Heavy-duty tires

Abstract

The present invention aims to provide a heavy-duty tire that enhances the cooling effect of the belt through grooves in the width direction. [Solution] The heavy-duty tire of the present invention is provided with a plurality of widthwise grooves extending in the tire width direction on the tread surface, and cooling promotion sections are provided in the widthwise grooves.

Description

Technical Field

[0001] The present invention relates to a heavy-duty tire.

Background Art

[0002] Conventionally, in heavy-duty tires, particularly tires for construction and mining vehicles, when the tire rotates, the tread surface deforms and the belt also deforms, causing heat to accumulate in the belt. Therefore, the belt tends to have the highest temperature and become a heat source. The heat generation of the belt has been the cause of tire failure.

[0003] In response to this, widthwise grooves are provided on the tread surface, and the belt is cooled by the air flowing through the groove bottom of the widthwise grooves near the belt. For example, in Patent Documents 1 and 2, it has been proposed to increase the amount of air introduced into the widthwise grooves by providing slopes in the widthwise grooves, thereby enhancing the cooling effect of the belt at the groove bottom.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technologies of Patent Documents 1 and 2, the cooling effect of the belt was not sufficient.

[0006] Therefore, an object of the present invention is to provide a heavy-duty tire with enhanced cooling effect of the belt by widthwise grooves.

Means for Solving the Problems

[0007] The gist configuration of the present invention is as follows. (1) A heavy-duty tire having multiple widthwise grooves extending in the tire width direction on the tread surface, An air guide groove is provided in the widthwise groove, communicating with the widthwise groove. A heavy-duty tire characterized in that a cooling promotion section is provided in the widthwise groove.

[0008] Here, "tread surface" refers to the entire circumferential surface of the outer tread of a heavy-duty tire that comes into contact with the road surface when the tire is mounted on an applicable rim, filled to the specified internal pressure, and subjected to the maximum load. Unless otherwise specified, the dimensions and shape of each element refer to those of a heavy-duty tire mounted on an applicable rim, filled to the specified internal pressure, and under no load.

[0009] In this specification, "applicable rim" refers to the standard rim for the applicable size (Measuring Rim in the ETRTO STANDARDS MANUAL, Design Rim in the TRA YEAR BOOK) which is an industrial standard valid in the region where the tire is produced and used, and which is listed or will be listed in the future in the STANDARDS MANUAL of the ETRTO (The European Tyre and Rim Technical Organisation) in Japan, the STANDARDS MANUAL of the ETRTO (The European Tyre and Rim Technical Organisation) in Europe, and the YEAR BOOK of the TRA (The Tire and Rim Association, Inc.) in the United States, etc. (That is, the "rim" in "wheel" above includes not only current sizes but also sizes that may be included in the above industrial standards in the future. An example of "sizes to be listed in the future" is the size listed as "FUTURE DEVELOPMENTS" in the ETRTO 2013 edition.) However, in the case of a size not listed in the above industrial standards, it refers to a rim with a width corresponding to the tire bead width. Furthermore, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel in the applicable size and ply rating as described in JATMA, etc., and in the case of sizes not listed in the above industrial standards, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle on which the tire is mounted. Furthermore, "maximum load capacity" refers to the load corresponding to the maximum load capacity mentioned above.

[0010] (2) The heavy-duty tire according to (1), wherein the cooling promotion portion is a paddle groove portion in cross-sectional view, consisting of a straight portion, a slanted portion connected to the straight portion, and an arc-shaped bottom portion connected to the slanted portion.

[0011] (3) The heavy-duty tire according to (2), wherein the ratio of the total depth of the paddle groove portion to the depth at the boundary between the straight portion and the slanted portion of the paddle groove portion is 1.5 or more and 2.5 or less.

[0012] (4) The heavy-duty tire according to (2) or (3), wherein, when the heavy-duty tire is mounted on an applicable rim, filled to the specified internal pressure, and unloaded, the slanted portion is inclined at an angle of 2° to 30° with respect to the tire diameter.

[0013] (5) The widthwise groove is provided with an air introduction groove that communicates with the widthwise groove, The air guide groove is a heavy-duty tire according to any one of (1) to (4) above, and is opposite to the air introduction groove.

[0014] (6) The heavy-duty tire according to (5), wherein a notch is provided at the corner of the end of the air intake groove opposite to the widthwise groove.

[0015] (7) The heavy-duty tire according to (5) or (6), wherein the length of the air intake groove at the center in the width direction is longer than the length of the air intake groove at the end in the width direction.

[0016] (8) The air introduction groove is trapezoidal in plan view as seen from the tread surface, and is the heavy-duty tire according to any one of (5) to (7) above.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a heavy-duty tire with enhanced cooling effect of the belt by the width-direction grooves.

Brief Description of the Drawings

[0018] [Figure 1] It is a cross-sectional view of the tire width direction of the heavy-duty tire according to an embodiment of the present invention. [Figure 2] It is a developed view showing the tread surface of the heavy-duty tire according to an embodiment of the present invention. [Figure 3] It is a partial perspective view showing an example of the slope and the air guide groove. [Figure 4] It is a plan view showing an example of the slope. [Figure 5] It is a plan view schematically showing the state of the slope of FIG. 4 under load. [Figure 6] It is a plan view showing another example of the slope. [Figure 7] It is a cross-sectional view for explaining the shape of the paddle groove portion. [Figure 8] It is a diagram schematically showing the flow of air in the prior art. [Figure 9] It is a diagram for explaining the action and effect of the heavy-duty tire of the present embodiment. [Figure 10] It is a diagram for explaining the action and effect of the heavy-duty tire of the present embodiment. [Figure 11] It is a diagram for explaining the action and effect of the heavy-duty tire of the present embodiment. [Figure 12] It is a partial perspective view showing the slope, the air guide groove, and the paddle groove portion. [Figure 13] It is a partial cross-sectional view showing the air guide groove and the paddle groove portion. [Figure 14]This is a cross-sectional view showing a first modified example of the cooling promotion section. [Figure 15] This is a cross-sectional view showing a second modified example of the cooling promotion section. [Modes for carrying out the invention]

[0019] Embodiments of the present invention will be described in detail below with reference to the drawings. The heavy-duty tire of this embodiment (hereinafter also simply referred to as "tire") is a tire for construction and mining vehicles. This tire has, for example, a cross-sectional width of 450 to 1550 mm and an outer diameter of 1750 to 4100 mm. In this specification, the notation "X to Y" (where X and Y are numerical values) means between X and Y.

[0020] Figure 1 is a cross-sectional view in the tire width direction of a heavy-duty tire according to one embodiment of the present invention. As shown in Figure 1, the tire 10 of this embodiment includes, as an example, a pair of bead portions 20, a pair of sidewall portions 30 connected to the bead portions 20, and a tread portion 40 connected between the pair of sidewall portions 30. In the illustrated example, a bead core 20a is embedded in the bead portion 20. Although not shown, a bead filler may be arranged on the radially outer side of the bead core 20a. Furthermore, as shown in the figure, this tire 10 further includes a carcass 50 that toroidally spans between the pair of bead portions 20. The number of carcass plies is not particularly limited, but can be one. Also, a belt 60 made of belt layers is arranged on the radially outer side of the carcass 50. In the illustrated example, there are four belt layers, but it is preferable to have four to six layers. The width of each belt layer in the tire width direction is not limited to the illustrated example, and can have various size relationships.

[0021] Figure 2 is an exploded view showing the tread surface 1 of a heavy-duty tire according to one embodiment of the present invention. As shown in Figure 2, the tire 10 has one or more (three in the illustrated example) circumferential grooves 2 on the tread surface 1. In the illustrated example, one circumferential groove 2b extends along the tire equatorial plane CL, one circumferential groove 2a is located in one half of the tire width direction with the tire equatorial plane CL as the boundary, and one circumferential groove 2c is located in the other half of the tire width direction with the tire equatorial plane CL as the boundary. In this disclosure, the tire 10 does not have to have circumferential grooves 2, and even if it does have circumferential grooves 2, the number of circumferential grooves 2 and the position in which the circumferential grooves 2 extend are not particularly limited. By arranging such circumferential grooves 2, the heat dissipation of the tread can be further improved.

[0022] The groove width (opening width) of the circumferential groove 2 is not particularly limited, but can be, for example, 3 to 10 mm. The groove depth (maximum depth) of the circumferential groove 2 is also not particularly limited, but can be, for example, 20 to 120 mm. In the illustrated example, the circumferential groove 2 extends without inclination with respect to the tire circumferential direction, but it may also extend with an inclination angle of 5° or less with respect to the tire circumferential direction. In the illustrated example, the circumferential groove 2 extends straight in the tire circumferential direction, but it may also extend in a zigzag or curved manner.

[0023] As shown in the illustration, in this tire 10, multiple (four in the illustrated example) land areas 3 are partitioned by the tread edge and the circumferential groove 2. In the illustrated example, the outermost land area 3a (3d) in the width direction is partitioned by the tread edge and the circumferential groove 2a (2c). In addition, a central land area 3b is partitioned between the circumferential grooves 2a and 2b, and a central land area 3c is partitioned between the circumferential grooves 2b and 2c.

[0024] The tire 10 of this embodiment has multiple widthwise grooves 4 extending in the tire width direction on the tread surface 1. In the illustrated example, the tire 10 has widthwise grooves 4 in the central land areas 3b and 3c, but it is sufficient if the widthwise grooves 4 are formed in any of the land areas 3. In the illustrated area, four widthwise grooves 4 are formed in each of the central land areas 3b and 3c, but the number of widthwise grooves 4 is not particularly limited as long as there are multiple grooves.

[0025] The groove width (opening width) of the lateral groove 4 is not particularly limited, but can be, for example, 3 to 10 mm. The groove depth (maximum depth) of the lateral groove 4 is not particularly limited, but can be, for example, 20 to 120 mm. In the illustrated example, all of the lateral grooves 4 are in communication with the circumferential grooves 2b that extend in the circumferential direction of the tire, but they do not have to be in communication with the circumferential grooves 2. In the illustrated example, lateral grooves 4 that are in communication with the circumferential grooves 2 at both ends and lateral grooves 4 that are in communication with the circumferential grooves 2b at one end and terminate at the other end within the land portion 3b (3c) are arranged alternately in the circumferential direction of the tire.

[0026] In the illustrated example, the widthwise groove 4, which has both ends communicating with the circumferential groove 2, consists of an inclined portion that extends inclined with respect to the tire width direction and two non-inclined portions that communicate with both ends of the inclined portion and extend substantially in the tire width direction, with the non-inclined portions communicating with the circumferential groove 2. Also, the widthwise groove 4, which has only one end communicating with the circumferential groove 2, consists of an inclined portion that extends inclined with respect to the tire width direction and one non-inclined portion that communicates with one end of the inclined portion and extends substantially in the tire width direction, with the non-inclined portion communicating with the circumferential groove 2. On the other hand, in this disclosure, the widthwise groove 4 can have various shapes, and for example, it can have a shape consisting only of an inclined portion (consisting only of a portion that extends straight inclined with respect to the tire width direction). The inclination angle of the inclined portion with respect to the tire width direction is not particularly limited, but for example it can be greater than 0° and 60° or less.

[0027] In the illustrated example, the widthwise groove 4 located at the central land portion 3b and the widthwise groove 4 located at the central land portion 3c are arranged such that their communication points with the tire equatorial plane CL alternate in the circumferential direction of the tire. On the other hand, for example, the widthwise groove 4 located at the central land portion 3b and the widthwise groove 4 located at the central land portion 3c may be communicating at the tire equatorial plane CL. Furthermore, in the illustrated example, the widthwise groove 4 located at the central land area 3b and the widthwise groove 4 located at the central land area 3c extend in the same direction (from the lower left to the upper right in the illustration). On the other hand, the widthwise groove 4 located at land area 3b and the widthwise groove 4 located at land area 3c may extend in opposite directions.

[0028] In the illustrated example, multiple lug grooves 7 are arranged in the outermost land portions 3a and 3d in the width direction. The number of lug grooves 7 is not particularly limited. The groove width (opening width) of the lug grooves 7 is not particularly limited, but can be, for example, 20 to 80 mm. The groove depth (maximum depth) of the lug grooves 7 is not particularly limited, but can be, for example, 20 to 120 mm. In the illustrated example, the lug grooves 7 extend without inclination with respect to the tire width direction, but the lug grooves 7 may extend with respect to the tire width direction (not particularly limited, but for example, with an inclination angle of more than 0° and less than or equal to 60°). In the illustrated example, the lug grooves 7 are in communication with the width direction grooves 4, but they do not have to be in communication. Furthermore, in the illustrated example, the lug groove 7 located at the outermost land portion 3a in the width direction and the lug groove 7 located at the outermost land portion 3d in the width direction are positioned offset in the circumferential direction of the tire so that they do not overlap when projected in the tire width direction. However, the lug groove 7 located at the outermost land portion 3a in the width direction and the lug groove 7 located at the outermost land portion 3d in the width direction may be positioned so that they partially or completely overlap when projected in the tire width direction.

[0029] In the illustrated example, in the outermost land portions 3a and 3d in the width direction, a widthwise sub-groove 8 is positioned between two adjacent lug grooves 7 in the tire circumferential direction. In the illustrated example, one end of the widthwise sub-groove 8 communicates with the circumferential groove 2a (2c), and the other end terminates within the outermost land portion 3a (3d) in the width direction. In the illustrated example, the other end is circular in plan view, but this is not limited to this case. The other end may also extend through the outermost land portion 3a (3d) in the width direction without terminating therein. The groove width (opening width) of the widthwise sub-groove 8 (the straight portion) is not particularly limited, but can be, for example, 3 to 10 mm. The groove depth (maximum depth) of the widthwise sub-groove 8 is not particularly limited, but can be, for example, 20 to 120 mm.

[0030] In the tire 10 of this embodiment, air intake grooves 5 communicating with the widthwise grooves 4 are provided in the widthwise grooves 4. In this example, the air intake grooves 5 are slopes. In the illustrated example, two slopes 5 are provided for each widthwise groove 4, but only one or three or more may be provided, and it is not necessary to provide slopes 5 for all widthwise grooves 4. Also, in the illustrated example, all slopes 5 are provided to communicate with the inclined portion of the widthwise groove 4, but they may also be provided to communicate with the non-inclined portion.

[0031] The illustrated tire 10 has a non-directional pattern, and therefore, the two slopes 5 provided in one widthwise groove 4 are located on opposite sides of the widthwise groove 4 so that either slope 5 can adequately perform its function of introducing air regardless of the direction of rotation. On the other hand, in the case of a directional pattern, for example, it is preferable to provide multiple slopes 5 in one widthwise groove 4 on the same side of the tire in the circumferential direction relative to the widthwise groove 4, and this same side is preferably the forward side in the direction of rotation.

[0032] Figure 3 is a partial perspective view showing an example of a slope and air guide groove. Figure 4 is a plan view showing an example of a slope. The width a (see Figures 2 and 3) of the end of the slope 5 opposite to the widthwise groove 4 is smaller than the width b (see Figures 2 and 3) of the end on the widthwise groove 4 side. The ratio a / b is preferably 0.2 to 0.8. As shown in the figure, the width b at the end on the widthwise groove 4 side is the distance between the wall surfaces partitioned by the slope 5 along the groove wall of the widthwise groove 4, and the width a at the end opposite to the widthwise groove 4 side is the width at the connection point of the slope 5 with the tread surface, measured in the same direction as width b. Furthermore, it is preferable that the length of the air intake groove 5 (slope length) c (length in the inclination direction: see Figures 2 and 4) at the widthwise center position of the slope 5 (the position passing through the midpoint of the tire width direction at the maximum width position) is longer than the slope length d (length in the inclination direction: see Figures 2 and 4) at the widthwise end position of the slope 5. The ratio d / c is preferably 0.2 to 0.8. As shown in the figures, the slope lengths c and d refer to the distance from the connection point between the slope 5 and the tread surface to the connection point between the slope 5 and the widthwise groove 4, measured in directions perpendicular to the widths a and b at each respective position.

[0033] The slope 5 can have a polygonal shape in a plan view from the tread surface, and is preferably trapezoidal, as shown in Figures 4 and 6. On the other hand, in this disclosure, the slope 5 can have various shapes as long as the width a of the end opposite to the width groove 4 side is smaller than the width b of the end on the width groove 4 side.

[0034] Furthermore, as shown in the figure, notches 5a are provided at the corners of the end of the slope 5 opposite to the widthwise groove 4 (both corners in the illustrated example). The slope formed by the notches 5a is a slope that faces the slope 5. In the illustrated example, the slope formed by the notches 5a is triangular in shape. In the illustrated example, the slope 5 and the slope formed by the notches 5a have the same depth in the portion that communicates with the widthwise groove 4. In the example of Figure 3, the slope formed by the notches 5a is flat, but it may also be curved or stepped. Note that, as shown in Figure 6, the slope 5 does not have to have notches 5a. Alternatively, the slope 5 may have notches 5a at only one corner of the end opposite to the widthwise groove 4.

[0035] In the tire 10 of this embodiment, an air guide groove 6 is provided in the widthwise groove 4, communicating with the widthwise groove 4 and facing the slope 5. Specifically, the slope 5 and the air guide groove 6 are provided on opposite sides of the two side walls that define the widthwise groove 4. In this example, the air guide groove 6 is positioned so that it completely fits within and overlaps the slope 5 when projected in the circumferential direction of the tire (aligned in the widthwise direction).

[0036] The groove width w of the air guide groove 6 (see Figure 3) is preferably smaller than the width b of the end of the slope 5 on the widthwise groove 4 side. Specifically, the groove width w of the air guide groove 6 is preferably 25% to 75% of the width b of the end of the slope 5 on the widthwise groove 4 side. Furthermore, the depth length l of the air guide groove 6 (see Figure 3) is preferably 70% to 150% of the groove width of the widthwise groove 4. The groove depth of the air guide groove 6 is not particularly limited, but can be, for example, 20 to 120 mm.

[0037] Figure 7 is a cross-sectional view illustrating the shape of the paddle groove portion. The widthwise groove 4 has a paddle groove portion 4a, which in cross-sectional view consists of a straight portion 4b, a slanted portion 4c connected to the straight portion 4b, and a curved bottom portion 4d connected to the slanted portion 4c.

[0038] The ratio of the groove width (maximum width) x2 of the bottom portion 4d to the groove width x1 of the straight portion 4b of the paddle groove portion 4a is preferably 1.1 to 2. Furthermore, the ratio of the total depth y2 of the paddle groove portion 4a to the depth y1 at the boundary between the straight portion 4b and the hypotenuse portion 4c of the paddle groove portion 4a is preferably 1.5 to 2.5. When the heavy-duty tire 10 is mounted on the applicable rim, filled to the specified internal pressure, and unloaded, it is preferable that the slanted side portion 4c is inclined at an angle of 2 to 30° with respect to the tire's radial direction. The radius of curvature of the bottom 4d in the cross-sectional view is not particularly limited, but can be, for example, 1.6 to 10 mm.

[0039] The maximum groove width of the paddle groove portion 4a can be made smaller than the depth length l of the air guide groove 6.

[0040] The following describes the effects and advantages of the heavy-duty tire of this embodiment. Figure 8 is a schematic diagram illustrating the airflow in the prior art. The inventors' investigations revealed that the temperature at the bottom of the groove directly below the slope of the widthwise groove tends to be higher. Conventionally, it was thought that the air entering the slope cooled the bottom of the widthwise groove. However, in reality, as shown in Figure 8, it was found that there is air stagnation (circled area) at the bottom of the groove directly below the slope. The inventors believe the reason for this air stagnation is as follows: Although the slope pushes air to the bottom of the groove, air escapes in the widthwise direction (left and right in the figure). As a result, although there is air flowing to the bottom of the groove, the air velocity and volume of this air are insufficient. The stagnant air, as shown by the arrows in the figure, is only pushed by the air flowing straight down and the air flowing left and right, and its movement becomes small. In the tire 10 of this embodiment, the widthwise groove 4 is provided with an air guide groove 6 that communicates with the widthwise groove 4, and the widthwise groove 4 is provided with a cooling promotion section (paddle groove section 4a in this example). As schematically shown in Figure 10, air normally flows into the widthwise groove 4 when the widthwise groove 4 is located outside the contact surface, especially when it is facing the contact surface, and when the widthwise groove 4 is located within the contact surface, little air enters the widthwise groove 4. In contrast, in this embodiment, both an air guide groove 6 and a cooling promotion section are employed simultaneously. The paddle groove portion 4a, which is the cooling promotion section, has a bottom portion 4d, so there is a space that does not close even when in contact with the ground. As schematically shown in Figure 11, the opposing slanted sides 4c gradually come into contact from the point of contact with the ground to just below the load, and the volume of the space decreases. On the other hand, from just below the load to the push-off, the slanted sides 4c gradually separate, and the volume of the space increases. This pump effect caused by the change in the volume of the space promotes airflow at the bottom of the groove from the point of contact with the ground to the push-off, thereby improving the heat dissipation effect at the bottom of the groove. The "pump effect" referred to here is as follows: From the point of contact with the ground to the push-off of the tire, air entering the space that does not close at the bottom of the paddle groove portion 4a flows turbulently within the paddle groove portion 4a. Subsequently, as the paddle groove portion 4a separates from the contact surface, air escapes from the paddle groove portion 4a. This series of airflows cools the tire. Furthermore, even outside of the initial push-off and kick-off phases, the airflow within the paddle groove portion 4a can improve the heat dissipation effect at the bottom of the widthwise groove 4. Here, since the air guide groove 6 does not close even when in contact with the ground, air can be directed to the cooling promotion section (paddle groove portion 4a) by the air guide groove 6 from stepping down to pushing off, and the cooling promotion section (paddle groove portion 4a) can enhance the cooling effect of the groove bottom due to the pump effect described above. As described above, the heavy-duty tire 10 of this embodiment can enhance the cooling effect of the belt 60 by the widthwise grooves 4. In particular, when the widthwise groove 4 is in communication with the circumferential groove 2, air can be discharged from the circumferential groove 2 to cool the area around the circumferential groove 2. Furthermore, since the paddle groove portion 4a has an arc-shaped bottom portion 4d in cross-section, the occurrence of cracks at the bottom of the groove can be suppressed. On the tread surface 1 side, the groove width is narrow and the straight portion 4b can be narrowed, thus improving wear resistance.

[0041] The paddle groove portion 4a is provided in at least a part of the extending region of the widthwise groove 4, and in this example, the paddle groove portion 4a is present in the entire region except for the area where the air guide groove 6 is provided. Figure 13 is a partial cross-sectional view showing the air guide groove 6 and the paddle groove portion 4a. As shown in the figure, it is preferable that the bottom of the air guide groove 6 (solid line) is smoothly connected to the bottom of the paddle groove portion 4a (dashed line). This makes it easier for air to flow from the air guide groove 6 to the paddle groove portion 4a when in contact with the ground. The circumferential groove 2 can also be made to have a paddle groove portion.

[0042] Figure 12 is a partial perspective view showing the slope, air guide groove, and paddle groove section. The maximum groove width of the paddle groove section 4a (dashed line) can be made smaller than the depth length l of the air guide groove 6 (solid line). This is because the groove width of the air guide groove 6 is ensured, making it easier for air to flow from the tread surface 1 to the bottom of the widthwise groove 4. In addition, near the air introduction groove 5, there is turbulent air and air flowing from the tire tread surface to the paddle groove section 4a, and this ensures that air can be reliably directed to the bottom surface of the paddle groove section 4a in opposition to the turbulent air.

[0043] In particular, when a slope 5 communicating with the widthwise groove 4 is provided in the widthwise groove 4, and the air guide groove 6 is configured to face the slope 5, the slope 5 ensures that air flows in from the tread surface 1 at the locations where the slope 5 and air guide groove 6 are provided. The incoming air flows to the bottom of the groove via the air guide groove 6 (both during and outside of contact with the ground), and the pumping function of the paddle groove portion 4a suppresses air stagnation from the moment of contact with the ground to the moment of push-off. As a result, airflow can be ensured at all times during tire rolling, improving the cooling effect at the bottom of the groove.

[0044] Figure 14 is a cross-sectional view showing a first modified example of the cooling promotion section. The upper side of the figure is the tread surface 1 side and the lower side is the groove bottom side. As shown in the figure, the widthwise groove 4 can also have a widened section 4e for the cooling promotion section without a slanted side. This creates a step, and as shown in the figure, air collides with the upper surface of the step, ensuring airflow at the bottom and suppressing stagnation. Figure 15 is a cross-sectional view showing a second modified example of the cooling promotion section. As shown, a protruding portion 4f is formed in the groove wall partitioned by the widthwise groove 4, protruding into the groove wall (to narrow the groove width), and this protruding portion 4f can also be used as the cooling promotion section. As shown, air collides with the protruding portion 4f, ensuring airflow at the bottom and suppressing stagnation.

[0045] The inventors have found that by devising the shape of the slope, the airflow rate from the slope into the widthwise groove can be increased, preventing air from stagnating and further enhancing the cooling effect of the belt at the bottom of the widthwise groove.

[0046] Figure 9 is a diagram illustrating the effects and advantages of the heavy-duty tire of this embodiment. In the heavy-duty tire 10 of this embodiment, a slope 5 is provided in the widthwise groove 4 and communicates with the widthwise groove 4, and the width a of the end of the slope 5 opposite to the widthwise groove 4 is smaller than the width b of the end on the widthwise groove 4 side. First, the presence of the slope 5 allows air flowing near the tread surface 1 as the tire rotates to be guided into the lateral grooves 4 and air guide grooves 6. Furthermore, because the width a of the end of the slope 5 opposite to the lateral groove 4 side (the air inlet side of the slope 5) is smaller than the width b of the end on the lateral groove 4 side (the air outlet side of the slope 5), less air enters from the inlet of the slope 5 compared to conventional designs, resulting in lower air pressure in the slope 5. As a result, as schematically shown in Figure 9, the amount of air flowing above the tread surface 1 increases. Here, because the air pressure in the slope 5 is low and the amount of air flowing above the tread surface 1 increases, the air in the slope 5 is pushed in by the air flowing above the tread surface 1, as schematically shown in Figure 9. As a result, the airflow in the slope 5 accelerates. In addition, the amount of air entering the lateral grooves 4 directly from above the tread surface 1 without going through the slope 5 also increases. This increases the force that pushes the air trapped at the bottom of the widthwise groove 4, thereby enhancing the cooling effect of the belt at the bottom of the groove.

[0047] Furthermore, in this embodiment, since the slope length c at the widthwise center of the slope 5 is longer than the slope length d at the widthwise end of the slope, the airflow velocity at the widthwise center of the slope 5 can be increased. This increases the airflow rate directed to the widthwise groove 4 and the air guide groove 6, further strengthening the force pushing the air trapped at the bottom of the widthwise groove 4, and further enhancing the cooling effect of the belt at the bottom of the groove.

[0048] Furthermore, in this embodiment, a notch 5a is provided at the corner of the end of the slope 5 opposite to the widthwise groove 4. This increases the amount of air flowing from the notch 5a towards the slope 5, particularly increasing the airflow velocity at the widthwise center of the slope 5. This further strengthens the force pushing the air trapped at the bottom of the widthwise groove 4, thereby further enhancing the cooling effect of the belt at the bottom of the groove. To efficiently obtain such an effect, it is preferable that the slope formed by the notch 5a is a slope toward the slope 5.

[0049] Furthermore, in heavy-duty tires, a decrease in contact area generally leads to a deterioration in wear resistance. In this embodiment, the heavy-duty tire 10 is equipped with a slope 5, so the apparent contact area is reduced, but in reality, there is compression of the rubber within the tread surface 1, so a portion of the slope 5 (the portion to the right of the vertical line in Figure 5) is in contact with the ground. In conventional slopes 5, even if there is compression of the rubber within the tread surface 1, the shape of the slope 5 contributes little to the contact area. In this embodiment, the width a of the end of the slope 5 opposite to the widthwise groove 4 side is smaller than the width b of the end on the widthwise groove 4 side, so the reduction in contact area itself is small, and in addition, due to the tapered shape on the air inlet side and the shape of the inner slope of the slope 5, the contact area can be restored by the compression of the rubber within the tread surface 1, so the deterioration in wear resistance is less compared to conventional designs.

[0050] Furthermore, in this embodiment, the widthwise groove 4 is provided with an air guide groove 6 that communicates with the widthwise groove 4 and faces the slope 5. As a result, the air guided from the slope 5 to the air guide groove 6 does not dissipate near the tread surface 1 of the widthwise groove 4, but flows efficiently to the bottom of the groove 4, thereby improving the heat dissipation effect at the bottom of the groove. In addition, since the air guide groove 6 does not close when the foot touches the ground, air can flow from the moment of impact to the moment of push-off.

[0051] Here, it is preferable that the groove width w of the air guide groove 6 is 25% to 75% of the width b of the end of the slope 5 on the widthwise groove 4 side. By making the groove width w somewhat narrow as described above (75% or less of the width b), the air introduced into the air guide groove 6 is prevented from escaping in the extending direction of the widthwise groove 4, thereby increasing the amount of air heading towards the bottom of the groove. On the other hand, by making the groove width w somewhat wide as described above (25% or more of the width b), it is possible to secure the amount of air introduced into the air guide groove 6.

[0052] Furthermore, the depth l of the air guide groove 6 is preferably 70-150% of the groove width of the widthwise groove 4. Setting it to 70% or more ensures that a sufficient amount of air is introduced into the air guide groove 6, while setting it to 150% or less restricts the movement of the air introduced into the air guide groove 6 in the depth direction, thereby increasing the amount of air moving toward the bottom of the groove.

[0053] As in this embodiment, it is preferable that the widthwise groove 4, which is provided with a slope 5, is in communication with the circumferential groove 2 that extends in the circumferential direction of the tire. This is because the amount of air flowing from the circumferential groove 2 to the widthwise groove 4 can be increased by the air flowing toward the bottom of the widthwise groove 4.

[0054] Furthermore, the widthwise groove 4 has a paddle groove portion 4a in cross-sectional view, which consists of a straight portion 4b, a slanted portion 4c connected to the straight portion 4b, and an arc-shaped bottom portion 4d connected to the slanted portion 4c. This allows the aforementioned pump function to enhance the cooling effect of the belt at the bottom of the groove.

[0055] Here, the ratio of the groove width (maximum width) of the bottom portion 4d to the groove width of the straight portion 4b of the paddle groove portion 4a is preferably 1.1 to 2. By making the groove width of the bottom portion 4d 1.1 times or more the groove width of the straight portion 4b, the cooling effect of the groove bottom due to the pumping effect described above can be enhanced, and space for turbulent airflow within the paddle groove portion 4a can be secured. On the other hand, by making it 2 times or less, the volume of the straight portion 4b can be secured to ensure the airflow velocity, the wear resistance of the tire can be ensured, and the pumping effect described above can not be reduced when pushing off. Furthermore, the ratio of the total depth of the paddle groove portion 4a to the depth at the boundary between the straight portion 4b and the slanted portion 4c of the paddle groove portion 4a is preferably 1.5 to 2.5. This is because, by making the total depth of the paddle groove portion 4a 1.5 times or more the depth at the boundary, the volume of the widened groove area can be increased, thereby enhancing the cooling effect at the bottom of the groove due to the pumping effect, and increasing the airflow velocity in the straight portion 4b, thereby straightening the air flowing toward the slanted portion 4c and the bottom portion 4d. On the other hand, by making it 2.5 times or less, the volume of the straight portion 4b can be secured, ensuring the airflow velocity, and providing space for turbulent airflow within the paddle groove portion 4a, as well as ensuring the wear resistance of the tire. Furthermore, when a heavy-duty tire is mounted on the applicable rim, filled to the specified internal pressure, and unloaded, it is preferable that the slanted edges 4c are inclined at an angle of 2 to 30° with respect to the tire's radial direction. An angle of 2° or more increases the volume of the area where the groove width is widened, thereby enhancing the cooling effect at the bottom of the groove due to the pumping effect described above, and also ensures space for turbulent airflow within the paddle groove portion 4a. On the other hand, an angle of 30° or less ensures that the slanted edges 4c come into contact with each other under load. It also prevents excessive reduction in mold release performance and ensures the tire's wear resistance. [Explanation of Symbols]

[0056] 1: Tread surface, 2: Circumferential groove, 3: Rikube, 4: Width direction groove, 5: Air intake groove (slope), 6: Air guide groove, 7: Lug grooves, 8: Width direction minor groove, 10: Heavy-duty tires, 20: Bead section, 30: Sidewall section, 40: Tread section, 50: Carcass, 60: Belt, CL: Tire equatorial plane

Claims

1. A heavy-duty tire having multiple widthwise grooves extending in the tire width direction on the tread surface, An air guide groove is provided in the widthwise groove, communicating with the widthwise groove. A heavy-duty tire characterized in that a cooling promotion section is provided in the widthwise groove.

2. The heavy-duty tire according to claim 1, wherein the cooling promotion portion is a paddle groove portion that, in cross-sectional view, consists of a straight portion, a slanted portion connected to the straight portion, and an arc-shaped bottom portion connected to the slanted portion.

3. The heavy-duty tire according to claim 2, wherein the ratio of the total depth of the paddle groove portion to the depth at the boundary between the straight portion and the slanted portion of the paddle groove portion is 1.5 or more and 2.5 or less.

4. The heavy-duty tire according to claim 2 or 3, wherein when the heavy-duty tire is mounted on an applicable rim, filled to a specified internal pressure, and unloaded, the slanted portion is inclined at an angle of 2° to 30° with respect to the tire's radial direction.

5. The widthwise groove is provided with an air introduction groove that communicates with the widthwise groove. The heavy-duty tire according to claim 1 or 2, wherein the air guide groove faces the air introduction groove.

6. The heavy-duty tire according to claim 5, wherein a notch is provided at the corner of the end of the air intake groove opposite to the widthwise groove.

7. The heavy-duty tire according to claim 5, wherein the length of the air intake groove at the center in the width direction is longer than the length of the air intake groove at the end in the width direction.

8. The heavy-duty tire according to claim 5, wherein the air intake groove is trapezoidal in a plan view as seen from the tread surface.

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