LU82033A1 - DRAWING OF SIDE TRACKS - Google Patents

Abstract

A tyre tread comprises an elongate strip having a respective longitudinal groove (2) in each lateral portion of the strip constructed and arranged to partially close when the tread is subjected to tangential forces, e.g. during cornering, stiffening the tread in the contact area to reduce excessive movement of the tread in the contact area whilst maintaining the groove open at the tread surface. Partial closing is achieved by forming the groove as two tracts a first tract, which remains open during cornering, extending from the tread surface and a second tract, which closes during cornering, separated from the first tract by a sudden variation in groove width produced, for example, by a transverse step formed in one of the groove flanks or a protuberance projecting from the base of the groove. <IMAGE>

Description

ÎL-L? N / tM / M

- 1 T GRAND-DUCHY OF LUXEMBOURG

............... t "U ^ Q

from the Minister

Title issued · from the National Economy and the Middle Classes .............. Industrial Property Service

LUXEMBOURG

Invention Patent Application I. Application to the company known as INDUSTRIE PIRELLI S.p.A .. S Piazza Duca d'Aoeta, Milan. {1) Italy * ............................................. ............

. ........ 46. rue (2; ^ Cemetery, Luzenibourç. acting as agents .................................... ....

deposit this twentyzetr.mÆQ.eïïèr.e ... mil .... neuf .... omt .... 8.Qix <mte..A ........... <a> a · **> ................... hours, at the Ministry of National Economy and the Middle Classes, in Luxembourg: 1. this request for obtaining 'a patent for an invention relating to: ^^ n ... de.J> .e ^. ^ .. xmlmmt ^ â..j ^ mæÊ8 ..... lateral £ .......... .................................................. .......................... w declares, assuming responsibility for this declaration, that the inventor (s) is (are ):

QirVliam.GElLMOJj Italy ................. (5) 2. the delegation of power, dated _______ Mihûdî ................ ............................ on ..12 .... dê.C & tiL · VC ... 1 £? $ .. ...

3. description in language ............ frû0t ^ .t6j ^ ........................... ........_. of the invention in two copies; Λ 4 ........ <££.! &? .......... drawing boards, in two copies; 5. the receipt of the taxes paid to the Luxembourg Registration Office, ... diærhuii ^ Mi ^ ihre .... rnl-.neuf .cent seventy nine ............ .................................................. ..................

claims for the above patent application the priority of one (s) request (s) of (6) .................. hr.epei ...... .................................................. filed in (7) ......... Italy ................................... .................................................. ..............

le itàiïgPr & u ^ âêisæribrejRdljB ^^ (8) bous le .No 31.200 A / 78 ................................. .................................................. .................................................. .................................................. ................

in the name of ....... Id. applicant ................................................. ........................................... (9); elect domicile for him / her and, if designated, for his / her representative, in Luxembourg ................................ .......

• 46 ........ vm. ^^ ili ^ tièx & .yj ^ ss ^ saæg ........................... .................................................. .................................................. ........................ (îo) requests the grant of a patent for the invention for the subject described and represented in the abovementioned appendices, - with postponement of this issue to ................................... month.

l’m .. (ks ... Mæ: * àziair.c € .................

II. Deposit Minutes

The above patent application has been filed with the Ministry of National Economy and the Middle Classes, Industrial Property Service in Luxembourg, dated: December 21, 1578

Pr. The Minister at ... II..1 ............... hours / ..... "... ~ x \ of the National Economy and the Middle Classes , I, '' i τ '/, ”: <“ ·' .- y; P / <*.

h & c ^ __.......; _____‘_ j__ BP-687

PATENT

on behalf of: INDUSTRIE PIRELLI S.p.A.

"Tread design with lateral grooves" Inventor: Mr Giuliano GHILARDI

Priority: / Patent application filed in Italy under n ° 31 200 A / 78 on December 22, 1978.

J

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The present invention relates to tread patterns, in particular tread patterns of large tires suitable for heavy motor transport on smooth roads at high speeds.

It is known that tires have the most radially outer part of their surface, going axially from one shoulder to the other of the tire, provided with a design consisting of a series of grooves or channels 10 hollowed out in the thickness of the tread and arranged in a variable manner in order to subdivide the strip into cords and / or into blocks separated from each other by the aforementioned grooves or channels.

In the thickness of the beads and of the blocks 15, there is also generally dug what are called lamellae, that is to say thin notches directed from the surface towards the interior of the tire, of greater depth! OR less equal to that of the grooves and which can also lead to the sides of the cords and blocks.

The set of grooves or channels and the melles constitutes precisely the design of the tread, one of the characteristic and distinctive elements of the tire, which varies mainly depending on the use for which the tire is intended.

25 Thus, for example, the tires of the "winter" type have a tread pattern strongly provided with blocks and deep grooves to increase the handling on snowy and / or muddy soils, typical for the winter season, while the designs of the tires for use on the road under normal atmospheric conditions are generally characterized by large circumferential zigzag grooves, forming a small line with respect to the longitudinal direction, from which branch other transverse grooves more or less inclined and extended, which completely cross the longitudinal cords, the whole being integrated by a tight la-mellage.

The main purpose of this type of tread pattern is to break the film of liquid which forms, for example in rainy weather, between the tire and the wet road surface in order to avoid the phenomenon of aqua-planing; another object is also to contribute significantly to the road holding and driving stability of the tire.

Unfortunately, these requirements are contradictory. In fact, to guarantee the certain prevention of aqua-planing, very subdivided and layered designs are required, while to obtain good road handling read from the tire, rather compact designs are required because the grooves and the lamellae weakening the resistance of the blocks, give them a notable mobility under the contact surface of the tire which leads to more considerable and especially more irregular wear. This situation has the main consequence of making the tire, and therefore the vehicle, mobile transverse to the direction of travel and not very sensitive to the action of the steering mechanism.

The phenomenon is obviously accentuated in the case of tires of large dimensions which support heavy loads in which the forces involved thus have enormous values. It is particularly marked in the curvilinear trajectories where one must face the curves of the route of the road.

25 Under these conditions, the crown zone of the most stressed tire is obviously the shoulder which is in the external position relative to the arc of the curve. In fact, the composition of the weight of the vehicle and of the centrifugal force which acts on it gives rise to a force which is exerted on the ground and which is thwarted by a system of tangential forces of friction located entirely in the part lateral of the crown area of the tire and, moreover, generally on a surface which is smaller than the contact surface which corresponds to the rectilinear step of the vehicle.

This lateral part is generally provided with a circumferential groove of variable shape but substantially adapted to separate the tread from / the shoulder of the tire and, consequently, from the sidewall, for "r1 • _: 3 Λ take account of the types different stresses to which these areas are respectively subjected during the running of the vehicle.

However, when the tire traverses a curvilinear trajectory, the tangential forces acting on the surface of the crown and directed like the axis of the tire tend to close the circumferential groove of the shoulder above | mentioned. If the width of the groove is such, taking account of its depth as naturally, that it can effectively close under this thrust, the corresponding zone of the tread stiffens, accompanied by a gain in the stability and the precision of the driving i of the tire, but of a serious loss of grip on! wet floor due to the deficiency in the breaking action of the liquid film interposed between the tire and the road in the mutual contact zone.

If, on the contrary, the groove has a width j such that it cannot close, the phenomenon Ί j of 11aqua-planing is avoided but the corresponding zone of the strip of! 2Q bearing has excessive block mobility, which! leads to a loss of grip when cornering on dry ground! or wet.

The object of the present invention consists of a tread pattern which has, in the lateral zones of the crown of the tire, characteristics guaranteeing a certain prevention of the phenomenon of aqua-planing - even under conditions different from straight walking - and at the same time providing improved handling characteristics and | 30 of response to the direction of the tire.

The object of the present invention therefore consists of a tire for vehicle wheels, the crown portion of which extends axially from a sidewall | to the other and which presents towards the outside a strip of elastomeric material, comprises a central strip - designated by | 15 tread "- which corresponds substantially to the radially external surface of said crown and which yj is always in contact with the ground during the straight line operation of the tire in service, and two lateral bands 4 - designated by" shoulders "- which substantially correspond to the axially external surfaces of the said ring connecting the tread and the sidewalls and which are in contact only intermittently with the ground during the running of the tire in service, said tread being provided of a drawing produced by a plurality of grooves and notches hollowed out in the thickness of the strip from the external surface and directed radially towards the interior of the tire, said tire 10 being characterized in that the drawing has, in the lateral zones, a continuous circumferential groove which has along its radial development at least one zone of abrupt variation of its axial width which divides said groove into two sections respectively radially external and radially internal with respect to this zone, the minimum axial width of the radially external section being greater than the maximum axial width of the radially internal section.

Various embodiments can be re-2Q alized. Among these, a technician in the sector can choose, with the help of adequate experience, the one which provides the best results taking into account the dimensions of the tire and its structural characteristics, and also which best integrates with the overall characteristics 25 of the design of the tread to be adopted.

Thus, the axial width of the radially outer and radially inner groove sections can either be variable in the radial direction or be constant, and it may not be of the same type in the two sections.

These groove sections can be symmetrical with respect to a single equatorial plane, or they can each admit their own equatorial plane of symmetry or else admit none of these planes.

The abrupt variation in the axial width 35 of the groove can be concentrated at one point or else concern a certain part of the radial development of the groove, but in the latter case the relationship between the radial dimension of this part and the total dimension of the I groove must be between O and 1.

3 5 •

With regard to the values of the axial width, it is good to respect the conditions according to which the ratio between the maximum axial width and the maximum depth of the groove must be between 5 0.2 and 1; the ratio between the maximum axial widths of the radially outer and radially inner sections must be between 2 and 10.

In addition, it is also good that the ratio between the values of the radial development of the res-1Q pectively radially external and radially internal sections mentioned above is between 0.3 and 0.7.

Finally also, the distance between the equatorial plane of the tire and the meridian plane of the annular part

Area of the crown of the tire containing said groove 15 must be between 45% and 85% of the half-width of the tread.

In any case, the present invention will be better understood using the description below and the [appended drawings, given simply by way of examples but! 20 nonlimiting, in which: j - Figure 1 shows a plan view of a circumferential part of the design of the tread according to the invention, - Figure 2 shows a sectional view of the part of the 25 crown of the tire provided with the drawing of the above-mentioned tread, j - FIGS. 3, 4 and 5 represent three possible different cross-section views of the lateral grooves of the drawing of FIG. 1 and 130 - FIGS. 6, 7 and 8 show the sectional views of the above grooves, respectively along the planes VI-VI, VII-VII and VIII-VIII of FIG. gure 1.

The tread pattern shown in FIGS. 1 and 2, which extends axially from one shoulder to the other of the tire, comprises two large circumferential grooves 1, arranged in a zigzag in the central position, and two narrower grooves 2, in the lateral position, j also arranged in a zigzag. These grooves delimit, i 6 as a whole, a large central cord 3, two intermediate cords 4 and two lateral cords 5 called the "shoulder cords

The central bead 3 also has 5 notches 6 which start from the side of the groove at the level of radial cavities 7 provided in the side itself.

Similar cavities 8 are also provided in the sides of the radially external section of the grooves 2 and (as will be explained more fully below) other cavities 9 are also provided in the sides of the radially internal section of the grooves 2 above.

Furthermore, these grooves are located in a band 10 of the part of the crown delimited by two planes perpendicular to the axis of the tire indicated by the letters "r" and "s" and highlighted by the trace of their intersection. with the drawing plan.

The median plane of this strip 10 is indicated by the letter "p", while the letter "m" designates the 2Q equatorial plane of the tire.

As has already been said, during the straight line running of the tire in service, almost the entire radially outer surface of the crown portion of the tire and the corresponding drawing is in contact with one another. a permanent way with the ground. The width of this part, which will be called "tread" in the description of the present invention, is easily determined by measuring the width of the contact surface and is indicated by the letter "L" in FIGS. 1 and 30 2. The remaining lateral strips of the surface of said crown portion, oriented almost exclusively axially outwards, constitute the shoulders or shoulders of the tire.

According to the invention, the distance "£ / 2" between the planes "m" and "p" must be between 45% and 85% of "L / 2".

Turning now to the subsequent figures, it can be seen that FIG. 3 illustrates in detail a first form of cross-sectional view of the grooves 2 corresponding to 47 of the invention.

As already indicated previously, this sectional view comprises an abrupt variation in width along the radial development of the groove which forms subs-5 both in the cavity two sections respectively external "h" and radially internal "k". It should be specified here that by the expression "sudden variation in the width of the section" is meant a variation in the width of the groove delimited between two lines of 1Q discontinuity (points 11 and 12 on the sectional view of Figure 3) in the slope of a side of the groove, which - when they are not on the same surface perpendicular to the radial axis of the groove (as in Figures 4 to 8) - are spaced l from one another in the above-mentioned radial direction of a space "d" the length of which is not greater than 33% of the total radial development "H" of the groove (h + d + k).

According to the invention, there are also preferential ratios determined between the various characteristic di-2Q mensions of the above-mentioned groove; in particular - with reference to FIG. 3 - the ratio between the maximum width "a" and the maximum depth * 'H "of the groove must be between 0.2 and 1- In addition, the minimum width" b " of the distance "h“ which lies radially outside the zone of the said abrupt variation must be greater than the maximum width ”c” of the radially internal distance “k”

It is good that the ratio h / k is between 0.3 and 0.7 and that the ratio a / c is between 2 30 and 10.

In FIG. 3, the groove is symmetrical with respect to the median plane "t" and it has its sides inclined and flared towards the outside. However, these conditions are in no way restrictive characteristics. In fact, according to various embodiments of the groove, the latter can have distances "h" and "k" of constant width and admit for each of these a different plane of symmetry (m1 and m2 in FIG. 4) or else admit no plane of symmetry.

8 "

It is also possible to provide various combinations of the above characteristics. In particular, the sudden variation of the axial width can be determined by a double variation of the slope on a single flank of the groove, or else the two flanks of the groove can exhibit double variations of the slope, and even in zones which are not opposite one another, or finally there can exist in the groove many zones having an abrupt variation of the axial width.

1Ö In the latter case, it may be that all the preferential relationships specified above are not respected, given, moreover, that there may be an incompatibility between some of them, but in any case the general conditions ( that is, the ratios between the maximum values indicated above will be observed.

According to another embodiment, very suitable, of the invention, the aforementioned shoulder groove has a section which branches inwards, that is to say that the sudden variation in the width of the section is obtained by means of a protrusion 13 projecting radially outwards from the bottom of the groove 2 (FIG. 5) and separated from the two sides of said groove so as to produce for each radially external section two sections and k ^ radially internal which may possibly have a different radial development from each other.

This solution has been shown to be particularly useful in the field of the invention because of its additional effect of expelling pebbles or other materials 30 which are embedded in the groove 2 during service of the tire.

Figures 6,7 and 8 show the section of the groove 2 of the tread pattern of Figure 1 along three different section planes and they explain themselves without the need to give more details.

Apart from the fact that we can see the perfect correspondence of the geometric characteristics! and dimensional with the conditions set out above, one ß 9 can verify in FIGS. 7 and 8 the presence of the respective cavities 9 and 8 already represented in FIG. 1, dug in the side of the radially internal k and radially external groove sections h.

5 The lateral shoulder grooves (with their cross section in accordance with that shown above), placed on the crown portion of the tire in the interval mentioned according to the invention, have demonstrated that they are able to resolve very adequately problem 10 proposed.

It has already been said that in the presence of tangential forces directed like the axis of the tire and acting predominantly on the side cords, the shoulder grooves of conventional tires close.

15 In fact, these cords - which can be shown, even roughly, as beams recessed on the bottom and projecting radially outwardly from a surface located at the bottom of the grooves - under the effect of the above tangential forces flé-20. fall behind the innermost cord and thus close the shoulder groove, causing the serious drawbacks already reported.

On the contrary, due to the particular shape of the section of the groove according to the invention, 125 the bead 5 of the tire of the invention rests against the bead 4, starting from the radially innermost zone, and thus closes the section k of the groove.

Under these conditions, the section h is still open and, at the same time, the part of the cords which are in mutual contact behaves like a solid element which is not subsequently deformable. In this way, the surface from which the cord 5 protrudes at i; overhang comes to be the surface corresponding to the area S * of the sudden variation in the width of the section and, consequently 135, the radial development of the part of the bead which can still bend is almost reduced in half, compared to the cord considered in its entirety.

| In other words, the length of the cantilever beam is very considerably reduced - if one refers to the scheme adopted to study the phenomenon - and therefore, S equal intensity of forces in action , the displacement of the bead decreases much more than proportionally due to the deformation in bending.

5 In practice, the part of the cord 5 corresponding to the section "hn does not move later, thus keeping open the radially outer section of the groove 2 and, moreover, it acquires a very high rigidity which also eliminates mobility radial of the cor-10 donation under the contact surface, as well as all the harmful effects associated therewith.

Naturally, as the tire wears down, the depth of the radially external section "h" decreases until it is completely canceled out by carrying the mouth of the section "k" at the surface. of the road.

In this situation, what still has been said above about the new tire still occurs, that is to say that the length of the cantilever beam 20 then constituted by the section "k" is clearly diminished and is therefore able to resist without bending the stresses of the above tangential forces, as a result of which the section "k" will no longer be able to close.

Naturally, the width of this section 25 "k" of the groove is significantly smaller, due to the conditions imposed by the invention, than the minimum width of the section "h" (byc), as a result of which the action of prevention of aqua-planing - if it occurs despite everything - is less effective.

3Q It is for this reason that in order to restore the initial efficiency of the cavities (9 in FIG. 7) are hollowed out in the side of the above-mentioned section "k", at the level of the straight longitudinal sections of the groove, these cavities having a gradually decreasing volume towards the bottom of the groove and being as deep as the latter.

Similar cavities (8 in FIG. 8) can also be provided - in a manner known per se - in the sides of the radially external section "h”, in particular at the point of intersection of two sections * 7Γν '/ 4 11 j straight zigzag lines.

t j In conclusion, the tire designed in this way shows that it has to a high degree the two qualities of driving stability and handling on wet ground.

But, in a very surprising and entirely unpredictable manner, the drawing of the invention has proved capable of solving yet another problem.

The technicians in the branch know perfectly well that, especially for tires of large di-10 mensions, the lateral parts of the tread are subjected early to an irregular type of wear, usually called "stepped wear" which not only confers on the unattractive appearance which damages the image of product quality - with all the serious commercial consequences which results from it - but which also shortens the life of the tire.

This type of wear is probably due to the bending deformation of the shoulder cords during the curvilinear trajectories, as a result of which not only the shoulder grooves 20 close but also the radially external surface of the cords probably takes an orientation. particular with respect to the ground, which gives rise to a non-uniform distribution (of the friction forces acting on the bead, which results in irregular wear in steps.

| The Applicant has now found that the design of the invention also provides a great improvement in the aforementioned phenomenon, perhaps due to the increase in rigidity (mentioned above) of the cord which - while maintaining the radially external surface of it oriented cor-30 rectly with respect to the ground - would lead to a uniform distribution on this surface of the friction forces and would therefore make it possible to obtain uniform and regular wear.

It is understood that the present description is given only by way of nonlimiting example and that the invention also relates to all the modifications and variants which are not expressly stated but that a technician of the branch can easily deduce at the start of I the present inventive idea, jj .rf5 Κώ f

Claims (14)

12 1. A tire for vehicle wheels, the crown portion of which extends axially from one sidewall to the other and which presents towards the outside a strip 5 of elastomeric material, comprises a central strip - designated by "strip of bearing "- which corresponds substantially to the radially outer surface of said crown and which is always in contact with the ground during the rectilinear operation of the tire in service, and two lateral bands 10 - designated by" shoulders "- which correspond substantially to the surfaces axially external of said crown connecting the tread and the sidewalls and which are in contact only intermittently with the ground during the running of the tire in service, said tread 15 being provided with a design produced by a plurality of grooves and notches cut into the thickness of the strip from the external surface and directed radially towards the inside of the tire, characterized in that the design has, in the lateral zones, a continuous circumferential groove which has along its radial development at least one zone of abrupt variation of its axial width which divides said groove into two sections respectively radially external and radially internal with respect to this zone, the minimum axial width of the radially external section being greater than the maximum axial width of the radially internal section. 2. A tire according to claim 1 characterized in that the ratio between the maximum axial width of the radially external section and the maximum radial development 3Q of the groove is between 0.2 and 1. 3. A tire according to claim 1 characterized in that the ratio between the maximum axial widths of the radially external and radially internal sections respectively is between 2 and 10. 4. A tire according to claim 1 characterized in that the ratio between the radial develop- ments of the radially external and internal radial sections respectively is between 0.3 and 0.7. 5. A tire according to claim 1/13 characterized in that the axial width of the radially external section is constant along its entire radial development. 6. A tire according to claim 1 i 5 characterized in that the axial width of the radially internal section is constant along its entire radial development. 7. A tire according to claim 1 characterized in that the median plane of the section of the radially external section 1 „10 does not coincide with the median plane of the section of the radially internal section. 8. A tire according to claim 1 characterized in that the radial development of the zone in which the abrupt variation of the axial width of the groove occurs is not greater than 1 of the total radial development of the groove. 9. A tire according to claim 1 characterized in that the dull radially ex-4 groove section is common to two radially groove sections! 20 internal, each of these two sections having a flank in | j common with the corresponding flank of said cross section | radially external. i jj 10. A tire according to any one of; preceding claims characterized in that said continuous circumferential groove has a longitudinal I-zigzag pattern. 11. A tire according to claim 10! 1 characterized in that in each rectilinear part of said groove at least one of the sides of the radially internal section has at least one cavity having a radial development equal to that of the radially internal section. 12. A tire according to claim 10 characterized in that, at each intersection point of two rectilinear sections of the circumferential groove in a zigzag shape, there are cavities open on the radially section. external and having the same radial jj j development as this one. 13. Tire according to any one of 1 Ar; ί “14 • previous claims characterized in that the ratio between the axial distance, separating the median plane of the crown band of the tire containing said continuous circumferential groove of the equatorial plane of the pneumati-5, and the half-width of it is between 0.45 and 0.85. ^ -