Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2000-07-19
2003-06-03
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209220, C152S209230, C152S209270, C152S902000, C152SDIG003
Reexamination Certificate
active
06571844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic tire and more particularly to a pneumatic tire having a tread with a block pattern.
2. Description of the Related Art
Sipes formed in ribs and blocks of a tread exhibit the effect of cutting through water films on road surfaces, similar to edges of grooves. The sipes also facilitate deformation of ribs and blocks and help exhibition of rubber hysteresis loss. Therefore, sipes are widely used in studless tires.
As shown in
FIG. 3
, studless tires generally have zigzag or straight sipes
100
, extending substantially parallel to tire circumferential-direction end portions of blocks (i.e., the end portions of blocks which are continuous with the block end portions running along the circumferential direction of the tire). Alternatively, as shown in
FIG. 26
, studless tires generally have sipes
102
which are approximately perpendicular to the circumferential direction of the tire in each block
101
.
However, when the sipes incline in the same direction on each block as described above, and when tires are used on snowy or icy roads, the effects of the sipe is satisfactory only for driving direction. Moreover, the degree of deformation of the blocks during driving is markedly different depending on the direction of the applied force. This means that the conventional method of forming sipes is not effective for improving cornering property, although the method is effective for improving braking and traction properties on ice. Moreover, when the tires are used on dry or wet roads, the rigidity of the blocks with respect to forward or backward force is small. Therefore, controllability at small steering angles is often insufficient. Even if the angle of sipes with respect to tire circumferential direction is changed, it is difficult to obtain suitable properties for both of braking and traction because rigidity of the block with respect to the forward force is different from that with respect to the backward force.
To improve tire braking on icy roads, it is desirable to increase sipe density at the central portion of the blocks. However, when the density of the sipes in an entire block is increased, block rigidity decreases and there is the possibility that controllability for dry and wet roads, and abrasion resistance of the tire are adversely affected.
When the density of sipes on entire blocks is excessively increased, the area of the tread contacting road surfaces decreases due to blocks collapsing and the properties when driving on icy roads also deteriorate. Moreover, in the above case, defects such as bareness and chipping tend to be more frequent during tire production.
For simultaneous good block rigidity and sipe effect (edge effect and water removal), it is desirable that the density of sipes be increased in the central portion of a block and decreased in block peripheral portions (for example, Japanese Patent Application Laid-Open No. 9(1997)-164816). However, from the standpoint of production, it is difficult to satisfactorily produce such a tire using conventional technology.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the above problems of conventional methods of forming sipes and provide a pneumatic tire having improved properties for icy and snowy roads, and in particular, good properties when used on icy roads.
Another object of the present invention is to provide a pneumatic tire having a block pattern with suitable sipe effect in multiple directions, good block rigidity with respect to force in any direction, and high density of sipes in the central area of each block.
Still another object of the present invention is to provide a pneumatic tire having a block pattern with suitable sipe effect in multiple directions, good block rigidity with respect to force in any direction, high density of sipes, and good tire properties for both braking and traction.
Still another object of the present invention is to provide a pneumatic tire having a block pattern with satisfactory sipe effect in multiple directions, good block rigidity with respect to force in any direction, and good controllability and resistance to uneven wear.
Still another object of the present invention is to provide a pneumatic tire having a block pattern which provides improved properties when driving on icy and snowy roads without adverse effects to properties when driving on dry roads and wet roads.
As the first aspect, the present invention provides a pneumatic tire comprising a tread having blocks defined by a plurality of intersecting grooves, wherein each of the blocks have at least one pair of sipes which are formed from first and second sipes, the first sipe extends from one of two tire axial direction end portions of the block and is inclined with respect to a circumferential direction of the tire. The second sipe extends from the other tire axial direction end portion of the block and is inclined with respect to the circumferential direction of the tire. The first and second sipes are alternately disposed along the circumferential direction of the tire. An end portion of the first sipe in the vicinity of a center of the block, and an end portion of the second sipe in a vicinity of a center of the block, intersect an imaginary common line extending along the circumferential direction of the tire. Further, the first and second sipes are inclined in opposite directions.
In the block, the sipe edge effect can be obtained for force applied from any direction since the first and second sipes are disposed alternately and the first and second sipes are inclined in opposite directions. For example, when a force from a direction parallel to the first sipe is applied to the tire, the second sipe provides the edge effect, although there is substantially no sipe edge effect from the first sipe in this case. That the first and second sipes incline in opposite directions means that, in the portion of the tire contacting the road surface when the tire is used on a vehicle, the first sipe is inclined in a manner such that the end portion of the first sipe, which end portion is at the side of the center of the block is placed in the front or in the rear of the other end portion, the second sipe is inclined in a manner such that the end portion of the second sipe, which end portion is at the side of the center of the block is placed in the front or in the rear of the other end portion. The angle between the first sipe and the circumferential direction of the tire is not always the same as the angle between the second sipe and the circumferential direction of the tire. Therefore, the cornering property when driving on icy road, on which the sipe edge effect is particularly effective, can be improved.
Since the end portion of the first sipe which is at the side of the center of each block and end portion of the second sipe which is at the side of the center of each block intersect an imaginary common line extending along the circumferential direction of the tire, the number of sipes in the central area of the block is greater relative to that in the peripheral areas of the block (end portions of the block).
Since the density of sipes increases in the central area of the block in which, when driving on icy roads, water film forms more easily than in the peripheral areas of the block, the number of edge components is effectively increased, and water film absorption properties are enhanced, and braking and traction properties improve. Here, edge components designate portions of both sides of a groove and portions of both sides of a sipe which are substantially straight and which form an edge when the sipe is open.
Moreover, density of sipes in the peripheral areas of the block (end portions of the block) can be lower than density of sipes, formed by conventional methods, in the peripheral areas for providing sufficient block rigidity. More specifically, since rigidity at the central area of the block can be decreased while maintaining sufficient block rigidity in peripheral portions, a
Kawabe Hiroshi
Kimura Masaharu
Kurokawa Makoto
Ochi Naoya
Yoshida Hiroto
Bridgestone Corporation
Maki Steven D.
Sughrue & Mion, PLLC
LandOfFree
Pneumatic tire having tread including pairs of sipes does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pneumatic tire having tread including pairs of sipes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pneumatic tire having tread including pairs of sipes will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3099188