Tyre tread band, in particular for off-road motor-vehicles

Abstract: The described tread band (1) has laterally opposite transverse channels (6), each having a substantially rectilinear end stretch (6a) extending with an appropriate inclination from a respective outer side edge (1a), a connecting stretch (6c) of curvilinear extension and an inner end stretch (6b) terminating beyond the equatorial plane (X) and having a slightly inclined orientation relative the latter. The connecting stretch (6c) of each transverse channel (6) opens into the connecting stretch of a laterally opposite transverse channel, to define a transverse groove (3) of undulated extension. Also provided are two longitudinal grooves (2) consisting of substantially rectilinear stretches (2a) each extending between two transverse grooves (3) in a direction inclined to the equatorial plane (X). L-shaped auxiliary channels (8) are interposed in an alternate sequence relative to the transverse channels (6) defining grooves (3).

Description: The present invention relates to a tyre tread band, in particular for off-road motor-vehicles, of the type comprising at least two longitudinal grooves substantially parallel to each other and extending circumferentially on opposite sides of the equatorial plane of a tyre carrying said tread band; at least one series of transverse grooves crossing the longitudinal grooves, said transverse and longitudinal grooves delimiting at least two rows of shoulder blocks circumferentially distributed at opposite side edges, and at least one row of centre blocks disposed between said rows of shoulder blocks. In more detail, the invention relates to a tread band having a pattern of a bidirectional and/or symmetric type. The invention also pertains to a tyre, in particular for off-road motor-vehicles, provided with the tread band in reference. It is known that thread bands in tyres have a pattern suitably cut by a series of longitudinal and transverse grooves, adapted to normally define one or more rows of circumferentially distributed centre blocks alongside which, on respectively opposite sides, there are respective rows of shoulder blocks located close to the opposite side edges of the tread band. The geometrical and size features of the grooves and of further possible cuts provided in the tread band, and consequently of the blocks defined thereby, are selected each time during the planning step, depending on the performance features required from the tyre, based on the intended type of use. Usually, the longitudinal grooves perform the function of giving the tyre steering property and roadholding features in relation to transverse stresses, that is stresses directed parallelly to the rotation axis of the tyre. The transverse grooves in turn perform the function of giving the tyre good traction performances, in relation to the tangential thrusts directed parallelly to the running direction. In addition, longitudinal and transverse grooves cooperate in carrying out an efficient water-draining action from the ground-contacting area of the tyre when the vehicle is running on a wet road surface. After the above statements, in making tyres particularly adapted for use on off-road motor-vehicles, good traction performances are to be achieved above all with reference to muddy and snow-covered grounds or in any case grounds of low consistency. These requirements are presently met by providing a great number of grooves and longitudinal and transverse cuts of great width and depth. However this solution has a tendency to impair the tyre running behaviour on normally asphalted roadways. Actually, due to the presence of many big grooves, the sizes and stiffness of the blocks is greatly reduced. Consequently, the block can be unable to conveniently withstand stresses to which the tyre is submitted both when the vehicle is running on a straight stretch and during the cornering, thereby giving rise to a rather uncertain and imprecise behaviour on the road, as well as to early and/or uneven wear of the tread band. In addition, the presence of big transverse grooves has a tendency to give rise to an undesired increase in noise and in the rolling resistance force of the tyre and, as a matter of fact, the present market requirements attach an increasingly greater importance to these factors. EP-506,279 corresponding to the preamble of claim 1, concerns a tyre tread pattern suitable for vehicles running at high speed values (e.g. above 190 km/h) and which have good traction and braking characteristics both in wet and snow-covered roads. In particular, EP-506,279 discloses a tread having curved open-ended transverse tread grooves disposed obliquely to the circumferential direction, each transverse groove extending from the central region of the tread to a corresponding edge of the tread. Transverse ribs are formed between successive adjacent transverse groves, said transverse ribs being subdivided into individual blocks by the presence of longitudinal grooves. According to some embodiments, the centremost transverse rib sections adjacent to the tread strip centreline merges into corresponding transverse rib sections on the other side of the tread centreline so that a continuous longitudinal central rib is formed which extends substantially in zig-zag manner around the tyre. According to a further embodiments, the tread pattern is provided with a continuous longitudinal central groove or a sipe which so that the transverse rib sections are formed as individual blocks. In accordance with the present invention, there is the provision of a tyre tread band according to claim 1 Preferably, each transverse channel has a gradually decreasing width away from the corresponding side edge of the tread band and, in another aspect of the invention, it preferably terminates beyond the equatorial plane with a respective inner end stretch the axis of which is oriented at an angle included between 0° and 25°, relative to said equatorial plane. The outer end stretches of the transverse channels are in turn preferably inclined to an angle included between 0° and 20° on both sides relative to the direction normal to said equatorial plane. Advantageously, the connecting stretches of the transverse channels having a curved extension with a radius of curvature included between 10% and 40% of the tread width, mutually meet close to the equatorial plane of the tyre and have their mutual-intersection points lying in a common straight line oriented according to an inclination included between 15° and 45° with respect to the equatorial plane. In addition, it is preferably provided that auxiliary channels should be associated with each of said shoulder block rows, said auxiliary channels being each disposed at a position preferentially spaced apart the same distance from two circumferentially contiguous transverse channels. Each auxiliary channel advantageously has a first stretch extending from the corresponding side edge of the tread band in a direction substantially normal to the equatorial plane and/or parallel to the outer end stretches of the adjacent transverse channels, and a second stretch crossing an adjacent transverse channel in a direction substantially parallel to the equatorial plane, intersecting said channel close to the transition point between said outer end stretch and connecting stretch. More preferably, the axis of the second stretch in each auxiliary channel is inclined at an angle included between 0° and 25° relative to the equatorial plane and oriented in an opposite direction to the inner end stretch of the circumferentially adjacent transverse channels. Each auxiliary channel further has an intermediate stretch connecting the first and second stretches by a curved course. It is also preferably provided that at least one longitudinal cut should extend from the first stretch of each auxiliary channel, the longitudinal cut partly penetrating into an adjacent shoulder block. Advantageously, the transverse and auxiliary channels define first shoulder blocks each of which comprises an outer portion of an elongated conformation in a direction substantially perpendicular to the equatorial plane and an inner portion of an elongated conformation in a direction substantially parallel to the equatorial plane, as well as second blocks of same configuration as the outer portions of the first blocks. As regards centre blocks, each of them has a conformation substantially defined by a centre portion disposed diagonally at the equatorial plane and interconnected, at respectively opposite sides, with two side portions substantially parallel to the equatorial plane. In accordance with another preferential feature of the present invention, each of said longitudinal grooves consists of a series of stretches, preferably substantially rectilinear, each extending between two contiguous transverse grooves at an angle included between 0° and 10° relative to said equatorial plane, all preferably inclined in the same direction. In another aspect, the present invention relates to a tyre for motor-vehicle wheels, in particular off-road motor-vehicles, provided with a tread band having the above described features. Further features and advantages will become more apparent from the detailed description of a preferred but non-exclusive embodiment of a tyre tread band, in particular for off-road motor-vehicles, in accordance with the present invention. This description will be taken hereinafter with reference to the accompanying drawing, given by way of non-limiting example and showing a plan view of a portion of the tread band in accordance with the invention, generally denoted by 1. The tread band 1, of the so-called bidirectional type, i.e. free of a preferential rotation direction, and/or symmetric, i.e. without constraints as regards the (inner/outer) mounting side, has at least two longitudinal grooves 2 circumferentially extending on respectively opposite sides relative to the equatorial plane of the tyre to which the tread band 1 will be applied. In the figure said equatorial plane is identified by line "X" parallel to the circumferential extension direction of the tread band. The tread band 1 further has at least one series of transverse grooves 3 each extending between the opposite side edges 1a of the tread band 1 and crossing the longitudinal grooves 2. In a preferential solution, the longitudinal grooves 2, disposed symmetrically of the equatorial plane "X", are spaced apart from each other by a distance "d" included between 15% and 35% of the overall width "W" of the tread band 1, measured between the side edges 1a. It is also preferably provided that each longitudinal groove 2 be made up of a series of substantially rectilinear stretches 2a, each extending between two transverse grooves 2 that are contiguous in a circumferential direction, at an angle "α" included between 0° and 10°, and preferably of 3° relative to the equatorial plane "X". The assembly of transverse grooves 3 and longitudinal grooves 2 defines at least two rows of shoulder blocks 4, circumferentially distributed at the side edges 1a, and at least one row of centre blocks 5, located between the shoulder block 4 rows. Each of the transverse grooves 3 is advantageously defined by at least two transverse channels 6 that, starting from the opposite side edges 1a, respectively extend in the direction of the central portion of the tread band 1. Each transverse channel 6 has an outer end stretch 6a extending from the respective side edge 1a according to an orientation substantially transverse to the equatorial plane "X". In more detail, each outer end stretch 6a extends at an angle "β" included between 0° and 20°, and preferably of 12°, on either side relative to a direction "n" normal to the equatorial plane. Each transverse channel 6 preferably terminates beyond the equatorial plane "X", penetrating into the respective centre block 5 by an inner end stretch 6b substantially parallel to the equatorial plane. In more detail, the axis of each of the inner end stretches 6b is inclined to the equatorial plane "X" by an angle "δ" included between 0° and 25°, and preferably of 7°, and spaced apart from the equatorial plane by a distance "1" included between 3% and 15% of width "W" measured at the apex of said stretch. As can be easily viewed from the accompanying figure, each transverse channel 6 has a gradually decreasing width starting from the corresponding side wall 1a, where the value of this width is included, just as an indication, between 9 mm and 12 mm, until the apex of the inner end stretch 6b where this width is reduced to a value as low as 2 mm at most. The outer end stretch 6a and inner end stretch 6b of each transverse channel 6 are mutually connected in a continuity relationship by a connecting stretch 6c having a curvilinear extension of large curvature. In more detail, the connecting stretch 6c extends according to an arc of a circle of radius "R", preferably included between 10% and 40% of W, in particular between 45 and 80 mm. As clearly shown in the accompanying drawing, the connecting stretch 6c of each transverse channel 6 meets the connecting stretch of the laterally opposite transverse channel 6, so as to give rise to a continuous transverse groove 3 of a substantially undulated extension. Preferably these connecting stretches 6c of the two transverse channels 6 joined together, will form a concave stretch and a convex stretch respectively, relative to the circumferential direction of the tyre. The connecting stretches 6c also interconnect the end stretches 6b of the respective transverse channels 6 in a continuity relationship. The intersection points M and N of the axially opposite transverse channels lie in a common straight line "t" oriented according to an inclination "Ω" included between 15° and 45° relative to the equatorial plane "X". Due to the presence of the inner end stretches of the transverse channels 6, each of the centre blocks 5 takes a substantially Z-shaped conformation, seen in side view, defined by a centre portion 5a preferably disposed diagonally, at the equatorial plane "X", and interconnected, at respectively opposite sides, with two side portions 5b preferably extending in a direction substantially parallel to the equatorial plane. In addition, each centre block 5 is preferably passed through, along a median transverse line, by at least one central narrow cut 7 extending parallelly to the transverse grooves 3. This central narrow cut 7 has a width in the order of 1,5 mm, and at all events included between 0,8 and 2,5 mm and a depth substantially corresponding to half the depth of the transverse grooves and preferably the same depth as the longitudinal grooves 2. In accordance with a further feature of the present invention, auxiliary channels are associated with each row of the shoulder blocks 4. Each of these auxiliary channels 8 is preferably disposed at a position substantially spaced apart the same distance from two of the circumferentially contiguous transverse channels 6. Each auxiliary channel 8 preferably of the same depth as the transverse channels 6 or the longitudinal grooves 2, has one stretch 8a extending from the corresponding side edge 1a in a direction preferably parallel to the outer end stretches 6a of the transverse channels 6 and a second stretch 8b crossing an adjacent transverse channel 6 in a direction substantially parallel to the equatorial plane "X", and preferably opposite to that of the inner stretch 6b of said transverse channel 6. Preferably, the axis of the second stretch 8b of each auxiliary channel 8 is inclined by an angle "δ" included between 0° and 25° relative to the equatorial plane, in a direction opposite to the inclination of the inner end stretches 6b of the transverse channels 6, and crosses the corresponding transverse channel 6 close to the transition point between the outer end stretch 6a and the connecting stretch 6c thereof. Each auxiliary cut 8 further has an intermediate stretch 8c extending in a curved configuration between the first and second stretches 8a, 8b. Preferably, the intermediate stretch 8c extends in the form of an arc of a circle of a radius "r" included between 10 mm and 35 mm. In the same manner as described with reference to the transverse channels 6, each auxiliary channel 8 preferably has a gradually decreasing width starting from the corresponding side edge 1a where said width is included between 9 mm and 12 mm, until the apex of the second stretch 8b, where this width takes a value as low as 2 mm at most. Preferably, the maximum and minimum values of the width of each auxiliary channel 8 are substantially coincident with the maximum and minimum values of the width of the transverse channels 6. The presence of the auxiliary cuts 8 alternated with the transverse cuts 6 gives rise, in each of the shoulder block 4 rows, to first and second shoulder blocks 9a and 9b placed consecutively one after the other in an alternate sequence. The first shoulder blocks 9a have a substantially L-shaped configuration, an outer portion 10 of which has an elongated conformation substantially perpendicular to the equatorial plane "X" and an inner portion 11 of which has an elongated conformation in a direction substantially parallel to the equatorial plane. The apex of the second stretch 8b of each channel 8 causes a partial separation between the outer and inner portions of each of the first blocks 9a, thereby partly releasing one portion from the other portion. Further extending from the first stretch 8a of each auxiliary channel 8 is a blind longitudinal cut 12 preferably of a width corresponding to about half the depth of the auxiliary channel and spaced apart from the equatorial plane "X" by a distance D 2 included between 25% and 40% of "W". This longitudinal cut penetrates into the outer portion 10 of the adjacent first block 9a by about half its circumferential extension in order to reduce the overall stiffness of the first block 9a. In order to further increase flexibility of the first blocks 9a at the respective outer portions 10, it is contemplated that each of them be further provided with a first outer narrow cut 13 of a width preferably lower than 1.5 mm and extending in a direction substantially parallel to the outer end stretch 6a of the transverse channel 6 starting from the apex of the second stretch 8b of the auxiliary channel 8, and crossing the longitudinal cut 12 to terminate beyond the latter in the direction of the corresponding side edge 1a. Each of the second shoulder blocks 9b substantially has the same shape and sizes as the outer portion 10 of the first shoulder block 9a. Auxiliary longitudinal cuts 14, disposed and shaped in the same manner as the above described longitudinal cuts 12, extend from the outer end stretches 6a of the transverse channels 6 penetrating into the second shoulder blocks 9b. Each auxiliary longitudinal cut 14 is crossed, at the apex thereof, by a second outer narrow cut 15 terminating at the second stretch 8b of the auxiliary channel 8, and having the same shape and orientation as described with reference to the first outer narrow cuts 13. In a different preferred embodiment the substantially rectilinear stretches 2a provided on each longitudinal groove 2 can be inclined in the opposite direction so as to obtain a directional pattern. Preferably, also the second stretches 8b present in the shoulder block 4 rows are disposed in the same direction, in accordance with the inclination direction of the rectilinear stretches 2a so as to more clearly accomplish a directional pattern. Still more preferentially all stretches 6b too are disposed in the same direction as the second stretches 8b. In a further different embodiment, the longitudinal and transverse groove stretches can be also combined so as to make a pattern of an asymmetric type. By way of example only, some dimension features of a prototype tyre, size 275/55R17, embodying a tread band in accordance with the invention, are reproduced hereinafter. It is to point out that the tyre in question is a radial tyre of the traditional type, commonly known by technicians: it comprises a radial carcass having a reinforcing structure formed of at least one ply of rubberized fabric, the ends of which are each turned up about an anchoring core provided on its radially outer surface with a rubber filling. Preferably the turned-up flaps of the carcass ply radially go up outwardly along at least part of the side of said filling. It is known that the tyre area comprising the anchoring core and filling forms the tyre bead intended for anchoring the tyre to a corresponding mounting rim. Disposed on the carcass in known manner is a tread band provided with a raised pattern, intended for bringing the tyre into rolling contact with the ground, said raised pattern being in this case the tread pattern of the invention, as previously described. This kind of tyre also comprises a belt structure disposed crown-wise to the carcass, interposed between the carcass and tread band and substantially extending between the two tyre sidewalls, that is as wide as the tread band. Said belt structure comprises two radially superposed layers of reinforcing cords, preferably of metal material, parallel to each other in each layer and in crossed relationship with those of the adjacent layer relative to the equatorial plane of the tyre, and a radially outermost layer of reinforcing cords, preferably of textile material, and still more preferably of heat-shrinkable (nylon) material, oriented at 0°, i.e. in a circumferential direction. Variant versions of the above described solution are commonly known and intended for specific uses of the tyre and can be applied to the tyre of the invention as well. Said prototype has the following features: Overall width of the tread band: "W" = 293.7 mm Inclination of the outer end stretches 6a of the transverse channels 6: "β" = 12° Inclination of the inner end stretches 6b of the transverse channels 6: "δ" = 7° Radius of curvature of the connecting stretches 6c of the transverse channels: "R" = 65 mm Distance of the apex of the inner end stretch 6b from the equatorial plane "X": "l" =9.4% of "W" Average inclination of the second stretch 8b of the auxiliary channel 8: "δ" = 7° Radius of curvature of the intermediate stretch 8c of the auxiliary channel 8: "r" = 18 mm Distance of the first and second longitudinal cuts 12, 14 from the equatorial plane "X": "D 2 " = 30% of "W" Width of each inclined stretch 2a of the longitudinal grooves 2: = 10 mm Inclination of the inclined stretches of the longitudinal grooves 2 "α" = 3° Depth of the longitudinal grooves 2, of the transverse and auxiliary channels 6 and 8, respectively: = 8,5 mm The tread band pattern in question has such geometrical features that, while the number and width of the transverse and auxiliary channels 6 and 8 respectively and the longitudinal grooves 2 are conveniently large so as to achieve the required performances on muddy, snow-covered and similar road surfaces, the tyre in any case has an excellent drive behaviour even on an asphalted road. In particular, the presence of the auxiliary channels 8 in the shoulder block 4 rows causes the pitch of the blocks at the tyre shoulders to be substantially doubled relative to the innermost areas of the tread band. This condition appears to be advantageous to the ends of the so-called "progressiveness" in the tyre ground-contacting, that is the tyre suitability, on reaching the adhesion limits in the cornering, to transmit the driver the feeling that this limit is reached without giving rise to sudden adhesion losses. The inner portions 11 of the first shoulder blocks 9a, prolonging in the circumferential direction to an extent equal to the pitch of the transverse channels 6, ensure excellent steering properties and roadholding features in connection with slip thrusts. In addition, interconnection between the outer portions 10 and inner portions 11 of the first shoulder blocks 9a ensures an excellent torsional stiffness of the blocks themselves, useful for achieving an even wear. The presence of the longitudinal grooves 2 consisting of rectilinear stretches 2a and second stretches 8b of the auxiliary channels 8, preferably substantially parallel to each other, ensures by itself, an efficient water draining when the vehicle is running on wet road surfaces. In addition, the thus shaped longitudinal grooves promote the steering property. An efficient water draining from the ground-contacting area of the tyre is further promoted by the particular conformation of the transverse channels 6 at the respective inner end stretches 6b, as well as by effect of the mutual intersection of the connecting stretches 6c. In this manner the water gathered in the central region of the ground-contacting area is easily caused to flow through the transverse channels 6 towards the longitudinal grooves 2 and the outer side edges 1a. In addition, due to the conformation of the centre blocks 5, a good stiffness of same is achieved, so that movements of said centre blocks, on their contacting the ground, is limited and in any case optimized, which will bring about an advantage in terms of evenness and low velocity of wear, without on the other hand impairing the tyre capability of absorbing the upward projecting bumps on the road, to advantage of the ride comfort. It is also to point out that blocks in the tread band in question have a gradually decreasing torsional stiffness from the equatorial plane towards the opposite side edges, to advantage of the performance and ride comfort features on an asphalted road surface. Reproduced in the following tables are the evaluations, indicated by a 1 to 7 score, of the behavioural features of a tyre provided with a tread band in accordance with the present invention (line A) as compared with a tyre of known type (line B). In more detail, the tyre of known type is the best tyre, based on tests carried out by the Applicant, presently available on the market, sold for the same use as the tyre made in accordance with the invention. 1 2 3 4 5 6 7 8 A 7 6 6 6.5 7 7 6.5 6 B 6.5 6 6 6 6 6 6 5 Table 1 refers to a behaviour on a dry road surface. In this table scores under columns 1 and 2 refer to steering property on a straight stretch and steering rigidity, respectively. Scores under columns 3 and 4 in turn refer to the void in the middle of steering and steering quickness. By "void in the middle", as known to those skilled in the art, is intended the tyre capability of reacting to minimum rotations of the steering wheel relative to the straight neutral position. Columns 5 and 6 refer to the steering property in the cornering and readiness in realignment, respectively. Scores under columns 7 and 8 refer to the capability of absorbing shocks when obstacles present on the road surface are stepped over and to the running noise. The following Table 2 refers instead to a behaviour on a wet road. 1 2 3 4 A 6.5 7 7 7 B 5 6 6.5 6.5 In Table 2, scores in columns 1 and 2 point out balancing between the tyre features and those of the vehicle suspension system, between the front and back axles, under understeering (column 1) and oversteering (column 2) conditions respectively, that is the positive or negative tyre influence on the vehicle behaviour (under the above running conditions). Items in columns 3 and 4, in turn, concern how the tyre can be controlled in slip, at the adhesion limit, and the tyre behaviour on decreasing of the speed, in slip and at the end of a bend. From the above tables it is possible to see that the tyre provided with a tread band in accordance with the invention has, on an average, obtained higher scores than the tyre of known type. Finally, referring again to Fig. 1, it is possible to see that preferably the two connecting stretches 6a of each continuous transverse groove 3 form a stretch of substantially sinusoidal course. This sinusoid is preferably inclined at an angle included between about 10° and about 40° relative to the axis perpendicular to the equatorial plane X of the tyre. More preferably, it is clockwise or anticlockwise rotated by an angle included between about 18° and about 28° and most preferably between about 21° and about 25°. The outer end stretches 6a extend said sinusoid in a transverse direction. The sinusoid angle and width are capable of forming a groove 3 of great transverse extension, together with stretches 6a. Preferably said groove 3 includes two stretches of substantially horizontal extension, limited in the middle by the longitudinal (or substantially longitudinal: to the ends of the present invention the two terms are intended as equivalent) grooves 2 constituting more than the two thirds of the whole groove 3.

Claims: A tyre tread band (1) comprising: at least two longitudinal grooves (2) substantially parallel to each other and extending circumferentially on opposite sides of the equatorial plane (X) of a tyre carrying said tread band (1); at least one series of transverse grooves (3) crossing the longitudinal grooves, said transverse (3) and longitudinal (2) grooves delimiting at least two rows of shoulder blocks (4) circumferentially distributed at the opposite side edges, and at least one row of centre blocks (5) disposed between said rows of shoulder blocks (4), each of said transverse grooves (3) comprising at least two transverse channels (6) which mutually meet to give said transverse groove (3) an axially continuous course extending between opposite side edges (1a) of the tread band (1), each of said transverse channel (6) comprising: an outer end stretch (6a) extending from the respective side edge (1a) of the tread band (1) in an orientation substantially perpendicular to the equatorial plane (X); a curvilinear connecting stretch (6c) that, by joining to the corresponding curvilinear connecting stretch (6c) of the laterally-opposite transverse channel (6), gives said transverse groove (3) said continuous course, characterized in that at least one of said transverse channels (6) further comprises an inner end stretch (6b) penetrating into a respective block of said centre blocks (5), said connecting stretch (6c) interconnecting said outer end stretch (6a) with said inner end stretch (6b) in a continuity relationship. Tread band according to claim 1, characterized in that each inner end stretch (6b) is oriented in a direction substantially parallel to the equatorial plane (X). Tread band according to claim 1, characterized in that said connecting stretches (6c) meet each other close to the equatorial plane (X) of the tyre. Tread band according to claim 1, characterized in that each transverse channel (6) terminates beyond the equatorial plane (X) by a respective inner end stretch (6b). Tread band according to claim 1, characterized in that the outer end stretches (6a) of said transverse channels (6) are inclined at an angle (β) included between 0° and 20° on both sides relative to a direction (n) normal to said equatorial plane (X). Tread band according to claim 1, characterized in that the axis of said inner end stretches (6b) is oriented at an angle (δ) included between 0° and 25°, relative to said equatorial plane (X). Tread band according to claim 1, characterized in that said connecting stretch (6c) has a curved extension according to a radius of curvature (R) included between 45 mm and 80 mm. Tread band according to claim 1, characterized in that each of said transverse channels (6) has a gradually decreasing width away from the corresponding side edge (1a) of the tread band. Tread band according to claim 1, characterized in that the intersecting points (M and N) of said transverse channels (6) lie in a common straight line (t) oriented with an inclination (Ω) included between 15° and 45° with respect to the equatorial plane (X). Tread band according to claim 1, characterized in that auxiliary channels (8) are associated with each of said shoulder block (4) rows, each of said auxiliary channels being disposed at a position spaced apart the same distance from two circumferentially-contiguous transverse channels (6). Tread band according to claim 10, characterized in that each auxiliary channel (8) has one stretch (8a) extending from the corresponding side edge (1a) of the tread band in a direction substantially parallel to the outer end stretches (6a) of said transverse channels (6), and a second stretch (8b) crossing the adjacent transverse channel (6) in a direction substantially parallel to the equatorial plane (X). Tread band according to claim 11, characterized in that the second stretch (8b) of each auxiliary channel (8) intersects said transverse channel (6) close to the transition point between the outer end stretch (6a) and the connecting stretch 8(6c) of the transverse channel itself. Tread band according to claim 11, characterized in that each auxiliary channel (8) further has an intermediate stretch (8c) connecting the first and second stretches (8a, 8b) following a curved course. Tread band according to claim 11, characterized in that the axis of the second stretch (8b) of each auxiliary channel (8) is inclined at an angle (δ') included between 0° and 25° relative to the equatorial plane (X) and oriented in a direction opposite to the inner end stretch (6b) of the contiguous transverse channel (6). Tread band according to claim 11, characterized in that the second stretches (8b) of each auxiliary groove (8) associated with the same row of shoulder blocks (4) extend substantially in the same direction relative to the circumferential direction. Tread band according to claim 11, characterized in that the second stretches (8b) of the auxiliary grooves (8) associated with two different rows of shoulder blocks (4) extend all in the same direction relative to the circumferential direction. Tread band according to claim 11, characterized in that extending from the first stretch (8a) of each auxiliary channel (8) there is at least one longitudinal cut (12) partly penetrating into an adjacent shoulder block (9a). Tread band according to claim 11, characterized in that said transverse (6) and auxiliary (8) channels define first shoulder blocks (9a) comprising an outer portion (10) having an elongated conformation in a direction substantially perpendicular to the equatorial plane (X) and an inner portion (11) having an elongated conformation in a direction substantially parallel to the equatorial plane itself, as well as second blocks (9b) of same conformation as the outer portions (10) of the first blocks (9a). Tread band according to claim 1, characterized in that each of said centre blocks (5) has a substantially Z-shaped conformation defined by a centre portion (5a) disposed diagonally at the equatorial plane (X) and interconnected on respectively opposite sides with two side portions (5b) substantially parallel to the equatorial plane (X). Tread band according to claim 1, characterized in that each of said longitudinal grooves (2) is comprised of a series of rectilinear stretches (2a) each extending between two contiguous transverse grooves (3) at an angle (α) included between 0° and 10° relative to said equatorial plane. Tread band according to claim 10, wherein said grooves (2, 3, 8) are disposed according to a bi-directional pattern. Tread band according to claim 10 or claim 21, wherein said grooves (2, 3, 8) are disposed according to a symmetric pattern. Tread band according to claim 10, wherein said grooves (2, 3, 8) are disposed according to a directional pattern. Tread band according to claim 1, wherein each of said transverse grooves (3) comprises at least one concave and one convex transverse stretches (6a, 6c) relative to the circumferential direction of the tyre. Tread band according to claim 1, wherein at least one of said transverse grooves (3) comprises at least one first and one second inner end stretches (6b) substantially extending in opposite ways along a circumferential direction. A tyre for motor-vehicle wheels provided with a tread band according to one or more of the preceding claims.

Inventors: NICOTINA DOMENICO, NICOTINA, DOMENICO
Applicants: PIRELLI, PIRELLI PNEUMATICI SOCIETA PER AZIONI
Application year: 1997
Main classification: B60C11
IPC codes: B60C11