Note: Descriptions are shown in the official language in which they were submitted.
2180771
A TIRE WITH TIRE TREAD ELEMENTS C~AMFERED TO MODIFY
~ K RCF or RSAT OR BOTH RCF AND RSAT
Cross-References to Related Applications
Commonly owned application Attorney Docket No.
95434A to Hubbell et al., filed of even date herewith
relates to a specific tire m--ade using the method
disclosed herein. Further this method is disclosed
and claimed in copending patent application TIRE TREAD
ELEMENT MOLD CHAMFER TO MODIFY RCF AND/OR RSAT USING
THE EXISTING MOLD Serial Number 08/588,036 (Attorney
docket number 95012A) which has been filed
concurrently herewith and is hereby incorporated by
reference.
Back~round of the Invention
This invention pertains generally to the art of
methods and apparatuses for molding pneumatic tires,
and more particularly to a tire mold feature which
creates chamfers on the edges of tire tread elements
to vary the level of residual cornering force (also
known as RCF) or residual self-aligning torque (also
known as RSAT) in tires.
The chamfer feature may be built into a mold and
then ground out wherever the chamfer is not desirable.
Alternatively, the same effect can be obtained by
adding chamfer inserts to the interior of a mold.
At a tire's point of contact with a road, also
known as the contact patch, a tire experiences a
mompnt about its vertical axis. This mompnt is
referred to as a self-aligning torque. At a small
slip angle where the self-aligning torque is zero, an
additional horizontal force, referred to as residual
cornering force, or RCF, is present. Even when
lateral forces such as those relating to plysteer and
conicity are reduced to zero, residual self-aligning
torque, or RSAT may remain.
The level of RCF and/or RSAT of a tire varies
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with the shape and profile of the individual elements
of the tire tread. In the past, one method employed
by tire designers to vary RCF and/or RSAT of a certain
tire design was to obtain a new tire mold with
alterations, which may have included changes to the
tire tread elements, to modify the original tread
pattern. Manufacturing a new mold can be costly and
time consuming, thereby slowing the development of new
tire designs.
Applicants recognized a need for a more cost-
effective solution to the RCF and/or RSAT problem than
redesigning and modifying entire existing molds that
produce tires with unacceptable RCF and/or RSAT.
Applicants have developed a new mold and tire made
there from that enables the tire designer to change
the RCF and/or RSAT in tires from a mold by adding
chamfer inserts to the mold to create the chamfer in
the tire or more preferably by designing the mold with
selected tread elements chamfered, and then modifying
that mold to adjust the RCF or RSAT of the tire by
selectively removing the mold material which created
the chamfer.
The present invention contemplates a new and
improved tire have chamfers selected for modifying RCF
and/or RSAT of a tire which is simple in design,
effective in use, and overcomes the foregoing
difficulties and others while providing better and
more advantageous overall results.
Summary of the Invention
In accordance with the present invention, a new
and improved tire can be made utilizing a method and
apparatus for modifying RCF and/or RSAT which can be
utilized with existing tire molds 30 or built into new
molds.
The pneumatic tire 12 has a pair of annular beads
2, at least one radial carcass ply 4 wrapped around
said beads 2, a belt reinforcing structure 8, a tread
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10 radially above a crown portion of said tire and
sidewalls 6 disposed between said tread 10 and said
beads 2. The tread 12 has lateral grooves 27. At
least some tread elements 22 defined by the
circumferential grooves 28 and lateral grooves 27 have
a chamfer on at least one side thereof on at least a
portion thereof in a shoulder region of the tread 10,
take placement of the chamfers 46 being determined by
the RCF or RSAT requirement of the tire 12.
In a preferred embodiment, the tire 12 according
to the invention has the chamfers 46 being about
2mm x 2mm or less more preferably about lmm x lmm and
the chamfers 46 extend inclined generally laterally a
distance of greater than 30% to 100~ of the lateral
extent of the tread element 22.
The preferred apparatus for forming the tire
according to the present invention includes a tire
mold 30 for modifying the residual cornering force or
residual self-aligning torque of a tire 12. The mold
30 has a molding means for molding treads. The
molding means has a plurality of recesses 38 for
forming tread elements 22, each tread element 22
having two or more edges 44. A plurality of the tread
element forming recesses 38 have one or more portions
150 for forming chamfered edges 46 along the edge of
the tread element 22 edges. Some of the chamfer
forming portions 150 are selectively removed for
modifying the residual cornering force or self-
aligning torque of the molded tire 12. In one mold 30
a majority of tread element forming recess are
initially fabricated having a chamfer forming portion
150 at one or more edges 44 of the respective tread
element forming recess. The preferred method is to
then choose predetermined chamfer forming portions 150
to modify the residual cornering force or residual
self-aligning torque and to remove the chosen
predetermined portions 150 of the mold such that
selected edges 44 of the tread elements 22 are
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partially or completely unchamfered. Preferably the
portions 150 are removed using a grinding procedure.
The chamfer portion 46 can extend circumferentially or
laterally or at any angle anywhere in between,
depending on the angle of the tread element. The
chamfer portion 46 as shown in Fig. 3 extends
generally laterally along the edge of tread element
22. For the purpose of this invention a chamfer
portion extends along an edge 44 of the tread element
22, the edge 44 being the intersection of a groove
wall and the ground contacting surface 48 of the
element 22. This chamfer portion can enable the tire
designer to alter or modify a tire's performance
without requiring a new mold to be built.
More particularly, in accordance with the present
invention, a method of molding a tire for modifying
residual cornering force of a tire includes the steps
of providing chamfering means in the mold interior
surface, measuring residual cornering force for tires
produced by the tire mold, comparing measured residual
cornering force for tires produced by the tire mold to
a specification range, and selectively removing some
or all of the chamfering means from the mold if
measured residual cornering force is outside the
specification range, thereby, removing the chamfering
of the tread elements of the tire, which alters the
RCF level of the tire.
According to another aspect of the present
invention, the chamfering means comprises an insert
insertable in the mold for chamfering an edge of a
tread of a tire.
According to another aspect of the present
invention, a method for modifying residual self-
aligning torque of a tire, the tire being molded by a
tire mold, the tire mold comprising a plurality of
recesses for forming a tire tread, the method
comprising the steps of measuring residual self-
aligning torque for tires produced by the tire mold,
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comparing measured residual self-aligning torque for
tires produced by the tire mold to a specification
range, providing chamfering means for chamfering the
tire tread produced by the tire mold if measured
residual self-aligning torque is outside the
specification range, and, chamfering the treads.
According to another aspect of the present
invention, an insert for use with a tire mold for
modifying residual cornering force or residual self-
aligning torque of a tire, the insert comprising afirst side and a second side, a chamfer edge, the
chamfer edge being disposed on the first side, and,
attaching means for attaching the second side to the
tire mold.
One advantage of the present invention is the
ability to modify rather than replace a tire mold to
adjust RCF and/or RSAT of a tire.
Another advantage of the present invention is to
reduce tire development costs by giving the tire
engineer the capability of placing chamfer inserts
into the tire molds, rather than replacing the entire
tire mold.
Another advantage of the present invention is
time savings derived from giving the tire designer the
capability of modifying existing molds, rather than
having to design, build, and receive new tire molds.
Still other benefits and advantages of the
invention will become apparent to those skilled in the
art upon a reading and understanding of the following
detailed specification.
Brief Description of the Drawings
The invention may take physical form in certain
parts and arrangement of parts. A preferred
embodiment of these parts will be described in detail
in the specification and illustrated in the
accompanying drawings, which form a part of this
disclosure and wherein:
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Fig 1 is a plan view of a portion of a tire tread
extending between a first tread edge and a second
tread edge;
Fig 2 is a cross-sectional view of a tire mold
for a tire 10 according to the invention;
Fig 3 is a plan view of the portion of the tire
tread illustrated in Fig 1 after application of the
invention and Fig. 3A is a cross section of the tread
taken along line 3A-3A of Fig. 3;
Fig 4 is an enlarged view of a portion of the
mold illustrated in Fig 2;
Fig 5 is a perspective view of an insert to form
the chamfer according to the invention;
Fig 6 is an enlarged view of a portion of a tire
mold utilizing a preferred embodiment of the
invention; and,
Fig 7 is a graph showing some experimental
results of tires incorporating the invention.
Fig 8 is a cross-sectional view of a tire 12
according to the present invention.
Detailed Description of the Invention
Referring now to the drawings, which are for
purposes of illustrating a preferred embodiment of the
invention only, and not for purposes of limiting the
invention, Fig 1 shows a portion of a tire tread 10
that stretches across a tire from the first tread edge
14 to the second tread edge 18. Grooves 27,28 in the
tread 10 channel water away from the contact patch to
improve traction on wet road surfaces. Between the
grooves 27,28 are tread elements 22 which extend
radially outwardly of the tread 10. The tread 10 has
sipes 26, or smaller grooves, to improve traction and
other tire performance parameters.
With reference to Figs 1 and 2, the tire 12 and
tire tread 10, is formed and vulcanized in the
conventional manner by molding the tire 12 in a tire
mold 30. The tire 12 is vulcanized within the mold 30
21~0771
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during the curing process.
One important and commonly monitored aspect of
tire performance is the magnitude of certain forces
and torques generated by rotation of the tire 12
against the road surface. Two of these are referred
to as "residual cornering force" (RCF) and "residual
self-aligning torque" (RSAT). Because these forces
and torques are well known in the tire art, only a
brief discussion will be made here.
Although the lateral forces generated by a tire
can be reduced to zero with respect to a forward
velocity vector at a small slip angle (called the
neutral slip angle), RSAT remains about the axis
vertical to the contact patch of the tire. At a slip
angle where self-aligning torque is zero, a lateral
force, RCF, exists and may cause the tire to drift in
a lateral direction. RCF or RSAT may be affected by
the shape and design of the tread 10. RCF or RSAT may
be reduced or increased by chamfering or otherwise
modifying certain areas of the tire treads elements
22.
Fig 2 shows a cross-sectional view of a schematic
of a tire mold 30. The right side of the tire mold 30
in Fig 2 is shown with a tire 12 mounted therein
while, for ease of illustration, the left side of the
tire mold 30 is shown without the tire 12. The
interior surface of the tire mold 30 is the negative
impression of the tire tread 10. Because the tire
mold 30 is the negative impression of the molded tire
tread 10, recesses 38 in the tire mold 30 form the
radially-protruding tread elements 22 in the tread 10.
Likewise, the protruding extensions 42 in the tire
mold 30 form the grooves 27,28 in the tire around the
tread 10.
RCF or RSAT may be adjusted and controlled by
chamfering or beveling certain portions of the tire
tread 10. Fig 3 shows a tire tread 10 with certain
edges 46 chamfered. The chamfering of the edges 46
2180771
can affect the RCF and/or RSAT levels in the tire. In
the specific tread configuration of Fig 3, chamfering
the edges 46 creates a negative shift in the tire RCF
and/or RSAT level. Tire treads 22 may be chamfered by
grinding the tire after unacceptable levels of RCF
and/or RSAT have been measured, but such grinding is
costly and time-consuming.
Tire RCF and/or RSAT can be modified by using a
mold with a modified tread pattern, but the design and
manufacture of a new tire mold takes a significant
period of time. This delay could idle expensive
production equipment and delay the delivery of the
finished product to the consumer. The invention
herein described eliminates both of these expensive
and time-consuming alternatives by providing a third
and fourth alternative. In the third alternative,
inserts 50 are placed within an existing tire mold to
modify the RCF and/or RSAT characteristics of a tire.
As illustrated in Figs 2, 4 and 5, the inserts 50 may
be mounted into a tire mold 30 using any acceptable
mounting means, including adhesives or mechanical
fasteners such as a bolt or screw 56.
With reference to Fig 5, a typical insert 50 is
shown. The insert 50 has a first side 64, a second
side 66 and a chamfer side 60. The chamfer side 60 is
the portion of the insert 50 which contacts the tire
tread 10 in the mold 30 during the curing process and
alters the shape of the tire tread 10. In the
preferred embodiment, the insert 50 includes a hole or
bore 70 through which an associated screw 56 or bolt
can be received for securing the insert 50 to the tire
mold 30.
Another important advantage of the invention is
the savings in tire development time. Also, the cost
of tire development may be reduced by a decrease in
hardware costs, such as the cost of a new tire mold
30. Finally, the tire inserts 50 may be used in tire
production molds 30 to slightly alter existing tire
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type production to bring production tires within
industry specifications for RCF and/or RSAT.
With reference to Fig. 4, the inserts 50 are
typically made of the same material as the mold with
which they are intended to be used. For example, one
preferred material for the inserts 50 is aluminum.
The angle ~ that the chamfer surface 60 of the insert
50 makes with the tire mold's surface 38 is chosen for
each tire application, but is generally between 40
degrees and 85 degrees. While the insert 50 has been
shown as mounted in the outermost recesses 38 of the
tire mold 30, inserts 50 can be utilized in any
portion of the tire mold 30, and inserts 50 can be
used in multiple recesses 38 of a tire mold 30 at the
same time.
With reference to Fig 6, in the fourth and
preferred alternative, the tire mold 30 is originally
produced with chamfering means for chamfering the
tread elements. The chamfering means takes the form
of mold portions 150 which are located in the tire
mold at points where a chamfer might be later
required. Preferably, a number of the edges of the
tire tread elements 22 are chamfered as the edges 46
in Fig 3. To adjust or modify RCF and/or RSAT,
selected mold portions 150 may be partially or
entirely removed from the mold by grinding the mold
portions 150 out of the tire mold 30 along dotted line
152. This has essentially the same effect of altering
the tire RCF and/or RSAT as adding inserts 50 as
described above, but is generally more efficient for
the tire manufacturing and development process.
In either inventive approach it will be
appreciated that the resultant chamfer portion 46 need
not and preferably does not extend to the full depth
of the tread element 22. The tread elements 22 when
new have a more flexible structure which is believed
to be a factor which can effect the RCF or RSAT more
dramatically when the tread is new and at full depth.
2180771
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As the tire 12 wears the effect of RCF or RSAT as it
relates to tread element flexibility is reduced.
Therefore, the chamfer portion 46 must perform its
modifying RCF or RSAT function most when the tread 12
is new. As the tread elements 22 wear down, the
chamfer portion 46 decreases in size to the point of
nonexistence. As this occurs, the ground contacting
surface 48 of the element 22 increases tending to
retard the rate of tread wear. This feature is
considered an important benefit on those treads 10
where the RCF and RSAT modification requirements
~;m;n;sh as a function of increased tread wear.
With reference to Fig 7, tires incorporating the
invention have demonstrated excellent results. In
Fig. 7, the term "CONT" refers to a control tire, the
term "OSSH" refers to the tire's outside shoulder, the
term ~TRAIL~ refers to the trailing edge of an
element, the term "LEAD" refers to the leading edge of
the element, and the term "RCF~ refers to residual
cornering force. The "y axis" of the graph lists the
force of the RCF in newtons. Experimental test
results utilizing a Goodyear Tire and Rubber Company
Eagle RS-A tires of size P205/55R16 tires are
illustrated. In each case discussed herein or
illustrated in Fig 7, the terminology is defined as
looking at a tire mounted on the right hand side of a
vehicle.
As illustrated in Fig 7, tread elements having no
chamfering was a control tire and generated RCF values
in the amount of about 30 newtons. The chamfers were
2 mm by 2 mm at an ~ angle of 45.
Tread elements having similar chamfering on the
tire's outside shoulder, trailing edge produced a
moderate negative shift in the RCF value in the amount
of 15 to 35 newtons.
Tread elements having chamfering on the tire's
inside shoulder, trailing edge produced a moderate
positive shift in the RCF value in the amount of about
21807~1
.
43 newtons.
Using a combination of the above chamfer
locations provides the capability to increase or
decrease the RCF or RSAT characteristics of the tire.
Tread elements having chamfering on the tire's
inside shoulder, leading edge produced a moderate
negative shift in the RCF value in the amount of about
30 newtons.
The above described test results, along with Fig
7, demonstrates that the invention is effective to
modify, either in the positive or negative direction,
a tire's RCF values.
With reference to Fig 8, a tire 12 of the present
invention is shown in cross-section. The tire 12 has
a pair of annular beads 2, at least one radial carcass
ply 4 wrapped around said beads 2, a belt reinforcing
structure 8 radially outward of the at least one ply
4, a tread 12 radially above a crown portion of said
tire 10 and sidewalls 6 disposed between said tread 12
and said bead 2. The tread 12 has circumferential
grooves 28 and lateral groove 27 defining tread
elements 22, at least some of the tread elements 22
have chamfers 46 which are employed to modify the RCF
or RSAT requirements.
The invention has been described with reference
to the preferred embodiment. Obviously, modifications
and alterations will occur to others upon a reading
and underst~nA;ng of the specification. It is
intended by applicant to include all such
modifications and alterations insofar as they come
within the scope of the appended claims or the
equivalents thereof.
Having thus described the invention, it is now
claimed:
