JP6340057B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire with improved wear resistance while maintaining on-ice performance.

  Conventionally, in order to improve running performance on ice (hereinafter referred to as performance on ice), a pneumatic tire having a sipe provided on a block has been proposed (for example, see Patent Document 1 below). Such a pneumatic tire has improved performance on ice due to the sipe edge effect and the water absorption effect.

JP 2009-190677 A

  However, the block provided with sipes has a low rigidity. The block having low rigidity has a problem that deformation during traveling is large and wear easily. If the length and depth of the sipe are reduced in order to improve the wear resistance performance of the block, there is a problem that the performance on ice decreases.

  The present invention has been devised in view of the above circumstances, and provides a pneumatic tire capable of improving wear resistance performance while maintaining on-ice performance based on the improvement of sipes and tie bars in the block. The main purpose is to do.

  The present invention is a pneumatic tire in which a tread portion is provided with a block divided by a longitudinal groove extending in the tire circumferential direction and a lateral groove extending in the tire axial direction, the block extending in the tire axial direction, and A plurality of sipes having both ends opened at block edges on both sides in the tire axial direction, the sipe having a depth including a base portion having a substantially constant depth and a shallow bottom portion having a depth smaller than the base portion. The depth change sipe includes a first depth change sipe and a second depth change sipe, and the shallow bottom portion of the first depth change sipe includes the second depth sipe. The lateral sipe is opposed to the base of the sipe in the tire circumferential direction, the lateral groove includes a tie bar having a raised groove bottom surface, and the tie bar is adjacent to the base of the depth sipe in the tire circumferential direction and the tire circumferential direction. Face, characterized in that is.

  In the pneumatic tire according to the present invention, the block is provided on both sides in a tire circumferential direction across a lateral groove, and the lateral groove includes a main portion having a depth larger than that of the tie bar. It is desirable to face the shallow bottom portion of each of the depth changing sipes adjacent on both sides in the circumferential direction.

  In the pneumatic tire according to the present invention, a shoulder main groove extending continuously in the tire circumferential direction at the tread ground end side most continuously on the tread portion, and continuously in the tire circumferential direction on the outer side in the tire axial direction than the shoulder main groove. And a shoulder narrow groove having a groove width smaller than that of the shoulder main groove, thereby providing an inner shoulder land portion between the shoulder main groove and the shoulder narrow groove, and a tire shaft of the shoulder narrow groove. An outer shoulder land portion that is separated from an outer side of the direction, and the lateral groove includes an inner shoulder lateral groove that extends between the shoulder main groove and the shoulder narrow groove, and an outer side that extends between the shoulder narrow groove and the tread grounding end. It is desirable that the inner shoulder lateral groove and the outer shoulder lateral groove are misaligned in the tire circumferential direction.

  In the pneumatic tire according to the present invention, the outer shoulder land is provided with an outer shoulder sipe extending from the outer edge in the tire axial direction toward the inner side in the tire axial direction and terminating in the outer shoulder land. It is desirable.

  In the pneumatic tire according to the present invention, it is desirable that the outer shoulder sipe bends and terminates in the tire circumferential direction within the outer shoulder land portion.

  The block of the pneumatic tire of the present invention is provided with a plurality of sipes extending in the tire axial direction and having both ends opened at the block edges on both sides in the tire axial direction. Such a sipe exhibits an excellent edge effect and water absorption effect, and improves the performance on ice.

  The sipe includes a plurality of depth changing sipes including a base portion having a substantially constant depth and a shallow bottom portion having a depth smaller than the base portion. Such a depth changing sipe reinforces the rigidity of the block by the shallow bottom while exhibiting an edge effect. For this reason, the wear resistance performance of the block is improved while maintaining the performance on ice.

  The depth change sipe includes a first depth change sipe and a second depth change sipe. The shallow bottom portion of the first depth changing sipe faces the base portion of the second depth changing sipe in the tire circumferential direction. Thereby, the rigidity fall of the block by the base of the 2nd depth change sipe is suppressed by the shallow bottom part of the 1st depth change sipe. Therefore, such a depth-changing sipe further improves the wear resistance performance while making the rigidity distribution of the block uniform.

  The lateral groove includes a tie bar having a raised groove bottom surface. The tie bar faces the base of the depth changing sipe adjacent in the tire circumferential direction in the tire circumferential direction. Thereby, a tie bar is provided in the vicinity of the base of the depth changing sipe with relatively large rigidity reduction. Therefore, the rigidity distribution of the tread portion becomes uniform, and the wear resistance performance is further improved.

  As described above, the pneumatic tire of the present invention can improve wear resistance while maintaining on-ice performance.

It is an expanded view of the tread part of the pneumatic tire of this embodiment. It is AA sectional drawing of FIG. It is the elements on larger scale of the center block of FIG. (A) is BB sectional drawing of FIG. 3, (b) is CC sectional drawing of FIG. It is DD sectional drawing of FIG. It is the elements on larger scale of the middle land part of FIG. It is the elements on larger scale of the inner side shoulder land part of FIG. It is the elements on larger scale of the outer side shoulder land part of FIG. It is the elements on larger scale of the block of other embodiments. (A) is EE sectional drawing of FIG. 9, (b) is FF sectional drawing of FIG. It is an expanded view of the tread part of other embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a pneumatic tire (hereinafter sometimes simply referred to as “tire”) 1 of the present embodiment. The pneumatic tire 1 of the present embodiment is suitably used as a heavy duty pneumatic tire for winter, for example. The tread portion 2 of the tire 1 is provided with a longitudinal groove 3 extending in the tire circumferential direction.

  The longitudinal groove 3 of the present embodiment includes a pair of center main grooves 4, a pair of shoulder main grooves 5, and a pair of shoulder narrow grooves 6.

  The center main groove 4 is provided on both sides of the tire equator C. The center main groove 4 extends continuously in the tire circumferential direction. The center main groove 4 of the present embodiment has a zigzag shape. The center main groove 4 may be linear.

  The shoulder main groove 5 is provided outside the center main groove 4 in the tire axial direction. The shoulder main groove 5 extends continuously in the tire axial direction. The shoulder main groove 5 of the present embodiment has a zigzag shape. The shoulder main groove 5 may be linear.

  FIG. 2 is a cross-sectional view taken along the line AA in FIG. As shown in FIG. 2, the groove width W1 of the center main groove 4 (meaning the groove width perpendicular to the center line of the groove) and the groove depth d1, and the groove width W2 and the groove depth of the shoulder main groove 5 are shown. The length d2 is variously determined according to the custom. However, when these groove widths or groove depths are small, the performance on ice and the performance on snow may be deteriorated. On the contrary, when these groove widths or groove depths are large, the rigidity of the tread portion 2 is lowered, and the steering stability performance may be lowered. For this reason, the groove width W1 of the center main groove 4 and the groove width W2 of the shoulder main groove 5 are preferably 3 to 7% of the tread grounding width TW, for example. The groove depth d1 of the center main groove 4 and the groove depth d2 of the shoulder main groove 5 are preferably, for example, 14.5 to 24.5 mm.

  The tread contact width TW is a distance in the tire axial direction between the tread contact ends Te and Te. The tread grounding end Te means a grounding end on the outermost side in the tire axial direction when a normal load is loaded on a normal tire and grounded on a flat surface with a camber angle of 0 degree.

  The “normal state” is a no-load state in which the tire 1 is assembled to a normal rim (not shown) and filled with a normal internal pressure. In the present specification, unless otherwise specified, the dimension of each part of the tire 1 is a value measured in a normal state.

  The “regular rim” is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, “Standard Rim” for JATMA, “Design Rim” for TRA, For ETRTO, "Measuring Rim".

  “Regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum value described in “VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO.

  “Regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. “JATMA” is “Maximum load capacity”, TRA is “TIRE LOAD LIMITS” The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”, “LOAD CAPACITY” in the case of ETRTO.

  As shown in FIG. 1, the shoulder narrow grooves 6 and 6 are provided outside the shoulder main groove 5 in the tire axial direction. The shoulder narrow groove 6 extends linearly continuously in the tire circumferential direction.

  As shown in FIG. 2, the groove width W <b> 3 of the shoulder narrow groove 6 is smaller than the groove width W <b> 2 of the shoulder main groove 5. The groove width W3 of the shoulder narrow groove 6 is preferably 0.10 to 0.15 times the groove width W2 of the shoulder main groove 5. Further, the groove depth d3 of the shoulder narrow groove 6 is preferably 0.50 to 0.70 times the groove depth d2 of the shoulder main groove 5. Such a shoulder narrow groove 6 increases the rigidity of the outer side in the tire axial direction of the tread portion 2 and improves the steering stability performance.

  As shown in FIG. 1, by providing the vertical groove 3 described above, the tread portion 2 includes a center land portion 7, a middle land portion 8, an inner shoulder land portion 9, and an outer shoulder land portion 10. Is divided.

  The center land portion 7 is provided between the pair of center main grooves 4. The middle land portion 8 is provided between the center main groove 4 and the shoulder main groove 5. The inner shoulder land portion 9 is provided between the shoulder main groove 5 and the shoulder narrow groove 6. The outer shoulder land portion 10 is provided between the shoulder narrow groove 6 and the tread grounding end Te.

  The tread portion 2 is further provided with a lateral groove 20 extending in the tire axial direction. The lateral groove 20 of the present embodiment includes a center lateral groove 21, a middle lateral groove 22, an inner shoulder lateral groove 23, and an outer shoulder lateral groove 24.

  The center lateral groove 21 communicates between the pair of center main grooves 4. The center lateral groove 21 extends linearly with a substantially constant width. The center lateral groove 21 is inclined with respect to the tire axial direction.

  The middle lateral groove 22 communicates between the center main groove 4 and the shoulder main groove 5. The middle lateral groove 22 extends linearly with a substantially constant width. The middle lateral groove 22 is inclined with respect to the tire axial direction.

  The inner shoulder lateral groove 23 communicates between the shoulder main groove 5 and the shoulder narrow groove 6. The inner shoulder lateral groove 23 extends linearly with a substantially constant width. The inner shoulder lateral groove 23 is inclined with respect to the tire axial direction.

  The outer shoulder lateral groove 24 communicates between the shoulder narrow groove 6 and the tread grounding end Te. The outer shoulder lateral groove 24 is substantially parallel to the tire axial direction. The outer shoulder lateral groove 24 includes, for example, a first outer shoulder lateral groove 24A and a second outer shoulder lateral groove 24B. The first outer shoulder lateral groove 24A has a substantially constant groove width. The second outer shoulder lateral groove 24B has a groove width that gradually increases toward the outer side in the tire axial direction.

  In the tire 1 of the present invention, a block 30 divided by a vertical groove 3 and a horizontal groove 20 is provided in the tread portion 2. The block 30 of this embodiment includes a center block 31, a middle block 32, an inner shoulder block 33, and an outer shoulder block 34. The center block 31 is divided by the center main groove 4 and the center lateral groove 21. The middle block 32 is divided into a center main groove 4, a shoulder main groove 5, and a middle lateral groove 22. The inner shoulder block 33 is divided by a shoulder main groove 5, a shoulder narrow groove 6, and an inner shoulder lateral groove 23. The outer shoulder block 34 is divided by a shoulder narrow groove 6 and an outer shoulder lateral groove 24.

  FIG. 3 shows a partially enlarged view of the block 30 of the present invention. FIG. 3 shows a center block 31 as the block 30. As shown in FIG. 3, the block 30 is provided with a plurality of sipes 40. In this specification, “sipe” means a cut having a width of 0.5 to 1.5 mm, and is distinguished from a drainage groove.

  The number Ns of sipes 40 provided in one block 30 is preferably 2 to 4, more preferably 2 to 3. In the present embodiment, two sipes 40 are provided in one block 30. Thereby, the outstanding edge effect is exhibited, without causing the rigidity reduction of the block 30. Therefore, the tire of the present embodiment achieves both on-ice performance and wear resistance performance.

  The sipe 40 extends in the tire axial direction. The sipe 40 of the present embodiment is, for example, wavy. Such a sipe 40 has a substantial length and improves water absorption performance. In addition, such a sipe 40 exhibits an edge effect in multiple directions, and the performance on ice is improved.

  Both ends 40e and 40e of the sipe 40 are opened at block edges 30e and 30e on both sides in the tire axial direction, respectively. Such a sipe 40 exhibits an excellent edge effect. Moreover, since the sipe 40 is opened at the block edge 30e, the sucked water is quickly discharged to the longitudinal groove 3 side during wet running. Therefore, such a sipe 40 exhibits an excellent water absorption effect.

  The sipe 40 includes a plurality of depth changing sipes 45 whose depths change.

  4A and 4B are sectional views of the depth changing sipe 45. FIG. As shown in FIG. 4A, the depth changing sipe 45 includes a base portion 46 and a shallow bottom portion 47.

  The base 46 has a substantially constant depth d4. The depth d4 of the base 46 is preferably 0.5 times or more, more preferably 0.55 times or more, and preferably 0.70 times or less the groove depth d1 (shown in FIG. 2) of the center main groove 4. More preferably, it is 0.60 times or less. Such a base 46 exhibits excellent water absorption performance while maintaining the rigidity of the block 30.

  The shallow bottom portion 47 has a depth d5 smaller than that of the base portion 46. The depth changing sipe 45 including the shallow bottom portion 47 reinforces the rigidity of the block 30 by the shallow bottom portion 47 while exhibiting an edge effect. For this reason, the wear resistance performance of the block 30 is improved while maintaining the performance on ice.

  The ratio d5 / d4 between the depth d5 of the shallow bottom portion 47 and the depth d4 of the base portion 46 is preferably 0.24 or more, more preferably 0.30 or more, preferably 0.42 or less, more preferably 0. .36 or less. When the ratio d5 / d4 is smaller than 0.24, the bottom surface 47d of the shallow bottom portion 47 is exposed to the ground contact surface early due to wear of the block 30. For this reason, there exists a possibility that the period when the outstanding performance on ice may be exhibited becomes small. Conversely, if the ratio d5 / d4 is greater than 0.42, the rigidity of the block 30 is not reinforced, and the wear resistance performance of the block 30 may not be improved.

  The ratio L2 / L1 between the length L2 of the shallow bottom portion 47 in the tire axial direction and the length L1 of the depth changing sipe 45 in the tire axial direction is preferably 0.10 or more, more preferably 0.15 or more, Preferably it is 0.25 or less, More preferably, it is 0.20 or less. When the ratio L2 / L1 is smaller than 0.10, the effect of reinforcing the rigidity of the block 30 may be reduced. On the contrary, when the ratio L2 / L1 is larger than 0.25, when the bottom surface 47d of the shallow bottom portion 47 is exposed to the grounding surface due to wear of the block 30, the performance on ice may be greatly deteriorated.

  As shown in FIG. 3, the depth changing sipe 45 includes a first depth changing sipe 48 and a second depth changing sipe 49.

  The inter-sipe circumferential distance L3 between the first depth changing sipe 48 and the second depth changing sipe 49 is, for example, constant in the tire axial direction. The first depth changing sipe 48 and the second depth changing sipe 49 make the rigidity distribution of the block 30 uniform. Thereby, especially heel and toe wear is effectively suppressed.

  FIG. 4A is a cross-sectional view of the first depth changing sipe 48 of the present embodiment. As shown in FIG. 4A, the shallow bottom portion 47a of the first depth changing sipe 48 is provided at one end 41 in the tire axial direction of the first depth changing sipe 48.

  FIG. 4B is a cross-sectional view of the second depth changing sipe 49 of the present embodiment. As shown in FIG. 4B, the shallow bottom portion 47 b of the second depth changing sipe 49 is provided at the other end 42 in the tire axial direction of the second depth changing sipe 49.

  As shown in FIG. 4B, the shallow bottom portion 47a of the first depth changing sipe faces the base portion 46b of the second depth changing sipe 49 in the tire circumferential direction. Thereby, the rigidity reduction of the block by the base part 46b of the 2nd depth change sipe 49 is suppressed by the shallow bottom part 47a of the 1st depth change sipe. Therefore, such a depth changing sipe 45 further improves the wear resistance performance while making the rigidity distribution of the block uniform.

  As shown in FIG. 3, a plurality of blocks 30 are provided in the tire circumferential direction with the lateral groove 20 interposed therebetween.

  FIG. 5 shows a cross-sectional view of the lateral groove 20. As shown in FIG. 5, the lateral groove 20 includes a main portion 25 and a tie bar 26.

  The main portion 25 has a substantially constant depth d6. The depth d6 of the main portion 25 is preferably 0.75 times or more, more preferably 0.78 times or more, preferably 0.90 times the groove depth d1 (shown in FIG. 2) of the center main groove 4. Below, more preferably 0.85 times or less. The lateral groove 20 including the main portion 25 exhibits excellent drainage performance while maintaining the rigidity of the tread portion in the tire circumferential direction.

  The tie bar 26 is a portion where the groove bottom surface 20d of the lateral groove 20 is raised. The main portion 25 and the tie bar 26 increase the rigidity between the blocks while maintaining the drainage performance of the lateral groove 20. For this reason, steering stability is improved while maintaining wet performance.

  The ratio d7 / d6 between the depth d7 of the tie bar 26 and the depth d6 of the main portion 25 is preferably 0.65 or more, more preferably 0.75 or more, preferably 0.95 or less, more preferably 0. .85 or less. When the ratio d7 / d6 is smaller than 0.65, the bottom surface 26d of the tie bar 26 is exposed to the ground contact surface early due to wear of the block 30. For this reason, there exists a possibility that the period when the outstanding performance on ice may be exhibited becomes small. Conversely, when the ratio d7 / d6 is greater than 0.95, the rigidity between the blocks does not increase, and the steering stability may be reduced.

  The ratio L5 / L4 of the length L5 of the tie bar 26 in the tire axial direction and the length L4 of the lateral groove 20 in the tire axial direction is preferably 0.30 or more, more preferably 0.45 or more, preferably 0.00. 70 or less, more preferably 0.55 or less. When the ratio L5 / L4 is smaller than 0.30, the rigidity of the block 30 may not be increased. Conversely, if the ratio L5 / L4 is greater than 0.70, the drainage performance of the lateral groove 20 may be degraded.

  As shown in FIG. 3, the tie bar 26 faces the base 46 of the depth changing sipe 45 adjacent in the tire circumferential direction in the tire circumferential direction. Thereby, the tie bar 26 is provided in the vicinity of the base portion 46 of the depth changing sipe 45 with relatively large rigidity reduction. Therefore, the rigidity distribution of the tread portion 2 becomes uniform, and the wear resistance performance is further improved.

  In the present embodiment, the main portion 25 of the lateral groove 20 faces the shallow bottom portion 47 of each of the depth changing sipes 45 adjacent on both sides in the tire circumferential direction. Such a lateral groove 20 makes the rigidity distribution between adjacent blocks uniform, and particularly suppresses heel and toe wear.

  From the same viewpoint, it is preferable that the shallow bottom portions 47 of the depth changing sipes 45 and 45 closest to the lateral groove 20 face each other on both sides in the tire circumferential direction of the lateral groove 20.

  FIG. 6 shows a partially enlarged view of the middle land portion 8. The middle land portion 8 is a block row in which middle blocks 32 are arranged in the tire circumferential direction. The middle block 32 of the present embodiment includes first middle blocks 32A and second middle blocks 32B alternately in the tire circumferential direction. In the first middle block 32A, the inter-sipe circumferential distance L3a gradually increases toward the shoulder main groove 5 side. In the second middle block 32B, the inter-sipe circumferential distance L3b gradually increases toward the center main groove 4 side. The first middle block 32A and the second middle block 32B exhibit the edge effect of the sipe 40 in multiple directions, and particularly improve the steering stability performance on an icy road.

  FIG. 7 shows a partially enlarged view of the inner shoulder land portion 9. The inner shoulder land portion 9 is a block row in which the inner shoulder blocks 33 are arranged in the tire circumferential direction. Edge edges 33e and 33e extending in the tire axial direction on both sides in the tire circumferential direction of the inner shoulder block 33 are parallel to each other, for example.

  An edge 33o extending in the tire circumferential direction on the outer side in the tire axial direction of the inner shoulder block 33 is linear. An edge 33i extending in the tire circumferential direction on the inner side in the tire axial direction of the inner shoulder block 33 is concave on the outer side in the tire axial direction. Such an inner shoulder block 33 exhibits an excellent snow column shear force in the tire axial direction, and improves on-snow performance.

  FIG. 8 shows a partially enlarged view of the outer shoulder land portion 10. As shown in FIG. 8, the outer shoulder land portion 10 is a block row in which outer shoulder blocks 34 divided by outer shoulder lateral grooves 24 are arranged in the tire circumferential direction.

  It is desirable that the outer shoulder lateral groove 24 and the inner shoulder lateral groove 23 are misaligned in the tire circumferential direction. Such outer shoulder lateral grooves 24 and inner shoulder lateral grooves 23 suppress local deformation of the block, and thus suppress heel and toe wear.

  The ratio L7 / L8 between the positional deviation L7 between the inner shoulder lateral groove 23 and the outer shoulder lateral groove 24 and the length L8 of the outer shoulder block 34 in the tire circumferential direction is preferably 0.30 or more, more preferably 0.35. It is above, Preferably it is 0.55 or less, More preferably, it is 0.50 or less. Thereby, the partial wear of a block is suppressed more effectively.

  For example, an outer shoulder sipe 35 is provided in the outer shoulder land portion 10. The outer shoulder sipe 35 extends from the edge 10e on the outer side in the tire axial direction toward the inner side in the tire axial direction. The outer shoulder sipe 35 terminates in the outer shoulder land portion 10. Such an outer shoulder sipe 35 increases the edge component while maintaining the rigidity of the outer shoulder land portion 10 on the inner side in the tire axial direction. For this reason, performance on ice and wear resistance are improved in a well-balanced manner.

  It is desirable that the outer shoulder sipe 35 bends and terminates in the tire circumferential direction within the outer shoulder land portion 10. Thereby, damage such as cracking of the outer shoulder block 34 starting from the inner end portion 35 i of the outer shoulder sipe 35 is suppressed.

  The ratio L6 / W4 between the length L6 of the outer shoulder sipe 35 in the tire axial direction and the width W4 of the outer shoulder block 34 in the tire axial direction is preferably 0.45 or more, more preferably 0.55 or more, Preferably it is 0.65 or less, More preferably, it is 0.60 or less. When the ratio L6 / W4 is smaller than 0.45, wandering performance may be deteriorated. Conversely, if the ratio L6 / W4 is greater than 0.65, the wear resistance performance of the outer shoulder block 34 may be reduced.

  As shown in FIG. 1, in the heavy duty pneumatic tire for winter of the present embodiment, the land ratio Lr of the tread portion 2 is preferably 74% or more, more preferably 74% or more, and preferably 84%. Below, more preferably 80% or less. When the land ratio Lr of the tread portion 2 is smaller than 74%, the steering stability performance may be lowered. On the contrary, when the land ratio of the tread portion 2 is larger than 84%, the wet performance and the performance on ice may be deteriorated. The land ratio Lr is a ratio of the total contact area of the actual tread portion 2 to the total contact area of the tread portion 2 measured with all the grooves filled.

  The number Nb of blocks 30 on the entire circumference of the tire in each land portion is preferably 70 or more, more preferably 74 or more, preferably 84 or less, more preferably 80 or less. When the number Nb is smaller than 70, the amount of the edge component of the block 30 is lowered, and the performance on ice may be lowered. On the other hand, when the number Nb is larger than 84, each block 30 is small, and there is a possibility that the wear resistance performance is lowered.

  The rubber hardness Hb of the block 30 is preferably 62 ° or more, more preferably 64 ° or more, preferably 70 ° or less, more preferably 68 ° or less. When the rubber hardness Hb of the block 30 is smaller than 62 °, the uneven wear resistance performance may be reduced. Conversely, when the rubber hardness Hb is greater than 70 °, the performance on ice and the performance on snow may be deteriorated. In this specification, the “rubber hardness” is the hardness according to durometer type A based on JIS-K6253.

  FIG. 9 shows a block 50 of another embodiment. FIG. 10A shows a cross-sectional view of the first depth changing sipe 51 of the block 50 of another embodiment. FIG. 10B shows a cross-sectional view of the second depth changing sipe 52 of the block 50 of another embodiment.

  As shown in FIG. 10A, in the first depth changing sipe 51 of the block 50 of another embodiment, a shallow bottom portion 53a is provided at a central portion 51c in the tire axial direction of the sipe. As shown in FIG. 10B, in the second depth changing sipe 52 of the block 50 of another embodiment, shallow bottom portions 53b are provided at both ends 52e and 52e of the sipe in the tire axial direction.

  As shown in FIG. 9, the block 50 including the first depth changing sipe 51 and the second depth changing sipe 52 as described above has three rigid reinforcement portions 55 by the shallow bottom portion 53 in the same block 50. become. For this reason, the torsional rigidity of the block 50 is effectively improved. Therefore, in particular, the steering stability performance when turning is improved.

  FIG. 11 shows a development view of the tread portion 2 of another embodiment. As shown in FIG. 11, the inner shoulder lateral groove 23 and the outer shoulder lateral groove 24 may face each other. Such inner shoulder lateral grooves 23 and outer shoulder lateral grooves 24 exhibit excellent wet performance and snow performance.

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, it cannot be overemphasized that this invention can be changed into various aspects, without being limited to said specific embodiment.

A heavy-duty pneumatic tire of size 11R22.5 based on the specifications in Table 1 was prototyped. Each sample tire was tested for performance on ice, performance on snow, wear resistance, and wet performance in a worn state. The common specifications and test methods for each tire are as follows.
Wearing rim: 8.25 × 22.5
Tire internal pressure: 900 kPa
Test vehicle: 10t truck, 50% of the standard load capacity is loaded at the center of the loading platform Tire mounting position: All wheels

<Performance on ice>
The driving performance on the icy road of the test vehicle equipped with each test tire was evaluated by the driver's sensuality. A result is a score which sets Example 1 to 100, and shows that the performance on ice is excellent, so that a numerical value is large.

<Snow performance>
The driving performance on snowy roads of test vehicles equipped with each test tire was evaluated by the driver's sensuality. A result is a score which sets Example 1 to 100, and shows that the performance on snow is excellent, so that a numerical value is large.

<Abrasion resistance>
The amount of wear of the test tire after traveling a certain distance on the dry road surface was measured. The result is the reciprocal of the amount of tire wear, and is displayed as an index with the value of Example 1 being 100. It shows that abrasion resistance performance is excellent, so that a numerical value is large.

<Wet performance in a worn state>
In the vehicle equipped with each worn test tire, the driving performance on the wet road surface was evaluated by the driver's sensuality. The test was conducted on a test tire in which the remaining groove depth of the center main groove was 20% of the new one. A result is a score which sets comparative example 1 as 100, and shows that wet performance is excellent, so that a numerical value is large.
The test results are shown in Table 1.

As is clear from Table 1, it was confirmed that the pneumatic tires of the examples had improved wear resistance performance while maintaining the performance on ice.

2 Tread 3 Vertical groove 20 Horizontal groove
26 Tie Bar 30 Block 40 Sipe 46 Base 47 Shallow Bottom 48 First Depth Change Sipe 49 Second Depth Change Sipe

Claims (5)

A pneumatic tire in which a tread portion is provided with a block divided by a longitudinal groove extending in the tire circumferential direction and a lateral groove extending in the tire axial direction,
The block is provided with a plurality of sipes extending in the tire axial direction and having both ends opened at the block edges on both sides in the tire axial direction,
The sipe includes a plurality of depth changing sipes including a base portion having a substantially constant depth and a shallow bottom portion having a depth smaller than the base portion,
The depth changing sipe includes a first depth changing sipe and a second depth changing sipe,
The shallow bottom portion of the first depth change sipe faces the base portion of the second depth change sipe in the tire circumferential direction,
The lateral groove includes a tie bar having a raised groove bottom surface,
The tie bar faces the base portion of the depth changing sipe adjacent in the tire circumferential direction in the tire circumferential direction,
In the tread portion, by providing a pair of center main grooves extending continuously in the tire circumferential direction on both sides of the tire equator, a center land portion between the pair of center main grooves is divided,
The lateral groove includes a plurality of center lateral grooves communicating between the pair of center main grooves,
The center land portion is divided into a plurality of center blocks by the center lateral groove,
The center block has a center portion having a maximum tire axial length sandwiched between block edges on both sides extending in the tire circumferential direction, and a tire axial length from the central portion toward both ends of the block. A gradually decreasing first end portion and a second end portion;
The first depth changing sipe is provided at the first end portion, the second depth changing sipe is provided at the second end portion, and any sipe is provided at the central portion. Pneumatic tire characterized by not.   The pneumatic tire according to claim 1, wherein the first depth change sipe and the second depth change sipe are provided in proximity to the central portion.   The pneumatic tire according to claim 1 or 2, wherein the first depth changing sipe and the second depth changing sipe are wave-like.   The pneumatic tire according to claim 3, wherein the center block is not provided with a linear sipe. The first depth changing sipe and the second depth changing sipe have both ends opened to the pair of center main grooves at the block edge,
5. The pneumatic tire according to claim 1, wherein the first depth change sipe and the second depth change sipe gradually increase in width toward the center main groove at the both ends.

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