Note: Descriptions are shown in the official language in which they were submitted.
1
PNEUMATIC VEHICLE TIRES
Field
The invention relates to a pneumatic vehicle tire, in particular for use in
winter driving conditions,
having a tread with profile positives, for example profile blocks, which are
separated from one
another by channels and in which sipes are formed, which sipes run
substantially in an axial
direction and extend in a radial direction in each case to a depth of 70% to
100% of the maximum
profile depth, which sipes have in each case two sipe walls which run
symmetrically with respect
to the central plane of the sipe, and which sipes are made up, in a radial
direction, of three sections
adjoining one another, with a radially outer section which is delimited
substantially by wall sections
running in a radial direction and which extends to a depth of 70% to 90% of
the depth of the sipe,
with a middle section running between the radially outer section and the
radially inner section,
and with a radially inner section which has wall sections which, in cross
section, run outward from
the central plane in a rounded manner.
Background
A tire as per the introduction is known from EP 2 072 286 B1 for example. The
tread of the tire
has profile blocks equipped with sipes. The sipes have an outer section of
constant width running
over the major part of their radial extent, and the radially innermost widened
section runs in a
circular-arc-shaped manner with an inner radius amounting to 0.5 mm to 5.0 mm.
A transition
section between said sections has sipe walls which in a cross section are
curved along an outer
radius, which amounts to 0.5 mm to 8.0 mm. Furthermore, the outer and the
inner radius have a
specific relationship with respect to one another. A mold segment suitable for
forming such sipes
and having a lamella is known from EP 2 517 867 B1.
The pneumatic vehicle tire known from EP 1 920 951 B1 has a tread with profile
blocks with an
inner and an outer sipe pair. The inner sipe pair is arranged in the middle
region of the profile
block. Of the outer sipe pair, in each case one sipe is situated outside the
inner sipe pair. Each
sipe has a widened section at the sipe base, wherein the widened sections of
the two sipe pairs
have different curvatures.
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During the use of tires in winter driving conditions, for example on roads
covered with ice, the
friction energy between the tread of the tire and the ice generates a
meltwater film, a "liquid layer",
which is for the most part wiped away by profile positive edges, in particular
by the block edges
in the case of transverse channels or sipes, such that it is also the case
that a major part of the
.. surface of the profile positives, for example of the profile blocks, comes
into direct frictional contact
with the underlying surface. The volume of the "liquid layer" to be wiped away
is dependent on
various factors, in particular the ambient temperatures, such as ice
temperature, tire temperature
and air temperature, and on the introduced friction energy, and is therefore
at its greatest in the
presence of temperatures around the freezing point. To ensure optimum
frictional contact
between the tread and the underlying surface, as much meltwater as possible
should be received
and discharged by the sipes, wherein, however, the size of the contact area of
the profile positives
or profile blocks with the underlying surface should remain as large as
possible.
The hitherto known sipes provided in profile blocks with widened sections at
the sipe base give
rise to a stress profile in the profile block which has proven to be
disadvantageous for the rolling
resistance and wet grip. In particular, there is resulting non-uniform bending
behavior of the block
elements between the sipes, along with a disadvantageous excessive compression
of the block
elements under pressure loads.
Summary
The invention is therefore based on the object of designing a tire of the type
mentioned in the
introduction such that the rolling resistance is reduced, and the wet grip
performance is improved.
The stated object is achieved according to the invention in that the middle
section running
between the radially outer section and the radially inner section extends to a
depth of 80 % to 95
% of the depth of the sipe and is delimited by wall sections which run in each
case at an angle of
50 to 60 with respect to the radial direction, giving rise to a widening of
the central section in the
direction of the sipe base, wherein the curved profile of the wall sections in
the radially inner
section is based on radii, the associated circle central points of which lie
along a line running
perpendicular to the central plane of the sipe, wherein the central point of
the circle belonging to
the smallest radius lies on the central plane, and said radius runs to the
lowest point of the sipe,
wherein the largest radius runs in each case to the radially outer end point
of each wall section,
and the central point of the circle thereof is the central point situated
furthest remote from the
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central plane, and wherein, between the points, the radii increase
continuously and the spacing
of the central points of the associated circles to the central plane becomes
larger.
Sipes designed according to the invention give rise to a considerable
reduction of the rubber
compression under pressure load and permit uniform bending and deformation
behavior of the
block elements of the profile blocks. In this way, the rolling resistance is
reduced, and the wet grip
performance is considerably improved. By means of the special design of the
radially inner
section, the form of the sipe at the sipe base, it is possible to obtain a
considerable improvement
in the bending behavior of the individual block elements, without the sipes
being excessively
widened in the region of the sipe base.
In a preferred embodiment, the spacing of the central point of the circle with
the largest radius to
the central plane amounts to 10 % to 50 % of the largest width of the radially
inner section. In a
further preferred embodiment, the smallest radius amounts to 40 % to 60 % of
the largest width
of the radially inner section, and the largest radius amounts to up to 2 times
the smallest radius,
in particular up to 1.5 times, particularly preferably up to 1.3 times. These
measures provide a
relatively large degree of design freedom with regard to the design of the
radially inner section,
wherein the effect of a considerable reduction of the rubber compression under
pressure load is
fully maintained.
Further special configurations of the sipes contribute to uniform bending and
deformation behavior
of the block elements of the profile blocks. Said configurations include the
radially inner section
having, at its widest point, a width of 150 % to 400 % of the width of the
radially outer section, and
the widest point of the radially inner section lying, in the radial direction,
at a depth which amounts
to 85% to 97% of the depth of the sipe.
The radially outer section, which has the greatest radial extent of all
sections, preferably has a
width of 0.30 mm to 0.80 mm, in particular of 0.40 mm to 0.60 mm.
Hence, according to a broad aspect, the invention provides a pneumatic vehicle
tire for use in
winter driving conditions, the tire having a tread with profile blocks, which
are separated from one
another by channels and in which sipes are formed, which sipes run
substantially in an axial
direction and extend in a radial direction in each case to a depth of 70% to
100% of a maximum
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profile depth, which sipes have in each case two sipe walls which run
symmetrically with respect
to a central plane of the sipe, and which sipes are made up, in a radial
direction, of three sections
adjoining one another, with a radially outer section which is delimited
substantially by wall sections
running in the radial direction and which extends to a depth of 70% to 90% of
the depth of the
sipe, with a middle section running between the radially outer section and the
radially inner
section, and with a radially inner section which has wall sections which, in
cross section, run
outward from the central plane in a rounded manner, wherein the middle section
running between
the radially outer section and the radially inner section extends to a depth
of 80 % to 95 % of the
depth of the sipe and is delimited by wall sections which run in each case at
an angle of 50 to 60
with respect to the radial direction, giving rise to a widening of the central
section in the direction
of the sipe base, wherein the curved profile of the wall sections in the
radially inner section is
based on radii, associated circle central points of which lie along a line
running perpendicular to
the central plane of the sipe, wherein the central point of the circle
belonging to a smallest radius
lies on the central plane, and the radius runs to a lowest point of the sipe,
wherein a largest radius
runs in each case to a radially outer end point of each wall section, and a
central point of a circle
thereof is a central point situated furthest remote from the central plane,
and wherein, between
the points, the radii increase continuously and the spacing of the central
points of the associated
circles to the central plane becomes larger.
Brief description of the drawings
Further features, advantages and details of the invention will now be
described in greater detail
with reference to the drawing, which schematically illustrates one exemplary
embodiment of the
invention. In the drawing:
figure 1 shows a view of a detail of a tread of a pneumatic vehicle tire
having a design
variant according to the invention, and
figure 2 shows a cross section through a sipe along the line II ¨ II in
figure 1.
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Detailed description of embodiments
Variants, examples and preferred embodiments of the invention are described
hereinbelow. In
the following description, the curvature is to be understood to mean the
reciprocal of the radius of
the circle that best approximates to the curvature profile at every curved
point.
Figure 1 illustrates four profile blocks 1 of a tread of a pneumatic vehicle
tire of radial type of
construction, in particular of a tire suitable for use in winter driving
conditions, for passenger motor
vehicles, vans or light trucks, wherein the circumferential direction of the
tire is denoted by the
double arrow U.
The profile blocks 1 belong to two profile block rows which each run in the
circumferential direction
U and which are separated from one another by a circumferential channel 2
which runs in a
straight manner in the exemplary embodiment shown, wherein the profile block
rows are
preferably delimited by further circumferential channels that are not
designated. The
circumferential channel 2 has, in the radial direction, a depth T of 7.0 mm to
10.0 mm, in particular
of up to 9.0 mm, wherein the depth T corresponds to the maximum profile depth
provided for the
respective pneumatic vehicle tire. Within the profile block rows, profile
blocks 1 which are adjacent
in the circumferential direction U are separated from one another in each case
by a transverse
channel 3, which preferably has a depth which at least substantially
corresponds to the
circumferential channel 2 or which is slightly shallower.
Each profile block 1 is equipped with a number of sipes 4, wherein, in the
design variant shown,
four correspondingly designed sipes 4 are provided per profile block 1. The
sipes 4 extend at least
substantially parallel to one another and at least substantially parallel to
the transverse channels
3, and extend in each case all the way through the profile block 1. The
spacings of the sipes 4 to
one another within a profile block 1 at least substantially correspond, and
are preferably
substantially equal to the spacings between the respective sipe 4 situated
furthest to the outside
in the circumferential direction U and the profile block edge at the
respective transverse channel
3.
As per figure 2, which shows a cross section through a sipe 4, each sipe 4
extends in a radial
direction to a depth t which amounts to 70% to 100%, in particular 80% to 90%,
of the depth T of
the circumferential channel 2. Each sipe 4 is delimited by two sipe walls 5,
which are of mirror-
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symmetrical design with respect to one another in relation to a central plane
E running through
the sipe 4. As will be discussed below, the two sipe walls 5 provide the sipe
4 with a width which
varies in a specific manner over the depth t of said sipe.
Each sipe 4 is made up of a radially outer section 4a, a middle section 4b and
a radially inner
section 4c, wherein the middle section 4b and the radially inner section 4c
provide the sipe 4 with
a pyriform design in cross section. The sipes 4a, 4b and 4c have wall sections
5a, 5b, 5c, wherein
in each case two wall sections 5a, 5b, 5c are situated opposite one another. A
bend is situated in
each case between the wall sections 5a and 5b, and the wall sections 5b and 5c
adjoin one
another without a bend.
The radially outer section 4a extends in a radial direction and to a depth ti,
which amounts to 70%
to 90% of the depth t, and the wall sections 5a run in a radial direction. The
radially outer section
4a therefore has a constant width B1, wherein the width B1 amounts to 0.30 mm
to 0.80 mm, in
particular 0.40 mm to 0.60 mm.
The middle section 4b directly adjoining the radially outer section 4a extends
to a depth t2, which
amounts to 80% to 95% of the depth t. The wall sections 5b delimiting the
middle section 4b run
at an angle a of 5 to 60 , preferably at most 45 , with respect to the radial
direction, wherein the
middle section 4b becomes continuously wider in the direction of the interior
of the sipe.
The wall sections 5c in the radially inner section 4c are specially curved and
adjoin one another
without a bend (tangentially) at the lowest point of the sipe 4, at the depth
t. The inner wall sections
5c have in each case a curvature which decreases continuously from their
radially outer end to
their radially inner end, such that their curvature is at its smallest at the
depth t. The radially inner
section 4c furthermore has, at a depth t3, its greatest width B2 of 150 % to
400 % of the width B1,
wherein the depth t3 amounts to 85 % to 97 % of the depth t.
As shown in figure 2, the special curvature profile of the wall sections 5c is
based on a continuous
displacement of the circle central points belonging to radii, wherein the
smallest radius r1 amounts
to 40 % to 60 % of the largest width B2 of the radially inner section 4c. The
central point of the
circle belonging to said radius ri lies on the central plane E, and the radius
ri runs to the deepest
point P1 of the sipe 4. The largest radius r2 runs in each case to the
radially outer end point P2 of
that wall section 5c of which the central point of its circle is situated on a
line Ii running
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perpendicular to the central plane E of the sipe 4 and is the central point
situated furthest remote
from the central plane E. Between the points Pi, P2, the radius increases
continuously, and the
spacing of the central points, situated on the line 11, of the associated
circles to the central plane
E becomes larger. The circle central points on the line II thus move away from
the respective wall
section 5c on the opposite side of the central plane E. The spacing of the
central point of the circle
with the largest radius r2 to the central plane E amounts to 10 % to 50 % of
the largest width B2
of the radially inner section 4c. The largest radius r2 amounts to up to 2
times the smallest radius
in particular up to 1.5 times, particularly preferably up to 1.3 times.
In one design variant, a small transition rounding is provided in each case
between the outer wall
sections 5a and the middle wall section 5b, which transition rounding ensures,
in the cross section,
a bend-free transition of the wall sections 5a and the wall sections 5b.
Furthermore, the outer wall
sections 5a may also, in the cross section, run at an angle of in particular
up to 5 with respect to
the radial direction, wherein the radially outer sections 4a becomes wider in
the direction of the
interior of the sipe.
Depending on the outer block shape, the sipes 4 may also run at an angle of up
to 45 with respect
to the transverse direction of the tire. Furthermore, the sipes 4 need not
extend parallel to one
another.
It is preferable for two to six sipes 4 to be provided per profile block 1,
wherein the sipes 4 provided
may also be of different designs, with preferably at least every second sipe
being designed
according to the invention.
List of reference numbers
1 ............. Profile block
2 ............. Circumferential channel
3 ............. Transverse channel
4 .......... Sipe
4a, 4b, 4c .... Section
5 ............. Sipe wall
5a, 5b, 5c .... Wall section
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B1, B2 ...... Width
E ............ Central plane
T ............ Depth
t, ti, t2, t3 .. Depth
a ....... Angle
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