Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1998-11-12
2002-11-19
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209210, C152S209220, C152S209250, C152S209270, C152S209280, C152S902000, C152SDIG003
Reexamination Certificate
active
06481480
ABSTRACT:
TECHNICAL FIELD
This invention relates to the field of heavy duty radial pneumatic tires for trucks and truck trailers.
BACKGROUND ART
In many areas of the world, heavy duty vehicles such as trucks must have superior traction performance on the drive axle positions of the vehicle. Tires having sufficiently aggressive tread patterns with block element type tread patterns seem to provide the best traction performance.
As the tread becomes about half worn these block elements can lose some of their traction capability or performance. Ideally, the drive axle tires would be replaced at that time. Unfortunately, for the vehicle owner this means that the tread still had a useful half life remaining if it could be used in a less traction sensitive wheel position. Unfortunately, the original tread pattern when worn was not conducive to such applications such as trailer tires.
The need was apparent that tread patterns must change or convert when worn partially to a different pattern if they were to be successfully used in other wheel positions.
The use of convertible truck tires which start out having one block type tread pattern and as the tire reached a certain level of wear changed to a rib type tire was taught in U.S. Pat. No. 4,223,712 wherein less than full depth inclined transverse grooves would disappear after the tire was 30% to 70% worn.
A later U.S. Pat. No. 4,732,195 issued Mar. 22, 1988, taught that the transverse grooves should disappear toward the axially outside of the tread so that the separated blocks change into continuous ribs from the axially outside to the inside of the tread in sequence as the tread wears.
In U.S. Pat. No. 4,854,384 issued Aug. 8, 1989, taught a block type tread pattern which is also converted to a rib type tire when the tire is worn in the range of 35% to 75% of the maximum depth. The tread has a plurality of circumferentially continuous zig-zag and straight grooves which have a total width equal to 15-35% of the entire tread width when the tire is new and 10-25% of the entire tread width when the tire is worn and the transverse grooves completely disappear to form a rib pattern consisting solely of zig-zag longitudinal grooves.
In these patents the tread pattern simply was converted from block elements to ribs by the loss of the transverse groove.
These rib type tires generally will exhibit uniform wear and can be used where traction must be achieved by zig-zagging the longitudinal grooves. Historically, such tires have relatively poor braking traction when used on wet or snowy roads.
The present invention in a unique way converts a block element tread pattern for drive axles of trucks when the tire is half worn to a combination of shoulder ribs and central rows of larger block elements which can exhibit substantially superior wet traction capability than the prior art ribbed type tires.
DISCLOSURE OF THE INVENTION
A radial ply pneumatic tire
10
for trucks or trailers having a tread
12
with at least three longitudinal grooves
20
,
22
that extend circumferentially to divide the tread
12
into at least four parts is disclosed, more preferably 5 parts divided by four longitudinal grooves
20
,
22
. The tread
12
has lateral grooves
30
,
31
,
32
,
33
,
34
extending across the at least four parts of the tread
12
to form at least four rows
1
,
2
,
3
,
4
,
5
of circumferentially separated blocks
40
including two shoulder rows
1
,
5
and at least two, preferably three central rows
2
,
3
,
4
. Each block
40
has a radially outer surface
42
.
The longitudinal grooves
20
,
22
have an average width W
1
between the radially outer surface
42
of the tread blocks
40
extending to a depth of less than 60% of the total tread depth D thereafter the average width of the longitudinal grooves
20
,
22
narrows to less than 50% of W
1
and the lateral grooves
30
,
34
in each shoulder row extends to a depth of less than 60% of the total tread depth.
The lateral grooves in the central rows
31
,
32
,
33
have an average length of L
1
between the radially outer surface
42
of the tread blocks
40
to a depth of less than 60% of the total depth D, thereafter the lateral grooves
31
,
32
,
33
average length increases to greater than L
1
, preferably to L
1
+50% of W
1
in length. The average groove width of the lateral grooves
31
,
32
,
33
in the central rows equals W
3
, the width W
3
being measured between the radially outer surface
42
of the block
40
to a depth of less than 60% of the total depth D, thereafter the lateral grooves narrow to an average width W
4
of less than 80% of W
3
for the remainder of the groove depth, preferably less than 50% of W
3
.
These changes in average groove widths W
1
of the longitudinal grooves
20
,
22
and the average groove widths W
3
of the central row lateral grooves
31
,
32
,
33
to less than 50% W
1
and less than 80% W
3
, respectively, preferably occurs at the same depth. Furthermore, it is preferred that the lateral grooves
30
,
34
in the shoulder rows
1
,
5
cease at the same depth wherein the longitudinal and the lateral grooves narrow.
It is further believed important that the longitudinal and lateral grooves change average width at 40% or more of the total depth D of the tread
12
.
In the preferred embodiment tire each block element has at least one sipe
51
,
52
,
53
and a portion of the sipe
51
,
52
,
53
remains in the tread
12
after the width of the longitudinal
20
,
22
and lateral grooves
31
,
32
,
33
narrows due to the tire
10
being worn.
The tire
10
when new preferably has a net-to-gross ratio of less than 70% which increases by at least 10% at the depth of the tread where the average groove widths narrow, preferably increasing by almost 20%.
Definitions
“Aspect ratio” of the tire means the ratio of its section height (SH) to its section width (SW) multiplied by 100% for expression as a percentage.
“Asymmetric tread” means a tread that has a tread pattern not symmetrical about the centerplane or equatorial plane EP of the tire.
“Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
“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 and pressure.
“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. Circumferentially and laterally extending grooves sometimes have common portions. The “groove width” is equal to the tread surface area occupied by a groove or groove portion, the width of which is in question, divided by the length of such groove or groove portion; thus, the groove width is its average width over its length. Grooves may be of varying depths in a tire. 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 the tire. If such narrow or wide grooves are of substantially reduced depth as compared to wide circumferential grooves which they interconnect, they are regarded as forming “tie bars” tending to maintain a rib-like character in the tread region involved.
“Inboard side” means the side of the tire nearest the vehicle when the tire is mounted on a wheel and the wheel is mounted on the vehicle.
“Lateral” means an axial direction.
“Net contact area” means the total area of ground contacting elements between defined boundary edges divided by the gross area between the boundary edges as measured around the entire circumference of the tread.
“Net-to-gross ratio” means the total area of ground contacting tread elements between the lateral edges around the entire circumference of the tread divided by the gross area of the entire tread between the lateral edges.
“Non-directional tread” means a tread that has no preferred direction of forward travel and
Schuster Daniel Edward
Serich John James
King David L.
Maki Steven D.
The Goodyear Tire & Rubber Company
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