Power transmission belt and related transmission system

Abstract

A power transmission belt comprising a body (102) made of a compound comprising a main elastomer, a toothing (104) and a plurality of longitudinal cords (103) embedded in the belt body and a backing (107), wherein: - the main elastomer constitutes at least 70% by weight of all the elastomeric materials of the body - the main elastomer is a copolymer of ethylene alpha olefin - the body comprises at least 12% by weight of fibres - the fibres are selected from the group consisting of glass, aramid, polyester, carbon, poly(p-phenylene-2,6-benzobisoxazole) PBO, polyamide, polyether ether ketone (POK), polyether ether ketone (PEEK), polyvinyl acetate (PVA), liquid crystal (LPC), polyethylene naphthalate (PEN), aliphatic polyamide - the fibres are between 1 and 6 mm in size - the teeth are covered with a covering material (108) selected from the group consisting of woven fabric, knitted fabric, non-woven fabric - the covering material is treated with a polymer containing nitrile groups - the covering material is coated with a second treatment (109) comprising an elastomer and an anti-friction material.

Description

[0001] POWER TRANSMISSION BELT AND RELATED TRANSMISSION SYSTEM

[0002] Cross-Reference o Related Applications

[0003] This Patent Application claims priority from Italian Patent Application No . 102023000015384 filed on July 21 , 2023 , the entire disclosure of which is incorporated herein by reference .

[0004] Technical Sector

[0005] The present invention relates to a power transmission belt and, in particular, to a toothed belt and the related transmission system .

[0006] State of the Prior Art

[0007] The present invention is preferably used for the transmission of motion in a transmission assembly comprising a motor .

[0008] The transmission of motion preferably takes place by using synchronous power transmission belts , also referred to as toothed belts .

[0009] The belt can be used both for motion transmission in motor vehicles and for industrial applications .

[0010] Transmission belts generally comprise a body made of elastomeric material, preferably of HNBR for toothed belts, a plurality of threadlike resistant inserts embedded longitudinally in the body, and a coupling portion integrally connected to the body and comprising a plurality of teeth that are transverse to the sliding direction of the belts in use in the case of toothed belts .

[0011] A typical problem of toothed belts is that they must be oil-resistant .

[0012] Recently, automotive engines have been developed that include a timing transmission system in which chains have been replaced by power transmission belts in the same working environment and thus in continuous contact with oil or an oil mist .

[0013] Such systems have been illustrated in patents by the applicant , such as W02005 / 080820 . In these drive systems , the power transmission belt is known as a "belt in oil" or "wet belt" and must be able to meet the same longevity requirements as equivalent chain drive systems . In the context of the present invention, "belt in oil" or "wet belt" means a power transmission belt used in power transmission systems in which it is at least partially immersed in oil at rest and / or during operation, or in transmission systems in which the power transmission belt is continuously in contact with oil or with a mist of oil , for example systems in which oil is supplied to the power transmission belt , for example in the form of a spray by means of a specially designed noz zle or by shaking due to the action of the power transmission belt and the pulleys .

[0014] In particular, in these transmission systems there are no separation means between the oil lubricating the engine and the transmission system .

[0015] Oil drive belts must therefore withstand continuous contact with the high-temperature oil during engine operation and not be damaged, either at high operating temperatures or at very low temperatures .

[0016] In particular, it is therefore crucial that the body compound, which must be oil-resistant even at high temperatures , avoids or at least reduces oil absorption and maintains good abrasion resistance . To this end, drive belts must have a better combination of oil swell characteristics and low temperature resistance than those currently on the market .

[0017] Drive systems in which the power transmission belt is wet with oil and / or runs continuously in oil are generally very similar to those in which a chain is used for the transmission of motion .

[0018] Materials suitable for use in drive belt housings , e . g . hydrogenated nitrile rubber (HNBR) or HNBR terpolymers , are well known .

[0019] A further disadvantage of known drive belts is that their excellent flexibility and resistance to oil swelling cannot be adj usted independently of each other . Generally, in HNBR there are relationships between the acrylonitrile monomer (ACN for short ) content , glass transition temperature and oil swelling . This means that oil swelling decreases with increasing ACN content , i . e . with increasing polarity . At the same time , however, there is an increase in the glass transition temperature . However, known HNBR polymers are still very expensive and do not always allow for ideal belt operation in contact with oil and particularly at low temperatures .

[0020] Due to supply di f ficulties , the use of nitrile rubbers has become more and more di f ficult and is now an obstacle to the use of nitrile rubber-based products .

[0021] Therefore , the belts currently used do not completely solve the problems mentioned .

[0022] Therefore , there is a constant search for drive belts that meet the increasingly stringent speci fications imposed by car manufacturers and, in particular, still allow for a high service li fe .

[0023] Summary of the Invention

[0024] The obj ect of the present invention is to provide a drive belt which solves the above-mentioned problems and is achieved by a belt according to claim 1 and the transmission system of claim 10 .

[0025] Brief Description of the Drawings

[0026] - Figure 1 is a schematic and partial view of a portion of a toothed belt ;

[0027] - Figure 2 a graph of the swelling pattern in oil of belts with di f ferent fibre percentages ;

[0028] - Figure 3 is a table showing a durability test for di f ferent comparison belts and according to the invention; and

[0029] - Figure 4 is a graph representing a constant torque noise test ; and

[0030] - Figure 5 represents a diagram of the transmission system for the noise test in Figure 4 .

[0031] Description of the Invention

[0032] A "main elastomer" is defined as an elastomer in the compound constituting the belt body constituting more than 70% by weight of the sum of elastomers in the compound constituting the body . Further components such as additives or fillers are then added to the elastomers .

[0033] The term " first elastomeric material essentially consists of" means that the elastomeric material is the only elastomer that determines the physical and chemical characteristics and performance of the compound constituting the body, even i f , in addition to the normal additives , further small percentages of other elastomeric polymers or copolymers can be added to the compound without adversely af fecting the functionality and chemical compatibility between the body compound and the other elements making up the toothed belt , and thus without departing from the scope of the present invention .

[0034] In the following, "elastomeric material additive" refers to a type of material that is added to the elastomeric material to modi fy its chemical and physical characteristics .

[0035] Use " in oil" or " in oil mist" means that the power transmission belt is used partially immersed in an oil bath or is continuously in direct contact with oil or oil mist . Generally, the oil drive belt in use is inside the engine block, e . g . as a replacement for chain or gear systems .

[0036] In the following, the names of the polymer acronyms follow ISO 1043- 1 : 2011 .

[0037] In an embodiment of the invention in Figure 1 , 101 denotes a toothed belt as a whole .

[0038] The toothing can optionally be helical , preferably with a helix angle comprised between 1 ° and 15 ° .

[0039] The belt 101 comprises a body 102 made of a main elastomer . A plurality of longitudinally threadlike resistant inserts 103 also alternatively referred to as "cord" are embedded in the body 102 .

[0040] The belt further comprises a toothing 104 composed of a plurality of teeth 106 which in use constitute the working surface 105 , i . e . the surface that meshes on a corresponding pulley of the transmission system .

[0041] The toothed belt further comprises a back 107 opposite the working surface 105 . The body 102 comprises an ethylene-alpha-olef in copolymer as the main elastomer.

[0042] Preferably, the main elastomer is present for more than 90% by weight of the total weight of the elastomers in the compound body.

[0043] Even more preferably, the main elastomer is present for more than 95% by weight of the total weight of elastomers in the compound body.

[0044] The main elastomer is present for more than 30% by weight of the total weight of the compound, even more preferably for more than 40%, and even more preferably between 40% and 50%.

[0045] The sum of the weight of the main elastomer and the fibres is more than 50% by weight of the total weight of the compound, even more preferably more than 60% by weight.

[0046] Preferably the ethylene-alpha-olef in copolymer is EPDM (ethylene-propylene-diene-monomer) or EPM (ethylene- propylene-monomer ) .

[0047] In addition to the elastomeric materials, the body compound may comprise conventional additives such as, for example, reinforcing agents, fillers, pigments, stearic acid, accelerators, vulcanizing agents, antioxidants, activators, initiators, plasticizers, waxes, prevulcanization inhibitors, antidegradants, process oils, and the like.

[0048] Advantageously, the body compound also comprises reinforcing fibres, more advantageously the compound comprises between 12 and 30% by weight of fibres, more preferably between 12 and 18% by weight.

[0049] The reinforcing fibres are comprised between 0.1 and 10 mm in length, preferably between 1 and 6 mm, even more preferably between 1 and 3 mm .

[0050] The use of fibres makes it possible to further increase the mechanical characteristics of the mixture that makes up the body .

[0051] The fibres are therefore present throughout the body, including the region surrounding the cords , which allows for greater rigidity .

[0052] Preferably, the fibres are fibres cut to a certain length or " staple" . "Staple" fibres are defined as textile fibres of discrete length .

[0053] The reinforcing fibres preferably comprise at least one substance selected from the group consisting of polyamide , aromatic polyamide , polyester, glass , PBO carbon fibres , more advantageously aliphatic polyamides , even more so polyamide 6 or polyamide 66 , which can be made to adhere to the mixture by means of a treatment , preferably RFL-based .

[0054] The treatment used may also have a base of VP-SBR, i . e . a copolymer of vinylpyridine and styrene-butadiene .

[0055] The cords 103 are formed by a plurality of threads or burrs or yarn and each thread is formed by a plurality of filaments .

[0056] Cord 103 preferably comprises high-modulus fibres , plus preferably at least one material chosen from the group consisting of carbon, PBO, aramid, polyamide , glass or polyester fibres .

[0057] Cords can advantageously be of the "hybrid" type , i . e . composed of at least a first fibrous material and a second fibrous material .

[0058] The use of cords 103 made up of two materials in the form of di f ferent fibres or filaments allows for better adhesion of the cord 3 to the mixture that constitutes the belt body .

[0059] The cords 103 are preferably treated with an aqueousbased treatment known as reactive impregnation, but can also be treated in a similar manner or with RFL, i . e . a composition based on latex, resorcinol and formaldehyde .

[0060] In the case of cords 103 comprising two fibrous materials , both the first and second materials are preferably chosen from the group consisting of glass fibres , aramid fibres , polyester fibres , carbon fibres , PBO fibres , polyamide fibres , polyketone ( POK) fibres , PEEK fibres , polyvinyl acetate ( PVA) fibres , liquid crystal fibres ( LPC ) and PEN fibres .

[0061] The first material preferably has a lower modulus than the second material and is preferably wound around the second material .

[0062] Preferably, in the cross-section the second material occupies between 15 and 75% of the total cross-sectional area . Even more preferably, the second material occupies between 45 and 55% of the total surface area .

[0063] Even more advantageously, in cross- section the f ibres of the two materials occupy similar surface areas , so that the positive characteristics of both are balanced as much as possible to achieve the best performance on the belt .

[0064] The first material is preferably glass fibre and the second material is preferably carbon fibre .

[0065] Preferably, the fibres of the first material are wound around the fibres of the second material in such a way that the fibres of the first material are at least partially coated externally, and even more preferably so that the fibres of the second material are entirely coated .

[0066] Preferably, the cords 103 have a Lang ' s twist , i . e . two twists in the same direction .

[0067] The number of fi laments forming the cord, as wel l as the number of base filaments or the count or the entire implementation of the insert , can be varied .

[0068] In order to achieve the best performance , the number of strands formed by the fibres of the first material is preferably comprised between 3 and 18 , and preferably between 8 and 15 .

[0069] Both the toothing 104 and the backing 107 can be covered with a covering material 108 that is generally used to modi fy the mechanical properties of the surface . The covering material can for example be a fabric, polymer film, treatment , anti- friction coating, etc .

[0070] Alternatively, it is also possible to use several covering materials such as , for example , a fabric onto which a layer of a mixture of elastomeric material and PTFE is calendared .

[0071] Advantageously, the working surface of the drive belt 101 is covered with a covering material 108 chosen more from the group consisting of woven fabric, knitted fabric or nonwoven fabric .

[0072] The covering material 108 covering the toothing 105 or the optional fabric covering the backing 110 preferably consist of a fabric formed by one or more layers and may be obtained by di f ferent weaving techniques , for example , by the weaving technique known as 2x2 twill .

[0073] The covering fabrics preferably have a structure consisting of a warp and weft .

[0074] More advantageously in the case of use of a woven fabric, the covering material 108 , 110 comprises threads extending substantially in the longitudinal direction of the toothed belt . Generally, such longitudinal threads are the weft threads .

[0075] Advantageously, the weft threads comprise at least one elastic thread and at least one thread with high thermal and mechanical resistance , such as for example aliphatic polyamide , aromatic polyamide or aramid, PET , polyesters , but also natural-based fabrics like cotton possibly also in complex or mixed structures with multiple threads of a chemical nature wound one on top of the other .

[0076] Even more advantageously the weft threads comprise an elastic thread and at least a f irst and a second thread, more preferably the first and the second thread are polyamides , even more preferably they are made of an aliphatic polyamide such as polyamide 6 , 6 and an aromatic polyamide , such as for example a para-polyaramide , as for example shown in patent EP0965271 .

[0077] In a preferred embodiment both threads winding the elastic thread ( s ) are made of polyaramide .

[0078] In a particularly preferred embodiment of the invention, the work surface is covered with a fabric in which a first strand of polyaramide fibres is wound around an elastic thread in a first direction S and a second strand of polyaramide fibres is wound in the opposite direction Z around the first strand .

[0079] Advantageously, the weft threads comprise para- polyaramide fibres . For example , the weft threads can be formed by winding a pair of para-polyamide threads , e . g . Technora threads , around a polyurethane thread .

[0080] Advantageously, the warp threads comprise meta- polyaramide fibres .

[0081] The fabric 108 , 110 generally undergoes a plurality of treatments .

[0082] Such treatments have proven to be very advantageous for the belt to have a long li fe in continuous contact with oil at high temperature .

[0083] Advantageously, an initial treatment can be based on poly-isocyanates useful for making the polyaramide fibres and thus the entire fabric adhere to the elastomers of the body .

[0084] Advantageously, the fabric 108 , 110 is subsequently subj ected to a second treatment with RFL .

[0085] Also in this case , preferably the latex i s an elastomeric material formed by a mixture of one or more copolymers , obtained from a diene monomer and a monomer containing nitrile groups , modi fied with a salt of an unsaturated carboxylic acid .

[0086] Advantageously, the fabric 108 , 110 is further subj ected to a third treatment based on a rubber, also known as a cement , preferably comprising an elastomeric material , more preferably a hydrogenated nitrile rubber, even more preferably an elastomeric material formed by a mixture of one or more copolymers , obtained from a diene monomer and a monomer containing nitrile groups , modi fied with a salt of an unsaturated carboxylic acid, and even more preferably the same elastomeric material constituting the body . Furthermore , preferably the fabric of the working surface 105 of the toothed belts 101 of the present invention is covered with a fourth treatment , even more preferably this treatment forms a layer 109 which is , for example , calendered on top of the fabric to form a separate layer .

[0087] This layer 109 preferably comprises an anti- friction material .

[0088] An anti- friction material is defined as a material that is capable of varying the friction between the working surface of the belt and the pulley .

[0089] Examples of anti- friction materials are fluorinated polymers , molybdenum sulphide , copper powder .

[0090] Preferably it is a fluorinated polymer, e . g . PTFE .

[0091] Advantageously, the layer 109 also comprises a treatment elastomer, e . g . a material similar to that used for the body compound or a fluoroelastomer .

[0092] Thus , one or more copolymers formed by a monomer containing nitrile groups and a diene , and more preferably an elastomeric material formed by a mixture of one or more copolymers , obtained from a diene monomer and a monomer containing nitrile groups , modi fied with a salt of an unsaturated carboxylic acid, and even more preferably the same elastomeric material used as the main elastomer in the body compound, may be used as elastomers for the fourth treatment .

[0093] By appropriately choosing the quantities of the materials of which the fourth treatment is composed, a covering layer is conveniently formed that is distinct and separate from the fabric itsel f , also referred to hereafter as the resistant layer 109 . Advantageously, the elastomeric material is present in the resistant layer 109 in greater quantities in phr than the sum of the fluorinated elastomer and the second elastomeric material .

[0094] The thickness of the resi stant layer 109 is advantageously comprised between 0 . 03 mm and 0 . 3 mm .

[0095] The resistant layer 109 can be arranged on top of the fabric 108 in di f ferent ways . It is preferably arranged by means of a calendering step .

[0096] An adhesive material can be placed between the fabric 109 and the resistant layer 108 to improve the adhesion of the resistant layer 109 onto the fabric 108 .

[0097] Preferably the resistant layer 108 has a weight comprised between 200 and 400 g / m2to ensure the necessary resistance .

[0098] Preferably, the backing 107 of the belt is also covered with a fabric, even more preferably the fabric on the working surface 105 and on the backing 107 are the same and are treated with the same materials .

[0099] Preferably, the fabric covering the backing 107 is also treated with di fferent treatments . It proved particularly advantageous to treat the backing 107 with a treatment similar to the fourth treatment of the fabric 108 covering the working surface 105 described above . More advantageously, this fourth treatment forms a resistant layer on top of the fabric . Even more preferably, the resistant layer covering the fabric 110 covering the backing 107 is the same as the one covering the fabric 108 covering the teeth .

[0100] From an examination of the characteristics of the belt made according to the present invention, the advantages that it allows obtaining are evident .

[0101] Considerable improvements have been obtained by using a toothed drive belt according to the present invention and, in particular, the problems set out above have been overcome . In particular, optimum belt life combined with limited oil absorption can be achieved.

[0102] The invention will be described below by means of examples , but is not intended to be limited to them.

[0103] Example 1

[0104] Belts are made that are distinguished by the composition of the body compound.

[0105] The fabric covering the belt is made of polyamide 66 with a raw weight of 380 g / m2and is treated with an HNBR compound .

[0106] The toothing is non-helical . The cord is type K glass with RFL treatment .

[0107] The belt also comprises a nylon polyamide 66 backing fabric with a raw weight of 380 g / m2.

[0108] The comparative belt of Example 1 comprises a body made from the compound in Table 1 .

[0109] Table 1 The belt of the invention of Example 1 comprises a body made from the compound in Table 2 .

[0110] Table 2 The table in Figure 3 shows oil contamination tests on belts with a high fibre content according to the present invention and belts comprising lower fibre percentages as shown in the graph .

[0111] Belts according to the present invention comprise 15% by weight of nylon fibres , whereby the percentage is given with respect to the total weight of the body compound .

[0112] The comparison belts comprise 4% fibres and 8% fibres , respectively .

[0113] The bar graph expressing the duration shows that the solution with 15% fibres allows a minimum performance of more than 60 hours , the minimum duration required to consider the test passed.

[0114] Example 2 Figure 3 shows a graph with so-called drag tests including average values and the dispersion for the four belt types in

[0115] Figure 2 .

[0116] The test is performed on the 4-cylinder VW EA189 type engine with a belt of the same dimensions as those sold with part number 160CWC150 . The temperature is set to 140 °C, the belt tension is set to 1700N . The motor speed is 3750 rpm.

[0117] The example according to the invention with 15% by weight fibres enables similar performance to belts with HNBR . Belts with lower fibre percentages do not actually achieve sufficient performance to pass the 60-hour limit .

[0118] It is clear that below a certain fibre % , the belt does not guarantee the required minimum service life .

[0119] Example 3

[0120] Figure 4 shows the result of a comparative test between a belt made according to the invention ( line A) and a comparison belt ( line B) subj ected to a timing belt endurance test, with the layout shown in Figure 5.

[0121] The parameters for the test are : belt type 150 - pitch 8 - 150 , 150 teeth and 15 mm width .

[0122] The temperature is room temperature ( 20 °C)

[0123] The toothed pulleys have 22 teeth .

[0124] The motor pulley speed is set to 6000 rpm

[0125] The system comprises a three-toothed pulley layout, with a drive pulley, a driven pulley and an idler, the latter being adjustable to set a suitable tension on the belt before starting the test .

[0126] The bench allows torque transmission in a range between 7 and 25 Nm. The torque to be transmitted is considered a test parameter and an appropriate mounting voltage is also associated with it, chosen in such a way as to prevent tooth j umps during the test . Each test corresponds to a torque to be transmitted and thus to a branch tension . As the torque to be transmitted increases, there is obviously a reduction in duration (power transmission always takes place under stationary conditions ) .

[0127] The graph in Figure 4 therefore shows the distribution of durations , obtained for a reference structure ( line B) and the structure according to the new invention ( line A) , when both are subj ected to the same stationary loading conditions . This shows the performance advantage of the belt according to the new invention ( line A) .

Claims

CLAIMS1. A power transmission belt comprising a body (102) made of a compound comprising a main elastomer, a toothing(104) and a plurality of longitudinal cords (103) embedded in the belt body and a backing (107) , characterised in that- said main elastomer constitutes at least 70 % by weight of all elastomeric materials of the body- said main elastomer is a copolymer of ethylene alpha olefin- said body comprises at least 12 per cent by weight of fibres- said fibres are selected from the group consisting of glass, aramid, polyester, carbon, poly(p- phenylene-2 , 6-benzobisoxazole ) PBO, polyamide, polyether ether ketone (POK) , polyether ether ketone (PEEK) , polyvinyl acetate (PVA) , liquid crystal (LPC) , polyethylene naphthalate (PEN) , aliphatic polyamide- said fibres are between 1 and 6 mm in size- the teeth are covered with a covering material (108) selected from the group consisting of woven fabric, knitted fabric, non-woven fabric- said covering material is treated with a polymer containing nitrile groups- said covering material is coated with a second treatment (109) comprising an elastomer and an antifriction material.

2. Transmission belt (101) according to claim 1, characterised in that said ethylene alpha olefin copolymer is ethylene propylene diene monomer (EPDM) or ethylenepropylene monomer (EPM) .

3. Transmission belt (101) according to claim 1 or 2, characterised in that said main elastomer is present for more than 90% by weight.

4. Transmission belt (101) according to claim 1 or 2, characterised in that it comprises fibres for at least 14% by weight.

5. Transmission belt (101) according to any one of the preceding claims, characterised in that said fibres are of nylon.

6. Transmission belt (101) according to any one of the preceding claims, characterised in that said fibres have a length between 1 and 3 mm.

7. Transmission belt (101) according to any one of the preceding claims, characterised in that said fibres are staple fibres.

8. Transmission belt (101) according to any one of the preceding claims, characterised by the fact that said main elastomer is present for more than 30% by weight with respect to the total weight of the compound.

9. Transmission belt (101) according to any one of the preceding claims, characterised in that the sum of the weight of said main elastomer and the weight of said fibres is more than 45 % by weight with respect to the total weight of the compound.

10. A power transmission system comprising a drive belt according to any one of claims 1 to 9 in continuous contact with oil or an oil mist.

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