JP2015221650A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve drainage performance, on-snow road performance and on-ice road performance in good balance.SOLUTION: In the pneumatic tire, a center land part 5 is provided with a plurality of center lug grooves 9 that extend across a center thin groove 8 from center main grooves 3 and have terminals positioned in the center land part 5. The center lug grooves 9 extend between the center main grooves 3 and the center thin groove 8, and have main parts 11 that incline on the side of arrival in a rotation direction toward inside in a tire shaft direction and have angles of 20-40° relative to the tire shaft direction, and sub parts 12 that extend from the center thin groove 8 to terminals 10, incline in a direction opposite to the direction of the main parts 11 and have angles 20-40°relative to the tire shaft direction. Groove depths at positions 9e where the center lug grooves 9 are communicated with the center main grooves 3 are larger than groove depths at inner ends 11i in the tire shaft direction of the main parts 11 and groove depths at the terminals 10 of the center lug grooves 9.

Description

  The present invention relates to a pneumatic tire in which snow / ice road performance, in particular, brake performance on snow road and ABS brake performance is improved in a well-balanced manner.

  A pneumatic tire having a plurality of lug grooves extending in the tire axial direction in the center land portion of the tread portion is known. This pneumatic tire obtains a large snow column shear force by the lug groove, and exhibits excellent snow road performance.

  With respect to this pneumatic tire, for example, it has been proposed to increase the volume of the lug groove and further increase the snow column shear force in order to improve the braking performance on snowy roads. However, with this method, the rigidity of the center land portion is reduced.

  FIG. 6 shows a graph showing the relationship between the friction coefficient and the slip ratio, where the vertical axis represents the friction coefficient and the horizontal axis represents the slip ratio. In the graph of FIG. 6, a tire having a high rigidity in the center land portion of the tread portion is indicated by a solid line, and a tire having a low rigidity is indicated by a broken line. A tire with a low rigidity at the center land portion has a lower coefficient of friction at a slip rate of 20 to 30%, which is a practical range of ABS brake operation, than a tire with a high rigidity. For this reason, a tire with low rigidity in the center land portion has a wheel speed that is less likely to follow the vehicle body speed than a tire with high rigidity. As a result, a tire having a low rigidity at the center land portion has a slower recovery of the wheel speed (that is, a reduction in the slip ratio) and a longer time for releasing the ABS than a tire having a high rigidity. It stretches. Therefore, a tire having a low rigidity at the center land portion has a problem that the braking performance at the time of ABS operation is deteriorated as compared with a tire having a high rigidity. Related technologies include the following.

JP 2009-269500 A

  The present invention has been devised in view of the above-described actual situation, and is based on improving the center lug groove provided in the center land portion. The main purpose is to provide a pneumatic tire that improves the braking performance during operation (hereinafter sometimes referred to as “ABS braking performance”) in a well-balanced manner.

  The present invention comprises a center land portion partitioned between the center main grooves by providing a pair of center main grooves extending continuously in the tire circumferential direction on both sides of the tire equator in the tread portion, and A pneumatic tire having a designated rotational direction, wherein the center land portion includes one center narrow groove extending continuously on the tire equator in the tire circumferential direction, and the center narrow groove extending from the center main groove. There are provided a plurality of center lug grooves extending beyond the center land portion and having terminal ends, and the center lug groove extends between the center main groove and the center narrow groove, and extends inward in the tire axial direction. A main portion that is inclined toward the first arrival side in the rotational direction and has an angle of 20 to 40 ° with respect to the tire axial direction, extends from the center narrow groove to the terminal end, and is inclined in a direction opposite to the main portion. And an angle with respect to the tire axial direction is 20 to 40 °, and a groove depth at a position where the center lug groove communicates with the center main groove is an inner diameter of the main portion in the tire axial direction. The groove depth at the end is larger than the groove depth at the end of the center lug groove.

  In the pneumatic tire according to the present invention, it is desirable that siping is provided in the center land portion.

  In the pneumatic tire according to the present invention, the groove width of the center lug groove is preferably 0.85 to 1.15 times the groove width of the center narrow groove.

  In the pneumatic tire according to the present invention, it is preferable that the groove depth of the main portion gradually decreases from the communication position of the center lug groove toward the tire equator.

  In the pneumatic tire according to the present invention, it is preferable that the groove depth of the sub-portion is 0.85 to 1.15 times the groove depth of the center narrow groove.

  In the center land portion of the pneumatic tire of the present invention, there is one center narrow groove extending continuously in the tire circumferential direction on the tire equator, extending from the center main groove beyond the center narrow groove and located in the center land portion. And a plurality of center lug grooves each having a terminating end.

  The center lug groove extends between the center main groove and the center narrow groove, is inclined toward the first arrival side in the rotational direction toward the inner side in the tire axial direction, and has a main portion whose angle with respect to the tire axial direction is 20 to 40 °, It extends from the center narrow groove to the terminal end, and has a sub part that is inclined in the opposite direction to the main part and has an angle of 20 to 40 ° with respect to the tire axial direction. Such a center lug groove can form a large and strong snow column extending in the tire axial direction in the center land portion where a large contact pressure acts. Further, since the main part and the sub part are inclined in the opposite directions, the lateral force acting on the snow column formed in the main part and the sub part is canceled during traveling. Since the main part is inclined toward the first arrival side in the rotation direction toward the inner side in the tire axial direction, the snow in the main part is smoothly discharged to the center main groove using the rotation force of the tire. On the other hand, a strong snow column is formed during braking. For this reason, in particular, braking performance on snowy roads is improved.

  The groove depth at the communication position of the center lug groove with the center main groove is larger than the groove depth at the inner end of the main portion in the tire axial direction and the groove depth at the end of the center lug groove. As a result, the rigidity in the vicinity of the tire equator of the center land portion that greatly contributes to the braking performance on snowy roads is enhanced. For this reason, the braking performance on snowy roads is further improved.

  Further, since the rigidity in the vicinity of the tire equator in the center land portion is enhanced, shear deformation in the vicinity of the tire equator in the center land portion is suppressed. As a result, the friction coefficient of the tire is increased, and the recovery of the wheel speed is accelerated at the time of braking when the ABS is operated. Accordingly, the ABS brake performance is improved.

It is an expanded view of the tread part which shows one Embodiment of this invention. It is AA sectional drawing of FIG. It is an enlarged view of the center block of FIG. It is BB sectional drawing of FIG. It is an expanded view of the tread part which shows embodiment of a comparative example. It is a figure which shows the relationship between a friction coefficient and a slip ratio.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1 and FIG. 2, the pneumatic tire of this embodiment (hereinafter simply referred to as “tire”) is preferably used as a winter tire, for example, and the rotation direction R of the tire is designated. It has a line-symmetric tread pattern. The rotation direction R of the tire is displayed in characters or the like on a sidewall portion (not shown), for example.

  The tread portion 2 of the tire of the present embodiment is provided with a pair of center main grooves 3, 3 and a pair of shoulder main grooves 4, 4 extending continuously in the tire circumferential direction. The pair of center main grooves 3 and 3 are arranged on both sides of the tire equator C. The shoulder main groove 4 is disposed on the outer side in the tire axial direction of the center main groove 3. As a result, the tread portion 2 of the present embodiment has one center land portion 5 divided between the center main grooves 3 and 3, and a pair of middle land portions divided by the center main groove 3 and the shoulder main grooves 4. A pair of shoulder land portions 7 and 7 are provided which are divided by the portions 6 and 6 and the shoulder main groove 4 and the ground contact Te.

  “Grounding end” Te is a normal load applied 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 °. 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. When there is no notice in particular, the dimension of each part of a tire, etc. are values measured in this normal state.

  “Regular rim” is a rim that is defined for each tire in the standard system including the standard on which the tire is based. “Standard Rim” for JATMA, “Design Rim” for TRA, For ETRTO, it is “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, and is “maximum air pressure” for JATMA, table “TIRE LOAD LIMITS” for TRA. 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.

  The center main groove 3 of the present embodiment extends in a zigzag shape. Since the center main groove 3 has a tire axial direction component, it exerts a snow column shear force. The center main groove 3 has an edge component in the tire axial direction. Therefore, braking performance on snowy roads and icy roads is improved.

  The shoulder main groove 4 of the present embodiment extends linearly along the tire circumferential direction. Such a shoulder main groove 4 ensures high rigidity in the tire circumferential direction in the vicinity of the shoulder main groove 4 of the middle land portion 6 and the shoulder land portion 7.

  The groove widths W1 and W2 and the groove depths D1 and D2 (shown in FIG. 2) in the tire axial direction of the main grooves 3 and 4 can be variously determined according to the custom. However, if these groove widths or groove depths are reduced, snow road performance may be deteriorated. Conversely, if these groove widths or groove depths are increased, the rigidity of the land portions 5 to 7 may be reduced, and ice road performance may be deteriorated. For this reason, the groove widths W1 and W2 of the main grooves 3 and 4 are preferably 2% to 8% of the tread ground contact width TW, for example. As for groove depth D1, D2 of each main groove 3 and 4, 8.0-14.0 mm is desirable, for example.

  FIG. 3 shows an enlarged view of the center land portion 5. As shown in FIG. 3, the center land portion 5 is provided with one center narrow groove 8 and a plurality of center lug grooves 9.

  The center narrow groove 8 extends continuously on the tire equator C in the tire circumferential direction. Thereby, the center land portion 5 has a first land portion 5A on one side (right side in FIG. 3) in the tire axial direction from the center narrow groove 8 and the other side in the tire axial direction from the center narrow groove 8 (FIG. 3). The left side is divided into the second land portion 5B.

  The center narrow groove 8 of this embodiment extends in a zigzag shape. The center narrow groove 8 is connected to the first portion 8a inclined to the one side (right side in FIG. 3) in the tire axial direction toward the rotation direction R, and connects between the first portions 8a and 8a and the first portion 8a. Includes a second portion 8b inclined in the opposite direction. Such center narrow groove 8 has an edge component in the tire axial direction, and can improve ice road performance.

  The first portion 8a and the second portion 8b of the present embodiment have the same angles α1a, α1b and lengths L1a, L1b in the tire circumferential direction with respect to the tire circumferential direction. Thereby, the rigidity in the tire circumferential direction and the tire axial direction of the center land portion 5 is ensured with a good balance.

  In order to effectively exhibit the above-described action, the angles α1a and α1b of the first portion 8a and the second portion 8b are preferably 3 to 10 °. The lengths L1a and L1b in the tire circumferential direction of the first portion 8a and the second portion 8b are preferably 5% to 11% of the tread contact width TW (shown in FIG. 1).

  From the viewpoint of ensuring high rigidity in the vicinity of the tire equator C of the center land portion 5 and improving braking performance on snowy roads and ABS braking performance, the groove width W3 of the center narrow groove 8 (perpendicular to the longitudinal direction of the groove). In the following, the same applies to other grooves.) Is preferably 0.5% to 1.5% of the tread ground contact width TW. The groove depth D3 (shown in FIG. 2) of the center narrow groove 8 is preferably 20% to 50% of the groove depth D1 of the center main groove 3.

  In the present embodiment, the center narrow groove 8 and the center main groove 3 have different zigzag shapes. Accordingly, the first land portion 5A and the second land portion 5B have different tire axial lengths along the tire circumferential direction. The maximum length L2 in the tire axial direction of the first land portion 5A and the second land portion 5B is preferably 5% to 10% of the tread contact width TW. When the maximum length L2 is less than 5% of the tread contact width TW, the rigidity in the tire axial direction of the land portions 5A and 5B is reduced, and the braking performance on snowy roads and the ABS braking performance on iced roads are deteriorated. There is a fear. When the maximum length L2 exceeds 10% of the tread contact width TW, the rigidity in the tire axial direction of the middle land portion 6 or the shoulder land portion 7 becomes small, and the turning performance on an icy road may be deteriorated.

  From the same viewpoint, the minimum length L3 in the tire axial direction of the first land portion 5A and the second land portion 5B is preferably 3% to 8% of the tread ground contact width TW.

  The center lug groove 9 has a terminal end 10 that extends from the center main groove 3 over the center narrow groove 8 and is located in the center land portion 5. Such a center lug groove 9 can form a solid snow column extending greatly in the tire axial direction across the tire equator C in the center land portion where a large contact pressure acts. Accordingly, braking performance on snowy roads is improved.

  The center lug groove 9 includes a first center lug groove 9A having a terminal end 10a located in the first land portion 5A, and a second center lug groove 9B having a terminal end 10b located in the second land portion 5B. Yes. In the present embodiment, the first center lug grooves 9A and the second center lug grooves 9B are alternately provided in the tire circumferential direction. Thereby, the edge component of the tire circumferential direction of the center lug groove 9 is ensured with sufficient balance, and ice road performance improves.

  The center lug groove 9 has a main portion 11 extending between the center main groove 3 and the center narrow groove 8 and a sub-portion 12 extending from the center narrow groove 8 to the terminal end 10.

  The main portion 11 is inclined toward the first arrival side in the rotation direction R toward the inner side in the tire axial direction. Thereby, the snow in the main part 11 is discharged | emitted smoothly to the center main groove 3 using the rotational force of a tire. On the other hand, a strong snow column is formed during braking. Therefore, the edge effect and the snow column shear force are effectively enhanced, and snow road performance is improved.

  The main portion 11 communicates with the apex 8 c of the center narrow groove 8 on the main portion 11 side of the zigzag. Thereby, the rigidity of the tire land equator C vicinity of the center land part 5 is ensured largely. Moreover, the axial direction length of the main part 11 can be shortened, and the snow removal effect can be further enhanced while increasing the rigidity. For this reason, the braking performance and the ABS braking performance on snowy roads are improved.

  An angle α2 of the main portion 11 with respect to the tire axial direction is 20 to 40 °. When the angle α2 of the main part 11 is less than 20 °, the rotational force of the tire cannot be effectively used, and the snow in the main part 11 cannot be discharged smoothly. When the angle α2 of the main portion 11 exceeds 40 °, the edge effect in the tire axial direction becomes small, and the ice road performance deteriorates. In addition, the tire axial direction component is reduced, the snow column shear force is not exhibited, and snow road performance is deteriorated. For this reason, the angle α2 of the main portion 11 is preferably 25 to 35 °.

  The sub part 12 is inclined in the direction opposite to the main part 11. For this reason, the lateral force acting on the snow column formed in the main part 11 and the sub part 12 is canceled during traveling. Accordingly, braking performance on snowy roads is improved.

  The sub-portion 12 communicates with the zigzag apex 8 c of the center narrow groove 8. Thereby, the rigidity of the tire equator C vicinity of the 1st land part 5A and the 2nd land part 5B is ensured largely. For this reason, braking performance and ABS braking performance on snowy roads are further improved.

  The angle α3 of the auxiliary portion 12 with respect to the tire axial direction is 20 to 40 °. Such a sub-portion 12 has a tire circumferential component and a tire axial component in a well-balanced manner. Therefore, ice road performance and snow road performance are improved in a well-balanced manner.

    It is desirable that the angle α3 of the sub part 12 is the same as the angle α2 of the main part 11. Thereby, the lateral force acting on the snow column formed in the main part 11 and the sub part 12 is effectively offset.

  The distance L4 in the tire axial direction between the terminal end 10 of the center lug groove 9 and the center main groove 3 is preferably 10% to 40% of the maximum length L2 in the tire axial direction of the first land portion 5A or the second land portion 5B. It is. That is, when the distance L4 is less than 10% of the maximum length L2 of the first land portion 5A, the rigidity of the center land portion 5 is reduced, and the ABS brake performance may be deteriorated. When the distance L4 exceeds 40% of the maximum length L2 of the first land portion 5A, the length of the snow column formed in the center lug groove 9 is reduced, and the snow road performance may be deteriorated.

  The groove width of the center lug groove 9 (average groove width obtained by dividing the groove areas of the main portion 11 and the sub portion 12 by the length of the groove center line) W4 is 0. It is desirable that it is 85 to 1.15 times. When the groove width W4 of the center lug groove 9 is less than 0.85 times the groove width W3 of the center narrow groove 8, the snow column shear force is reduced, and the snow road performance may be deteriorated. When the groove width W4 of the center lug groove 9 exceeds 1.15 times the groove width W3 of the center narrow groove 8, the rigidity of the center land portion 5 is reduced, and there is a possibility that the ice road performance is deteriorated. From this point of view, the groove width W4 of the center lug groove 9 is more preferably 0.95 to 1.05 times the groove width W3 of the center narrow groove 8, and more preferably the same as the groove width W3 of the center narrow groove 8. It is.

  In order to effectively exhibit the above-described action, the groove width W4 of the center lug groove 9 is desirably 6% to 10% of one pitch P of the center lug groove 9.

  The groove width W4 of the center lug groove 9 is gradually increased toward the outer side in the tire axial direction in the main portion 11. Further, the groove width W4 of the center lug groove 9 is constant in the sub-portion 12. Thereby, the rigidity in the vicinity of the tire equator C of the center land portion 5 is ensured, and the snow in the center lug groove 9 can be smoothly discharged to the center main groove 3.

  FIG. 4 shows a BB cross section of FIG. As shown in FIG. 4, the groove depth D4b of the center lug groove 9 at the communication position 9e with the center main groove 3 is the groove depth D5a at the inner end in the tire axial direction of the main portion 11 and the center lug groove. 9 is larger than the groove depth D4a at the terminal end 10. As a result, the rigidity in the vicinity of the tire equator C of the center land portion 5 that greatly contributes to the braking performance on snowy roads is increased. For this reason, the braking performance on snowy roads is further improved.

  When the groove depth D4b at the communication position 9e of the center lug groove 9 is excessively larger than the groove depth D5a at the inner end of the main portion 11 and the groove depth D4a at the terminal end 10 of the center lug groove 9, The rigidity on the outer side in the tire axial direction of the center land portion 5 may be reduced, and the ice road performance may be deteriorated. Therefore, the groove depth D4b of the center lug groove 9 at the communication position 9e is preferably 2 of the groove depth D5a at the inner end of the main portion 11 and the groove depth D4a at the end 10 of the center lug groove 9. 0.0 to 2.5 times.

  In the present embodiment, the groove depth D5 of the main portion 11 is gradually reduced from the communication position 9e of the center lug groove 9 toward the tire equator C. Thereby, the snow in the main part 11 is smoothly discharged to the center main groove 3. Further, the rigidity in the vicinity of the tire equator C of the center land portion 5 that greatly contributes to the braking performance on snowy roads is increased. For this reason, the braking performance on snowy roads is further improved. In order to effectively enhance the above action, it is desirable that the groove depth D5 of the main portion 11 is gradually reduced from the communication position 9e to the inner end 11i of the main portion 11.

  The maximum depth D5b of the main portion 11 (in FIG. 4, the same as the groove depth D4b of the center lug groove 9 at the communication position 9e) is preferably 70% to 100% of the groove depth D1 of the center main groove 3. It is.

  The groove depth D6 of the sub-portion 12 is preferably 0.85 to 1.15 times the groove depth D3 of the center narrow groove 8. If the groove depth D6 of the sub-portion 12 is less than 0.85 times the groove depth D3 of the center narrow groove 8, the snow column shear force may be reduced. When the groove depth D6 of the sub part 12 exceeds 1.15 times the groove depth D3 of the center narrow groove 8, the rigidity of the center land part 5 may be reduced. From such a viewpoint, the groove depth D6 of the sub-portion 12 is more preferably 0.9 to 1.1 times the groove depth D3 of the center narrow groove 8, and further preferably the groove depth of the center narrow groove 8 is. Same as D3.

  In this embodiment, the groove depth D6 of the sub part 12 is constant along the longitudinal direction of the sub part 12. Such sub part 12 maintains the rigidity of the center land part 5 further higher.

  As shown in FIG. 3, the center land portion 5 is provided with a plurality of sipings 13. The siping 13 in the present embodiment is an open type that connects between the center narrow groove 8 and the center main groove 3. The siping 13 extends in a zigzag shape. Such a siping 13 has edge components in the tire circumferential direction and the tire axial direction. Therefore, ice road performance is improved. In addition, the siping 13 provided in the center land part 5 is not limited to such an aspect, For example, a semi-open type or a closed type may be used.

  The siping 13 of this embodiment is inclined in the same direction as the main part 11 and the sub part 12. Thereby, the rigidity of the center land part 5 is ensured highly. In order to exhibit such an effect more effectively, it is desirable that the angle α4 of the siping 13 with respect to the tire axial direction is the same as the angles α2 and α3 of the main portion 11 and the sub portion 12. Note that the angle α4 of the siping 13 of the present embodiment is specified by a virtual straight line 13e passing through the center of the zigzag amplitude.

  As shown in FIG. 1, the middle land portion 6 is provided with a plurality of middle lateral grooves 15 that connect between the center main groove 3 and the shoulder main groove 4. Thereby, the middle land portion 6 is formed as a block row in which a plurality of middle blocks 6A divided between the middle lateral grooves 15 and 15 are provided in the tire circumferential direction.

  The middle lateral groove 15 extends from the center main groove 3 toward the shoulder main groove 4 while being inclined toward the rear arrival side in the rotation direction R. Such middle lateral grooves 15 smoothly discharge the snow in the grooves using the rotation of the tires to the shoulder main grooves 4. Therefore, the snow road performance is further improved.

  The groove width W7 and the groove depth D7 of the middle lateral groove 15 are preferably 10.0 to 12.0 mm. The groove depth D7 (shown in FIG. 2) is preferably 80% to 120% of the groove depth D1 of the center main groove 3. Thereby, a large snow column formed by the middle lateral groove 15 can be secured while securing the rigidity of the middle block 6A.

  The middle block 6A is provided with a middle vertical groove 16 having one end communicating with the middle lateral groove 15 and the other end terminating in the middle block 6A, and a middle siping 17.

  The middle vertical narrow groove 16 is inclined with respect to the tire circumferential direction. For this reason, the middle vertical narrow groove 16 has a tire axial direction component. Therefore, the traction performance on snowy roads is further improved.

  From the viewpoint of securing a large snow column in the middle vertical groove 16 while ensuring the rigidity of the middle block 6A, the groove width W8 of the middle vertical groove 16 is preferably 3.0 to 4.5 mm. The groove depth D8 of the middle vertical groove 16 is 6 to 12 mm.

  The middle siping 17 is an open-type siping whose both ends communicate with the center main groove 3, the shoulder main groove 4, the middle horizontal groove 15, or the middle vertical groove 16.

  The shoulder land portion 7 is provided with a plurality of shoulder lateral grooves 18 that connect between the shoulder main groove 4 and the ground contact Te. Thus, the shoulder land portion 7 is formed as a block row provided with a plurality of shoulder blocks 7A divided between the shoulder lateral grooves 18 and 18.

  In the present embodiment, the shoulder lateral groove 18 extends in a zigzag shape. Such a shoulder lateral groove 18 has a tire circumferential direction component, and can improve turning performance on an icy road. The groove width W9 of the shoulder lateral groove 18 is preferably 2% to 4% of the tread ground contact width TW in order to ensure a good balance between the snow column shearing force and the rigidity of the shoulder block 7A. The groove depth D9 (shown in FIG. 2) is preferably 80% to 120% of the groove depth D2 of the shoulder main groove 4.

  Further, the shoulder block 7A is provided with a semi-open type shoulder siping 19 that extends outward from the shoulder main groove 4 in the tire axial direction and terminates in the shoulder block 7A without reaching the ground contact Te. Since such shoulder siping 19 secures a large edge component while suppressing a decrease in rigidity of the shoulder block 7A, it improves ice road performance.

  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 based on the specifications shown in Table 1, and the braking performance and ABS braking performance of each sample tire were tested. The common specifications are as follows.
Tread contact width TW: 180mm
Center main groove depth D1: 11.2mm
Shoulder main groove depth D2: 11.2mm
Center narrow groove depth D3: 4.0 mm
Middle lateral groove depth D7: 11.2mm
Middle vertical groove depth D8: 9.1mm
Shoulder lateral groove depth D9: 11.2mm
Groove depth D6 of sub part: constant in tire axial direction Depth of each siping: 7.5mm
* 1: D4b is the depth of the center lug groove at the communication position with the center main groove.
The test method is as follows.

<Brake performance on snowy roads>
Each sample tire was mounted on all wheels of a 3500cc four-wheel drive vehicle under the following conditions. One test driver made the test vehicle run on a test course on a snowy road (excluding a snowy snowy road), and the running characteristics related to the braking force at this time were evaluated by the sensuality of the test driver. The results are displayed with a score of Example 1 being 100. The larger the value, the better.
Rim: 17 × 6.5J
Internal pressure: 220kPa (4 wheels)

<ABS brake performance>
In the above test vehicle, the test driver runs on a mirror-burn-shaped ice road test course at an air temperature of 0 ° C, operates ABS from a speed of 30 km / h, applies sudden braking, and brakes until the car stops. The distance was measured. The result is evaluated by the reciprocal of the braking distance, and is 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 tests, it can be confirmed that the brake performance on the snow road and the ABS brake performance are significantly improved in the tires of the examples as compared with the comparative example. The same test was performed with different tire sizes, but the same results were obtained.

3 Center main groove 5 Center land part 8 Center narrow groove 9 Center lug groove 10 End of center lug groove 11 Main part 11i Inner end 12 of main part Sub part

Claims (5)

The tread part is provided with a pair of center main grooves extending continuously in the tire circumferential direction on both sides of the tire equator, so that the tread part has a center land part divided between the center main grooves, and the rotation direction is specified. A pneumatic tire,
The center land portion has one center narrow groove extending continuously in the tire circumferential direction on the tire equator, and a terminal end extending from the center main groove beyond the center narrow groove and located in the center land portion. And having a plurality of center lug grooves,
The center lug groove extends between the center main groove and the center narrow groove, is inclined toward the first arrival side in the rotational direction toward the inner side in the tire axial direction, and has an angle of 20 to 40 ° with respect to the tire axial direction. The main part,
Extending from the center narrow groove to the terminal end, and having a sub-part inclined in the opposite direction to the main part and having an angle of 20 to 40 ° with respect to the tire axial direction,
The groove depth at the position where the center lug groove communicates with the center main groove is determined by the groove depth at the inner end of the main portion in the tire axial direction and the groove depth at the end of the center lug groove. Pneumatic tire characterized by being large.   The pneumatic tire according to claim 1, wherein the center land portion is provided with siping.   The pneumatic tire according to claim 1 or 2, wherein a groove width of the center lug groove is 0.85 to 1.15 times a groove width of the center narrow groove.   The pneumatic tire according to any one of claims 1 to 3, wherein a groove depth of the main portion is gradually reduced from the communication position of the center lug groove toward the tire equator.   The pneumatic tire according to any one of claims 1 to 4, wherein a groove depth of the sub-portion is 0.85 to 1.15 times a groove depth of the center narrow groove.

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