Field of the Invention
The present invention is directed to a pneumatic tire.
More specifically, the present invention is directed to the tread of a tire and
the sipes in the tire tread.
Background of the Invention
The tread portion of a pneumatic tire generally comprises
a plurality of circumferentially and laterally extending grooves defining ground
engaging rubber elements, the elements being in the form of blocks or ribs or combinations
thereof. The particular size and shape of the tread elements contribute significantly
to the overall performance of the tire and are for that reason designed to achieve
the desired tire characteristics.
Winter type tires, as well as all-season type tires, usually
have multiple sipes. Usually, a sipe is a groove having a width in the range of
0.1% to 1% of the tread width, i.e. the arc length of the tread surface in the axial
direction. The sipe tends to close when it is located in the tire footprint at zero
speed and under normal load and pressure. Sipes are typically formed by steel blades
inserted into a cast or machined mold or tread ring therefor.
A sipe may extend circumferentially or laterally the tread
in a straight, curved, or zigzag manner and may be as deep as the primary tread
grooves or have a depth that is greater than the groove depth. The sipes can pass
through the sides of the ribs and tread blocks or be confined to the interior of
the tread elements. It is also known to have sipes lying in planes which are not
perpendicular to tangents to the surface of the tread at their point of intersection;
the inclination of the planes defining neighboring sipes can be identical or differ
step wise along the tread element length. It is further known to use sipes having
a depth that varies along its length.
The presence of sipes in a tread increases the number of
biting edges in the tread. The local high pressure at each biting edge improves
the wiping and digging action of the tread surface, conferring to a tire excellent
traction on snow and ice. Furthermore, sipes improve the flexibility of the tread
elements without destroying their solidity. The easy relative longitudinal sliding
between the opposed faces of the sipe weakens the resistance of the tread elements
to flexing in the contact area between tread and road and therefor slows down the
heat buildup of the tire; however, the sliding of the opposed faces of the sipes
creates friction between the opposing sipe faces and can lead to wear of the sipes.
discloses a tire with a rib having a plurality of sipes formed therein.
The sipes have a three-dimension aspect, wherein a plurality of peaks and valleys
are defined though a sipe centerline. The peaks and valleys formed are either a
single point of maximum depth or a line of maximum depth. Due to the sharp lines
forming the sipe configuration, while the opposing sides of the sipe interlock,
there is increased abrasion at the points.
discloses a three-dimensional sipe for tire treads. The protrusions and
cavities formed all have a domed configuration. The rounded opposing edges of the
sipe reduces rubbing but doesn't eliminate the movement of the opposing sipe faces.
shows circular 3-d siping with flat spaces therebetween. The flat portions
of the sipe are still subject to rubbing and wear.
Summary of the Invention
The present invention is directed to a tire molded with
three-dimensional sipes, and tire molding blades for forming such three-dimensional
sipes. The tire has blocks and tread elements that are stiffer than conventional
two-dimensional sipes and provide the tire with improved tire characteristics, such
as handling and stability.
The present invention includes a tire tread, the tread
having a plurality of ground engaging elastomeric elements, whereby at least one
of the elements has a sipe. The sipe has a radial depth, a first sipe face, a second
opposing sipe face, and a multiple dimension centerplane located equidistant from
the sipe faces. The sipe centerplane has at least two radially adjacent rows of
projections, the radially adjacent rows being separated by a planar section. The
planar section has a zigzag configuration of defined length and width.
In one aspect of the invention, in the sipe centerplane,
the projections in either row may having different period lengths in the depth direction
of the sipe centerplane, different heights in the vertical direction, or different
widths in the horizontal direction. In one aspect, the differing period depths alternate
in the depth direction Z. The differences in the length, height, or width may alternate
in a set pattern or may increase or decrease progressively, or in any type of ordered
or random pattern.
In another aspect of the invention, either row of projections
in the sipe centerplane may be a series of projections separated by a second planar
In another aspect of the invention, the radially outermost
row of projections comprises a plurality of half cylindrical tubes, the projections
being separated by planar sections.
In another aspect of the invention, the radially inner
row of projections comprises projections having configurations selected from the
group consisting of frustums, hemispheres, and half cylindrical tubes
Also disclosed is a mold blade for mounting inside a tire
mold to form a sipe in a tire tread. The blade is defined by a centerline, planar
portions and at least one three-dimensional portion. The three-dimensional portion
of the plane has at least two radially adjacent rows of projections, the radially
adjacent rows being preferably separated by a planar section. The separating planar
section has a defined length and width.
In one aspect, the radially outer row of projections is
a series of projections separated by a second planar section.
In one aspect of the mold blade, the projections in at
least one of the rows of projections have variations in the depth direction of the
mold, variations in the vertical direction of the mold, or variations in the width
direction of the mold.
In another aspect, the radially outermost row of projections
comprises a plurality of half-cylindrical tubes, the projections being separated
by planar sections.
In another aspect, the projections in at least one of the
rows of projections have configurations selected from the group consisting of frustums,
hemispheres, and half cylindrical tubes.
In another aspect of the invention, at least one of the
rows of projections comprises projections having frustum configurations wherein
the base of the frustum has at least three sides.
In another aspect, the blade has a constant thickness.
The following definitions are controlling for the disclosed
"Axial" and "axially" are used herein to refer to lines
or directions that are parallel to the axis of rotation of a tire.
"Blade" means a protrusion in a tire curing mold that forms
part of the tread design. The protrusion forms a corresponding depression in the
finished tire tread.
"Radial" and "radially" are used to mean directions radially
toward or away from the axis of rotation of the tire.
"Sipes" refer to small grooves molded into tread elements
of a tire that subdivide the tread elements and improve traction characteristics.
Sipes have a width typically in the range of 0.1 % to 1% of the tread width and
tend to close completely in a tire footprint. The depth of a sipe may vary around
the circumference of the tread, or the depth of one sipe may be constant but vary
from the depth of another sipe in the tire.
Brief Description of the Drawings
The invention will be described by way of example and with
reference to the accompanying drawings in which:
Detailed Description of the Invention
- FIG. 1A illustrates a blade in accordance with the present invention;
- FIG. 1B is a sectional view of the blade along line 1 B-1 B in FIG. 1A;
- FIG. 1C is a schematic view of the blade of FIG. 1A;
- FIG. 2 is a cut view of a tread element showing the opposing sipe faces and
the centerplane formed between the opposing sipe faces;
- FIG. 3 is another embodiment of a blade used to make a multi-dimensional sipe;
- FIG. 4 is another embodiment of a blade;
- FIG. 5 illustrates a blade and tread portion during molding; and
- FIGS. 6 and 7 are further embodiments of blades in accordance with the present
FIG. 1A illustrates a blade 10 in accordance with the present
invention. The blade 10 is used to form a sipe in a tire tread during molding of
a tire. The blade 10 has a three-dimensional portion 12 comprising a plurality of
adjacent or spaced projections 14, seen on one side of the blade as protrusions
and on the other side of the blade as recesses. The blade 10 is made of metal, preferably
steel, and the projecting elements 14 are made by stamping or embossing the steel
sheet. Such a blade 10 is mounted into a tire mold such that the top 16 of the blade
10 is closer to the mold and the projections 14 are in the open space of the mold
to form a three-dimensional sipe in a tire tread. The blade 10 has a horizontal
direction H and a vertical direction V. The projections, extending from at least
one side the blade, also provide the blade with a depth direction Z (see FIG. 1B).
The open holes in the various blades illustrated are for mounting of the blade in
the tire mold.
The blade 10, and as discussed further herein the correspondingly
formed sipe 20 of the present invention, as illustrated in the embodiment of FIG.
1A, has two radially adjacent rows 22, 24 of three-dimensional projections 14. In
regards to the blade 10, the radial direction is synonymous with the vertical direction
V. The radially adjacent rows 22, 24 are separated by a planar section 26, the planar
section 26 having a defined height in the vertical direction V and a defined length
in the horizontal direction H, but which does not have any depth variation in the
third direction Z. The planar section 26 can have any two dimensional configuration
such as a plate, sheet, or straight line having a defined height. Preferably, the
planar section 26 has a zigzag configuration having a defined height in the vertical
direction V and having a defined length in the horizontal direction H, as seen in
FIG. 1A. The defined height in the vertical direction V is greater than a single
point, and preferably has a value equal or greater than the actual thickness of
material forming the blade 10.
The radially outermost row 22 of three-dimensional projections
14 is a series of spaced projections 14, the projections 14 being separated by a
second two-dimensional planar section 30. The three-dimensional projections 14 have
a half tubular or half cylindrical configuration. The depth of the projections 14
in the depth direction Z may be different than the full blade depth in the Z direction.
The adjacent projections 14 may also have differing heights in the vertical direction.
As seen in FIG. 1A, the projections increase in vertical height along the horizontal
direction H of the blade 10. While not illustrated, the adjacent projections may
also increase in length in the horizontal direction H of the blade 10, wherein each
adjacent projection has a greater width in the horizontal length or the length varies
in another manner; alternatively, the projections 14 may vary in the depth direction
in any consecutive or nonconsecutive manner.
The radially inner row 24 of projections 14 is a series
of half tubular or half cylindrical configurations. Similar to the radially outer
row 22, the tubes may have differing period lengths in the depth direction Z. Also
similar to the radially outer row 22, the radially inner row projections 14 may
vary in the vertical direction and/or the horizontal direction and/or the depth
direction. Such variations may be dependent upon the selected configuration for
the radially outer row 22.
Alternatively, the blade 10 may be defined as comprising
an open, two layer honeycomb structure containing projections therein. Along the
same plane as the two-dimensional end portions of the blade, two stacked open honeycomb
layers are present along a two-dimensional plane, see the schematic representation
illustrated in FIG. 1C.
When molding a tire using the blade 10, the extent of the
blade 10 entering into the tread rubber, and the top 16 of the blade configuration
may be varied depending on the desired tire characteristics. For a summer tire,
the top 16 of the blade 10 may be formed with a two-dimensional planar section,
and the blade 10 is inserted to a depth until the top planar section enters the
tread rubber. For such a formed sipe, when the tread is unworn, the sipe presents
itself as a straight line. Following tread wear, the sipe presentation changes.
For a winter tire, the blade 10 may be inserted into the tread rubber to a depth
forming an initial sipe having multiple edges at the tread surface for an unworn
tire. Such multiple edges increase the number of biting edges in the tread. For
the summer tire, it is desired that wear takes the summer tire to the winter tire
tread depth to provide the additional biting surfaces.
FIG. 2 shows a tread element with a sipe 20 formed by the
blade 10 of FIG. 1. The single elastomeric tread element is a portion of a tread
pattern and is shown after the tire vulcanization step wherein the sipe 20 is formed
into the tread rubber. The neighboring tread elements or ribs of the tread pattern
have not been represented for simplicity. Also, for simplicity, the tread element
is shown with only a single sipe 20; the tread element may be provided with multiple
sipes 20 at any inclination angle relative to adjacent grooves.
The tread element is divided into two portions 32', 32"
at the location of the sipe 20, showing the opposing faces 20', 20" of the sipe
20. The protrusion 34 in each sipe face 20 , 20 cooperates with the recesses 36
in the opposing sipe face 20', 20". During normal operation of the tire, when the
sipe 20 enters the contact patch, the sipe 20 closes and the opposing sipe faces
20', 20" interlock, reducing slippage of the two opposing sipe faces 20', 20". A
centerplane is formed equidistant from the opposing sipe faces. The centerplane
is multi-dimensional and mimics the configuration of the blade 10 forming the sipe
20. The dimensions of the centerplane 38 are a) the vertical direction V, also conventionally
referred to as the radial direction of the tire, having a defined height, b) the
horizontal direction H, parallel to the longest plane of the centerplane regardless
of orientation of the sipe in the tread element, having a defined length, and c)
the depth direction Z, parallel to the short plane of the centerplane 38 regardless
of orientation of the sipe 20 in the tread element 32 and corresponding to the variation
in the centerplane 38 forming the recesses 36 and protrusions 34 of the spaced projections
14. As the centerplane 38 mimics the configuration of the sipe blade 10, each sipe
face 20', 20" also mimics one side of the blade 10.
The sipe 20 has a defined width, preferably in the range
of 0.1 % to 1% of the tread width; the width permitting the sipe 20 to close completely
when the tread element 32 enters the contact patch during tire rotation. The sipe
width is preferably constant, though portions of the sipe 20 are three-dimensional
Another embodiment of the sipe blade is shown in FIG. 3.
Similar to the blade 10 of FIG. 1A, the blade 10 has two radially adjacent rows
22, 24 of three-dimensional projections 14. The radially adjacent rows 22, 24 are
separated by a planar section 26; the planar section 26 having a zigzag configuration.
The radially outer row 22 of projections 14 is similar to that of FIG. 1A, while
the radially inner row 24 of projections 14 has a set of projections having a half-spherical
or hemisphere configuration, having a circular base 40 and a domed shaped projection
42, the domed shaped projections 42 being separated by a planar section 46.
Another variation of the sipe blade is illustrated in FIG.
4. The radially inner row 24 of three-dimensional projections 14 contains projections
44 having the configuration of a frustum of a four-sided element wherein the top
portion is round to form a hemispherical projection. The base of the frustum, while
illustrated as four-sided, may have any number of sides or have any polygonal configuration,
such as triangular (see FIG. 7), pentagonal, hexagonal, heptagonal. The polygonal
configuration may be a regular polygon wherein all of the sides are of equal length
and all of its vertices have the same angle.
FIG. 5 illustrates another molding scenario using a blade
of the present invention. The blade 50 has the same overall configuration as that
illustrated in FIG. 1, wherein the depth of the blade 50 increases from one side
edge to the opposing blade edge. The projection configurations of the blade 50 are
similar to the blade of FIG. 6. The tread rubber 52 to be molded is not flat, but
instead is defined by at least one radius of curvature. During molding of the tread
rubber 52, only a portion of the blade 50 is inserted into the tread rubber 52.
Because only a portion of the blade 50 is inserted into the tread rubber 52, the
radially outer row of projections 22 does not need to extend to the top edge of
the blade 50.
FIG. 6 illustrates another variation on the blade 56. The
projections 14 in both projection rows 22, 24 all have the same height in the vertical
direction V. Additionally, at least one of the spaces between similar projections
14 may be planar, instead of having continuously alternating projections. In the
blade 60 of FIG. 7, the radially inner row 24 of projections 14 have configurations
of a three-sided based frustum. The projection rows 22, 24 are separated by a zigzag
planar section 62.
Tires were molded using the blade of FIG. 1A and compared
against standard two-dimensional sipes. The tires tested were all of the same construction
and the tread configurations were identical so that the only difference is in the
sipe configuration. The conventional tires were tested in three groups, A, B, C,
as were the tires having the inventive three-dimensional sipes 1, 2, 3, with groups
A and 1, B and 2, C and 3 being directly tested against each other. Test results
under different operating conditions are presented below. The conventional tires
are given the base rating of 100 and the three-dimensional sipe tires are judged
against the conventional tires.
@ 55 km/h
@ 55 km/h
The majority of the above tests results are subjective
results of the drivers. The noise test results were achieved by placing microphones
next to the tires at the noted speeds.
The results show that the tires with the inventive sipes
have improved dry handling, especially in steering and stability area. Additionally,
the wet handling times and wet braking are comparable to conventional sipes. In
testing for noise, only one set of conventional tires were tested against the inventive
tires; but at both 55 km/h and 80 km/h, the inventive tires tested as quieter tires.
The present invention results in a tire having improved
tire characteristics, including tire blocks that have an increased stiffness provided
by the interlocking aspect of the sipes.