JP7255371B2 - pneumatic tire - Google Patents

Description

The present disclosure relates to a pneumatic tire with well-balanced improvements in rolling resistance performance, tire noise performance, and crack resistance performance.

In order to improve fuel efficiency, it is important to reduce rolling resistance in tires. For example, in order to lower the rigidity of the tread portion and arrange low heat generation rubber for the purpose of reducing rolling resistance, a method of increasing the thickness of the undertread rubber is adopted. However, when the undertread rubber is thickened, there is a problem that cracks occur in the tread portion.

Various techniques have been proposed to simultaneously reduce rolling resistance and improve crack resistance. For example, Patent Document 1 discloses a ratio CR2/CR1 of the curvature radius CR1 of the shoulder region when filled with air pressure equivalent to 5% of the nominal maximum air pressure and the curvature radius CR2 of the shoulder region when filled with the nominal maximum air pressure. is 0.70 to 0.95, the pneumatic tire is configured such that the shoulder region expands outward in the tire radial direction due to inflation. With such a configuration, the pneumatic tire described in Patent Document 1 achieves a reduction in rolling resistance and an improvement in crack resistance.

JP-A-1-9002

By the way, in the tread portion, the load tends to be concentrated on the land portion extending in the tire circumferential direction and located near the outermost main groove in the tire width direction. Cracks are likely to occur in the land portion located near the formed main groove. The occurrence of cracks in the land portion near the main groove formed on the outermost side in the tire width direction is caused not only by changes in the amount of growth of the shoulder region due to changes in tire air pressure, but also by the amount of growth between the center region and the shoulder region of the tire. However, Patent Literature 1 does not disclose any findings regarding such a relationship between the amount of growth between the center region and the shoulder region. Therefore, there is room for further improvement in the technique described in Patent Document 1.

Moreover, in recent years, not only reduction in rolling resistance and improvement in crack resistance, but also reduction in tire noise is often demanded at the same time in order to contribute to the local environment.

In view of the above circumstances, an object of the present disclosure is to provide a pneumatic tire that has improved rolling resistance performance, tire noise performance, and crack resistance performance in a well-balanced manner.

The gist of the present disclosure is as follows.

A pneumatic tire comprising a tread rubber including an undertread rubber and a cap tread rubber, and at least two circumferential main grooves extending in the tire circumferential direction formed on the surface of the tread rubber,
The total width of the at least two circumferential main grooves is 15% or more of the ground contact width in a load state of 70% of the maximum load capacity when incorporated in a specified rim and filled with specified internal pressure,
In the meridional cross-sectional view of a tire assembled in a specified rim and filled with an internal pressure of 5% of the specified internal pressure, the point on the tire surface in the tire equatorial plane is P0, and the position in the tire width direction is the tire of the pneumatic tire belt. When the point on the profile line of the surface of the tread rubber equal to the position in the tire width direction of the outermost position in the width direction is defined as P1, the angle formed by the line segment connecting the points P0 and P1 with respect to the tire width direction. is θ, the tire section height is SH, and the tire radial height to the tire maximum width position is SWH,
θ is 4° or more and 7° or less,
The ratio SWH/SH is 0.4 or more and 0.55 or less,
The total tire width SW is equal to or greater than the standard median value,
A tire width direction region inside the tire width direction outer end portion of the outermost circumferential main groove located on the outermost side in the tire width direction of the circumferential main grooves is defined as a center region, and the end portion is defined as a center region. to the point P1 is defined as a shoulder region, and in the shoulder region, the dimension in the tire width direction is 0.3 times the dimension from the end to the point P1, and the point P1 is defined as an out-shoulder region, and when the tire radial growth amounts in the center region and the out-shoulder region are CG and SOG, respectively, when the internal pressure is set from 50 kPa to 230 kPa in an unloaded state, the ratio CG/SOG is 0.25 or more and 0.55 or less.

According to the pneumatic tire according to the present disclosure, it is possible to improve rolling resistance performance, tire noise performance, and crack resistance performance in a well-balanced manner by focusing on the relationship between the amount of growth between the center region and the shoulder region. .

FIG. 1 is a tire meridian sectional view showing a pneumatic tire according to a basic embodiment. FIG. 2 is a plan view showing an example of the tread surface of the pneumatic tire according to the basic embodiment. FIG. 3 is a tire meridian sectional view showing the overall configuration of the pneumatic tire according to the basic embodiment. FIG. 4 is an enlarged view of the vicinity of the outermost circumferential main groove in a state where the internal pressure is 50 kPa and 230 kPa, respectively. FIG. 5 is a diagram showing the relationship between the distortion of the belt cover 16 and the stress applied to each of the center region Ce and the shoulder regions Sh.

Hereinafter, embodiments of the pneumatic tire according to the present disclosure (basic mode and additional modes 1 to 5 shown below) will be described in detail based on the drawings. Note that these embodiments do not limit the present disclosure. In addition, the components of the above embodiments include components that can be easily replaced by those skilled in the art, or components that are substantially the same. Further, the various forms included in the above embodiments can be arbitrarily combined within the scope obvious to those skilled in the art.

≪Basic form≫
The basic configuration of the pneumatic tire according to the present invention will be described below. In the following description, the tire radial direction refers to the direction perpendicular to the rotation axis of the pneumatic tire, the tire radial direction inner side refers to the side facing the rotation axis in the tire radial direction, and the tire radial direction outer side refers to the tire radial direction. The side away from the rotation axis. In addition, the tire circumferential direction refers to a circumferential direction around the rotation axis. Furthermore, the tire width direction refers to a direction parallel to the rotation axis, the tire width direction inner side refers to the side facing the tire equatorial plane (tire equator line) in the tire width direction, and the tire width direction outer side refers to the direction in the tire width direction. The side away from the tire equatorial plane. The tire equatorial plane CL is a plane perpendicular to the rotation axis of the pneumatic tire and passing through the center of the tire width of the pneumatic tire.

FIG. 1 is a tire meridian sectional view showing a pneumatic tire according to the present basic embodiment. Note that FIG. 1 shows a pneumatic tire 10 in an unloaded state assembled on a specified rim and filled with an internal pressure of 5% of the specified internal pressure. Here, the specified rim means the "applicable rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. The specified internal pressure means the maximum air pressure specified by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or "INFLATION PRESSURES" specified by ETRTO.

A pneumatic tire 10 shown in FIG. 1 includes a carcass 12 , a belt 14 , a belt cover 16 and a tread rubber 18 .

The carcass 12 is a member that spans between bead cores on both sides in the tire width direction (not shown) and forms the frame of the tire. The carcass 12 includes at least one carcass layer (one layer in FIG. 1).

The belt 14 is a member that is arranged outside the carcass 12 in the tire radial direction, tightens the carcass 12 strongly, and increases the rigidity of the tread portion T. As shown in FIG. The belt 14 is composed of two or more layers, ie, two belt layers 14a and 14b in the example shown in FIG. The belt layers 14a and 14b have a structure in which belt cords cross each other.

The belt cover 16 is arranged on the outer side of the belt 14 in the tire width direction so as to cover the outer ends of the belt layers 14a and 14b in the tire width direction. It is a suppressing member. The belt cover 16 is composed of a plurality of belt covers 16a and 16b, two in the example shown in FIG. 1, which are sequentially formed from the inner side to the outer side in the tire radial direction. As a result, it is possible to mainly prevent peeling failures at the ends of the belt 14 and improve high-speed durability.

The tread rubber 18 is mainly a member arranged outside the carcass 12 and the belt 14 in the tire radial direction and in contact with the road surface. As shown in FIG. 1, the tread rubber 18 includes an undertread rubber 18a (hatched portion in the figure) and a cap tread rubber 18b formed outside the undertread rubber 18a in the tire radial direction.

FIG. 2 is a plan view showing the tread pattern of the pneumatic tire of this basic embodiment shown in FIG. Reference numerals E1 and E2 in FIG. 2 each indicate a grounding edge line (a line in which continuous grounding edges are connected in the tire circumferential direction). As shown in FIG. 2, the tread portion T of the pneumatic tire 10 has at least two circumferential main grooves 22 (four circumferential main grooves 22a to 22d in the figure) extending in the tire circumferential direction. formed. The total width of these four circumferential main grooves 22 is 15% or more of the ground contact width when the rim is assembled in a specified rim and filled with a specified internal pressure and a load of 70% of the maximum load capacity is applied.

Here, the main groove is a groove that is required to display a wear indicator as defined by JATMA, and generally refers to a groove having a groove width of 2% or more of the tread width TW. Further, the groove width refers to the dimension between adjacent land portions measured in the direction perpendicular to the extending direction of the groove at the opening of the groove. In addition, the maximum load capacity refers to the "maximum load capacity" specified by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "LOAD CAPACITY" specified by ETRTO. .

Then, as shown in FIG. 2, the pneumatic tire 10 of the present embodiment has the tire width direction outside of the outermost circumferential main grooves 22a and 22d located on the outermost side in the tire width direction among the circumferential direction main grooves 22a to 22d. , a plurality of lug grooves 24 inclined with respect to the tire width direction are formed at regular intervals in the tire circumferential direction. In the example shown in FIG. 2 , the circumferential main grooves extend inward in the tire width direction from each of the two outermost circumferential main grooves 22 a and 22 d on the outer side in the tire width direction. A pair of first narrow grooves 26a and 26b communicating with the respective grooves 22b and 22c are formed at regular intervals in the tire circumferential direction. Furthermore, in the example shown in FIG. 2 , second grooves extending inward in the tire width direction from each of the two circumferential main grooves 22 b and 22 c on the inner side in the tire width direction are inclined with respect to the tire width direction and terminate in land portions. Two narrow grooves 28 are formed at regular intervals in the tire circumferential direction.

Below, the dimensions of each groove are shown in a non-loaded state in which the tire is assembled in a specified rim and filled with an internal pressure of 5% of the specified internal pressure. The groove width of the circumferential main grooves 22 is, for example, 6 mm to 12 mm, the groove depth of the circumferential main grooves 22 is, for example, 6 mm to 9 mm, and the interval between the circumferential main grooves 22 is, for example, 10 mm. ~35 mm. The groove width of the lug grooves 24 is, for example, 1.5 mm to 4 mm, the groove depth of the lug grooves 24 is, for example, 4.4 mm to 7.4 mm, and the interval between the lug grooves 24 is, for example, 12 mm. ~40 mm. The groove widths of the first fine grooves 26a, 26b and the second fine grooves 28 are, for example, 0.5 mm to 1.5 mm, and the groove depths of the first fine grooves 26a, 26b, and the second fine grooves 28 are, for example, , 4.4 mm to 7.4 mm. The interval between adjacent first fine grooves 26a and 26b is, for example, 12 mm to 25 mm, the interval between adjacent pairs of first fine grooves 26a and 26b is, for example, 8 mm to 20 mm, and the adjacent second The interval between the fine grooves 28 is, for example, 12 mm to 40 mm. Here, the groove width is the maximum dimension in the direction perpendicular to the extending direction of the groove, and the groove depth is the diameter measured from the tire profile line to the groove bottom in the tire radial direction when there is no groove. Maximum size.

FIG. 3 is a tire meridian sectional view showing the overall configuration of the pneumatic tire according to the present basic embodiment. As shown in FIG. 3, in a meridional cross-sectional view of a tire assembled on a specified rim and filled with 5% of the specified internal pressure in a no-load state, the point on the tire surface in the tire equatorial plane CL is P0, and the position in the tire width direction is the belt 14. Let the point on the profile line of the tread surface equal to the tire width direction position of the tire width direction outermost position be P1, and let the angle formed by the line segment connecting the points P0 and P1 with the tire width direction be θ, When the cross-sectional height is SH, and the tire radial height to the tire maximum width position is SWH, the pneumatic tire 10 according to the present basic embodiment is:
θ is 4° or more and 7° or less,
The ratio SWH/SH is 0.4 or more and 0.55 or less,
The total tire width SW is equal to or greater than the standard median value,
is configured as

Here, the standard means JATMA, TRA, or ETRTO mentioned above. Further, the standard median value refers to the value located in the center when a plurality of tire total widths listed in JATMA or the like are arranged in ascending order.

Further, as shown in FIG. 3, the outermost circumferential main grooves 22a and 22d of the circumferential main grooves 22a to 22d located on the outermost side in the tire width direction are positioned on the inner side in the tire width direction of the ends 23 on the outer side in the tire width direction. is defined as a center region Ce, the tire width direction region from the end portion 23 to the point P1 is defined as a shoulder region Sh, and the tire width direction region from the end portion 23 to the point P1 in the shoulder region Sh A region having a dimension 0.3 times the dimension and including the point P1 is defined as a shoulder outer region Sh _out , and a region on the inner side of the shoulder outer region Sh _out in the tire width direction is defined as a shoulder inner region Sh _in . At this time, when the pneumatic tire 10 according to the present basic embodiment is mounted on a specified rim and the internal pressure is set from 50 kPa to 230 kPa in an unloaded state, the tire radial growth amount in the center region Ce and the shoulder outside region Sh is When CG and SOG, the ratio CG/SOG is configured to be 0.25 or more and 0.55 or less.

Here, each of the tire radial direction growth amounts CG and SOG is determined, for example, by arbitrary three points in each of the center region Ce and the shoulder outer region Sh _out (portions where grooves are formed) in a meridional cross-sectional view of the tire in an unloaded state. ), the average value of each amount of change in the tire radial direction between the case of filling with an internal pressure of 50 kPa and the case of filling with an internal pressure of 230 kPa. In particular, the arbitrary three points in each of the center region Ce and the shoulder outer region Sh _out are, for example, when viewed in a meridional cross-section of the tire in an unloaded state, each of the center region Ce and the shoulder outer region Sh _out are defined by the grooves. It can be set to three points that are equally divided into three except for the formed portion. Note that each tire radial direction growth amount CG and SOG is not limited to this, and the tire radial direction growth amount at at least one arbitrary point excluding the portion where the groove is formed in each of the center region Ce and the shoulder outer region Sh _out Variation may be used. Alternatively, as the SOG, an average value of the amount of change in the tire radial direction in the two shoulder outer regions Sh _out on both sides in the tire width direction may be used.

In addition, in the present invention, the dimensions of the pneumatic tire 10 are measured in an unloaded state when the tire is filled with an internal pressure within the range normally used. In this basic configuration, an internal pressure of 5% of the specified internal pressure is selected to define the dimensions of the pneumatic tire. However, the pneumatic tire 10 according to the present basic embodiment is effective as long as the internal pressure is within the range normally used. Therefore, it should be noted that it is not essential for the implementation of the present invention that the pneumatic tire 10 is filled with an internal pressure of 5% of the specified internal pressure.

The pneumatic tire according to the present basic embodiment described above includes the usual manufacturing processes, that is, the tire material mixing process, the tire material processing process, the green tire molding process, the vulcanization process, and the inspection process after vulcanization. etc. When manufacturing the pneumatic tire of this basic form, the inner wall of the mold for vulcanization is formed with, for example, projections and recesses corresponding to the tread pattern shown in FIG. I do.

(action, etc.)
According to the pneumatic tire 10 according to this basic embodiment, the following effects can be obtained.

The pneumatic tire 10 according to the present basic embodiment is configured such that θ is 4° or more and 7° or less in an unloaded state in which the tire is assembled on a specified rim and filled with 5% of the specified internal pressure.

In the tread portion T, from the center region Ce to the shoulder region Sh is inclined inward in the tire radial direction in a meridional cross-sectional view of the tire. Due to the deformation of the shoulder region Sh, a load is applied to the land portions located in the vicinity of the outermost circumferential main grooves 22a and 22d located at the boundary between the center region Ce and the shoulder region Sh among the circumferential main grooves 22a to 22d. As a result, cracks are likely to occur in land portions near the outermost circumferential main grooves 22a and 22d. By setting θ to 4° or more, it is possible to smooth the change in thickness (that is, the change in rigidity) from the tread portion T to the shoulder region Sh. Such a smooth change in rigidity suppresses the local load from being applied particularly to the land portions near the outermost circumferential main grooves 22a and 22d. It is possible to suppress the occurrence of cracks in the part (effect 1).

On the other hand, by setting θ to 7° or less, the load dependence of the contact width does not become excessively large, and the contact area does not excessively increase, so the rolling resistance can be reduced under load ( Function and effect 2).

Here, if θ is smaller than 4°, the shoulder region Sh becomes too flat, resulting in an increase in the contact length and the contact width, resulting in an excessive contact area. Therefore, air column resonance due to natural vibration of the air in the lug grooves 24 of the shoulder region Sh, which is excited by vibration of the tread portion T, etc., increases, and as a result, tire noise performance deteriorates. The contact length is the maximum length in the tire circumferential direction of the contact area of the tire. On the other hand, if θ is larger than 7°, the shoulder region Sh becomes too round, and the shoulder region Sh is largely deformed by the input during running, and the rigidity is lowered, resulting in deterioration of rolling resistance. .

The pneumatic tire 10 according to the present basic embodiment is mounted on a specified rim and filled with 5% of the specified internal pressure in an unloaded state so that the ratio SWH/SH of SWH to SH is 0.40 or more and 0.55 or less. It is configured. By setting the ratio SWH/H to 0.40 or more, excessive increase in the tire radial dimension from the tire maximum width position to the tire radial outermost position in the tire meridional cross-sectional view in FIG. 3 can be suppressed. can be done. As a result, large deformation of mainly the shoulder region Sh due to input during running is suppressed, and in particular, local load applied to the land portions near the outermost circumferential main grooves 22a and 22d is suppressed. Therefore, it is possible to suppress the occurrence of cracks in the land portions near the outermost circumferential main grooves 22a and 22d (effect 3).

On the other hand, by setting the ratio SWH/SH to 0.55 or less, the tire radial dimension from the tire maximum width position to the radial outermost position of the tire is sufficiently secured in the tire meridional cross-sectional view in FIG. be able to. This makes it possible to smooth the change in thickness (that is, the change in rigidity) from the tread portion T to the shoulder region Sh in a tire meridional cross-sectional view. Such a smooth change in rigidity suppresses the local load from being applied particularly to the land portions near the outermost circumferential main grooves 22a and 22d. It is possible to suppress the occurrence of cracks in the part (effect 4).

Here, if SWH/SH is smaller than 0.4, mainly the shoulder region Sh is greatly deformed by the input during running, and the rigidity is lowered, resulting in deterioration of rolling resistance. On the other hand, when SWH/SH is greater than 0.55, the tire radial dimension from the maximum tire width position to the radial outermost position of the tire cannot be sufficiently secured, and the tire radial growth amount in the shoulder region Sh is insufficient. be enough. As a result, the land portions near the outermost circumferential main grooves 22a and 22d are particularly likely to be locally loaded, so cracks are sufficiently suppressed in the land portions near the outermost circumferential main grooves 22a and 22d. I can't.

The pneumatic tire 10 according to this basic embodiment is constructed so that the total tire width SW shown in FIG. . Making the total tire width SW equal to or larger than the standard median value, in other words, by increasing the total tire width SW to some extent, ensuring a sufficient volume of the tire cavity and reducing tire deflection under load. and thus rolling resistance can be reduced in a load-applied state (effect 5). Note that if SW is smaller than the standard median value, the volume of the tire cavity cannot be sufficiently ensured, and the amount of growth in the tire radial direction in the shoulder region Sh becomes insufficient. As a result, the land portions near the outermost circumferential main grooves 22a and 22d are particularly likely to be locally subjected to a load, so that the occurrence of cracks in the land portions near the outermost circumferential main grooves 22a and 22d is sufficiently suppressed. I can't.

The pneumatic tire 10 according to the present basic embodiment has a CG/SOG ratio of 0.25 or more to 0.55 or less in an unloaded state in which the pneumatic tire 10 is mounted on a prescribed rim and filled with 5% of the prescribed internal pressure. It is configured. By setting the ratio CG/SOG to 0.25 or more, it is possible to secure a sufficient amount of growth in the tire radial direction in the shoulder region Sh. As a result, the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d are particularly prevented from being locally subjected to a load, so cracks are prevented from occurring in the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d. can be suppressed (effect 6).

On the other hand, by setting the ratio CG/SOG to 0.55 or less, the contact length and contact width in the shoulder region Sh can be sufficiently reduced, and the contact area in the shoulder region Sh can be sufficiently reduced. Therefore, it is possible to reduce the air column resonance sound caused by the natural vibration of the air in the lug grooves 24 of the shoulder region Sh, which is excited by the vibration of the tread portion T or the like, and thus the tire noise can be reduced (Effect 7). .

Here, when the ratio CG/SOG is less than 0.25, the tire radial growth amount in the shoulder region Sh becomes too large compared to the tire radial growth amount in the center region Ce, and the shoulder region Sh becomes flat. As a result, the contact length and the contact width in the shoulder region Sh increase, and the contact area in the shoulder region Sh increases. Therefore, air column resonance due to natural vibration of the air in the lug grooves 24 of the shoulder region Sh, which is excited by vibration of the tread portion T, etc., increases, and as a result, tire noise performance deteriorates. On the other hand, when the ratio CG/SOG is greater than 0.55, the amount of tire radial direction growth in the shoulder region Sh is too small, and the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d in particular tend to be locally subjected to load. Therefore, it is not possible to sufficiently suppress the occurrence of cracks in the land portions near the outermost circumferential main grooves 22a and 22d.

As described above, in the pneumatic tire of the present embodiment, improvements are made to θ, the ratios SWH/SH, SW, and the ratio CG/SOG. Tire noise performance and crack resistance performance can be improved in a well-balanced manner.

≪Additional forms≫
Next, additional modes 1 to 5 that can optionally be implemented with respect to the basic mode of the pneumatic tire according to the present invention will be described.

(Additional form 1)
FIG. 4 is an enlarged view of the vicinity of the outermost circumferential main groove 22 when the inner pressures are 50 kPa and 230 kPa, respectively. In FIG. 4 , the solid line represents the state in which the tire is installed in the specified rim and filled with an internal pressure of 230 kPa, and the dotted line represents the state in which the seat is installed in the specified rim and filled with an internal pressure of 50 kPa.

As shown in FIG. 4, in the pneumatic tire 10 according to the additional embodiment 1, the tire width direction dimension of the outermost circumferential main groove 22 is set to GW50 and the internal pressure is 230 kPa in a state in which the pneumatic tire 10 is assembled on a regular rim and filled with an internal pressure of 50 kPa. When GW230 is the tire width direction dimension of the outermost circumferential main groove 22 filled with is preferred. Here, the tire width direction dimension of the outermost circumferential main groove 22 is the dimension between the inner end and the outer end in the tire width direction of the outermost circumferential main groove 22 (the outermost circumferential main groove 22 is If chamfered, the dimension between the inner end and the outer end in the tire width direction including the chamfered portion). Also, the tire width direction dimension of the outermost circumferential main groove 22 may be set using an average value of the tire width direction dimensions of the two outermost circumferential direction main grooves 22a and 22d.

By setting the ratio GW50/GW230 to 0.92 or more, the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d can be sufficiently deformed in the tire width direction when the internal pressure is filled. A sufficient tire radial growth amount can be ensured. As a result, the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d are particularly prevented from being locally subjected to a load, so cracks are prevented from occurring in the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d. can be suppressed.

On the other hand, by setting the ratio GW50/GW230 to 0.96 or less, the contact length and contact width in the shoulder region Sh are sufficiently reduced when the internal pressure is filled, and thus the contact area in the shoulder region Sh is sufficiently reduced. . Therefore, it is possible to reduce the columnar resonance noise caused by the natural vibration of the air in the lug grooves 24 of the shoulder region Sh, which is excited by the vibration of the tread portion T or the like, thereby improving the tire noise performance. Moreover, since the contact area does not increase excessively, the rolling resistance can be reduced under load.

Here, if the ratio GW50/GW230 is smaller than 0.92, the amount of deformation in the tire width direction of the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d when the internal pressure is filled is too small, and the shoulder region Sh. Since a sufficient tire radial growth amount cannot be ensured at , it is not possible to sufficiently suppress the occurrence of cracks in the land portions near the outermost circumferential main grooves 22a and 22d. On the other hand, if GW50/GW230 is greater than 0.96, the amount of deformation in the tire width direction of the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d when the internal pressure is filled becomes too large, resulting in a large contact area. Since it increases excessively, rolling resistance increases.

(Additional form 2)
As shown in FIG. 1, if UGG is the thickness of the cap tread rubber 18b under the circumferential main groove 22 in the no-load state in which 5% of the specified internal pressure is filled with the specified rim, the air according to the additional mode 2 The padded tire 10 is preferably configured such that the thickness UGG is 0.3 [mm] or more and 1.5 [mm] or less. Here, the thickness UGG is the dimension in the tire radial direction from the center position of the groove bottom of the circumferential main groove 22 in the tire width direction to the undertread rubber 18a.

By setting the thickness UGG to 0.3 [mm] or more, the cap tread rubber 18b under the circumferential main groove 22 can be made sufficiently thin. Large deformation of the tread rubber 18b can be suppressed. As a result, sufficient rigidity can be ensured in the cap tread rubber 18b below the circumferential main groove 22, so rolling resistance can be reduced.

On the other hand, by setting the thickness UGG to 1.5 [mm] or less, the vibration width in the tire radial direction of the cap tread rubber 18b under the circumferential main groove 22 can be sufficiently reduced, so that the tire Noise can be reduced.

If the thickness UGG is less than 0.3 [mm], the cap tread rubber 18b under the circumferential main groove 22 becomes too thin, and the cap tread rubber 18b under the circumferential main groove 22 cannot obtain sufficient durability. Therefore, cracks are likely to occur in the land portions near the circumferential main grooves 22 . On the other hand, if the UGG is greater than 1.5 [mm], the rigidity of the cap tread rubber 18b under the circumferential main groove 22 becomes too small, resulting in increased rolling resistance.

(Additional form 3)
Assuming that the hardness of the cap tread rubber 18b is CHS and the hardness of the undertread rubber 18a is UHS, in the pneumatic tire 10 according to the additional embodiment 3, the difference CHS-UHS between the hardness CHS and the hardness UHS is the JIS hardness, It is preferably configured to be greater than 5 and less than 15. Here, JIS hardness is a value measured by a method using a durometer as a measuring instrument, as specified in JIS K6253.

Moreover, the pneumatic tire 10 according to the present basic embodiment is preferably configured such that tan δC of the cap tread rubber 18b at 60°C is greater than tan δU of the undertread rubber 18a at 60°C.

Further, in the pneumatic tire 10 according to the present basic embodiment, the ratio UA/TA of the cross-sectional area UA of the undertread rubber 18a to the cross-sectional area TA of the tread rubber 18 is 0.2 or more and 0.4 or less in the tire meridional cross-sectional view. It is preferably configured to be

When the hardness difference CHS-UHS is greater than 5 and less than 15 in JIS hardness, especially in the shoulder region Sh, when the cap tread rubber 18b receives an input from the road surface while the vehicle is running, the undertread rubber 18a is sufficient. It can be deformed by following. As a result, the local load is suppressed particularly on the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d, so cracks are prevented from occurring in the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d. can be suppressed.

Since tan δC of the cap tread rubber 18b at 60°C is larger than tan δU of the undertread rubber 18a at 60°C, rolling resistance can be reduced and heat build-up resistance can be enhanced.

When the ratio UA/TA is 0.2 or more, the ratio of the undertread rubber 18a in the tread rubber 18 is sufficiently large, and when the belt 14 and the cap tread rubber 18b behave differently during running, the undertread rubber The tread rubber 18a can play a cushioning role against these behaviors. Therefore, tire noise can be reduced.

On the other hand, when the ratio UA/TA is 0.4 or less, the ratio of the undertread rubber 18a in the tread rubber 18 is not excessively increased, and sufficient rigidity can be secured in the entire tread rubber 18. Therefore, rolling resistance can be reduced.

If the ratio UA/TA is less than 0.2, the ratio of the undertread rubber 18a in the tread rubber 18 becomes too small. The undertread rubber 18a cannot act as a buffer against these behaviors. Therefore, tire noise increases. In addition, as a result of the cap tread rubber 18b having an excessively large proportion in the tread rubber 18, the rigidity of the tread rubber 18 increases, resulting in a smaller ground contact area and increased contact pressure during rolling, resulting in increased rolling resistance. increase.

On the other hand, if the ratio UA/TA is greater than 0.4, the ratio of the relatively soft undertread rubber 18a in the tread rubber 18 becomes too large, and the tread rubber 18 as a whole cannot ensure sufficient rigidity. As a result, sufficient durability cannot be ensured particularly in the land portions near the outermost circumferential main grooves 22a and 22d, which are likely to be locally loaded. Cracks are likely to occur in the part.

(Additional form 4)
FIG. 5 is a diagram showing the relationship between the distortion of the belt cover 16 and the stress applied to each of the center region Ce and the shoulder regions Sh. As shown in FIG. 5, when the belt cover 16 is distorted by 1% of its total length in a non-loaded state in which it is assembled in a specified rim and filled with 5% of the specified internal pressure, the stress applied to the center region Ce and the belt cover 16 are deformed. Let CS be the gradient of the stress in the center region Ce due to the stress applied to the center region Ce when the belt cover 16 is distorted by 3% of the total length, and the stress applied to the shoulder region Sh when the belt cover 16 is distorted by 1% of the total length and the stress applied to the belt cover 16. When the stress applied to the shoulder region Sh when is distorted by 3% of its total length and the slope of the stress in the shoulder region Sh due to SS, the pneumatic tire 10 according to the additional embodiment 4 has a ratio CS/SS of 2 or more It is preferably configured to be 3 or less. Here, the smaller the stress gradients CS and SS, respectively, the weaker the restraint by the belt cover 16 in that area, and when stress is applied to each area, the area is more likely to be distorted, and the amount of deformation in that area is reduced. growing. Further, the larger the stress gradients CS and SS, respectively, the stronger the restraint by the belt cover 16 in that area, and when stress is applied to each area, the area is less likely to be distorted, and the amount of deformation in that area is smaller. Become.

When the ratio CS/SS is 2 or more, the restraint of the shoulder region Sh by the belt cover 16 can be sufficiently weakened. A radial growth amount can be secured. As a result, the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d are particularly prevented from being locally subjected to a load, so cracks are prevented from occurring in the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d. can be suppressed.

On the other hand, when the ratio CS/SS is 3 or less, the restraint of the shoulder region Sh by the belt cover 16 is not excessively weakened, and sufficient rigidity can be secured in the tread portion T, thereby reducing rolling resistance. can be reduced.

If the ratio CS/SS is less than 2, the belt cover 16 restricts the shoulder region Sh too strongly, so that a sufficient amount of tire radial deformation is obtained in the shoulder region Sh relative to the amount of tire radial growth in the center region Ce. can't As a result, the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d are particularly likely to be locally subjected to a load, so that the occurrence of cracks in the land portions in the vicinity of the outermost circumferential main grooves 22a and 22d is sufficiently suppressed. Can not do it.

On the other hand, when the ratio CS/SS is greater than 3, the restraint of the shoulder region Sh by the belt cover 16 is too weak, and the amount of growth in the tire radial direction of the shoulder region Sh is greater than the amount of growth in the tire radial direction of the center region Ce. too much. Therefore, as a result of the shoulder region Sh becoming too flat, the contact length and contact width of the shoulder region Sh increase, and the contact area of the shoulder region Sh increases. Therefore, air column resonance due to natural vibration of the air in the lug grooves 24 of the shoulder region Sh, which is excited by vibration of the tread portion T, etc., increases, and as a result, tire noise performance deteriorates.

(Additional form 5)
Let GR be the groove area ratio of the first thin grooves 26a, 26b and the second thin grooves 28 in the tread surface to the area of the center region Ce. It is preferably configured to be 0.02 or more and 0.07 or less.

When the groove area ratio GR is 0.02 or more, the contact area in the center region Ce becomes sufficiently small when the internal pressure is filled. Therefore, air column resonance due to natural vibration of the air in the first fine grooves 26a, 26b and the second fine grooves 28 in the center region Ce, which is excited by vibration of the tread portion T, etc., is reduced, and tire noise is reduced. can be reduced.

On the other hand, when the groove area ratio GR is 0.07 or less, the ground contact area in the center region Ce can be sufficiently reduced, so that rolling resistance can be reduced.

When the groove area ratio GR is less than 0.02, the rigidity of the blocks near the first narrow grooves 26a and 26b is high, and the amount of tire radial deformation in the tread portion T is small, so the tread portion T is difficult to deform. As a result, the heat generation of the tread portion T increases, so the rolling resistance cannot be reduced. On the other hand, if the groove area ratio GR is greater than 0.07, the ground contact area in the center region Ce becomes too large when the internal pressure is filled. Air column resonance due to natural vibration of the air in the grooves 26a, 26b and the second narrow groove 28 increases, resulting in increased tire noise.

Here, it is preferable that a total of 70 to 120 first fine grooves 26a, 26b and second fine grooves 28 are arranged for each rib. When the groove is divided in the middle like the second narrow groove 28, the number of grooves may be the count number of grooves divided in the middle×0.5.

≪Example≫
Pneumatic tires of Examples 1 to 6 and a conventional pneumatic tire having a tire size of 185/60R15 84H and having the tire meridional cross-sectional shape shown in FIGS. 1 and 3 and the tread pattern shown in FIG. 2 were produced. The detailed conditions of these pneumatic tires are as shown in Tables 1 and 2 below.

The pneumatic tires according to Examples 1 to 6 and the pneumatic tires according to the conventional example thus produced are assembled on a specified rim, and a load (330 kg) of 66% of the maximum load capacity is applied, and the displacement ( 1300 cc) test vehicle, and the rolling resistance, tire noise and groove cracks were evaluated according to the following procedures.

(Performance related to rolling resistance)
Rolling resistance was measured for each test tire by the force method according to ISO 28580. Based on this measurement result, an index evaluation was performed using the conventional example as a standard (100). This evaluation indicates that the higher the index, the higher the performance in terms of rolling resistance.

(Performance related to tire noise)
Evaluation was made based on the loudness of the sound that passed outside the vehicle when traveling on a road surface that satisfies the ISO 10844:1994 regulations. Specifically, a test vehicle equipped with each test tire was run on a test course at a speed of 50 km/h, tire noise was measured eight times from both sides in the width direction of the vehicle, and the average value was calculated. Then, the measurement results were evaluated with an index based on the conventional example (100). Since the tire noise index indicates the sound pressure level difference, the smaller the index, the better the tire noise.

(Crack resistance performance)
Each test tire was evaluated for crack resistance performance. Specifically, each test tire was mounted on a specified rim and exposed to an environment of an internal pressure of 50 kPa, a temperature of 50° C. and an ozone concentration of 100 pphm for 8 hours each for 3 days, and then the number of cracks finally generated was counted. Then, the measurement results were evaluated with an index based on the conventional example (100). In this evaluation, the higher the index, the higher the crack resistance.

According to Tables 1 and 2, it is within the technical scope of the present invention (that is, the relationship between θ, the ratio SWH/SH, the total tire width SW and the ratio CG/SOG, the relationship between the ratio GW50/GW230, the circumferential main groove 22 Improvements were made to the relationship between the thickness UGG of the lower cap tread rubber 18b, the hardness difference CHS-UHS, tan δC, tan δU and the ratio UA/TA, the relationship CS/SS, and the relationship GR. All of the pneumatic tires of Examples 1 to 6 had better rolling resistance performance, tire noise performance, and crack resistance than the pneumatic tires of the conventional example, which do not belong to the technical scope of the present invention. It can be seen that the balance has been improved.

10 pneumatic tire 12 carcass 14 belt 16 belt cover 18 tread rubber 22 circumferential main groove Ce center region Sh shoulder region CL tire equatorial plane T tread

Claims (6)

A pneumatic tire comprising a tread rubber including an undertread rubber and a cap tread rubber, and at least two circumferential main grooves extending in the tire circumferential direction formed on the surface of the tread rubber,
The total width of the at least two circumferential main grooves is 15% or more of the ground contact width in a load state of 70% of the maximum load capacity when incorporated in a specified rim and filled with specified internal pressure,
In the meridional cross-sectional view of a tire assembled in a specified rim and filled with an internal pressure of 5% of the specified internal pressure, the point on the tire surface in the tire equatorial plane is P0, and the position in the tire width direction is the tire of the pneumatic tire belt. When the point on the profile line of the surface of the tread rubber equal to the position in the tire width direction of the outermost position in the width direction is defined as P1, the angle formed by the line segment connecting the points P0 and P1 with respect to the tire width direction. is θ, the tire section height is SH, and the tire radial height to the tire maximum width position is SWH,
θ is 4° or more and 7° or less,
The ratio SWH/SH is 0.4 or more and 0.55 or less,
The total tire width SW is equal to or greater than the standard median value,
A tire width direction region inside the tire width direction outer end portion of the outermost circumferential main groove located on the outermost side in the tire width direction of the circumferential main grooves is defined as a center region, and the end portion is defined as a center region. to the point P1 is defined as a shoulder region, and in the shoulder region, the dimension in the tire width direction is 0.3 times the dimension from the end to the point P1, and the point P1 is defined as an out-shoulder region, and the tire radial growth amounts in the center region and the out-shoulder region are CG and SOG, respectively, when the internal pressure is from 50 kPa to 230 kPa in an unloaded state, and the ratio CG/SOG is 0.25 or more and 0.55 or less. In an unloaded state, the width of the outermost circumferential main groove when filled with an internal pressure of 50 kPa is GW50, and the width of the outermost circumferential main groove when filled with an internal pressure of 230 kPa is GW230. The pneumatic tire according to claim 1, wherein GW230/GW50 is 0.92 or more and 0.96 or less. The dimension in the tire radial direction from the center position of the tire width direction center position of the groove bottom of the circumferential main groove to the undertread rubber in an unloaded state filled with 5% of the specified internal pressure is the cap tread under the circumferential main groove The pneumatic tire according to claim 1 or 2, wherein the thickness UGG of rubber is 0.3 [mm] or more and 1.5 [mm] or less. The difference CHS-UHS between the hardness CHS of the cap tread rubber and the hardness UHS of the undertread rubber is greater than 5 and less than 15 in JIS hardness,
tan δC of the cap tread rubber at 60°C is greater than tan δU of the undertread rubber at 60°C,
The ratio UA/TA of the cross-sectional area UA of the undertread rubber to the cross-sectional area TA of the tread rubber in a meridional cross-sectional view of the tire in an unloaded state filled with 5% of the specified internal pressure is 0.2 or more and 0.4 or less. 4. The pneumatic tire according to any one of claims 1 to 3. further comprising at least one layer of belt cover covering the belt;
Stress applied to the center region when the belt cover is distorted by 1% of its total length and when the belt cover is distorted by 3% of its total length in a no-load state where the belt cover is assembled in a specified rim and filled with 5% of the specified internal pressure. Let CS be the stress applied to the center region due to the stress applied to the center region and the stress applied to the center region when the belt cover is distorted by 1% of its total length. 5. The air according to any one of claims 1 to 4, wherein the ratio CS/SS is 2 or more and 3 or less, where SS is the gradient of the stress in the shoulder region due to the stress applied to the shoulder region in the case of entered tire. a first narrow groove extending inward in the tire width direction from the outermost circumferential main groove at an angle to the tire width direction and communicating with the circumferential main groove;
a second narrow groove extending inward in the tire width direction from the circumferential main groove at an angle to the tire width direction and terminating in a land portion;
is formed in the center region,
6. The method of any one of claims 1 to 5, wherein GR is a groove area ratio of the first fine groove and the second fine groove to the area of the center region, and the groove area ratio GR is 0.02 or more and 0.07 or less. A pneumatic tire according to any one of the preceding paragraphs.

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