Note: Descriptions are shown in the official language in which they were submitted.
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62-125, 272
HEAVY DUTY PNEUMATIC RADIAL TIRES
This invention relates to heavy duty pneumatic
radial tires for use in, for example, truck, bus and so
on, and more particularly to a heavy duty pneumatic
radial tire comprising a tread provided with plural ribs
05 extending circumferentially of the tire and many open
sipes (hereinaEter referred to as sipe unless otherwise
specified) crossing the tread.
As the heavy duty pneumatic radial tire running
on good road at a high speed, there have hitherto been
10 used some tires, wherein the tread is divided inio
plural ribs by main wide grooves extending zigzag
circumferentially of the tire and many sipes each
crossing the tread to extend between both side ends or
the tread and having a thin width are arranged in the
tread in the circumferential direction of the tire.
In these tiresr however, the amplitude and pitch of
zigzag in the sipe and the main groove are not still
optimized.
The invention will be described with reference
to the accompanying drawings, wherein:
Figs. l to 3 are partial plan views of some
embodiments of the conventional heavy duty pneumatic
radial tire, respectively;
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Fig. 4 is a graph showing a relation between
pitch number of main groove in one pitch of open sipe
and time of uneven wear generated in the heavy duty
pneumatic radial tire according to the invention;
05 Fig. 5 is a partial plan view of a first
embodiment of the heavy duty pneumatic radial tire
according to the invention; and
Figs. 6 and 7 are partial plan views of the
other embodiments of the heavy duty pneumatic radial
tire ascording to the invention, respectively.
For example, the conventional heavy duty
pneumatic radial tires are shown in Figs. l to 3.
The heavy duty pneumatic radial tire l shown in Fig. l
comprises a tread 2 divided into five ribs 5 by four
15 main wide grooves 3 each extending zigæag circumfer-
entially of the tire. The amplitude W~ of the zigzag
main groove 3 in widthwise direction of the tire is
large, and the repeated pitch P3 of the zigzag main
groove in circumferential direction is lon~. Numeral 6
2~ is a sipe. The sipe 6 crosses the tread 2 and extends
between both side ends 2a of the tread 2 so as to have
predetermined inclinin~ direction S and inclination
angle ~6 of the sipe 6 with respect to the circumfer-
ential direction C. Furthermore, the pitch P6 of the
sipe 6 in the circumferential direction C is approxi-
mately e~ual to the groove pitch P3 of the main
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groove 3. The construction other than the above is the
same as in the ordinary tire. However, in the heavy
, duty pneumatic radial tire 1 comprising such a tread 2,
rigidities of portions SA and 5B at a side end part 5a
05 of the rib 5 sandwiching the sipe 6 become ununiform, so
that the wearing of the portion 5A ( shadowed region
partially shown in Fig. 1) becomes faster than that of
the portion 5B during the running and consequently
uneven wear producing a stepped difference prematurely
10 generates at the side end part 5a of the rib 5.
The heavy duty pneumatic radial tire 8 shown in
Fig. 2 is a case that the inclination angle ~6 of the
sipe 6 crossing the tread 2 is made smaller than that of
the heavy duty penumatic radial tire 1 shown in Fig. 1.
1~ Even in the heavy duty radial tire 8, the premature
occurrence of uneven wear is caused at the side end part
5a of the rib 5 likewise the heavy duty pneumatic radial
tire 1 of Fig. 1.
The heavy duty peunmat1c radial tire 9 shown in
20 Fig. 3 i5 a case that the inclination angle ~6 of the
sipe 6 crossing the tread 2 is made larger than that of
the heavy duty pneumatic radial tire 1 shown in Fig. 1
and is perpendicular to the circumEerential direction of
the tire. Even in the heavy duty pneumatic radial
25 ~tire 9, the rigidities of convex portion 5c and concave
portion 5D at the side end part Sa of the rib 5 become
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ununiform and the wear.ing of the convex portion 5C iS
faster than that of the concave portion 5D likewise the
case of Fig. 1, so that the uneven wear prematurely
occurs.
05 It is, therefore, an object of the invention to
provide a heavy duty pneumatic radial tire haviny a
considerably improved resistance to uneven wear by
regulating the amplitude and pitch of the main zigzag
groove to the pitch oE the open sipe crossing the tread
10 provided with plural ribs to thereby make the rigidity
at the side end part of the rib in the vicinity of the
open sipe uniform and largely delay the time of uneven
wear produced in the side end part of the rib.
According to the invention, there is the provi-
sion of a heavy duty pneumatic radial tire comprising a
tread divided into plural ribs by plural main grooves
each extending zigzag circumferentially of the tire,
characterized in that each of open sipes crossing said
tread and having a thin width is arranged at a sipe
20 pitch Ps of 10~40 mm in the circumferential direction,
and said main zigzag groove has an amplitude of 1~10 mm,
and a ratio of said pitch Ps of said sipe to groove
pitch PG of said main groove is within a range of 1.5~20.
The term "open sipe" used herein means a thin
2~ slit extending between both side ends of the tread
provided with plural ribs defined by plural main qrooves
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extending circumferentially of the tire, wherein both
ends of the slit open to the groove wall face of the
main groove or the outside wall face of the tread end
without terminating in the rib.
05 The reason why the sipe pitch Ps of the sipe
(open sipe) in the circumferential direction is limited
to a range of 10~40 mm is due to the fact that when the
sipe pitch is less than 10 mm, the rigidity of rib
blocks cut by ~he sipes too lowers to advance the
10 generation tlme of uneven wear, while when it exceeds
40 mm, the rigidity of the block becomes too large and
the effect by the arrangement of the sipe reduces to
advance the generation time of uneven wear.
Furthermore, the reason why the amplitude of the
main groove is limited to a range of 1~10 mm is due to
the fact that when the amplitude is less than 1 mm, the
rigidity of that portion of the rib which projects
toward the main groove becomes too large, while when it
exceeds 10 mm, the rigidities of rib portions near to
the sipe become ununiform and the generation time of
uneven wear is advanced in both cases.
Moreover, the reason why the ratio (PSips) of
the sipe pitch Ps to the groove pitch PG of the main
groove is limited to a range of 1.5~20 is due to the fact
that when PS/PG is less than 1.5, the rigidity of a side
end portion of the rib near to the sipe becomes
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ununiform to advance the generation time of uneven wear
as shown in Fig. 4, while when it exceeds 20, the
rigidity of the side end portion of the rib too lowers
to advance the generation time of uneven wear as shown
o~ in Fig. 4.
In a preferred embodiment of the invention, the
inclination angle ~ between the cutting direction S of
the sipe and the circumferential direction C of the tire
is preferable to be 55~90. When the inclination angle
10 is less than 55, the rigidity of the side end portion
of the rib near to the sipe becomes ununiform to advance
the generation time of uneven wear.
In another preferred embodiment of the inven-
tion, the depth of the sipe is favorable to correspond
1~ to 50~38% of the depth of the main groove. When the
depth of the sipe is less than 50%, the rigidity of the
rib blocks cut by the sipes are not sufficiently lowered
and the generation time of uneven wear is advanced.
While, when it exceeds 98%, cracks are caused in the
20 groove bottom of the main groove by the sipe.
And also, the sipe is preferable to have a width
of not more than 1 mm. When the width is more than
1 mm, the movement of the rib blocks cut by the sipes
becomes too large to advan¢e the generation time of
2~ uneven wear.
In Fig. 5 is shown a first embodiment of the
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heavy duty pneumatic radial tire according to the
invention, wherein numeral 11 is a heavy duty pneumatic
radial tubeless tire having a tire size oE E13.50/80R16.
The tire 11 comprises a tread 15 divided into five ribs
o5 13 by four main wide grooves 12 each extending zigzag
circumferentially of the tire. The main groove 12 has a
groove width Wl2 of 6.0 mm, a zigzag amplitude V12 in
widthwise direction of tire of 3.0 mm and a repetitive
ziyzag pitch PG in circumferential direction C of
10 9.5 mm. Numeral 16 is an open sipe (merely referred to
as a sipe hereinafter). The sipe 16 crosses the tread
15 and extends between both side ends 15a of the
tread 15. The sipes 16 are arranged so as to have an
inclination angle ~15 between the cutting direction S
15 of the sipe 16 and the circumferential direction C of
the tire of 75 and a sipe pitch Ps in the circumfer-
ential direction C of the tire of 19.5 mm. Moreover,
the ratio PS/PG of the sipe pitch Ps to the groove pitch
P~ of the main groove 12 is 2.05. The sipe 16 opens to
the groove wall face of the main groove 12 at the side
end 13a of the rib 13 and the outside wall face of the
tread 15 at the side end 15a of the tread 15, respec-
tively. The sipe has a width of 0.7 mm and a depth of
8.0 mm corresponding to 82% of the groove depth oE the
25 main groove 12 (g.7 mm).
The construction of the tire 11 other 'chan the
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above is the same as in the ordinary pneumatic radial
tire, and the details thereof are omitted.
The function of the tire 11 will be described in
detail below.
05 In the heavy duty pneumatic radial tire 11
according to the invention, the amplitude V12 and pitch
PG of the main groove 12 in the tread 15 are 3.0 mm and
9.5 mm, respectively, and the pitch Ps of the sipe 16 is
19.5 mm, and the ratio PS/PG of the sipe pitch Ps to the
10 groove pitch PG is 2.05, so that the rigidities of side
end portions 13b of the rib 13 in the vicinity 16a of
the sipe 16 become approximately equal and uniform.
Therefore, even when the tire 11 is run on good road at
a high speed under a heavy loading, the wearing of these
1~ side end portions 13b in the vicinity 16a of the sipe 16
are approximately equal and consequently the occurrence
of uneven wear causing premature wear in only one of the
side end portions 13b near to the sipe 16 is largely
suppressed to largely delay the generation time of
uneven wear, whereby the resistance to uneven wear can
considerably be improved. Furthermore, the sipe 16 has
an inclination angle Hl6 of 75, a width of 0.7 mm and a
depth of 8.0 mm corresponding to 82% of the groove depth
; of the main groove 12 (9.7 mm)~ so that the above effect
2~ o~ suppressing the occurrence of uneven wear is further
increased to largely ~delay the generation time of uneven
wear, whereby the resistance to uneven wear can be more
improved.
The effect of -the invention will be described
with reference to the following test experiment.
05 There were provided six test tires 1 to 6
(corresponding to first to third embodiments and
Comparative Examples 1 to 3) having a dimension of each
part of the tread as shown in the following Table 1.
The test tire 1 was the same as in the first
10 embodiment of Fig. 5. The test tires 2 and 3 were
second and third embodiments as shown by 21 and 31 in
Figs. 6 and 7, whose construction being the same as in
the first embodiment except that the inclination angle
~16 of the sipe 16 was 60 and 90 r respectively.
1~ The test tires 4 to 6 (Comparative Examples 1 to
3) were the conventional tires as shown in Figs. 1 to 3.
In the test tires 4 to 6, the main groove had a width of
7~0 mm, an amplitude of 7.0 mm and a pitch of 28.0 mm
and the inclination angle ~6 of the sipe 6 was 75, 60
and 90, respectively~ as shown in Table 1. The con-
struction of these test tires 4 to 6 other than the
above was the same as in the first embodiment.
Moreover, the test tires 1 to 6 were produced in the
same manner.
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Table 1
~est Test 5'est Test Test Test
tire 1 tire 2 tire 3 tire 4 tire 5 tire 6
First Second Third Compar- Compar- Compar-
embodi- embodi- ~mbodi- atlve 2xample ative
ment ment ment 1 2 3
Corresponding
figure Fig.5 Fig.6 Fig.7 Fig.l Fig.2 Fig.3
Width of main 6.0 6 0 6.0 7.0 7.0 7.0
groove (mm)
Amplitude of
main groove (mm) 3.0 3.0 3.0 7.0 7.0 7.0
_
Pitch of 9.5 9 5 9.5 28.028.0 28.0
main groove (mm)
..._
Pitch of sipe (mm)19.5 19.5 19.528.0 28.0 28.0
_ _
Inclinatlon angle 75 60 90 ... _ _ 60 90
PS/PG 2.052.05 2.05 1.0 1.0 1.0
_ _
Running distance
t'll the occur- 100 100 100 80 80 80
wear (index)
. . .
The test was carried out as follows. That is,
each of the above test tires subjected to an internal
pressure of 9.0 kg/cm2 was mounted onto a rim of
9.5 V x 16 T/L in a rear wheel of a test truck.
The test tire was run on a test course at a running
speed of 80 km/hr under a loading of 4,300 kg to measure
a running distance till the occurrence of uneven wear.
The test result was represented by an index on
the basis that the first embodiment was 100 in Table lo
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The larger numerical value of the index, the better the
resistance to uneven wear.
As seen from the results of Table l, the
generation time of uneven wear in the first to third
05 embodiments is considerably slower than that of
Comparative Examples l to 3, from which it is apparent
that the effect of suppressing the occurrence of uneven
wear in the tread of the heavy duty pneumatic radial
tire according to the invention is large. That is,
10 according to the invention, the resistance to uneven
wear is largely improved to considerably prolong the
wear life of the tire.
As mentioned above, according to the invention,
the rigidities of side end portions of the rib ln the
1~ vicinity of the sipe are made uniform by regulating the
pitch of the open sipe arranged in the tread as well as
the amplitude and pitch of the main groove to this sipe
pitch, whereby the generation time of uneven wear at the
side end portion of the rib can be largely suppressed to
2~ considerably improve the resistance to uneven wear and
the wear life of the tire.
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