Low edge tooth profile v-belt and method of using same and belt drive

Abstract

The present invention relates to a low edge profile V-belt having at least a tooth portion in which tooth crests and tooth roots are alternately arranged in a belt length direction on an inner peripheral side, wherein the tooth portion on the inner peripheral side is formed of a compression rubber layer and a fabric layer covering an inner peripheral side surface of the compression rubber layer, the top of the tooth crest on the inner peripheral side is flat, and the length of each top in the belt length direction is 18 to 65% with respect to a tooth pitch.

Description

Technical Field

[0001] This invention relates to a low-edge toothed V-belt for use in a belt-driven continuously variable transmission (CVT), a method of using the belt, and a belt drive mechanism. Background Technology

[0002] Among V-belts that transmit power through friction, there are two types: raw-edge V-belts (where the rubber layer with an exposed friction drive surface (V-shaped side)) and wrapped V-belts (where the friction drive surface is covered by a cover fabric). These are distinguished by their application based on the surface properties of the friction drive surface (the coefficient of friction between the rubber layer and the cover fabric). Raw-edge V-belts include those without teeth, as well as toothed raw-edge V-belts with teeth only on the inner circumference to improve flexibility, and toothed raw-edge V-belts with teeth on both the inner and outer circumferences to improve flexibility (such as double-toothed raw-edge V-belts).

[0003] Low-edge V-belts are mainly used for driving general industrial machinery, agricultural machinery, and auxiliary equipment in automobile engines. Among them, low-edge toothed V-belts are used for other purposes, such as the transmission belts (CVT belts) in belt-type continuously variable transmissions (CVTs) of motorcycles (scooters), snowmobiles (small snow vehicles), and four-wheel off-road vehicles (ATVs).

[0004] Figure 1 This is a schematic diagram used to illustrate the transmission mechanism of a CVT. For example... Figure 1 As shown, the belt-type CVT 20 has a mechanism that winds a V-belt 23 onto a drive pulley 21 and a driven pulley 22, allowing for stepless changes in the gear ratio. Each pulley 21, 22 has a fixed pulley half 21a, 22a whose axial movement is restricted or fixed, and a movable pulley half 21b, 22b that can move axially. The inner peripheral walls of the fixed pulley half 21a, 22a and the inner peripheral walls of the movable pulley half 21b, 22b form V-groove-shaped inclined opposing surfaces. Each pulley 21, 22 has a structure that allows for continuous changes in the width of the V-groove formed by these fixed pulley half 21a, 22a and movable pulley half 21b, 22b. The two end faces of the V-belt 23 in the width direction are formed as conical surfaces that are inclined in the same direction as the V-groove-shaped inclined opposing surfaces of each pulley 21, 22, and can be embedded in any vertical position of the V-groove opposing surfaces according to the changed V-groove width. For example, by narrowing the V-groove width of the drive pulley 21 and widening the V-groove width of the driven pulley 22, from Figure 1 The state shown in (a) changes to Figure 1In the state shown in (b), the V-belt 23 moves above the V-groove on the side of the drive pulley 21 and below the V-groove on the side of the driven pulley 22, so that the winding diameter of each pulley 21 and 22 changes continuously, thereby enabling stepless change of the gear ratio.

[0005] For example, a motorcycle's CVT has: a drive pulley fixed around the crankshaft of the engine, a driven pulley connected to the drive shaft of the rear wheel via gears, and a V-belt wound around the drive pulley and the driven pulley.

[0006] At low speeds, the movable pulley half of the drive pulley moves away from the fixed pulley half, reducing the winding diameter of the drive pulley. Simultaneously, the movable pulley half of the driven pulley moves closer to the fixed pulley half, increasing the winding diameter of the driven pulley. Therefore, the rear pulley is driven with higher torque at low speeds. Conversely, at high speeds, the movable pulley half of the drive pulley moves closer to the fixed pulley half, increasing the winding diameter of the drive pulley. Simultaneously, the movable pulley half of the driven pulley moves away from the fixed pulley half, reducing the winding diameter of the driven pulley. Therefore, the rear pulley is driven with lower torque at high speeds.

[0007] On the other hand, motorcycles differ from snowmobiles and ATVs in their clutch mechanisms (mechanisms that temporarily interrupt power transmission) at idle speed.

[0008] In other words, in a motorcycle's CVT, an automatic centrifugal clutch is installed between the rear wheel and the driven pulley. This clutch cuts off torque transmission from the driven pulley to the rear wheel at idle speed. Therefore, even if the driven pulley rotates at idle speed, the rear wheel does not rotate.

[0009] On the other hand, in CVTs used in snowmobiles or four-wheel-drive vehicles, an automatic centrifugal clutch is not installed. Instead, at idle speed, the torque transmission from the drive pulley to the V-belt is cut off by moving the movable pulley half until it completely separates from the side of the V-belt. That is, in this CVT, at idle speed, the V-belt falls into the groove bottom (shaft portion) of the pulley, whereby the lower surface (inner circumferential surface) of the V-belt contacts the shaft portion, thus functioning as a belt clutch to temporarily interrupt power transmission (the shaft portion of the drive pulley functions as an idler pulley). This type of transmission is called a belt-clutch-engaged CVT.

[0010] Figure 2 This is a schematic diagram showing the idling state of a CVT with clutch engagement. Figure 2 As shown, in this clutch-engaged CVT 30, the V-belt 33 does not contact either the movable pulley half 31b or the fixed pulley half 31a in the drive pulley 31, but instead contacts the pulley shaft portion 31c of the drive pulley 31. That is, in the automatic centrifugal clutch mode of a motorcycle CVT, the V-belt also... Figure 1In that case, the belt contacts the pulley half of the pulley, while in a clutch-type CVT in a snowmobile or four-wheel off-road vehicle, the inner circumferential surface of the V-belt contacts the outer circumferential surface of the pulley shaft (a typical pulley shaft with a smooth outer circumferential surface).

[0011] The following belts are known as clutch-engaged CVTs, which are transmission belts specifically designed for use where the bottom surface (inner circumferential surface) of the belt contacts the pulley shaft, such as when the engine is idling.

[0012] Japanese Patent Application Publication No. 2004-188776 (Patent Document 1) discloses a method for manufacturing a V-belt, which is used as a gear belt for transmissions of two-wheeled vehicles, off-road vehicles, snowmobiles, etc. By attaching a canvas to the bottom surface through a rubber layer, the bottom surface is prevented from becoming rubber, thereby preventing the bottom rubber from adhering to the shaft.

[0013] Japanese Patent Application Publication No. 2006-2836 (Patent Document 2) discloses a low-edge belt in which the bottom surface of the belt that contacts and slides with the pulley half shaft is made of a canvas surface without rubber coating. As a result, the coefficient of friction of the bottom surface is less than 0.1, and there is no rubber shedding (rubber powder falling off). Therefore, the fallen rubber will not intrude into the gap around the pulley half shaft and cause malfunctions.

[0014] Japanese Patent Application Publication No. 2006-226420 (Patent Document 3) discloses a power transmission belt in which the surface of a compressed rubber layer that abuts against the recess of a pulley is exposed. In the canvas, no rubber is attached to the part that abuts against the recess of the pulley, thereby eliminating the rubber attached to the belt surface that abuts against the recess of the pulley, reducing the coefficient of friction, and preventing noise.

[0015] Japanese Patent Application Publication No. 2007-144714 (Patent Document 4) discloses a V-belt that prevents rubber from seeping onto the canvas surface by covering the bottom surface of the belt with a canvas coating applied only to the belt body side, thereby suppressing noise and the generation of driving force.

[0016] Japanese Patent Application Publication No. 2009-51204 (Patent Document 5) discloses a toothed V-belt. In the process of winding canvas around a mold and temporarily fixing it, by using a tubular canvas with elastic filaments as the filaments in the belt circumference direction, it is possible to manufacture the belt without rubber adhering to the canvas. Even when the belt falls in a clutch-connected CVT, it can suppress the scattering of rubber shavings.

[0017] Japanese Patent Application Publication No. 2009-156289 (Patent Document 6) discloses a V-belt in which Teflon (registered trademark) is coated on the lower canvas, and the rubber used to bond the lower canvas to the bottom rubber is penetrated to the surface, thereby reducing the coefficient of friction with the crankshaft and reducing the torque transmitted from the crankshaft to the V-belt at idle speed.

[0018] On the other hand, compared with the automatic centrifugal clutch method, the engine braking performance of the clutch engagement method is lower. Therefore, a mechanism that functions as an engine braking system (EBS) is being studied. This mechanism utilizes the contact between the idler pulley and the inner circumferential surface of the transmission belt at idle speed to brake the driven pulley (rear pulley) through friction.

[0019] WO2011 / 046740 (Patent Document 7) and WO2019 / 209739 (Patent Document 8) disclose a continuously variable transmission engine braking system that adds braking function by engaging with an idler wheel (shaft), wherein the idler wheel (shaft) is provided with protrusions and concaves corresponding to the protrusions and concaves (teeth) provided on the inner circumferential surface of the V-belt.

[0020] Japanese Patent Application Publication No. 2023-169113 (Patent Document 9) discloses a braking system for a continuously variable transmission with a clutch engagement type, which uses a low-edge toothed V-belt as the transmission belt. The low-edge toothed V-belt is configured with a compression rubber layer as a combination of a main body of the compression rubber layer and an inner surface layer. The inner surface layer covers the inner peripheral side surface of the main body of the compression rubber layer and has a surface with a friction coefficient greater than that of the main body surface of the compression rubber layer.

[0021] Existing technical documents

[0022] Patent documents

[0023] Patent Document 1: Japanese Patent Application Publication No. 2004-188776

[0024] Patent Document 2: Japanese Patent Application Publication No. 2006-2836

[0025] Patent Document 3: Japanese Patent Application Publication No. 2006-226420

[0026] Patent Document 4: Japanese Patent Application Publication No. 2007-144714

[0027] Patent Document 5: Japanese Patent Application Publication No. 2009-51204

[0028] Patent Document 6: Japanese Patent Application Publication No. 2009-156289

[0029] Patent Document 7: WO2011 / 046740

[0030] Patent Document 8: WO2019 / 209739

[0031] Patent Document 9: Japanese Patent Application Publication No. 2023-169113 Summary of the Invention

[0032] The problem that the invention aims to solve

[0033] In the V-belts of Patent Documents 1-6, to prevent adverse conditions (noise, driving force generation, rubber scattering, etc.) caused by friction between the belt bottom surface and the pulley shaft, the aim is to facilitate sliding of the belt bottom surface (reduce the coefficient of friction), and therefore, engine braking performance (braking function) in the belt clutch engagement method is not described. Furthermore, the V-belts in Patent Documents 1-6 cannot obtain sufficient frictional force to achieve adequate braking function, thus failing to perform the braking function effectively. Therefore, the challenge lies in achieving braking function by shortening the braking distance and time, and in maintaining braking function, requiring the development of V-belts with high braking capacity (high friction).

[0034] On the other hand, the continuously variable transmission (CVT) engine braking systems in patent documents 7 and 8 require pulleys of a special shape.

[0035] Furthermore, in low-edge V-belts, CVT applications require the highest resistance to lateral pressure. To suit this application, the compression rubber layer needs to be highly rigid compared to other applications. Therefore, insufficient flexibility is inevitable in CVT applications, making teeth essential. In other words, high-rigidity rubber and teeth are necessary components for CVT applications. On the other hand, a belt with a flat (toothless) inner circumferential surface and a larger contact area is advantageous for braking (friction) by contacting the inner circumferential surface of the belt with the pulley shaft. However, since it is a CVT application and teeth are necessary, the contact point between the inner circumferential surface (bottom surface) of the belt and the pulley shaft (a conventional pulley shaft with a smooth outer circumferential surface and no irregularities for engagement with the belt) is only the top of the teeth, making it difficult to improve friction (braking function). In other words, in low-edge V-belts used in CVT applications, improving lateral pressure resistance and braking function is a difficult trade-off.

[0036] In response, Patent Document 9 enhances the braking function of the inner circumferential surface of the V-belt by configuring an inner surface layer (rubber layer) with a high coefficient of friction on the inner circumferential surface of the compression rubber layer body in the low-edge toothed V-belt. However, in the low-edge V-belt of Patent Document 9, the inner surface layer (rubber layer) is also prone to disappearing due to wear accompanying driving, and the braking function also disappears, thus posing a problem with durability (wear resistance).

[0037] Therefore, the object of the present invention is to provide a low-edge toothed V-belt that is applicable to braking systems of continuously variable transmissions with clutch engagement and has excellent durability such as wear resistance, as well as a method of using the same and a belt drive mechanism.

[0038] Methods for solving problems

[0039] In order to achieve the aforementioned goal, the inventors conducted in-depth research and discovered that in a low-edge toothed V-belt having teeth with alternating tooth tips and tooth roots in the belt length direction (or circumferential direction) at least on the inner circumferential side, the teeth are formed by a compressed rubber layer and a fabric layer covering the inner circumferential surface of the compressed rubber layer. The top of the tooth tip is formed to be flat, and the length of each top in the belt length direction is adjusted to 20-60% relative to the tooth pitch. This makes it suitable for braking systems of continuously variable transmissions with clutch engagement, and also improves durability such as wear resistance, thus completing the present invention.

[0040] That is, the present invention includes the following methods.

[0041] Method [1]: A low-edge toothed V-belt, having at least on the inner circumferential side teeth arranged alternately with tooth tips and tooth roots in the belt length direction, wherein, The teeth on the inner circumferential side are formed of a compressed rubber layer and a fabric layer, the fabric layer covering the inner circumferential surface of the compressed rubber layer. The top of the tooth tip on the inner circumferential side is flat, and, The length of each top band in the longitudinal direction is 18-65% of the tooth pitch.

[0042] Method [2]: A low-edge toothed V-belt according to the aforementioned method [1], wherein the tooth pitch is 6 to 17 mm.

[0043] Method [3]: A low-edge toothed V-belt according to method [1] or [2], wherein the fabric layer contains aramid fibers.

[0044] Method [4]: ​​A low-edge toothed V-belt according to any one of methods [1] to [3], wherein the cross-sectional shape of the tooth root on the inner circumferential side in the belt length direction is a shape having a bottom and a sidewall portion, the bottom being formed by an arc with a radius of curvature of 2 to 4 mm, and the sidewall portion being inclined relative to the belt thickness direction or extending from the bottom along the belt thickness direction.

[0045] Method [5]: A low-edge toothed V-belt according to any one of methods [1] to [4], wherein, The cross-sectional shape of the tooth root on the inner circumferential side along the length direction is a shape having a bottom and a sidewall portion. The bottom is formed by combining multiple consecutive arcs, and the sidewall portion is inclined relative to the thickness direction of the belt or extends from the bottom along the thickness direction of the belt. The radius of curvature of the plurality of arcs decreases as they move away from the deepest part of the tooth root. The radius of curvature of the first arc passing through the deepest part of the plurality of arcs is larger than the radius of the imaginary circle tangent to the deepest part and the sidewalls on both sides, and is 2 to 4 mm.

[0046] Method [6]: A belt drive mechanism comprising a low-edge toothed V-belt and pulley according to any one of methods [1] to [5], wherein the low-edge toothed V-belt is a speed belt for a continuously variable transmission with clutch engagement.

[0047] Method [7]: According to the belt drive mechanism of Method [6], wherein the continuously variable transmission with clutch engagement is a continuously variable transmission in which the inner circumferential surface of the belt contacts the pulley shaft at idle speed.

[0048] Method [8]: According to the belt drive mechanism of Method [6] or [7], wherein the continuously variable transmission with clutch engagement is a continuously variable transmission equipped with a braking system that utilizes the friction between the inner circumferential surface of the belt and the pulley shaft.

[0049] Method [9]: A method of using a low-edge toothed V-belt, wherein the low-edge toothed V-belt is a low-edge toothed V-belt according to any one of the methods [1] to [5], wherein, in a continuously variable transmission with clutch engagement, the low-edge toothed V-belt participates in all of the continuously variable transmission, clutch engagement and braking.

[0050] In addition, the numerical range represented by "A~B" in this application refers to "above A and below B", and is used to include the meaning of the numerical values ​​A and B at both ends.

[0051] Invention Effects

[0052] In this invention, a low-edge toothed V-belt with teeth arranged alternately at the top and bottom of the teeth in the belt length direction on at least the inner circumferential side, wherein the teeth are formed by a compressed rubber layer and a fabric layer covering the inner circumferential surface of the compressed rubber layer, wherein the top of the tooth is formed to be flat, and the length of each top in the belt length direction is adjusted to 18-65% (e.g., 20-60%) relative to the tooth pitch, thus making it suitable for braking systems of continuously variable transmissions with clutch engagement, and improving durability such as wear resistance. Attached Figure Description

[0053] [ Figure 1 ] Figure 1 This is a schematic diagram used to illustrate the transmission mechanism of a belt-driven continuously variable transmission (CVT).

[0054] [ Figure 2 ] Figure 2 This is a schematic diagram showing the idling state of a continuously variable transmission (CVT) with clutch engagement.

[0055] [ Figure 3 ] Figure 3 This is a schematic partial cross-sectional perspective view showing an example of a low-edge double-tooth V-belt of the present invention.

[0056] [ Figure 4 ] Figure 4 It is Figure 3 A schematic cross-sectional view of a low-edge double-tooth V-belt cut along its length.

[0057] [ Figure 5 ] Figure 5 It is used to describe the shape of the inner circumferential tooth root. Figure 4 Enlarged image.

[0058] [ Figure 6 ] Figure 6 This is a diagram showing the layout of the testing machine used in the durability test (Top durability test) of the low-edge double-tooth V-belt obtained in the embodiment.

[0059] [ Figure 7 ] Figure 7 This is a diagram showing the layout of the testing machine used in the low-endurance test of the low-edge double-tooth V-belt obtained in the embodiment.

[0060] [ Figure 8 ] Figure 8 This is a schematic diagram of the cross-sectional shape of the low-edge double-tooth V-belt obtained in Comparative Examples 1-8 and Comparative Examples 1-5.

[0061] [ Figure 9 ] Figure 9 This is an FEM analytical diagram showing the tooth interference state generated when the low-edge double-tooth V-belt obtained in Comparative Example 4 is bent.

[0062] [ Figure 10 ] Figure 10 This is a schematic diagram of the cross-sectional shape of the low-edge double-tooth V-belt obtained in Comparative Examples 9-21 and Comparative Examples 6-7. Detailed Implementation

[0063] [Structure of low-edge toothed V-belt]

[0064] In the low-edge toothed V-belt of the present invention, the teeth formed on the inner circumferential side are formed by a compressed rubber layer and a fabric layer covering the inner circumferential surface of the compressed rubber layer. In this invention, since the inner circumferential surface of the compressed rubber layer is covered by the fabric layer, wear resistance is improved. Furthermore, in low-edge V-belts, CVT applications require the highest resistance to lateral pressure; to suit this application, the compressed rubber layer requires high rigidity compared to other applications. Therefore, in CVT applications, by forming teeth on the compressed rubber layer formed on the inner circumferential side using high-rigidity rubber, flexibility can be improved.

[0065] Thus, the low-edge toothed V-belt of the present invention is used for CVT applications. Since the teeth on the inner circumferential side are essential, the portion of the inner circumferential surface (bottom surface) of the belt that contacts the pulley shaft is only the top of the tooth tip. Therefore, in the low-edge toothed V-belt of the present invention, the top is formed into a flat shape (a flat shape along a surface perpendicular to the belt thickness direction). Furthermore, in the present invention, the length of the top in the belt length direction is adjusted to 18% or more relative to the tooth pitch, thereby increasing the area of ​​the inner circumferential surface of the V-belt that can contact the outer circumferential surface of the pulley shaft, and ensuring friction-based braking performance. Furthermore, in the present invention, the length of the top in the belt length direction is adjusted to 65% or less relative to the tooth pitch, thereby ensuring braking performance without compromising belt flexibility and durability.

[0066] The low-edge toothed V-belt of the present invention is not particularly limited as long as it has such a shape. It can be a low-edge toothed V-belt with teeth formed only on the inner circumferential side, or a low-edge double-toothed V-belt with teeth formed on both the inner and outer circumferential sides. Among these, from the viewpoint that the present invention is more effective in use under more severe conditions and requires a high level of both lateral pressure resistance and flexural fatigue resistance, the low-edge double-toothed V-belt is particularly preferred.

[0067] Figure 3 This is a schematic partial cross-sectional perspective view showing an example of a low-edge double-tooth V-belt of the present invention. Figure 4 It is Figure 3 A schematic cross-sectional view of a low-edge double-tooth V-belt cut along its length.

[0068] In this example, the low-edge double-tooth V-belt 1 has an inner circumferential tooth portion formed by alternating inner circumferential tooth tops 1a and inner circumferential tooth bottoms 1b along the belt length direction (direction A in the figure) on the inner circumferential surface of the compressed rubber layer 4. The cross-sectional shape of the inner circumferential tooth top 1a in the belt length direction is approximately inverted trapezoidal, and the cross-sectional shape in the direction orthogonal to the belt length direction (width direction or direction B in the figure) is approximately inverted trapezoidal.

[0069] On the other hand, the outer peripheral surface also has an outer peripheral tooth portion formed by the alternating arrangement of outer peripheral tooth tips 1c and outer peripheral tooth roots 1d along the belt length direction. The cross-sectional shape of the outer peripheral tooth tip 1c in the belt length direction is approximately trapezoidal, and the cross-sectional shape in the direction orthogonal to the belt length direction (width direction or direction B in the figure) is approximately rectangular. That is, each outer peripheral tooth tip 1c protrudes approximately trapezoidally from the outer peripheral tooth root 1d in the cross-section in direction A in the belt thickness direction.

[0070] The low-edge double-tooth V-belt has a layered structure, consisting of an elongated rubber layer 2, a core layer (adhesive rubber layer) 3, a compression rubber layer 4, and a fabric layer 5, stacked sequentially from the outer periphery to the inner periphery. The cross-sectional shape in the belt width direction is an approximately inverted trapezoid, with the belt width decreasing from the outer periphery to the inner periphery. Furthermore, a core 3a is embedded within the core layer 3. The inner peripheral teeth are formed on the compression rubber layer 4, which is covered by the fabric layer 5, using a toothed forming mold, while the outer peripheral teeth are formed on the elongated rubber layer 2 using a toothed forming mold.

[0071] In particular, each inner circumferential tooth tip 1a protrudes in a generally inverted trapezoidal shape from the inner circumferential tooth root 1b in the A-direction cross section in the belt thickness direction. That is, in this invention, the top 11 of the inner circumferential tooth tip 1a is formed into a flat shape along the belt length direction, and the length L of the top 11 in the belt length direction (circumferential direction) is adjusted to 20-60% relative to the inner circumferential tooth pitch P (the shortest distance between the deepest parts of adjacent tooth roots).

[0072] In this invention, by forming the top 11 as flat (having a flat shape with a surface substantially perpendicular to the belt thickness direction), friction is ensured by guaranteeing the frictional area with the pulley shaft. Figure 4 As shown, the ratio (proportion) of the length L of the top (flat top) 11 relative to the inner circumferential tooth pitch P becomes an indicator of the area of ​​the flat shape (flat portion) of the top 11 used to ensure friction.

[0073] That is, when the inner circumferential surface of the belt has no teeth, the concept of "tooth pitch" = "circumferential length of the flat portion" is adopted, and the area of ​​the flat portion is the largest. However, since teeth are necessary in this invention, the area of ​​the flat portion cannot be maximized. By setting teeth (valve), the flat surface is missing, and the area of ​​the flat portion is reduced. When the above-mentioned maximum area is set to 100, the proportion of the area of ​​the remaining flat portion is an indicator of the area of ​​the flat portion, which has the same meaning as "the ratio (proportion) of the circumferential length of the flat top of the tooth tip relative to the tooth pitch".

[0074] That is, multiplying this ratio by the number of teeth in the belt means "the sum of the circumferential lengths of all flat tops relative to the full circumference of the inner circumference when there are no teeth," and multiplying this ratio by the belt width means "the full area of ​​flat tops relative to the full area of ​​the inner circumferential surface when there are no teeth." Therefore, in this application, the ratio of the length L of the top (flat top) of the inner circumferential tooth pitch P is also called the inner circumferential flatness ratio.

[0075] On the other hand, from the viewpoint of ensuring braking performance (inner circumferential surface friction), it is preferable to maximize the area of ​​the inner circumferential surface of the V-belt that can contact the outer circumferential surface of the pulley shaft (i.e., inner circumferential flatness). To increase the contact area with the pulley shaft, it is necessary to narrow the inner circumferential tooth pitch to increase the number of teeth, or to reduce the tooth angle to increase the inner circumferential flatness. However, these methods reduce the width of the teeth (recesses). On the other hand, if the width of the teeth (recesses) is too small, the teeth will interfere with each other during bending, becoming an obstacle to bending. In addition, the stress generated at the tooth root increases, making the tooth root prone to cracking. Furthermore, early tooth root cracking leads to a shortened service life.

[0076] That is, in the braking system of a continuously variable transmission with clutch engagement, the braking function and durability (resistance to tooth root cracks) are inversely related. Therefore, the area of ​​the inner circumferential surface of the belt needs to be set within a range that can balance both aspects.

[0077] From this perspective, in this invention, the length L of each top section in the longitudinal direction is adjusted relative to the inner circumferential tooth pitch P to be 18-65% (particularly 20-60%), preferably 25-63%, more preferably 30-62%, further preferably 35-61%, and most preferably 38-60%. Furthermore, the length L relative to the inner circumferential tooth pitch P is preferably 25-55%, more preferably 30-50%, further preferably 35-45%, and most preferably 35-40%. When the ratio of the length L relative to the inner circumferential tooth pitch P (inner circumferential flatness) is lower than the lower limit of 18%, the contact area is insufficient, and the braking function cannot be fully exerted; when it exceeds the upper limit of 65%, the width of the inner circumferential tooth (recess) is too small, and the durability (resistance to tooth root cracking) decreases.

[0078] The inner circumferential tooth pitch P is, for example, 6–17 mm, preferably 7–15 mm, more preferably 8–14 mm, even more preferably 9–13 mm, and most preferably 10–12.5 mm. If the inner circumferential tooth pitch P is too small, it may not be able to adequately ensure the teeth (recesses) and create obstacles to bending; if it is too large, the inner circumferential flatness decreases, and it may not be able to adequately ensure braking performance (friction force on the inner circumferential surface).

[0079] Figure 5 It is used to describe the shape of the bottom of the inner circumferential teeth. Figure 4 An enlarged image. For example... Figure 4 and Figure 5 As shown, in this example, the cross-sectional shape of the tooth root 1b is a shape having a bottom 13 and sidewall portions 12, 12. The bottom 13 is formed by combining three arcs: a first arc 13a and a pair of second arcs 13b, 13b. The sidewall portions 12, 12 are relative to the thickness direction ( Figure 4 and Figure 5The direction (indicated by the single-dot dashed line) is inclined towards the inner circumference of the tooth root 1b in a direction that expands with respect to the tooth angle θ (the inclination angle of the single-sided sidewall) and extends from the bottom 13. For example... Figure 4 and Figure 5 As shown, in the unbent state of the low-edge toothed V-belt 1, the radii of curvature of the plurality of arcs (first arc 13a and second arc 13b) constituting the bottom 13 decrease as they move away from the deepest part A of the tooth root 1b.

[0080] Specifically, the first arc 13a is represented by a circle C1 with a center O1 on a vertical line VL (in the direction of strip thickness) orthogonal to the strip length direction, but using a circle smaller than the imaginary circle VC ( Figure 5 The imaginary circle VC is formed with a larger diameter than the circle with a dotted line having a radius of curvature R0. The imaginary circle VC has a center O0, passes through the deepest part A of the tooth root 1b, and is tangent to the deepest part A of the tooth root 1b and the two sidewall portions 12 at three points (the deepest part A and the tangent points B of the pair of sidewall portions, totaling three points). Furthermore, in this application, an imaginary circle refers to a circle equivalent to an imaginary arc when the bottom is composed of a single arc.

[0081] Furthermore, the second arc 13b is located between the first arc 13a and the sidewall portion 12. The radius of curvature R2 of the second arc 13b is formed to be smaller than the radius of curvature R1 of the first arc 13a.

[0082] In this invention, the shape of the bottom of the inner circumferential tooth root is not limited to the shape formed by combining the first arc and a pair of second arcs, and can also be a shape formed by a single arc. However, from the viewpoint of improving durability (resistance to tooth root cracking), it is preferable to have a shape formed by combining multiple consecutive arcs, and particularly preferable to have a shape formed by combining the first arc and a pair of second arcs.

[0083] When the bottom of the tooth root is designed as a combination of multiple continuous arcs, it is preferable that the radius of curvature of the first arc located at the deepest part of the tooth root is larger than that of an imaginary arc, and the radius of curvature decreases as it moves away from the deepest part. By designing it as a multi-segment arc, the stress at the bottom of the tooth root, which is prone to stress concentration due to bending deformation, can be mitigated and dispersed, thus suppressing the formation of cracks at the tooth root. Furthermore, compared to the case where the bottom is formed by a single arc (equivalent to an imaginary arc), the circumferential length of the tooth (the length of the flat top) can be increased, ensuring a wider contact area with the pulley shaft.

[0084] The radius of curvature R1 of the first arc is, for example, 1 to 5 mm, preferably 1.5 to 4.8 mm (e.g., 1.5 to 4.5 mm), more preferably 2 to 4.7 mm (e.g., 2 to 4 mm), even more preferably 2.5 to 4.6 mm (e.g., 2.5 to 4 mm), and most preferably 3 to 4.5 mm (e.g., 3 to 4 mm). If the radius of curvature R1 is too small, durability (resistance to tooth root cracking) may decrease; if it is too large, the inner circumferential flatness decreases, which may not adequately ensure braking performance (friction force on the inner circumferential surface). These ranges of the radius of curvature R1 of the first arc can also be the ranges of the radius of curvature of the arc when the bottom of the tooth root is formed by a single arc.

[0085] The radius of curvature R2 of the second arc is, for example, 0.1–3 mm, preferably 0.15–2 mm, more preferably 0.2–1.5 mm, even more preferably 0.25–1.3 mm, and most preferably 0.5–1.2 mm. If the radius of curvature R2 is too small, the bending resistance may decrease, leading to reduced durability. If it is too large, the flatness of the inner circumference decreases, which may not be able to adequately ensure braking performance (friction force on the inner circumferential surface).

[0086] In the cross-sectional shape of the tooth root, the sidewall is not limited to a shape that is inclined at a tooth angle θ and extends from the bottom relative to the direction of the belt thickness toward the inner circumference of the tooth root diameter, but can also be a shape that extends from the bottom (parallel) along the direction of the belt thickness.

[0087] The tooth angle θ of the sidewall portion can be 30° or less (especially 25° or less), for example, 20° or less, preferably 15° or less (e.g., 1 to 15°), more preferably 12° or less (e.g., 3 to 12°), and even more preferably 10° or less (especially 4 to 10°). The tooth angle θ is, for example, 8° or less, preferably 5° or less. If the tooth angle θ is too small, tooth interference is likely to occur; if it is too large, the inner circumferential flatness decreases, which may not adequately ensure braking performance (friction force on the inner circumferential surface).

[0088] In the low-edge toothed V-belt of the present invention, from the viewpoint of preventing edge breakage, a C-surface chamfer of C0.5mm to C2.0mm or an R-surface chamfer of R0.5mm to R2.0mm is preferably applied at the intersection of the flat top 11 and the sidewall portion 12. In the present invention, the inner circumferential flatness can be adjusted by performing C-surface chamfering and R-surface chamfering on the intersection. For example, in the R-surface chamfering, the inner circumferential flatness can be adjusted by adjusting the radius of curvature R3 of the R-surface chamfer within the range (0.5 to 2.0mm). That is, the radius of curvature R3 can be increased to decrease the inner circumferential flatness, or decreased to increase the inner circumferential flatness. Furthermore, in the present invention, the inner circumferential flatness can also be adjusted by combining such adjustments of C-surface chamfering or R-surface chamfering with adjustments of the radius of curvature R1, the radius of curvature R2, or the tooth angle θ.

[0089] The overall thickness, tooth height, and bottom thickness of the low-edge toothed V-belt (low-edge double-toothed V-belt) of the present invention are defined as follows: Figure 4 As shown.

[0090] The overall thickness H (average thickness) of the low-edge toothed V-belt of the present invention is, for example, 8 to 19 mm, preferably 10 to 19 mm, more preferably 13 to 18 mm, and even more preferably 14 to 17 mm. If the thickness is too small, the resistance to lateral pressure may be reduced; if the thickness is too large, the flexibility may be reduced, which may lead to a decrease in transmission efficiency, and at the same time, the resistance to bending fatigue may be reduced.

[0091] like Figure 4 As shown, in this application, when the compression rubber layer 4 and the elongation rubber layer 2 have teeth, the overall thickness H of the belt refers to the thickness at the top of the teeth (the maximum thickness of the belt). That is, the thickness H of the low-edge toothed V-belt 1 refers to the shortest distance (the distance perpendicular to the thickness direction) from the top of the teeth of the fabric layer 5 (the top of the inner circumferential side) to the top of the teeth of the elongation rubber layer 2 (the top of the outer circumferential side).

[0092] Furthermore, in this application, the inner circumferential tooth bottom of the inner circumferential tooth refers to the portion of the thin-walled portion that forms the fabric layer and the compressed rubber layer having the inner circumferential tooth, and generally refers to the curved valley or groove (curved groove) located between the adjacent inner circumferential tooth tops protruding towards the inner circumferential side of the belt.

[0093] The height H1 of the inner peripheral teeth formed on the inner peripheral surface (the shortest distance from the deepest part of the inner peripheral tooth base to the top of the inner peripheral tooth in the thickness direction) can be selected from, for example, a range of 4 to 8 mm, preferably 5 to 7 mm, and the height H4 of the outer peripheral teeth formed on the outer peripheral surface (the shortest distance from the deepest part of the outer peripheral tooth base to the top of the outer peripheral tooth in the thickness direction) can be selected from, for example, a range of 2 to 5 mm, preferably 3 to 4 mm.

[0094] The inner core thickness H2 of the inner circumferential surface (the shortest distance from the central axis of the core wire to the deepest part of the inner tooth root in the thickness direction) can be selected from, for example, a range of 2 to 7 mm, preferably 3 to 5 mm, and the outer core thickness H3 of the outer circumferential surface (the shortest distance from the central axis of the core wire to the deepest part of the outer tooth root in the thickness direction) can be selected from, for example, a range of 0.5 to 4 mm, preferably 1 to 3 mm.

[0095] In the low-edge toothed V-belt of the present invention, the belt width and V-angle are not particularly limited and can be appropriately selected according to the design of the belt drive mechanism. Generally, the belt width, for example, the upper width (the belt width on the outer periphery) can be selected from a range of 20 to 50 mm, preferably 30 to 44 mm. The angle of the V-shaped side, i.e., the V-angle, can be selected from a range of 20 to 35°, preferably 24 to 32°.

[0096] [Compression rubber layer]

[0097] In the low-edge toothed V-belt of the present invention, the compression rubber layer body is formed of a rubber composition (crosslinked rubber composition) containing a first rubber component.

[0098] (A1) Rubber component 1

[0099] The first rubber component can be a vulcanizable or cross-linkable rubber, such as diene rubbers [natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), chloroprene rubber (CR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (H-NBR), etc.], ethylene-α-olefin elastomers [ethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer (EPDM), etc.], chlorosulfonated polyethylene rubber, alkylated chlorosulfonated polyethylene rubber, epichlorohydrin rubber, acrylic rubbers, silicone rubber, polyurethane rubber, fluororubber, etc. These rubber components can be used alone or in combination of two or more.

[0100] Among them, ethylene-α-olefin elastomer and chloroprene rubber are preferred. From the point of view that they have a good balance of heat resistance, abrasion resistance, oil resistance and high productivity, chloroprene rubber is particularly preferred.

[0101] When the first rubber component contains chloroprene rubber, the proportion of chloroprene rubber in the first rubber component can be 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more (especially 90 to 100% by mass), and most preferably 100% by mass (chloroprene rubber only) from the viewpoint of improving the aforementioned properties and productivity. When the first rubber component contains ethylene-α-olefin elastomer, the proportion of ethylene-α-olefin elastomer in the first rubber component is also the same as the proportion of chloroprene rubber.

[0102] (A2) First short fiber

[0103] The rubber composition forming the compression rubber layer may further contain a first short fiber. Examples of the first short fibers include polyamide short fibers (aliphatic polyamide short fibers such as polyamide 6, polyamide 66, and polyamide 46, and aramid short fibers), polyalkylene arylide short fibers (e.g., polyethylene terephthalate (PET) short fibers, polyethylene naphthalate (PAN) short fibers), liquid crystal polyester short fibers, polyaryl ester short fibers (amorphous fully aromatic polyester short fibers), vinylon short fibers, polyvinyl alcohol-based short fibers, poly(p-phenylene benzobisoxazole) (PBO) short fibers, and other synthetic short fibers; natural short fibers such as cotton, linen, and wool; and inorganic short fibers such as carbon short fibers. These first short fibers can be used alone or in combination of two or more. Among these, aramid short fibers and PBO short fibers are preferred, with aramid short fibers being particularly preferred.

[0104] The first short fiber can be a short fiber cut from fibrous, stretched fibers into a specified length. To suppress compression deformation of the belt caused by lateral pressure from the pulley (improving lateral pressure resistance), the first short fiber is preferably oriented along the belt width direction and embedded in the main body of the compression rubber layer. Furthermore, to reduce the coefficient of friction of the surface in contact with the pulley, thereby suppressing noise (sound emission), or to reduce wear caused by friction with the pulley, the short fiber is preferably protruding from the surface of the compression rubber layer.

[0105] The average fiber length of the first short fiber is, from the viewpoint of improving lateral pressure resistance and abrasion resistance without reducing flexibility, for example, 0.1 to 20 mm, preferably 0.5 to 15 mm (e.g., 0.5 to 10 mm), and more preferably 1 to 6 mm (especially 2 to 4 mm). If the fiber length of the first short fiber is too short, the mechanical properties in the fiber orientation direction cannot be sufficiently improved, and the lateral pressure resistance and abrasion resistance may decrease. Conversely, if it is too long, the orientation of the short fibers in the rubber composition decreases, and thus the flexibility may decrease.

[0106] The monofilament fineness of the first short fiber is chosen from the viewpoint of providing high reinforcement without reducing flexibility, for example, 1 to 12 dtex, preferably 1.2 to 10 dtex (e.g., 1.5 to 8 dtex), and more preferably 2 to 5 dtex (especially 2 to 3 dtex). If the monofilament fineness is too large, the resistance to lateral compression and abrasion per compound may decrease; if the monofilament fineness is too small, the dispersibility of the rubber decreases, and thus the flexibility may decrease.

[0107] To improve adhesion to the first rubber component, the first short fiber can undergo a general bonding treatment. Examples of such bonding treatments include impregnation in a treatment solution containing an epoxy compound or polyisocyanate compound, impregnation in an RFL treatment solution containing resorcinol, formaldehyde, and latex, and impregnation in a rubber paste. These treatments can be applied individually or in combination.

[0108] The proportion of the first short fiber relative to 100 parts by weight of the first rubber component is, for example, 5 to 50 parts by weight, preferably 5 to 40 parts by weight (e.g., 8 to 35 parts by weight), more preferably 10 to 30 parts by weight, and even more preferably 15 to 25 parts by weight. If the first short fiber is too small, the resistance to lateral pressure and abrasion may decrease; if it is too large, the processability may decrease, or the flexibility of the belt may decrease, leading to a decrease in durability.

[0109] (A3) Other ingredients

[0110] The rubber composition forming the compression rubber layer may contain conventional additives, such as crosslinking agents or vulcanizing agents (sulfur-based crosslinking agents, organic peroxides, etc.), co-crosslinking agents (bismaleimides, etc.), crosslinking aids or crosslinking accelerators (thiuram-based accelerators, etc.), crosslinking delay agents, metal oxides (zinc oxide, magnesium oxide, calcium oxide, barium oxide, iron oxide, copper oxide, titanium oxide, aluminum oxide, etc.), and fillers [reinforcing fillers such as carbon black and silica (hydrated silica, etc.); extenders such as clay, calcium carbonate, talc, and mica (non-reinforcing fillers or inert fillers), etc.]. Plasticizers (or softeners) [oils (paraffin oil, naphthenic oil, etc.), aliphatic carboxylic acid plasticizers, aromatic carboxylic acid ester plasticizers, oxycarboxylic acid ester plasticizers, phosphate ester plasticizers, ether plasticizers, ether ester plasticizers, etc.], processing agents or processing aids (stearic acid, metal stearate salts, waxes, paraffin, fatty acid amides, etc.), antioxidants (antioxidants, heat aging inhibitors, flexural cracking inhibitors, ozone degradation inhibitors, etc.), adhesion improvers, colorants, tackifiers, coupling agents (silane coupling agents, etc.), stabilizers (UV absorbers, heat stabilizers, etc.), flame retardants, antistatic agents, etc. These additives can be used alone or in combination of two or more. Additionally, metal oxides can also act as crosslinking agents.

[0111] The proportion of fillers such as carbon black or silica (first filler) relative to 100 parts by mass of the first rubber component is, for example, 10 to 200 parts by mass, preferably 20 to 100 parts by mass, more preferably 30 to 80 parts by mass, and even more preferably 40 to 70 parts by mass.

[0112] The proportion of the plasticizer (first plasticizer) relative to 100 parts by weight of the first rubber component can be less than 10 parts by weight, for example, 0.1 to 10 parts by weight, preferably 1 to 8 parts by weight, and more preferably 3 to 7 parts by weight. If the proportion of plasticizer is too high, the compression rubber layer will be excessively softened, and the resistance to lateral pressure may be reduced.

[0113] The total proportion of the other components (A3) relative to 100 parts by mass of the first rubber component is, for example, 5 to 300 parts by mass, preferably 10 to 200 parts by mass, more preferably 30 to 150 parts by mass, and even more preferably 50 to 100 parts by mass.

[0114] (A4) Characteristics of the compressed rubber layer

[0115] The compression rubber layer uses a high-rigidity (high elastic modulus) rubber composition and has high rubber hardness to improve lateral pressure resistance. The rubber hardness can be 89° or higher, for example, 90–99°, preferably 91–98°, more preferably 92–97°, and even more preferably 93–96°. If the rubber hardness of the main body of the compression rubber layer is too low, the lateral pressure resistance may decrease; if it is too high, the flexibility is insufficient, and the durability (resistance to tooth root cracking) may decrease.

[0116] In addition, in this application, the rubber hardness of each rubber layer refers to the value Hs (Type A) measured using a Type A durometer based on the hardness test of a spring-type durometer as specified in JIS K 6253 (2012) (Vulcanized rubber and thermoplastic rubber - Method for determination of hardness -), sometimes simply referred to as rubber hardness. More specifically, it can be measured using the methods described in the examples below.

[0117] The tensile strength of the compressed rubber layer is, for example, 25–50 MPa in the width direction, preferably 30–40 MPa, and more preferably around 30–35 MPa. If the tensile strength is too low, the resistance to lateral pressure may decrease; conversely, if it is too high, the flexibility is insufficient and the durability (resistance to tooth root cracks) may decrease.

[0118] Furthermore, in this application, the tensile strength of each rubber layer can be measured using the tensile strength T value of each rubber layer, determined based on the method of JIS K 6251 (2017), as an index value of tensile strength. Specifically, it can be measured using the method described in the embodiments below.

[0119] The average thickness of the compression rubber layer is, for example, 7 to 13 mm, preferably 8 to 12 mm, and more preferably 9 to 11 mm. Furthermore, in this application, the thickness of the compression rubber layer refers to the thickness at the top of the teeth.

[0120] [Fabric layer]

[0121] In this invention, from the viewpoint of ensuring braking performance, improving durability (resistance to tooth root cracking), and wear resistance, the inner circumferential surface of the compression rubber layer is covered by a fabric layer. The fabric layer can be formed from conventional fabrics.

[0122] Commonly used fabrics include woven fabrics, knitted fabrics (weft-knitted fabrics, warp-knitted fabrics), and nonwoven fabrics. Among these, woven fabrics such as plain weave, twill weave, and satin weave, as well as woven fabrics and knitted fabrics with a cross angle exceeding 90° but less than approximately 120°, are preferred. Woven fabrics widely used as cover fabrics for transmission belts in general industrial or agricultural machinery are particularly preferred [plain weave fabrics with a right-angle cross angle, and plain weave fabrics with a cross angle exceeding 90° but less than approximately 120° (wide-angle canvas)]. Furthermore, for applications requiring durability, the fabric can be wide-angle canvas.

[0123] The fibers constituting the fabric can be exemplified by fibers such as the first short fiber constituting the compressed rubber layer. These fibers can be single yarns using only one type of fiber, or composite yarns (blended yarns, etc.) combining two or more fibers. From the viewpoint of improving abrasion resistance, aramid fibers are preferred.

[0124] Aramid fibers can be either para-aramid fibers or meta-aramid fibers.

[0125] Examples of para-aramid fibers include poly(p-phenylene terephthalamide) fibers (e.g., Teijin Corporation's "Twaron (registered trademark)", Toray DuPont Corporation's "Kevlar (registered trademark)", etc.) and copolymer fibers of poly(p-phenylene terephthalamide) and 3,4'-oxodiphenylene terephthalamide (e.g., Teijin Corporation's "Technora (registered trademark)").

[0126] Meta-aramid fibers include, for example, poly(m-phenylene isophthalamide) fibers (such as Teijin Corporation's "Conex (registered trademark)").

[0127] These aramid fibers can be used alone or in combination of two or more. Para-aramid fibers are preferred.

[0128] The fabric layer can be a single layer or multiple layers (e.g., two to five layers, preferably two to four layers), but from the point of view of productivity, a single layer (1 layer) or a double layer (2 layers) is preferred.

[0129] The fabric layer can be bonded as needed, for example, treated with RFL liquid (impregnation treatment, etc.), or the adhesive rubber can be rubbed into the fabric, or the adhesive rubber and the fabric can be stacked in a stacked form or embedded in the compression rubber layer.

[0130] The average thickness of the fabric layer is, for example, 0.1 to 1.5 mm, preferably 0.2 to 1 mm, and more preferably 0.3 to 0.7 mm. If the fabric layer is too thin, braking performance may not be adequately ensured due to early wear of the fabric; if it is too thick, flexibility may be reduced.

[0131] [Elongated rubber layer]

[0132] The low-edge toothed V-belt of the present invention may further contain an elongated rubber layer formed of a rubber composition (crosslinked rubber composition) containing a second rubber component.

[0133] The second rubber component may preferably be selected from the rubber components exemplified as the first rubber component. The second rubber component may be a different rubber component from the first rubber component, but is generally the same as the first rubber component.

[0134] From the viewpoint of further improving lateral pressure resistance and abrasion resistance, the rubber composition forming the elongated rubber layer preferably contains a second short fiber. When both the compression rubber layer and the elongated rubber layer contain the second short fiber as a short fiber, lateral pressure resistance and abrasion resistance are further improved. The second short fiber may be selected from the short fibers exemplified by the first short fiber, including a preferred embodiment. The second short fiber may be a different short fiber from the first short fiber, but is generally the same as the first short fiber. The proportion of the second short fiber may include a preferred proportion, selected from the proportion of the first short fiber.

[0135] The rubber composition forming the elongated rubber layer may further contain other components exemplified in the rubber composition forming the compression rubber layer.

[0136] The properties of the elongated rubber layer can be selected from the properties of the aforementioned compressed rubber layer (hardness, tensile strength, coefficient of friction, etc.) within a preferred range.

[0137] The average thickness of the elongated rubber layer is, for example, 2 to 10 mm, preferably 2.5 to 8 mm, and more preferably 3 to 7 mm. Furthermore, in this application, the thickness of the elongated rubber layer refers to the thickness at the top of the teeth.

[0138] [Core Layer]

[0139] The core layer only needs to contain a core, and it can be a core layer formed by the core alone. However, from the viewpoint of suppressing interlayer delamination and improving belt durability, it is preferable to form a core layer (adhesive rubber layer) formed by a cross-linked rubber composition in which a core is embedded. The adhesive rubber layer is located between the elongated rubber layer and the main body of the compression rubber layer, bonding the elongated rubber layer and the main body of the compression rubber layer together, while the core is embedded in the adhesive rubber layer.

[0140] (Adhesive rubber layer)

[0141] The low-edge toothed V-belt of the present invention may further contain an adhesive rubber layer formed from a cured product (crosslinked rubber composition) of a rubber composition containing a third rubber component.

[0142] The third rubber component may preferably be selected from the rubber components exemplified as the first rubber component. The third rubber component may be a different rubber component from the first rubber component, but is generally the same as the first rubber component.

[0143] The rubber composition forming the adhesive rubber layer may further contain short fibers and other components as exemplified by the rubber composition forming the compression rubber layer.

[0144] The adhesive rubber layer preferably has a lower rubber hardness than the compression rubber layer. The rubber hardness of the adhesive rubber layer is, for example, 60–85°, preferably 65–84°, more preferably 70–83°, and even more preferably 75–82°. If the rubber hardness is too low, the resistance to lateral pressure may be insufficient; if it is too high, the adhesion may decrease. By adjusting the adhesive rubber layer to such a low hardness, it can deform significantly under shear stress, thus suppressing delamination between the core and the compression and elongation rubber layers.

[0145] The average thickness of the adhesive rubber layer is, for example, 0.8 to 3 mm, preferably 1.2 to 2.8 mm, and more preferably 1.5 to 2 mm.

[0146] (Core)

[0147] The core is not particularly limited, and core threads (twisted cords) arranged at predetermined intervals along the width direction of the belt can generally be used. The core threads extend along the length direction of the belt, and multiple core threads parallel to the belt length direction can be arranged, but from a productivity point of view, they are generally arranged in a spiral configuration, parallel to the approximate belt length direction of the low-edge toothed V-belt, with predetermined intervals. In a spiral configuration, the angle 18 relative to the belt length direction of the core threads can be, for example, less than 5°; from a belt travel perspective, the closer to 0°, the better. Furthermore, the spacing between the core threads is preferably set to a range of 1.5 to 2.5 mm, more preferably a range of 1.8 to 2.2 mm. The spacing between the core threads is the distance between the centers of adjacent core threads.

[0148] The core wire only needs to have at least a portion in contact with the adhesive rubber layer. This can be any of the following configurations: the core wire embedded in the adhesive rubber layer, the core wire embedded between the adhesive rubber layer and the elongated rubber layer, or the core wire embedded between the adhesive rubber layer and the compression rubber layer. From the viewpoint of improving durability, the configuration of embedding the core wire in the adhesive rubber layer is preferred.

[0149] The fibers constituting the core wire can be exemplified by fibers constituting the first short fiber, etc. Among these fibers, from the viewpoint of high modulus, polyethylene terephthalate, polyethylene 2,6-naphthalate, etc., are commonly used. 2-4 Alkylene-C 6-12 Synthetic fibers such as polyester fibers (polyalkylene arylide fibers) and aramid fibers, and inorganic fibers such as carbon fibers, with aryl compounds as the main constituent unit, are preferred. Polyester fibers (polyethylene terephthalate fibers, polyethylene naphthalate fibers, etc.) and aramid fibers are also preferred. The fibers can be multifilament yarns. For example, multifilament yarns may contain 100 to 5000 monofilaments, preferably 500 to 4000, and more preferably approximately 1000 to 3000 monofilaments.

[0150] The core yarn can typically be a twisted cord made of multifilament yarn (e.g., double twist, single twist, Langevin twist, etc.). The average diameter of the core yarn (the diameter of the twisted cord) can be, for example, 0.5–3 mm, preferably 0.6–2 mm, and more preferably around 0.7–1.5 mm. The total fineness of the core yarn (twisted cord) can be, for example, 2000–17000 dtex, preferably 4000–15000 dtex, and more preferably 5000–13000 dtex (especially around 6000–8000 dtex).

[0151] To improve adhesion to the rubber component, the core wire can be bonded (or surface-treated) using the same method as the first short fiber. Preferably, the core wire is bonded using at least RFL liquid.

[0152] [Reinforced Fabric]

[0153] The low-edge toothed V-belt of the present invention may contain reinforcing fabric. Examples of the reinforcing fabric's form include, for instance, being laminated on the outer peripheral surface of the elongated rubber layer, or being embedded in the elongated rubber layer.

[0154] The reinforcing fabric can be formed from conventional fabrics. Examples of conventional fabrics include fabrics used as fabric layers. The reinforcing fabric can also be bonded as needed, for example, treated with RFL liquid (impregnation treatment, etc.), or subjected to friction treatment by rubbing adhesive rubber into the fabric, or the adhesive rubber and the fabric are laminated together or embedded in a compression rubber layer.

[0155] The average thickness of the reinforcing fabric is, for example, 0.1 to 1.5 mm, preferably 0.2 to 1 mm, and more preferably 0.3 to 0.7 mm.

[0156] [Manufacturing method of low-edge toothed V-belt]

[0157] The manufacturing method of the low-edge toothed V-belt of the present invention is not particularly limited. Regarding the lamination process of each layer (the manufacturing method of the sleeve), conventional methods can be used depending on the type of belt.

[0158] The following describes a representative manufacturing method for low-edge toothed V-belts. First, a laminate of a fabric precursor and a sheet of uncrosslinked rubber for compression is placed in contact with a flat belt tooth mold, with the fabric precursor facing down and alternating teeth and grooves corresponding to the inner circumferential teeth. Pressure is applied at a temperature of 60–120°C (particularly 80–100°C) to create a toothed pad (not fully crosslinked, in a semi-crosslinked state) with the inner circumferential teeth molded on it. Then, both ends of the toothed pad are vertically cut at appropriate positions (particularly the top of the tooth tip) to obtain the desired length.

[0159] Next, an inner mold with alternating teeth and grooves corresponding to the inner circumference teeth is covered on the outer periphery of the cylindrical metal mold, so that the tooth pad engages and winds with the teeth and grooves of the inner mold, and joins at both ends (especially the top of the tooth tip). After the first adhesive rubber layer sheet (lower adhesive rubber: uncrosslinked rubber sheet) is stacked on the outer periphery of the tooth pad, the core wire (twisted cord) forming the core body is spirally wound. The second adhesive rubber layer sheet (upper adhesive rubber: uncrosslinked rubber sheet) and the elongated rubber layer sheet (uncrosslinked rubber sheet) are then wound sequentially on its outer periphery to produce an uncrosslinked molded body.

[0160] Subsequently, with the uncrosslinked molded body covered by an outer jacket, it is placed in a known crosslinking apparatus (vulcanizing tank, etc.) and crosslinked molded at a temperature of 120–200°C (especially 150–180°C) to produce a crosslinked belt sleeve. Then, it is processed by V-shaped cutting using a cutting machine or the like to obtain an annular low-edge toothed V-belt.

[0161] In the case of a low-edge double-tooth V-belt, under the condition that the outer mold of the uncrosslinked molded body is covered with an outer mold in which the corresponding teeth and grooves of the outer peripheral teeth are alternately arranged, the outer jacket is crosslinked and molded to obtain a crosslinked belt sleeve with outer peripheral teeth also formed on the outer peripheral surface. The sleeve is then processed by V-shaped cutting to obtain a low-edge double-tooth V-belt.

[0162] In addition, the adhesive rubber layer can be formed from multiple adhesive rubber layer sheets, and the core wire (twisted cord) forming the core can be wound in relation to the stacking sequence of the multiple adhesive rubber layer sheets according to the embedding position of the adhesive rubber layer.

[0163] Example

[0164] The present invention will be described in more detail below based on embodiments, but the present invention is not limited to these embodiments. Furthermore, details of the materials used in the embodiments, the method for manufacturing the uncrosslinked rubber sheet, and the methods for measuring or evaluating various physical properties are shown below.

[0165] [Materials Used]

[0166] Chloroprene rubber: DENKA Corporation, "PM-40"

[0167] Magnesium oxide: Kyowa Chemical Industry Co., Ltd., "Kyowamag 30"

[0168] Stearic acid: "Stearic Acid" manufactured by Nippon Oil Co., Ltd.

[0169] Anti-aging agent: NONFLEX OD-3 manufactured by Seiko Chemical Co., Ltd.

[0170] Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd.

[0171] Silica: "ULTRASIL (registered trademark) VN3" manufactured by Evonik Japan Co., Ltd., with a BET specific surface area of ​​175 m² / g.

[0172] Plasticizer 1: Naphthenic oil, Idemitsu Kosan Co., Ltd.'s "NS-900"

[0173] Plasticizer 2: RS-700 manufactured by ADEKA Corporation

[0174] Crosslinking accelerator: Tetramethylthiuram disulfide (manufactured by Ouchi Shinsei Chemical Co., Ltd., "NoccelerTT")

[0175] Zinc oxide: "Three types of zinc oxide" manufactured by Zhengtong Chemical Industry Co., Ltd.

[0176] Sulfur: Sulfur produced by Meiyuan Chemical Co., Ltd.

[0177] N,N'-m-phenylene bismaleimide: Manufactured by Ouchi Shinsei Chemical Co., Ltd., under the brand name "Vulnoc PM".

[0178] Resorcinol-formaldehyde copolymer (resorcinol resin): a resorcinol-formaldehyde copolymer containing less than 20% by mass of resorcinol and less than 0.1% by mass of formalin.

[0179] Hexamethoxymethyl melamine: "POWERPLAST PP-1890S" manufactured by Singh Plasticisers & Resins Pvt. Ltd.

[0180] Aramid staple fiber: "Conex staple fiber" manufactured by Teijin Co., Ltd., with an average fiber length of 3mm, an average fiber diameter of 14μm, and a solid component adhesion rate of 6% by mass after being bonded with RFL solution (2.6 parts by mass of resorcinol, 1.4 parts by mass of 37% formalin, 17.2 parts by mass of vinylpyridine-styrene-butadiene copolymer latex (manufactured by Zeon Co., Ltd., Japan), and 78.8 parts by mass of water).

[0181] Core cord: A twisted cord with a total fineness of 6600 dtex, consisting of aramid fibers with a fineness of 1100 dtex twisted in a 2×3 twist pattern and an upper twist coefficient of 3.0 and a lower twist coefficient of 3.0, is treated with bonding (core cord diameter 1.28 mm).

[0182] Fabric (reinforcing fabric): Aramid canvas (thickness 0.30-0.50 mm) bonded with RFL liquid.

[0183] [Preparation of uncrosslinked rubber sheet for the rubber layer]

[0184] The rubber compositions used to form the compression rubber layer, elongation rubber layer, and adhesive rubber layer are prepared according to the proportions listed in Table 1 below. The rubber compositions forming each layer are respectively compounded using a Banbury mixer, and the resulting compounded rubber is passed through calendering rolls to produce calendered rubber sheets (uncrosslinked rubber sheets). In this specification, each rubber composition is designated as R1 to R7.

[0185] [Table 1]

[0186] Table 1

[0187] [Rubber hardness Hs of cross-linked rubber]

[0188] Each rubber layer was heated under pressure at 160°C for 30 minutes using an uncrosslinked rubber sheet to produce a crosslinked rubber sheet (100mm×100mm×2mm thickness). The stack of three crosslinked rubber sheets was used as a sample, and the hardness of the crosslinked rubber sheet was determined using a Type A hardness tester based on the spring-type hardness test specified in JIS K6253 (2012).

[0189] [Tensile strength of cross-linked rubber]

[0190] Cross-linked rubber sheets prepared for determining the rubber hardness Hs of cross-linked rubber were used as samples. Test pieces were prepared in a dumbbell shape (size 5) according to JIS K6251 (2017). In samples containing short fibers, dumbbell-shaped test pieces were collected with the fiber orientation direction as the stretching direction. The test pieces were then clamped at both ends and stretched at 500 mm / min until cut. The maximum tensile force recorded was divided by the initial cross-sectional area of ​​the test piece (tensile strength T) and taken as the tensile strength.

[0191] [Fabrication of low-edge double-tooth V-belt]

[0192] Using the method described in the foregoing embodiments, a low-edge double-tooth V-belt (dimensions: top width 38.5mm, thickness (H) 16.7mm, tooth height (inner circumferential side: H1) 6.8mm, tooth height (outer circumferential side: H4) 3.8mm, pitch height (H3+H4) 5.4mm, inner circumferential core thickness (H2) 4.5mm, belt outer circumference length 1158mm, V angle 26°) was manufactured.

[0193] [Analysis based on the three-dimensional finite element method (FEM)]

[0194] Based on the method described in the embodiment of Japanese Patent No. 7256249, a three-dimensional finite element model is created for the obtained low-edge double-tooth V-belt (both the belt in a tension-free state and the belt in a state with applied tension of 1000N) to confirm whether adjacent teeth interfere with each other when the belt bends (tooth interference). Furthermore, in the case where no tooth interference occurs, the maximum value of the Mises stress generated at the deepest part of the inner circumferential tooth root is calculated using the finite element model. On the other hand, in the case where tooth interference occurs, the following evaluation of the low-edge double-tooth V-belt is not performed.

[0195] [Evaluation of low-edge double-tooth V-belt]

[0196] (1) Durability test (Top durability test)

[0197] As a test used to confirm resistance to tooth root cracking (bending fatigue resistance), such as Figure 6 As shown, a two-axis running test machine with a drive (DR) pulley with a diameter (pitch diameter) of 178 mm and a driven (DN) pulley with a diameter (pitch diameter) of 140 mm was used. A low-edge double-tooth V-belt was wound around each pulley, the drive pulley speed was 6000 rpm, the axle load (dead weight) was 1.2 kN, and a load of 60 Nm was applied through a loading device (power generating device). The belt was run at an ambient temperature of 115°C, and the running time until the crack at the tooth root reached the core wire and the life was reached was measured as the running life.

[0198] (Judgment criteria for Top Durability Test)

[0199] a: Service life of 130 hours or more (qualified)

[0200] b: Service life of 110 hours or more but less than 130 hours (qualified)

[0201] c: Service life less than 110 hours (unqualified)

[0202] (2) Endurance driving test (Low endurance test)

[0203] As a test to confirm the core wire stripping resistance (lateral pressure resistance), such as Figure 7 As shown, a two-axis running test machine with a drive (DR) pulley with a diameter (pitch diameter) of 92 mm and a driven (DN) pulley with a diameter (pitch diameter) of 208 mm was used. A low-edge double-tooth V-belt was wound around each pulley, the drive pulley speed was 5000 rpm, the axle load (dead weight) was 2.2 kN, and a load of 50 Nm was applied through a loading device (power generating device). The belt was made to run at an ambient temperature of 60°C, and the running time until the core wire peeled off was measured as the running life.

[0204] (Judgment criteria for the Low Durability Test)

[0205] a: Walking lifespan of 30 hours or more (qualified)

[0206] b: Walking lifespan of 10 hours or more but less than 30 hours (qualified)

[0207] c: Walking life less than 10 hours (unqualified)

[0208] (3) Braking performance test (engine braking performance of the actual vehicle)

[0209] A low-edge double-tooth V-belt was installed on the CVT of a 1000cc four-wheel off-road vehicle for a real-vehicle test. While the vehicle was in motion, the throttle was released from the highest speed without applying the brakes, and the time it took for the driven pulley to rotate from 478 rpm to 0 rpm was measured.

[0210] (Judgment criteria for braking performance test)

[0211] a: The time to reach 0 rpm is less than 7 seconds (acceptable)

[0212] b: The time to reach 0 rpm is more than 7 seconds but less than 8 seconds (pass).

[0213] c: The time to reach 0 rpm exceeds 8 seconds (unacceptable)

[0214] (4) Braking continuity test (engine braking continuity of the actual vehicle)

[0215] After 500 miles of driving in harsh road conditions (off-road) on the vehicle that underwent the aforementioned braking performance test, the braking performance was confirmed using the methods described in the braking performance test. Braking continuity was determined based on the following criteria, considering whether the braking performance after 500 miles maintained a high level or declined compared to the initial braking performance (before 500 miles). Furthermore, if the vehicle failed the aforementioned braking performance test (judgment c), the braking continuity test was not conducted.

[0216] (Judgment criteria for continuous braking test)

[0217] a: Braking performance before and after 500 miles of driving is at a high level (maintain judgment a).

[0218] b: Braking performance after 500 miles of driving is judged as b (from a to b, or remaining at b).

[0219] c: Braking performance after 500 miles of driving is rated as c (degradation from a or b to c).

[0220] (5) Comprehensive judgment

[0221] Based on the results of endurance tests (Top endurance test, Low endurance test), braking performance tests, and braking continuity tests, and considering the need to ensure the required levels of bending fatigue resistance (resistance to tooth root cracking) and lateral pressure resistance (resistance to core wire stripping) of the transmission belt while maintaining braking performance, the overall quality (graded) is determined according to the criteria shown in Table 2. Then, from the perspective of product usability, grades A, B, and C are set as acceptable, and grade D as unacceptable. Furthermore, if tooth interference is confirmed during FEM analysis, the overall assessment at that point is graded as D (unacceptable).

[0222] [Table 2]

[0223] Table 2

[0224] <Belts with a tooth pitch of 11.8 mm (Comparative Examples 1-5 and Examples 1-8)>

[0225] [Comparative Example 1]

[0226] In a band with an inner tooth pitch of 11.8 mm and a radius of curvature of 2.3 mm for the arc forming the bottom of the inner tooth root, a band is made with the tooth tip formed by a curve (an arc with a radius of curvature of 2.8 mm) and without a flat top.

[0227] [Comparative Example 2]

[0228] Compared to the belt of Comparative Example 1, a belt with a flat top of 1.1 mm circumferential length was made on the inner circumferential tooth tip, and the inner circumferential flatness was adjusted to 9%. As the bottom arc forming the tooth root, two consecutive arcs based on the imaginary arc R0 = 2.5 mm were formed (the deepest first arc R1 = 3.9 mm, and a pair of second arcs R2 = 1.0 mm).

[0229] [Comparative Example 3]

[0230] Compared to Comparative Example 2, a belt was fabricated by reducing the radius of curvature of the tooth tip R-face chamfer to R3=2.1mm, increasing the circumferential length of the flat top to 1.8mm, and adjusting the inner circumferential flatness to 15%.

[0231] [Example 1]

[0232] Compared to Comparative Example 2, a belt was fabricated by reducing the radius of curvature of the tooth tip R-face chamfer to R3=1.8mm, adjusting the circumferential length of the flat top to 2.4mm, and adjusting the inner circumferential flatness to 20%.

[0233] [Example 2]

[0234] Compared to Comparative Example 2, a strip was fabricated with the circumferential length of the flat top increased to 4.5 mm and the inner circumferential flatness increased to 38%.

[0235] [Example 3]

[0236] In Example 2, where the inner circumferential flatness is adjusted to 38%, an arc is made as the bottom of the tooth root, and the radius of curvature of the first arc, which is the deepest part of two consecutive arcs with a radius of curvature R0 = 2.5 mm based on the imaginary arc, is changed to a strip with a radius of curvature R1 = 3.0 mm.

[0237] [Example 4]

[0238] In Example 2, where the inner circumferential flatness is adjusted to 38%, an arc is made as the bottom of the tooth root, and the curvature radius of the first arc of the deepest part of two consecutive arcs with a curvature radius R0 = 2.5 mm based on the imaginary arc is changed to a strip with a curvature radius R1 = 4.0 mm.

[0239] [Example 5]

[0240] In Example 2, where the inner circumferential flatness is adjusted to 38%, an arc is made as the bottom of the tooth root, and the radius of curvature of the first arc, which is the deepest part of two consecutive arcs based on the imaginary arc curvature radius R0 = 2.5 mm, is changed to a band with a curvature radius of R1 = 4.5 mm.

[0241] [Example 6]

[0242] Compared to Example 2, the radius of curvature of the imaginary arc on which the bottom two consecutive arcs forming the tooth root (the radius of curvature of the deepest first arc R1=3.9mm and the radius of curvature of the pair of second arcs R2=1.0mm) are based is reduced to R0=1.1mm, the tooth angle is changed to θ=20°, and the inner circumferential flatness is adjusted to 38%.

[0243] [Example 7]

[0244] Compared to Example 2, a belt was fabricated with the radius of curvature of the imaginary arc reduced to R0=0.5mm, the radius of curvature of the second arc changed to R2=0.5mm, the tooth angle changed to θ=24°, and the inner circumference flatness adjusted to 38%.

[0245] [Example 8]

[0246] Compared to Example 2, a strip is fabricated by reducing the radius of curvature of the imaginary arc to R0=1.5mm, reducing the tooth angle to θ=4°, thereby adjusting the circumferential length of the flat top to 7.1mm and increasing the inner circumferential flatness to 60%.

[0247] [Comparative Example 4]

[0248] Compared to Example 2, a strip is fabricated by reducing the radius of curvature of the imaginary arc to R0=1.4mm, reducing the tooth angle to θ=1°, thereby adjusting the circumferential length of the flat top to 7.9mm and increasing the inner circumferential flatness to 67%.

[0249] [Comparative Example 5]

[0250] The belt is made in the same manner as in Example 2, except that a fabric layer covering the inner circumferential surface of the belt is not provided.

[0251] The evaluation results of the strips obtained in Comparative Examples 1-5 and Examples 1-8 are shown in Table 3. Furthermore, the approximate cross-sectional shapes of the strips obtained in the Comparative Examples and Examples are shown in... Figure 8 .

[0252] [Table 3]

[0253] Table 3

[0254] In Comparative Example 1, the stress generated at the tooth root is small, and the durability (resistance to tooth root cracks) is rated as a. However, since there is no flat section, the engine braking performance is rated as c. The overall rating is D.

[0255] Compared with Comparative Example 1, the belts of Comparative Examples 2 and 3 have less stress generated at the tooth root and their durability (resistance to tooth root cracking) is rated as a. However, since the inner circumference flatness is relatively small at 9% (Comparative Example 2) and 15% (Comparative Example 3), their engine braking performance is rated as c. The overall rating is D.

[0256] The belt of Example 1 is at the same level as Comparative Examples 2 and 3. The stress generated at the tooth root is small, and the durability (resistance to tooth root cracks) is rated as a. However, due to the increase in the inner circumference flatness to 20%, the engine braking performance is improved to rated as b. The engine braking continuity is also good (rated as b). The overall rating is improved to B.

[0257] Furthermore, in the belt of Example 2, the stress generated at the tooth root is small, the durability (resistance to tooth root cracks) is rated as A, and the inner circumferential flatness is increased to 38%. Therefore, the engine braking performance is improved to rated A, the engine braking continuity is also good (rated A), and the overall rating is improved to A level.

[0258] In Example 2, where the inner circumferential flatness was increased to 38%, the radius of curvature R1 of the first arc, which is the deepest part of two consecutive arcs based on the imaginary arc R0=2.5mm, was changed as the bottom arc forming the tooth root. In Examples 3 (R1=3.0mm), 4 (R1=4.0mm), and 5 (R1=4.5mm), the same results as in Example 2 were also obtained.

[0259] Compared to Example 2, which increases the inner circumferential flatness to 38%, Example 6, which reduces the radius of curvature of the imaginary arc on which the two consecutive arcs forming the bottom of the tooth root are based to R0=1.1mm (and changes the tooth angle to θ=20° to adjust the inner circumferential flatness to 38%), achieves engine braking performance rating a, but the stress generated at the tooth root increases, and the durability (resistance to tooth root cracking) decreases to rating b, thus the overall rating is B. Furthermore, in Example 7, which reduces the radius of curvature of the imaginary arc to R0=0.5mm (and changes the tooth angle to θ=24° to adjust the inner circumferential flatness to 38%), engine braking performance also achieves rating a, but the stress generated at the tooth root increases, and the durability (resistance to tooth root cracking) decreases to rating c, thus the overall rating is C.

[0260] On the other hand, in Example 8, where the inner circumferential flatness was increased to 60% by reducing the radius of curvature R0 of the imaginary arc and the tooth angle θ (R0=1.5mm, θ=4°), the stress generated at the tooth root was small, and the durability (resistance to tooth root cracking) and engine braking performance were both rated as A, resulting in an overall rating of A. However, in Comparative Example 4, where the inner circumferential flatness was increased to 67% by further reducing the radius of curvature R0 of the imaginary arc and the tooth angle θ (R0=1.4mm, θ=1°), interference between adjacent teeth when bent was confirmed in the FEM analysis, thus resulting in a rating of D (unacceptable). Figure 9 The image shows an FEM diagram illustrating the interference between the inner circumferential teeth of the low-edge double-tooth V-belt obtained in Comparative Example 4. Figure 9 It can be seen that in Comparative Example 4, the inner circumferential teeth on the upper side of the belt are deformed due to bending, and the adjacent inner circumferential teeth come into contact with each other.

[0261] The results above show that, from the perspective of product practicality, the belts of Examples 1-8, with an inner circumferential flatness of 20-60%, are qualified grades A, B, and C, respectively. It can be said that setting the inner circumferential flatness in this range is suitable for balancing the "performance of braking function" and "durability (resistance to tooth root cracking)" which are opposite in nature.

[0262] Furthermore, compared to the belt of Example 2, which had an inner circumferential flatness of 38% and an overall rating of A, the belt of Comparative Example 5, which did not have a fabric layer covering the inner circumferential surface of the belt, had a braking performance rating of A in the initial stage of driving (before 500 miles of driving), but decreased to a rating of C after driving, thus the engine braking continuity was rated C. In addition, durability (resistance to tooth root cracking) also decreased to a rating of C. As a result, the overall rating was D. From this result, it can be seen that the fabric layer covering the inner circumferential surface of the belt is effective in terms of engine braking continuity and durability (resistance to tooth root cracking).

[0263] <Belts with a tooth pitch of 9.44 mm (Comparative Examples 6-7 and Examples 9-21)>

[0264] [Comparative Example 6]

[0265] A strip with an inner circumferential tooth pitch of 9.44 mm is fabricated, and a flat top with a circumferential length of 1.4 mm is set at the inner circumferential tooth tip (the radius of curvature of the tooth tip R-surface chamfer R3 = 2.4 mm). The inner circumferential flatness is adjusted to 15%. As the bottom arc forming the tooth root, two consecutive arcs with a radius of curvature R0 = 1.1 mm based on the imaginary arc are formed (the radius of curvature of the deepest first arc is R1 = 2.5 mm, and the radius of curvature of the pair of second arcs is R2 = 0.3 mm).

[0266] [Example 9]

[0267] Compared to Comparative Example 6, a belt was fabricated by reducing the radius of curvature of the tooth tip R-face chamfer to R3=2.0mm, adjusting the circumferential length of the flat top to 1.9mm, and adjusting the inner circumferential flatness to 20%.

[0268] [Example 10]

[0269] Compared to Comparative Example 6, a belt was fabricated by reducing the radius of curvature of the tooth tip R-face chamfer to R3=0.5mm, adjusting the circumferential length of the flat top to 4.6mm, and adjusting the inner circumferential flatness to 48%.

[0270] [Example 11]

[0271] In Example 10, where the inner circumferential flatness is adjusted to 48%, an arc is made as the bottom of the tooth root, and the radius of curvature of the first arc at the deepest part of two consecutive arcs is changed to a strip with R1=1.5mm.

[0272] [Example 12]

[0273] In Example 10, where the inner circumferential flatness is adjusted to 48%, a strip is fabricated in which the radius of curvature of the first arc is changed to R1 = 2.0 mm (and the radius of curvature of the second arc is R2 = 0.75 mm).

[0274] [Example 13]

[0275] In Example 10, where the inner circumferential flatness is adjusted to 48%, a strip is fabricated with the radius of curvature of the first arc changed to R1 = 2.75 mm.

[0276] [Example 14]

[0277] In Example 10, where the inner circumferential flatness is adjusted to 48%, a strip is fabricated with the radius of curvature of the first arc changed to R1=3.0mm (the radius of curvature of the second arc R2=0.25mm).

[0278] [Example 15]

[0279] In Example 10, where the inner circumferential flatness is adjusted to 48%, a strip is fabricated with the radius of curvature of the first arc changed to R1 = 3.9 mm.

[0280] [Example 16]

[0281] In Example 10, where the inner circumferential flatness is adjusted to 48%, a strip is fabricated with the radius of curvature of the first arc changed to R1 = 4.5 mm.

[0282] [Example 17]

[0283] Compared to Example 10, the radius of curvature of the imaginary arc on which the two consecutive arcs forming the bottom of the tooth root are based is increased to R0=1.5mm, and the radius of curvature of the first arc is changed to R1=3.9mm and the radius of curvature of the second arc is changed to R2=1.0mm, and the inner circumferential flatness is adjusted to 41%.

[0284] [Example 18]

[0285] Compared to Example 17, the fabrication process involves increasing the radius of curvature of the imaginary arc on which the two consecutive arcs forming the bottom of the tooth base are based to R0=1.8mm, reducing the tooth angle to θ=1°, and adjusting the inner circumferential flatness to 41%.

[0286] [Example 19]

[0287] Compared to Example 17, the fabrication process involves reducing the radius of curvature of the imaginary arc on which the two consecutive arcs forming the bottom of the tooth base are based to R0=0.5mm, increasing the tooth angle to θ=17°, and adjusting the inner circumferential flatness to 41%.

[0288] [Example 20]

[0289] Compared to Example 17, the fabrication process involves increasing the radius of curvature of the imaginary arc on which the two consecutive arcs forming the bottom of the tooth base are based to R0=1.9mm, reducing the tooth angle to θ=0°, and adjusting the inner circumferential flatness to 49%.

[0290] [Example 21]

[0291] Compared to Example 10, a strip is made by reducing the radius of curvature of the imaginary arc to R0=0.5mm, reducing the radius of curvature of the first arc to R1=1.5mm, and reducing the radius of curvature of the second arc to R2=0.25mm, thereby adjusting the circumferential length of the flat top to 5.6mm and increasing the inner circumferential flatness to 59%.

[0292] [Comparative Example 7]

[0293] Compared to Example 21, a belt is fabricated by reducing the tooth angle to θ=6°, thereby adjusting the circumferential length of the flat top to 6.3 mm and increasing the inner circumferential flatness to 67%.

[0294] The evaluation results of the strips obtained in Comparative Examples 6-7 and Examples 9-21 are shown in Table 4. Furthermore, the approximate cross-sectional shapes of the strips obtained in Comparative Examples 6-7 and Examples 9-21 are shown in... Figure 10 .

[0295] [Table 4]

[0296] Table 4

[0297] In Comparative Example 6, the stress generated at the tooth root is small, and the durability (resistance to tooth root cracks) is rated as a. However, since the inner circumference flatness is relatively small at 15%, the engine braking performance is rated as c. The overall rating is D.

[0298] The belt of Example 9 is at the same level as that of Comparative Example 6. The stress generated at the tooth root is small, and the durability (resistance to tooth root cracking) is rated as a. However, since the inner circumferential flatness is increased to 20%, the engine braking performance is improved to rated as b. The engine braking continuity is also good (rated as b). The overall rating is improved to B.

[0299] Furthermore, in the belt of Example 10, the stress generated at the tooth root is small, the durability (resistance to tooth root cracks) is rated as A, and the inner circumferential flatness is increased to 48%. Therefore, the engine braking performance is improved to rated A, the engine braking continuity is also good (rated A), and the overall rating is improved to A level.

[0300] In Example 10, where the inner circumferential flatness is increased to 48%, the radius of curvature R1 of the first arc, the deepest part of two consecutive arcs based on an imaginary arc R0 = 1.1 mm, is changed in Examples 12 (R1 = 2.0 mm), 13 (R1 = 2.75 mm), 14 (R1 = 3.0 mm), 15 (R1 = 3.9 mm), and 16 (R1 = 4.5 mm), which form the bottom arc of the tooth root. In these examples, durability (resistance to tooth root cracking), engine braking performance, and engine braking continuity are all good (judged as a or b), and are comprehensively rated as A or B. In Example 11 (R1 = 1.5 mm), where R1 is set to the minimum, durability (resistance to tooth root cracking) decreases (judged as c), but is still rated as a satisfactory level (C).

[0301] In Example 10, where the inner circumferential flatness was increased to 48%, the radius of curvature of the imaginary arc was increased to R0 = 1.5 mm, and the radius of curvature of the first arc was changed to R1 = 3.9 mm and the radius of curvature of the second arc was changed to R2 = 1.0 mm. In Example 17, where the inner circumferential flatness was adjusted to 41%, the same good results as in Example 10 were also obtained. Furthermore, in Example 18, where the radius of curvature of the imaginary arc was increased to R0 = 1.8 mm (and the tooth angle was reduced to θ = 1° to adjust the inner circumferential flatness to 41%), the same good results as in Example 17 were also obtained compared to Example 17. Furthermore, in Example 19, which reduces the radius of curvature of the imaginary arc to R0=0.5mm (and increases the tooth angle to θ=17° to adjust the inner circumferential flatness to 41%) compared to Example 17, the stress generated at the tooth root increases, but the durability (resistance to tooth root cracking) is judged as b, and the overall judgment is B grade.

[0302] Furthermore, in Example 20, which increased the radius of curvature of the imaginary arc to R0=1.9mm (and reduced the tooth angle to θ=0° to adjust the inner circumferential flatness to 49%) compared to Example 17, the same good results as in Example 17 were also obtained.

[0303] On the other hand, compared to Examples 10 and 17, in Example 21, where the inner circumferential flatness was increased to 59% by reducing the radius of curvature of the imaginary arc and the first arc (R0=0.5mm, R1=1.5mm), the stress generated at the tooth root was large, and the durability (resistance to tooth root cracking) was judged as C, but the overall judgment was a qualified level C grade. However, in Comparative Example 7, where the inner circumferential flatness was increased to 67% by further reducing the tooth angle (θ=6°), interference between adjacent teeth when bent was confirmed in FEM analysis (tooth interference), therefore it was a level D (unqualified).

[0304] The results above show that, from the perspective of product practicality, the belts of Examples 9-21 with an inner circumferential flatness of 20-59% are qualified grades A, B, and C, respectively. It can be said that setting the inner circumferential flatness in this range is suitable for balancing the opposite relationships of "braking function" and "durability (resistance to tooth root cracking)".

[0305] As can be seen from the above, the following low-edge toothed V-belt has been confirmed to be suitable for the braking system of a continuously variable transmission with clutch engagement, and its durability, such as wear resistance, can also be improved: at least on the inner circumferential side, there are teeth with alternating tooth tops and tooth bottoms arranged in the belt length direction, the teeth are formed by a compressed rubber layer and a fabric layer covering the inner circumferential surface of the compressed rubber layer, the top of the tooth top is formed to be flat, and the length of each top in the belt length direction is adjusted to 20-60% relative to the tooth pitch.

[0306] Industrial availability

[0307] The low-edge toothed V-belt of the present invention is suitable as a transmission V-belt for transmission mechanisms requiring high friction on the inner circumferential surface. In particular, it can be used as a gear belt in clutch-connected CVTs such as snowmobiles (small snowmobiles) or ATVs, and is suitable as a gear belt in clutch-connected CVTs where the inner circumferential surface of the belt contacts the pulley shaft at idle speed. It can also be used as a gear belt involved in all aspects of continuously variable transmission, clutch engagement, and braking in clutch-connected CVTs.

[0308] While the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications and alterations can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2024-046651, filed March 22, 2024, and Japanese Patent Application No. 2025-038669, filed March 11, 2025, the contents of which are incorporated herein by reference.

[0309] Explanation of reference numerals in the attached figures

[0310] 1…Low-edge toothed V-belt

[0311] 1a…Inner circumferential tooth tip

[0312] 1b…Inner circumferential tooth base

[0313] 1c…external tooth tip

[0314] 1d… peripheral tooth root

[0315] 2…Elongated rubber layer

[0316] 3…Core layer (adhesive rubber layer)

[0317] 3a…Core (core wire)

[0318] 4…Compression rubber layer

[0319] 5…fabric layer

Claims

1. A low-edge toothed V-belt, having at least on its inner circumferential side teeth arranged with alternating tooth tips and tooth roots along the belt length direction, wherein, The teeth on the inner circumferential side are formed of a compressed rubber layer and a fabric layer, the fabric layer covering the inner circumferential surface of the compressed rubber layer. The top of the tooth tip on the inner circumferential side is flat, and, The length of each top band in the longitudinal direction is 18-65% of the tooth pitch.

2. The low-edge toothed V-belt according to claim 1, wherein, The tooth pitch is 6–17 mm.

3. The low-edge toothed V-belt according to claim 1 or 2, wherein, The fabric layer contains aramid fibers.

4. The low-edge toothed V-belt according to any one of claims 1 to 3, wherein, The cross-sectional shape of the tooth root on the inner circumference side along the length direction is a shape having a bottom and a sidewall portion. The bottom is formed by an arc with a radius of curvature of 2 to 4 mm, and the sidewall portion is inclined relative to the thickness direction of the belt or extends from the bottom along the thickness direction of the belt.

5. The low-edge toothed V-belt according to any one of claims 1 to 4, wherein, The cross-sectional shape of the tooth root on the inner circumferential side along the length direction is a shape having a bottom and a sidewall portion. The bottom is formed by combining multiple consecutive arcs, and the sidewall portion is inclined relative to the thickness direction of the belt or extends from the bottom along the thickness direction of the belt. The radius of curvature of the plurality of arcs decreases as they move away from the deepest part of the tooth root. The radius of curvature of the first arc passing through the deepest part of the plurality of arcs is larger than the radius of the imaginary circle tangent to the deepest part and the sidewalls on both sides, and is 2 to 4 mm.

6. A belt drive mechanism comprising a low-edge toothed V-belt and a pulley as described in any one of claims 1 to 5, wherein, The low-edge toothed V-belt is a transmission belt used in continuously variable transmissions with clutch engagement.

7. The belt drive mechanism according to claim 6, wherein, The continuously variable transmission with clutch engagement is a continuously variable transmission in which the inner circumferential surface of the belt contacts the pulley shaft at idle speed.

8. The belt drive mechanism according to claim 6 or 7, wherein, The continuously variable transmission with clutch engagement is a continuously variable transmission equipped with a braking system, which utilizes the friction between the inner circumferential surface of the belt and the pulley shaft.

9. A method of using a low-edge toothed V-belt, wherein the low-edge toothed V-belt is a low-edge toothed V-belt according to any one of claims 1 to 5, wherein... In a continuously variable transmission (CVT) with clutch engagement, the low-edge toothed V-belt is involved in all aspects of continuously variable transmission, clutch engagement, and braking.

Images