The present invention relates to a combination of a pneumatic
tyre and a rim to assemble the pneumatic tyre to and a producing method thereof,
capable of suppressing disturbance of the carcass cord arrangement generated when
a green tyre is vulcanised and formed, and improving the uniformity.
Normally, when a pneumatic tyre is produced, a green tyre
(t1) made on a forming drum, is vulcanised and formed in a tyre vulcanising mould
(b), thereby making a finished tyre (t2) having final a shape very close to the
tyre outline shape when assembled onto a rim as shown in Figs. 7(A) and 7(B).
In the green tyre (t1), sidewall portions (c) and bead
portions (d) spread outwards in the axial direction of the tyre as the sidewalls
extend radially inwards. Therefore, when the green tyre (t1) is (t1) is vulcanised
and formed, the bead cores (d1) are moved axially inwards beyond the sidewall maximum
width positions (p) of the finished tyre (t2).
At that time, as shown in Fig. 8(A), a compression force
(x) which becomes greatest when the bead cores (d1) pass through the sidewall maximum
width positions (p) is temporarily applied to the carcass (e). As a result, as shown
in Fig. 8(B), a disturbance of the cord arrangement such as a meander (k) is generated
in the carcass cords (e1), and this is a cause of deterioration in the uniformity
which results in increased tyre noise and lowering of the steering stability of
If Wc is designated as the difference between the axial
distance Wa of the tyre inner peripheral surface and the distance Wb of the bead
portion inner surface, both from the tyre centreline, and h is the height of the
tyre cross-section then a bead offset ratio can be set as Wc/h. In the prior art
Japanese Patent Application Laid Open No HO6-228104 this was set at 0.2 or smaller
whereas in normal tyres it is typically 0.5.
However, although the distance between the beads is increased
and the offset ratio Wc/h of 0.5 is reduced in this prior art, since the difference
Wc exists, a portion (g) exists which bend backwards so at least the tyre inner
surface is inclined inwards in the axial direction of the tyre toward the radially
inner direction. Thus, since the compressing force is still naturally applied, there
is still disturbance of the carcass cord arrangement such as meander.
FR 2699 121 discloses a tyre, a mounting rim therefore
and a circumferentially unstretchable ring for supporting the tread of the tyre
when running at low or zero pressure. The inner surface of the tyre in a tyre meridian
cross-section has a substantially spread form and remains in this form when mounted
on the rim. The tyre mounted on the rim does thus not present a conventional form.
It is an object of the present invention to provide a combination
of a pneumatic tyre and a rim to assemble the pneumatic tyre to and a producing
method thereof, capable of improving the uniformity, reducing the noise and improving
the steering stability according to the above problems.
This object is achieved by a combination of a pneumatic
tyre and a rim to assemble the pneumatic tyre to according to claim 1 and a producing
method for a pneumatic tyre according to claim 2.
A tyre vulcanising mould used for the method according
to claim 2 comprises a tyre forming surface having a substantially spread shape
inwardly in the tyre's radial direction in its region from a tread forming surface
portion forming an outer surface of a tread portion to a bead forming surface portion
forming an outer surface of a bead portion through a sidewall forming surface portion
forming an outer surface of a sidewall portion, and said tyre forming surface has
a maximum width at a bead heel corresponding portion for forming a bead heel.
The tyre vulcanising mould may have an angle &agr; which
is 85 degrees or smaller, where said angle &agr; is defined between a tyre axial
direction line and a line segment extending from said bead heel corresponding portion
through a position of intermediate height of a curved surface of a minimum radius
between said tread forming surface portion and said sidewall forming surface portion.
As a result of the present invention, it is possible to
reliably prevent the disturbance of the carcass cord arrangement at the time of
the vulcanising and final forming process, to improve the uniformity, to reduce
noise in service and to improve the steering stability on a vehicle.
These objects as well as other objects, features and advantages
of the present invention will become more apparent to those skilled in the art from
the following description with reference to the accompanying drawings in which:
- Fig. 1 is a sectional view of a tyre of an embodiment of the present invention;
- Fig. 2 is a sectional view showing a state in which the tyre is assembled on
- Figs. 3(A) and 3(B) are diagrams for explaining a forming method for a green
- Fig. 4 is a sectional view of a vulcanising mould of the embodiment of the invention;
- Fig. 5 is a diagram showing a tyre forming surface of the vulcanising mould
at an, enlarged scale;
- Fig. 6 is a sectional view for explaining one of the problems of a conventional
- Figs. 7(A) and 7(B) are sectional views for explaining the producing method
of the conventional tyre;
- Figs. 8 (A) and 8(B) are diagrams for explaining the main problem of the conventional
- Fig. 9 is a sectional view of the conventional tyre for explaining one of the
Fig. 1 is a meridian cross-sectional view of a pneumatic
tyre 1 after being vulcanised and formed. In Fig. 1, the pneumatic tyre 1 is a radial
tyre for a passenger car, and includes a tread portion 2, a pair of sidewall portions
3 extending from opposite ends of the tread portion 2 in a radially inward direction
of the tyre, and bead portions 4 located at the inner ends of the sidewall portions
3. A carcass 6 is provided between the bead portions 4, 4 of the pneumatic tyre
1, and the tread portion 2 is reinforced by a belt layer 7 disposed outside the
carcass 6 and inside of the tread portion 2.
The belt layer 7 comprises two or more (two, in the present
embodiment) belt plies 7a, 7b whose belt cords are disposed at 30° or less
with respect to the tyre equator C, and the belt cords are superposed such that
they intersect each other between the plies. Steel cord is preferable as the belt
cord, but the belt cord may be an organic fibre cord such as nylon, polyester, rayon
and aromatic polyamide.
The belt layer 7 has at its outer side with a band layer
9 for preventing lifting of the belt layer 7. The band layer 9 comprises a continuous
ply formed by helically winding an organic fibre cord such as nylon substantially
parallel to the tyre equator C, and the band layer 9 is formed such as to cover
at least an outer edge portion of the belt layer 7.
The carcass 6 is formed of one or more carcass plies 6a
having a ply body 6A extending from the tread portion 2 to the bead portion 4 through
the sidewall portion 3 and reaching a bead core 5, and a ply turn-up portion 6B
continuously formed with the ply body 6A and folded back from the inner side of
the tyre around the bead core 5.
The carcass ply 6a includes carcass cords disposed at 70
to 90° with respect to the tyre equator C. An organic fibre cord such as nylon,
polyester, rayon and aromatic polyamide, or a metal fibre cord such as steel is
employed as the carcass cord. In the case of the present embodiment, one carcass
ply 6a is used comprising an organic fibre cord disposed at substantially 90°
with respect to the tyre equator C.
A bead apex rubber 8 extending from the bead core 5 outwardly
in the tyre radial direction is disposed between the ply body 6A and the ply turn-up
portion 6B. An inner surface and an outer surface of the bead apex rubber 8 in the
tyre axial direction contact the ply body 6A and the ply folding portion 6B respectively
and or extend substantially parallel to the ply body 6A and the ply folding portion
6B as a reinforcing layer. In order to obtain the necessary rigidity of the bead,
it is preferable that the bead apex rubber 8 has a height H1 from a cross-section
centre 5P of the bead core 5 which is 30% or more of a tyre height HT at the cross-section
centre 5P, and is made of a hard rubber having a JIS A hardness of 60 to 90 degrees.
For the bead core 5, there is employed a core capable of
rotating around its own circumferential centre line. In other words, the cross-section
of the core has substantially symmetrical shape around its cross-section centre
point 5P, i.e., a core having a structure which does not have directivity around
the cross-section centre point 5P in terms of strength. For such a core, it is possible
to employ various structures of circularly cross-section such as a so-called bunched
type in which a large number of filaments are bound together, and a so-called cable
type formed with a sheath layer comprising a plurality of sheath wires helically
wound around the periphery of the core in the manner a cable.
Inside the carcass 6, an inner liner layer 11 forming a
tyre inner barrel, i.e., a tyre inner surface IS is provided between the bead portions
4, 4 along the ply body 6A.
The tyre inner surface IS is in a substantially spread
form inward in the radial direction in its region from the tread portion 2 to the
toe tip ends 4A of the bead portions 4 through the sidewall portions 3.
The expression "substantially spread form" used in the
present application means a shape of an outward inclining state in which the tyre
inner surface IS extends substantially obliquely outwards in the tyre axial direction
towards the radially inner direction. In such a "substantially spread form", the
tyre width Wi between the tyre inner surfaces IS gradually increases in the radially
inward direction to form a maximum width Wil between the toe tip ends 4A and 4A.
In the pneumatic tyre 1, since the inner liner rubber layer
11 has a substantially constant thickness, the tyre inner surface IS is substantially
parallel to the ply body 6A of the carcass 6 and the inner surface of the bead apex
rubber 8. Therefore, the inner surfaces of the ply body 6A and the bead apex rubber
8 are also in the substantially spread form.
The toe tip end 4A corresponds to an inner end of the tyre
inner surface IS in the radial direction. The bead portion 4 comprises a bead bottom
surface portion S1 extending from the toe tip end 4A for sitting on a wheel rim
seat, and a flange contact surface portion S3 connected to an outer side of the
bead bottom surface portion S1 through a convex arc bead heel S2.
In the present embodiment, the tyre outer surface OS is
also in a substantially spread form in its region from the tread portion 2 to the
bead heel S2 of the bead portion 4 through the sidewall portion 3. Therefore, the
tyre width Wo between the tyre outer surfaces OS also gradually increases in the
radially inward direction to reach a maximum width Wo1 between the bead heels S2
As shown in Fig. 2, when this pneumatic tyre 1 is mounted
in its standard rim specified by specifications such as JATMA, TRA or ETRTO, the
pneumatic tyre 1 assumes a conventional tyre shape, wherein the tyre maximum width
WT is provided at a substantially intermediate portion of the sidewall portion 3,
and the bead portion 4 is disposed axially inside the maximum width position P.
As described above, the pneumatic tyre 1 is in the substantially
spread form close to the green tyre, which is vulcanised. Therefore, in the vulcanising
and formation process, the carcass 6 does not receive compression deformation in
the radial direction and so it is possible to reliably and effectively prevent disturbance
of the cord arrangement such as meander of the carcass cord due to no compression
deformation being generated. It is therefore possible to greatly improve the uniformity
and to reduce noise in service and to improve the steering stability on a vehicle.
When the tyre is assembled to its rim, the bead portion
4 is deformed to turn inwards from is maximum width position P. However, since the
bead core 5 does not have directivity around the cross-section centre in terms of
strength as described above, it is possible to stably secure the rigidity of the
bead. To the contrary, internal stress from the bead portion 4 to the sidewall portion
3 is increased due to the deformation and the rigidity is increased, which contribute
to the improvement of the steering stability.
As shown in Figs. 3 (A) and 3(B), the tyre assembly process
is basically like a conventional tyre. The green tyre 1A is formed such that a tyre
covering rubber 12 comprising the inner liner rubber 11, a chafer rubber 4G and
sidewall rubber 3G are assemble together on a building drum and the carcass ply
6a and the like are sequentially wound to form a cylindrical base 13 and then, bead
cores 5 on which bead apex rubbers 8 are mounted are set to opposite sides of the
cylindrical base 13. Then, a main portion 13A of building drum cylindrical base
13 between the bead cores 5 and 5 is expanded to bring the main portion 13A into
contact under pressure with an inner peripheral surface of an annular tread ring
15 including a pre-assembled belt layer 7, a band layer 9 and a tread rubber 2G,
and the side portions 13B outside the bead core 5 are folded up to contact the main
portion 13A, thereby forming the green tyre 1A in its spread form.
As shown in Fig. 4, the vulcanising mould 20 comprises
a mould body 21 having a tyre forming surface 23, and a bladder 22 for pressing
the tyre inner surface of a green tyre 1A mounted in the tyre forming surface 23.
In the present embodiment, the vulcanising mould body 21
comprises an upper mould 21U for forming one of the tyre outside surfaces, a lower
mould 21L for forming the other tyre outside surface, and a plurality of segments
21T capable of forming the tread surface. By mounting the upper mould 21U and the
segments 21T to a ram of a press, and by mounting the lower mould 21L to a bed,
the upper mould 21U, the lower mould 21L and the segments 21T can be united together
or separated from one another by the vertical movement of the ram. By uniting the
upper mould 21U, the lower mould 21L and the segments 21T together, a forming chamber
surrounded by the tyre forming surface 23 is formed.
The bladder 22 is a bag-like resilient sheet body formed
using rubber, synthetic resin or the like. By charging high temperature and high
pressure gas or liquid into the bladder 22, the bladder 22 is expanded, and this
presses the green tyre 1A against the tyre forming surface 23. Thus the vulcanising
process and the forming process are carried out simultaneously.
Here, as shown in Fig. 5, the tyre forming surface 23 comprises
a tread forming surface portion 23A forming an outer surface of the tread portion
2, a sidewall forming surface portion 23B forming an outer surface of the sidewall
portion 3, and a bead forming surface portion 23C forming an outer surface of the
bead portion 4. The bead forming surface portion 23C comprises a bottom surface
corresponding portion 23C1 forming the bead bottom surface portion S1, a bead heel
corresponding portion 23C2 forming the bead heel S2, and a flange contact surface
corresponding portion 23C3 forming the flange contact surface portion S3.
The tyre forming surface 23 has substantially the same
outline as that of the unvulcanised green tyre outer surface OS. Therefore, the
tyre forming surface 23 has a substantially spreading shape in the radially inward
direction over a region from the tread forming surface portion 23A to the bead heel
corresponding portion 23C2 through the sidewall forming surface portion 23B, and
a width W of the tyre forming surface 23 between the bead heel corresponding portions
23C2 and 23C2 is the maximum width W1.
According to the present embodiment, in the tyre forming
surface 23, the angle &agr; defined between a tyre axial direction line and a
line segment N extending from the bead heel corresponding portion 23C2 through a
position Q is set to 85 degrees or smaller. The position Q is the position of intermediate
height of a curved surface of a minimum diameter portion 23D between the tread forming
surface portion 23A and the sidewall forming surface portion 23B. This angle &agr;
is an index of the spreading degree, and by setting this angle at 85 degrees or
smaller to increase the spreading degree, the outward projection from the maximum
width position P of the bead portion 4 can be set greater and more reliably, and
it is then possible to further improve the suppressing effect of the disturbance
of the cord arrangement. If the angle &agr; is greater than 85 degrees, the suppressing
effect might be insufficient.
In order to obtain the pneumatic tyre 1, in the pressing
state by the bladder 22, it is necessary to previously form the tyre inner surface
IS of the green tyre 1A such that the tyre inner surface IS substantially spreads
radially inward in a region from the tread portion 2 to the two tip end 4A of the
bead portion 4 through the sidewall portion 3. This can be carried out by controlling
the thickness of each of the constituent members of the tyre.
By forming the tyre inner surface IS in the substantially
spreading shape, as shown in Fig. 6, it is possible to prevent the bladder 22 from
needing on over-hang portion 30 in the tyre axially outward direction for expanding,
unlike the conventional tyre. When there is an over-hang portion 30, at the time
of vulcanisation, trapped air 16 is prone to be held in a position of the over-hang
portion 30 between the green tyre 1A and the bladder 22, and there is a tendency
that the tyre shaping precision is lowered and uniformity is deteriorated. Therefore,
by forming the pneumatic tyre 1 into the above-mentioned outline, the uniformity
can further be enhanced.
The present application is not be limited to a tyre for
a passenger car, and can be applied to tyres for various purposes such as a heavy
load tyres and small truck tyre, and a bias structure other than the radial structure
can also be employed as the carcass.
To show the effectiveness of the invention tyres for a
passenger car having a tyre size of 195/65R16 were made based on the specifications
shown in Table 1, and the noise and steering stability of the tyres were measured.
The tyres were produced by vulcanising and forming substantially the same green
tyres, and only the outline shapes at the time of the vulcanisation were different
and other specifications were all the same.
Road Noise: The sample tyres were mounted on all the wheels
of a passenger car (2000 cc) each on a rim (6JJ x 16) and at standard internal pressure
(200 kpa). The passenger car was run on a hot rolled road (asphalt road surface)
and on a bitumen road (road surface on which chesils are spread) at a speed of 60
km an hour, and the over all (O.A.) and the noise level (dB(A)) at 160Hz were measured
by a microphone set at the side of a right ear portion of a driving seat. On the
hot rolled road, the noise level at 250 Hz was also measured.
Pass-by Noise: Using the above-mentioned car, the maximum
level (dB(A)) of the passing noises at the passing speed of 60- km/h and 80 km/h
were measured in accordance with actual coasting test specified by JASO/C/606.
(2) Steering stability
The above-mentioned car was run on a tyre test course,
and the steering wheel response performance, turning performance, wet grip performance
and riding comfort degree were evaluated each on a scale of 10 by the driver's sensory
evaluation. The result is better as the score is higher.
The weight of the sample tyre, the vertical spring coefficient,
the lateral spring coefficient, the cornering power (CP), the cornering force (CF),
the self aligning torque power (SATP), the rolling resistance coefficient (RRC),
the projection climbing over performance, and resonance frequency of the tyre were
measured by laboratory test, and the results are shown in Table 1. The RRC is a
value obtained by dividing the rolling resistance value by a load at that time.
@1° and @12° in CP, CF and SATP show slip angle.
Concerning the projection climbing over performance, a
tyre having a rim (6JJ × 16) and internal pressure (200 kpa) and supported
by a fixed shaft was allowed to run on a drum provided with a projection having
a height of 5 mm and a width of 25 mm while stepwisely changing the speed from 20
km/h to 100 km/h by 20 km/h each, and the difference of reaction force (kgf), which
was applied to the fixed shaft when climbing the above mentioned projection, between
the maximum value and the minimum value in the vertical direction and the longitudinal
direction and to-and-fro direction at each of the speed was calculated and was compared
with the average value. The projection climbing over performance is more excellent
as the P-P value is smaller.
The resonance frequency of the tyre was calculated such
that a tread centre of a tyre having a rim (6JJ x 16) and internal pressure (200
kpa) therein was vibrated by an impact hammer (input of ,about 20 kgf), its output
is detected by, e.g., a piezoelectric triaxial load cell, and the correlation between
these input and output is analysed by a computer, thereby calculating resonance
frequency in the circumferential direction and the radial direction which are inherent
in a tyre.
Further, the cord shrinkage ratio during the vulcanisation
formation (180°C) of the carcass, and the cord pass (cord length) between the
bead cores of the carcass cord after the vulcanisation formation were also measured.
Bead width W1 <mm>
Angle &agr; (degree
of spread) <degree>
Size after being assembled
• Outer diameter
• Tyre maximum
width WT <mm>
Vertical spring coefficient
Lateral spring coefficient
CP @1° <kgf>
CF @12° <kgf>
SATP @1° <kgf•m>
RRC @80 km/h
• p-p vertical
• p-p to-and-fro
• Radial direction
(1) Road noise
• Hot roll
• Hot roll
• Bitumen road
(2) Pass-by noise
• @ 60 km/h
• @ 80 km/h
• Dry responding
• Dry turning
• Wet grip
• Riding comfortable
As shown in Table 1, it was confirmed that the cord distribution
of the tyre of the embodiment was smaller than that of the conventional product
and that wave of the carcass cord is suppressed and the uniformity is improved.
Further, it was confirmed that the tyre of the embodiment was excellent in respect
of tyre noise and steering stability, especially the steering wheel response performance
on a dry road surface.