Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2000-01-27
2001-09-25
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209120, C152S209220, C152S902000
Reexamination Certificate
active
06293323
ABSTRACT:
TECHNICAL FIELD
This invention relates to a pneumatic tire and, more particularly, to a pneumatic tire for off-road use.
BACKGROUND ART
Tire designers are continuously working to improve a tire's working footprint. The working footprint affects the following tire variables: traction, noise, vibration, and handling. Although these variables are the same for all types of tires, the importance of each variable is dependent upon the type of tire. For example, in off-road tires, users are primarily concerned with the traction and vibration of the working footprint.
FIG. 4
shows the Goodyear RL-2 Radial Semi Xtra Tread Traction tire as seen in the 1984 Tread Design Guide at page 205. The RL-2 is an off-road tire used on articulated dump trucks, loaders, graders, and other off-road machinery. The RL-2 provides excellent traction, especially circumferential traction. However, in some applications the RL-2's tread design causes a higher than desired vibration.
A large portion of the vibration caused by a tire occurs when a lug either enters the footprint or leaves the footprint. Upon entering the footprint, the tread lug is compressed causing an impact vibration. When a tread lug leaves the footprint, the lug snaps back to its original position causing additional vibration. The amplitude of the vibration is highest when the footprint length is such that an entering lug impacts at the same time that a leaving lug snaps back to its original position.
Two major factors contributing to the high vibration of the RL-2 are the nearly axal alignment of the lugs and the width of the lateral grooves. The nearly axial alignment of the lugs allows a large percentage of each lug to enter the footprint at once. This causes an instantaneous compression of a large percentage of the lug and results in increased vibration. The RL-2 also has wide lateral grooves. Since wider grooves lower a tire's bending stiffness, the wide lateral grooves of the RL-2 result in a low circumferential bending stiffness allowing the tread to easily bend in a circumferential direction. The more the tread bends, the greater the lugs protrude from the tread surface and the greater the amplitude of the vibration caused by their impact and release. In addition to lowering a tire's bending stiffness, the wider grooves reduce the area of the lugs in the footprint of the tire. As a result, the pressure distributed upon each lug in the footprint is increased. As the pressure upon each lug is increased, the amount of deformation of the respective lug is increased, resulting in an increase in the amplitude of the vibration.
U.S. Pat. No. 4,649,976 discloses a tread with a plurality of series of independent tread elements separated by curved grooves, shown in FIG.
5
. Each series of independent tread elements extends in a curved path across the width of the tread. Each tread element, in a respective series, is separated from the other tread elements by a straight groove. These straight grooves are of the same depth as the curved grooves. The tire disclosed in this patent provides a smoother ride than the RL-2 because the curved path allows the series of independent tread elements to overlap one another as they enter or leave the footprint. This overlap results lower vibrations because there is less compression as each tread element enters the footprint and less snap back as each element leaves the footprint.
This invention makes further improvements to the working footprint of an off-road tire. The tire of this invention provides excellent traction, yet lower vibration than the tires disclosed in the prior art.
SUMMARY OF THE INVENTION
This invention relates to a pneumatic tire for off-road use. The pneumatic tire has a tread with a plurality of lugs. Each lug extends across the tread from a first shoulder to a second shoulder. The tire also has a plurality of wide grooves, which separate circumferentially adjacent lugs.
The tire has at least first and second lugs. The lugs alternate circumferentially between a first lug and a second lug. Each first lug has three tread elements. The free tread elements in the first lug are separated by a first and a second narrow groove. Each second lug has two tread elements. The two tread elements of the second lug are separated by a third narrow groove.
DEFINITIONS
For ease of understanding this disclosure, the following terms are disclosed.
“Axi” and “Axially” are used to refer to lines or directions that are parallel to the axis of rotation of the tire.
“Circumferential” means lines or directions extending along the perimeter of the surface of the annular tire parallel to the equatorial plane (EP) and perpendicular to the axial direction.
“Crown” refers to the circumferentially outermost portion of the carcass substantially within the width limits of the tread.
“Equatorial plane” (EP) means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread.
“Footprint” means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load pressure or under specified pressure and speed conditions.
“Groove” means an elongated void area in a tread that may extend circumferentially or laterally about the tread in a straight, curved or zigzag manner. The groove width is equal to the tread surface area occupied by a groove or groove portion, divided by the length of such groove or groove portion; thus, the groove width is its average width over its length. Grooves, as well as voids, reduce the stiffness of tread regions in which they are located. The depth of a groove may vary around the circumference of the tread, or the depth of one groove may be constant but vary from the depth of another groove in a tire.
“Lateral” means an axial direction.
“Leading” refers to a portion or part of the tread that contacts the ground first, with repect to a series or such parts or portions, during rotation of the tire in the preferred direction of travel.
“Lugs” means a radial rows of tread rubber extending across the width of the tire. At least part of the lug is in direct contact with the ground or road surface. A lug can be made up of a plurality of tread elements that are separated by grooves.
“Nonskid” means the depth of grooves in a tire tread.
“Pitch” means the difference from one peak in the tread pattern to the next. Pitch refers to the circumferential distance from one design feature in the tread pattern to the next similar design feature.
“Pneumatic tire” means a laminated mechanical device of generally toroidal shape, usually an open torous, having beads and a tread and made of rubber, chemicals, fabric and steel or other materials. When mounted on a wheel of a motor vehicle, the tire through its tread, provides traction and contains the fluid that sustains the vehicle load.
“Stiffness” means the measure of a tire's ability to act like a spring.
“Tie Bar” refers to an extra thickness of rubber at the bottom of a groove such that, in the location where the extra rubber is present, the groove depth is less than the groove depth at all other locations. Tie bars stabilize a lug by limiting the independent movement of two portions of a lug that are separated by a groove. Tie bars can also be present between two adjacent lugs.
“Trailing” refers to a portion or part of the tread that contacts the ground last, with respect to a series of such parts or portions, during rotation of the tire in the preferred direction of travel.
“Tread” means a molded rubber component that when bonded to a tire casing, includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load.
“Tread Centerline” refers the intersection of the equatorial plane (EP) with the tread.
“Tread Width” means the arc length of the tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire.
REFERENCES:
patent: D. 53693 (1919-08-01), Stokes
patent: D. 57124 (1921-02-01), Githens
patent: D. 177233 (1956-03-01), Hawkinson
patent: D. 367448
Brown R W
King David L.
Maki Steven D.
The Goodyear Tire & Rubber Company
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