JP7234756B2 - pneumatic tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pneumatic tire, and more particularly, a pneumatic tire capable of suppressing uneven shoulder wear of a tread portion while maintaining excellent steering stability on wet road surfaces and improving ride comfort. Regarding.

A pneumatic tire generally includes a tread portion extending in the tire circumferential direction and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of sidewall portions arranged radially inward of the sidewall portions. A structure comprising a pair of bead portions, a carcass layer mounted between the pair of bead portions, and a plurality of belt layers arranged outside the carcass layer in the tread portion in the tire radial direction. are doing.

In such pneumatic tires, improvement in wear characteristics is required as a permanent issue. As a technique for improving wear characteristics, for example, increasing the hardness of the cap tread rubber to increase the rigidity of the tread portion has been proposed (see, for example, Patent Document 1). However, if the hardness of the cap tread rubber is simply increased, there is a problem that the increased rigidity of the tread portion increases the impact received from the road surface during running, degrading the ride comfort (mild feeling). Therefore, it is necessary to achieve both wear characteristics and riding comfort, which are in a trade-off relationship.

By the way, techniques have been proposed for improving various performances of a pneumatic tire by defining the ground contact shape of the pneumatic tire (see Patent Documents 2 to 4, for example). However, these techniques do not aim to achieve both wear characteristics and riding comfort.

Japanese Unexamined Patent Application Publication No. 2017-203080 JP-A-6-8710 JP-A-8-108710 JP 2009-78790 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic tire capable of suppressing uneven shoulder wear of a tread portion while maintaining excellent steering stability on wet road surfaces and improving ride comfort.

The pneumatic tire of the present invention for achieving the above object comprises a tread portion extending in the tire circumferential direction and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and these sidewall portions. and a pair of bead portions arranged radially inward of the tire, and a plurality of main grooves extending in the tire circumferential direction are formed in the tread portion, and the main grooves define a plurality of rows of land portions. in tires,
The maximum contact length in the tire circumferential direction when the pneumatic tire is filled with air pressure of 230 kPa and is grounded under conditions of loading 40%, 75%, and 100% of the maximum load capacity specified by the standard. are respectively LA1, LB1, and LC1, and the maximum ground contact widths in the tire width direction are WA1, WB1, and WC1, respectively. When the outer contact lengths in the tire circumferential direction are LA2, LB2, and LC2, respectively, the maximum contact lengths LA1, LB1, LC1 and the outer contact lengths LA2, LB2, LC2 are 1.02≤(LB2/LB1)/(LA2). /LA1)≦1.25, 1.00≦(LC2/LC1)/(LB2/LB1)≦1.20,
When the tread portion is divided into a center region having a width equivalent to 53% of the maximum ground contact width WB1 centered on the tire equator and a shoulder region outside the center region in the tire width direction within the maximum ground contact width WB1. , a plurality of sipes are formed in at least one row of the land portion included in the shoulder region, the sipe has a chamfered portion at its edge, and the maximum depth x (mm) of the sipe and the chamfered portion The maximum depth y (mm) satisfies the relationship x×0.1≦y≦x×0.3+1.0.

In the present invention, a plurality of sipes are formed in at least one row of the land portion included in the shoulder region, the sipe has a chamfered portion at its edge, and the maximum depth x (mm) of the sipe and the chamfered portion Maximum depth y (mm) satisfies the relationship x x 0.1 ≤ y ≤ x x 0.3 + 1.0 to ensure steering stability on wet road surfaces based on these chamfered sipes At the same time, the rigidity in the shoulder region of the tread portion can be ensured to suppress uneven shoulder wear. Further, the maximum ground lengths LA1, LB1, LC1 and the external ground lengths LA2, LB2, LC2 are 1.02≤(LB2/LB1)/(LA2/LA1)≤1.25, 1.00≤(LC2/LC1)/ By satisfying the relationship of (LB2/LB1) ≤ 1.20 and defining the ground contact shape in consideration of load fluctuations, it is possible to improve riding comfort (mild feeling) while maintaining the effect of suppressing uneven shoulder wear. can.

In the present invention, it is preferable that the maximum contact length LB1 and the external contact length LB2 satisfy the relationship 0.65≤LB2/LB1≤0.95. Also, the maximum ground lengths LA1, LB1, LC1 and the external ground lengths LA2, LB2, LC2 can satisfy the relationship of (LC2/LC1)/(LB2/LB1)≤(LB2/LB1)/(LA2/LA1). preferable. Thereby, it is possible to improve the ride comfort based on the shape of the ground contact.

In the present invention, it is preferable that the maximum width w of the chamfered portion satisfies the relationship of t×0.8≦w≦t×5 with respect to the sipe width t of the sipe. By appropriately setting the maximum width w of the chamfer with respect to the sipe width t in this manner, both steering stability on wet road surfaces and uneven wear resistance in the shoulder region can be achieved at a higher level.

The inclination angle θ of the sipe on the acute side with respect to the tire circumferential direction is preferably in the range of 70° to 90°. By setting the inclination angle θ of the sipes within the above range, both steering stability on wet road surfaces and uneven wear resistance in the shoulder region can be achieved at a higher level.

At least part of the sipe is preferably curved or bent in plan view. Since at least a portion of the sipe is curved or bent in plan view, the total amount of edges of each sipe increases, and steering stability on wet road surfaces can be further improved.

At least one end of the sipe is preferably open to the main groove. As a result, steering stability on wet road surfaces can be further improved.

By curving or bending at least part of the contour of the chamfered portion in a cross section perpendicular to the sipe, the actual cross-sectional area of the chamfered portion is larger than the imaginary cross-sectional area of the chamfered portion when the contour of the chamfered portion is straight. Larger is preferred. In this case, the steering stability on wet road surfaces can be further improved by increasing the actual cross-sectional area of the chamfered portion.

Alternatively, by curving or bending at least a part of the contour of the chamfered portion in a cross section perpendicular to the sipe, the actual cross-sectional area of the chamfered portion is larger than the imaginary cross-sectional area of the chamfered portion when the contour of the chamfered portion is straight. A small area is preferred. In this case, by reducing the actual cross-sectional area of the chamfered portion, the uneven wear resistance in the shoulder region can be further improved.

The chamfer preferably extends parallel to the sipe. As a result, steering stability on wet road surfaces and uneven wear resistance in the shoulder region can be further improved.

In the contact area of the tread portion defined by the maximum contact width WB1, the groove area Sm including the chamfered portion and the groove area Sa not including the chamfered portion satisfy the relationship of 1.01≤Sm/Sa≤1.50. is preferred. By setting the ratio Sm/Sa within the above range, the total amount of chamfered portions can be sufficiently secured, and both steering stability on wet road surfaces and uneven wear resistance in the shoulder region can be achieved at a higher level.

The ratio Sar of the groove area excluding the chamfered portion in the shoulder region is preferably in the range of 10% to 25%. By setting the ratio Sar of the groove area excluding the chamfered portion in the shoulder region to the above range and making the ratio Sar of the groove area relatively smaller than in a tread pattern that depends on normal lug grooves, Uneven wear resistance can be sufficiently improved.

The loads corresponding to 40%, 75%, and 100% of the maximum load capacity specified by the standard are W40, W75, and W100 (kN), respectively. Let CP40, CP75, and CP100 (kN/°) be the cornering powers measured under the condition of loading W100, R be the aspect ratio of the pneumatic tire, D (mm) be its outer diameter, and D (mm) be its cross-sectional width. When the nominal is A (mm), loads W40, W75, W100 and cornering power CP40, CP75, CP100 are 0.05≦(R×D/2A) ² ×[(CP100-CP75)/(W100-W75) ]/[(CP75-CP40)/(W75-W40)]≦0.50. As a result, it is possible to suppress an excessive increase in cornering power in the high-load region and improve steering stability on wet road surfaces. In particular, the easiness of outputting cornering power varies depending on the tire size, so the above relational expression is corrected by the value of (R×D/2A) ² . In other words, the lower the aspect ratio and the smaller the outer diameter of the tire, the lower the contribution of cornering power on the high load side.

In the present invention, when a plurality of belt layers including a plurality of belt cords inclined with respect to the tire circumferential direction are embedded in the tread portion, and the belt cords intersect each other between the layers, the belt cords are located at the center position of the tire. with respect to the tire circumferential direction satisfies the relationship of 21°≦α≦30°. By not making the inclination angle α of the belt cord at the center position of the tire extremely low, it is possible to suppress an increase in the rigidity of the belt layer and improve riding comfort.

In the present invention, the cornering power is measured under the condition that the tire is mounted on a regular rim and filled with a predetermined air pressure and a predetermined load is applied, the camber angle is 0 °, the speed is 10 km / h, and the slip The cornering force is measured while changing the angle, and the cornering force is calculated based on the cornering force in the range where the slip angle is 0° to 1°. The contact shape of the tread portion is measured under the condition that the tire is mounted on a regular rim, filled with a predetermined air pressure, placed vertically on a flat surface, and a predetermined load is applied. The outer diameter of a pneumatic tire is measured at the center position of the tire in a state in which the tire is mounted on a regular rim and filled with a predetermined air pressure. "Regular rim" is a rim defined for each tire in a standard system including the standard on which the tire is based. For example, JATMA is a standard rim, TRA is a "Design Rim", or ETRTO. If so, it should be "Measuring Rim". Air pressure is 230 kPa. The predetermined load is 40%, 75%, or 100% of the maximum load capacity determined for each tire by each standard in the system of standards including the standards on which tires are based.

1 is a meridian sectional view showing a pneumatic tire according to an embodiment of the invention; FIG. FIG. 2 is a developed view showing a tread pattern of the pneumatic tire of FIG. 1; FIG. 2 is a plan view showing the ground contact shape (40% load) of the pneumatic tire of FIG. 1; FIG. 2 is a plan view showing the ground contact shape (75% load) of the pneumatic tire of FIG. 1; FIG. 2 is a plan view showing the ground contact shape (100% load) of the pneumatic tire of FIG. 1; FIG. 4 is a plan view showing an example of a sipe having a chamfered portion; It is a cross section taken along the line VII-VII in FIG. (a), (b) is a top view which shows the modification of the sipe which has a chamfered part, respectively. (a) to (h) are plan views showing further modified examples of sipes each having a chamfered portion. FIG. 4 is a plan view showing the inclination angle of a sipe having a chamfered portion; FIG. 11 is a cross-sectional view showing a further modified example of a sipe having chamfers; FIG. 11 is a cross-sectional view showing a further modified example of a sipe having chamfers; 1] is a developed view showing a belt layer constituting the pneumatic tire of the present invention. [FIG.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. 1 and 2 show a pneumatic tire according to an embodiment of the invention. In FIG. 2, CL is the tire center position, Tc is the tire circumferential direction, and Tw is the tire width direction.

As shown in FIG. 1, the pneumatic tire of this embodiment includes a tread portion 1 extending in the tire circumferential direction and forming an annular shape, and a pair of sidewall portions 2, 2 arranged on both sides of the tread portion 1. and a pair of bead portions 3 , 3 arranged radially inward of the sidewall portions 2 .

A carcass layer 4 is mounted between the pair of bead portions 3,3. The carcass layer 4 includes a plurality of carcass cords extending in the tire radial direction, and is folded back from the tire inner side to the outer side around the bead cores 5 arranged in the respective bead portions 3 . A bead filler 6 made of a rubber composition having a triangular cross section is arranged on the outer circumference of the bead core 5 .

On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1 . These belt layers 7 include a plurality of belt cords inclined with respect to the tire circumferential direction, and are arranged so that the belt cords intersect each other between the layers. Steel cords are preferably used as the belt cords forming the belt layer 7 . At least one belt reinforcing layer 8 including a plurality of band cords oriented in the tire circumferential direction is arranged on the outer peripheral side of the belt layer 7 . It is desirable that the belt reinforcing layer 8 have a jointless structure in which a strip material formed by arranging at least one band cord and covering it with rubber is continuously wound in the tire circumferential direction. Organic fiber cords such as nylon and aramid cords are preferably used as the band cords forming the belt reinforcing layer 8 .

As shown in FIG. 2, the tread portion 1 has a pair of central main grooves 11, 11 extending in the tire circumferential direction at positions on both sides of the tire center position CL, and a pair of central main grooves 11, 11 extending outward in the tire width direction from the central main grooves 11, 11. A pair of outer main grooves 12, 12 extending in the tire circumferential direction are formed at positions of . The central main groove 11 and the outer main groove 12 may have a straight shape, or may have a zigzag shape. Thus, a land portion 20 is defined between the central main grooves 11, 11, a land portion 30 is defined between the central main groove 11 and the outer main groove 12, and a land portion 30 is defined outside the outer main groove 12. A land portion 40 is defined. These land portions 20, 30, and 40 may be ribs extending continuously along the tire circumferential direction, or may be block rows composed of a plurality of blocks arranged in the tire circumferential direction. good.

A plurality of lug grooves 31 extending in the tire width direction are formed in each of the land portions 30 . The lug groove 31 has a groove width in the range of 2.0 mm to 9.0 mm. A circumferential narrow groove 32 extending in the tire circumferential direction and having a zigzag shape is formed in one of the pair of land portions 30 .

A plurality of sipes 41 extending in the tire width direction are formed in each of the land portions 40 . The sipe 41 has a groove width of less than 2.0 mm and has a chamfer 42 on at least one edge (see FIGS. 6 and 7). The chamfered portions 42 are not necessarily provided on all the sipes 41. For example, the sipes 41 having the chamfered portions 42 and the sipes 41 not having the chamfered portions 42 may be alternately arranged along the tire circumferential direction.

3 to 5 show the ground contact shapes (40% load, 75% load, 100% load) of the pneumatic tire of FIG. 1, respectively. In the above pneumatic tire, the pneumatic tire is filled with air pressure of 230 kPa, and the tire when grounded under the conditions of loading 40%, 75%, and 100% of the maximum load capacity specified by the standard. The maximum ground contact lengths in the circumferential direction are LA1, LB1, and LC1 (mm), and the maximum ground contact widths in the tire width direction are WA1, WB1, and WC1 (mm), respectively. Let LA2, LB2, and LC2 (mm) be the outer contact lengths in the tire circumferential direction at 40% positions of the widths WA1, WB1, and WC1, respectively.

That is, as shown in FIG. 3, the pneumatic tire is filled with air pressure of 230 kPa, and the maximum load in the tire circumferential direction when the tire is grounded under the condition of loading 40% of the maximum load capacity specified by the standard. Let LA1 be the contact length, WA1 be the maximum contact width in the tire width direction, and LA2 be the external contact length in the tire circumferential direction at a position 40% of the maximum contact width WA1 from the tire center position CL toward the outside in the tire width direction. . The outer contact length LA2 is the average value of the measured values on both sides of the tire center position CL.

Further, as shown in FIG. 4, when the pneumatic tire is filled with air pressure of 230 kPa and is grounded under the condition of loading 75% of the maximum load capacity specified by the standard, the maximum pressure in the tire circumferential direction Let LB1 be the ground contact length, WB1 be the maximum ground contact width in the tire width direction, and LB2 be the external contact length in the tire circumferential direction at a position 40% of the maximum contact width WB1 from the tire center position CL toward the outside in the tire width direction. . The outer contact length LB2 is the average value of the measured values on both sides of the tire center position CL.

Furthermore, as shown in FIG. 5, when the pneumatic tire is filled with air pressure of 230 kPa and is grounded under the condition of loading 100% of the maximum load capacity specified by the standard, the maximum in the tire circumferential direction Let LC1 be the contact length, WC1 be the maximum contact width in the tire width direction, and LC2 be the external contact length in the tire circumferential direction at a position 40% of the maximum contact width WC1 from the tire center position CL toward the outside in the tire width direction. . The outer contact length LC2 is the average value of the measured values on both sides of the tire center position CL.

Here, the maximum ground lengths LA1, LB1, LC1 and external ground lengths LA2, LB2, LC2 satisfy the following relationships.
1.02≤(LB2/LB1)/(LA2/LA1)≤1.25
1.00≦(LC2/LC1)/(LB2/LB1)≦1.20

Further, as shown in FIG. 4, the tread portion 1 is arranged within the maximum contact width WB1 and a center region Xc having a width corresponding to 53% of the maximum contact width WB1 around the tire equator (that is, the tire center position CL). When the center region Xc is divided into the shoulder region Xs, which is located outside the center region Xc in the tire width direction, at least one row of land portions included in the shoulder region Xs, that is, the land portion 40 has a plurality of chamfered portions 42 as described above. are formed, and as shown in FIG. 7, the maximum depth x (mm) of the sipe 41 and the maximum depth y (mm) of the chamfered portion 42 are x×0.1≦y≦x×0 .3+1.0 is satisfied. The sipe 41 having the chamfered portion 42 can be arranged not only in the shoulder region Xs but also in the center region Xc.

In the pneumatic tire described above, a plurality of sipes 41 are formed in the land portion 40 included in the shoulder region Xs. mm) and the maximum depth y (mm) of the chamfered portion 42 satisfies the relationship x×0.1≦y≦x×0.3+1.0. While securing steering stability on the road surface, it is possible to secure rigidity in the shoulder region Xs of the tread portion 1 and suppress uneven shoulder wear.

Here, if y<x×0.1, the drainage effect based on the chamfered portion 42 is reduced, resulting in insufficient steering stability on a wet road surface, whereas y>x×0.3+1.0. As a result, the resistance to uneven wear in the shoulder region Xs decreases due to the decrease in the rigidity of the land portion. In particular, it is desirable to satisfy the relationship y≦x×0.3+0.5.

Further, in the pneumatic tires described above, the maximum contact lengths LA1, LB1, LC1 and the outer contact lengths LA2, LB2, LC2 are 1.02≤(LB2/LB1)/(LA2/LA1)≤1.25, 1.00. By satisfying the relationship ≤(LC2/LC1)/(LB2/LB1)≤1.20 and defining the shape of the ground contact in consideration of load fluctuations, while maintaining the effect of suppressing uneven shoulder wear, ride comfort (mild feeling) can be improved. In other words, in a general vehicle with the engine mounted in the front, (LB2/LB1)/(LA2/LA1) is set within a predetermined range in consideration of the load fluctuations of the rear-mounted tires having a relatively small load. By setting (LC2/LC1)/(LB2/LB1) within a predetermined range in consideration of the load fluctuations of the front-mounted tires, which have a relatively large load, the effect of suppressing uneven shoulder wear and improving ride comfort is achieved. The improvement effect can be optimized.

Here, if (LB2/LB1)/(LA2/LA1) is less than 1.02, the effect of improving ride comfort is insufficient, and conversely, if it is greater than 1.25, the effect of suppressing uneven shoulder wear is insufficient. be enough. Similarly, if (LC2/LC1)/(LB2/LB1) is less than 1.00, the effect of improving ride comfort will be insufficient, and conversely, if it is greater than 1.20, the effect of suppressing uneven shoulder wear will be insufficient. be enough. In particular, it is desirable to satisfy the relationships of 1.03≤(LB2/LB1)/(LA2/LA1)≤1.15 and 1.02≤(LC2/LC1)/(LB2/LB1)≤1.10.

In the pneumatic tire described above, the maximum contact length LB1 and the outer contact length LB2 preferably satisfy the relationship 0.65≤LB2/LB1≤0.95. By controlling the shape of the ground when a load of 75% of the maximum load capacity is applied, good riding comfort can be exhibited during steady running. In particular, in the range of 0.70≤LB2/LB1≤0.88, the envelope characteristics of the tread portion 1 are improved, and the ride comfort is effectively improved.

In the above pneumatic tire, the maximum contact lengths LA1, LB1, LC1 and the outer contact lengths LA2, LB2, LC2 satisfy the relationship of (LC2/LC1)/(LB2/LB1)≤(LB2/LB1)/(LA2/LA1). Satisfaction is good. By optimizing the contact shape of the rear-mounted tire and the front-mounted tire in this manner, the ride comfort can be improved.

In the above pneumatic tire, as shown in FIG. 7, the maximum width w of the chamfered portion 42 and the sipe width t of the sipe 41 preferably satisfy the relationship t×0.8≦w≦t×5. By appropriately setting the maximum width w of the chamfered portion 42 with respect to the sipe width t in this way, it is possible to achieve both steering stability on wet road surfaces and uneven wear resistance in the shoulder region Xs at a higher level. can. Here, if the maximum width w of the chamfered portion 42 is smaller than 0.8 times the sipe width t of the sipe 41, the effect of improving the steering stability on wet road surfaces is reduced. If it is more than 0.0 times, the effect of improving the uneven wear resistance in the shoulder region Xs is lowered. In particular, it is desirable to satisfy the relationship t×1.2≦w≦t×3.

FIGS. 8(a), (b) and FIGS. 9(a)-(h) each show a further modification of the sipe having a chamfer. In the example of FIG. 6, the sipe 41 has chamfered portions 42 on both edges, but as shown in FIGS. can be 9(a) to 9(h), in forming a pair of chamfered portions 42 on both edges of the sipe 41, each chamfered portion 42 is made shorter than the sipe 41, and one chamfered portion 42 is A structure in which the sipe 41 is unevenly distributed on one side in the longitudinal direction and the other chamfered portion 42 is unevenly distributed on the other side in the longitudinal direction of the sipe 41 may be employed. In this case, the drainage effect of the chamfered portion 42 and the edge effect of the portion without the chamfered portion 42 can be exhibited in a well-balanced manner.

For example, in FIG. 9( a ), the sipe 42 opens into the main groove 11 or 12 while the chamfered portion 42 does not communicate with the main groove 11 or 12 . 9(a), (c) to (h), the pair of chamfered portions 42 overlap each other along the longitudinal direction of the sipe 41, but in FIG. They do not overlap each other along the longitudinal direction. Although the sipe 41 is linear in FIG. 9(e), the sipe 41 is arcuate in FIG. 9(f). 9A to 9D and 9H, the chamfered portion 42 is arranged on the side where the sipe 41 forms an acute angle, but in FIG. 9G, the chamfered portion 42 is arranged on the side where the sipe 41 forms an obtuse angle. are placed. In FIG. 9(h), the portion where the pair of chamfered portions 42 overlap each other along the longitudinal direction of the sipe 41 is offset to one side of the land portion 40 in the width direction.

In the above pneumatic tire, as shown in FIG. 10, the inclination angle θ of the sipe 41 with respect to the tire circumferential direction is preferably 70° to 90°, more preferably 75° to 90°. This inclination angle θ is an acute angle formed by an imaginary line (broken line) connecting both end portions of the sipe 41 with respect to the tire circumferential direction. When the pitch variation is adopted, the inclination angle θ is the inclination angle of the sipe 41 at the intermediate pitch. By setting the inclination angle .theta. In particular, by bringing the inclination angle θ of the sipe 41 closer to 90°, the rigidity of the land portion 40 against the input in the tire width direction can be increased, and the uneven wear resistance in the shoulder region Xs can be improved. Here, if the inclination angle θ is less than 70°, the effect of improving the steering stability on wet road surfaces and the uneven wear resistance in the shoulder region Xs decreases.

In the pneumatic tire described above, at least a portion of the sipe 41 is preferably curved or bent in plan view. Since at least a part of the sipe 41 is curved or bent in plan view, the total amount of edge of each sipe 41 is increased, and the steering stability on wet road surfaces can be further improved.

In the pneumatic tire described above, at least one end of the sipe 41 is preferably open to the main groove 12 . As a result, the sipes 41 having the chamfered portions 42 function to effectively guide water on the road surface to the main grooves 12, so that steering stability on wet road surfaces can be further improved.

In the above pneumatic tire, as shown in FIG. 11, when at least a part of the contour of the chamfered portion 42 in the cross section perpendicular to the sipe 41 is curved or bent so that the contour of the chamfered portion 42 is straight (broken line ), the real cross-sectional area of the chamfered portion 42 (the area of the region surrounded by the dashed-dotted line and the solid line) is larger than the virtual cross-sectional area of the chamfered portion 42 (the area of the region surrounded by the dashed-dotted line and the broken line). May be set. In this case, by increasing the actual cross-sectional area of the chamfered portion 42, the steering stability on wet road surfaces can be further improved.

In the above pneumatic tire, as another aspect, as shown in FIG. 12, at least a part of the contour of the chamfered portion 42 in the cross section perpendicular to the sipe 41 is curved or bent so that the contour of the chamfered portion 42 is straightened. In the case of (dashed line), the actual cross-sectional area of the chamfered portion 42 (the area surrounded by the dashed-dotted line and the solid line) is larger than the virtual cross-sectional area of the chamfered portion 42 (the area of the region surrounded by the dashed-dotted line and the dashed line). area) may be set smaller. In this case, by reducing the actual cross-sectional area of the chamfered portion 42, the uneven wear resistance in the shoulder region Xs can be further improved.

In the pneumatic tire described above, the chamfered portion 42 does not necessarily have to extend parallel to the longitudinal direction of the sipe 41 , but the chamfered portion 42 preferably extends parallel to the sipe 41 . As a result, steering stability on wet road surfaces and uneven wear resistance in the shoulder region Xs can be further improved.

In the above pneumatic tire, in the contact area of the tread portion 1 defined by the maximum contact width WB1, the groove area Sm including the chamfered portion 42 and the groove area Sa not including the chamfered portion 42 are 1.01≦Sm/Sa≦ It is good to satisfy the relationship of 1.50. The groove area Sm means the total area of the groove components (including the chamfered portion 42) formed in the ground contact area on the tire circumference, and the groove area Sa means the total area of the groove components (chamfered portion 42) formed in the contact area on the tire circumference. ) means the total area of
By setting the ratio Sm/Sa within the above range, the total amount of the chamfered portion 42 can be sufficiently secured, and both steering stability on wet road surfaces and uneven wear resistance in the shoulder region Xs can be achieved at a higher level. can. Here, if the ratio Sm/Sa is less than 1.01, the total amount of the chamfered portions 42 is insufficient, so that the effect of achieving both of the above performances is reduced. Therefore, the effect of achieving both of the above performances is reduced. In particular, it is desirable to satisfy the relationship 1.05≤Sm/Sa≤1.30.

In the pneumatic tire described above, the ratio Sar of the groove area not including the chamfered portion 42 in the shoulder region Xs is preferably in the range of 10% to 25%. By setting the ratio Sar of the groove area excluding the chamfered portion 42 in the shoulder region Xs within the above range, the uneven wear resistance in the shoulder region Xs can be sufficiently improved. Here, if the ratio Sar of the groove area excluding the chamfered portion 42 in the shoulder region Xs is less than 10%, the steering stability on the wet road surface is reduced, and conversely, if it is greater than 25%, the durability in the shoulder region Xs is reduced. Uneven wear resistance is lowered.

The loads corresponding to 40%, 75%, and 100% of the maximum load capacity specified by the standard are W40, W75, and W100 (kN), respectively. Let CP40, CP75, and CP100 (kN/°) be the cornering powers measured under the condition of loading W100, R be the aspect ratio of the pneumatic tire, D (mm) be its outer diameter, and D (mm) be its cross-sectional width. When the nominal is A (mm), loads W40, W75, W100 and cornering power CP40, CP75, CP100 are 0.05≦(R×D/2A) ² ×[(CP100-CP75)/(W100-W75) ]/[(CP75-CP40)/(W75-W40)]≦0.50. As a result, it is possible to suppress an excessive increase in cornering power in the high-load region and improve steering stability on wet road surfaces. In particular, since the above relational expression is corrected by the value of (R×D/2A) ² , the lower the aspect ratio and the smaller the ratio of the outer diameter to the nominal section width, the greater the contribution of cornering power on the high load side. Lower. Therefore, it is possible to exhibit moderate cornering power according to the tire size.

Here, when (R×D/2A) ² ×[(CP100-CP75)/(W100-W75)]/[(CP75-CP40)/(W75-W40)] is smaller than 0.05, the low load region Conversely, if it is greater than 0.50, the cornering power becomes excessive in the high-load region, and in either case, the effect of improving steering stability on wet road surfaces is reduced. In particular, satisfying the relationship 0.10≦(R×D/2A) ² ×[(CP100-CP75)/(W100-W75)]/[(CP75-CP40)/(W75-W40)]≦0.40 It is desirable to

In the pneumatic tire described above, when a plurality of belt layers 7 including a plurality of belt cords C that are inclined with respect to the tire circumferential direction and in which the belt cords C intersect each other are embedded in the tread portion 1, As shown in FIG. 13, the inclination angle α of the belt cord C at the tire center position CL with respect to the tire circumferential direction preferably satisfies the relationship of 21°≦α≦30°. By not making the inclination angle α of the belt cord C at the tire center position CL extremely low, it is possible to suppress an increase in the rigidity of the belt layer 7 and improve riding comfort. Here, if the inclination angle α is smaller than 21°, the rigidity of the belt layer 7 increases and the effect of improving ride comfort is reduced. not targeted.

Further, the inclination angle α of the belt cord C with respect to the tire circumferential direction at the tire center position CL and the inclination angle β of the belt cord C with respect to the tire circumferential direction at the belt end position BE have a relationship of 18°≦β<α≦30°. Satisfied and good. By reducing the inclination angle β of the belt cord C at the belt end position BE, uneven shoulder wear can be effectively suppressed, and the inclination angle α of the belt cord C at the tire center position CL can be reduced. By not making the angle extremely low, it is possible to suppress an increase in the rigidity of the belt layer 7 in the center region Xc of the tread portion 1 and maintain good riding comfort. In particular, it is preferable that the difference between the inclination angle α and the inclination angle β is 3° or more. A structure in which the inclination angle β of the belt cord C with respect to the tire circumferential direction at the belt end position BE is preferably smaller than the inclination angle α with respect to the tire circumferential direction of the belt cord C at the tire center position CL is preferable. The belt cord C may be inclined at a constant angle with respect to the tire circumferential direction over the entire width, and the inclination angles α and β may be set to the same value, or α<β may be established.

As shown in FIG. 13, the belt layer 7 has a high-angle area Ac on the center side where the belt cord C has an inclination angle of α±1° and a shoulder area where the belt cord C has an inclination angle of β±1°. The width Lc of the high angle region Ac is 1/2 or more of the total width L of the belt layer 7, and the width Ls of each low angle region As is 1 of the total width L of the belt layer 7. /8 or more is preferable. By setting the high-angle area Ac on the center side of the belt layer 7 and the low-angle area As on the shoulder side of the belt layer 7 as described above, the rigidity distribution of the tread portion 1 can be optimized. Here, if the width Lc of the high-angle area Ac is smaller than 1/2 of the total width L of the belt layer 7, the function of the belt layer 7 is deteriorated, and the width Ls of the low-angle area As is the total width of the belt layer 7. If it is less than 1/8 of L, the rigidity in the tire circumferential direction in the shoulder region Xs of the tread portion 1 cannot be sufficiently increased. The width Lc of the high-angle area Ac and the width Ls of the low-angle area As are set based on the total width L of each belt layer 7 .

The pneumatic tire described above is suitable as a passenger car tire having an aspect ratio of 0.65 or less. In a tire for a passenger car, which is strictly required to improve ride comfort, it is possible to achieve both uneven wear resistance and ride comfort.

In the above-described embodiment, a tread pattern including four main grooves in the tread portion has been described. It is also applicable to tread patterns including

The tire size is 205/55R16 91V, a carcass layer is mounted between a pair of bead portions, two belt layers are embedded outside the carcass layer in the tire radial direction in the tread portion, and a plurality of belt layers extend in the tire circumferential direction in the tread portion. In a pneumatic tire in which two main grooves are formed and a plurality of rows of land portions are defined by these main grooves, a conventional example in which lug grooves are provided in the center region and the shoulder region of the tread portion, and Comparative Example 1 having a sipe without a chamfered portion and a lug groove in the center region, and Example 1 having a sipe with a chamfered portion in the shoulder region of the tread portion and a lug groove in the center region. Tires of Example 11 and Example 12 having sipes with chamfered portions in the center region and shoulder region of the tread were manufactured.

In the conventional example, Comparative Example 1, and Examples 1 to 12, the inclination angle α of the belt cord with respect to the tire circumferential direction at the tire center position, the inclination angle β of the belt cord with respect to the tire circumferential direction at the belt end position, and the maximum depth of the sipe width x, presence/absence of chamfer, maximum depth y of chamfer, inclination angle θ of sipe, curvature of sipe, opening of sipe to main groove, cross-sectional shape of chamfer, maximum width w of chamfer and sipe of sipe Ratio w/t to width t, plan view shape of chamfered portion (vs. sipe), arrangement region of sipe having chamfered portion, ratio Sm of groove area Sm including chamfered portion and groove area Sa not included chamfered portion /Sa, ratio Sar of the groove area not including the chamfered portion in the shoulder region, (LB2/LB1)/(LA2/LA1), (LC2/LC1)/(LB2/LB1), LB2/LB1 (rectangular ratio), low Load area CP variation coefficient X=[(CP75-CP40)/(W75-W40)], high load area CP variation coefficient Y=[(CP100-CP75)/(W100-W75)], (R×D/2A) ² ×(Y/X) was set as shown in Table 1.

These test tires were evaluated for uneven wear resistance (shoulder area), riding comfort, and steering stability on wet road surfaces by the following test methods. Table 1 also shows the results.

Uneven wear resistance (shoulder area):
Each test tire was mounted on a wheel with a rim size of 16 x 6.5J and mounted on a friction energy measurement tester, and the average friction energy in the shoulder region of the tread was measured under the conditions of air pressure of 230 kPa and load of 4.5 kN. bottom. The measured value is obtained by measuring the frictional energy at a total of four points, two points in the tire width direction and two points in the tire circumferential direction, at intervals of 10 mm in each region, and averaging these values. The evaluation results are shown as indices with the conventional example being 100, using the reciprocal of the measured value. It means that the larger the index value, the better the uneven wear resistance.

Ride comfort:
Each test tire was mounted on a wheel with a rim size of 16 x 6.5J, mounted on a front-wheel drive vehicle with a displacement of 2 liters, filled with the specified air pressure for the vehicle, and paneled on a test course with protrusions on the road surface. A running test was carried out by using the sensor, and a sensory evaluation was performed on the ride comfort (mild feeling) considering the input of the protrusions. The evaluation results are shown as indices with the conventional example being 100. A larger index value means better riding comfort.

Steering stability on wet roads:
Each test tire was mounted on a wheel with a rim size of 16 x 6.5J, mounted on a front-wheel drive vehicle with a displacement of 2 liters, inflated to the specified air pressure for the vehicle, and run by a panelist on a water-sprinkled test course. , sensory evaluation of steering stability on wet roads. The evaluation results are shown as indices with the conventional example being 100. A larger index value means better steering stability on a wet road surface.

As can be seen from Table 1, the tires of Examples 1 to 12 were superior in uneven wear resistance, ride comfort, and steering stability on wet road surfaces in comparison with the conventional tire. On the other hand, in the tire of Comparative Example 1, since the lug grooves in the shoulder region were merely replaced with normal sipes, the steering stability on wet road surfaces deteriorated.

REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt reinforcing layer 11 central main groove 12 outer main groove 20, 30, 40 land portion 31 lug groove 32 circumferential narrow groove 41 sipe 42 Chamfer

Claims (14)

A tread portion extending in the tire circumferential direction and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged inside the tire radial direction of the sidewall portions. A pneumatic tire in which a plurality of main grooves extending in the tire circumferential direction are formed in the tread portion, and a plurality of rows of land portions are defined by the main grooves,
The maximum contact length in the tire circumferential direction when the pneumatic tire is filled with air pressure of 230 kPa and is grounded under conditions of loading 40%, 75%, and 100% of the maximum load capacity specified by the standard. are respectively LA1, LB1, and LC1, and the maximum ground contact widths in the tire width direction are WA1, WB1, and WC1, respectively. When the outer contact lengths in the tire circumferential direction are LA2, LB2, and LC2, respectively, the maximum contact lengths LA1, LB1, LC1 and the outer contact lengths LA2, LB2, LC2 are 1.02≤(LB2/LB1)/(LA2). /LA1)≦1.25, 1.00≦(LC2/LC1)/(LB2/LB1)≦1.20,
When the tread portion is divided into a center region having a width equivalent to 53% of the maximum ground contact width WB1 centered on the tire equator and a shoulder region outside the center region in the tire width direction within the maximum ground contact width WB1. , a plurality of sipes are formed in at least one row of the land portion included in the shoulder region, the sipe has a chamfered portion at its edge, and the maximum depth x (mm) of the sipe and the chamfered portion A pneumatic tire, characterized in that the maximum depth y (mm) of the satisfies the relationship x x 0.1 ≤ y ≤ x x 0.3 + 1.0. 2. The pneumatic tire according to claim 1, wherein said maximum contact length LB1 and said outer contact length LB2 satisfy a relationship of 0.65≤LB2/LB1≤0.95. The maximum ground lengths LA1, LB1, LC1 and the external ground lengths LA2, LB2, LC2 satisfy the relationship (LC2/LC1)/(LB2/LB1)≤(LB2/LB1)/(LA2/LA1). 3. The pneumatic tire according to claim 1 or 2. The air according to any one of claims 1 to 3, wherein the maximum width w of the chamfered portion satisfies a relationship of t x 0.8 ≤ w ≤ t x 5 with respect to the sipe width t of the sipe. entered tire. The pneumatic tire according to any one of claims 1 to 4, characterized in that an acute angle side inclination angle θ of the sipe with respect to the tire circumferential direction is in the range of 70° to 90°. The pneumatic tire according to any one of claims 1 to 5, wherein at least part of said sipe is curved or bent in plan view. The pneumatic tire according to any one of claims 1 to 6, wherein at least one end of said sipe is open to the main groove. By curving or bending at least a part of the contour of the chamfered portion in a cross section perpendicular to the sipe, the actual cross section of the chamfered portion is larger than the imaginary cross-sectional area of the chamfered portion when the contour of the chamfered portion is straight. The pneumatic tire according to any one of claims 1 to 7, characterized in that the area is increased. By curving or bending at least a part of the contour of the chamfered portion in a cross section perpendicular to the sipe, the actual cross section of the chamfered portion is larger than the imaginary cross-sectional area of the chamfered portion when the contour of the chamfered portion is straight. The pneumatic tire according to any one of claims 1 to 7, characterized in that the area is reduced. The pneumatic tire according to any one of claims 1 to 9, wherein the chamfer extends parallel to the sipe. In the contact area of the tread defined by the maximum contact width WB1, the relationship between the groove area Sm including the chamfered portion and the groove area Sa not including the chamfered portion satisfies 1.01≤Sm/Sa≤1.50. The pneumatic tire according to any one of claims 1 to 10, wherein The pneumatic tire according to any one of claims 1 to 11, wherein a groove area ratio Sar not including the chamfered portion in the shoulder region is in the range of 10% to 25%. Loads corresponding to 40%, 75%, and 100% of the maximum load capacity specified by the standard are W40, W75, and W100 (kN), respectively. Let CP40, CP75, and CP100 (kN/°) be the cornering powers measured under the conditions of loading W75 and W100, respectively, let R be the aspect ratio of the pneumatic tire, let D (mm) be its outer diameter, and When the nominal cross-sectional width is A (mm), the loads W40, W75, W100 and the cornering powers CP40, CP75, CP100 are 0.05≦(R×D/2A) ² ×[(CP100−CP75)/ (W100-W75)]/[(CP75-CP40)/(W75-W40)]≦0.50. In the tread portion, a plurality of belt layers including a plurality of belt cords inclined with respect to the tire circumferential direction and intersecting belt cords are embedded in the tire circumferential direction at the tire center position of the belt cords. 14. The pneumatic tire according to any one of claims 1 to 13, wherein the inclination angle α with respect to the angle satisfies a relationship of 21°≦α≦30°.

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