CN114599528A

CN114599528A - Pneumatic tire

Info

Publication number: CN114599528A
Application number: CN202080074749.4A
Authority: CN
Inventors: 芝井孝志
Original assignee: Yokohama Rubber Co Ltd
Current assignee: Yokohama Rubber Co Ltd
Priority date: 2019-11-01
Filing date: 2020-09-29
Publication date: 2022-06-07
Anticipated expiration: 2040-09-29
Also published as: CN114599528B; FI20225425A1; FI130329B; WO2021085005A1; JP7172954B2; JP2021070450A

Abstract

Provided is a pneumatic tire, wherein a tread surface of a tread portion is provided with a stud, and the riding comfort performance on a dry road surface can be improved while the performance on ice is improved. In a pneumatic tire in which cleats (P) are implanted on a tread surface of a tread portion (1), when a region defined between a pair of tire meridians arranged at an interval of 1/4 of a tire contact patch length on a tire equator (CL) is defined as a band-shaped region (A), and a plurality of band-shaped regions (A) are arranged in the tire circumferential direction sequentially shifted by 1 degree over the entire circumference of the tire, the number N of cleats (P) included in each band-shaped region (A) is 4.0% or less of the total number N of cleats (P) over the entire circumference of the tire in all band-shaped regions of the plurality of band-shaped regions (A), and the number N of cleats included in the band-shaped region (A) is 2.0% or more of the total number N in band-shaped regions of 2/3 or more of the plurality of band-shaped regions (A).

Description

Pneumatic tire

Technical Field

The present invention relates to a pneumatic tire in which a cleat is implanted on a tread surface of a tread portion.

Background

In severe winter regions such as northern europe and russia, studded tires (studded tires) are mainly used as winter tires. In a studded tire, a tread portion is provided with a plurality of insertion holes for inserting studs, and the studs are inserted into the insertion holes (see, for example, patent document 1). When the anti-skid nails run on the ice and snow road surface, the anti-skid nails can play the effect of grabbing the ice and snow road surface, so the performance on the ice can be improved. On the other hand, when the vehicle is traveling on a road surface other than ice or snow (particularly, a dry paved road surface), the impact of the hard stud hitting the paved road surface is transmitted as a feeling of impact, which may cause deterioration of riding comfort. In addition, even in winter in severe winter, there is a chance that the vehicle will travel on a paved road surface (dry road surface) other than an icy or snowy road surface at a not-infrequent frequency. Therefore, in the studded tire, a measure for improving the riding comfort performance on a dry road surface while effectively exhibiting the running performance on an icy or snowy road surface (particularly, the traction performance on ice) is demanded.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2018-187960

Disclosure of Invention

Problems to be solved by the invention

The invention aims to provide a pneumatic tire which is provided with a stud implanted on a tread surface of a tread portion and can improve the performance on ice and the riding comfort performance on a dry road surface.

Means for solving the problems

The pneumatic tire of the present invention for achieving the above object includes: a tread portion extending in a tire circumferential direction and having a ring shape; a pair of side wall portions disposed on both sides of the tread portion; and a pair of bead portions disposed on the inner side of the sidewall portion in the tire radial direction, wherein studs are implanted on the tread surface of the tread portion, wherein, when a region defined between a pair of tire meridians disposed at a distance of 1/4 from the tire equator line is a band-shaped region and a plurality of band-shaped regions are arranged in the tire circumferential direction with an angle of 1 degree sequentially shifted over the entire circumference of the tire, the number N of studs included in each band-shaped region is 4.0% or less of the total number N of studs in the entire circumference of the tire in all band-shaped regions of the plurality of band-shaped regions, and the number N of studs included in the band-shaped region is 2.0% or more of the total number N in the band-shaped region of 2/3 or more of the plurality of band-shaped regions.

ADVANTAGEOUS EFFECTS OF INVENTION

In the present invention, by providing the stud as described above, it is possible to effectively improve the on-ice performance and to satisfactorily exhibit the riding comfort performance on a dry road surface. Specifically, in all the belt-shaped regions, the ratio of the number N of the studs to the total number N of the studs is suppressed to 4.0% or less, so that the feeling of impact when the studs come into contact with the road surface when running on a dry road surface can be suppressed, and the ride comfort can be improved. On the other hand, since the band-shaped region in which the ratio of the number N of the studs to the total number N of the studs is set to an appropriate range of 2.0% or more is sufficiently provided over the entire circumference of the tire, the on-ice performance can be satisfactorily exhibited.

In the present invention, it is preferable that the total number of the cleats is 135 to 250. By providing an appropriate number of cleats in this manner, it is advantageous to improve the riding comfort on dry roads while effectively exhibiting the traction performance on ice.

In the present invention, it is preferable that a concentrated region of 1 or more and 1/3 or less out of the plurality of band-shaped regions is present among the plurality of band-shaped regions, and the concentrated region is a band-shaped region in which the number N of cleats included in the band-shaped region is 3.0% or more of the total number N. By providing the concentrated region in which the number of cleats is large and the performance on ice is excellent in this manner, the performance on ice can be further improved. On the other hand, since the number of concentrated regions is suppressed to 1/3 or less among the plurality of belt-like regions, the ride comfort on a dry road surface can be satisfactorily exhibited even if concentrated regions are provided.

At this time, it is preferable that 2 or more dense regions exist in the concentrated region, and the interval between the dense regions adjacent in the tire circumferential direction is 100% or more of the tire contact patch length, and the dense region is a band region in which the number N of cleats included in the band region is 3.5% or more of the total number N. The dense region is particularly excellent in on-ice performance also in the concentrated region, so that further improvement in on-ice performance can be achieved. On the other hand, since the distance between the dense regions is set to be larger than the tire contact patch length, the dense region existing in the contact patch when the tire rolls is always 1 spot or less, and the riding comfort performance on a dry road surface can be satisfactorily exhibited even if the dense region is provided.

Further, it is preferable that the average protrusion amount Px of the cleats included in the concentrated region and the average protrusion amount Pav of the cleats in the region other than the concentrated region satisfy the relationship of Px ≦ 0.9 × Pav. By setting the projecting amount of the stud in this manner, the projecting amount of the stud can be suppressed to be low in a concentrated region where the number of studs is relatively large, which is advantageous for the comfortable ride performance on a dry road surface to be exhibited well.

In the present invention, when a region located on the tire equator among regions obtained by dividing the tread surface of the tread portion by 3 in the tire width direction is set as a center region and a pair of regions located on both sides of the center region in the tire width direction are set as shoulder regions, it is preferable that at least 1 stud is present in each of the center region and the pair of shoulder regions in a band-shaped region in which the number n of studs is 3 or more. By arranging the studs in a distributed manner in the tire width direction in this manner, a force for scraping an icy or snowy road surface can be effectively obtained over the entire region in the tire width direction, which is advantageous for improving the on-ice performance. Further, uniformity in the tire width direction can be improved.

In the present invention, the "ground contact length" refers to a length in the tire circumferential direction on the tire equator of a ground contact area formed when a normal load is applied while a tire rim is assembled to a normal rim and the normal internal pressure is applied. The "ground contact ends" refer to both ends of the ground contact region in the tire axial direction. The "regular rim" is a rim specified for each tire in a specification system including a specification based on which the tire is based, and for example, is a standard rim in the case of JATMA, a "design rim" in the case of TRA, or a "measurement rim" in the case of ETRTO. The "normal internal PRESSURE" is an air PRESSURE specified for each TIRE in a specification system including a specification based on the TIRE, and is set to a maximum air PRESSURE in the case of JATMA, a maximum value in the table "TIRE LOAD limit AT variance with VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and an "INFLATION PRESSURE" in the case of ETRTO, but is set to 250kPa in the case of a passenger vehicle. The "normal LOAD" is a LOAD specified for each TIRE in a specification system including a specification based on the TIRE, and is a maximum LOAD capacity in the case of JATMA, a maximum value in the table "TIRE LOAD limit AT variance stability requirements" in the case of TRA, and a LOAD capacity in the case of ETRTO, but is a LOAD corresponding to 80% of the LOAD in the case of a passenger vehicle.

Drawings

Fig. 1 is a radial cross-sectional view of a pneumatic tire constituted by an embodiment of the present invention.

Fig. 2 is a front view showing a tread surface of a pneumatic tire constituted by an embodiment of the present invention.

Fig. 3 is a cross-sectional view schematically showing an example of a stud planted in a tread portion.

Fig. 4 is an explanatory diagram schematically showing a variation in the number of cleats per strip-shaped zone.

Detailed Description

Hereinafter, the configuration of the present invention will be described in detail with reference to the drawings.

As shown in fig. 1, the pneumatic tire of the present invention includes a tread portion 1, a pair of side wall portions 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3 disposed on the inner side of the side wall portions 2 in the tire radial direction. In fig. 1, reference symbol CL denotes a tire equator, and reference symbol E denotes a ground contact end. Fig. 1 is a meridian cross-sectional view, and therefore is not depicted, but the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction and are annular, thereby constituting an annular basic structure of the pneumatic tire. In the following, the description using fig. 1 is based on the illustrated meridian cross-sectional shape, but each tire constituting member extends in the tire circumferential direction and is annular.

A carcass layer 4 is provided between the pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the vehicle inner side to the outer side around bead cores 5 arranged in the respective bead portions 3. Further, a bead filler 6 is disposed on the outer periphery of the bead core 5, and the bead filler 6 is enclosed by the main body portion and the folded-back portion of the carcass layer 4. On the other hand, a plurality of (2 in fig. 1) belt layers 7 are embedded in the tread portion 1 on the outer circumferential side of the carcass layer 4. Each belt layer 7 includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and is disposed such that the reinforcing cords intersect with each other between layers. In the belt layer 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set to a range of, for example, 10 ° to 40 °. Further, a belt reinforcing layer 8 is provided on the outer peripheral side of the belt layer 7. The belt reinforcing layer 8 includes organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer 8, the angle of the organic fiber cord with respect to the tire circumferential direction is set to, for example, 0 ° to 5 °.

The present invention is applied to a pneumatic tire having such a general cross-sectional structure, but the basic structure thereof is not limited to the above structure. In addition, the present invention relates to the arrangement of the studs P in the pneumatic tire in which the studs P are implanted on the tread surface of the tread portion 1, and therefore, the structure (tread pattern) of the grooves and land portions formed on the surface of the tread portion 1 is not particularly limited.

Further, the pneumatic tire shown in fig. 2 has a tread pattern in which a plurality of land portions 13 are defined by a plurality of lateral grooves 11 extending in the tire width direction and a plurality of circumferential grooves 12 extending in the tire circumferential direction. In the illustrated example, the lateral grooves 11 include a first lateral groove 11a extending obliquely with respect to the tire width direction, one end of the first lateral groove 11a being located on the tire equator CL, the other end thereof extending across the ground contact edge E on one side in the tire width direction, and a second lateral groove 11b extending obliquely with respect to the tire width direction, one end thereof being located on the tire equator CL, the other end thereof extending across the ground contact edge E on the other side in the tire width direction. The first lateral grooves 11a and the second lateral grooves 11b are arranged such that one ends of the first lateral grooves 11a and one ends of the second lateral grooves 11b are alternately arranged in the tire circumferential direction on the tire equator CL, and the first lateral grooves 11a and the second lateral grooves 11b are substantially V-shaped. The circumferential groove 12 extends obliquely with respect to the tire circumferential direction at a middle portion in the longitudinal direction of each lateral groove 11 so as to connect the lateral grooves 11 adjacent to each other in the tire circumferential direction. A center land portion 13a is defined on the inner side of the circumferential groove 12 in the tire width direction, and a shoulder land portion 13b (shoulder block) is defined on the outer side of the circumferential groove 12 in the tire width direction. In the illustrated example, an auxiliary groove 14 is provided at a middle portion in the longitudinal direction of each circumferential groove 12, and one end of the auxiliary groove 14 communicates with the circumferential groove 12, extends from the circumferential groove 12 toward the tire equator CL, and terminates at the other end in the center land portion 13 a. Further, a plurality of sipes 14 are provided in each land portion 13. The stud P can be planted in any land portion 13.

The stud P is fitted into a fitting hole for a stud provided on the tread surface of the tread portion 1. The insertion of the stud P is performed by inserting the stud P into the insertion hole in a state where the insertion hole is expanded, and then releasing the expansion of the insertion hole. Fig. 3 is a sectional view schematically showing a state where the stud P is planted in the planting hole of the tread portion 1. In the illustrated example, a stud P of a double flange type is described as the stud P, but a stud P of another structure such as a single flange type may be used.

As illustrated in fig. 3, the cleat P is composed of a cylindrical body portion P1, a tread-side flange portion P2, a bottom-side flange portion P3, and a top portion P4. The diameter of the tread-side flange portion P2 and the bottom-side flange portion P3 is larger than the diameter of the body portion P1, the tread-side flange portion P2 is formed on the tread side (outer side in the tire radial direction) of the body portion P1, and the bottom-side flange portion P3 is formed on the bottom side (inner side in the tire radial direction) of the body portion P1. The apex P4 projects radially outward from the tread-side flange P2 at the pin (center of the stud P). In a state where the stud P is planted in the tread portion 1, the top portion P4 protrudes beyond the tread surface, and therefore, the stud P can dig into an icy or snowy road surface and exhibit on-ice traction. The top portion P4 is made of a material (e.g., tungsten compound) harder than the other portions (the body portion P1, the tread-side flange portion P2, and the bottom-side flange portion P3) made of aluminum or the like, for example. In the present invention, the number of cleats P included in a band-shaped area described later is defined, and when at least a part of the apex portion P4 is present in the band-shaped area described later, the number is calculated as the number included in the band-shaped area.

In the present invention, a region defined between a pair of tire meridians arranged so that a distance on the tire equator CL is 1/4 of the tire contact patch length is defined as a band-shaped region a (for example, see a hatched portion in fig. 2) independently of a tread pattern formed on the surface of the tread portion 1. As schematically shown in fig. 4, a plurality of band-shaped regions a (a1, a2, A3 · · · · · · · · · are arranged over the entire circumference of the tire with an angle offset by 1 ° in order in the tire circumferential direction, and the number n of the studs P included in each band-shaped region a (a1, a2, A3 · · · · · · · · · · · · · · · · is measured. Fig. 4 schematically shows the arrangement of the band-shaped regions a, and details of the tread pattern formed in the tread portion 1 and a specific arrangement of the stud P are omitted. Note that the band-shaped region a after the reference symbol a3 is omitted. Reference symbol R in the drawing denotes a tire circumferential direction.

In all the band-shaped regions a thus defined, the number N of the studs P included in each band-shaped region a is set to 4.0% or less of the total number N of studs P over the entire circumference of the tire. For example, in the example shown in fig. 4, the number n of the cleats P is 7 or less. In the example of fig. 4, the total number N is 190, and 4.0% of the total number N is 7.6, so that the example of fig. 4 satisfies the above-described conditions. In the example of fig. 2, when the total number N is 190, the number N of the cleats P in the 3-point strip-shaped region a (hatched portion) surrounded by the one-dot chain line is 7 or less, and the above-described condition is satisfied. On the other hand, in the band-shaped region a of 2/3 or more out of the plurality of band-shaped regions a, the number N of the cleats P included in the band-shaped region a is set to 2.0% or more of the total number N of the cleats P. For example, when the total number N is 190, 2.0% of the total number N is 3.8, and therefore, in the example of fig. 4, the above condition is satisfied if the band-shaped region a in which 4 or more cleats P are provided is 2/3 or more out of the plurality of band-shaped regions a. In this way, in all the belt-shaped regions a, the ratio of the number N of the cleats P to the total number N of the cleats P is suppressed to 4.0% or less, which is low, so that the feeling of impact when the cleats P are in contact with the road surface when running on a dry road surface can be suppressed, and the riding comfort can be improved. On the other hand, since the band-shaped region a in which the ratio of the number N of the studs P to the total number N of the studs P is set to an appropriate range of 2.0% or more is sufficiently provided over the entire circumference of the tire, the on-ice performance can be satisfactorily exhibited.

Further, in the plurality of band-shaped regions a, if a region in which the number N of the cleats P included in the band-shaped region a is 3.0% or more of the total number N of the cleats P is divided as the concentrated region a ', the concentrated region a' preferably exists at 1 or more in the tire circumferential direction. In the example shown in fig. 4, as described above, the total number N is 190, and 3.0% of the total number N is 5.7, so that the band-shaped region a provided with 6 or more cleats P corresponds to the concentrated region a' in the example of fig. 4. In the 3-point band-shaped region a (hatched portion) shown in fig. 2, a region where the number n of the cleats P is 6 or 7 corresponds to the concentrated region a'. In fig. 2, the region where the number n of cleats P is 7 also corresponds to a dense region a ″ described later, and therefore the reference numeral in the drawing is denoted by a (a ″), and this region also corresponds to a concentrated region a'. In the case where a plurality of concentration regions a 'are provided, it is preferable to suppress the concentration regions a' to 1/3 or less among the plurality of strip regions a. Since the number n of the cleats P is larger in the concentrated region a 'than in the other band-shaped regions a and the on-ice performance is excellent, the on-ice performance can be further improved by providing such concentrated region a'. On the other hand, since the number of the concentrated regions a 'is suppressed to 1/3 or less among the plurality of belt-shaped regions a, the ride comfort on a dry road surface can be satisfactorily exhibited even if the concentrated regions a' are provided. If the number of the concentrated regions a 'exceeds 1/3 in the plurality of belt-shaped regions a, the concentrated regions a' in which the number of the cleats P is large, which may cause a feeling of impact during traveling, increase, and it is difficult to exhibit a good riding comfort.

In the concentrated region a', if a region in which the number N of the cleats P included in the band-shaped region is 3.5% or more of the total number N of the cleats P is divided into the dense regions a ″, it is preferable that the dense regions a ″ exist at 1 or more positions in the tire circumferential direction. In the example shown in fig. 4, as described above, the total number N is 190, and 3.5% of the total number N is 6.7, so that the band-shaped region a provided with 7 or more cleats P corresponds to the concentrated region a' in the example of fig. 4. In the 3-point band-shaped region a (hatched portion) shown in fig. 2, a region where the number n of the cleats P is 7 corresponds to the concentrated region a ″. When a plurality of dense regions a "are provided, the interval between the adjacent dense regions a" in the tire circumferential direction is preferably 100% or more of the tire contact patch length. The dense region a ″ is also excellent particularly in the on-ice performance in the concentrated region a', so that further improvement in the on-ice performance can be achieved. On the other hand, since the interval between the dense areas a "is made larger than the tire contact patch length, the dense area a" existing in the contact patch when the tire rolls is 1 or less, and the riding comfort performance on a dry road surface can be satisfactorily exhibited even if the dense area a "is provided. If the interval between the dense areas a "is smaller than 100% of the contact patch length, a large number of dense areas a" in which the cleats P are likely to cause a feeling of impact during traveling may be present in the contact patch, and it is therefore difficult to exhibit satisfactory riding comfort. Further, the intervals of the dense regions a "from each other are lengths in the tire circumferential direction between tire meridian lines opposed between adjacent dense regions a".

The studs P may be arranged as described above, but the total number of studs in the entire tire is preferably 135 to 250, and more preferably 135 to 200. By providing an appropriate number of cleats P on the entire tire as described above, it is advantageous to effectively exhibit the on-ice performance and to exhibit the riding comfort performance satisfactorily. If the total number of the studs is less than 135, the traction performance on ice cannot be sufficiently improved. If the total number of the cleats exceeds 250, the riding comfort performance cannot be sufficiently exhibited.

As shown in fig. 2, in the case where the region on the tire equator CL in the region obtained by dividing the tread surface (the region between the ground contact edges E on both sides in the tire width direction) of the tread portion 1 by 3 in the tire width direction is defined as the center region Ce, and the pair of regions on both sides in the tire width direction of the center region Ce are defined as the shoulder regions Sh, it is preferable that at least 1 stud P is present in each of the center region Ce and the pair of shoulder regions Sh in the band-shaped region a in which the number n of studs P is 3 or more. By disposing the studs in a distributed manner in the tire width direction in this manner, a force for scratching an icy or snowy road surface can be effectively obtained over the entire region in the tire width direction, which is advantageous in improving the on-ice performance. Further, uniformity in the tire width direction can be improved. For example, when the total number N of the studs P is 135, the number N of the studs P is 3 or more (135 × 0.020 — 2.7) in the band-shaped region a in which the number N of the studs P is 2.0% or more of the total number N. In this case, if the above-described dispersed arrangement of the studs P is adopted, at least 1 stud P is disposed in each of the central region Ce and the pair of shoulder regions Sh in the band-shaped region of not less than 2/3 of the plurality of band-shaped regions a. Therefore, it is very effective for improving the on-ice performance.

The amounts of projection h of the studs P may be uniform, but when the average of the amounts of projection h of the studs P included in the concentrated region a 'is defined as the average amount of projection Px and the average of the amounts of projection h of the studs P disposed in the regions other than the concentrated region a' is defined as the average amount of projection Pav, it is preferable that Px is less than or equal to 0.9 × Pav. By setting the projecting amount h of the stud P in this manner, the projecting amount of the stud can be suppressed low in the concentrated region a' where the number of studs is relatively large, which is advantageous for improving the riding comfort. Further, from the viewpoint of sufficiently securing the on-ice performance, it is preferable that the relation Px ≧ 0.7 XPav is satisfied.

The present invention will be further described with reference to the following examples, but the scope of the present invention is not limited to these examples.

Examples

11 kinds of pneumatic tires of conventional example 1, comparative examples 1 to 2, and examples 1 to 8, each having a tire size of 205/55R 1694T, a basic structure illustrated in FIG. 1, and a structure set as shown in Table 1 based on the tread pattern of FIG. 2, were produced.

In table 1, "total number N" is the total number of studs provided in the entire tire, and "N" is the number of studs included in each dense region. The "maximum value of N in the band-like region" shows the condition of the upper limit value defined in the present invention (4.0% of the total number N is 0.04N), the measured value in each tire, and the relationship of the magnitudes thereof. In particular, regarding the magnitude relation, the case where the measurement value is equal to or less than the upper limit condition (0.04N) is represented by "good", and the case where the measurement value exceeds the upper limit condition (0.04N) is represented by "x". The "standard disposition region" means a band-shaped region satisfying the condition that the number N of the cleats is 2.0% or more of the total number N of the cleats. The "standard placement region" indicates conditions of the lower limit value defined in the present invention (2.0% of the total number N is 0.02N), the presence/absence of the standard placement region, and the ratio of the standard placement region to all the band-shaped regions. The "concentrated region" indicates the condition of the lower limit value defined in the present invention (3.0% to 0.03N of the total number N), the presence or absence of a concentrated region, and the ratio of the concentrated region to all the band-shaped regions. As for the "dense region", the conditions of the lower limit value defined in the present invention (3.5% of the total number N is 0.035N), the presence or absence of the dense region, and the minimum interval (ratio with respect to the ground contact length) between the dense regions adjacent in the tire circumferential direction are shown. "arrangement in the width direction of the studs" means arrangement in the tire width direction of the studs in a band-shaped region where the number n of studs is 3 or more, and indicates "scattering" when at least 1 stud is present in each of the center region and the pair of shoulder regions, and indicates "unevenness" when no stud is present in either of the center region and the pair of shoulder regions. "Px/Pav" is the ratio of the average protrusion amount Px of the studs included in the concentrated region to the average protrusion amount Pav of the studs disposed in the regions other than the concentrated region.

In the 11 types of pneumatic tires (conventional example 1, comparative examples 1 to 2, and examples 1 to 8), the ground contact length was 120mm, which is common. That is, in each example, the tire circumferential direction length (1/4 of the tire contact patch length) of the band-shaped region was 30 mm.

The pneumatic tires were evaluated for on-ice steering stability performance, ride comfort performance on dry road surfaces, and low vibration performance on dry road surfaces by the following evaluation methods, and the results are shown in table 1.

Stability of operation on ice

Each test tire was assembled to a wheel having a rim size of 16 × 6.5J, filled with a vehicle specified air pressure, and mounted to a front wheel drive vehicle having an air displacement of 1.4L, and steering stability performance was evaluated by a test driver on a test route (turning site) formed on an icy or snowy road surface. The evaluation results are expressed by an index with the value of conventional example 1 being 100. The larger the index value is, the more excellent the steering stability performance on ice is.

Ride comfort on dry road

Each test tire was assembled to a wheel having a rim size of 16 × 6.5J, filled with a vehicle specified air pressure, mounted to a front wheel drive vehicle having an air displacement of 1.4L, and subjected to sensory evaluation of ride comfort (impact) by a test driver on a test route constituted by a dry road surface. The evaluation results are expressed by an index with the value of conventional example 1 being 100. The larger index value means that the smaller the impact feeling, the more excellent the ride comfort on dry road.

Low vibration performance on dry road

Each test tire was assembled to a wheel having a rim size of 16 × 6.5J, filled with a vehicle specified air pressure, mounted on a front wheel drive vehicle having an air displacement of 1.4L, and subjected to sensory evaluation with respect to vibration on a test route constituted by a dry road surface. The evaluation results are expressed by an index with the value of conventional example 1 being 100. The larger the index value is, the smaller the vibration is, the more excellent the low vibration performance on a dry road surface is. The more excellent the low vibration performance, the more excellent the weight balance of the tire and the more excellent the uniformity.

As is clear from table 1, examples 1 to 8 all exhibited good on-ice handling stability performance, good ride comfort performance on dry roads, and low vibration performance, compared to conventional example 1, and both of these performances were highly achieved. On the other hand, in comparative example 1, the band-shaped region satisfying the condition that the number N of the cleats is 2.0% or more of the total number N of the cleats is small, and therefore the grip stability on ice is deteriorated. In comparative example 2, since there is a band-shaped area in which the number of studs is more than 4.0% of the total number N, the ride comfort performance and the low-vibration performance on a dry road surface are deteriorated.

Description of the reference numerals

1: a tread portion;

2: a sidewall portion;

3: a bead portion;

4: a carcass layer;

5: a bead core;

6: a bead filler;

7: a belt ply;

8: a belt reinforcement layer;

11: a transverse groove;

12: a circumferential groove;

13: a land portion;

14: an auxiliary groove;

15: a sipe;

p: anti-skid nails;

a: a band-shaped region;

a': a concentration area;

a': a dense region;

ce: a central region;

sh: a shoulder region;

CL: the tire equator;

e: ground terminal

Claims

1. A pneumatic tire is provided with:

a tread portion extending in a tire circumferential direction and having a ring shape; a pair of side wall portions disposed on both sides of the tread portion; and a pair of bead portions disposed on the inner side of the sidewall portion in the tire radial direction, the pneumatic tire having a tread surface on which cleats are implanted,

the pneumatic tire is characterized in that it is,

when a region defined between a pair of tire meridians arranged at an interval on the tire equator line of 1/4 corresponding to the tire contact patch length is a belt-shaped region, and a plurality of belt-shaped regions are arranged over the entire circumference of the tire with angles sequentially shifted by 1 degree in the tire circumferential direction,

in all the band-shaped regions, the number N of the studs included in each band-shaped region is 4.0% or less of the total number N of the studs in the entire circumference of the tire, and in the band-shaped region of 2/3 or more of the band-shaped regions, the number N of the studs included in the band-shaped region is 2.0% or more of the total number N.

2. A pneumatic tire according to claim 1,

the total number of the anti-skid nails is 135-250.

3. A pneumatic tire according to claim 1 or 2,

among the plurality of band-shaped regions, a concentrated region in which the number N of cleats included in the band-shaped region is 3.0% or more of the total number N is present at 1 point or more and 1/3 points or less among the plurality of band-shaped regions.

4. A pneumatic tire according to claim 3,

in the concentrated region, there are 2 or more dense regions in which the number N of cleats included in the band-shaped region is 3.5% or more of the total number N, and the interval between the dense regions adjacent to each other in the tire circumferential direction is 100% or more of the tire contact patch length.

5. A pneumatic tire according to any one of claims 1 to 4,

the average protrusion amount Px of the stud included in the concentrated region and the average protrusion amount Pav of the stud in the region other than the concentrated region satisfy a relationship of Px ≦ 0.9 xPav.

6. A pneumatic tire according to any one of claims 1 to 5,

in a region obtained by dividing the tread surface of the tread portion by 3 equally in the tire width direction, when a region located on the tire equator is a central region and a pair of regions located on both sides of the central region in the tire width direction are shoulder regions, at least 1 stud is present in each of the central region and the pair of shoulder regions in a band-shaped region in which the number n of studs is 3 or more.