JP5926714B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire having improved turning performance and uneven wear resistance performance while ensuring straight running stability performance.

  A pneumatic tire is known in which a plurality of middle lateral grooves are provided in the middle land portion of the tread portion, and the depth of the middle lateral groove in the tire axial direction is smaller than the depth of the middle lateral groove in the tire axial direction outer side. . Such a pneumatic tire can exhibit excellent straight running stability performance by increasing the rigidity inside the tire axial direction of the middle land portion where a large contact pressure acts during straight running.

  However, in recent years, it has been desired to improve, for example, turning performance and uneven wear resistance performance of this type of pneumatic tire.

JP 2009-269500 A

  The present invention has been devised in view of the above circumstances, and based on the improvement of the middle lateral groove, the pneumatic tire has improved turning performance and uneven wear resistance performance while ensuring straight running stability performance. The main purpose is to provide

  In the present invention, a pair of inner main grooves extending continuously in the tire circumferential direction on both sides of the tire equator on the tread portion, and a pair extending continuously in the tire circumferential direction on the outer side of the inner main groove in the tire axial direction. A pneumatic tire in which a pair of middle land portions are provided between the inner main groove and the outer main groove, and the middle land portion is formed on the inner main groove. A plurality of middle lateral grooves that connect the main groove and the outer main groove are provided. The middle lateral groove includes an inner portion on the inner main groove side, an outer portion on the outer main groove side, and the inner portion and the outer portion. A groove depth of the inner portion and the outer portion is smaller than a groove depth of the intermediate portion.

  In the pneumatic tire according to the present invention, it is preferable that the groove width of the inner portion is smaller than the groove width of the outer portion.

  In the pneumatic tire according to the present invention, it is preferable that the middle land portion is divided into substantially parallelogram-shaped middle blocks arranged in the tire circumferential direction when the middle lateral groove is inclined with respect to the tire axial direction. .

  In the pneumatic tire according to the present invention, the middle block has an outer block edge along the outer main groove and an inner block edge along the inner main groove, and the tire circumferential direction of the inner block edge The length is preferably 105% to 115% of the length of the outer block edge in the tire circumferential direction.

  The pneumatic tire according to the present invention is divided into an outer block piece and an inner block piece by providing a circumferential groove that connects between the middle lateral grooves adjacent to each other in the tire circumferential direction. The outer block piece is provided with an outer siping, and the inner block piece is preferably provided with an inner siping, and the outer siping and the inner siping preferably extend in different directions.

  In the pneumatic tire according to the present invention, it is preferable that the inner block piece is provided with a concave portion recessed inward in the tire radial direction at a corner portion where the inner main groove and the middle lateral groove intersect at an obtuse angle.

  In the pneumatic tire according to the present invention, the circumferential groove preferably joins the intermediate portion adjacent in the tire circumferential direction.

  In the pneumatic tire according to the present invention, it is preferable that the groove depth of the intermediate portion is 80% to 100% of the groove depth of the inner main groove.

  In the pneumatic tire according to the present invention, the groove depth of the outer portion is preferably 40% to 60% of the groove depth of the outer main groove.

  In the pneumatic tire according to the present invention, the intermediate portion joins the equal width portion having a constant groove width, the inner portion and the equal width portion, and the gradually increasing portion in which the groove width gradually increases toward the equal width portion. The length in the tire axial direction including the inner portion and the gradually increasing portion is preferably 24% to 34% of the maximum width in the tire axial direction of the middle land portion.

  The middle land portion of the pneumatic tire of the present invention is provided with a plurality of middle lateral grooves that connect the inner main groove and the outer main groove. The middle lateral groove includes an inner portion arranged on the inner main groove side, an outer portion arranged on the outer main groove side, and an intermediate portion connecting the inner portion and the outer portion. The groove depth of the inner part is smaller than the groove depth of the intermediate part. As a result, the rigidity inside the tire block in the tire axial direction of the middle block to which a large contact pressure acts during straight traveling is ensured higher than the rigidity in the middle of the middle block in the tire axial direction, so that the straight running stability performance is improved.

  The groove depth of the outer portion is smaller than the groove depth of the intermediate portion. As a result, the rigidity of the middle block on the outer side in the tire axial direction of the middle block to which a large contact pressure acts during turning is ensured higher than the rigidity of the middle block in the tire axial direction center, thereby improving the turning performance.

  Further, the rigidity of both sides of the middle block in the tire axial direction is higher than the rigidity of the middle block of the middle block in the tire axial direction. For this reason, since the rigidity of the middle block is ensured in a well-balanced manner in the tire axial direction, the uneven wear resistance is improved.

It is an expanded view of the tread part which shows one Embodiment of this invention. It is an enlarged view of the middle land part of FIG. It is AA sectional drawing of FIG. It is an expanded view of the tread part which shows other embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a developed view of a tread portion 2 of a pneumatic tire showing an embodiment of the present invention. The pneumatic tire of the present embodiment (hereinafter sometimes simply referred to as “tire”) is suitably used as a studless tire, for example.

  As shown in FIG. 1, the tread portion 2 includes a pair of inner main grooves 3 and 3 extending continuously in the tire circumferential direction on both sides of the tire equator C, and an outer side in the tire axial direction of the inner main groove 3. A pair of outer main grooves 4, 4 extending continuously in the tire circumferential direction are provided.

  The inner main groove 3 is inclined in multiple directions with respect to the tire axial direction. The inner edge 3x that is the groove edge on the inner side in the tire axial direction of the inner main groove 3 and the outer edge 3y that is the groove edge on the outer side in the tire axial direction of the inner main groove 3 have different zigzag shapes. For this reason, the groove edges 3x and 3y of the inner main groove 3 have multidirectional edge components. Such an inner main groove 3 improves the turning performance.

  The outer main groove 4 extends linearly in this embodiment. Such an outer main groove 4 can increase the rigidity of the tread portion 2 in the tire circumferential direction and improve the straight running stability performance. The inner main groove 3 and the outer main groove 4 are not limited to such a mode.

  Various groove widths (average groove width in the tire axial direction) W1 and W2 and groove depths D1 and D2 (shown in FIG. 3) of the main grooves 3 and 4 can be determined in accordance with common practice. The groove widths W1 and W2 of the main grooves 3 and 4 are preferably 2 to 7% of the tread ground contact width TW, for example. As for groove depth D1, D2 of each main groove 3 and 4, 8-12 mm is desirable, for example.

  The tread portion 2 is provided with a plurality of land portions by the inner main groove 3 and the outer main groove 4. The land portion of this embodiment includes a center land portion 5, a pair of middle land portions 6, 6, and a pair of shoulder land portions 7, 7.

  The center land portion 5 is divided between the pair of inner main grooves 3 and 3. The middle land portion 6 is divided between the inner main groove 3 and the outer main groove 4. The shoulder land portion 7 is divided between the outer main groove 4 and the ground contact Te. The shape of the land portion of the tread portion 2 is not limited to such a mode, and can take various forms.

  The “ground contact end” is a normal load state in which a normal load is loaded on a normal rim that is assembled with a normal rim and filled with a normal internal pressure, and a normal load is applied to a flat surface with a camber angle of 0 degrees. Is determined as the ground contact position on the outermost side in the tire axial direction. In the normal state, the distance in the tire axial direction between the ground contact ends Te and Te is determined as the tread ground contact width TW. Unless otherwise noted, the dimensions and the like of each part of the tire are values measured in a normal state.

  The “regular rim” is a rim defined by each standard for each tire in the standard system including the standard on which the tire is based. For example, “Standard Rim” for JATMA and “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. “JAMATA” is the “maximum air pressure”, TRA is the table “TIRE LOAD LIMITS” The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” in the case of ETRTO. When the tire is for a passenger car, the normal internal pressure is 180 kPa.

  “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” The maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “LOAD CAPACITY” in the case of ETRTO. When the tire is for a passenger car, the normal load is a load corresponding to 88% of the load.

  FIG. 2 shows an enlarged view of the middle land portion 6 on the right side of FIG. As shown in FIG. 2, the middle land portion 6 is provided with a plurality of middle lateral grooves 8 that connect the inner main groove 3 and the outer main groove 4.

  The middle lateral groove 8 of the present embodiment is inclined with respect to the tire axial direction. Since such middle lateral grooves 8 have edge components in the tire axial direction and the tire circumferential direction, the turning performance and straight running stability performance can be improved in a well-balanced manner.

  The middle lateral groove 8 is inclined in the same direction over the entire length. The middle lateral groove 8 of the present embodiment is inclined upward to the right. Thereby, the fall of the rigidity of the middle land part 6 is suppressed, and high uneven wear-proof performance is ensured. The middle lateral groove 8 is not limited to such an aspect, and may be, for example, a V-shape extending in a direction different from the tire axial direction.

  The middle lateral groove 8 includes an inner portion 11 on the inner main groove 3 side, an outer portion 12 on the outer main groove 4 side, and an intermediate portion 13 that connects the inner portion 11 and the outer portion 12.

  The inner part 11 of this embodiment extends linearly. Such an inner portion 11 ensures a high rigidity on the inner side in the tire axial direction of the middle land portion 6 where a large contact pressure acts during straight traveling. Therefore, the straight running stability performance is improved.

  The inner portion 11 communicates with the inner main groove 3. Thereby, the above-mentioned operation is effectively exhibited.

  FIG. 3 shows an AA cross section of FIG. As shown in FIG. 3, the groove depth D3 of the inner part 11 is smaller than the groove depth D5 of the intermediate part 13. Thereby, the rigidity inside the tire axial direction of the middle land portion 6 can be effectively ensured, and the straight running stability performance is further improved.

  If the groove depth D3 of the inner portion 11 is excessively smaller than the groove depth D5 of the intermediate portion 13, the water in the middle lateral groove 8 may not be smoothly drained into the inner main groove 3. Moreover, the snow pillar formed in the middle horizontal groove 8 becomes small, and there is a possibility that the braking performance on the snowy road is deteriorated. For this reason, the groove depth D3 of the inner portion 11 is preferably 45% to 65% of the groove depth D5 of the intermediate portion 13.

  In order to exhibit the above-mentioned action more effectively, the groove depth D3 of the inner portion 11 is preferably 40% to 60% of the groove depth D1 of the inner main groove 3.

  As shown in FIG. 2, the groove width W <b> 3 of the inner part 11 is smaller than the groove width W <b> 4 of the outer part 12. Thereby, since the rigidity inside the tire axial direction of the middle land portion 6 can be further ensured, the straight running stability performance is further improved.

  When the groove width W3 of the inner portion 11 is excessively smaller than the groove width W4 of the outer portion 12, the balance between the rigidity on the inner side in the tire axial direction of the middle land portion 6 and the rigidity on the outer side in the tire axial direction of the middle land portion 6 However, the uneven wear resistance may be deteriorated. Moreover, there exists a possibility that drainage performance may deteriorate. For this reason, the groove width W3 of the inner part 11 is preferably 50% to 80% of the groove width W4 of the outer part 12.

  The angle α1 of the inner portion 11 with respect to the tire axial direction is preferably 22 to 32 °. Such an inner portion 11 has an edge component in the tire circumferential direction while ensuring high rigidity of the middle land portion 6, and can improve turning performance. The angle α1 is an angle of the groove center line 8c of the middle lateral groove 8.

  The outer portion 12 extends linearly. Such an outer portion 12 ensures high rigidity on the outer side in the tire axial direction of the middle land portion 6.

  The outer portion 12 communicates with the outer main groove 4. Thereby, the rigidity in the tire axial direction on the outer end side in the tire axial direction of the middle land portion 6 is ensured high, and the turning performance is effectively improved.

  As shown in FIG. 3, the groove depth D4 of the outer portion 12 is smaller than the groove depth D5 of the intermediate portion 13. That is, during turning, the rigidity on the outer side in the tire axial direction of the middle land portion 6 where a large lateral force acts is ensured, so that the turning performance is improved. The middle lateral groove 8 has a groove depth on both sides in the tire axial direction that is smaller than the groove depth in the central portion in the tire axial direction. Thereby, since the rigidity of the middle land portion 6 is leveled over the tire axial direction, uneven wear resistance is improved.

  From the viewpoint of effectively exhibiting the above-described action, the groove depth D4 of the outer portion 12 is preferably 45% to 65% of the groove depth D5 of the intermediate portion 13. If the groove depth D4 of the outer portion 12 is excessively smaller than the groove depth D5 of the intermediate portion 13, the water in the middle lateral groove 8 may not flow smoothly into the outer main groove 4.

  From the same viewpoint, the groove depth D4 of the outer portion 12 is preferably 40% to 60% of the groove depth D2 of the outer main groove 4.

  As shown in FIG. 2, the angle α2 of the outer portion 12 with respect to the tire axial direction is smaller than the angle α1 of the inner portion 11. Such an outer portion 12 exhibits a large snow column shearing force, and thus improves braking performance on snowy roads. In addition, it improves drainage performance during turning. When the angle α2 of the outer portion 12 is excessively smaller than the angle α1 of the inner portion 11, the edge component in the tire circumferential direction becomes small, and the turning performance may be deteriorated. For this reason, the angle α2 of the outer portion 12 is preferably 5 to 15 °.

  The length L1 of the outer portion 12 in the tire axial direction is preferably 21% to 31% of the maximum width Wa of the middle land portion 6 in the tire axial direction. If the length L1 of the outer portion 12 in the tire axial direction is less than 21% of the maximum width Wa of the middle land portion 6, the inner rigidity of the middle land portion 6 in the tire axial direction cannot be effectively increased, and turning Performance may deteriorate. When the length L1 of the outer portion 12 in the tire axial direction exceeds 31% of the maximum width Wa of the middle land portion 6, the drainage performance during turning may be deteriorated.

  The intermediate portion 13 includes a constant width portion 13A having a constant groove width, and a gradually increasing portion 13B in which the groove width gradually increases toward the equal width portion 13A by joining the inner portion 11 and the constant width portion 13A. Such a gradually increasing portion 13B smoothly connects the inner portion 11 and the equal width portion 13A, eliminates a rigid step at the connection position between the inner portion 11 and the equal width portion 13A, and ensures high uneven wear resistance performance. .

  In the present embodiment, the equal width portion 13A and the outer portion 12 have different angles with respect to the tire axial direction. Thereby, the middle lateral groove 8 has edge components in different directions, and can improve the turning performance.

  In order to ensure high rigidity on the middle side in the tire axial direction of the middle land portion 6, the angle α3 of the equal width portion 13A with respect to the tire axial direction is preferably the same angle as the angle α1 of the inner portion 11.

  The groove width W5 of the equal width portion 13A is preferably 90% to 110% of the groove width W4 of the outer side portion 12. Thereby, the equal width part 13A and the outer side part 12 are smoothly connected, and the rigidity of the middle land part 6 can be ensured high. More preferably, the equal width portion 13 </ b> A has the same groove width as that of the outer side portion 12.

  The length Lw in the tire axial direction of the narrow groove portion 14 combining the gradually increasing portion 13B and the inner portion 11 is preferably 24% to 34% of the maximum width Wa of the middle land portion 6 in the tire axial direction. When the length Lw of the narrow groove portion 14 in the tire axial direction is less than 24% of the maximum width Wa of the middle land portion 6 in the tire axial direction, it is possible to effectively increase the rigidity of the middle land portion 6 on the inner side in the tire axial direction. It may not be possible. If the length Lw in the tire axial direction of the narrow groove portion 14 exceeds 34% of the maximum width Wa of the middle land portion 6 in the tire axial direction, there is a possibility that water in the middle lateral groove 8 cannot be smoothly discharged into the inner main groove 3. is there.

  As shown in FIG. 3, in the gradually increasing portion 13B of the present embodiment, the groove depth gradually increases toward the equal width portion 13A.

  In order to balance the rigidity of the middle land portion 6 in the tire axial direction and demonstrate excellent uneven wear resistance performance, in addition to improving high drainage performance and braking performance on snowy roads, the groove depth D4 of the intermediate portion 13 is Preferably, it is 80% to 100% of the groove depth D1 of the inner main groove 3.

  As shown in FIG. 2, the middle land portion 6 is divided into middle blocks 9 arranged in the tire circumferential direction by the inner main groove 3, the outer main groove 4, and the middle lateral groove 8. In the present embodiment, the middle block 9 has a substantially parallelogram shape. As a result, during cornering when a large lateral force acts, the middle blocks 9 and 9 adjacent to each other in the tire circumferential direction support each other, and the middle block 9 has a large apparent rigidity in the tire axial direction. Therefore, turning performance and uneven wear resistance are improved.

  The middle block 9 is provided with a circumferential groove 10 that connects between the middle lateral grooves 8 and 8 adjacent in the tire circumferential direction.

  The circumferential groove 10 of the present embodiment extends linearly. Such a circumferential groove 10 ensures a large rigidity of the middle block 9.

  The circumferential groove 10 connects between the intermediate portions 13 and 13 adjacent to each other in the tire circumferential direction, more specifically, between the equal width portions 13A and 13A. The circumferential groove 10 is provided near the center of the middle block 9 in the tire axial direction. Thereby, the rigidity of both sides in the tire axial direction of the middle block 9 is ensured with a good balance.

  The circumferential groove 10 of the present embodiment is inclined with respect to the tire circumferential direction. Since such a circumferential groove 10 has edge components in the tire circumferential direction and the tire axial direction, it improves the turning performance and straight running stability performance on ice roads in a well-balanced manner.

  In order to effectively exhibit the above-described action, the angle α4 of the circumferential groove 10 with respect to the tire circumferential direction is preferably 3 to 10 °.

  The groove width W6 of the circumferential groove 10 is preferably 3% to 13% of the maximum width Wa of the middle land portion 6 in the tire axial direction. When the groove width W6 of the circumferential groove 10 is less than 3% of the maximum width Wa of the middle land portion 6, the drainage performance may be deteriorated. When the groove width W6 of the circumferential groove 10 exceeds 13% of the maximum width Wa of the middle land portion 6, the rigidity of the middle block 9 is excessively lowered, and the uneven wear resistance performance and the turning performance may be deteriorated. The groove width W6 of the circumferential groove 10 is more preferably 5% to 11% of the maximum width Wa of the middle land portion 6.

  As shown in FIG. 3, the groove depth D6 of the circumferential groove 10 is preferably 80% to 100% of the groove depth D1 of the inner main groove 3 in order to exhibit the above-described action more effectively. is there.

  As shown in FIG. 2, the middle block 9 is divided into an outer block piece 9 </ b> A and an inner block piece 9 </ b> B by a circumferential groove 10. That is, the outer block piece 9A is divided into middle lateral grooves 8, 8 that are adjacent to each other in the tire circumferential direction, the outer main groove 4, and the circumferential groove 10. The inner block piece 9B is divided into middle lateral grooves 8 and 8, the inner main groove 3 and the circumferential groove 10 which are adjacent to each other in the tire circumferential direction.

  An outer siping 17 is provided on the outer block piece 9A. The outer siping 17 of the present embodiment has a zigzag shape. The outer siping 17 is not limited to a zigzag shape, and may be, for example, a straight shape or a wave shape.

  An inner siping 18 is provided on the inner block piece 9B. The inner siping 18 of the present embodiment has a zigzag shape, but may be a linear shape or a wave shape, for example.

  The outer siping 17 and the inner siping 18 extend in different directions. That is, the outer block piece 9A and the inner block piece 9B have edge components in different directions, respectively, and the turning performance on ice roads is improved.

  The outer siping 17 is inclined upward in the present embodiment. In the present embodiment, the inner siping 18 is inclined upward to the left. That is, the outer siping 17 and the inner siping 18 extend in opposite directions with respect to the tire axial direction. As a result, the mutually opposite lateral forces generated at the edges of the sipes 17 and 18 are canceled out, so that the straight running stability performance on the icy road is improved. In order to exhibit such an action more effectively, it is desirable to make the angle θ1 of the outer siping 17 with respect to the tire axial direction and the angle θ2 of the inner siping 18 with respect to the tire axial direction equal. The angles θ1 and θ2 of the sipings 17 and 18 are defined by zigzag centerlines.

  In order to improve the straight running stability performance and turning performance on an icy road with a good balance, the angles θ1 and θ2 of the sipings 17 and 18 are preferably 10 to 30 °.

  The depth (not shown) of the outer siping 17 and the inner siping 18 is preferably the groove depth of the inner main groove 3 in order to ensure the edge component until the late stage of wear while ensuring the uneven wear resistance performance of the middle block 9. It is 50 to 90% of the length D1.

  The outer siping 17 and the inner siping 18 are provided on the outer block piece 9A or the inner block piece 9B, respectively. When the number of the outer siping 17 and the inner siping 18 exceeds seven, the rigidity of the middle block 9 is reduced, and the uneven wear resistance may be deteriorated. Further, when the number of the outer siping 17 and the inner siping 18 is less than 3, the edge component may be small.

  The inner block piece 9B is further provided with a recess 19 that is recessed inward in the tire radial direction. The recessed part 19 of this embodiment is elliptical. Such a recess 19 has multidirectional edge components while ensuring the rigidity of the inner block piece 9B. For this reason, turning performance improves.

  The recess 19 is provided in a corner portion K where the inner main groove 3 and the middle lateral groove 8 intersect at an obtuse angle. Moreover, the recessed part 19 is terminated in the inner block piece 9B without communicating with another groove. Thereby, the rigidity of inner block piece 9B is ensured high, and uneven wear-proof performance is maintained.

  In order to effectively exhibit the above-described action, the depth (not shown) of the recess 19 is preferably 1 to 3 mm.

  The middle block 9 has an inner block edge 9 x along the inner main groove 3 and an outer block edge 9 y along the outer main groove 4.

  The tire circumferential direction length La of the inner block edge 9x is preferably 105% to 115% of the tire circumferential direction length Lb of the outer block edge 9y. When traveling straight ahead, a larger ground pressure acts on the inner side of the middle block 9 in the tire axial direction than on the outer side in the tire circumferential direction. For this reason, when the tire circumferential direction length La of the inner block edge 9x is less than 105% of the tire circumferential direction length Lb of the outer block edge 9y, the rigidity of the inner side of the middle block 9 in the tire axial direction cannot be secured greatly. The straight running stability performance and uneven wear resistance performance may be deteriorated. When the tire circumferential direction length La of the inner block edge 9x exceeds 115% of the tire circumferential direction length Lb of the outer block edge 9y, the outer side of the middle block 9 in the tire axial direction where a large contact pressure acts during turning There is a possibility that the rigidity of the wheel will be reduced and the turning performance may be reduced. For this reason, the tire circumferential direction length La of the inner block edge 9x is more preferably 108% to 112% of the length Lb of the outer block edge 9y in the tire circumferential direction.

  From the viewpoint of ensuring a good balance between the rigidity in the tire axial direction and the rigidity in the tire circumferential direction, the maximum width Wa in the tire axial direction of the middle land portion 6 is preferably 105% to the length Lb of the outer block edge 9y. 115%.

  As shown in FIG. 1, the center land portion 5 is provided with a plurality of center lateral grooves 20 that connect between the pair of inner main grooves 3 and 3. The center lateral groove 20 of the present embodiment is opposite to the first center lateral groove 20A and the first center lateral groove 20A inclined upward (to the right in FIG. 1). And the second center lateral groove 20B which is inclined toward the center.

  The first center lateral grooves 20A and the second center lateral grooves 20B are alternately arranged in the tire circumferential direction. As a result, the lateral forces in the opposite directions generated at the groove edges of the center lateral grooves 20A and 20B are canceled out, so that the straight running stability performance is further improved.

  The center land portion 5 is provided with a center siping 21 extending substantially parallel to the first center lateral groove 20A or the second center lateral groove 20B. As a result, the straight running stability performance and the turning performance are improved in a well-balanced manner.

  The shoulder land portion 7 is provided with a shoulder lateral groove 22 that connects between the outer main groove 4 and the ground contact end Te and is spaced in the tire circumferential direction.

  The shoulder land portion 7 is provided with a shoulder siping 23 extending substantially parallel to the shoulder lateral groove 22. Thereby, the turning performance on an icy road is further improved.

  As for the tire of this embodiment, as a studless tire for winter, it is desirable that the land ratio is set to 60 to 70%. As a result, the turning performance on the icy road and the uneven wear resistance are improved in a well-balanced manner without lowering the straight running stability. The land ratio is the total surface area Mb of the treads of all the land portions 5 to 7, all the grooves 3, 4, 8, 10, 20, and 22 of the tread portion 2, the concave portion 19, and the sipings 17, 18, 21, and 23 is a ratio (Mb / Ma) with the virtual surface area Ma of the virtual tread obtained by filling 23 or the like.

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, this invention is changed and implemented in various aspects, without being limited to said specific embodiment.

A pneumatic tire of size 225 / 65R17 having the basic pattern shown in FIG. 1 was prototyped according to the specifications in Table 1, and the ice tire braking performance, the turning performance on the ice road, the straight running stability performance of the ice road, the snow Road braking performance, drainage performance, and uneven wear resistance were tested. The common specifications and test methods for each sample tire are as follows.
Tread contact width TW: 180mm
Inner main groove width W1: 8mm
Inner main groove depth D1: 11 mm
Groove width W2 of outer main groove: 8mm
Groove depth D2 of outer main groove: 11 mm
Inner groove width W3: 3.5 mm
Inner groove depth D3: 6 mm
Circumferential groove depth D6: 9 mm
Center lateral groove width: 3.5mm
Center lateral groove depth: 6mm
Shoulder width groove width: 6.5mm
Shoulder lateral groove depth: 10mm
Depth of each siping / groove depth of inner main groove: 64%

<Brake performance on icy roads>
Each test tire was mounted on all wheels of a four-wheel drive passenger car with a displacement of 2400 cc under the following conditions. Then, the test driver drove the iceburn test course, and the running characteristics related to the braking force at this time were evaluated by the test driver's sensuality. The results are displayed as a score with the value of Example 1 being 100. The larger the value, the better.
Rim (all wheels): 17 × 6.5J
Internal pressure (all wheels): 220 kPa

<Turning performance on icy road>
In the test vehicle, a test driver traveled the test course of the ice burn, and the running characteristics related to the steering wheel response, rigidity, grip, and the like during turning were evaluated by the test driver's sensuality. The results are displayed as a score with the value of Example 1 being 100. The larger the value, the better.

<Straight running stability performance on icy roads>
The test driver ran the test vehicle on the test course of the ice burn, and the running characteristics related to the steering stability and grip during the straight running at this time were evaluated by the test driver's sensuality. The results are displayed as a score with the value of Example 1 being 100. The larger the value, the better.

<Brake performance on snowy roads>
In the above test vehicle, the test driver drove the test course on the snowy road, and the running characteristics related to the braking force at this time were evaluated based on the sensuality of the test driver. The results are displayed as a score with the value of Example 1 being 100. The larger the value, the better.

<Drainage performance>
The test driver entered the above-mentioned test vehicle on the asphalt road surface with a radius of 100 m on a test course provided with a puddle with a depth of 6 mm while gradually increasing the speed. Then, the average lateral acceleration (lateral G) of the front wheels at a speed of 50 to 80 km / h was calculated. The results are displayed as an index with Example 1 as 100. The larger the value, the better.

<Uneven wear resistance>
The test driver ran the test vehicle for 8000 km on the dry asphalt road test course. Thereafter, the amount of wear at both ends of the middle block in the tire axial direction was measured at eight locations in the tire circumferential direction. Then, the average of the differences in the amount of wear at each of the eight locations was calculated. The results are displayed as an index with the value of Example 1 being 100. The larger the value, the better.
The test results are shown in Table 1.

  As a result of the test, it was confirmed that each performance of the tire of the example was improved in a balanced manner as compared with the comparative example.

3 Inner main groove 4 Outer main groove 6 Middle land 8 Middle lateral groove 9 Middle block
11 Inner part 12 Outer part 13 Middle part

Claims (9)

In the tread portion, a pair of inner main grooves extending continuously in the tire circumferential direction on both sides of the tire equator, and a pair of outer main grooves extending continuously in the tire circumferential direction on the outer side of the inner main groove in the tire axial direction. Is a pneumatic tire provided with a pair of middle land portions between the inner main groove and the outer main groove,
The middle land portion is provided with a plurality of middle lateral grooves that connect the inner main groove and the outer main groove,
The middle lateral groove includes an inner part on the inner main groove side, an outer part on the outer main groove side, and an intermediate part connecting the inner part and the outer part,
The groove depth of the inner part and the outer part is smaller than the groove depth of the intermediate part,
The groove width of the inner portion, rather smaller than the groove width of the outer portion,
The intermediate portion content is equal width portion groove width is constant, and, and a gradually increasing section which groove width toward the fixed-width portion joint and the like width portion and the inner portion gradually increases,
The pneumatic tire according to claim 1, wherein a groove width of the equal width portion is 90% to 110% of a groove width of the outer portion . The pneumatic tire according to claim 1 , wherein a groove width of the equal width portion is the same as a groove width of the outer portion . The middle land portion is divided into substantially parallelogram-shaped middle blocks arranged in the tire circumferential direction by inclining the middle lateral groove with respect to the tire axial direction,
The middle block has an outer block edge along the outer main groove, and an inner block edge along the inner main groove,
The pneumatic tire according to claim 1 or 2 , wherein a tire circumferential length of the inner block edge is 105% to 115% of a tire circumferential length of the outer block edge . The middle block is provided with a circumferential groove that connects between the middle lateral grooves adjacent to each other in the tire circumferential direction.
It is divided into an outer block piece and an inner block piece,
The outer block piece is provided with an outer siping,
The inner block piece is provided with an inner siping,
The pneumatic tire according to claim 3 , wherein the outer siping and the inner siping extend in different directions . The pneumatic tire according to claim 4 , wherein the inner block piece is provided with a concave portion recessed inward in the tire radial direction at a corner portion where the inner main groove and the middle lateral groove intersect at an obtuse angle . The pneumatic tire according to claim 4 or 5, wherein the circumferential groove joins the intermediate portion adjacent in the tire circumferential direction . The pneumatic tire according to any one of claims 1 to 6 , wherein a groove depth of the intermediate portion is 80% to 100% of a groove depth of the inner main groove . The pneumatic tire according to any one of claims 1 to 7 , wherein a groove depth of the outer portion is 40% to 60% of a groove depth of the outer main groove . The air according to any one of claims 1 to 8 , wherein a length in a tire axial direction of the inner portion and the gradually increasing portion is 24% to 34% of a maximum width in a tire axial direction of the middle land portion. Enter tire.

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