JP2020172152A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire reduced in rolling resistance in a normal load bearing state and yet enhanced in dry braking performance and wet braking performance.SOLUTION: In a tire meridian cross-sectional view, in a state where a pneumatic tire is assembled to a normal rim and is filled with 5% of specified inner pressure, a relational expression of 0.8≤TW/SW≤0.95 is satisfied, a relational expression of 1.04≤CW100/CW70≤1.15 is satisfied, a relational expression of 27≤GR70≤40 is satisfied and a relational expression of GRB<GRA is satisfied, where TW shows a tread width, SW shows tire total widths, CW100(CW70) shows a grounding width at the time of load bearing of 100% (70%) of maximum load capacity, GR70 shows a groove area ratio in the grounding width CW70, GRA shows a groove area ratio excluding a main groove, GRB shows a groove area ratio in a difference region between the grounding width CW70 and the grounding width CW100.SELECTED DRAWING: Figure 2

Description

The present invention relates to a pneumatic tire in which rolling resistance under a normal load state is reduced and dry braking performance and wet braking performance are improved.

Since the reduction of rolling resistance is an important factor for improving fuel efficiency, various technologies have been proposed so far.

For example, a technique has been proposed in which the rolling resistance is reduced by reducing the weight by reducing the thickness of the rubber forming the shoulder region (Patent Document 1). In addition, by setting the ratio TR3 / TR2 of the radius of curvature TR2 at 230 kPa, which is an internal pressure that approximates the normal internal pressure and the specified air pressure of passenger car tires, to the radius of curvature TR3 at 300 kPa, which is a high internal pressure setting, to 1.10 to 1.50. , A technique has been proposed in which rolling resistance is reduced by bulging the tread central region TC in a well-balanced manner even when a high internal pressure is applied (Patent Document 2).

Japanese Patent No. 5469692 Japanese Patent No. 5952587

In recent years, there has been an increasing demand not only for reducing rolling resistance under a normal load and thus improving fuel efficiency, but also for quicker and more accurate rest under a braking load.

From this point of view, if the thickness of the rubber forming the shoulder region is reduced as in the technique of Patent Document 1, the ground contact width cannot be sufficiently secured, so that the frictional force under the braking load state is sufficient. May not be available. Further, when the ratio TR3 / TR2 is 1.10 to 1.50 as in the technique of Patent Document 2, the tread central region TC bulges too much in the air-filled state above the specified air pressure, so that the ground contact width cannot be sufficiently secured. , Braking load There is a possibility that sufficient frictional force cannot be obtained under load. As described above, in all of Patent Documents 1 and 2, there is room for improvement in increasing the frictional force in the braking load load state, and by extension, in improving the dry braking performance and the wet braking performance.

The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce rolling resistance under a normal load condition and to improve dry braking performance and wet braking performance in a well-balanced manner. To provide tires.

The pneumatic tire according to the present invention includes a pair of left and right bead portions, a sidewall portion connected radially outward of the bead portion, and a tread portion straddling between the sidewall portions, and has a tread shape between the pair of left and right bead portions. A carcass composed of at least one carcass ply extending to the tire, a belt including at least one belt layer including a cord arranged outside the tire radial direction of the carcass, and a belt arranged outside the tire radial direction of the belt. , The tread rubber that forms a part of the above tread part is provided, and the tread width is TW and the total tire width is SW in the state where the tire is incorporated into the regular rim and filled with 5% of the specified internal pressure. When 0.80 ≤ TW / SW ≤ 0.95 is satisfied, the ground contact width at a load of 100% of the maximum load capacity is CW100, and the ground contact width at a load of 70% of the maximum load capacity is CW70. When 1.04 ≤ CW100 / CW70 ≤ 1.15 is satisfied and the groove area ratio in the ground width CW70 is GR70, 27 ≤ GR70 ≤ 40 is satisfied, the groove area ratio excluding the main groove is GRA, the ground width CW70 and the ground width CW100. When the groove area ratio in the difference region with is set to GRB, GRB <GRA is satisfied.

In the pneumatic tire according to the present invention, the ratio of the tread width to the total tire width, the ratio of the contact width under the braking load state to the contact width under the normal load load state, the groove area ratio under the normal load load state, In addition, improvements have been made to the magnitude relationship of the groove area ratio between predetermined regions in the tire width direction. As a result, according to the pneumatic tire according to the present invention, it is possible to improve the rolling resistance under a normal load state and the dry braking performance and the wet braking performance in a well-balanced manner.

FIG. 1 is a cross-sectional view of a tire meridian showing a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a plan view of the pneumatic tire shown in FIG. FIG. 3 is a cross-sectional view of the tire meridian showing only one side in the tire width direction from the tire equatorial plane CL from the sidewall portion to the tread portion of the pneumatic tire of the present embodiment shown in FIG. FIG. 4 is a modified example of the pneumatic tire of the present embodiment shown in FIG. 1, and is a cross-sectional view of the tire meridian showing only one side in the tire width direction from the tire equatorial plane CL from the tread portion to the shoulder portion. is there. FIG. 5 is a cross-sectional view of the tire meridian showing only one side of the pneumatic tire of the present embodiment shown in FIG. 1 from the tread portion to the shoulder portion in the tire width direction from the tire equatorial plane CL. FIG. 6 is a cross-sectional view of the tire meridian showing only one side in the tire width direction from the tire equatorial plane CL from the tread portion to the shoulder portion of the pneumatic tire of the present embodiment shown in FIG.

Hereinafter, embodiments of the pneumatic tire according to the present invention (basic and additional embodiments 1 to 11 shown below) will be described in detail with reference to the drawings. It should be noted that these embodiments do not limit the present invention. In addition, the components of the embodiment include those that can be easily replaced by those skilled in the art, or those that are substantially the same. Further, the various embodiments included in the embodiment can be arbitrarily combined within the scope of those skilled in the art.

[Basic form]
The basic form of the pneumatic tire according to the present invention will be described below. In the following description, the tire radial direction means a direction orthogonal to the rotation axis of the pneumatic tire, the inner side in the tire radial direction is the side toward the rotation axis in the tire radial direction, and the outer side in the tire radial direction is the tire radial direction. The side away from the axis of rotation. The tire circumferential direction refers to a circumferential direction centered on the rotation axis. Further, the tire width direction means a direction parallel to the rotation axis, the inside in the tire width direction is the side toward the tire equatorial plane (tire equatorial line) in the tire width direction, and the outside in the tire width direction is in the tire width direction. The side of the tire away from the equatorial plane. The tire equatorial plane is a plane that is orthogonal to the rotation axis of the pneumatic tire and passes through the center of the tire width of the pneumatic tire.

FIG. 1 is a cross-sectional view of a tire meridian showing a pneumatic tire according to an embodiment of the present invention. The pneumatic tire 10 shown in FIG. 1 includes a pair of left and right bead portions 12, a sidewall portion 14 connected to the outer side in the radial direction of the bead portion 12, and a tread portion 16 straddling between the sidewall portions 14.

Further, the pneumatic tire 10 shown in FIG. 1 has a carcass 22 composed of at least one carcass ply (one in the figure) extending in a toroid shape between a pair of left and right bead portions 12, 12 and a carcass 22. A belt 24 including at least one layer (three layers in the figure) including a cord, which is arranged outside in the tire radial direction, and a belt 24 which is arranged outside the tire width direction of the belt 24 and has a tread portion 16. It is equipped with a tread rubber 26 that constitutes a part.

Under the above premise, the pneumatic tire 10 of the present embodiment is incorporated into a regular rim and filled with 5% of the specified internal pressure, and as shown in FIG. 1, the tread width is measured in a cross-sectional view of the tire meridian. When TW and the total tire width are SW, the relationship of 0.80 ≤ TW / SW ≤ 0.95 is satisfied.

FIG. 2 is a plan view of the pneumatic tire shown in FIG. The pneumatic tire 10 of the present embodiment has a ground contact width (the dimension of the ground contact surface in the tire width direction, the same applies hereinafter) at a load load of 100% of the maximum load capacity as CW100, and a ground contact at a load load of 70% of the maximum load capacity. When the width is CW70, 1.04 ≤ CW100 / CW70 ≤ 1.15 is satisfied. The load of 100% of the maximum load capacity is assumed to be the load during braking, and the load of 70% of the maximum load capacity is assumed to be the load during normal use (when starting and using other than braking). It was done.

Here, the specified rim means the "applicable rim" specified in JATMA, the "Design Rim" specified in TRA, or the "Measuring Rim" specified in ETRTO. The specified internal pressure means the "maximum air pressure" specified in JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified in TRA, or "INFLATION PRESSURES" specified in ETRTO. Furthermore, the maximum load capacity means the "maximum load capacity" specified in JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified in TRA, or the "LOAD CAPACITY" specified in ETRTO. ..

Further, the pneumatic tire 10 of the present embodiment satisfies 27 ≦ GR70 ≦ 40 when the groove area ratio in the ground contact width CW70 shown in FIG. 2 is GR70.

Further, the pneumatic tire 10 of the present embodiment has a groove area ratio excluding the main groove in the entire region including the region X of the ground contact width CW70 in FIG. 2 and the difference region Y between the ground contact width CW70 and the ground contact width CW100. Is GRA, and when the groove area ratio in the difference region Y is GRB, GRB <GRA is satisfied. Here, the main groove is a groove that is obliged to display the wear indicator specified in JATMA, and generally means a groove having a width of 2% or more of the tread width TW. The groove also includes a sipe. The groove width refers to the dimension between adjacent land portions measured in a direction perpendicular to the extending direction of the groove at the opening of the groove.

(Action, etc.)
In general, it is desirable to reduce the ground contact area and thus the rolling resistance to reduce fuel consumption in the normal load load state, while in the braking load load state, the ground contact area is increased to improve braking performance so that reliable stopping can be realized. desired.

Therefore, in the present embodiment, in order to obtain the following actions 1 to 7, the ratio of the tread width TW and the total tire width SW, the ground contact width CW100 under the braking load state, and the ground contact width CW70 under the normal load load state. The ratio with, the groove area ratio in the ground contact width CW70, and the relationship between the groove area ratio excluding the main groove and the groove area ratio in the difference region between the ground contact width CW70 and the ground contact width CW100 have been improved.

By setting the ratio TW / SW of the tread width TW and the total tire width SW shown in FIG. 1 to 0.80 or more, the ground contact width, and by extension, the so-called shoulder portion 18 near the boundary between the sidewall portion 14 and the tread portion 16. A sufficient ground contact area can be secured. As a result, the frictional force under the braking load state can be increased (action 1). On the other hand, by setting the ratio TW / SW of the tread width TW and the total tire width SW to 0.95 or less, it is possible to suppress an excessive increase in the contact pressure at the shoulder portion 18 (action 2).

The ratio TW / SW of the tread width TW to the total tire width SW is preferably 0.83 or more and 0.92 or less, and more preferably 0.85 or more and 0.9 or less.

In addition, the ground contact width under load of 100% of the maximum load capacity (ground contact width under braking load load state) CW100 and the ground contact width at 70% of the maximum load capacity under load (ground contact width under normal load load state). ) By setting CW100 / CW70 to 1.04 or more with CW70, a sufficient ground contact width can be secured in the braking load load state, and the frictional force in the braking load load state can be increased (action 3). On the other hand, by setting the above ratio CW100 / CW70 to 1.15 or less, it is possible to prevent the ground contact length (the tire circumferential dimension in the ground contact state) from becoming excessively small under normal load (action 4).

The ratio CW100 / CW70 of the ground contact width CW100 to the ground contact width CW70 is preferably 1.06 or more and 1.13 or less, and more preferably 1.08 or more and 1.11 or less.

Furthermore, by setting the groove area ratio GR70 in the ground contact width CW70 to 27 or more, it is possible to secure a sufficient groove area in the ground contact area and improve the drainage performance when a normal load is applied (action 5). On the other hand, by setting the groove area ratio GR70 in the ground contact width CW70 to 40 or less, it is possible to suppress the groove area from becoming excessively high in the ground contact region (action 6).

The groove area ratio GR70 in the ground contact width CW70 is preferably 29 or more and 38 or less, and more preferably 31 or more and 36 or less.

In addition, in FIG. 2, when the groove area ratio excluding the main groove in all the regions including the regions X and Y is GRA, and the groove area ratio in the difference region Y between the ground contact width CW70 and the ground contact width CW100 is GRB. By satisfying GRB <GRA, the groove area ratio in the tire width direction outer region (the difference region Y) of the ground contact surface is substantially changed from the groove area ratio in the tire width direction central region (region X of the ground contact width CW70). Is also made smaller. As a result, excellent drainage can be realized especially in the region X of the ground contact width CW70, and the rigidity can be increased in the difference region Y (action 7).

As shown above, in the pneumatic tire of the present embodiment, by improving the TW / SW, CW100 / CW70, GR70, and the relationship between GRB and GRA, respectively, the normal load is applied by the above actions 2 and 6. While the rolling resistance in the state can be reduced, the braking performance (dry braking performance and / or wet braking performance) can be improved by the above actions 1, 3, 4, 5, and 7.

The pneumatic tire of the present embodiment shown above is a normal manufacturing process, that is, a tire material mixing process, a tire material processing process, a green tire molding process, a vulcanization process, and a post-vulcanization inspection process. It is obtained through the above. When manufacturing the pneumatic tire of the present embodiment, for example, a convex portion and a concave portion corresponding to the groove and the convex portion formed in the tread portion shown in FIG. 2 are formed on the inner wall of the vulcanization die. Vulcanization is performed using this mold.

[Additional form]
Next, additional embodiments 1 to 11 which can be arbitrarily and selectively implemented with respect to the above-mentioned basic embodiment of the pneumatic tire according to the present invention will be described.

(Additional form 1)
FIG. 3 is a cross-sectional view of the tire meridian showing only one side in the tire width direction from the tire equatorial plane CL from the sidewall portion 14 to the tread portion 16 of the pneumatic tire of the present embodiment shown in FIG. In the basic form, as shown in FIGS. 1 and 3, the tire radial dimension of the tire radial outermost point P1 of the tire equatorial plane CL and the tire width direction end point P2 of the tread rubber 26 is D, and the tire cross-sectional height is When SH, the height in the tire radial direction to the maximum tire width position is SWH, and the radius of curvature of the arc of the shoulder part is R1,
TW x 0.04- (SWH / SH-0.5) x 15 ≤ D ≤ TW x 0.07- (SWH / SH-0.5) x 15 and 5 mm ≤ R1 ≤ 30 mm,
The ratio BW / TW of the width BW of the effective belt layer 24c to the tread width TW satisfies 0.80 ≤ BW / TW ≤ 0.90, and the belt cover 28 is formed on the outer side of the maximum width belt layer 24a in the tire width direction. That (additional form 1) is preferable. In the example shown in FIG. 3, the belt cover 28 is composed of two belt cover layers 28a and 28b which are continuous in the tire radial direction.

Here, the tire cross-sectional height SH refers to the tire radial dimension from a part of the contact point between the bead portion 12 and the rim to the outermost position of the tread portion 16 in the tire radial direction, up to the maximum tire width position. The tire radial height SWH is the tire radial dimension from a part of the contact point between the bead portion 12 and the rim to the maximum tire width position, and the arc of the shoulder portion is the shoulder portion shown in FIGS. The arc that constitutes the outer contour of 18.

Further, the effective belt layer means the belt layer 24c in which the outer position in the tire width direction is located on the innermost side in the tire width direction among the belt layers 24a, 24b, and 24c constituting the belt 24.

By setting the tire radial dimension D to [TW x 0.04- (SWH / SH-0.5) x 15] or more, the ground contact width (tire width direction dimension in the ground contact state) is not excessively increased, and by extension, the normal load load state. The rolling resistance at the tire can be further reduced.

On the other hand, by setting the tire radial dimension D to [TW x 0.04- (SWH / SH-0.5) x 15] or less, the ground contact width, especially the ground contact area of the shoulder part, is sufficiently secured and the braking load is applied. The frictional force in the state can be further enhanced, and thus the dry braking performance and the wet braking performance can be further enhanced.

Further, by setting the radius of curvature R1 of the arc of the shoulder portion to 5 mm or more, the ground contact width can not be excessively increased, and the rolling resistance under a normal load state can be further reduced.

On the other hand, by setting the radius of curvature R1 of the arc of the shoulder part to 30 mm or less, the ground contact width and eventually the ground contact area of the shoulder part are sufficiently secured, the frictional force under the braking load state is further increased, and dry braking is performed. Performance and wet braking performance can be further improved.

The radius of curvature R1 is more preferably 8 mm or more and 27 mm or less, and extremely preferably 10 mm or more and 25 mm or less.

Further, when the ratio BW / TW is 0.80 or more, the belt 24 can be sufficiently secured on the outer side of the tread portion 16 in the tire width direction, and the durability performance can be improved. On the other hand, when the ratio BW / TW is 0.90 or less, the weight of the belt 24 can be reduced without making it excessively long, and the rolling resistance can be further reduced.

The ratio BW / TW is more preferably 0.82 or more and 0.88 or less, and extremely preferably 0.83 or more and 0.87 or less.

In addition, since the belt cover 28 is formed on the outer side of the maximum width belt layer 24a in the tire width direction, bending of the shoulder portion 18 during tire rolling is suppressed, and cracks originating from the end of the belt 24 are cracked. The occurrence can be suppressed.

(Additional form 2)
In the basic form and the form in which the additional form 1 is added to the basic form, the groove area ratio other than the main groove in the region between the main groove 32b and the main groove 32d is set to GR1 in FIG. 2, and the entire region shown in the figure is shown. Of these, when the groove area ratio in the tire width direction outer region than the main grooves 32b and 32d is GR2, it is preferable that 1.00 <GR1 / GR2 ≦ 2.00 is satisfied (additional form 2).

By setting the ratio GR1 / GR2 to more than 1.00, the groove area ratio is increased especially inside the tire width direction to improve drainage, while the groove area ratio is decreased outside the tire width direction. Rigidity is increased, and in combination with these, wet braking performance can be further improved. On the other hand, by setting the ratio GR1 / GR2 to 2.00 or less, it is possible to suppress an excessive rigidity difference between the inner region and the outer region in the tire width direction with the main grooves 32b and 32d as boundaries. As a result, the tread portion smoothly deforms between both ground contact ends, especially when a braking load is applied, thereby realizing a gentle change in the ground contact surface pressure in the tire width direction, which further enhances dry braking performance and wet braking performance. Can be able to

The ratio GR1.00 / GR2.00 is more preferably 1.10 or more and 1.90 or less, and extremely preferably 1.15 or more and 1.85 or less.

(Additional form 3)
In the basic form and the form in which at least one of the additional forms 1 and 2 is added to the basic form, the average thickness TG of the tread rubber shown in FIG. 1 is 7.0 mm or more and 9.5 mm or less (additional form 3). Is preferable. It should be noted that such a tread rubber thickness TG assumes a pneumatic tire for a general passenger car, not a pneumatic tire for a truck bus in particular. The average thickness TG of the tread rubber is the average tread thickness measured at five points located at approximately equal intervals in the area of the ground contact width CW100 shown in FIG. 2 avoiding the main groove 32 in the tire width direction. Means a value.

By setting the average thickness TG to 7.0 mm or more, it is possible to secure excellent out-of-plane bending rigidity of the tread, secure a sufficient ground contact area, and further improve dry braking performance and wet braking performance. On the other hand, by setting the average thickness TG to 9.5 mm or less, heat generation during running can be suppressed, and by extension, rolling resistance under a normal load state can be further reduced.

The average thickness TG is more preferably 7.2 mm or more and 9.3 mm or less, and extremely preferably 7.4 mm or more and 9.1 mm or less.

(Additional form 4)
FIG. 4 is a modified example of the pneumatic tire of the present embodiment shown in FIG. 1, and is a cross-sectional view of the tire meridian showing only one side in the tire width direction from the tire equatorial plane CL from the tread portion to the shoulder portion. is there. In the basic form and the form in which at least one of the additional forms 1 to 3 is added to the basic form, as shown in FIG. 4, at least two main grooves extending in the tire circumferential direction are provided in the tread portion (the same figure). In the example shown in, two tires 32a and 32b on one side in the tire width direction are displayed, so there are practically four tires), and of these main grooves 32a and 32b, the tire with the outermost main groove 32b in the tire width direction. The center position P3 in the width direction is located at a distance of 1/4 or less of the tread width TW from the tire equatorial plane CL, is located outside the outermost main groove 32b in the tire width direction, and is located outside in the tire width direction. It is preferable that the circumferential fine groove 34 having a depth smaller than that of the main groove 32b is formed (additional form 4). Here, the tire direction center position P3 of the main groove 32b means the tire width direction center position on the groove surface.

The center position of the outermost main groove 32b in the tire width direction in the tire width direction is located at a distance of 1/4 or less of the tread width TW from the tire equatorial plane CL, so that it is mainly on the shoulder portion 18 side of the tread surface. A sufficient ground contact area of the shoulder portion 18 can be secured without forming a groove, the frictional force under a braking load load state can be further enhanced, and thus the dry braking performance and the wet braking performance can be further enhanced.

The center position P3 in the tire width direction is more preferably located at a distance of 23/100 or less of the tread width TW from the tire equatorial plane CL, and may be present at a distance of 21/100 or less. Very preferable.

Further, since the pneumatic tire of the present embodiment has a relatively wide tread width TW (0.80 ≤ TW / SW ≤ 0.95), the energy loss in the shoulder portion 18 is large during traveling. For this reason, by forming a new circumferential narrow groove 34 on the outer side in the tire width direction from the outermost main groove 32b in the tire width direction, the focus is on improving drainage rather than rigidity in the shoulder portion 18. Ultimately, it is possible to efficiently secure rigidity and drainage. In the present embodiment, since the circumferential fine groove 34 has a smaller depth than the main groove 32b, consideration is also given to avoiding an excessive decrease in the rigidity of the shoulder portion 18.

(Additional form 5)
In the basic form and the form in which at least one of the additional forms 1 to 4 is added to the basic form, as shown in FIG. 4, the tire width direction position is the outermost main groove 32b in the tire width direction. When the outer position is set to position 0 and the outermost position in the tire width direction of the contact width CW70 region is set to position 100, the center position of the circumferential groove 34 in the tire width direction shall be from position 15 to position 80. (Additional form 5) is preferable.

By setting the center position of the circumferential groove 34 in the tire width direction from the position 15 to the outside in the tire width direction, the rigidity of the land portion formed between the circumferential main groove 32b and the circumferential groove 34 is sufficient. It is possible to further improve the dry braking performance and the wet braking performance by ensuring the above, and by extension, suppressing the deformation of the land portion during traveling. On the other hand, by setting the center position of the circumferential groove 34 in the tire width direction from the position 80 to the inside in the tire width direction, the drainage performance of the circumferential groove 34 is sufficiently ensured, and the wet braking performance is further improved. be able to.

The center position of the circumferential groove 34 in the tire width direction is more preferably from position 20 to position 75, and extremely preferably from position 25 to position 70.

(Additional form 6)
In the basic form and the form in which at least one of the additional forms 1 to 5 is added to the basic form, it is preferable that the main grooves 32 (32a to 32d) shown in FIG. 2 are chamfered (additional form 6).

By chamfering the main groove 32 (32a to 32d), the groove volume is increased, the drainage performance is improved, and the ground contact pressure of the land portion adjacent to the main groove 32 can be improved, so that the wet braking performance is particularly high. Can be further enhanced.

As shown in Fig. 2, when there are multiple main grooves in the circumferential direction, chamfering the main grooves 32a and 32c near the tire equatorial plane CL to increase the groove volume improves drainage performance efficiently. Is preferable. This is because if the same circumferential main grooves are arranged, the closer to the tire equatorial plane CL, the higher the drainage performance.

Further, if the main grooves in the circumferential direction exist at the same position in the tire width direction, it is more preferable to chamfer the wall surface closer to the tire equatorial plane CL. This is because when the wall surface closer to the tire equatorial plane CL is chamfered, the position of the circumferential main groove in the tire width direction substantially moves to the inside in the tire width direction (tire side equatorial plane CL side), and the drainage performance is improved. This is to increase.

(Additional form 7)
FIG. 5 is a cross-sectional view of the tire meridian showing only one side in the tire width direction from the tire equatorial plane CL from the tread portion 16 to the shoulder portion 18 of the pneumatic tire of the present embodiment shown in FIG. In the basic form and the form in which at least one of the additional forms 1 to 6 is added to the basic form, as shown in FIG. 5, the outer contour 42 of the tread portion 16 is a central arc located in the central portion in the tire width direction. 0.4 ≤ L / (TW / 2) when the length of the central arc 42a in the tire width direction is 2L, including the 42a and a pair of shoulder arcs 42b connected to the outside of the central arc 42a in the tire width direction. It is preferable that ≤0.7 is satisfied (additional form 7). In FIG. 5, the central arc 42a is shown only on one side of the tire equatorial plane CL, and in reality, the half portion is also present on the other side of the tire equatorial plane CL.

By setting the ratio L / (TW / 2) to 0.4 or more, the ground contact width and the ground contact area of the shoulder part are further secured to further increase the frictional force under the braking load state, and eventually the dry braking performance and wet braking. Performance can be further improved.

On the other hand, by setting the ratio L / (TW / 2) to 0.7 or less, the ground contact width cannot be excessively increased, and the rolling resistance under a normal load state can be further reduced.

The ratio L / (TW / 2) is more preferably 0.45 or more and 0.65 or less, and extremely preferably 0.50 or more and 0.60 or less.

(Additional form 8)
In the basic form and the form in which at least one of the additional forms 1 to 7 is added to the basic form, it is preferable that the tire outer diameter is equal to or more than the standard median value (additional form 8).

Here, the standard means the above-mentioned JATMA, TRA, or ETRTO. Further, the standard median value means a value located at the center when a plurality of outer diameters listed in JATMA and the like are arranged in ascending order.

By setting the tire outer diameter to be equal to or higher than the standard median value, in other words, by increasing the tire outer diameter to some extent, a sufficient volume of the tire inner cavity is secured, and not only the tire bends under normal load, but also braking. It is also possible to reduce the bending of the tire under load, and thus the rolling resistance under both loads.

By setting the tire outer diameter to a value 3 mm smaller than the standard maximum value and a value equal to or less than the standard maximum value, the above effect can be achieved at a higher level.

(Additional form 9)
In the basic form and the form in which at least one of the additional forms 1 to 8 is added to the basic form, it is preferable that the total tire width SW shown in FIG. 1 is equal to or more than the standard median value (additional form 9).

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

By setting the total tire width to the standard median value or higher, in other words, by increasing the total tire width to some extent, a sufficient volume of the cavity inside the tire is secured, and not only the tire bends under normal load, but also braking. It is also possible to reduce the bending of the tire under load, and thus the rolling resistance under both loads.

By setting the total tire width to a value 3 mm or more smaller than the standard maximum value and a standard maximum value or less, the above effect can be achieved at a higher level.

(Additional form 10)
FIG. 6 is a cross-sectional view of the tire meridian showing only one side in the tire width direction from the tire equatorial plane CL from the tread portion 16 to the shoulder portion 18 of the pneumatic tire of the present embodiment shown in FIG. In the basic form and the form in which at least one of the additional forms 1 to 9 is added to the basic form, as shown in FIG. 6, the distance between the belt edges ES between the maximum width belt layer 24a and the minimum width belt layer 24c is ES. However, it is preferable that 5 mm <ES <15 mm (additional form 10).

Here, the width of the belt layer means the dimension of the belt layer in the tire width direction. The distance between the belt edges ES refers to the distance between the outermost point in the tire width direction of the belt layer 24a having the maximum width and the outermost point in the tire width direction of the belt layer 24c having the minimum width.

By setting the distance ES between the belt edges to more than 5 mm, it is possible to prevent the minimum width of the belt layer 24c from being excessively increased in the tire width direction. Therefore, the shoulder portion 18 can be sufficiently bent when filled with air pressure, and the ground contact width can be further reduced, so that the rolling resistance under a normal load can be further reduced.

On the other hand, by setting the distance ES between the belt edges to less than 15 mm, the existing region of the belt in the outer portion of the tread portion 16 in the tire width direction can be reduced. Therefore, when the sidewall portion 18 bends, it is possible to suppress the occurrence of cracks starting from the end portion of the belt 24.

The distance ES between the belt edges is more preferably 7 mm or more and 13 mm or less, and extremely preferably 8 mm or more and 12 mm or less.

(Additional form 11)
In the basic form and the form in which at least one of the additional forms 1 to 10 is added to the basic form, for example, as shown in FIGS. 1, 3 and 6, a belt cover 26 is provided on the outer side of the belt 24 in the tire radial direction to provide a tire. It is preferable that the tire radial dimension MG of the carcass 22, the belt 24, and the belt cover 26 on the equatorial plane CL satisfies 3.0 mm ≤ MG ≤ 5.5 mm (additional form 11). It should be noted that such a tire radial dimension MG is assumed to be a pneumatic tire for a general passenger car, not a pneumatic tire for a truck bus in particular.

Excellent durability can be achieved by setting the tire radial dimension MG to 3.0 mm or more. On the other hand, by setting the tire radial dimension MG to 5.5 mm or less, the rigidity of the tread as a whole does not increase too much. As a result, the tread portion can be sufficiently deformed during traveling, and a sufficient ground contact area can be secured, so that the dry braking performance and the wet braking performance can be further improved.

The tire radial dimension MG is more preferably 3.5 mm or more and 5.0 mm or less, and extremely preferably 3.7 mm or more and 4.8 mm or less.

The tire size was 205 / 60R16 92V, and the pneumatic tires of Invention Examples 1 to 12 and the conventional pneumatic tires having the tire meridional cross-sectional shape shown in FIGS. 1 and 2 (in some cases, FIG. 4) were produced. The detailed conditions of these pneumatic tires are shown in Tables 1 and 2 below. In Tables 1 and 2, TW is the tread width, SW is the total tire width, CW100 is the ground contact width at 100% of the maximum load capacity, and CW70 is the 70% of the maximum load capacity. GR70 is the groove area ratio in the grounding width CW70, GRA is the groove area ratio excluding the main groove, GRB is the groove area ratio in the difference region between the grounding width CW70 and the grounding width CW100, and D is the tire. The tire radial dimension of the outermost point of the equatorial surface in the tire radial direction and the end point of the tread rubber in the tire width direction, SH is the tire cross-sectional height, SWH is the tire radial height up to the tire maximum width position, and R1 is. The radius of curvature of the arc of the shoulder part, BW is the half width of the effective belt layer, GR1 is the groove area ratio other than the main groove in the area surrounded by the main groove in the area of the ground contact width CW70, and GR2 is the ground contact width. The groove area ratio in the region outside the tire width direction from the main groove in the region of CW70, TG is the average thickness of the tread rubber, and position N (N is a specific numerical value) is the tire width in the region of the ground contact width CW70. When the outermost position in the direction is position 100, the center position in the tire width direction of the circumferential narrow groove, L is half the length of the central arc in the tire width direction, and ES is the maximum width belt layer and minimum width. The distance between the belt edges and the belt layer of the tire is shown. All of these codes and the like are based on the above-mentioned description of the present specification.

The rolling resistance, dry braking performance, and wet braking performance of the pneumatic tires of Invention Examples 1 to 12 and the conventional pneumatic tires produced in this manner were evaluated according to the following procedure.

(Rolling resistance)
Each test tire was assembled on a wheel with a rim size of 16 x 6J and mounted on a drum tester, and the rolling resistance coefficient (RRC) was measured in accordance with ISO25280 under the conditions of an air pressure of 210 kPa and a load of 4.94 kN. The evaluation result is shown by an index of 100 in the conventional example using the reciprocal of the measured value. The larger the exponential value, the smaller the rolling resistance. The results are also shown in Tables 1 and 2.

(Dry braking performance and wet braking performance)
Each test tire is attached to a wheel with a rim size of 16 x 6J and attached to a passenger car. The air pressure (F / R) after warming up is 240kPa / 240kPa, and braking from an initial speed of 100km / h to a complete stop on a dry or wet road surface. Distance measurements were performed. The evaluation result is shown by an index of 100 in the conventional example using the reciprocal of the measured value. The larger the index value, the better the braking performance on a dry road surface or a wet road surface. These results are also shown in Tables 1 and 2.

According to Table 1, it belongs to the technical scope of the present invention (that is, the ratio of the tread width to the total tire width, the ratio of the ground contact width under the braking load load state to the ground contact width under the normal load load state, and the braking load. Improvements have been made to the ratio of the ground contact width between the load state and the normal load load state, the groove area ratio under the normal load load state, and the groove area ratio between predetermined regions in the tire width direction.) Invention Examples 1 to 12 In all of the pneumatic tires of the present invention, rolling resistance, dry braking performance, and wet braking performance are improved in a well-balanced manner as compared with the conventional pneumatic tires, which do not belong to the technical scope of the present invention. I understand.

10 Pneumatic tires
12 bead part
14 sidewall part
16 tread section
18 Shoulder
22 Carcass
24 belt
26 tread rubber
28 Belt cover
32 Main groove
34 Circumferential groove
42 Outer contour
CL tire equatorial plane
TW tread width
SW tire total width
SH tire cross-section height
SWH Tire radial height to the maximum tire width position
X Ground width CW70 area
Y Difference area between the ground width CW70 and the ground width CW100

Claims (12)

It is provided with a pair of left and right bead portions, a sidewall portion connected radially outward of the bead portion, and a tread portion straddling between the sidewall portions.
A carcass composed of at least one carcass ply extending in a toroid shape between a pair of left and right bead portions, a belt including at least one belt layer including a cord arranged outside the tire radial direction of the carcass, and the above. A pneumatic tire provided with a tread rubber which is arranged outside the tire radial direction of the belt and constitutes a part of the tread portion.
When the tread width is TW and the total tire width is SW, 0.80 ≤ TW / SW ≤ 0.95 is satisfied in the tire meridional cross-sectional view with the tire incorporated into the regular rim and filled with 5% of the specified internal pressure.
When the ground contact width at a load of 100% of the maximum load capacity is CW100 and the ground contact width at a load of 70% of the maximum load capacity is CW70, 1.04 ≤ CW100 / CW70 ≤ 1.15 is satisfied.
When the groove area ratio in the ground contact width CW70 is GR70, 27 ≤ GR70 ≤ 40 is satisfied.
A pneumatic tire characterized in that GRB <GRA is satisfied when the groove area ratio excluding the main groove is GRA and the groove area ratio in the difference region between the ground contact width CW70 and the ground contact width CW100 is GRB. The tire radial dimension of the tire equatorial outermost point and the tire width direction end point of the tread rubber is D, the tire cross-sectional height is SH, the tire radial height to the maximum tire width position is SWH, and the shoulder. When the radius of curvature of the arc of the part is R1,
TW x 0.04- (SWH / SH-0.5) x 15 ≤ D ≤ TW x 0.07- (SWH / SH-0.5) x 15 and 5 mm ≤ R1 ≤ 30 mm,
Claim that the ratio BW / TW of the width BW of the effective belt layer to the tread width TW satisfies 0.80 ≤ BW / TW ≤ 0.90, and the belt cover is formed on the outer side of the maximum width belt layer in the tire width direction. Item 1. The pneumatic tire according to item 1. In the tread portion, the groove area ratio other than the main groove in the region surrounded by the main groove in the region of the ground contact width CW70 is set to GR1, and the region outside the tire width direction from the main groove in the region of the ground contact width CW70. The pneumatic tire according to claim 1 or 2, which satisfies 1.00 <GR1 / GR2 ≤ 2.00 when the groove area ratio in the above is GR2. The pneumatic tire according to any one of claims 1 to 3, wherein the average thickness TG of the tread rubber is 7.0 mm or more and 9.5 mm or less. The tread portion has at least two main grooves extending in the tire circumferential direction, and the center position of the outermost main groove in the tire width direction among the main grooves in the tire width direction is the tread width TW from the tire equatorial plane. It exists at a distance of 1/4 or less of
According to any one of claims 1 to 4, a circumferential fine groove is formed that is located outside the tire width direction and has a depth smaller than the main groove that is the outermost in the tire width direction. Pneumatic tires listed. Regarding the position in the tire width direction, when the outermost position in the tire width direction of the main groove in the tire width direction is set to position 0 and the outermost position in the tire width direction in the area of the contact width CW70 is set to position 100, the circumference The pneumatic tire according to claim 5, wherein the center position of the directional groove in the tire width direction is from position 15 to position 80. The pneumatic tire according to any one of claims 1 to 6, wherein the main groove is chamfered. The outer contour of the tread portion includes a central arc located at the center in the tire width direction and a pair of shoulder arcs connected to the outside of the center arc in the tire width direction, respectively, in the tire width direction of the center arc. The pneumatic tire according to any one of claims 1 to 7, which satisfies 0.4 ≤ L / (TW / 2) ≤ 0.7 when the length is 2 L. The pneumatic tire according to any one of claims 1 to 8, wherein the tire outer diameter is equal to or more than the standard median value. The pneumatic tire according to any one of claims 1 to 9, wherein the total tire width is equal to or more than the standard median value. The pneumatic tire according to any one of claims 1 to 10, wherein the distance ES between the belt edges of the maximum width belt layer and the minimum width belt layer satisfies 5 mm <ES <15 mm. A claim that a belt cover is provided on the outer side of the belt in the tire radial direction, and the tire radial dimension MG of the carcass, the belt, and the belt cover on the tire equatorial plane satisfies 3.0 mm ≤ MG ≤ 5.5 mm. The pneumatic tire according to any one of 1 to 10.

Images