Patent Application
20070158009
The present invention relates to a pneumatic tyre particularly suitable for equipping two-wheeled vehicles.
It is known that a tyre generally comprises: a carcass structure provided with at least one carcass ply the ends of which are in engagement with respective circumferential annular reinforcing structures integrating annular elements usually called “bead cores”; a belt structure applied at a radially external position relative to the carcass structure, a pair of sidewalls applied at an axially external position to side surfaces of the carcass structure and each extending radially away from one of the annular anchoring structures towards said belt structure; a tread band currently consisting of a strip of elastomer material of appropriate thickness applied to the belt structure, at a radially external position and in which, following a moulding operation carried out concurrently with tyre vulcanisation, longitudinal and/or transverse grooves are formed that are disposed to define a desired “tread pattern”.
The carcass structure can be possibly coated on the inner walls thereof, with a so-called “liner” essentially consisting of an airtight layer of elastomer material that in tubeless tyres is adapted to ensure a hermetic seal of the tyre itself once it has been inflated.
In the so-called “radial” tyres each of the cords arranged in the carcass ply or plies lies in a plane substantially radial to the rotation axis of the tyre, i.e. it has an orientation substantially perpendicular to the circumferential extension direction.
In accordance with recent production processes, as described in document EP 928 680 in the name of the same Applicant for example, a pneumatic tyre can be directly built on a toroidal support. A first carcass ply is formed by laying a plurality of “strip-like elements” on said toroidal support, each strip-like element comprising longitudinal thread-like elements incorporated in a layer of elastomer material. Said strip-like elements are sequentially laid down so as to form a carcass structure in which the strip-like elements are partly overlapped at side portions of the tyre and disposed in circumferential side by side relationship with each other at the crown region of the tyre itself. Associated with the carcass ply are annular reinforcing structures for example comprising a first and a second circumferential annular inserts and an elastomer filler interposed therebetween. A second carcass ply can be made in superposed relationship with the first carcass ply and with said annular structures. Then a belt structure, also made by laying of strip-like elements, is associated with the carcass structure thus formed. Subsequently, a tread band and a pair of sidewalls are applied through superposition in coils disposed in axial side by side and/or radial superposed relationship, of an elementary semi-finished product of elastomer material in the form of an elongated element of suitable sizes. This process therefore contemplates use of at least two different types of elementary semi-finished products and more particularly: the elongated element, i.e. a section member of elastomer material alone and of substantially rectangular section; the strip-like element, i.e. a strip of elastomer material into which elongated reinforcing elements, typically textile or metallic cords are incorporated.
Document WO 00/38906 in the name of the same Applicant discloses a method of making a pneumatic tyre in which a carcass ply is formed by laying on a toroidal support, a first and a second series of sections alternated with each other and having side portions terminating on opposite sides relative to first primary portions of annular reinforcing structures to the beads. Subsequently, a second ply is formed in the same manner as the first ply, with a third and a fourth series of elongated sections superposed on opposite sides over second primary portions of the annular reinforcing structures. The sections forming the first and second carcass plies are laid in respective deposition planes parallelly offset on opposite sides relative to a meridian plane of the toroidal support, and have mutually-crossed side portions and radially-disposed crown portions.
As compared with tyres for four-wheeled vehicles, a quite particular performance involving many structural differences is required from tyres for two-wheeled vehicles. The most important differences result from the fact that during running on a bend a motorcycle must greatly incline relative to its position during running on a rectilinear stretch, forming an angle with the perpendicular to the ground (called “camber angle”) that usually reaches 45° but can even be as wide as 65° under extreme drive conditions. Therefore, when the motorcycle is running on a bend, the contact area of the tyre progressively moves from the central region of the tread to the axially outermost region in the direction of the bend centre. For this reason tyres for two-wheeled vehicles are distinguishable from the others due to the marked transverse curvature. This transverse curvature is usually defined by the particular value of the ratio of the distance between the radially outer point of the tread and the line passing by the laterally opposite extremities of the tread itself, measured on the equatorial plan of the tyre, to the distance measured along the tyre chord between said extremities. In tyres for two-wheeled vehicles, the value of the curvature ratio is generally at least as high as 0.15 and is currently in the order of about 0.3 for rear tyres and even higher, until about 0.45 for front tyres, against a value usually in the order of about 0.05 in the case of motor-vehicle tyres.
Presently, tyres for two-wheeled vehicles usually have a radial carcass structure associated with a belt structure that can comprise one or more belt layers shaped as a closed ring and essentially made up of textile or metallic cords suitably oriented relative to the cords belonging to the adjacent carcass structure.
In particular, the belt structure can be made of one or more continuous cords wound into coils that are disposed in axial side by side relationship and are substantially parallel to the circumferential extension direction of the tyre (the so-called “zero-degree belt”). Alternatively, the belt structure may consist of two radially superposed layers, each made up of elastomer material reinforced with cords disposed parallel to each other, said layers being such arranged that the cords of the first belt layer are oriented obliquely to the equatorial plane of the tyre, whereas the cords of the second layer have an oblique orientation as well, which however is symmetrically crossed with respect to the cords of the first layer (the so-called “crossed-belt”).
It is the Applicant's feeling that tyres for two-wheeled vehicles with crossed belt are characterised by a high bending rigidity in the region occupied by the tread band, which ensure an optimal behaviour on a bend. However, since the side rigidity at the sidewalls is relatively low as compared with the high bending rigidity in the region of the tread band, vibrations are likely to arise during running on a rectilinear stretch, which vibrations can reduce the vehicle stability at high speed.
On the contrary, in tyres for two-wheeled vehicles with a zero-degree belt, the bending rigidity at the tread band region is not substantially increased, so that during running on a rectilinear stretch, in particular at high speed, vibrations are controlled and gripping to the ground is improved. However, when a tyre is run on a bend the side rigidity may be insufficient and, in addition, in particular in the case of two-wheeled vehicles of big sizes, transmission of the torque onto the ground by the tyre may decrease.
In trying to combine an optimal behaviour during running both on a rectilinear stretch and on a bend, tyres for two-wheeled vehicles have been proposed in which the belt structure combines a zero-degree spiralling with a pair of crossed layers; see document GB 2 157 239, for example. These embodiments have seldom brought to a real balancing of the tyre behaviour, and at all events they involve a greater construction complexity and an important weight increase.
The Applicant has therefore felt the necessity to simplify the overall structure of the tyre, without on the other hand adversely affecting the behavioural features of same, maintaining ride comfort and stability substantially constant while reducing the weight. In addition, a simplified structure enables the building time to be reduced and, as a result, the production costs to be reduced as well.
The Applicant could ascertain that a carcass structure made with a single radial carcass ply makes the tyre structure lighter and simpler, but under some operating conditions, when high performance and high stability on a bend or on a rectilinear stretch are required from a tyre for example, the resulting tyre structure offers a poor performance above all with motorcycles of big sizes.
The Applicant has found that said problem can be solved by making a tyre having a carcass structure comprising at least one carcass ply in which each cord of said ply lies in a plane that is substantially perpendicular to the equatorial plane of the tyre and forms with the corresponding radial plane passing by the intersection point of said cord with the equatorial plane of the tyre, a lying angle different from zero. In this way the cords of the carcass ply are such arranged that they are submitted, during rolling of the tyre and as better illustrated in the following, to a force hindering deflection of the tyre itself.
A carcass ply thus made ensures accomplishment of a tyre with a carcass structure having a weight reduction even reaching 50%, the carcass rigidity being the same. Finally the tyre keeps excellent directional-stability qualities and a high capability of absorbing the disturbing energy resulting from ground unevennesses, thereby attenuating the so-called “kick-back” phenomenon.
As better illustrated in the following, this solution is particularly advantageous when the belt structure consists of one or more continuous cords spiralled along a direction substantially parallel to the equatorial plane of the tyre. In fact this belt structure enables the features of the carcass structure during running on a rectilinear stretch and on a bend to be enhanced as above illustrated, without making the overall structure of the tyre heavier.
In a first aspect, the present invention relates to a pneumatic tyre for two-wheeled vehicles comprising:
According to a preferred embodiment, said belt structure comprises a layer having a plurality of circumferential coils disposed in axial side by side relationship and spirally wound with a substantially zero angle with respect to said equatorial plane of said tyre.
According to a further embodiment, in said carcass structure one carcass ply is provided.
According to a different embodiment of the tyre in reference, in said carcass structure provision is made for a first carcass ply and a further carcass half-ply associated with each other.
According to another preferred embodiment, said lying angle is included between about 1 and about 12 degrees.
In a further aspect, the invention relates to a pair of tyres for a two-wheeled vehicle, a front and a rear tyre respectively, each tyre comprising:
Further features and advantages of the invention will become more apparent from the detailed description of some preferred, but not exclusive, embodiments of a tyre for two-wheeled vehicles in accordance with the present invention. This description will be set out hereinafter with reference to the accompanying drawings, given by way of non-limiting example, in which:
With reference to the drawings, a tyre for two-wheeled vehicles has been generally identified by reference numeral 1; it comprises a carcass structure including at least one carcass ply 2 preferably having a first and a second carcass half-plies 3, 4, said carcass ply 2 being shaped in a substantially toroidal configuration and being in engagement, by its opposite circumferential edges, with at least one annular reinforcing structure 9 so as to form a structure usually identified as “bead”.
Circumferentially applied to the carcass structure, at a radially external position, is a belt structure 5, on which a tread band 6 is circumferentially superposed, in said tread band longitudinal and transverse grooves being formed, by a moulding operation carried out concurrently with the tyre vulcanisation, which grooves are such arranged as to define a desired “tread pattern”.
Tyre 1 also comprises a pair of sidewalls 7 laterally applied on opposite sides to said carcass structure.
The carcass structure may possibly be coated on its inner walls with a so-called “liner”, essentially consisting of a layer of an air-tight elastomer material adapted to ensure a hermetic seal to the tyre itself once it has been inflated.
Preferably, the belt structure 5 comprises a layer that has a plurality of circumferential coils 5a disposed in axial side by side relationship and formed of a rubberized cord or a strip-like element including some rubberized cords (preferably 2 to 5), spirally wound with a substantially zero angle, with respect to the equatorial plane X-X of the tyre. In other words, said cords form a plurality of circumferential coils 5a substantially oriented towards the rolling direction of the tyre usually referred to as “0 degree” arrangement with reference to its position relative to the equatorial plane X-X of tyre 1.
In a preferred embodiment, the circumferential coils are wrapped on said carcass ply 2 with a variable pitch so as to preferably obtain a greater density of the cords on the opposite side portions than at the central portion of the belt structure 5.
It is to be pointed out here and in the following that even if the spiralling operation and any pitch variation can give rise to deposition angles different from zero, these angles are so small that they can be always considered as substantially equal to zero.
Generally said cords are textile or metallic cords. Preferably said cords are steel cords having such a behaviour that in a stress-strain diagram said cords have a percent elongation higher than 0.4%, more preferably included between 0.5 and 4%, with a load smaller than 5% relative to the breaking load.
Preferably said cords consist of high-carbon steel wires (HT), i.e. steel wires the carbon content of which is greater than 0.9%.
If textile cords are used, they can be made of a synthetic fibre, nylon, rayon, PEN, PET, for example, preferably a synthetic fibre having a high modulus, in particular an aramidic fibre (Kevlar® fibres, for example). Alternatively hybrid cords can be employed which comprise at least one low-modulus thread (a nylon or rayon thread, for example) twisted with at least one high-modulus thread (a Kevlar® thread, for example).
Optionally, tyre 1 may also comprise a layer 10 of elastomer material disposed between said carcass structure and belt structure 5 formed of said circumferential coils 5a, said layer 10 preferably extending over a surface substantially corresponding to the extension surface of said belt structure 5. Alternatively, said layer 10 extends on a smaller surface than the extension surface of the belt structure 5, only on opposite side surfaces thereof, for example.
In a further embodiment, an additional layer of elastomer material (not shown in
In a preferred embodiment, at least one of said layer 10 and additional layer comprises short aramidic fibres, Kevlar® fibres for example, dispersed in said elastomer material.
Said carcass ply 2, as above illustrated, is preferably formed of two carcass half-plies 3, 4. Each of said half-plies 3, 4 has a plurality of cords oriented in such a manner that each of them crosses the equatorial plane of the tyre in accordance with the invention preferably at an angle substantially equal to 90°. In addition, the lying plane of each cord is substantially perpendicular to the equatorial plane X-X of said tyre 1, has an orientation relative to a radial plane R passing by the crossing point of said cord with the equatorial plane X-X, and forms an angle α with said radial plane R which is substantially different from 0° (lying angle).
Preferably, the carcass ply 2 is built in accordance with the process disclosed in the already mentioned document WO 00/38906. As shown in
In this way each cord of the carcass ply crosses the equatorial plane X-X at a point belonging to a radial plane R of said tyre, each cord lying in a plane forming an angle α with said radial plane that is different from 0°.
Preferably, in the tyre in accordance with the invention said lying angle α is included between about 1 and about 12 degrees, more preferably between about 2 and about 8 degrees.
Said strip-like elements 21, as shown in
Said deposition can be carried out by a single rotation of the toroidal support 20 thanks to a continuous side-by-side positioning of each strip-like element relative to the preceding one.
In principle, it is possible to make each carcass ply with a number of rotations greater than or equal to (as previously illustrated) two rotations of the toroidal support 20, each strip-like element being laid, with respect to the preceding one, with an interval in a circumferential direction corresponding to the number of said rotations less one, multiplied by the transverse size of said strip-like element.
Preferably the strip-like elements, of a width included between 5 mm and 20 mm, and of a thickness included between 0.5 mm and 2 mm, contain a number of cords of between 4 and 40, with a density preferably in the range of 60 to 180 cords/dm, measured on the carcass ply, in a circumferential direction, close to the equatorial plane of tyre 1.
The carcass ply in accordance with the present invention preferably comprises textile cords selected from those usually adopted when carcasses for tyres are manufactured, made of nylon, rayon, PET, PEN, for example, with a strand of a diameter included between 0.35 mm and 1.5 mm.
As an alternative to the strip-like elements, a single continuous cord can be used, which cord by an appropriate deposition consisting of successive side-by-side positionings on said toroidal support forms said carcass ply 2 with the same geometry. In this case therefore a plurality of cords in the strict sense of the word is no longer present, but there is a single cord having a plurality of stretches or segments from bead to bead which are joined to each other, each stretch being substantially equivalent to each cord belonging to the above illustrated strip-like element.
Therefore in the present description and in the following claims, by the term “plurality of cords” it is intended both a true multiplicity of cords and a plurality of stretches belonging to the same cord, substantially extending from bead to bead, that are joined together.
Preferably, each annular reinforcing structure 9 has at least one annular insert made of an elongated, preferably metallic, element disposed in substantially concentric coils, each coil being alternatively defined either by a stretch of a continuous spiral or by concentric rings formed of respective thread-like elements.
Preferably, as shown in
The constituent material of said thread-like element can be any textile or metallic material or a material of other nature provided with appropriate features of mechanical resistance; preferably this material is standard or high-carbon steel preferably employed in the form of a metal cord.
In a different embodiment of the tyre in accordance with the invention a carcass structure is provided which has a first carcass ply associated with a further half-ply.
More specifically, subsequent to deposition of the liner and one possible filler of elastomer material, the first carcass ply is laid which may for example consist of two half-plies made in succession through two rotations of the toroidal support about an axis substantially coincident with the rolling axis of the finished tyre. Then a first annular insert, another filler of elastomer material, and a further carcass half-ply are laid in the described order. The strip-like elements of the last half-ply are preferably laid spaced out by a distance in a circumferential direction substantially corresponding to their transverse size; in addition each of them is substantially radially superposed on a corresponding strip-like element of the carcass ply already built on the toroidal support, i.e. the lying plane N will be the same.
Finally, a second annular insert and a further filler will complete building of the carcass structure.
In the same manner it is then possible to make a carcass structure having two carcass plies in which the second ply is built by superposing each strip-like element of the second ply on a strip-like element of the first ply in a substantially radial direction.
In a preferred embodiment, the mono-ply carcass structure or a carcass structure consisting of a ply and a half-ply, is coupled with a belt structure 5 only consisting of said coils 5a.
The tyre in accordance with the invention, employed on a two-wheeled vehicle both as a front tyre 100 and as a rear tyre 200 has a rotation direction of its own that must be coincident with the rotation due to the forward movement direction of the vehicle. For example, the vehicle diagrammatically shown in
For what has been previously illustrated, it is to be pointed out that the lying plane of each cord with the radial plane passing by the intersection point of said cord with the equatorial plane X-X of the tyre determines said lying angle α. This, as can be seen from said
The applicant, without wishing to be bound to any interpretative theory, points out that this geometric difference, as better clarified in the following, substantially depends on the forces acting on said tyres as a consequence of the fact that the front wheel is a driven wheel, whereas the rear wheel is a driving wheel.
In more detail, the Applicant has noticed that in the case of the front tyre 100, the force tangent to tyre 100 at the contact point with the ground (force transmitted from the road to the tyre and directed in a direction opposite to the drive direction) gives rise on each cord in contact with the ground to a compression force that is an obstacle to deflection, so that tyre 100 increases its rigidity upon rolling on the ground. The rear tyre 200 is mounted, as previously noticed, in such a manner that it presents the lying angle α2 of each cord oriented in the opposite direction (
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/IB03/01092 | Mar 2003 | IB | international |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB03/02089 | 5/30/2003 | WO | 6/15/2006 |
