WO2009066492A1

WO2009066492A1 - V-ribbed belt

Info

Publication number: WO2009066492A1
Application number: PCT/JP2008/064673
Authority: WO
Inventors: Hideaki Kawahara; Atsuya Taniguchi
Original assignee: Bando Chemical Industries Ltd
Current assignee: Bando Chemical Industries Ltd
Priority date: 2007-11-21
Filing date: 2008-08-12
Publication date: 2009-05-28
Anticipated expiration: 2010-05-21
Also published as: JP2009127691A

Abstract

An object is to improve the mounting operability of a V-ribbed belt while suppress occurrence of misalignment noise. A V-ribbed belt (1) has a belt body (10) made of a rubber composition and a core wires embedded in the belt body in the belt longitudinal direction. The V-ribbed belt has a tensile elastic modulus in a range greater than 200 N/% AND BELOW 350 N/% per lcm of belt width in the belt longitudinal direction.

Description

DESCRIPTION

V-RIBBED BELT

FIELD OF THE INVENTION [0001]

The present invention relates to a V-ribbed belt and more specifically a V-ribbed belt that has a belt body made by a rubber composition and core wires embedded in the belt body in a longitudinal direction of the belt. BACKGROUND OF THE INVENTION [0002]

Hitherto, as a means for transmitting power from a driving side to a driven side, transmission belts are widely used, and recently there is a demand for high load transmission of synchronous belts, V-belts or V-ribbed belts designed for automobiles or general industries.

As such, a transmission belt is required to have an appropriate stretchability (elasticity), and for this, the body portion is usually made of a rubber composition.

Also, in order to impart a tensile strength to a belt in its longitudinal direction, a belt having a tensile resistant member called as core wires embedded in a belt body is widely used.

For example, for a V-ribbed belt or the like, a belt, which includes a belt body having a compression rubber layer with plural ribs formed thereon in a longitudinal direction of the belt (hereinafter referred as a belt longitudinal direction) for friction transmission to a pulley, an adhesive rubber layer laminated onto the compression rubber layer and core wires embedded in the adhesive rubber layer or between the adhesive rubber layer and the compression rubber layer, is widely used. [0003]

This V-ribbed belt is generally wound around plural shafts when in use, and is mounted to a device or the like while being wound around grooved pulleys provided on the respective shafts. For example, in an automobile, a V-ribbed belt is wound around plural pulleys for driving accessories of the automobile, such as an alternator pulley, an air conditioner pulley, a power steering pulley and a water pump pulley, and transmits driving power to these pulleys from a crankshaft pulley. [0004] When the V-ribbed belt is used in a layout of fixed shafts while being wound around these plural grooved pulleys, it is conventional that the V-ribbed belt as used has a circumferential length longer than the distance along which the belt is wound between the shafts and is subjected to a tensile force by an auto-tensioner after being wound between the shafts (cf. Patent Document l). Alternative to the above arrangement employing the auto-tensioner, there is another arrangement conventionally employed, in which a V-ribbed belt has a high stretchability and a circumference length slightly shorter than the distance along which the belt is wound between the shafts, and is stretched by a jig and then mounted between the shafts, which is called, such as snap-on mounting. [0005]

A V-ribbed belt capable of being served to this snap-on mounting method is also called as an elastic-type belt. This type of belt does not need an auto-tensioner, therefore contributes to reduction of machine costs, is excellent in mounting and dismounting operability, and thus is widely used in these days. For example, the following Patent Document 2 describes that the necessity to use an auto-tensioner can be omitted by using a V-ribbed belt having a low tensile elastic modulus. [0006] Meanwhile, recently, a transmission belt is generally required to reduce noises caused during the operation, and especially, a strong demand exists for a V-ribbed belt for an automobile to reduce noises during belt driving as a counter-measure for noise when in driving the automobile. It is known that a V-ribbed belt causes unusual noises when the shafts around which the belt is wound are misaligned to each other.

Especially, in an automobile, plural shafts for driving plural accessories are separately provided and therefore a V-ribbed belt for use in this arrangement is easy to be influenced by the misalignment when in use. [0007]

Therefore, noises can be expected to be reduced by suppressing the occurrence of unusual noise due to misalignment (hereinafter simply referred as misalignment noise). However, little study was made for a V-ribbed belt of the elastic type to suppress the occurrence of misalignment noise, and no countermeasure has yet been established.

In other words, a conventional V-ribbed belt has a problem in that it is difficult to suppress occurrence of misalignment noise while improving the mounting operability.

This problem is common not only for a V-ribbed belt for automobile, but also for a V-ribbed belt for general use.

[0008]

[Patent Document l] Japanese Patent Application Laid-open No. Her 5- 164206

[Patent Document 2] Japanese Patent Application Laid-open No. Sho-63- 195447

SUMMARY OF THE INVENTION [Problems to be Solved by the Invention]

[0009] It is an object of the present invention to improve the mounting operability of a V-ribbed belt while suppressing occurrence of misalignment noise. [Means of Solving the Problems]

[0010] According to the present invention, there is provided a V-ribbed belt having a belt body made of a rubber composition and core wires embedded in the belt body in the belt longitudinal direction, characterized in that the V-ribbed belt has a tensile elastic modulus in a range greater than 200 N/% and below 350 N/% per 1 cm of belt width in the belt longitudinal direction. [Advantages of the Invention]

[0011]

According to the present invention, it is possible to improve the mounting operability of the V-ribbed belt while at the same time suppress occurrence of misalignment noise. [Brief Description of the Drawings]

[0012]

FIG. 1 is a cross sectional perspective view of a V-ribbed belt of one embodiment of the present invention.

FIG. 2 is a cross sectional view illustrating the size of each element of the V-ribbed belt.

FIG. 3 is a schematic view illustrating a method for evaluation of misalignment noise. [Description of the Reference Codes]

[0013] 1^" belt body, 10^: compression rubber layer, 11: groove, 12: rib, 20: adhesive rubber layer, 30: cover rubber layer, 40: core wire [Best Mode for Carrying out the Invention]

[0014] Now, the description will be made for a preferred embodiment of the present invention.

A V-ribbed belt of this embodiment has a belt body formed into an endless shape, and core wires embedded in the belt body in the belt longitudinal (circumferential) direction.

The V-ribbed belt of this embodiment is formed to have a tensile elastic modulus in a range greater than 200 N/% and below 350 N/% per 1 cm of belt width in the belt longitudinal direction.

[0015] The tensile elastic modulus in the belt longitudinal direction can be determined by carrying out a tensile test, following the standard of Society of Automotive Engineers of Japan (JASO) "E109-94, Automotive V-ribbed belts".

More specifically, a V-ribbed belt is held for 24 hours at a temperature of 23 ±2 ⁰C and a relative humidity of 50 ±5 %, and cut into a strip-shaped specimen having a length of 400 mm in the belt longitudinal direction. A tensile test is conducted by using this strip-shaped specimen to investigate the relationship between stretch (%) of the belt and load (N) required for causing this stretch. The measured result for the range of the stretch from 1 % to 10 % is linearly regressed by the least square method to determine the inclination of the straight line. Thus, the tensile elastic modulus (N/%) can be determined.

The relationship between the stretch and the load can be determined through a step including: marking two lines on the strip-shaped specimen around a center portion thereof at 100 mm distance away from each other in the longitudinal direction of the specimen; gripping the specimen by two chucks located at 200 mm away from each other with an area of the specimen between the marks being positioned substantially at the center between the marked lines! carrying out a tensile test at a tensile rate of 50 ±5 mm/min; and measuring a load applied between the chucks every time the distance between the marked lines is stretched 1 mm (1%).

Then, the obtained tensile elastic modulus (N/%) of the V-ribbed belt is divided by the belt width (cm), and thereby the tensile elastic modulus per 1 cm of belt width can be determined. [0016]

The V-ribbed belt of this embodiment is designed to have a tensile elastic modulus in a range greater than 200 N/% and below 350 N/% per 1 cm of belt width in the belt longitudinal direction, for the reason that, when this tensile elastic modulus is 200 N/% or below, misalignment noise may not be satisfactorily suppressed, and when this tensile elastic modulus is 350 N/% or greater, a great force is required to stretch the V-ribbed belt, which makes it hard to carry out mounting and dismounting operations of the belt for the plural shafts.

[0017]

Now, a more detailed description will be made for the V-ribbed belt of this embodiment with reference to FIG. 1 attached hereto.

FIG. 1 illustrates a cross sectional perspective view of the V-ribbed belt.

As illustrated in FIG. 1, the V-ribbed belt of this embodiment has a three-layer structure of a compression rubber layer 10, an adhesive rubber layer 20 and a cover rubber layer 30 laminated in this order from the inner circumferential surface to the outer circumferential surface, of the belt.

The core wires 40 are embedded in the adhesive rubber layer 20 of the belt body 1.

[0018]

The compression rubber layer 10 of the V-ribbed belt of FIG. 1 is formed with two grooves 11 continuously extending in the belt longitudinal direction and each having a substantially V-shaped cross section so as to have three ribs 12 extending in the belt longitudinal direction and separated from each other by the grooves 11. These ribs 12 each are formed to have a width gradually reduced towards the inner circumferential surface and have a substantially isosceles trapezoidal cross section.

This compression rubber layer 10 is made of a rubber composition. [0019]

Specifically, this compression rubber layer 10 may be made of a rubber composition used for a conventional transmission belt, such as a resin composition that contains a reinforcing agent, such as a base rubber, a vulcanizing agent, a cross linking auxiliary agent, short fibers, inorganic particles and resin particles. [0020]

Examples of the base rubber include a natural rubber, a polyisoprene rubber, an epoxidized natural rubber, a styrene-butadiene copolymer rubber, a polybutadiene rubber, an acrylonitrile-butadiene copolymer rubber, a hydrogenated acrylonitrile-butadiene copolymer rubber, an ethylene -α -olefin rubber, a butyl rubber, chlorosulfonated polyethylene, alkylated chlorosulfonated polyethylene, chlorinated polyethylene, or a mixture thereof.

Among them, by using an ethylene-crolefin rubber, a V-ribbed belt can be imparted with an excellent heat resistance and an excellent cold resistance.

[0021] As the vulcanizing agent, sulfur or organic peroxide may be used.

Examples of this organic peroxide include di-t-butylperoxide, dicumylperoxide, t-butylcumylperoxide, 1, 1 -t-butylperoxy-3, 3,5-trimethylcyclohexane, 2, 5 ^■ dimethyl-2,5 - di(t-butylperoxy)hexane,

2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3, bis(t-butylperoxydϋsopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxy benzoate, and t-butylperoxy2-ethylhexyl carbonate.

[0022]

As the vulcanization accelerator, thiazole, thiuram or sulfonamide type may be used. Examples of the thiazole-type vulcanization accelerator include 2-mercaptobenzothiazole, 2-mercaptothiazoline, dibenzothiazyl disulfide, and zinc salt of 2-mercaptobenzothiazole. Examples of the thiuraπrtype vulcanization accelerator include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and N,N'-dimethyl-N,N'-diphenylthiuram disulfide. Examples of the sulfonamide -type vulcanization accelerator include N-cyclohexyl-2-benzothiazolesulfenamide, and N,N'-cyclohexyl-2-benzothiazolesulfenamide.

Examples of the other type vulcanization accelerator include bismaleimide and ethylenethiourea.

These vulcanization accelerators may be used alone or in combination of two or more types.

[0023]

Examples of the cross linking auxiliary agent include triallylcyanurate, triallylisocyanurate, 1,2-polybutadiene, a metallic salt of an unsaturated carboxylic acid, oxime, guanidine, trimethylolpropane trimethacrylate, ethylene glycol dimethacrylate, N,N'-m-phenylenebismaleimide, and sulfur.

[0024]

Examples of the short fibers include polyester fibers, polyvinyl alcohol fibers, polyamide fibers, cotton fibers, silk fibers, linen fibers, wool fibers, cellulose fibers, aromatic polyamide fibers, wholly aromatic polyester fibers, poly(para-phenylenebenzobisoxazole) fibers, carbon fibers, polyketone fibers, and basaltic fibers.

Among them, it is possible to further suppress occurrence of misalignment noise by mixing 10 wt. % or more of polyamide fibers in a rubber composition of the compression rubber layer.

From the view point of the effect of suppressing occurrence of misalignment noise, a larger amount of polyamide short fibers are preferably contained. However, when the amount is excessive, the bending fatigue resistance of rubber is deteriorated and hence rib cracking may be caused at an early stage. Therefore, the amount of polyamide short fibers contained in the rubber composition is preferably 30 wt. % or lower. [0025]

Examples of the inorganic particles include graphite, molybdenum disulfide, mica, talc, antimony trioxide, molybdenum diselenide, and tungsten disulfide. Examples of the resin particles include fine particles of polyterafluoroethylene (PTFE), ultra high molecular weight polyethylene resin, cross-linked acrylic resin or cross-linked rubber.

As described in JIS K 6936-1, -2, the term of the "ultra high molecular weight polyethylene" is intended to be a polyethylene material, in which the melt flow rate of the polyethylene material cannot be measured according to JIS K 7210, and even when the melt mass-flow rate (MFR) of the polyethylene material is measured at 190⁰C and 21.6 kg load, the measured value becomes less than 0.1 g/10 min.

[0026]

Although no detailed description will be made herein, the aforesaid rubber composition may be appropriately mixed with carbon black, plasticizer, age resistor, or processing material. [0027]

The adhesive rubber layer 20, the cover rubber layer 30, etc. may be made of the same rubber composition as the rubber composition used in making the aforesaid compression rubber layer. For example, the adhesive rubber layer 20 may be made of the materials of the above-exemplified rubber composition excluding the short fibers. The cover rubber layer 30 may be formed by lining cloth or the like with the above-exemplified rubber composition. [0028]

For the core wires 40, it is preferable to use materials having a low stretching elastic modulus among those conventionally used as core wires, and preferable to use polyamide fibers, for the reason that the tensile elastic modulus can be easily adjusted into a range greater than 200 N/% and below 350 N/% per 1 cm of belt width in the belt longitudinal direction of the V-ribbed belt.

This tensile elastic modulus can be measured by the method according to, for example, JIS L1013. [0029] When core wires are formed by using fibers having a low stretching elastic modulus such as polyamide fibers and fibers having a stretching elastic modulus higher than the aforesaid fiber having a low stretching elastic modulus, the tensile elastic modulus per 1 cm of belt width of a V-ribbed belt can be more easily adjusted into the above range. As fibers having a higher stretching elastic modulus to be used in combination with the polyamide fibers, polyester fibers are preferable for the reason that they are widely used for V-ribbed belts and therefore fibers having desirable characteristics can be easily obtained.

Although a method for forming core wires by using both fibers having a low stretching elastic modulus and fibers having a high stretching elastic modulus is not limited to a specific method, it is possible to employ a method in which intermediate yarns unified according to the stretching elastic modulus obtained by such a method in which a yarn formed of plural fibers having a low stretching elastic modulus is twisted with a yarn formed of plural fibers having a high stretching elastic modulus, thereby forming each intermediate yarn, and these intermediate yarns are interlaced with each other, or to employ a method in which plural yarns, each being formed by twisting plural fibers having different stretching elastic moduli, are twisted together. [0030]

When the intermediate yarns unified according to the stretching elastic modulus are interlaced with each other and core wires are formed of fibers having different stretching elastic moduli, the stretching elastic modulus of core wires can be easily adjusted according to the combination of these intermediate yarns, and the tensile elastic modulus per 1 cm of belt width in the belt longitudinal direction of a V-ribbed belt can be more easily adjusted into the range greater than 200 N% and below 350 N/%.

On the other hand, when core wires are formed by twisting together plural yarns, each being formed by twisting plural fibers having different stretching elastic moduli, the entire core wires can have homogeneous characteristics. [0031]

When the belt body with these core wires embedded therein is made of a rubber composition containing an ethylene-crolefin rubber, the core wires are used preferably after they are predipped in isocyanate for surface treatment, and then coated with solution prepared by dissolving chlorosulfonated polyethylene by solvent, and then coated with chlorosulfonated polyethylene by drying the solution.

Thus, by using an ethylene -α -olefin rubber as a base rubber of the rubber composition of the belt body, it is possible to impart a V-ribbed belt with an excellent heat resistance and an excellent cold resistance, while on the other hand, the rubber composition, which contains an ethylene-α-olefϊn rubber, has a low adhesiveness to other members and easy to cause a so-called pop-out of core wires in a V-ribbed belt. On the other hand, by using the core wires, which have been subjected to surface treatment by isocyanate and then coated with chlorosulfonated polyethylene, it is possible to suppress occurrence of the pop-out.

That is, when the belt body is made of a rubber composition containing an ethylene -α-olefin rubber and the core wires are embedded in the belt body after they are subjected to surface treatment and then coated with chlorosulfonated polyethylene, it is possible to suppress occurrence of pop-out while imparting the V-ribbed belt with an excellent heat resistance and an excellent cold resistance, thereby ensuring the reliability of the V-ribbed belt over a prolonged time.

[0032]

Accordingly, it can be said that the V-ribbed belt of this embodiment, especially the V-ribbed belt that has the belt body made of a rubber composition containing an ethylene-α-olefin rubber, and has the core wires embedded therein, which are subjected to surface treatment and then coated with chlorosulfonated polyethylene, is appropriately used for automobiles.

Specifically, when the V-ribbed belt of the present invention is used for driving accessories of an automobile and is mounted around fixed shafts without using an autertensioner, a significant effect of the present invention can be further demonstrated. EXAMPLES

[0033]

Now, the description of the present invention will be made for the present invention by citing Examples without intention to limit the present invention thereto.

[0034]

(Example l)

As shown in Table 1, a V-ribbed belt of Example 1 is prepared by preparing a belt body having core wires embedded in the inside thereof made of a rubber composition, which has a base rubber of an ethylene-α-olefin rubber (an ethylene propylene diene rubber: EPDM) and contains 20 wt. % of polyamide short fibers.

The core wires used are marketed under the name of "Stanyl (470 dtex)" manufactured by DSM based on polyamide 46 fibers, in which four yarns thereof are grouped together, and primarily twisted in the S-direction at a pitch of 17.8 times/10 cm, thereby obtaining three yarns, and these three yarns are grouped together and finally twisted in the Z-direction at a pitch of 10.3 times/10 cm. The core wires are immersed in a toluene solution of isocyanate

(isocyanate solid content 16 wt. %) and is subjected to surface treatment in which they are dried for 40 seconds at a temperature of 245 °C, then coated with a chlorosulfonated polyethylene solution, then dried four 40 seconds at a temperature of 60 "C, and then embedded in the belt body. The core wires are embedded in the belt body to have a distance of 1.3 mm between the adjacent core wires (hereinafter referred also as a "twist pitch").

The structure (size) of the prepared V-ribbed belt is illustrated in FIG. 2, in which six ribs are formed at a pitch of 3.56 mm, each having a width of about 21.4 mm, a thickness of about 4.8 mm and a circumferential length of 1117 mm. [0035]

(Examples 2-5, Comparative Examples 1*5)

V-ribbed belts of Examples 2-5 and Comparative Examples 1*5 each are prepared in the same manner as Example 1, except that the structure of core wires and the twist pitch are changed as shown in Table 1. In the V-ribbed belt of Comparative Example 1, in place of coating with a chlorosulfonated polyethylene solution, the core wires are immersed in a resorcin formalin latex (RFL) solution and dried at a high temperature, thereby processing the core wires. Thus, the respective V-ribbed belts are prepared. [0036] Table 1

*1 represents that two poly amide 66 fibers (400 dTex) are grouped together and S-twisted and three polyester fibers (polyethylene terephthalate^ PET, 1110 dTex) are grouped together and S-twisted, and these twisted fibers are Z-twisted. *2 represents that polyamide 66 fibers (930 dTex) and polyester fibers (PET, 1110 dTex) are grouped together and S-twisted, thereby preparing three yarns, which are then Z-twisted. [0037]

(Measurement of Tensile Elastic Modulus)

The tensile elastic modulus in the belt longitudinal direction of a V-ribbed belt of each of Examples and Comparative Examples are determined by carrying out a tensile test, following the standard of Society of Automotive Engineers of Japan (JASO) "E109-94, Automotive V-ribbed belts."

More specifically, each V-ribbed belt is held for 24 hours at a temperature of 23+2 ⁰C and a relative humidity of 50±5 %, and cut into a strip-shaped specimen having a length of 400 mm in the belt longitudinal direction. A tensile test is conducted by using this strip-shaped specimen to investigate the relationship between stretch (%) of the belt and load (N) required for causing this stretch. The measured result for the range of the stretch from 1 % to 10 % is linearly regressed by the least square method to determine the inclination of the straight line. Thus, the tensile elastic modulus (N/%) is determined. The relationship between the stretch and the load is determined by marking two lines on the strip-shaped specimen around a center portion thereof at 100 mm distance away from each other in the longitudinal direction of the specimen, gripping the specimen by two chucks located at 200 mm away from each other with an area of the specimen between the marks being positioned substantially at the center between the marked lines, carrying out a tensile test at a tensile rate of 50 ±5 mm/min, and measuring a load applied between the chucks every time the distance between the marked lines is stretched 1 mm (1%).

Then, the obtained tensile elastic modulus (N/%) of the V-ribbed belt is divided by the belt width (21.4 cm), and thereby the tensile elastic modulus per 1 cm of belt width is obtained.

The result is shown in Table 2.

[0038]

(Misalignment Noise) The evaluation of misalignment noise is carried out based on an arrangement, in which a V-ribbed belt of each of Examples and Comparative Examples is wound around four pulleys in total which are respectively held in abutting engagement with the inner side (a compression rubber layer side) and the rear side (a canvas side), of the V-ribbed belt, as illustrated in FIG. 3. [0039]

Specifically, the pulleys held in abutting engagement with the belt inner circumferential surface include a driving pulley having a diameter of 80 mm ("Pd" in FIG. 3), a tension pulley having a diameter of 60 mm ("Pt" in FIG. 3), to which a load is applied to apply a tension to the belt, and a resin-made pulley having a diameter of 130 mm ("Pr" in FIG. 3) for water injection. The pulley held in abutting engagement with the belt outer circumferential surface includes an idler pulley having a diameter of 80 mm ("Pi" in FIG. 3). The evaluation is carried out by using these pulleys. [0040]

In the evaluation of misalignment noise, the resin-made pulley (Pr) is held in position with a misalignment of 3.5 degrees (misalignment angle), the tension pulley (Pt) is subjected to a tension load of 300 N by a dead weight (DW) loading system, and the driving pulley (Pd) is rotated at 750 rpm. The evaluation of misalignment noise is carried out at an atmospheric temperature of 5 degrees. First, each V-ribbed belt is driven under the above conditions, and then water is sprayed onto the resin-made pulley (Pr). It is evaluated whether the belt makes a screeching noise within three minutes before the surface of the resin-made pulley (Pr) is dried out. According to the evaluation, a symbol "O" represents that the belt makes no screeching noise, a symbol "Δ" represents that the belt makes a slight screeching noise, a symbol " x " represents that the belt makes a screeching noise at a low level, and a symbol " X X" represents that the belt makes a screeching noise at a high level.

The result is also shown in Table 2.

[0041]

(Evaluation of Belt Mounting Operability) Two shafts are disposed in parallel to each other and pulleys each having a diameter of 120 mm are respectively mounted to these shafts. Each V-ribbed belt is wound around the pulleys. The shafts are moved away from each other with the V-ribbed belt kept wound therearound until the tension force applied to the V-ribbed belt reaches 588 N and fixed at this position. Then, the V-ribbed belt is dismounted under the above condition, and it is evaluated whether this V-ribbed belt can be manually wound around the shafts while the shafts are held at the above position.

According to the evaluation, a symbol "®" represents that the V-ribbed belt can be easily mounted and hence an excellent operability can be achieved, a symbol "O" represents that a mounting operation can be made without any trouble although it is felt that the belt has some stiffness, and a symbol " x " represents that the belt cannot be mounted around the shafts.

The result is also shown in Table 2.

[0042] Table 2

*V Tensile elastic modulus per 1 cm of belt width in the belt longitudinal direction

[0043]

It is apparent from the result shown in Table 2 that the V-ribbed belt of the present invention is excellent in operability as an elastic belt enabling snap -on mounting, and satisfactorily suppresses occurrence of misalignment noise.

Claims

1. A V-ribbed belt having a belt body made of a rubber composition and core wires embedded in the belt body in the belt longitudinal direction, characterized in that the V-ribbed belt has a tensile elastic modulus in a range greater than 200 N/% and below 350 N/% per 1 cm of belt width in the belt longitudinal direction.

2. The V-ribbed belt according to claim 1, wherein polyamide fiber is used in the core wires.

3. The Vribbed belt according to any one of claims 1 and 2, wherein the core wires are made of fibers having different stretching elastic moduli.

4. The V-ribbed belt according to claim 3, wherein the core wires are made of the polyamide fiber and fiber having a stretching elastic modulus higher than that of the polyamide fiber.

5. The Vribbed belt according to claim 4, wherein the fiber having a stretching elastic modulus higher than that of the polyamide fiber is polyester fiber.

6. The Vribbed belt according to any one of claims 3 to 5, wherein the core wires each are made of a first yarn formed of twisted plural fibers having a uniform stretching elastic modulus, and a second yarn formed of twisted plural fibers having a stretching elastic modulus higher than the stretching elastic modulus of the fibers of the first yarn, the first yarn and the second yarn being interlaced with each other.

7. The V-ribbed belt according to any one of claims 3 to 5, wherein the core wires each are made of plural yarns twisted together, and each of the plural yarns is made of plural fibers having different stretching elastic moduli.

8. The V-ribbed belt according to any one of claims 1 to 7, wherein the belt body is made of a rubber composition containing an ethylene-crolefin rubber, and the core wires are embedded in the belt body after they are subjected to surface treatment by isocyanate and then coated with chlorosulfonated polyethylene.

9. The V-ribbed belt according to any one of claims 1 to 8 used for driving an accessory of an automobile and mounted around fixed shafts without using an auto-tensioner.