Pneumatic tire

Abstract

To provide a pneumatic tire that achieves enhanced traveling performance on both icy / snowy road surfaces and dry road surfaces.SOLUTION: A tread surface includes a circumferential groove 1 extending in a tire circumferential direction, lateral grooves 3 extending in a direction intersecting the circumferential groove 1, and a block row composed of blocks 4 partitioned by the circumferential grooves 1 and the lateral grooves 3, the blocks being arranged along the tire circumferential direction. Each block 4 is provided with sipes 5, shallow grooves 6 that are shallower than the sipes 5, and auxiliary grooves 7 that are wider than both the sipes 5 and the shallow grooves 6. The auxiliary groove 7 extends in a tire axial direction in a circumferential central region 4C of the block 4 and ends without connection to the circumferential groove 1 or the lateral groove 3.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

[0002] Generally, on the surface of a new tire, there are attached mold release agents, oil components, etc. during the tire vulcanization molding process. In order to exhibit the original performance of the tire, a running-in of about several tens to several hundreds of kilometers is recommended. Therefore, in addition to the cut-shaped sipes, it is known to form shallower grooves than the sipes on the land portions of the tread surface so that the performance can be exhibited even in the initial state where sufficient running-in has not been performed (especially when new). On the tread surface of the tires described in Patent Documents 1 and 2, blocks provided with such sipes and shallow grooves are arranged.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, in studless tires, not only the running performance on icy and snowy roads but also the requirements for the running performance on dry roads have been increasing. In order to improve these running performances, it is effective to improve the grounding property of the blocks, that is, to make the grounding pressure approach a uniform state while ensuring the grounding area of the blocks. However, since the mechanisms for reducing the grounding property of the blocks are different between icy and snowy roads and dry roads, although it is necessary to improve the grounding property in accordance with each of them, no specific structure suitable for this has been known.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a pneumatic tire capable of improving running performance on both snowy and icy roads and dry roads.

Means for Solving the Problems

[0006] The pneumatic tire of the present invention includes a circumferential groove extending along the tire circumferential direction in a tread surface, a lateral groove extending in a direction intersecting with the circumferential groove, and a block row in which blocks defined by the circumferential groove and the lateral groove are arranged along the tire circumferential direction. The block is provided with a sipe, a shallow groove shallower than the sipe, and a sub-groove formed wider than the sipe and the shallow groove. The sub-groove extends along the tire axial direction in a circumferential central region of the block and terminates without being connected to the circumferential groove and the lateral groove.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0008] An embodiment of the present invention will be described with reference to the drawings.

[0009] FIG. 1 is a plan view showing an example of the tread surface of a pneumatic tire according to the present embodiment. The pneumatic tire T is a studless tire for automobiles, including a pair of bead portions (not shown), a pair of sidewall portions (not shown) extending radially outward in the tire diameter direction from each of the pair of bead portions, and a tread portion 10 connected to the radially outer ends of each of the pair of sidewall portions in the tire diameter direction. The tread surface Tr constitutes the outer peripheral surface of the tread portion 10. The tire T shown in FIG. 1 is new, and the tread surface Tr is in an unworn state.

[0010] The tread surface Tr is provided with a plurality of circumferential grooves 1 extending in the tire circumferential direction and a plurality of land portions 2 defined thereby. The number of the circumferential grooves 1 is, for example, 3 to 5. In the example of FIG. 1, five land portions 2 are defined by four circumferential grooves 1. The five land portions 2 include a pair of shoulder land portions 21, 22 adjacent to the ground contact end TE, a pair of mediate land portions 23, 24 adjacent to the shoulder land portions 21, 22 with the circumferential grooves 1 interposed therebetween, and a center land portion 25 adjacent to the mediate land portions 23, 24 with the circumferential grooves 1 interposed therebetween. The shoulder land portions 21, 22 are the land portions arranged at the outermost side in the tire axial direction among the plurality of land portions 2.

[0011] Here, the tire circumferential direction is the direction around the central axis (tire rotation axis) of the tire T. The tire radial direction is the direction along the diameter of the tire T. The side approaching the central axis of the tire T is the inner side in the tire radial direction, and the side away from the central axis of the tire T is the outer side in the tire radial direction. The tire axial direction is the direction parallel to the central axis of the tire T. The side approaching the center in the tire axial direction of the tire T is the inner side in the tire axial direction, and the side away from the center in the tire axial direction of the tire T is the outer side in the tire axial direction.

[0012] The ground contact end TE is the outermost position in the tire axial direction of the ground contact surface in a state where the tire T mounted on a standard rim is filled with a standard internal pressure, placed vertically on a flat road surface, and a standard load is applied. Unless otherwise specified, the dimensions, angles, positional relationships, etc. of each part of the tire are defined in a non-loaded state where the tire T mounted on a standard rim is filled with a standard internal pressure.

[0013] The regular rim is the rim defined for each tire in a standard system including the standards on which the tire is based. For example, it is the standard rim in JATMA, and it is the "Measuring Rim" in TRA and ETRTO.

[0014] The regular internal pressure is the air pressure defined for each tire in a standard system including the standards on which the tire is based. In the case of tires for trucks and buses and light trucks, in JATMA it is the maximum air pressure, in TRA it is the value corresponding to the Load Index described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in ETRTO it is the "INFLATION PRESSURE". In the case of passenger car tires, it is usually 180 kPa, but in the case of tires marked as Extra Load or Reinforced, it is 220 kPa.

[0015] The regular load is the load defined for each tire in a standard system including the standards on which the tire is based. In JATMA it is the "maximum load capacity", in TRA it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in ETRTO it is the "LOAD CAPACITY". In the case of passenger car tires, it is the load corresponding to 88% of the said load.

[0016] The tread surface Tr includes a circumferential groove 1 extending along the tire circumferential direction, a lateral groove 3 extending in a direction intersecting the circumferential groove 1, and a block row in which blocks divided by the circumferential groove 1 and the lateral groove 3 are arranged along the tire circumferential direction. In the present embodiment, each land portion 2 is formed by the block row. Among them, the shoulder land portions 21 and 22 have characteristic structures described later, and hereinafter, mainly the shoulder land portion 21 will be described. Since the shoulder land portion 22 has a shape symmetrical to the shoulder land portion 21, the description regarding the shoulder land portion 21 also applies to the shoulder land portion 22.

[0017] The shoulder land portion 21 is formed by a row of blocks 4 arranged along the tire circumferential direction. The block 4 is divided by a circumferential groove 1 and a transverse groove 3 extending in a direction intersecting with the circumferential groove 1. The groove width W1 (see FIG. 2) of the circumferential groove 1 is, for example, 4.0 mm or more, preferably 6.0 mm or more. The groove width W3 (see FIG. 2) of the transverse groove 3 is larger than the groove width W7 (see FIG. 4) of the sub-groove 7 described later. The transverse groove 3 extends from the circumferential groove 1 to the outside in the tire axial direction to reach the grounding end TE, and completely divides the block 4. However, it is not limited to this, and a shape in which a part of the transverse groove 3 is interrupted and the blocks 4 are partially connected may also be acceptable.

[0018] FIG. 2 is a plan view of the block 4. The shoulder land portion 21 is formed by an array (i.e., a row of blocks) of the blocks 4 shown in FIG. 2. The block 4 is provided with sipes 5, shallow grooves 6 shallower than the sipes 5, and sub-grooves 7 formed wider than the sipes 5 and the shallow grooves 6. FIG. 3 is a plan view of the same block 4 as FIG. 2, but for the sake of explanation, the illustration of the sipes 5 and the shallow grooves 6 is partially omitted. FIG. 4(A) is a cross-sectional view of the shallow groove 6, corresponding to the cross-section taken along the X-X arrow view of FIG. 3. FIG. 4(B) is a cross-sectional view of the sub-groove 7, corresponding to the cross-section taken along the Y-Y arrow view of FIG. 3.

[0019] The sipes 5 are formed in a cut shape. The sipes 5 exhibit an edge effect and a water drainage effect, and have a function of enhancing the driving performance (e.g., handling stability performance and braking performance) on icy and snowy road surfaces. The groove width W5 of the sipes 5 is not particularly limited, but is, for example, 0.1 mm or more, preferably 0.2 mm or more, more preferably 0.3 mm or more. Also, the groove width W5 is, for example, 1.0 mm or less, preferably 0.8 mm or less, more preferably 0.6 mm or less. The depth of the sipes 5 is preferably 3.0 mm or more, more preferably 4.0 mm or more. The depth of the sipes 5 is set to be equal to or less than the depth of the circumferential groove 1, and is, for example, 6.5 mm or less.

[0020] The siping 5 is formed by a corrugated siping with a siping surface shape appearing on the tread surface of the block 4 that extends in a wavy shape. The wavy shape here may be a sine wave shape, a triangular wave shape (zigzag shape), etc., and is not particularly restricted. The siping 5 may have a siping surface shape that extends linearly. The extending direction, inclination angle, etc. of the siping 5 having an amplitude like a corrugated siping are defined based on the amplitude center line AC. The siping 5 is a three-dimensional siping including a portion where the cross-sectional shape along a plane parallel to the tread surface of the block 4 changes along the depth direction, but is not limited thereto, and may also be a two-dimensional siping where the cross-sectional shape is constant along the depth direction.

[0021] The shallow groove 6 exhibits an edge effect and a water drainage effect, and has a function of enhancing the running performance on an ice and snow road surface in an initial state where sufficient bedding running has not been performed. The groove width W6 of the shallow groove 6 is not particularly limited, but is, for example, 0.3 mm or more, preferably 0.5 mm or more. Also, the groove width W6 is, for example, 1.5 mm or less, preferably 1.0 mm or less. The groove width W6 is preferably the same as or larger than the groove width W5. The depth D6 of the shallow groove 6 is, for example, 0.1 mm or more, preferably 0.2 mm or more. Also, from the viewpoint of suppressing a decrease in the rigidity of the surface portion of the block 4, the depth D6 is, for example, 2.0 mm or less, preferably 1.5 mm or less.

[0022] The sub-groove 7 is formed wider than the siping 5 and the shallow groove 6. That is, the groove width W7 of the sub-groove 7 is larger than the groove width W5 (W5 < W7) and also larger than the groove width W6 (W6 < W7). The groove width W7 is, for example, 0.4 mm or more, preferably 0.6 mm or more. Also, the groove width W7 is, for example, 2.0 mm or less, preferably 1.8 mm or less. The groove width W7 is larger than the groove width W6 by, for example, 0.3 mm or more, preferably 0.5 mm or more. The groove width W7 is defined based on a pair of groove edges extending parallel to each other on the tread surface of the block 4, and this point is the same for the other groove widths W1, W3, W5, W6 as well.

[0023] The secondary groove 7 extends along the tire axial direction in the circumferential central region 4C of the block 4 (hereinafter, may be simply referred to as the "central region 4C") and terminates without connecting to the circumferential groove 1 and the lateral groove 3. The central region 4C is defined as, for example, a region sandwiched by the regions 4E at both ends when the maximum length L4 of the block 4 in the tire circumferential direction is divided into four equal parts. In the present embodiment, the secondary groove 7 is completely contained within the central region 4C, but it is not limited thereto, and a part of the secondary groove 7 may protrude into one or both of the regions 4E at both ends.

[0024] As described in [A] and [B] below, although the mechanism for reducing the grounding performance of the block is different between the ice and snow road surface and the dry road surface, according to the pneumatic tire T of the present embodiment, the grounding performance can be improved by adapting to each of them, so that the running performance on both the ice and snow road surface and the dry road surface can be improved.

[0025] [A] Ice and snow road surface When driving on an ice and snow road surface, a water film intervenes between the tread surface of the block 4 and the road surface. If the water removal by the sipes 5 and the shallow grooves 6 is not sufficient, it will cause a substantial reduction in the contact area, and the grounding performance tends to decrease. Therefore, in order to improve the running performance on the ice and snow road surface, it is considered effective to suppress the formation of such a water film. In particular, on an ice and snow road surface with a low friction coefficient, the grounding pressure is relatively high at the center of the block 4 and relatively low at the peripheral portion surrounding it. Therefore, it is effective to promote the water removal at the center portion.

[0026] [B] Dry road surface On a dry road surface with a high friction coefficient, contrary to the ice and snow road surface, the grounding pressure is relatively low at the center of the block 4 and relatively high at the peripheral portion surrounding it. Therefore, due to such a non-uniform grounding pressure distribution, the grounding performance tends to decrease. Therefore, in order to improve the running performance on the dry road surface, it is considered effective to make the grounding pressure of the block 4 uniform. Also, when the block 4 is likely to fall over, it will cause a reduction in the contact area. Therefore, it is desirable to ensure the rigidity of the block 4 as much as possible.

[0027] In the tire T of the present embodiment, in addition to the sipes 5 and the shallow grooves 6, the auxiliary grooves 7 are provided in the blocks 4, so that the edge effect by the auxiliary grooves 7 is exhibited when driving on an icy or snowy road surface. Moreover, the auxiliary grooves 7 are formed wider than the sipes 5 and the shallow grooves 6 and extend along the tire axial direction in the central region 4C including the central portion of the block 4, so that water intervening between the tread surface of the block 4 and the road surface becomes a path to escape to the outside of the circumferential groove 1 and the grounding end TE, and promotes water drainage at the central portion of the block 4. Therefore, regarding the above [A], according to the tire T of the present embodiment, the driving performance on an icy or snowy road surface can be improved.

[0028] Furthermore, in this tire T, due to the provision of the auxiliary grooves 7 as described above, the flexibility of the central portion of the block 4 is increased. Therefore, when driving on a dry road surface, the grounding pressure of the central portion of the block 4 is increased, and consequently, the effect of equalizing the grounding pressure of the block 4 is achieved. Moreover, the auxiliary grooves 7 have a closed structure that terminates without being connected to either the circumferential groove 1 or the lateral groove 3, and such a closed structure is effective in suppressing the reduction in the rigidity of the block 4 due to the auxiliary grooves 7. Therefore, regarding the above [B], according to the tire T of the present embodiment, the driving performance on a dry road surface can be improved.

[0029] As described above, the auxiliary grooves 7 terminate without being connected to either the circumferential groove 1 or the lateral groove 3 and have a closed end 7a that closes within the block 4. The closed end 7a corresponds to the inner end in the tire axial direction of the auxiliary groove 7. In the present embodiment, the auxiliary groove 7 terminates without reaching the grounding end TE and has a closed end 7b that closes within the block 4. The closed end 7b corresponds to the outer end in the tire axial direction of the auxiliary groove 7. In order to effectively suppress the reduction in the rigidity of the block 4 due to the auxiliary grooves 7, it is preferable that both ends of the auxiliary groove 7 are closed within the block 4 in this way. However, it is not limited to this, and the auxiliary groove 7 may extend across the grounding end TE.

[0030] The secondary groove 7 is preferably shallower than the sip 5 and deeper than the shallow groove 6. The fact that the secondary groove 7 is formed shallower than the sip 5 is advantageous for suppressing the reduction in the rigidity of the block 4. Further, the fact that the secondary groove 7 is formed deeper than the shallow groove 6 (D6 < D7) is advantageous for ensuring the water drainage effect by the secondary groove 7. The depth D7 of the secondary groove 7 is, for example, less than 3.0 mm, preferably less than 2.0 mm. Further, the depth D7 is, for example, 0.5 mm or more, preferably 0.8 mm or more.

[0031] As shown in FIG. 4(A), in the present embodiment, an example is shown in which the shallow groove 6 is formed in a semi-circular cross-sectional shape. However, the present invention is not limited to this, and the cross-sectional shape of the shallow groove 6 may be other shapes such as a rectangle or a triangle. Further, as shown in FIG. 4(B), in the present embodiment, an example is shown in which the secondary groove 7 is formed in a rectangular cross-sectional shape, and the corner 7c formed by the bottom surface and the side surface of the secondary groove 7 is formed in an arc shape. However, the present invention is not limited to this, and the cross-sectional shape of the secondary groove 7 may be other shapes such as a semi-circular shape or a triangular shape.

[0032] In the present embodiment, the sips 5 and the shallow grooves 6 are arranged side by side at regular pitch intervals. The pitch interval P6 of the shallow grooves 6 is smaller than the pitch interval P5 of the sips 5, but the present invention is not limited to this. From the viewpoint of suppressing the reduction in the rigidity of the surface portion of the block 4, the pitch interval P6 is preferably 1.5 mm or more, more preferably 2.0 mm or more. Further, from the viewpoint of ensuring the function of enhancing the running performance on an icy snow road surface in the initial state, the pitch interval P6 is preferably 3.5 mm or less, more preferably 3.0 mm or less.

[0033] The sip 5 extends in a direction inclined with respect to the tire axial direction. The angle θ5 of the sip 5 with respect to the tire axial direction is preferably 45 degrees or less, more preferably 40 degrees or less, and still more preferably 30 degrees or less. The angle θ5 may be zero, but is preferably 5 degrees or more so that the edge effect is appropriately exhibited not only in the tire circumferential direction but also in the tire axial direction. The sip 5 is inclined in the same direction as the transverse groove 3 with respect to the tire axial direction, and such a configuration is advantageous for arranging the sips 5 in the block 4 at an appropriate density.

[0034] The shallow groove 6 extends in a direction inclined with respect to the tire axis direction. The angle θ6 of the shallow groove 6 with respect to the tire axis direction is preferably 45 degrees or less, more preferably 40 degrees or less, and still more preferably 30 degrees or less. The angle θ6 may be zero, but is preferably 5 degrees or more so that the edge effect is appropriately exhibited not only in the tire circumferential direction but also in the tire axis direction. In the present embodiment, the shallow groove 6 does not form a mesh shape by itself, and thus does not have an intersection that intersects another shallow groove 6 in a cross shape or an X shape.

[0035] The shallow groove 6 extends in a direction intersecting the sipe 5. In the present embodiment, the shallow groove 6 is inclined in a direction opposite to the sipe 5 with respect to the tire axis direction. According to such a configuration, the region where the sipe 5 and the shallow groove 6 interfere with each other can be reduced as much as possible, which is advantageous for appropriately exhibiting the edge effect of each of the sipe 5 and the shallow groove 6. The shallow groove 6 may be inclined in the same direction as the sipe 5 with respect to the tire axis direction, but in that case, it is preferable that the angle θ5 and the angle θ6 are different from each other from the viewpoint of reducing the interfering region as described above.

[0036] As shown in FIG. 2, the shallow groove 6 has a cut portion 6B in a part of the extending direction of the shallow groove 6, and the sub-groove 7 is disposed in the cut portion 6B and is separated from the shallow groove 6. Therefore, a clearance is provided between the end of the shallow groove 6 and the sub-groove 7, and the shallow groove 6 and the sub-groove 7 do not have an intersection. According to such a configuration, the reduction in the rigidity of the block 4 due to the sub-groove 7 is suppressed, which is advantageous for improving the running performance on a dry road surface. In the present embodiment, a part of the plurality of shallow grooves 6 arranged in parallel with each other is made discontinuous via the cut portion 6B. The shallow groove 6 terminates without being connected to the circumferential groove 1 and the transverse groove 3, but is not limited thereto.

[0037] In the present embodiment, one sub-groove 7 is provided for one block 4. Such a configuration is effective in suppressing the reduction in the rigidity of the block 4 due to the sub-groove 7. However, it is not limited thereto, and a plurality of sub-grooves 7 may be provided for one block 4.

[0038] The secondary groove 7 extends in a direction inclined with respect to the tire axial direction. Therefore, in the present embodiment, the sipes 5, the shallow grooves 6, and the secondary groove 7 are each inclined with respect to the tire axial direction. A part or all of the secondary groove 7 may have a shape extending parallel to the tire axial direction, but by being inclined with respect to the tire axial direction in this way, the edge effect is exerted not only in the tire circumferential direction but also in the tire axial direction. The secondary groove 7 is formed by a plurality of portions having different extending directions from each other as will be described later, and each of them is inclined with respect to the tire axial direction.

[0039] The secondary groove 7 has a bent shape including a first portion 71 extending in a first direction and a second portion 72 extending in a second direction intersecting the first direction. According to such a configuration, the length of the secondary groove 7 becomes larger than that in the case where it is not bent, and consequently the groove area increases, so that the water drainage effect by the secondary groove 7 is enhanced. In the present embodiment, the first direction and the second direction are each a direction inclined with respect to the tire axial direction. Also, the first direction and the second direction are each a direction inclined with respect to the tire circumferential direction. The first direction and the second direction are inclined in opposite directions with respect to the tire axial direction.

[0040] The secondary groove 7 is bent at a plurality of locations (specifically, two locations), but it may be bent at one location. In the present embodiment, an example in which the secondary groove 7 is formed in a crank shape in plan view is shown. The secondary groove 7 includes a pair of first portions 71 forming both sides of the crank shape and a second portion 72 connecting between them. From the viewpoint of facilitating the escape of water to the outside of the circumferential groove 1 or the grounding end TE, it is preferable that the angle θ71 is the same as or smaller than the angle θ72. Also, it is preferable that the length of the first portion 71 along the tire axial direction is larger than the length of the second portion 72 along the tire axial direction.

[0041] From the perspective of facilitating water drainage to the outside of the circumferential groove 1 or the grounding end TE, the angle θ71 of the first portion 71 extending in the first direction with respect to the tire axis direction is preferably 45 degrees or less, more preferably 40 degrees or less, and still more preferably 30 degrees or less. The angle θ71 may be zero, but it is preferably 5 degrees or more so that the edge effect is appropriately exerted not only in the tire circumferential direction but also in the tire axis direction. The angle θ72 of the second portion 72 extending in the second direction with respect to the tire axis direction may be 90 degrees, but it is preferably 80 degrees or less so that the edge effect is appropriately exerted not only in the tire circumferential direction but also in the tire axis direction.

[0042] The intersection angle θ7 formed by the first portion 71 and the second portion 72 is preferably 90 degrees or more, more preferably 100 degrees or more, in order to facilitate water drainage through the secondary groove 7. Also, the intersection angle θ7 is preferably 160 degrees or less, more preferably 140 degrees or less, in order to increase the length of the secondary groove 7 by the bent shape. The intersection angle θ7 is the smaller angle among the angles formed by the first portion 71 and the second portion 72.

[0043] The shallow groove 6 extends in a third direction, and it is preferable that the first direction and the second direction intersect the third direction, respectively. That is, the first portion 71 and the second portion 72 preferably extend in directions intersecting the shallow groove 6, respectively. According to such a configuration, the region where the shallow groove 6 and the secondary groove 7 interfere with each other can be reduced as much as possible, which is convenient for appropriately exerting the edge effect of the shallow groove 6. In the present embodiment, the shallow groove 6 is inclined in a direction opposite to the first portion 71 with respect to the tire axis direction. The shallow groove 6 is inclined in the same direction as the second portion 72 with respect to the tire axis direction, but the angle θ6 is different from the angle θ72.

[0044] As described above, in the present embodiment, the shoulder land portions 21 and 22 adjacent to the ground contact end TE are each formed by a block row in which the above-described blocks 4 are arranged. Such a block row may be applied to at least one of the plurality of land portions 2, and may be applied to other land portions instead of or in addition to the shoulder land portions 21 and 22. However, from the viewpoint of enhancing the running performance on an icy or snowy road surface, it is preferably applied to a shoulder land portion where a large water removal effect can be obtained by discharging water outside the ground contact end TE. Therefore, it is preferably applied to at least one of the pair of shoulder land portions 21 and 22.

[0045] Those skilled in the art will understand that the above-described embodiments are specific examples of the following aspects.

[0046] [1] The pneumatic tire of the present invention includes a circumferential groove extending along the tire circumferential direction on the tread surface, a lateral groove extending in a direction intersecting with the circumferential groove, and a block row in which blocks defined by the circumferential groove and the lateral groove are arranged along the tire circumferential direction. The block is provided with a sipe, a shallow groove shallower than the sipe, and a sub-groove formed wider than the sipe and the shallow groove. The sub-groove extends along the tire axial direction in the circumferential central region of the block and terminates without being connected to the circumferential groove and the lateral groove. According to such a configuration, the running performance on both an icy or snowy road surface and a dry road surface can be improved.

[0047] [2] In the pneumatic tire of [1] above, the sub-groove may be shallower than the sipe and deeper than the shallow groove. The fact that the sub-groove is formed shallower than the sipe is advantageous for suppressing a decrease in the rigidity of the block. Also, the fact that the sub-groove is formed deeper than the shallow groove is advantageous for ensuring the water removal effect by the sub-groove.

[0048] [3] In the pneumatic tire of [1] or [2] above, the shallow groove may have a discontinuous portion in a part of the extending direction of the shallow groove, and the sub-groove may be disposed in the discontinuous portion and separated from the shallow groove. According to such a configuration, since the reduction in the rigidity of the block due to the sub-groove is suppressed, it is convenient for improving the running performance on a dry road surface.

[0049] [4] In the pneumatic tire of any one of [1] to [3] above, the sub-groove may have a bent shape including a first portion extending in a first direction and a second portion extending in a second direction intersecting the first direction. According to such a configuration, the length of the sub-groove becomes larger compared to the case where it is not bent, and consequently the groove area increases, so that the water drainage effect by the sub-groove is enhanced.

[0050] [5] In the pneumatic tire of [4] above, the first direction and the second direction may each be a direction inclined with respect to the tire axis direction. According to such a configuration, in the sub-groove having a bent shape, the edge effect is appropriately exhibited not only in the tire circumferential direction but also in the tire axis direction.

[0051] [6] In the pneumatic tire of [4] or [5] above, the shallow groove may extend in a third direction, and the first direction and the second direction may each be a direction intersecting the third direction. According to such a configuration, since the region where the shallow groove and the sub-groove interfere with each other can be reduced as much as possible, it is convenient for appropriately exhibiting the edge effect by the shallow groove.

[0052] [7] In the pneumatic tire of any one of [1] to [6] above, the shoulder land portion adjacent to the grounding end may be formed by the block row. According to such a configuration, since the shoulder land portion that can obtain a large water drainage effect by discharging water to the outside of the grounding end is formed by the above block row, the running performance on an icy or snowy road surface can be improved well.

[0053] The pneumatic tire of the present invention is equivalent to a normal pneumatic tire except that a block row in which blocks provided with the above-described sipes, shallow grooves, and sub-grooves are arranged is provided on the tread surface, and any conventionally known materials, shapes, structures, etc. can be adopted in the present invention. Therefore, for example, in the present embodiment, a tread pattern asymmetric with respect to the center in the tire axial direction of the tread surface Tr is formed (see FIG. 1), but the present invention is not limited thereto.

[0054] Since the pneumatic tire of the present invention can improve the running performance on both snowy and icy road surfaces and dry road surfaces, it is useful as a studless tire or an all-season tire.

[0055] Although the embodiments of the present invention have been described with reference to the drawings, the specific configuration should not be considered to be limited to this embodiment. The scope of the present invention is shown not only by the description of the above-described embodiment but also by the claims, and further includes all modifications within the meaning and scope equivalent to the claims.

[0056] The pneumatic tire according to the present invention is not limited to the above-described embodiment at all, nor is it limited to the above-described effects. The pneumatic tire according to the present invention can be variously improved and modified without departing from the gist thereof. In addition, each configuration employed in the above-described embodiment can be arbitrarily combined and employed.

Explanation of reference numerals

[0057] 1 Circumferential groove, 2 Land portion, 3 Lateral groove, 4 Block, 4C Central circumferential region, 5 Sipe, 6 Shallow groove, 6B Discontinuous portion, 7 Sub-groove, 21 Shoulder land portion, 71 First portion, 72 Second portion, Tr Tread surface

Claims

1. A pneumatic tire comprising a circumferential groove extending along the circumferential direction of the tire tread, a lateral groove extending in a direction intersecting the circumferential groove, and a block row in which blocks defined by the circumferential groove and the lateral groove are arranged along the circumferential direction of the tire, wherein the block is provided with a sipe, a shallow groove shallower than the sipe, and a secondary groove formed wider than the sipe and the shallow groove, wherein the secondary groove extends along the tire axial direction in a central region in the circumferential direction of the block and terminates without connecting to the circumferential groove and the lateral groove.

2. The pneumatic tire according to claim 1, wherein the secondary groove is shallower than the sipe and deeper than the shallow groove.

3. The shallow groove has a break portion in a part of the extending direction of the shallow groove, The pneumatic tire according to claim 1, wherein the secondary groove is disposed at the break portion and is separated from the shallow groove.

4. The pneumatic tire according to claim 1, wherein the secondary groove has a bent shape including a first portion extending in a first direction and a second portion extending in a second direction intersecting the first direction.

5. The pneumatic tire according to claim 4, wherein the first direction and the second direction are respectively directions inclined with respect to the tire axial direction.

6. The shallow groove extends in a third direction, The pneumatic tire according to claim 4, wherein the first direction and the second direction are respectively directions intersecting the third direction.

7. The pneumatic tire according to any one of claims 1 to 6, wherein a shoulder land portion adjacent to the grounding end is formed by the block row.

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