BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a radial tire that is
particularly suitable for use in motorcycles and that is capable of improving tire
durability and steering stability.
Radial tires for use in motorcycles in which band layers
with band cords of organic fiber being spirally wound around along a circumferential
direction of tires are disposed outside of carcasses of radial structure are suggested
in, for instance,
Japanese Patent Laid-Open Publication No. 4-278805 (1992
Japanese Patent Laid-Open Publication No. 7-96710 (1995
In radial tires for motorcycles employing organic fiber
cords as band cords, it is being attempted to use material of high elasticity such
as aramid. However, since the extension of cords are large, effects of restricting
uplifting of tread portions when the tires are performing high-speed rotation (so-called
a lifting phenomenon) are not sufficient. Drawbacks were thus exhibited that disadvantages
in steering stability were found and that deflected wear was apt to occur. In view
of those facts, radial tires for motorcycles employing steel cords as the band cords
were suggested in, for instance,
Japanese Patent Laid-Open Publication No. 4-362402 (1992
Japanese Patent Laid-Open Publication No. 7-96712 (1995
Japanese Patent Laid-Open Publication No. 4-362402
, there is recited a band cord that is obtained by twining three shaped
metallic wires. However, when employing metallic wires having a wire diameter of
approximately 0.15 mm, it is generally the case that it is apt to lack in bending
strength and that there is still room for improvements in durability and wear resistance.
The suggested steel cords of 3 by 3 arrangement require complicated twining processes
so that costs are increased.
Japanese Patent Laid-Open Publication No. 7-96712
, there is described a metallic cord as a band cord in which sheaths comprised
of one to four metallic wires are twined around a core comprised of one or two metallic
wires. However, such a metallic cord will have a large cord diameter and permeability
of rubber into the area between the metallic wires is insufficient. It is therefore
likely that the cords become rusty and that degradation in bonding power between
the cords and rubber, degradation in the strength of the cords or cutting of cords
is caused through the spread of such rust. Moreover, since a load-extension curve
of such a cord is determined depending on the shape of the core, the extension characteristic
of the cords is apt to become unstable. Particularly in case a large extension is
to be obtained, it will be necessary to set the shape of the core to be large, which
makes the configuration of the cords unstable.
EP 1270 270
discloses a tire comprising a band layer having a band cord made of steel
filaments twisted together, wherein the steel filaments includes two-dimensional
zigzag waved filament.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above
cases, and it is an object thereof to provide a radial tire that is particularly
suitable for use in motorcycles and in which the durability and steering stability
has been further improved by improving band cords.
The present invention is a radial tire comprising a carcass
that extends from a tread portion over sidewall portions up to bead cores of bead
portions, and a band layer disposed outside the carcass in the tread portion wherein,
BRIEF DESCRIPTION OF THE DRAWINGS
the band layer is formed of a band ply in which a band cord is wound around in a
spiral manner along a circumferential direction of the tire,
the band cord comprises total nine metallic wires including at least five shaped
wires, and is formed by twining two to four wire bundles composed of a plurality
of said metallic wires twined while twisting each wire thereof,
each shaped wire is formed in a two-dimensional shape with repeated peaks and troughs
in a condition prior to the twisting, and
the metallic wires of each wire bundle are revolved around the center of the wire
bundle while rotating on its own axis through the twining.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
- Fig. 1 is a sectional view of a radial tire for motorcycles illustrating an
embodiment of the present invention;
- Fig. 2 is a partial perspective view illustrating one example of a belt-like
- Fig. 3 is a sectional view illustrating one example of a band cord;
- Fig. 4 is a plan view illustrating one example of a shaped wire;
- Fig. 5 is a diagram illustrating a basic structure of a twining machine in conceptual
- Fig. 6(A) is a diagram illustrating a wire bundle that is formed by twining
metallic wires while twisting each wire thereof, and Fig. 6 (B) is a diagram illustrating
a wire bundle formed by twining metallic wires without twisting each wire thereof;
- Fig. 7 is a plan view for explaining processes of forming a band cord.
An embodiment of the present invention will now be explained
on the basis of the drawings.
Fig. 1 is a sectional view in which the radial tire of
the present invention is a radial tire for motorcycles.
In the drawing, a radial tire 1 for motorcycles comprises
a tread portion 2 in which tread surface 2S curves in an arc-like manner, a pair
of sidewall portions 3 that extends radially inward from both ends of the tread
portion 2, and bead portions 4 that are located at radially inner ends of the respective
sidewall portions 3. In the tire 1, a tread width TW, a tire axial distance between
tread ends Te, Te, is a maximum width of the tire.
The tire 1 also comprises a carcass 6 that extends from
the tread portion 2 over the sidewall portions 3 to bead cores 5 of the bead portions
4 and a band layer 7 that is disposed outside of the carcass 6 in the tread portion
2. In the present example, the carcass 6 and the band layer 7 form a frame portion
of the tire.
The carcass 6 comprises more than one (wherein one is employed
in the present example) carcass ply 6A in which carcass cords are aligned at an
angle of 70 to 90°, and preferably 80 to 90°, with respect to the peripheral
direction of the tire. Favorably used carcass cords may be organic fiber cords such
as nylon, polyester, rayon or aromatic polyamide. The carcass ply 6A is integrally
formed with ply turnup portions 6b that are turned up from inside to outside of
the bead cores 5 and secured on each end of a main body portion 6a extended between
the bead cores 5, 5, forming a toroidal shape. A bead apex rubber 8 that extends
from the bead cores 5 to radially outward in a tapered manner is disposed between
the main body portion 6a and the turnup portions 6b. With this arrangement, regions
extending from the bead portions 4 to the sidewall portions 3 are reinforced.
The band layer 7 is comprised of more than one (wherein
one is employed in the present example) carcass ply 7A that is obtained by spirally
winding band cords along the tire circumferential direction. In the present example,
the band layer 7 is directly formed outside of the carcass 6, while it is also possible
to provide a band layer 9 with a belt layer (not shown) being interposed between
when the tire is for use in passenger cars.
In the present example, the band ply 7A is formed by using
a belt-like ply 9 as will be described below. As illustrated in Fig. 2, the belt-like
ply 9 assumes an elongated belt-like shape of small width in which one band cord
10, preferably a plurality number thereof are embedded into a topping rubber G in
a parallel manner. This belt-like ply 9 is spirally wound outside of the carcass
6 to thereby form the band ply 7A. In this respect, the band ply 7A may assume various
forms beside the case in which a single belt-like ply 10 is spirally wound in a
successive manner from one end side of the tread end Te to the other end side, and
may alternatively be arranged in that two belt-like plies 10, 10 are spirally wound
from proximate of the tire equator C towards respective tread ends Te on both sides.
A band width BW, which represents an axial width of the
band ply 7A, is preferably set to, for instance, approximately 80 to 95% of the
tread width TW. When the band width BW is less than 80% of the tread width TW, it
is impossible to obtain a sufficient rigidity at proximate of the tread end Te so
that, for instance, no sufficient camber thrust can be generated upon application
of a large camber angle so that turning properties tend to be degraded. On the other
hand, when it becomes larger than 95%, the outer end of the band ply 7A will approach
the tread end Te so that peeling from the rubber and other defects are apt to occur.
The band cord 10, whose cross-sectional surface is illustrated
in Fig. 3, is formed by twining two to four wire bundles B, which have been formed
by twisting a plurality of metallic wires F while twisting each wire thereof. At
this time, the total number of metallic wires F forming the band cord 10 will be
nine, including at least five shaped wires FA, wherein each of the shaped wires
FA is formed in a two-dimensional wave-like shape in which peaks and troughs are
repeated in a condition prior to twisting.
Such a band cord 10 prevents overlapping of waves of the
shapes employing wire bundles B which have been bundled upon preliminarily performing
twisting at long pitches so as to make the cord diameter compact and enables forming
of large airspaces between metallic wires F, F. With this arrangement, the permeability
of the topping rubber to inside of the cord will be increased to effectively prevent
occurrence and expansion of rust, and high adhesive power between the metallic wires
F and the rubber can be maintained over a long period of time. It is accordingly
possible to remarkably improve the durability of the band ply 7A, and consequently
the durability of the tire. Since the band cord 10 is formed by twining wire bundles
B that have been obtained by twisting metallic wires F, the wire bundles B that
have been applied with twist will function as resistances against extension of the
cords. Accordingly, the band cords 10 will be restricted in extensibility while
being of open structure, and they exhibit large constraining force with respect
to lifting at the time when the tire performs high-speed running for reliably restricting
the same. The steering stability can thus be improved as well.
As for the metallic wires F, it is preferable to employ
a hard steel wire material having a carbon content of, for instance, 0.65 to 0.88
wt%, and more preferably, 0.70 to 0.88 wt%. When the carbon content of the metallic
wires F falls below 0.65%, the strength of the wires tends to degrade, and on the
other hand, when it exceeds 0.88 wt%, the hardness of the wires will be too high
so that degradations in strength when forming shapes will tend to be large. In this
respect, it is possible to perform surface treatments (plating) using metal or resin
for the purpose of improving the adhesive power with rubber compositions.
While not particularly limited, the wire diameter d of
the metallic wires F shall desirably be 0.15 to 0.2 mm. When the wire diameter d
is less than 0.15 mm, the rigidity tends to be insufficient as band cords of radial
tires when using nine wires. On the other hand, when the wire diameter d is larger
than 0.20 mm, the rigidity of the band cord 10 will be excess so that the steering
stability and riding comfort tends to be worsened. While the present embodiment
illustrates a case in which all metallic wires F forming the band cord 10 are of
the same wire diameter d, it is possible to make metallic wires F of different wire
diameters within the above range coexist.
While one to four of the nine metallic wires F may be non-shaped
wires (not shown) in the band cord 10, it is preferable that all of the nine metallic
wires F are shaped wires FA therein.
Fig. 4 illustrates a condition of a shaped wire FA prior
to twisting as in a planar form. The shaped wire FA includes a two-dimensional wave-like
shape in which peaks U and troughs D of waves are alternately repeated. Two-dimensional
shapes can be easier processed when compared to three-dimensional, for instance,
spiral-like shapes, and clearances between wires F, F can be easily formed and serve
to secure a sufficient permeability of rubber to the interior of the cord even when
the wave heights h are relatively small. Also in case a plurality of wires F is
included, it serves to form the clearances while achieving a compact cord diameter
for improving the rubber permeability. The present example illustrates a zigzag-like
example in which a straight portion 13 is interposed between a peak U and a trough
D. This serves to further improve the permeability of rubber to the interior of
the cords. It is also possible to employ sine waveforms in which the peaks U and
troughs D are connected through smooth curve portions.
It is desirable that the shaped wires FA is formed with
a wave pitch Pw of 1 to 5 mm and a wave height h of 0.18 to 0.65 mm. As illustrated
in Fig. 4, the wave pitch Pw is measured from peak-to-peak of the peaks U or the
troughs D, while the wave height h is measured as a right-angled distance between
a peak U and a trough D. When the wave pitch Pw is less than 1 mm, damages that
the metallic wires F receive at the time of processing the shapes will be large
so that the strength of the wires may be degraded. On the other hand, when it becomes
larger than 5 mm, the permeability of rubber tends to be degraded. When the wave
height h is less than 0.18 mm, it will be difficult to secure permeability of rubber.
On the other hand, when it is larger than 0.65 mm, the cord diameter will become
large and damages that the shaped wires FA receive at the time of processing the
shapes will be large, which may lead to degradations in strengths of the wires.
The shaped wires FA preferably include two or more types
of shaped wires FA1, FA2 whose wave pitches Pw and/or wave heights h differ. This
advantageously serves to achieve shifts in phases and heights of waves when performing
twining of a relatively large number of metallic wires F (namely, nine) and consequently
to improve the permeability of rubber within the cords.
The number of metallic wires F forming a single wire bundle
B is preferably two to five, and more preferably two to four. While the number of
wire bundles B forming a single band cord 10 is in the range of two to four, it
is preferably three. Fig. 3 illustrates an example in which a band cord 10 is formed
by twining three wire bundles B1 to B3. In this respect, each of the wire bundles
B1 to B3 is formed of three metallic wires F. Table 1 illustrates structures of
the band cord 10 of the present invention, wherein the structures of cord No. 5
and No. 6 are particularly preferable.
Band cord structure
Number of wire bundles
Number of wires
included in a wire bundle
Wire bundle B1
Wire bundle B2
Wire bundle B1
Wire bundle B2
Wire bundle B3
Wire bundle B1
Wire bundle B2
Wire bundle B3
Wire bundle B4
The difference between conventional "twining" and "twining
while twisting each wire" applied in the present invention will now be explained.
Fig. 5 illustrates a basic structure of a twining machine for manufacturing cords
in conceptual form. Reference numeral 30 is a fixed gear that does not rotate, and
reference numerals 31, 32 are planetary gears that are mounted to a rotating disk
33 so that they may go around the fixed gear 30 together with the rotating disk
33. The metallic wires F are held by bobbins 34 that are provided on the respective
planetary gears 32. The metallic wires F will be wound back from the respective
bobbins 34 accompanying the rotation of the rotating disk 33 so that the respective
metallic wires F are twined to be tied into a single strand or a cord.
At this time, since the number of gears of the fixed gear
30 and that of the planetary gears 32 are identical, the planetary gears 32 will
revolve around the fixed gear 30 without rotating on their own axes. Accordingly,
while performing conventional "twining", the metallic wires F of the wire bundle
B will revolve around a center n of the wire bundle B without rotating on their
own axes as illustrated in Fig. 6(B).
In contrast thereto, in performing "twining while twisting
each wire" of the present invention, the number of gears of the fixed gear 30 and
that of the planetary gears 32 is, for instance, made different so that a twist
is applied to the respective metallic wires F when performing twining. Thus, the
metallic wires F of the wire bundle B will be revolved around the center n of the
wire bundle B while rotating around their own axes as illustrated in Fig. 6 (A).
This is similar that the earth revolves both on its own axis and around the Sun.
Through the above-mentioned rotation around their own axes,
which are not found in the conventional "twining", the two-dimensional shape of
the shaped wires FA is changed into a complicated three-dimensional shape. With
this arrangement, the wire bundle B is compactly bundled while securing large clearances
between the metallic wires F, F. The twist pitch Pf when performing twisting is
preferably set to be extremely large, namely three to twenty times the final twine
When the twist pitch Pf is less than three times than the
final twine pitch Pc, untwining torque that acts to feaze the wire bundle B will
become large so that the shape retention consequently tends to be worsened (for
instance, feazing of the band cord 10 is apt to occur). On the other hand, when
it exceeds twenty times, the twist pitch Pf will be remarkably large so that the
wire bundle B becomes large-sized and is apt to feazing. Shapes of respective shaped
wires FA, FA are also apt to be overlapped in the wire bundle B.
As illustrated in Fig. 7, the wire bundles B1 to B3 are
twined at a final twine pitch Pc of preferably 5 to 20 mm for forming the band cord
10. When the twine pitch Pc becomes less than 5 mm, the strength tends to be degraded
and on the other hand, when it exceeds 20 mm, the permeability of rubber tends to
be inferior. The present embodiment is arranged in that the twisting direction and
the final twining direction for forming the wire bundle B are made to identical
directions in the band cord 10. Alternatively, they may be opposite directions.
Such a case will function to balance the untwining torque of the cord 10 and to
stabilize the shape of the cord.
While a particularly preferred embodiment of the present
invention has so far been explained in details, the present invention is not to
be limited to the illustrated embodiment alone, and it may be executed upon modifying
the same into various forms, for instance, upon application thereof to band layers
of tires for automobiles.
For confirming the effects of the present invention, various
metallic cords have been sampled according to the specifications of Table 2, and
comparisons and evaluations of characteristics of sample cords and of performances
of radial tires for motorcycles when the sample cords were used as band cords have
In this respect, the radial tires for motorcycles comprise
the basic structure as illustrated in Fig. 1 wherein only the band cords were differed.
Common specifications were such that the tire size was 180/55ZR17 and such that
the carcass was comprised of a single carcass ply in which carcass cords of nylon
66 (1400 dtex/2) were aligned at 90° with respect to the tire equator. In this
respect, the number of implanted carcass cords was 38 (one per each 5 cm) at positions
inside of the bead core. The band layer was formed by spirally winding a belt-like
ply outside of the carcass in each of the sample tire.
Test methods were as follows.
<Permeability of Rubber>
Radial tires for motorcycles comprising a band ply utilizing
sample metallic cords were manufactured, and band cords taken out from the tires
were disassembled. It was then observed whether rubber was completely filled between
the wires within the band cords, and ratios of lengths of portions at which rubber
was filled with respect to observation lengths (10 cm) were defined to be the permeability
of rubber. Such measurements were performed for ten cords, and an average value
thereof was defined as a measured value of the cords. In this respect, observation
was performed by cutting sections of cords by a knife for removing two adjoining
wires from among the wires whereupon clearances between the removed two wires and
the remaining wires were observed.
<Hygroscopic High-speed Durability>
Sample tires were left in an atmosphere of high temperature
and high humidity (temperature: 70°C, humidity 98% RH) for seven days whereupon
durability tests were performed by using a drum running tester. The durability test
was performed under conditions of an air pressure of 250 kPa and a load of 2.45
kN, wherein running was started at a velocity of 80 km/H with the velocity being
increased by 10 km/H each 24-hour period, and the running distance until the tire
was damaged was obtained. Evaluations are displayed using indices with the Comparative
Example 2 being 100, and the larger the numeric values are, the more favorable it
<Steering Stability (Stability of Straight-ahead high-speed
Running/Sense of Grip of Turning Movements>
Sample tires were mounted as rear tires of a motorcycle
having an engine displacement of 750 cm3 and were made to run on paved
roads for evaluating stability of straight-ahead high-speed running and sense of
grip when performing turning movements through senses of a driver. Evaluations are
displayed using indices with the Comparative Example 2 being 100, and the larger
the numeric values are, the more favorable it is.
The sample vehicle was made to run on a general road, and
the running distance required for 1 mm wear of the tread rubber was measured. Evaluations
are displayed using indices with the Comparative Example 2 being 100, and the larger
the numeric values are, the more favorable it is.
Comparative Example 1
Comparative Example 2
Comparative Example 3
Physicality of cord
Number of implantation (number/5 cm)
Carbon content (wt%)
Number of waving (number)
Wave pitch Pw (mm)
Wave height h (mm)
0.15 (6) 0.25(3)
Twine pitch Pc (mm) *2
Twist pitch Pf (mm)
Structure of wire bundle *3
3, 3, 3
3, 3, 3
4, 3, 2
Cord diameter (mm)
Permeability of rubber (%)
Stability of straight-ahead high-speed running (index)
Sense of grip when performing turning movement (index)
Wear resistance (index)
Hygroscopic high-speed durability (index)
*1 Open structure
*2 S: strand C: cord
*3 Number of wires included in each wire bundle
As explained so far, the radial tire according to the present
invention is capable of improving the steering stability and durability, and when
particularly employing the same as a radial tire for use in motorcycles, it is possible
to exhibit extremely favorable stability of straight-ahead high-speed running and
sense of grip when performing turning movements.