CA2903360A1

CA2903360A1 - Pneumatic tire

Info

Publication number: CA2903360A1
Application number: CA2903360A
Authority: CA
Inventors: Kazutaka Matsuzawa
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 2013-03-13
Filing date: 2014-03-13
Publication date: 2014-09-18
Anticipated expiration: 2034-03-13
Also published as: CA2903360C; RU2602619C1; BR112015022869A2; JP2014177150A; CL2015002573A1; BR112015022869A8; WO2014141715A1; JP5785577B2

Abstract

A pneumatic tire has the following structure. Narrow grooves are arranged in a tread surface at intervals in a tire circumferential direction, each of the narrow grooves extending at an angle with the tire circumferential direction and having a groove width smaller than a groove depth. In one end portion of the narrow groove, an inflow part extending in the tire circumferential direction, communicating with the narrow groove at one end, and terminating at the other end is provided in a groove wall surface that is on an end point side of a tire circumferential component of a first vector from among groove wall surfaces of the narrow groove that face each other in the tire circumferential direction, the first vector being from one end of the narrow groove to the other end of the narrow groove.

Description

- I -PNEUMATIC TIRE
TECHNICAL FIELD
100011 The disclosure particularly relates to a pneumatic tire having a tread with enhanced heat dissipation.
BACKGROUND

[0002] A tire attached to a vehicle generates heat due to repeated expansion and contraction associated with load rolling. The heat generation is especially noticeable in the tread that comes into contact with the road surface, and causes various failures (such as heat separation) of the tread. There is accordingly a need to dissipate heat generated in the tread of the pneumatic tire.

[0003] To fulfill the need, a pneumatic tire in which grooves are formed in the tread surface has been conventionally used. The grooves of the tire reduce the tread itself which is a heat source, and also increase the surface area of the tread. The heat dissipation of the tread of the pneumatic tire can thus be enhanced.
CITATION LIST
Patent Literature

[0004] PTL 1: JP 2003-205706 A
SUMMARY
(Technical Problem)

[0005] In the conventional pneumatic tire, the overall volume of grooves needs to be increased in order to further improve the effect of enhancing the heat dissipation. Increasing the overall volume of grooves, however, may cause lower stiffness of the land portion and impair the wear performance or operation stability of the tire.
It could therefore be helpful to provide a pneumatic tire having a tread with enhanced heat dissipation while suppressing an increase in overall volume of grooves.

(Solution to Problem)

[0006] We provide the following.
A pneumatic tire has the following structure. Narrow grooves are arranged in a tread surface at intervals in a tire circumferential direction, each of the narrow grooves extending at an angle with the tire circumferential direction and having a groove width smaller than a groove depth. In one end portion of the narrow groove, an inflow part extending in the tire circumferential direction, communicating with the narrow groove at one end, and terminating at the other end is provided in a groove wall surface that is on an end point side of a tire circumferential component of a first vector from among groove wall surfaces of the narrow groove that face each other in the tire circumferential direction, the first vector being from one end of the narrow groove to the other end of the narrow groove.
With this structure, the tire circumferential projection length of the part combining the narrow groove and the inflow part can be relatively reduced. This prevents the position of a joint of tread molds from coinciding with the position of the narrow groove or inflow part, and suppresses flash above the narrow groove and/or the inflow part. Such a pneumatic tire has a tread with enhanced heat dissipation while an increase in overall volume of grooves is suppressed.
Here, the "tread surface" is the outer circumferential surface of the whole tire, which comes into contact with the road surface when the tire attached to an applicable rim and filled to a specified internal pressure rolls in a state of being placed under a load corresponding to a maximum load capacity. The "applicable rim" is a standard rim defined in any of the below-mentioned standards according to the tire size ("design rim" in Year Book of TRA, "measuring rim" in Standards Manual of ETRTO). The "specified internal pressure" is the air pressure corresponding to the maximum load capacity as defined in the standard. The "maximum load capacity" is the maximum mass permitted to be loaded onto the tire in the standard. The standard is determined according to an effective industrial standard in areas where tires are produced or used. Examples of the standard include Year Book of the Tire and Rim Association, Inc. (TRA) in the United States, Standards Manual of the European Tyre and Rim Technical Organisation -.3 -(ETRTO) in Europe, and JATMA Year Book of the Japan Automobile Tyre Manufacturers Association (JATMA) in Japan.
The "groove depth (of the narrow groove)" is the maximum depth of the narrow groove in the tire radial direction. The "groove width (of the narrow groove)" is the width of the narrow groove in the tire circumferential direction.
It is assumed that each dimension of the disclosed pneumatic tire is measured in a state where the tire is attached to the applicable rim, filled to the specified internal pressure, and placed under no load, unless otherwise noted.

[0007] Preferably, a tire circumferential projection length Lx of a part combining the narrow groove and the inflow part is smaller than a tire circumferential projection length Lx' of a part combining the narrow groove and a virtual inflow part in the case where, at the same position in a tire width direction as the inflow part, the virtual inflow part is provided in a groove wall surface that is on a start point side of the tire circumferential component of the first vector. This range facilitates the effect of enhancing the heat dissipation of the tread.

[0008] Preferably, a distance from the one end of the narrow groove to a position of the inflow part along an extension direction of the narrow groove is 0% to 35% of an extension length of the narrow groove. This structure facilitates the effect of enhancing the heat dissipation of the tread.

[0009] Preferably, the inflow part is provided at the one end of the narrow groove. This structure further facilitates the effect of enhancing the heat dissipation of the tread.

[0010] Preferably, an angle 02 between the first vector and a second vector that is from the one end of the inflow part to the other end of the inflow part is less than 90 . This structure further facilitates the effect of enhancing the heat dissipation of the tread.

[0011] Preferably, the angle 02 is 50 to 70 . This structure further facilitates the effect of enhancing the heat dissipation of the tread.

[0012] Preferably, the inflow part is provided in both of the groove wall surfaces of the narrow groove that face each other in the tire circumferential direction. This structure further increases the effect of enhancing the heat dissipation of the tread.
(Advantageous Effect)

[0013] It is possible to provide a pneumatic tire having a tread with enhanced heat dissipation while suppressing an increase in overall volume of grooves.
BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In the accompanying drawings:
FIG. 1(a) is a partial development view illustrating the tread surface of a pneumatic tire according to one of the disclosed examples, and FIG. 1(b) is a sectional view of the tire illustrated in FIG. 1(a) taken along line A-A
extending in the tire circumferential direction;
FIG. 2 is a diagram for describing the operation of the disclosed pneumatic tire;
FIG. 3(a) is an enlarged view of a narrow groove and inflow part ((i) to (iv)) that may be used in the tire illustrated in FIG. 1 and a narrow groove and virtual inflow part ((i)) used in a tire according to a comparative example, FIG. 3(b) is a diagram illustrating a first vector whose start point is one end of the narrow groove illustrated in FIG. 3(a) and whose end point is the other end of the narrow groove, and FIG. 3(c) is a diagram illustrating, together with the first vector in FIG. 3(b), a second vector whose start point is one end of the inflow part in (i) to (iv) illustrated in FIG. 3(a) and whose end point is the other end of the inflow part;
FIG. 4(a) is an enlarged view of a narrow groove and inflow part that may be used in the tire illustrated in FIG. 1, FIG. 4(b) is a diagram illustrating the first vector for the narrow groove illustrated in FIG. 4(a), and FIG. 4(c) is a diagram illustrating, together with the first vector in FIG. 4(b), the second vector for the narrow groove illustrated in FIG. 4(a);
FIG. 5 is an enlarged view of a narrow groove and inflow part that may be used in the tire illustrated in FIG. 1 in the case where the inflow part is provided in both groove wall surfaces of the narrow groove;
FIG. 6 is a diagram schematically illustrating the numerical analysis result of wind speed vectors inside the narrow groove and inflow part illustrated in FIG. 5;
FIG. 7 is a diagram illustrating examples of the shape of the inflow part on the tread surface;
FIG. 8 is a diagram illustrating examples of the shape of the inflow part in a cross section along a plane perpendicular to the extension direction of the narrow groove; and FIG. 9 is a sectional view of the pneumatic tire according to one of the disclosed examples in the tire width direction.
DETAILED DESCRIPTION

[0015] The following describes an embodiment of the disclosed pneumatic tire in detail with reference to drawings.
FIG. 1(a) is a partial development view illustrating the tread surface of a pneumatic tire according to one of the disclosed examples.
A pneumatic tire 1 (hereafter also referred to as "tire 1") according to one of the disclosed examples has, in a tread surface 2: a pair of center circumferential grooves 13 opposite to each other with the tire equator C in between and extending along the tire circumferential direction; and a pair of side circumferential grooves 14 extending along the tire circumferential direction on the outer sides of the center circumferential grooves 13 in the tire width direction. The pneumatic tire 1 also has, in the tread surface 2:
intermediate widthwise grooves 15 extending along the tire width direction and communicating with the center circumferential grooves 13 and the side circumferential grooves 14; and side widthwise grooves 16 extending along the tire width direction to the tread ground contact ends TG and communicating with the side circumferential grooves 14.
The tread ground contact ends TG mentioned here are the ends of the tread surface in the tire width direction.

[0016] The tire 1 also has: a rib-like center land portion 17 defined by the center circumferential grooves 13 and including the tire equator C; block-like intermediate land portions 18 defined by the center circumferential grooves 13, the side circumferential grooves 14, and the intermediate widthwise grooves 15; and block-like side land portions 19 defined by the side circumferential grooves 14, the side widthwise grooves 16, and the tread ground contact ends TG.

[0017] The tire 1 further has, in the rib-like center land portion 17 in the tread surface 2, narrow grooves 3 extending at an angle with the tire circumferential direction and terminating within the rib-like center land portion 17 at both ends 3a and 3b.
FIG. 1(b) is a sectional view of the tire illustrated in FIG. 1(a) taken along line A-A extending in the tire circumferential direction. As illustrated in FIG. 1(b), the groove width w3 of the narrow groove 3 is smaller than the groove depth d3 of the narrow groove 3.
In the tire 1, the narrow grooves 3 are arranged with a fixed pitch Lp in the tire circumferential direction.

[0018] The tire 1 further has, in a groove wall surface 3w (3we) of each narrow groove 3, an inflow part 4 extending in the tire circumferential direction. The inflow part 4 communicates with the narrow groove 3 at one end 4a, and terminates at the other end 4b.
The expression "extending in the tire circumferential direction" does not only mean extending exactly in the tire circumferential direction but also means extending in a direction that has a component of the tire circumferential direction.

[0019] When the tire rolls, wind flows in the direction opposite to the rotating direction of the tire, as illustrated in FIG. 2(a). This wind flows into each groove provided in the tread surface and then flows out of the groove, as a result of which the heat of the tread is dissipated to cool the tread.
If the groove has a larger width, the amount of wind (indicated by the arrow in (i) in FIG. 2(b)) flowing into the groove increases and so the tread cooling effect is enhanced, but the stiffness of the land portion decreases and the wear resistance or operation stability of the tire is impaired (see (i) in FIG.
2(b)). If the groove has a smaller width, the decrease in stiffness of the land portion is suppressed and the wear resistance or operation stability of the tire is not impaired, but the amount of wind (indicated by the arrow in (ii) in FIG.
2(b)) flowing into the groove decreases and so the tread cooling effect is reduced (see (ii) in FIG. 2(b)).

[0020] In the tire 1 according to one of the disclosed examples in which the inflow part is provided in addition to the narrow groove having a relatively small groove width, wind is easily taken into the narrow groove 3 through the inflow part 4 when the tire rolls, so that the amount of wind (indicated by the arrow in FIG. 2(c)) flowing into the narrow groove 3 increases (FIG. 2(c)).
Thus, the disclosed pneumatic tire attains the tread cooling effect by the narrow groove and the inflow part.

[0021] FIG. 3(a) is an enlarged view of the narrow groove 3 and inflow part 4 that may be provided in the tire 1 in each of (i) to (iv). The following description concerns the development view representing the tread surface, unless otherwise noted.
Let the vector from one end 3a of the narrow groove 3 to the other end 3b of the narrow groove 3 be a first vector V1, as illustrated in FIG. 3(b).
At one end 3a of the narrow groove 3 in the tire 1, the inflow part 4 extending in the tire circumferential direction is provided in the groove wall surface 3we of the narrow groove 3 that is on the end point Vice side of the tire circumferential component Vic of the first vector V1 from among the groove wall surfaces 3we and 3ws (3w) of the groove wall 3 facing each other in the tire circumferential direction, as illustrated in (ii) to (iv) in FIG. 3(a).
In other words, the inflow part is provided in the groove wall surface 3we of the narrow groove 3 that is in the upstream in the direction of the tire circumferential component Vic of the first vector V1 from among the groove wall surfaces 3we and 3ws (3w) of the groove wall 3 facing each other in the tire circumferential direction.
In the disclosed pneumatic tire, the inflow part 4 is provided in one end portion 3ap of the narrow groove 3, as illustrated in (i) to (iv) in FIG.
3(a).
In the tire 1, the inflow part 4 extends from the groove wall surface 3w (3we) in the direction of the tire circumferential component Vlc of the first vector VI.
100221 In the examples illustrated in (i) to (iv) in FIG. 3(a), the first vector V1 is a vector whose start point is the midpoint X of the line segment extending in the tire circumferential direction and forming one end 3a of the narrow groove 3 and whose end point is the midpoint Y of the line segment extending in the tire circumferential direction and forming the other end 3b of the narrow groove 3. In the disclosed pneumatic tire, however, the first vector V1 may be a vector whose start point is the outermost point in the tire width direction in one end portion 3ap of the narrow groove 3 and whose end point is the outermost point in the tire width direction in the other end portion - 8 -3bp of the narrow groove 3.
[0023] The following describes the working effects of the tire 1 according to one of the disclosed examples.
In a tire which is a comparative example to the tire 1 according to one of the disclosed examples where the narrow groove 3 and the inflow part 4 are provided as illustrated in (i) in FIG. 3(a), an inflow part is provided in the groove wall surface 3ws of the narrow groove 3 that is on the start point Vlcs side of the tire circumferential component Vic of the first vector VI, at the same position in the tire width direction as the inflow part 4 of the tire 1 (indicated as a virtual inflow part 4' in FIG. 3(a)).
In one end portion 3ap of the narrow groove 3, the tire circumferential projection length Lx (illustrated in (i) in FIG. 3(a) as a typical example) of the part combining the narrow groove 3 and the inflow part 4 in the tire 1 according to one of the disclosed examples where the inflow part 4 is provided in the groove wall surface 3we of the narrow groove 3 that is on the end point Vice side of the tire circumferential component Vic of the first vector V1 is smaller than the tire circumferential projection length Lx' (illustrated in (i) in FIG. 3(a)) of the part combining the narrow groove 3 and the inflow part 4 in the pneumatic tire according to the comparative example where the virtual inflow part 4' is provided in the groove wall surface 3ws of the narrow groove 3 that is on the start point Vlcs side of the tire circumferential component Vlc of the first vector VI.
Note that the position of the inflow part 4 denotes the midpoint P of the line forming one end 4a of the inflow part 4 between the point 4aoo nearest one end 3a of the narrow groove 3 and the point 4aoi nearest the other end 3b of the narrow groove 3, as illustrated in (i) in FIG. 3(a). The position of the virtual inflow part 4' denotes the equally defined point P' (see (i) in FIG. 3(a)). Here, the straight line passing through the point P in the tire 1 according to one of the disclosed examples and the point P' in the pneumatic tire according to the comparative example is parallel to the tire circumferential direction, that is, the inflow part 4 and the virtual inflow part 4' have the same position in the tire width direction.
A pneumatic tire is typically manufactured by vulcanization using tire molds. A tread is molded by arranging a plurality of tread molds along the whole tire circumference (using sectors separated in the tire circumferential direction). At a joint of tread molds, a slight amount of tread rubber may leak out of the molds. This locally causes flash (excess rubber) on the tread surface of the vulcanized pneumatic tire. In the case where the position of the joint of the tread molds coincides with the position of the narrow groove and/or inflow part formed in the tread surface, flash occurs above the narrow groove and/or the inflow part, and partly fills the narrow groove and/or the inflow part. In view of this, in the case where the same number of narrow grooves having inflow parts are formed in the tread surface, a smaller tire circumferential projection length of the part combining the narrow groove and the inflow part lowers the possibility that the position of the joint of the tread molds coincides with the position of the narrow groove or inflow part, and reduces changes in shape of the narrow groove and inflow part due to the above-mentioned flash.
Hence, the tire I according to one of the disclosed examples in which the tire circumferential projection length Lx of the part combining the narrow groove 3 and the inflow part 4 is relatively small easily attains the tread cooling effect by the narrow groove 3 and the inflow part 4.
[0024] Moreover, the tire 1 according to one of the disclosed examples has the following working effect in the case where the rotating direction of the tire is the direction (the direction from one end to the other end of the inflow part) of the tire circumferential component Vic of the first vector Vl. Air flowing from the other end 4b of the inflow part 4 open to the tread surface 2 into the inflow part 4 and then flowing from one end 4a of the inflow part 4 communicating with the narrow groove 3 into the narrow groove 3 in one end portion 3ap of the narrow groove 3 flows from one end portion 3ap of the narrow groove 3 to the other end portion 3bp of the narrow groove 3 throughout most of the extension length L3 of the narrow groove 3. Thus, air flows through a relatively large area inside the narrow groove 3.
In the tire 1 according to one of the disclosed examples, in the case where the rotating direction of the tire is the direction (the direction from the other end to one end of the inflow part) opposite to the direction of the tire circumferential component Vic of the first vector V1, air flowing into the narrow groove 3 in the other end portion 3bp of the narrow groove 3 can flow out of the inflow part 4 provided in one end portion 3ap of the narrow groove 3.
Therefore, the tire 1 according to one of the disclosed examples easily attains the tread cooling effect by the narrow groove 3 and the inflow part 4.
[0025] As described above, the disclosed pneumatic tire has a tread with enhanced heat dissipation.
[0026] Moreover, as described above, the disclosed pneumatic tire is unlikely to have flash above the narrow groove and/or the inflow part, which improves the tire manufacturing efficiency.
[0027] In the disclosed pneumatic tire, the distance M1 from one end 3a of the narrow groove 3 to the position of the inflow part 4 along the extension direction of the narrow groove 3 is preferably 0% to 35% of the extension length L3 of the narrow groove 3.
In this case, air flowing from the inflow part 4 into the narrow groove 3 flows from a position nearer one end 3a of the narrow groove 3 to a position nearer the other end 3b of the narrow groove 3, substantially throughout most of the extension length L3 of the narrow groove 3. Thus, air flows through a larger area inside the narrow groove 3. This facilitates the effect of enhancing the heat dissipation of the tread. In addition, a decrease in tire circumferential distance between narrow grooves 3 adjacent in the tire circumferential direction can be reduced.
[0028] Here, the distance M1 from one end 3a of the narrow groove 3 to the position of the inflow part 4 along the extension direction of the narrow groove 3 is the distance between the midpoint P and the point X along the extension direction of the narrow groove 3.
The extension length L3 of the narrow groove 3 is the straight-line distance between the point X and the point Y, i.e. the length of the first vector VI.
[0029] Since the inflow part 4 is provided at one end 3a of the narrow groove 3 in the tire 1 as illustrated in (ii) to (iv) in FIG. 3(a), air flowing from the inflow part 4 into the narrow groove 3 flows from one end 3a of the narrow groove 3 to the other end 3b of the narrow groove 3 substantially throughout the whole extension length L3 of the narrow groove 3, as mentioned above.
Thus, air flows through a larger area inside the narrow groove 3. This further facilitates the effect of enhancing the heat dissipation of the tread.
In addition, a decrease in tire circumferential distance between narrow grooves 3 adjacent in the tire circumferential direction can be minimized.
[0030] The expression "the inflow part 4 is provided at one end 3a of the narrow groove 3" means that the point 4aoo of the line forming one end 4a of the inflow part 4, which is nearest one end 3a of the narrow groove 3, matches the tire widthwise outer point of one end portion 3ap of the narrow groove 3.
In the tire 1, one end 3a of the narrow groove 3 is a straight line parallel to the tire circumferential direction. Accordingly, any point on the end 3a can be the tire widthwise outer point of one end portion 3ap of the narrow groove 3.
[0031] Let the vector from one end 4a of the inflow part 4 provided in one end portion 3ap of the narrow groove 3 to the other end 4b of the inflow part be a second vector V2, as illustrated in FIG. 3(c).
(i) to (iv) in FIG. 3(c) illustrate the first vector V1 and the second vector V2 for the narrow groove 3 and the inflow part 4 illustrated in (i) to (iv) in FIG. 3(a), respectively.
The second vector V2 is a vector whose start point V2s is the midpoint P of the line forming one end 4a of the inflow part 4 between the point 4aoo nearest one end 3a of the narrow groove 3 and the point 4aoi nearest the other end 3b of the narrow groove 3, and whose end point V2e is the midpoint Q of the line forming the other end 4b of the inflow part 4 between the point 4boo nearest one end 3a of the narrow groove 3 and the point 4boi nearest the other end 3b of the narrow groove 3.
[0032] In the tire 1, the angle 02 between the first vector V1 and the second vector V2 is preferably less than 900 (acute angle), as illustrated in (iv) in FIG.
3(c). In other words, the tire 1 preferably has the narrow groove 3 and inflow part 4 illustrated in (iv) in FIG. 3(a), rather than the narrow groove and inflow part 4 illustrated in any of (i) to (iii) in FIG. 3(a).
[0033] When the angle 02 is acute, air flowing from the other end 4b of the inflow part 4 open to the tread surface 2 into the inflow part 4 and then flowing from one end 4a of the inflow part 4 communicating with the narrow groove 3 into the narrow groove 3 in one end portion 3ap of the narrow groove 3 concentrates in one end portion 3ap of the narrow groove 3, rather than flowing from one end portion 3ap of the narrow groove 3 to the other end portion 3bp of the narrow groove 3. The air that has concentrated in one end portion 3ap of the narrow groove 3 flows inward in the tire radial direction in one end portion 3ap of the narrow groove 3, and reaches the groove bottom 3bo of the narrow groove 3. The air then flows from one end portion 3ap of the narrow groove 3 toward the other end portion 3bp of the narrow groove 3 and reaches the other end portion 3bp of the narrow groove 3, and flows outward in the tire radial direction in the other end portion 3bp of the narrow groove 3. Thus, the air travels in the deep part of the narrow groove 3 and then flows out to the tread surface 2. The generation of heat in the tread is noticeable in the tread portion inward in the tire radial direction, as compared with the tread portion outward in the tire radial direction. Accordingly, the flow of air through the deep part of the narrow groove 3 can more effectively dissipate heat generated in the tread.
Therefore, setting the angle 02 to less than 900 further facilitates the effect of enhancing the heat dissipation of the tread.
[0034] The angle 02 is preferably 50 to 70 .
This range of the angle 02 further facilitates the effect of enhancing the heat dissipation of the tread.
[00351 In the disclosed pneumatic tire, one end and the other end of the narrow groove 3 illustrated in FIG. 3(a) may be replaced so that, at one end 3a of the narrow groove 3, the inflow part 4 extending in the tire circumferential direction is provided in the groove wall surface 3we of the narrow groove 3 that is on the end point Vice side of the tire circumferential component Vic of the first vector V1 from among the groove wall surfaces 3we and 3ws (3w) of the groove wall 3 facing each other in the tire circumferential direction, as illustrated in FIG. 4(a). FIG. 4(b) illustrates the first vector V1 in this case, and FIG. 4(c) illustrates the second vector in this case.
[0036] A preferred embodiment of the inflow part 4 in FIG. 3 may be the same as a preferred embodiment of the inflow part 4 in FIG. 2.
[0037] In the disclosed pneumatic tire, the inflow part 4 is preferably provided in both groove wall surfaces 3w of the narrow groove 3 facing each other in the tire circumferential direction, as illustrated in FIG. 5.
[0038] By providing the inflow part 4 in both groove wall surfaces 3w of the narrow groove 3, air flowing into the narrow groove 3 from the inflow part 4 located in one end portion 3ap of the narrow groove 3 can flow out of the inflow part 4 located in the other end portion 3bp of the narrow groove 3.
The heat dissipation of the tread can be further enhanced in this way.
Moreover, by providing the inflow part 4, the effect of enhancing the heat dissipation of the tread can be achieved regardless of whether the rotating direction of the tire is the direction of the tire circumferential component of the first vector V1 or the direction opposite to the direction of the tire circumferential component of the first vector Vi.
[00391 FIG. 6(a) and 6(b) schematically illustrates the numerical analysis result of wind speed vectors inside the narrow groove 3 and inflow part 4 illustrated in FIG. 5.
As a model, the narrow groove 3 with the extension length L3 = 200 mm, the groove width w3 = 10 mm, the groove depth d3 = 100 mm, and 01 =
300 and the inflow part 4 with the extension length L4 = 50 mm, the width w4 = 50 mm, the depth d4 = 20 mm, and 02 = 60 were used.
In the tire which is the comparative example where the virtual inflow part 4' illustrated in (i) in FIG. 3(a) is provided in both groove wall surfaces 3w of the narrow groove 3 facing each other in the tire circumferential direction, air flowing from the other end 4b of the inflow part 4 open to the tread surface 2 into the inflow part 4 and then flowing from one end 4a of the inflow part 4 communicating with the narrow groove 3 into the narrow groove 3 flows from the tread surface 2 toward the groove bottom 3bo and reaches the groove bottom 3bo of the narrow groove 3 around the center part of the narrow groove 3, and subsequently flows from the groove bottom 3bo toward the tread surface 2, as illustrated in FIG. 6(a). In the disclosed tire having the narrow groove 3 and inflow part 4 illustrated in FIG. 5, on the other hand, air flowing from one end 4a of the inflow part 4 into the narrow groove 3 flows from the tread surface 2 toward the groove bottom 3bo and reaches the groove bottom 3bo of the narrow groove 3 before passing through the center part of the narrow groove 3, keeps flowing in the groove bottom 3bo, and flows from the groove bottom 3bo toward the tread surface 2 after passing through the center part of the narrow groove 3, as illustrated in FIG. 6(b).
This result demonstrates that the disclosed tire can more effectively dissipate heat generated in the tread.
[0040] In the tire 1, the narrow grooves 3 are arranged with the fixed pitch Lp in the tire circumferential direction, as illustrated in FIG. 1(a). The disclosed pneumatic tire is, however, not limited to such, as long as the narrow grooves are arranged at intervals in the tire circumferential direction.
Arranging the narrow grooves at intervals in the tire circumferential direction prevents the position of a joint of tread molds from coinciding with the position of the narrow groove or inflow part, and suppresses flash above the narrow groove and/or the inflow part. The effect of enhancing the heat dissipation of the tread can be achieved in this way.
[0041] The disclosed pneumatic tire has the effect of enhancing the heat dissipation of the tread as long as the narrow groove 3 and the inflow part 4 are provided in any part of the tread surface 2.
In the tire 1, the narrow groove 3 and the inflow part 4 are located in the rib-like center land portion 17 including the tire equatorial plane CL. In the rib-like center land portion 17, the ground contact pressure when the tire rolls is particularly high, and the expansion and contraction of the tread rubber are particularly large. Hence, the effect of enhancing the heat dissipation of the tread by the narrow groove 3 and the inflow part 4 is facilitated by providing the narrow groove 3 and the inflow part 4 in the rib-like center land portion 17.
[0042] In the disclosed pneumatic tire, the smaller angle 01 (illustrated in FIG. 1(a) as a typical example) of the angles between the extension direction of the narrow groove 3 and the tire circumferential direction is preferably 45 to 70 , and more preferably 55 to 65 . This range ensures that wind flows into the narrow groove 3.
[0043] In the tire 1, the ratio (w4/w3) of the tire circumferential length w4 (see FIG. 1(b)) of the inflow part 4 to the groove width w3 of the narrow groove 3 is preferably 3 to 7. With this range of w4/w3, the stiffness of the land portion in which the narrow groove 3 and the inflow part 4 are provided can be ensured and also the heat dissipation of the tread can be improved.
The ratio (d4/d3) of the depth d4 (see FIG. 1(b)) of the inflow part 4 to the groove depth d3 of the narrow groove 3 is preferably 1/7 to1/3. With this range of d4/d3, the stiffness of the land portion in which the narrow groove 3 and the inflow part 4 are provided can be ensured and also the heat dissipation of the tread can be improved.
[0044] In the tire 1, the ratio (L3/L4) of the extension length L3 of the narrow groove to the extension length L4 of the inflow part is preferably 2.0 or more, in terms of further enhancing the cooling effect.
[0045] In the tire 1, the ratio (w4/d4) of the tire circumferential length w4 of the inflow part to the depth d4 of the inflow part is preferably 1.0 or more, in terms of further enhancing the cooling effect.
[0046] The width w3 of the narrow groove 3 is preferably 10 mm to 20 mm.
With this range, the narrow groove 3 is closed and the land portion is continuous during ground contact. This enhances the stiffness of the land portion, and improves wear performance.
[0047] In the tire 1, the shape of the inflow part 4 on the tread surface 2 is a parallelogram including a pair of sides parallel to the extension direction of the narrow groove 3, as illustrated in (i) to (iii) in FIG. 3(a). The disclosed pneumatic tire is, however, not limited to such a shape, and may take any shape.
[0048] FIG. 7(a) to 7(e) illustrates examples of the shape of the inflow part on the tread surface 2.
Examples of the shape of the inflow part 4 include, in addition to a parallelogram: a trapezoid whose lower base is open to the wall surface of the narrow groove 3 and whose upper base is away from the wall surface of the narrow groove 3 where the tire widthwise length gradually decreases from the wall surface side of the narrow groove 3 (FIG. 7(a)); a trapezoid whose upper base is open to the wall surface of the narrow groove 3 and whose lower base is away from the wall surface of the narrow groove 3 where the tire widthwise length gradually increases from the wall surface side of the narrow groove 3 (FIG. 7(b)); a shape in which two sides other than the upper base and lower base of the trapezoid illustrated in FIG. 7(b) are curves (FIG. 7(c)); a semicircle (FIG. 7(d)); and a triangle (FIG. 7(e)).
[0049] The inflow part 4 in a cross section along a plane perpendicular to the extension direction of the narrow groove 3 is preferably shaped to gradually increase in depth from the other end 4b of the inflow part 4 toward one end 4a of the inflow part 4 and reach the maximum depth at one end 4a of the inflow part 4, as illustrated in FIG. 1(b).
[0050] In the tire 1, the shape of the inflow part 4 in the cross section along the plane perpendicular to the extension direction of the narrow groove 3 is a straight line connecting one end 4a and the other end 4b of the inflow part 4, as illustrated in FIG. 1(b). The disclosed pneumatic tire is, however, not limited to such a shape, and may take any shape.
[0051] FIG. 8(a) to 8(h) illustrates examples of the shape of the inflow part in the cross section along the plane perpendicular to the extension direction of the narrow groove 3.
Examples of the shape of the inflow part 4 include, in addition to a straight line: various curves (FIG. 8(a) to 8(c)); a curve in which the depth of the inflow part 4 increases stepwise from the other end 4b to one end 4a (FIG.

8(d)); a curve in which the depth of the inflow part 4 is constant from the other end 4b to an intermediate point M and gradually increases from M to one end 4a (FIG. 8(e) and 8(f)); a curve in which the depth of the inflow part 4 gradually increases from the other end 4b to an intermediate point M and is constant from M to one end 4a (FIG. 8(g)); and a curve in which the depth of the inflow part 4 is constant from the other end 4b to one end 4a (FIG. 8(h)).

[0052] Although the tread pattern of the tire 1 has the rib-like land portion and the block-like land portions, the tread pattern of the disclosed pneumatic tire is not limited to such, and may be any pattern.
Although both ends 3a and 3b of the narrow groove are terminated within the rib-like center land portion 17, at least one end of the narrow groove may be open to another groove (e.g. the circumferential groove) in the disclosed pneumatic tire.
[0053] Although the narrow groove 3 and the inflow part 4 are located in the rib-like center land portion 17 including the tire equator C in the tire 1, the narrow groove 3 and the inflow part 4 may be located in any part of the tread surface 2 in the disclosed pneumatic tire.
[0054] The disclosed pneumatic tire is particularly suitable as a tire having a relatively large tread, such as a tire for a construction vehicle or a tire for a truck or a bus.
[0055] FIG. 9 is a sectional view of the pneumatic tire 1 according to one of the disclosed examples in the tire width direction.

As illustrated in FIG. 9, the tire 1 includes a tread portion 500 with a thicker rubber gauge (larger rubber thickness) than a pneumatic tire attached to a passenger vehicle or the like.
[0056] In detail, the tire I satisfies DC/OD 0.015, where OD is the tire outer diameter and DC is the rubber gauge of the tread portion 500 in the position of the tire equatorial plane C.
[0057] The tire outer diameter OD (in mm) is the diameter of the tire 1 in the part where the outer diameter of the tire 1 is largest (typically, the tread portion 500 near the tire equatorial plane C). The rubber gauge DC (in mm) is the rubber thickness of the tread portion 500 in the position of the tire equatorial plane C. The rubber gauge DC does not include the thickness of a belt 300. In the case where the circumferential groove is formed in the position including the tire equatorial plane C, the rubber gauge DC is the rubber thickness of the tread portion 500 in the position adjacent to the circumferential groove.
[0058] The tire 1 includes a pair of bead cores 110, a carcass 200, and the belt 300 made up of a plurality of belt layers, as illustrated in FIG. 9. Although only one half of the width of the tire 1 is illustrated in FIG. 9, the other half of the width of the tire 1 not illustrated has the same structure.
[0059] Each bead core 110 is provided in a bead portion 120. The bead core 110 is made of bead wires (not illustrated).
[0060] The carcass 200 is the framework of the tire 1. The carcass 200 extends from the tread portion 500 to the bead portion 120 through a buttress portion 900 and a sidewall portion 700.
[0061] The carcass 200 toroidally extends between the pair of bead cores 110.
In this embodiment, the carcass 200 includes each bead core 110. The carcass 200 is in contact with each bead core 110. Both ends of the carcass 200 in the tire width direction twd are supported by the pair of bead portions 120.
[0062] The carcass 200 has carcass cords extending in a predetermined direction in a plan view from the tread surface 2. In this embodiment, the carcass cords extend along the tire width direction twd. The carcass cords are steel wires as an example.
[0063] The belt 300 is placed in the tread portion 500. The belt 300 is located outside the carcass 200 in the tire radial direction trd. The belt 300 extends in the tire circumferential direction. The belt 300 has belt cords extending at an angle with the predetermined direction in which the carcass cords extend. The belt cords are steel cords as an example.
[0064] The belt 300 made up of the plurality of belt layers includes a first belt layer 301, a second belt layer 302, a third belt layer 303, a fourth belt layer 304, a fifth belt layer 305, and a sixth belt layer 306.
[0065] The first belt layer 301 is located outside the carcass 200 in the tire radial direction trd. The first belt layer 301 is located innermost in the belt 300 made up of the plurality of belt layers, in the tire radial direction trd.
The second belt layer 302 is located outside the first belt layer 301 in the tire radial direction trd. The third belt layer 303 is located outside the second belt layer 302 in the tire radial direction trd. The fourth belt layer 304 is located outside the third belt layer 303 in the tire radial direction trd. The fifth belt layer 305 is located outside the fourth belt layer 304 in the tire radial direction trd. The sixth belt layer 306 is located outside the fifth belt layer 305 in the tire radial direction trd. The sixth belt layer 306 is located outermost in the belt 300 made up of the plurality of belt layers, in the tire radial direction trd. The first belt layer 301, the second belt layer 302, the third belt layer 303, the fourth belt layer 304, the fifth belt layer 305, and the sixth belt layer 306 are arranged in this order outward in the tire radial direction trd.
[0066] In this embodiment, the width (the width measured along the tire width direction twd, hereafter the same) of the first belt layer 301 and second belt layer 302 in the tire width direction twd is 25% or more and 70% or less of the tread width TW. The width of the third belt layer 303 and fourth belt layer 304 in the tire width direction twd is 55% or more and 90% or less of the tread width TW. The width of the fifth belt layer 305 and sixth belt layer 306 in the tire width direction twd is 60% or more and 110% or less of the tread width TW.
[0067] In this embodiment, the width of the fifth belt layer 305 is larger than the width of the third belt layer 303, the width of the third belt layer 303 is larger than or equal to the width of the sixth belt layer 306, the width of the sixth belt layer 306 is larger than the width of the fourth belt layer 304, the width of the fourth belt layer 304 is larger than the width of the first belt layer 301, and the width of the first belt layer 301 is larger than the width of the second belt layer 302 in the tire width direction twd. In the belt 300 made up of the plurality of belt layers, the width of the fifth belt layer 305 is largest and the width of the second belt layer 302 is smallest in the tire width direction twd. The belt 300 made up of the plurality of belt layers accordingly includes a shortest belt layer (i.e. the second belt layer 302) that is shortest in the tire width direction twd.
[0068] The second belt layer 302 which is the shortest belt layer has a belt end 300e which is an end edge in the tire width direction twd.
[0069] In this embodiment, in a plan view from the tread surface 2, the inclination angle of the belt cords of the first belt layer 301 and second belt layer 302 with respect to the carcass cords is 70 or more and 85 or less.
The inclination angle of the belt cords of the third belt layer 303 and fourth belt layer 304 with respect to the carcass cords is 50 or more and 75 or less.
The inclination angle of the belt cords of the fifth belt layer 305 and sixth belt layer 306 with respect to the carcass cords is 50 or more and 70 or less.
[0070] The belt 300 made up of the plurality of belt layers includes an inner crossing belt group 300A, an intermediate crossing belt group 300B, and an outer crossing belt group 300C. Each of the crossing belt groups 300A to 300C is a group of a plurality of belt layers in which the belt cords of adjacent belt layers cross each other (preferably with the tire equatorial plane in between) in the plan view from the tread surface 2.
[0071] The inner crossing belt group 300A is a set of belt layers, and is located outside the carcass 200 in the tire radial direction trd. The inner crossing belt group 300A is made up of the first belt layer 301 and the second belt layer 302. The intermediate crossing belt group 300B is a set of belt layers, and is located outside the inner crossing belt group 300A in the tire radial direction trd. The intermediate crossing belt group 300B is made up of the third belt layer 303 and the fourth belt layer 304. The outer crossing belt group 300C is a set of belt layers, and is located outside the intermediate crossing belt group 300B in the tire radial direction trd. The outer crossing belt group 300C is made up of the fifth belt layer 305 and the sixth belt layer 306.

[0072] The width of the inner crossing belt group 300A is 25% or more and 70% or less of the tread width TW in the tire width direction twd. The width of the intermediate crossing belt group 300B is 55% or more and 90% or less of the tread width TW in the tire width direction twd. The width of the outer crossing belt group 300C is 60% or more and 110% or less of the tread width TW in the tire width direction twd.
[0073] The inclination angle of the belt cords of the inner crossing belt group 300A with respect to the carcass cords is 70 or more and 850 or less in the plan view from the tread surface 2. The inclination angle of the belt cords of the intermediate crossing belt group 300B with respect to the carcass cords is 500 or more and 75 or less in the plan view from the tread surface 2. The inclination angle of the belt cords of the outer crossing belt group 300C with respect to the carcass cords is 500 or more and 70 or less in the plan view from the tread surface 2.
[0074] The inclination angle of the belt cords with respect to the carcass cords is largest in the inner crossing belt group 300A, in the plan view from the tread surface 2. The inclination angle of the belt cords of the intermediate crossing belt group 300B with respect to the carcass cords is larger than or equal to the inclination angle of the belt cords of the outer crossing belt group 300C with respect to the carcass cords.
[0075] The center circumferential groove 13 is formed so that the length DL
along the tire width direction twd from the belt end 300e to the tire widthwise innermost position (i.e. the position of bending inward in the tire width direction) of the groove width center line WL passing through the widthwise center of the center circumferential groove 13 in the plan view from the tread surface 2 of the tire 1 is 200 mm or less.
EXAMPLES
[0076] Non-limiting examples according to the disclosure are described below.
[0077] In this example, a tire was molded and then vulcanized using a typical technique in the tire industry, to produce a vulcanized tire including the narrow groove and the inflow part and having the specifications shown in Table I. A vulcanizer for vulcanizing the tread with a plurality of molds was used for the vulcanization.
[0078] The produced tire was attached to the applicable rim (53/80R63) defined in JATMA, the rim was assembled, and the internal pressure was set to 600 kPa. Wind flowing in the tire circumferential direction was applied to the tire. The thermal conductivity inside the narrow groove was evaluated by applying heat into the narrow groove from a film heater placed on the downwind groove wall surface of the narrow groove of the tire and measuring the heat at one point around the center of the upwind groove wall surface of the narrow groove. In detail, the relative evaluation index with the evaluation result of Comparative Example 1 being 100 was calculated. A
larger index represents a greater effect of enhancing the heat dissipation of the tread. Table I shows the detailed conditions and results.
[0079] [Table 1]
Comparative Example 1 Example I Example 2 Example 3 Example 4 View illustrating narrow groove and inflow portion (i) in FIG. 3(a) (i) in FIG. 3(a) (ii) in FIG 3(a) (iii) in FIG. 3(a) (iv) in FIG. 3(a) Groove width w3 of narrow groove a I 0.1 DI a 1 / groove depth d3 of narrow groove Groove wall where inflow portion is provided V Is side V le side V
lc side V le side Vie side Tire circumferential width Lx of narrow groove and inflow portion in Example 0.56 056 056 0.56 / tire circumferential width Lx of narrow groove and inflow portion as Comparative Example I
Distance MI /extension length L3 0.3 0(3 013 013 Inflow portion at end of narrow groove Not present Present Present Present Angle 02 between first vector VI and second vector V2 ( ) 100 110 Angle 01 between extension direction of narrow groove and ire 30' 30 30. 30.
width direction ( ) Tire circumferential length w4 of inflow portion / groove width w3 of narrow groove Depth d4 of inflow portion 0.2 0.2 0.2 / groove depth d3 of narrow groove Distance M2 between point X and point P along extension direction of narrow groove (nim) Index of thermal conductivity inside narrow groove IfX) 99 98 Flash in narrow WOOVe or inflow portion Present Not present Not present Not present Not present [0080] The comparison between Example 1 and Comparative Example 1 indicates that flash above the narrow groove and/or the inflow part is suppressed when the features set forth in claim 1 and/or claim 2 are satisfied.
The comparison between Example 3 and Examples 1, 2, and 4 indicates that the effect of enhancing the heat dissipation of the tread is further increased when the features set forth in claim 6 are satisfied in addition to the features set forth in claims 1 to 5.
INDUSTRIAL APPLICABILITY
[0081] The disclosed pneumatic tire has a tread with enhanced heat dissipation while an increase in overall volume of grooves is suppressed.

- 22 -The disclosed pneumatic tire is particularly suitable as a tire for a construction vehicle or a tire for a truck or a bus.
REFERENCE SIGNS LIST
[0082] 1 pneumatic tire 2 tread surface 3 narrow groove 3a (3e) one end of narrow groove 3b (3e) other end of narrow groove 3ap (3ep) one end portion of narrow groove 3bp (3ep) other end portion of narrow groove 3bo groove bottom of narrow groove 3w groove wall surface of narrow groove 3we (3w) groove wall surface of narrow groove on end point side of tire circumferential component of first vector 3ws (3w) groove wall surface of narrow groove on start point side of tire circumferential component of first vector 4 inflow part 4' virtual inflow part 4a (4e) one end of inflow part 4b (4e) other end of inflow part 4aoo point of line forming one end of inflow part nearest one end of narrow groove 4aoi point of line forming one end of inflow part nearest other end of narrow groove 4boo point of line forming other end of inflow part nearest one end of narrow groove 4boi point of line forming other end of inflow part nearest other end of narrow groove 13 center circumferential groove 14 side circumferential groove 15 intermediate widthwise groove 16 side widthwise groove 17 rib-like center land portion

- 23 -18 block-like intermediate land portion 19 block-like side land portion 120 bead portion 200 carcass 300 belt 301 first belt layer 302 second belt layer 303 third belt layer 304 fourth belt layer 305 fifth belt layer 306 sixth belt layer 300A inner crossing belt group 300B intermediate crossing belt group 300C outer crossing belt group 300e belt end 500 tread portion 700 sidewall portion 900 buttress portion d3 groove depth of narrow groove d4 depth of inflow part w3 groove width of narrow groove in tire circumferential direction w4 tire circumferential length of inflow part tire equator (equatorial plane) CL tire equatorial plane M1 distance from one end of narrow groove to position of inflow part along extension direction of narrow groove L3 extension length of narrow groove L4 extension length of inflow part Lx tire circumferential projection length of part combining narrow groove and inflow part Lx' tire circumferential projection length of part combining narrow groove and virtual inflow part midpoint between point 4aoo and point 4aoi

- 24 -Q midpoint between point 4boo and point 4boi Tw tread ground contact width TG tread ground contact end VI first vector Vlc tire circumferential component of V
Vice end point of Vic VI cs start point of Vic V2 second vector V2e end point of V2 V2s start point of V2 01 angle between extension direction of narrow groove and tire circumferential direction 02 angle between VI and V2

Claims

1. A pneumatic tire, wherein narrow grooves are arranged in a tread surface at intervals in a tire circumferential direction, each of the narrow grooves extending at an angle with the tire circumferential direction and having a groove width smaller than a groove depth, and in one end portion of the narrow groove, an inflow part extending in the tire circumferential direction, communicating with the narrow groove at one end, and terminating at the other end is provided in a groove wall surface that is on an end point side of a tire circumferential component of a first vector from among groove wall surfaces of the narrow groove that face each other in the tire circumferential direction, the first vector being from one end of the narrow groove to the other end of the narrow groove.

2. The pneumatic tire according to claim 1, wherein a tire circumferential projection length Lx of a part combining the narrow groove and the inflow part is smaller than a tire circumferential projection length Lx' of a part combining the narrow groove and a virtual inflow part in the case where, at the same position in a tire width direction as the inflow part, the virtual inflow part is provided in a groove wall surface that is on a start point side of the tire circumferential component of the first vector.

3. The pneumatic tire according to claim 1 or 2, wherein a distance from the one end of the narrow groove to a position of the inflow part along an extension direction of the narrow groove is 0% to 35% of an extension length of the narrow groove.

4. The pneumatic tire according to any one of claims 1 to 3, wherein the inflow part is provided at the one end of the narrow groove.

5. The pneumatic tire according to any one of claims 1 to 4, wherein an angle .theta.2 between the first vector and a second vector that is from the one end of the inflow part to the other end of the inflow part is less than 90°.

6. The pneumatic tire according to claim 5, wherein the angle .theta.2 is 50° to 70°.

7. The pneumatic tire according to any one of claims 1 to 6, wherein the inflow part is provided in both of the groove wall surfaces of the narrow groove that face each other in the tire circumferential direction.