CA1054914A

CA1054914A - Tire tread structure

Info

Publication number: CA1054914A
Application number: CA250,972A
Authority: CA
Inventors: Henri J. Mirtain
Original assignee: Uniroyal SA
Current assignee: Uniroyal SA
Priority date: 1975-05-30
Filing date: 1976-04-26
Publication date: 1979-05-22
Also published as: BE841650A; FR2312385B1; DE2621905C2; GB1549347A; DE2621905A1; FR2312385A1

Abstract

TIRE TREAD STRUCTURE

Abstract of the Disclosure A tread for a pneumatic vehicle tire, characterized by improved wear, is disclosed. The tread includes a plura-lity of lugs separated by grooves and a plurality of cir-cumferentially continuous ribs. Each edge of the lugs and ribs is chamfered. The width of each chamfer as pro-jected onto the radially outward surface of the tread is between about 0.15L and about 0.5L, where L is the dimen-sion of the unchamfered lug or rib measured perpendicu-larly to the chamfered edge and parallel to the surface of the tread. The depth of each chamfer is between about 0.2Z and about 0.4Z, where Z is the depth of the groove adjacent to the chamfered edge measured to the radially outward surface of the tread.
This abstract is not to be taken either as a com-plete exposition or as a limitation of the present in-vention, however, the full nature and extent of the in-vention being discernible only by reference to and from the entire disclosure.

Description

Back~ound of the Xnvention This invention relate~ to a tread structure for pneumatic vehi~le tires and more particularly to ~uch a tread structure having cham~ered lugs and ribsO
Con~entional pneumatic vehicle tires of the typ~ presently in use g~nerally have tread constructions which include a plurality of longitudinally extendlng rows o~ lugs and r_bs which are separated from one ~nother by longitudinally extending grooves, the lugs being ~urther separa-ted ~rom one another by transversely extending grooves. Such tires, which have grooves which extend radially ~rom with1n the tread body to the radially outward surface thereof hav~ been found to be generally satisfactory for in-service use sn a vehicle, that iS5 they have been found to be generally satis~actory ~or I thelr intended ~unctions such as vehicle support~ trac-; tion etc~ me treads are, however, as is weil known~
sub~ect to substantial wear, which wear ultimately re~
~uires either the retreading or replacement o~ the tire~
both of which entail substant~al expense. In this regard it ha~ been noted that the- aforementioned conventlonally tread d tires~ tha~ is, tires having treads in which t~e grooves separating the ribs and lugs extend radlally to the radially outward sur~ace o~ the tread exhibit a deleterious wear phenomenon peculiar to the outer edges of the ribs and lugs~ More p~rticularly, this wear pr~marily occurs at the rearward edge~ with respect to the rolling direction of the tire~ of the tread pro-~ections . Thi s wear therefore is primarily con~ined to those portions o~ the pro~ections OL the tread which are . , ~ 1-'~ ~

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~L0549~l4 dlscontlnuous and are conventlonally re~erred to as lugs and this we~r does not occur where the tread pro-~ection is circumferentially continuous, such a pro-~ection being conventionally referred to a5 a rib.
~ear o~ the kind here being discussed, which is æuperimposed over the general wear that is t~king place in the tread, is caused by the ru~ber~ material lugs of the tread, which are in contact wit~ the road surface7 being longitudinally deformed during operation~
mis longitudinal deformation takes the form o~ the lugs being flexed obliquely toward the rear relative to the directlon of motion of the vehicle on which the ; tires are mounted becausP of the twisting torque be-tween the tire rim and the road surface, and the longi-tudinally deformed lugs resume their initial state only when the lugs are displaced rearwardly and upwardly as the tire rolls. me lugs there~ore are subjected to a movement, i.e.~ a deformation~ in addition to the conventional rolling movement. r~he addition~l move-ment or de~ormation which a~ects each lug occurs~clearl~g only during a fraction o~ each re~olution of the wheel and it corresponds to a slippage o~ the rear portion relative to the direction o~ rotation o~ the tire) ~
o~ the lugs which are pressed against the road sur~ace ~ -

2~ -by a pressure ~orce that is weaker than the pressure ~orce acting against the front or ~orward portion o~
the lug and the localized wear at the rear portion of the ~ -lug results ~rom the slippage due to the lower pressure ~orceO
At this point it is appropriate to note that ~2-the transverse edges of the lugS3 and the transverse edges o~ the ribs as well, o~ the tread are al~o subjected to wear whlch~ although o~ the same type, is 1lbstantially less severe. mis transverse edge or side wear of the lugs and ribs ~s ~aused by the lateral deformation o~
the lugs and ribs during turns and by the lateral de-~ormations to which the lugs and ribs are subjected during straight line travel because of tire squirm and because o~t~e flexibilty ~e.,elasticityg o~ the tread rubberO
Clearly, a tire tread structure which was as satisfactory as conventionally tread~d tires for its intended ~unctions and which additionally exhibited improved wearing characteristics relative to kno~n tread structures by eli~inating3or at least minimizing, rlb and lug outer edge wear woulcl be most desirable.

Summary of the Invention __ It is, there~ore~ an important ob~ect of the pre~ent invention to provide an improved tread structure ~or pneumat~c vehicle tires by means of which the a~ore-said drawbacks and disadvantages may be most e~ficaciously avoided.
It is a further ob~ect o~ this invention to pro-vide a tread structure ~or pneumatic vehicle tires charac-:
terized by improved resistance to wear.
Generally speaking, the ob~ectives of the present -~
invention are attained by the provision of a tread for a pneumatic vehicle tire, the tread comprising a plurality of lugs separàted by grooves, wherein at least one edge of ea~h o~ the lugs iæ chamfered, the width of the cham~er ~ 5 ~

as pro~ected onto the radially outward surface of the tread being between about 0~15L and about 0~5Lg where L is the dimension of the unchamfered lug measured per-pendicularly to the chamfered edge and parallel to th~
surface o~ the tread, and the depth of the ch~m~r is between about 002Z and about 0.4Z~ where Z is the depth of the groove adjacent to the chamfered edge measured to the radially outward surface of the treadO
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.. 0 The ~oregoing and other objects and ~eatures of the present invention will be more clearly understood ~rom the following detailed description thereof when read in conjunction with the accompanying drawings, in . which:
Figure 1 is a schematic plan view of a portion ~ o~ the surface of a t.read illustrating the wear pattern . o~ conventional lugs;
Figure 2 is a schematic sectional view of a portion of a conventional tire tread in contact with a road sur-~ace~ w~ich view is taken along the median equatorial plane o~ the tire;
Figure 3 is similar to Figure 2 exceptin~ that the deformation o~ the tread lugs when the tire is rolling is here illustrated;
F~gure 4 is a schematic sectional view of a portion of a conventional tread, taken along the median e~uatorial : plane of a tire, after use;
Figure 5 is slmilar to Figure 4 exceptlng that ; tread lug wear after the tire has been in-s~rvice in 30 both the forward and rearward directions is here illu-, --4--.

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~ I~S~strated;
Figure 6 is a broken cross-sectional view of a portion of a tire tread taken along either o~ the llnes 6-6 in Figure 8 lllustrating a lug stI~cture in accordance with a first embodiment of the invention;
Figure 7 is similar to Figure 6 and illustrates a lug strueture in accordance with a second embodiment o~ the invention; and Figure 8 is a plan view o~ a portion of a tread, the lugs and ribs o~ whlch are structured in accordance with the invention.
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Description of the Preferred Embodir.ent ~ ~ ~ . . .
Turning now to Figure 1 -there is illustrated a schematic plan view of a portio:n o~ a conventional tire tread 1 which includes a plurality of lugs 3, 5 and 7 ~hich are independent of, and separated frQm~ one another by grooves 9 and 11 and a lug 13 having a di~ferent shape than that o~ the lugs 3~ 5 and 7. The tread will also cQnventionally include a plurality o~ continuous cir-cum~erential rlbs not here illustrated.
The direction o~ rolling of the ~read is indicated by the words FORWAR3 and REAR~ARD and the wear pattern of . -~he lugs ~relative to the type of wear here under discussion) which is caused by rolling in the forward direction is indicated at the rear of the ~ugs at 3a, 5~, Ta and 13a.
With respect to the lug 13 there is also illustrated~ at 13b, the wear pattern which will result fro~ a reversal o~ the rolling direction~ Such a reve~sal might oceur~
for exampleg when, ~or purposes of periodic maintenance, the tires are shi~ted to the opposite side of the vehicl~

" ' ' 1,~

on which the~ are mountedr Turning now to ~'igs. 2-5, each of which is a schematic cross-~ectional view of a portion of a tread taken through the median equatorial plane o~ a tire, the cause ~nd the mode of occurrence of the aforementioned wear will now be described~ Referring first to Figure 2, there are illustrated lugs 15, 17, 19, 219 23 and 253 each o~ which is similar to the lugs 3~ 5, 7 and 13 lllustrated in Figur~ 1. Agaln~ as ln Figure 1, the lugs are separated by grooves, here indicated at 27, 29~ 31, 33 ~nd 35.
Flgure ~ illustrates the tire treads in contact with a road sur~ace 37, the tire being in contact with the road sur~ace but not undergoing rotation. Under these conditions it wiil be noted that the grooves, indicated at 27, 29 31 and 33 are not deformed and the region or portion o~
the tread which is in contact with the road surface 37 has virtually the sam~ configura~ion as those portions o~ the tire tread which are not in contact wlth the road sur~ace, with the exception, of course3 that those portions which are in contact with the road sur~ace 37 are slightly M attened due to loading.
Ref~rring now to Figure 3 ~hich shows the same tread portion as illustrated in Figure 2, with the excep~
tion that the tread section of ~igure 3 is shown in the 25 con~iguration achieved during rotation of the tire, it c~n be seen that the lugs 17~ 19 and 21 have been de~ormed so that the groo~es 29 and 31 no longer extend radially of the tire9 but rather3 are oblique with respect thereto.
ThUBg the open portion o~ the ~roove, i.e., that portion ad~acent the road surface, is shifted in the forward ~ S~
direction while the bottom of the groove, i.e~ the r~dially inward portion thereof, is shi~ted rearwardly.
It will also be noted that the groove 35 which has been, but no longer is, in contact with the road surface 37 has resumed lts "normal"~ that is, radially extending~
state. Thus, groove 35 extends radially o~ the tire;
the grooves 27 and 33 are in an intermediate state of de~ormation; the groove 27 is going toward the state of maximum deformationi and the groove 33 is going toward the normal condition~
The deformation of the lugs is caused by the force indicated at F in Fig. 3, which force is a result of the torque between the tire rim and the tread surface, the ~or~ue being a ~unction o~ the elasticity o~ the rubbery material o~ the tread ancl the adhesion between the tread and the road surface 37'. In going ~rom the con~iguration o~ lug 19 ~hlch is in its de~ormed state to the configuration o~ lug 25 which is in its normal state, each lug undergoes, an addition to the general rolling movement, a slippage movement which af~ects the ~ront and rear portions of the lug dif~erently. mus, the localized wear which has been said to occur at the rearward portion o~ each 1U8 is caused by the fact that th~ rear portion o~ each lug3 indicated at 21a with respect to lug 21, is sub~ected to less compression then the front edge thereof, indicated at 21b with respect to lug 21, during the a~orenoted slippage movement.
Iurning now to Figure 4 there is illustrated a v1ew of the tread portions illustrated in Figs. 2 ~nd 3 after their ~n~service use in the forward direction :

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onlyO It w~ll bP noted that the lugs 17~ 19 and 21 exhibit a saw-tooth profile showing asymmetric wear of the lugs~ Thus, the rear edges of lugs ~79 19 ~nd 21~ indicated at 17a, l9a and 21a, respectively, ; 5 are worn whereas the front edges o~ the lugs are not worn~
Figure 5 illustrates the tread portion shown in Figure 4 a~ter the tread has been in use in both the forward and rearward directions. Figure 5 shows that i~ the tread is used in-service in both dlrections under similar conditions and ~r equal distances, the tread will show a generally symmetrical wear profile with ~he edges l9a and l9b of the lug 19 showing virtually identical wear.
It has been ~ound that the type o~ lug edge wear illustrated in Figures 4 and 5 will, i~ initiated, ~ continue idefinitely without stabilizing. That is~ once ; this type o~ wear has begun it will continue and will not reach a point o~ wear at which the lug rear edge wear will çease. It has ~urther been found~ however, that, where the edges of the lugs and ribs have been chamfered ! ` :
to provlde the structure o~ the invent~n, this type o*
edge wear is not initiated and tread life ~s there~ore substantially extended. Further, the e~fectiveness o~
the tread ls lmproved due to the fact that tread wear ls trans~erred to the central portion of the lugs and ribs thereby providing a more uni~orm wearing o~ the tread. It has ~urther been ~ound that the optimum pro~ile of the cham~ers corresponds to a curve which is a function o~ numerous par~meters, one o~ which parameters relates to the mode o~ operation o~ the vehicle on which the inventively treaded tire is mounted. It may therefore be seen that it is not possible to establish an opti~um profile ~or all tires which are used for all purposes, but rather, that a structure having a profile within a range o~ limits is pre~erably provided. In thls regard it is apprepriate to note that, within the ranges provided, the pro~iles actually adopted will suitably be those re~uiring less complex constructlons andgin particular, will be those which take into account tire molding re-; quirements and di~ficulties~
Turnlng now to Figure 6 there is sho~ a bro~en cross-sectional view taken along either o~ the lines 6-6 in ~igure 8, o~ a portion o~ the tire tread~ which cross-section may be taken as shown i~Pi~ 8~ either along a `~ plane parallel to the median equatorial plane of the tire or parall~l to one o~ the grooves o~ the tread, as will be more ~ully discussed belowl In accordance with one embodiment o~ the invention, the lugs 39, 41 and 43 illustrated ln Figure 6 ha~e cham~ered edges. The depth ; o~ the cham~er ln a radial direction is indicated at D, the width of the cham~er is lnd~cated at W and L indicate~
the length o~ the uncham~ered lug measured in a direction parallel to the surface of the tread and perpendicular to the edge o~ the lug to be chamfered. In Figure 6 the grooves separating the lugs 39~ 41 and 43, each of .~ .
~rhich grooves has a depth indicated at Z, are indicated at 45 and 47, respectively, and the chamfers are indicated at 49~ 51, 53 and 55, respectively. In this embodiment the cham~ers 49, 51~ 53 and 55 are linear and are obll~ue .
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~L054914 with respect to the plane of the grooves 45 and 47 as well as with respect to the sur~ace of the treadO Where, : ~or example~ Figure 6 represents a cross-section of t~e tread taken along a plane parallel to the median equatorial plane of the tire~L reprissents th2 length o~ the lug 41 taken along the circumference o~ the tread. It has been f~ud that the desired reduction in lug and rib wear is attained, where, in accordance with the invention, the d~mensions of the cham~ers are such that the width W of ~ 10 the chamfer is between about 0.15L and about 0~5L and : the depth D of the cham~er is between about 0.2Z and about 0.4Z, and more speci~ically where the width W of the chamfer is between about 0.18L and a~out 0 26L and the depth D o~ the chamfer î~ between about 0.26Z and ~ou~ 0.34Z.
In accordanc~ with the second embodiment of the ~nvention there is illustratlsd in Figure 7 the same :~ :
portion o~ tread as is illustrated in Figure 6 with the exception that the cham~ers o~ the lugs 399 41 and 43, cham~ers 57, 5g, 61 and 63, respecti~ely, are rounded or curvilinear rather than being flat or linear as in the embodlment illustr~ted in ~igure 6. The profile Of tha ch~mfers in Figure 7 is that o~ the arc o~ a circle ~ having a radius o~ cur~ature indicated at R. In this `` 25 em~odiment R is equal to L ~hich~as in Flgure 6, re~
presents the length of the unchamfered lug as measured . parallel to the sur~ace of the tread, which surfare is here.indicated at 65, ~nd perpendicular to the plane o* the edge to be ch~mfered. As illustrated in Figure 7, wlth the radius o~ curvature R o~ the chamfer being equal ' ' .~ .

, .

~s~
to L, the width W of the cham~ers 57, 599 61 and 63 are equal to L/2. It will~ o~ course, be realiz~d that the embodiment illustrated in Figure 7 is subject to modi-fication in that each of the cham~ers could extend a distance somewhat less than L/2 which would result in a - substantially flat zone situated in the plane 65 de~ining the surface o~ the tread. mus, for example~ with re-spect to lug 41, the radius o~ curvature R o~ each of the cham~ers 59 and 61 could be les~ than L/2 and lug 41 would therefore include a flat portion9 located ; in the plane 65, bet~een cham~ers 59 and 61.
As previously indicated~ the optimum profile of the cham~ers is a curve which is a ~unction of numerous pa~ &ters and which is related, among other things, to the mode of operation o~ the vehicle on which the in-ventlvely treaded tire is mounted. Further, ~or reasons o~ practicality, the cham~er profile selected must take lnto account tire molding considerations and limitations.
merefore, rather than specifically delineating the paramater~ defining the chamfers in the embodiment illu-str~t~d in Figure 7, a range o~ paramaters is provided.
mus~ in the embodiment illustrated in Figure 7~ it has been found desirable that the radius of curvature R
o~ the cham~ers be between about o.8L and about 1.2L and ~
more specifically that the radius o~ curva~ure R be be- -~ween about 0~95L ~nd about 1.05L. In any eventa and reg~rdless o~ the radius of curvature R selected, the -` width ~ o~ the chamfer in the direction ~ must nevertheless ba between about 0.15L ~nd about 0.5L and the depth D of chamfer must be between about 0.2Z and about O.~Z.
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~2 ~ ~ 5 ~
Turning now to Figure 8~ there is shown a plan view of a portion of a tread 69. m e dashed line X-Y
indicates the median equatorial plane of the tire of which the tread 69 ~orms a part. The tread 69 in~ludes a plura-lity of ~ugs indicated at 71, 735 75 and 77 which, as indicated, are independent of, and ~eparated from~one another. For examplejthe lugs 71 and 73 are separated by a groove 79 and the lugs 75 and 77 are separated by a groove 811 r~he tread 69 ~urther includes a plurality of circumferentially continuous ribsg one of which, rib 83, ls illustrated~ The rib 83 is separated from the:lugs 71-77 by rooves 85 and 87. As illustrated, the ad~acent sides o~ each of the lugs~indicated at 86, 88, 90 and 92~ ~:
are ob~lque relative to one another ~nd the ~ides o~ the ribs 83gindicated at 94 and 96, are in a zig~zag con-figuration. In the description provided above with respect : to Flgures 2-5, the wear of the :rearward portion of each o~ the lugs was discussed and, in ~igures 6 and 7, the ,1 .
;:. cham~ering o~ this portion of each o~ the lugs was em-~hasized~ Eoweverg as p~.~eviously indicatad, the lateral edges of the lugs and the edges o~ the ribs also undergo wear o~ the type here under discussion ~nd both the forward and re~rward edges o~ the lugs undergo wear due to rev~rsal of the direction o~ rotatiQn of the tire. Therefore~ it has been found advant~geous to cham~er all the radially outwa~d edges of the tread, i.e., both the forward and rearward edges o~ the lugs and the lateral edges of the ~ lug~ and edges o~ the rlbs. In accordance with this ob~ective all the edges of the lugs ~nd of the rlbs illu-.30 s~rated in Figure 8 are cham~ered~ each o~ these cham~ers .
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~ .C3 5~
being indicated at 890 It w~ll be realize~ o~ course~
that each o~ the chamfers 89 must satis~y the relation-ships previously set forth~ mus, the width W o~ each of the chamfers must be between about 0.15L and about 0.5L and the depth D o~ each of the chamfers must be between about 0.2Z and about Oa4Z~ Clearly, o~ course, the structure of the chamfers may meet the more limited relationships discussed above with respec-t to depth and width and may, in addition, be either curvilinear or linear It has been found that the inventive tread structure serves to prevent or to minimize the commencement of loca-li2ed tread edge wear and therefore has resulted in a sub-stantial extension of tread life~
It will be understood that the ~oregoing description o~ the preferred embodiments o~ the present invention is ~or purposes of illustration only, and that ~he various ætructural and operational ~eatures as herein disclosed are susceptible to a ~umber of modi~ications ~nd changes, none of which entail any departure ~rom the spirit and scope of the present inventlon ~s de~ined in the hereto appended claims.
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Claims

WHAT IS CLAIMED IS:

1. A tread for a pneumatic vehicle tire, said tread comprising a plurality of lugs separated by grooves having straight sides wherein at least one edge of each of the said lugs is chamfered, the width of said chamfer as projected onto the radially outward surface of said tread being between approx-imately 0.15L and 0.5L where L is the dimension of said un-chamfered lug measured perpendicularly to said chamfered edge and parallel to the surface of said tread, and the depth of said chamfer is between approximately 0.2Z and 0.4Z, where Z
is the depth of the groove adjacent to said chamfered edge measured to the radially outward surface of said tread.

2. A tread according to claim 1 wherein the width of said chamfer is between approximately 0.18L and 0.26L.

3. A tread according to claim 1 wherein the depth of said chamfer is between approximately 0.26Z and 0.34Z.

4. A tread according to claim 1 wherein said chamfers are linear.

5. A tread according to claim 1 wherein said chamfers are curvilinear and their radius of curvature is be-tween approximately 0.8L and 1.2L.

6. A tread according to claim 5 wherein the radius of curvature is between approximately 0.95L and 1.05L.

7. A tread according to claim 5 wherein said radius of curvature is substantially equal to L.

8. A tread according to claim 1 wherein said tread further comprises at least one circumferentially continuous rib, the sides of which are in a zig-zag configuration, said rib being separated from said plurality of lugs by grooves.

9. A tread according to claim 8 wherein a plurality of the edges of said rib are chamfered, the width of said chamfer as projected onto the radially outward surface of said tread being between approximately 0.15L and 0.5L, where L is the dimension of said unchamfered rib measured perpendicularly to said chamfered edge and parallel to the surface of said tread, and the depth of said chamfer is between 0.2Z and ap-proximately 0.4Z, where Z is the depth of the groove adjacent to said chamfered edge measured to the radially outward sur-face of said tread.

10. A tread according to claim 9 wherein said rib chamfers are linear.

11. A tread according to claim 9 wherein said rib chamfers are curvilinear and their radius of curvature is be-tween approximately 0.8L and 1.2L.

12. A tread according to claim 11 wherein the radius of curvature is between approximately 0.95L and 1.05L.