DRIVE BELTS, USE OF SUCH A DRIVE BELTS AS A V-RIBBED BELT AND MANUFACTURING METHOD

Description

[0001] The invention relates to a drive belt according to the preamble of claim 1. Furthermore, the invention relates to a use and manufacture of such a drive belt.

[0002] Drive belts, especially multi-ribbed belts for belt-driven starter generators in modern hybrid or mild hybrid vehicles, are subjected to very high loads. Therefore, in recent years, tensile cords made of para-aramid in cord construction have increasingly been embedded in the core of drive belts. Para-aramid cords give the drive belt particularly high tensile strength, dimensional stability, and longitudinal stiffness.

[0003] For example, WO 2006 / 102641 A1 and WO 2012 / 143241 A1 each disclose drive belts with tension strands made of para-aramid in cord constructions. Each tension strand has twisted strands, each formed from at least one twisted yarn. The direction of twist of each strand is opposite to the direction of twist of the cord.

[0004] For the purposes of this application, the term "yarn" refers to any linear structure made from textile fibers. Such fibers can be fibers, in particular staple fibers, or filaments. Filaments specifically refer to fibers with a length of at least 1000 mm. A strand, in turn, is formed from one or more yarns.

[0005] Preferably, strands are formed by twisting one or more yarns together. This twisting is also called plying. A twist of untwisted yarns, or a single untwisted yarn, is called a pre-twist. The result of a pre-twist can be a strand. Twisting one or more pre-twists, for example, one or more strands, produces the final ply. A cord or a drawstring made of one or more strands can be the result of the final ply.

[0006] In the following, the term "cord" is used synonymously for two-stage twisted cords. These cords have strands twisted together, with the twist being referred to as "twisting." The strands themselves are formed by twisting one or more yarns together. Their twist is referred to as "pre-twisting."

[0007] Prior art has shown that the twisting and untwisting of the pre-twisted and untwisted strands can significantly influence the properties of a drive belt. Therefore, a twist factor was defined in the prior art, recognizing the high importance of the ratio between the twist factor of the strands and the twist factor of the cords with regard to the properties of the resulting drive belt. The prior publications WO 2006 / 102641 A1 and WO 2012 / 143241 A1 use different formulas for calculating the twist factor or twist multiplier. This application uses the calculation according to WO 2006 / 102641 A1. The twist factor TM is therefore calculated as follows: TM = TPM / 39 , 4 5905 / T

[0008] In this context, TM denotes the twist factor, TPM the twist in turns per meter, and T the yarn fineness or titer in the unit dtex.

[0009] From WO 2018 / 074471 A1 and EP 3 530 783 A1, a drive belt with tensile strands embedded in cord construction is known, although the yarn factor is calculated according to a different formula and therefore has values ​​that differ from the rest of the prior art.

[0010] Although conventional drive belts already exhibit high tensile strength, dimensional stability, and longitudinal stiffness, the ongoing development of vehicle technology, particularly for belt-driven starter generators, is placing higher demands on drive belts. It has been shown that even drive belts with para-aramid tensile cords can break relatively quickly during operation. This is especially true under dynamic stress, which is particularly high in belt-driven starter generators. Furthermore, tensile cords of drive belts subjected to high dynamic loads tend to unwind from the unprotected belt edge. This often results in belt failure during operation.

[0011] Drive belts are typically manufactured as a continuous tube and then cut into individual belt sections. This ensures that the drive belt itself remains seamless and therefore exhibits high stability. However, drive belts with tensile cords made of para-aramid are very difficult to cut. The cut edges of these belts often appear fuzzy, which customers consider a defect. Furthermore, overload tests of otherwise comparable belts (with identical para-aramid cords) have shown a tendency towards shorter service life for those belts with noticeably fuzzy cut edges.

[0012] Against this background of the increased demands on drive belts, especially with regard to their stability under high dynamic stress, their resistance to the unwinding of tension strands and with regard to an aesthetically pleasing belt edge, there was a need for further development.

[0013] The basis for further development is the objective of providing a drive belt in which the tension strands do not unwind under high dynamic stress and high load transmission, which also exhibits high durability, in particular preventing the drive belt from tearing, and which has a low-linting belt edge, i.e., it can be cut with minimal linting during the production process. Furthermore, it is an object of the invention to provide the use of such a drive belt as a multi-ribbed V-belt and a method for manufacturing such a drive belt.

[0014] According to the invention, this problem is solved with regard to the drive belt by the subject matter of claim 1, with regard to the use by the subject matter of claim 12 and with regard to the manufacturing process by the subject matter of claim 13.

[0015] The invention is based on the concept of a drive belt with a base body in which one or more tensile strands made of para-aramid in a cord construction are embedded. Each tensile strand has twisted strands, each formed from at least one twisted yarn. The direction of twist of each strand is opposite to the direction of twist of the cord. According to the invention, the tensile strands each have at least four strands, wherein the twist factor TM1 of the strands (pre-twist) is between 4.5 and 5.4 and the twist factor TM2 of the cord (out-twist) is between 2.7 and 3.8. The ratio of the twist factor of the strands (pre-twist) to the twist factor of the cord (out-twist) is, according to the invention, between 1.3 and 1.5.

[0016] Numerous trials and long-term tests have shown that the drive belt according to the invention has significantly improved properties compared to drive belts from the prior art and is thus able to meet the increased requirements for drive belts for modern belt starter generators or hybrid vehicles.

[0017] The use of at least four strands for the tensile cord, in contrast to the two or three strands used for the tensile cord of the drive belt according to WO 2012 / 143241 A1, results in improved resistance of the drive belt to tension cord unwinding. Surprisingly, several test series have also shown that a narrow range for the ratio of the twist factors, namely between 1.3 and 1.5, leads to a significant improvement in the fatigue strength of the drive belt. The drive belt according to the invention can therefore withstand very high dynamic loads. In particular, the tensile cords do not unwind even under high load transmission. In the endurance test, longer service lives were achieved compared to prior art drive belts before belt failure occurred (e.g., due to backing material failure after dynamic fatigue and / or thermal aging of the backing material).No further belt tearing during operation was observed.

[0018] Particularly good properties of the drive belt are achieved when the ratio of the twist factor of the strands to the twist factor of the cord is between 1.35 and 1.45.

[0019] To achieve these twist factors and, moreover, to positively influence the properties of the drive belt, the invention provides that each strand has a twist between 410 m and 490 m. The cords (twist) can advantageously each have a twist between 125 m and 175 m. It is particularly preferred if the cords each have a twist between 150 m and 170 m.

[0020] Furthermore, tests with different grid densities have shown that the desired high-quality properties of the drive belt for use in automotive belt-driven starter-generator applications are achieved when the strands each have a density between 800 dtex and 1200 dtex. A density of 1100 dtex is particularly preferred.

[0021] Although the properties of the drive belt, particularly with regard to tensile strength, dimensional stability, and longitudinal stiffness, are largely determined by the material and the structure of the tensile cords, it is nevertheless advantageous if the main body has a fiber-reinforced cover layer and / or a fiber-reinforced base compound. The cover layer and the fiber-reinforced base compound can each be made of a polymeric material with elastic properties. It is particularly preferred if the cover layer and / or the base compound are made of a peroxide-crosslinked ethylene-propylene rubber or an ethylene-propylene diene rubber.

[0022] The top layer and the base layer can together form the core material, preferably in the form of a vulcanized rubber compound comprising at least one rubber component and additives. The rubber component can be, in particular, an ethylene propylene rubber, an ethylene propylene diene rubber, a (partially) hydrogenated nitrile rubber, a chloroprene rubber, a chlorosulfonated polyethylene, a fluorocarbon rubber, a natural rubber, a styrene-butadiene rubber, or butadiene rubber. The rubber component can be unblended or blended with at least one other rubber component.

[0023] The additives may include at least one crosslinking agent or crosslinking system. Furthermore, fillers and / or processing aids and / or a plasticizer and / or an antioxidant and / or fibers and / or color pigments may be used as additives.

[0024] The cover layer and / or the backing compound may contain fibers made of aramid, polyester, polyamide, poly-p-phenylenebenzobisoxazole, cotton, linen, rayon, fiberglass, metal fiber, silicate fiber, or other fiber materials commonly used in the rubber industry. The fibers may be oriented parallel to the longitudinal or transverse direction of the belt's circumference. It is also possible for the fiber orientation to differ between the cover layer and the backing compound of the belt.

[0025] It is also preferred if the tensile cords are embedded in the base body in a tensile cord layer between the cover layer and the base material. In this process, the cover layer and the base material can be bonded together in such a way that, in the finished drive belt, the cover layer is indistinguishable from the base material. The tensile cords can thus be completely embedded in the uniform base body.

[0026] The tensile cords can generally be provided with a strip preparation and / or coated with an adhesive to facilitate or improve embedding in the base body.

[0027] It is particularly preferred that the tensile cord density in the drive belt is between 80 and 130 tensile cords per 100 mm belt width. In particular, between 90 and 120, preferably between 100 and 110, and especially preferably 105, tensile cords per 100 mm belt width can be provided. It has been shown that such a tensile cord density represents a good compromise between the tensile strength and lateral stability of the drive belt.

[0028] In a particularly preferred embodiment of the invention, the strands have a twist of 450 m and the cords each have a twist of 160 m. In this embodiment, it is particularly advantageous for the strands to each have a density of 1100 dtex. The drawstring preferably comprises exactly four strands, each formed from a single twisted yarn. Therefore, it is preferred if the drawstring is formed from a cord 1100x1x4, 450 / 160 sZ (and / or zS). Thus, the strands are twisted in the S-direction (and / or in the Z-direction), and the cords are each twisted in the Z-direction (and / or in the S-direction). Preferably, for drive belts according to the invention, in particular multi-ribbed belts, two cords with opposite rotations (i.e. sZ and zS) are installed in one belt, wherein both cords are wound in parallel (onto the top layer) during the manufacturing process.

[0029] A secondary aspect of the invention relates to the use of a previously described drive belt as a multi-ribbed belt in a motor vehicle engine, in particular for a belt-driven starter generator.

[0030] Furthermore, the present invention relates to a method for manufacturing a drive belt as previously described, wherein four individual yarns or yarn bundles are each twisted individually with a twist between 410 m -1< and 490 m -1< to form a strand, the four strands are then combined and twisted with an opposite twist between 125 m -1< and 175 m -1< to form a cord, wherein a twisting factor TM 1 between 4.5 and 5.4 is set for the strands and a twisting factor TM 2 between 2.7 and 3.8 is set for the cords and a ratio of the twisting factor of the strands to the twisting factor of the cords (TM 1 / TM 2 ) between 1.3 and 1.5 is set.

[0031] Preferably, in one embodiment of the manufacturing process according to the invention, a rotation of 450 m -1< is set for each of the four strands and a rotation of 160 m -1< is set for the cords.

[0032] The invention is explained in more detail below using an exemplary embodiment with reference to the accompanying schematic drawings. These show Fig. 1 shows a partial cross-section through a drive belt according to a preferred embodiment of the invention; Fig. 2 shows a roller arrangement of a mild hybrid test for the drive belt according to Fig. 1 ; and Fig. 3 a roller arrangement of a constant high load test for the drive belt according to Fig. 1 .

[0033] In Fig. 1A drive belt is shown in partial section, comprising a base body formed from a cover layer 2 and a base material 4. A tension member layer consisting of several tension members 3 extends between the cover layer 2 and the base material 4. The tension members 3 are preferably arranged parallel to each other. It is also conceivable that the tension members 3 are arranged offset from each other.

[0034] The in Fig. 1 The drive belt 1 shown is designed as a multi-ribbed V-belt. For this purpose, the substructure 4 has several parallel ribs 5, which are separated from each other by grooves 6. The side of the substructure compound 3 opposite the tension members 3 or the cover layer 2 forms a force transmission surface 7, which extends over the ribs 5 and through the grooves 6.

[0035] The force transmission surface 7 can have a coating 8. The coating 8 can be a flocking, in particular with a cotton or aramid flock. It is also possible to use a textile covering as the coating 8. The textile covering can be in the form of a woven, knitted, or crocheted fabric. The coating 8 preferably provides wear protection and noise reduction.

[0036] The improved properties of the drive belt 1 compared to the prior art are primarily due to the formation of the individual tensile strands 3. Preferably, each tensile strand 3 has at least four, and in particular exactly four, strands. The twist factor TM1 of the strands is between 4.5 and 5.4, and the twist factor TM2 of the cords is between 2.7 and 3.8. In particular, for the tensile strands 3 of the drive belt 1 according to the invention, the ratio of the twist factor of the strands to the twist factor of the cords (TM1 / TM2) is between 1.3 and 1.5, preferably between 1.35 and 1.45.

[0037] In the process of developing the present invention, several multi-ribbed V-belts were constructed with a fiber-containing cover layer and a fiber-containing core compound using various aramid tensile cords. The cover layer and / or the core compound consist of peroxide-crosslinked ethylene propylene diene monomer (EPDM) rubber. The aramid yarn used was type T1008 (1100 dtex) from Teijin Limited. The tensile cord layer was produced by parallel winding of two cords with opposite directions of rotation (sZ and zS) with a construction of 1100x1x4. The cords were each provided with a stripping preparation and coated with an adhesive.

[0038] For all tested drive belts, the tensile cord density was 105 cords per 100 mm belt width. Drive belts of varying widths were cut from the feed tube, and the cut edges were visually inspected. The length of each drive belt was approximately 1,200 mm. Furthermore, the drive belts were tested for dynamic service life in a mild hybrid test and a constant high load test, and their resistance to cord unwinding was evaluated.

[0039] Specifically, the drive belts were each subjected to a mild hybrid test (CT Mild Hybrid Test, 6PK1196) and a constant high load test (Constant High Load Test, 4PK1196).

[0040] In the mild hybrid test, the drive belt runs alternately with its top layer and its underlayer compound over six rollers of varying diameters. The arrangement of the rollers in the mild hybrid test shows Fig. 2A drive pulley (BSG) applies torque to the drive belt according to a defined test cycle. Each test cycle comprises a start section, a boost section, a recuperation section, and a base load section. The total duration of the test cycle is 20 seconds. During the start and boost sections of the test cycle, the drive pulley accelerates the belt, while during the recuperation and base load sections, it brakes the belt.

[0041] The starting phase is relatively short, but a high torque from the generator pulley, specifically around 60 Nm, is applied to the drive belt. During the longer boost phase, a weaker torque acts on the belt, amounting to only about half the starting torque, or approximately 30 Nm. The recuperation phase lasts a similar amount of time to the boost phase, with a torque of approximately 30 Nm. The longest phase is the base load phase, during which a constant torque of approximately 5 Nm is maintained. The ambient temperature during the mild hybrid test was set to 130 °C.

[0042] In the constant high-load test, the drive belt runs alternately with its top layer and its underlayer compound over four rollers, with one drive roller applying a constant torque of 20 Nm at a rotational speed of 5000 revolutions per minute. The arrangement of the rollers in the mild hybrid test shows Fig. 3The ambient temperature during the constant high load test was set to 100 °C.

[0043] All drive belts were subjected to the same tests, with the test cycle being repeated until the drive belt broke, the tensile cords unwound from the drive belt, or the belt's substructure exhibited at least three cracks or a complete break. The test results are shown in the following table, where the drive belt with test number 6 is constructed according to the invention. These drive belts achieved the best overall results. This is clearly evident from the final run times in the various tests. The comparison drive belts could not achieve such long test run times. Trial code Rotation advance TM1 [m -1< ] Rotation Auszwim TM2 [m -1< ] Rotation factor pre-twitch TM1 Twist factor unwinding TM2 Quotient TM1 / TM2 CT Mild Hybrid Test, 6PK1196, runtime [h] Constant High Load Test, 4Pk1196, running time [h] Optical assessment of the cut edge Target runtime > 150 h > 70 h 1 270 270 2,96 5,91 0,50 74...84 h 38...48h + 2 300 105 3,28 2,30 1,43 74... 94 h 124...163 h - 3 360 126 3,94 2,76 1,43 50...291 h 161...18 2h o 4 360 200 3,94 4,38 0,90 - 58...64 h + 5 450 100 4,93 2,19 2,25 164...40 0 h 8...63 h - 6 450 160 4,93 3,50 1,41 224...42 1 h 74...184 h + 7 450 190 4,93 4,16 1,18 44...96 h 1...20 h +

[0044] In particular, test belt no. 5, which has a thread ratio according to WO 2006 / 102641 A1, shows a significant deviation in the final running times of the two tests, especially in the constant high load test, as well as a lint-rich belt edge. With the drive belt according to the invention (test belt no. 6), higher final running times are achieved in both the mild hybrid test and the constant high load test. Furthermore, the drive belt designed in this way exhibits a very low-lint cut edge. Reference symbol list (Part of the description)

[0045] 1 Drive belt 2 Cover layer 3 Tension member 4 Base compound 5 Rib 6 Groove 7 Power transmission surface 8 Coating

Claims

1. A drive belt (1) having a base body in which one or more tension cords (3) of para-aramid are embedded in cord construction, each strand (3) having twisted strands, each of which is formed of at least one twisted yarn, and wherein the direction of rotation of the respective strand (pre-thread) is opposite to the direction of rotation of the cord (twisting), wherein the tensile strands (3) each have at least four strands, wherein the thread factor TM1 of the strands (pre-thread) is between 4.5 and 5.4 and the thread factor TM2 of the cord (thread) is between 2.7 and 3.8 and the ratio of the twist factor of the strands to the thread factor of the cord (TM1 / TM2) is between 1.3 and 1.5, and where the strands have a twist (pre-thread) between 410 m-1 and 490 m-1.

2. Drive belt (1) according to claim 1, characterized in that the ratio of the twist factor of the strands to the twist factor of the cords (TM1 / TM2) is between 1.35 and 1.45.

3. Drive belt (1) according to claim 1 or 2, characterized in that the cord has one twist (twist) between 125 m-1 and 175 m-1.

4. Drive belt (1) according to any of the preceding claims, characterized in that the cords each have a twist (twisting) between 150 m-1 and 170 m-1.

5. Drive belt (1) according to any one of the preceding claims, characterized in that the strands each have a titer between 800 dtex and 1200 dtex, in particular 1100 dtex.

6. Drive belt (1) according to any of the preceding claims , characterized in that the base body has a fibrous top layer (2) and a fibrous substructure compound (4), each of which is formed of a polymeric material having elastic properties, preferably of a peroxide-crosslinked ethylene-propylene rubber or ethylene-propylene-diene rubber.

7. Drive belt (1) according to claim 7, characterized in that the tension cords (3) are embedded in the base body in a tensile strand position between the top layer (2) and the substructure mixture (4).

8. Drive belts (1) according to any of the preceding claims, characterized in that the tension cords (3) are provided with a grazing preparation and / or coated with an adhesive agent.

9. Drive belt (1) according to any one of the preceding claims, characterized in that a tensile cord density between 80 and 130, in particular between 90 and 120, in particular between 100 and 110, preferably 105, is tensile cords per 100 mm belt width.

10. Drive belt (1) according to any of the preceding claims , characterized in that the belt is a V-ribbed belt.

11. Drive belt (1) according to any of the preceding claims, characterized in that the strands have a rotation of 450 m-1 and the cords each have a rotation of 160 m-112. The use of a drive belt according to any of the preceding claims as a V-ribbed belt in a motor vehicle engine, in particular for a belt-starter-alternator.

13. A method for producing a tensile cord for a drive belt according to any one of claims 1 to 11, wherein four yarns or bundles of yarn are individually twisted with a twist (pre-thread) between 410 m-1 and 490 m-1 to form a strand each, the four strands are then combined and twisted with an opposite twist (twisting) between 125 m-1 and 175 m-1 are twisted into a cord, whereby a twist factor TM1 between 4.5 and 5.4 is set for each strand and a TM2 twist factor between 2.7 and 3.8 for the cord and a ratio of the twist factor of the strands to the twist factor of the cord (TM1 / TM2) between 1.3 and 1.5.

14. The method of claim 13, wherein a rotation of 450 m-1 is set for each of the four strands and a rotation of 160 m-1 for the cords.