Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1997-07-14
2001-11-27
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C057S902000, C152S451000
Reexamination Certificate
active
06321810
ABSTRACT:
BACKGROUND OF THE INVENTION
In the bias-ply automotive pneumatic tire, carcass-protective reinforcing layers, known as breakers, are interposed between the carcass and the tread. In the radial-ply tire, reinforcing layers called “belts” are interposed between the carcass and the tread and serve to brace up the carcass in the radial direction. In such a pneumatic tire, it is common practice to increase the service life of the tire by embedding steel cords in the breakers or belts.
This invention relates to a pneumatic tire in which the rubber layer, i.e. said breaker or belt, between the carcass and tread has been reinforced with steel cords.
The breaker or belt is often constructed in a plurality of layers. Particularly when the anti-cut property of a pneumatic tire must be increased, a plurality of steel cords capable of sufficient elongation are embedded at appropriate spacings in the outermost, i.e. adjacent to the tread, layer of the aforementioned breaker or belt.
In the conventional steel cord, it is common practice, as explained below, to implement a large elongation value by adopting a multi-strand structure.
FIGS. 9 and 10
are cross-section views showing the multi-strand steel cords heretofore used in the conventional pneumatic tire; thus,
FIG. 9
represents the 4×4×0.23 construction, while
FIG. 10
represents the 3×7×0.22 construction.
Referring to
FIG. 9
, a steel cord
10
is an assembly of four strands
16
twisted together and each strand
16
, in turn, is an assembly of four constituent wires
12
, each constituent wire
12
being a steel wire with a diameter of 0.23 mm. The twisting pitch of these constituent wires
12
is 3.5 mm and that of the strands
16
is 5.5 mm.
The steel cord
10
illustrated in
FIG. 10
is an assembly of three strands
16
twisted together. Each strand
16
is an assembly of seven constituent wires
12
and each of the wires
12
is a steel wire with a diameter of 0.22 mm. The twisting pitch of the wires
12
is 4.0 mm and that of the strands
16
is 7.5 mm.
Since each of these steel cords
10
is a low-pitch multi-ply structure, it has a large elongation and is flexible, insuring a large impact-absorbing or damping capacity. Therefore, the conventional pneumatic tires utilizing these steel cords
10
had high anti-cut properties.
The conventional tires employing steel cords of the above-described constructions present the following problems, however.
Thus, in the conventional multi-strand steel cords
10
, the degree of so-called “twisting loss” of tenacity or strength is high and the strength of the respective wires
12
cannot be effectively utilized. In order to obtain a desired strength for steel cord
10
, an increased number of constituent wires
12
is required but the use of so many wires
12
adds to the overall weight of the steel cord
10
. Moreover, since the steel cord
10
used heretofore is a flexible steel cord, the pneumatic tire is markedly deformed on the tread to create a large rolling resistance, thus detracting from milage.
Furthermore, as will be apparent from
FIGS. 9 and 10
, the wires
12
in the conventional construction are round in section and disposed in close contact and, for this reason, a closed air space
18
is created in the approximate center of the constituent wires. Therefore, in this steel cord
10
, rubber does not easily enter and fill the space
18
. In other words, the resulting breaker or belt will have the space
18
unfilled with rubber. If the tread of the tire is damaged and consequently water finds its way from the site of injury into the space
18
, the invading water migrates within the space
18
along the length of steel cord
10
and, also, remains entrapped therein. Consequently the steel cord
10
becomes rusted with time, detracting from the strength of bond to the rubber. If this decrease in bond strength progresses, there occurs the trouble known as “separation”.
Therefore, the present applicant previously proposed, in the copending Japanese Patent Application No. 79399/1988, “a pneumatic tire in which the rubber layer between the carcass and tread has been reinforced with single-strand steel cords with an elongation at break of not less than 4%”.
FIG. 11
is a cross-section view showing the steel cord used in the pneumatic tire according to the above patent application which remains yet to be laid open.
This steel cord
10
is a single-strand cord of 1×5×0.38 construction. Thus, it is an assembly of five wires
12
each having a diameter of 0.38 mm. The twisting pitch is 6.5 mm and the elongation at break of the cord is 6.5%.
Despite being a single-strand cord, this steel cord
10
has an elongation at break of not less than 4% and, therefore, offers an anti-cut performance comparable to that of a multi-strand steel cord. Furthermore, because of the very single-strand construction, the rate of wire tenacity utilization is high. This means that the desired tire strength is attainable even if the overall weight of the tire cord is decreased, and that accordingly a lightweight pneumatic tire can be implemented. Moreover, because of the adequate flexural hardness of the steel cord
10
, the rigidity of the pneumatic tire is enhanced. Therefore, the deformation and, hence, rolling resistance of the tire are reduced, thus contributing to milage. Furthermore, since clearances are created between constituent wires
12
at intervals along the length of the steel cord, the space
14
enclosed by the wires
12
is exposed to the atmosphere. Therefore, in the vulcanization of the pneumatic tire having a breaker or belt in which this steel cord
10
has been embedded, the rubber finds its way readily into the space
14
and as the space is thus filled with the rubber, the incidence of “separation” is virtually inhibited.
However, even in the case of a steel cord having the same 1×5×0.38 construction, its anti-cut property is poor when its twisting pitch is as large as 18.0 mm and its elongation is as small as, for example, 2.5%. In addition, as illustrated in
FIG. 12
, a closed space
18
is formed by and among the wires
12
. Therefore, in the result of arresting the entry of rubber into the space
18
, this cord is equivalent to the aforementioned multi-strand cord.
In the pneumatic tire disclosed in the copending patent application mentioned above, the wires
12
are identical in diameter and shaping rate so that all the wires
12
form one common circumcircle
22
. Therefore, though the incidence of separation is inhibited, the effect of anchoring the steel cord in the rubber constituting the breaker or belt is so small that the separation once started tends to grow easily.
Having been accomplished in view of the above situation, this invention has as its object to provide a pneumatic tire in which the strength or tenacity of material wires is effectively exploited, while maintaining the anti-cut property of the tire at a level comparable to that of the conventional tire, to thereby improve the rigidity of the tire while the incidence and growth of separation having been successfully inhibited.
SUMMARY OF THE INVENTION
This invention relates to a pneumatic tire characterized in that, of the breaker or belt consisting of a plurality of rubber layers which is disposed between the carcass and the tread, at least the outermost layer has been reinforced with a plurality of steel cords, each of which is a single-strand cord with an elongation at break of at least 4 percent, with the constituent wires of the cord forming no single common circumcircle. The shaping rate is a ratio of a diameter of a circumcircle defined by a hypothetical cord formed of a plurality of wires, with the plurality of wires being shaped, to a diameter of a circumcircle defined by the hypothetical cord with the plurality of wires not being shaped and each of the plurality of wires contacting neighboring ones of the plurality of wires.
The steel cord made up of constituent wires forming no single common tangent circle, that is to say a steel cord in which the cur
Johnstone Adrienne C.
Jordan and Hamburg LLP
Toyo Tire & Rubber Co., Ltd.
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