CA1057636A - Pneumatic tire - Google Patents

Abstract

ABSTRACT

A pneumatic tire having a reinforcement belt dis-posed between a tread and a carcass includes a projecting median tread portion and lateral recessed tread portions.
The tire can also include in cross section, first and second axially directed protruberances at the sidewalls extending from the lateral recessed portions, with extremities of the reinforcement belt extending into the protruberanres. The projecting median portion of the tread is connected to the lateral recessed portions through a pair of continuous circumferential grooves which constitute flexible articulate links between the respec-tive lateral portions and the projecting median portion.

Description

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; This inYentlon rel~te~ to pneumatlc tires and more partlcularly to Qn impro~ed tire construction for obtaining increased tread llfe in relation to the tread e of a standard type o~ tire. The invention is appli-cable to su~h vehicles aæ cars~ buses or the like. I
A radial carcass pneumatic tire having a rein- ~-~orcement belt and a tread thatg ln cross-section, ~s substantially in the shape o~ a curved trapezoid normally ¦
makes complete contact with the ground over subst~ntially the entire cross-~ectional width of its tread. Such a tire can be characteri~ed as one of usual, standard or ¦~
ordinary confi~uration.
When a standard pneuma~ic t~re is mounted on a :.
, wheel that is load bearing but is not being steered, as : .
.¦ 15 on.*he rear wheel.of an automobile or truck, the---tread :1 layer ~s norm~lly worn ln a substantlally e~en manner across the entire tread w~dth. Thus the cross-æectional ~J ' fih~pe 0~ ~he tread l~yer~ a~ it gradually wears down, ~ substan~ial1y-corresponds to the-cross-sec~ional shape o~
;1 20 the tread-in~its unNorn ~ate.
il A ~tandard:-tire:h~ing a tre~d~-that-is-:eve~ly.
..
worn to a theoretical- maximum ~lowa~le-~ear depth generall~r .~ attain~ an optimum- di6t~ce endura~ce. One known-~ an-~i dard tire~ ~o~-exa~le~ as an~p-t;~ d~s-~-a~ee--endurGnce ~;
-~. 2~ of approx:tmatel~ lOO,ûOO-k~lometers ~62,500 miles) correspondin~;-to.~he.theore~ical max~mum allowable-wear -A i dep.th o~ it~ -tread. -Ho~ever,. w}len a.siGalldard pneuma~c *lre-i~ mou~ted cn a ~teere~-~he~l,~such~a~ a front wheel ~ ~L.autc~mobile :
or- ~--*ruck, -~he - tread -layer-ls -:geIIe~ally -ws~ =une~ ly ;~
. ~ ~
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~2- ~5763~

across lt6 entire cross-~ectional width, with wear at the ~ :
. lateral shoulder areas being more pronounced than at an intermediate portion between the shoulders. Shoulder , wear is thus accelerated in relation to wear at the medlan portion o~ the tread, whlch tends to wear in a slower and subst~ntially more even manner. This pattern of wear is attributable in part to the beha~ior of the pneumatie tire ~n turns or in ~urves ~hen the angular orientation . o~ the steered wheel varies with respeet to a fixed axis such as a ~heel axle. As a consequence the maximum allowable wear depth is often reached in the shoulder -~
areas be~ore such wear occurs ~n the median portion of the treadO It is thus necessary to replace the pneumatic ~ '.
tlre while it ~till has a considerable residual amount of theoretically useable tread such as approximately 4 ~ un- ;
used residual tread ma~erial. Moreover, the distance ~1 endurance of a pneumatic tlre ha~ing uneven wear i~ pro--`~ port1onately reduced ln an amount *hat correspondsi with .
the resldu 1 amoun~ o~ theoreticall~ useable tread. ~or ~ 20 example the distance endurance of the known ~tandard-tire :1 havlng 4 ~ ~nu~ed--re~idual tread ~ approx-imately 60-~000 kllometer~ 37,500 miles).
Another unde8~reable result-of une~en tread-xear- -- -~
iB ~hat;a-re~reading.opera~ion ~ually re~uires remo~al of the re~idual amount--~-theoretically-u~eable tread layer by rasping, grinding or other simllar stripp~ng or abradng procedure. Such an-operation-~ tedlous a~d~
co~tly. There~ore, a ~ire_*hat iB ~orn-un~Yen3y not~ly - ---pro~des less- dl~ta~c~ nduranc~ ~ ~a t~re---hasr~ng--w :i 30 - ~orm- ~e~ren -~ar but r~Quir~ a -more- co~tly retreading-- - ' -", . ~

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ope.r~tion. '~
It iZ3 thus desireable to minimize or eliminate : uneven tread wear i.n tires.
v A primary ob~ective of the present lnvent~on i~
to pro~ide a novel tire constructlon whereln a ma~or por- ~
t~on o~ the tread material in the lateral shoulder areas ~ :
o~ a standard tire that experlences accelerated wear is eliminated to provide a pro~ecting median tread portion of the tire that wears evenly on a steered or unsteered ` ::
~ 10 ~heel 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 ap~ent and in part pointed -out hereinafter. .
The pneum~tic tire of the present invention is :
~ 15 characterized by a tread l~yer having a med~n ground con-;Z tacting portlon pro~ecting radially beyond oppos~e ter~l shoulder ~ortions ~n step-like fa~hion. ~he cross-wise width of ~he median pro~ecting portion substant~ ~lly $~ corresponds wlth the cros~wise w~dth of the evenly worn ~;' 20 median-portion of a ~tandard-tire mounted on a steered wheel. The opposite lateral shoulder portions are sub-Z ~ta~tially symmetrical to an e~uatorlal plane of the ;~
t~re ~nd do not- normall~r-contact the ground while there 1~ useable-material-in the median tread portion of the ,.¦ 25 t~re.
`J ~he shape of the median portion, in croæs-sect~on, :
3 ~' ~
u~stantii~l-ly that o~ a cur~red rectangle or tr~pezoid ::.
!, and pro~ects--beyond the ~houlder portion~ by ~Ln ~wun~ :~
¦ e~u-~valent- to at least a predeterm~ned theoretical maxi- ~
30-~ allowa~e ~-read wear depth ffl a 6tandard tir~, - :.~ , . . - .
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-4- lV5763~ ~ ~

Preferably the lateral shoulder portions have a pre-determined minimum allowable amowlt of tread material covering the reinforcing belt. This construction per- .
mits substi~nti~lly un~form e~en and complete wear of the j totiRl available useable amount of the tread regardless of ~hether the tire is mounted on a isteered or unsteered wheel, because it allows a substantially un~orm even 11 :
wear of the protruberant median portion o~ the tread. I --- The amount o~ material in the median tread por-tion ci~n vary from any given amount o~ unevenly worn tread material on a s~andard tire to the theoreticial i maximum useable quantity o~ tread material on the stan-`, dard tire. As a practical matter, a concentration o~ ~he : ' entire theoretical useable tread material o~ a standard 3 15 tire in the median tread porticn of the present tire wou;d ~ubject the tread to excess heat-up through intra-mole~ular frlction o~ the rubber and result in acceler-ated wear. Preferably the projecting median portion has a i tread thic~ness tha~ is substantia1ly the same as that o~ a standard tire and a cross~ise width appro~imately 60~ ~s wide a~ that of a standard tire. There~ore, the ~olume of the pro~ecting median tread portion of the presen~
tlre is generally less th~n~the volume of the theoretical maximum useable quantity Or ~resd in the standard pneu-~ 25 m~tic tire. `
;1 S~nce the distQnce endurance of 2 standard t~re ', sub~ect to une~en wear substAntially corre~ponds to an ~certainable ~olume Or worn a~ay tread~ the pre~ent tlre~will a~tain a~ lea~t an equ~a~ent di~tance endur-~nce-~hen the-ascertain&bl~ Yol~me of~tread 1~
'1 .
.,~ .
~, :3LU157636 concentrated in the protuberant mediarl tread portion.
The distance endurance of the present tire is exten~ed in a further embodiment by enlarging the lateral shoulder portions in a substantially axi~al directIon, so as to project beyond the outs~de sidewall surfaces, and by extending opposite side edges of the reinforcement belt into the two projecting shoulder enlargements. The crosswise width o the ' median projecting portion is also enlarged. The resulting ':
arrangement serves to stiffen the tread in the lateral _ 10 direction thereby improving the skid strength around curves and promotes even wear of the projecting median tread portion .~1' on a steered wheel.
'`'.~. Preerably 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 , ,;
~:i .
and the projecting median portion of the tread. The'grooves, :
:::
in cross-section, are wider than any grooves in the median ,:

, projecting portion and have at least the same radial depth as : '~:~ , ::
,~ 20 the grooves in.the median portion. ~ .' ' In accordance with one broad aspect, the invention '.'' relates to a pneumatic tire-having sidewalls ~nd an axis o~ ;

,;',1 rotation including, in cross-section, a carcass, a tread having .'.

~ , a projecting median portion intermediate said s~dewal'ls with a ,,.il - ground contact surace, opposite lateral portions discontinuous ;,:

from said ground contact surface and extending from said median ~', ' portion to the respective said sidewalls and a reInforcing belt ~

~.; ~ disp~sed between sa~d tread and-~sa~-car~ass, the-improvement ..

mpE-ising ~ -f ist- and-second--axially,dir,ected,.protuberances at s ~
the sidewalls of said tire extending from the'lateral portions, : ~.

.'-', the -reinforaing b~lt hav~ng,.opposite.edge port~ons ext~nding .-. into the axia~ly d~re~ed.protuberances, said opposite la~eral ~ :
~ ' ~

~ 5- ~
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portions being recessed from the ground contact surface in step-l~ke fashion and wherein the lateral recessed portions respectively include a free surface spaced from the edge portions of said reinforcing belt by a predetermined min~mum allowable thickness of tire material, and the projecting median port~on of said ¢~read ~s connected to said lateral recessed portions by circumferential grooves of uniform width that form an articulate link between said median portion and said respective lateral recessed portions said grooves having a common arc of tangency at a radially innermost port~on of said grooves, said arc continuing below the free surfaces of the lateral portions such that a maximum allowable wear aepth of said projecting median portion is along sai~d common arc of . . .
- tangency.
~, The invention accordingly comprises the constructions hereinafter described, the scope of the invènt~on ~eing indicated in the following claims.
: ;~-;. .. ~
¢ In the accompanying drawings in which various possible `~

i embodiments of the invention are illustrated: I

' 20 ~ig. 1 is a fragmen~ary sect-ional view of a known ¦ standard pn umatic tire; ~ `

1 Fig. 2 shows the tire of---Fig. 1 with lateral--shoulder : :i : :
portions o~ the tread recessed to provide a relatively narrow projecting median portion; ;~
`~ ~' : .
, i 1 30 _ ', ' i . .

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-6- iO57636 ~

Flg. 3 shows a tire similar ~o that of Fig. 2 wlth I
,an enlarged median portion, pro~ecting shoulders, enlarged I :
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 ind~cate corre~ , ~ sponding par~s throughout the several ~iews o~ the drawings. ~ , '- Referring now to the drawings, Fig. 1 in part~- :
' 10 cular, a standard pneumat~c ~ire generally indicated by ', reference number 101 comprises a radial carcass 102 and a ':, , reinforcement be~t 103. The reinforcement belt has a ~
~'-' width c in cross-section and includes a plurality o~ indi- ~, vidual plies disposed between the crown of the carcass ~ .
~3 15 102 and a tread 104 ha~ng a width b in cross-section. :
~-`,., Indentat~ons formed in the tread 104, such as a palr o~
grooves 105j are ~ubstankially synunetrical with respect to , a median equaborial plane 106 o~ the standard tlre 101.
The--m~ximum allowah~-e wea~ dept~.o~ he-~-re~--104-- -~:~ 2~---- ' is indicated at lo7..-- When the standard ~ire lOl is- mounted on ~n unsteered-wheel of a hea~y,duty.~ehicl-e, such &~ - ~:
~ a rear wheelj- the traad 10~ generall~- wears.in-~a s~bstan- .. ' '':. ' tially- even manner. Even wearing---o~-the tread -104 can occur, for example, from a periphera-l---ro~ling contact sur-25- ~ce 108 to-t~e max~mum-~l~owabi-e-we&r--dept~ limit 107. :
I ~hl8 zone-o~ e~en wear-l~-~or ~enera~ly-curved trapezoidal ah~pe -indicated:~y-the.re~erence ~umber---lQ9--and the-let~er~-- :~
, AEFD. ~he ev~n-tr~d-~aar--zon'~-AEFD-represe~ts--~he--theo- ' ' , reti~al-maximum--u~able ar~a o~ ~h~ tread 104,- ~nd , 30~=-- corre~ponds-to .-&- dl$~an~e ~ndurance ~ -for---ex¢mple~
s^.'.,'~ .
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-7- ~.~s~636 100, 000 kilometer~ (62, 500 mile~
When the ~tandard tlre 101 i8 mounted Otl a ~teered wheel, such as a front wheel of a heavy duty vehicle, the tread 104 ususally wears in a substantially : 5 uneven manner. A typ~cal uneven tread wear pattern i8 ¦`
. indicated by the widely spaced cross-hatched area 110, I :
....
de~lned by the letters ABCDFE~ representing material ~:~ that is unevenly worn away, and the densely eross-hatched area 111 de~ined by the letters ABCD and the l~ne l:
107, repre~enting unus~d residual mater~al. As a result ~ o~ uneven tread wear, the sidewall~ at A and D are worn ; ~o the maximum allowable depth 107 whlle there is still a i~u~st~ntial amount of unu~ed residual material 111.
Thus the tread wear is accelerated at the ~idewall~ in ~j 15 relatlon to other portions o~ the tread 104 : .1 i ~'.,',',7, On the average, an unevenly worn tire re~u~res : :
1 replacement after only 60~ of the available tread ha~
.~ been worn. ~he diætance endurance of the tire 101 cor- .
1 respondlng to 6uch uneven tread wear is, ~or ex~mp~e, ~::
~ . ...
~i 20 approximately 60,000 kilometers (37,500 miles - corre- ;~
.. ~ponding to the zone ABCDFE~ ~nd represents a loss o~
approximately 40,000 kilometers (25,000 miles - corre-'3 sponding to the zone ABCD and the line 107) in compari-, ¦ ~on wi$h ~he distance endurance o~ the t~re 101 when sub~ected to even wear. :
.1 It will be noted ~ha~ the unevenly worn aw ~ .
~, area 110 (ABCDFE) comprlses ~ median por~ion BCKJ that 'i is substantially of a curved rectangular or trapezold~l .
' ~1 .
h~pe e~iden~ing sub~tantially e~en wear o~r a cross ~::
~ 30 wi~ w~dt~ a. ~he unused residual portl~n 111 comprises .,,.' ~ .
~,.,i, ~ I' ~
~ 7 ! ~

", . . .

-8- 1(157636 a median por~ion BCGH that ~8 also ~ubst~ntially o~ a .
curved rectQngular or trapezoldal 6hape and ha~ a cross-wise width a identical to the portlon BCICJ in the tread portion 110~ The residual portion 111 also includes curved triangular portions ABH and DCG, which include generally acute angle portlons at A and D respectlvely.
Re~erring now to Fig. 2, a tire lOla include~ a medlan portion 112 of tread 104' having ~ ground contaet sur~ace 108~ pro~ecting beyond opposite rece~sed :
lateral portions 113 and 114. The pro~ecting ~nedian portion 112~ defined by the letters GHJ'K', is sub-stantially o~ a curved trapezoidal or a curved rect~,~u-lar ~hape in cross-section and has a crosswiae width a identlcal to the curved rectanguIar central port-lons ~
BCKJ and BCGH of Fig. 1. Preferabl~ the pro~ecting :
1 ~
~, median portion 112 ls of substantially identical th~ck- .
, nea6 as the ~tandard tread 104 and represents an accum- ~ :~
-~ ul~tion of substantially ~11 the material in the une~en ~i, t~ead wear æone 110 (~BCDFE) o~ the standard tire 101, ~:
20 - ~h~ch cQrrespond~ to a distance endurance o~ 60,000 ,,,, .
~ kilometers (37,500 miles) when the tire 101 is unevenly ':' wor~. ~ , I ~,,;1 ~he receæsed l-ateral portions 113 and 1~4, which I c~incide with the line 1~7 and do not contact the ground, ~:
^.~ 25 are defined b~ the letters AH and DG and ~orm ob~u~e 1 anglea with the portiona HJ' and-GK'~ o~ the pro~ecting .:1 median portlon 112.
~;1 Slnce ~he cros~wise width a of ~he med~n portion .
;, 112 ~G~J'K~ identlc~l to the croæ~lse ~id~h a of :`
.1 30 t~ evenly ~orn portion BCXJ of a ~tandard tIr~ mount~d ' 1 ':

':' ~L~5~763~ ~

on an unsteered wheel, the med~an portion 112 ~ear~ sub- :
stantially evenly ~nd substantlally completely to the maximum allowable wear limit 107, whether the tlre lOla G. is mounted on a s~teered or un~teered wheel. Complete use of the proJecting median por~ion 112 to the line 107 correspond~, for example, to a distance endurance -~ o~ approximatel~ 60,000 kilometers (37,500 miles3. I~
~ desired the concentration o~ rubber in the pro~ecting :
:~ portion 112 can be lncreased beyond tha~ of the portion G~JK o~ Fig. 1 b~ providing 6roo~es 105' ~Fig. 2) that '. are narrower than the groove~ 105 ln Flg. 1, but have the same depth.
' The full shoulder area of a standard treadg such `
-~ . as 104 in Fig. 1~ hav~ng a radial thicXness corresponding .~ 15 to the pro~ecting portion 112 and a width b in cross-~ection, is shown in dotted outline on each side of the ` ~
~i pro~ectlng portion 112~ ~he cros~-sectional width a o~ ~ ~;
~ ~. ,j . .
~ ! the pro~ecting central portlon 112 is approximately 6 ''~,',J 0~ the cross~ectlonal w~dth ~ v~ a standard tread 1~4, ~ 20~ and the cross-sectional~width c o~ the reinforcing belt .l. 103 ~s approxlmately~9 ~ of th~ width b. The width a o~
.;~ the central portion 112 is thu~ approximately 2/3 the :~
~3, width c o~ the reinforcing belt 103. The~;e relationfihips are æet forth b~low:
: a ~ 6 ~ b 9 ~ b a ~ 2~3 ~ .
It wlll ~e noted th~t in the ~tandard pneumati~
ire 101 o~ Fig. 1 th~ gr~und contac~ sur~a~e 108 extendæ ;
30 -- beyona t~e extr~mlties-or -~he reln~orceme~ beIt`103. ; ~`
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.()5'7636 :
The ~tre~es impo~ed on the tread dur~n~ movement o~ the tire ~ubJect the ed~e~ of the belt 103 to continuous mo~ement and heat-up, and at high speeds, to eventual ~- separation ~rom the tire carca~s lOQ, However in the t~re lOla of Fig. 2 the median pro~ectlng portion 112 generally receives the grea-test magnitude of stresses due to rolling contact between the - :
tread 104' and the ground. The extremities of the rein- ;
-~ forcement belt 103, being remotely positioned beyond the ; -l~teral lim~ts HJ' and GK' of the median projecting por-~ tion 112, are there~ore a~fected to a lesser extent by ~:
;~, the ~olling contact stresses than the pro~ecting portion 112.
Referring now to Fig. 3, a tire lOlb includes an ,, .
enlarged pro~ecting msdian portion 117 compri~ing the ; - .
!;~"`;, ~ortion 112 (G~J'K') and lateral enlargements 115, 116 :~
.. 1 respectively de~ined by LMJ'H and PNK'&. The enlarged pro~ecting median portion 117, defined by the letter~
has ~ ~verall cro~ sectional width a' that i8 . :~
~i, 20~ - approxi-~tely~7 ~ ~or the width-b` o~ ~he ~tand~rd tread , 104~-- Moreover, the-pro~ecting median port-ion 117 i8 1.:-appro~imAtely 25% la~ger:~n ~ros~-section than the portion 112 and a~ords-~he tlre--lOlb=:a-25% -increase-in d~-~tance endurance---over- the~--tire lOla-=to extend the use~ul li~e l;
o~ the-tire lOlb to approximately 75,000 kilometers t46j-875-mi-le~-unt-il the portion-117-is-completely worrl ¦
to the line-lt~7 :o~- maxlmum--all-owab~e--depthv- . ¦:
The- ~lre--lOlb also--inc~lu~es-laterally pro~ecting ~;
~ "1 t ~
shoulder~ 118 Qnd ll9--const~u~lng-enlargement~ of t~e ..
~: ' 30~- ,; recessed-Ia~eral-portisns-~ 3-and--~-1-14_-of~Figv--2 ~lon~the : ., '. :

0- ' ;
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line 107 by amounts AA' and DD' respect.ively. The lateral portions 113 and 114 are inclined at an angle alpha (OC ) 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 with ~ :~
an overall width b' at the line 107 of maximum allowable depth .
1 : , .
representing approximately a 27~ increase in wid~h over the ' ;2 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 ~2% of the width b', and the width a is .
approximately 47% of the width b'. ::
., A reinforcement belt 103' in the tire lOlb has i opposite edges extending into the projecting shoulders 118 and 119. The cross-sectional width c' of the belt 103' is, for example, 27% wider than width c of the belt 103 in Fig. 1, l 45~ wider than the cross-sectional width a' of the projecting .. ~ .
; 3 central portion 117, and approximately 10~ shorter than the ,:
.~i width b' of the tread 104'.
The laterally projecting shoulders 118 and 119, and :, the enlarged reinforcement ~elt 103 extend the distance . endurance gain of the tire approximately 5% to a useful life of approximately 80,000 kilometers (50,000 miles).
The elevation or radial thickness of the projecting ':,:' :
.l median portion 117, indicated by el, is measured between the ~:1 ground contact surface~108' and the line 107 of maximum :

:.1 allowable wear. Although the thickness of the tire lOlb at the .:l equatorial plane 106 is substantially :; .:1 , ' l ,,,:.~ .
, ., -, ~12- ~V ~ 6 ~

:
equivalent to the thickness of the standard tire 101 at said plane, it is feasible to provide the t~re lOlb with ~ ~ approx~mately 4% greater thickness at the plane 106. A
: predetermined minimum allowable material thickne~s e~
covers the extremitles o~ the belt 103' in the ~houlder area~ whereby the overall material thicXness el + e2 in the median portion of the tire lOlb over the belt 103 is : ~ndicated by h. . ~:
;~ ~e~erring now to Fig. 4~ a tire lOlc include~
circum~erential grooves 120 and 121 ~oining the pro~ect-ing central portion 117 to the respective recessed lateral portion 113 ~nd 114 to form an articulate f~exi-ble connection therebetween. , :~
. I The radial th~ckness e~ o~ the pro~ecting central .:
~ll15 portion 117~ which corresponds to the maximum allowable .l wear limit depth, is measured between the ground conta~t sur~ace 108i and a maximum allowable wear limit line 1~7' :~
~, defined along a curved line tangent to the bottom of the articulation-groove~-120 and 1~ Xe minlmum---al~owab~-e - ~
materlal thickness e2 eovers th-e~extrem~tie~ ~ the belt- .
1 103' in the shoulder areas 113 and ll~j and a materii~l ~ :
1 thlckne~ e3 ~n the median portion o~ the tlre between :~
1 the bel-t 103 and the pro~ecting portion 117 pro~ide an .t overall thickness ~ ~ el ~ e3 in the median-portion o~ ~ :
the tire lOlc oYer the belt 103. It will be apparent tha~
iB or les~er magni~ude ~han h in Fig. 3 be~ause e3 iæ
of le~er ma~nltude than e~.
Th~ ra~ at ~hich a tread wear~ i8 o~ten a runctlon Or ~he d~tance ~et~een the-trea~ and_~h~ rei~Qx~ement ~ 30 belt. aenerally ~he abllity o~ a tlre to re~l~t skidd~ng ~:

~ -12- i -13- .

1057G~G
incr~ses aB the dlstance between the belt and th tread decreases to a minimum allowable distanceO M~reoverg a ~
reduced amount of rubber between the belt and the tread ;
provides a cooler running tire because there is le8s heat produced by lntramolecular frict~on during movement of the tire. Tread wear 7 S thus reduced-because the -:
. resistance to skidding increases and les~ heat i~ gener-ated within the tire. :
It is there~ore desireable to provide the smallest allowable thickness between the tread and the re~n~orce- :
ment belt 103'. Thus, the embodiment of F~g. 4 is :
pre*erable to the embodiment ~ Fig. 3 because e3 is less , than e2 and hl ls le~s than h~
., The inclination of the lateral portionæ 113 an~
114 at an angle alpha (OC ) helpæ reduce de~ormat~on of ~:
.`1 the pro~ecting ~entral portion 117 and the pro~ecting .;1 shoulders 118 and 119. `
:J Although the rein~orcement belts 103 and 103' are `! ~hown as ha~lng three ply l~yersg any feasible number of ~ 20 plies can be used. For example, a ~ourth ply o~ approxi- ~:
,'7 matelg 44% ~he width of c' can constitute the radial~y ., extreme outer ply layer. ~he position o* th~ lateral :~, edges of the ~ourth ply l~yer Will a~fect the ~lexibility .
~ Or the tire at the artieulation grooves 120 and 121. :
i 25 ~herefore these edge~ ~hould be o~ le~ser axi 1 extent than the arti~ulation grooves 120 and 121 to a~oid the possl~ility o~ crack~ forming at the articulation grooves.
~- Pre~erably the ~our~h ply l~yer ~hould not pro~ect ax~lly ~' beyond the articulation groo~es to ma nta~n the rlexl- :
! 30 bility thereo -13- , f ~

: `~
During construction o~ a tire having a rein~orce- .
ment belt one or more of the belt plies may ~hl~t slight- ~:
ly in loc~lized areas with respect to the equatorial .
[ plane of the tire. The amount of off-center shlft can ; 5 vary at di~ferent locations around the tire circumference.
A belt ply that is cut unevenly prior to itæ installation ln the tire can also be considered off-center.
:
In a standard pneumatic tlre where the re~nforcing .
, belt is gener~lly o~ lesser ~dth than the ground con- ~
.~, 70 tacting tread surface, the of~-center de~ects can affect ~ .
the roundness o~ the tire and cause excess variations :
in la~eral and ~ert~cal ~orces on the tire during its :
movement on the ground. ~hese ~orce variatlons lead .
to meandering and squirm which result in ~ibrations, deviations~ de~lections and skidding of the tire.
~ However~ in the present tire construction the :i effects o~ the o~-center de~ects attributable to the -¦ reinforcement belt are now localized in the lateral ~houlder- portions where there ~ s no grcNnd contact~.ng ~, - 20--- tread area. Consequently, ally off-center de:E ects ha~re less harm~ul afi~ect on the road holding ability o~ the tire, e~ren at high speeds, resulting in less meandering, ~ :
: ~ sguirm and vibrat-ions, etc, Reaction ~orce variation~ ,.
are thus reduced, especially lateral forces, thereby mini-'~ ~5 mlz~ng the rolling resistance of the tîre ar~d permitting;::
a vehicle incorporati~g- said ~ires~;o aoh-~-eve--a-g-reater uel economy. ~ .
; 'f For-exan~ple, in a st~dard--tire the lateral ~orce--- :;
wa~ fo~d to var~r b~r approximately 30 ~o 35 kilogr~n~
~30 ~round i~- aver~ge ~ralu~ nd the vertic~L-- ~orce--was I

, : `~

-15- 10S7~i36 , . .
found to vary rrom approximately 90 to 130 lcilogr~n~
around its aVerAge ~alue. In the present tire, corre- ;
sponding variatlons were respectiv~ly 11 to 20 kilograms ~ .
~- with regard to the lateral force and approximately 60 ~o 108 kilograms in the case o~ the vertical force. .
Maneuver~bility of a ~ehicle e~ploying the tireæ of the :
,. ~.
present in~ention ls thus ~acilltated, ,:
The ~ollowing temperature measurements show the relative hea~-up characteristlcs o~ a standard tire lncorporating the present in~ention.
3 ~ ~:~1 TE~RATURE TEST .
Measurement Zone :
.~ On the Tire Standard Tire Present Tire Crown, Equatorial 93C 90C :~

Shoulder 110C 101C ~: .
.;, Bel~ Extremitie~ 110C 80C ~`
.-3 ;~
,: The test results ~ndica~e approximately 8% cooler ~: :
1 ~ ; temp-eratures--at~he-la~eral--shoulder:portion and:-approxi-mately-27~.cooler:.temperatures-at t~e extremities of the . reln~orcement bel~ in a tire-o~-the pre~ent invention.-, The ~ollowing set-up was.used to evaluate the:............ ~!
;~ rela~Ye load endurance o~ a re~n~orclng belt in a æ*an- . ;;
dard tlre~ nd the rein~orcing belt of the-present inve~ ~:
~on-.- On a wheel rim having a diameker~--of-l~6 meteræ , ' there are-plaeed three bars o~ a thic~ne~ ~f.l~ mlll~me~e.r~ .-.~ angul~rly spacea ~part--b~ i20~ wl~h--respect to one------ ~
i ~nother, one or the bars being oriented-para~ o--t-he~ . - 1;
, axi-s-~r--~he--wheel--while ~he--o~he~--two bar~-for~-a-45~--.' 30~-:- angle ~ltb-~6id R~i8~ Th~-wheel:is ro~ted--~t ~.
f,.'"l, j ' . ~ ' ' :
. -~5-.. , . . . , . . ~ . .. .

.' peripheral linear ~ipeed o~ 60 kilometer~i per hour (37.5 miles per hour). The tests were performed on two radial carcass pneum~tic tires of ~ size of 10.00 R 20 in~lated to a pressure of 6 bars and mounted on a 20 x 7.33 V rim, one o~ ~hich was a standard t~re acting as a control -, whereas the other was a tire ~ncorporating the present ~n~ention. Eaeh tlre wa~i sub~ected to a load o~ 1500 kilograms with the load being periodically increased by -~_ 200 kilograms e~ery 24 hours. On the ~tandard tire it ;
was noted that a separation o~ the belt ex~remities occurred between 168 and 192 hours o~ testing~ correspond- ~
lng to a load of approximately 2700~ilograms. In the ;
tire of the present invention the belt extremities separated after a test period o~ 260 hours which corre-sponded to a load o~ approx~mately 3500 kilograms, Some a~vantages of the present invention evident from the foregoing descr~ption include a tire wherein wear of the tread is limited essentlally to ~ts median ~ --~ portion and i~i at all times uni~orm or even to perm~t com-~ 20 plete wear and the a~taiNment of a distance endurance ;` correæponding to such complete wear. Since ~he shoulder -;
portions do not ordinarily touch the ~round they are not ;~
~, sub~ect to an~ appreciable wear, and are less prone to heat up during movement o~ the tire because they conta~n a relati~el~ reduc~d mass o~ laubber, are not sub~ect to the buckllng stres~ies tha~ occur during contact of the ~, tread with the ground and are sub~ect to improved cooling through the alr ~urrents tha~ en~elop each recessed lateral portlon. Because o~ ~he reduced heat-up and wear ~n the la~er~l shoulder area there i8 a correspond~ng ~ncrease ,.~ . ~' ;~ ' . . ~ :

-17- 105~636 in ~uel economy ~or a motor vehicle incorpor~ting tires of the present in~ention.
Travelling comfort is improved because the lateral ~- pro~ecting shoulders can elastically flex without con-: 5 ta~ing the ground thereby prov~ding an elastic suspen-`. sion effec~. Driving a vehicle incorporating the present :-,i . .
t~e also becomes an easier taæk because the reaction to ` steering is smoother resulting in easier handling of the :
_ steering Yheel~ Moreo~er high speed driving can b~
~`~ 10 accomplished with grea~er assurance o~ sa~ety due to -.i improved security against belt separation at ~he outer ~, edges. ~;
``~ In view of the above, lt wlll be seen that the ~everal ob~ects o~ the invention are achieved and other advantageous results attained. 'i I A~ vari~us changes could be made in the above ;~, constructions wi~hout departing ~rom the scope of the ~:~
i. inve~tion, it i~ lntended tha~ all matter contalned in ~: the abo~e de~criptlon or ~hown ln the accompanying draw-~,'`fl 20 ings shall be in~erpreted as illu~trati~e and not in a - ~:
' limitlng sense.
..
i','~''~' ~l .
" ' 'I .
j . ~ ~
~'' ~ ~ .

~, 1 ' - :-:
' : ! :~

~ 17-

Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a pneumatic tire having sidewalls and an axis of rotation including, in cross-section, a carcass, a tread having a projecting median portion intermediate said sidewalls with a ground contact surface, opposite lateral portions discontinuous from said ground contact surface and extending from said median portion to the respective said sidewalls and a reinforcing belt disposed between said tread and said carcass, the improvement comprising, first and second axially directed protuberances at the sidewalls of said tire extending from the lateral portions, the reinforcing belt having opposite edge portions extending into the axially directed protuberances, said opposite lateral portions being recessed from the ground contact surface in step-like fashion and wherein the lateral recessed portions respectively include a free surface spaced from the edge portions of said reinforcing held by a predetermined minimum allowable thickness of tire material, and the projecting median portion of said tread is connected to said lateral recessed portions by circumferential grooves of uniform width that form an articulate link between said median portion and said respective lateral recessed portions said grooves having a common arc of tangency at a radially innermost portion of said grooves, said arc continuing below the free surfaces of the lateral portions such that a maximum allowable wear depth of said projecting median portion is along said common arc of tangency.

2. The pneumatic tire of claim 1 wherein said median portion has a crosswise width approximately 62% the crosswise width of said tire between said axially directed protuberances.