Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1999-06-15
2002-12-03
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209160, C152S209180, C152S209270, C152S901000, C152SDIG003
Reexamination Certificate
active
06488064
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to vehicle tires, and more particularly to heavy duty truck tires. The invention is particularly useful with long haul trucking operations in reducing the irregular wear of front axle tires.
The problem of irregular wear in long haul truck tires is well known in the art. Truck tires that experience straight ahead driving for a large portion of their life develop wear patterns which are different. Tire stresses from turning and maneuvering the vehicle only exist for a limited time compared with tire stresses from straight ahead highway driving. The axle alignment of the truck as well as compliance of truck suspension and steering linkages become much more important in producing tire wear. Normal stresses can also become as important as the longitudinal and lateral stresses in producing tire wear.
Those patents which disclose various solutions for the problem of irregular wear and endurance in steer axle truck tires include U.S. Pat. Nos. 4,214,618; 4,480,671; 4,890,658; 5,010,936; 5,099,899 and 5,131,444, French Patent No. 2,303,675 (FR675), British Patent No. 2,027,649 (GB649), Japanese Patent No. 3-253408 (JP408) and PCT Patent Application No. 9202380-A (PCT380). These references disclose means to control the shape of a shoulder area of a tire's tread in an effort to limit the onset of irregular changes in the tread shape as the tire wears (i.e. railway wear). The use of shoulder grooves of various sizes and at various locations where the contact area of the tread transitions into the shoulder area is disclosed. However, none of these references disclose a shoulder rib that will reduce the stresses on the first interior rib to delay the onset and reduce the growth of irregular wear over a substantial portion of the life of the tire's tread.
The use of narrow shoulder ribs on the front steer axle truck tire to control wear on the main circumferential ribs is known in the art. The general problem with the teachings of the art is characterized by the fact that relatively narrow shoulder ribs and narrow grooves separating the narrow shoulder rib from the first interior rib is only effective when the tire is relatively new. The narrow shoulder ribs quickly wear producing and a relatively large recess so that the narrow shoulder rib does not carry a large enough portion of the tire load after initial wear is experienced. This problem is not solved with either no initial recess or a large initial recess as the shoulder rib of the tire develops its own stable recess magnitude during the initial wearing process. To improve rib wear and endurance of the tire the use of wider shoulder ribs and somewhat narrower grooves have been disclosed in Australian Patent No. 622983 (AU983), PCT Application No. 9202380-A (PCT380) and Japanese Patent No. 2-253408 (JP408). These references are discussed in more detail in the following paragraphs.
The Australian Patent AU983 discloses a tire for vehicles traveling long distances at sustained speed with medium to high loads on the tire. The wear life of the tread is improved by including narrow shoulder grooves having a width of 3.5 millimeters, wide shoulder ribs each having a width at least 13 percent of the total contact width and a shoulder rib recess having a value between 0.5 and 5.0 millimeters. The disclosed shoulder rib width is relatively large; being at least 35 millimeters for a tire with a main tread width of 200 millimeters.
In the PCT application PCT380 a truck tire is disclosed for long runs at sustained speeds which has increased resistance to separation between the layers of subtread reinforcement. Resistance to separation is improved by a narrow shoulder grooves having a width between 0.6 and 8 millimeters, wide shoulder ribs having a width between 17 and 34 millimeters and a shoulder rib recess having a value of less than 40 percent of the depth of the main tread grooves. Once again the shoulder rib width is relatively large and the preferred recess is also relatively large.
The Japanese Patent JP408 discloses a tire with reduced shoulder abrasion and gravel biting. Resistance to abrasion is realized by including thin narrow shoulder grooves with a groove width from 0.2 to 3 percent of the main tread width, the shoulder ribs have a width greater than 90 percent of the main groove depth of the main tread portion with a sloping contact surface area between 20 and 60 degrees, but the patent is silent about the magnitude of the shoulder rib recess. The sloping contact surface area of the shoulder rib is at least 20 degrees to help prevent gravel biting as well as groove cracking and tearing.
Another design feature known in the art to assist the tire tread in increasing tread life by reducing irregular wear is the addition of spaced apart sipes which extend laterally into the main ribs from the main grooves, as well as from the narrow shoulder grooves into the first interior ribs. This siping can be further enhanced by inclined sipes which are inclined in the depth direction from a normal line to the tread surface of the tire. Inclined siping is disclosed in Japanese Patent No. 5-338418 (JP418) and in AU983. In JP418 the inclined sipes are placed so that the sipes have an inner end which trails the surface end during forward rotation of the tire. This inclined sipe is used to lower rib rigidity. No siping is indicated adjacent the narrow shoulder end part 2 (FIG. 1). The inclined siping disclosed in AU983 is inclined at an angle to the normal line at the tread surface between 5 and 25 degrees. The siping of this reference is used in combination with a very wide shoulder rib as previously discussed.
In yet another design feature, known in the art to assists the tire tread to increase tread life by reducing irregular wear, the tread design controls the amount of normal load on the main ribs by the addition of a stepped rib which is placed adjacent to the rib or ribs to be protected. In the disclosure of US444, the stepped rib zones contact the ground within the main tread width land portion to help support the load of the tire. The total width of the stepped zones is in a range from 5 to 25 percent of the tread ground contact area and the stepped zones have a recess which is proportional to the load on the tire and the tread gage and inversely proportional to the tread contact area and the modulus of elasticity of the tread rubber. Recessed values of 2 millimeters or greater are used. Contact of the stepped zone with the ground is based on contact with at least 50 percent but less than 200 percent of the maximum load on the tire tread. Each stepped zone is inside the land portion of the tread and is limited by two narrow grooves or narrow cuts and the load supporting land portions encompass the full lateral width of the tire. The US444 disclosure is silent about the width of narrow grooves and cuts, and about the use of stepped zones at the lateral edges of the tire tread.
Another patent that discloses a tread design that controls the amount of normal load taken by a stepped rib which is placed adjacent to the rib or ribs to be protected is British Patent No. 532,534 (GB534). Grooves between the load bearing ribs have thinner ribs which are separated from the load bearing ribs by narrow grooves about 0.8 millimeters in width. The thinner ribs may be recessed but no values are given for the magnitude of the recesses. The GB534 patent is silent about recessed ribs on the lateral edges of the tread.
A need remains to have a shoulder rib which becomes a sacrificial rib that maintains contact with the ground surface to reduce the loads taken by the main tread width, especially the first interior rib. A means for maintaining a load on the shoulder ribs can effectively reduces the stresses on the main ribs of the steer axle truck tire during straight ahead driving. The need is to cause tread wear to be more uniform across the tire's tread. The first interior rib of the tread width on each lateral side of the tire is subjected to high loads which produce relatively high stresses whi
Csontos Alan A.
Farrell Martin
Maki Steven D.
Michelin & Recherche et Technique S.A.
Remick E. Martin
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