Patent Description:
A pneumatic tire having stud pins inserted into a tread is also referred to as a studded tire or a spiked tire, and is mainly used for traveling on an icy and snowy road. In general, since the stud pin is formed of a metal material, the insertion of a large number of stud pins may deteriorate uniformity of the tire. It is therefore desirable that a structure that takes this point into consideration be employed, but no specific configuration suitable for the structure has not been proposed.

Patent Document <NUM> proposes a studded tire in which, when an area between a pair of tire meridians arranged at intervals of <NUM> % of a tire circumferential length on a tire equator line is defined as a band-shaped area, and a plurality of the band-shaped areas are arranged over the entire circumference of the tire so as to be shifted by one degree along a tire circumferential direction, the plurality of band-shaped areas include a dense area having four or more stud pins and a sparse area having three or less stud pins, and the dense area is intermittently present along the tire circumferential direction. Such intermittent presence of the dense area possibly causes deterioration of uniformity of the tire.

Further pneumatic tires with staggered insertion holes and studs in the tread surface are known from documents <CIT>, <CIT>, <CIT> and <CIT>.

It is therefore an object of the present invention to provide a pneumatic tire capable of suppressing deterioration of uniformity caused by the insertion of a stud pin.

A pneumatic tire according to the present invention includes a tread in which an insertion hole into which a stud pin is inserted is formed, in which the tread includes a plurality of main grooves continuously extending along a tire circumferential direction, and is divided into a shoulder area located on an outer side in a tire axial direction and a center area located on an inner side in the tire axial direction relative to a groove width center of a shoulder main groove located on an outermost side in the tire axial direction among the plurality of main grooves, and when an area of <NUM> % of a ground contact width centered on a tire equator in the center area is defined as an equatorial area, and an area between the equatorial area and the shoulder main groove is defined as an equatorial neighboring area, the insertion hole formed in the equatorial neighboring area located on one side in the tire axial direction and the insertion hole formed in the equatorial neighboring area located on an other side in the tire axial direction are arranged in a staggered manner along the tire circumferential direction and no main groove is provided in the equatorial area.

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

As illustrated in <FIG>, a pneumatic tire T (hereinafter, may be simply referred to as a "tire T") according to the present embodiment includes a pair of bead portions <NUM>, sidewalls <NUM> each extending outward in a tire radial direction from a corresponding one of the bead portions <NUM>, and a tread <NUM> connected to an outer end of each of the sidewalls <NUM> in the tire radial direction. The tire T further includes a carcass <NUM> provided between the pair of bead portions <NUM>, a belt <NUM> laminated on an outer side of the carcass <NUM> in the tire radial direction, and an inner liner <NUM> disposed on a tire inner surface.

Here, the tire radial direction is a direction along a diameter of the tire T and corresponds to a vertical direction in <FIG>. In <FIG>, an upper side is an outer side in the tire radial direction, and a lower side is an inner side in the tire radial direction. A tire axial direction is a direction parallel to a rotation axis of the tire T and corresponds to a horizontal direction in <FIG>.

A side adjacent to a tire equator TC is an inner side in the tire axial direction, and a side remote from the tire equator TC is an outer side in the tire axial direction. The tire equator TC is a virtual line located at a center of the tire T in the tire axial direction and orthogonal to the tire rotation axis as viewed from above. A tire circumferential direction is a direction around the rotation axis of the tire T.

A bead core 1a having an annular shape is embedded in each bead portion <NUM>. The bead core 1a includes a bundle member such as steel wires covered with rubber. A bead filler 1b is disposed adjacent to an outer side of the bead core 1a in the tire radial direction. The bead filler 1b includes rubber having a triangular cross section extending outward in the tire radial direction from the bead core 1a. A rim strip rubber <NUM> forming an outer surface of each bead portion <NUM> is provided on an outer side of the bead core 1a and an outer side of the bead filler 1b in the tire axial direction.

The carcass <NUM> extends in a toroidal shape across the pair of bead portions <NUM>. The carcass <NUM> is wound up from the inside to the outside in the tire axial direction so as to surround the bead cores 1a and the bead fillers 1b. The carcass <NUM> includes a carcass ply formed by coating carcass cords with rubber. The carcass cords are paralleled in a direction intersecting the tire circumferential direction (for example, in a direction at an angle of <NUM>° to <NUM>° with respect to the tire circumferential direction). A sidewall rubber <NUM> forming an outer surface of each sidewall <NUM> is provided on the outer side of the carcass <NUM> in the tire axial direction.

The belt <NUM> includes a plurality of belt plies 5a and 5b laminated on each other. Each of the belt plies 5a and 5b includes belt cords paralleled in a direction inclined relative to the tire circumferential direction and covered with rubber. The belt plies 5a and 5b are laminated such that their respective belt cords extend in different directions to intersect each other. A tread rubber <NUM> forming an outer surface of the tread <NUM> is provided on an outer side of the belt <NUM> in the tire radial direction. The inner liner <NUM> includes rubber that is highly airtight, such as butyl rubber. The inner liner <NUM> holds an internal pressure of the tire T.

An insertion hole <NUM> into which a stud pin is inserted is formed in the tread <NUM>. The tire T having a stud pin (not illustrated) inserted into each insertion hole <NUM> acts as a studded tire (also referred to as a spiked tire). In general, the stud pin is formed of a metal columnar member. The shape, material, size, and the like of the stud pin inserted into the tire T are not particularly limited. In the present embodiment, the insertion hole <NUM> is flask-shaped in cross section, but is not limited to such a shape.

A tread pattern illustrated in <FIG> is formed on an outer circumferential surface of the tread <NUM>. In the present embodiment, a tread pattern that is line-symmetric with respect to the tire equator TC and is shifted in phase in the tire circumferential direction is used. The tire T is a tire of a specified rotation direction type whose tire rotation direction is specified. An arrow RD indicates a tire rotation direction at the time of forward movement.

A front side RD1 in the rotation direction is also referred to as a leading side, and a rear side RD2 in the rotation direction is also referred to as a trailing side. The tire T need not necessarily have such a directional pattern, and may have a non-directional pattern. For example, the tire T may have a tread pattern formed point-symmetric with respect to a center point on the tire equator TC.

The tread <NUM> includes a plurality of main grooves <NUM> continuously extending along the tire circumferential direction. A groove width W <NUM> of the main grooves <NUM> on the outer circumferential surface of the tread <NUM> is, for example, equal to or greater than <NUM>. Of the plurality of main grooves <NUM>, a main groove <NUM> located on an outermost side in the tire axial direction is referred to as a shoulder main groove <NUM>. In the present embodiment, the number of the main grooves <NUM> included in the tread <NUM> is two, and these main grooves correspond to the shoulder main grooves <NUM>. Note that the tread <NUM> may include three or more main grooves. The tread <NUM> is divided into a shoulder area SA located on the outer side in the tire axial direction and a center area CA located on the inner side in the tire axial direction relative to a groove width center of the shoulder main groove <NUM>.

The pair of shoulder main grooves <NUM> are arranged with the tire equator TC interposed between the shoulder main grooves <NUM>. A distance D11 from the groove width center of the shoulder main groove <NUM><NUM> to the tire equator TC is, for example, <NUM> % to <NUM> % of a ground contact half width HW. The ground contact half width HW corresponds a distance in the tire axial direction from the tire equator TC to a ground contact end TE.

The ground contact end TE corresponds to an outermost position of a ground contact surface in the tire axial direction in a case where the tire T mounted on a normal rim and inflated to a normal internal pressure is placed perpendicularly to a flat road surface, and a normal load is applied to the tire T. A ground contact width TW corresponds to a distance in the tire axial direction between the pair of ground contact ends TE, and a half of the ground contact width TW corresponds to the ground contact half width HW.

The normal rim is a "standard rim" in JATMA standard, a "Design Rim" in TRA standard, or a "Measuring Rim" in ETRTO standard. The normal internal pressure corresponds to a "maximum pneumatic pressure" in JATMA standard, a "maximum value" described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA standard, or "INFLATION PRESSURE" in ETRTO standard.

The normal load is a load defined for each tire by each standard in the standard system including the standard on which the tire is based. The normal load is the maximum load capacity in the case of JATMA, the maximum value described in the above table in the case of TRA, and "LOAD CAPACITY" in the case of ETRTO, and when the tire is for a passenger car, the normal load is <NUM> % of the above-described load.

<FIG> is an enlarged view of a main part of <FIG>, illustrating extracted lands provided in the center area CA. In the tire T, when an area of <NUM> % of the ground contact width TW centered on the tire equator TC in the center area CA is defined as an equatorial area RA, and an area between the equatorial area RA and the shoulder main groove <NUM> is defined as an equatorial neighboring area NA, the insertion hole <NUM> formed in the equatorial neighboring area NA located on one side in the tire axial direction and the insertion hole <NUM> formed in the equatorial neighboring area NA located on the other side in the tire axial direction are arranged in a staggered manner along the tire circumferential direction.

Such a configuration can prevent uneven distribution of the insertion holes <NUM> in the center area CA of the tread <NUM> and thus can suppress deterioration of uniformity caused by the insertion of the stud pins. In particular, deterioration of uniformity in tire shape in the tire circumferential direction can be suppressed, so that it is possible to suppress deterioration of fuel efficiency (rolling resistance) or deterioration of noise performance. Further, the stud pins are evenly arranged in the tread <NUM>, so that it is possible to enhance a scratching effect of the stud pins on an icy and snowy road.

The equatorial area RA is provided with a rib <NUM> continuously extending in the tire circumferential direction. This makes it possible to ensure the ground contact surface of the equatorial area RA to which a high load is applied during driving or braking on the icy and snowy road and satisfactorily enhance grip. Instead of the rib <NUM>, a block array in which a plurality of blocks is arranged may be provided in the equatorial area RA.

According to the invention, no insertion hole <NUM> is formed in the equatorial area RA. Therefore, the insertion holes <NUM> formed in the center area CA are arranged not in the equatorial area RA but in the equatorial neighboring area NA. The configuration where no stud pin is disposed in the equatorial area RA is suitable for ensuring the ground contact surface of the equatorial area RA to which a high load is applied during driving or braking on the icy and snowy road. Furthermore, in order to ensure the ground contact surface of the equatorial area RA, no main groove is provided in the equatorial area RA.

A center point CP (midpoint) between the insertion holes <NUM> formed in the equatorial neighboring area NA located on one side in the tire axial direction and a center point CP between the insertion holes <NUM> formed in the equatorial neighboring area NA located on the other side in the tire axial direction are alternately arranged in the tire circumferential direction such that a line sequentially connecting the center points CP along the tire circumferential direction becomes a wavy line (zigzag line).

As illustrated in <FIG>, the insertion hole <NUM> formed in the equatorial neighboring area NA and the insertion hole <NUM> formed in the shoulder area SA adjacent to the equatorial neighboring area NA with the shoulder main groove <NUM> interposed between the equatorial neighboring area NA and the shoulder area SA are arranged in a staggered manner along the tire circumferential direction. This makes it possible to effectively suppress deterioration of uniformity caused by the insertion of the stud pins. In the present embodiment, such a staggered arrangement of the insertion holes <NUM> is applied to each of a pair of tread half portions, which enhances the above-described improvement effect.

As illustrated in <FIG> and <FIG>, the tread <NUM> includes a lateral groove <NUM> extending across the shoulder main groove <NUM> and dividing the tread <NUM> into a plurality of band-shaped areas BA within a range where the lateral groove <NUM> extends. A groove width W12 of the lateral groove <NUM> at a connection portion between the lateral groove <NUM> and the main groove <NUM> is, for example, equal to or greater than <NUM>. A plurality of the lateral grooves <NUM> are formed at intervals in the tire circumferential direction.

The lateral groove <NUM> extends outward in the tire axial direction from one end located in the center area CA to the ground contact end TE across the shoulder main groove <NUM>. The lateral groove <NUM> extends obliquely relative to the tire axial direction. The lateral groove <NUM> is gently curved so as to be a protruding shape toward the trailing side (the rear side RD2 in the rotation direction) as a whole.

<FIG> is an enlarged view of the main part of <FIG>, schematically illustrating the band-shaped area BA defined by the lateral groove <NUM>. The band-shaped area BA is included in each of the pair of tread half portions defined by the tire equator TC, but <FIG> illustrates the band-shaped area BA included in one of the pair of tread half portions (the tread half located on the right side of <FIG>).

As described above, the lateral groove <NUM> divides the tread <NUM> into the plurality of band-shaped areas BA within the range where the lateral groove <NUM> extends. The band-shaped area BA extends in a band shape across the center area CA and the shoulder area SA. The band-shaped areas BA are curved along the lateral groove <NUM>. Each band-shaped area BA includes one shoulder block <NUM> and one block-shaped land <NUM> to be described later.

The band-shaped area BA includes a band-shaped area BAs including the insertion hole <NUM> formed in the shoulder area SA and a band-shaped area BAc including the insertion hole <NUM> formed in the center area CA. The band-shaped area BAs includes no insertion hole <NUM> formed in the center area CA, and the band-shaped area BAc includes no insertion hole <NUM> formed in the shoulder areas SA.

In the tire T, in at least one of the pair of tread half portions defined by the tire equator TC, the band-shaped areas BAs including the insertion hole <NUM> formed in the shoulder area SA and the band-shaped areas BAc including the insertion hole <NUM> formed in the center area CA are alternately arranged along the tire circumferential direction.

<FIG> illustrates an example where the band-shaped areas BAs and the band-shaped areas BAc are alternately arranged on a one-to-one basis, but the present invention is not limited to such an example. For example, as illustrated in <FIG>, a plurality of the band-shaped areas BAs may be arranged between the band-shaped areas BAc in the tire circumferential direction.

Alternatively, a plurality of the band-shaped areas BAc may be arranged between the band-shaped areas BAs in the tire circumferential direction. In this case, it is preferable that the number of the band-shaped areas BAs or the band-shaped areas BAc arranged continuously be equal to or less than three. That is, it is preferable that the band-shaped areas BAs and the band-shaped areas BAc be alternately arranged on a one-to-one, one-to-two, one-to-three, two-to-two, two-to-three or three-to-three basis.

The band-shaped area BA may include a band-shaped area in which the insertion hole <NUM> is formed in both the shoulder area SA and the center area CA, or a band-shaped area in which the insertion hole <NUM> is formed in neither the shoulder area SA nor the center area CA. Note that, in the tread half portion, the number of such band-shaped areas is preferably less than <NUM> % and more preferably less than <NUM> % of the number of the band-shaped areas BA on the entire circumference of the tire. That is, in the tread half portion, <NUM> % or more of the band-shaped areas BA on the entire circumference of the tire is preferably occupied by the band-shaped areas BAs and the band-shaped areas BAc.

The number of the insertion holes <NUM> formed in the shoulder area SA is preferably greater than the number of the insertion holes <NUM> formed in the center area CA. This makes it possible to enhance the scratching effect of the shoulder area SA to which a high load is applied during turning and enhance steering stability. It is sufficient that such a relationship be satisfied when at least one (preferably both) of the tread half portions is viewed along the entire circumference of the tire. In the tread half portion, a difference between the number of the insertion holes <NUM> formed in the shoulder area SA and the number of the insertion holes <NUM> formed in the center area CA is, for example, preferably equal to or greater than three, and more preferably equal to or greater than five.

As illustrated in <FIG>, in the present embodiment, the insertion hole <NUM> (strictly speaking, the center of the insertion hole <NUM>) formed in the shoulder area SA is disposed in a section S interposed in the tire circumferential direction between the center point CP between the insertion holes <NUM> formed in the center area CA and the insertion hole <NUM> adjacent to the trailing side (the rear side RD2 in the rotation direction) of the center point CP. Such a configuration can enhance the scratching effect during driving on the icy and snowy road and satisfactorily enhance grip.

In the shoulder area SA, the plurality of shoulder blocks <NUM> defined by the lateral groove <NUM> are arranged in the tire circumferential direction. As a result, a block edge of each shoulder block <NUM> exerts an edge effect to enhance traveling performance on the icy and snowy roads. In the shoulder area SA, shoulder blocks <NUM> in which the insertion hole <NUM> is formed and shoulder blocks <NUM> in which no insertion hole <NUM> is formed are alternately arranged in the tire circumferential direction.

Such shoulder blocks <NUM> are alternately arranged on a one-to-one basis, or may be alternately arranged on a one-to-two, one-to-three, two-to-two, two-to-three or three-to-three basis. In order to suppress deterioration of uniformity, the number of the insertion holes <NUM> formed in each shoulder block <NUM> is preferably equal to or less than one.

In the center area CA, the plurality of the block-shaped lands <NUM> defined by the lateral groove <NUM> are arranged in the tire circumferential direction. As a result, a block edge of each block-shaped land <NUM> exerts an edge effect to enhance traveling performance on the icy and snowy roads. In the center area CA, block-shaped lands <NUM> in which the insertion hole <NUM> is formed and block-shaped lands <NUM> in which no insertion hole <NUM> is formed are alternately arranged in the tire circumferential direction.

Such block-shaped lands <NUM> are alternately arranged on a one-to-one basis, or may be alternately arranged on a one-to-two, one-to-three, two-to-two, two-to-three or three-to-three basis. In order to suppress deterioration of uniformity, the number of the insertion holes <NUM> formed in each block-shaped land <NUM> is preferably equal to or less than one.

The shoulder block <NUM>, the block-shaped land <NUM>, and the rib <NUM> each have a plurality of sipes <NUM> formed therein. The sipes <NUM> are each constituted by a cut-away portion having a width equal to or less than <NUM>. Each of the sipes <NUM> may have a two-dimensional shape with no change in shape in a depth direction, or may have a three-dimensional shape with a portion changed in shape in the depth direction.

In each shoulder block <NUM>, a sipe <NUM> extending along the tire axial direction is formed. The plurality of sipes <NUM> extending approximately in parallel to the lateral groove <NUM> that define the shoulder block <NUM> are formed at intervals in the thickness direction thereof. A sipe extending in parallel to the tire circumferential direction or a sipe extending obliquely relative to the tire circumferential direction may be formed in the shoulder block <NUM>.

In a case where the shoulder blocks <NUM> are arranged at variable pitches in the tire circumferential direction, that is, in a case where a pitch element, which is the basis of repetition of a pattern design, has various pitch lengths (lengths in the tire circumferential direction), the number of the sipes <NUM> in a shoulder block <NUM> having the smallest length in the tire circumferential direction is preferably less than the number of the sipes <NUM> in a shoulder block <NUM> having the largest length in the tire circumferential direction. Such a configuration makes a difference in ground contact area per unit area in the shoulder block <NUM> due to the difference in pitch smaller, so that it is suitable for reducing uneven wear of each block.

The center area CA is provided with a land including the rib <NUM> located at the center and an array of the block-shaped lands <NUM> located on both sides of the rib <NUM>. In the center area CA, lateral grooves <NUM> extending approximately linearly and lateral grooves <NUM> bent in an L shape are alternately arranged in the tire circumferential direction, and the block-shaped land <NUM> is defined by such lateral grooves <NUM>. In the equatorial neighboring area NA, block-shaped lands <NUM> including a sipe <NUM> inclined in the same direction as the direction of the lateral groove <NUM> defining the block-shaped land <NUM> and block-shaped lands <NUM> including a sipe <NUM> inclined in the opposite direction are alternately arranged in the tire circumferential direction. The rib <NUM> has a sipe <NUM> extending approximately in parallel to the tire axial direction.

The pneumatic tire T according to the present embodiment is equivalent of a normal studded tire (under a condition where no stud pins are inserted into the insertion holes <NUM>) except that the insertion holes <NUM> are arranged as described above, and any known material, shape, structure, and the like may be used. The pneumatic tire T may have the stud pins inserted into the insertion holes <NUM> of the tread <NUM>.

The embodiment according to the present invention has been described with reference to the drawings. However, this embodiment should not limit specific configurations according to the present invention.

Claim 1:
A pneumatic tire (T) comprising a tread (<NUM>) in which an insertion hole (<NUM>) into which a stud pin is inserted is formed,
wherein the tread (<NUM>) includes a plurality of main grooves (<NUM>) continuously extending along a tire circumferential direction, and is divided into a shoulder area (SA) located on an outer side in a tire axial direction and a center area (CA) located on an inner side in the tire axial direction relative to a groove width center of a shoulder main groove (<NUM>) located on an outermost side in the tire axial direction among the plurality of main grooves (<NUM>), and
when an area of <NUM> % of a ground contact width (TW) centered on a tire equator (TC) in the center area (CA) is defined as an equatorial area (RA), and an area between the equatorial area (RA) and the shoulder main groove (<NUM>) is defined as an equatorial neighboring area (NA), the insertion hole (<NUM>) formed in the equatorial neighboring area (NA) located on one side in the tire axial direction and the insertion hole (<NUM>) formed in the equatorial neighboring area (NA) located on an other side in the tire axial direction are arranged in a staggered manner along the tire circumferential direction,
where:
the ground contact width (TW) corresponds to a distance in the tire axial direction between a pair of ground contact ends (TE);
the ground contact end (TE) corresponds to an outermost position of a ground contact surface in the tire axial direction in a case where the tire (T) mounted on a normal rim and inflated to a normal internal pressure is placed perpendicularly to a flat road surface, and a normal load is applied to the tire (T);
the normal rim is a "standard rim" in JATMA standard, a "Design Rim" in TRA standard, or a "Measuring Rim" in ETRTO standard;
the normal internal pressure corresponds to a "maximum pneumatic pressure" in JATMA standard, a "maximum value" described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA standard, or "INFLATION PRESSURE" in ETRTO standard;
the normal load is the maximum load capacity in the case of JATMA, the maximum value described in the above table in the case of TRA, and "LOAD CAPACITY" in the case of ETRTO, and when the tire is for a passenger car, the normal load is <NUM> % of the above-described load,
characterised in that
no main groove is provided in the equatorial area (RA).