Patent Description:
An off-the-road tire (OR Tire) mountable on a construction or industrial vehicle includes an auxiliary belt disposed between a carcass layer and a pair of reinforcing belts as an additional reinforcing material for improving the durability of the tire. An example of a conventional OR tire that is configured in this manner is the technology described in Patent Document <NUM>.

<CIT> and <CIT> disclose both a pneumatic tire comprising a carcass layer, a belt layer disposed on the outer side of the carcass layer and a tread rubber disposed on the outer side of the belt layer, wherein the belt layer comprises a first and a second reinforcing belt and an auxiliary belt, wherein the second reinforcing belt is narrower than the first reinforcing belt and the auxiliary belt is spaced apart from a tire equatorial plane and is disposed between the first reinforcing belt and the carcass layer, wherein the first and the second reinforcing belt have cord angles between <NUM>° and <NUM>° and the auxiliary belt has a cord angle between <NUM>° and <NUM>°.

<CIT> discloses a pneumatic tire comprising a carcass layer, a belt layer disposed on the outer side of the carcass layer, a tread disposed on the outer side of the belt layer. The belt layer comprises a first reinforcing belt, a second reinforcing belt, which is narrower than the first reinforcing belt. An auxiliary belt is provided, wherein the auxiliary belt is spaced apart from a tire equatorial plane and disposed between the carcass layer and the first reinforcing belt.

<CIT> discloses a pneumatic tire comprising a carcass layer, a belt layer disposed on the outer side of the carcass layer, a tread disposed on the outer side of the belt layer. The belt layer comprises a first reinforcing belt, a second reinforcing belt, which is narrower than the first reinforcing belt and an auxiliary belt, wherein the auxiliary belt is spaced apart from a tire equatorial plane and disposed between the carcass layer and the first reinforcing belt.

<CIT> and <CIT> both disclose a pneumatic tire comprising a carcass layer, a belt layer disposed on the outer side of the carcass layer and a tread rubber disposed on the outer side of the belt layer, wherein the belt layer comprises a first and a second reinforcing belt and an auxiliary belt, wherein the second reinforcing belt is narrower than the first reinforcing belt and the auxiliary belt is disposed between the first reinforcing belt and the carcass layer, wherein the first and the second reinforcing belt have cord angles between <NUM>° and <NUM>° and the auxiliary belt has a cord angle between <NUM>° and <NUM>° and the carcass layer has a cord angle between <NUM>° and <NUM>°.

Meanwhile, in recent years, OR tires have been developed with lowered aspect ratios in response to the evolution of heavy or construction machinery. An OR tire with a low aspect ratio can provide improved applied load capacity while maintaining the tire outer diameter, however, such a tire also increases the load index (k-factor) and thus the deflection amount of the tire. Accordingly, there is a problem that separation of the peripheral rubber tends to occur at end portions of the belt plies.

In light of the foregoing, an object of the invention is to provide a pneumatic tire with improved belt edge durability performance.

To achieve the object described above, the pneumatic tire according to an embodiment of the invention includes a carcass layer, a belt layer disposed on an outer side of the carcass layer in a radial direction, and a tread rubber disposed on an outer side of the belt layer in the radial direction, the carcass layer having a cord angle of <NUM> ° or more and <NUM> ° or less, the belt layer being formed by layering a first reinforcing belt, a second reinforcing belt that is narrower than the first reinforcing belt, and an auxiliary belt that is spaced apart from a tire equatorial plane and disposed between the carcass layer and the first reinforcing belt, the first reinforcing belt and the second reinforcing belt having cord angles of <NUM> ° or more and <NUM> ° or less, and the auxiliary belt having a cord angle of <NUM> ° or more and <NUM> ° or less.

According to an embodiment, a distance De5 from the tire equatorial plane to an outer end portion of the auxiliary belt in a tire width direction has a relationship <NUM> ≤ De5/(TDW/<NUM>) ≤ <NUM> with respect to a developed tread half-width TDW/<NUM>.

According to an embodiment, a distance De5 from the tire equatorial plane to an outer end portion of the auxiliary belt in a tire width direction has a relationship <NUM> ≤ De5/De1 ≤ <NUM> with respect to a distance De1 from the tire equatorial plane to an end portion of the first reinforcing belt.

According to an embodiment, a distance De5' from the tire equatorial plane to an inner end portion of the auxiliary belt in a tire width direction has a relationship <NUM> ≤ De5'/(TDW/<NUM>) ≤ <NUM> with respect to a developed tread half-width TDW/<NUM>.

According to an embodiment, a width Wb5 of the auxiliary belt has a relationship <NUM> ≤ Wb5/(TDW/<NUM>) ≤ <NUM> with respect to a developed tread half-width TDW/<NUM>.

According to an embodiment, a cord diameter of a belt cord forming the auxiliary belt is in a range of <NUM> or more and <NUM> or less.

According to an embodiment, a distance De1 from the tire equatorial plane to an end portion of the first reinforcing belt has a relationship <NUM> ≤ De1/(TDW/<NUM>) ≤ <NUM> with respect to a developed tread half-width TDW/<NUM>.

According to an embodiment, a distance De2 from the tire equatorial plane to an end portion of the second reinforcing belt has a relationship <NUM> ≤ De2/(TDW/<NUM>) ≤ <NUM> with respect to a developed tread half-width TDW/<NUM>.

According to an embodiment, the belt layer comprises a protection belt disposed on an outer side of the first reinforcing belt and the second reinforcing belt in the radial direction, wherein the protection belt has a cord angle of <NUM> ° or more and <NUM> ° or less, and wherein a distance De3 from the tire equatorial plane to an end portion of the protection belt has a relationship De1 < De3 with respect to a distance De1 to an end portion of the first reinforcing belt and a relationship De2 < De3 with respect to a distance De2 to an end portion of the second reinforcing belt.

According to an embodiment, a distance De3 from the tire equatorial plane to an end portion of the protection belt has a relationship <NUM> ≤ De3/(TDW/<NUM>) ≤ <NUM> with respect to a developed tread half-width TDW/<NUM>.

According to an embodiment, a shoulder drop amount Dt of a tread profile when the tire is mounted on a specified rim and inflated to a specified internal pressure has a relationship <NUM> ≤ Dt/SH ≤ <NUM> with respect to a tire cross-sectional height SH.

According to an embodiment, a distance Gca1 from a tread profile to a carcass profile on the tire equatorial plane has a relationship <NUM> ≤ Gca1/Gca2 ≤ <NUM> with respect to a distance Gca2 from a tread edge to a carcass profile.

According to an embodiment, a gauge Gtr1 of the tread rubber on the tire equatorial plane has a relationship <NUM> ≤ Gtr1/Gtr2 ≤ <NUM> with respect to a gauge Gtr2 of the tread rubber at an end portion position of an outermost layer of the belt layer.

According to an embodiment, the pneumatic tire is an OR tire for a construction or industrial vehicle having an aspect ratio of <NUM>% or less.

According to an embodiment, an aspect ratio of the carcass layer is <NUM>% or less.

According to the pneumatic tire according to embodiments of the invention, an auxiliary belt having a cord angle of <NUM> ° or more and <NUM> ° or less is advantageous in that the cord angle of the auxiliary belt is appropriately set to improve the belt edge durability performance of the tire. Specifically, the lower limit described above allows for the difference in cord angles between adjacent auxiliary belts and carcass layers to be reduced, and the interlayer strain to be reduced, thereby suppressing separation of the peripheral rubber at end portions of the auxiliary belt. Also, the upper limit described above allows for radial growth in the shoulder region in the tread portion to be suppressed, thereby suppressing separation of the peripheral rubber at end portions of the belt layer.

Embodiments of the invention are described in detail below with reference to the drawings. However, the invention is not limited to these embodiments. Moreover, constituents of the embodiments include elements that are substitutable while maintaining consistency with the invention as claimed. Furthermore, the modified examples described in the embodiments can be combined as desired within the scope of the appended claims.

<FIG> is a cross-sectional view in a tire meridian direction illustrating a pneumatic tire according to an embodiment of the invention. The same drawing illustrates a cross-sectional view of a half region in the tire radial direction. The same drawing illustrates an OR tire mountable on a construction or industrial vehicle as an example of the pneumatic tire according to an embodiment of the invention.

In reference to the same drawing, "cross section in a tire meridian direction" refers to a cross section of the tire taken along a plane that includes the tire rotation axis (not illustrated). Reference sign CL denotes the tire equatorial plane and refers to a plane normal to the tire rotation axis that passes through the center point of the tire in the tire rotation axis direction. "Tire width direction" refers to the direction parallel with the tire rotation axis. "Tire radial direction" refers to the direction perpendicular to the tire rotation axis.

A pneumatic tire <NUM> has an annular structure with the tire rotation axis as its center and includes: a pair of bead cores <NUM>, <NUM>, a pair of bead fillers <NUM>, <NUM>, a carcass layer <NUM>, a belt layer <NUM>, a tread rubber <NUM>, a pair of sidewall rubbers <NUM>, <NUM>, and a pair of rim cushion rubbers <NUM>, <NUM> (see <FIG>).

The pair of bead cores <NUM>, <NUM> are formed by winding one or a plurality of bead wires made of steel by multiple times in an annular shape and are embedded in the bead portion to constitute a core of the left and right bead portions. The pair of bead fillers <NUM>, <NUM> are disposed on an outer circumference of the pair of bead cores <NUM>, <NUM> in the tire radial direction and reinforce the bead portions.

The carcass layer <NUM> has a single layer structure made from one carcass ply or a multilayer structure made from a plurality of stacked carcass plies and spans between the left and right bead cores <NUM>, <NUM> in a toroidal shape to form the framework of the tire. Additionally, both end portions of the carcass layer <NUM> are turned back to an outer side in the tire width direction so as to wrap around the bead cores <NUM> and the bead fillers <NUM> and fixed. The carcass ply of the carcass layer <NUM> is formed by performing a rolling process on coating rubber-covered carcass cords made from steel and has a cord angle (defined as the inclination angle in the longitudinal direction of the carcass cords with respect to the tire circumferential direction) being <NUM> ° or more and <NUM> ° or less. Also, a cord diameter of the carcass cord is in a range of <NUM> or more and <NUM> or less.

The belt layer <NUM> is a multilayer structure including a plurality of belt plies <NUM> to <NUM> and is disposed around the outer circumference of the carcass layer <NUM>. These belt plies <NUM> to <NUM> include two or more reinforcing belts <NUM>, <NUM>, one or more protection belts <NUM>, <NUM>, and one or more auxiliary belts <NUM>. A detailed configuration of each of the belt plies <NUM> to <NUM> is described below.

The tread rubber <NUM> is disposed on the outer circumference of the carcass layer <NUM> and the belt layer <NUM> in the tire radial direction and constitutes a tread portion. The pair of sidewall rubbers <NUM>, <NUM> are disposed on an outer side of the carcass layer <NUM> in the tire width direction and constitute left and right sidewall portions. The pair of rim cushion rubbers <NUM>, <NUM> are disposed on an inner side in the tire radial direction of the turned back portions of the carcass layer <NUM> and the left and right bead cores <NUM>, <NUM> to form a rim-fitting surface of the bead portion.

<FIG> is an explanatory diagram illustrating the belt layer of the pneumatic tire illustrated in <FIG>. The same drawing illustrates a half region of a tread portion demarcated by the tire equatorial plane CL.

As described above, the belt layer <NUM> is formed by layering a plurality of belt plies <NUM> to <NUM> including two or more reinforcing belts <NUM>, <NUM>, one or more protection belts <NUM>, <NUM>, and one or more auxiliary belts <NUM>.

Each of the belt plies <NUM> to <NUM> extends continuously in the tire width direction across the tire equatorial plane CL. Additionally, each of the belt plies <NUM> to <NUM> has a left-right symmetrical structure centered on the tire equatorial plane CL. Furthermore, adjacent belt plies <NUM>, <NUM>; <NUM>, <NUM>; <NUM>, <NUM> have cord angles (defined as the inclination angle in the longitudinal direction of the belt cords with respect to the tire circumferential direction) of opposite signs and are stacked so that the longitudinal directions of the belt cords intersect each other (having so-called a crossply structure).

The first reinforcing belt <NUM> is made by performing a rolling process on coating rubber-covered belt cords made of steel and has a cord angle, as an absolute value, of <NUM> ° or more and <NUM> ° or less, preferably, <NUM> ° or more and <NUM> ° or less. Additionally, the first reinforcing belt <NUM> is disposed on an outer side of the carcass layer <NUM> in the tire radial direction.

The second reinforcing belt <NUM> is made by performing a rolling process on coating rubber-covered belt cords made of steel and has a cord angle, as an absolute value, of <NUM> ° or more and <NUM> ° or less, preferably, <NUM> ° or more and <NUM> ° or less. Also, the second reinforcing belt <NUM> is disposed in a layered manner on an outer side of the first reinforcing belt <NUM> in the tire radial direction.

Additionally, an outer diameter of a belt cord forming the reinforcing belts <NUM>, <NUM> is in a range of <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less. Additionally, the number of ends of the belt cords forming the reinforcing belts <NUM>, <NUM> is in a range of <NUM> ends/<NUM> or more and <NUM> ends/<NUM> or less, preferably, <NUM> ends/<NUM> or more and <NUM> ends/<NUM> or less.

In a configuration in which the cord is formed of a plurality of twisted wires, the cord diameter is measured as the diameter of a circumscribed circle of the cord in a radial cross-sectional view.

Also, in the configuration of <FIG>, the narrower second reinforcing belt <NUM> is disposed in a layered manner on an outer side of the wider first reinforcing belt <NUM> in the tire radial direction. However, no such limitation is intended, and the narrower second reinforcing belt <NUM> may be disposed in a layered manner on an inner side of the wider first reinforcing belt <NUM> in the tire radial direction (not illustrated).

Furthermore, a third reinforcing belt (not illustrated) may be disposed in a layered manner. In this case, the third reinforcing belt may be disposed on an inner side or on an outer side (not illustrated) of the first reinforcing belt <NUM> and the second reinforcing belt <NUM> in the radial direction. Alternatively, the third reinforcing belt may be disposed to be interposed between the first reinforcing belt <NUM> and the second reinforcing belt <NUM> (not illustrated). In these cases, the widest reinforcing belt is defined as the first reinforcing belt <NUM> described above, and the narrowest reinforcing belt is defined as the second reinforcing belt <NUM> described above.

The first protection belt <NUM> is made by performing a rolling process on coating rubber-covered belt cords made of steel and has a cord angle, as an absolute value, of <NUM> ° or more and <NUM> ° or less, preferably, <NUM> ° or more and <NUM> ° or less. Also, the first protection belt <NUM> is disposed in a layered manner on an outer side of the first reinforcing belt <NUM> and the second reinforcing belt <NUM> in the radial direction. Also, the first protection belt <NUM> is wider than the first reinforcing belt <NUM> and the second reinforcing belt <NUM> as described below, and disposed to entirely cover these reinforcing belts <NUM>, <NUM> from an outer side in the radial direction. Also, a cord diameter of a belt cord forming the first protection belt <NUM> is narrower than the cord diameter of the belt cords of the first reinforcing belt <NUM> and the second reinforcing belt <NUM>. Additionally, a difference between the cord diameters of the first reinforcing belt <NUM> and the second reinforcing belt <NUM> and the cord diameter of the first protection belt <NUM> preferably is in a range of <NUM> or more and <NUM> or less.

The second protection belt <NUM> is made by performing a rolling process on coating rubber-covered belt cords made of steel and has a cord angle, as an absolute value, of <NUM> ° or more and <NUM> ° or less, preferably, <NUM> ° or more and <NUM> ° or less. Also, the second protection belt <NUM> has a cord angle with an opposite sign with respect to the first protection belt <NUM>, and the belt cords are layered so that the longitudinal directions of the belt cords intersect each other. Also, the second protection belt <NUM> is narrower than the first protection belt <NUM>, and is disposed in a layered manner on an outer side of the first protection belt <NUM> in the radial direction.

Additionally, an outer diameter of a belt cord forming the protection belts <NUM>, <NUM> is in a range of <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less. Additionally, the number of ends of the belt cords forming the protection belts <NUM>, <NUM> is in a range of <NUM> ends/<NUM> or more and <NUM> ends/<NUM> or less, preferably, <NUM> ends/<NUM> or more and <NUM> ends/<NUM> or less.

Note that the second protection belt <NUM> may be omitted, and only the first protection belt <NUM> may be disposed (not illustrated).

Additionally, in <FIG>, a distance De1 from a tire equatorial plane CL to an end portion of the first reinforcing belt <NUM> preferably has a relationship <NUM> ≤ De1/(TDW/<NUM>) ≤ <NUM>, more preferably, <NUM> ≤ De1/(TDW/<NUM>) ≤ <NUM>, with respect to a developed tread half-width TDW/<NUM>.

The distance to an end portion of a belt ply is the distance in the tire width direction from the tire equatorial plane to the outermost belt cord of the belt ply in the tire width direction, measured when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state.

The developed tread width TDW is the linear distance between the two ends of the tread pattern portion of the tire in a developed view, measured when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state.

Also, as illustrated in <FIG>, the second reinforcing belt <NUM> is narrower than the first reinforcing belt <NUM> and the first protection belt <NUM>, and the end portion of the second reinforcing belt <NUM> is disposed to be interposed between the first reinforcing belt <NUM> and the first protection belt <NUM>. Additionally, a distance De2 from the tire equatorial plane CL to the end portion of the second reinforcing belt <NUM> preferably has a relationship <NUM> ≤ De2/(TDW/<NUM>) ≤ <NUM>, more preferably, <NUM> ≤ De2/(TDW/<NUM>) ≤ <NUM>, with respect to the developed tread half-width TDW/<NUM>.

Furthermore, the distance De2 of the second reinforcing belt <NUM> preferably has a relationship <NUM> ≤ De2/De1 ≤ <NUM>, more preferably, <NUM> ≤ De2/De1 ≤ <NUM>, with respect to the distance De1 of the first reinforcing belt <NUM>.

Also, as illustrated in <FIG>, the first protection belt <NUM> is wider than the first reinforcing belt <NUM> and the second reinforcing belt <NUM>, and disposed to entirely cover these reinforcing belts <NUM>, <NUM> from an outer side in the radial direction. Additionally, a distance De3 from the tire equatorial plane CL to an end portion of the first protection belt <NUM> preferably has a relationship <NUM> ≤ De3/(TDW/<NUM>) ≤ <NUM>, more preferably, <NUM> ≤ De3/(TDW/<NUM>) ≤ <NUM>, with respect to the developed tread half-width TDW/<NUM>.

Also, the distance De3 of the first protection belt <NUM> preferably has a relationship <NUM> ≤ De3/De1 ≤ <NUM>, more preferably, <NUM> ≤ De3/De1 ≤ <NUM>, with respect to the distance De1 of the first reinforcing belt <NUM>. In this way, separation of the peripheral rubber occurring at end portions of the belt plies is suppressed.

Also, as shown in <FIG>, the second protection belt <NUM> is narrower than the first protection belt <NUM>, and the end portion of the second protection belt <NUM> is disposed on an outer circumferential surface of the first protection belt <NUM>. Additionally, a distance De4 from the tire equatorial plane CL to an end portion of the second protection belt <NUM> preferably has a relationship <NUM> ≤ De4/(TDW/<NUM>) ≤ <NUM>, more preferably, <NUM> ≤ De4/(TDW/<NUM>) ≤ <NUM>, with respect to the developed tread half-width TDW/<NUM>. In this way, the distance De4 of the second protection belt <NUM> is appropriately set.

Also, the distance De4 of the second protection belt <NUM> preferably has a relationship <NUM> ≤ De4/De3 ≤ <NUM>, more preferably, <NUM> ≤ De4/De3 ≤ <NUM>, with respect to the distance De3 of the first protection belt <NUM>.

Also, in the configuration of <FIG>, the end portions of the first reinforcing belt <NUM> and the second reinforcing belt <NUM>, as well as the end portions of the first protection belt <NUM> and the second protection belt <NUM> are disposed to be offset from each other in the tire width direction. In this way, stress concentration at belt end portions is mitigated.

As illustrated in <FIG>, the belt layer <NUM> includes a single layer auxiliary belt <NUM>. The auxiliary belt <NUM> has a split structure that is spaced apart from the tire equatorial plane CL and is disposed between the carcass layer <NUM> and the first reinforcing belt <NUM>. Additionally, the pair of auxiliary belts <NUM> are disposed having left-right symmetry about the tire equatorial plane CL (see <FIG>).

Also, the auxiliary belt <NUM> is made by performing a rolling process on coating rubber-covered belt cords made of steel and has a cord angle, as an absolute value, of <NUM> ° or more and <NUM> ° or less, preferably, <NUM> ° or more and <NUM> ° or less. Accordingly, the cord angle of the auxiliary belt <NUM> is smaller than the cord angle of the adjacent carcass layer <NUM> (<NUM> ° or more and <NUM> ° or less), and is greater than the cord angle of the adjacent first reinforcing belt <NUM> (<NUM> ° or more and <NUM> ° or less). Also, a difference between the cord angle of the auxiliary belt <NUM> and the cord angle of the carcass layer <NUM> is preferably <NUM> ° or more and <NUM> ° or less, more preferably, <NUM> ° or more and <NUM> ° or less. Also, a difference between the cord angle of the auxiliary belt <NUM> and the cord angle of the first reinforcing belt <NUM> is preferably <NUM> ° or more and <NUM> ° or less, more preferably, <NUM> ° or more and <NUM> ° or less. In this way, the cord angle of the auxiliary belt <NUM> is appropriately set.

Additionally, an outer diameter of a belt cord forming the auxiliary belt <NUM> is in a range of <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less. Additionally, the number of ends of the belt cords forming the auxiliary belt <NUM> is in a range of <NUM> ends/<NUM> or more and <NUM> ends/<NUM> or less, preferably, <NUM> ends/<NUM> or more and <NUM> ends/<NUM> or less.

Also, as illustrated in <FIG>, the auxiliary belt <NUM> is narrower than the first reinforcing belt <NUM>, and the two end portions of the auxiliary belt <NUM> are interposed between the first reinforcing belt <NUM> and the carcass layer <NUM>. Also, a distance De5 from the tire equatorial plane CL to an outer end portion of the auxiliary belt <NUM> in the tire width direction preferably has a relationship <NUM> ≤ De5/(TDW/<NUM>) ≤ <NUM>, more preferably, <NUM> ≤ De5/(TDW/<NUM>) ≤ <NUM>, with respect to the developed tread half-width TDW/<NUM>.

Additionally, the distance De5 from the tire equatorial plane CL to the outer end portion of the auxiliary belt <NUM> in the tire width direction has a relationship <NUM> ≤ De5/De1 ≤ <NUM>, preferably, <NUM> ≤ De5/De1 ≤ <NUM>, with respect to the distance De1 of the first reinforcing belt <NUM>. Accordingly, the auxiliary belt <NUM> is completely disposed on the tire equatorial plane CL side of the end portion of the first reinforcing belt <NUM>.

Also, in the configuration of <FIG>, the outer end portion of the auxiliary belt <NUM> is disposed on the tire equatorial plane CL side of the end portion of the narrower second reinforcing belt <NUM>. However, no such limitation is intended, and the outer end portion of the auxiliary belt <NUM> may be disposed further to an outer side in the tire width direction than the end portion of the narrower second reinforcing belt <NUM> (not illustrated). Specifically, the outer end portion of the auxiliary belt <NUM> is preferably disposed to be offset with respect to the end portions of the first reinforcing belt <NUM> and the second reinforcing belt <NUM> in the tire width direction.

Also, a distance De5' from the tire equatorial plane CL to an inner end portion of the auxiliary belt <NUM> in the tire width direction preferably has a relationship <NUM> ≤ De5'/(TDW/<NUM>) ≤ <NUM>, more preferably, <NUM> ≤ De5'/(TDW/<NUM>) ≤ <NUM>, with respect to the developed tread half-width TDW/<NUM>.

Additionally, the distance De5' from the tire equatorial plane CL to the inner end portion of the auxiliary belt <NUM> in the tire width direction has a relationship <NUM> ≤ De5'/De5 ≤ <NUM>, preferably, <NUM> ≤ De5'/De5 ≤ <NUM>, with respect to the distance De5 of the outer end portion of the auxiliary belt <NUM>.

Also, a width Wb5 (= De5 - De5') of the auxiliary belt preferably has a relationship <NUM> ≤ Wb5/(TDW/<NUM>) ≤ <NUM>, more preferably, <NUM> ≤ Wb5/(TDW/<NUM>) ≤ <NUM>, with respect to the developed tread half-width TDW/<NUM>.

Note that in the configuration of <FIG>, a single layer and a pair of left and right auxiliary belts <NUM>, <NUM> are disposed as described above. However, no such limitation is intended, and two or more auxiliary belts may be layered and disposed left and right.

<FIG> is an enlarged view illustrating the tread portion of the pneumatic tire illustrated in <FIG>. The same drawing illustrates a half region of a tread portion demarcated by the tire equatorial plane CL.

In <FIG>, a shoulder drop amount Dt of a tread profile when the tire is mounted on a specified rim and inflated to a specified internal pressure preferably has a relationship <NUM> ≤ Dt/SH ≤ <NUM>, more preferably, <NUM> ≤ Dt/SH ≤ <NUM>, with respect to a tire cross-sectional height SH.

Additionally, a shoulder drop amount Dt' of a tread profile when the tire is mounted on a specified rim and inflated to an internal pressure of <NUM> kPa preferably has a relationship <NUM> ≤ Dt'/SH' ≤ <NUM>, more preferably, <NUM> ≤ Dt'/SH' ≤ <NUM>, with respect to a tire cross-sectional height SH'. The tread profile when the tire is inflated to the internal pressure of <NUM> kPa corresponds to the shape of the tire mold.

Moreover, in <FIG>, a distance Gca1 from a tread profile to a carcass profile on the tire equatorial plane CL preferably has a relationship <NUM> ≤ Gca1/Gca2 ≤ <NUM>, more preferably, <NUM> ≤ Gca1/Gca2 ≤ <NUM>, with respect to a distance Gca2 from a tread edge T to a carcass profile.

The distance from the tread profile to the carcass profile is measured when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state.

A profile is a contour line in a cross-sectional view along the tire meridian direction, and is measured using a laser profiler in an unloaded state with the tire mounted on a specified rim and inflated to the specified internal pressure. The laser profiler used may be, for example, a tire profile measuring device (available from Matsuo Co.

Additionally, in <FIG>, a gauge Gtr1 of the tread rubber <NUM> on the tire equatorial plane CL preferably has a relationship <NUM> ≤ Gtr1/Gtr2 ≤ <NUM>, more preferably, <NUM> ≤ Gtr1/Gtr2 ≤ <NUM>, with respect to a gauge Gtr2 of the tread rubber <NUM> at an end portion position of the outermost layer (that is, the second protection belt <NUM> in <FIG>) of the belt layer <NUM>. Additionally, the gauge Gtr1 of the tread rubber <NUM> on the tire equatorial plane CL is in the range of <NUM> ≤ Gtr1 ≤ <NUM>.

When viewed in a cross-sectional view in the tire meridian direction, a gauge of the tread rubber is measured as the length of a perpendicular line drawn from a tread profile to a belt cord surface of the outermost layer of the belt layer. The belt cord surface is defined as a surface connecting the end portions that are on an outer side in the tire radial direction of the plurality of belt cords forming the belt ply.

As described above, the pneumatic tire <NUM> includes a carcass layer <NUM>, a belt layer <NUM> disposed on an outer side of the carcass layer <NUM> in the radial direction, and a tread rubber <NUM> disposed on an outer side of the belt layer <NUM> in the radial direction (see <FIG>). Additionally, the carcass layer <NUM> has a cord angle of <NUM> ° or more and <NUM> ° or less. Additionally, the belt layer <NUM> is formed by layering a first reinforcing belt <NUM>, a second reinforcing belt <NUM> that is narrower than the first reinforcing belt <NUM>, and an auxiliary belt <NUM> that is spaced apart from the tire equatorial plane CL and disposed between the carcass layer <NUM> and the first reinforcing belt <NUM> (see <FIG>). Additionally, the first reinforcing belt <NUM> and the second reinforcing belt <NUM> have cord angles of <NUM> ° or more and <NUM> ° or less, and the auxiliary belt <NUM> has a cord angle of <NUM> ° or more and <NUM> ° or less.

In such a configuration, (<NUM>) the auxiliary belt <NUM> is disposed between the carcass layer <NUM> and the reinforcing belts <NUM>, <NUM>, and thus radial growth in the shoulder region in the tread portion is suppressed. In this way, there is an advantage that separation of the peripheral rubber at end portions of the belt layer <NUM> is suppressed and the belt edge durability performance of the tire is improved. Additionally, (<NUM>) the auxiliary belt <NUM> has a so-called split structure in which the auxiliary belt <NUM> is spaced apart from the tire equatorial plane CL, and thus increase in the gauge of the center region in the tread portion due to the arrangement of the auxiliary belt <NUM> is suppressed. In this way, there is an advantage that the heat build-up when the tire is rolling is suppressed, and thus heat build-up resistance performance of the tire is ensured. Additionally, (<NUM>) the auxiliary belt <NUM> having a cord angle of <NUM> ° or more and <NUM> ° or less is advantageous in that the cord angle of the auxiliary belt <NUM> is appropriately set. In other words, the lower limit described above allows for the difference in cord angles between adjacent auxiliary belts <NUM> and carcass layers <NUM> to be reduced, and the interlayer strain to be reduced, thereby suppressing separation of the peripheral rubber at end portions of the auxiliary belt <NUM>. Also, the upper limit described above ensures the effect of suppressing radial growth in the shoulder region in the tread portion by the auxiliary belt <NUM> described above.

Also, in the pneumatic tire <NUM>, a distance De5 from the tire equatorial plane CL to an outer end portion of the auxiliary belt <NUM> in the tire width direction has a relationship <NUM> ≤ De5/(TDW/<NUM>) ≤ <NUM> with respect to the developed tread half-width TDW/<NUM> (see <FIG>). The lower limit described above ensures the effect of suppressing radial growth in the shoulder region in the tread portion by the auxiliary belt <NUM>. The upper limit described above suppresses separation of the peripheral rubber at the outer end portion of the auxiliary belt <NUM>.

Additionally, in the pneumatic tire <NUM>, the distance De5 from the tire equatorial plane CL to the outer end portion of the auxiliary belt <NUM> in the tire width direction has a relationship <NUM> ≤ De5/De1 ≤ <NUM> with respect to the distance De1 from the tire equatorial plane CL to the first reinforcing belt <NUM> (see <FIG>). The lower limit described above ensures the effect of suppressing radial growth in the shoulder region in the tread portion by the auxiliary belt <NUM>. The upper limit described above suppresses separation of the peripheral rubber at the outer end portion of the auxiliary belt <NUM>.

Also, in the pneumatic tire <NUM>, a distance De5' from the tire equatorial plane CL to an inner end portion of the auxiliary belt <NUM> in the tire width direction has a relationship <NUM> ≤ De5'/(TDW/<NUM>) ≤ <NUM> with respect to the developed tread half-width TDW/<NUM> (see <FIG>). The lower limit ensures an advantage due to the auxiliary belt <NUM> having the split structure. The upper limit described above suppresses separation of the peripheral rubber at the outer end portion of the auxiliary belt <NUM>.

Also, in the pneumatic tire <NUM>, a width Wb5 of the auxiliary belt <NUM> has a relationship <NUM> ≤ Wb5/(TDW/<NUM>) ≤ <NUM> with respect to the developed tread half-width TDW/<NUM> (see <FIG>). The lower limit described above allows for the width Wb5 of the auxiliary belt <NUM> to be ensured. The upper limit described above ensures an advantage due to the auxiliary belt <NUM> having the split structure.

Additionally, in the pneumatic tire <NUM>, a cord diameter of a belt cord forming the auxiliary belt <NUM> is in a range of <NUM> or more and <NUM> or less. In this way, the cord diameter of the auxiliary belt <NUM> is appropriately set.

Additionally, in the pneumatic tire <NUM>, a distance De1 from the tire equatorial plane CL to an end portion of the first reinforcing belt <NUM> has a relationship <NUM> ≤ De1/(TDW/<NUM>) ≤ <NUM> with respect to the developed tread half-width TDW/<NUM> (see <FIG>). The lower limit described above ensures the hoop effect of the first reinforcing belt <NUM>, and thus the tire shape is appropriately maintained. The upper limit described above suppresses separation of the peripheral rubber at end portions of the first reinforcing belt <NUM>.

Additionally, in the pneumatic tire <NUM>, a distance De2 from the tire equatorial plane CL to an end portion of the second reinforcing belt <NUM> has a relationship <NUM> ≤ De2/(TDW/<NUM>) ≤ <NUM> with respect to the developed tread half-width TDW/<NUM> (see <FIG>). The lower limit described above ensures the hoop effect of the second reinforcing belt <NUM>, and thus the tire shape is appropriately maintained. The upper limit described above suppresses separation of the peripheral rubber at end portions of the second reinforcing belt <NUM>. Furthermore, in a configuration in which the narrower second reinforcing belt <NUM> is disposed on an outer side of the wider first reinforcing belt <NUM> in the radial direction (see <FIG>), the pressing down action of the internal pressure by the second reinforcing belt <NUM> is increased and the edge strain of the wider first reinforcing belt <NUM> is effectively reduced in comparison to a configuration in which the narrower reinforcing belt is disposed on an inner side of the wider reinforcing belt in the tire radial direction.

Additionally, in the pneumatic tire <NUM>, the belt layer <NUM> includes the protection belt <NUM> disposed on an outer side of the first reinforcing belt <NUM> and the second reinforcing belt <NUM> in the radial direction (see <FIG>). Furthermore, the protection belt <NUM> has a cord angle of <NUM> ° or more and <NUM> ° or less. Also, a distance De3 from the tire equatorial plane CL to an end portion of the protection belt <NUM> has a relationship De1 < De3 with respect to the distance De1 to the end portion of the first reinforcing belt <NUM> and a relationship De2 < De3 with respect to the distance De2 to the end portion of the second reinforcing belt <NUM>. In such a configuration, separation of the peripheral rubber at end portions of the first reinforcing belt <NUM> and the second reinforcing belt <NUM> is suppressed by the protection belt <NUM>.

Additionally, in the pneumatic tire <NUM>, a distance De3 from the tire equatorial plane CL to an end portion of the protection belt <NUM> has a relationship <NUM> ≤ De3/(TDW/<NUM>) ≤ <NUM> with respect to the developed tread half-width TDW/<NUM> (see <FIG>). The lower limit described above ensures the effect of suppressing separation of the peripheral rubber by the protection belt <NUM>. The upper limit described above suppresses the occurrence of strain due to the protection belt <NUM> itself being excessively large.

Additionally, in the pneumatic tire <NUM>, a shoulder drop amount Dt of a tread profile when the tire is mounted on a specified rim and inflated to a specified internal pressure has a relationship <NUM> ≤ Dt/SH ≤ <NUM> with respect to a tire cross-sectional height SH (see <FIG>). The lower limit described above allows for the tread gauge in the center region and the shoulder region of the tread portion to be appropriately set, and thus the heat build-up performance of the tire is improved. The upper limit described above allows for the amount of strain in the shoulder region in the tread portion when the tire is rolling to be reduced, and thus the belt edge durability performance of the tire is improved.

Moreover, in the pneumatic tire <NUM>, a distance Gca1 from a tread profile to a carcass profile on the tire equatorial plane CL has a relationship <NUM> ≤ Gca1/Gca2 ≤ <NUM> with respect to a distance Gca2 from a tread edge T to a carcass profile (see <FIG>). The lower limit described above suppresses rising of the shoulder region in the tread portion, and thus the amount of strain in the shoulder region is reduced. In this way, the belt edge durability performance of the tire is improved. The upper limit described above allows for the tread gauge in the center region and the shoulder region of the tread portion to be appropriately set, and thus the heat build-up performance of the tire is improved.

Additionally, in the pneumatic tire <NUM>, a gauge Gtr1 of the tread rubber on the tire equatorial plane CL has a relationship <NUM> ≤ Gtr1/Gtr2 ≤ <NUM> with respect to a gauge Gtr2 of the tread rubber at an end portion position of the outermost layer of the belt layer. The lower limit described above suppresses rising of the shoulder region in the tread portion, and thus the amount of strain in the shoulder region is reduced. In this way, the belt edge durability performance of the tire is improved. The upper limit described above allows for the tread gauge in the center region and the shoulder region of the tread portion to be appropriately set, and thus the heat build-up performance of the tire is improved.

The configuration of the pneumatic tire <NUM> is preferably applied to a low aspect ratio tire for a construction or industrial vehicle. Specifically, the intended tire is an OR tire having an aspect ratio of <NUM>% or less, preferably <NUM>% or less. Such an OR tire with a low aspect ratio can provide improved applied load capacity while maintaining the tire outer diameter, however, such a tire also increases the load index (k-factor) and thus the deflection amount of the tire. Accordingly, there is a problem that separation of the peripheral rubber tends to occur at belt end portions and the amount of heat generation is large. As such, having such an OR tire with low aspect ratio as the target of application produces a remarkable effect of improvement to the belt edge durability performance and heat build-up resistance performance of the tire as described above.

Also, the configuration of the pneumatic tire <NUM> is preferably applied for an OR tire having an aspect ratio of the carcass layer <NUM> of <NUM>% or less.

The aspect ratio of the carcass layer is calculated as a ratio of a distance Hca from the maximum diameter position of a rim flange portion of a specified rim to the maximum diameter position of the carcass layer in the radial direction to the maximum width Wca of the carcass layer when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state.

<FIG> is a table showing the results of performance tests of pneumatic tires according to embodiments of the invention.

In the performance tests, (<NUM>) heat build-up resistance performance and (<NUM>) belt edge durability performance were evaluated for a plurality of types of test tires. Test tires having a tire size of <NUM>/65R9 were assembled on a rim having a rim size of <NUM> × <NUM> - <NUM>, and an internal pressure of <NUM> kPa and a load of <NUM> were applied to the test tires.

The test tires of Examples <NUM> to <NUM> had the configuration illustrated in <FIG> and <FIG>, and the belt layer <NUM> was formed by layering a pair of reinforcing belts <NUM>, <NUM>, a pair of protection belts <NUM>, <NUM>, and a single layer and a pair of left and right auxiliary belts <NUM>. Additionally, the reinforcing belts <NUM>, <NUM> and the auxiliary belt <NUM> were made from steel cords having a cord diameter of <NUM>, and the pair of protection belts <NUM>, <NUM> were made from steel cords having a cord diameter of <NUM>. Additionally, the developed tread half-width TDW/<NUM> was <NUM>, and the tire cross-sectional height SH was <NUM>. Additionally, the cord angle of the carcass layer <NUM> was <NUM>°, and the aspect ratio of the carcass layer <NUM> was <NUM>%.

The test tire of the Conventional Example does not include the auxiliary belt <NUM> in the configuration of <FIG> and <FIG>. In the test tires of the Comparative Example, in the configurations illustrated in <FIG> and <FIG>, the cord angles of the first reinforcing belt <NUM> and the auxiliary belt <NUM> were outside the predetermined range.

Claim 1:
A pneumatic tire (<NUM>), comprising:
a carcass layer (<NUM>);
a belt layer (<NUM>) disposed on an outer side of the carcass layer (<NUM>) in a radial direction; and
a tread rubber (<NUM>) disposed on an outer side of the belt layer (<NUM>) in the radial direction,
the carcass layer (<NUM>) having a cord angle of <NUM> ° or more and <NUM> ° or less,
the belt layer (<NUM>) being formed by layering a first reinforcing belt (<NUM>), a second reinforcing belt (<NUM>) that is narrower than the first reinforcing belt (<NUM>), and an auxiliary belt (<NUM>) that is spaced apart from a tire equatorial plane (CL) and disposed between the carcass layer (<NUM>) and the first reinforcing belt (<NUM>),
the first reinforcing belt (<NUM>) and the second reinforcing belt (<NUM>) having cord angles of <NUM> ° or more and <NUM> ° or less, and
the auxiliary belt (<NUM>) having a cord angle of <NUM> ° or more and <NUM> ° or less,
wherein a distance De5 from the tire equatorial plane (CL) to an outer end portion of the auxiliary belt (<NUM>) in a tire width direction has a relationship <NUM> ≤ De5/De1 ≤ <NUM> with respect to a distance De1 from the tire equatorial plane (CL) to an end portion of the first reinforcing belt (<NUM>),
characterized in that, a distance De5' from the tire equatorial plane (CL) to the inner end portion of the auxiliary belt (<NUM>) in the tire width direction has a relationship <NUM> ≤ De5'/De5 ≤ <NUM> with respect to the distance De5.