Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a pneumatic tire
having a good high-speed running performanee, and more
particularly to a pneumatic radial tire for passenger
cars having an improved steering response during
05 a high-speed running.
In general, tire tread rubbers are required
to have characteristics such as wet resistance, cut
resistance, slip resistance and the like, and also
substantially affect a rolling resistance which is
0 elosely related to a fuel consumption of an automobile
vehicle. Among these characteristics, the slip
resistance (wet skid resistance, ete) particularly
tends to be eonflictive to the rolling resistance, so
that the use of a rubber advantageous for the former
becomes disadvantageous for latter, and to the contrary,
the wse of a rubber advantageous for the latter becomes
disadvantageous for the former. In order to improve
such conflicting characteristics simultaneously, there
have been known tread rubbers having such a composite
structure that a rubber having an exeellent wear
resistance is definitely used in a portion particulary
exposed to wearing during the running and a rubber
suitable for the rolling resistanee is used in the
other portions.
With respeet to the eomposite strueture of
the tread rubber, in addition to the above, as deseribed
in, for example, United States Patent Speeifieation
No. 3,759,~06 there is proposed a strueture that a rubber
2 r ~
32~3;2
having a considerably high stretch modulus is used
in a base portion bounded by bottoms of tread grooves
for preventing the wrenching out of tread ribs from
their root during the running of passenger tire at
05 a high speed and a rubber having an excellent wear
resistance and a relative low stretch modulus is usually
used in portions exposed to wearing.
The invention is different from the above
mentioned prior composite structure, and is to largely
o improve the steering response at high-speed of radial
tires by composing a par-ticular composite tread struc-
ture consisting of an inner layer having a properly
high modulus of elasticity in portions forming the base
such as rib, block, lug or the like cast into the tread
portion, and an outer layer arranged on the inner layer
and having a particularly improved gripping property on
road surface and a modulus of elasticity controlled in
a given ratio with respect to the inner layer.
According to the invention, there is the
provision of in a pneumatic radial tire having a good
high-speed running performance, comprising a tread
portion, a pair of sidewall portions toroidally
extending from the both sides of the tread portion,
a carcass reinforcing these portions and composed of at
least one ply containing cords arranged in a direction
perpendicular to the equational plane of the tire, and
a belt disposed between the carcass and the tread
portion and composed of plural inextensible cord layers,
-- 3 --
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the improvement wherein said tread portion is divided
into at least two composite rubber layers in a direction
of the thickness, in which an inner rubber layer near
to the belt has a dynamic modulus (E') of 100-250 kg/cm2
os and an outer rubber layer has a dynamic modulus (E') of
70-150 kg/cm2 and a loss tangent (tan ~) of at least
0.25, and a ratio in dynamic modulus (E') of the inner
rubber layer to the outer rubber layer is at least 1.15.
The invention is particularly useful for
lo application to tires having an aspect ratio of not more
than 70%, preferably 60%, more preferably 50%.
A single figure is a right half cross-sectional
view of an embodiment of the pneumatic radial tire
according to the invention.
1S In the single figure is shown a radial
right-half section of the pneumatic radial`tire according
to the invention. In the tire 1, a pair of right and
left sidewall portions 2 are toroidally connected to
both sides of a tread portion 3. Although the left-half
section is omitted, tire 1 is, of course, symmetrical
with respect to an equational plane O-O.
A bead ring 4 is embedded in an inwardly and
part of each of the sidewall portions 2 in the radial
. direction in the conventional manner, and a carcass 5
is extended between both the bead rings ~ to wholly
reinforce the sidewall and tread portions.
The carcass 5 is composed of one ply or
plural plies, each ply containing cords of an organic
-- 4 --
~ L;2,Z~3Z8;2
fiber such as polyester fiber, nylon Eiber, rayon fiber
or the like arranged in a direction substantially
perpendicular to the equational plane O-O. In the
lllustrated embodiment, the carcass 5 is one ply, both
05 end portions of which are wound outwardly around the
bead rings 4 to form turnup portions 6, respectively.
Further, a hard rubber filler 7 is disposed in a space
defined by the carcass 5, turnup portion 6 and bead
ring 4 and tapered toward the direction of the -tread
lo portion.
As the rubber filler 7, it is better to use
rubber having a dynamic modulus of 600-1,500 kg/cm2.
Since a so-called radial structure as mentioned
above is used as the carcass 5, a belt 8 composed of
lS inextensible cord layers is disposed between the
carcass 5 and the tread portion 3 in the usual manner,
whereby the rigidity of the tread portion is enhanced
as a whole.
The reinforcing element for the belt 8 is
a metal cord such as steel and the like or a high
elastic fiber cord such as glass, polyester, rayon,
aromatic polyamide and the like. These cords may be
~ used alone or particularly in combination of metal cord
; with fiber cord. The belt 8 is composed of plural cord
layers each containing such cords arranged at an
inclination angle of 5-25 with respect to the
equational plane O-O, the cords of which being crossed
with each other.
-- 5 --
~2;2~3Z8;~
Although the belt 8 is constructed by merely
laminating two steel cord layers 8-1 and 8-2 one upon
the other in the illustrated embodiment, there may
be a so-called fold belt structure wherein the cord
05 layer 8-1 is made wider and both side ends thereof are
folded and piled on the cord layer 8-2, or a structure
tha~ one layer or at most two layers containing heat
shrinkable fiber cords such as nylon cord arranged in
parallel to or at a slight inclination angle with
0 respect to the equational plane O-O may directly be
disposed on the belt shown in the figure to partially
or wholly cover it therewith.
The tread portion 3 is composed of a composite
rubber layer comprising an outer rubber layer 9 directly
contacted fitted with road surface during the running
and an inner rubber layer 10 supporting the outer
rubber layer 9 on the belt 8.
The outer rubber layer 9 has a loss tangent
(tan ~) of at least 0.25 and a dynamic modulus (E') of
70-150 kg/cm2. While, the inner rubber layer 10 has
a dynamic modulus (E') of 100-250 kg/cm2. Then, a ratio
: of the inner rubber layer 10 to the outer rubber layer
9 in dynamic modulus (E') is required to be at least 1.15.
According to the invention, the outer rubber
layer 9 is a rubber having an improved gripping property
against road surface in addition to wear resistance,
and it has been confirmed from the experiments by the
inventors that when the ratio in dynamic modulus between
~L22~28Z
the outer rubber layer 9 and the inner rubber layer 10
is within the above defined range, the gripping property
is more enhanced together with a suitable flexibility
effect of tread rubber (actually rib, block, lug or the
05 like) at the ground contact area in the steering during
the running. In this case, the outer rubber layer 9
has a loss tangent (tan ~) of at least 0.25, preferably
of 0.3-0.5 and a dynamic modulus of 70-150 kg/cm2,
preferably of 80-140 kg/cm2, and the inner rubber layer
has a dynamic modulus (E'~ of 100-250 kg/cm2,
preferably of 110-200 kg/cm2. Further, the ratio in
dynamic modulus of inner rubber layer 10 -to outer
rubber layer 9 is at least 1.15, preferably 1.25-2Ø
Moreover, as to a ratio of thickness between the inner
rubber layer 10 and the outer rubber layer 9, good
results are obtained when an average thickness of the
inner rubber layer 10 is within a range of 0.15-0.35
relative to 1 of that of the outer rubber layer 9.
The reason why the thickness of each rubber layer is
expressed on average is due to the fact that when the
tread portion 3 is composed of, for example, ribs 14
divided by a large number of grooves 13, the joint
surface between the inner and outer rubber layers 10, 9
becomes wavy as shown in the figure.
Though the composite rubber layer composed of
two inner and outer layers is shown in the illustrated
embodiment, a third or fourth rubber layer may be added
as far as the object is maintained.
~2X:~3282
As shown in this embodiment, it is preferable
that the outer rubber layer 9 and the inner rubber
layer 10 are substantially piled one upon the other
over the whole of the tread portion, and both side end
05 portions thereof are e~tend in wedge form in-to rubbers
12 of the sidewall portions having a good flexing
property at positions of tire shoulders 11. Moreover,
numeral 15 is an inner liner having an excellent air
impermeability.
lo In order to confirm the performances of the
tire according to the invention, the actual running
test was carried out on a circuit course (2.04 km) by
using a test tire with a size of 205/60R 15, during
which a lap time was actually measured and also the
steering response, stability, wet skid resistance and
riding comfort in the high-speed running and in the
running on usual road were estimated by feeling.
Moreover, the ~eeling in the running on the
circuit is based on a total evaluation of driving and
braking properties, steering response, gripping
property against road surface during the steering and
controllability beyond slip limit.
As a test tire were used tires A, B and C
according to the invention and control tire D.
All of these tires had a common feature that
two rubberized plies each containing polyester cords
arranged in a direction perpendicular to the equational
plane O-O of the tire were wound around the bead ring 4
~z~
from inside to outside as shown in the figure, and the
bead filler rubber 7 having a considerably high dynamic
modulus was interposed between the carcass ply and its
turnup portion. ~oreover, as the belt 8, two layers
8-1 and 8-2 each containing metal cords arranged at
an inclination angle of 20 with respect to the
equational plane O-O were laminated so as to cross the
cords of these layers with each other as shown in the
figure, and two reinforcing layers each containing
nylon cords arranged at an angle of 0 with respect to
the equatorial plane O-O (not shown) were arranged on
each side end portion of the layer 8-2 to particularly
reinforce both the side end portions of the belt 8.
The structure and compounding recipe of the
tread rubber in each test tire are shown in the following
Tables 1 and 2, respectively.
Table 1
Kinds of tire A B C D
_ .
Tread rubber
Outer rubber-layer 9_) W X Y On1y W
Inner rubber layer 10 Z Z Z
Average thickness of
rubber (mm)
Outer rubber laYer 9 8.0 8.0 8.0 ,~ ~
(Inner rubber layër 10~ 2.0 2.0 2.0 lU . U
8~
Table 2
_
Kind of rubber W X Y Z
Butadiene-styrene
copolymer rubber 50 _ _ 100
(Styrene 23.5%)
Butadiene-styrene
copolymer rubber 50 100 100
(Styrene 35%)
Carbon black (HAF~ 80 85 _ 90
Carbon black (ISAF) _ _ 85
Aromatic process oil 40 45 45 35
Stearic acid 1 1 1
Antioxidant (IPPD) 1 1
Zinc white 3 3 3 3
Accelerator _
PPG 0.5 0.5 0.7 0.6
DM 1.0 1.0 0.8 1.2
Sulfur 5 1.5 1.5 1.7
(kg/cm2) 116 97 130 173
Loss tangent 0.340 0.43 0.49
Note: The dynamic modulus and loss tangent were
measured with respect to a strip specimen
of width 5 mmxlength 20 mmxthickness 2 mm
using a viscoelastic spectrometer made by
Iwamoto Seisakusho under the test conditions
of a frequency of 50 Hz, a dynamic strain
of 1% and a temperature of 25C.
The test tire assembled onto a rim and
subjected to an internal pressure of 2.2 kg/cm2 was
mounted on a vehicle and actually run to obtain results
as shown in the following Table 3.
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Table 3
Kind of tire D
~ _
(circuit) 1' 15" 81 1' 15" 10 1' 14" 70 1' 16" 25
tcircuit) 104 105 107 100
.
Steering response 104 105 106 100
Stability 105 105 107 100
Wet skid resistance 100 103 104 100
Riding comfort 100 100 99 100
against vibration
Note: The properties otner than the lap time are
expressed as an index when the tire D is
regarded as 100. The large the index value,
the better the property.
As mentioned above, according to the invention,
the steering response in the high-speed running can
considerably be improved synthetically.
