threads are wound with an overall tensile strength of the fabric pretreatments in the longitudinal direction of the belt ranging from <NUM> to <NUM> N/<NUM>, even more advantageously from <NUM> to <NUM> N/<NUM>.

Advantageously fabrics are used which have warp threads composed of a poly meta-aramid thread with an overall elasticity of the fabric in the latitudinal direction ranging from <NUM> to <NUM> N/<NUM>, even more advantageously from <NUM> to <NUM> N/<NUM>.

Advantageously fabrics are used having a post-treatment weight ranging from <NUM> to <NUM> grams/m<NUM>. Even more advantageously from <NUM> to <NUM> grams/m<NUM>.

The fabric <NUM>, <NUM> generally undergoes a first, a second, third and fourth treatment.

Said treatments have proved to be very advantageous, ensuring long life of the belt in continuous contact with oil at high temperature.

Advantageously the first treatment is based on poly-isocyanates.

The first treatment proved to be particularly effective in ensuring adhesion of the polyaramid fibers, and therefore in the case of the present invention the entire fabric, to the body elastomers.

Advantageously the fabric <NUM>, <NUM> subsequently undergoes a second treatment with RFL.

Advantageously the fabric <NUM>, <NUM> subsequently undergoes a third rubber-based treatment, also called cement, preferably a hydrogenated nitrile rubber, for example a Zetpol.

Furthermore preferably the fabric <NUM> of the work surface <NUM> of the toothed belts <NUM> of the present invention is covered with a fourth treatment, even more preferably said treatment forms a layer <NUM> which is for example calendered over the fabric to form a separate layer.

Said layer <NUM> preferably comprises a fluorinated polymer, for example PTFE, and a treatment elastomer, for example a material similar to the one used for the body compound or a fluoroelastomer.

Advantageously one or more copolymers formed from a monomer containing nitrile groups and a diene can be used as elastomers for the fourth treatment.

Advantageously the monomers containing the nitrile groups are in a percentage ranging from <NUM> to <NUM>% with respect to the total final copolymers.

More advantageously they are between <NUM> and <NUM>% by weight for cold applications with temperatures down to -<NUM>, between <NUM> and <NUM>% by weight for belts with dry applications and between <NUM> and <NUM>% by weight for applications in oil.

Even more advantageously for applications in oil they are between <NUM> and <NUM>% by weight, for example <NUM>% by weight, while for dry applications they are between <NUM> and <NUM>% by weight, for example <NUM>% by weight.

More advantageously the treatment copolymer(s) used are nitrile rubbers and/or fluoroelastomers, even more advantageously they are acrylonitrile butadiene rubbers, known under the acronym NBR. Even more advantageously they are hydrogenated acrylonitrile butadiene rubbers or HNBR or they are also XHNBR, namely carboxylated hydrogenated acrylonitrile butadiene rubbers.

By appropriately choosing the quantities of the materials composing the fourth treatment, a covering layer is formed distinct and separate from the fabric, below also called resistant layer <NUM>. Advantageously the fluorinated polymer is present in the resistant layer <NUM> in a quantity greater in phr than the sum of the fluorinated elastomer and the second elastomeric material.

The thickness of the resistant layer <NUM> advantageously ranges from <NUM> to <NUM>.

The resistant layer <NUM> can be arranged over the fabric <NUM> in different ways. Preferably it is arranged by means of a calendering step.

Between the fabric <NUM> and the resistant layer <NUM> an adhesive material can be arranged to improve the adhesion of the resistant layer <NUM> on the fabric <NUM>.

Preferably, to ensure the necessary resistance, the resistant layer <NUM> has a weight ranging from <NUM> to <NUM>/m<NUM>.

Preferably also the back <NUM> of the belt is covered by a covering fabric <NUM> comprising at least an elastic thread made of elastolefin, even more preferably the fabrics on the work surface <NUM> and on the back <NUM> are identical.

Preferably also the covering fabric <NUM> of the back <NUM> is treated with different treatments. Treating the back <NUM> with a treatment similar to the fourth treatment of the fabric <NUM> covering the work surface <NUM> described above was found to be particularly advantageous. More advantageously said fourth treatment forms a resistant layer over the fabric. Even more preferably the resistant layer that covers the covering fabric <NUM> of the back <NUM> is identical to the one that covers the covering fabric <NUM> of the teeth.

Preferably both in warp and weft a fabric is used with dtex ranging from <NUM> to <NUM> dtex, more preferably from <NUM> to <NUM> dtex.

Preferably the weft elongation is greater than <NUM>% % at <NUM> N and greater than <NUM>% % at <NUM> N. The sample is raw. It is tested on dynamometer as a sample of a <NUM> wide fabric and the distance between the two dynamometer clamps is <NUM>. It is elongated at a speed of <NUM>/min.

From an examination of the characteristics of the belt produced according to the present invention, the advantages it offers are evident.

Using a transmission belt, both poly-V and toothed, according to the present invention considerable improvements have been obtained and, in particular, it has been possible to overcome the problems described above. In particular, thanks to the use of a fabric <NUM>, <NUM>, <NUM>, <NUM> as fibrous covering material it is possible to obtain at low cost an elastic fabric that adapts optimally to the profile of the ribs <NUM> or the teeth <NUM>.

Claim 1:
A power transmission belt (<NUM>, <NUM>) comprising a body (<NUM>, <NUM>) in a first elastomeric material, a plurality of cords (<NUM>, <NUM>) embedded in the body of the belt, a back (<NUM>, <NUM>) and a plurality of ribs (<NUM>) or teeth (<NUM>), said back (<NUM>) or said ribs (<NUM>) or teeth (<NUM>) are covered with a covering material (<NUM>, <NUM>, <NUM>, <NUM>) selected from the group consisting of woven fabric, knitted fabric, characterized in that said covering material comprises elastolefin fibers.