Friction transmission belt

Abstract

To provide a frictional transmission belt capable of reducing noise generating when being wetted.SOLUTION: A frictional transmission belt includes a belt main body transmitting power to a pulley by frictional force generated by contact with the pulley. In a relation between a slip speed as a difference between a speed of the belt main body and a speed of the pulley, and a friction coefficient, a reduction rate Dm of the friction coefficient indicated by a following formula (1), in which a maximum friction coefficient is μx and a reference friction coefficient is μr, is 20% or less, when the slip speed indicating the maximum friction coefficient is a first slip speed, the friction coefficient in increasing the slip speed from the first slip speed to a second slip speed is a reference friction coefficient, and a difference between the second slip speed and the first slip speed is 500 mm / s. Dm=(μx-μr) / μx×100 ... (1)SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a friction power transmission belt. [Background technology]

[0002] Conventionally, as a means for transmitting rotational power from an engine, motor, etc., a method has been widely used in which pulleys are fixed to the rotating shafts of the driving and driven sides, and a friction transmission belt such as a V-ribbed belt is stretched across each pulley.

[0003] It is known that friction transmission belts (hereafter referred to as transmission belts) can experience a phenomenon known as stick-slip when they are submerged in water during operation, and that this phenomenon can sometimes be accompanied by an abnormal noise, in other words, a slipping noise.Since the slipping noise of transmission belts can cause noisy equipment, various countermeasures are being considered.

[0004] For example, Patent Document 1 proposes that in a friction transmission belt in which the surface of the belt body that comes into contact with a pulley is covered with a knitted fabric, the knitted fabric is made of yarn that extends while reversing its direction of travel so as to move back and forth in the width direction of the friction transmission belt, and has an inverted portion that reverses the direction of travel and a straight portion that extends connecting the inverted portions, and the surface that comes into contact with the pulley is covered with this knitted fabric so that the straight portion is located closer to the surface than the inverted portion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 142843 Summary of the Invention [Problem to be solved by the invention]

[0006] Various methods have been proposed to reduce the noise generated when water gets in. However, the current noise reduction effect is not satisfactory, and further improvement is required.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a friction power transmission belt that can reduce abnormal noise generated when it is wet. [Means for solving the problem]

[0008] The inventors conducted a detailed investigation into the generation of abnormal noise when wet, and discovered that in the relationship between sliding speed and friction coefficient, the rate of decrease in the friction coefficient in the zone from when the friction coefficient reaches its maximum until the sliding speed increases by 500 mm / s is closely related to the generation of abnormal noise, which led to the completion of the present invention.

[0009] (1) The friction transmission belt of the present invention is A friction power transmission belt including a belt body that transmits power to a pulley by frictional force generated by contact with the pulley, In the relationship between the sliding speed, which is the difference between the speed of the belt body and the speed of the pulley, and the friction coefficient, the sliding speed that exhibits the maximum friction coefficient is defined as a first sliding speed, and the friction coefficient when the sliding speed is increased from the first sliding speed to a second sliding speed is defined as a reference friction coefficient, and when the difference between the second sliding speed and the first sliding speed is 500 mm / s, When the maximum friction coefficient is μx and the reference friction coefficient is μr, the reduction rate Dm of the friction coefficient shown by the following formula (1) is 20% or less. Dm=(μx-μr) / μx×100 (1)

[0010] The friction transmission belt described above suppresses the decrease in the friction coefficient in the zone from when the friction coefficient reaches its maximum to when the sliding speed increases by 500 mm / s. The friction transmission belt described above is less likely to experience stick-slip when exposed to water. This reduces the abnormal noise that occurs when the belt is exposed to water.

[0011] (2) In the above-mentioned friction drive belt, when the zone from the first sliding speed to the second sliding speed is equally divided into n sections (n is a natural number of 2 or more), the sliding speed at the start of each section is defined as the start speed, the friction coefficient at the start speed is defined as the start friction coefficient, the sliding speed at the end of each section is defined as the end speed, and the friction coefficient at the end speed is defined as the end friction coefficient, it is preferable that the start friction coefficient and the end friction coefficient in the m-th section (m is a natural number of 1 to n) be μsm and μem, respectively, and that the reduction rate Dsm of the friction coefficient, as expressed by the following formula (2), is 20 / n% or less in all of the sections. Dsm=(μsm-μem) / μsm×100 (2) In this case, a significant decrease in the coefficient of friction is prevented in all sections that make up the above zone. The coefficient of friction gradually decreases in the above zone. In the above friction transmission belt, the occurrence of stick-slip due to exposure to water is effectively suppressed. Therefore, abnormal noise is less likely to occur when the belt is exposed to water.

[0012] (3) In the above-mentioned friction transmission belt, the belt body preferably includes a compressed rubber layer that contacts the pulley, and the compressed rubber layer preferably includes a rubber layer body made of a rubber composition and a fibrous material layer laminated on the rubber layer body. In this case, the fibrous material layer absorbs water. Therefore, a water film is less likely to form between the belt body and the pulley. In the above-mentioned friction transmission belt, a significant decrease in the coefficient of friction is prevented.

[0013] (4) In the above-mentioned friction transmission belt, the porosity of the surface layer of the compressed rubber layer is preferably 10% or more. In this case, the voids formed in the surface layer contribute to water absorption. In the above-mentioned friction transmission belt, a water film is unlikely to form between the belt body and the pulley.

[0014] (5) In the above-mentioned friction transmission belt, the porosity is more preferably 20% or more. In this case, water is effectively absorbed by the voids formed in the surface layer. In the above-mentioned friction transmission belt, a water film is unlikely to form between the belt body and the pulley.

[0015] (6) In the above-mentioned friction transmission belt, the fibrous member layer is preferably made of a knitted fabric, and the knitted fabric preferably contains cellulosic fibers as a main fiber. Cellulosic fibers have excellent water absorption properties. In the above-mentioned friction transmission belt, a water film is unlikely to form between the belt body and the pulley.

[0016] (7) In the above-mentioned friction transmission belt, it is preferable that the compression rubber layer has a plurality of V-ribs extending downward toward the inner periphery. This friction transmission belt is a V-ribbed belt. The above-mentioned friction transmission belt is less susceptible to stick-slip caused by exposure to water. Therefore, noise generated when the belt is exposed to water is reduced. [Effects of the Invention]

[0017] In the friction transmission belt of the present invention, the decrease in the friction coefficient is suppressed in the zone from when the friction coefficient reaches its maximum to when the sliding speed increases by 500 mm / s. The friction transmission belt is less likely to experience stick-slip when exposed to water. As a result, noise generated when exposed to water is reduced. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram schematically illustrating a portion of a V-ribbed belt according to an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing the pulley layout of a belt running test machine for evaluating the dynamic friction coefficient when wetted. [Figure 3A] 1 is a graph showing the measurement results of the coefficient of friction. [Figure 3B] FIG. 3B is an enlarged view of the graph shown in FIG. 3A. [Figure 4A] FIG. 2 is a diagram for explaining a method for measuring porosity. [Figure 4B] FIG. 2 is a diagram for explaining a method for measuring porosity. [Figure 4C] FIG. 2 is a diagram for explaining a method for measuring porosity. [Figure 5A] FIG. [Figure 5B]FIG. 5B is an enlarged cross-sectional view of a portion of the bridging device shown in FIG. 5A. [Figure 6A] 2A to 2C are diagrams for explaining a method of manufacturing the V-ribbed belt shown in FIG. [Figure 6B] 2A to 2C are diagrams for explaining a method of manufacturing the V-ribbed belt shown in FIG. [Figure 6C] 2A to 2C are diagrams for explaining a method of manufacturing the V-ribbed belt shown in FIG. [Figure 7] FIG. 10 is a diagram showing the pulley layout of a belt running test machine for evaluating abnormal noise when wetted. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (friction transmission belt) FIG. 1 schematically shows a portion of a friction transmission belt B according to one embodiment of the present invention. This friction power transmission belt B is a V-ribbed belt used, for example, in an accessory drive belt transmission device installed in the engine compartment of an automobile. This V-ribbed belt B has, for example, a belt circumference of 700 mm or more and 3000 mm or less, a belt width of 10 mm or more and 36 mm or less, and a belt thickness of 3.5 mm or more and 5.0 mm or less.

[0020] This V-ribbed belt B includes an endless belt body 10. In this V-ribbed belt B, the belt body 10 transmits power to the pulley by the frictional force generated when the inner peripheral surface of the belt body 10 comes into contact with the pulley. The belt body 10 includes a compressed rubber layer 11 located on the inner circumferential side of the belt, an adhesive rubber layer 12 located in the middle, and a back reinforcing fabric 13 located on the outer circumferential side of the belt.

[0021] The compressed rubber layer 11 extends in the length direction of the belt. The compressed rubber layer 11 comes into contact with a pulley such as a driving pulley or a driven pulley. The compressed rubber layer 11 is composed of a rubber layer main body 14 and a fiber member layer 15. The rubber layer body 14 is also referred to as a compressed rubber layer body. The thickness of the rubber layer body 14 is, for example, 2.0 mm or more and 3.2 mm or less. The rubber layer main body 14 is made of a rubber composition containing a crosslinked rubber component (hereinafter referred to as a crosslinked rubber composition). The rubber composition is a crosslinked product obtained by heating and pressurizing an uncrosslinked rubber composition (raw material composition) in which various rubber compounding ingredients including a crosslinking agent are blended and kneaded with the rubber component, and the rubber component is crosslinked by the crosslinking agent.

[0022] Examples of the rubber component contained in the raw material composition include ethylene-α-olefin elastomers such as ethylene-propylene-diene terpolymer (EPDM), ethylene-propylene copolymer (EPM), ethylene-butene copolymer (EDM), and ethylene-octene copolymer (EOM); chloroprene rubber (CR); chlorosulfonated polyethylene rubber (CSM); and hydrogenated acrylonitrile rubber (H-NBR). The rubber component preferably uses one or more of these, more preferably an ethylene-α-olefin elastomer, and even more preferably EPDM.

[0023] Examples of the crosslinking agent contained in the raw material composition include sulfur and organic peroxides. Examples of rubber compounding agents other than the crosslinking agent include reinforcing materials such as carbon black, fillers, antioxidants, softeners, vulcanization accelerators, vulcanization accelerator assistants, co-crosslinking agents, and short fibers.

[0024] The fibrous material layer 15 is laminated on the inner circumferential surface of the rubber layer body 14. The fibrous material layer 15 forms the inner circumferential surface of the belt body 10. The thickness of the fibrous material layer 15 is, for example, 0.1 mm or more and 1.5 mm or less. In this V-ribbed belt B, the fiber member layer 15 covers the entire inner peripheral surface of the rubber layer main body 14. The fiber member layer 15 may be laminated on the inner peripheral surface so as to cover a part of the inner peripheral surface.

[0025] The fiber member layer 15 may be made of either a woven fabric or a knitted fabric. Examples of the weave of the woven fabric include plain weave, twill weave, satin weave, and variations thereof. Examples of the knitted fabric include plain knit, rib knit, purl knit, and other variations in the weft knitting, and single Denbigh knit, single Van Dyke knit, and other variations in the warp knitting. From the viewpoint of being highly elastic and being able to uniformly cover the rubber layer main body 14, the fiber member layer 15 is preferably made of a knitted fabric. In this V-ribbed belt B, the fibrous member layer 15 may be a crosslinked rubber composition containing short fibers.

[0026] When the fiber member layer 15 is made of a woven fabric or a knitted fabric, the V-ribbed belt B may use a fiber member layer 15 that has been subjected to an adhesive treatment, or may use a fiber member layer 15 that has not been subjected to an adhesive treatment. From the viewpoints of the following (1) and (2), when the V-ribbed belt B uses a fiber member layer 15 that has not been subjected to an adhesive treatment, the V-ribbed belt B preferably uses a fiber member layer 15 that has not been subjected to an adhesive treatment, when the fiber member layer 15 is made of a woven fabric or a knitted fabric. (1) In the V-ribbed belt B, the rubber layer main body 14 of the compressed rubber layer 11 is made of a cross-linked rubber composition, so that the rubber layer main body 14 and the fiber material layer 15 are bonded with sufficient adhesive strength even if the fiber material layer 15 is not subjected to an adhesive treatment. (2) Furthermore, the V-ribbed belt B having an unbonded fiber member layer 15 suppresses the generation of abnormal noise when wetted compared to the V-ribbed belt B having an bonded fiber member layer 15. This is presumably because the unbonded fiber member layer 15 tends to have better water absorption properties than the bonded fiber member layer 15.

[0027] In the friction transmission belt B of the present invention, the fact that the fiber component layer 15 has not been subjected to an adhesive treatment means that the fiber component layer 15 has not been subjected to an adhesive treatment in which it is immersed in an adhesive, and no adhesive is attached to the surface of the fiber component layer 15. In the present invention, "adhesion treatment by immersion in an adhesive" refers to a treatment of immersing in an epoxy resin solution or an isocyanate resin solution and heating, a treatment of immersing in an RFL aqueous solution and heating, and a treatment of immersing in rubber cement and drying.

[0028] When the fiber material layer 15 is made of a woven fabric, warp yarns and weft yarns are used to form the fiber material layer 15. When the fiber material layer 15 is made of a knitted fabric, knitting yarns are used to form the fiber material layer 15. Examples of fibers constituting the threads used to form the fiber member layer 15 include natural fibers such as cellulose fibers, wool, and silk; and synthetic fibers such as polyurethane fibers, aliphatic polyamide fibers (nylon 66 fibers), aromatic polyamide fibers (para- and meta-based), polyester fibers, acrylic fibers, and polyvinyl alcohol fibers. The reinforcing fabric may be made of one type of fiber or two or more types of fibers. The fibers constituting the fibrous material layer 15 are preferably cellulosic fibers, from the viewpoint of good water absorption performance.

[0029] In this V-ribbed belt B, the fiber member layer 15 preferably contains cellulosic fibers as the main fibers, as this is suitable for ensuring good water absorption properties. As described above, the fiber member layer 15 is preferably made of a knitted fabric, from the viewpoint of being highly elastic and being able to uniformly cover the rubber layer main body 14. Therefore, in this V-ribbed belt B, it is more preferable that the fiber member layer 15 is a knitted fabric, and that this knitted fabric contains cellulosic fibers as the main fibers.

[0030] When the fibrous material layer 15 contains cellulosic fibers as the main fibers, the proportion of cellulosic fibers in the fibers constituting the fibrous material layer 15 is preferably 50% by mass or more, more preferably 70% by mass or more. The proportion of cellulosic fibers may be 100% by mass. When the fibrous material layer 15 contains cellulosic fibers as the main fibers, it is preferable that the cellulosic fibers are exposed on the surface of the fibrous material layer 15 (the inner peripheral surface of the belt body 10) in order to ensure excellent water absorption properties.

[0031] When the fibrous material layer 15 contains cellulosic fibers as the main fibers, the fibrous material layer 15 may contain fibers other than cellulose fibers. In this case, the other fibers are preferably polyurethane fibers and aliphatic polyamide fibers. From the viewpoint of ensuring stretchability, polyurethane fibers are more preferable as the other fibers.

[0032] Examples of cellulosic fibers include cellulose fibers derived from natural plants such as wood pulp from conifers and broad-leaved trees, bamboo fiber, sugarcane fiber, cotton fiber, kapok seed hair fiber, hemp, paper mulberry, and Mitsumata gin bark fiber, and Manila hemp and New Zealand hemp leaf fiber; cellulose fibers derived from animals such as sea squirt cellulose; bacterial cellulose fiber; algae cellulose fiber; cellulose ester fiber; and regenerated cellulose fibers such as rayon, cupra, and lyocell. Among these, cotton fiber is preferred from the viewpoint of practicality as a fiber material.

[0033] The adhesive rubber layer 12 is a strip extending in the belt length direction and having a horizontally elongated rectangular cross section. The thickness of the adhesive rubber layer 12 is, for example, 1.0 mm to 2.5 mm. The adhesive rubber layer 12 is composed of an adhesive rubber layer main body 16 and a core wire 17 covered by the adhesive rubber layer main body 16.

[0034] The adhesive rubber layer main body 16 is made of a cross-linked rubber composition. As described above, the compressed rubber layer main body 14 is also made of a cross-linked rubber composition. In this V-ribbed belt B, the compressed rubber layer main body 14 and the adhesive rubber layer main body 16 may be made of the same rubber composition or different rubber compositions.

[0035] The cord 17 is located in the middle in the belt thickness direction of the adhesive rubber layer 12. The cord 17 is wound so as to form a spiral having a pitch in the belt width direction, and is embedded in the adhesive rubber layer main body 16.

[0036] The core wires 17 are made of twisted yarns of polyamide fiber, polyester fiber, aramid fiber, polyamide fiber, etc. The diameter of the core wires 17 is, for example, 0.5 mm or more and 2.5 mm or less. The shortest distance between adjacent core wires 17 in the cross section of the adhesive rubber layer 12 is, for example, 0.05 mm or more and 0.20 mm or less. Preferably, the core wire 17 is subjected to one or more of the following adhesive treatments: an adhesive treatment in which the core wire 17 is immersed in an epoxy resin solution or an isocyanate resin solution and heated; an adhesive treatment in which the core wire 17 is immersed in an RFL aqueous solution and then heated; and an adhesive treatment in which the core wire 17 is immersed in rubber cement and then dried.

[0037] The back reinforcing fabric 13 is made of, for example, a plain weave, twill weave, satin weave, knitted fabric, nonwoven fabric, etc., fabric material using threads such as cotton, polyamide fiber, polyester fiber, aramid fiber, etc. The thickness of the back reinforcing fabric 13 is, for example, 0.4 mm or more and 1.2 mm or less. To impart adhesion to the adhesive rubber layer 12, the back reinforcing fabric 13 may be subjected to an adhesion treatment in which it is immersed in an RFL aqueous solution and heated before molding, and / or an adhesion treatment in which rubber cement is coated on the outer circumferential surface of the adhesive rubber layer 12 and dried. The back reinforcing fabric 13 may be attached to the adhesive rubber layer 12 via a rubber layer (not shown).

[0038] In this V-ribbed belt B, a back rubber layer having a thickness of, for example, 0.4 mm to 0.8 mm may be used instead of the back reinforcing fabric 13. In this case, the texture of the woven fabric is preferably transferred to the surface of the back rubber layer in order to suppress noise generation during back drive. In order to suppress adhesion caused by contact between the back surface of the belt and the flat pulley, the back rubber layer is preferably made of a rubber composition that is slightly harder than the adhesive rubber layer main body 16. Furthermore, when a back rubber layer is provided, this back rubber layer may be made of the same rubber composition as one or both of the compressed rubber layer main body 14 and the adhesive rubber layer main body 16, or may be made of a rubber composition different from either the compressed rubber layer main body 14 or the adhesive rubber layer main body 16. When the back rubber layer is made of a rubber composition different from that of the adhesive rubber layer main body 16, it is preferable that the back rubber layer be made of a rubber composition that is slightly harder than that of the adhesive rubber layer main body 16, in order to prevent adhesion caused by contact between the back surface of the belt and the flat pulley.

[0039] As shown in Figure 1, in this V-ribbed belt B, a plurality of V-ribs 18 are formed on the compressed rubber layer 11 of the belt body 10, hanging down toward the inner periphery. The V-ribs 18 are ridges that extend in the belt length direction and have a cross section that is approximately an inverted triangle. The V-ribs 18 are arranged side by side in the belt width direction. Each V-rib 18 has a rib height of 2.0 mm to 3.0 mm and a base-to-base width of 1.0 mm to 3.6 mm. The number of V-ribs 18 is, for example, 3 to 10 (6 in FIG. 1).

[0040] In this V-ribbed belt B, a plurality of V-rib bodies 14a are formed hanging down toward the inner periphery of the rubber layer body 14 of the compressed rubber layer 11. Each of the plurality of V-rib bodies 14a is covered with a fiber material layer 15 to form a V-rib 18. In this V-ribbed belt B, the surface of the V-rib 18 covered with this fiber material layer 15 becomes the pulley contact surface.

[0041] The inventors conducted a detailed investigation into the generation of abnormal noise when friction drive belt B was exposed to water, and discovered that, in the relationship between the sliding speed and the friction coefficient, the rate of decrease in the friction coefficient in the zone from when the friction coefficient reaches its maximum to when the sliding speed increases by 500 mm / s is deeply involved in the generation of abnormal noise, which led to the completion of the present invention. The relationship between the sliding speed and the friction coefficient of the friction transmission belt B shown in Figure 1 will be explained below. Before that, the belt running tester used to obtain this relationship and the evaluation method for obtaining this relationship will be explained.

[0042] (Belt running tester) 2 shows an example of the pulley layout of a belt running tester 20 for evaluating the dynamic friction coefficient when wet. This belt running tester 20 (hereinafter referred to as the tester) is configured to be able to evaluate the dynamic friction coefficient when wet of a friction transmission belt B, which is a V-ribbed belt B (belt length = 1080 mm) configured with six V-ribs 18. By changing the pulley specifications, this tester 20 can also evaluate other friction transmission belts B, such as V-belts and flat belts. The testing machine 20 includes four pulleys 21. The four pulleys 21 are (1) a first drive pulley 22, which is a ribbed pulley; (2) The second drive pulley 23, which is a ribbed pulley and is located to the right of the first drive pulley 22; (3) a driven pulley 24, which is a ribbed pulley and is located above the second driving pulley 23; and (4) Idler pulley 25, which is a flat pulley, is located to the lower left of driven pulley 24. The pulley diameter of each pulley 21 is 50 mm. Each pulley 21 is made of SUS. The surface roughness (arithmetic mean roughness Ra) of the contact surface of each pulley 21 with the V-ribbed belt B is 3.2 μm. In this testing machine 20, the rib side of the V-ribbed belt B contacts the first driving pulley 22, the second driving pulley 23, and the driven pulley 24. The back side of the V-ribbed belt B contacts the idler pulley 25. A motor and a torque meter are connected to each of the first drive pulley 22 and the second drive pulley 23. This testing machine 20 is capable of controlling the rotation speeds of the first drive pulley 22 and the second drive pulley 23 and measuring the torques generated in the first drive pulley 22 and the second drive pulley 23. A weight is connected to the driven pulley 24 so that a constant tension is applied to the V-ribbed belt B. In this testing machine 20, the dead load DW is set so that a tension of 10 kgf (98 N) is generated per V-rib 18. Table 1 below shows the exact location of each pulley 21. Table 1 also shows the center coordinates of each pulley 21 when the center of the first driving pulley 22 is set as the origin (0,0) of the XY coordinates in Fig. 2. For example, the center coordinates (200,308.91) of the driven pulley 24 indicate a position 200 mm to the right and 308.91 mm above the center of the first driving pulley 22, which is the origin.

[0043] [Table 1]

[0044] In this testing machine 20, the pulleys 21 are arranged as shown in Table 1, so that the contact angle between the friction transmission belt B (V-ribbed belt B) and the second drive pulley 23 is set to 90 degrees.

[0045] (Evaluation method) The relationship between the sliding speed and the friction coefficient of the V-ribbed belt B as the friction transmission belt B is obtained as follows: This evaluation method is carried out at an ambient temperature of 18°C to 28°C. (1) The V-ribbed belt B shown in FIG. 1 is wound around each pulley 21. (2) A weight is connected to the driven pulley 24. Since this V-ribbed belt B has six V-ribs 18, the tension of the V-ribbed belt B is set to 588 N (60 kgf). (3) The motor is driven to rotate the first drive pulley 22 and the second drive pulley 23. (4) At the entrance of the V-ribbed belt B to the first drive pulley 22, water is dripped onto the rib side of the V-ribbed belt B at a rate of 40 ml per minute. (5) The rotation speed of each of the first drive pulley 22 and the second drive pulley 23 is set to 1000 rpm, and the V-ribbed belt B is made to run at a constant speed. (6) 30 seconds after the start of constant speed traveling, the rotational speed of the second drive pulley 23 is decelerated at a constant acceleration to 500 rpm over 30 seconds, and the torque of the second drive pulley 23 during this deceleration process is measured. (7) From the measured torque, the tension side tension T1 (N) represented by the tension between the first drive pulley 22 and the second drive pulley 23 and the slack side tension T2 (N) represented by the tension between the second drive pulley 23 and the driven pulley 24 are calculated, and the dynamic friction coefficient (hereinafter referred to as the friction coefficient) is calculated using Euler's equation. This gives the relationship between the slip speed, which is the difference between the speed of the belt body 10 and the speed of the second drive pulley 23, and the friction coefficient.

[0046] (Relationship between sliding speed and friction coefficient) FIG. 3A shows the results of measurements of the friction coefficient of the friction transmission belt B (V-ribbed belt B) shown in FIG. 1, obtained using the belt running tester 40 shown in FIG. 2. FIG. 3A shows the relationship between the sliding speed and the friction coefficient. In FIG. 3A, the horizontal axis V represents the sliding speed (mm / s). The sliding speed V when the second drive pulley 23 starts to decelerate is 0 mm / s. The vertical axis μ represents the friction coefficient.

[0047] As shown in FIG. 3A, in the friction drive belt B, when the second drive pulley 23 begins to decelerate and the sliding speed V increases, the friction coefficient μ increases rapidly. Thereafter, the rate of increase of the friction coefficient μ gradually decreases. After reaching a maximum friction coefficient, the friction coefficient μ gradually decreases as the sliding speed V increases. In FIG. 3A, μx represents the maximum friction coefficient, and V1 represents the sliding speed at which the maximum friction coefficient μx is reached, i.e., the first sliding speed. V2 represents the second sliding speed, and μr represents the friction coefficient when the sliding speed V increases from the first sliding speed V1 to the second sliding speed V2, i.e., the reference friction coefficient. As shown in FIG. 3A, the reference friction coefficient μr is lower than the maximum friction coefficient μx.

[0048] In this friction transmission belt B, in the relationship between the sliding speed V and the friction coefficient μ, the reduction rate Dm of the friction coefficient μ is expressed by the following equation (1), where μx is the maximum friction coefficient and μr is the reference friction coefficient. Dm=(μx-μr) / μx×100 (1) In this friction transmission belt B, when the difference (V2-V1) between the second sliding speed V2 and the first sliding speed V1 is 500 mm / s, the reduction rate Dm of the friction coefficient μ expressed by equation (1) is 20% or less.

[0049] In this friction drive belt B, the decrease in the friction coefficient μ is suppressed in the zone from when the friction coefficient μ reaches its maximum friction coefficient μx until the sliding speed V increases by 500 mm / s. This friction drive belt B is less likely to experience stick-slip when exposed to water. As a result, the abnormal noise that occurs when exposed to water is reduced.

[0050] Figure 3B is an enlarged view of the graph shown in Figure 3A, which shows the relationship between sliding speed V and friction coefficient μ in the zone from first sliding speed V1 to second sliding speed V2 (hereinafter referred to as the evaluation zone).

[0051] As shown in Figure 3B, for this friction drive belt B, the change in the friction coefficient μ is kept small within the evaluation zone. Therefore, this friction drive belt B is less likely to experience stick-slip due to water exposure, and is less likely to generate abnormal noise when wet. However, even if the reduction rate Dm of the friction coefficient μ shown in the above equation (1) is 20% or less, it cannot be denied that there are cases where there are sections within the evaluation zone where the friction coefficient μ drops significantly. In such cases, there is concern that stick-slip will occur due to water exposure, resulting in abnormal noise. Therefore, when the evaluation zone is divided into n equal sections (n is a natural number of 2 or more), the sliding speed at the start of each section is defined as the start speed, the friction coefficient μ at this start speed is defined as the start friction coefficient, the sliding speed at the end of this section is defined as the end speed, and the friction coefficient μ at this end speed is defined as the end friction coefficient, In the m-th section Sm (m is a natural number between 1 and n), the start friction coefficient is μsm and the end friction coefficient is μem. It is preferable that the decrease rate Dsm of the friction coefficient μ, as shown in the following formula (2), is 20 / n% or less in all sections. Dsm=(μsm-μem) / μsm×100 (2)

[0052] 3B shows a case where the evaluation zone is divided into five equal sections. Using this case as an example, we will explain below how the decrease rate Dsm of the friction coefficient μ expressed by the above formula (2) is 20 / n% or less in all sections.

[0053] In Figure 3B, the regions denoted by symbols S1 to S5 represent sections formed by dividing the evaluation zone into five equal parts. The section with the first sliding speed V1 as the start speed is the first section S1, and the section with the second sliding speed V2 as the end speed is the fifth section S5. Since the width of the evaluation zone is 500 mm / s, when the evaluation zone is divided into five equal sections, the width of each section Sm is 100 mm / s.

[0054] Symbol Vs1 is the start speed of the first section S1. Symbol μs1 is the friction coefficient at the start speed Vs1, and this friction coefficient μs1 is the start friction coefficient of the first section S1. Since the first section S1 is the section where the start speed Vs1 is the first sliding speed V1, the start friction coefficient μs1 is also the maximum friction coefficient μx. Symbol Ve1 is the end speed of the first section S1. Symbol μe1 is the friction coefficient at the end speed Ve1, and this friction coefficient μe1 is the end friction coefficient of this first section S1. Therefore, the decrease rate Ds1 of the friction coefficient μ in the first section S1 is expressed by the following equation (2a). Ds1=(μs1-μe1) / μs1×100 (2a)

[0055] Symbol Vs2 is the start speed of the second section S2. Symbol μs2 is the friction coefficient at the start speed Vs2, and this friction coefficient μs2 is the start friction coefficient of the second section S2. Since the start speed Vs2 is the end speed Ve1 described above, the start friction coefficient μs2 is also the end friction coefficient μe1 described above. Symbol Ve2 is the end speed of the second section S2. Symbol μe2 is the friction coefficient at the end speed Ve2, and this friction coefficient μe2 is the end friction coefficient of the second section S2. Therefore, the decrease rate Ds2 of the friction coefficient μ in the second section S2 is expressed by the following equation (2b). Ds2=(μs2-μe2) / μs2×100 (2b)

[0056] Symbol Vs3 is the start speed of the third section S3. Symbol μs3 is the friction coefficient at the start speed Vs3, and this friction coefficient μs3 is the start friction coefficient of the third section S3. Since the start speed Vs3 is the end speed Ve2 described above, the start friction coefficient μs3 is also the end friction coefficient μe2 described above. Symbol Ve3 is the end speed of the third section S3. Symbol μe3 is the friction coefficient at the end speed Ve3, and this friction coefficient μe3 is the end friction coefficient of the third section S3. Therefore, the decrease rate Ds3 of the friction coefficient μ in the third section S3 is expressed by the following equation (2c). Ds3=(μs3-μe3) / μs3×100 ····(2c)

[0057] Symbol Vs4 is the start speed of the fourth section S4. Symbol μs4 is the friction coefficient at the start speed Vs4, and this friction coefficient μs4 is the start friction coefficient of the fourth section S4. Since the start speed Vs4 is the end speed Ve3 described above, the start friction coefficient μs4 is also the end friction coefficient μe3 described above. Symbol Ve4 is the end speed of the fourth section S4. Symbol μe4 is the friction coefficient at the end speed Ve4, and this friction coefficient μe4 is the end friction coefficient of the fourth section S4. Therefore, the decrease rate Ds4 of the friction coefficient μ in the fourth section S4 is expressed by the following equation (2d). Ds4=(μs4-μe4) / μs4×100 (2d)

[0058] Symbol Vs5 is the start speed of the fifth section S5. Symbol μs5 is the friction coefficient at the start speed Vs5, and this friction coefficient μs5 is the start friction coefficient of the fifth section S5. Since the start speed Vs5 is the end speed Ve4 described above, the start friction coefficient μs5 is also the end friction coefficient μe4 described above. Symbol Ve5 is the end speed of the fifth section S5. Symbol μe5 is the friction coefficient at the end speed Ve5, and this friction coefficient μe5 is the end friction coefficient of the fifth section S5. Since the fifth section S5 is the section in which the second sliding speed V2 is the end speed Vs5, the end friction coefficient μe5 is also the reference friction coefficient μr. Therefore, the decrease rate Ds5 of the friction coefficient μ in the fifth section S5 is expressed by the following equation (2e): Ds5=(μs5-μe5) / μs5×100 (2e)

[0059] In this friction drive belt B, the reduction rate Ds1 of the friction coefficient μ in the first section S1, the reduction rate Ds2 of the friction coefficient μ in the second section S2, the reduction rate Ds3 of the friction coefficient μ in the third section S3, the reduction rate Ds4 of the friction coefficient μ in the fourth section S4, and the reduction rate Ds5 of the friction coefficient μ in the fifth section S5 are preferably 4% or less. In other words, in all sections constituting the evaluation zone, the reduction rate Dsm of the friction coefficient μ expressed by the above formula (2) is preferably 20 / 5%, i.e., 4% or less. This prevents a significant reduction in the friction coefficient μ in all sections constituting the evaluation zone. The friction coefficient μ gradually decreases throughout the entire evaluation zone. In this friction drive belt B, fluctuations in the friction coefficient μ are kept small, effectively suppressing the occurrence of stick-slip due to exposure to water. Therefore, abnormal noise is less likely to occur when the belt is exposed to water.

[0060] In this friction transmission belt B, from the viewpoint of effectively suppressing the generation of abnormal noise when wetted, the number n of sections constituting the evaluation zone is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. The larger the number n, the better, but if this number n is too large, noise due to the measurement accuracy of the sliding speed V and the friction coefficient μ increases. From the viewpoint of being able to accurately determine the effect of suppressing the generation of abnormal noise when wetted, this number n is preferably 15 or less, more preferably 12 or less, and even more preferably 10 or less.

[0061] In this friction transmission belt B, from the viewpoint of effectively suppressing the generation of abnormal noise when wetted and improving power transmission efficiency, the upper limit of the reduction rate Dm of the friction coefficient μ shown in the above formula (1) may be set to 15%. In this case, it is more preferable that the reduction rate Dsm of the friction coefficient μ shown in the above formula (2) be 15 / n% or less in all sections. From the viewpoint of more effectively suppressing the generation of abnormal noise when wetted and further improving power transmission efficiency, the upper limit of the reduction rate Dm of the friction coefficient μ shown in the above formula (1) may be set to 10%. In this case, it is more preferable that the reduction rate Dsm of the friction coefficient μ shown in the above formula (2) be 10 / n% or less in all sections.

[0062] As described above, in this friction transmission belt B, the compressed rubber layer 11 is composed of a rubber layer main body 14 and a fiber material layer 15. This fiber material layer 15 forms the inner peripheral surface of the belt main body 10 that contacts the pulley 21. In this friction transmission belt B, the fiber material layer 15 absorbs water. Therefore, a water film is unlikely to form between the belt main body 10 and the pulley 21. In this friction transmission belt B, a significant decrease in the friction coefficient μ is prevented. In this friction transmission belt B, fluctuations in the friction coefficient μ are kept small, so the occurrence of stick-slip due to exposure to water is effectively suppressed. Therefore, abnormal noise is unlikely to occur when exposed to water. From this perspective, it is preferable that the belt main body 10 includes a compressed rubber layer 11 that contacts the pulley 21, and that this compressed rubber layer 11 is composed of a rubber layer main body 14 and a fiber material layer 15 laminated on the rubber layer main body 14.

[0063] In this friction transmission belt B, the surface of the compressed rubber layer 11 comes into contact with the pulley 21. When the surface of the compressed rubber layer 11 is formed of a fiber member layer 15, as in the V-ribbed belt B shown in Fig. 1, voids are formed in the surface layer portion of the compressed rubber layer 11 due to the presence of this fiber member layer 15. These voids contribute to the absorption of water.

[0064] In this friction transmission belt B, when the portion extending from the surface of the compressed rubber layer 11 to 200 μm in the depth direction is defined as the surface layer, the void ratio in this surface layer is preferably 10% or more. As a result, the voids formed in the surface layer contribute to water absorption. In this friction transmission belt B, a water film is less likely to form between the belt body 10 and the pulley 21. In this friction transmission belt B, a significant decrease in the friction coefficient μ is prevented. Because fluctuations in the friction coefficient μ are kept small, the occurrence of stick-slip due to exposure to water is effectively suppressed. As a result, abnormal noise is less likely to occur when exposed to water. From this perspective, a void ratio of 20% or more is more preferable. From the perspective of ensuring the rigidity of the surface layer, the void ratio is preferably 70% or less.

[0065] The void ratio in the surface layer portion of the compressed rubber layer 11 can be calculated using, for example, a cross-sectional image of the friction transmission belt B taken by a computer tomography device (Toshiba Corporation's "TOSCANER-30902μhd"). In calculating the void ratio, for example, a three-dimensional image of the surface layer portion is obtained by trimming the photographed cross-sectional image of the friction transmission belt B.

[0066] FIG. 4A shows a schematic representation of a three-dimensional image of the surface layer K obtained by trimming. In FIG. 4A, the length indicated by the symbol T is the thickness of the surface layer K used to calculate the porosity. This thickness T corresponds to the depth from the surface of the compressed rubber layer 11 and is set to 200 μm. The length indicated by the symbol W is the width of the surface layer K. This width W is set to 800 μm. The length indicated by the symbol L is the length of the surface layer K. This length L is set to 2000 μm. The volume of the surface layer K obtained by this trimming is expressed as the product of the thickness T, width W, and length L.

[0067] Once a three-dimensional image of the surface layer K is obtained, the stack histogram binarization method is used to separate this three-dimensional image into an image of the object portion made of rubber or fiber and an image of the remaining void portion. Based on the image of the void portion thus obtained, the volume of the void portion in the surface layer K is calculated, and the void ratio of the surface layer K of the compressed rubber layer 11, which is expressed as the ratio of the volume of the void portion to the volume of the surface layer K, is calculated. Note that FIG. 4B shows an image of the object portion obtained by binarizing the three-dimensional image. FIG. 4C shows an image of the void portion obtained by removing the image of the object portion from the three-dimensional image.

[0068] Next, a method for manufacturing the above-described V-ribbed belt B will be described with reference to the drawings. 5A and 5B are views showing a cross-linking device 30 used in manufacturing the V-ribbed belt B according to this embodiment. FIGS. 6A, 6B, and 6C are views for explaining the manufacturing method of the V-ribbed belt B according to this embodiment.

[0069] The cross-linking device 30 includes a base 31, a cylindrical expansion drum 32 erected on the base 31, and a cylindrical mold 33 provided on the outside thereof.

[0070] The expansion drum 32 has a hollow cylindrical drum body 32a and a cylindrical rubber expansion sleeve 32b fitted around the drum body 32a. The outer periphery of the drum body 32a is formed with a number of vent holes 32c that communicate with the interior. Both ends of the expansion sleeve 32b are sealed between the drum body 32a and the expansion sleeve 32b by fixing rings 34 and 35, respectively. The bridging device 30 is provided with a pressurizing means (not shown) that introduces pressurized air into the drum body 32a to apply pressure. The bridging device 30 is configured so that when pressurized air is introduced into the drum body 32a by the pressurizing means, the pressurized air passes through the vent holes 32c and enters between the drum body 32a and the expansion sleeve 32b, causing the expansion sleeve 32b to expand radially outward.

[0071] The cylindrical mold 33 is configured to be detachable from the base 31. The cylindrical mold 33 attached to the base 31 is provided concentrically with the expansion drum 32 at a distance. The cylindrical mold 33 has a plurality of circumferentially extending V-rib forming grooves 33a formed continuously in the axial direction (groove width direction) on its inner peripheral surface. Each V-rib forming groove 33a is formed to narrow toward the groove bottom, and specifically, its cross-sectional shape is formed to be the same shape as the V-rib 18 of the V-ribbed belt B to be manufactured. The cross-linking device 30 is provided with heating means and cooling means (neither shown) for the cylindrical mold 33, and is configured so that the temperature of the cylindrical mold 33 can be controlled by these heating means and cooling means.

[0072] In the manufacturing method of the V-ribbed belt B according to the embodiment, first, rubber compounding ingredients including a crosslinking agent are blended with the rubber component and kneaded in a kneading machine such as a kneader or a Banbury mixer. The resulting uncrosslinked rubber composition is formed into a sheet by calendar molding or the like to prepare an uncrosslinked rubber sheet 14' for the rubber layer main body 14 of the compressed rubber layer 11. Similarly, an uncrosslinked rubber sheet 16' for the rubber layer main body 16 of the adhesive rubber layer 12 is also prepared. Furthermore, a fibrous member layer 15 made of a woven or knitted fabric and a back reinforcing fabric 13 made of a woven or knitted fabric are prepared and subjected to an adhesive treatment as needed. In this manufacturing method, the fibrous member layer 15 is formed into a cylindrical shape in advance. The back reinforcing fabric 13 may also be formed into a cylindrical shape in advance. Furthermore, a core wire 17 is prepared and subjected to an adhesive treatment as needed.

[0073] 6A, a rubber sleeve 37 is placed on a cylindrical drum 36 having a smooth surface, and then the back reinforcing fabric 13 and the uncrosslinked rubber sheet 16' for the adhesive rubber layer main body 16 are wound on top of the rubber sleeve 37 in this order to form a laminate, and then the core wire 17 is spirally wound on top of that, and then the uncrosslinked rubber sheet 16' for the adhesive rubber layer main body 16 and the uncrosslinked rubber sheet 14' for the compressed rubber layer main body 14 are wound on top of that in this order. Finally, a cylindrical fiber member layer 15 is placed on top of the uncrosslinked rubber sheet 14' to form an uncrosslinked slab S'.

[0074] Next, the rubber sleeve 37 with the uncrosslinked slab S' is removed from the cylindrical drum 46 and fitted into the inner surface of the cylindrical mold 33 as shown in Figure 6B.The cylindrical mold 33 with the uncrosslinked slab S' is then attached to the base 31 so as to cover the expansion drum 32.

[0075] Next, the cylindrical mold 33 is heated, and as shown in Fig. 6C, high-pressure air is injected through the air vent 32c between the drum body 32a and the expansion sleeve 32b of the expansion drum 32 to expand the expansion sleeve 32b. At this time, the uncrosslinked slab S' is pressed against the cylindrical mold 33, and the uncrosslinked rubber sheets 14', 16' press and stretch the fiber material layer 15 while flowing into the V-rib forming grooves 33a. The crosslinking of the rubber components progresses, and the uncrosslinked rubber sheets are integrated and compounded with the fiber material layer 15, the cords 17, and the back reinforcing fabric 13, and finally, a cylindrical belt slab S is molded. The molding temperature for this belt slab S is, for example, 100°C to 180°C, the molding pressure is, for example, 0.5 MPa to 2.0 MPa, and the molding time is, for example, 10 minutes to 60 minutes.

[0076] Then, after the high-pressure air is released from between the drum body 32a and the expansion sleeve 32b of the expansion drum 32, the belt slab S molded on the inner peripheral surface of the cylindrical mold 33 is removed, and the belt slab S is sliced into a predetermined number of V-ribs 18 and turned over to obtain the V-ribbed belt B.

[0077] The porosity of the surface layer K of the compressed rubber layer 11 can be controlled by adjusting the elongation rate of the fibrous material layer 15 and the molding pressure. The elongation rate of the fibrous material layer 15 is adjusted by stretching the fibrous material layer 15 in the height direction or circumferential direction of the cylindrical mold 33. This elongation rate is expressed as the ratio of the width of the fibrous material layer 15 after stretching to the width or circumferential length of the fibrous material layer 15 before stretching.

[0078] Up to this point, a V-ribbed belt has been described as an embodiment of the friction transmission belt according to the present invention, but the friction transmission belt according to the embodiment of the present invention is not limited to this and may be a V-belt, a flat belt, etc. [Example]

[0079] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. Here, V-ribbed belts of Examples 1 to 6 and Comparative Example 1 were produced and evaluated.

[0080] <Materials for fiber component layers> To form the fiber member layer, the following three types of knitted fabrics were prepared without any adhesive treatment. (Knitted Fabric A) Circular knitted fabric made of knitting yarn consisting of cotton fiber and polyurethane fiber (Knitted Fabric B) Circular knitted fabric made of yarn consisting of cotton, nylon and polyurethane fibers (Knitted Fabric C) Circular knitted fabric made of knitting yarn consisting of nylon fiber and polyurethane fiber The proportion of cellulosic fibers (cotton fibers) in the fibers constituting the fiber component layer was 84% for knitted fabric A, 47% for knitted fabric B, and 0% for knitted fabric C.

[0081] <Materials for the compressed rubber layer body and adhesive rubber layer body> An uncrosslinked rubber composition containing EPDM and a rubber compounding agent containing sulfur was kneaded and then rolled with a calendar roll to prepare an uncrosslinked rubber sheet for the main body of the compression rubber layer and an uncrosslinked rubber sheet for the main body of the adhesive rubber layer.

[0082] <Materials for the core wire> As the material for the core wire, a twisted yarn of polyester fiber was prepared, which was immersed in an RFL aqueous solution and then subjected to an adhesive treatment by heating and drying.

[0083] <Material for back reinforcement fabric> The back reinforcing fabric was prepared by immersing a woven fabric made of a cotton-polyester blended yarn in an RFL aqueous solution and then subjecting it to a bonding treatment of heating and drying.

[0084] [Example 1] A V-ribbed belt having the same configuration as the above embodiment, using knitted fabric A as the fiber component layer, and using the above-mentioned compressed rubber layer main body material, adhesive rubber layer main body material, core wires, and back reinforcing fabric, was produced by the manufacturing method described with reference to Figures 5A to 6C, and was named the V-ribbed belt of Example 1. In Example 1, the elongation ratio of the fiber member layer was set to 180%, and the molding pressure was set to 0.7 MPa. The porosity of the surface layer portion of the compressed rubber layer was 38%.

[0085] [Examples 2 to 4 and Comparative Example 1] V-ribbed belts of Examples 2 to 4 and Comparative Example 1 were produced in the same manner as in Example 1, except that the stretching ratios and molding pressures were as shown in Table 2 below. The porosity of the surface layer portion in each of Examples 2 to 4 and Comparative Example 1 was as shown in Table 2.

[0086] [Example 5] A V-ribbed belt of Example 5 was produced in the same manner as in Example 1, except that knitted fabric B was used for the fiber member layer and the stretch ratio and molding pressure were set as shown in Table 2 below. In Example 4, the porosity of the surface layer was 22%.

[0087] [Example 6] A V-ribbed belt of Example 6 was produced in the same manner as in Example 1, except that knitted fabric C was used for the fiber member layer and the stretch ratio and molding pressure were set as shown in Table 2 below. In Example 6, the porosity of the surface layer was 20%.

[0088] <Evaluation of dynamic friction coefficient when wet> Using the belt running tester 20 shown in Figure 2 and according to the evaluation method described above, the relationship between sliding speed and friction coefficient was obtained for Examples 1 to 6 and Comparative Example 1, and the friction coefficient reduction rate Dm, shown in the above-mentioned formula (1), was calculated. Furthermore, the zone from the first sliding speed V1 to the second sliding speed V2 was equally divided into five sections, and the friction coefficient reduction rate Dsm, shown in the above-mentioned formula (2), i.e., reduction rates Ds1, Ds2, Ds3, Ds4, and Ds5, was calculated for each section. The results are shown in Table 2 below.

[0089] <Evaluation of abnormal noise when submerged in water> 7 shows the layout of pulleys in a belt running test machine 40 for evaluating abnormal noise when wetted. In FIG. 7, symbol B denotes a V-ribbed belt.

[0090] The belt running tester 40 for evaluating abnormal noise when wetted includes a drive pulley 41 which is a ribbed pulley with a pulley diameter of 140 mm, a first driven pulley 42 which is a ribbed pulley with a pulley diameter of 75 mm provided to the right of the drive pulley 41, a second driven pulley 43 which is a ribbed pulley with a pulley diameter of 50 mm provided above the first driven pulley 42 and diagonally above the right of the drive pulley 41, and an idler pulley 44 which is a flat pulley with a pulley diameter of 75 mm provided between the drive pulley 41 and the second driven pulley 43. The belt running tester 40 for evaluating abnormal noise when wetted is configured so that the V-ribbed belt's V-ribbed side contacts the drive pulley 41 and the first and second driven pulleys 42 and 43 which are ribbed pulleys, and its back surface contacts and is wound around the idler pulley 44 which is a flat pulley.

[0091] Example 1 6The V-ribbed belts of Comparative Example 1 and Comparative Example 2 were set in the belt running tester 40 for evaluating abnormal noise when exposed to water, and the pulleys were positioned so that a belt tension of 49 N per rib was applied. Resistance was applied to the second driven pulley 43 so that a current of 60 A would flow through the alternator to which it was attached. The drive pulley 41 was rotated at 800 rpm at room temperature, and water was dripped at a rate of 1,000 ml per minute onto the V-rib side of the V-ribbed belt where the V-ribbed belt entered the drive pulley 41. The occurrence of abnormal noise during belt running was evaluated on a five-point scale: "S: No abnormal noise was observed; A: Slight abnormal noise was observed; B: Slight abnormal noise was observed; C: Clear abnormal noise was observed; and D: Severe abnormal noise was observed."

[0092] [Table 2]

[0093] As shown in Table 2, the V-ribbed belt according to the embodiment of the present invention suppresses a decrease in the coefficient of friction and achieves a reduction in abnormal noise generated when wet. It has also been confirmed that the greater the void ratio in the surface layer of the compressed rubber layer, the smaller the rate of decrease in the friction coefficient can be kept. [Industrial Applicability]

[0094] The V-ribbed belt of the present disclosure is useful, for example, in an accessory drive belt transmission device for an automobile. [Explanation of symbols]

[0095] 10 Belt body 11 Compressed rubber layer 12 Adhesive rubber layer 13 Back reinforcement fabric 14 Rubber layer body (compressed rubber layer body) 14a V-rib body 15 Fiber member layer 16 Adhesive rubber layer body 17 Core Wire 18 V-Rib 20, 40 running test machine 30 Crosslinking device 14', 16' uncrosslinked rubber sheet B. Friction transmission belt (V-ribbed belt) K Surface layer

Claims

1. A friction power transmission belt including a belt body that transmits power to a pulley by frictional force generated by contact with the pulley, the belt body includes a compression rubber layer that contacts the pulley, the compression rubber layer is composed of a rubber layer main body made of a rubber composition and a fiber member layer laminated on the rubber layer main body, the fiber material layer is a woven fabric or a knitted fabric, the fiber member layer contacts the pulley; In the relationship between the slipping speed, which is the difference between the speed of the belt body and the speed of the pulley, and the friction coefficient when the belt is wet, the slipping speed that exhibits the maximum friction coefficient is defined as a first slipping speed, and the friction coefficient when the slipping speed is increased from the first slipping speed to a second slipping speed is defined as a reference friction coefficient, and when the difference between the second slipping speed and the first slipping speed is 500 mm / s, the reference coefficient of friction is lower than the maximum coefficient of friction; The reduction rate Dm of the friction coefficient expressed by the following formula (1), where μx is the maximum friction coefficient and μr is the reference friction coefficient, is 20% or less. Friction transmission belt. Dm=(μx-μr) / μx×100 (1)

2. When the zone from the first sliding speed to the second sliding speed is equally divided into n sections (n is a natural number of 2 or more), the sliding speed at the start of each section is defined as the start speed, the friction coefficient at the start speed is defined as the start friction coefficient, the sliding speed at the end of each section is defined as the end speed, and the friction coefficient at the end speed is defined as the end friction coefficient, In an m-th section (m is a natural number of 1 to n), the start friction coefficient is μm and the end friction coefficient is μem, and a reduction rate Dsm of the friction coefficient expressed by the following formula (2) is 20 / n% or less in all the sections. The friction power transmission belt according to claim 1. Dsm=(μsm-μem) / μsm×100 (2)

3. the porosity of the surface layer of the compression rubber layer is 10% or more; The friction power transmission belt according to claim 1 or 2.

4. The porosity is 20% or more. The friction power transmission belt according to claim 3.

5. The surface layer portion is a portion extending from the surface of the compression rubber layer to a depth of 200 μm. The friction power transmission belt according to claim 3 or 4.

6. The fiber material layer is made of a knitted fabric, The knitted fabric contains cellulosic fibers as the main fibers. The friction power transmission belt according to any one of claims 1 to 5.

7. The compression rubber layer is formed with a plurality of V-shaped ribs extending downwardly toward the inner periphery. The friction power transmission belt according to any one of claims 1 to 6.

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