Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1999-12-16
2001-10-09
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209120, C152S209220, C152S902000, C152S903000
Reexamination Certificate
active
06298890
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.
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.
The Goodyear RL-2 Radial Semi Xtra Tread Traction tire as seen in the 1984 Tread Design Guide at page 205 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 higher than desired vibration.
Two major factors contributing to the high vibration of the RL-2 are the nearly axial 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.
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
10
for off-road use. The pneumatic tire
10
has a tread
12
. The tread
12
has a plurality of lugs
14
extending from a first shoulder
16
to a second shoulder
18
. The plurality of lugs
14
are separated by a plurality of wide grooves
20
.
Each lug
14
of the tread
12
has a wide section
22
near at least one of the respective shoulders and a narrow section
24
near a centerline of the tire. Each lug
14
may extend straight across the tread
12
or may be inclined from the first shoulder
16
to the second shoulder
18
.
Definitions
For ease of understanding this disclosure, the following terms are disclosed:
“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.
“Footprint” means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load in pressure or under specified load, 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 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 on the tire.
“Lateral” means in an axial direction.
“Leading” refers to a portion or part of the tread that contacts the ground first, with respect to a series of 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.
“Non-skid” means the depth of grooves in a tire tread.
“Pitch” means the distance from one peak in the tread pattern to the next. Pitch refers to the circumferential distance from one design feature in a 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 the wheel of a motor vehicle, the tire though its tread provides a traction and contains the fluid that sustains the vehicle load.
“Shoulder” means the upper portion of the sidewall just below the tread edge.
“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 other locations. Tie bars stabilize a lug by limiting the independent movement of two portions of a lug that are separated by the 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 Centerline” refers to the intersection of the equatorial plane (EP) with the tread.
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Brown Robert W
King David L
Maki Steven D.
The Goodyear Tire & Rubber Company
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