Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2006573
(a) TITLE OF THE INVENTION
PNEUMATIC TIRE WITH SIDEWALL PROTRUSIONS FOR ENHANCED
OPERATION ON SNOW COVERED TERRAIN
(b) TECHNICAL FIELD TO WHICH THE INVENTION RELATES
The present invention relates to a pneumatic tire having improved road grip
performance on snowy roads.
(c) BACKGROUND ART
Hitherto, many efforts have been made to improve road grip performance of
snow tires on snowy roads, e.g., traction performance and breaking
performance.
Among such efforts were providing blocks on the tread, providing sipes on the
tread
elements, and varying these shapes thereof, etc. Such efforts were generally
devoted
to designing a tread pattern, in other words, to designing a tread structure
at the tread
face. However, a further improvement in the road grip performance is required.
(d) DESCRIPTION OF THE INVENTION
An object of one aspect of the present invention is therefore to provide a
pneumatic tire having improved road grip performance on snowy roads, which is
formed according to a new conception of the road grip such that a further
gripping
force can be obtained by providing gripping means in the so-called "buttress"
parts as
well as the tread face.
The present invention was made after noting the fact that the radially-
outermost part of the tire sidewall, which is generally called the tire
buttress part,
contacts with the sidewall of a rut when running on a snowy road, in
particular, one
which is covered by packed snow.
According to one aspect of the present invention, a pneumatic tire is provided
including a tread portion, and a pair of sidewall portions extending radially-
inwardly
from an associated tread edge to an associated bead portion, wherein the tread
portion
includes primary, circumferentially-extending main grooves which are disposed
on
each associated side of the equator of the tire, and lateral grooves extending
from the
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main grooves to the tread edges to open at the axially-outer end thereof at
the face of
the sidewall portion, thereby forming, in each shoulder region, a row of
shoulder
blocks which is arranged circumferentially of the tire along each tread edges,
wherein
the face of the tread portion includes indentations, and each face of the
sidewall
portions includes associated protrusions, whereby a pair of the indentations
and the
protrusions make up a gripping means, and wherein each indentation extends
both
radially-inwardly from the surface of the tread portion and axially-inwardly
from the
face of the sidewall, thereby to extend from the tread edge to a point which
is axially-
inward thereof, the axially outer end thereof being open at the face of the
sidewall,
and the axially-inner end terminating an axial distance inwardly of the tread
edge at
the top of the shoulder block.
By one variant of this aspect of the invention, the number of the shoulder
blocks in each row is in the range of 25 to 60.
By another variant of this aspect of the invention or of variants thereof, the
face of the tread portion which is occupied by the shoulder blocks is between
45
and 75 % , whereby the total area of the tops of the shoulder blocks is 0.45
to 0.75
times the area of the face of the tread portion if no tread grooves were to be
formed.
By another variant of this aspect of the invention or of variants thereof, the
edges of each shoulder block are respectively formed in a zigzag or stepwise
configuration, whereby the performance of the shoulder block to engage with
snow or
ice is effectively improved.
By yet another variant of this aspect of the invention or of variants thereof,
the
axial distance from the equator of the tire to each indentation at the face of
the tread
portion is 0.460 to 0.4975 times the width of the tread portion between the
tread
edges. By one variation thereof, the axial distance is between 1.5 and 8 mm.
By a further variant of this aspect of the invention or of variants thereof,
each
protrusion extends radially-inwardly from a position inwardly of the face of
the tread
portion to beyond a position which is 15 % of the distance of the lateral
groove depth
from the face of the tread portion.
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By still a further variant of this aspect of the invention or of variants
thereof,
each indentation has a bottom extending between the top and the axially-outer
side of
the shoulder block, and the bottom is inclined at an angle of 35 ° to
55 ° to the
equatorial plane of the tire. By one variation thereof, the inclination is
40°.
By yet a further variant of this aspect of the invention or of variants
thereof,
each protrusion extends radially-outer surface which is inclined at an angle
of 35 ° to
55 ° to the equatorial plane of the tire.
By a still further variant of this aspect of the invention or of variants
thereof,
each protrusion has a radially-inner surface, the inner edge of which being
joined to
the face of the sidewall portion, an axially-outer surface thereof extending
parallel
with the face of the sidewall portion between the radially-outer surface and
the
radially-inner surface, and having side surfaces at a right angle thereto.
By still another variant of this aspect of the invention or of variants
thereof,
the projecting amount of the protrusion constituting the distance which is
measured
axially from the tread edge to the circumferential edge is not less than 0.01
times the
tread width between the tread edges.
By a still further variant of this aspect of the invention or of variants
thereof,
two angled edges are formed in a region around each tread edge by each
indentation,
and wherein two angled edges are formed radially-inwardly of the tread edge by
each
protrusion. By one variation thereof, the gripping means is provided by four
angled
edges which provide a road grip. By another variation thereof, five gripping
means
are formed on each shoulder block, and four angled edges are provided on each
shoulder block.
(e) DESCRIPTION OF THE FIGURES
In the accompanying drawings:
Fig. 1 is a partial plan view showing an embodiment of one aspect of the
present invention.
Fig. 2 is a sectional view thereof;
Fig. 3 is a perspective view showing a shoulder block thereof;
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Fig. 4 is a sectional view of the shoulder block;
Fig. 5 is a graph showing the relationship between braking distance in index
and the axial distance from the equator of the tire to the indentation at the
tread face;
Fig. 6 is a graph showing the relationship between braking distance in index
and the amount of the protrusion;
Fig. 7 is a graph showing the relationship between heel and toe wear and the
above-mentioned axial distance;
Figs. 8 and 9 are perspective views each showing embodiments of other
aspects of the present invention.
(t~ AT LEAST ONE MODE FOR CARRYING OUT THE INVENTION
In Figs. 1 - 4, a pneumatic tire 1 has a tread portion 2, and a pair of
sidewall
portions extending radially-inwardly one from each tread edge to a bead
portion (not
shown). The tire is provided with a block pattern in the tread portion as
shown in
Fig. 1.
The tread portion is provided with circumferentially-extending main grooves
G2 disposed one on each side of the tire equator CO, and lateral grooves K
extending
from the main grooves G2 to the tread edges T to open the axially outer end
thereof
at the sidewall face 3, thereby forming, in each shoulder region, a row US of
shoulder blocks BS which are arranged circumferentially of the tire along each
tread
edge T.
Further the tread portion in this embodiment is provided, between the above-
mentioned main grooves G2, with circumferentially-extending main grooves G1
and
with lateral grooves, so as to form a row UC of central blocks BC which is
arranged
circumferentially on the centre line of the tread or the equator CO, and a row
UM of
middle blocks BM which is arranged circumferentially between the central block
row
UC and each of the shoulder block rows US.
The number of the shoulder blocks in each row UC, UM, US is preferably set
in the range of 25 to 60.
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Further, the occupation of the tread face by the above-mentioned shoulder
blocks BC, BM and BS is arranged between 45 % and 75 % , that is, the total
area SA
of the tops of the shoulder blocks BC, BM and BS is 0.45 to 0.75 times the
area S of
the tread face obtained, assuming that no tread groove is formed. When the
SANS
5 ratio is more than 0.75, while the wear resistance is improved, the traction
performance is impaired. On the other hand, when the SANS ratio is less than
0.45,
wear resistance is greatly reduced.
The edges S 1 and S2 of each shoulder block BC, BM and BS, in particular
side edges 52, are respectively formed in a zigzag or stepwise configuration
as shown
in Fig. 1, whereby the performance of the shoulder block to engage with or to
scratch
the snow and ice is effectively improved.
The tread face is provided with indentations 10, and each sidewall face 3 is
provided protrusions 11 pairing with the respective indentations. A pair of an
indentation and a protrusion make up a gripping means 7. A plurality of
gripping
means, in this embodiment, five gripping means, is formed on each shoulder
block
BS.
The indentation sinks both radially-inwardly from the tread surface and
axially-
inwardly from the sidewall face 3. In other words, the indentation extends
from the
tread edge T to a point 9 which is axially-inward thereof. The axially-outer
end
thereof is opened at the sidewall face 3, and the axially-inner end is
terminated an
axial distance 11 inward of the tread edge at the top of the shoulder block
BS.
The distance L of the point 9 from the tire equator CO must be 0.46 to 0.4975
times the tread width WT between the tread edges T, and generally and
preferably,
the distance 11 is set in the range between 1.5 mm and 8 mm.
The indentation shown in Figs. 1 - 4 is provided with an inclined bottom l0A
extending from the tread face to sidewall face 3 at an angle (theta) of 40
° .
The protrusion 11 projects axially-outwardly from the sidewall face 3 by a
distance 12. The radially-outer surface 11A thereof is located radially-
inwardly of the
bottom 10A. In this embodiment, the surface 11A is inclined at the same angle
as the
bottom 10A, which is 40° in this example.
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Further, the protrusion has a radially-inner surface, the inner edge of which
is
joined to the sidewall face 3, an axially-outer surface 11B extending parallel
with the
sidewall face 3 between the radially-outer surface and the radially-inner
surface, and
side surfaces 11C at a right angle thereto.
The distance 12 measured axially from the tread edge T to the circumferential
edge lla between the surfaces 11A and 11B, that is, the projecting amount of
the
protrusion, is not less than 0.01 times the tread width WT between the tread
edges.
Accordingly, as shown in Figs. 3 and 4, in a region around each tread edge,
two angled edges l0a are formed by each indentation 10, and two angled edges l
la
radially-inward of the tread edge T are formed by each protrusion 11. The
edges l0a
and lla can engage with the base and sidewall of the rut respectively, with
shaving or
scratching the snow to generate traction or breaking force. Thus, the gripping
means
can provide four angled edges which provide a road grip. In this embodiment,
since
five gripping means are formed on each shoulder block, forty angled edges are
provided on every shoulder block.
In Fig. 4, the line X is a 15 % wear line, that is, an imaginary line drawn at
15 % distance of the lateral groove depth H from the tread face. In this
embodiment,
the main groove depth is equal to the lateral groove depth. The protrusion 11
preferably extends radially-inwardly beyond the line X so as to have a part 12
inwardly thereof which projects from the sidewall face 3, thereby maintaining
the
road grip performance through the tire wear life.
Figs. 5 and 7 show the results of various tests, wherein test tires of size
10.00
R 20 (Tread width WT=200 mm) having the tread pattern shown in Fig. 1 were
prepared.
Fig. 5 shows the relationship between the above-mentioned distance L and
braking distance on a road covered by flatly packed snow. In the tests, the
distance L
was varied, while the distance 12 was kept constant at O.O1WT (=2.0 mm). The
test
tires of each distance L were mounted on all the wheels of a 2-D4 type truck.
Fig. 8 shows the relationship between the above-mentioned distance 12 and
braking distance on a road covered by rutted packed snow. In the tests, the
distance
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12 was varied, while the distance L was kept constant at 0.48WT (=96mm). The
test
tires of each distance 12 were mounted on all the wheels of a 2-D4 type truck.
Fig. 7 shows the relationship between the above-mentioned distance L and heel
& toe wear around the edges l0a of the indentations after a field test of
30,OOOkm
running. In the tests, the distance L was varied, while the distance 12 was
kept
constant at O.O1WT (=2.Omm). The test tires of each distance L were mounted on
the front wheels of a 2-D4 type truck.
As shown in Fig. 5, when the distance L was more than 0.4975WT, the road
grip performance deteriorated. Also, as shown in Fig. 6, when the distance 12
was
less than 0.01 WT, the road grip performance deteriorated. On the other hand,
as
shown in Fig. 7, when the distance L was less than 0.46WT, the wear resistance
was
impaired.
In Fig. 8, the gripping means 7 is substantially the same as that as explained
above with the exception that the circumferential width of the protrusion 11
is larger
than the indentation 10, while the protrusions are formed in a same width in
Figs. 1-
4.
In Fig. 9, the protrusion 11 is formed of the same width as the indentation
10,
but the bottom l0A of the indentation which connects to the inclined radially
outer
surface 11A of the protrusion, is parallel with the tread face.
As explained above, in aspects of the present invention, the tire is provided
with indentations and protrusions in the tire shoulder region. Accordingly,
when
running on a packed snow road, in addition to the engaging force between the
tread
and the base of the rut, an engaging force is further produced between the
tire
sidewalk and the rut sidewalk. As the result, the road grip performance can be
effectively improved to upgrade the running performance on that snowy road.
Further, by regulating the axial extent of the indentation and the radial
extent of the
protrusion as mentioned above, the grip performance is maintained through the
wear
life of the tire without generating uneven wear.
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