Patent ID: 12246560

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure can be applied to tires for passenger cars, heavy duty vehicles and the like, but suitably applied to tires for light trucks (including commercial vehicles).

Taking a pneumatic tire for light trucks as an example, an embodiment of the present disclosure will be described in detail in conjunction with accompanying drawings.

FIG.1is a tire meridian sectional view including the tire rotation axis (not shown) of a pneumatic tire1as an embodiment of the present disclosure.

As well known in the art, a pneumatic tire comprises a tread portion whose radially outer surface defines the tread, a pair of axially spaced bead portions mounted on rim seats, a pair of sidewall portions extending between the tread edges and the bead portions, a carcass extending between the bead portions through the tread portion and the sidewall portions, and a tread reinforcing belt disposed radially outside the carcass in the tread portion.

InFIG.1, shown is the tire under its a normal state.

Here, the normal state is such that the tire is mounted on a standard wheel rim R and inflate to a standard pressure but loaded with no tire load.

The undermentioned normally inflated loaded condition 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.

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.

In this application including specification and claims, various dimensions, positions and the like of the tire refer to those under a normal state unless otherwise noted.

As shown inFIG.1, the tire1in the present embodiment comprisesa pair of bead portions4each with a bead core5embedded therein, anda carcass6extending between the bead cores5.

The carcass6comprises at least one carcass ply (6A,6B).

The carcass ply (6A,6B) extends between the bead portions4and is turned up around the bead core5in each bead portion4from the inside to the outside in the tire axial direction so as to form a pair of turnup portions6bextending radially outwardly and a main portion6atherebetween.
The carcass6may be composed of only one carcass ply6A.
In the present embodiment, the carcass6is composed of two carcass plies6A and6B arranged radially inside and outside in the tread portion.

At least one of the bead portions4is provided with a reinforcing rubber portion10adjacent to the axially outer side of the turnup portion6b.

The reinforcing rubber portion10increases the rigidity of the bead portion4, suppresses deflection during running, and improves bead durability.

In the present embodiment, each of the bead portions4is provided with the reinforcing rubber portion10.

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

The reinforcing rubber portion10comprises an inner rubber layer11and an outer rubber layer12disposed on the axially outside of the inner rubber layer11.

In addition, the reinforcing rubber portion10may include one or more intermediate rubber layers (not shown) disposed between the inner rubber layer11and the outer rubber layer12.

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

Such outer rubber layer12further increases the rigidity of the bead portion4and improves the bead durability.

Further, the outer rubber layer12prevents contact between the radially outer end11eof the inner rubber layer11and a sidewall rubber3G and a clinch rubber4G which will be described later, and

reduces the number of stepped portions formed by the reinforcing rubber portion10and the rubbers3G and4G. This suppresses the occurrence of bareness of rubber, namely, rubber unfilled part.
Furthermore, since the radially outer end11eof the inner rubber layer11and the radially outer end12eof the outer rubber layer12come into contact with the carcass ply6A at two different positions, stress concentration on the carcass ply6A is alleviated, and loosening of the ply6A is suppressed.
Therefore, the tire1of the present disclosure can further improve the bead durability.

In the present embodiment, each of the bead portions4is provided with a bead apex rubber8and a clinch rubber4G, andeach of the sidewall portions is provided with a sidewall rubber3G.

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 extended to the bead portion so as to be adjacent to a radially outer portion of the clinch rubber4G.

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

The radially outer end12eof the outer rubber layer12is positioned at a radial height H1 from the bead base line BL, andthe radial height H1 is preferably 25% or more, more preferably 50% or more, but preferably 75% or less of the tire cross-sectional height H.
Since the radial height H1 is 25% or more of the tire section height H, it is possible to maintain high lateral rigidity against the load applied during running.
Since the radial height H1 is 75% or less of the tire section height H, strain at the radially outer end12eof the outer rubber layer12in the buttress portion B is reduced, and damage is suppressed.

The tire section height H is the distance in the tire radial direction from the bead base line BL to the radially outermost position on the tire.

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

In the present embodiment, the radially outer end12eof the outer rubber layer12is positioned radially inward of the radially outer end6tof the turnup portion6bof the inner carcass ply6A. Thereby, the outer rubber layer12will be less likely to have a level difference and damage will be suppressed.

In each bead portion, the radially inner end12iof the outer rubber layer12and the radially inner end11iof the inner rubber layer11are displaced in the tire radial direction from each other. This suppresses concentration of strain on the carcass ply6A at the radially inner ends11iand12i.

The radial height H2 of the radially outer end11eof the inner rubber layer11from the bead base line BL is preferably 25% or more, more preferably 30% or more, but preferably 60% or less, more preferably 55% or less of the tire section height H. Since the radial height H2 is 25% or more of the tire section height H, it is possible to maintain high lateral rigidity against the load applied during running.

Since the radial height H2 is 60% or less of the tire section height H, excessive increase in rigidity of the bead portion4is suppressed.

The first distance (H1−H2) in the tire radial direction between the radially outer end12eof the outer rubber layer12and the radially outer end11eof the inner rubber layer11is preferably 10% or more, more preferably 15% or more, preferably 30% or less, but more preferably 25% or less of the tire section height H.

Thereby, the strain generated at the outer ends11eand12eis appropriately dispersed, and the effect of improving the lateral rigidity by the reinforcing rubber portion10is highly exhibited.

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

As shown inFIG.2, the radially inner end12iof the outer rubber layer12is positioned radially outside the radially outer end5eof the bead core5. Thereby, the rigidity in the vicinity of the bead core5is suppressed from becoming excessively high, thereby suppressing deterioration in fitting of the bead portion to the wheel rim.
The radially inner end11iof the inner rubber layer11is located radially inside the radially outer end5eof the bead core5. Thereby, the lateral rigidity of the bead portion4is maintained high.
Thus, the radially inner end12iof the outer rubber layer12is located radially outside the radially inner end11iof the inner rubber layer11in the present embodiment.
The radially inner end12iportion of the outer rubber layer12overlaps withthe bead apex rubber8in the tire radial direction.

The second distance Hb in the tire radial direction between the radially inner end12iof the outer rubber layer12and the radially inner end11iof the inner rubber layer11is preferably 5% or more, more preferably 7% or more, but preferably 15% or less, more preferably 13% or less of the first distance (H1−H2).

Thereby, the rigidity in the vicinity of the bead core5can be effectively increased.

It is preferable that the loss tangent δ2 of the outer rubber layer12is larger than the loss tangent δ1 of the inner rubber layer11.

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

Since the inner rubber layer11has a smaller hysteresis loss than the outer rubber layer12, the amount of heat generated is suppressed. Thereby, the inner rubber layer11suppresses the heat of the outer rubber layer12from being transferred to the carcass ply6A, and the separation between the inner rubber layer11and the carcass ply6A is suppressed. Therefore, the bead durability is greatly improved.

In order to effectively derive the above effects, the loss tangent δ2 of the outer rubber layer12is preferably 0.12 or more, more preferably 0.14 or more, but preferably 0.25 or less, more preferably 0.20 or less.

The loss tangent δ1 of the inner rubber layer11is preferably 60% or more, more preferably 65% or more, but preferably 90% or less, more preferably 85% or less of the loss tangent δ2 of the 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*2of the outer rubber layer12is preferably 60% or more of the complex elastic modulus E*1 of the inner rubber layer11.

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

If the complex elastic modulus E*2 of the outer rubber layer12is excessively larger than the complex elastic modulus E*1 of the inner rubber layer11,

stepped difference in rigidity at the radially outer end12eand the radially inner end12iof the outer rubber layer12become large, andthere is a possibility that the bead durability may deteriorate.
For this reason, it is preferable that the complex elastic modulus E*2 of the outer rubber layer12is larger than the complex elastic modulus E*1 of the inner rubber layer11. And the complex elastic modulus E*2 is preferably 200% or less, more preferably 190% or less of the complex elastic modulus E*1.
Although not particularly limited, the complex elastic modulus E*2 of the outer rubber layer12is preferably 60 MPa or more, more preferably 80 MPa or more, but preferably 140 MPa or less, more preferably 120 MPa or less.

Each of the inner rubber layer11and the 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 inner rubber layer11and a second sheet-shaped rubber member13bfor forming the 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 inner rubber layer11and the outer rubber layer12.

As shown inFIG.2, the inner rubber layer11has a constant-thickness portion14having a constant thickness, and reduced-thickness portions15whose thickness decreases toward its radially inner end11iand radially outer end11e, andthe 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 rigidity stepped difference and improve the bead durability.
Here, the constant-thickness portion is a portion where the thickness variation is at most 0.2 mm per 1 mm in the tire radial direction.
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 portion10hasa first portion17where the two sheet-shaped rubber members13are laminated, anda 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 inner rubber layer11and the outer rubber layer12.
In the present embodiment, the second portion18includesa radially inner second portion18aformed by only the inner rubber layer11, anda radially outer second portion18bformed by only the outer rubber layer12.
In the present embodiment, the first portion17is positioned between the second inner portion18aand the second outer portion18b.

The first portion17includes a maximum thickness portion17a.

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

The maximum thickness portion17adoes not include

the portion19awhere the reduced-thickness portion15of the inner rubber layer11and the constant-thickness portion14of the outer rubber layer12overlap, andthe portion19bwhere the reduced-thickness portion15of the outer rubber layer12and the constant-thickness portion14of the inner rubber layer11overlap.

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 radial outer end21of the contact position between the tire1and the normal 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 is further improved.

In order to drive 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 of the constant-thickness portion14of the inner rubber layer11.

The thickness Tb of the second portion18may be the thickness of the constant-thickness portion14of the 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 T1 of the inner rubber layer11and the thickness T2 of the outer rubber layer12are 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.

The bead apex rubber8in this example is formed in a triangular shape in a tire meridian cross section as shown inFIG.2.

Although not particularly limited, it is preferred that, at a radial position at a radial height of the radially outer end8eof the bead apex rubber8, there are the inner rubber layer11and the outer rubber layer12.

In the present embodiment, at a radial position at a radial height of the radially outer end8eof the bead apex rubber8, there is disposed the maximum thickness portion17a.

The complex elastic modulus E*3 of the bead apex rubber8is preferably smaller than the complex elastic modulus E*1 of the inner rubber layer11.

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

The complex elastic modulus of each of the sidewall rubber3G and the clinch rubber4G is smaller than the complex elastic modulus E*1 of the inner rubber layer11. Thereby, basic ride comfort performance is exhibited.

The complex elastic modulus E*b of the sidewall rubber3G is preferably not less than 5%, more preferably not less than 10%, but preferably not more than 50%, more preferably not more than 40% of the complex elastic modulus E*1 of the inner rubber layer11.

The complex elastic modulus E*c of the clinch rubber4G is preferably not less than 10%, more preferably not less than 20%, but preferably not more than 70%, more preferably not more than 60% of the complex elastic modulus E*1 of the inner rubber layer11.

While detailed description has been made of a preferable embodiment of the present invention, the present invention 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, and tested for the bead durability and steering stability.

Specifications of the pneumatic tires are shown in Table 1, wherein

the values of tan δ1 and tan δ2 are indicated by an index based on the value of tan δ1 of Comparative Example 1 being 100, andthe values of complex elastic moduli E*1 and E*2 are indicated by an index based on the value of E*1 of Comparative Example 1 being 100, whereintan δ1 of the inner rubber layer of Comparative Example 1 was 0.10, andE*1 of the inner rubber layer of Comparative Example 1 was 20 MPa.
<Bead Durability Test>
Using a tire test drum, each tire was run under the following conditions, andthe running distance until the bead portion(s) was damaged was measured.Tire inflation pressure: 220 kPaVertical tire load: 19.84 kNRunning speed: 20 km/hWheel rim size: 6.0 J
The results are indicated in Table 1 by an index based on the running distance of Comparative Example 1 being 100, wherein the larger the numerical value, the better the bead durability.
<Steering Stability Test>

Using a test vehicle (2000cc small truck) on all wheels of which test tires were mounted, the test driver evaluated steering stability performance based on stability and maneuverability when running on a dry asphalt test course at high speed.

The results are indicated in Table 1 by an index based on Comparative Example 1 being 100, wherein the higher the value, the better the steering stability performance.

TABLE 1ComparativeTireexample 1Example 1Example 2H1/H (%)252555H2/H (%)207575tanδ11008080tanδ2100130130E*11008080E*2100130130Ta (mm)333Tb (mm)1.511Bead durability100120120Steering stability6080100

From the test results, it was confirmed that the bead durability of Example tires according to the present disclosure were improved as compared to Comparative example tire, and the steering stability performance of Examples tires was maintained.

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 cores, and comprising a carcass ply, the carcass ply comprising a main portion extending between the bead cores, and a turnup portion turned up around the bead core in each bead portion from the axially inside to the axially outside and extending outwardly in the tire radial direction,
whereinat least one of the bead portions is provided with a reinforcing rubber portion adjacent to the axially outer side of the turnup portion,the reinforcing rubber portion comprises an inner rubber layer and an outer rubber layer adjacent to the axially outer side of the inner rubber layer, andthe radially outer end of the outer rubber layer is positioned radially outside the radially outer end of the inner rubber layer.
Disclosure 2: The pneumatic tire according to Disclosure 1, wherein the height in the tire radial direction, of the radially outer end of the outer rubber layer from a bead base line is 25% to 75% of the section height of the tire.
Disclosure 3: The pneumatic tire according to Disclosure 1 or 2, wherein the radially inner end of the outer rubber layer is located radially outside the radially inner end of the inner rubber layer.
Disclosure 4: The pneumatic tire according to Disclosure 3, wherein each of the inner rubber layer and the outer rubber layer is made of a sheet-shaped rubber member, and the reinforcing rubber portion includes a first portion where the sheet-shaped rubber members are laminated, andthe first portion is positioned across a straight line which is drawn parallel to the tire axial direction, passes through a radially outer end of a contact position between the tire and a standard wheel rim under a normal state such that the tire is mounted on the standard wheel rim, and inflated to a standard pressure but loaded with no tire load.
Disclosure 5: The pneumatic tire according to Disclosure 4, wherein a thickest portion of the first portion is positioned across the straight line.
Disclosure 6: The pneumatic tire according to Disclosure 4 or 5, wherein the 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, wherein the 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, wherein the loss tangent δ2 of the outer rubber layer is larger than the loss tangent δ1 of the inner rubber layer.
Disclosure 9: The pneumatic tire according to any one of Disclosures 1 to 8, wherein the complex elastic modulus E*2 of the outer rubber layer is 60% or more of the complex elastic modulus E*1 of the inner rubber layer.
Disclosure 10: The pneumatic tire according to Disclosure 9, wherein the complex elastic modulus E*2 of the outer rubber layer is greater than the complex elastic modulus E*1 of the inner rubber layer.
Disclosure 11: The pneumatic tire according to any one of Disclosures 1 to 10, wherein the outer rubber layer and the inner rubber layer each include a constant-thickness portion having a constant thickness.

DESCRIPTION OF THE REFERENCE SIGNS

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