Note: Descriptions are shown in the official language in which they were submitted.
~LZ~
This invention relates to a pneumatic radial
tire, and more particularly to a radial tire for
passenger cars which is used at an internal pressure
higher than an ordinarily normal internal pressure.
05 It is well-known that the internal pressure
of the tire used is made higher for reducing the rolling
resistance. However, such a rising of the internal
pressure for the ordinary tire is accompanied with the
following drawbacks:
(a) The spring constant in the radial direction
of the tire is increased to degrade the ride comfort-
ability against vibration; and
(b) The ground contact area is decreased to
reduce a restoring torque (self-aligning torque) when a
slip angle is given to the tire, resulting in the
deterioration of the steering stability such as poor
reaction force in the steering during the high-speed
running or the like. For this reason, it is impossible
to use the tire at a higher internal pressure up to now.
It is, therefore, an obJect of the invention
to provide a pneumatic radial tire for use in passenger
cars under a high internal pressure, wherein the radial
profile of the carcass is adequately changed not only
to minimize the reduction of the restoring torque due
to the high internal pressure but also to more enhance
the improvement of the rolling resistance and also-the
width of the tread is made narrow not only to improve
the degradation of the ride comfortability against
.. , ~"
vibration but also to increase the restoring torque.
According to the invention, there is the
provision of a pneumatic radial tire for passenger car
comprising a pair of sidewall portions each provided at
05 its inner end with a bead portion, a tread portion
extending across the sidewall portions at their outer
ends in the radial direction, a reinforcement for these
portions composed of a toroidal carcass of at least one
ply containing organic fiber cords embedded therein in a
substantially radial direction of the tire and extending
across two bead cores embedded in the bead portions and
turning up around each of the bead cores ~rom inside
toward outside and a belt of at least two rubberized
layers, each layer containing high modulus cords embedded
therein, superimposed about a crown region of the
carcass and crossing with each other at a relatively
small angle with respect to the mid-circumferential
line of the tire, and a rubber filler disposed between
the carcass and the turnup thereof to enhance the
2~ rigidity of the bead portion, characterized in that the
carcass has such a radial profile of a carcass line in
tire section that when the tire is mounted on a normal
rim and inflated at a working internal pressure, a
-ratio of radii R/R' is within a range of 0.65-0.85 and
f is within a range of 5-lO mm, where R' is a radius of
a standard arc passing through points B, E and C,
point B is an intersection of the carcass line and
a straight line in parallel with the rotatig axis of
~2~
the tire passing an alienating point A of a flange o~
the rim to the outer surface of the bead portion,
point C is an intersection of the carcass line and a
line segment drawn from the intersection B perpendicular
o5 to the straight line, point E is an intersection of a
line extending through a middle point D of the line
segment BC as a chord and in parallel with the rotating
axis and a line extending through a maximum width
poin~ F of the carcass line and perpendic~llar to the
rotating axis and in parallel with the line segment BC,
R is a radius of curvature in a curved line of a shoulder
profile of the carcass line passing through the point C,
and f is a maximum distance between the standard arc
and the remaining carcass line smoothly extending from
the curved line of the shoulder prorile to -the point B
and having a single inflection point, and that the
tread has a width corresponding to 55-62% of the maximum
tire width, and that the working internal pressure is
higher by 25-50% than a normal internal pressure.
The invention will now be described in detail
with reference to the accompanying drawing, wherein:
Fig. 1 is a schematic view illustrating a
relation between a radial profile of a tire according
to the invention (a solid line) and a standard arc
(a broken line);
Fig. 2 is a schematically sectional view of
the tire of Example 1 (after inflated at an internal
pressure);
Fig. 3 is a schematically sectional view of
the tire of E~ample 2 (after inflated at an internal
pressure);
Fig. 4 is a schematically sectional view of
05 the tire of Example 3 (after inflated at an internal
pressure); and
Fig. 5 is a schematically sectional view of
the tire of Comparative Example l (after inflated at an
internal pressure).
In Fig. l is shown a radial profile of a
carcass in the tire according to the invention obtained
by adequately changing from a natural equilibrium
curve. The term "natural equilibrium curve" used
herein means a shape of a carcass line or a middle line
in the thickness of the carcass ply come out in the
radial section of the tire including a meridional line
thereof which can stand against the effect of the
internal pressure only by the tension bearing of the
carcass ply without being subjected to bending force
and shearing force.
That is, according ~o the invention, it is
necessary that a curvature in a curved line of a
shoulder profile of the carcass corresponding to the
upper region of the sidewall portion is made large with
respect to the standard arc BEC of Fig. l, i.e. a ratio
of radius of curvature R in the shoulder profile to
radius R' of the standard arc is within a range of
0.65-0.85, while a curvature of the carcass corresponding
'7~5
to the lower region of the sidewall portion is made
small or into a reversed R-shape, i.e. a maximum
distance f between the carcass line FB and the arc BE
in Fig. l is within a range of 5 l0 mm.
05 The arc BEC shown in Fig. l is a more standard
arc and is originally different from the radial profile
of the carcass based on the so-called natural equilibrium
curve. However, the upper region of the sidewall
portion is relatively thin in the thickness and low in
the rigidity, so that the radial profile of this region
based on the natural equilibri.um curve becomes very
approximate to a part EC of ~he above arc. Therefore,
it should be noticed that the ratio R/R' of 0.65-0.85
will be obtained~only insofar the carcass line is
lntentionally precluded from the natural equilibrium
curve.
On the other hand, the lower region of the
sidewall portion is a region having a relatively large
rigidity because the carcass ply is turned up around
the bead core from inside toward outside in the radial
direction and ~he rubber filler is disposed between the
carcass ply and the turnup thereof. to strengthen the
bead portion. In any case~ such a lower region is
generally existent inside the arc BE in the radial
profile of the carcass based on the natural equilibrium
curve. According to the invention, however, the f value
of 5-l0 mm is first given by intentionally and largely
precluding the carcass line from the natural equilibrium
~2~
curve, i.e. only by making the curvature of the carcass
at the lower region of the sidewall portion small or
into the reversed R-shape, which can completely be
distinguished from the conventional natural equilibrium
05 curve.
The reason why the rolling resistance is
improved in the tire having the carcass radial profile
obtained by intentionally precluding from the natural
equilibrium curve is disclosed in detail in EPC Publica-
tion No. 103,984 and also the means disclosed in the
same publication is required in the invention for the
manufacture of such tires.
When the ratio R/R' is more than 0.85, it is
impossible to obtain the effect for reducing the rolling
15 resistance by reducing the shearing deformation in the
upper region of the sidewall portion by intentionally
precluding from the natural e~uilibrium curve as shown
in the EPC Publication No. 103,984, while when the
ratio R/R' is less than 0.65, the bending deformation
20 concentrates in relatively thick buttress portion to
cancel the effect for reducing the rolling resistance
resulting from the reduced shearing deforma~ion. t
On the other hand, when the value of f is less than
5 mm, the effect for reducing the consumed energy
25 according to the principle disclosed in the EPC Publica-
tion No. 103,984 cannot be sufficiently achieved, while
when the value of f exceeds ~0 mm, the tension in the
carcass in the lower region of the sidewall portion
when filled with the internal pressure is too high to
adversely affect the durability of the tire, and as the
carcass enters inside oE the tire, the outer surface of
the tire locates on the relatively inner side to
05 adversely affect the fitting of the rim.
In the tire of the above configuration, the
tension of the carcass in the upper region of the
sidewall portion becomes relatively low, which contri-
butes to increase a pneumatic trail when being subjected
to a slip angle, i.e. a distance between the center of
the ground contact surface and the working point of the
cornering force located therebehind to thereby increase
the restoring torque.
In Fig. 2 is shown a first embodiment of the
tire shape according to the invention, wherein a tread
width TW is made narrower to a tire width SW as compared
with the case of the ordinarily used radial tire.
Fig. 3 shows a second embodiment of the tire according
to the invention having the same structure as in Fig. 2
except that the tread portion has a cap and base
structure, and Fig. 4 shows a third embodiment of the
tire according to the invention having the same structure
as in Fig. 3 except that the rubber filler has a compo-
site struc-ture of hard rubber stock and soft rubber
stock. In these figures, numeral l is a bead portion,
numeral 2 an annular sidewall portion, numeral 3 a
tread portion, numeral 4 a carcass, numeral 5 a belt,
numeral 6 a rubber filler, numeral 7 a bead core,
numeral 8 a rim and numeral 9 a rim flange. For the
comparison, the ordinarily used radial tire is shown in
Fig. 5.
When the tread width TW is made narrower to
05 the tire width SW, the length of the ground contact
surface of the tire under loading becomes relatively
longer as compared with the case of the ordinarily used
radial tire and as a result, the enveloping property
against irregular road surface is enhanced even under a
higher internal pressure to improve the deterioration
of the ride comfortability produced under the high
internal pressure, and also the restoring force when
giving the slip angle is increased. Further, the
volume of the tread rubber can be reduced, so that the
tread rubber gauge is made uniform over the whole of
the tread width to reduce the rolling resistance.
According to the invention, a ratio TW/SW of
tread width to tire width is necessary to be within a
range of 55%-62%. When the ratio e~ceeds 62%, it is
difficult to obtain the aforementioned effect, while
when the ratio is less than 55%, the width o~ the
ground contact surface under loading is too narrow,
resulting in the occurrence of trouble in view of the
s~ability.
Moreover, the reason why the tire according
to the invention is used at a working internal pressure
being higher by 25-50% than a normal internal pressure
(about 1.7 kg/cm2) results from the reduction of the
'7~i
rolling resistance. When the working internal presswre
is not higher by 25% than the normal internal pressure,
the sufficient effect for the reduction of the rolling
resistance can not be obtained, while when the working
05 internal pressure exceeds 50% higher than the normal
internal pressure, the effect of reducing the rolling
resistance is saturated and rather the durability of
the tire is adversely affected.
The invention will be described below while
comparing the tires shown in Figs. 2-4 as Examples 1-3
with the tire of Fig. 5 as Comparative Example 1 and a
tire formed by intentionally precluding only the radial
profile of the carcass in the ordinarily used radial
tire from the natural equilibrium curve as Comparative
Example 2.
The structure of each tire of Examples 1-3
and Comparative Examples 1-2 is shown in the following
Table 1.
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Table 1
_
¦ d ~ Structure Structure
Kln of R/R'¦f (mm) TW/SW of tread of bead
tire rubber filler
_ _
Comparat ve 1.02 3.0 65%single rubber
Comparative 0.80 6.0 65b "
I .
0.80 6.0 59% " "
Example 2 0.80 6.0 59D/two layer "
hard and
Example 3 0.80 7.5 59% " soft rubber
Note: tire size ... P175/70R13
normal rim ... 5J-13
In these tires, the carcass 4 was a single
ply containing polyester cords of 1500 d/2 arranged at
90 with respect to the equator of the tire, and the
belt 5 was composed of two cord layers each containing
steel cords (twisting construction : 1 x 5 x 0.25 mm~
arranged at a cord angle of 20 with respect to the
equator of the tire, the cords of which layers being
crossed with each other. Further, the rubber of the
tread portion (3, 3a) had a loss tangent of 0.110 as
measured by means of a spectrometer, made by Iwamoto
Seisakusho, under the conditions of 50 Hz, 1% tensile
strain and 60C, and a Shore A hardness of 57, while
the under tread rubber (3b) in the cap and base structure
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of Figs. 3 and 4 had a loss tangent of 0.06 and a
Shore A hardness of 56. As the rubber of the bead
filler 6 was used rubber having a Shore A hardness of
95 except for the case of Fig. 4. The bead filler of
05 Fig. 4 was composed of a hard rubber stock 6a having a
Shore A hardness of 95 and a soft rubber stock 6b
having a Shore A hardness of 7~.
The rolling resistance was measured with
respect to these tires under internal pressures of
2.5 kg/cm2 and 2.~ kg/cm2 to obtain results as shown in
the following Tables 2 and 3, respectively, wherein the
rolling resistance was represented by an index on a
basis that the value of the rolling resistance of
Comparative Example 1 under an internal pressure of
1.7 kg/cm2 is 100. The larger the i.ndex value, the
more the reduction of the rolling resistance. Moreover,
the evaluation of the rolling resistance was performed
as follows: that is, the tire was pushed against a drum
of 1,707 mm in diameter and rotated up to a predetermined
speed together with the drum by the driving of a motor,
and then the driving of the motor was stopped to run
the drum by inertia, during which the rolling resistance
- was calculated by a degree of deceleration during the
rotation of the drum and tire.
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As apparent from Tables 2 and 3, the tires of
Examples 1-3 have such an effec~ that the rolling
resistance under the high internal pressure is reduced
as much as 30-50% in comparison with the rolling
05 resistance of Comparative Example 1 under the internal
pressure of 1.7 kg/cm2, and show the improving effect
of 20-30% to the case of Comparative Example 1 under
the high internal pressure (2.2 or 2.5 kg/cm2).
Particularly, the tires of Examples 2 and 3 have most
excellent results on the rolling resistance.
Then, the restoring torque was measured with
respect to the tires to obtain results as shown in the
following Tables 4 and 5.
The evaluation o~ the restoring torque was
made as follows: that is, the tire subjected to the
predetermined internal pressure (1.7, 2.2 or 2.5 kg/cm2)
was pushed against a drum of 1,707 mm in diameter and a
slip angle given to the tire was changed while rotating
the tire, during which a maximum value of the restoring
2~ torque (self-aligning torque) was measured and
represented by an index on a basis that the maximum
value of Comparative Example l under an internal pressure
of 1.7 kg/cm2 is 100. The larger the index value, the
better the restoring torque.
- 15 -
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- 17 -
-' ~l2~7~S
As apparent from Tables 4 and 5, in the tires
of Examples 1-3 according to the invention, the reduction
of the restoring torque is not substantially accomplished
even with the rising of the internal pressure.
05 Further, the test for the ride comfortability
was made with respect to the tires to obtain results as
shown in the following Tables 6 and 7.
In this case, the degree of force produced on
the rotating axis of the tire was measured during the
rotation of the tire on a test drum provided with
protrusions, from which the ride comfortability against
vibration was evaluated by an index on a basis that the
value of Comparative Example 1 under an internal pressure
of 1.7 kg/cm2 is 100. The largér the index value, the
better the ride comfortability against vibration.
- 18 -
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- 19 -
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- 20 -
P7~
As apparent from Tables 6 and 7, in the tires
of Examples 1-3 according to the invention, the ride
comfortability against vibration under the high internal
pressure is not substantially deteriorated and is
05 approximately equal to that under the normal internal
pressure (1.7 kg/cm2).
As mentioned above, according to the invention,
the largely reduction of the rolling resistance can
advantageously be realized under an internal pressure
Of 20-50% higher than the normal internal pressure by
adequately determining the radial profile of the carcass
and making the tread width narrow to the tire width
without causing the deterioration of the ride comfort-
ability against vibration and the reduction of the
restoring torque, which have been produced when the
ordinarily used tire is merely used under an internal
pressure higher than the normal internal pressure.
~5
- 21 -
