U.S. patent application number 10/615239 was filed with the patent office on 2004-01-22 for pneumatic tire for passenger cars and method of manufacturing the same.
Invention is credited to Hanada, Ryoji.
Application Number | 20040011450 10/615239 |
Document ID | / |
Family ID | 30002370 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040011450 |
Kind Code |
A1 |
Hanada, Ryoji |
January 22, 2004 |
Pneumatic tire for passenger cars and method of manufacturing the
same
Abstract
A pneumatic tire for passenger cars has a tread and left and
right beads, the beads each having a bead core embedded therein
with a bead filler disposed on the outer circumferential side of
the bead core, at least one carcass ply being arranged to extend
between the beads, the carcass ply having reinforcing cords which
extend in a width direction of the tire and are aligned at a
predetermined interval along a circumferential direction of the
tire, and two belt plies being disposed on the outer
circumferential side of the carcass ply in the tread. An average of
residual strain of the reinforcing cords of an innermost carcass
ply is set to -10% to 5% in each side region located between an
outer circumferential end of the bead filler and an end of an
overlapping portion of the two belt plies.
Inventors: |
Hanada, Ryoji;
(Hiratsuka-shi, JP) |
Correspondence
Address: |
RADER FISHMAN & GRAUER PLLC
LION BUILDING
1233 20TH STREET N.W., SUITE 501
WASHINGTON
DC
20036
US
|
Family ID: |
30002370 |
Appl. No.: |
10/615239 |
Filed: |
July 9, 2003 |
Current U.S.
Class: |
152/556 ;
156/110.1; 156/123; 156/130.5 |
Current CPC
Class: |
B29D 2030/0623 20130101;
B60C 13/00 20130101; B29D 30/0601 20130101; B29D 30/0602 20130101;
B29D 2030/0621 20130101; B60C 9/08 20130101; B29D 30/0005
20130101 |
Class at
Publication: |
152/556 ;
156/110.1; 156/123; 156/130.5 |
International
Class: |
B60C 009/04; B60C
009/00; B29D 030/00; B29D 030/08; B29D 030/06; B29D 030/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 17, 2002 |
JP |
JP2002-208449 |
Jul 17, 2002 |
JP |
JP2002-208469 |
Claims
What is claimed is:
1. A pneumatic tire for passenger cars having a tread and left and
right beads, the beads each having a bead core embedded therein
with a bead filler disposed on the outer circumferential side of
the bead core, at least one carcass ply being arranged to extend
between the beads, the carcass ply having reinforcing cords which
extend in a width direction of the tire and are aligned at a
predetermined interval along a circumferential direction of the
tire, and two belt plies being disposed on the outer
circumferential side of the carcass ply in the tread, wherein an
average of residual strain of the reinforcing cords of an innermost
carcass ply is set to -10% to 5% in each of side regions located
between an outer circumferential end of the bead filler and an end
of an overlapping protion of the two belt plies.
2. A pneumatic tire for passenger cars according to claim 1,
wherein the average of residual strain of the reinforcing cords is
set to --10% to 3%.
3. A pneumatic tire for passenger cars according to claim 2,
wherein the average of residual strain of the reinforcing cords is
set to -10% to 0%.
4. A pneumatic tire for passenger cars having a tread and left and
right beads, the beads each having a bead core embedded therein
with a bead filler disposed on the outer circumferential side of
the bead core, at least one carcass ply being arranged to extend
between the beads, the carcass ply having reinforcing cords which
extend in a width direction of the tire and are aligned at a
predetermined interval along a circumferential direction of the
tire, and two belt plies being disposed on the outer
circumferential side of the carcass ply in the tread, wherein an
average of residual strain of the reinforcing cords of an innermost
carcass ply is set to -5% to 1% in a overlapping region
corresponding to an overlapping portion of the two belt plies.
5. A pneumatic tire for passenger cars according to claim 4,
wherein the average of residual strain of the reinforcing cords is
set to -5% to -1%.
6. A pneumatic tire for passenger cars according to claim 5,
wherein the average of residual strain of the reinforcing cords is
set to -5% to -3%.
7. A pneumatic tire for passenger cars according to claim 4,
wherein an average of residual strain of the reinforcing cords of
the innermost carcass ply is set to -10% to 5% in each of side
regions located between an outer circumferential end of the bead
filler and an end of an overlapping portion of the two belt
plies.
8. A pneumatic tire for passenger cars according to claim 7,
wherein the average of residual strain of the reinforcing cords is
set to -10% to 3% in each of the side regions.
9. A pneumatic tire for passenger cars according to claim 8,
wherein the average of residual strain of the reinforcing cords is
set to -10% to 0% in each of the side regions.
10. A method of manufacturing a pneumatic tire for passenger cars,
comprising the steps of: setting a green tire in a shaping mold for
pre-shaping green tires, the green tire having a tread and left and
right beads, the beads each having a bead core embedded therein
with an unvulcanized bead filler disposed on the outer
circumferential side of the bead core, at least one unvulcanized
carcass ply being arranged to extend between the beads, the carcass
ply having reinforcing cords which extend in a width direction of
the tire and are aligned at a predetermined interval along a
circumferential direction of the tire, and two unvulcanized belt
plies being disposed on the outer circumferential side of the
unvulcanized carcass ply in the tread, the shaping mold having
shaping surfaces which can shape a green tire having a size close
to that of the green tire which is being pressed against molding
surfaces of a vulcanization mold; inflating the set green tire so
that the set green tire is pressed against the shaping surfaces of
the shaping mold to form a shaped green tire; and setting the
shaped green tire in the vulcanization mold; and curing the shaped
green tire after inflating the shaped green tire so as to press
against the molding surfaces of the vulcanization mold.
11. A method of manufacturing a pneumatic tire for passenger cars
according to claim 10, wherein the green tire is set in the shaping
mold after preheated.
12. A method of manufacturing a pneumatic tire for passenger cars
according to claim 11, whrein the green tire is preheated so that a
surface temperature of the green tire is 40.degree. C. to
90.degree. C. when set in the shaping mold.
13. A method of manufacturing a pneumatic tire for passenger cars
according to claim 11, wherein the green tire is cooled down after
inflated in the shaping mold.
14. A method of manufacturing a pneumatic tire for passenger cars
according to claim 13, wherein the shaped green tire is cooled down
so that the surface temperature of the shaped green tire is
30.degree. C. or lower when removed from the shaping mold.
15. A method of manufacturing a pneumatic tire for passenger cars
according to claim 10, wherein the shaping mold has the shaping
surfaces extending from the beads of the set green tire to at least
intersections where vertical lines perpendicularly drawn to a tread
surface of the tread from ends of a widest belt ply of the
unvulcanized belt plies meet the tread surface.
16. A method of manufacturing a pneumatic tire for passenger cars
according to claim 15, wherein each of the shaping surfaces extends
tire-inward along the tire width direction to a position which is
located at 20% or more of the width of the widest belt ply from the
end of the widest belt ply.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to pneumatic tires for
passenger cars and methods of manufacturing the same. More
specifically, the present invention relates to a pneumatic tire for
passenger cars and a method for manufacturing thereof, in which
braking performance can be improved.
[0002] Tire performance of pneumatic tires for passenger cars is
typically improved by changing materials and structures thereof.
Conventionally, in order to advance braking performance of the
tires, there has been proposed a technique to use high-grip rubber
compounds in the tire tread. The use of such rubber compounds,
however, deteriorates rolling resistance and further causes
degradation of wear characteristics.
[0003] Another technique of improving braking performance is that a
new reinforcing ply is disposed to enhance rigidity of the tire.
The placement of such a new component, however, incurs increases in
cost and weight.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide a
pneumatic tire for passenger cars and a method of manufacturing the
same, in which braking performance can be improved without using
high-grip rubber compounds in a tread and without placing any new
component.
[0005] In order to achieve the above object, the present invention
provides a pneumatic tire for passenger cars having a tread and
left and right beads, the beads each having a bead core embedded
therein with a bead filler disposed on the outer circumferential
side of the bead core, at least one carcass ply being arranged to
extend between the beads, the carcass ply having reinforcing cords
which extend in a width direction of the tire and are aligned at a
predetermined interval along a circumferential direction of the
tire, and two belt plies being disposed on the outer
circumferential side of the carcass ply in the tread, wherein an
average of residual strain of the reinforcing cords of an innermost
carcass ply is set to -10% to 5% in each of side regions located
between an outer circumferential end of the bead filler and an end
of an overlapping portion of the two belt plies.
[0006] The present invention provides another pneumatic tire for
passenger cars having a tread and left and right beads, the beads
each having a bead core embedded therein with a bead filler
disposed on the outer circumferential side of the bead core, at
least one carcass ply being arranged to extend between the beads,
the carcass ply having reinforcing cords which extend in a width
direction of the tire and are aligned at a predetermined interval
along a circumferential direction of the tire, and two belt plies
being disposed on the outer circumferential side of the carcass ply
in the tread, wherein an average of residual strain of the
reinforcing cords of an innermost carcass ply is set to -5% to 1%
in a overlapping region corresponding to an overlapping portion of
the two belt plies.
[0007] The present invention also provides a method of
manufacturing a pneumatic tire for passenger cars comprising the
steps of: setting a green tire in a shaping mold for pre-shaping
green tires, the green tire having a tread and left and right
beads, the beads each having a bead core embedded therein with an
unvulcanized bead filler disposed on the outer circumferential side
of the bead core, at least one unvulcanized carcass ply being
arranged to extend between the beads, the carcass ply having
reinforcing cords which extend in a width direction of the tire and
are aligned at a predetermined interval along a circumferential
direction of the tire, and two unvulcanized belt plies being
disposed on the outer circumferential side of the unvulcanized
carcass ply in the tread, the shaping mold having shaping surfaces
which can shape a green tire having a size close to that of the
green tire which is being pressed against molding surfaces of a
vulcanization mold; inflating the set green tire so that the set
green tire is pressed against the shaping surfaces of the shaping
mold to form a shaped green tire; setting the shaped green tire in
the vulcanization mold; and curing the shaped green tire after
inflating the shaped green tire so as to press against the molding
surfaces of the vulcanization mold.
[0008] According to the present invention described above, by
specifying the average of residual strain of the reinforcing cords
of the carcass ply, as described above, braking performance can be
improved due to rigidity of the carcass ply greater than that of
the conventional carcass ply. Since it is not required to change a
high-grip rubber compound in the tread or provide any new
component, problems does not arise such as degradation of rolling
resistance and wear characteristics, and increases in cost and
weight.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a tire meridian half cross sectional view
illustrating an embodiment of a pneumatic tire for passenger cars
according to the present invention.
[0010] FIG. 2 is an explanatory view of carcass and belt plies
shown in FIG. 1.
[0011] FIG. 3 is an explanatory half cross sectional view
illustrating an example of a shaping device used for manufacturing
a pneumatic tire for passenger cars according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] The embodiments of the present invention will be described
in detail below with reference to the attached drawings.
[0013] FIGS. 1 and 2 show an example of a pneumatic tire for
passenger cars according to the present invention, in which the
reference numeral 1 denotes a tread, the reference numeral 2 a
sidewall, the reference numeral 3 a bead, and the reference symbol
CL a tire center line.
[0014] A bead core 5 with a bead filler 4 disposed on the outer
circumferential side thereof is embedded in each of the left and
right beads 3. Two carcass plies 6A and 6B are arranged to extend
between the beads 3, the carcass plies 6A and 6B each comprising a
rubber layer and reinforcing cords f aligned therein, the
reinforcing cords being constituted of organic fiber cords (twisted
cords), extending in a width direction of the tire and being
arranged at a predetermined interval along a circumferential
direction T of the tire. The carcass plies 6A and 6B have end
portions 6a and 6b, which are turned up around the bead cores 5
from the inner side to the outer side of the tire.
[0015] Arranged on the outer circumferential side of the carcass
plies 6 in the tread 1 are two belt plies 7A and 7B, each of which
comprises reinforcing cords e, made of steel cords, which extend in
a slanted manner relative to the tire circumferential direction T
and are aligned at a predetermined interval along the tire
circumferential direction T. The first belt ply 7A on the side of
the carcass plies 6 is formed to be wider in width than the second
belt ply 7B, in which the reinforcing cords e of the belt plies 7A
and 7B are intersected to each other so that they are oriented in
opposing directions with respect to the tire circumferential
direction T.
[0016] Provided radially outwardly of the second belt ply 7B are
two belt cover plies 8 each of which comprise an organic fiber cord
spirally wound in the tire circumferential direction T. An inner
liner ply 9 is disposed on the inner side of the carcass ply 6A.
The reference numeral 10 denotes a main groove extending along the
tire circumferential direction T on the tread surface 1A.
[0017] The two carcass plies 6A and 6B described above has an
average of residual strain of the reinforcing cords f which is set
in a range from -10% to 5% in each side region X located between
the outer circumferential end 4a of the bead filler 4 and the
overlapping portion end m of the two belt plies 7A and 7B (an edge
position of the second belt ply 7B). In an overlapping region Y
corresponding to the overlapping portion of the two belt plies 7A
and 7B, an average of residual strain of the reinforcing cords f is
set in a range from -5% to 1%.
[0018] The inventor of the present invention has intensely studied
ways to improve braking performance without changing of a rubber
compound of the tread, which incurs deterioration of rolling
resistance and wear characteristics, and without provision of any
new component. As a consequence, the inventor of the present
invention focused on carcass plies arranged to extend between the
left and right beads.
[0019] Carcass plies include reinforcing cords. If the tension of
the reinforcing cords is increased, the rigidity of the carcass
plies can be increased. Thus, it is possible to improve braking
performance without changing a rubber compound of the tread or
providing any new component.
[0020] A pneumatic tire is manufactured through a vulcanization
process. Accordingly, residual strain is usually observed on the
reinforcing cords of carcass plies after curing. A study of a
relationship between residual strain and rigidity of the carcass
ply revealed that the reinforcing cords with less residual strain
have lower effect of untwisting. Thus, rigidity of a carcass ply
can be enhanced by utilizing rigidity of the reinforcing cords. The
less the residual strain is, the further the rigidity of the
reinforcing cords can be utilized to increase rigidity of a carcass
ply. Preferably, the value of the residual strain is a minus value.
It has been found that rigidity of a carcass ply can be greatly
increased especially in the overlapping region Y.
[0021] When measurements of residual strain of the reinforcing
cords of the innermost carcass ply of the conventional tire were
carried out, the average of residual strain was approximately 2% in
the belt ply overlapping region in the tread and the average of
residual strain is approximately 8% in the rest of the region.
Accordingly, if the average values of residual strain of the
reinforcing cords can be less than the values, it becomes possible
to improve braking performance without using a high-grip rubber
compound in the tread or disposing any new component.
[0022] Thus, as described above, the averages of residual strain of
the reinforcing cords f are set in a range from -10% to 5% in the
side region X and -5% to 1% in the overlapping region Y. The
average of residual strain of the reinforcing cords f in the bead 3
side region positioned radially inwardly of the side region X may
be set in the same range from -10% to 5% as in the side region X.
However, the bead filler 4, made of rubber with higher rigidity
than the rubber constituting the sidewall 2, is usually disposed in
the region, thus providing high rigidity to the region. Therefore,
even if the rigidity of the carcass plies 6A and 6B is increased in
the region, this increase will not play a part in improvement of
braking performance.
[0023] If the average of residual strain of the reinforcing cords f
is less than the foregoing range in either or both of the regions X
and Y, uniformity will greatly decrease. In order to obtain an
effect of highly improved braking performance, it is preferable
that the averages of residual strain be set in the above ranges in
both regions X and Y. However, setting of an average of the
residual strain to the above range in either of the regions can
improve braking performance.
[0024] The pneumatic tire described above can be produced as
follows: a green tire is shaped to have an size close to that of
the green tire pressed against the molding surfaces of a
vulcanization mold to form a shaped green tire; the shaped green
tire is set in the vulcanization mold before inflated; the shaped
green tire is vulcanized by heating; and the vulcanized pneumatic
tire is cooled down in a post cure inflation process in which, as
required, air pressure which is supplied is adjusted.
[0025] To form the shaped green tire, a shaping device, for
example, shown in FIG. 3 having a shaping mold can be used. A green
tire G shown in FIG. 3 comprises left and right beads G1 and G2 and
a tread G3, the beads G1 and G2 each having a bead core Gc embedded
therein with an unvulcanized bead filler Gd disposed on the outer
circumferential side of the bead core, an unvulcanized carcass ply
Gb being arranged to extend between the beads G1 and G2, the
carcass ply Gb having reinforcing cords which extend in a width
direction of the tire and are aligned at a predetermined interval
along a circumferential direction of the tire, and two unvulcanized
belt plies Ga being disposed on the outer circumferential side of
the unvulcanized carcass ply Gb in the tread G3.
[0026] The reference numeral 11 denotes a shaping mold for shaping
the green tire G. The shaping mold 11 comprises upper and lower
circular mold sections 12 and 13 disposed on the upper and lower
sides of the shaping mold 11.
[0027] The lower mold section 13 is fixed onto a base plate 14. A
lower mold bead ring B1 is fastened to the inner surface of the
inner circumferential side of the lower mold section 13 to shape
one bead G1 of the green tire G. The upper mold section 12 can
ascend and descend in directions indicated by an arrow a by
ascending and descending means (not shown). An upper mold bead ring
B2 is fixed onto the inner surface of the inner circumferential
side of the upper mold section 12 to shape the other bead G2 of the
green tire G.
[0028] Shaping surfaces 12A and 13A of the upper and lower mold
sections 12 and 13 extend from the beads G1 and G2 of the green
tire G to the tread G3. As shown in FIG. 3, the upper and lower
mold sections 12 and 13 are not abutted on each other and separated
apart when the green tire G is set, so as to open the central side
of the tread G3. This can easily release strain of the reinforcing
cords of the unvulcanized belt plies Ga and the unvulcanized
carcass ply Gb which is generated when pressing the green tire G
against the shaping surfaces 12A and 13A by inflation of the green
tire G. Therefore, this structure is preferable in terms of
improving uniformity. However, it may be constructed such that the
upper and lower mold sections 12 and 13 are abutted on each other
when the green tire G is set.
[0029] As described above, in the case where the upper and lower
mold sections 12 and 13 are structured so as to be spaced apart
from each other, it is preferable to have the shaping surfaces 12A
and 13A each of which extends from the bead G1, G2 of the green
tire G to at least a intersection P where a vertical line M
intersects with the tread surface G3a. The vertical line M is
perpendicularly drawn to the tread surface G3a from the end s of
the widest belt ply Ga.sub.1 having the largest width.
[0030] Preferably, the shaping surfaces 12A and 13A extend
tire-inward (towards the tire center line CL) along the tire width
direction to positions which are located at 20% or more of the
width W of the widest belt ply Ga.sub.1 from the ends s of the
widest belt ply Ga.sub.1. This structure is preferable for
effectively preventing the tread G3 from expanding out of a space
between the upper and lower mold sections 12 and 13 during
inflation of the green tire G.
[0031] Holding means 30 for holding the beads G1 and G2 of the
green tire G is provided in the center side of the shaping mold 11.
The holding means 30 includes lifting means 15 at the center of the
shaping mold 11. The lifting means 15 comprises a hydraulic
cylinder actuated with pressurized oil. The hydraulic cylinder has
a upstanding cylinder body 15A and a vertically extending rod 15B
which protrudes upwardly from the upper end of the cylinder body
15A and is vertically moved.
[0032] A circular upper member 16 is hermetically engaged with and
fastened to the upper end of the rod 15B. The upper member 16 is
enabled to move up and down with raising and lowering of the rod
15. A circular lower member 17 is fixed to the base plate 14 and
hermetically engaged with the cylinder body 15A. The lower plate 17
is disposed on the inner circumferential side of the lower mold
section 13.
[0033] Cylindrically formed rubber sealing member 20A and 20B are
provided such that one end portion of the sealing member 20A and
one end portion of the sealing member 20B are securely attached
between the upper mold bead ring B2 and the upper member 16 and
between the lower mold bead ring B1 and the lower member 17,
respectively. The sealing members 20A and 20B each have the other
end portion which expands outwardly so that the diameter of the
other end is larger.
[0034] Holding mechanisms 18 for holding the beads G1 and G2 are
provided at a plurality of locations at a predetermined interval
along a circumferential direction of the circular mold between the
upper member 16 and the lower member 17. Each of the holding
mechanisms 18 comprises an upper support arm 18A protruding
downward from the upper member 16, a lower support arm 18B
protruding upward from the lower member 17 , and holding arms 18C
and 18D for holding the beads G1 and G2. The holding arms 18C and
18D are connected to the upper support arm 18A and the lower
support arm 18B, respectively.
[0035] The holding arms 18C and 18D have bend end portions 18C1 and
18D1, end surfaces 18C2 and 18D2 of which hold the inner surfaces
of the beads G1 and G2 of the green tire G, set to the upper and
lower bead rings B1 and B2, by pressing the inner surfaces of the
beads G1 and G2 via the sealing members 20A and 20B.
[0036] A connecting arm 18E connects the holding arms 18C and 18D
at their middle parts. The upper and lower support arms 18A and
18B, the upper and lower holding arms 18C and 18D and the
connecting arm 18E constitute a link mechanism. When the rod 15B is
raised, holding by the holding mechanisms 18 is released, and the
holing mechanisms 18 hold beads G1 and G2 in a lowered position
shown in FIG. 3.
[0037] Formed in the base plate 14 and the lower plate 17 are a
supply path (not shown) which supplies a pressure medium into the
green tire G set in the shaping mold 11 and a discharge path (not
shown) which discharges the pressure medium therefrom. The green
tire G is inflated by the pressure medium supplied from a pressure
medium supply source (not shown) through the supply path while the
pressure medium is constantly supplied from the supply path.
Meanwhile, a constant pressure is maintained in the green tire G
while the pressure medium is discharged from the discharge path.
Thus, the inflated green tire G is cooled down by the pressure
medium.
[0038] As described above, it is preferable to directly inflate the
green tire G with a pressure medium in order to uniformly press the
green tire G against the shaping surfaces 12A and 13A of the upper
and lower mold sections 12 and 13. However, instead of the sealing
members 20A and 20B, a cylindrical bladder can be attached and the
green tire G may be inflated by supplying a pressure medium into
the bladder and by expanding the bladder.
[0039] In order to set the averages of residual strain of the
reinforcing cords fin the aforementioned ranges, the dimensions of
the shaping surfaces 12A and 13A are adjusted. To reduce the
averages of residual strain of the reinforcing cords f, the
dimensions of the shaping surfaces 12A and 13A are set to the
dimensions of the molding surfaces of the vulcanization mold as
closely as possible. To reduce only the average of residual strain
of the reinforcing cords in the side regions X, the dimensions of
parts of the shaping surfaces 12A and 13A corresponding to the side
regions X are set to the dimensions of the molding surfaces of the
vulcanization mold as closely as possible. To reduce only the
average of residual strain of the reinforcing cords in the
overlapping region Y, the dimensions of parts of the shaping
surfaces 12A and 13A corresponding to the overlapping region Y are
set to the dimensions of the molding surfaces of the vulcanization
mold as closely as possible.
[0040] It is preferable that treatment of the shaping surfaces 12A
and 13A of the upper and lower mold sections 12 and 13 be carried
out to reduce friction against the green tire G. For example, a
silicon-based solution can be applied to the shaping surfaces 12A
and 12B before setting the green tire G.
[0041] The green tire G will be shaped using the aforementioned
shaping device as follows. First, the green tire G is preheated.
The preheating temperature is preferably set so that the surface
temperature of the green tire G is in a range from 40.degree. C. to
90.degree. C. when set in the shaping mold 11. If the temperature
is lower than 40.degree. C., it is difficult to give unvulcanized
rubber a creep strain. As a result, it is hard to give the green
tire G some predetermined deformation. If the temperature exceeds
90.degree. C., the rigidity of the green tire G rapidly decreases.
Accordingly, there is a possibility that the green tire G bursts
during inflation.
[0042] The green tire G is set to the lower mold section 13 after
preheated. At this time, the upper mold section 12 stays in a
waiting position above. The rod 15B is in the elevated position,
and holding by the holding mechanisms 18 are released.
[0043] After the green tire G is set in the lower mold section 13,
the rod 15B descends, and holding mechanisms 18 hold the beads G1
and G2 through the sealing members 20A and 20B, as shown in FIG. 3.
Subsequently, the upper mold section 12 in the waiting position
descends to be set to the green tire G (the state of the upper mold
section in FIG. 3)
[0044] After completion of the setting of the green tire G in the
shaping mold 11, a pressure medium is supplied to the inside as
indicated by arrows, and the green tire G is inflated. Owing to
this, the green tire G is pressed against the shaping surfaces 12A
and 13A of the upper and lower mold sections 12 and 13 to be shaped
(the state in FIG. 3). For the pressure medium, a medium which can
cool down the preheated green tire G is employed. For example, air
at a room temperature and preferably cooled down air at a
temperature lower than the room temperature can be used.
[0045] The green tire G is cooled down for a predetermined time
period by supplying the pressure medium while maintained in a state
in which the green tire G is being pressed against the shaping
surfaces 12A and 13A. The cooling temperature of the green tire G
may be such that a surface temperature of the tire is 30.degree. C.
or lower when removed from the shaping mold 11. If the tire surface
temperature is higher than 30.degree. C., the elasticity of the
unvulcanized rubber recovers. Thus, there is a possibility that the
shape of the green tire G regains the shape before shaping.
[0046] After cooling, the upper mold section 12 ascends to the
waiting position above. Subsequently, the rod 15B is elevated to
release the holding by the holding mechanisms 18, and the green
tire G is removed. The green tire G obtained is formed into a
shaped green tire which is close in size to the green tire in the
state of being pressed against the molding surfaces of the
vulcanized mold. The shaped green tire is, as in a conventional
method, pressed and heated inside the mold of a vulcanization
machine to cure the shaped green tire.
[0047] According to the present invention described above, by
setting the averages of residual strain of the reinforcing cords f
of the carcass plies 6A and 6B lower than conventional ones, it is
possible to increase rigidity of the carcass plies 6A and 6B. As a
consequence, braking performance can be improved. Since it is not
required to use a high-grip rubber compound in the tread 1, rolling
resistance and wear characteristics can not be deteriorated. It is
not required to provide any new component, thereby preventing
increases in cost and weight.
[0048] In addition, by setting the average of residual strain of
the reinforcing cords f of the carcass plies 6A and 6B in the side
regions X as previously mentioned, a side rigidity of the tire can
be enhanced. Accordingly, it is possible to increase steering
stability.
[0049] In the present invention, the average of residual strain of
the reinforcing cords f of the carcass plies 6A and 6B in the side
regions X is preferably set to -10% to 3% in order to further
improve braking performance, and desirably -10% to 0%.
[0050] The average of residual strain of the reinforcing cords f of
the carcass plies 6A and 6B in the overlapping region Y is
preferably set to -5% to -1% in order to further improve braking
performance, and desirably -5% to -3%.
[0051] In the foregoing embodiment, the averages of residual strain
of the reinforcing cords f of the carcass plies 6A and 6B are set
in the ranges described above. However, at least the averages of
residual strain of the reinforcing cords f of the inner most
carcass ply 6A may be set in the above-mentioned ranges.
[0052] It is preferable to specify the averages of residual strain
of the reinforcing cords f of the carcass plies, as described
above, in the side regions X and the overlapping region Y in order
to further improve braking performance. However, braking
performance can be improved by specifying, as described above, of
the average of residual strain of the reinforcing cords f in either
of the side regions X or the overlapping region Y.
[0053] In FIG. 1, an embodiment of a pneumatic tire for passenger
cars having two carcass plies is described, but the present
invention is applicable to ones which have at least one carcass
ply.
[0054] According to the present invention, the average of residual
strain of the reinforcing cords f will be measured as follows.
[0055] First, an inner liner ply 9 is removed from the pneumatic
tire to expose the inner carcass ply 6A. Second, a plurality of
reinforcing cords f (2 to 5 cords) of the carcass ply 6A, which are
arbitrary targets for measuring, are marked at positions
corresponding to the tire center line CL, the opposed ends m of the
overlapping portion and the outer circumferential ends 4a of the
bead fillers 4. Third, a non-expandable tape is stuck along the
marked reinforcing cords f, and the markings are made to transfer
to the non-expandable tape. Thereafter, the plurality of marked
reinforcing cords f are extracted from the tire. Each residual
strain value is calculated based on a distance between the markings
of the extracted reinforcing cords f and a distance between the
corresponding markings transferred onto the non-expandable
tape.
[0056] More specifically, values (%) of residual strain of the
reinforcing cords f in the side regions X and in the overlapping
region Y are calculated by equations 100 (M-M')/M' and 100
(N-N')/N', respectively, where M is a distance between the marking
positions of the extracted reinforcing cords f corresponding to the
tire center line CL and the overlapping portion end m, N is a
distance between the marking positions of the extracted reinforcing
cords f corresponding to the overlapping portion end m and the
outer circumferential end 4a of the bead filler 4, M' is a distance
between the marking positions, corresponding to the tire center
line CL and the overlapping portion end m, of the non-expandable
tape to which the markings have been transferred, and N' is a
distance between the marking positions, corresponding to the
overlapping portion end m and the outer circumferential end 4a of
the bead filler 4, of the non-expandable tape to which the markings
have been transferred.
[0057] The foregoing measurement is performed at six spots at an
approximate regular interval along the entire circumference of the
tire. The values of residual strain obtained in each region are
averaged to be specified as an average of residual strain.
EXAMPLE 1
[0058] Test tires according to the present invention tires 1 to 5,
comparative tire 1 and conventional tire were produced having the
same tire size of 225/55R16 and a construction of a pneumatic tire
shown in FIG. 1, in which the reinforcing cords of the carcass
plies were polyester cords. The test tires each had averages of
residual strain of the carcass plies shown in Table 1, in which the
averages of residual strain of the reinforcing cords in the
overlapping region were constant and the averages of residual
strain of the reinforcing cords of the carcass plies in each of
side regions were varied.
[0059] Each test tire was attached to a rim with a rim size of
16.times.7.5 JJ, and air pressure was set to 200 kPa. The
evaluation tests of braking performance and uniformity were
conducted in the following testing method, obtaining the results
shown in Table 1.
[0060] [Braking Performance]
[0061] Each test tire was fit to a passenger car of 3000 cc
displacement with an anti-lock braking system. When running the
test course with a wet surface at 100 km/h, braking was applied to
stop the car, and the braking distance up to stopping was measured
seven times. The mean value of five braking distances except
maximum and minimum braking distances was calculated, and each
result of the present invention tires and comparative tire was
evaluated in the index, on the basis of the conventional tire as
100. The greater the index is, the shorter the braking distance is.
Accordingly, braking performance is better with the larger index.
The index value of 105 or more indicates that there is an effective
improvement.
[0062] [Uniformity]
[0063] Radial force variations (RFV) of each lot of ten test tires
were measured with a load of 5.0 kN based on JASO 0607-87. The
average of the measurements of ten test tires of each lot was taken
as RFV thereof. The results were evaluated by the index value,
where the conventional tire had the index value of 100. The smaller
the value is, the better the uniformity is. The index value of 104
or less indicates that the uniformity is within the scope of the
conventional level.
1 TABLE 1 OVERLAP- PING SIDE BRAKING UNI- REGION REGION PERFORM-
FORM- (%) (%) ANCE ITY CONVENTIONAL 2 8 100 100 TIRE PRESENT 2 5
105 100 INVENTION TIRE 1 PRESENT 2 3 108 100 INVENTION TIRE 2
PRESENT 2 0 116 101 INVENTION TIRE 3 PRESENT 2 -5 119 103 INVENTION
TIRE 4 PRESENT 2 -10 120 104 INVENTION TIRE 5 COMPARATIVE 2 -15 121
112 TIRE
[0064] As can be seen from Table 1, it is understood that the
present invention tires which have averages of residual strain of
the reinforcing cords of the carcass plies in the side regions, set
in a range from -10% to 5%, can improve braking performance while
maintaining uniformity at a conventional level.
EXAMPLE 2
[0065] Test tires according to the present invention tires 6 to 10
and comparative tire 2 were produced having the same tire size as
in Example 1 and a construction of a pneumatic tire shown in FIG.
1, in which the reinforcing cords of the carcass plies were
polyester cords. The test tires each had averages of residual
strain of the carcass plies shown in Table 2, in which, according
to the present invention tires 6 to 9 and comparative tire 2, the
averages of residual strain of the reinforcing cords in the side
regions were constant and the averages of residual strain of the
reinforcing cords of the carcass plies in the overlapping region
were varied, and according to the present invention tire 10, the
averages of residual strain of the reinforcing cords in the side
regions and in the overlapping region were within the ranges of the
present invention.
[0066] As in Example 1, the evaluation tests of braking performance
and uniformity were carried out, obtaining the results shown in
Table 2.
2 TABLE 2 OVER- LAPPING SIDE BRAKING UNI- REGION REGION PERFORM-
FORM- (%) (%) ANCE ITY PRESENT 1 8 108 101 INVENTION TIRE 6 PRESENT
-1 8 122 101 INVENTION TIRE 7 PRESENT -3 8 127 102 INVENTION TIRE 8
PRESENT -5 8 130 104 INVENTION TIRE 9 COMPARATIVE -7 8 131 115 TIRE
2 PRESENT -3 0 131 102 INVENTION TIRE 10
[0067] As can be seen from Table 2, it is understood that the
present invention tires which have averages of residual strain of
the reinforcing cords of the carcass plies in the overlapping
region, set in a range from -5% to 1%, can improve braking
performance while maintaining uniformity at a conventional
level.
[0068] As explained above, according to the present invention, by
specifying, as mentioned above, the average of residual strain of
the reinforcing cords of the carcass ply in the side regions or in
the overlapping region, braking performance can be improved without
using ahigh-grip rubber compound in the tread and without disposing
any new component.
* * * * *