Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2000-07-05
2002-09-17
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S902000
Reexamination Certificate
active
06450221
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a non-directional pneumatic agricultural tire for use on farm tractors and similar agricultural type vehicles. Tractor tires must have good vibration characteristics on and off the road while maintaining good traction or drawbar characteristics. Such tires must also provide for the removal of soil, mud, etc., during in-field use.
In the past, agricultural vehicles were horse drawn. With the introduction of motorized tractors in the early 1900's, the farm wheels were made of steel with traction cleats extending across the steel wheel. E. J. Farkas in 1922 patented a detachable tread for tractor wheels. U.S. Pat. No. 1,423,519 describes a rubber tread member that could be added to the steel cleat thus making it possible to cross a road without destroying the paved surface. These historical vehicles were greatly underpowered for the task of farming. Accordingly, the wheels were generally designed to be somewhat, if not entirely, non-directional with cleats inclined or normal to the direction of travel. The non-directional characteristic was helpful when the tractor became stuck In such cases, horses would be hooked to the rear of the vehicle and the tractor with the assistance of added horsepower could reverse itself out of the muck.
As tractor motors improved, the tires became directional in design. The tractor's primary function required forward pulling power and tires were accordingly designed to enhance this feature.
In November 1995, U.S. Pat. No. 5,464,050 issued to Mark Leonard Bonko describing a novel non-directional tread having a set of at least three lugs having substantially parallel lug centerlines oriented at about 45° and lug centers that lie along a substantially straight line across the tread edges.
This tire had lugs of substantially equal lengths and were relatively short when compared to the long bar lugs of the prior art directional tractor tires. The advantage of short lug lengths was greatly improved flexibility resulting in less soil compaction.
While the use of many short lugs has many beneficial features particularly dry traction performance, such a tire has room for improvement.
In particular the tire disclosed in the Bonko patent was best suited for four or more rows of lugs to avoid a low speed lug induced vibration that was evidenced when only three lugs rows were employed. The reason such a phenomena was occurred was related to the fact that as the tire rolled at certain axial locations only the center lug supported the load. On a hard road-like surface at high tire inflation, this makes the tire “duck walk” a term commonly referred to in the tire art. To avoid these phenomena it is desirable to have at least two lugs always contacting the ground in any axial path of the tires contact patch perpendicular to the direction of tire rotation. The Bonko patent requiring the lug centerlines to be parallel prevented or at least greatly limited the three-row lug pattern from achieving this result while still maintaining the open space between lugs for good wet traction. For that reason, Bonko choose a four-row lug pattern as his preferred tire.
That non-directional tire had excellent dry traction with acceptable wet traction. The farmer was very pleased with the ability to have good forward and reverse directional pulling power.
One perceived drawback of the design was that the tire looked slightly unbalanced and that under severe pulling or pushing loads, the tractor may see a sideways slippage. Bonko noted in his earlier patent that a mirror image tire could be made to create offsetting lateral forces to eliminate this concern, if needed. His test data showed an added cost of having both left side and right side tire molds was unnecessary. Nevertheless, to some farmers how the tire looks establishes how the tire will perform. Farmers, maybe more than any other group of tire buyers, are actually as a group very sophisticated and quite adept at understanding how mechanical devices work. They have an on the job engineering sense about them and they tend to network They communicate about what works and what is just a gimmick. They tend to want improved products, but they don't want to risk their livelihood on products that even hint that they don't work. Thus to gain wide acceptance of a new product, the engineers must make a product that looks like it will do the job. The challenge here was to develop a tire that has both actual and perceived advantages.
In DE 89 07 334U discloses an eastmover tire having the features described in the preamble of claim
1
.
Bonko in this next generation of non-directional tires set out to increase the lug lengths and open the tread pattern by going to three rows of lugs. The resultant design had to avoid the “duck walk” phenomena, look aggressive and be directional, and provide superior mud traction and at the same time increasing the uniformity of tread wear over his predecessor non-directional tire. The inventive tire described below has exceeded all of the above mentioned design requirements and in very novel way.
SUMMARY OF THE INVENTION
A non-directional pneumatic agricultural tire (
20
) having a maximum section width (W), an axis of rotation, an equatorial plane perpendicular to the axis, a casing having a carcass (
21
) reinforced with rubber coated cord, a rubber tread (
32
) disposed radially outwardly of the carcass is disclosed.
The tread (
32
) includes an inner tread and a plurality of tread lugs (
50
A,
50
B,
50
C), the lugs respectively have a surface (
58
) with a length (l
l
) and a width (l
w
) defined as the distance between a first edge (
52
) and a second edge (
54
) wherein the length (l
l
) is at least three times the width (l
w
) and the length (l
l
) of the lugs (
50
A,
50
B,
50
C) are respectively at least 20% of the maximum section width (W).
Each lug has a centerline (
63
) defined by a line bisecting the lug surface along the length of the lug.
The tread (
32
) has a first and a second tread edge (
33
A,
33
B) and a net-to-gross ratio, the net-to-gross ratio being defined as the ratio of the surface area of the normally loaded and normally inflated tire tread rubber that makes contact with a hard, flat surface, divided by the area of the tread (
32
), including non-contacting portions such as grooves as measured around the entire circumference of the tire.
The tread (
32
) has sets (
60
) of three lugs, each set having two lugs being shoulder lugs (
50
A and
50
B) having substantially parallel centerlines (
63
) and one central lug (
50
C) having a centerline (
63
) substantially perpendicular to the centerlines (
63
) of the shoulder lugs (
50
A,
50
B). The set (
60
) is repeated a plurality of times circumferentially about the tread (
32
). The set (
60
) extends along a line (
63
) through the lug centers (
61
) in a substantially straight line across the tread (
32
) from the first tread edge (
33
A) to the second tread edge (
33
B). The line (
62
) passing approximately through the center (
61
) of each lug of a set (
60
) forms an acute angle &thgr;
c
with the equatorial plane of about 45°or more.
The tread (
32
) is characterized by a net-to-gross ratio of 30% or less, preferably 20% or less wherein the lugs (
50
A,
50
B,
50
C) have a ratio of the lug width (l
w
) to lug radial height (1
h
) being less than two-thirds over 70% of the lug length (l
l
) and the lug (
50
A) are circumferentially offset relative to the lugs (
50
B) by a distance X as measured between axial lines (
90
) tangent to an end (
51
) of lug (
50
A) and an axial line (
92
) tangent to end (
51
) of lug (
50
B), X being a circumferential distance of less than the width of the lugs (l
w
) and wherein the set (
60
) is oriented such that the axially inner ends (
51
) of lugs (
50
A) when extended by the dashed lines to end (
53
) of lug (
50
C) creates an asymmetric chevron (
70
) having an apex (
73
) and lug (
50
B) has an end (
51
) when extended by dashed lines to the end (
51
) of lug (
50
C) forms an asymmetric chevron (
72
) having an ap
King David L.
Maki Steven D.
The Goodyear Tire & Rubber Company
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