Patent Description:
Conventionally, a tire has been known which includes a tread including a tread surface which contacts the road surface. This tread has a so-called block pattern in which a plurality of blocks are defined by a plurality of grooves extending in the tire-circumferential direction or in a direction intersecting the tire-circumferential direction. The blocks are arranged in the tire-circumferential direction. Patent Document <NUM> discloses a pneumatic tire in which a plurality of thin grooves called sipes are formed in such a block. Sipes have a wavy shape with amplitude in a tire surface view. Sipes increases the edge effect and improves grip performance of the tire.

Document <CIT> describes a tread for a pneumatic tire comprising raised elements which are provided with incisions having wavy or broken line paths. The incisions have a wide less than <NUM> and have lower amplitudes at the bottom of the incisions than at the surface of the tread.

Document <CIT> describes a pneumatic vehicle tire with a tread with profile elements, such as profile blocks, which are provided with incisions extending parallel to one another in a plan view and to the axial direction at an angle of <NUM>° to <NUM>°. Each incision in the plan view runs over at least a section in the form of a harmonic wave and each incision extends radially inwards from the outer surface of the profile element with a continuous reduction in the amplitude of the harmonic wave shape. The amplitude of the harmonic waveform of the incision decreases progressively from the outer surface of the profile element radially inwards.

Document <CIT> describes a tread kerf of a snow tire which easily discharges snow trapped in the kerf. The tread kerf is formed on an outer surface of a block of a tread of the snow tire and has a trapezoidal wave structure extending along the surface and formed in a depth direction of the block, and an amplitude of the trapezoidal wave structure is gradually decreased in a direction from a tire surface to a tire base. Since the amplitude of the tread kerf is gradually decreased in the direction from the tire surface to the tire base, the tread kerf may easily discharge snow trapped in the kerf to the outside of the tire block through the tire surface, even if a small space formed by the kerf is filled with snow when the tire is rotated on a snowy road.

However, for the above sipes shown in Patent Document <NUM>, the amplitude is largest at the tire surface, and the amplitude decreases as approaching the bottom. In a cross-sectional view in the depth direction, the sipe gently curves at the middle in the depth direction. Rubber between sipes tends to deform at and around the curving point of the sipe at the middle in the depth direction during braking and starting off of the vehicle. For this reason, the contact area of the rubber surface between sipes decreases and the traction declines, and block chipping occurs and the durability declines.

Therefore, the present invention has an object of providing a pneumatic tire having wavy-shaped sipes with improved traction and durability.

The present invention makes it possible to provide a pneumatic tire having wavy-shaped sipes with improved traction and durability.

Hereinafter, an embodiment will be described while referencing the drawings. <FIG> is a view expanding a part of the outer circumferential surface of a tire <NUM> in a plan view, the tire <NUM> being a pneumatic tire according to the embodiment. The tire <NUM> according to the embodiment can be applied to a tire for passenger vehicles; however, besides this, it can be also applied to a tire for various vehicles such as light trucks, trucks, and buses.

<FIG> shows a tire-axial direction X and a tire-circumferential direction C. In the tire <NUM> according to the embodiment, one side of the tire-circumferential direction is defined as a rotational direction during forward advancement of the vehicle on which the tire <NUM> is mounted, and a C1 direction shown in <FIG> corresponds to this rotational direction. It should be noted that the front side referred to in the following description is the right side of <FIG>, and indicates a side in the advancing direction of the vehicle defined as the tire rotation direction C1. The rear side is the left side in <FIG>, and indicates the reverse direction of the vehicle defined as the rotation direction C2 which is the opposite direction to the tire rotation direction C1.

<FIG> shows the tread <NUM> of the tire <NUM>, and shoulders <NUM> on both tire-axial sides of the tread <NUM>. The shoulder <NUM> is a portion transitioning from the tread <NUM> to each of the sidewalls (not shown) on both sides in the tire axial direction, and is a portion corresponding to the shoulder of the tire <NUM>. The shoulder <NUM> includes a first shoulder <NUM> on the upper side in <FIG>, and a second shoulder <NUM> on the lower side in <FIG>.

The tread <NUM> has a tread surface <NUM> to be in contact with the road surface. A tread pattern <NUM> is formed on the tread surface <NUM>. The tread pattern <NUM> is mainly designed by a plurality of grooves <NUM> and a plurality of blocks <NUM> defined by the grooves <NUM>. <FIG> shows a tire equatorial plane S1, which is a virtual line extending at the tire-axial center of the tread surface <NUM> along the tire circumferential direction.

When defining the tire axial direction as the left/right direction, the tread pattern <NUM> is substantially left/right symmetrical with the tire equatorial plane S1 as the symmetrical line, except that the tread pattern <NUM> is somewhat displaced in the tire circumferential direction. The tread surface <NUM> includes a first tread surface <NUM> close to the first shoulder <NUM>, and a second tread surface <NUM> close to the second shoulder <NUM>, with the tire equatorial plane S1 as a boundary.

The grooves <NUM> of the tread pattern <NUM> include a plurality of slanted grooves <NUM> and a plurality of communication grooves <NUM>. The slanted grooves <NUM> and the communication grooves <NUM> according to the embodiment are grooves having a groove width exceeding <NUM>.

The slanted grooves <NUM> are grooves extending from both tire-axial sides toward the tire equatorial plane S1. These slanted grooves <NUM> are arranged at intervals in the tire-circumferential direction. The plurality of slanted grooves <NUM> includes first slanted grooves <NUM> extending from the first shoulder <NUM> toward the tire equatorial plane S1, and second slanted grooves <NUM> extending from the second shoulder <NUM> toward the tire equatorial plane S1. The first slanted groove <NUM> is formed mainly on the first tread surface <NUM>, and the second sloped groove <NUM> is mainly formed on the second tread surface <NUM>.

The communication grooves <NUM> include first communication grooves <NUM> and second communication grooves <NUM>. Each of the first communication groove <NUM> communicates with the pair of first slanted grooves <NUM> adjacent in the tire-circumferential direction. Each of the second communication grooves <NUM> communicates with the pair of second slanted grooves <NUM> adjacent in the tire-circumferential direction.

The first communication grooves <NUM> are formed in the first tread surface <NUM>, and the second communication grooves <NUM> are formed in the second tread surface <NUM>.

Since the tread pattern <NUM> is left/right symmetrical, the first slanted grooves <NUM> and second slanted grooves <NUM> have similar features, and the first communication grooves <NUM> and second communication grooves <NUM> have similar features.

The first slanted grooves <NUM> are grooves extending from the first shoulder <NUM> toward the tire equatorial plane S1, in which the slanted grooves <NUM> generally slope relative to the tire-circumferential direction while gradually curving so that the slanted grooves <NUM> extend toward the front side and is convex toward the rear side. The second slanted grooves <NUM> are grooves extending from the second shoulder <NUM> toward the tire equatorial plane S1, in which the slanted grooves <NUM> generally slope relative to the tire-circumferential direction while gradually curving so that the slanted grooves <NUM> extend toward the front side and is convex toward the rear side. Herein, each slanted grooves <NUM>, <NUM> has an end close to the shoulder <NUM> (first shoulder <NUM>, second shoulder <NUM>) defined as a base end, and an end close to the tire equatorial plane S1 defined as a leading end.

The first slanted groove <NUM> includes a base-end side curved part <NUM> and a leading-end side curved part <NUM>. The base-end side curved part <NUM> extends from the base end to a portion beyond the tire-width center of the first tread surface <NUM>. The leading-end side curved part <NUM> curves from an end close to the tire equatorial plane S1 of the base-end side curved part <NUM> toward the tire equatorial plane S1 to the leading end. The base-end side curved part <NUM> curves with a relatively small curvature, and is slightly sloped toward the front side. The leading-end side curved part <NUM> curves with a similar curvature to the base-end side curved part <NUM>, and slopes to the front side at a sharper angle than the base-end side curved part <NUM>.

The second slanted groove <NUM> has a similar form to the first slanted groove <NUM>. In other words, the second slanted groove <NUM> includes a based-end curved part <NUM> and a leading-end side curved part <NUM>. The base-end curved part <NUM> extends from the base end to a portion beyond the tire-width center of the second tread surface <NUM>. The leading-end side curved part <NUM> curves from an end close to the tire equatorial plane S1 of the base-end side curved part <NUM> toward the tire equatorial plane S1 to the leading end.

The plurality of first slanted grooves <NUM> arranged in the tire-circumferential direction have alternately different lengths. The leading end of the shorter first slanted grooves <NUM> terminates such that it merges with the second slanted groove <NUM> immediately before the tire equatorial plane S1. The leading end of the longer first slanted groove <NUM> passes through the tire equatorial plane S1, and then terminates after crossing the leading-end side curved part <NUM> of the two second slanted grooves <NUM> adjacent in the tire-circumferential direction.

The length of the second slanted grooves <NUM> also differ alternately in the tire-circumferential direction similarly to the first slanted grooves <NUM>. In other words, the leading end of the shorter second slanted groove <NUM> terminates such that it merges with the first slanted groove <NUM> immediately before the tire equatorial plane S1. The leading end of the longer second slanted groove <NUM> passes through the tire equatorial plane S1, and then terminates after crossing the leading-end side curved part <NUM> of the two first slanted grooves <NUM> adjacent in the tire-circumferential direction.

The first communication groove <NUM> extends from the end of the leading-end side curved part <NUM> of the first slanted groove <NUM> close to the base-end side curved part <NUM>, straight toward a bending point of the first slanted groove <NUM> on the front side in the tire-circumferential direction. The bending point is a point where the first slanted groove <NUM> transitions from the base-end side curved part <NUM> to the leading-end side curved part <NUM>.

The second communication groove <NUM> is similar to the first communication groove <NUM>, and extends from the end of the leading-end side curved part <NUM> of the second sloped groove <NUM> close to the base-end side curved part <NUM>, straight to a bending point of the second slanted groove <NUM> on the front side in the tire-circumferential direction. The bending point is a point where the second sloped groove <NUM> transitions from the base-end side curved part <NUM> to the leading-end side curved part <NUM>.

The first communication groove <NUM> and second communication groove <NUM> both slope relative to the tire-circumferential direction so as to be directed toward the outer side in the tire-circumferential direction, as extending from the rear side to the front side.

The blocks <NUM> of the tread pattern <NUM> include a plurality of shoulder blocks <NUM> arranged in the outermost positions in the tire-axial direction, a plurality of central blocks <NUM> arranged at the center in the tire-axial direction, and a plurality of intermediate blocks <NUM> arranged between the should blocks <NUM> and the central blocks <NUM> in the tire-axial direction.

The shoulder blocks <NUM> include first shoulder blocks <NUM> close to the first shoulder <NUM>, and second shoulder blocks <NUM> close to the second shoulder <NUM>.

Each of the first shoulder blocks <NUM> are defined as an approximately rectangular shape, by the pair of first slanted grooves <NUM> adjacent in the tire-circumferential direction and the first communication groove <NUM>. The edge of the first shoulder block <NUM> close to the first shoulder <NUM> continues to the outer surface of the first shoulder <NUM>. The plurality of first shoulder blocks <NUM> are arranged in the tire-circumferential direction to sandwich the base-end side curved parts <NUM> of the first slanted grooves <NUM>.

Each of the second shoulder blocks <NUM> is defined as an approximately rectangular shape, by the pair of second slanted grooves <NUM> adjacent in the tire-circumferential direction and the second communication groove <NUM>. The edge of the second shoulder block <NUM> close to the second shoulder <NUM> continues to the outer surface of the second shoulder <NUM>. The plurality of second shoulder blocks <NUM> are arranged in the tire-circumferential direction to sandwich the base-end side curved parts <NUM> of the second slanted grooves <NUM>.

The first shoulder blocks <NUM> and the second shoulder blocks <NUM>, which are arranged in the tire-circumferential direction to sandwich the base-end side curved parts <NUM> of the slanted grooves <NUM>, may be arranged at equal intervals in the tire-circumferential direction, or may be arranged at variable pitch, which are irregular intervals.

The central blocks <NUM> are arranged in a manner such that they span both the first tread surface <NUM> and second tread surface <NUM>. In other words, the tire equatorial plane S1 passes through all of the central blocks <NUM>. The plurality of central blocks <NUM> includes a plurality of first central blocks <NUM> existing mainly on the first tread surface <NUM>, and a plurality of second central blocks <NUM> existing mainly on the second tread surface <NUM>.

The first central block <NUM> has a larger proportion occupying the surface area in the first tread surface <NUM> than in the second tread surface <NUM>. Each of the first central blocks <NUM> is defined as a substantially rectangular shape by the leading-end side curved parts <NUM> of the pair of first slanted grooves <NUM> adjacent in the tire-circumferential direction, and the leading-end side curved part <NUM> of the second slanted groove <NUM> having a greater length among the plurality of second slanted grooves <NUM>.

The second central block <NUM> has a greater proportion occupying the surface area in the second tread surface <NUM> than in the first tread surface <NUM>. Each of the second central blocks <NUM> is defined as a substantially rectangular shape, by the leading-end side curved parts <NUM> of the pair second slanted grooves <NUM> adjacent in the tire-circumferential direction, and the leading-end side curved part <NUM> of the first slanted groove <NUM> having a larger length among the plurality of first slanted grooves <NUM>.

Each of the plurality of the first central blocks <NUM> and each of the plurality of second central blocks <NUM> are alternately arranged in the tire-circumferential direction.

The intermediate block <NUM> includes a first intermediate block <NUM> close to the first tread surface <NUM>, and a second intermediate block <NUM> close to the second tread surface <NUM>.

Each of the first intermediate blocks <NUM> is defined as an approximately rectangular shape, by the leading-end side curved parts <NUM> of the pair of first slanted grooves <NUM> adjacent in the tire-circumferential direction, the first communication groove <NUM>, and the leading-end side curved part <NUM> of the second slanted groove <NUM> having a longer length. The plurality of first intermediate blocks <NUM> are arranged in the tire-circumferential direction to sandwich the leading-end side curved parts <NUM> of the first slanted grooves <NUM>.

Each of the second intermediate blocks <NUM> is defined as an approximately rectangular shape, by the leading-end side curved parts <NUM> of the pair of second slanted grooves <NUM> adjacent in the tire-circumferential direction, the second communication groove <NUM>, and the leading-end side curved part <NUM> of the second slanted groove <NUM> having a longer length. The plurality of second intermediate blocks <NUM> are arranged in the tire-circumferential direction to sandwich the leading-end side curved parts <NUM> of the second slanted grooves <NUM>.

The first intermediate blocks <NUM> are arranged between the shoulder blocks <NUM> and the central blocks <NUM> in the tire-axial direction. The second intermediate blocks <NUM> are arranged between the shoulder blocks <NUM> and the central blocks <NUM> in the tire-axial direction.

As described above, the tire equatorial plane S1 passes through all of the central blocks <NUM>. On the other hand, the tire equatorial plane S1 neither passes through the shoulder blocks <NUM> nor the intermediate blocks <NUM>.

In the first tread surface <NUM>, as the plurality of blocks <NUM> along the first slanted groove <NUM>, block columns 13A and block columns 13B are alternately arranged in the tire-circumferential direction. The block column 13A includes, as the three blocks <NUM>, a first shoulder block <NUM>, a first intermediate block <NUM>, and a first central block <NUM> extending in this order from the first shoulder <NUM> toward the tire equatorial plane S1. The block column 13B includes, as the two blocks <NUM>, a first shoulder block <NUM> and a first intermediate block <NUM> extending in this order from the first shoulder <NUM> toward the tire equatorial plane S1.

Similarly, in the second tread surface <NUM>, as the plurality of blocks <NUM> along the second slanted groove <NUM>, the block columns 13A and the block columns 13B are alternately arranged in the tire-circumferential direction. The block column 13A includes, as the three blocks <NUM>, the second shoulder block <NUM>, the second intermediate block <NUM>, and the second central block <NUM> extending in this order from the second shoulder <NUM> toward the tire equatorial plane S1. The block column 13B includes, as the two blocks <NUM>, the second shoulder block <NUM> and the second intermediate block <NUM> extending in this order from the second shoulder <NUM> side toward the tire equatorial plane S1.

In both the first tread surface <NUM> and the second tread surface <NUM>, the intermediate block <NUM> in the column without the central block <NUM> has a longer length in the extending direction along the slanted groove <NUM>, than the intermediate block <NUM> in the column with the central block <NUM>.

On the other hand, the shoulder block <NUM> and the central block <NUM> have the equal length in the extending direction along the slanted grooves <NUM>.

As shown in <FIG>, each of the blocks <NUM> of the tread <NUM> has a plurality of sipes <NUM>. The plurality of sipes <NUM> includes shoulder sipes <NUM>, central sipes <NUM>, and intermediate sipes <NUM>. The shoulder sipes <NUM> are respectively formed in the first shoulder blocks <NUM> and the second shoulder blocks <NUM> (hereinafter, may be collectively called "shoulder block <NUM>"). The central sipes <NUM> are respectively formed in the first central blocks <NUM> and the second central blocks <NUM> (hereinafter, may be collectively called "central block <NUM>"). The intermediate sipes <NUM> are respectively formed in the first intermediate blocks <NUM> and the second intermediate blocks <NUM> (hereinafter, may be collectively called "intermediate block <NUM>"). All sipes have a smaller groove width than the aforementioned slanted grooves <NUM> and the communication grooves <NUM>, and this groove width is no more than <NUM>. The number of sipes <NUM> per each blocks <NUM> is arbitrary; however, sipes <NUM> of the number on the order of <NUM> to <NUM>, for example, are arranged in one block <NUM>.

The shoulder sipes <NUM>, the central sipes <NUM>, and the intermediate sipes <NUM> respectively open in the surfaces of the blocks <NUM>, <NUM>, and <NUM>, and have a wavy shape as a whole in a tire surface view. The depth direction of the sipes <NUM>, <NUM>, <NUM> substantially follows the tire-radial direction.

As shown in <FIG>, the shoulder block <NUM> has a plurality of shoulder sipes <NUM>. The shoulder sipes <NUM> extend almost straight as a whole. In each of the shoulder blocks <NUM>, the plurality of shoulder sipes <NUM> are arranged in parallel to each other at intervals. The plurality of shoulder sipes <NUM> extend substantially in parallel to the extending direction of the shoulder blocks <NUM> along the slanted groove <NUM>. In other words, the shoulder sipes <NUM> extend in the direction intersecting the tire-circumferential direction. The end on the tire-axial inner side (tire equatorial plan S1 side) of the shoulder sipe <NUM> communicates with the first communication groove <NUM> and the second communication groove <NUM> (hereinafter, may be collectively called "communication groove <NUM>"). The end on the tire-axial outer side (shoulder <NUM> side) of the shoulder sipe <NUM> terminates without reaching the end on the tire-axial outer side of the shoulder block <NUM>.

<FIG> is a perspective view showing one shoulder sipe <NUM>. <FIG> is an arrow view along IIIA-IIIA in <FIG>. <FIG> is a cross-sectional view along the line IIIB-IIIB in <FIG>. <FIG> is a cross-sectional view along the line IIIC-IIIC in <FIG>. <FIG> is a cross-sectional view along the line IIID-IIID in <FIG>. <FIG> is a cross-sectional view along the line IV-IV in <FIG>.

As shown in <FIG>, the shoulder sipe <NUM> has a wavy-shaped part <NUM> and a sipe bridge <NUM>. The wavy-shaped part <NUM> is formed in a wavy shape extending along the extending direction. The sipe bridge <NUM> extends straight from an end of the wavy shaped part <NUM> to the communication groove <NUM>, and has a smaller depth than that of the wavy shaped part <NUM>. In addition, the shoulder sipe <NUM> has an opening 113A in the surface of the shoulder block <NUM>, and a bottom 113B. The wavy shaped part <NUM> occupies a large portion, e.g., at least <NUM>% of the extending direction length of the shoulder sipe <NUM>. The depth of the wavy shaped part <NUM>, a length between the opening 113A and the bottom 113B of is set on the order of <NUM> to <NUM>, for example, and the depth of the sipe bridge <NUM> is set on the order of <NUM> to <NUM>, for example; however, they are not limited thereto.

As shown in <FIG> and <FIG>, the wavy shaped part <NUM> of the shoulder sipe <NUM> is formed in a wavy shape having a fixed period and the wavy shape extends from the opening 113A to the bottom 113B. The amplitude of the wavy shape part <NUM> is largest at the opening 113A and smallest at the bottom 113B. In other words, the shoulder sipe <NUM> has a wavy shape at the bottom 113B, and the bottom 113B does not have a linear shape. The amplitudes of the openings 113A at the surface of the shoulder block <NUM> of the plurality of shoulder sipes <NUM> are equal to each other. Furthermore, the amplitude of the shoulder sipe <NUM> decreases at a fixed or constant rate of change from the opening 113A to the bottom 113B. In addition, as shown in <FIG>, the width of a gap between opposing inner surfaces of the shoulder sipe <NUM> has a substantially fixed dimension from the opening 113A to the bottom 113B. Accordingly, in a cross-sectional view in the depth direction which is substantially orthogonal to the extending direction of the shoulder sipe <NUM>, as shown in <FIG>, the shoulder sipe <NUM> is linear from the opening 113A to the bottom 113B. The width of the shoulder sipe <NUM> is preferably at least <NUM> and no more than <NUM>.

It should be noted that the shoulder sipe <NUM> of the present embodiment has a portion in which part of the wavy shape part <NUM> is not continuous in the extending direction, i.e., a part is missing, as shown in <FIG> and <FIG> to 3D. This is an example of some aspects of the shoulder sipe <NUM>. The shoulder sipe <NUM> is not to be limited to this, and may have a continuous wavy shape.

As shown in <FIG>, each of the central blocks <NUM> has a plurality of central sipes <NUM>. The central sipes <NUM> extend straight as a whole. In each of the central blocks <NUM>, the plurality of central sipes <NUM> are arranged in parallel to each other at intervals. The plurality of central sipes <NUM> extend substantially in parallel with the tire-axial direction. In other words, the central sipe <NUM> extends in a direction intersecting the tire-circumferential direction. Each of both ends of the central sipe <NUM> is continuous with either the first slanted groove <NUM> or the second slanted groove <NUM> (hereinafter, may be collectively called "slanted groove <NUM>").

<FIG> is a perspective view showing one central sipe <NUM>. <FIG> is an arrow view along VIA-VIA in <FIG>. <FIG> is a cross-sectional view along the line VIB-VIB in <FIG>. <FIG> is a cross-sectional view along the line VIC-VIC in <FIG>. <FIG> is a cross-sectional view along the line VID-VID in <FIG>. <FIG> is a cross-sectional view along the line VII-VII in <FIG>.

As shown in <FIG>, the central sipe <NUM> includes a wavy shape part <NUM>, a first sipe bridge <NUM>, and a second sipe bridge <NUM>. The wavy shape part <NUM> is formed in a wavy shape along the extending direction. The first sipe bridge <NUM> extends straight from one end of the wavy shape part <NUM> to the slanted groove <NUM>, and has a smaller depth than the wavy shape part <NUM>. The second sipe bridge <NUM> extends straight from the other end of the wavy shape part <NUM> to the slanted groove <NUM>, and has a smaller depth than the first sipe bridge <NUM>.

In addition, the central sipe <NUM> includes an opening 123A at the surface of the central block <NUM>, and a bottom 123B. The wavy shape part <NUM> occupies at least <NUM>%, for example, of the length in the extending direction of the central sipe <NUM>. The depth of the wavy shape part <NUM>, i.e., a length between the opening 123A and the bottom 123B is set on the order of <NUM> to <NUM>, for example, the depth of the first sipe bridge <NUM> is set on the order of <NUM>, for example, and the depth of the second sipe bridge <NUM> is set on the order of <NUM>, for example; however, they are not limited thereto.

As shown in <FIG> and <FIG>, the wavy shape part <NUM> of the central sipe <NUM> is formed in a wavy shape having a fixed period and the wave shape extends from the opening 123A to the bottom 123B. The amplitude of the wavy shape part <NUM> is largest at the opening 123A and smallest at the bottom 123B. In other words, the central sipe <NUM> has a wavy shape at the bottom 123B, and the bottom 123B does not have a linear shape. The amplitudes of the openings 123A in the surfaces of the central blocks <NUM> of the plurality of central sipes <NUM> are equal to each other. Furthermore, the amplitude of the central sipe <NUM> decreases at a fixed rate of change from the opening 123A to the bottom 123B. In addition, as shown in <FIG>, the width of a gap between opposing inner surfaces of the central sipe <NUM> has a substantially fixed dimension from the opening 123A to the bottom 123B. Accordingly, in the cross-sectional view in the depth direction which is substantially orthogonal to the extending direction of the central sipe <NUM> as shown in <FIG>, the central sipe <NUM> is linear from the opening 123A to the bottom 123B. The width of the central sipe <NUM> is preferably at least <NUM> and no more than <NUM>.

As shown in <FIG>, each of the intermediate blocks <NUM> has a plurality of intermediate sipes <NUM>. The intermediate sipe <NUM> extends straight as a whole. In each of the intermediate blocks <NUM>, the plurality of intermediate sipes <NUM> are arranged in parallel to each other at intervals. The plurality of intermediate sipes <NUM> all slant relative to the tire-circumferential direction so as to be directed to the outer side in the tire-circumferential direction, as extending from the rear side to the front side. In other words, the intermediate sipe <NUM> extends in a direction which intersects the tire-circumferential direction. Each of both ends of the intermediate sipe <NUM> communicate with either the slanted groove <NUM> or the communication groove <NUM>.

The intermediate sipe <NUM> has a similar configuration to the aforementioned central sipe <NUM>. In other words, although omitted from illustration, the intermediate sipe <NUM> has similar portions to the wavy shape part <NUM>, the first sipe bridge <NUM>, and the second sipe bridge <NUM> of the central sipe <NUM>. Then, the period of the wavy shape part of the intermediate sipe <NUM> is fixed, and the amplitude is largest at the opening at the surface of the central block <NUM> and smallest at the bottom. The amplitudes of the openings, at the surfaces of the intermediate blocks <NUM>, of the plurality of intermediate sipes <NUM> are equal to each other. The width of the intermediate sipe <NUM> is substantially fixed from the opening to the bottom. Accordingly, in a cross-sectional view in the depth direction which is substantially orthogonal to the extending direction of the intermediate sipe <NUM>, the intermediate sipe <NUM> is linear from the opening to the bottom. The width of the intermediate sipe <NUM> is preferably at least <NUM> and no more than <NUM>.

<FIG> is a plan view schematically showing an opening 113A of a wavy shape in the shoulder sipe <NUM>, and shows amplitude ShA of the opening 113A. <FIG> is a plan view schematically showing a bottom 113B of a wavy shape in the shoulder sipe <NUM>, and shows amplitude ShB of the bottom 113B. <FIG> is a plan view schematically showing an opening 123A of a wavy shape in the central sipe <NUM>, and shows amplitude CeA of the opening 123A. <FIG> is a plan view schematically showing a bottom 123B of a wavy shape in the central sipe <NUM>, and shows amplitude CeB of the bottom 123B. <FIG> is a plan view schematically showing an opening 133A of a wavy shape in the intermediate sipe <NUM>, and shows amplitude MeA of the opening 133A. <FIG> is a plan view schematically showing a bottom 133B of a wavy shape in the intermediate sipe <NUM>, and shows amplitude MeB of the bottom 133B.

In the present embodiment, the above-mentioned amplitudes ShA, CeA, and MeA are not equal. Specifically, the amplitude ShA of the shoulder sipe <NUM> is the smallest. The amplitude CeA of the central sipe <NUM> and the amplitude MeA of the intermediate sipe <NUM> are equal to each other, or the amplitude CeA of the central sipe <NUM> is greater than the amplitude MeA of the intermediate sipe <NUM>. In other words, it is specified as "CeA ≧ MeA > ShA".

With the condition of "CeA ≧ MeA > ShA", these amplitudes CeA, MeA and ShA are preferably each at least <NUM> and no more than <NUM>.

In addition, the amplitude ShB of the bottom 113B of the shoulder sipe <NUM>, the amplitude CeB of the bottom 123B of the central sipe <NUM>, and the amplitude MeB of the bottom 133B of the intermediate sipe <NUM> are preferably each at least <NUM> and no more than <NUM>.

In addition, the ratio A/B for each sipe is preferably at least <NUM> and no more than <NUM>, where A is the amplitudes of the openings 113A, 123A, 133A of the respective sipes <NUM>, <NUM>, <NUM>, and B is the amplitudes of the bottoms 113B, 123B, 133B of the respective sipes <NUM>, <NUM>, <NUM>. In other words, each of ShA/ShB of the shoulder sipe <NUM>, CeA/CeB of the central sipe <NUM>, and MeA/MeB of the intermediate sipe <NUM> is preferably at least <NUM> and no more than <NUM>.

According to the claimed invention, the following effects are exerted.

The bottom of each of the sipes <NUM> in the present embodiment does not have a linear shape along the extending direction of the sipe <NUM>, but rather has a wavy shape. Upon stress acting on the block <NUM> of the tread surface <NUM> such as during braking or during starting off of the vehicle, both side portions on the sipe <NUM> of the block <NUM> tend to collapse according to the direction in which this stress acts. At this time, the bottom of the sipe <NUM> which has a wave shape as in the embodiment produces a force resisting stress and the forces is higher than that of the bottom of the sipe which has a linear shape. Therefore, the block <NUM> hardly distorts, and the decline in contact area of the surface of the block <NUM> is suppressed. For this reason, the traction improves. In addition, since distortion of the block <NUM> is suppressed, defects such as block chipping where a part or the entirety of the block <NUM> comes off is suppressed, whereby durability of the tire <NUM> improves.

In each of the sipes <NUM> of the present embodiment, the amplitude decreasing at a fixed rate of change from the opening to the bottom in the surface of each block <NUM> allows each sipe <NUM> to be linear from the opening to the bottom, in a cross-sectional view in the depth direction which is substantially orthogonal to the extending direction of each sipe <NUM>.

Accordingly, the bottom of the sipe <NUM> functions as the aforementioned starting point for collapse of the block <NUM>. In addition, since both side portions of the sipe <NUM> of the block <NUM> tend to engage, the traction improves. The improvement in traction improves cornering performance and handling stability.

It should be noted that the present invention is not limited to the above-mentioned embodiment, and even if performing modifications, improvements, etc. in the scope of the claims, it will be encompassed in the scope of the present invention.

Claim 1:
A pneumatic tire (<NUM>) comprising a tread (<NUM>), wherein:
the tread (<NUM>) includes blocks (<NUM>) having sipes (<NUM>) extending in a direction which intersects a tire-circumferential direction,
each of the sipes (<NUM>) has a wavy shape in an extending direction of the sipe (<NUM>), the sipe (<NUM>) has an opening at a surface of the block (<NUM>) and a bottom, and the wavy shape continues from the opening to the bottom, and
amplitude of the sipe (<NUM>) is largest at the opening and smallest at the bottom, and the amplitude decreases at a fixed rate of change from the opening toward the bottom, whereby the sipe (<NUM>) is linear from the opening to the bottom, in a cross-sectional view in a depth direction which is substantially orthogonal to the extending direction of the sipe (<NUM>),
characterized in that
a ratio As/Ab is at least <NUM> and no more than <NUM>, where AS is amplitude of the opening of the sipe (<NUM>) and Ab is amplitude of the bottom of the sipe (<NUM>).