Resilient tires and wheels – Tires – resilient – Anti-skid devices
Patent
1997-11-03
1999-09-28
Maki, Steven D.
Resilient tires and wheels
Tires, resilient
Anti-skid devices
152902, 152DIG3, B60C 1111, B60C 1112, B60C 1113, B60C10700
Patent
active
059571802
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a pneumatic tire for a passenger car. More particularly, this invention relates to a pneumatic tire for a passenger car which improves driving performance on snow and dirt roads without lowering dry performance.
BACKGROUND ART
In pneumatic tires for passenger cars in general, the increase of an edge quantity by increasing the number of blocks and the number of kerfs disposed on the blocks is effective for improving driving performance such as braking/driving performance during driving on snow roads and dirt roads. If the number of blocks is simply increased, however, the blocks are divided into finer blocks and block rigidity drops, so that dry performance drops. The same problem occurs when the number of kerfs is increased.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a pneumatic tire for a passenger car capable of improving driving performance on snow and dirt roads without deteriorating dry performance.
In a pneumatic tire for a passenger car including a plurality of grooves disposed on a tread surface thereof, land portions divided and defined by the grooves and kerfs disposed on the land portions and opening at at least one of the ends thereof to the grooves, the pneumatic tire for a passenger car for accomplishing the object described above is characterized in that at least one stage of step portion is disposed in a step shape on at least one of the grooves walls of the grooves, and kerfs are disposed on this step portion with smaller gaps than those between the kerfs disposed on the land portions.
In the present invention, the grooves described above include at least one main groove extending in a tire circumferential direction and a plurality of transverse grooves extending in a tire width-wise direction.
In the pneumatic tire for a passenger car according to the present invention, the step portion is formed on the groove walls of the grooves, and the kerfs are disposed on the upper surface of the step portion in greater number and with smaller gaps than those between the kerfs disposed on the land portions. Therefore, the kerfs disposed on the step portion exhibit an edge effect against the snow and mud entering the grooves during driving on the snow road and the dirt road.
When the kerfs extending in the tire width-wise direction are disposed on the land portions divided by the main grooves and the kerfs extending in the same direction as the kerfs on the land portions are disposed on the step portion disposed on the wall grooves of the main grooves with smaller gaps than those between the kerfs of the land portions, braking/driving performance on the snow road and the dirt road can be improved.
On the other hand, when the kerfs extending in the tire circumferential direction are disposed on the land portions divided by the transverse grooves and the kerfs extending in the same direction are disposed on the step portion formed on the groove walls of the transverse grooves with smaller gaps than those between the kerfs of the land portions, turning performance on the snow road and the dirt road can be improved by the edge effect of the kerfs extending in the tire circumferential direction. This effect becomes remarkable particularly when the construction described above is provided to the land portions disposed in the shoulder zones of the tread.
The effect of the improvement in braking/driving performance and turning performance on the snow road and the dirt road can be accomplished without increasing the number of blocks and the number of kerfs on the blocks irrespective of these numbers. Therefore, dry performance (dry road maneuvering stability), which is governed mainly by the surface area of the land portions and the degree of rigidly, is not spoiled.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a front view of principal portions and shows an example of a tread pattern of a pneumatic tire for passenger cars according to the present invention;
FIG. 2 is an enlarged sectional view and shows an example of step por
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patent: 4703788 (1987-11-01), Kusube et al.
patent: 4854358 (1989-08-01), Takeuchi
patent: 5492161 (1996-02-01), Fuchikami et al.
patent: 5814169 (1998-09-01), Yamaguchi et al.
Kuramochi Izumi
Tokieda Akinori
Maki Steven D.
The Yokohama Rubber Co. Ltd.
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