Patent ID: 12194785

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present disclosure will now be described in detail in conjunction with accompanying drawings.

FIG.1is a meridian cross-sectional view of a pneumatic tire1as an embodiment of the present disclosure under its normal state.

The present disclosure can be applied to tires for light trucks (including commercial vehicles).

Further, the present disclosure may be applied to tires for passenger cars and heavy duty vehicles such as trucks and buses.

Here, the normal state is a no-load state in which the tire is mounted on a regular rim R and inflated to a standard pressure.

In this application including the description and claims, dimensions, positions and the like relating to the tire are refer to those under the normal state unless otherwise noted.

The regular rim R 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. For example, the regular 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 for the tire specified by the same organization in the Air-pressure/Maximum-load Table or similar list.

For example, 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.

As shown inFIG.1, the tire1comprises a pair of bead portions4each with a bead core5embedded therein, and a carcass6extending between the bead portions4.

The carcass6comprises at least one carcass ply (6A,6B) extending between the bead portions4through a tread portion2and sidewall portions3, and turned up around the bead core5in each bead portion4from the axially inside to the axially outside so as to form a pair of turnup portions6bextending radially outwardly and a main portion6atherebetween.

In the present embodiment, the carcass6is composed of two carcass plies6A and6B arranged radially inside and outside in the tread portion2.

The radially outer end6eof the turnup portion6bof the inner carcass ply6A is positioned radially inside the radially outer end6iof the turnup portion6bof the outer carcass ply6B.

The carcass6may be composed of only one carcass ply6A.

One of or each of the bead portions4is provided with a reinforcing rubber portion10adjacent to the axially outer side of the axially outer turnup portion6b.

The reinforcing rubber portion10is to enhance the rigidity of the bead portion4, suppress deflection during running and improve bead durability performance.

In the present embodiment, the reinforcing rubber portion10is disposed in each of the bead portions4.

The reinforcing rubber portion10is disposed on the axially outer side of the turnup portion6bof the inner carcass ply6A.

The reinforcing rubber portion10is composed of an axially inner rubber layer11and an axially outer rubber layer12which is disposed on the axially outer side of the axially inner rubber layer11.

The reinforcing rubber portion10may include one or more intermediate rubber layers (not shown) arranged between the axially inner rubber layer11and the axially outer rubber layer12.

The radially outer end12eof the axially outer rubber layer12is positioned radially outside the radially outer end11eof the axially inner rubber layer11.

The radially inner end12iof the axially outer rubber layer12is positioned radially inside the radially inner end11iof the axially inner rubber layer11.

Such axially outer rubber layer12enhances the rigidity of the bead portion4, especially the lateral rigidity, thereby improving the bead durability performance.

The axially outer rubber layer12prevents contact between a sidewall rubber3G or a clinch rubber4G which will be described later, and the axially inner rubber layer11, so that the number of steps formed by the reinforcing rubber portion10and the sidewall rubber3G or the clinch rubber4G is decreased to suppress the occurrence of space not filled with rubber.

Therefore, in the tire according to the present disclosure, the bead durability performance can be further improved.

On the radially outer side of the reinforcing rubber portion10, the two outer ends11eand12ecome into contact with the carcass ply6A or6B. On the radially inner side of the reinforcing rubber portion10, the two inner ends11iand12icome into contact with the carcass ply6A. Therefore, strain concentration on the carcass ply6A is relaxed as compared with the case where only the radially outer end11eand the inner end11iof the axially inner rubber layer11are in contact with the carcass ply6A (for example, when the length of the axially inner rubber layer11is greater than the length of the axially outer rubber layer12). As a result, the looseness of the carcass ply6A is suppressed. Therefore, the tire1according to the present disclosure is further improved in bead durability performance.

In each of the bead portions4in the present embodiment, the bead apex rubber8, the sidewall rubber3G, and the clinch rubber4G are disposed.

The bead apex rubber8extends radially outwardly from the bead core5.

The clinch rubber4G is disposed axially outside the reinforcing rubber portion10.

The sidewall rubber3G is disposed adjacently to the radially outer side of the clinch rubber4G.

The sidewall rubber3G and the clinch rubber4G form a part of the outer surface of the tire1.

The distance D1 in the tire radial direction between the radially outer end11eof the axially inner rubber layer11and the radially outer end12eof the axially outer rubber layer12is preferably not less than 3 mm.

Thereby, between the radially outer ends11eand12e, a certain distance is secured, and the change in rigidity of the bead portion4in the tire radial direction is reduced, so the bead durability performance is further improved.

The distance D1 is more preferably not less than 5 mm, but preferably not more than 15 mm, more preferably not more than 10 mm.

From the same point of view, the distance D2 (shown inFIG.2) in the tire radial direction between the radially inner end11iof the axially inner rubber layer11and the radially inner end12iof the axially outer rubber layer12is preferably not less than 3 mm, more preferably not less than 5 mm, but preferably not more than 10 mm, more preferably not more than 7 mm.

The height H1 from the bead baseline BL to the radially outer end12eof the axially outer rubber layer12is preferably not less than 20%, more preferably not less than 30%, but preferably not more than 50%, more preferably not more than 45% of the tire section height H.

Since the height H1 is not less than 20% of the tire section height H, it is possible to exhibit high lateral rigidity against the load applied during running.

Since the height H1 is not more than 50% of the tire sectional height H, damage at the buttress portion B to which a relatively large load is applied is suppressed.

Here, the tire section height H is the distance in the tire radial direction from the bead base line BL to the radially outermost position of the tread portion2.

The bead base line BL is a straight line extending parallel to the tire axial direction, passing through the radial position corresponding to the rim diameter determined by the standard (for example, JATMA) on which the tire is based.

In the present embodiment, the radially outer end12eof the axially outer rubber layer12is positioned radially inward of the radially outermost end6tof the turnup portions6b.

Thereby, undesirable steps are eliminated, and the occurrence of space not filled with rubber, namely, space filled with air can be suppressed. And sufficient bead durability performance can be ensured.

FIG.2is an enlarged view of the bead portion4.

In the present embodiment, the radially inner end12iof the axially outer rubber layer12is positioned radially inward of the radially outer end5eof the bead core5as shown inFIG.2. Thereby, the axially outer rubber layer12and the bead core5overlap in the tire radial direction, and deformation of the axially outer rubber layer12is further suppressed, thereby improving bead durability performance.

The radially inner end12iof the axially outer rubber layer12in this example is positioned radially inside the center5cin the tire radial direction of the bead core5.

The radially inner end12iof the axially outer rubber layer12in this example is preferably positioned radially outside the radially inner end5iof the bead core5.

Thereby, the fitability with the wheel rim is maintained at a high level, while maintaining the bead durability performance.

The radially inner end11iof the axially inner rubber layer11in this example is positioned radially inward of the radially outer end8eof the bead apex rubber8.

As a result, the bead apex rubber8and the axially inner rubber layer11overlap in the tire radial direction, and deformation of the axially inner rubber layer11is suppressed, thereby further improving bead durability performance.

The radially inner end11iof the axially inner rubber layer11is preferably positioned radially outside the radially outer end5eof the bead core5.

As a result, the fitability to the wheel rim is maintained at a high level, while maintaining the bead durability performance.

The loss tangent62of the axially outer rubber layer12is preferably larger than the loss tangent61of the axially inner rubber layer11.

Such axially outer rubber layer12has higher rigidity, and exerts an effect of suppressing strain and an effect of improving lateral rigidity.

Since the axially inner rubber layer11has a smaller hysteresis loss than the axially outer rubber layer12, the amount of heat generated is suppressed.

As a result, the axially inner rubber layer11suppresses the heat of the axially outer rubber layer12from being transferred to the carcass ply6A, and the separation between the axially inner rubber layer11and the carcass ply6A is suppressed. Therefore, the bead durability performance is greatly improved.

In order to effectively derive such advantageous effect, the loss tangent62of the axially outer rubber layer12is preferably 0.07 or more, more preferably 0.12 or more, but preferably 0.20 or less, more preferably 0.18 or less.

The loss tangent61of the axially inner rubber layer11is preferably not less than 50%, more preferably not less than 55%, but preferably not more than 70%, more preferably not more than 65% of the loss tangent62of the axially outer rubber layer12,

In this specification, the loss tangent δ and the complex elastic modulus E* described later are measured using a dynamic viscoelasticity measuring device (Iplexer series manufactured by GABO) under the following conditions in accordance with the provisions of JIS-K6394 “Rubber, vulcanized or thermoplastic—Determination of dynamic properties—General guidance”.Initial strain: 10%Dynamic strain amplitude: +/−2%Frequency: 10 HzDeformation mode: StretchMeasurement temperature: 70 deg. C

The complex elastic modulus E*2 of the axially outer rubber layer12is preferably not less than 120% of the complex elastic modulus E*1 of the axially inner rubber layer11.

As a result, the lateral rigidity of the axially outer rubber layer12disposed on the outer side in the tire axial direction is maintained high, and deformation under high load conditions is suppressed, thereby improving bead durability performance.

If the complex elastic modulus E*2 of the axially outer rubber layer12is excessively larger than the complex elastic modulus E*1 of the axially inner rubber layer11, then the stepped rigidity change at the radially outer end12eand the radially inner end12iof the axially outer rubber layer12becomes large.

Thus, there is a possibility that the bead durability performance may deteriorate.

For this reason, the complex elastic modulus E*2 of the axially outer rubber layer12is preferably larger than the complex elastic modulus E*1 of the axially inner rubber layer11, and the complex elastic modulus E*2 is preferably not more than 200%, more preferably not more than 190% of the complex elastic modulus E*1.

Although not particularly limited, the complex elastic modulus E*2 of the axially outer rubber layer12is preferably 40 MPa or more, more preferably 50 MPa or more, but preferably 150 MPa or less, more preferably 120 MPa or less.

Preferably, the adhesive force f2 of the axially outer rubber layer12is not less than 1.3 times the adhesive force f1 of the axially inner rubber layer11.

Such axially outer rubber layer12has high adhesiveness to the sidewall rubber3G or the clinch rubber4G, and helps to improve the bead durability performance.

Although not particularly limited, the adhesive force f2 of the axially outer rubber layer12is more preferably not less than 1.4 times, but preferably not more than 2.0 times, more preferably not more than 1.8 times the adhesive force f1 of the axially inner rubber layer11.

The adhesive force f2 of the axially outer rubber layer12is preferably not less than 150N, more preferably not less than 180N.

Although not particularly limited, considering the attachment work of the axially outer rubber layer12, the adhesive force f2 is preferably not more than 350N, more preferably not more than 300N.

The adhesive force is of the rubber layers11and12in the state before vulcanization (namely, sheet-shaped rubber members described later), and is measured under the following conditions, using a PICMA tack tester manufactured by Toyo Seiki Co., Ltd.Load for pressure bonding: 4.9 NPressurizing time: 30 secondsPeeling speed: 15 mm/minTemperature: 20 degrees C.Humidity: 55%

Each of the axially inner rubber layer11and the axially outer rubber layer12is made of a sheet-shaped rubber member13(shown inFIG.3).

The sheet-shaped rubber member13is obtained, for example, by cutting a raw rubber sheet (not shown) extruded by a rubber extruder.

Such sheet-shaped rubber member13facilitates the production of the reinforcing rubber portion10for various tire sizes and enhances its versatility.

FIG.3is a perspective view of each sheet-shaped rubber member13.

As shown inFIG.3, in the present embodiment, the sheet-shaped rubber member13includes a first sheet-shaped rubber member13afor forming the axially inner rubber layer11and a second sheet-shaped rubber member13bfor forming the axially outer rubber layer12.

In the present embodiment, the reinforcing rubber portion10is formed by laminating these sheet-shaped rubber members13aand13bin the tire axial direction.

Each sheet-shaped rubber member13is vulcanized to form the axially inner rubber layer11and the axially outer rubber layer12.

As shown inFIG.2, the axially inner rubber layer11has a constant-thickness portion14having a constant thickness, and reduced-thickness portions15whose thickness decreases toward its radially inner end11iand radially outer end11e, and the axially outer rubber layer12has a constant-thickness portion14having a constant thickness, and reduced-thickness portions15whose thickness decreases toward its radially inner end12iand its radially outer end12e.

The reduced-thickness portion15serves to alleviate the stepped rigidity difference and improve the bead durability performance.

Here, the constant-thickness portion is a portion where the thickness variation is at most 0.2 mm per 1 mm length along the longitudinal direction (tire radial direction) of the axially inner rubber layer11and the axially outer rubber layer12.

For example, the length Lc of each reduced-thickness portion15is preferably not more than 5 mm, more preferably not more than 3 mm.

The reinforcing rubber portion10have a first portion17where the two sheet-shaped rubber members13are laminated, and a second portion18where the two sheet-shaped rubber members13are not laminated (namely, a portion18is formed by only one sheet-shaped rubber member13).

In the present embodiment, the first portion17is composed of the axially inner rubber layer11and the axially outer rubber layer12which are laminated.

In the present embodiment, the second portion18is composed of only the axially outer rubber layer12.

The second portion18comprises an inner second portion18aextending radially inwardly from the radially inner end11iof the axially inner rubber layer11, and an outer second portion18bextending radially outwardly from the radially outer end11eof the axially inner rubber layer11.

In the present embodiment, the first portion17is positioned between the inner second portion18aand the outer second portion18b.

The first portion17includes a maximum thickness portion17a.

The maximum thickness portion17ais formed by overlapping the constant-thickness portion14of the axially inner rubber layer11and the constant-thickness portion14of the axially outer rubber layer12.

The maximum thickness portion17adoes not includethe portion19awhere the reduced-thickness portion15of the axially inner rubber layer11including the radially outer end11eand the constant-thickness portion14of the axially outer rubber layer12overlap, andthe portion19bwhere the reduced-thickness portion15of the axially inner rubber layer11including the radially inner end11iand the constant-thickness portion14of the axially outer rubber layer12overlap.

It is preferable that the first portion17is positioned across a straight line K, which is drawn parallel to the tire axial direction, passing through the radially outer end21of the contact area between the tire1and the regular rim R under the normal state of the tire.

The vicinity of the radially outer end21is a portion to which a large bending load acts while the vehicle is running.

By disposing the first portion17in the same position in the tire radial direction as the radially outer end21, deformation at the radially outer end21is suppressed, and the bead durability performance is further improved.

In order to derive this effect more effectively, it is preferred that the maximum thickness portion17ais positioned across the straight line K.

The difference (Ta−Tb) between the thickness Ta of the first portion17and the thickness Tb of the second portion18is preferably 1 mm or more.

Since the difference (Ta−Tb) is 1 mm or more, the rigidity of the first portion17is increased and the durability is improved.

If the difference (Ta−Tb) is excessively large, the rigidity of the first portion17becomes too large, and there is a possibility that ride comfort performance is deteriorated.

From this point of view, the difference (Ta−Tb) is preferably 3.5 mm or less, more preferably 3.0 mm or less.

The thickness Ta of the first portion17is the thickness of the maximum thickness portion17a.

The thickness Tb of the second portion18is the thickness T2 of the constant-thickness portion14of the axially outer rubber layer12.

In order to effectively derive the above effects, the thickness Ta of the first portion17is preferably not less than 1.5 times, more preferably not less than 1.8 times, but preferably not more than 2.5 times, more preferably not more than 2.3 times the thickness Tb of the second portion18.

The thickness T2 of the constant-thickness portion14of the axially outer rubber layer12is preferably larger than the thickness T1 of the constant-thickness portion14of the axially inner rubber layer11.

As a result, the reinforcing rubber portion10can suppress the occurrence of bareness of rubber, while ensuring sufficient durability, so the appearance of the tire can be improved.

Although not particularly limited, the thickness T2 of the axially outer rubber layer12is preferably not less than 120%, more preferably not less than 150%, but preferably not more than 350%, more preferably not more than 300% of the thickness T1 of the axially inner rubber layer11.

The thickness T2 of the axially outer rubber layer12is preferably 0.5 mm or more, more preferably 0.8 mm or more, but preferably 2.0 mm or less, more preferably 1.5 mm or less. When the thickness T2 of the constant-thickness portion14of the axially outer rubber layer12is the same as the thickness T1 of the constant-thickness portion14of the axially inner rubber layer11, the axially inner rubber layer11and the axially outer rubber layer12may be manufactured by cutting one sheet of the sheet-shaped rubber member13.

The bead apex rubber8in this example has a triangular shape in the meridian cross section of the tire.

Although not particularly limited, at a radial position corresponding to the radial height of the radially outer end8eof the bead apex rubber8, both the axially inner rubber layer11and the axially outer rubber layer12exist.

In the present embodiment, at the radial position corresponding to the radial height of the radially outer end8eof the bead apex rubber8, the maximum thickness portion17aexists.

The complex elastic modulus E*3 of the bead apex rubber8is preferably equal to the complex elastic modulus E*1 of the axially inner rubber layer11, for example.

The complex elastic modulus E*3 of the bead apex rubber8is preferably smaller than the complex elastic modulus E*2 of the axially outer rubber layer12, for example.

As shown inFIG.1, the complex elastic modulus E* of the sidewall rubber3G and the clinch rubber4G are both smaller than the complex elastic modulus E*1 of the axially inner rubber layer11. As a result, basic ride comfort performance is provided.

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

Comparison Tests

Based on the structure shown inFIG.1, pneumatic tires were experimentally manufactured as test tires (Comparative examples Ref.1-Ref.4 and Examples Ex.1-Ex.5 according to the present disclosed) and tested for the bead durability performance and appearance.

Specifications of the test tires are shown in Table 1, whereinthe values of δ1 and δ2 are indicated by an index based on the value of δ1 of Ref.1 being 100,the values of E*1 and E*2 are indicated by an index based on the value of E*1 of Ref.1 being 100,the values of f2/f1 are indicated by an index based on the value of f1 of Ref.1 being 100,the loss tangent δ1 of the axially inner rubber layer of Ref.1 was 0.10,the complex elastic modulus E*1 of the axially inner rubber layer of Ref.1 was 20 MPa, andthe adhesive force f1 of the axially inner rubber layer of Ref.1 was 150 N.
<Bead Durability Test>

Using a tire test drum, each test tire was run under the following conditions, and the running distance until the bead portion broke was measured.

The results are indicated in Table 1 by an index based on Comparative Example Ref.1 being 100, wherein the larger the numerical value, the better, the bead durability performance.Rim size: 6.0 JInternal pressure: 220 kPavertical tire load: 19.84 kNRunning speed: 20 km/h
<Appearance Test>

The outer surface of the region of each test tire where the sidewall rubber or the clinch rubber was disposed was visually evaluated by a tester.

The results are indicated in Table 1 by an index based on Comparative Example Ref.1 being 100, wherein the larger the numerical value, the better the appearance.

TABLE 1TireRef. 1Ref.2Ref.3Ref.4Ex. 1Ex.2Ex.3Ex.4Ex.5D1(mm)00001.53533D2(mm)00001.53533Ta(mm)333333333Tb(mm)1.511111111tanδ110010080808080808080tanδ2100100100130100100100100100E*110010080808080808080E*2100100100130100100100100100f2/f1100100100100100100100130150Bead100110120120130140140150150durabilityAppear-100100100100110110110110110ance

From the test results, it was confirmed that Example tires according to the present disclosure had improved bead durability performance as compared to Comparative example tires, and maintained good appearance.

STATEMENT OF THE PRESENT DISCLOSURE

The present disclosure is as follows:

Disclosure 1: A pneumatic tire comprising:a pair of bead portions each with a bead core embedded therein, anda carcass extending between the bead portions, the carcass comprising a carcass ply extending between the bead portions and turned up around the bead core in each bead portion from the axially inside to the axially outside so as to form a pair of turnup portions extending radially outwardly, and a main portion therebetween,
whereinone of or each of the bead portions is provided with a reinforcing rubber portion disposed adjacently to the axially outer side of the turnup portion,the reinforcing rubber portion includes an axially inner rubber layer, and an axially outer rubber layer which is adjacent to the axially outer side of the axially inner rubber layer,the radially outer end of the axially outer rubber layer is positioned radially outside the radially outer end of the axially inner rubber layer, andthe radially inner end of the axially outer rubber layer is positioned radially inside the radially inner end of the axially inner rubber layer.

Disclosure 2: The pneumatic tire according to Disclosure 1, whereinthe distance D1 in the tire radial direction betweenthe radially outer end of the axially inner rubber layer andthe radially outer end of the axially outer rubber layer is 3 mm or more.

Disclosure 3: The pneumatic tire according to Disclosure 1, whereinthe distance D2 in the tire radial direction betweenthe radially inner end of the axially inner rubber layer andthe radially inner end of the axially outer rubber layer is 3 mm or more.

Disclosure 4: The pneumatic tire according to any one of Disclosures 1 to 3, whereinthe axially inner rubber layer and the axially outer rubber layer are made of sheet-shaped rubber members, andthe reinforcing rubber portion includes a first portion where the sheet-shaped rubber members are laminated, andthe first portion extends across a straight line drawn in parallel to the tire axial direction, passing through the radially outer end of a contact area between the pneumatic tire and a regular rim in a state of the tire which is mounted on the regular rim, and inflated to a standard pressure, but loaded with no tire load.

Disclosure 5: The pneumatic tire according to Disclosure 4, whereina thickest portion of the first portion exists on the straight line.

Disclosure 6: The pneumatic tire according to Disclosure 4 or 5, whereinthe reinforcing rubber portion includes a second portion where the sheet-shaped rubber members are not laminated, andthe difference (Ta−Tb) between the thickness Ta of the first portion and the thickness Tb of the second portion is 1 mm or more.

Disclosure 7: The pneumatic tire according to Disclosure 6, whereinthe thickness Ta of the first portion is 1.5 to 2.5 times the thickness Tb of the second portion.

Disclosure 8: The pneumatic tire according to any one of Disclosures 1 to 7, whereina loss tangent δ2 of the axially outer rubber layer is greater than a loss tangent δ1 of the axially inner rubber layer.

Disclosure 9: The pneumatic tire according to any one of Disclosures 1 to 8, whereina complex elastic modulus E*2 of the axially outer rubber layer is not less than 60% of a complex elastic modulus E*1 of the axially inner rubber layer.

Disclosure 10: The pneumatic tire according to Disclosure 9, whereinthe complex elastic modulus E*2 of the axially outer rubber layer is greater than the complex elastic modulus E*1 of the axially inner rubber layer.

Disclosure 11: The pneumatic tire according to any one of Disclosures 1 to 10, whereinthe axially outer rubber layer and the axially inner rubber layer each include a constant-thickness portion having a constant thickness.

Disclosure 12: The pneumatic tire according to any one of Disclosures 1 to 11, whereinan adhesive force of the axially outer rubber layer is not less than 1.3 times an adhesive force of the axially inner rubber layer.

DESCRIPTION OF THE REFERENCE SIGNS

1Pneumatic tire4Bead portion6A Carcass ply10Reinforcing rubber portion11Inner rubber layer11eRadially outer end of Inner rubber layer11iRadially inner end of Inner rubber layer12Outer rubber layer12eRadially outer end of Outer rubber layer12iRadially inner end of Outer rubber layer