Note: Descriptions are shown in the official language in which they were submitted.
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3-84, 569
A COMBINATION OF E~EAVY DUTY PNEUMATIC
RA~IAL TIRES FOR USl~ 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
effectively improving resistance to wondering while
05 sufficiently maintaining high running performances on
snow and ice road surfaces.
For exampIe, 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-
lO driven steering shaft and four tires are mounted on eachof 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
15 possible. In this case, the ratio of ground contacting
width to maximum tire width in the tire, for example, a
studless tire having a tire size of 10.00 R20 is usually
about 0.82.
According to such a conventional technique~
however, the braking performance on snow and ice~road
surfaces, traction performance and the like can
effectively be improved because the tread width of the
tire is wide, but there is caused a problem as to the
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resistance to wondering during the running on snow road
and tracked road. That is, since the tread width of the
tire mounted on the steering shaft largely exerting on
the wondering is also wide likewise the tire mounted on
o~ the driving shaft, it is obliged to degrade the
resistance to wonderin~.
It is, therefore, an object of the invention to
advantageously solve the above problems of the
conventional technigue and to provide a combination of
~0 heavy duty pneumatic radiaI tires for use in winter
season capable of ensuring excellent running
performances on snow and ice road surfaces while
improving the resistance to wondering.
The invention is based on a discovery that the
1~ resistance to wondering is improved by making the ground
contacting width of the tire mounted on the steering
: shaft narrower than that of the conventional tire, while
the reduced amount of the ground contacting width in the
tire mounted on the steering shaft is compensated by
increasing the ground contacting width of the tire
mounted on the driving shaft totally considering the
tires mounted on the steering shaft and the driving
shaft, whereby excellent running performances on snow
and ice road surfaces as a whole of the vehicle can
sufficiently be maintained.
According to the invention, there is the
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According to the invention, at least one sipe is
formed in each block constituting each block row
whereby excellent performances on ice based on the
biting of the sipe edge into ice can be developed.
Ob On the other hand, considering only the
performances on ice, it is effective to reduce the
negative ratio to increase actual ground contacting
area, but if the negative ratio is too small, the block
edge component becomes less and the amount of the block
bitten into snow during the running on snow road is
lacking to lower the running performances on snow road.
According to the invention, therefore, the development
of high performances on snow road can be ensured by
rendering the negative ratio into not less than 30%.
lb In the invention, the ratio of ground contacting
width to maximum tire width (TW/SW)F in the tire to be
mounted on the non-driven steering shaft of the vehicle
is within a range of 0.66-0.8, which is sufficiently
smaller than that of the conventional tire, whereby the
excellent resistance to wondering is obtained while
ensuring the performances on snow road required on the
tire.
: When the ratio (TW/SW)F exceeds 0.8, the
resistance to wondering is close to that of the
: a6 conventional tire and can not be improved up to an
expected extent, while when it is less than 0.66, the
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According to the invention, at least one sipe is
formed in each block constituting each block row:
whereby excellent performances on ice based on the
biting of the sipe edge into ice can be developed.
On the other hand, considering only the
performances on ice, it is effective to reduce the
negative ratio to increase actual ground contacting
area~ but if the negative ratio is too small, the block
edge component becomes less and the amount of the block
1~ bittPn into snow during the running on snow road is
lacking to lower the running performances on snow road.
According to the invention, therefore, the development
of high performances on ~now road can be ensured by
rendering the negative ratio into not less than 30%.
lb In the invention/ the ratio of ground contacting
width to maximum tire width (TW~SW)F in the tire to be
:
~; mounted on the non-driven steerlng shaft of the vehicle
is within a range of 0.66-0.8, which is sufficiently
smaller than that of the conventional tire, whereby the
excellent resistance to wondering is obtained while
ensuring the performances on snow road required on the
tire.
When~the ratio (~W/SW)F exceeds 0.8, the
resistance to wondering is close to that of the
2~ conventional tire and can not be~improved up to an
expected extent, while when it~is less than 0.66, the
:
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friction force of the tire on snow and ice roads is too
low and hence the turning performance and other
performances are degraded.
In the tire to be mounted on the driving shaft
0~ of the vehicle, in order to make the ground contacting
area of the tire as a whole of the vehicle larger than
total ground contacting area of the conventional tires
to ensure the high performances on snow and ice roads,
the ratio of ground contacting width to maximum tire
width (TW/SW)D of the tire is not less than
1.21-1/2(TW/SW)F but not more than 1 for preventing the
heat generation of the belt portion to enhance the tire
durability.
That is, the ground contacting width of the tire
1~ mounted on the non-driven steering shaft is made
narrower than that of the conventional tire within a
particular range, whereby the resistance to wondering
: can largely be improved while ensuring necessary
performances on snow and ice roads. On the other hand,
the ground contacting width of the tire mounted on the
driving shaft is made wider than that of the conven-
tional tire within a particular range to compensate the
reduced amount of the ground contacting width in the
tire mounted on the non-driven steering shaft, whereby
: ~ the performances on snow and ice roads as a whole of the
vehicle can sufficiently be maintained at a high level.
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2~3~49
The invention will be described with reference
to the accompanying drawings r wherein:
Fig. 1 is a diagrammatically plan view of a
tread pattern used in the tire according to the
o~ invention;
Fig. 2 is a graph showing a relation between
ground contacting width ratio and resist.ance to
wondering; and
Fig. 3 is a graph showing a relation between
ground contacting width ratio and braking performance on
ice road.
In Fig. 1 is shown a plan view of the tread
pattern used ln the practice of the invention. This
tread pattern is common in the tire mounted on the non-
1~ driven steering shaft and the tire mounted on thedriving shaft~
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 lal 3a, 4a in the respec-
tive block rows 1, 3, 4 other than the shoulder block row
2 lS provided with a sipe 5, 6, 7 substantially extend-
.ing in the widthwise direction of the tread portion,
while each of the blocks 2a in the shoulder block row 2
is pr~vided with two sipes 8 substantially extendlng in
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the widthwise direction of the tread portion. 2063 9~ 9
In the illustrated tire having such a tread
pattern, the negative ratio is 33% and the tire maximum
width SW is 271 mm irrespectively of the non-driven
o0 steering shaft and the driving shaft.
Furthermore, the ground contacting width TW of
the tire to be mounted on the non-driven steering shaft
is 200 mm, and the ground contacting width TW of the tire
to be mounted on the driving shaft is 234 mm. ~hat is,
the ratio of ground contacting width to maximum tire
width (TW/SW)F of the tire mounted on the non-driven
steering shaft in the above embodiment is about 0.74 and
the ratio of ground contacting width to maximum tire
width of the tire mounted on the driving shaft is about
1~ U.86.
In Fig. 2 are shown test results on the
resistance to wondering when the tire of the above
structure having a tire size of lO.00 R20 and a maximum
tire width of 271 mm is mounted on a non-driven steering
shaft of a vehicle and run on wondering road by changing
the ground contacting width of the tread within a range
of 180 mm - 240 mm.
In this test~ the ground contacting width of the
tire mounted on the non-driven steerlng shaft is
changed, but the ground contacting width of each of four
tires mounted on the driving shaft is constant (224 mm).
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The vehicle is straightly run on wondering road over a
distance of 5 km, during which the number of handle
corrected is measured. In Fig. 2, the measured result
is represented by an index value.
0~ As the index value, a case that the straight
running is possible with necessitating slight handle
correction is 100. The larger the index value, the
better the result.
According to the graph shown in ~ig. 2, it is
apparent that when the ground contacting width of the
tread exceeds 220 mm or the ratio of ground contacting
width to maximum tire width (~W/SW)F exceeds 0.81, the
improvement of the resistance to wondering can not be
expected.
lS On the other hand, when the ratio (TW/SW)F is
less than 0.66, or the ground contacting width of the
tread is less than 180 mm, it is confirmed from
experiments that the friction force of the tire on snow
and ice roads is too small as previously mentioned and
hence the turning performance and other running
performances largely lower.
In the invention, therefore, the ratio (TW/SW)F
in the tire mounted on the non-driven steering shaft is
within a range of about 0.66-0.8.
When the resistance to wondering is improved as
mentioned above, if the ground contacting width of each
g
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of the four tires mounted on the driving shaft is ~3~9
to that of each of the two tires mounted on the non-
driven steering shaft, the performances on snow and ice
roads as a whole of the vehicle are gradually lowered
o~ accompanied with the decrease of the ground contacting
width as compared with the resistance to wondering.
This is shown in Fig. 3 relating to the braking
performance on ice. In this case, the distance from the
starting full braking to the stopping of the vehicle
running at 20 km/hr is measured and the performance on
ice is represented by an index on the basis that the
tire having the stopping distance of 32m, i.e. the tire
haviny the ground contacting width of 220 mm i8 100.
According to this graph, when the ground
1~ contacting width of each of the tires mounted on the
non-driven steering shaft and the driving shaft i8
224 mm, and when the ground contacting widths of both
tlres are 220 mm, the sufficiently large ground
contacting width as a while of the vehicle can be
2~ ensured and consequently the performance on ice
represented by the index value of not less than 100 can
be obtained as shown by white s~uares in Fig. 3 aside
from the resistance to wondering. On the other hand,
when the ground contacting widths of both tires are
gradually decreased to 212 mm, 196 mm and I80 mm for
improving the refiistance to wondering, the ground
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contacting width as a whole of ~he vehicle is too small
as shown by black circles in Fig. 3, and hence the
performances on ice rapidly lower.
According to the invention, therefore, the
0~ ground contacting width of the tire mounted on the non~
driven steering shaft is maintained at the narrow value
for improving the resistance to wondering, while the
ratio of ground contacting width to maximum tire width
~TW/SW)D of each of the tires mounted on the driving
1~ shaft is limited to a range of 1.21-1/2(TW/SW)F~
(TW/SW)D~1, whereby the decreased quantity of ground
contacting width viewing the whole of the vehicle is
sufficiently compensated while improviny the resistance
to wondering, whereby the effective improvement of the
1~ performances on ice is obtained.
As shown by white circles in Fig. 3, when the
ratio (TW/SW)F is constant or the ground contacting
width of the tire mounted on the non-driven steering
shaft is constant and the ground contacting width of the
tire mounted on the driving shaft is changed from 212 mm
to 224 mm, from 196 mm to 232 mm and 240 mm or from
180 mm to 240 mm, the high performances represented by
an index value of not less than lO0 can be obtained.
As seen from the above, according to the
invention, the resistance to wonderlng can effectively
be improved by narrowing the ground contacting width of
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the tire mounted on the non~driven steering shaft within
a constant range as compared with the conventional tire,
and also the high performances on snow and ice roads as
a whole of the vehicle can suficiently be maintained by
widening the ground contacting width of the tire mounted
on the driving shaft to sufficiently compensate the
decreased quantity of the ground contacting width of the
tire mounted on the non-driven~steering shaft.
When two t.ires are mounted on the single non-
driven steering shaft~ four tires are mounted on the
single driving shaft and four tires are mounted on the
single non-driven and non-steering shaft located behind
the driving sha~t, the relation among the ground
contacting width, the resistance to wondering and the
braking per~ormances on ice is shown in Table 1.
Table l
_ ~i ~ .h ~ . '. . .~ ~t. . 7. ~ ~d~ t .;. . Res ist- ~aiting
steering on driving non-driven wondering on ice
sha~t shaft shat
_ . _ _ _ . .
Com~ar-
tire I220 mm 220 mm 220 mm 100 100
Com~ar-
: atlve196 mm 196 mm 196 mm 130 90
: : Invention 196 mm 232 mm 232 mm 130 102
_
tire ~196 mm 240 mm 240 mm 130 105
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As seen from Table 1, even when the constructio2n~ 3 ~9
of the inventlon is applied to the vehicle provided with
the non-driven and non~steering shaft, the resistance to
wondering can efectively be improved while maintaining
o~ high performances on snow and ice roads.
Thus, according to the invention, the ratio of
ground contacting width to maximum tire width (TW/SW)F
of the tire mounted on the non-driven steering shaft is
within a range of 0.66-0.8 smaller than that of the
conventional tire, and the ratio of ground contacting
width to maximum tire width (TW/SW)D of the tire mounted
on the driving shaft is within a range of
1.21-l/2(TW/SW)FS(TW/SW)D~l larger than that of the
conventional tire, whereby the performances on snow and
1~ ice roads are sufficiently developed and further the
resistance to wondering can effectively be improv~d.
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