Patent Description:
<CIT> discloses a pneumatic tyre. The pneumatic tyre includes a circumferentially extending band-shaped noise damper that is made of sponge material. The noise damper is fixed to the inner surface of the tread portion in the tyre radial direction.

<CIT> discloses a pneumatic tyre according to the preamble of claim <NUM>. <CIT> and <CIT> respectively disclose a pneumatic tyre having a noise damper made of a sponge and disposed in an inner space of the tyre.

The noise damper can convert the vibration energy of the air in the tyre cavity into heat energy to reduce tyre noise such as resonance noise. Thus, the tread rubber to which the noise damper is fixed easily stores heat during running. As the heat storage property of the tread rubber is increased, there is a problem that the durability of the tread portion may deteriorate.

The present invention has been made in view of the above circumstances and has a maj or object to provide a pneumatic tyre capable of improving noise performance and durability.

A pneumatic tyre according to the present invention is defined in claim <NUM> and includes a tread portion having a tread rubber and a tyre inner cavity surface, and a noise damper made of a porous material fixed to the tyre inner cavity surface. The tread rubber includes an outer tread rubber having a ground-contacting surface, and an inner tread rubber disposed inwardly in the tyre radial direction of the outer tread rubber and outwardly in the tyre radial direction of the noise damper. A loss tangent tan δ of the inner tread rubber at <NUM> degrees C is smaller than a loss tangent tan δ of the outer tread rubber at <NUM> degrees C. A pair of ends in a tyre axial direction of the inner tread rubber is arranged inwardly in the tyre axial direction of a pair of outer ends in the tyre axial direction of the noise damper.

Preferable embodiments are defined in the dependent claims.

Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings.

Note that the drawings may contain exaggerated representations that differ from the actual structural dimensional ratios to aid in understanding the content of the invention. Further, throughout the embodiments, the same or common elements are denoted by the same reference numerals, and duplicate description may be omitted. Furthermore, the specific configurations shown in the embodiments and drawings are for understanding the contents of the present invention, and the present invention is not limited to the specific configurations shown but to the embodiments covered by the scope of the appended claims.

<FIG> is a tyre meridian cross-sectional view showing an embodiment of a pneumatic tyre (hereinafter, simply referred to as "tyre") <NUM>. The tyre <NUM> according to the present embodiment is exemplified as a pneumatic tyre for passenger car, for example. However, the tyre <NUM> is not limited to such an aspect, and may be a pneumatic tyre for heavy load and the like, for example.

As illustrated in <FIG>, the tyre <NUM> includes a tread portion <NUM>. Further, the tyre <NUM> according to the present embodiment includes a carcass <NUM> and a belt layer <NUM>.

In the present embodiment, the carcass <NUM> extending between a pair of bead portions <NUM>. In the present embodiment, the carcass <NUM> includes at least one carcass ply. In this embodiment, the carcass <NUM> is composed of a single carcass ply 6A.

In the present embodiment, the carcass ply 6A includes a main portion 6a extending between bead cores <NUM> each disposed in a respective one of the bead portions <NUM>, through the tread portion <NUM> and a pair of sidewall portions <NUM>, and a pair of turned-up portions 6b connected to the main portion 6a and each turned up around the bead core <NUM> from axially inside to outside of the tyre. In each bead portion <NUM>, a bead apex rubber <NUM> which extends from the bead core <NUM> is disposed between the main portion 6a and the turn-up portion 6b.

In the present embodiment, the carcass ply 6A, for example, includes a plurality of carcass cords (not illustrated) oriented at an angle of from <NUM> to <NUM> degrees with respect to the tyre equator C. As the carcass cords, organic fiber cords such as aromatic polyamides and rayon may be used, for example.

In the present embodiment, an inner liner rubber <NUM> which forms a tyre inner cavity surface <NUM> is arranged inside the carcass <NUM>. The inner liner rubber <NUM> is composed of airimpermeable rubber such as butyl rubber so that the filled air of the tyre <NUM> can be kept airtight.

In the present embodiment, the belt layer <NUM> is disposed outwardly in the tyre radial direction of the carcass <NUM> in the tread portion <NUM>. In the present embodiment, the belt layer <NUM> is composed of two belt plies consisting of a radially inner belt ply 7A and a radially outer belt ply 7B.

In the present embodiment, each of the belt plies 7A and 7B has a plurality of belt cords (not illustrated) which, for example, is oriented at an angle of from <NUM> to <NUM> degrees with respect to the tyre circumferential direction. These belt piles 7A and 7B are superimposed such that the belt cords of the belt ply 7A and the belt cords of the belt ply 7A cross with each other. As the belt cords, for example, steel, aramid, rayon, etc. may be preferably adopted.

In the present embodiment, the tread portion <NUM> has a pair of tread edges 2t. The pair of tread edges 2t is the axial outermost edges of the tread ground-contacting surface <NUM> of the tyre <NUM> which occurs under the condition such that the tyre <NUM> under a normal state is grounded on a plane with a standard tyre load at zero camber angles. In the normal state, the distance between the tread edges 2t and 2t in the tyre axial direction is defined as the tread ground-contacting width TW.

As used herein, the "normal state" is such that the tyre <NUM> is mounted onto a standard wheel rim with a standard pressure but loaded with no tyre load. As used herein, unless otherwise noted, dimensions of portions of the tyre are values measured under the normal state. In addition, the dimensions of each portion of the tyre shall allow the normal error contained in a rubber molded product.

As used herein, the "standard wheel rim" is a wheel rim officially approved for each tyre by standards organizations on which the tyre <NUM> is based. For example, the standard wheel rim is the "standard rim" specified in JATMA, the "Design Rim" in TRA, and the "Measuring Rim" in ETRTO.

As used herein, the "standard pressure" is a standard pressure officially approved for each tyre by standards organizations on which the tyre <NUM> is based. For example, the standard pressure is the "maximum air pressure" in JATMA, the maximum pressure given in the "Tire Load Limits at Various Cold Inflation Pressures" table in TRA, and the "Inflation Pressure" in ETRTO.

As used herein, the "standard tyre load" is a tyre load officially approved for each tyre by the standards organization in which the tyre <NUM> is based. For example, the standard tyre load is the "maximum load capacity" in JATMA, the maximum value given in the above-mentioned table in TRA, and the "Load Capacity" in ETRTO, for example.

In the present embodiment, the tyre <NUM> includes a tread rubber <NUM> and a noise damper <NUM>.

In the present embodiment, the noise damper <NUM> is fixed to a tyre inner cavity surface <NUM> of the tread portion <NUM>. In the present embodiment, the noise damper <NUM> is formed in a band shape with a bottom surface fixed to the tyre inner cavity surface <NUM> and extends in the tyre circumferential direction. Further, the noise damper <NUM> includes a pair of outermost ends (not illustrated) on both sides in the tyre circumferential direction, which is butt-jointed with each other to form a substantially annular shape. The pair of outermost ends may be separated in the tyre circumferential direction.

In the present embodiment, the noise damper <NUM> has substantially the same cross-sectional shape at each position in the tyre circumferential direction except for the pair of outer ends (not illustrated) in the tyre circumferential direction. However, the noise damper is not limited to such an aspect. In addition, the cross-sectional shape of the noise damper <NUM> can be set as appropriate. In the present embodiment, the noise damper <NUM> has a flat horizontal shape (in this embodiment, a horizontally long rectangular shape) in which a thickness in the tyre radial direction (the maximum thickness T1) is smaller than a width in the tyre axial direction (the maximum width W1). As a result, the noise damper <NUM> can be prevented from collapsing or deforming during tyre running.

In the present embodiment, the noise damper <NUM> is made of a porous material. As the porous material, a porous sponge material may be exemplified. The sponge material has a spongy porous structure. In addition, the sponge material includes, for example, the so-called sponge itself obtained by foaming rubber or synthetic resin, as well as those in which animal fibers, plant fibers, synthetic fibers, etc. are entwined and integrally connected.

As the sponge material, synthetic resin sponges such as ether-based polyurethane sponges, ester-based polyurethane sponges, and polyethylene sponges, and chloroprene rubber sponges (CR sponges) may be adopted. Other examples of sponge materials may include ethylene propylene rubber sponge (EDPM sponge) and nitrile rubber sponge (NBR sponge). In particular, polyurethane-based or polyethylene-based sponges including ether-based polyurethane sponges are preferable from the viewpoints of sound control (noise performance), light weight, controllability of foaming, and durability.

The porous material (sponge material in this example) is easily deformed by shrinkage or bending. Thus, the noise damper <NUM> can deform flexibly following the deformation of the inner liner rubber <NUM> during running.

The noise damper <NUM> made of such a porous material can convert the air vibration in the tyre cavity <NUM> into heat energy to reduce it by its surface and internal holes (cells). This can reduce the noise inside the vehicle due to the resonance of the air. Further, the noise damper <NUM> can alleviate the impact received from the tread portion <NUM> while running, and the road noise can be reduced. Thus, in the present embodiment, the tyre <NUM> can improve noise performance.

The noise damper <NUM> generates heat during running because it converts the air vibration in the tyre cavity <NUM> into heat energy to exert a sound control effect. When the heat of the noise damper <NUM>, for example, is propagated to the tread edge 2t sides of the tread rubber <NUM>, which tend to generate a large amount of heat during running, the heat storage amount of the tread rubber <NUM> on the tread edge 2t sides may increase and be difficult to improve durability. Thus, it is preferable that outer ends 14t of the noise damper <NUM> in the tyre axial direction are arranged inside the tyre axial direction rather than the tread edges 2t. As a result, the tyre <NUM> according to the present embodiment can suppress the increase in the amount of heat storage on the tread edge 2t sides of the tread rubber <NUM>, and the durability can be improved.

Preferably, a maximum width W1 in the tyre axial direction of the noise damper <NUM> is in a range from <NUM>% to <NUM>% of the tread ground-contacting width TW. By setting the maximum width W1 of the noise damper equal to or less than <NUM>% of the tread ground-contacting width TW, the heat of the noise damper <NUM> can be suppressed from being propagated to the tread edge 2t sides of the tread rubber <NUM>, and the durability can be improved. By setting the maximum width W1 of the noise damper <NUM> equal to or more than <NUM>% of the tread ground-contacting width TW, air vibration in the tyre cavity <NUM> can be absorbed effectively and the noise performance can be improved. From this point of view, the maximum width W1 of the noise damper <NUM> is more preferably equal to or less than <NUM>% of the tread ground-contacting width TW, also preferably equal to or more than <NUM>%.

Preferably, the maximum thickness T1 of the noise damper <NUM> in the tyre radial direction is equal to or less than <NUM>. As a result, it is possible to suppress the increase in heat generation of the noise damper <NUM>, and the durability can be improved. Preferably, the maximum thickness T1 is equal to or more than <NUM>. As a result, the noise damper <NUM> can efficiently absorb the air vibration in the tyre cavity <NUM>, and the noise performance can be improved. From this point of view, the maximum thickness T1 is preferably <NUM> or less, and preferably <NUM> or more.

In the present embodiment, the tread rubber <NUM> is disposed in the tread portion <NUM>. In the present embodiment, the tread rubber <NUM> is disposed outwardly in the tyre radial direction of the belt layer <NUM>.

In the present embodiment, the tread rubber <NUM> includes an outer tread rubber 13A and an inner tread rubber 13B. Further, in the present embodiment, the tread rubber <NUM> includes a middle tread rubber 13C. <FIG> is a partial enlarged view of the tread portion <NUM> with a noise damper <NUM> of <FIG>.

In the present embodiment, the outer tread rubber 13A constitutes the tread ground-contacting surface <NUM>. In the present embodiment, the outer tread rubber 13A extends outwardly in the tyre axial direction beyond both outer ends 7t of the belt layer <NUM> in the tyre axial direction.

The inner tread rubber 13B is disposed inwardly in the tyre radial direction of the outer tread rubber 13A and is disposed outwardly in the tyre radial direction of the noise damper <NUM>. In the present embodiment, the inner tread rubber 13B is arranged adjacent to the belt layer <NUM>.

The middle tread rubber 13C is disposed between the outer tread rubber 13A and the inner tread rubber 13B. In the present embodiment, the middle tread rubber 13C extends in the tyre axial direction beyond the outer ends 13Bt in the tyre axial direction of the inner tread rubber 13B as well as the outer ends 7t in the tyre axial direction of the belt layer <NUM>.

Rubber compositions of the outer tread rubber 13A, the inner tread rubber 13B and the middle tread rubber 13C are not particularly limited. The rubber compositions include a rubber base material, a reinforcing agent (filler), a cross-linking agent, and a vulcanization accelerator. As the rubber base material, for example, diene-based rubbers such as natural rubber, butadiene rubber, isoprene rubber, and styrene-butadiene rubber, and a mixture thereof can be adopted. As the reinforcing agent (filler), for example, carbon, silica, or the like can be adopted. As the cross-linking agent, for example, sulfur can be adopted. As the vulcanization accelerator, for example, thiazole-based, guanidine-based, sulfenamide-based, thiuram-based, etc. can be adopted.

As mentioned above, the noise damper <NUM> generates heat while running. Thus, the tread rubber <NUM> to which the noise damper <NUM> is fixed easily stores heat by transmitting heat from the noise damper <NUM>. When the heat storage property of the tread rubber <NUM> becomes large, the durability of the tread portion <NUM> tends to deteriorate.

In the present embodiment, a loss tangent tan δ of the inner tread rubber 13B at <NUM> degrees C is set smaller than a loss tangent tan δ of the outer tread rubber 13A at <NUM> degrees C. The loss tangent tan δ at <NUM> degrees C can be set, for example, by adjusting the amount of the above-mentioned reinforcing agent or cross-linking agent added, and the type and amount of vulcanization accelerator added.

In this specification, a loss tangent tan δ at <NUM> degrees C is a value measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co. under the following conditions in accordance with the provisions of JIS-K6394.

In the present embodiment, since a loss tangent tan δ at <NUM> degrees C of the inner tread rubber 13B is set smaller than a loss tangent tan δ at <NUM> degrees C of the outer tread rubber 13A, the heat generation of the inner tread rubber 13B at the start of running can be suppressed compared to the outer tread rubber 13A. Thus, by arranging the inner tread rubber 13B made of such a low heat generation rubber outward in the tyre radial direction of the noise damper <NUM>, the heat stored in the tread rubber <NUM> can be suppressed by receiving the heat from the noise damper <NUM>, which generates heat while running. As a result, in the present embodiment, the tyre <NUM> can suppress the increase in heat storage property of the tread rubber <NUM>, and the durability of the tread portion <NUM> can be improved. Thus, in the present embodiment, the tyre <NUM> can improve the noise performance and durability.

In order to further improve the above-mentioned effect, the loss tangent tan δ of the inner tread rubber 13B at <NUM> degrees C is preferably equal to or less than <NUM>. By setting the loss tangent tan δ of the inner tread rubber 13B at <NUM> degrees C being equal to or less than <NUM>, the inner tread rubber 13B can further suppress heat generation while running. This can reduce the heat storage of the tread rubber <NUM> and improve the durability of the tread portion <NUM>. From this point of view, the loss tangent tan δ of the inner tread rubber 13B at <NUM> degrees C is preferably equal to or less than <NUM>.

Further, the loss tangent tan δ of the inner tread rubber 13B at <NUM> degrees C is preferably equal to or more than <NUM>, for example. As a result, the deformation of the inner tread rubber 13B during running can be suppressed from becoming smaller than necessary, and steering stability can be maintained.

On the other hand, if the loss tangent tan δ of the outer tread rubber 13A at <NUM> degrees C is larger than the loss tangent tan δ of the inner tread rubber at <NUM> degrees C, the value can be set appropriately. In the present embodiment, the loss tangent tan δ of the outer tread rubber 13A at <NUM> degrees C can be set to, for example, <NUM> to <NUM> from the viewpoint of improving steering stability.

Preferably, a pair of outer ends 13Bt in the tyre axial direction of the inner tread rubber 13B is located inwardly in the tyre axial direction of the tread edges 2t of the tread portion <NUM>. As a result, it is possible to suppress the placement of the inner tread rubber 13B, which has a relatively small deformation (loss tangent tan δ), on the tread edges 2t side where the ground pressure is relatively large during cornering. Thus, the tyre has a larger grip when cornering and the steering stability can be maintained.

Further, the pair of outer ends 13Bt of the inner tread rubber 13B is located inwardly in the tyre axial direction of the pair of outer ends 14t in the tyre axial direction of the noise damper <NUM>. As a result, the tyre axial region of the inner tread rubber 13B with respect to the noise damper <NUM> may be suppressed from becoming larger than necessary, and the steering stability can be maintained.

Preferably, the maximum width W2 in the tyre axial direction of the inner tread rubber 13B is in a range from <NUM>% to <NUM>% of the maximum width W1 in the tyre axial direction of the noise damper <NUM>. By setting the maximum width W2 of the inner tread rubber 13B to <NUM>% or less of the maximum width W1 of the noise damper <NUM>, the inner tread rubber 13B does not become larger than necessary and the steering stability can be maintained. Further, by setting the maximum width W2 of the inner tread rubber 13B to <NUM>% or more of the maximum width W1 of the noise damper <NUM>, it can be suppressed that the heat storage property of the tread rubber <NUM> increases, and the durability of tread portion <NUM> can be improved. From this point of view, the maximum width W2 of the inner tread rubber 13B is preferably equal to or less than <NUM>% of the maximum width W1 of the noise damper <NUM>, and preferably equal to or more than <NUM>%.

Preferably, the maximum thickness T2 (the maximum thickness in the tyre radial direction) of the inner tread rubber 13B is equal to or less than <NUM>% of the maximum thickness T3 (the maximum thickness in the tyre radial direction) of the tread rubber <NUM>. As a result, the ratio of the inner tread rubber 13B in the tread rubber <NUM> can be suppressed from becoming more than necessary, and the steering stability can be maintained. Further, the maximum thickness T2 of the inner tread rubber 13B is preferably equal to or more than <NUM>% of the maximum thickness T3 of the tread rubber <NUM>. This can suppress the increase in heat storage of the tread rubber <NUM> and improve the durability of the tread portion <NUM>. From this point of view, the maximum thickness T2 of the inner tread rubber 13B is preferably equal to or less than <NUM>% and preferably equal to or more than <NUM>% of the maximum thickness T3 of the tread rubber <NUM>.

In the present embodiment, a loss tangent tan δ of the inner tread rubber 13B at <NUM> degrees C is set smaller than a loss tangent tan δ of the middle tread rubber 13C at <NUM> degrees C. As a result, the inner tread rubber 13B can suppress heat generation from the start of running compared to the middle tread rubber 13C. Thus, the inner tread rubber 13B can suppress the heat storage of the tread rubber <NUM> due to the heat generated from the noise damper <NUM> during running, and the durability of the tyre can be improved.

Preferably, a loss tangent tan δ of the middle tread rubber 13C at <NUM> degrees C is set larger than a loss tangent tan δ of the outer tread rubber 13A at <NUM> degrees C. As a result, in the outer tread rubber 13A, the inner tread rubber 13B and the middle tread rubber 13C which constitute the tread rubber <NUM>, the loss tangent tan δ of the middle tread rubber 13C at <NUM> degrees C is set to be the largest. Thus, the heat generation in the outer tread rubber 13A can be suppressed. With this, heat transfer from the noise damper <NUM> to the tread rubber <NUM> can be suppressed, and the durability of the tread portion <NUM> can be improved. In order to effectively exert such an effect, the loss tangent tan δ of the middle tread rubber 13C at <NUM> degrees C is set to, for example, <NUM> to <NUM>.

The tread rubber <NUM> in accordance with the previous embodiment is provided with the middle tread rubber 13C between the outer tread rubber 13A and the inner tread rubber 13B, but is not limited to such an embodiment. For example, the middle tread rubber 13C may be omitted. In such a tyre <NUM>, similar to the tyre <NUM> of the previous embodiment, a loss tangent tan δ of the inner tread rubber 13B at <NUM> degrees C is set smaller than a loss tangent tan δ of the outer tread rubber 13A at <NUM> degrees C. This can suppress the increase in heat storage of the tread rubber <NUM> and improve the durability of the tread portion <NUM>.

Pneumatic tyres shown in <FIG> were prepared based on the specifications in Table <NUM> (Examples <NUM> to <NUM>). For comparison, a pneumatic tyre with the same loss tangent tan δ at <NUM> degrees C of the inner tread rubber and the loss tangent tan δ at <NUM> degrees C of the outer tread rubber was also prepared (comparative example).

Then, durability, noise performance and steering stability performance were evaluated for each test tyre. The specifications of each tyre are the same except for the configurations shown in Table <NUM>, and the tyre sizes, etc. are as follows. Further, the test methods are as follows.

In a drum running tester, each test tyre filled with the above internal pressure was run with a load of <NUM> kN, and the speed is increased by <NUM>/h every <NUM> minutes from <NUM>/h. Then, the running time until the tyre was damaged was measured. The evaluation is shown by an index with the running time of Example <NUM> as <NUM>. The larger the value, the higher the durability (high-speed durability). The evaluation <NUM> or more indicates better durability.

The noise (vehicle exterior noise) when the above-mentioned vehicle equipped with each test tyre set under the above conditions was run on a test course on a dry road (running speed: <NUM>/h) was evaluated by the driver's sensory. The evaluation is shown by a score with Example <NUM> as <NUM>. The larger the value, the better. The evaluation <NUM> or more indicates better noise performance.

The above-mentioned vehicle equipped with each test tyre set under the above conditions was run on a test course on a dry road (running speed: <NUM> to <NUM> / h). Then, the steering stability (responsiveness, rigidity, grip force, stability, and transient characteristics) at that time was evaluated by the sensuality of the test driver. The evaluation is shown by a score with Example <NUM> as <NUM>, and the larger the value, the better. The evaluation <NUM> or higher indicates that the vehicle has the required performance.

As a result of the test, it was confirmed that Examples <NUM> to <NUM> were able to improve the noise performance and the durability (improve the overall evaluation) compared to the comparative example. Furthermore, some Examples which have a better loss tangent tan δ of the inner tread rubber, a better ratio of the maximum width W1 of the noise damper to the tread ground width TW, and a better maximum thickness T1 of the noise damper could improve noise performance, durability, and steering stability in a well-balanced manner as compared to the others.

Pneumatic tyres shown in <FIG> were prepared based on the specifications in Table <NUM> (Example <NUM> to Example <NUM>). Then, durability, noise performance and steering stability performance were evaluated for each test tyre. The specifications of each tyre are the same except for the configuration shown in Table <NUM>, and the tyre size etc. are the same as in Example A except for the following. The test method is the same as in Example A.

Claim 1:
A pneumatic tyre (<NUM>) comprising:
a tread portion (<NUM>) having a tread rubber (<NUM>) and a tyre inner cavity surface (<NUM>); wherein
the tread rubber (<NUM>) comprises an outer tread rubber (13A) having a ground-contacting surface (<NUM>), and an inner tread rubber (13B) disposed inwardly in a tyre radial direction of the outer tread rubber (13A), and
a loss tangent tan δ of the inner tread rubber (13B) at <NUM> degrees C is smaller than a loss tangent tan δ of the outer tread rubber (13A) at <NUM> degrees C, wherein loss tangent tan δ at <NUM> degrees C is a value measured using a viscoelastic spectrometer under the provisions of JIS-K6394 at an initial distortion of <NUM>%, a frequency of <NUM>, an amplitude of +/-<NUM>% , under tension deformation mode and at a temperature of <NUM> degrees C,
characterized by a noise damper (<NUM>) made of a porous material fixed to the tyre inner cavity surface (<NUM>), wherein
the inner tread rubber (13B) is disposed outwardly in the tyre radial direction of the noise damper (<NUM>), and
a pair of ends (13Bt) in a tyre axial direction of the inner tread rubber (13B) is arranged inwardly in the tyre axial direction of a pair of outer ends (14t) in the tyre axial direction of the noise damper (<NUM>).