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Title:
WOVEN FABRIC FOR TRANSMISSION BELT COMPRISING TEXTURIZED YARN AND LOW FRICTION YARN
Document Type and Number:
WIPO Patent Application WO/2014/191723
Kind Code:
A1
Abstract:
The fabric (1) comprises a warp yarn (2) woven with a yarn bundle comprising a first yarn (3) and a second, different yarn (4) with one of the two yarns in the weft yarn bundle comprising a friction reducing substance. The fabric (1 ) is particularly suited for use on the surface of a toothed belt such as a transmission or timing belt and exhibits enhanced abrasion resistance.

Inventors:
FRY ELIZABETH (GB)
ROOCROFT BRIAN THOMAS (GB)
Application Number:
PCT/GB2014/051579
Publication Date:
December 04, 2014
Filing Date:
May 22, 2014
Export Citation:
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Assignee:
HEATHCOAT FABRICS LTD (GB)
International Classes:
D03D15/58; D03D1/00; F16G1/28
Domestic Patent References:
WO2011003090A12011-01-06
Foreign References:
EP1436450A12004-07-14
EP1813835A22007-08-01
Attorney, Agent or Firm:
PERKINS, Sarah et al. (London EC4A 3BG, GB)
Download PDF:
Claims:
CLAIMS

1. A woven fabric for use in a transmission or timing belt, the woven fabric comprising:

a first yarn; and

a yarn bundle woven with the first yarn, the yarn bundle comprising at least second and third yarns, the second yarn being a texturized thermoplastic yarn and the third yarn comprising a friction reducing substance and wherein the second and third yarns are not separated from one another in the yarn bundle by the first yarn.

2. A woven fabric according to claim 1 , wherein neither the second yarn nor the third yarn includes an elastic core thread. 3. A woven fabric according to any preceding claim, wherein the second yarn comprises texturized Nylon.

4. A woven fabric according to any preceding claim, wherein the friction reducing substance of the third yarn has a coefficient of friction of less than 0.5.

5. A woven fabric according to any preceding claim, wherein the friction reducing substance of the third yarn is PTFE. 6. A woven fabric according to any preceding claim, wherein the first yarn is a non-thermoplastic yarn.

7. A woven fabric according to any preceding claim, wherein the first yarn is present in the warp direction of the fabric and the yarn bundle is present in the weft direction of the fabric. A woven fabric according to any preceding claim, wherein the first yarn and the yarn bundle form a twill or non-directional weave construction..

A belt for use as a transmission or timing belt, comprising a substrate with the fabric according to any one of claims 1-8 on at least a part of at least one surface of the belt.

10. A belt according to claim 9, wherein the fabric is adhered or otherwise attached to the substrate.

11. A belt according to either of claim 9 or 10, wherein the fabric forms the working surface of the belt

A belt according to claim 11 , wherein the working surface of the belt includes a plurality of regularly spaced protrusions.

A method of forming a woven fabric, comprising weaving a first yarn and a yarn bundle together, wherein the yarn bundle comprises at least second and third yarns, the second yarn being a texturised thermoplastic yarn and the third yarn comprising a friction reducing substance; and subsequently finishing the woven fabric to realise the bulking properties of the textured yarn.

A method as claimed in claim 13 wherein the first yarn and the yarn bundle are woven in a twill or non direction weave construction.

Description:
WOVEN FABRIC FOR TRANSMISSION BELT COMPRISING TEXTURIZED YARN AND LOW FRICTION YARN

[0001] This invention relates to a fabric particularly, although not exclusively, one which can be incorporated in a transmission or timing belt (herein generally referred to as belts). The belts may be used in automobile engines as well as in other industrial uses. Such belts include toothed belts, V belts and multi-ribbed V belts.

[0002] Some conventional transmission or timing belts include a fabric covering at least a portion of one or both main surfaces of the belt. The fabric is used to increase the durability of the belt and to reduce noise (squealing or squeaking during use) particularly at start-up. Nylon is known for use in belt fabrics but, particularly in the case of toothed belts, such belts remain prone to failure. Alternative materials have also been considered for use in belt fabrics for providing belts with improved performance characteristics and durability.

[0003] In US 2010/0197435 a thermoplastic belt is described with a wear resistant, anti-static fabric on its surface such as a fabric containing silver-coated polymeric fibre.

[0004] Woven fabric has been used for either the back or working surface of the belt. Thus US 2008/0261739 describes a V-ribbed belt that includes a textile warp knitted fabric which has two different yarn substances on the working surface of the belt. On the other hand, in EP 1643157 a transmission belt is described comprising a woven fabric for use as a backing fabric on a toothed belt. The fabric uses the same yarn substance for all of the weft yarns but uses both an S-twisted yarn and a Z-twisted yarn side-by- side in a Panama or twill weave.

[0005] It is also known to include in the belt fabric a friction-reducing substance. In EP 1035353 a power transmission belt is described which includes polytetrafluoroethylene (PTFE) fibres dispersed throughout a composition forming an outer surface of the belt. In contrast, in US 4302197 a fabric is described which has different characteristics on either surface: one surface has a high adhesive characteristic whereas the other surface has a low-friction characteristic. [0006] EP 1436450 describes a yarn for use in a belt fabric in which the yarn comprises an elastic core around which is wrapped PTFE. This yarn is one of two different weft yarns used in the woven fabric, with each weft being separated from adjacent wefts by the warp yarn. Where PTFE is wrapped around an elastic core, commonly the other one or more weft yarns used in the woven fabric will have a similar construction, namely an elastic core around which is wound Polyamide or Polyester, for example, to maintain the amount of extension available in the resultant woven fabric. In Figures 1a, 1 b, and 1 c examples of a toothed belt are shown in each case with a woven fabric on the belt's toothed surface and with the woven fabric formed of two different weft yarns but with both of the weft yarns having an elastic core. As can be seen clearly in these Figures the yarns of the woven fabric are susceptible to fraying.

[0007] The present invention seeks to mitigate problems encountered to date with transmission belts having a fabric surface.

[0008] The present invention also seeks to provide an improved fabric suitable for forming at least a portion of at least one surface of a transmission belt. The present invention further seeks to provide a woven fabric which is suitable for forming at least a portion of at least one surface of a transmission belt and which avoids or reduces fraying of the woven fabric yarns during use of the transmission belt in contrast to existing woven fabrics.

[0009] According to a first aspect of the present invention, there is provided a woven fabric for use in a transmission or timing belt, the woven fabric comprising: a first yarn; and a yarn bundle woven with the first yarn, the yarn bundle comprising at least second and third yarns, the second yarn being a texturized thermoplastic yarn and the third yarn comprising a friction reducing substance wherein the second and third yarns are not separated from one another in the yarn bundle by the first yarn.

[0010] In a particularly preferred embodiment neither the second yarn nor the third yarn includes an elastic core thread.

[0011] The fabric according to the present invention has a low-friction surface which is soft or yielding due to its bulk but which is also extensible i.e. stretchable. This enables the fabric to conform, for example, to the 3D structure of a toothed belt without significant loss of bulk and thereby substantially maintain the durability and other performance characteristics of the fabric when forming the surface of a transmission or timing belt.

[0012] The fabric is suited for use on either or both of part or all of the tooth-facing surface and the opposing back surface of a transmission or synchronous timing belt.

[0013] The second yarn, which is a texturized thermoplastic material, is preferably Nylon 66.

[0014] The third yarn which comprises a low-friction substance ideally includes a substance preferably having a coefficient of friction of less than 0.5, in accordance with A.S.T.M. D.1984 method. In a preferred embodiment the substance is PTFE.

[0015] Preferably the first yarn is a continuous filament material. Ideally, the first yarn is selected from the following group: Polyamide, Polyester or other thermoplastic materials, aramids, PPS, PEEK , PTFE.

[0016] In a preferred embodiment the yarn bundle comprises an equal number of second yarns and third yarns.

[0017] In a second preferred embodiment the yarn bundle comprises more second yarns than third yarns. For example, the yarn bundle may comprise two second yarns and one third yarn.

[0018] In a further preferred embodiment the yarn bundle may comprise at least a fourth yarn which is different to the second and third yarns.

[0019] The first yarn may be present in the warp direction of the fabric with the yarn bundle present in the weft direction of the fabric, or vice versa.

[0020] In a further preferred embodiment, the first yarn and the yarn bundle form a twill weave or a non-directional weave.

[0021] According to a second aspect of the present invention, there is provided a belt comprising a fabric described above.

[0022] The belt preferably further comprises a substrate to which the fabric described above is adhered or otherwise attached. In one embodiment the fabric may be adhered or otherwise attached to the working surface of the belt. Also, the working surface of the belt may include a plurality of protrusions, that may be regularly spaced, for example in the form of teeth, intended for contact with the moving parts of an engine or the like. The substrate may additionally comprise a filler material.

[0023] The belt may further comprise a core material, which can be any material known in the art, examples being resilient glass fibre, para-aramid, PBO (Poly-p-phenylobenzobisthiazole) (Zylon™) or the like. The belt is preferably, but not exclusively, for use in automotive applications, particularly automobile engines or the like. The belt is preferably adapted for use as a transmission or timing belt.

[0024] In a yet further aspect of the present invention, there is provided a method of forming a fabric a method of forming a woven fabric, comprising weaving a first yarn and a yarn bundle together, wherein the yarn bundle comprises at least second and third yarns, the second yarn being a texturised thermoplastic yarn and the third yarn comprising a friction reducing substance and wherein the second and third yarns are not separated from one another in the yarn bundle by the first yarn; and subsequently finishing the woven fabric to develop the bulking characteristics of the textured yarn.

[0025] In a preferred embodiment the first yarn and the yarn bundle are woven in a twill or non directional weave construction.

[0026] It is to be understood that reference herein to a yarn bundle or a weft bundle is to be understood as reference to two or more yarns jointly functioning as a single weft or warp in the woven fabric whereby at no point in the fabric is the weft bundle broken or separate by the warp or vice versa. Moreover, the two or more yarns forming the yarn bundle are preferably arranged side-by-side.

[0027] The present invention will now be described, by way of example only, with reference to the following drawings, in which:

Figures 1 a, 1 b and 1 c are photographic images of conventional transmission belts with a woven fabric on the toothed surface; Figure 2 illustrates a weave pattern for a fabric according to the present invention;

Figure 3 is a view of a typical second yarn according to the present invention; Figure 4 is a view of a typical third yarn according to the present invention; Figure 5 shows a first outer surface of a fabric according to the present invention;

Figure 6 shows a second surface of a fabric according to the present invention;

Figure 7 shows a cross-section through a transmission belt with a fabric according to the present invention; and

Figure 8 is a photographic image of a timing belt in accordance with the claimed invention with a woven fabric on the toothed surface.

[0028] A woven fabric 1 suitable for use in forming a surface of a transmission or timing belt is illustrated in Figure 2. The fabric 1 has a twill weave with a warp yarn 2 and a weft bundle of first and second yarns 3, 4 in each weft line. In Figure 2 the two yarns 3, 4 in each weft bundle are different from one another and the two yarns 3, 4 of each weft bundle are woven in the fabric side-by-side so that within the body of the fabric at no point are the individual yarns of the weft bundle separated from one another by the warp yarn. Although Figure 2 shows only two weft yarns in the weft bundle, each weft bundle may comprise more than two threads. Thus, the weft bundle may include a third weft yarn which is different to the first and second weft yarns, such as a low melt yarn, and / or the weft bundle may include multiples of either or both of the different weft yarns. Also each weft bundle may comprise at least an equal number of the two different first and second weft yarns or may comprise a different number of first yarns to second yarns.

[0029] Although one particular twill weave is illustrated in Figure 2, the fabric may be manufactured using alternative weaves including, but not limited to, basket or Panama weave, or other non directional weave constructions. In all cases, however, each weft line of the fabric weave comprises a plurality of yarns consisting of at least two different yarns. [0030] The first yarn 3 is shown in Figure 3 which has been extracted from the woven fabric after the fabric finishing process or processes. The first yarn 3 is a thermoplastic yarn such as, but not limited to, Nylon 66. The first yarn 3 preferably does not contain or comprise PTFE or another low-friction substance. The first yarn 3 also does not contain or comprise a core of an elastic material. As may be clearly seen in Figure 3 the first weft yarn 3 has been texturized, which has the effect of forming crimps or crinkles in the filaments of the yarn and bulks out the yarn and contributes to the stretch of the resultant woven fabric.

[0031] The second weft yarn 4 is shown in Figure 4, which has also been extracted from the woven fabric after the fabric finishing process or processes. The second weft yarn 4 is a low friction yarn (i.e. having a yarn surface which presents a lower friction in comparison to the thermoplastic yarn) and does not have an elastic core. The low friction yarn 4 preferably comprises PTFE but alternative low friction yarns are also envisaged. The yarn should be sufficiently flexible to be susceptible to the contractive force of the accompanying nylon yarn so that the nylon yarn is able to force the low friction yarn into a crimped state, which delivers the required stretchability of the resultant fabric.

[0032] It is preferable that the warp yarn 2 in the woven fabric is a continuous filament type (Nylon 66 for example, Polyamide, Polyester or other thermoplastic materials, aramids, PPS, PEEK, PTFE). This enables the weft yarns 3, 4 to pass over the warp yarns 2 easily when crimping / bulking of the weft yarns occur during the one or more fabric finishing processes thus providing the necessary stretch in the resultant fabric to enable it to follow the profile of timing belt teeth in a mould.

[0033] During the fabric finishing process the thermoplastic yarn 3 contracts which adds bulk to the fabric whereas the low-friction yarn 4 becomes crimped but does not bulk out in the manner of the thermoplastic yarn 3. This ensures that the resultant woven finished fabric, as shown in Figures 5 and 6, is flexible and can be stretched but remains compressible even when stretched. Moreover the flexibility and stretchability of the fabric is possible without the use of elastane or other elastic core yarns and so avoids the need for yarn wrapping processes. This, in turn, ensures that transmission or timing belts having this woven fabric on their working surfaces have improved durability and improved performance characteristics in comparison to conventional belts.

[0034] When the woven fabric is intended for use on the tooth-side of the belt, the fabric has a stretch capability in the range 30-200%, more preferably in the range 50-150%, more preferably still >60% at 2 kg using a 25 mm strip.

[0035] The woven fabric may be, but need not be, treated with a RFL dip. The latex part is optionally carboxylated HNBR, VP-SBR, CR, CS or VP. RFL is a system for providing adhesion of textiles to other substrates such as rubbers. RF is resorcinol formaldehyde resin and a latex is added to that resin which is suitable or compatible for the particular rubber to be adhered to. Alternative conventional processes for improving the adhesion or attachment of the woven fabric to the belt substrate are also envisaged.

[0036] Figure 7 illustrates diagrammatically a synchronous timing belt 5 comprising the fabric 1 described above. The belt 5 comprises a rubber substrate 6 with a fabric covered working surface 7. Tension members 8, such as glass cord, are provided within the substrate 6. The working surface 7 includes teeth 9 for cooperating with a pulley system or the like in use.

Example

An exemplary twill weave fabric construction is as follows:

Warp yarn: 235f34x1 HT PA66 heat protected

First weft yarn: 1 17f 17x4HT PA66 heat protected textured

Second weft yarn: 440 d'tex PTFE

Weft extension @ 2 kg 1 18%

Warp tensile 1453 N

Weft tensile 1233 NWeight 449gms/m 2

Gauge 1.22 mm [0037] Woven fabric according to the above Example (T-07282) was subjected to the standard abrasion resistance test for coated fabrics ASTM D3389-10. The standard abrasion resistance test employs a rotary platform abrader available from Taber Industries which has a circular specimen holder adapted to rotate within its own plane about a central axis. A flat sample of the woven fabric is mounted on the specimen holder and a pair of abrasive wheels are pivoted into position to form peripheral engagement with the upper surface of the sample and to apply a predetermined loading to the surface of the sample. The direction of travel of the periphery of the abrasive wheels is at an acute angle to the rotation of the sample with the angle of travel of one wheel being opposite to that of the other. Each abrasive wheel is 13 mm thick, has a diameter of approximately 50 mm and the contacting surface of the wheel has a predetermined grade of abrasive quality. A vacuum nozzle is also provided immediately above the sample to capture and remove abraded particles that may be produced. During the test the starting weight of the sample is measured and the sample is then rotated under the abrasive wheels for a predetermined number of revolutions. Periodically during the test rotation may be stopped to enable any loose abraded particles lying on the surface of the sample to be removed. Once the predetermined number of revolutions is reached, any remaining loose abraded particles are removed from the surface of the sample and the end weight of the sample is measured.

[0038] The results of this test are set out below in Tables 1 and 2 along with comparable data for a woven fabric containing the same warp yarn and a single textured Nylon 66 weft yarn but no PTFE (T-00770) and for a woven fabric again with the same warp yarn but with two weft yarns both being textured Nylon 66 (T-00717) i.e. the PTFE yarn being replaced by a second Nylon weft yarn.

Table 1

Test Conditions:

Cycles: 150

Load: 1000 grams

Abrasive wheels: H-18 (vitrified wheel) Specimen type: Fabric, cut to 4 inch squares and adhered to a piece of cardboard with double sided tape

Vacuum Status: On

Vacuum nozzle height: 0.25 in

Test conditions: 23°C ± 2°C / 50% ± 10% RH

Conditioning: 40+ hours at 23°C ± 2°C / 50% ± 10% RH

Test Results:

Table 2

Test Conditions:

Cycles: 300

Load: 1000 grams

Abrasive wheels: H-18 (vitrified)

Specimen type: Fabric, cut to 4 inch squares and adhered to a piece of cardboard with double sided tape

Vacuum Status: On

Vacuum nozzle height: 0.25 in

Test conditions: 23°C ± 2°C / 50% ± 10% RH

Conditioning: 40+ hours at 23°C ± 2°C / 50% ± 10% RH

Test Results:

For both Test Results:

Weight loss = Initial weight - Final weight, and Wear Index = (Weight loss x 1000)/number of cycles of revolution.

[0039] The above Test Results show clearly a surprisingly large improvement in the wear resistance of the fabric of the above Example for both 150 and 300 cycles. Indeed the test results show a reduction of roughly around 50% in wear for the fabric of the above Example in comparison to the other two sample fabrics. This enhanced wear resistance is also clearly evident in Figure 8 which is a photographic image of a timing belt 5 with the woven fabric of the above Example. The timing belt shown in Figure 8 has been in use for the same length of time as the belts Figures 1a, 2b and 1c and yet, unlike the belts of Figures 1a-1c, the belt in Figure 8 shows no evidence of fraying.

[0040] The PTFE yarn in the woven fabric 1 is believed to provide a lubrication effect resulting in PTFE material transferring to adjacent thermoplastic yarns. It is reasonable to assume that this lubrication/smearing effect would also be transferred to the pulley surfaces within a timing belt system, thus further reducing the co-efficient of friction of the timing belt, when entering and exiting the pulleys.

[0041] Although reference has been made to the woven fabric comprising a warp yarn and two or more different weft yarns, it is to be understood that these could be swapped and that the woven fabric may comprise a weft yarn and a warp bundle of two or more different warp yarns woven such that the weft yarn does not separate the warp yarns.

[0042] It will, of course, be apparent that modifications may be made to the specific fabric and to the belt described above. For example, the yarn bundle may include more than a single thread of Nylon 66 and a single thread of PTFE and whilst it is preferred that there is an equal number of threads of each material in the yarn bundle, this is not an essential feature. Also, both the Nylon 66 and the PTFE may be replaced by other materials having similar characteristics. Thus changes may be made to the fabric and to the belts described herein may include without departing from the scope of the invention as defined in the accompanying claims.