A tire with a tread reinforcing layer that includes a ply reinforcing structure formed by winding a cord-embedded rubber tape circumferentially of the tire. The ply reinforcing structure includes first oblique segments and second oblique segments which intersect with each other to form a mesh structure having rhombic spaces. The circumferential lengths of the rhombic spaces are less than ⅔ times the maximum circumferential length of the ground contacting patch of the tire in its normally loaded state.

TECHNICAL FIELD

The present invention relates to a tire having a tread reinforcing layer.

BACKGROUND ART

Patent Document 1 below describes a pneumatic tire including a tread reinforcing band. This band comprises first main portions and second main portions of a narrow strip of rubber coated cords, wherein the first main portions are inclined with respect to the circumferential direction, and the second main portions are inclined in the opposite direction to the first main portions to intersect with the first main portions. Such intersections improve the cornering performance because they increase the rigidity of the band and can produce large cornering power.

Patent Document 1: Japanese Patent Application Publication No. 2015-174569

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, it was found that the pneumatic tire of Patent Document 1 has room for improvement in the cornering performance as a result of experiments conducted by the present inventor.

The inventor studied the pneumatic tire disclosed in Patent Document 1 and found that rhombic spaces formed by being surrounded by the first main portions and second main portions contribute an improvement of the cornering performance.

In view of the above circumstances, the present invention has been devised, and its primary objective is to provide a tire capable of improving the cornering performance.

According to the present invention, a tire comprises a toroidal carcass and a tread reinforcing layer disposed radially outside the carcass in a tread portion of the tire,

wherein

the tread reinforcing layer comprises a ply reinforcing structure in which a long tape of at least one reinforcing cord coated with topping rubber is wound,

the ply reinforcing structure comprises

a plurality of first oblique segments in which the tape is inclined with respect to the tire circumferential direction to one side in the tire axial direction, and

a plurality of second oblique segments in which the tape is inclined with respect to the tire circumferential direction to the other side in the tire axial direction

so that the second oblique segments intersect the first oblique segments, and

the first oblique segments are arranged so that the side edges thereof do not contact with each other, and the second oblique segments are arranged so that the side edges thereof do not contact with each other, whereby the intersecting first and second oblique segments form a mesh structure having rhombic spaces, wherein

circumferential lengths of the rhombic spaces are less than ⅔ times a maximum circumferential length of a ground contacting patch of the tread surface of the tread portion when the tire in its normally loaded state is contacted with a flat horizontal surface at a camber angle of 0 degree.

In the tire according to the present invention, the circumferential lengths of the rhombic spaces are preferably not less than ⅖ times the maximum circumferential length of the ground contacting patch of the tread surface.

Preferably, axial lengths of the rhombic spaces are less than ⅔ times the maximum circumferential length of the ground contacting patch of the tread surface.

Preferably, the axial lengths of the rhombic spaces are not less than ⅖ times the maximum circumferential length of the ground contacting patch of the tread surface.

Preferably, the mesh structure is disposed in a middle region between the tire equator and a tread edge.

It is preferable that the ply reinforcing structure comprises, in a crown region including the tire equator, a center spiral structure in which the tape extends circumferentially of the tire and spirally one or more turns.

Preferably, the ply reinforcing structure comprises, in a shoulder region including the tread edge, a lateral spiral structure in which the tape extends circumferentially of the tire and spirally one or more turns.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention can be applied to various tires such as pneumatic tires for passenger cars, motorcycles, heavy duty vehicles and the like, as well as non-pneumatic tires.

Taking a pneumatic tire as an example, embodiments of the present invention will now be described in conjunction with accompanying drawings.

FIG. 1shows a meridian cross-section including a tire rotational axis (not shown) of a motorcycle tire as an embodiment of the present invention in its normally inflated unloaded state.

In the case of a pneumatic tire, the normally inflated unloaded state is such that the tire is mounted on a standard wheel rim and inflate to a standard pressure but loaded with no tire load.

The normally loaded state is such that the tire is mounted on the standard wheel rim and inflated to the standard pressure and loaded with the standard tire load.

In this application including specification and claims, various dimensions, positions and the like of a pneumatic tire refer to those in the normally inflated unloaded state of the tire unless otherwise noted.

The standard wheel rim is a wheel rim officially approved or recommended for the tire by standards organizations, i.e. JATMA (Japan and Asia), T&RA (North America), ETRTO (Europe), TRAA (Australia), STRO (Scandinavia), ALAPA (Latin America), ITTAC (India) and the like which are effective in the area where the tire is manufactured, sold or used.
The standard pressure and the standard tire load are the maximum air pressure and the maximum tire load for the tire specified by the same organization in the Air-pressure/Maximum-load Table or similar list.
For example, the standard wheel rim is the “standard rim” specified in JATMA, the “Measuring Rim” in ETRTO, the “Design Rim” in TRA or the like. The standard pressure is the “maximum air pressure” in JATMA, the “Inflation Pressure” in ETRTO, the maximum pressure given in the “Tire Load Limits at various Cold Inflation Pressures” table in TRA or the like. The standard load is the “maximum load capacity” in JATMA, the “Load Capacity” in ETRTO, the maximum value given in the above-mentioned table in TRA or the like.

As shown inFIG. 1, the tire1of the present embodiment comprises: a tread portion2whose radially outer surface defines the tread surface2acontacting with the ground, a pair of axially spaced bead portions4mounted on rim seats, a pair of sidewall portions3extending between the tread edges TE and the bead portions4, a toroidal carcass6extending between the bead portions through the tread portion and the sidewall portions, and a tread reinforcing layer7disposed radially outside the carcass6in the tread portion2.

As a characteristic of a motorcycle tire, the tread portion2(inclusive of the carcass6, tread reinforcing layer7and a tread rubber thereon) is convexly curved so that the tread surface2abetween the tread edges Te is curved like an arc swelling radially outwardly, and the maximum cross sectional width of the tire1occurs between the tread edges TE.

The tread portion2compresses a crown region2C centered on the tire equator C, a pair of shoulder regions2S extending axially inwardly from the respective tread edges TE, and a pair of middle regions2M between the respective shoulder regions2S and the crown region2C. The crown region2C is a region contacting with the ground mainly during straight running. The middle region2M is a region contacting with the ground when the motorcycle is leant to initiate a turn and during cornering. The shoulder region2sis a region contacting with the ground when the motorcycle is leant largely during cornering.

The carcass6is composed of at least one carcass ply6A. The carcass ply6A is made of carcass cords rubberized with topping rubber and arranged radially at an angle in a range from 75 to 90 degrees with respect to the tire equator C, for example. The carcass ply6A extends between the bead portions4through the tread portion2and the sidewall portions3, and is turned up around a bead core5in each bead portion so as to form a pair of turned up portions6band a main portion6atherebetween.

The tread reinforcing layer7is curved along the tread portion2and extends over the substantially entire width of the tread portion2. As a result, the tread reinforcing layer7can increase the rigidity of the tread portion2over the entire width of the tread portion2.

From such viewpoint, it is preferable that, in the tire meridian cross section, the developed width Wt of the tread reinforcing layer7measured therealong is set in a range from 75% to 95% of the developed tread width TW measured between the tread edges TE along the tread surface2a.

The tread reinforcing layer7comprises a ply reinforcing structure8formed by winding a tape9around the carcass6.

FIG. 2shows an example of the tape9. The tape9is one reinforcing cord or plural parallel reinforcing cords10coated with a topping rubber11. In this example, the tape9includes a plurality of parallel reinforcing cords10.

For example, a steel cord or an organic fiber cord is suitably used as the reinforcing cord10.

The tape9has side edges9sextending in the longitudinal direction of the tape, and the or each reinforcing cord10therein extends parallel with the side edges9s. In this example, the cross sectional shape of the tape is substantially rectangle. The width W1of the tape9is preferably set in a range from 2.5 to 12.0 mm, for example. The thickness t1of the tape9is preferably set in a range from 0.6 to 3.0 mm, for example.

The ply reinforcing structure8includes a mesh structure13where the wound tape9intersects itself.

FIG. 3is an developed view of a circumferential part of the mesh structure13developed in the tire circumferential direction and axial direction.

As shown, the mesh structure13comprises a plurality of first oblique segments16and a plurality of second oblique segments17.

In the first oblique segments16, the wound tape9is inclined with respect to the tire circumferential direction toward one side in the tire axial direction (diagonally right up in the figure).

In the second oblique segments17, the wound tape9is inclined with respect to the tire circumferential direction in the opposite direction to the first oblique segments16, namely, toward the other side in the tire axial direction (diagonally right down in the figure).
Thus, the first oblique segments16intersect the second oblique segments17to form the mesh structure13.

In the mesh structure13, the side edges16sof the first oblique segments16are arranged without contacting with each other, and also side edges17sof the second oblique segments17are arranged without contacting with each other, so rhombic spaces19surrounded by the intersecting first and second oblique segments16and17are formed.

When the tread portion2is subjected to a torsional force during running, the mesh structure13having such rhombic spaces19can effectively resist against torsional deformation of the tread portion2to enable a smooth or stable turning and cornering. Further, the intersecting portions20between the first oblique segments16and the second oblique segments17can increase the rigidity of the tread reinforcing layer7, so the cornering performance can be improved.

In the present invention, the “rhomboid shape” includes not only those formed by four sides which are straight lines having the same length but also those formed by four sides which are not straight lines including a curved line such as an arc as far as the above-described function can be obtained.

The circumferential lengths La of the rhombic spaces19are set to be less than ⅔ times the maximum circumferential length LA of a ground contacting patch S (shown inFIG. 5) of the tread surface2aof the tread portion2occurred when the tire1in its normally loaded state is contacted with a flat horizontal surface at a camber angle of 0 degree.

FIG. 4(a)schematically shows an example of the ground contacting patch Sa.

When the mesh structure13is positioned in the ground contacting patch Sa during running, by limiting the circumferential lengths La as described above, at least one rhombic space19is positioned in the ground contacting patch Sa. Here, the expansion “at least one rhombic space19is positioned in the ground contacting patch Sa” means not only that the entire shape of one rhombic space19is positioned in the ground contacting patch Sa as shown inFIG. 4(a)but also that a part of a rhombic space19and a part of another rhombic space19—as shown in the center ofFIG. 4(b)above and below, which form one rhombic space19or more part of the rhombic space19when combined into one—is positioned in the ground contacting patch Sa.

As a result, the mesh structure16can exert a large hoop effect in the ground contacting patch Sa, so a smooth turning or cornering becomes possible. Thus, according to the present invention, the cornering performance can be improved. Further, in the case of a motorcycle tire as in the present embodiment, the change in the contour shape of the ground contacting patch becomes particularly small between axially inside and outside of the tread portion2.

Preferably, the circumferential lengths La of the rhombic spaces19are set to be not less than ⅖ times the maximum circumferential length LA of the ground contacting patch S. If the length La is less than ⅖ times the length LA, the total number of the first oblique segments16and second oblique segments17increases, and the mass of the tire1excessively increases. Thus, the cornering performance may be worsened.

Preferably, the axial lengths Wa of the rhombic spaces19are set to be less than ⅔ times the maximum axial length WA of the ground contacting patch S. As a result, one or more rhombic spaces19(in the above-explained sense) are positioned in the ground contacting patch Sa when the mesh structure13is positioned in the ground contacting patch Sa during running, and the cornering performance may be further improved.

However, from the viewpoint of suppressing an excessive increase in the mass of the tire, it is preferable that the axial lengths Wa of the rhombic spaces19are set to be not less than ⅖ times the maximum axial length WA of the ground contacting patch S.

It is preferable that the first oblique segments16have an inclination angle θ1of not less than 1 degrees, more preferably not less than 3 degrees, still more preferably not less than 5 degrees with respect to the tire circumferential direction, and

the second oblique segments17have an inclination angle θ2of not less than 1 degrees, more preferably not less than 3 degrees, still more preferably not less than 5 degrees with respect to the tire circumferential direction.

The angle θ1and the angle θ2are preferably not more than 20 degrees, more preferably not more than 15 degrees, and still more preferably not more than 10 degrees.

Incidentally, the angle of the tape9may be an average angle obtained by averaging over the circumference of the ply reinforcing structure8.

It is preferable that the angle θ1of the first oblique segments16is set to be equal to the angle θ2of the second oblique segments17so that cornering power of the same magnitude may be generated when turning right and left to thereby allow a smoother turning.

The mesh structure13in this embodiment comprises a plurality of circumferential segments18extending substantially parallel with the tire circumferential direction.

The circumferential segments18suppress deformation of the carcass6to improve high-speed stability performance.

The circumferential segments18have an angle θ3of not more than 5 degrees, preferably not more than 2 degrees with respect to the tire circumferential direction. In this example, the angle θ3is set to a most preferable value of 0 degree.

The circumferential segments18are disposed at both ends13sin the width direction of the mesh structure13.

Both ends in the tire circumferential direction of each of the circumferential segments18are respectively connected to one of the first oblique segments16and one of the second oblique segments17.

Such circumferential segments18lessen the bending stress acting on the cord(s)10of the tape9as compared with the case where the first oblique segment16and the second oblique segment17are directly connected. As a result, it is possible to suppress the bent portions of the tape9from being separated from the underlying structure at the time of winding the tape.

In the present embodiment, at each end13sin the width direction of the mesh structure13, the circumferential segments18are extend linearly in the tire circumferential direction. More specifically, the circumferential segments18which are parallel with the tire circumferential direction, are arranged in line in the tire circumferential direction forming a linear arrangement18A like a circumferentially continuous tape. Such linear arrangement18A can hoop the carcass6to effectively suppress deformation of the carcass6. Since the linear arrangement18A is formed on both sides of the mesh structure13, the deformation is further effectively suppressed.

As shown inFIG. 3, the linear arrangement18A in this example is provided with reentrant portions22toward the widthwise center of the mesh structure13.

Such reentrant portions22suppress an excessive increase in the rigidity caused by the overlapping of the circumferential segments18adjacent to each other in the tire circumferential direction, and as a result, it is possible to improve the rigidity balance of the mesh structure13between both end (13) portions and a portion therebetween.

When the circumferential length Lb of the reentrant portions22becomes excessively large, there is a possibility that the above-described hooping force to the carcass6becomes small. In addition, since the positions of the axially outermost rhombic spaces19shift toward the inside in the width direction of the mesh structure13, the range where the hooping effect is exerted may be reduced.

Therefore, the circumferential length Lb of the reentrant portion22is preferably not less than 5%, more preferably not less than 10% of the lengths La of the outermost spaces19cadjacent to the reentrant portion22in the tire axial direction. And the circumferential length Lb is preferably not more than 25%, more preferably not more than 20% of the lengths La of the rhombic spaces19c.

The mesh structure13may be formed by winding one continuous tape9or winding the tape9formed by connecting plural separate pieces.

FIG. 5shows the entire width of the ply reinforcing structure8of the present embodiment.

In addition to the mesh structure13, the ply reinforcing structure8includes a spiral structure14in which the tape9is wound spirally and circumferentially of the tire at least one turn. Such spiral structure14exerts a great hooping force on the carcass6.

In the spiral structure14, the angle θ4with respect to the tire circumferential direction of the tape9is smaller than the angle θ1of the first oblique segments16and the angle θ2of the second oblique segments17, and

the angle θ4is preferably not more than 5 degrees, more preferably not more than 2 degrees including 0 degree.

In the present embodiment, the mesh structure13is mainly formed in each middle region2M. This greatly improves the cornering performance.

The width Wm of each mesh structure13measured therealong is preferably not less than 20%, more preferably not less than 25%, but preferably not more than 48%, more preferably not more than 40% of the developed tread width TW.

The spiral structure14includes a center spiral structure24formed in the crown region2cand a lateral spiral structure25formed in each shoulder region2s.

The center spiral structure24exerts a large hooping force on the crown region2C which contacts with the ground during straight running which is mainly a high-speed running, therefore, the high-speed stability performance is improved.

The lateral spiral structure25reduces the torsional rigidity of the shoulder region2S as compared with the case where the mesh structure is formed, therefore, relatively small cornering power is generated. For this reason, the reaction force and vibrations caused by, for example, gaps of the road surface etc. are reduced, so the ground contact feeling is improved. As a result, the lateral spiral structure25enables stable cornering with a large leaning angle of the motorcycle, and thereby the cornering performance can be improved.

In this example, the outer edge25ein the tire axial direction of the lateral spiral structure25forms the outer edge7eof the tread reinforcing layer7.

The center spiral structure24and each lateral spiral structure25are each formed by one tape9. Thereby, the above-described function is effectively exhibited.

However, the center spiral structure24and each lateral spiral structure25may be formed by a plurality of tapes9.

In the spiral structure14in this example, the side edges9sof the tape9contact with each other between the axially adjacent turns of the tape9.

Further, it is also possible that the side edges9sare overlapped with each other between the axially adjacent turns of the tape9.

The spiral structure14is separated in the tire axial direction from the mesh structure13. Thereby, it is possible to suppress an excessive increase in the rigidity caused by the tape9of the spiral structure14and the adjacent tape9in the circumferential segments18which basically extend in the tire circumferential direction.

Specifically, in the present embodiment, the center spiral structure24and each mesh structure13are separated in the tire axial direction. Each second spiral structure25and the adjacent mesh structure13are separated in the tire axial direction.

During straight running, the crown region2C is subjected to a higher ground pressure as compared with the shoulder regions2S. Therefore, the crown region2C is required to have a higher circumferential rigidity than in the shoulder regions2S. It is thus, preferred that the shortest distance W3between the center spiral structure24and each mesh structure13is set to be smaller than the shortest distance W4between the mesh structure13and the adjacent lateral spiral structure25, wherein the shortest distance W3is the distance in the tire axial direction between the outer end24ein the tire axial direction of the center spiral structure24and the inner end13iin the tire axial direction of the mesh structure13, and the shortest distance W4is the distance in the tire axial direction between the inner end25iin the tire axial direction of the lateral spiral structure25and the outer end13ein the tire axial direction of the mesh structure13.

If the difference (W4−W3) between the shortest distance W3and the shortest distance W4is large, the rigidity in the border area between the shoulder region2S and the middle region2M is decreased, and the cornering performance when the motorcycle is leant largely is liable to deteriorate.

From such a viewpoint, the difference (W4−W3) is preferably not less than 1 mm, more preferably not more than 4 mm.

The shortest distance W3between the center spiral structure24and the mesh structure13may be set to 0 mm. That is, the center spiral structure24and the mesh structure13may be in contact with each other. In this case, the circumferential rigidity in the border area between the crown region2C and the middle region2M is increased, and high-speed stability performance is improved.

The width Wc of the center spiral structure24measured therealong is preferably not less than 3%, more preferably not less than 10%, but preferably not more than 30%, more preferably not more than 25% of the developed tread width TW.

The width Ws of each lateral spiral structure25measured therealong is preferably not less than 2%, more preferably not less than 7%, but preferably not more than 20%, more preferably not more than 15% of the developed tread width TW.

In the present embodiment, the mesh structure13is disposed in each middle region2M. However, it may be also possible to dispose the mesh structure13in each of the crown region2C and the shoulder regions2S. Further, it may be possible to dispose the mesh structure13over two or more of the crown region2C, middle region2M and shoulder region2S.

While detailed description has been made of an especially preferable embodiment of the present invention, the present invention can be embodied in various forms without being limited to the illustrated embodiment.

Comparison Tests

Motorcycle tires having the internal structure shown inFIG. 1and tread reinforcing layers based on that shown inFIG. 5were experimentally manufactured as test tires (practical examples Ex1-Ex8 and comparative example REF1).

The tread reinforcing layers had specifications shown in Table 1. Common specifications are as follows.

width Wt of Tread reinforcing layer: 90% of TW

width Wm of Mesh structure: 40% of TW

width Wc of Center spiral structure: 6.0% of TW

width Ws of Lateral spiral structure: 2.0% of TW

The tires were tested for the high speed stability performance and cornering performance as follows.

The test tires were mounted on a 1000 cc motorcycle, and the motorcycle was run on a dry asphalt road of a test course.

Rear Wheel:Tire size 180/55ZR17, Rim size 17M/CxMT5.50,Tire pressure 250 kPa
During running, the test rider evaluated high-speed stability performance based on high-speed running characteristics such as handle stability, grip and the like.
The results are indicated in Table 1 by an index based on Comparative example REF1 being 100, wherein the larger the numerical value, the better the performance.
<Cornering Performance Test>

using an indoor tire testing machine, the test tires were measured for the cornering force under the following conditions and then cornering power was calculated.

The cornering power is obtained from the equation {CF(+1 degree)−CF(−1 degree)}/2, namely, by subtracting a cornering force value CF(−1 degree) at the slip angle of −1 degree from a cornering force value CF(+1 degree) at the slip angle of +1 degree in order to obtain their difference, and then dividing the difference by 2. Thus, the cornering power is the cornering force per 1 degree of the slip angle.
The results are indicated in Table 1 by an index based on Comparative example REF1 being 100, wherein the larger the numerical value, the higher the cornering power.

From the test results, it was confirmed that the tires according to the present invention were improved in the cornering performance as compared with the comparative example.

DESCRIPTION OF THE REFERENCE SIGNS