Patent Application
20100024949
The present invention relates to a process of manufacturing tyres. Specifically, the present invention relates to a process of manufacturing tyres comprising application of strip-like elements having different widths. Moreover, the present invention further relates to a tyre comprising at least one reinforcing component formed by approaching strip-like elements having different widths.
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite ends associated with annular anchoring structures, each of said anchoring structures being usually made up of a substantially circumferential annular insert onto which at least one filling insert is applied, at a radially external position thereof. The carcass ply or plies typically comprise(s) reinforcing textile or metal (e.g. steel) reinforcing thread-like elements (such as wires and/or cords) disposed on a plane substantially orthogonal to a travel direction of the tyre in so-called radial tyres, more generally at an angle between 70° and 110°.
A belt (or breaker) structure is associated with the carcass structure. The belt structure comprises one or more belt layers, arranged in radial superposed relationship with each other and with the carcass structure, and having textile or metal reinforcing thread-like elements of crossed orientation (typically between 15° and 65° versus a travel direction of the tyre). A tread band is applied to the belt structure, at a radially external position thereof, made of elastomeric material, like other constituent parts of the tyre.
In most of the known processes for tyre manufacture, the carcass structure and the belt structure (together with the respective tread band) are provided to be made separately of each other in respective work stations, to be mutually assembled at a later time.
More particularly, manufacture of the carcass structure first contemplates deposition of the carcass ply or plies on a first drum usually identified as “building drum” to form a cylindrical sleeve. The annular anchoring structures at the beads are fitted or formed on the opposite ends of the carcass ply or plies, which are turned up around the annular structures themselves so as to enclose the latter ones.
At the same time, on a second drum, or auxiliary drum, an outer sleeve is made which comprises the belt layers laid down in radially superposed relationship with each other, and the tread band applied to the belt layers at a radially external position thereof. The outer sleeve is then picked up from the auxiliary drum to be coupled with the carcass sleeve. For that purpose, the outer sleeve is disposed in coaxial relation around the carcass sleeve, afterwards the carcass ply or plies are shaped into a toroidal conformation by axially moving the beads close to each other and simultaneously admitting fluid under pressure into the carcass sleeve, so as to determine application of the belt structure and the tread band to the carcass structure of the tyre at a radially external position thereof.
Assembling of the carcass sleeve with the outer sleeve can be carried out on the same drum as used for building the carcass cylindrical sleeve, in which case reference is made to a “unistage building process”. Alternatively, assembling may be carried out on a so-called “shaping drum” onto which the carcass cylindrical sleeve is transferred and then expanded to obtain a toroidal shape and to couple with the outer sleeve, according to a so-called “two-stage building process”.
According to conventional techniques, each of the carcass plies and/or the belt layers can be formed as a sheet component applied as a single piece on the building drum and/or on the auxiliary drum.
Alternatively, according to recently developed processes, the carcass plies and the belt layers are produced by application of a series of strip-like elements, or strips. In order to form a belt layer or a carcass ply the strips can be either arranged side-by-side or by overlapping an edge portion thereof.
As observed in EP 1652658, a single layer applied as non-overlapped strips enhances uniformity and consistency of the tyre construction across the tyre radial width. However, merely applying the strips edge-to-edge across the tread region rather than by overlapping causes a new set of difficulties and can result in material waste. Still with reference to EP 1652658, for example, a typical passenger tyre may require 20 to 60 strips. Applying the strips in an edge-to-edge, zero clearance configuration would require cutting a 21st or 61st strip to fill a final gap. Destruction of a strip in order to fill a remainder gap on each tyre results in an unacceptable level of scrap and high manufacturing costs.
In principle, strips of a precise and prescribed width could be utilized in an edge-to-edge non-overlapping layer in order to leave no remainder gap. However, according to EP 1652658, such an approach would necessitate expensive production and inventorying of strips of varying widths in order to accommodate tyres of varying sizes.
In order to solve the above problems, EP 1652658 suggests a method and a corresponding apparatus for applying a breaker or another reinforcement layer strip by strip. The method of EP 1652658 comprises:
EP 1568476 discloses a method of forming a cord-reinforced tire structural member, including the steps of: forming strips of a predetermined width reinforced by a predetermined number of cords of a type, and forming a tyre structural member by successively arranging a predetermined number of the strips, which is specified for a tyre size, and joining together side edge parts of adjacent strips. According to an embodiment, the strips are formed in a width of about π inches, and a tyre structural member for a tyre of a size of n inches (n is an integer) is formed by successively connecting the n strips.
EP 1698490 discloses a pneumatic tyre in which formation of a belt layer is realized by using an integer number of strip pieces and without causing any overlap between the strip pieces, and a method of manufacturing the same. In the method, the belt layer is formed by aligning N strip pieces on a molding drum in the circumferential direction of the tyre with equal spaces disposed between adjacent strips pieces, wherein N is selected as an integer satisfying (N+1)×A/sin(θ)>L>N×A/sin(θ), and wherein A, θ, and L respectively denote a width of the respective strip pieces, a cord angle of the belt layer with respect to a circumferential direction of the tyre, and a circumferential length of the belt layer.
For manufacturing a tyre with two belt layers, the method of EP 1698490 includes the steps of: setting an applicable number of strip pieces N2 equal to an applicable number of strip pieces N1 while selecting an integer N1 satisfying L1=N1×A/sin(θ) as the applicable number N1; forming the inner belt layer by joining the N1 strips pieces to one another in a manner that each of both sides of each strip piece is butted with one side of another strip piece; and forming the outer belt layer by aligning the N2 strip pieces on the inner belt layer in a circumferential direction of the tyre with spaces, which are equivalent to 2πG/N2, disposed between adjacent ones of these N2 strip pieces, wherein A, G, θ, L1 and L2 respectively denote a width of the respective strip pieces, a thickness of the respective strip pieces, a cord angle of the respective belt layers with respect to a circumferential direction of the tyre, and circumferential lengths of the respective inner and outer belt layers.
The Applicant observes that a complete tyre production line requires a high level of flexibility. In fact, an efficient management of the manufacturing steps is required in order to cope with the different tyre sizes and models to be produced, without introducing substantial increase of costs, waste, and/or manufacturing time.
The Applicant further observes that the length of each reinforcing component of a tyre (i.e. each tyre component comprising reinforcing thread-like elements, such as the layers forming the carcass structure and/or the belt structure) should match, as far as possible, a respective given target circumference, i.e. a circumferential length measured on a manufacturing drum on which the reinforcing component should be applied at a given manufacturing step (either a building drum, or an auxiliary drum, or, in general, any kind of drum used during the manufacturing of a green tyre).
In this respect, it is observed that an incorrect matching of the target circumference to be covered may lead to unacceptable non-uniformities in the finished tyre. The presence of such non-uniformities could be particularly detrimental to the quality of tyres (either car tyres, or motorcycle tyres, or truck/bus tyres), in particular for high or ultra high performance (HP/UHP) tyres, which should be suitable for supporting high speeds and/or extreme driving conditions. For example, non-uniformities in the carcass structure may lead to an irregular wear of the tyre tread during use. As another example, a scarce matching of the target circumference when forming a belt layer, corrected by forcing the ends of the layer for joining the same with each other, could lead to various problems, including: resulting angle of the reinforcing thread-like elements with respect to the equatorial plane of the tyre different from the one specifically designed for the tyre; non-uniformity of the same angle along the circumference of the tyre; differences from tyre to tyre in the same production lot.
Thus, complexity arises in a complete tyre production line, since many different target circumferences should be matched, depending on several factors, including: the tyre model, the tyre size, the diameter of the manufacturing drum, the shape of the manufacturing drum, the thickness of underlying layers already applied on the drum, etc.
The Applicant further observes that known methods for defining an optimal arrangement, number, and/or size of strips to be used for forming reinforcing components of the tyres often refer to the manufacturing of a single tyre size, and/or of a single reinforcing layer. Thus, these methods may fail in case tyres of different models and/or sizes have to be produced, since a strip arrangement, or a strip size, being optimal for matching a target circumference for a certain tyre size, or for a certain layer to be formed, could be far from being optimal for matching the target circumference for a different tyre size, or for a different layer to be formed.
In particular, as far as the width of the strip is concerned, it cannot be guaranteed that a strip of given width, optimized for forming a given layer in a tyre of a given size substantially without any final gap between the first and the last strip, could be used for forming another layer in the same tyre and/or the same layer in another tyre size substantially without any final gap between the first and the last strip. For example, a certain strip width may lead to perfectly match the target circumference when forming a first carcass ply, but not when forming a second carcass ply to be superposed to the first in the same tyre. As another example, a certain strip width could lead to perfectly match the target circumference when forming a carcass ply or a belt layer to be used for one tyre size or model, but not when forming a carcass ply or a belt layer to be used for another tyre size or model.
A possible solution to the above could be to set the strip width to π inches, and to form a reinforcing component for a tyre of a size of n inches by successively connecting n strips, as suggested in EP 1568476. This solution could be useful for producing reinforcing components for tyres of different sizes by using the same strip width. However, it is observed that this solution disadvantageously imposes a strong constraint in the choice of the diameter of the manufacturing drum, which should be equal to the rim diameter for all the tyre sizes to be produced in order to have a target circumference (expressed in inches) equal to an integer number of π.
On the contrary, it would be advantageous to freely choose the diameter of the manufacturing drum, for example in order to reduce the extent of the shaping of the carcass structure for the coupling with the belt structure. As a consequence, the target circumference to be covered with the strips could be very different from an integer number of π. The flexibility in the choice of the diameter of the manufacturing drum thus imposes additional complexity in the setting of an optimal width for the strips to be used.
The Applicant has understood that in order to combine the flexibility required by a complete tyre production line with a high quality of the produced tyres, without introducing disadvantageous increase of costs, material waste and/or manufacturing time, a further degree of freedom is needed for the application of strip-like elements. In particular, the Applicant has understood that the use of strip-like elements of different widths for the formation of the reinforcing layers of a tyre could provide an effective solution to cope with the required production flexibility and tyre quality. In particular, it has been found that a complete tyre production line (i.e. a production line suitable for producing tyres of different sizes and/or models) could be advantageously achieved by using strips of two different widths for the formation of the reinforcing components of the tyres.
In a first aspect, the invention relates to a process for manufacturing a tyre comprising:
For the purposes of the present invention, the term “plurality” should be interpreted as meaning “at least two”.
For the purposes of the present invention, the expression “strip-like element” indicates an elongated element of elastomeric material incorporating reinforcing thread-like elements generally disposed substantially parallel to each other along the longitudinal direction of the elongated element. For the purposes of the present invention, the expression “reinforcing thread-like element” includes a wire or a cord (typically made of a textile or metal material).
For the purposes of the present invention, the “effective width” of a strip-like element indicates the width (measured in an orthogonal direction versus the thread-like element direction) of the portion of the strip-like element actually contributing to the circumferential length of the formed reinforcing component. The effective width of a strip-like element practically corresponds to the maximum width of the strip-like element in case the strip-like element is abutted to the adjacent strip-like element, with no overlapping; on the other hand, in case of overlapping, the effective width of a strip-like element practically corresponds to the maximum width of the strip-like element minus the width of the side edge portion of the strip-like element destined to overlap the adjacent strip-like element.
For the purposes of the present invention, the expression “each substantially having the same width” referred to the strip-like elements of the first plurality or of the second plurality indicates that all the strip-like elements of the respective plurality have the same width but for typical fabrication tolerances (e.g. within 0.3 mm, preferably within 0.1 mm).
The use of strip-like elements of different widths for manufacturing the reinforcing layers of a tyre may provide the level of flexibility requested by a complete production line. With this choice, the manufacturing process could be designed with reduced design constraints, without the need of large inventories of strips of different sizes, and/or without the need of continuously modifying the strip width in order to cope with a tyre size change and/or with a different target circumference to be covered. In particular, it has been found that practically all the reinforcing layers of a tyre could be formed by using strip-like elements of two different widths, substantially for any practical tyre size to be produced, with a dramatic reduction in manufacturing complexity.
The number of reinforcing thread-like elements in the strip-like elements of the first plurality typically results in being different from the number of reinforcing thread-like elements in the strip-like elements of the second plurality. However, the reinforcing thread-like elements may be arranged in the strip-like elements of the first and of the second plurality with substantially the same pitch (i.e. the same distance between thread-like elements). This advantageously results in the same reinforcing thread-like element pitch in the formed reinforcing component, thus avoiding undesirable non-uniformities in the produced tyre.
The at least one reinforcing component of the tyre to be produced in the process according to the present invention may comprise at least one carcass ply, and/or at least one belt layer.
The approaching of the side edge portions of the strip-like elements of the first plurality and of the second plurality may be either performed by abutting side edges of the strip-like elements to one another, or by overlapping side edge portions of the strip-like elements to the adjacent ones. It is noticed that uniformity of the finished tyre could be improved by abutting side edges of the strip-like elements to one another.
Advantageously, the arranging of the strip-like elements of the first plurality and of the second plurality may comprise arranging strip-like elements of the first plurality alternated with strip-like elements of the second plurality in at least one portion of the at least one reinforcing component of the tyre. The arranging of the strip-like elements of the first plurality alternated with the strip-like elements of the second plurality may lead to a finished tyre having reduced vibrational effects caused by harmonic components due to the joins between the various strip-like elements.
Alternatively, the arranging of the strip-like elements of the first plurality and of the second plurality may comprise:
In order to improve uniformity, the total length of the at least one reinforcing component formed by the arranged strip-like elements of the first plurality and of the second plurality can be made to be substantially equal to a respective target circumference of said at least one reinforcing component. For the purposes of the present invention, the target circumference of a reinforcing component corresponds to the circumference to be covered by the reinforcing component when applied on a manufacturing drum (possibly over underlying layers), during preparation of a green tyre.
In particular, the length of the at least one reinforcing component formed by the arranged strip-like elements of the first plurality and of the second plurality can be made to differ from the target circumference by a value being lower than a preset threshold value. An acceptable threshold value could be, for example, 0.5% of the target circumference.
The process of the invention may give particular advantages in case of use of strip-like elements (for both the first and the second plurality) having a high width. A “high width” may correspond to at least 1% of the target circumference (e.g. at least 15 mm). The use of high width strip-like elements could speed up the process of manufacturing of a tyre. However, joins between high width strip-like elements are more far to each other. In such situation, less-than-perfect join between the strip-like elements leads to “isolated” non-uniformities, which tend to give a worst effect on the performance of the tyre.
Being N1 a first integer number of the strip-like elements of the first plurality and N2 a second integer number of the strip-like elements of the second plurality, it may be preferably provided that both N1 and N2 be greater than or equal to (N1+N2)/5 (i.e. both N1 and N2 are greater than 20% of the sum of N1 and N2).
More preferably, it may be provided that both N1 and N2 be greater than or equal to 2(N1+N2)/5 (i.e. both N1 and N2 are greater than 40% of the sum of N1 and N2).
Even more preferably, it may be provided that N1 and N2 differ by at most one, i.e. N2=N1 or N2=N1+1.
The arranging of the strip-like elements of the first plurality and of the second plurality is performed on a surface of the support used for arranging the strip-like elements. The surface of the support may be a cylindrical or toroidal surface (e.g. the support may be a manufacturing drum, and the arranging of the strip-like elements is performed on an external surface thereof). Alternatively, the surface of the support may be a plane surface (e.g. the support may be a conveyor belt). In case of deposition on a toroidal surface, the target circumference could be chosen in any convenient manner, for example at the equatorial plane.
It may be convenient to set the first effective width, i.e. the effective width of the first plurality of strip-like elements, and the second effective width, i.e. the effective width of the second plurality of strip-like elements, so that they slightly differ from each other, e.g. so that they differ from each other of at most 5 mm, or, more preferably, of at most 2 mm. By using strip-like elements having slightly differing effective width, the response of the finished tyre to the forces developed by the interaction with the ground during rolling may advantageously result to be more uniform, with a significant improvement in the performance of the tyre during use.
In a second aspect, the invention relates to a tyre comprising at least one reinforcing component formed by approached strip-like elements, wherein said strip-like elements comprise a first plurality of strip-like elements, each substantially having a first effective width, and a second plurality of strip-like elements, each substantially having a second effective width, wherein said first effective width is different from said second effective width.
The reinforcing thread-like elements comprised within the strip-like elements can have substantially the same pitch in both the strip-like elements of the first plurality and the strip-like elements of the second plurality.
The at least one reinforcing component of the tyre may comprise at least one carcass ply, and/or at least one belt layer.
In one embodiment, the strip-like elements of the first plurality and of the second plurality are alternated with each other in at least one portion of the at least one reinforcing component.
Being N1 a first integer number of the strip-like elements of the first plurality and N2 a second integer number of the strip-like elements of the second plurality, it may be preferably provided that both N1 and N2 be greater than or equal to (N1+N2)/5 (i.e. both N1 and N2 are greater than 20% of the sum of N1 and N2).
More preferably, it may be provided that both N1 and N2 be greater than or equal to 2(N1+N2)/5 (i.e. both N1 and N2 are greater than 40% of the sum of N1 and N2).
Even more preferably, it may be provided that N1 and N2 differ by at most one, i.e. N2=N1 or N2=N1+1.
The first effective width, i.e. the effective width of the first plurality of strip-like elements, and the second effective width, i.e. the effective width of the second plurality of strip-like elements, can be such that they slightly differ from each other, e.g. such that they differ from each other of at most 5 mm, or, more preferably, of at most 2 mm.
The first and the second effective widths may be, for example, higher than or equal to 15 mm.
The features and advantages of the present invention will be made apparent by the following detailed description of some exemplary embodiments thereof, provided merely by way of non-limitative examples, description that will refer to the attached drawings, wherein:
With reference to
The tyre 1 comprises a carcass structure 2 having one or more carcass plies, each comprising thread-like elements (schematically shown) consecutively adjacent to each other and placed in substantially radial planes containing the rotation axis of the tyre. A belt structure, indicated in a general way by 3, is applied circumferentially around the carcass structure 2, in a centered position with respect to the equatorial plane p-p of the tyre, and a tread band 4 is placed in a position radially external to the belt structure.
The belt structure 3 has at least a first belt layer 5 in a position radially external to the carcass 2, a second belt layer 7 placed in a position radially external to said first layer 5, and a reinforcing layer 10 in a position radially external to said second ply 7. The first belt layer 5 and the second belt layer 7 comprise thread-like elements 6, 8 adjacent to each other and orientated obliquely with respect to the equatorial plane p-p of the tyre. Moreover, the thread-like elements 8 of the second belt layer 7 are inclined in the opposite direction with respect to the thread-like elements 6 of the first belt layer 5. Differently, the thread-like elements 11 of the reinforcing layer 10 are substantially parallel to each other and orientated in a direction substantially parallel to the equatorial plane p-p of the tyre.
As explained above in the summary, according to the invention strip-like elements of different effective widths are used to form at least one reinforcing component of a tyre comprising reinforcing thread-like elements disposed along a transverse direction with respect to the equatorial plane p-p of the tyre. The at least one reinforcing component may be a carcass ply of the carcass structure 2, and/or a belt layer 5, 7, and/or any other reinforcing component of the tyre comprising reinforcing thread-like elements orientated obliquely with respect to the equatorial plane p-p of the tyre. Preferred embodiments may provide that strip-like elements of two different effective widths be used to form all the reinforcing layers of the tyre (each layer comprising the strip-like elements of both different widths). In particular, it may be provided that the reinforcing layer(s) of the carcass structure and the reinforcing layers of the belt structure are formed with strip-like elements of respective effective widths. In other words, the carcass ply or plies could be formed by strip-like elements having effective widths W1, W2 (with W1≠W2), whereas the belt layers could be formed by strip-like elements having effective widths W3, W4 (with W3≠W4), wherein W3 and W4 could be respectively equal to W1 and W2, or wherein at least one of W3, W4 could be different from at least one of W1, W2.
With reference to
An inserter 15 is disposed behind the die 14 of the extruder 12. A plurality of reinforcing thread-like elements 21, such as steel cords or textile cords, unwound from a plurality of reels 16 disposed behind the inserter 15, are arranged parallel to each other in a horizontal plane (i.e. a plane orthogonal to
The cord-reinforced continuous strip 22 of a predetermined width extruded by the extruder 14 is guided by pulling through a pull drum 17. The cord-reinforced continuous strip 22 is further delivered through an idle roller 19 towards a support 25, such as a belt conveyor, or a cylinder manufacturing drum, or a toroidal manufacturing drum. A festoon 18 is formed between the pull roller 17 and the idle roller 19.
A cutter 20 is disposed in front of the support 25. The cutter 20 cuts the cord-reinforced continuous strip 22 into strips 23 of a predetermined length. The strips 23 are delivered successively onto the support 25 by conventional means, not shown in
In an alternative configuration, not shown in
In operation, the strip 23 is delivered onto the support 25, the support 25 is driven to advance the strip 23 by a predetermined distance, and then the next strip 23 is delivered onto the support 25 so that a front side edge portion of the subsequent strip 23 is approached to a back side edge portion of the preceding strip 23. The approaching may be either performed by overlapping the side edge portions, or by abutting the side edges of the strips 23. The approached side edge portions of the adjacent strips 23 are then joined together. These steps are repeated until a target length for the reinforcing layer being formed is reached.
The carcass ply of
Alternatively, a single extruding line could be used for manufacturing a strip of cumulative effective width W1+W2, which is then longitudinally cut to result in two continuous strips having effective widths W1 and W2, before cutting the strips to the length needed by the reinforcing layer being prepared and feeding of the strips on the conveyor belt.
In further embodiments, the strips A and B could be provided by unwinding of a continuous strip prepared in advance from suitable reels, cut to length and fed to the conveyor belt (either from two reels carrying continuous strips respectively of effective width W1 and W2, or from one reel continuous strip of cumulative effective width W1+W2 longitudinally cut to form the continuous strips having effective widths W1 and W2).
In order to improve production efficiency, the provision of the plurality of strips A and of the plurality of strips B to the conveyor belt could be performed in parallel. For example, while a strip A is being applied to the conveyor belt and joined to the previous strip B, the subsequent strip B is being drawn and cut. Advantageously, application of the strips A and B on the conveyor belt could be provided from opposite sides of the conveyor belt. Advance of the conveyor belt could be suitably controlled in order to allow the alternated deposition of the strips A and B.
The carcass ply of
For example, the first and the second portions of the carcass ply and/or of the belt layer could be formed on two respective conveyor belts (not shown). The feeding to the respective conveyor belt of the strips A could be provided by a first extruding line, and the feeding to the respective conveyor belt of the strips B could be provided by a second extruding line, the first and the second extruding lines being for example similar to those shown in
Alternatively, a single extruding line could be used for manufacturing a strip of cumulative effective width W1+W2, then suitably longitudinally cut to result in two continuous strips having effective widths W1 and W2, before cutting the strips to the length needed by the reinforcing layer being prepared and feeding of the strips on the respective conveyor belts.
In further embodiments, the strips A and B could be provided by unwinding of a continuous strip prepared in advance from suitable reels, cut to length and fed to the respective conveyor belts (either from two reels carrying continuous strips respectively of effective width W1 and W2, or from one reel continuous strip of cumulative effective width W1+W2 longitudinally cut to form the continuous strips having effective widths W1 and W2).
In order to improve production efficiency, the application of the plurality of strips A and of the plurality of strips B to the conveyor belts could be performed in parallel on the two conveyor belts.
Strips A and B respectively have effective width W1 and W2, with W1≠W2. The number of applied strips A is N1 and the number of applied strips B is N2. In the embodiment shown in
In operation, the first application apparatus 51 and the second application apparatus 53 may apply at the same time respectively a strip A and a strip B, so as to increase efficiency of the application process. The encircled numbers shown in
In operation, the first application apparatus 51 and the second application apparatus 53 may apply at the same time respectively a strip A and a strip B, so as to increase efficiency of the application process. This could be accomplished only for a certain number of pairs of strips A, B (at most until exhausting of the N2 strips B to be laid down). The encircled numbers shown in
The Applicant has found that the use of strip-like elements of different effective widths for manufacturing the reinforcing components of a tyre may provide the level of flexibility requested by a complete production line. With this choice, the manufacturing process could be designed with fewer design constraints, without the need of large inventories of strips of different sizes, and/or without the need of continuously modifying the strip effective width in order to cope with a tyre size change and/or with a different target circumference to be covered.
By indicating with D the diameter of a generic target circumference to be covered by the strip-like elements for forming a given reinforcing layer, and with W1, W2 the effective widths of the strip-like elements used, the number N1 of the strip-like elements of effective width W1 and the number N2 of the strip-like elements of effective width W2 to be applied for covering the target circumference corresponding to the diameter D shall satisfy the following relationship [1]:
W1N1+W2N2=Dπ [1]
Equation [1] holds in case the reinforcing layer being prepared is a carcass ply, whereas for the preparation of a belt layer the following relationship should be satisfied:
W1/sin(θ)N1+W2/sin(θ)N2=Dπ [1′]
wherein θ represents the angle of the reinforcing thread-like elements of the belt layer with respect to the equatorial plane of the tyre. In the following, Equation [1] will be taken as reference. However, the same considerations could be applied for Equation [1′] obtaining corresponding results.
The value of the effective widths W1, W2 of the strip-like elements could always be chosen or expressed, at least as an approximation, as an integer number. Furthermore, the value of Dπ, i.e. the value of the target circumference to be covered by the strip-like elements for forming the given reinforcing layer, could also be expressed, at least as an approximation, as an integer number. This could be easily accomplished by expressing the effective width and target circumference values in the above relationship [1] in mm, for example. The accuracy of the approximation may define a tolerance for the calculation, so that the cumulative value W1 N1+W2 N2 (i.e. the length of the layer formed by the joining of the N1 strip-like elements of effective width W1 and the N2 strip-like elements of effective width W2) differs from the target circumference to be covered by the reinforcing layer being formed by a value being controllable, in order to keep it under a preset threshold value. Preferred embodiments could provide a practical whole coverage of the target circumference by suitable choice of the target diameter D.
Equation [1] can thus be re-written as
W1N1+W2N2=C [2]
where C represents the integer approximation to the target circumference. Equation [2] contains only integer numbers (with N1 and N2 being the unknown quantities to be determined), and is known in mathematical literature as Diophantine equation. Conventional mathematical methods could be exploited for solving Equation [2] for any practical value of the approximated target circumference C, i.e. for any reinforcing layer and/or tyre size. For example, according to the Eulerian method, Equation [2] could be progressively transformed in equations with lower integer coefficients, being more easily solvable, and then, by progressive back transformations, finding the solution of Equation [2], i.e. determining the unknown N1 and N2.
The solutions to the Equations [1] or [2] could be found in principle for any value of target circumference, once the values of the effective widths W1 and W2 have been fixed. In practice, “any value of target circumference” in the framework of a tyre production means any target circumference to be matched for any tyre size, and/or model, and/or reinforcing layer to be applied on manufacturing drums of any convenient size. Thus, a convenient choice of the effective widths W1 and W2 may lead to the provision of a series of pairs (N1, N2) adapted for applying any reinforcing layer in any tyre size and/or model on manufacturing drums of any convenient size.
Once the number N1 of strip-like elements having effective width W1 (strip-like elements A) and the number N2 of strip-like elements having effective width W2 (strip-like elements B) have been determined, the particular arrangement sequence of the strip-like elements A and B on the suitable support used during manufacturing of the tyre can be determined in the manner most convenient to the manufacturer. For example, production effectiveness and/or reduction of the whole cycle time for forming each reinforcing layer could be pursued in order to find the best application sequence for each pair (N1, N2). The embodiments disclosed above with reference to
As it is well known, tyre sizes are represented by rim bead seat design diameters, expressed in inches. For example, there are tyres respectively having bead seat diameters of 15 inches, 16 inches, 17 inches and so on. Coming back to Equation [2], when the manufacturing of the same reinforcing layer with the same strip-like elements for two different sizes is considered, the following relationships could be written:
1st size: W1N1+W2N2=C1 [3]
2nd size: W1N3+W2N4=C2 [4]
wherein C1=D1π and C2=D2π, D1 and D2 being related to the two tyre sizes. Let's assume that the 2nd size is greater than the 1st size. If the two tyre sizes are subsequent to each other, and D1 and D2 are expressed in inches, it follows that D2=D1+1, so that C2=C1+π, if expressed in inches, or, in other words, C1 and C2 differ with each other by about 80 mm (more precisely about 79.76 mm). Furthermore, since N1, N2, N3, N4 are all integers, and N3 and N4 refer to a greater tyre size, the following relationships could be written:
N3=N1+inc1 [5]
N4=N2+inc2 [6]
wherein inc1 and inc2 are integer numbers representing the difference in number between the strip-like elements needed for forming the reinforcing layer in the 1st tyre size and in the 2nd tyre size.
All this being taken into account, Equation [4] could be re-written as:
W1(N1+inc1)+W2(N2+inc2)=C1+π [4′]
which (see Equation [3]) could be also written as
W1 inc1+W2 inc2=π [7]
Equation [7] gives a rule which could be followed to suitably choose the effective widths W1 and W2 of the strip-like elements. For example, by considering inc1=1 and inc2=1, and by approximating the value of π as being 79 mm, one can choose W1=40 mm and W2=39 mm. As another example, by considering inc1=1 and inc2=2, and by approximating the value of π as being 80 mm, one can choose W1=27 mm and W2=26 mm.
In the following Table 1, results are reported for preparing a carcass ply in different tyre sizes, ranging from 17 inches to 23 inches. It is assumed that the carcass ply should be formed by strip-like elements having effective widths W1=40 mm and W2=39 mm, and that the strip-like elements are applied to a cylinder support having a diameter starting from 490 mm at 17 inches (the diameters of the cylinder supports to be used for manufacturing the tyres of the other sizes could be easily derived, since they lead to target circumferences differing with each other by a value of π, as disclosed above). The table reports, for each tyre size (TS), the number of needed strip-like elements of effective width W1=40 mm (N1), the number of needed strip-like elements of effective width W2=39 mm (N2), the target circumference to be covered (TC), the cumulative sum of the effective widths of the (N1+N2) strip-like elements (CS). As it can be seen, the carcass ply could be advantageously produced with a minimum difference (within few millimeters) between the cumulative sum of the effective widths of the strip-like elements and the target circumference to be covered. It is noticed that the table could be completed for any practical tyre size, even lower than 17 inches or higher than 23 inches.
In the above examples, the effective widths (expressed in mm) of the strip-like elements were chosen so as W2=W1−1. In this particular case, the solutions to Diophantine Equation [2] could explicitly be written as:
N1=C+kW2 [8]
N2=−C−kW1 [9]
wherein k is any integer non-zero number. In fact, by substituting expressions [8] and [9] and reminding that W2=W1−1, Equation [2] could be rewritten as:
W1(C+kW2)+W2(−C−kW1)=C==>W1C−W2C=C==>W1C−(W1−1)C=C==>C=C
which is always verified. Thus, by appropriately choosing the value of the parameter k one can find the numbers N1 and N2 in the most convenient way.
In the following Table 2, results are reported for preparing a carcass ply in different tyre sizes, ranging from 17 inches to 23 inches. It is assumed that the carcass ply should be formed by strip-like elements having effective widths W1=27 mm and W2=26 mm, and that the strip-like elements are applied to a cylinder support having a diameter starting from 472.3 mm at 17 inches (the diameters for the other sizes could be easily derived, as observed above). The table reports, for each tyre size (TS), the value of the parameter k, the number of needed strip-like elements having effective width W1=27 mm (N1), the number of needed strip-like elements having effective width W2=26 mm (N2), the target circumference (TC), the cumulative sum of the effective widths of the (N1+N2) strip-like elements (CS). As it can be seen, the carcass ply could be advantageously produced with a number N1=N2 or N1=N2+1 of strip-like elements of different effective width, with a minimum difference (almost always within 1 mm) between the cumulative sum of the effective widths of the strip-like elements and the target circumference to be covered.
As shown with the above examples, a carcass ply could be conveniently formed by using two strip-like elements having different effective widths. For the preparation of a second carcass ply to be superposed to the first (prepared with N1 strip-like elements of effective width W1 and N2 strip-like elements of effective width W2), the increase in the target circumference to be covered due to the thickness of the first carcass ply should be taken into account. Being G the thickness of the first carcass ply, the increase (versus C) of the target circumference is given by 2πG. Such an increase could be managed by modifying the numbers N1 and N2 and taking into account of the difference between the effective widths W2−W1.
For example, by considering a thickness of the first carcass ply of 1 mm and a difference between the effective widths of the strip-like elements of 1 mm (as in the above examples), the increase in the target circumference becomes about 6 mm, which could be managed by applying (N1+6) strip-like elements of effective width W1 and (N2−6) strip-like elements of effective width W2 (assuming that W2<W1).
Alternatively, the second carcass ply could be formed by using the same number N1 and N2 of strip-like elements of the first carcass ply, by calculating from the target circumference increase a distributed gap to be applied between the N1+N2 strip-like elements.
In any case, once the effective widths W1 and W2 of the strip-like elements have been chosen, any carcass ply for any tyre size could be prepared with a suitable combination of the strip-like elements.
The above examples were disclosed with reference to the preparation of a carcass ply. As already said, similar considerations could be performed for the preparation of the belt layers, starting from Equation [1′] instead of Equation [1]. The effective widths of the strip-like elements to be used for the preparation of the belt layers could be the same as the effective widths of the strip-like elements to be used for the preparation of the carcass ply or plies, or they can be different.
The above considerations on the Diophantine equations and related examples could refer to an application of the strip-like elements performed by abutting side edges of the strip-like elements with each other. In such case, the effective widths W1 and W2 could correspond to the actual widths of the strip-like elements. In case an overlapping between side edge portions of the strip-like elements is used during the application thereof, the effective widths W1 and W2 correspond to the widths of the portions of the strip-like elements not being destined to overlap adjacent strip-like elements. A width of overlapping portion is summed to the effective widths in order to find the actual widths of the strip-like elements to be prepared for the formation of the reinforcing layers.
For example,
On the other hand, as another example,
It is noticed that the invention is not limited to any particular shape of strip-like element transverse section, so that the shapes shown in
The invention advantageously allows overcoming many problems involved in a complete tyre production line, as disclosed above. In addition, it is further noticed that an improvement to the tyres manufactured according to the above could also be obtained. In fact, a greater uniformity could be obtained due to the matching of the target circumference for any reinforcing layer and/or for any tyre size. Moreover, the use of strip-like elements of different effective widths for the formation of the reinforcing layers may reduce the occurrence of vibrational effects due to harmonic components caused by jointed portions regularly disposed along the circumference of the tyre, especially with alternated configurations between the strip-like elements of a first effective width and the strip-like elements of a second, different effective width.
Although the present invention has been disclosed and described by way of some embodiments, it is apparent to those skilled in the art that several modifications to the described embodiments, as well as other embodiments of the present invention are possible without departing from the scope thereof as defined in the appended claims.
For example, while the detailed description always made reference to two pluralities of strip-like elements, it is noticed that the same or similar considerations could be repeated in case of use of more than two pluralities of strip-like elements. As another example, while the detailed description always made reference to the manufacturing of carcass plies for radial tyres, it is noticed that the same or similar considerations could be repeated for the manufacturing of carcass plies for non-radial (e.g. cross-ply) tyres. As another example, while the detailed description always made reference to the preparation of reinforcing layers (carcass plies, belt layers) of the tyre, it is noticed that the same or similar considerations could be repeated for the preparation of other reinforcing components of the tyre including reinforcing thread-like elements, such as, e.g., a chafer provided for bead reinforcement.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/012452 | 12/22/2006 | WO | 00 | 8/11/2009 |
