VULCANISING MOULD FOR MANUFACTURING TYRES FOR VEHICLE WHEELS

Abstract

A green tyre has a symmetric profile in radial section having a radially outer tread band, two radially inner beads and two sidewalls each extended from one edge of the tread band to one of the beads. During a moulding and vulcanisation treatment of the green tyre, a movement is imposed to the tread band with respect to the beads along a direction parallel to a rotation axis of the tyre, to obtain a moulded and vulcanised tyre having an asymmetric profile in radial section. A mould for vulcanizing tyres for vehicle wheels is also described, having a tread wall axially asymmetric with respect to a middle line plane of the mould.

Claims

1-32. (canceled)

33. A mould for vulcanizing tyres for vehicle wheels, comprising a moulding cavity having a plurality of sectors configured for operating against a tread band, two bead seats configured for operating against beads of a tyre, and two sidewall plates each extending between said plurality of sectors and one of the bead seats, wherein said plurality of sectors in its entirety defines a tread wall whose geometric conformation is a copy of a geometric conformation of the tread band of the moulded and vulcanized tyre, said tread wall being axially asymmetric with respect to a middle line plane of the mould axially equidistant from axially outer edges of the bead seats.

34. The mould as claimed in claim 33, wherein each bead seat has a radially inner surface and an axially outer surface respectively converging towards an axially outer edge of the bead seat.

35. The mould as claimed in claim 34, wherein said tread wall is axially asymmetric with respect to a middle line plane of the moulding cavity, axially equidistant from axially outer edges of the bead seats.

36. The mould as claimed in claim 35, wherein said tread wall has a middle circumferential line that is axially offset at a predefined distance with respect to a middle line plane of the moulding cavity axially equidistant from axially outer edges of the bead seats.

37. The mould as claimed in claim 35, wherein said tread wall has a middle circumferential line that is axially offset by a predefined distance with respect to a middle line plane of the moulding cavity axially equidistant from radially inner edges of the sidewall plates.

38. The mould as claimed in claim 37, wherein axial terminal portions of said tread wall are radially equidistant from a geometric axis of the moulding cavity.

39. The mould as claimed in claim 37, further comprising: axial movement devices for axially arranging said bead seats adjacent to each other; and radial movement devices for centripetally moving at least a part of said plurality of sectors.

40. The mould as claimed in claim 39, wherein the radial movement devices are configured for centripetally moving the sectors after the axial movement devices have axially arranged said bead seats adjacent to each other.

41. The mould as claimed in claim 39, wherein the radial movement devices are configured for centripetally moving the sectors before the axial movement devices have completed the adjacent axial arrangement of said bead seats.

42. The mould as claimed in claim 37, further comprising: axial movement devices for axially arranging two sidewall plates adjacent to each other; and radial movement devices for centripetally moving at least a part of said plurality of sectors.

43. The mould as claimed in claim 42, wherein the radial movement devices are configured for centripetally moving the sectors after the axial movement devices have axially arranged the sidewall plates adjacent to each other.

44. The mould as claimed in claim 42, wherein the radial movement devices are configured for centripetally moving the sectors before the axial movement devices have completed the axial adjacent arrangement of the sidewall plates.

45. The mould as claimed in claim 44, wherein each bead seat has a radially inner surface and an axially outer surface respectively converging towards an axially outer edge of the bead seat.

46. The mould as claimed in claim 45, wherein said tread wall has a middle circumferential line axially equidistant from axially opposed edges of said tread wall and axially offset at a predefined distance with respect to a middle line plane of the mould axially equidistant from the axially outer edges of the bead seats.

47. The mould as claimed in claim 46, wherein terminal axial portions of said tread wall are radially equidistant from a rotation axis of the tyre.

Description

[0082] Such description will be set forth hereinbelow with reference to the set of drawings, provided only for exemplifying and hence non-limiting purposes, in which:

[0083] FIG. 1 shows, in partial radial section, a built green tyre, introduced into a vulcanising mould predisposed in open condition, in accordance with the present invention;

[0084] FIG. 2 shows the tyre of FIG. 1 in a closed condition of the mould;

[0085] FIG. 3 shows the tyre during an action of pressing an action of pressing of the green tyre closed in the mould;

[0086] FIG. 4 shows a partial radial section of a wheel for motor vehicles obtained in accordance with the present invention;

[0087] FIGS. 5 and 6 schematically shows a motor vehicle provided with the wheel of FIG. 4 in respective operating conditions and with the ground footprints.

[0088] With particular reference to FIGS. 4 to 6, reference number 1 overall indicates a wheel for motor vehicles comprising a tyre 2.

[0089] The tyre 2 has a carcass structure 3 which comprises at least one carcass ply 3a preferably internally covered by a layer of impermeable elastomeric material or so-called liner 4. Two anchoring annular structures 5each comprising a reinforcement annular insert or so-called bead core 5a preferably bearing an elastomeric filler 5b in radially outer position with respect to the bead core itselfare engaged with respective end flaps of the carcass ply/plies 3a. The filler 5b has a radially outer apex, being tapered in moving away from the bead core 5a. The anchoring annular structures 5 are integrated in proximity to zones normally identified with the name beads 6, at which the engagement between the tyre 2 and a respective mounting rim 7 normally occurs, according to a fitting diameter determined by the inner diameter size of the anchoring annular structures 5. Each bead 6 is extended from one radially inner edge of the tyre to the radially outer apex of the filler 5b.

[0090] A crown structure 8 normally comprising one or more belt layers 8a is circumferentially applied around the carcass ply/plies 3a, and a tread band 9 is circumferentially superimposed on the belt layers 8a. Two sidewalls 10, each being extended from the corresponding bead 6 to a corresponding lateral edge of the tread band 9, are applied in laterally opposite positions on the carcass ply/plies 3a.

[0091] The rim 7, per se known, has a substantially cylindrical body 11 provided with a radially outer channel, where the tyre 2 is placed. The substantially cylindrical body 11 delimits an axially outer housing 12ai.e. directed towards the exterior of a motor vehicle when the rim is mounted on said motor vehicleand an axially inner housing 12bi.e. directed towards the motor vehicle side when the rim is mounted on said motor vehicle, defined by respective radially outer annular slots symmetric with respect to a middle line plane P.sub.W orthogonal to a rotation axis X-X of the wheel 1 (here substantially coinciding with the rotation axis of the tyre 2 and indicated in the same manner. The axially outer housing 12a and the axially inner housing 12b are each adapted to receive a respective bead 6 of the tyre 1.

[0092] The rim 7 also comprises a radially inner body 13, with respect to the substantially cylindrical body 11, in which devices are obtained (not illustrated and for example defined by holes and relative bolts) for coupling the wheel 1 to the hub. In the illustrated embodiment, the radially inner body 13 is non-aligned with respect to the middle line plane P.sub.W and moved towards the axially outer housing 12a of the rim 7 in a manner so as to form the necessary space inside the substantially cylindrical body 11 for the placement of the hub and the braking devices (e.g. brake discs and callipers).

[0093] The geometry of the rim 7, in particular with reference to the radially inner body 13 adapted to receive the hub, is such to render two housings unambiguously identified: axially outer housing 12a and axially inner housing 12b.

[0094] The radial distance r of each of the two axially outer/inner housings respectively 12a, 12b, from the rotation axis X-X, measure along a diameter of the rim 7, is the same. The axial distance x measured parallel to the rotation axis X-X, of each of the two axially outer/inner housings respectively 12a, 12b from the middle line plane P.sub.W, is the same.

[0095] The two beads 6 of the tyre 1, each installed in a respective axially outer/inner housing 12a, 12b are also symmetric with respect to the middle line plane P.sub.W (or P.sub.T). The radial distance r of each of the two beads 6 from the rotation axis X-X, measured along a diameter of the rim 7, is the same. The axial distance x of each of the two beads 6 measured parallel to the rotation axis X-X from the middle line plane P.sub.W (or P.sub.T) is the same.

[0096] When the tyre 2 is not mounted on the rim and when it is mounted on the rim, inflated to the operating pressure but not subjected to external stress forces, said tyre 2 has a non-symmetric geometry in a radial section (FIG. 4).

[0097] In particularexcluding the beads 6the carcass structure 3, the belt structure 8, the tread band 9 and the sidewalls 10 of the tyre 2 are asymmetric with respect to the middle line plane P.sub.W (or P.sub.T). The tread band 9 is translated, with respect to a symmetric conventional tyre, along an axial direction towards the axially outer housing 12a of the rim 7.

[0098] In a radial section (FIG. 4), the two opposite axial ends 9a and 9b of the tread band 9 have the same radial distance d, measured along a diameter of the wheel 1, from the rotation axis X-X. In other words, the medium line lm of the tread band 9 is parallel to said rotation axis X-X.

[0099] The tread band 9 has middle circumferential line 14 thereof (constituted by the points equidistant from the two opposite axial ends 9a and 9b) moved, with respect to the middle line plane P.sub.W (or P.sub.T), by a predefined distance D. As is visible in FIG. 4, in the illustrated embodiment, the tread band 9 is also symmetric with respect to a plane of symmetry M. In other words, the middle circumferential line 14 lies on the plane of symmetry M which is orthogonal to the rotation axis X-X and is moved, with respect to the middle line plane P.sub.W (or P.sub.T), by the predefined distance D.

[0100] The wheel 1 is mounted on the automobile C with a predefined camber angle and the middle circumferential line 14 (or plane of symmetry M) thereof moved, with respect to the middle line plane P.sub.W (or P.sub.T), towards the exterior of the automobile C itself.

[0101] Preferably said camber angle is substantially zero.

[0102] With vehicle stopped during straight line travel (FIG. 5), even if the tyre 2 is subjected to centrifugal forces, which increase the diameter thereof, and to ground interaction forces, the tread band 9 maintains its non-alignment with respect to the middle line plane P.sub.W (or P.sub.T) also at the portion directly set on the ground; this is due to the non-alignment of the middle circumferential line with respect to the middle line plane P.sub.W (or P.sub.T), in which the vertical force transmitted by the hub acts. In such operating condition, the footprint d.sub.1 is also non-aligned with respect to the line of intersection between the ground and the middle line plane P.sub.W (or P.sub.T), in which the vertical force F.sub.1 lies which is transmitted from the hub. Due to such asymmetry, the length g.sub.1 of the ground footprint d.sub.1 is slightly greater towards the inner sidewall (towards the automobile C) of the tyre 2 than towards the outer sidewall. Such asymmetry is in any case less than the asymmetry of the footprint of a wheel with negative camber angle, optimal for a corresponding tyre with symmetric cross section. Such asymmetry is less because it lacks the contribution given (in tyres with symmetric profile with negative camber angle) by the greater crushing of the inner sidewall (motor vehicle side) with respect to the outer sidewall due to the tilt (equal to the camber angle) of the medium line of the tread band with respect to the ground.

[0103] While the automobile follows a curve (FIG. 6), each tyre that is external with respect to the curve (on which most of the centripetal force that acts on that axis of the automobile is unloaded) is deformed and the footprint assumes a configuration that decreases the initial asymmetry (with respect to the middle line plane P.sub.W) characteristic of the straight line travel with non-zero camber angle.

[0104] More particularly, the force F.sub.2 which passes from the hub to the wheel 1 tends to move the rim 7 towards the exterior while the tyre portion 2 which adheres to the ground remains adherent thereto. It follows that the tyre 2 is deformed at the portion directly set on the ground and those immediately adjacent portions. The tread band portion 9 in contact with the ground reduces or cancels its non-alignment with respect to the middle line plane P.sub.W (or P.sub.T) (the plane of symmetry M and the middle line plane P.sub.W (or P.sub.T) approach each other until they are possibly superimposed) while the diametrically-opposite tread band portion 9 maintains the abovementioned predefined distance D. Due to such deformation, the length g.sub.2 of the footprint d.sub.2 is substantially constant along the entire axial extension of the footprint d.sub.2 itself.

[0105] In accordance with the present invention, a process for obtaining a tyre according to that described above provides for building a green tyre 2, having a symmetric profile in radial section, with the tread band 9 in radially outer position, the two beads 6 in radially inner position and the two sidewalls 10 each being extended from one edge of the tread band 9 to one of the beads 6. The building of the green tyre 2 can be executed in any manner, even per se known and conventional, and therefore it is not described in detail herein.

[0106] The built green tyre 2 is introduced into a moulding cavity 15 of a vulcanisation mould 16, illustrated in FIGS. 1 to 3, in order to be subjected to a moulding and vulcanisation treatment. The moulding cavity 15 has a plurality of sectors 17 configured for operating against the tread band 9 of the tyre 2, two bead seats 18 configured for operating against the beads 6, and two sidewall plates 19 each being extended between said plurality of sectors 17 and one of the bead seats 18, in order to operate against the sidewalls 10 of the tyre 2.

[0107] Each of the bead seats 18 has a radially inner surface 20 and axially outer surface 21, respectively converging towards an axially outer edge 22 of the bead seat 18. In the illustrated example, each of the bead seats 18 is defined by an annular element operatively couplable to one of the sidewall plates 19, for example against a radially inner edge 23 of the latter. In a possible modified embodiment, the bead seats 18 can be obtained directly in one piece in the sidewall plates 19.

[0108] The plurality of sectors 17 in its entirety defines a tread wall 17a whose geometric conformation is a copy, in negative, of that of the tread band 9 of the vulcanised tyre.

[0109] The sidewall plates 19 define respective sidewall walls 19a which, with closed mould, are extended from respective axially opposite edges 27 of the tread wall 17a to the respective bead seats 18.

[0110] The mould 16 also comprises axial movement devices, for example represented by two columns 24 of which at least one is axially movable with respect to the other, for axially arranging the bead seats 18 and/or the sidewall plates 19 respectively fixed thereto adjacent to each other.

[0111] Radial movement devices provide to centripetally move the plurality of sectors 17 or at least a part thereof. For example, the movement devices, can comprise a pair of half-shells 25 respectively carried by the columns 24, and internally having tilted guide surfaces 26 cooperating with the sectors 17 so as to determine a mutually approaching or moving-apart radial movement thereof, simultaneously with the mutual axial approaching and moving-apart motion of the columns 24.

[0112] In a further embodiment, not illustrated since it can also be obtained in a known manner, the radial movement devices can be configured for centripetally moving the sectors 17 after the axial movement devices have axially arranged the bead seats 18 and/or the sidewall plates 19 adjacent to each other.

[0113] The movement of the bead seats 18, sidewall plates 19 and/or sectors 17 occurs between an open condition, in which the columns 24 and the parts borne thereby are mutually moved apart in order to allow the introduction of the green tyre 2 and the extraction of the moulded and vulcanised tyre 2, and a closure condition in which the sectors 17, the sidewall plates 19 and the bead seats 18 delimit contours of the moulding cavity 15, as in FIGS. 2 and 3.

[0114] FIG. 1 represents an intermediate condition in which the columns 24 have been partially approached until a mutual mating has been determined of the sectors 17 respectively borne by one half-shell 25 and the other.

[0115] As is clearly illustrated in FIG. 1, the built green tyre 2, before reaching the closure condition, and in any case before being introduced into the moulding cavity 15, is symmetric with respect to the middle line plane P.sub.T thereof.

[0116] More particularly, the beads 6, the carcass structure 3, the belt structure 8, the tread band 9 and the sidewalls 10 of the green tyre 2 are symmetric with respect to the middle line plane P.sub.T.

[0117] In a radial section (FIG. 1), the two opposite axial ends 9a and 9b of the tread band 9 have the same axial distance from the middle line plane P.sub.T.

[0118] The opposite axial ends 9a and 9b of the tread band 9 also have the same radial distance d, measured radially from the rotation axis X-X. In other words, the medium line Im of the tread band 9 is parallel to said rotation axis X-X.

[0119] The middle circumferential line 14 of the tread band 9 coincides with the middle line plane P.sub.T, with respect to which the entire tread band 9 is symmetric.

[0120] In accordance with the present invention, during the moulding and vulcanisation treatment of the tyre 2 in the moulding cavity 15, a movement is imposed to the tread band 9 with respect to the beads 6, along a direction parallel to the rotation axis of the tyre 2, in a manner such that the moulded and vulcanised tyre have an asymmetric profile in radial section, as previously described.

[0121] For such purpose, it is preferably provided that the tread wall 17a defined by the plurality of sectors 17, in its entirety, is axially asymmetric with respect to a middle line plane of the mould 16, axially equidistant from axially outer edges 22 of the bead seats 18 and/or from radially inner edges 23 of the sidewall plates 19, and hence coinciding with the middle line plane P.sub.T of the tyre 2 closed in the mould itself.

[0122] More particularly, the tread wall 17a has a middle circumferential line 14a, axially equidistant from the axially opposite edges 27 of said plurality of sectors 17 in its entirety, axially offset at a predefined displacement distance D.sub.1 with respect to the middle line plane of the mould 16. Such displacement distance D.sub.1 can be equal to or different from, for example greater than, the predefined distance D detectable on the vulcanised tyre 2, mounted on the rim 7 in operating conditions.

[0123] Axial terminal portions of the plurality of sectors 17 in its entirety, bearing the aforesaid axially opposite edges 27, are radially equidistant from a geometric axis of the moulding cavity 15, preferably coinciding with the rotation axis X-X of the tyre 2 closed in the moulding cavity itself. The position of the axial terminal portions coincides with the position of the two opposite axial ends 9a and 9b of the tread band 9 in the vulcanised tyre 2, and/or causes the orientation of the aforesaid medium line Im in operating condition.

[0124] The movement of the tread band 9 with respect to the beads 6 can be partially or totally obtained simultaneously with the closure of the green tyre 2 inside the moulding cavity 15.

[0125] More particularly, during the mutual approaching of the columns 24 and of the half-shells 25, it may be provided that the sidewall plates 19 and/or the bead seats 18 come into contact against the sidewalls 10 and/or the beads 6 of the tyre 2. An axial deformation is therefore imposed on the tyre 2, in the section comprised between the beads 6 and the respective opposite axial ends 9a, 9b of the tread band 9, the axial deformation such to determine the axial movement of the tread band 9 with respect to the beads 6, simultaneously with mutual axial approaching of the sidewall plates 19 and/or of the bead seats 18.

[0126] During such deformation, the sectors 17 can remain spaced from the surfaces of the tread band 9, such that the movement of the tread band 9 with respect to the beads 6 is executed in the absence of mechanical interferences between the plurality of sectors 17 and the tread band 9 themselves.

[0127] During the approaching of the sidewall plates 19 and/or the bead seats 18, a progressive centripetal approaching of the sectors 17 can in any case be actuated, until they come into contact with the tread band 9 upon completion of the closure of the mould 16.

[0128] The configuration of the mould 16, for example obtained by arranging a suitable tilt of the guide surfaces 26, can nevertheless be suitable for determining a contact between sectors 17 and tread band 9 before the start or the conclusion of the movement of the tread band 9 and/or before the completion of the closure of the mould 16. In this situation, the sectors 17 are adapted to carry out a gripping action on the tread band 9 which fixes the positioning thereof inside the mould 16 during the lateral deformation that determines the movement of the tread band 9 with respect to the beads 6.

[0129] Once the closure of the mould 16 has been completed, an action of vulcanisation of the tyre 2 is conducted, simultaneously with an action of pressing of the same against the inner surfaces of the moulding cavity 15.

[0130] For example, for such purpose it can be provided to use an expandable chamber 28 inside the tyre 2, in which vapour or another pressurised fluid for determining the action of pressing and the administration of heat is introduced.

[0131] The action of the expandable chamber 28 can increase or, in a possible modified embodiment of the invention, determine the movement of the tread band 9 with respect to the beads 6, simultaneously with pressing.

[0132] In a possible modified embodiment of the invention the movement of the tread band 9 with respect to the beads 6 can be mainly or exclusively attained simultaneously with the action of pressing, rather than due to the closure of the mould 16.

[0133] During vulcanisation or at least part thereof, the tread band 9, moved axially with respect to the beads 6, is retained in accordance with an axially asymmetric position with respect to a middle line plane P.sub.T of the tyre 2, with the middle circumferential line 14 thereof moved axially according to the predefined distance of displacement D.sub.1 with respect to the middle line plane of the moulding cavity 15 and the tyre 2.

[0134] The molecular cross-linking induced in the elastomeric material due to the vulcanisation permanently stabilizes the structure of the tyre 2 according to the desired asymmetric configuration.