Note: Descriptions are shown in the official language in which they were submitted.
046390 -1-
' :
This invention relates to pneumatic tires and
more particularly to an impro~ed tire construction for
obtaining increased tread li~e in relation to the tread
life o~ a standard type of tire. The invention is appli-
cable to ~uch vehicles as cars, buseæ or the like.
A radial carcass pneumatic tire having a rein-
forcement belt and a tread that, in cross-section, is
substantially in the shape o~ a curved trapezoid normally
makes complete contact with the ground over substantially
the entire cross-sectional width of its tread. Such a
tire can be characterized as one of u~ual, standard or
ordil.ary configuration.
When a standard pneumatic tlre is mounted on a
wheel that is load bearing but is not being steered, as
on the rear wheel of an automobile or truck, the tread
layer is normally worn in a substantially even manner
across the entire tread width. Thus the cross-sectional
8hape o~ the tread layer, as it gradually wears down,
~ubstantially corresponds to the cross-sectional shape of
` 20 the tread in its unworn state.
A standard tire having a tread that is evenly
worn to a theoretical maximum allowable wear depth generally
attains an optimum distance endurance. One known stan-
dard tire, ~or example, has an optimum distance endurance
o~ approximatel~ 100,000 kllometers (62,500 miles)
corresponding to the theoretical maximum allowable wear
depth o~ itæ tread.
However, when a standard pneumatic tlre is mounted
on Q steered wheel, æuch as a ~ront wheel of an automobile
or a truck, the tread layer is generally worn unevenly
~b~
10 46 39 -2-
across its entire crosæ-sect~onal wldth, with wear at the
lateral shoulder areas be~ng more pronounced than at an
intermediate portion between the shoulders. Shoulder
wear i8 thus accelerated in relation to wear at the median
portion of the tread, which tends to wear in a slo~er and
substantially more even manner. This pattern of wear is
attributable in part to the behavior of the pneumatic
tire in turns or ln curves when the angular orientation
of the steered wheel varies with respect to a fixed
axis such as a wheel axle. As a consequence the maximum
allowable wear depth ls often reached in the shoulder
areas before such wear occurs in the median portion of
the tread. It is thus necessary to replace the pneumatic
tire while it still has a considerable residual amount of
theoretically useable ~read such as approximately 40% un-
used residual tread material. Moreover, the distance
endurance of a pneumatic tire having uneven wear is pro-
portionately reduced in an amount that corresponds with
the residual amount of theoretically useable tread. For
example the distance endurance of the known standard tire
having 40% unused residual tread is approximately 60,ooo
kilometers (37,500 miles).
Another undesireable result of uneven tread wear
ls that a retreading operation usually requires removal
of the residual amount of theoretically useable tread
layer by rasping, grinding or other similar stripping or
abrading procedure. Such an operation is tedious and
c06tly Therefore, a tire that is worn unevenly not only
provide3 less distance endurance than a tire having uni-
form even wear but requires a more costl~ retreading
. .
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10~6390
operation,
It is thus desireable to minimlze or eliminate
uneven tread wear in tires.
A primary ob~ective of the present invention ls
to provide a novel tire constructlon wherein a ma~or por-
tion of the tread material in the lateral shoulder areas
of a standard tire that experiences accelerated wear is
eliminated to provide a pro~ecting median tread portion
of the tire that wears evenly on a steered or unsteered
wheel and permits optimum use of the tire to the maximum
allowable depth of the tread layer, Other ob~ects and
features will be in part apparent and in part pointed
out hereinafter,
The pneumatic tire of the present invention is
characterized by a tread layer having a median ground con-
tacting portion pro~ecting radially beyond opposite
lateral shoulder portions in step-like fashion. The croæs-
uise width of the median pro~ecting portion substantially
corresponds with the crosswise width of the evenly worn
median portion of a ætandard tire mounted on a steered
wheel. The opposite lateral shoulder portions are sub-
stantially symmetrical to an equatori~l plane of the
tire and do not normally contact the ground while there
ls useable material in the median tread portion of the
tire.
The 8hape of the median portion, in cross-section,
i8 substantially that of a curved rectangle or trapezoid
and pro~ects beyond the shoulder portions by an amount
equivalent to at least a predetermined theoretical maxi-
mum allowable tread wear depth of a standard tlre,
10~6390 'I
Preferably the lateral shoulder portions have a pre-
determined minimum allowable amount of tread material
covering the reinforcing belt. This construction per-
mits substantially uniform even and complete wear of the
total available useable amount of the tread regardless
o~ whether the tire is mounted on a steered or unsteered
wheel, because it allows a substantially uni~orm even
wear of the protruberant median portion of the tread.
The amount of material in the median tread por-
tion can vary from any given amount of unevenly worn
tread material on a standard tire to the theoretical
maximum useable quantity o~ tread material on the stan-
dard tire. Aæ a practical matter, a concentration o~ the
entire theoretical useable tread material of a standard
tire in the median tread portion of the present tire
would sub~ect the tread to excess heat-up through intra-
molecular friction of the rubber and result in acceler-
ated wear. Preferably the pro~ecting median portion has a
tread thickness that i8 substantially the same as that of a
standard tire and a crosswise width approximately 60% as
wlde as that of a standard tire. Therefore, the volume
of the pro~ecting median tread portion of the present
tire is generally less than:the volume of the theoretical -
maximum useable quantity of tread in the standard pneu-
matic tire.
Since the distance endurance of a standard tire
sub~ect to uneven wear substantially corresponds to an
ascertainable volume o~ worn away tread, the present
tire will attain at least an equivalent distance endur-
ance when the ascertainable volume of tread is
--4--
,.
104~390
concentrated in the protuberant median tread portion.
The distance endurance of the present tire is
extended in a further embodiment by enlarging the lateral
shoulder portions in a substantially axial direction, so as
to pro~ect beyond the outside sidewall surfaces, and by
extending opposite side edges of the reinforcement belt into
the two projecting shoulder enlargements. The crosswise width
of the median projecting portion is also enlarged. The
resulting arrangement ser~es to stiffen the tread in the lateral
1 n direction thereby improving the skid strength around curves
and promotes even wear of the projecting median tread portion on
a steered wheel.
Preferably the lateral shoulder portions connect to
the projecting median portion of the tread through a pair of
continuous circumferential grooves which constitute flexible
articulate links between the respective shoulder portions and the
pro~ecting median portion of the tread. The grooves, in cross-
section, are wider than any grooves in the median pro~ecting
portion and have at least the same radial depth as the groo~es
in the median portion.
In accordance with one broad aspect, the invention
relates to a pneumatic tire having opposite sidewall and an axis
of rotation, including in cross-section, a carcass, a tread
having a pro~ecting median portion intermediate said sidewalls
with a ground contact surface, opposite lateral recessed portions
discontinuous from said ground contact surface and normally
unengageable with the ground, said lateral recessed portions
extending from said median portion to respective said sidewalls,
a reinforcing belt disposed between said tread and said carcass,
first and second axially directed protuberances at the sidewalls
of said tire extending from the lateral portions to approximately
88~ of the maximum cross-sectional width of said tire, said
~ .b
~ -5-
104~390
median portion having a crosswise width approximately 62~ the
crosswise width of said tire between said axially directed
protuberances and wherein said reinforcement belt has opposite
end portions extending into said axially directed protuberances.
The invention accordingly comprises the constructions
hereinafter described, the scope of the invention being
indicated in the ~ollowing claims.
In the accompanying drawings in which various possible
embodiments o~ the invention are illustrated;
Fig. 1 is a ~ragmentary sectional view of a known
standard pneumatic tire;
Fig. 2 shows the tire of ~ig, 1 with lateral ~; ;
shoulder portions of the tread recessed to provide a relatively
narrow projecting median portion;
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.
10463~0
--6--
Flg. 3 shows a tire similar to that of Fig. 2 w~th
an enlarged median portion, pro~ecting shoulders, enlarged
reinforcement belt and a superimposed dotted outline of
the tire of Fig. l; and,
Fig. 4 is a view similar to Fig. 3 showing a modi-
fied tread and belt construction.
Corresponding reference characters indicate corre~
sponding parts throughout the several views of the drawings.
Referring now to the drawings, Fig. 1 in parti-
cular, a standard pneumatic tire generally indicated by
reference number 101 comprises a radial carcass 102 and a
reinforcement belt 103. The reinforcement belt has a
width c in cross-section and includes a plurality of indi-
vidual plies disposed between the crown of the carcass
102 and a tread 104 having a width b in cross-section.
Indentations formed in the tread 104, such as a pair of
grooves 105, are substantially symmetrical with respect to
a median equatorial plane 106 of the standard tire 101.
The maximum allowable wear depth of the tread 104
i8 indicated at 107. When the standard tire 101 is mounted
on an unsteered wheel of a heavy duty vehicle, such as
a rear wheel, the tread 104 generally wears in a substan-
tially even manner, Even wearing of the tread 104 can
occur, ~or example, from a peripheral rolling contact sur-
face 108 to the maximum allowable wear depth limit 107.
This zone of even wear is of generally curved trapezoidal
~hape indicated by the reference number 109 and the letters
AEFD. The even tread wear zone AEFD represent~ the theo-
retical maximum u~eable area of the tread 104, and
corresponds to a distance endura~ce o~, for example,
--6--
1 0~6 39 _7_
100,000 kilometers t62,500 miles).
~Jhen the stan~ard tire 101 16 mounted on a
steered wheel, such as a front wheel of a heavy duty
vehicle, the tread 104 ususally wears in a substantially
uncven manner. A typical uneven tread wear pattern is
indicated by the widely spaced cross-hatched area 110,
defined by the letters ABCDFE, representing material
that is unevenly worn away, and the densely cross-
hatched area 111 defined by the letters ABCD and the line
107, representing unused residual material. As a result
of uneven tread wear, the sidewalls at A and D are worn
to the maximum allowable depth 107 while there is still
a substantial amount o~ unused residual material 111.
Thus the tread wear is accelerated at the sidewalls in
relation to other portions of the tread 104.
On the average, an unevenly worn tire requires
replacement after only 60% of the available tread has
been worn. The distance endurance of the tire 101 cor-
responding to such uneven tread wear is, for example,
approximately 60,000 kilometers (37,500 miles - corre-
sponding to the zone ABCDFE) and represents a loss of
approximately 40,000 kilometers (25,000 miles - corre-
sponding to the zone ABCD and the line 107) in compari-
son with the distance endurance of the tire 101 when
sub~ected to e~en wear.
It will be noted that the unevenly worn away
area 110 (A~CDFE) comprises a median portion BCKJ that
i8 substantially o~ a curved rectan~ular or trapezoidal
shape evidencing substantially even wear over a cross- ~-
wise width a. The unused residual portlon 111 comprises
-7-
-, . -. . . , , . . ~
. .
.
1046390
--8--
a median portion BCGH that is also substantially of a
curved rectangular or trapezoidal shape and has a cross-
wlse width a ldentical to the portion BCKJ in the tread
portion 110. The residual portion 111 also includes
curved triangular portions ABH and DCG, which include
generally acute angle portions at A and D respecti~ely.
Referring now to Fig. 2, a tire lOla includes a
median portion 112 of tread 104' having a ground contact
surface 108~ pro~ecting beyond opposite recessed
lateral portions 113 and 114, The pro~ecting median
portion 112, deflned by the letters GHJ'K', is sub-
stantially of a curved trap~oidal or a curved rectangu-
lar shape in cross-section and has a crosswise width a
identlcal to the curved rectangular central portions
BCKJ and BCGH of Fig. 1, Preferably the pro~ccting
medlan portlon 112 ls of substantlally identical thick-
ne~s as the standard tread 104 and represents an accum-
ulatlon of substantially all the materlal in the uneven
tread wear zone 110 (ABCDFE) of the standard tire 101,
which corresponds to a distance endurance of 60,000
kilometers (37,500 miles) when the tlre 101 is unevenly
i worn.
The recessed lateral portionæ 113 and 114, whlch
colnclde with the llne 107 and do not contact the ground,
are deflned by the letters AH and DG and form obtuse
angles with the portlons HJ' and GK' of the pro~ecting
median portlon 112.
Since the crosswise width a of the median portion
112 (GHJ'K') is identical to the crosswise width _ of
the evenly worn portion BCKJ of a standard tlre mounted
-8-
. .
1046390 9
on an unsteered wheel, the median portion 112 wears sub-
stantially evenly and substantlally completely to the
maximum allowable wear llmit 107, whether the tire lOla
iB mounted on a steered or unsteered wheel. Complete
use of the pro~ecting median portion 112 to the line
107 corresponds, for example, to a distance endurance
of approximately 60,000 kilometers (37,500 miles). If
desired the concentration of rubber in the projecting
portion 112 can be increased beyond that o~ the portion
GHJK of Fig. 1 by providing groo~es 105' (Fig 2~ that
are narrower than the grooves 105 in Fig. 1, but have
the same depth.
The full shoulder area of a standard tread, such
as 104 in Fig. 1, having a radial thickness corresponding
to the pro~ecting portion 112 and a width b in cross-
section, is shown in dotted outline on each slde of the
proJecting portion 112. The cross-sectional width _ of
~ the proJecting central portion 112 is approximately 60%
i o~ the cross-sectional width b of Q standard tread 104,
; 20 and the cross-sectional width c of the rein~orcing belt
103 is approximately 90% of the width b. The width a of
the central portlon 112 is thus approximately 2/3 the
width c of the reinforcing belt 103. These relationships
are set forth below:
a . 60% b
c = 90% b
a ~ 2/3 c
It wlll be noted that in the standard pneumatlc
tire 101 of Flg. 1 the ground contact surface 108 extends
~ 30 beyond the extremltles of the reinforcement belt 103.
., .
_g_
. - . , . ~ : ~.
~0~6390
-10-
The stresses imposed on the tread during mo~ement of the
tlre sub~ect the edges of the belt 103 to continuous
movement and heat-up, and at high speeds, to eventual
separation from the tire carcass 102.
However in the tire lOla o~ Fig. 2 the median
pro~ecting portion 112 generally receives the greatest
magnitude of stresses due to rolling contact between the
tread 104' and the ground. The extremities of the rein-
forcement belt 103, belng remotely posLtioned beyond the
lateral limits HJ' and GK' of the median pro~ecting por-
tion 112, are therefore affected to a lesser extent by
the rolling contact stresses than the pro~ecting por~ _n
112.
Referring now to Fig. 3, a tire lOlb includes an
enlarged pro~ecting median portion 117 comprising the
portion 112 (GHJ'K') and lateral enlargements 115, 116
respectively defined by LMJ'H and PNK'G. The enl&rged
proJecting median portion 117, defined by the letters
PI.~, has an overall cross-sectional width a' that is
approximately 79% of the width b of the standard tread
104. Moreover, the pro~ecting median portion 117 is
approximately 25~ larger in cross-section than the portion
112 and affords the tire lOlb a 25% increase in distance
endurance over the tire lOla to extend the useful li~e
of the tire lOlb to approximately 75~000 kilometers
t46,875 miles) until the portion 117 is completely worn
:. to the line 107 of maximum allowabIe depth.
: The tire lOlb also includes laterally pro~ecting
shoulders 118 and 119 constltuting enlargements of the
recessed lateral portlons 113 and 114 of Fig. 2 along the
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1046390
-11-
line 107 by amounts AA' and DD' respectively. me
lateral portions 113 and 114 are inclined at an angle
alpha (o~) measuring between 0 and 20 with respect
to the axis of rotation of the tire lOlb in its inflated
and unloaded state. The projecting shoulders 118 and
119 provide the tire lOlb w~ith an overall width b' at
the line 107 of maxlmum allowable depth representing ap-
proximately a 27% increase in width over the width b of
the standard tire tread 104 in Fig. 1. The width b' is
approximately 88% of the maximum overall width of the
tire. In accordance with the foregoing relationships
the width a' is approximately 62% of the width b', and
the width a is approximately 47~ of the width b'.
A reinforcement belt 103' in the tire lOlb has
opposite edges extending into the projecting shoulders
118 and 119. me cross-sectional width c' of the belt
103' is, for example, 27% wider than w~idth c of the belt
103 in Fig. 1, 45% wider than the cross-sectional width
a' of the pro~ecting central portion 117, and approxi-
mately 10~ shorter than the width b' of the tread 104'.
The laterally pro~ecting shoulders 118 and 119,
and the enlarged reinforcement belt 103 extend the dis-
tance endurance gain of the tire approximately 5% to a
useful liie of approximately 80,000 kilometers (50~000
miles).
The elevation or radial thickness of the pro-
~ecting median portion 117, indicated by el, is measured
between the ground contact surface 108' and the line 107
of maximum allowable wear. Although the thickness of the
tire lOlb at the equatorial plane 106 is substantially
--11 -
'
10463~0 -12-
equivalent ~co the thickness of the standard tire 101 at
~aid plane, it ls feasible to provide the tire lOlb with
approximately 4% greater thickness at the plane 106. A
predetermined minimum allowable material thickness e2
covers the extremities of the belt 103' in the shoulder
area, whereby the overall material thickness el + e2 in
the median portion of the tire lOlb over the belt 103 is
indicated by h.
Referring now to Fig. 4, a tire lOlc include~
circumferential grooves 120 and 121 ~oining the pro~ect-
ing central portion 117 to the respective recessed
lateral portion 113 and 114 to ~orm an articulate flexi-
ble connection therebetween.
The radial thickness el of the pro~ecting central
portion 117, which corresponds to the m~ximum allowable
wear limit depth, is measured between the ground contact
~urface 108' and a maximum allowable wear limit line 107
de~ined along a curved line tangent to the bottom of the
articulation grooves 120 and 121. The minimum allowable
ma~erial thickness e2 covers the extremities of the belt
103' in the shoulder area~ 113 and 114, and a material
thickness e3 in the median portion of the tire between
the belt 103 and the pro~ecting portion 117 provide an
overall thickness hl = el + e3 in the median portion of
the tlre lOlc over the belt 103. It will be apparent that
i8 0~ lesser magnitude than h in Fig. 3 because e3 is
of lesser magnitude than e2.
The rate at which a tread wears i8 often a ~unction
of the distance between the tread and the reinforcement
belt. Generally the ability of a tire to resist skidding
-12-
. ~ .
104~3~30 -13-
increases as the distance between the belt and the tread
decreases to h minimum allowable distance. Moreover, a
reduced amount Or rubber between the belt and the tread
provides a cooler running tire because there is less
heat produced by intramolecular fric~on during movement
of the tire. Tread wear is thus reduced because the
resistance to skidding increases and less heat is gener-
ated within the tire.
It is therefore desireable to provide the smallest
allowable thickness between the tread and the reinforce-
ment belt 103'. Thus, the embodiment of Fig. 4 is
preferable to the embodiment of Fig. 3 because e3 is less
tha~l e2 ~d hl is less than h.
The inclination of the lateral portions 113 and
114 at an angle alpha ~oC ) helps reduce deformation of
the pro~ecting central portion 117 and the pro~ecting
shoulders 118 and 119.
Although the reinforcement belts 103 and 103' are
: ~hown aa having three ply layers, any feasible number of
plles can be uæed. For example, a fourth ply of approxi-
mately 44~ the width of c' can constitute the radially
extreme outer ply layer. The position of the lateral
edges of the fourth ply layer will affect the flexibility
of the tire at the articulation grooves 120 and 121.
T~erefore theæe edges æhould be o~ lesser axial extent
than the articulation grooves 120 and 121 to avoid the
: possibility of cracks forming at the articulation grooves.
Preferably the fourth ply layer should not pro~ect axially
beyond the articulation grooves to maintain the flexi-
bility thereof.
13
,.
046 39 0 -14-
During construction of a tire having a reinforce-
ment belt one or more of the belt plies may shift slight-
ly in localized areas with respect to the equatorial
plane of the tire. The amount of off-center shift can
vary at different locations around the tire circum~erence.
A belt ply that is cut unevenly prior to its installation
in the tire can also be considered off-center.
In a standard pneumatic tire where the reinforcing
belt is generally of lesser width than the ground con-
tacting tread surface, the off-center defects can affect
the roundness of the tire and cause excess variations
in lateral and vertical forccD on the tire during its
movement on the ground. These force variations lead
to meander~ng and squirm which result in vibrations,
deviatlons, deflections and skidding of the tire.
However, in the present tire construction the
effects of the off-center defects attributable to the
reinforcement belt are now localized in the lateral
~houlder portions where there i8 no ground contact~ng
tread area. Consequently, any off-center defect~ ha~e
a lesæ harmful affect on the road holdine ability of the
tire, even at high speeds, resulting in less meandering,
squirm and vibrations, etc. Reaction force variations
are thus reduced, especially lateral forces, thereby mini-
mizing the rolling resistance of the tire ~nd permittlng
a vehicle incorporating said tires to achieve a greater
fuel economy.
For example, in a standard tire the lateral force
was found to vary by approximately 30 to 35 kilograms
around its average value, and the vertical force was
-14-
-15- 1046390
found to vary from approximately 90 to 130 kilograms
around its average value. In the present tire, corre-
sponding vQriations were respectively 11 to 20 kilogr~ns
with regard to the lateral force and approximately 60
to 108 kilograms in the case of the vert~cal force.
Maneuver~bility of a vehicle employing the tires of the
present invention is thus facilitated.
The following temperature measurements show the
relative heat-up characteristics of a standard tire
incorporating the present invention.
TEMPERATURE TEST
Measurement Zone
On the TireStandard Tire Present Tire
Crown, Equatorial
Plane 93C 90C
Shoulder 110C 101C
Belt Extremities 110C 80C
The test results indicate approximately 8% cooler
temperatures at the lateral shoulder portion and approxi-
mately 27% cooler temperatures at the extremities of the
reinforcement belt in a tire of the present invention.
The following set-up was used to evaluate the
relative load endurance of a reinforcing belt in a stan-
dard tire and the reinforcing belt of the present inven-
tion. On a wheel rim having a diameter of 1,6 meters
there are placed three bars of a thickness of 19 millimeters
angularly spaced apart by 120 with respect to one
another, one of the bars being oriented parallel to the
axi6 of the wheel while the other two bars form a 45
~ngle with said a~is. The wheel is rotated at a
-15-
-16- 104~390
peripheral linear speed of 60 kilometers per hour (37.5
mlles per hour). The tests ~Jere performed on two radial
carcass pneumatic tires of a size of 10.00 R 20 inflated
to a pressure of 6 bars and mounted on a 20 x 7.33 V rim,
one of ~hich was a standard tire acting as a control
whereas the other was a tire incorporating the present
invention. Each tire was sub~ected to a load of 1500
kilograms with the load being periodically increased by
200 kllograms every 24 hours. On the standard tire it
was noted that a separation of the belt extremities
occurred between 168 and 192 hours of testing, correspond-
ing to a load of approximately 2700~kilograms. In the
tire of the present invention the belt extremit~es
separated after a test period o~ 260 hours which corre-
sponded to a load of approximately 3500 kilograms.
Some advantages of the present in~ention evident
from the foregoing description lnclude a tire wherein
wear of the tread i8 llmlted es~entially to lts median
portlon and is at all times uniform or even to per~-~t com-
plete wear and the attainment of a distance endurance
corresponding to such complete wear. Since the shoulder
portions do not ordinarily touch the ground they are not
subJect to any appreciable wear, and are les6 prone to
heat up during movement of the tire because they contaln
a relatlvely reduced mass of rubber, are not sub~ect to
the buckllng stresses that occur during contact of the
tread with the ground and are sub~ect to improved cool~ng
through the alr currents that envelop each recessed lateral
portion. Because of the reduced heat-up and wear ln the
lateral shoulder area there ls a correspond~ng increase
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,
.
-17- iO46390
in fuel econo.~y for a motor vehicle incorporating tires
of the present invention.
Travelling comfort is improved because the lateral
pro~ectlng shoulders can elastically flex without con-
tacting the ground thereby providing an elastic suspen-
sion effect. Driving a vehicle incorporating the present
tire also becomes an easier task because the reaction to
steering is smoother resulting in easier handling of the
steering wheel. Moreover high speed driving can be
accomplished with greater assurance of saPety due to
improved security against belt separation at the outer
ed~
In view of the above, it will be seen that the
~everal ob~ects of the invention are achieved and other
advantageous results attained.
AB various changes could be made in the above
constructions without departing from the scope of the
invention, it is intended that all matter contained in
the above description or shown in the accompanying draw-
ings~shall be interpreted as illustrative and not in a
ll~ltln_ sense.
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