PNEUMATIC TIRE

A pneumatic tire has a bead portion provided with a bead core and a bead apex rubber. The bead apex rubber extends radially outward from the radially outer surface of the bead core, and has a radially outer end not positioned in a first region. The first region is defined between a first radial line and a second radial line. The first radial line extends straight through a radially outer end of a contact area where the bead portion comes into contact with a flange of a wheel rim. The second radial line extends straight through a position spaced 10 mm axially outward from the radially outer end of the contact area.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a pneumatic tire.

Background Art

Patent document 1 below discloses a pneumatic tire for a small shuttle bus with a gross vehicle weight exceeding 3 tons. This type of pneumatic tire has a small diameter in order to secure a wide riding space. In addition, the pneumatic tire of Patent Document 1 has increased load bearing capacity by specifying the arrangement of the circumferential grooves, the ratio of the outer diameter of the tire to the wheel rim diameter, and the like.

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

Since the pneumatic tire as described above has a small diameter, the air volume for supporting the weight of the vehicle is reduced, and the tire cross-sectional height is small. For this reason, the pneumatic tire as described above has a problem that strain is concentrated on the bead portions during running with heavy loads, and damage starting from the bead portion is likely to occur.

The present disclosure was made in view of the situation as described above, and a primary objective of the present disclosure is to improve the durability of the bead portions of a pneumatic tire mounted on a wheel rim whose rim diameter is 12 to 17 inches.

Means for Solving the Problems

According to the present disclosure, a pneumatic tire configured to be mounted on a wheel rim whose rim diameter is in a range from 12 to 17 inches,

has a ratio (SH/SW) of the cross-sectional height SH of the tire to the cross-sectional width SW of the tire which is in a range from 0.30 to 0.45, and
a ratio (RW/SW) between the width RW of the wheel rim and the cross-sectional width SW of the tire which is in a range from 0.78 to 0.99, and
comprises a pair of bead portions each with a bead core embedded therein, and a bead apex rubber disposed in one of or each of the bead portions and extending radially outwardly from a radially outer surface of the bead core so as to have a radially outer end not positioned within a first region, wherein
the first region is defined between a first tire radial direction line and a second tire radial direction line, when the tire is mounted on a wheel rim and inflated to a specified internal pressure,
the first tire radial direction line is a straight line extending in the tire radial direction through a radially outer end of a contact area where the bead portion comes into contact with a flange of the wheel rim, and
the second tire radial direction line is a straight line extending in the tire radial direction through a position spaced 10 mm axially outward from the radially outer end of the contact area.

Effects of the Invention

The pneumatic tire according to the present disclosure can improve the durability of the bead portion by adopting the above configuration.

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

In the present embodiment, the tire1is used in a new small shuttle bus which focuses on transporting people and goods within cities. Buses of this type are required to have a large boarding space, and some of them have a gross vehicle weight exceeding 3 tons. Such bus may be an electric vehicle equipped with an in-wheel motor (not shown) and equipped with an automatic driving function. The present disclosure however, may be applied to tires for passenger cars, heavy duty vehicles and the like.

FIG.1shows the tire1mounted on a wheel rim R and inflated to a specified internal pressure.

The specified internal pressure refers to the internal pressure at which the tire1exhibits the best performance, for example, 400 to 1100 kPa, or 500 to 900 kPa.

When the tire1is for passenger cars or heavy duty vehicles, the prescribed internal pressure is air pressure specified for the tire by a standard included in a standardization system on which the tire is based, for example, the “maximum air pressure” in JATMA, maximum value listed in the “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” table in TRA, and “INFLATION PRESSURE” in ETRTO.

In this application including specification and claims, various dimensions, positions and the like of the tire refer to those under the standard state unless otherwise noted, wherein the standard state is such a state that the tire is inflated to the prescribed internal pressure, and loaded with no tire load.

As for the wheel rim R, one that fits the tire1is adopted. When the tire1is for passenger cars or heavy duty vehicles, the wheel rim R is a wheel rim specified for the tire by a standard included in a standardization system on which the tire is based, for example, the “normal wheel rim” in JATMA, “Design Rim” in TRA, and “Measuring Rim” in ETRTO.

The tire1is mounted on a wheel rim R whose rim diameter RD in a range from 12 to 17 inches. Thus, the tire1of the present disclosure has a small diameter for the vehicle size.

The tire1has a ratio (SH/SW) of the tire cross-sectional height SH to the tire cross-sectional width SW which is in a range from 0.30 to 0.45, and

a ratio (RW/SW) of the rim width RW of the wheel rim R to the tire cross-sectional width SW which is in a range from 0.78 to 0.99.
Thereby, the tire1of the present disclosure can secure a low aspect ratio and an air volume for supporting the weight of the vehicle.
As such tire1, for example, a size of 205/40R15 or 215/45R12 is suitable.
On the other hand, the rim width of a wheel rim R suitable for the tire1of these sizes is 7.0 J or 7.5 J.
In addition, in the tire1of the present disclosure, it is preferable that the wheel rim R has a large space for accommodating an in-wheel motor

The rim diameter RD is the outer diameter of the main portion (or bead seat) Rh (flange Rf is not included) of the wheel rim R.

The cross-sectional width SW of the tire is the maximum axial width of the tire1excluding axially protruding rim protectors (not shown).

The cross-sectional height SH of the tire is the radial distance between the radially outermost end of the tread portion2of the tire1, and a radial position corresponding to the wheel rim diameter RD. A line extending parallel to the tire axial direction through the above-said radial position is known as the bead base line.

The wheel rim width RW is the axial distance between the radially inner ends of the flanges Rf on both sides in the tire axial direction. When the tire1is for passenger cars or heavy duty vehicles, the rim diameter RD and rim width RW may be determined on the basis of the JATMA standard on which the wheel rim R is based.

The tire1comprises a pair of bead portions4each with a bead core5embedded therein. One of or each of the bead portions4is provided with a bead apex rubber8extending radially outwardly from the radially outer surface5aof the bead core5.

In the present embodiment, the bead apex rubber8is disposed in each of the bead portions4. Structurally, strain tends to concentrate on the radially outer end8eof the bead apex rubber8.

FIG.2is an enlarged view of the bead portion4shown inFIG.1.

In the present disclosure, a first region10is defined in the bead portion4as shown inFIG.2. The first region10is defined between a first tire radial direction line n1and a second tire radial direction line n2.
The first tire radial direction line n1is a straight line extending in the tire radial direction through the radially outer end11eof the contact area11where the bead portion4comes into contact with the flange Rf of the wheel rim R.
The second tire radial direction line n2is a straight line extending in the tire radial direction through an axial position12spaced 10 mm axially outward from the radially outer end11eof the contact area11.
The first region10is a region where large strain concentrates during running with heavy loads.
In the present embodiment, the radially outer end11eof the contact area11is positioned radially inside the radially outer end5jof the bead core5.

According to the present disclosure, the radially outer end8eof the bead apex rubber8is not located within the first region10. Therefore, damage starting from the radially outer end8eis suppressed, and the durability of the bead portion4is improved.

As shown inFIG.1, the tire1comprises a carcass6extending between the bead cores5in the present embodiment.

Further, the tire1comprises a tread reinforcing belt7, an outside apex rubber9, a sidewall rubber3G, a clinch rubber4G, and a chafer13.

The carcass6comprises at least one carcass ply (6A,6B) made of rubberized carcass cords (not shown) and extending between the bead portions4through the tread portion2and the sidewall portions3, and turned-up around the bead core5in each of the bead portions4from the inside to the outside in the tire axial direction so as to form a pair of turned-up portions6band a main portion6atherebetween.

In the present embodiment, the carcass6is composed of two carcass plies6A and6B arranged inside and outside in the tire radial direction in the tread portion2although the carcass6may be composed of a single carcass ply (6A,6B).
Each of the turned-up portions6bextends radially outwardly, and the radially outer end6ethereof is positioned radially outside the radially outer end8eof the bead apex rubber8in the present embodiment.

In the present embodiment, the tread reinforcing belt7is disposed in the tread portion2and composed of a radially inner belt ply7aand a radially outer belt ply7b.

The axial edges7hof the radially inner belt ply7aare respectively positioned axially outside the axial edges7kof the radially outer belt ply7b.
Each of the belt plies7aand7bis made of rubberized parallel belt cords (not shown), for example, steel cords. As to the structure of the belt, those for general truck/bus tires may be adopted.

As shown inFIG.2, the bead apex rubber8is disposed between the main portion6aand each of the turned-up portion6bof the radially outer carcass ply6B so that the bead apex rubber8is in contact with the axially outer side of the main portion6aand the axially inner side of the turned-up portion6b.

In the present embodiment, the radially outer end8eof the bead apex rubber8is located axially inside than the first region10. That is, the bead apex rubber8does not exist in the first region10. Accordingly, the interface between the bead apex rubber8and the carcass ply is not formed in the first region10, so damage due to carcass play separation does not occur, and the durability of the bead portion4is further improved. If the radially outer end8eof the bead apex rubber8is positioned axially outside the first region10, the interface is formed, but damage originating from the radially outer end8eis suppressed, therefore, the durability of the bead portion4may be improved.

It is preferable that the axial distance La between the radially outer end8eof the bead apex rubber8and the radially outer end11eof the contact area11is 2 mm or less. If the radially outer end8eof the bead apex rubber8is disposed at a position more than 2 mm axially inward of the radially outer end11eof the contact area11, it becomes difficult to increase the rigidity around the radially outer end lie where a particularly large strain occurs, and thereby the durability may not be improved.

It is preferable that the bead apex rubber8has complex elastic modulus E* of 25 MPa or more, more preferably 30 MPa or more, but 40 MPa or less, more preferably 35 MPa or less.

The complex elastic modulus E* was measured under the following conditions according to the Japanese Industrial Standard (JIS) K6394 by using a spectrometer manufactured by Ueshima Seisakusho Co., Ltd.

amplitude of dynamic strain: 1%

The bead apex rubber8has its radially outer portion8A positioned axially outside the axially outer end5eof the bead core5as shown inFIG.2.

In the tire meridian cross section, the ratio (So/S) of the cross-sectional area So of the radially outer portion8A to the cross-sectional area S of the bead apex rubber8is preferably 0.2 or more. Since the ratio (So/S) is 0.2 or more, the rigidity of the portion axially outside the bead core5is maintained, thereby distortion due to running is suppressed, and durability is improved.

In order to enhance such action, the ratio (So/S) is more preferably 0.25 or more.
If the ratio (So/S) is excessively large, a large load due to running may be applied to the radially inner portion of the bead apex rubber8, and as result, the durability may be deteriorated. Therefore, the ratio (So/S) is preferably 0.35 or less, more preferably 0.30 or less.

As shown inFIG.1, the radial height HA of the bead apex rubber8is preferably not less than 175%, more preferably not less than 200%, but preferably not more than 275%, more preferably not more than 250% of the radial height HC of the bead core5.

As a result, the above effects are effectively exhibited.

The radially outer ends8eof the bead apex rubbers8are respectively positioned axially inside the axial edges7hof the radially inner belt ply7a. And the radially outer ends8eof the bead apex rubbers8are respectively positioned axially outside the axial edges7kof the radially outer belt ply7bin the present embodiment.

The outside apex rubber9is disposed axially outside the turned-up portion6b. In the present embodiment, the outside apex rubber9is disposed adjacently to the axially outer side of the turned-up portion6bof the inner carcass ply6A.

In the present embodiment, the outside apex rubber9has a complex elastic modulus E* which is the same as that of the bead apex rubber8. As a result, the difference in the amount of strain between the bead apex rubber8and the outside apex rubber9is reduced, so strain is less likely to occur in the entire bead portion, and the effect of improving durability is exhibited.

FIG.3is an enlarged view of the bead portion4. As shown inFIG.3, the outside apex rubber9is formed in a sheet shape with a thickness “d” of 40% or less of the maximum axial width Wa of the bead apex rubber8.

Such outside apex rubber9maintains the width of the bead portion4small to ensure deformation (deflection) during running, and disperses the load to enhance the durability.

The radially inner end9iof the outside apex rubber9is positioned radially inside a radial position P1which is 2 mm radially outward from the radially outer end5jof the bead core5. As a result, the rigidity step difference in the vicinity of the bead core5is reduced, and the durability of the bead portion4is further improved.

In the present embodiment, the radially inner end9iof the outside apex rubber9is located radially outside the radially outer end5jof the bead core5.
In addition, the radially inner end9iof the outside apex rubber9is located radially outside the radially outer end lie of the contact area11.

The radially outer end9eof the outside apex rubber9is disposed at a position axially outwardly spaced apart from the first region10by 10 mm or more. As a result, the rigidity of the bead portion4is enhanced, and the durability is further improved.

The axial distance Lb between the radially outer end9eof the outside apex rubber9and the first region10(the position12shown inFIG.2) is preferably not less than 160%, more preferably not less than 180%, but preferably not more than 240%, more preferably not more than 220% of the maximum width Wa of the bead apex rubber8.
In the present embodiment, the radially outer end9eof the outside apex rubber9is located radially outside the radially outer end4eof the clinch rubber4G.

The distance L1in the tire radial direction between the radially outer end9eof the outside apex rubber9and the radially outer end8eof the bead apex rubber8is 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 radial height HB of the outside apex rubber9.

The radial height HB of the outside apex rubber9is preferably not less than 200%, more preferably not less than 220%, but preferably not more than 280%, more preferably not more than 2600% of the radial height HA (shown inFIG.1) of the bead apex rubber8.
As a result, the above effects are effectively exhibited.

In the present embodiment, the sidewall rubber3G and the clinch rubber4G may be made of various well-known materials.

The clinch rubber4G is, for example, disposed adjacently to the radially inner side of the sidewall rubber3G.
The clinch rubber4G comprises a portion coming into contact with the wheel rim.
The radially inner end4iof the clinch rubber4G is positioned radially inside the radially inner end5iof the bead core5as shown inFIG.3.

In the present embodiment, the chafer13is formed in a U shape composed of a first portion13a, a second portion13band a third portion13c.

The third portion13cis positioned radially inside the radially inner end5iof the bead core5, and extends along the bead base so as to be able to contact with the bead seat of the wheel rim R.
The first portion13aextends radially outwardly from the axially inner end of the third portion13c, facing the inner cavity of the tire1.
The second portion13bextends radially outwardly from the axially outer end of the third portion13c. In the present embodiment, the second portion13bextends between the turned-up portion6bof the inner carcass ply6A and the outside apex rubber9,

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 Example and Examples 1-7 according to the present disclosure), and tested for the bead durability.

Specifications of the test tires are shown in Table 1.
Common specifications to all the test tires and the test method are as follows.

Using test vehicles, the test tires were run under the following conditions to measure the running distance until damage was occurred in the bead portions.

Test vehicle: E-Pallet manufactured by Toyota Motor Corporation The results are indicated in Table 1 by an index based on Example 1 being 100, wherein values of 95 or higher are acceptable.

In Table 1, the minus sign “−” of La means that the radially outer end8eof the bead apex rubber8was positioned axially outside the radially outer end11eof the contact area11. In Table 1, “*1” means that the radially inner end9iof the outside apex rubber9was positioned 5 mm radially outward from the radially outer end5jof the bead core5. In Table 1, “*2” means that the radially outer end9eof the outside apex rubber9was positioned 5 mm axially outward from the radially outer end11eof the contact area11.

TABLE 1ComparativeTireexampleExample 1Example 2Example 3Example 4Example 5Example 6Example 7La (mm)−5.02.02.02.02.02.02.0−15.0Ratio (Sa/S)0.250.250.10.250.250.250.250.25Outside apex rubberAbsenceAbsenceAbsencePresencePresencePresencePresencePresenceSecond apex rubber———at P1*1at P1at P1at P1inner end positionLb (mm)———10105*210Durability9010095110105105100108
From the test results, it was confirmed that Example tires according to the present disclosure were improved in bead durability as compared to Comparative example tire.

Statement of the Present Disclosure

The present disclosure is as follows:
Disclosure 1. A pneumatic tire configured to be mounted on a wheel rim whose rim diameter is in a range from 12 to 17 inches, wherein a ratio (SH/SW) of the cross-sectional height SH of the tire to the cross-sectional width SW of the tire which is in a range from 0.30 to 0.45, and a ratio (RW/SW) between the width RW of the wheel rim and the cross-sectional width SW of the tire which is in a range from 0.78 to 0.99,
the pneumatic tire comprising a pair of bead portions each with a bead core embedded therein, and a bead apex rubber disposed in one of or alternatively each of the bead portions and extending radially outwardly from a radially outer surface of the bead core so as to have a radially outer end not positioned within a first region, wherein

the first region is defined between a first tire radial direction line and a second tire radial direction line, when the tire is mounted on a wheel rim and inflated to a specified internal pressure,

the first tire radial direction line is a straight line extending in the tire radial direction through a radially outer end of a contact area where the bead portion comes into contact with a flange of the wheel rim, and
the second tire radial direction line is a straight line extending in the tire radial direction through a position spaced 10 mm axially outward from the radially outer end of the contact area.
Disclosure 2. The pneumatic tire according to Disclosure 1, wherein the radially outer end of the bead apex rubber is positioned axially inside than the first region.
Disclosure 3. The pneumatic tire according to Disclosure 1, wherein
the axial distance La between the radially outer end of the bead apex rubber and the radially outer end of the contact area is not more than 2 mm.
Disclosure 4. The pneumatic tire according to Disclosure 1, 2 or 3, wherein
the bead apex rubber has its radially outer portion positioned axially outside the axially outer end of the bead core, and
in a meridian cross section of the tire, the cross-sectional area So of the radially outer portion is not less than 0.2 times the cross-sectional area S of the bead apex rubber.
Disclosure 5. The pneumatic tire according to any one of Disclosures 1 to 4, which comprises 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 outside so as to form a pair of turned-up portions extending radially outward and a main portion therebetween, and an outside apex rubber is disposed axially outward of each of the turned-up portions.
Disclosure 6. The pneumatic tire according to Disclosure 5, wherein the outside apex rubber is sheet-shaped and has a thickness of not more than 40% of a maximum axial width of the bead apex rubber.
Disclosure 7. The pneumatic tire according to Disclosure 5 or 6, wherein the radially inner end of the outside apex rubber is positioned radially inward than a radial position 2 mm radially outward from the radially outer end of the bead core.
Disclosure 8. The pneumatic tire according to Disclosure 5, 6 or 7, wherein the radially outer end of the outside apex rubber is disposed at an axial position at least 10 mm axially outward from the first region.

DESCRIPTION OF THE REFERENCE SIGNS