JPH11157308A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To regain the edge-effect (of a tire) and to restrict a lowering of the performance of the tire on the ice due to wear by making new, sharp block- edges appear in turn as the wear progresses. SOLUTION: Sipings are formed in a block partitioned by a longitudinal groove and a lateral groove 4. The lateral groove wall face 5 is provided with a step-region RS, which has a stepped surface Si and which extends like a staircase from a tread surface 2, and a non-step region RN, which extends down to the bottom of the groove. In this case, the length of projection Xi of the stepped surface Si should be equal or longer than 0.2 mm and moreover it should be shorter than 0.25 times the lateral groove width Wa at the tread surface. Moreover, the sum of the length of projection of the step surface on both sides should be equal or greater than 0.4 mm and moreover it should be smaller than 0.3 times the lateral groove width Wa. On the other hand, the length of the step region RS should be 0.3 to 0.75 times the depth D of the lateral groove.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire for traveling on snow and ice roads, and more particularly to a studless tire.

[0002]

2. Description of the Related Art In recent years, studless tires have become mainstream as tires used during snowfall in winter and when the road surface is frozen.

[0003] In this studless tire, a high shearing force is generated by a snow column stepped between blocks to secure performance on snow. For the performance on ice, the block is provided with a plurality of sipes, the road surface is dug up by each edge of the block and the siping, the frictional force (edge effect) is increased, and the tread is formed of soft rubber, so that the tread is formed. Increasing the adhesive friction has been performed.
In particular, in recent years, there has been a strong demand for an improvement in grip force on a frozen and ice-burned road surface, and the increase in the number of sipes and the softening of tread rubber have been further promoted.

[0004]

However, the increase in the number of sipes and the softening of the tread rubber decrease the wear resistance of the tread rubber. Furthermore, if the tire travels a short distance on the dry road, the edges at both ends in the circumferential direction of each block are worn round. In addition, the contribution of the block edge to the road surface excavation friction force (edge effect) is extremely large as compared with other siping edges, and therefore, the wear of the block edge causes a significant decrease in performance on ice. Becomes

Japanese Patent Application Laid-Open No. 2-283507 discloses that
In order to improve the traction performance on snow, a technique of forming a groove wall in a step shape has been disclosed. This is intended to improve the compaction effect of the snow column in the groove, that is, to improve the shearing force of the snow column. Become. As a result, there is a problem that the wet grip performance is reduced due to a decrease in the lateral groove volume, and uneven wear is caused by the step surface.

Accordingly, the present invention aims at recovering the edge effect by successively generating new sharp block edges as the wear progresses, and in particular, aims to suppress the deterioration of the performance on ice due to wear, as well as the wet grip performance and the uneven wear resistance performance. The purpose of the present invention is to provide a pneumatic tire in which the deterioration of the tire is prevented.

[0007]

In order to achieve the above object, a pneumatic tire according to the present invention comprises at least one longitudinal groove extending in the tire circumferential direction on a tread surface and a plurality of lateral grooves communicating with the longitudinal groove. By providing, the tread surface is divided into a plurality of blocks, and the block includes a sipe-equipped block having a siping opening at least one end in the vertical groove, and lateral groove wall surfaces on both sides of the lateral groove,
A step region having a step surface protruding toward the groove center side and extending stepwise radially inward from the tread surface, and a non-step region extending from the inner edge of the lowermost step surface to the groove bottom in the step region And the vertical wall portion except the step surface of the horizontal groove wall surface is inclined at a right angle to the tread surface or in a direction to decrease the horizontal groove width W from the tread surface toward the groove bottom,
The projecting length Xi of the step surface toward the center of the groove is 0.2
mm and not more than 0.25 times the width Wa of the lateral groove on the tread surface, and the sum ΣXi of the protruding lengths Xi of the step surfaces X on the side walls of the lateral grooves is 0.4 mm or more and not more than 05 times the width Wa of the lateral groove. In addition, the step region length, which is the radial distance from the tread surface to the lowermost step surface, is 0.3 mm of the lateral groove depth from the tread surface.
It is not less than twice and not more than 0.75 times.

In the step region thus formed on the lateral groove wall surface, even if the block edge is rounded due to abrasion and the edge effect is once reduced, new sharp edges appear sequentially and the edge effect can be maintained. .

[0009]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 illustrates the simplest tread pattern 1 for a studless tire that can be employed in the pneumatic tire of the present invention. The effect of the present invention was evaluated using this pattern 1.

The tread surface 2 has at least one longitudinal groove 3 extending in the tire circumferential direction, and a plurality of lateral grooves 4 communicating with the longitudinal groove 3.
, The tread surface 2 is divided into a plurality of blocks B. In this example, as the longitudinal grooves 3, four longitudinal grooves 3A, 3A, 3
Although B and 3B are shown, for example, zigzag grooves may be used, and the number thereof may be appropriately selected from one or more according to the required tire performance, tire size, and the like.

Similarly, in the present embodiment, as the lateral grooves 4, a central lateral groove 4A connecting between the inner vertical grooves 3A and 3A, an intermediate lateral groove 4B connecting between the inner and outer vertical grooves 3A and 3B, and an outer A lateral groove 4C extending between the vertical groove 3B and the tread edge Te is provided. In this example, the lateral grooves 4A, 4A,
By arranging B and 4C substantially in a line, the tread edge Te,
One linear lateral groove extending between Te and substantially parallel to the tire axis is formed. These lateral grooves 4 are not necessarily parallel to the tire axis, and the inclination angle and the inclination direction with respect to the tire axis can be different for each lateral groove 4, and can be shifted in the tire circumferential direction so that the opening ends do not coincide. May also be changed for each block row.

Also in the block B, in this example,
Although a rectangular shape is illustrated, various block shapes can be employed without being limited thereto.

The block B includes a sipe-attached block Bk having a sipe K whose longitudinal groove 3 opens at least one end. The siping K has a narrow groove shape or a notch shape with a groove width of 2.0 mm or less. In this example, a case where all blocks B have the same number of the sipes K whose both ends are opened at the vertical groove 3 or the tread edge Te. Is shown. Note that the tread center area Y greatly affects grip performance on snow and ice.
It is also possible to improve the rigidity of the shoulder region Y2 by providing the siping K only in the block B in No. 1 and not providing the siping K in the outer block B serving as the shoulder region Y2 or by reducing the number of sipings.

FIG. 2 shows a cross section taken along a line II, which is perpendicular to the groove center line of the lateral groove 4 and is, in this example, a circumferential direction. The lateral groove wall surfaces 5, 5 on both sides of the lateral groove 4 extend stepwise from the tread surface 2 radially inward in a stepwise manner, and extend from the inner edge of the lowermost step surface Sn in the step region RS to the groove bottom. And a non-step region RN including only the vertical wall surface portion 6.

As shown in an enlarged view in FIG. 5, the step region RS has a vertical wall portion 7 extending downward toward the groove bottom.
And step surfaces Si (i = 1 to n) that protrude inward from the lower end of the vertical wall surface portion 7 toward the groove center side. S
One having 1, S2, and S3 (n = 3) is disclosed. The radial direction length R1 of the step region RS, that is, the tread surface 2 to the lowermost step surface S3 (S
The radial distance to n) needs to be 0.3 times or more and 0.75 times or less the transverse groove depth D. In other words, the radial length R2 of the non-step region RN is determined by the transverse groove depth. Is set in the range of 0.7 to 0.25 times of.

FIG. 3 schematically shows the block B as viewed from the side of the tire. When traveling on an icy and snowy road surface, an edge effect (road surface digging friction force) by the block edge BE is important for securing friction on a high slip surface such as a snow surface or an ice surface. However, in the block B of a tire in which the rigidity of the block B is set to be low, such as a studless tire, the movement of the block edge BE during rolling of the tire is large, and the contact with the road surface causes the edge BE to move as shown in FIG.
, And the edges are easily lost.

In the tire according to the present invention, the stepped region RS is provided in the lateral groove wall surfaces 5 and 5 of the lateral groove 4,
A new edge is exposed on the tread surface 2 immediately after the edge is worn round, so that the edge effect can be maintained.

In winter tires for running on icy and snowy roads, a platform is formed at a position half the groove depth of the main groove.
Ice and snow road running performance is guaranteed up to 50% wear,
After this 50% wear, it is used for running on a normal road surface without snow or ice. The coefficient of friction on a normal road surface is significantly higher than on snow or ice, so the step surface Si is likely to cause uneven wear on a normal road, and the step surface Si near the groove bottom may cause cracks. Cheap.

Therefore, in the present invention, the non-step region RN is provided on the lateral groove wall surface 5 so that, after the wear of the step region RS, the non-step region RN can be shifted to the non-step region RN. The evil has been eliminated.

Here, the step region length R1 is equal to the lateral groove depth D.
Is less than 0.3 times, the edge effect is not sufficiently maintained by the above-described step region RS, and if it exceeds 0.75 times to reach the vicinity of the groove bottom, it tends to cause the uneven wear and cracks described above. Become. Therefore, it is necessary to secure a range of 0.70 to 0.25 times the horizontal groove depth D from the groove bottom as the non-step region RN. Still more preferably, FIG.
As shown in FIG.
The step area RS is set up to the% position.

Next, FIG. 5 shows details of the step area RS. The step surface Si is formed from a horizontal plane substantially parallel to the tread surface 2. The vertical wall portions 6 and 7 of the horizontal groove wall 5 excluding the step surface Si have a direction perpendicular to the tread surface 2 (90 degrees) or a direction in which the horizontal groove width W decreases from the tread surface 2 toward the groove bottom. It is inclined. This provides a sharp edge with an apex angle of approximately 90 degrees at the inner edge of the step surface Si, secures the rigidity of the block B, and makes it difficult for cracks to occur at the groove bottom. Preferably, vertical wall portion 7 in step region RS is formed at 90 degrees with respect to tread surface 2. This is because, when the step surface Si is formed on the inclined groove wall surface as in the related art, the reduction of the groove width due to wear becomes too fast, and the reduction of the wet grip due to wear is promoted.

In this embodiment, the vertical wall 6 of the non-step region RN is replaced with a steeply inclined surface 6a substantially parallel to the vertical wall 7.
And a gentle inclined surface portion 6b which has a gentler inclination than the steeply inclined surface portion 6a and has a radius of curvature of 1.0 mm or more and which is smoothly connected to the groove bottom to prevent the occurrence of cracks. .

Each of the projecting lengths Xi of the step surface Si formed in the step region RS toward the center of the groove is set to 0.1.
2 mm or more is required. If the thickness is less than 0.2 mm, it is difficult to prepare the tire mold due to processing, and the block edge BE is affected by the round wear, and the step surface Si is already roundly worn before the step surface Si is exposed on the tread surface. Is lost and the effect of the step is lost.

If the projection length Xi of each step surface Si exceeds 0.25 times the width Wa of the lateral groove on the tread surface, the width W of the lateral groove, that is, the volume of the lateral groove is excessively reduced, and the shear force of the snow column is reduced. It has a negative effect on traction performance on snow.

For the same reason, the sum ΣXi of the protruding lengths Xi of each step Si is 0.4 mm or more and the width of the lateral groove Wa is
Is set to a range of 0.5 times or less.

FIG. 6 is a view of the block B as viewed from the tire lateral direction. A plurality of sipes K extending in the tire axial direction are formed in the block B sandwiched between the lateral grooves 4,4. Although the depths of the sipings K may all be the same, the rigidity of the block small portion b divided between the sipes K, K and between the siping K and the lateral groove 4 is made uniform,
As shown in FIG. 6, the siping K1 closest to the lateral groove 4 can be formed shallower than other sipes K, as shown in FIG. In this case, it is desirable that the step region length R1 of the lateral groove 4 is 0.5 times or more the depth Lk of the siping K1 closest to the lateral groove 4 in the block. If the ratio is less than 0.5 times, the small block b1 between the lateral groove 4 and the siping K1 is greatly inclined and the edge is likely to be rounded.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Using the pattern shown in FIG. 1, the change in friction coefficient μ based on the amount of wear was measured for a tire having a step region according to the present invention and a tire having no step region, and the results are shown in Table 1.

Measurement method: Rim (15 × 6)
1/2 JJ), internal pressure (200 kpa), using a vehicle mounted on all wheels (2500 cc domestic passenger car), at a speed of 30 km / h, four-wheel full-lock braking on ice, and braking distance to stop Was measured, and an average friction coefficient μ was calculated by the following equation (1). Coefficient of friction μ = (entry speed) ² / {2 x 9.8 x (braking distance)} ---- (1) Measurement conditions are weather (sunny) and road surface (ice plate: Nayoro Test, Sumitomo Rubber Industries, Ltd.) Course) Temperature (-6 ° C), temperature on ice (-3 ° C).

[0029]

[Table 1]

The use of the tire used in this test is shown below.

[0031]

[Table 2]

[0032]

As described above, according to the present invention, it is possible to suppress a decrease in the edge effect of the lateral groove due to the progress of abrasion without deteriorating other performances, and to maintain a high performance on ice and snow.

[Brief description of the drawings]

FIG. 1 is a plan view showing a tread pattern to which the present invention is applied.

FIG. 2 is a cross-sectional view showing a lateral groove of the tread pattern of the present invention.

FIG. 3 is a diagram showing a block for explaining an effect of the present invention as viewed from a tire lateral direction.

FIG. 4 is a diagram showing a block for explaining the effect of the present invention as viewed from a tire lateral direction.

FIG. 5 is an enlarged sectional view showing a lateral groove wall surface of the present invention.

FIG. 6 is a sectional view showing a block according to an embodiment of the present invention.

[Explanation of symbols]

 2 Tread surface 5 Lateral groove wall surface 6, 7 Vertical wall portion B block Bk Block with sipe K siping K1 siping closest to lateral groove LS siping depth R1 step region length RS step region RN non-step region Si step surface Sn step surface

Claims (2)

[Claims] 1. The tread surface is divided into a plurality of blocks by providing at least one vertical groove extending in the tire circumferential direction and a plurality of horizontal grooves communicating with the vertical grooves on the tread surface. The longitudinal groove includes a sipe block having a siping opening at least one end, and the lateral groove wall surfaces on both sides of the lateral groove have a step surface protruding toward the groove center side and are radially inward from the tread surface. A step region extending stepwise, and a non-step region extending from the inner edge of the lowermost step surface to the groove bottom in the step region, and the vertical wall surface portion of the lateral groove wall surface excluding the step surface is the tread. While it is inclined at right angles to the surface or in a direction to decrease the lateral groove width W from the tread surface toward the groove bottom, while the protrusion length of the step surface toward the groove center side Xi is, 0.2
mm and not more than 0.25 times the width Wa of the lateral groove on the tread surface, and the sum ΣXi of the protruding lengths Xi of the step surfaces X on the side walls of the lateral grooves is 0.4 mm or more and not more than 05 times the width Wa of the lateral groove. And the step region length, which is the radial distance from the tread surface to the lowermost step surface, is 0.3 times or more and 0.75 times or less the transverse groove depth from the tread surface. A pneumatic tire characterized by the following. 2. The length of the step region of the lateral groove is at least 0.5 times the depth of the sipe closest to the lateral groove among the sipes arranged in the sipe-equipped block. Pneumatic tires.