JP4589719B2 - Pneumatic tire - Google Patents

Description

  The present invention is particularly suitable for a four-wheel drive vehicle, and relates to a pneumatic tire in which a plurality of sipings are arranged in parallel on a block surface to improve performance on snow and ice.

  In a four-wheel drive vehicle, since all four wheels function as drive wheels, the drivability is greatly improved compared to other rear-wheel drive and front-wheel drive vehicles. Therefore, it tends to fall into the illusion that it is excellent in overall grip performance including drivability and braking performance. However, in actuality, at the time of braking, the rear wheel drive and the like function as brake wheels in the same manner as a four-wheel drive vehicle, so that the merit of the four-wheel drive is not obtained in terms of braking performance.

  Therefore, in a four-wheel drive vehicle, in order to compensate for the insufficient braking performance associated with the illusion and improve the safety of traveling, a tire having a directional pattern that has a relatively improved braking performance compared to the driving performance is desired. Yes. The demand is particularly strong in winter tires such as studless tires with improved running performance on snowy and icy roads that are likely to slip.

  In view of such a situation, as shown in FIG. 11A, the present inventor spreads siping b arranged in parallel on the surface of the block a from the top of the block center side toward the tire arrival direction rear arrival side. It has been proposed to form a substantially V-shape extending in the direction. Such a siping b has a V-shaped spreading direction during braking as shown in FIG. 11B, so that the block small piece b1 (part partitioned by the siping b) is not easily deformed and the frictional force is increased. . On the other hand, since the V-shape is closed as shown in FIG. 11C during driving, the block small piece b1 is easily deformed, and the frictional force is relatively small compared with that during braking. Thus, the braking performance can be relatively improved.

  However, with the stronger demand in recent years, further improvement in braking performance is desired. Further, when the substantially V-shaped siping b is provided on the block a, there is a new problem that uneven wear is likely to occur in the region c on the rear side in the rotation direction of the block a and on both outer sides in the block width direction. appear. This uneven wear is presumed to occur for the following reason. Normally, the tire travels in a driving state, but at this time, the deformation of the block a on the arrival side in the rotation direction is large. At the time of driving, as shown in FIG. 11C, the V-shaped direction is closed, so that the compressive force is high at the center side of the block a, and the rigidity at both outer sides in the block width direction is relatively low. By these interactions, it is estimated that the region c becomes more slippery with the road surface, and uneven wear occurs remarkably.

  Patent Document 1 describes that a substantially V-shaped siping is formed on a circumferential rib.

JP 2003-11618 A

  According to the present invention, on the basis of arranging substantially V-shaped siping on the block surface side by side, on the wall surface of at least the first-arrival side siping, an inclined wall portion inclined toward the first-arrival side toward the sipe bottom is basically provided. An object of the present invention is to provide a pneumatic tire that can improve the braking performance on the road more than the drivability and that can suppress uneven wear caused by the substantially V-shape.

In order to achieve the above object, the invention of claim 1 of the present application is a pneumatic tire having a siping block in which a plurality of sipings are arranged in parallel in the tire circumferential direction on a surface of a block defined by a tread groove.
The siping has a substantially V-shape extending in a direction extending from the top to the block side edge on both sides in the tire axial direction toward the rear arrival side in the tire rotation direction from the top to the block side edge including the width center line of the block. Shape
Each sipes, have a sloping wall portion inclined in arrival side to the sipe bottom siping wall,
The width W in the block width direction of the inclined wall portion of the siping adjacent on the first arrival side is sequentially larger than the width W in the block width direction of the inclined wall portion adjacent on the rear arrival side . .

The invention according to claim 2 is characterized in that the inclination angles θ of the respective sipings with respect to the normal line of the block surface of the inclined wall portion are equal to each other .

In the invention according to claim 3, the block with siping is characterized in that the block wall surfaces on the first arrival side and the rear arrival side have a V-shape parallel to the siping .

  According to a fourth aspect of the present invention, the inclined wall portion is formed on a central side including the top portion.

  Further, in the invention of claim 5, the first-sided siping is that the entire siping wall surface is composed of the inclined wall part, and the last-sided siping is inclined to the center side including the top part of the siping wall surface. It features a wall.

  In the invention according to claim 6, the siping block has an inclination angle αa with respect to the normal of the block surface of the first block wall surface, and an inclination angle αb with respect to the normal of the block surface of the second block wall surface. It is characterized by being large.

  Since the present invention is configured as described above, the braking performance on snowy and icy roads can be further improved compared to the driving performance. In addition, it is possible to suppress uneven wear resulting from the siping being substantially V-shaped.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a development view of a tread pattern when the pneumatic tire of the present invention is a studless tire for a four-wheel drive vehicle.
In FIG. 1, a pneumatic tire 1 has a tread groove 5 including a plurality of vertical main grooves 3 extending in the tire circumferential direction and a horizontal main groove 4 extending in a direction intersecting with the vertical main grooves 3 in a tread portion 2. Prepare. Thereby, the tread portion 2 is partitioned into, for example, four block rows in which the blocks 6 are spaced apart in the tire circumferential direction. The tread pattern may be a rib / block pattern in addition to the block pattern as in this example. The tread groove 5 preferably has a groove width of 3.5 mm or more in order to improve drainage performance.

  The block 6 includes a siping block 8 in which a plurality of sipings 7 are arranged on the block surface S in the tire circumferential direction. In this example, all of the blocks 6 are composed of blocks 8 with siping, and four sipings 7 are arranged in parallel with the block 8. However, some of the blocks 6 are blocks 8 with siping. The number of sipings 7 may be different for each block 8. In addition, when distinguishing each siping 7, it may be described as siping 7A, 7B, 7C, 7D in order from the tire rotation direction first arrival side FS.

  As shown in an enlarged view in FIG. 2, the siping 7 has a top Q located in a block central area Yc including the width center line C of the block 8, and block side edges on both sides in the tire axial direction from the top Q. It is formed in a substantially V-shape consisting of inclined lines 7a, 7a extending in a direction extending toward the rear arrival side FK in the tire rotation direction up to 8e.

The “block central region Yc” means a width region that is 30% of the width BW of the block 8 with the width center line C as the center. Further, the sipe width, sipe depth h, and circumferential interval P of the sipe 7 are not particularly restricted, but in the case of a passenger car tire, the sipe width is 1.0 mm or less, further 0.5 mm or less (for example, 0. 2 to 0.4 mm) is preferable, and as the sipe depth h (shown in FIG. 6), when the block height is H so that the siping 7 can remain even at the end of wear, A range of (0.5H−1.0 mm) to (H + 1.0 mm) is preferable. Further, the circumferential distance P between the sipes 7 and 7 is preferably in the range of 3.0 to 7.0 mm, more preferably 4.0 to 6.0 mm, in view of the balance between the edge effect and the block rigidity.

  In the block 8 provided with such a substantially V-shaped siping 7, the block small piece portion 8A is deformed in a direction in which the V-shape spreads during braking, as shown in FIGS. 3 (A) and 3 (B). Deforms in the closing direction. The block rigidity at the time of braking can be made higher than the block rigidity at the time of driving due to the difference in restraining force of each part at this time. Further, the increase in the block rigidity suppresses the block deformation and increases the road surface frictional force, so that the braking performance can be enhanced as compared with the driving performance. Such an effect is particularly effective when the angle β (V-shaped opening angle β) between the inclined lines 7a and 7a in the siping 7 is in the range of 120 to 150 °.

  In the present invention, in order to increase the braking performance as compared with the driving performance, at least the first sipe 7A is inclined to the sipe wall 7S toward the sipe bottom Bo as shown in FIG. An inclined wall portion 9 is provided.

  Here, the block usually has insufficient rigidity on the first arrival side, such as large deformation on the first arrival side during braking. As a result of the inventor's research, when the substantially V-shaped siping 7 is formed on the block, the block rigidity at the time of braking can be increased as compared with that at the time of driving, but the rigidity difference between the first arrival side and the rear arrival side is further increased. Turned out to be. This is presumably because the rigidity improvement effect by the substantially V-shaped siping 7 is different between the first arrival side and the later arrival side, and a greater rigidity improvement effect is exhibited on the later arrival side. Then, due to the large rigidity difference, the road surface friction force is not sufficiently increased on the first arrival side, and the effect of improving the braking performance is low.

  Therefore, the inclined wall portion 9 is formed on at least the first arrival side siping 7A. Since the inclined wall portion 9 is inclined toward the first arrival side FS toward the sipe bottom Bo, the siping edge at the inclined wall portion 9 can be deformed to stand on the road surface during braking, and the edge effect can be enhanced. . Thereby, the shortage of the road surface frictional force on the first arrival side can be compensated, and the grip performance (braking performance) during braking of the block 8 as a whole can be improved.

At this time, it is preferable to increase the edge effect on the first arrival side and maintain a balance between the edge effect and the road surface frictional force. Therefore, in this example, as shown to FIGS. 5-6, while providing the inclined wall part 9 in the siping wall surface 7S of each siping 7, in each siping 7,
(1) The inclination angle θ of the inclined wall portion 9 of the siping 7 adjacent on the first arrival side is sequentially made larger than the inclination angle θ of the inclined wall portion 9 of the adjacent siping 7 on the rear arrival side, and / or
(2) The width W in the block width direction of the inclined wall portion 9 of the siping 7 adjacent on the first arrival side is sequentially increased from the width W in the block width direction of the inclined wall portion 9 of the adjacent siping 7 on the rear arrival side. Yes.

More specifically, the inclined wall portions of the sipings 7A, 7B, 7C, and 7D are 9A, 9B, 9C, and 9D, the inclination angles are θA, θB, θC, and θD, and the widths of the inclined wall portions are WA and WB. , WC, WD,
θA>θB>θC> θD and / or
WA>WB>WC> WD
It is said. 4, the inclination angle θ means an angle on the acute angle side where the inclined wall portion 9 makes a normal to the block surface S in a cross section orthogonal to the inclined wall portion 9, as representatively shown in FIG.

In this example, the inclination angles θ of the sipings 7 are equal to each other, and the width W in the block width direction of the inclined wall portion 9 of the siping 7 adjacent on the first arrival side is equal to the block of the inclined wall portion of the siping adjacent on the rear arrival side. Sequentially larger than the width W in the width direction, that is, θA = θB = θC = θD and WA>WB>WC> WD
This is illustrated as an example.

  Thus, by comprising, the balance of an edge effect and a road surface frictional force can be maintained, and it becomes possible to improve braking performance more. If the inclination angle θ is too large or too small, the edge effect during braking is reduced. Therefore, the lower limit value of the tilt angle θ is larger than 0 °, more preferably 10 ° or more, and the upper limit value is preferably 30 ° or less, more preferably 20 ° or less.

  Here, in the first arrival side siping 7A, it is preferable to form the entire siping wall surface 7S with the inclined wall portion 9 in order to further improve the braking performance. At this time, other sipings including the last arrival side siping 7D. In 7B-7D, the inclined wall part 9 is arranged on the center side including the top part Q, and the non-inclined wall part 10 is formed on both outer sides in the width direction. This is because, as far as the width direction of the block 8 is concerned, the block rigidity decreases as the inclination direction θ becomes smaller as the width direction becomes both outer sides, and accordingly, by arranging the inclined wall portion 9 on the center side, The advantage is that the block rigidity can be made uniform in the width direction while minimizing the decrease in the overall block rigidity. It should be noted that the WD of the inclined wall portion 9D in the last landing side siping 7D is 40 to 60% of the width BW of the block 8, that is, the width wd of the non-inclined wall portion 10 in the block width direction of the inclined line 7a. A range of 40 to 60% of the length L (= 0.5 × BW) is preferable. The width w of the non-inclined wall portion 10 at the sipings 7B and 7C between the last arrival side and the first arrival side is {wd × (n−1) in order from the rear arrival side when the number of formations of the sipings 7 is n. ) / N}, {wd × (n−2) / n}, {wd × (n−3) / n}... As a reference value, and set within a range of ± 10% of the reference value. preferable.

  Further, as shown in FIG. 7, the inclined wall portion 9 can be formed by a plurality of wall portions 9 i and 9 j having different inclination angles θ as the siping 7, and in such a case, the wall portion having a large inclination angle θ. 9i is formed on the center side (top Q side).

  Next, in the block 8 provided with the substantially V-shaped siping 7, as shown in FIG. 11A, uneven wear tends to occur in the area c on the rear side in the rotation direction of the block and on the outer side in the block width direction. Become. Normally, the tire is running in a driving state, but at this time, the deformation of the block 8 on the rear arrival side FK in the rotation direction is large. Further, during the driving, the V-shape is deformed in the closing direction, so that the compressive force is high on the center side of the block 8 and the rigidity on the outer sides in the block width direction is relatively low. Due to these interactions, slippage with the road surface increases in the region c, and uneven wear occurs. However, in this example, the non-inclined wall portion 10 having a large rigidity is arranged on both outer sides in the width direction, and the formation width becomes larger toward the rear arrival side FK in the rotation direction. Therefore, deformation in the region c can be effectively suppressed, and uneven wear can be prevented.

  At the time of driving, on the contrary, the deformation at the rear landing side FK is large and the road surface frictional force is insufficient as compared with the first landing side FS, but the inclined wall portion 9 is inclined in the direction in which the edge lies at the time of driving. Therefore, by adopting the above-described configuration (1) and / or (2), the edge effect of the rear arrival side FK during driving can be enhanced as compared with the first arrival side FS. It can be compensated, and the grip performance can be made uniform, and the drivability can be improved although not as much as the braking performance.

  In the present example, as shown in FIG. 6, the block 8 with siping has an inclination angle αa of the block wall surface 8Sa on the first arrival side larger than an inclination angle αb of the block wall surface 8Sb on the rear arrival side. As a result, deformation on the first landing side of the block 8 during braking is suppressed, grip performance (braking performance) is further improved, and slippage with the road surface on the first landing side is reduced, and uneven wear on the first landing side during braking is suppressed. Yes. The inclination angle αa is preferably in the range of 20 to 10 °, and the difference (αa−αb) from the inclination angle αb is preferably 5 ° or more. Note that the inclination angles αa and αb mean angles on the acute angle side that are normal to the block surface S in a cross section orthogonal to the wall surface 8Sa and the wall surface 8Sb.

FIG. 8 shows a reference example of the block 8 . In this example, the width W of the inclined wall portion 9 in each siping 7 is made equal to each other, and the inclination angle θ of the inclined wall portion 9 of the adjacent siping 7 on the first arrival side is set to the inclined wall of the adjacent siping 7 on the rear arrival side. The inclination angle θ of the portion 9 is sequentially set to be larger. That is,
WA = WB = WC = WD and
θA>θB>θC> θD
It is said.

  Further, the shape of the block 8 is not particularly restricted. In addition to the rectangular shape as in this example, the block wall surfaces 8Sa and 8Sb on the first arrival side and the rear arrival side are parallel to the siping 7 as shown in FIG. It can also be formed in a letter shape. In such a case, there is little difference in rigidity in each part, which is advantageous for uneven wear.

  The siping 7 has an “substantially V-shape” as well as a case where the inclined line 7a extends in an arc as shown in FIG. 10A in addition to the case where the inclined line 7a extends in a straight line. included. Further, as shown in FIG. 10B, if the center line i extends linearly or arcuately in a direction spreading toward the rear arrival side FK, a zigzag pattern in which the valleys are repeated with the center line i interposed therebetween as the inclined line 7a. Those (including wavy shapes) are also included in a substantially V-shape.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  Using the tread pattern shown in FIG. 1 as a basic pattern, a tireless tire size 195 / 65R15 with V-shaped siping having the specifications shown in Table 2 formed on the surface of each block was prototyped, and the braking performance of each prototype tire on an icy road Then, driving performance and uneven wear were tested and compared with each other. The size of each block is the same (width (32 mm) x length (40 mm) x height (10 mm)), and each siping has a sipe width (0.3 mm), a sipe depth h (8.2 mm), The interval p (5 mm) is the same as the V-shaped opening angle β (135 °).

(1) Braking property:
The test tire is mounted on the four wheels of a four-wheel drive vehicle (2000 cc) with a rim (15 × 6.5) and internal pressure (200 kPa), and it is 30 km / H on an icy road in an environment with a temperature of 0 ° C. The reciprocal of the braking distance until the car stops after applying a sudden brake with the four-wheel lock from the running speed is displayed as an index. In addition, an index | exponent is set as 100 for the comparative example 1, and it is so favorable that a value is large.

(2) Drive performance:
Using the vehicle, the vehicle was started on the ice path, and the time required to travel 25 m was evaluated by an index with Comparative Example 1 taken as 100. The higher the value, the better.

(3) Uneven wear:
The vehicle was used to travel about 10,000 km on a dry pavement test course, and the wear state of the block was evaluated in five stages by visual inspection. The larger the value, the better the less uneven wear.

  As shown in the table, it can be confirmed that the tires of the examples can greatly improve the braking performance while maintaining the driving performance and can suppress the uneven wear.

It is an expanded view of the tread pattern which shows one Example of the pneumatic tire of this invention. It is a top view which shows siping with a block. (A), (B) is a top view explaining the deformation | transformation state of the block at the time of braking and a drive. It is a perspective view which shows the siping of the earliest arrival side. (A)-(C) are perspective views which show another siping. It is the sectional view on the AA line of FIG. 2 which shows an inclination wall part. It is a perspective view which shows the other example of an inclined wall part. It is sectional drawing which shows the other example of siping. It is a top view which shows the other example of a block. (A) (B) is a top view explaining the substantially V shape of siping. (A)-(C) is a top view explaining the subject which an invention is going to solve.

Explanation of symbols

5 Tread Grooves 6, 8 Block 7 Siping 7A First landing side siping 7S Siping wall surface 9 Inclined wall portion 8Sa, 8Sb Block wall surface Bo Sipe bottom C Width center line FK Rear landing side FS First landing side Q Top Yc Block central area

Claims (6)

A pneumatic tire having a block with siping in which a plurality of sipings are juxtaposed in the tire circumferential direction on the surface of the block defined by the tread groove,
The siping has a substantially V-shape extending in a direction extending from the top to the block side edge on both sides in the tire axial direction toward the rear arrival side in the tire rotation direction from the top to the block side edge including the width center line of the block. Shape
Each sipes, have a sloping wall portion inclined in arrival side to the sipe bottom siping wall,
The width W in the block width direction of the inclined wall portion of the sipe adjacent on the first arrival side is sequentially larger than the width W in the block width direction of the inclined wall portion of the sipe adjacent on the rear arrival side. Pneumatic tire. 2. The pneumatic tire according to claim 1 , wherein the inclination angles θ with respect to the normal of the block surface of the inclined wall portion of each siping are equal to each other . 3. The pneumatic tire according to claim 1, wherein the block with siping has a V-shaped parallel wall with the siping on the first and second block walls . The inclined wall portion, the pneumatic tire according to claim 1, characterized in that it is formed in the central side including the top. As for the first arrival side siping, the entire siping wall surface is composed of the inclined wall portion, and the last arrival side siping is characterized in that the inclined wall portion is arranged on the center side including the top portion of the siping wall surface. The pneumatic tire according to claim 1 .   The block with siping is characterized in that the inclination angle αa of the first block wall surface with respect to the normal of the block surface is larger than the inclination angle αb of the block wall surface of the rear arrival side with respect to the normal of the block surface. The pneumatic tire according to any one of claims 1 to 5.

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