Note: Descriptions are shown in the official language in which they were submitted.
`` 2018~6~
1-145268
HEAVY DUTY P~EUUATIC TIRE
This invention relates to a heavy duty pneumatic
tire applicable to trucks, buses and the like, and more
particularly to a pneumatic tire whose wear-resistance
is improved without detrimentally affecting wet
05 performance, or performance on wet roads.
With heavy duty pneumatic tires for use in heavy
vehicles such as trucks, buses and the like, there has
developed recently great requirement for wear-
resistan~e, particularly irregular wear-resistance which
is a performance for wear called as railway wear or
river wear. A tire having a tread pattern shown in
Fig. 1 is one of proposals to fulfill such a
requirement.
In the tire 10 shown in Fig. 1, a tread 12 is
formed with a plurality of circumferential main grooves
14 spaced apart from each other and extending in a
circumferential direction of the tire, pairs of narrow
grooves 16 formed in ends of the tread 12, respectively,
and extending in the circumferential direction, and
sipes 18 formed in shoulders and extending in a radial
direction of the tire. A radial length of rib 20
defined by each pair of narrow grooves 16 is made
shorter than a radial length of ribs 22 and 24 adjacent
`` 201856~
the rib 20 to cause forces in braking directions of the
tire or negative shearing forces in the ribs 20, thereby
effectively preventing irregular wear from occurring in
the ribs 22 and 24.
With such a tire 10, however, although the
irregular wear is effectively prevented by forming the
narrow grooves 16 in the tread 12 of the tire 10,
sufficient drainage could not be ensured because of the
narrow width of the narrow grooves 16. Therefore, this
tire 10 is inferior in steering stability on wet roads
to a tire 10' having circumferential main grooves 14 as
shown in Fig. 2. Such a problem of the tire 10 has not
yet been solved sufficiently irrespective of various
efforts.
1~ On the other hand, although the tire 10' shown
in Fig. 2 is superior in drainage, the tire 10' is
likely to suffer irregular wear.
It is an object of the invention to provide a
heavy duty pneumatic tire improved in wear-resistance
without detrimentally affecting steering stability on
wet roads.
In order to accomplish this object, a heavy duty
pneumatic tire for a vehicle such as a truck, bus and
the like according to the invention comprises two pairs
of narrow grooves spaced in a width direction and
extending in a circumferential direction and a plurality
201856~
of sipes formed between two narrow grooves positioned on
an inner side of the width direction with a constant
interval in the circumferential direction, and
dimensions of the narrow grooves and the sipes
fulfilling the following relations,
C = (0.10-0.30) x T
W = (0.03-0.14) x T
K = (0.05-0.50) x A,
where T is a width of a tread of the tire, C is a
distance from a tread end to the narrow groove
positioned on an outer side, W is a distance between
each pair of the narrow grooves, A is a distance between
the narrow grooves positioned on the inner side, and K
is a distance between the sipes in the circumferential
1~ direction.
The tire according to the invention can
effectively prevent irregular wear on ribs except narrow
ribs defined by the two pairs of the narrow grooves and
effect drainage along the sipes formed in zones defined
by the two pairs of the narrow grooves, while
maintaining the draining performance along
circumferential directions of the tire.
According to the invention, the narrow grooves
positioned on the outer side of the width direction are
located at the distance C = (0.10-0.30) x T from the
tread ends, where T is the tread width. If the C is
``` 201856~
less than 0.10 x T, the rigidity of ribs from the tread
ends is too low so that negative shearing forces are
ineffective. On the other hand, if the C is more than
0.30 x T, the narrow grooves are positioned too near the
center of the tire so that the effect of preventing
irregular wear at shoulders will decrease.
The reason why the narrow grooves are formed in
pairs is as follows. Relatively large negative shearing
force components are caused in the ribs formed between
the narrow grooves, while shearing forces occurring in
the other ribs except the ribs defined by the pairs of
the narrow grooves are effectively shifted into positive
directions, thereby preventing occurrence and
development of cores causing irregular wear occurring
1~ along edges of the other ribs resulting f rom drag of
tread rubber forming the ribs.
The reason why the distance W between the narrow
grooves is (0.03-0.14) x T is that if the W is less than
0.03 x T, the negative shearing forces caused in the
ribs defined between the pairs of the narrow grooves are
insufficient so that negative shearing forces are also
caused in the other ribs, with the result that the other
ribs are also dragged and hence occurrence and
development of cores of irregular wear in the other ribs
cannot be effectively prevented.
On the other hand, if the W is more than
`` 20~ 8~
0.14 x T, the negative shearing forces caused in the
ribs defined by the pairs of the narrow grooves become
too large so that the other ribs are affected by the
large shearing forces to promote occurrence and
0~ development of cores of irregular wear.
In the zone between the narrow grooves
positioned on the inner side of the width direction,
sipes are formed spaced apart in the circumferential
direction and the distance K between the adjacent sipes
in the circumferential direction is (0.05-0.50) x A,
where A is the distance between the narrow grooves
positioned on the inner side.
With the distance X thus determined, the
drainage through the sipes is ensured and so-called edge
16 effect and increase of contacting area with a road are
accomplished. The edge effect means to cut water films
formed on a road by edges of plural rubber blocks
defined by the sipes. If the K is less than 0.05 x A,
the requisite draining performance is maintained, but
the rigidity of rubber blocks defined by the adjacent
sipes becomes too low, with the result that the steering
stability on a dried road is lowered and so-called
polygonal wear is likely to occur in cornering. On the
other hand, if the K is more than 0.5 x A, the rigidity
of the rubber blocks defined by the ad~acent sipes
becomes too high, with the result that contacting area
20~8~6~
with a road decreases and the steering stability on a
wet road lowers.
The zone between the narrow grooves positioned
on the inner sides of the width direction may of course
0~ be formed with one or more circumferential main grooves
extending in the circumferential direction, if required,
The drainage is more improved with this arrangement.
In order that the invention may be more clearly
understood, preferred embodiments will be described, by
way of example, with reference to the accompanying
drawings.
Figs. la and lb and 2 illustrate tread patterns
of the prior art;
Figs. 3a and 3b illustrate a preferred
1~ embodiment of the tire according to the invention;
Figs. 4a and 4b illustrate another preferred
embodiment of the tire according to the invention;
Figs. 5a and 5b illustrate a further preferred
embodiment of the tire according to the invention; and
Fig. 6 is a view illustrating relations between
running distances and widths of irregular wear with
tires according to the invention shown in Figs. 3a, 4a
and 5b and tires of the prior art.
Fig. 3a illustrates part of a tread pattern of a
pneumatic tire according to the invention. As the inner
construction of the tire is a general radial
20:l856~
construction, it will not be described in further
detail.
The tread 12 is formed with two circumferential
grooves 14 spaced apart from each other and extending in
a circumferential direction in a center portionl and two
pairs of narrow grooves 16a and 16b formed in ribs
defined by the circumferential grooves 14 and tread
edges, respectively. As a result of these grooves,
there are formed ribs 32 between the circumferential
grooves 14, and ribs 34 between the circumferential
grooves 14 and the narrow grooves 16a. Moreover, sipes
36 are formed in the ribs 32 and the ribs 34, which are
spaced in circumferential directions with a constant
interval K.
1~ Each of the narrow grooves 16b positioned on an
outer side of a width direction and extending in the
circumferential direction is so formed that a distance C
from the tread end to an inner wall of the narrow groove
16b on an outer side of the width direction is within a
range fulfilling a relation (0.10-0.30) x T. The T is
a width of the tire tread 12.
Moreover, a distance W between each pair of the
narrow grooves 16a and 16b or a distance between
adjacent inner walls of each pair of the narrow grooves
16a and 16b is within a range fulfilling a relation
(0.03-0.14) x T.
2~18~6~
It should be noticed in this case that a width
of the narrow grooves 16a and 16b depends upon a depth h
of the narrow grooves, but should fulfill a relation
d = (0.05-0.3) x h, preferably d = (0.1-0.2) x h, when
o~ h = 0.072 x T.
The reason why the narrow grooves are formed to
fulfill the above relations is that when the tire
contacts a ground, the opposed inner walls of each of
the narrow grooves are brought into contact with each
other so that movements of the tread rubbers at edges of
the ribs defined by these narrow grooves are restrained,
thereby effectively preventing occurrence and
development of cores of irregular wear at the edges of
the ribs.
1~ Moreover, as can be seen from Fig. 3b
illustrating a section of the tread taken along the line
~b-~b in Fig. 3a, outer surfaces of the ribs 20 formed
between the narrow grooves 16a and 16b are radially
inward of surfaces of the ribs 32 and 34 and the ribs 35
defined by the narrow grooves 16b and the tread edges.
As a result, although the ribs 20 defined between the
narrow grooves abut against a road surface similarly to
the other ribs when the tread contacts the road surface,
the ribs 20 on a side leaving the road surface are
subjected to a large negative shearing forces so that
drag at edges of the other ribs is prevented to
201856~
effectively prevent irregular wear of the tire.
As above described, ribs 32 bet~een the two
circumferential main grooves 14 and ribs 34 between the
main grooves 14 and the narrow grooves 16a are formed
with sipes 36 oblique to an equatorial plane of the
tire. Such sipes 36 are so formed to fulfill a relation
K = (0.05-0.50) x A, where A is a distance between the
narrow grooves 16a on the inner side of the width
direction, and K is a distance between the sipes 36 in
the circumferential direction. By forming the sipes 36
in the ribs 32 and 34, rigidities of tread rubbers in
the respective ribs become proper values.
A depth t of the sipes 36 should be determined
to fulfill a relation t = (0.6-1.0) x h and equal to or
1~ shallower than the depth of the circumferential main
grooves 14, where h is the depth of the narrow grooves.
Moreover, an angle 0 of the sipes 36 made with
the equatorial plane of the tire is freely selected
within 0=0-90. In other words, the sipes 36 may
extend in directions between in parallel with the
equatorial plane and substantially at right angles to
the equatorial plane.
Although the circumferential main grooves 14 are
two in this embodiment, the number of the grooves is not
limited to two. ~hey may be one or more than three in
consideration of drainage performance of the tire.
- 10 -
2018565
Figs. 4a and 4b illustrate another embodiment of
the tire according to the invention. In this
embodiment, a rib 32 defined by narrow grooves 16a on an
inner side of a width direction i5 not formed with
o~ circumferential main grooves, but is formed with sipes
36 oblique relative to an equatorial plane of the tire
and spaced with a constant interval in a circumferential
direction of the tire. As can be seen from Fig. 4b
illustrating a section of the tire along one sipe, the
tire is substantially similar to the tire shown in
Figs. 3a and 3b in the distance C between the tread end
and the narrow groove 16b positioned on the outer side
of the width direction, the distance W between the pair
of narrow grooves 16a and 16b, and the intervals K in
1~ circumferential directions between the adjacent sipes,
with exception of protrusions 38 spaced from each other
in the extending directions of the sipes. Therefore,
these similar features will not be explained for the
sake of simplicity.
In this embodiment, the two protrusions 38 are
provided spaced in the extending direction of the sipes
36. One or more than three protrusions may be formed
dependently upon lengths of the sipes or angles ~ of the
sipes made with the equatorial plane of the tire.
By changing the number of the protrusions 38, the
rigidity of blocks defined by the adjacent sipes 36 and
201856~
the narrow grooves 16a can be freely changed.
The tire of this embodiment is somewhat inferior
in wet performance to the tire shown in Figs. 3a and 3b
in as much as the tire of this embodiment does not have
the circumferential main grooves. ~owever, it is
possible to mitigate occurrence of cores of wear at
edges of the rubber blocks along the circumferential
main grooves to improve the wear-resistance of the tire.
Figs. 5a and 5b illustrate a further embodiment
of the tire according to the invention. Although it has
circumferential main grooves 14 similar to those of the
tire shown in Figs. 3a and 3b, it has particular sipes
36 which are formed in ribs 32 and 34 defined by
circumferential main grooves 14 and narrow grooves 16a
1~ positioned on an inner side of a width direction.
The extending directions of the sipes 36 are changed
with the respective ribs so as to be substantially in
symmetry with respect to the circumferential main
grooves 14 associated therewith. In order to improve
the drainage of the tire by the sipes, widths of the
sipes formed in the ribs 34 are uniformly widened from
intermediate portions of the sipes to outer ends opening
in the narrow grooves 16a, and depths of the widened
portions of the sipes are narrower than those of the
sipes according to this embodiment.
In this embodiment, the sipes 36 formed in the
2018~6~
ribs is formed with protrusions 38 spaced in extending
directions of the sipes 36 to improve the rigidity of
the rubber blocks defined by the sipes 36, the
circumferential main grooves 14 and the narrow grooves
16a on the inner side of the width direction in the same
manner as the embodiment shown in Figs. 4a and ~b.
The tire of this embodiment exhibits the good
drainage performance and sufficient wear-resistance as
in the embodiment shown in Figs. 3a and 3b. Moreover,
abutment of the surface of the tire against a road
surface is insured with the aid of the edge effect of
the edges of the rubber blocks so that the wet
performance and steering stability of the tire are
improved.
1~ Although the sipes 36 formed in the rib 32
defined by the two circumferential main grooves 14 have
uniform widths along the extending directions of the
sipes 32, the widths of the sipes may be modified in
following manner. For example, widths of the sipes are
widened from intermediate portions of the sipes to ends
opening in the circumferential main grooves, or widths
of the sipes formed in the ribs 32 and 34 are
substantially e~ual. Moreover, the ribs 32 and 34
defined by the circumferential main grooves 14 and the
narrow grooves 16a positioned on the inner side of the
width direction are formed in edges with further sipes
201~6~
extending in the width direction and spaced in the
circumferential direction with a constant interval.
Test on the wet performance and wear-resistance
was carried out with the tires according to the
invention and tires of the prior art, which will be
explained hereinafter.
Tires for the test
Tires were used which had the general radial
construction and whose sizes were lOOOR/20.
1~ Tire 1 according to the invention (Invention tire 1)
The tires 1 used for the test had the pattern
shown in Fig. 3 and had dimensions, the tread width T of
210 mm, distance C of 25 mm from the tread end to the
narrow grooves positioned on the outer side of the width
1~ direction, distance W of 15 mm between each pair of
narrow grooves, depth h of 15 mm of the narrow grooves,
distance A of 120 mm between the narrow grooves
positioned on the inner side of the width direction, and
hence width d of 2.5 mm of the narrow grooves, distance
K of 10 mm between the adjacent sipes in the
circumferential direction, depth t of 13.5 mm of the
sipes, width of 14 mm and depth of 15 mm of the
circumferential main grooves.
Tires 2 according to the invention (Invention tire 2)
The tires 2 had the tread pattern shown in
Fig. 4a. The tires 2 had dimensions, the width T of
-14-
2 ~ 6 ~
210 mm of the tread, distance C of 24 mm between the end
of the tread and the narrow groove positioned on the
outer side of the width direction, distance W of 25 mm
between the each pair of narrow grooves, depth h of
14 mm of the narrow grooves, distance A of 100 mm
between the narrow grooves positioned on the inner side
of the width direction or width d of 3 mm of the narrow
grooves, distance K of 30 mm between the adjacent sipes,
and depth t of 12 mm of the sipes.
Tires 3 according to the invention (Invention tire 3)
The tires 3 had the tread pattern shown in
Fig. 5a. The tire 3 had dimensions, the tread width T
of 215 mm, distance C of 34 mm between tread end and
narrow grooves positioned on the outer side of the width
1~ direction, distance W of 12 mm between each pair of
narrow grooves, depth h of 14 mm of the narrow grooves,
distance A of 110 mm between the narrow grooves
positioned on the inner side of the width direction or
width d of 32.5 mm of the narrow grooves, distance K of
ao 25 mm between the adjacent sipes in the circumferential
direction, depth t of 14 mm of the sipes, width of 12 mm
of circumferential main grooves, and depth of 14.5 mm of
the circumferential main grooves.
Comparative example tire 1
The comparative example tire 1 had the tread
pattern shown in Fig. la and had dimensions, the tread
2018~6~
width T of 215 mm, distance of 42 mm from the tread ends
to centers of zigzags of narrow grooves positioned on
the outer side of the width direction, distance of 9 mm
between each pair of narrow groovesr depth of 15.2 mm of
0~ the narrow grooves, distance of 16.5 mm between
circumferential main grooves, depth of 15.2 mm of the
main grooves, and distance of 50 mm between centers of
zigzags of the circumferential main grooves.
Comparative example tire 2
The comparative example tire 2 had the tread
pattern shown in Fig. 2 and had dimensions, the tread
width T of 205 mm, distance of 13.5 mm between the
circumferential main grooves, depth of 15.2 mm of the
main grooves, and distance of 40.5 mm between centers of
1~ zigzags of the circumferential main grooves.
Method of testing
The tires above described were filled with
normal pressure and alternately eguipped on a vehicle.
The vehicle equipped with the tires was driven under
110% normal load on a road with water films of 1.2 mm at
40 km/h, 60 km/h and 80 km/h, respectively. Wet limit
performance was measured by feeling and estimated by
indexes. In this case, the higher the index, the
performance is higher.
Wear resistance
The tires filled with the normal inner pressure
- 16-
201~6~
were equipped on the vehicle. The vehicle equipped with
the tires was driven under the normal load. After
running 60,000 km, widths of irregular wears occurred
were measured.
Result of the test
Result of wet performance test is shown in the
following table and result of the irregular wear test is
shown in Fig. 6.
Table
Wet limit performance
Invention tire 1 115
Invention tire 2 95
Invention tire 3 ~ 110
Comparative example tire 1 80
Comparative example tire 2 100
As can be seen from the Table and Fig. 6, all
the tires according to the invention have the improved
wet performance or the improved irregular wear-
resistance without substantial lowering of the wet
performance in comparison with the tire having tread
patterns of the prior art.
Therefore, the invention can provide an improved
heavy duty pneumatic tire having balanced wet
performance and wear-resistance as shown in the Table
-` 201856~
and Fig. 6.
It is further understood by those skilled in the
art that the foregoing description is that of preferred
embodiments of the disclosed tires and that various
changes and modifications may be made in the invention
without departing from the spirit and scope thereof.
2~
- 18-
