Power transmission belt

Abstract

Power transmission belt comprising a body (2) formed of a compound comprising a main elastomer, and a plurality of longitudinal cords (3) embedded in the belt body and a back (7). The cords have an elastic modulus varying less than 10% in a range of tension applied to the cord between 4.5% and 8.5% of the breaking load of the cord itself.

Description

[0001] "POWER TRANSMISSION BELT"

[0002] Cross-Reference to Related Applications

[0003] This Patent Application claims priority from Italian Patent Application No. 102023000026424 filed on December 12, 2023, the entire disclosure of which is incorporated herein by reference.

[0004] Technical Sector

[0005] The present invention relates to a reinforcement insert for a power transmission belt and, in particular, to the corresponding transmission belt.

[0006] Background

[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 toothed transmission belts, also referred to as polyV.

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

[0010] Transmission belts generally comprise a body of elastomeric material, a plurality of resistant thread-like inserts embedded longitudinally in the body also called cords, and a coupling portion integrally connected to the body.

[0011] In the case of polyV belts, the coupling portion comprises a plurality of ribs, hereafter referred to as V-shaped ribs, arranged side by side and alternated with V-shaped grooves. The resistant inserts or cords particularly contribute to ensuring to the belt the necessary mechanical characteristics and contribute in an essential way to determining the modulus of the belt itself and, in particular, ensure the maintenance of performance over time. The cords are generally obtained by twisting high modulus fibres several times.

[0012] The resistant inserts are normally treated with compounds adapted to increase the compatibility of the fibres with the body compound surrounding the cords themselves.

[0013] The body compound makes it possible to connect the various aforesaid elements and ensure that they contribute synergistically to the final performance of the belt itself.

[0014] Finally, the fabric covering the working surface of the belts has the task of increasing the abrasion resistance and therefore protects the working surface of the belt from wear.

[0015] The wrapping step of a belt is one of the critical moments in the process of making transmission belts. In fact, despite all the attempts to standardize production and to understand the effects of the various steps on the life of the belts, the belts produced are still inexplicably different in terms of life due to different factors that interact during the steps of making the belt.

[0016] The methods for making belts that are currently used evidently do not allow to completely solve the problems mentioned, but it is not clear how to act on the different production steps and on the materials used to improve the situation.

[0017] It is known that the processes for making the belts comprise a series of manual, semi-automatic or automatic steps, during which the materials used to form the belts are subjected to a variety of physical and chemical type stresses.

[0018] A very important step is the deposition of the cord on the layers of body or fabric mixture wound or fitted on suitably sized cylinders.

[0019] The deposition step depends on the nominal development of the belt defined in the drawing.

[0020] The cord is unwound from its own reel and runs along a circuit consisting of rollers and guides, which allow it to be deposited on the materials, be they fabrics or layers of compound, already wound on the wrapping cylinders with an appropriate spiral pitch and with an appropriate laying tension.

[0021] Laying control is of particular importance for compliance with the dimensional specifications of the finished product.

[0022] The control of these delicate steps affects the performance of the belt in a way that is not entirely clear Lo da.e.

[0023] Therefore, there is a constant search for methods for making or wrapping transmission belts and the corresponding belts that enable to meet the increasingly stringent specifications imposed by the users and that, in particular, still allow for a high durability.

[0024] Summary of the Invention

[0025] Aim of the present invention is the realization of a transmission belt of a corresponding transmission system and of a process of making a transmission belt.

[0026] This aim is achieved by a transmission belt according to claim 1, by a transmission system according to claim 11 and by a process of making a belt according to claim 12.

[0027] Brief Description of the Drawings

[0028] - Figure 1 is a schematic view of a polyV belt according to the present invention;

[0029] Figure 2 is a table reporting some physical characteristics of a cord according to the invention and of a comparison cord as reported in examples 1 and 2;

[0030] - Figure 3 is a graph reporting the trend of the elastic modulus of the cord of the invention and of a comparison cord plotted with respect to a percentage of the breaking load of the cords;

[0031] - Figure 4 represents a diagram of the transmission system for the fatigue test from which the elongation results are extracted at the end of the test of Fig. 5;

[0032] - Figure 5 is a graph representing the result of the bending fatigue test to which the belts have been subjected and reports the % elongation values of the belts at the end of the comparison test between a belt according to the invention and a comparative belt; and

[0033] - Figure 6 is a graph reporting the result of the bending fatigue test to which the belts have been subjected, in particular it reports the decay values of the breaking load [%] of the belts at the end of the comparison test between a belt according to the invention and a comparative belt.

[0034] Description of the Invention

[0035] A "main elastomer" is defined as an elastomer in the compound constituting the belt body constituting more than 50% 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.

[0036] The term "first elastomeric material essentially consists of" is intended to mean that the elastomeric material is the only elastomer that determines the physical and chemical characteristics and performance of the compound constituting the body, even if, in addition to the normal additives, further small percentages of other elastomeric polymers or copolymers can be added to the compound without adversely affecting 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.

[0037] In the following, "elastomeric material additive" refers to a type of material that is added to the elastomeric material to modify its chemical and physical characteristics thereof.

[0038] "Textured" means that the fabric comprises a heat and mechanically treated yarn so that it assumes a structure or conformation of the individual filaments adapted to increase its extensibility and its elastic memory.

[0039] "Warp" in the context of the present invention means the set of threads that in use in the belt are positioned in the direction in which a high extensibility of the fabric is not required.

[0040] "Weft" means the set of threads that in use in the belt are positioned in the direction in which a high extensibility of the fabric is required during the moulding step.

[0041] "Polyaramide" or "aromatic polyamide" means a polyamide obtained from at least one monomer containing an aromatic ring.

[0042] "Para-aramide" means a polyamide containing at least two aromatic rings side by side in the polymer chain, which are bonded in the para position (atom 1 and 4). Examples of such materials are Kevlar®, Technora®, Heracron® and Twaron®.

[0043] "Meta-aramid" means a polyamide containing at least two aromatic rings side by side in the polymer chain which are bonded in the meta position (atom 1 and 3).

[0044] Examples of such materials are Conex® and Nomex®.

[0045] In the following, the names of the acronyms of the polymers follow ISO 1043-1:2011.

[0046] The belt is preferably a polyV belt.

[0047] In the embodiment of the invention of Figure 1, 1 denotes as a whole a polyV belt.

[0048] With reference to Figure 1, 1 denotes a poly-V belt comprising a body 2 comprising a first elastomeric material, a plurality of thread-like resistant inserts 3 embedded longitudinally in the body, and a coupling portion 4 integrally connected to the body and comprising a plurality of ribs, hereinafter referred to as V-shaped ribs 5 arranged side by side and alternated with V-shaped grooves 6. The belt also has a back 7.

[0049] The poly-V belt may further comprise a layer of a thermoplastic material that at least partially covers the ribs 5 and / or a fabric.

[0050] The body 2 comprises as main elastomer an elastomer selected from the group consisting of natural rubber (NR), polychloroprene (CR), acrylonitrile butadiene (NBR) and relative hydrogenated elastomers known as hydrogenated acrylonitrile butadiene (HNBR) or zinc salts of hydrogenated acrylonitrile butadiene grafted with unsaturated carboxylic acid esters, polyisoprene, styrene-butadiene rubbers, ethylene-alpha-olefin elastomers, EPDM, polyurethane, fluoroelastomers, ethylene-acrylic elastomers (AEM), bromine-butyl, chlorosulfonated polyethylene (CSM) or alkylchlorosulfonated one, chlorinated polythene, epoxidized natural rubber, SBR, carboxylated NBR, carboxylated HNBR, ACM and mixtures of these compounds.

[0051] More preferably the main elastomer comprises as first or as further elastomeric material at least a polyolefin copolymer or a rubber containing acrylonitrile units.

[0052] For example, elastomers or rubbers containing EPDM acronym for Ethylene propylene diene monomer or EPM acronym for Ethylene propylene monomer.

[0053] 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.

[0054] The cords 3 are formed by a plurality of threads or filaments or strands or yarns twisted together to form the cord and each thread is formed by a plurality of filaments or yarns twisted together to form the strands.

[0055] Each strand is formed of at least a plurality of twisted filaments or yarns.

[0056] The direction of rotation of the respective strand is equal to or opposite to the direction of rotation of the filament.

[0057] In the context of the present invention, any linear structure consisting of textile fibres is referred to as a filament.

[0058] Such fibrous materials may be fibres, in particular staple fibres or filaments.

[0059] The filaments usually refer to fibres at least 1000 mm long.

[0060] The strands are preferably formed by torsion of one or more filaments. This torsion is also called twisting.

[0061] Hereinafter, the term "cord" is used as a synonym for 2-stage twisted cord.

[0062] In a first step, the strands are formed by torsion of one or more filaments. Their torsion is called "pre-torsion" or initial torsion.

[0063] The cords are composed of strands twisted together and the torsion is called torsion or "twist level"

[0064] The mode of rotation or torsion of the initial torsion and final torsion can significantly affect the properties of a transmission belt.

[0065] The ratio between the initial twist factor and the ultimate twist factor is of great importance with regard to the properties of a transmission belt.

[0066] In the context of the present application, the twist factor TM, acronym of twist multiplier, is calculated as follows:

[0067] TM=TPM / 39.4 / (5905 / T)

[0068] TM indicates the twist factor,

[0069] TPM the torsion in torsions per metre (turns per metre) and

[0070] T the fineness of the bundle of filaments or the count in the dtex unit.

[0071] The twist factor of the filaments of the single strand is referred to below as TM1, while the twist factor of the cords starting from the individual strands is referred to as TM2.

[0072] In a preferred embodiment the cords are formed by 4 strands, i.e. a number of strands that allows to correctly balance the necessary mechanical characteristics with the correct dimensions of the cords.

[0073] Advantageously, the cords have a diameter between 0.2 and 2 mm, more advantageously between 0.5 and 1 mm. For example, the cords had particularly optimal results with a diameter of 0.8 mm. The cords preferably have an initial torsion per metre to form the strands from the filaments of between 300 and 500 more preferably, between 350 and 450, even more preferably between 360 and 380.

[0074] The initial twist factor is defined as TM1 and calculated with the formula:

[0075] TM1=TPM / 39.4) / (5905 / T) wherein

[0076] TM1 indicates the factor of torsion of the strands

[0077] TPM the torsion in torsions per metre or turns per metre of the filaments to form the strands

[0078] T the fineness of the yarn in the dtex unit

[0079] The value of the initial twist factor TM1 is preferably between 3.60 and 4.80, more preferably between 3.80 and 4.50.

[0080] The ultimate twist factor is defined as TM2 and calculated with the formula

[0081] TM2= (TPM / 39.4) / (5905 / T) wherein

[0082] TM2 indicates the factor of torsion of the cord

[0083] TPM the torsion in torsions per metre or turns per metre of the strands to form the cords

[0084] T the fineness of the bundle of filaments in the dtex unit.

[0085] The cords preferably have an ultimate torsion per metre TM2 to form the cords from the strands of between 100 and 300, more preferably, between 150 and 200, even more preferably between 160 and 180.

[0086] The value of the ultimate twist factor TM2 is preferably between 2.80 and 4.80, more preferably between 3.00 and 4.50, even more preferably between 3.50 and 4.00.

[0087] The torsion value TM1 is calculated as an average of the values for the single strand (starting from the filaments) while the torsion value TM2 is calculated as an average of the values of the cord starting from the strands.

[0088] The helix angle alphal is the angle at which the strands are wound or twisted to obtain the strands, while the helix angle alpha2 is the angle at which the strands are wound or twisted to obtain the cords.

[0089] The angle alphal is also referred to as twisting or torsion of the filaments in strands, while the angle alpha2 is also referred to as twisting or torsion of the strands to obtain the cords.

[0090] The angles alpha 1 and alpha 2 can be calculated as:

[0091] Alphal=arctg (n*D*Nl) wherein D is the diameter of the cord

[0092] N1 the number of torsions per mm of the filaments to obtain the strands.

[0093] While alpha2 is calculated as

[0094] Alpha2=arctg (n*D*N2) wherein D is the diameter of the cord N2 the number of torsions per mm of the strands to obtain the cords.

[0095] The helix angle of the torsions for the strands, also called alphal or al is preferably between 35° and 50°, more preferably between 42° and 45°.

[0096] The helix angle of the torsions for the cords, also called alpha2 or a2 is preferably between 20° and 30°, more preferably between 20° and 26.5°.

[0097] The ratio between al and a2 is preferably between 1.5 and 2.5, more preferably between 1.6 and 2.3.

[0098] The count or fineness of the cord according to a preferred form of the present invention is between 800 and 1300 dtex, more preferably between 1000 and 1200 dtex, particularly optimal performances were obtained with cord having dtex of 1100.

[0099] It has surprisingly been found that by selecting cords having a stable elastic modulus measured in N / mm, i.e. varying by less than 15%, more preferably less than 10%, more preferably less than 5%, in a range of tension applied to the cord between 4 and 12, preferably between 4.5% and 8.5%, even more preferably between 5% and 7% of the breaking load of the cord itself, more performing belts are obtained in terms of the lifespan thereof.

[0100] The tension applied is similar to that applied during the belt wrapping step. This result was particularly innovative as there is no mention in the literature of the effects of the stabilisation of the elastic modulus on the wrapping step of a belt and of the consequent increased useful life of the belt itself.

[0101] The number of filaments forming the strands or the count or the whole realization of the cord, can however be slightly varied as long as the values of the elastic modulus of the cord remain stable as defined below.

[0102] To better highlight this technical effect and to visualise the elastic modulus values with different tensions, the single load curve was first calculated with a polynomial of the third order and the first derivative was subsequently extracted, thus extracting the elastic modulus in a known way.

[0103] The elastic module was plotted as a function of the tension applied to the cord, during the load-elongation test, as depicted in Figure 3.

[0104] The measurements of the elastic modulus are expressed as an average of the measurements obtained on 5 samples to have a better comparable test.

[0105] The average value of the curve obtained was reported in the graph of Figure 3.

[0106] Advantageously the cords are entirely made of aromatic polyamide, more preferably of para-aromatic polyamide.

[0107] From an examination of the characteristics of the belt made according to the present invention, the advantages that it allows obtaining are evident.

[0108] Considerable improvements have been obtained by using a transmission belt according to the present invention and, in particular, the problems set out above have been overcome. In particular, a very good durability of the belt can be obtained.

[0109] The invention will be described below by means of examples, but is not intended to be limited to them.

[0110] Examples 1 e 2 A first belt according to the invention and a second comparison belt are made differing only in the characteristics of the cords having the characteristics reported in Figure 2.

[0111] The fabric covering the belt is made of polyamide 66 with a weight of about 185 gr / sqm and is treated with an EPDM-based compound.

[0112] The belt comprises a body made with the compound of Table

[0113] 1.

[0114] Table 1

[0115] The cords of the two belts are made entirely of aramid, in of particular para-aramid and differ in the values of torsion or twist, angle alpha and other characteristics that allow to obtain a stabilization of the elastic modulus in a predetermined tension range as reported in Figure 2.

[0116] The endurance test was performed on the transmission system depicted in Figure 4 having a development of 1205-1210 mm. The belt has a rib number equal to 5. The belt width is 17.8 mm + / - 0.3 and the section is known and already marketed as Section pVk profile.

[0117] The pulley (outer) diameters of the transmission system depicted are

[0118] Dl=60 mm (pulley with ribs) D2=D5=50 mm (smooth pulleys)

[0119] D3=D4=50 mm (pulleys with ribs)

[0120] The rotation speed of the pulley (D3) is preset to 4250 rpm. The temperature is ambient at 22-25 °C. The Weight for tensioning is: 320 N (also called dead weight) The specific load applied to the belt is therefore equal to 320 N / (5*2) = 32 N / (rib*branch).

[0121] The bending fatigue strength of the transmission belts was evaluated. In this case, truncation tests were carried out.

[0122] The test is suspended at 100 hours for the evaluation of belt elongation (%) and decay (%) of the breaking load at the end of the test.

[0123] The graph of Figure 5 shows the results of the truncation endurance test after 100 hours. The belt of comparison example 2 and that 1 according to the invention have a superimposable elongation at the end of the test.

[0124] The bar graph of Figure 6 shows that the decay of the breaking load of a belt built with the cord according to the invention is decidedly lower than the decay suffered by the belt built with comparison cord. The breaking load values were extracted from the belts subjected to the aforesaid truncation endurance test after 100 hours.

Claims

C L A I M S1. A power transmission belt (1) comprising a body (2) formed of a compound comprising a main elastomer, and a plurality of longitudinal cords (3) embedded in the belt body and a back (7), characterised in that said cords have an elastic modulus varying less than 10 % in a range of tension applied to the cord between 4,5 % and 8,5 % of the breaking load of the cord body.

2. A transmission belt (1) according to claim 1, characterised in that each of said cords consists of 4 strands twisted together obtained each twisted by twisting a plurality of filaments.

3. A transmission belt (1) according to claims 1 to 2, characterised in that that said filaments are made of aromatic polyamide.

4. A transmission belt (1) according to any one of the preceding claims, characterised in that each of said cords has a diameter between 0,5 and 1 mm.

5. A transmission belt (1) according to any one of the preceding claims, characterised in that each of said strands is formed by a plurality of twisted filaments with a twist per metre of between 300 and 500.

6. A transmission belt (1) according to any one of the preceding claims, characterised in that the strands have an initial twist factor defined as TM1 and comprised between3,80 and 4,50 and calculated according to the formula:TM1= (TPM / 39.4) / (5905 / T) whereinTM1 indicates the factor of torsion of the strandsTPM the torsion in torsions per metre or turns per metre of the filaments to form the strandsT the fineness of the bundle of filaments in the dtex unit.

7. A transmission belt (1) according to any one of the preceding claims, characterised in that each of said cords is formed by said twisted strands with a twist per metre of between 150 and 200.

8. A transmission belt (1) according to any one of the preceding claims, characterised by the fact that the cords have an ultimate twist factor defined as TM2 between 3,00 and 4,50 and calculated by the formulaTM2= (TPM / 39,4) / (5905 / T) whereinTM2 indicates the factor of torsion of the cordTPM the torsion in torsions per metre or turns per metre of the strands to form the cordsT the bundle fineness of filaments in the dtex unit.

9. A transmission belt (1) according to any one of the preceding claims, characterised by defining as helix angle al the angle of torsion of the filaments to obtainstrands according to the formula al=arctg (n*D*Nl) wherein D is the diameter andN1 the number of twists of the filaments per mm, said angle al is preferably between 42° and 45°.

10. A transmission belt (1) according to any one of the preceding claims, characterised in that defined as helix angle 2 the angle of torsion of the strands to obtain the cord according to the formulaA2 =arctg (n*D*N2) wherein D is the diameter andN2 the number of twists per mm of the strands to obtain the cords, said angle a2 is preferably between 20° and 26,5°.

11. A transmission belt (1) according to any one of the preceding claims, characterised by the fact that said cords have an elastic modulus varying less than 10 % in a range of tension applied to the cord between 5 % and 7 % of the breaking load of said cord.

12. A transmission belt (1) according to any one of the preceding claims, characterised by the fact that said cords have an elastic modulus varying less than 5 % in a range of tension applied to the cord between 4,5 % and 8,5 % of the breaking load of said cord.

13. A transmission belt (1) according to any one ofthe preceding claims, characterised by the fact that said cords have an elastic modulus varying less than 5 % in a range of tension applied to the cord between 5 % and 7 % of the breaking load of the cord itself.

14. A power transmission system comprising a power transmission belt according to any one of claims 1 to 13.

15. Process of making a power transmission belt comprising the wrapping step of a power transmission belt according to any one of claims 1 to 13.

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