Patent Publication Number: US-2005143209-A1

Title: Friction drive belt and method for fabricating the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2003-299737 filed in Japan on Aug. 25, 2003, the entire contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      (a) Field of the Invention  
      This invention relates to friction drive belts and methods for fabricating the same.  
      (b) Description of the Related Art  
      V-ribbed belts are generally used as automotive engine accessory drive belts. V-ribbed belts have a belt body made of rubber, of which a ribbed rubber layer (working part) contacting with a pulley contains short fibers oriented along the width of the belt. Furthermore, the short fibers contained in the belt body project beyond the belt surface. This reduces the friction resistance of the belt surface, leading to reduction of abnormal sounds produced between the belt and the pulley and reduction of abrasion at the belt surface.  
      Japanese Unexamined Utility Model Publication No. 6-40497 discloses a V-ribbed belt having a double-layered, ribbed rubber in which short fibers embedded into a rib top-side portion are oriented substantially along the length of the belt and short fibers embedded into the remaining rib root-side portion are oriented substantially orthogonally to the length direction of the belt. The document describes that when the belt is wrapped around a flat pulley in order to use it as a flat belt, an unpleasant stick-slip sound can be prevented from being produced in the belt travel.  
      Japanese Unexamined Patent Publication No. 7-63242 discloses a V-ribbed belt comprising a ribbed rubber layer formed of hydrogenated acrylonitrile-butadiene rubber (H-NBR), a tension member layer adjoining the ribbed rubber layer, and a top fabric layer adjoining the tension member layer, wherein part of the H-NBR rubber forming each rib root of the ribbed rubber layer is compounded with short fibers oriented substantially along the width of the belt, and part of the H-NBR rubber forming each rib top of the ribbed rubber layer is compounded with unsaturated carboxylic acid&#39;s metal salt. This document describes that the V-ribbed belt has excellent heat resistance, abrasion resistance and flex fatigue resistance even when used under severe conditions such as increasing atmospheric temperature, is free from troubles such as abrasion-induced failures, and therefore has a long life.  
      Japanese Examined Utility Model Publication No. 7-29330 discloses a V-belt for power transmission in which an adhesion rubber layer contains short fibers oriented along the belt width, a tension member layer is formed of a tension cord embedded in the adhesion rubber layer, a tension layer is laid on the tension member layer, and a compression rubber layer is laid under the tension rubber layer. Furthermore, a cord fabric is embedded in the rubber forming the compression rubber layer, a reinforcing rubber layer is formed, between the tension member layer and the cord fabric, with short fibers of the same type as in the adhesion rubber layer mixed thereinto in an orientation along the belt width and in higher volume per unit rubber weight than that of the short fibers in the adhesion rubber layer. The document describes: that the existence of the reinforcing rubber layer prevents the cord fabric from causing their abnormal approach to the tension cord and their disordering in embedded arrangement during the vulcanization of the belt, and absorbs the difference in the resistance against a lateral force from extremely sideward between the tension member layer and the cord fabric during the belt travel; and that since the reinforcing rubber layer exists to have a definite hardness difference from the adhesion rubber layer by intentionally increasing the amount of short fibers therein over that in the adhesion rubber layer, this contributes to avoidance of direct contact between the tension cord and the transversely parallel-arranged cords and suppresses the occurrence of delamination therebetween and, in the worst case, protrusion of the tension cord, resulting in enhanced belt durability.  
      Japanese Unexamined Patent Publication No. 10-338377 discloses an endless conveyer belt having a belt body formed of an elastic material and short fibers dispersed into the elastic material, wherein the short fibers have a length of 1 mm to 10 mm and a fineness of 0.5 denier to 30 denier, are mixed into the elastic material at a weight % of 1 to 30, and are dispersed into the whole belt body in an orientation along the belt length. The document describes that the belt is relatively thin and relatively high in coefficient of friction at its one side.  
      Japanese Unexamined Patent Publication No. 2001-146942 discloses a drive belt in which a cord is embedded along the belt length into an adhesion rubber layer, a cover fabric is stacked on the surface of the adhesion rubber layer, a compression rubber layer is disposed adjacent the adhesion rubber layer, and the compression rubber layer is formed so that at least one particle-dispersed rubber layer composed of rubber containing dispersed particulate inorganic material is interbedded in a short-fiber-mixed rubber layer composed of rubber containing dispersed short fibers. The document describes that since the drive belt includes the particle-dispersed rubber layer capable of keeping high the thicknesswise surface roughness of the belt working flank contacting with a pulley, it can exhibit high power transmission performance even with water on the working flank, has enhanced running life in a high temperature atmosphere and in a low temperature atmosphere, and is excellent in weather resistance.  
      Japanese Unexamined Patent Publication No. 2001-317595 discloses a drive belt having a V-rib provided along the belt length, wherein a plurality of rubber layers composed of those of rubber type compounded with short fibers and those of rubber type compounded with no short fiber are stacked, and the V-rib is formed of a combination of stacking of both types of rubber layers to control the coefficient of friction of the belt side ace. The document describes that various kinds of V-ribs can be produced using multiple levels of coefficients of friction without the need for design change in composition of the rubber compound for the V-rib.  
      Meanwhile, a V-ribbed belt is fabricated by wrapping around a molding drum materials including an unvulcanized rubber sheet, a woven fabric and a cord and then applying heat and pressure to the wrapped materials. In this case, used as the unvulcanized rubber sheet forming a ribbed rubber layer of the belt body is one containing short fibers oriented substantially perpendicularly to the direction of wrapping around the molding drum.  
      Such an unvulcanized rubber sheet as containing short fibers oriented in a single direction is produced by extending an unvulcanized rubber mass containing short fibers in the form of a sheet by a calender roll or other means. The unvulcanized rubber sheet thus produced contains short fibers oriented in the longitudinal direction of the sheet.  
      Therefore, in fabricating a V-ribbed belt, the elongate, short-fiber-containing, unvulcanized rubber sheet cannot be used as it is with its lengthwise direction aligned with the direction of wrapping around the molding drum, but needs to be cut in a slightly shorter length than the axial length of the drum and used as wrapped around the molding drum to align both the cut ends with both ends of the molding drum.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to provide a friction drive belt having a novel construction that uses no short fiber-containing rubber, and a method for fabricating the same.  
      The present invention is directed to a friction drive belt, used by being wrapped around a plurality of pulleys, for transmitting power by friction between its belt body and each of the pulleys. In the friction drive belt, a working part of the belt body through which power is transmitted has a structure in which one or more rubber layers and one or more non-woven fabric layers are alternately stacked along the thickness of the belt.  
      According to the friction drive belt having the above structure, the non-woven fabric layer or layers exposed at the belt surface reduce the friction resistance at the belt surface, and therefore suppress abnormal sounds produced between the belt surface and the pulley and friction at the belt surface. That is, the friction drive belt of this invention has the same belt performance as a friction drive belt in which the working part of its belt body is formed of short-fiber-containing rubber.  
      The non-woven fabric layer or layers of the working part preferably have a total thickness of 15% to 75%, both inclusive, of the thickness of the working part.  
      When the total thickness of the non-woven fabric layer or layers is 15% to 75%, both inclusive, of the thickness of the working part, the belt can play a fundamental role of power transmission and effectively reduce the coefficient of friction at the belt surface. More specifically, as described later with reference to Examples, if the total thickness of non-woven fabric layers is less than 15% of the thickness of the working part, abrasion at the belt surface during travel is significantly increased. On the other hand, if the total thickness of non-woven fabric layers is more than 75% of the thickness of the working part, the belt flex resistance is extremely deteriorated.  
      A friction drive belt of the present invention as described above can be fabricated by forming, on the outer periphery of a molding drum, a structure in which one or more unvulcanized rubber layers and one or more non-woven fabric layers are alternately stacked to cover the whole circumference of the molding drum; and applying heat and pressure to the layered structure of the unvulcanized rubber layer or layers and the non-woven fabric layer or layers to provide an integral lamination. Therefore, there is no need to cut a short-fiber-containing unvulcanized rubber sheet in an appropriate length and align the orientation of short fibers with the belt widthwise direction, unlike the case of fabricating a friction drive belt in which the working part of its belt body is made from short-fiber-containing rubber.  
      The types of friction drive belts according to the present invention are not particularly limited, but include friction drive belts in which the belt body is that of a raw edge plane V-belt, that of a raw edge laminated V-belt, that of a raw edge cogged V-belt, or that of a V-ribbed belt. V-ribbed belts are generally used for automotive accessory drive and produced much more than the other types of belts. Therefore, when the friction drive belt of the present invention is a V-ribbed belt, general belt productivity growth can be best achieved.  
      Other objects, features and benefits will be apparent from the following description referring to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view showing a V-ribbed belt according to an embodiment of the present invention.  
       FIGS. 2A and 2B  are diagrams illustrating a method for fabricating a V-ribbed belt.  
       FIG. 3  is a diagram illustrating the layout of a serpentine accessory drive system in which a V-ribbed belt is wrapped around pulleys.  
       FIGS. 4A  to  4 K are cross-sectional views showing various modifications of the inventive V-ribbed belt.  
       FIG. 5  illustrates a belt coefficient-of-friction measurement tester used for measuring the coefficient of friction at the ribbed rubber layer surface.  
       FIG. 6  is a diagram illustrating the layout of a belt run tester for evaluating V-ribbed belts based on an abrasion resistance test.  
       FIG. 7  is a diagram illustrating the layout of a belt run tester for running durability evaluation on V-ribbed belts.  
       FIG. 8  is a diagram illustrating the layout of a belt run tester for noiselessness evaluation on V-ribbed belts.  
       FIGS. 9A and 9B  are graphs showing the relation between the total thickness of non-woven fabric layers and coefficient of friction.  
       FIGS. 10A and 10B  are graphs showing the relation between the total thickness of non-woven fabric layers and rate of abrasion.  
       FIGS. 11A and 11B  are graphs showing the relation between the total thickness of non-woven fabric layers and durability.  
       FIGS. 12A and 12B  are graphs showing the relation between the total thickness of non-woven fabric layers and noiselessness.  
       FIG. 13  is a table showing belt structures and test evaluation results. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.  
       FIG. 1  shows a V-ribbed belt B according to an embodiment of the present invention.  
      The V-ribbed belt B is composed of an adhesion rubber layer  11 , a tension rubber layer  12  provided integrally on the upper face of the adhesion rubber layer  11 , a back face reinforcing fabric  13  attached integrally to the upper face of the tension rubber layer  12 , i.e., provided on the belt back face side thereof, a ribbed rubber layer  14  provided integrally on the lower face of the adhesion rubber layer  11 , i.e., on the belt inner face side thereof, a cord  16  disposed to form helical turns extending substantially along the length of the belt in the middle of the thickness of the adhesion rubber layer  11  and spaced at regular intervals in the belt widthwise direction. Among these members, the adhesion rubber layer  11 , the tension rubber layer  12  and the ribbed rubber layer  14  constitute a V-ribbed belt body.  
      The adhesion rubber layer  11  forms a flat looped strip located in the middle of the V-ribbed belt body to extend along the length of the belt, is made from a rubber composition containing a rubber component such as chloroprene rubber (CR), ethylene-propylene-diene monomer (EPDM) or hydrogenated acrylonitrile-butadiene rubber (H-NBR), and serves as a layer for retaining the cord.  
      The tension rubber layer  12  forms a flat looped strip located on the adhesion rubber layer  11  in the V-ribbed belt body to extend along the length of the belt, and is made from a rubber composition containing a rubber component such as chloroprene rubber (CR), ethylene-propylene-diene monomer (EPDM) or hydrogenated acrylonitrile-butadiene rubber (H-NBR).  
      The back face reinforcing fabric  13  is formed by subjecting a woven fabric of warps and wefts made from nylon fibers, cotton or the like to adhesion treatment with rubber cement obtained by solving rubber in a solvent, and constitutes a reinforcing member for reinforcing the belt back face.  
      The ribbed rubber layer  14  is a portion of the V-ribbed belt body in which six ribs  15  are disposed, under the adhesion rubber layer  11 , at regular pitches in the belt widthwise direction to extend along the length of the belt. The ribbed rubber layer  14  has a structure in which rubber layers  14   a  and non-woven fabric layers  14   b  are alternately stacked, and constitutes a working part for transmitting power to a pulley by directly contact with it. Each rubber layer  14   a  forming the ribbed rubber layer  14  is made from a rubber composition containing a rubber component such as chloroprene rubber (CR), ethylene-propylene-diene monomer (EPDM) or hydrogenated acrylonitrile-butadiene rubber (H-NBR), like the adhesion rubber layer  11 . The rubber composition forming the rubber layer  14   a  may contain short fibers. The non-woven fabric layer  14   b  is formed by subjecting, prior to the molding of a belt, a sheet of non-woven fabric made of chemical fibers such as nylon fibers, polyester fibers or aramid fibers, or natural fibers such as cotton to adhesion treatment with, for example, resorcinol-formaldehyde latex (RFL) liquid or rubber cement. The proportion of non-woven fabric layers  14   b  that is contained in the ribbed rubber layer  14  is greater toward the belt inner periphery than toward the belt outer periphery, and the rib top is constituted by a non-woven fabric layer  14   b.  The total thickness of the non-woven fabric layers  14   b  is 15% to 75%, both inclusive, of the thickness of the ribbed rubber layer  14 , i.e., the rib height.  
      The cord  16  is formed by subjecting, prior to the molding of a belt, a twist yarn (Z-twisted) made of polyethylene terephthalate (PET) fibers, polyethylene naphthalate (PEN) fibers or polyvinyl alcohol (PVA) fibers to adhesion treatment with resorcinol-formaldehyde latex (RFL) liquid or the like and stretch thermoforming process, and constitutes a tension member that gives strength and tensile strength to the belt.  
      According to the V-ribbed belt B having the above structure, the non-woven fabric layers  14   b  of the ribbed rubber layer  14  reduce the friction resistance at the belt surface, and therefore suppress abnormal sounds produced between the belt surface and the pulley and friction at the belt surface. That is, the V-ribbed belt B has the same belt performance as a V-ribbed belt in which a ribbed rubber layer serving as a working part is formed of short-fiber-containing rubber.  
      The shearing force acting on the belt becomes larger, in the working part, toward the belt outer periphery than toward the belt inner periphery. Therefore, if the proportion of non-woven fabric layers  14   b  contained in the ribbed rubber layer  14  becomes greater toward the belt outer periphery, the risk of delamination is increased. Since in this embodiment, however, the proportion of non-woven fabric layers  14   b  contained in the ribbed rubber layer  14  is greater toward the belt inner periphery than toward the belt outer periphery, delamination is less likely to occur.  
      Furthermore, since the total thickness of the non-woven fabric layers  14   b  is 15% to 75%, both inclusive, of the thickness of the ribbed rubber layer  14 , the belt can play a fundamental role of power transmission and effectively reduce the coefficient of friction at the belt surface.  
      Next, a description will be made of a method for fabricating the V-ribbed belt B with reference to  FIGS. 2A and 2B .  
      First, materials for the fabrication of a V-ribbed belt B are prepared as follows: a first unvulcanized rubber sheet  12 ′ for the formation of a tension rubber layer  12 , two second unvulcanized rubber sheets  11 ′ for the formation of an adhesion rubber layer  11 , a plurality of third unvulcanized rubber sheets  14   a ′ for the formation of rubber layers  14   a  in a ribbed rubber layer  14 , a plurality of adhesion-treated (or non-adhesion-treated) non-woven fabric sheets  14   b ′ (of 0.02 mm to 1.50 mm thickness) for the formation of non-woven fabric layers  14   b  in the ribbed rubber layer  14 , an adhesion-treated woven fabric  13 ′ for the formation of a back face reinforcing fabric  13 , and an adhesion-treated twist yarn  16 ′ for the formation of a cord  16 .  
      Next, the woven fabric  13 ′ formed in a cylinder is wrapped over the molding drum  80  to fit on it, the first unvulcanized rubber sheet  12 ′ is then wrapped around the woven fabric  13 ′ a predetermined number of times, and one of the second unvulcanized rubber sheets  11 ′ is then wrapped around a predetermined number of times.  
      Then, the twist yarn  16 ′ is wound around the second unvulcanized rubber sheet  11 ′ on the molding drum  80  to form helical turns at regular pitches from one end to the other end of the molding drum  80 .  
      Thereafter, the other second unvulcanized rubber sheet  11 ′ is wrapped around the layer of the twist yam  16 ′ a predetermined number of times.  
      Next, one of the third unvulcanized rubber sheets  14   a ′ is wrapped around the second unvulcanized rubber sheet  11 ′ a predetermined number of times, and one of the non-woven fabric sheets  14   b ′ is then wrapped therearound. This alternate wrapping of a third unvulcanized rubber sheet  14   a ′ and a non-woven fabric sheet  14   b ′ is repeated a predetermined number of times (one to thirty times). As a result of the above process, as shown in  FIG. 2A , a stack is formed on the outer periphery of the molding drum  80 , and is as follows, in the order from nearest to farthest from the molding drum: the woven fabric  13 ′, the first unvulcanized rubber sheet  12 ′, the second unvulcanized rubber sheet  11 ′, the twist yarn  16 ′, the second unvulcanized rubber sheet  11 ′, and a layered structure of the third unvulcanized rubber sheets  14   a ′ and the non-woven fabric sheets  14   b ′ ( FIG. 2A  shows the case where four non-woven fabric sheets  14   b ′ are contained in the stack.  
      Next, the molding drum  80  wrapped with the stack is covered with a rubber sleeve, put into a vulcanizer, and cured therein under predetermined temperature and pressure conditions for a predetermined time. During the time, the first to third unvulcanized rubber sheets  11 ′,  12 ′ and  14   a ′ are fluidized and crosslinked so that the woven fabric  13 ′, the non-woven fabric sheets  14   b ′ and the twist yarn  16 ′ are bonded together with the rubber materials to form an integral cylindrical slab. As a result, as shown in  FIG. 2B , a lamination is formed on the outer periphery of the molding drum  80  and is as follows, in the order from nearest to farthest from the molding drum: a back face reinforcing fabric  13 , a tension rubber layer  12 , an adhesion rubber layer  11  having a cord  16  embedded therein, and a ribbed rubber layer  14  in which rubber layers  14   a  and non-woven fabric layers  14   b  are alternately stacked.  
      Then, the molding drum  80  is taken out of the vulcanizer, the rubber sleeve is removed, and subsequently the molded slab is removed.  
      Next, the slab is cut into three or four axially even pieces, and the outer periphery of each piece is ground circumferentially to form ribs  15 .  
      Finally, each slab piece is cut into specified widths, and each cut piece is turned over to direct its side having the ribs  15  inward, thereby obtaining a V-ribbed belt B.  
      In fabricating the above V-ribbed belt B, the layered structure of the non-woven fabric sheets and the third unvulcanized rubber sheets may be formed firstly by alternately stacking one or more third unvulcanized rubber sheets and one or more non-woven fabric sheets to organize them into an elongate sheet, and then by wrapping the elongate sheet around the second unvulcanized rubber sheet a predetermined number of times. The elongate sheet may consist of a double-layered structure of a third unvulcanized rubber sheet and a non-woven fabric sheet, or a triple-layered structure with a non-woven fabric sheet sandwiched between two third unvulcanized rubber sheets, or a multi-layered structure. In this connection, if a non-woven fabric sheet  14   b ′ before molded has a thickness of about 0.20 mm or less, the non-woven fabric layer  14   b  obtained by molding it has substantially the same thickness.  
      As described above, according to the fabrication method of a V-ribbed belt B of the present invention, a ribbed rubber layer  14  is formed by one or more third unvulcanized rubber sheets  14   a ′ and one or more non-woven fabric sheets  14   b ′. Therefore, there is no need to cut a short-fiber-containing unvulcanized rubber sheet in an appropriate length and align the orientation of short fibers with the belt widthwise direction, unlike the case of fabricating a friction drive belt in which the ribbed rubber layer  14  is made from short-fiber-containing rubber.  
      Next, a description will be made of a belt drive system  30  using the V-ribbed belt B.  
       FIG. 3  shows a pulley layout of a serpentine belt drive system for automotive engine accessories, in which a V-ribbed belt B is wrapped around the pulleys.  
      This pulley layout for serpentine belt accessory drive is composed of an accessory A pulley  31  located at an uppermost position, an accessory B pulley  32  placed below the accessory A pulley  31 , a tensioner pulley  33  placed to the lower left of the accessory A pulley  31 , an accessory C pulley  34  placed below the tensioner pulley  33 , a crankshaft pulley  35  placed to the lower left of the tensioner pulley  33 , and an accessory D pulley  36  placed to the lower right of the crankshaft pulley  35 . All the pulleys other than the tensioner pulley  33  and the accessory C pulley  34 , which are both flat pulleys, are ribbed pulleys. The V-ribbed belt B is wrapped around the accessory A pulley  31  to make contact at its ribs  15 , then wrapped around the tensioner pulley  33  to make contact at its belt back face, then sequentially wrapped around the crankshaft pulley  35  and the accessory D pulley  36  to make contact at its ribs  15 , then wrapped around the accessory C pulley  34  to make contact at its belt back face, then wrapped around the accessory B pulley  32  to make contact at its ribs  15 , and finally returned to the accessory A pulley  31 . This V-ribbed pulley B is driven into clockwise rotation by the crankshaft pulley  35 , thereby driving the accessory pulleys including the accessory A pulley  31 .  
      V-ribbed belts according to other embodiments of the present invention include those containing a single non-woven fabric layer  14   b  as shown in  FIGS. 4A  to  4 C, those containing two non-woven fabric layers  14   b  as shown in  FIGS. 4D  to  4 G, and those containing three or more non-woven fabric layers  14   b  as shown in  FIGS. 4H  to  4 K. As described before, the shearing force acting on the belt is greater, in the ribbed rubber layer  14 , toward the belt outer periphery than toward the belt inner periphery. If the proportion of non-woven fabric layers  14   b  contained in the ribbed rubber layer  14  is greater toward the belt outer periphery, the risk of delamination is increased. Therefore, the preference in this respect among the above V-ribbed belts is not for those in which a non-woven fabric layer  14   b  is disposed toward the rib roots as shown in  FIGS. 4C, 4E ,  4 F,  4 I and  4 J, but for those in which a non-woven fabric layer  14   b  is disposed at the rib tops and rib mid-portions as shown in the other figures. Furthermore, since the traveling belt makes contact with a pulley beginning at the rib tops, a lower coefficient of friction at the rib tops leads to a greater suppression of occurrence of abnormal sounds during the belt travel. Therefore, the preference in this respect is not for V-ribbed belts in which a rubber layer  14   a  is disposed at the rib tops as shown in  FIGS. 4B, 4C ,  4 F,  4 G,  4 J and  4 K, but for those in which a non-woven fabric layer  14   b  is disposed at the rib tops as shown in the other figures. Considering both the respects together, V-ribbed belts as shown in  FIGS. 4A, 4D  and  4 H are preferable.  
      Although the above embodiments are directed to V-ribbed belts, applicable belts for this invention are not limited to V-ribbed belts but include other types of friction drive belts such as V-belts.  
     WORKING EXAMPLES  
      A description will be made of belt evaluations based on actually conducted tests.  
      (Belts for Test Evaluation)  
      V-ribbed belts for test evaluation were prepared as below. The belt structures are also shown in  FIG. 13 .  
     Example 1  
      Prepared as Example 1 was a V-ribbed belt (rib height: 2.00 mm) which has the same structure as in the first-mentioned embodiment and in which a single non-woven fabric layer was formed using a non-woven nylon fiber fabric sheet of 0.05 mm thickness subjected to adhesion treatment with resorcinol-formaldehyde latex (RFL) liquid and rubber cement. Chloroprene rubber (CR) was used as the rubber component of a rubber composition constituting each of the adhesion rubber layer, the tension rubber layer and the rubber layer of the ribbed rubber layer. The back face reinforcing fabric was formed using a woven nylon fiber fabric subjected to adhesion treatment with rubber cement. The cord was formed using a twist yarn (Z-twisted) of polyethylene terephthalate (PET) fibers subjected to adhesion treatment with resorcinol-formaldehyde latex (RFL) liquid and rubber cement and stretch thermoforming process.  
     Example 2  
      Prepared as Example 2 was a V-ribbed belt which has the same structure as in Example 1 except that three non-woven fabric layers were formed using non-woven nylon fiber fabric sheets of 0.05 mm thickness each.  
     Example 3  
      Prepared as Example 3 was a V-ribbed belt which has the same structure as in Example 1 except that six non-woven fabric layers were formed using non-woven nylon fiber fabric sheets of 0.05 mm thickness each.  
     Example 4  
      Prepared as Example 4 was a V-ribbed belt which has the same structure as in Example 1 except that ten non-woven fabric layers were formed using non-woven nylon fiber fabric sheets of 0.05 mm thickness each.  
     Example 5  
      Prepared as Example 5 was a V-ribbed belt which has the same structure as in Example 1 except that 19 non-woven fabric layers were formed using non-woven nylon fiber fabric sheets of 0.05 mm thickness each.  
     Example 6  
      Prepared as Example 6 was a V-ribbed belt which has the same structure as in Example 1 except that 30 non-woven fabric layers were formed using non-woven nylon fiber fabric sheets of 0.05 mm thickness each.  
     Example 7  
      Prepared as Example 7 was a V-ribbed belt which has the same structure as in Example 1 except that 32 non-woven fabric layers were formed using non-woven nylon fiber fabric sheets of 0.05 mm thickness each.  
     Example 8  
      Prepared as Example 8 was a V-ribbed belt which has the same structure as in Example 1 except that a single non-woven fabric layer was formed using a non-woven nylon fiber fabric sheet of 0.20 mm thickness.  
     Example 9  
      Prepared as Example 9 was a V-ribbed belt which has the same structure as in Example 1 except that two non-woven fabric layers were formed using non-woven nylon fiber fabric sheets of 0.20 mm thickness each.  
     Example 10  
      Prepared as Example 10 was a V-ribbed belt which has the same structure as in Example 1 except that four non-woven fabric layers were formed using non-woven nylon fiber fabric sheets of 0.20 mm thickness each.  
     Example 11  
      Prepared as Example 11 was a V-ribbed belt which has the same structure as in Example 1 except that seven non-woven fabric layers were formed using non-woven nylon fiber fabric sheets of 0.20 mm thickness each.  
     Example 12  
      Prepared as Example 12 was a V-ribbed belt which has the same structure as in Example 1 except that six non-woven fabric layers were formed using non-woven aramid fiber fabric sheets of 0.05 mm thickness each.  
     Example 13  
      Prepared as Example 13 was a V-ribbed belt which has the same structure as in Example 1 except that four non-woven fabric layers were formed using non-woven aramid fiber fabric sheets of 0.20 mm thickness each.  
     Example 14  
      Prepared as Example 14 was a V-ribbed belt which has the same structure as in Example 1 except that six non-woven fabric layers were formed using non-woven polyester fiber fabric sheets of 0.05 mm thickness each.  
     Example 15  
      Prepared as Example 15 was a V-ribbed belt which has the same structure as in Example 1 except that four non-woven fabric layers were formed using non-woven polyester fiber fabric sheets of 0.20 mm thickness each.  
     Example 16  
      Prepared as Example 16 was a V-ribbed belt which has the same structure as in Example 1 except that six non-woven fabric layers were formed using non-woven cotton fabric sheets of 0.05 mm thickness each.  
     Example 17  
      Prepared as Example 17 was a V-ribbed belt which has the same structure as in Example 1 except that four non-woven fabric layers were formed using non-woven cotton fabric sheets of 0.20 mm thickness each.  
     Example 18  
      Prepared as Example 18 was a V-ribbed belt which has the same structure as in Example 1 except that a ribbed rubber layer was formed from aramid short fiber-containing rubber.  
     Example 19  
      Prepared as Example 19 was a V-ribbed belt which has the same structure as in Example 1 except that a ribbed rubber layer was formed from a low-hardness rubber composition (containing no short fibers).  
     Example 20  
      Prepared as Example 20 was a V-ribbed belt which has the same structure as in Example 1 except that a ribbed rubber layer was formed from a high-hardness rubber composition (containing no short fibers).  
      (Test Evaluation Method)  
      &lt;Hardness of Ribbed Rubber Layer&gt; 
      For each of the V-ribbed belts of Examples 1 to 20, the hardness of the ribbed rubber layer was measured using an A-type spring hardness tester specified in JIS K6301.  
      &lt;Coefficient of Friction at Rib Surface&gt; 
       FIG. 5  shows a belt coefficient-of-friction measurement tester  40  used for measuring the coefficient of friction at the surface of the ribbed rubber layer. This belt coefficient-of-friction measurement tester  40  is composed of a ribbed pulley  41  of 60 mm diameter and a load cell  42  placed to the side of the ribbed pulley  41 . The load cell  42  is arranged so that the later-described specimen is wrapped around it after being extended horizontally toward the ribbed pulley  41 , i.e., so that the angle at which the specimen is wrapped around it is 90 degrees.  
      Strip-shaped specimens were produced from the V-ribbed belts of Examples 1 to 20. Each specimen was fixed at one end to the load cell  42  to direct its rib side downward, wrapped around the ribbed pulley  41  to make contact at its rib side, and then got down with a 1.75 kg weight  43  hung at the other end. Subsequently, the ribbed pulley  41  was rotated at 20 rpm in the direction of pulling up of the weight  43 , and during the time, the tension T 1  applied to the horizontal portion of the specimen between the load cell  42  and the ribbed pulley  41  was measured with the load cell  42 . In this case, the tension T 2  applied to the vertical portion of the specimen between the ribbed pulley  41  and the weight  43  is 17.15N corresponding to the weight  43 . Then, the coefficient of friction was calculated according to the following formula:  
         μ   ′     =       ln   ⁢       T   1       T   2         θ         
 
 &lt;Abrasion Rate of the Rib Surface&gt;
 
       FIG. 6  shows the layout of a belt run tester  50  for evaluating V-ribbed belts on an abrasion resistance test. This belt durability tester is composed of a pair of pulleys  51  and  52  of 60 mm diameter arranged to the right and left, wherein the left-side pulley is a drive pulley and the right-side pulley is a driven pulley.  
      After each of the V-ribbed belts of Examples 1 to 20 was measured in weight, it was subjected to a belt run test. In this test, each belt was wrapped around both the ribbed pulleys  51  and  52  to make contact at its rib side, the left-side ribbed pulley  51  which is a drive pulley was pulled sideward to impose a deadweight of 1177N thereon, a rotation load of 3.8 kW was applied to the right-side ribbed pulley  52  which is a driven pulley, the left-side ribbed pulley  51  was rotated at 3500 rpm for 24 hours under room temperature conditions. Then, each belt after 24 hours run was measured in weight, and its rate of abrasion was calculated according to the following formula:  
         Rate   ⁢           ⁢   of   ⁢           ⁢   abrasion     =           Initial   ⁢           ⁢   weight     -     afterrun   ⁢           ⁢   weight         Initial   ⁢           ⁢   weight       ×   100         
 
 &lt;Running Durability&gt;
 
       FIG. 7  shows the layout of a belt run tester  60  for durability evaluation on V-ribbed belts. This belt run tester  60  is composed of large-diameter ribbed pulleys  61  and  62  of 120 mm diameter disposed one above the other (the upper is a driven pulley and the lower is a drive pulley), an idler pulley  64  of 70 mm diameter placed to the right of and at a height intermediate the large-diameter ribbed pulleys, and a small-diameter ribbed pulley  63  of 45 mm pulley diameter disposed to the right of the idler pulley  64 . The idler pulley  64  is positioned so that the angle at which the belt is wrapped around it is 90 degrees.  
      A belt run test was conducted on each of the V-ribbed belts of the above Examples 1 to 20. In the belt run test, each belt was wrapped around the three ribbed pulleys  61  to  63  to make contact at its rib side and wrapped around the idler pulley  64  to make contact at its back face, the small-diameter ribbed pulley  63  was pulled sideward to impose a set weight of 834N thereon, and the lower ribbed pulley  62 , which is a drive pulley, was rotated at 4900 rpm in an atmosphere of 85° C.±3° C. The time from the start of the run until the occurrence of a crack was measured under these conditions, and the relative running durability was calculated with respect to the time data from Example 18 which is a reference value of 100.  
      &lt;Noiselessness&gt; 
       FIG. 8  shows the layout of a belt run tester  70  for noiselessness evaluation on V-ribbed belts. This belt run tester  70  is composed of a drive ribbed pulley  71  of 130 mm diameter, a larger driven ribbed pulley  72  of 120 mm diameter placed to the upper left of the drive ribbed pulley  71 , and a smaller driven ribbed pulley  73  of 70 nm diameter placed to the upper right of the drive ribbed pulley  71 .  
      A belt run test was conducted on each of the V-ribbed pulleys of Examples 1 to 20 by wrapping each belt around the three ribbed pulleys  71  to  73  to make contact at its rib side and rotating the drive ribbed pulley  71 . The noise production of each belt at the smaller drive ribbed pulley  73  was sensorily evaluated at five levels.  
      (Test Evaluation Results)  
      The test results are shown in  FIG. 13 . In this case, Example 18 in which the ribbed rubber layer is made of short fiber-containing rubber can be considered as an example of conventional V-ribbed belts.  
      &lt;Hardness of Ribbed Rubber Layer&gt; 
      In each of Example 1 to 17 in which the ribbed rubber layer has a rubber/non-woven fabric layered structure, the ribbed rubber layer has a hardness of 83. This shows that the hardness of the ribbed rubber layer does not depend on the type and thickness of non-woven fabric and the total thickness of non-woven fabric layers. In Example 18 (conventional example) in which the ribbed rubber layer is made of a rubber composite, i.e., short fiber-containing rubber, the ribbed rubber layer has a hardness of 85, which is slightly higher than those of Examples 1 to 17. Examples 19 and 20 in which the ribbed rubber layer is made of rubber show the results on which respective hardnesses of their rubber compositions reflected.  
      &lt;Coefficient of Friction at Ribbed Rubber Layer Surface&gt; 
       FIG. 9A  shows the relation between the total thickness of non-woven fabric layers and the coefficient of friction at the ribbed rubber layer surface for Examples 1 to 11 using nylon fiber non-woven fabrics, and for comparison, also that for Examples 18 to 20.  
      Referring to  FIG. 9A , it is shown that as the total thickness of the non-woven fabric layers is increased, the coefficient of friction is decreased. This is because the non-woven fabrics exposed at the surface of the ribbed rubber layer reduced the coefficient of friction. The effect of decreasing the coefficient of friction is outstanding for total thicknesses of non-woven fabric layers up to 0.5 mm (25% of the ribbed rubber layer thickness), but it is small for total thicknesses of non-woven fabric layers over 0.5 mm. Furthermore, as seen from Examples 1 to 7 having a non-woven fabric thickness of 0.05 mm and Examples 8 to 11 having a non-woven fabric thickness of 0.20 mm, the coefficient of friction is not affected by the thickness of each non-woven fabric, but given as an overall characteristic across the surface of the ribbed rubber layer by the total thickness of non-woven fabric layers. Example 18 (conventional example) in which the ribbed rubber layer is made of short fiber-containing rubber has a coefficient of friction of 0.900. In order to obtain an equivalent coefficient of friction, the total thickness of non-woven fabric layers needs to be 0.50 mm (25% of the ribbed rubber layer thickness) or more. Out of Examples 19 and 20 in which the ribbed rubber layer is made of rubber, Example 19 of low rubber hardness has a very high coefficient of friction, but Example 20 of high rubber hardness has an equivalent coefficient of friction to Example 18.  
       FIG. 9B  shows the relation between the total thickness of non-woven fabric layers ant the coefficient of friction at the surface of the ribbed rubber layer for Examples 1 to 7 and 12 to 17.  
      Referring to  FIG. 9B , it is shown that the coefficient of friction is not affected by which of nylon fibers, aramid fibers, polyester fibers and cotton is used for the non-woven fabric, i.e., the fiber type, but depends on the total thickness of non-woven fabric layers.  
      &lt;Abrasion Rate of Ribbed Rubber Layer&gt; 
       FIG. 10A  shows the relation between the total thickness of non-woven fabric layers and the rate of abrasion of the ribbed rubber layer for Examples 1 to 11, and for comparison, also that for Examples 18 to 20.  FIG. 10B  shows the relation between the total thickness of non-woven fabric layers and the rate of abrasion of the ribbed rubber layer for Examples 1 to 7 and 12 to 17.  
      As seen from  FIGS. 10A and 10B , the rate of abrasion is also given as an overall characteristic across the surface of the ribbed rubber layer like the coefficient of friction. Namely, there exists a correlation between the rate of abrasion and the coefficient of friction.  
      More specifically, reference to  FIG. 10A  shows that as the total thickness of the non-woven fabric layers is increased, the rate of abrasion is decreased. The effect of decreasing the rate of abrasion is outstanding for total thicknesses of non-woven fabric layers up to 0.5 mm (25% of the ribbed rubber layer thickness), but it is small for total thicknesses of non-woven fabric layers over 0.5 mm. Furthermore, as seen from Examples 1 to 7 having a non-woven fabric thickness of 0.05 mm and Examples 8 to 11 having a non-woven fabric thickness of 0.20 mm, the rate of abrasion is not affected by the thickness of each non-woven fabric, but given as an overall characteristic across the ribbed rubber layer by the total thickness of non-woven fabric layers. Example 18 (conventional example) in which the ribbed rubber layer is made of short fiber-containing rubber has a rate of abrasion of 2.02%. In order to obtain an equivalent rate of abrasion, the total thickness of non-woven fabric layers needs to be 0.50 mm (25% of the ribbed rubber layer thickness) or more. Out of Examples 19 and 20 in which the ribbed rubber layer is made of rubber, Example 19 of low rubber hardness has a very high rate of abrasion, but Example 20 of high rubber hardness has an equivalent rate of abrasion to Example 18. Moreover, it is seen from  FIG. 10B  that the rate of abrasion is not affected by which of nylon fibers, aramid fibers, polyester fibers and cotton is used for the non-woven fabric, i.e., the fiber type, but depends on the total thickness of non-woven fabric layers.  
      &lt;Running Durability&gt; 
       FIG. 11A  shows the relation between the total thickness of non-woven fabric layers and the running durability of the relevant belt for Examples 1 to 11 using nylon fiber non-woven fabrics, and for comparison, also that for Examples 18 to 20.  
      Referring to  FIG. 11A , it is shown that the running durability is improved with increasing total thickness of non-woven fabric layers up to 0.5 mm (25% of the ribbed rubber layer thickness), while on the other hand it is deteriorated with increasing total thickness of non-woven fabric layers over 0.5 mm. The running durability, in practice, needs to be 80 or more per cent of the running durability of Example 18 (conventional example), i.e., 80% or more, and therefore the total thickness of non-woven fabric layers needs to be at least 0.10 mm (5% of the ribbed rubber layer thickness) and at most 1.5 mm (75% of the ribbed rubber layer thickness). The running durability is preferably equal to or greater than that of Example 18, i.e., 100% or more, and in that case, the total thickness of non-woven fabric layers needs to be at least 0.3 mm (15% of the ribbed rubber layer thickness) and at most 0.7 mm (35% of the ribbed rubber layer thickness). Furthermore, as seen from Examples 1 to 7 having a non-woven fabric thickness of 0.05 mm and Examples 8 to 11 having a non-woven fabric thickness of 0.20 mm, the running durability is also not affected by the thickness of each non-woven fabric, but given as an overall characteristic across the ribbed rubber layer by the total thickness of non-woven fabric layers. Out of Examples 19 and 20 in which the ribbed rubber layer is made of rubber, Example 19 of low rubber hardness has a very low running durability, but Example 20 of high rubber hardness has an equivalent running durability to Example 18.  
       FIG. 11B  shows the relation between the total thickness of non-woven fabric layers and the running durability of the relevant belt for Examples 1 to 7 and 12 to 17.  
      Referring to  FIG. 11B , it is shown that the running durability is also not affected by which of nylon fibers, aramid fibers, polyester fibers and cotton is used for the non-woven fabric, i.e., the fiber type, but depends on the total thickness of non-woven fabric layers.  
      &lt;Noiselessness&gt; 
       FIG. 12A  shows the relation between the total thickness of non-woven fabric layers and the noiselessness of the relevant belt for Examples 1 to 11 using nylon fiber non-woven fabrics, and for comparison, also that for Examples 18 to 20.  
      Referring to  FIG. 12A , it is shown that the noiselessness is improved, i.e., abnormal sounds are reduced, with increasing total thickness of non-woven fabric layers up to 0.5 mm (25% of the ribbed rubber layer thickness), but increase in the total thickness of non-woven fabric layers over 0.5 mm does not lead to further improved noiselessness. Furthermore, as seen from Examples 1 to 7 having a non-woven fabric thickness of 0.05 mm and Examples 8 to 11 having a non-woven fabric thickness of 0.20 mm, the noiselessness is not affected by the thickness of each non-woven fabric, but given as an overall characteristic across the ribbed rubber layer by the total thickness of non-woven fabric layers. Example 18 (conventional example) in which the ribbed rubber layer is made of short fiber-containing rubber has a noiselessness level of 3. In order to obtain an equivalent noiselessness level, the total thickness of non-woven fabric layers needs to be 0.30 mm (15% of the ribbed rubber layer thickness) or more. Out of Examples 19 and 20 in which the ribbed rubber layer is made of rubber, Example 19 of low rubber hardness has a very poor noiselessness, but Example 20 of high rubber hardness has an equivalent noiselessness to Example 18.  
       FIG. 12B  shows the relation between the total thickness of non-woven fabric layers and the noiselessness of the relevant belt for Examples 1 to 7 and 12 to 17.  
      Referring to  FIG. 12B , it is shown that the noiselessness is also not affected by which of nylon fibers, aramid fibers, polyester fibers and cotton is used for the non-woven fabric, i.e., the fiber type, but depends on the total thickness of non-woven fabric layers.  
      The foregoing discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize, from such discussion and accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the present invention.