Pneumatic tyre

Abstract: A pneumatic tyre comprising a carcass (5) having at least one ply of cords extending between bead portions (4), and a band (7) disposed radially outside the carcass (5) and inside a tread (2) made of parallel cords wound spirally around a breaker (6), characterised in that the band (7) comprises two circumferential portions (J,K) which are a parallel cord portion (J) in which the windings of the band cords are laid parallel to the tyre equator (C) and an inclined cord portion (K) in which the windings of the band cords are laid at an inclination angle of 0.3 to 5 degrees to the tyre equator (C), the circumferential length of the inclined cord portion (K) being less than 50% of the whole circumferential length of the band (7).

Description: The present invention relates to a belted pneumatic tyre, more particularly an improvement in the belt structure, which is capable of improving tyre uniformity and high speed durability. In Japanese Utility Model Publication No. 61-15604, a belted radial tyre having a band belt made by spirally winding cords around a breaker belt is disclosed. Such a band provides a tight hooping effect, and thereby the so called tread lifting phenomenon due to the centrifugal force during high speed running can be effectively prevented, and durability is improved to a high level. However, recently the requirements for tyres have become very severe and are not satisfied by such a belt structure. In the above-mentioned belt structure, the cords are wound spirally such that the cords are inclined with respect to the tyre equator at a certain angle through the whole circumferential length of the band. As a result, the tyre uniformity is liable to be disturbed, uneven tyre deformation is caused and durability is lowered, these effects being particularly notable in high speed running. It is therefore, an object of the present invention to provide a pneumatic tyre in which high speed durability is improved by improving the uniformity of the belt reinforcements. According to one aspect of the present invention, a pneumatic tyre comprises a carcass having at least one ply of cords extending between bead portions, and a band disposed radially outside the carcass and inside a tread made of parallel cords wound spirally around a breaker, characterised in that the band comprises two circumferential portions which are a parallel cord portion in which the windings of the band cords are laid parallel to the tyre equator and an inclined cord portion in which the windings of the band cords are laid at an inclination angle of 0.3 to 5 degrees to the tyre equator, the circumferential length of the inclined cord portion being less than 50% of the whole circumferential length of the band. Preferably, in the major circumferential portion of the band the band cords are laid parallel to the tyre equator, and accordingly uniformity of the tread portion is best improved to improve high speed durability of the tyre. Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings, in which: Figure 1 is a cross sectional view of a tyre according to the present invention; Figure 2 is a developed plan view showing the carcass and band thereof; Figures 3 and 4 are respectively a side view and a developed partial plan view of another example of the band; Figure 5 is a perspective view of a ribbon of rubber used to form the band; and Figure 6 is a sectional view of a modification of the band. In Figures 1 and 2, a pneumatic tyre 1 is a passenger car tyre and has a tread portion 2, a pair of axially spaced bead portions 4, and a pair of sidewall portions 3 extending between the tread edges and the bead portions 4. The tyre 1 also has a pair of bead cores 4A disposed one in each of the bead portions 4, a toroidal carcass 5 extending between the bead portions 4 and turned up around the bead cores 4A, and belt reinforcements 6 and 7 disposed radially outside the carcass and inside a rubber tread. The carcass 5 comprises at least one ply of cords and forms two turned up portions and one main portion between the bead cores 4A. The carcass cords are arranged radially at 60 to 90 degrees with respect to the tyre equator C to provide a radial or so-called semiradial ply structure. For the carcass cords, organic fibre cords, e.g. nylon, aromatic polyamide or the like are used. The belt reinforcements in this embodiment comprise a breaker 6 and a band or bandage 7. The breaker 6 is disposed radially outside the carcass crown, and comprises radially inner and outer plies 6A and 6B, the radially inner breaker ply 6A being wider than the radially outer breaker ply 6B. The breaker cords in each ply are laid at an angle of 15 to 40 degrees with respect to the tyre equator C and parallel with each other, but crosswise to the cords in the next ply. For the breaker cords, high elastic modulus cords, e.g. steel cords, organic fibre cords such as aromatic polyamide fibre cords or the like are used. The band 7 is the radially outermost reinforcing cord layer and is disposed on the radially outer surface of the breaker 6 and extends axially across the whole width of the breaker 6 to reach the breaker edges. Thus the edges F1 and F2 of the band 7 in this embodiment are aligned with the breaker edges, but they can project outside the edges to give an edge overlap. The band 7 is made of parallel cords wound spirally around the breaker 6 continuously from one edge to the other edge thereof. The number of parallel cords is preferably in the range of 6 to 20. The band 7 in this embodiment composed as shown in Figure 2, is of two circumferential portions, a parallel cord portion J and an inclined cord portion K. The parallel cord portion J is such that the cords of the windings of the band are laid parallel to the tyre equator C. The inclined cord portion K is such that the cords in the windings of the band are laid in these portions at a small angle (alpha) of 0.3 to 5 degrees, more preferably 1 to 3 degrees, with respect to the tyre equator C. The circumferential length of the inclined cord portion K is 20 to 50% of the whole circumferential length. If the circumferential length of the inclined cord portion K is less than 20%, the inclination angle becomes excessively large, and it becomes too difficult to make such a band. If more than 50%, the parallel cord portion J becomes too short and uniformity is not be improved. Figures 3 to 4 show another example of the band, in which the band 7 is composed of alternate parallel cord portions and inclined cord portions. In this example, the band 7 is composed of alternate three parallel cord portions J1, J2 and J3 and three inclined cord portions K1, K2 and K3. The inclined cord portions K1-K3 have substantially the same circumferential lengths, the total of which is not more than 25% of the whole circumferential length of the band. Also the parallel cord portions J1-J3 have substantially the same circumferential lengths. If the total circumferential length of the inclined cord portions is more than 25%, sufficient uniformity is not be obtained, and durability is impaired. The inclined cord portions K1, K2 and K3 (and accordingly the parallel cord portions) are disposed symmetrically around the tyre axis at substantially regular pitch angles (in this example every 120 degrees). The windings of the band cords in each inclined cord portion are also laid at a small angle (alpha) of 0.3 to 5 degrees, more preferably 1 to 3 degrees, with respect to the tyre equator C, and those in each parallel cord portion are parallel with the tyre equator C. The above-mentioned bands 7 are formed by winding a ribbon of rubber 10 shown in Figure 5. The ribbon 10 is such that the band cords 11 are embedded in coating rubber 12 parallel to each other along the longitudinal direction thereof. The cross sectional shape of the ribbon 10 in this example is a flat rectangle. Preferably organic fibre cords having a heat shrinking nature such as 66-nylon are used. By using such cords, the band cords are shrunk during vulcanisation to increase the hoop force of the band, and the tyre uniformity is improved. In the widthwise direction of the ribbon 10, the cords 11 are laid at substantially regular intervals, and the number of cords is preferably in the range of 6 to 20 as explained above. When the cord number is less than 6, the width W1 of the ribbon 10 becomes too small and the winding number or the number of windings of the ribbon is increased, which lowers the productivity and increases the manufacturing cost of the tyre. When the number is more than 20, the width W1 of the ribbon 10 becomes too large, and as a result the cord inclination angle in the inclined cord portion is increased and the tyre uniformity is deteriorated. Starting from the band edge F1, the ribbon 10 is wound around the radially outside of the breaker 6 spirally and continuously to the other band edge F2. As shown in Figures 2 and 4, in the parallel cord portions J, J1-J3 the ribbon 10 is wound parallel to the tyre equator C, and in the inclined cord portions K, K1-K3 the ribbon is wound at the above mentioned small inclination angle (alpha). In the above-mentioned examples, the ribbon 10 is wound closely so that the windings are not overlapped except in the band edge portions. In the edge portion, the ribbon 10 is wound along the band edge F1, F2 for at least one turn to make the axially outermost winding, the whole of which is parallel with the tyre equator C, and which is overlapped with the next winding, so that the ends of the ribbon 10 are prevented from loosening, and to provide a further reinforcement at the breaker edges to prevent breaker edge separation failure. Passing through the sole inclined cord portion (Figures 1-2) or all of the inclined cord portions (Figures 3-4), the ribbon 10 is progressed by one spiral pitch. In other words, in order to progress the ribbon one spiral pitch, the width of the ribbon (or the number of the embedded cords), the overlap width and the like are determined based on the above-mentioned limitations for the inclination angle and the total circumferential length of the inclined cord portion(s). If the inclination angle (alpha) is more than 5 degrees, which means that the bent angle of the ribbon 10 at the boundary between the parallel and inclined cord portions is more than 5 degrees, an undesirable stress is caused around the boundary, and further it becomes difficult to make such a band. The joint of the tread rubber which is wound on to the outside of the band and the circumferential ends or joint of the breaker ply are preferably disposed within the parallel cord portion(s), whereby separation failure during high speed running can be avoided. As explained above, in the two examples, the windings of the ribbon 10 are not overlapped except in the band edge portions. However, it can be overlapped over all the width as shown in Figure 6. The overlap widths L can be constant through all the width, but it is also possible to vary the overlap widths in the axial direction such that the overlap widths increase gradually from the tread centre towards the tread edges, or the overlap widths in the tread shoulder regions are larger than those in the tread crown region. Further, it is possible to wind the ribbon in an opened state where adjacent turns have their edges spaced apart by a small distance. Furthermore, immediately inside the above explained band 7 a similar band can be disposed so as to provide the tyre with a double-layered band structure. As described above, in pneumatic tyres according to the present invention, the spiral cord band comprises the major parallel cord portion and the minor inclined cord portion, whereby tyre uniformity and high speed durability are improved.

Claims: A pneumatic tyre comprising a carcass (5) having at least one ply of cords extending between bead portions (4), and a band (7) disposed radially outside the carcass (5) and inside a tread (2) made of parallel cords wound spirally around a breaker (6), characterised in that the band (7) comprises two circumferential portions (J,K) which are a parallel cord portion (J) in which the windings of the band cords are laid parallel to the tyre equator (C) and an inclined cord portion (K) in which the windings of the band cords are laid at an inclination angle of 0.3 to 5 degrees to the tyre equator (C), the circumferential length of the inclined cord portion (K) being less than 50% of the whole circumferential length of the band (7). A pneumatic tyre according to claim 1 characterised in that the circumferential length of the inclined cord portion (K) being more than 20% of the whole circumferential length of the band (7). A pneumatic tyre according to claim 1 or 2 characterised in that the band (7) comprises a plurality of circumferential portions including at least two parallel cord portions (J1,J2,J3) in which the windings of the band cords are laid parallel to the tyre equator (C) and at least two inclined cord portions (K1,K2,K3) in which the windings of the band cords are laid at an inclination angle of 0.3 to 5 degrees of the tyre equator, said at least two inclined cord portions (K1,K2,K3) being disposed substantially symmetrically around the tyre axis, and the total circumferential length of said at least two inclined cord portions (K1,K2,K3) are not more than 25% of the whole circumferential length of the band (7). A tyre according to claim 3, characterised in that the inclined cord portions (K1,K2,K3) have substantially the same circumferential length the total of which is not more than 25% of the whole circumferential length of the band (7). A tyre according to claim 3 or 4, characterised in that the parallel cord portions (J1,J2,J3) have substantially the same circumferential length. A tyre according to claim 3, 4 or 5, characterised in that the inclined cord portions (K1,K2,K3) are disposed symmetrically around the tyre axis in substantially regular pitched angles. A tyre according to any one of claims 1 to 6, characterised in that the inclination angles is in the range of 0.3 to 5 degrees. A tyre according to any one of claims 1 to 7, characterised in that the inclination angle is in the range of 1 to 3 degrees.

Inventors: HIROSAWA YOUICHIRO, ONODA MAKOTO, SAKUNO HIROAKI - AZA-MIYAKOBAS, YAMAMORI SYUICHI, HIROSAWA, YOUICHIRO, ONODA, MAKOTO, SAKUNO, HIROAKI, 1-44 AZA-MIYAKOBASHIYAMA, YAMAMORI, SYUICHI
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1991
Main classification: B60C9
IPC codes: B60C9