Note: Descriptions are shown in the official language in which they were submitted.
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A COMBINATION OF HEAVY DUTY PNEUMATIC
RADIAL TIRES FOR US13 IN WINTER SEASON
This invention relates to a combination of heavy
duty pneumatic radial tires for use in winter season,
and more particularly to a radial tire combination
ef~ectively improving resistance to uneven wear while
05 highly maintaining traction performance on snow road.
For example, when a vehicle under a heavy duty
is provided with a non-driven steering shaft and one or
two driving shafts and two tires are mounted on the non-
driven steerlng shaft and four tires are mounted on each
of the driving shafts, it has been attempted to improve
running performances on snow and ice road surfaces in
winter season by rendering all tires into studless tires
having a wider ground contacting width as far as
possible. In this casel the groove depth of each of the
circumferential groove and the lateral groove in the
tires is generally the same irrespectively of the shaft
mounting the tire.
~ ccording to such a conventional technique,
however, the groove depth of the lateral groove is
particularly set to a deeper depth for enhancing the
traction performance of the tire on snow road, whereby
the bending deformation of the block by the friction
force acting on the block surface in the tire during the
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running is facilitated to en~ure the sufficient biting
of the block edge into snow.
As a result, the conventional technique has a
serious problem in the quality that the uneven wear is
0~ apt to be caused and particularly the violent heel and
toe wear occurs in the tire mounted on the non-driven
steering shaft.
It i~, therefore, an object of the invention to
advantageously solve the above problems of the
conventional technique and to provide a combination of
heavy duty pneumatic radial tires for use in winter
season capable o~ effectively improving the resistance
to uneven wear while sufficiently maintaining high
traction performance on snow as a whole of the vehicle.
1~ According to the invention, there is the
provision of a combination of heavy duty pneumatic
radial tires for use in winter season to be mounted on a
: non-driven steering shaft and a driving shaft of a
vehicle~ each tire comprising plural block rows located
: 20 in a surface of a tread portion and separated from each
othex in a widthwise direction of the tread, each of
which block row being defined by plural circumferential
grooves extending circumferentially of the tire and
plural lateral grooves extending in a direction crossing
~with the circumferential groove, in which each block
constituting each of the block rows is provided with at
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least one sipe, characterized in that a projection
length L~ of block edge in each block in the widthwise
direction of the tread portion per unit length in the
circumferential direction of the tire and a similar
o~ projection length Ls of ~he sipe satisfy the following
relation:
LS/LB '- 0.8
and a groove depth DF of the lateral groove in the tire
mounted on the non-driven steering shaft is shallower
1~ than a groove depth DD of the lateral groove in the tire
mounted on the driving shaft.
In a preferred embodiment of the invention, the
groove depths DF and DD satisfy the following relations
to a groove depth HF Of the circumferential groove in
1~ the tire mounted on the non driven steering shaft and a
groove depth HD of the circumferential groove in the
tire mounted on the driving shaft:
10/20 ~ DF/HF ~ 15/20
15/20 ~ DD/HD ~; 1-
In such a combination of the invention, thetires to be mounted on a vehicle are classified into a
tire for the non-driven stsering shaft and a tire for
the driving shaft. In the tire mounted on the non-
driven steerin~ shaft, the groove depth of the lateral
groove is made shallower to restrain the deformation of
blocks during the running of the tire, whereby the
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occurrence of heel and toe wear in the tire is
effectively prevented. On the other hand, the grQOVs
depth of the lateral groove in the tire mounted on the
driving shaft is made deeper for preventing the lowering
o~ of traction performance on snow as a while of the
vehicle, whereby the bending deformation of the block is
facilitated through shearing force of tire treading
surface from road surface to ensure sufficient biting of
block edge into snow.
Therefore, in the tire combination according to
the invention, the uneven wear of the tire mounted on
the non-driven steering shaft can effectively be
prevented, and also the lowering of the traction
performance on snow in this tire can be compensated by
1~ enhanciny the traction performance on snow in the tire
mounted on the driving shaft, whereby the traction
performance on snow as a whole of the vehicle can be
maintained at a sufficiently high level.
In the invention, the projection length LB of
block edge in each block in the widthwise direction of
the tread portion per unit length in the circumferential
direction of the tire and the similar projection length
s Of the sipe satisfy the relation of LSiLB 2 0.8, so
that the high traction performance of the tire mounted
8~ on the driving shaft is ensured while maintaining the
high braking performancs on snow in all tires.
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When the above ratio is less than 0.8, the above
performances can not sufficiently be enhanced.
In the preferable embodiment of the invention,
the groove depths DF and DD of the lateral grooves are
o~ restricted to satisfy the following relations to the
groove depths HF and HD of the circumferential grooves
in the tires to be mounted on the non-driven steering
shaft and the driving shaft:
10/20 ~ DF/HF < 15/20
15/20 ~ DD/HD ~ 1
, whereby the block edges are sufficiently bitten into
snow to bring about the high traction performance on
snow.
When DF/HF is le~s than 10/20, the lateral
grooves of the tire mounted on the non-driven steering
shaft are lost before the wear.ing degree of this tire
reaches S0~, whereby the running performances on snow
are largely deteriorated ana as a result an official
authorization as a snow tire can not be obtained.
While, when it is not less than 15/20, the rigidity of
the block in the circumferential direction i~ too small
and the saw-teethed uneven wear in the circumferential
direction or so-called heel and toe wear becomes
conspicuou~ in the tire mounted on the non-driven
steering shaft.
When DD/HD is less than 15/20, the rigidity of
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the block in the circumferential direction is too large
and the biting of the block edge into snow becomes
insufficient and as a result a large traction
performance on snow is not obtained. Whlle, when it
exceeds 1, the rubber gauge between outermost belt layer
and groove bottom is too small and the appearance at
last worn stage is poor and the more improvement of
performances on snow can not be expected.
The invention will be described with reference
to the accompanying drawing, wherein:
Fig. 1 is a diagrammatically plan view of a
tread pattern used in the tire according to the
invention.
In Fig. 1 is shown a plan view of the tread
1~ pattern used in the practice of the invention. This
tread pattern is common in the tire mounted on the non-
driven steering shaft and the tire mounted on the
driving shaft.
Moreover, the internal reinforcing structure of
the tire is the same as in the usual radial tire, so
that it is omitted in the drawing.
The tire having a ground contacting width TW
comprises a center block row 1, a pair of shoulder block
rows 2 and two pairs of block rows 3, 4 located between
the center block row and the shoulder block row at its
tread portion. Each of blocks la, 3al 4a in the
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respective block rows 1, 3, 4 other than the shoulder
block row 2 is provided with a sipe 5, 6, 7 substan-
tially extending in the widthwise direction of the tread
portion, while each of the blocks 2a ln the shoulder
o~ block row 2 is provided with two sipes 8 substantially
extending in the widthwise direction of t:he tread
portion.
These block rows 1-4 are separated in the
widthwise direction of the tread by a pair of circumfer-
ential middle grooves 9 located at a central region ofthe tread and extending zigzag in the circumferential
direction of the tire, a pair of circumferential large
grooves 10 located from the middle grooves 9 toward the
tread edge and extending zigzag in the circumferential
1~ direction of the tire, and a pair of circumferential
fine grooves 11 located at the tread shoulder regions
and extending zigzag in the circumferential direction of
the tire. The blocks la-4a of the block rows 1-4 are
separated in the circumferential direction of the tire
by two kinds of lateral grooves 12l 13 intersecting with
the circumferential grooves 9-11 and extending in the
widthwise direction of the tread.
In the illustrated tire having such a tread
pattern, the ground contacting width T~ i9 224 mm, the
2~ tire maximum width SW is 271 mm and the negative ratio
is 33~ irrespectively of the non-driven steering shaft
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and the driving shaft.
Moreover, the ratio (LS/LB) of projection length
Ls Of sipe to projection length LB of block edge in each
block in the widthwise direction of the tread portion
o~ per unit length in the circumferential direction of the
tire is 1.0 in each of the blocks la, 2a, 3a and 0.97 in
the block 4a.
In these tires, according to the invention, the
groove depths DF of the lateral grooves 12, 13 in the
tire mounted on the non-driven steering shaft are
shallower than the groove depths DD of the lateral
grooves 12, 13 in the tire mounted on the driving shaft.
More preferably, the groove depths DF~ DD have the
following relations to the groove depths HF, HD of the
1~ circumferential grooves 9-11 in the tires mounted on the
non-driven steering shaft and the driving shaft:
10/20 ~ DF/HF < 15/20
15/20 -~ DD/HD 5 1-
Thus, in the tire combination accordins to the
inventionl the traction performance on snow as a whole
of the vehicle i9 maintained at a sufficiently high
level and particularly the uneven wear of the tire
mounted on the non-driven steering shaft is effectively
prevented as previously mentioned.
The following examples are given in the
illustration of the invention and are not intended as
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limitations thereof. 2 0 ~ 4 9 ~ 2
A comparative test for resistance to uneven wear
and txaction performance on snow road will be described
with respect to the tire combination according to the
o~ invention, conventional tire combination and comparative
tire combination as mentioned below.
In all tire combinations, the test tire had a
tire size of 10.00R20, a tread pattern shown in Fig. 1
and a groove depth of each circumferential groove of
20 mm.
After two tires were mounted on a non-driven
steering shaft of a vehicle and four tires were mounted
on a driving shaft of the vehicle, they were actually
run under a 100% load. After the running over a
16 distance of 20000 km, the resistance to uneven wear was
evaluated by measuring a stepwise worn amount of heel
and toe wear and indicating the measured amount as an
index on the basis that ~he amount of 2.0 mm was 100.
On the other hand, the vehicle was run on a regulated
snow road at an empty state and then a traction force
thereof was measured. The traction performance was
evaluated by an index on the basis that the traction
force of the conventional tire combination I was 100.
The test results are shown in Table 1.
In Table 1, the larger the index value, the better the
result.
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able 1
Conven~ Conven- InYention Invention ~om~ar-
tional tional tire tire a lV~
tire combina~ tlon I combi- co bi~a-
tire mounted
Groove on non-driven 14 16 13 11 11
depth steering
of shaft
lateral _
groove tire moun~ed 1416 16 16 11
_ __ __
Resistance to 100 80 110 125 125
uneven wear _
Traction pPrformance 100 120 120 120 75
on snow _
As seen from Table 1, the traction performance
on snow as a whole of the vehicle and the resistance to
uneven wear can simultaneously be established at a high
level in the tire combination according to the
invention.
As mentioned above, according to the invention,
the groove depth of the lateral groove is properly
selected between the tire to be mounted on the non-
driven steering shaft and the tire to be mounted on the
driving shaft, whereby the traction performance on snow
as a whole of the vehicle is sufficiently maintained at
a higher level and also the resistance to uneven wear,
particularly heel and toe wear can effectively be
improved.
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