JP5219128B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire such as a truck / bus studless tire having a plurality of blocks in a tread portion and having sipes disposed in the blocks.

  As a result of restricting the use of spike tires having spikes or the like in the tread portion, pneumatic tires (so-called studless tires) that improve performance on ice and snow without providing them have become widespread. As such a tire tread pattern, a block pattern in which the tread portion is divided into blocks by a plurality of main grooves and a plurality of lug grooves extending in the tire circumferential direction, and various sipes are formed in each block is widely used. Has been. This block pattern increases the edge component (edge amount) by forming multiple blocks and sipes in the tread part, enhancing the edge effect, etc., improving the performance on ice and snow such as traction performance and braking performance on ice and snow road surface I am letting.

  By the way, pneumatic tires, such as heavy duty studless tires for trucks and buses, vary greatly depending on the load of the vehicle, and when the load is large, the contact area increases and the performance on ice and snow is high. On the contrary, when the load is small, the ground contact area tends to decrease and the performance on ice and snow tends to deteriorate. Therefore, in such a pneumatic tire, it is common to increase the number of blocks and sipes in the tread portion to ensure the performance on ice and snow particularly when the load is small (see Patent Document 1).

FIG. 3 is a plan view illustrating an example of a tread pattern of such a conventional pneumatic tire, and schematically shows a part of the tire circumferential direction.
As shown in the figure, the pneumatic tire 100 includes four main grooves 110 and 111 that are bent in a zigzag shape and extend in the tire circumferential direction (vertical direction in the figure), and five rows of land portions 120 that are partitioned by the main grooves 110 and 111. , 121, 122.

  In the pneumatic tire 100, a plurality of lug grooves 112 extending in the tire width direction (left-right direction in the drawing) and the like extending in the tire width direction (left-right direction in the figure) are arranged at predetermined intervals in the tire circumferential direction. These are partitioned into a plurality of blocks 120B, 121B, and 122B. Further, in each block 120B, 121B, 122B, a plurality of sipes 115 (both in this case) are arranged so as to extend substantially in the tire width direction while being bent in a zigzag manner. . Further, in the pneumatic tire 100, the blocks 120B, 121B, and 122B are formed in substantially the same or similar shape, and the phases of their arrangement positions are shifted from each other in the tire circumferential direction so that they are arranged substantially evenly on the tire tread. ing.

  In the pneumatic tire 100, the number of blocks in the tread portion and the edge component are increased by relatively shortening the arrangement interval of the main grooves 110 and 111 and the lug grooves 112, for example. In addition, a large number of sipes 115 are arranged in each of the blocks 120B, 121B, and 122B, thereby enhancing the edge effect exerted on the snow and ice road surface and improving the performance on snow and ice.

  However, as in the pneumatic tire 100, when the number of blocks is increased to reduce each of the blocks 120B, 121B, and 122B, or the number of sipes 115 is increased, the rigidity of each block is reduced and wear occurs. It tends to be easier. Therefore, in the conventional pneumatic tire 100, the wear resistance performance may be lowered, and it is difficult to achieve both the performance on ice and snow and the wear resistance performance. On the other hand, if the main grooves 110 and 111 and the lug groove 112 are narrowed (thinned) and the blocks 120B, 121B, and 122B are enlarged to cope with this, the ground contact area in the ground contact surface increases and the rigidity of the block increases. Thus, wear resistance and the like can be improved. However, in this case, the effect of discharging snow or the like in each of the grooves 110, 111, and 112 may be reduced, and sufficient performance on ice and snow may not be obtained.

In addition, conventionally, a plurality of blocks formed in the tread portion are linearly extended in the tire width direction, and two width direction sipes having both ends opened to main grooves on both sides are formed. There is also known a pneumatic tire that improves performance on ice and snow while maintaining the above (see Patent Document 2).
However, in this conventional pneumatic tire, the amount of the edge component that exerts an effect in the longitudinal direction of the vehicle is still not sufficient when traveling on ice and snow, and further improvement of performance on ice and snow is ensured while ensuring wear resistance performance. It is necessary to plan.

JP 2006-131148 A JP 2007-186121 A

  The present invention has been made in view of the above-described conventional problems, and its object is to improve the performance on ice and snow such as traction performance and braking performance on ice and snow while ensuring the wear resistance performance of the pneumatic tire. That is.

The present invention relates to a tread portion having two central main grooves disposed in the tire circumferential direction with the tire equatorial plane interposed therebetween, and a central land on the tire equatorial plane defined by the two central main grooves. And the central land portion is spaced apart in the tire circumferential direction in which one end opens in each of the central side main grooves and the other end terminates in the central land portion. The first and second lug grooves and the sipe connecting the first and second lug grooves are arranged in a plurality in the tire circumferential direction and partitioned into a plurality of large blocks. It is provided only in the central land portion, and is divided into a pair of small blocks by a circumferential sipe extending in the tire circumferential direction while being bent at least once, and in the small block, the circumferential sipe and the central side At least one width direction size opening in the main groove. And at least one each disposed between the width sipe and each lug groove, and a closed sipe that is bent at least once and extends in the tire width direction and ends in the small block. Features.

  Here, in the present invention, regarding the direction in which each groove or sipe extends, in the case of the tire circumferential direction, in addition to being parallel to the tire circumferential direction, it is inclined, curved, or bent at a predetermined angle with respect to the same direction. It extends extending including the elements of the tire circumferential direction. Similarly, in the case of the tire width direction, in addition to the case of being parallel to the tire width direction, the tire width direction includes elements in the tire width direction such as extending at a predetermined angle with respect to the same direction. It means extending.

  According to the present invention, it is possible to improve performance on ice and snow such as traction performance and braking performance on ice and snow while ensuring wear resistance performance of the pneumatic tire.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The pneumatic tire of the present embodiment is a studless tire for heavy loads such as trucks and buses and passenger cars, for example, a bead core disposed in a pair of tire bead portions, and at least one layer extending in a toroidal shape therebetween. It has a well-known tire structure including a carcass layer, a belt layer disposed on the outer peripheral side of the carcass layer of the tread portion, and a tread rubber formed with a predetermined tread pattern.

FIG. 1 is a plan view showing a developed tread pattern of the pneumatic tire of the present embodiment, and schematically shows a part in the tire circumferential direction.
As shown in the figure, this pneumatic tire 1 is provided with at least four main grooves 10 and 11 extending in the tire circumferential direction (vertical direction in the figure) in the tread portion 2, and is partitioned by them to extend in the tire circumferential direction. The existing five (5 rows) land portions 20, 21, and 22 are arranged. The pneumatic tire 1 is substantially linear in the direction intersecting the main grooves 10 and 11 disposed in the land portions 20, 21, and 22, for example, the tire width direction (left and right direction in the drawing), A plurality of lug grooves 30, 31, 32, 33, 34 extending by bending, bending or the like are provided. The pneumatic tire 1 is divided by the plurality of lug grooves 30, 31, 32, 33, 34, etc., and the land portions 20, 21, 22 are arranged in a plurality of blocks 20B, 21B arranged in the tire circumferential direction. , 22B.

  The main grooves 10 and 11 are two center-side main grooves 10 arranged across the tire equatorial plane CL, and two arranged on the tread end (tire width direction outer end) side on the outer side in the tire width direction. The outer main grooves 11 are arranged at predetermined substantially symmetrical positions in the tire width direction across the tire equatorial plane CL. The main grooves 10 and 11 are straight grooves that are slightly bent at a predetermined pitch and extend substantially linearly in the tire circumferential direction, and the groove width and the depth in the tire radial direction are substantially the same or similar. Is formed.

  The land portions 20, 21, 22 are partitioned by two central side main grooves 10, and the central land portion 20 located on the tire equatorial plane CL between them, the central side main groove 10, and the outer main groove 11 Between the two intermediate land portions 21 located in an intermediate region between them, and the outermost side in the tire width direction defined between the outer main groove 11 and the tread end (shoulder portion side) ) And two shoulder land portions 22 located in the middle. The width in the tire width direction of each of the land portions 20, 21, 22 corresponds to the arrangement of the main grooves 10, 11, etc. that divide them, and the central land portion 20 is the widest, the shoulder land portion 22, the intermediate land portion Narrow in the order of 21.

  The central land portion 20 includes a plurality of first lug grooves 30 and second lug grooves 31 extending substantially in the tire width direction, two types of sipes 40 and 41 extending substantially in the tire circumferential direction, and an approximate tire width. Two types of sipes 42 and 43 extending in the direction are repeatedly arranged in a predetermined pattern in the tire circumferential direction.

  Each of the first and second lug grooves 30 and 31 has an opening in each of the central main grooves 10 on both sides (in the drawing, the first lug groove 30 is on the left side and the second lug groove 31 is on the right side. The central side main groove 10 is opened), and the other end is formed in a predetermined length so as to terminate in the central land portion 20, and are arranged apart from each other in the tire circumferential direction. Further, the plurality of first lug grooves 30 and second lug grooves 31 are arranged at predetermined substantially identical intervals in the tire circumferential direction, respectively, and their arrangement positions (phases) are shifted in the tire circumferential direction, They are alternately arranged on the left and right along the tire circumferential direction. Further, the first and second lug grooves 30 and 31 are formed to have substantially the same groove width narrower than that of the main grooves 10 and 11, and each of the first and second lug grooves 30 and 31 extends inward in the tire width direction from the opening on the center side main groove 10 side. And terminates at or near the tire equatorial plane CL.

  In the present embodiment, the first and second lug grooves 30 and 31 are formed so as to extend in a substantially straight line inclined in the same direction with respect to the tire width direction and at a predetermined angle from the tire width direction. ing. Further, the plurality of first and second lug grooves 30 and 31 are formed symmetrically with respect to a point on the tire equatorial plane CL. In addition, the interval between the first lug groove 30 and the second lug groove 31 adjacent to each other in the tire circumferential direction is narrow on one side across the lug grooves 30, 31, and wide on the other side. Are alternately arranged along the tire circumferential direction.

  Sipes 40 and 41 arranged alternately along the tire circumferential direction are opened at the end portions of the first lug groove 30 and the second lug groove 31, respectively. These sipes 40 and 41 are located at substantially the center position in the tire width direction of the central land portion 20 (on the tire equatorial plane CL) and between the first and second lug grooves 30 and 31 adjacent to each other in the tire circumferential direction. Arranged in order. The two types of sipes 40 and 41 are provided on one side where the distance between the lug grooves 30 and 31 is narrow, and are mainly used to connect the first and second lug grooves 30 and 31 to each other. 40 and a circumferential sipe 41 that is provided on the other side having a large interval between the lug grooves 30 and 31 and mainly divides each block 20B in the central land portion 20 in the tire width direction. The connecting sipes 40 extend substantially linearly in the tire circumferential direction or inclined or curved at a predetermined angle (inclined in the upper right direction here), and the end portions of the lug grooves 30 and 31 near the tire equatorial plane CL. They are connected to each other, and together with them, the central land portion 20 is traversed in the tire width direction as a whole. On the other hand, the circumferential sipe 41 has a zigzag shape, a wave shape, or a meandering bent shape (here, these shapes are collectively referred to as a bend), and the tire circumferential direction is bent once or more (one bend). In addition, the lug grooves 30 and 31 extend at a predetermined angle in the same direction and open at the end portions of the lug grooves 30 and 31 near the tire equatorial plane CL.

  In the present embodiment, a plurality of sets of the connecting sipes 40 and the pair of first and second lug grooves 30 and 31 connected via the connecting sipes 40 are arranged at a predetermined interval in the tire circumferential direction, and thereby, the central land The portion 20 is divided in the tire circumferential direction and partitioned into a plurality of relatively large blocks 20B. Further, the large sipe 41 divides the large block 20B into two small blocks 20S having a substantially rectangular shape in a plan view and arranged to be shifted in the tire circumferential direction across the tire equatorial plane CL. It is divided into a pair of small blocks 20S. In FIG. 1, one large block 20 </ b> B is hatched with diagonal lines, and a pair of divided small blocks 20 </ b> S are hatched with diagonal lines inclined in opposite directions.

FIG. 2 is an enlarged plan view showing an area including one large block 20 </ b> B of the central land portion 20.
In the pneumatic tire 1, as shown in the figure, each of the left and right small blocks 20S includes at least one width-direction sipe 42 and closed sipe 43 provided on both sides in the tire circumferential direction with the two in between. A plurality of sipes 42 and 43 are further arranged. The width-direction sipe 42 is a both-side opening sipe whose ends on both sides open to the circumferential sipe 41 and the central main groove 10 that define the small blocks 20S, respectively. Alternatively, it extends by bending or the like, and is divided in the tire circumferential direction across the small block 20S. Here, two sipe 42 in the width direction are arranged at approximately the center in the tire circumferential direction of each small block 20S, and they are inclined in the same direction with respect to the tire width direction so as to be substantially spaced apart from each other. They are formed in parallel.

  On the other hand, the closed sipe 43 is a sipe that is bent at least once and extends in the tire width direction as a whole, with both ends terminating in the small block 20S and closed at both ends. At least one is arranged between each lug groove 30 or 31 on both sides in the tire circumferential direction. Here, the closed sipe 43 has two tires in the tire circumferential direction between the widthwise sipe 42 and the lug groove 30 or 31, one on each side across the two widthwise sipes 42. Inclined as a whole in the same direction with respect to the direction. In this pneumatic tire 1, the sipes 42 and 43 in the central land portion 20 are all formed so as to be inclined in the same direction (here, the same direction as the lug grooves 30 and 31) with respect to the tire width direction. Four sipes 42 and 43 are arranged in each small block 20S.

  On the other hand, the middle land portion 21 (see FIG. 1) on both outer sides in the tire width direction of the central land portion 20 includes a plurality of lug grooves 32 extending in the substantially tire width direction and two types of sipes 44 and 45, respectively. They are repeatedly arranged in a predetermined pattern in the tire circumferential direction. Each lug groove 32 is formed to have a narrower groove width than the main grooves 10 and 11 and incline in the tire width direction, and both ends of the main grooves 10 on both sides sandwiching the intermediate land portion 21. , 11 and cross the intermediate land portion 21 in the tire width direction. Here, the lug grooves 32 are inclined at a predetermined angle in the same direction with respect to the tire width direction at the middle land portions 21 on the left and right sides, and with respect to the lug grooves 30 and 31 in the central land portion 20 and the tire width direction. Are arranged in parallel in the tire circumferential direction at a predetermined interval substantially the same as the arrangement interval in each tire circumferential direction.

  The intermediate land portion 21 is divided by the plurality of lug grooves 32 in the tire circumferential direction and is partitioned into a plurality of blocks 21B having substantially the same shape. Further, in each block 21B, as in the small block 20S (see FIG. 2), at least one width-direction sipe 44, and closed sipe 45 provided on both sides in the tire circumferential direction across them. A plurality of sipes 44 and 45 are arranged. The width-direction sipe 44 is a both-side opening sipe whose end portions on both sides open to the central main groove 10 and the outer main groove 11 on both sides, respectively, and is straight, inclined, bent, or the like substantially in the tire width direction. It extends and crosses the block 21B and is divided in the tire circumferential direction. Here, two sipe 44 in the width direction are arranged at approximately the center in the tire circumferential direction of each block 21B, and they are inclined in the same direction with respect to the tire width direction so as to be substantially parallel to each other with a predetermined interval therebetween. And a pair of small blocks are defined on both sides thereof.

  On the other hand, the closed sipe 45 is a sipe that is bent at least once and extends in the tire width direction as a whole and has both ends terminated in the block 21B. At least one each is arranged between the lug grooves 32 on both sides in the tire circumferential direction. Here, one closed sipe 45 is provided in each of the small blocks on both sides across the two widthwise sipes 44, respectively, at the substantially central portion in the tire circumferential direction between the widthwise sipes 44 and the lug grooves 32. It is inclined as a whole in the same direction with respect to the width direction. In this pneumatic tire 1, the sipes 44 and 45 in the intermediate land portion 21 are formed so as to all be inclined in the same direction with respect to the tire width direction, and four each are arranged in each block 21 </ b> B. . Further, both sipes 44 and 45 extend in the same direction as the lug groove 32 in the intermediate land portion 21 and on both sides of the central land portion 20 in the same direction relative to the tire width direction. It is formed at a predetermined angle.

  Further, the shoulder land portion 22 on both outer sides in the tire width direction of each intermediate land portion 21 includes a plurality of lug grooves 33 and 34 extending in a direction intersecting with the outer main groove 11, a circumferential narrow groove 50, and Three types of sipes 46, 47, and 48 are repeatedly arranged in a predetermined pattern in the tire circumferential direction. Each lug groove 33, 34 extends incline in the tire width direction, and both ends open to the outer main groove 11 and the tread end side, respectively, and cross the shoulder land portion 22 in the tire width direction. Among these, one lug groove 33 is formed such that the end portion on the outer side in the tire width direction is widened in the same direction with respect to the inner side in the tire width direction where the groove width is narrower than that of the main grooves 10 and 11. The entire lug groove 34 is formed to have a narrower groove width than the main grooves 10 and 11. The lug grooves 33 and 34 are alternately arranged along the tire circumferential direction at a predetermined interval substantially the same as the arrangement interval of the other lug grooves 30, 31 and 32, and the shoulder land portion 22 is divided in the tire circumferential direction. Are divided into a plurality of blocks 22B.

  Each block 22B is divided at a substantially central portion in the tire width direction by a circumferential narrow groove 50 extending linearly in the tire circumferential direction, and is divided into an outer small block 22S1 and an inner small block 22S2 on the outer and inner sides in the tire width direction. Partitioned. In addition, each of the outer small blocks 22S1 has one sipe 46, one end of which opens into the wide portion of the lug groove 33, extends and inclines in the tire circumferential direction, then bends, and extends substantially linearly in the same direction. The other end is formed to terminate in the outer small block 22S1.

  On the other hand, each of the inner small blocks 22S2 includes at least one width-direction sipe 47 and closed sipe 48 provided on both sides in the tire circumferential direction with the at least one width-direction sipe 47 interposed therebetween. The configuration is similar to that of FIG. That is, the width-direction sipe 47 is a both-side opening sipe whose ends on both sides open to the outer main groove 11 and the circumferential narrow groove 50, respectively, and extends substantially incline in the tire width direction, and the inner small block 22S2. Is divided in the tire circumferential direction. Here, two width-direction sipes 47 are disposed at approximately the center portion of each inner small block 22S2 in the tire circumferential direction, and they are formed substantially in parallel to be inclined in the same direction with respect to the tire width direction. The inner small block 22S2 is further partitioned.

  The closed sipe 48 is a sipe that is bent at least once and extends in the tire width direction as a whole, with both ends terminating in the inner small block 22S2, and both ends closed. At least one is arranged between each of the lug grooves 33 and 34 on both sides. Here, the closed sipe 48 has one tire on both sides across the two widthwise sipes 47, and the tire width at the substantially central portion in the tire circumferential direction between the widthwise sipes 47 and the lug grooves 33 and 34, respectively. Inclined in the same direction with respect to the direction. In the pneumatic tire 1, the sipes 47 and 48 in the inner small block 22S2 are all inclined in the same direction with respect to the tire width direction, and in the substantially same direction as the lug grooves 33 and 34, and in the central land portion 20 The lug grooves 30 and 31 are formed so as to extend in substantially the same direction with respect to the tire width direction.

  In the pneumatic tire 1, the tire radial depths of the sipes 40 to 48 are all in the range of 50 to 100% of the tire radial depth of the central main groove 10 (and the outer main groove 11). It is formed to the depth of. Further, the phases of the first lug groove 30 and the second lug groove 31 in the central land portion 20, the lug groove 32 in the intermediate land portion 21, and the lug grooves 33 and 34 in the shoulder land portion 22 are set to each other. The tires are shifted in the circumferential direction by a predetermined distance, and the arrangement positions in the respective tire circumferential directions are sequentially shifted in the tire circumferential direction. Further, here, each main groove 10, so that the maximum width V of the intermediate land portion 21 in the tire width direction is in the range of 40 to 75% of the maximum width W of the central land portion 20 in the tire width direction. 11 is disposed to form land portions 20, 21, and 22.

  In the pneumatic tire 1 of the present embodiment described above, the central land portion 20 is partitioned into a relatively large block 20B by a plurality of sets of lug grooves 30, 31 and connecting sipes 40. Therefore, the block rigidity is also relatively high. And a sufficient edge component and edge amount (length) can be secured. Further, since each large block 20B is divided into small blocks 20S by the bent circumferential sipe 41, the edge components in the large block 20B can be further increased. At the same time, due to the shape of the circumferential sipe 41, when a force such as rolling under load is applied, the small blocks 20S on both sides sandwiching the sipe 41 are deformed from each other by contact with the bent sipe wall. It is possible to obtain the effect of suppressing the collapse and the like. Due to the mutual complementary effect between the adjacent small blocks 20S, it is possible to prevent the block rigidity from being lowered.

  In addition, in the pneumatic tire 1, a plurality of sipes each including a width-direction sipe 42 having both sides opened in each small block 20S and a bent sipe 43 having a large amount of edges that hardly reduce block rigidity. 42 and 43 are arranged. Therefore, the number of sipes in the large block 20B and the length of the large block 20B and the edge component that exerts an effect in the vehicle front-rear direction in running on ice and snow are increased, and the block effect is reduced while enhancing the edge effect. Can also be suppressed. Further, here, the small blocks 20S are arranged in two rows centering on the tire equatorial plane CL, and thus include the tire equatorial plane CL that has the longest contact length in the tire circumferential direction and has the greatest effect on the performance on ice and snow. Edge components extending in the tire width direction are concentrated in the center portion. As a result, in addition to maintaining the block rigidity, it is possible to effectively improve the performance on ice and snow.

  As described above, generally, when the edge length is increased, the block becomes smaller and the block rigidity is lowered. As a result, the wear resistance performance including uneven wear resistance is degraded. Then you can avoid them. That is, in the pneumatic tire 1, as described above, even if the edge component in the central land portion 20 that affects the performance on ice and snow is increased, it is possible to suppress the rigidity of the large block 20B from being lowered and wear occurs. The trouble which becomes easy can be prevented and the fall of wear resistance performance can be controlled. Therefore, according to the present embodiment, it is possible to improve the performance on ice and snow such as traction performance and braking performance on the snow and ice while ensuring sufficient wear resistance performance for the pneumatic tire 1 and to make them compatible with each other. it can.

  In the pneumatic tire 1, the intermediate land portion 21 and the shoulder land portion 22 are similarly divided into a plurality of blocks 21 </ b> B and 22 </ b> B, and a plurality of sipes 44 to 48 are arranged, which is sufficient as a studless tire. The edge amount (edge effect) can be ensured. Further, the block 21B of the intermediate land portion 21 is divided into small blocks by the width-direction sipes 44, and at least one bent-shaped closed sipe 45 is disposed in each small block on both sides thereof, so that the rigidity of the block 21B is reduced. It is possible to obtain a larger edge effect while suppressing.

  In addition, since the inclining direction with respect to the tire width direction of each of the lug grooves 30 to 34 is alternately formed in different directions for each of the land portions 20, 21, and 22, the edge effect is exhibited even in different directions, The performance can be improved effectively. Moreover, in this pneumatic tire 1, since each phase (arrangement position in the tire circumferential direction) of each of the lug grooves 30 to 34 is shifted from each other in the tire circumferential direction, the blocks 20B, 21B, 22B and the like are also different. It arrange | positions at a tire circumferential direction position. As a result, each element in the tread portion 2 is grounded sequentially at the time of tire rolling, and the edge effect is continuously exhibited, so that high performance on ice and snow can be constantly obtained.

  Here, when the maximum width V of the intermediate land portion 21 in the tire width direction is narrower than 40% of the maximum width W of the central land portion 20 in the tire width direction, the width of the intermediate land portion 21 is reduced. As a result, the rigidity of the block 21 </ b> B decreases, and there is a risk that uneven wear tends to occur in the intermediate land portion 21. On the other hand, when the maximum width V is made wider than 75% of the maximum width W, conversely, the width of the central land portion 20 becomes narrower, the rigidity of the block 20B decreases, and the central land portion 20 is biased. Wear may easily occur. Therefore, it is more desirable that the maximum width V of the intermediate land portion 21 is in the range of 40 to 75% of the maximum width W of the central land portion 20, thereby improving the wear resistance performance of the land portions 20 and 21. Both can be secured.

  Further, when the tire radial depth of each sipe 40 to 48 is shallower than 50% of the tire radial depth of the main grooves 10 and 11, the sipe 40 to 48 is brought into an early stage with wear of the tread portion 2. It may become shallower or disappear, and the performance on ice and snow may be reduced. In addition, the deformation of the blocks 20B, 21B, and 22B on which they are formed becomes smaller than necessary, and traction loss is likely to occur when traveling on a snowy and snowy road surface. is there. On the other hand, if the depth is deeper than 100%, the rigidity of each block becomes too low and the grounding property is lowered, the performance on ice and snow such as traction performance and brake performance is lowered, or sufficient resistance Wear performance may not be ensured. Therefore, each sipe 40 to 48 is more preferably formed to a depth in the range of 50 to 100% of the depth of the main grooves 10 and 11.

  In the present embodiment, each of the main grooves 10 and 11 is formed as a straight groove extending substantially linearly in the tire circumferential direction. For example, these main grooves 10 and 11 are bent in a zigzag shape with a larger amplitude in the tire width direction. For example, it may be formed to extend in the tire circumferential direction in another manner. However, when the main grooves 10 and 11 are formed as straight grooves, the snow drainage becomes higher and the performance on the snow of the pneumatic tire 1 can be further improved. Therefore, the main grooves 10 and 11 are formed as such. It is more desirable to do. Further, in this pneumatic tire 1, the sipes 40 and 41 in the central land portion 20 are arranged on the tire equatorial plane CL, but they are arranged at other positions in the tire width direction, such as being shifted in the tire width direction. May be. Furthermore, in the small block 20S of the central land portion 20, in addition to one closed sipe 43 disposed on both sides of the width direction sipe 42, a plurality of pieces may be disposed. Depending on the position and the like, different numbers of closed sipes 43 may be arranged on both sides thereof.

(Tire test)
In order to confirm the effect of the present invention, the pneumatic tire 1 of the embodiment (hereinafter referred to as an implementation product) having the tread pattern (see FIG. 1) described above and the conventional tread pattern (see FIG. 3) described above are used. A pneumatic tire 100 (hereinafter referred to as a conventional product) of a conventional example (comparative example) provided was made as a prototype, and a comparative test between performance on ice and snow and wear resistance performance was performed under the following conditions. Both the implementation product and the conventional product are radial ply tires for trucks and buses having a tire size of 11R22.5-16PR defined by JATMA YEAR BOOK (2007, Japan Automobile Tire Association Standard).

  In each test, the actual product and the conventional product were mounted on a rim of size 7.50 and the air pressure was set to 900 kPa, respectively, and 2-D · 4 (the front wheel was one shaft of two wheels, the rear wheel was a driving double wheel and a double wheel). It was attached to a vehicle with two wheels (two shafts) and a normal load was applied. Further, the performance on ice and snow was evaluated by testing the traction performance on ice and the brake performance on ice of the implemented product and the conventional product when new.

  On the ice traction performance test, on the test course (ice surface), the vehicle was started from a stopped state and the acceleration was measured, and the measurement results were compared and evaluated based on the conventional products. In addition, on-ice brake performance test is a test course (ice road surface) where the braking distance when a vehicle running at a predetermined speed is fully braked is measured to determine the deceleration, and the result is compared with the conventional product. evaluated. On the other hand, in the wear resistance performance test, the test course (dry road surface) is run under the same conditions with each new tire, the wear life (life) at that time is measured, and the result is compared with the conventional product as a reference. evaluated.

  Table 1 shows the results of these tests, all of which are expressed as an index with the result of the conventional product taken as 100, and the larger the value, the better the result and the higher the performance.

  As a result, as shown in Table 1, the starting acceleration index was as large as 115 in the actual product compared to 100 in the conventional product, and it was found that the traction performance on ice was greatly improved. Moreover, the deceleration index was as large as 115 for the actual product compared to 100 for the conventional product, indicating that the braking performance on ice was greatly improved. On the other hand, the wear life index was 101 for the actual product compared to 100 for the conventional product, and it was found that the wear resistance performance can be maintained at the same level.

  From the above results, it was proved by the present invention that the performance on ice and snow such as traction performance and brake performance on ice and snow can be improved while ensuring the wear resistance performance of the pneumatic tire 1.

It is a top view which expands and shows the tread pattern of the pneumatic tire of this embodiment. It is a top view which expands and shows the area | region containing one large block of a central land part. It is a top view which expands and shows an example of the tread pattern of the conventional pneumatic tire.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Pneumatic tire, 2 ... Tread part, 10 ... Central side main groove, 11 ... Outer side main groove, 20 ... Central land part, 20B ... Large block, 20S ...・ Small block, 21 ... Middle land, 21B ... Block, 22 ... Shoulder land, 22B ... Block, 22S1 ... Outer small block, 22S2 ... Inner small block, 30 ..Lug groove, 31 ... Lug groove, 32 ... Lug groove, 33 ... Lug groove, 34 ... Lug groove, 40 ... Connection sipe, 41 ... Circumferential sipe, 42 ..Sipe in the width direction, 43 ... Closed sipe, 44 ... Width sipe, 45 ... Closed sipe, 46 ... Sipe, 47 ... Sipe in the width direction, 48 ... Closed sipe, 50 ... circumferential narrow groove, CL: tire equatorial plane.

Claims (6)

Two central main grooves extending in the tire circumferential direction disposed across the tire equatorial plane in the tread portion, and a central land portion on the tire equatorial plane partitioned by the two central main grooves, A pneumatic tire provided,
The central land portion includes first and second lug grooves that are spaced apart from each other in the tire circumferential direction, with one end opening in each of the central side main grooves and the other end terminating in the central land portion, A plurality of sipes connecting the first and second lug grooves are arranged in the tire circumferential direction and partitioned into a plurality of large blocks,
The large block is provided only in the central land portion, and is divided into a pair of small blocks by a circumferential sipe extending in the tire circumferential direction while bending one or more times.
In the small block, at least one width-direction sipe opening to the circumferential sipe and the central main groove is disposed between the width-direction sipe and each lug groove. A pneumatic tire comprising: a closed sipe that is bent at least twice and extends in the tire width direction and ends in the small block. In the pneumatic tire according to claim 1,
A pneumatic tire comprising one closed sipe between each of the width direction sipes and each of the lug grooves. In the pneumatic tire according to claim 1 or 2,
Two outer main grooves extending in the tire circumferential direction, which are respectively arranged on the outer sides in the tire width direction of the respective central main grooves, and two intermediate lands partitioned between the central main grooves and the outer main grooves With
The intermediate land portion is partitioned into a plurality of blocks by a plurality of lug grooves extending in the tire width direction, and at least one width direction sipe that opens into the central main groove and the outer main groove in the block; A closed sipe that is disposed between the sipe in the width direction and the lug grooves on both sides and that is bent at least once and extends in the tire width direction and ends in the block. And pneumatic tires. In the pneumatic tire according to claim 3,
The pneumatic tire according to claim 1, wherein a maximum width in the tire width direction of the intermediate land portion is in a range of 40 to 75% of a maximum width in the tire width direction of the central land portion. In the pneumatic tire according to any one of claims 1 to 4,
A pneumatic tire characterized in that a tire radial depth of each sipe is in a range of 50 to 100% of a tire radial depth of the central main groove. In the pneumatic tire according to any one of claims 1 to 5,
The pneumatic tire is characterized in that the phases of the lug grooves are arranged so as to be shifted from each other in the tire circumferential direction.

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