Tubeless pneumatic tyre

Abstract: A tubeless pneumatic tyre including a carcass (11,16,22) having a carcass cord web (12) and topping rubber layers covering the opposite sides of the carcass cord web, the carcass (11) extending from a tread portion through a sidewall portion to a bead portion and turned up around a bead core outwardly from the inside of the tyre in the axial direction of the tyre, wherein only the inner one layer (13a) of the topping rubber layers which faces the inside of the tyre is made of a butyl-based rubber. The tubeless pneumatic tyre is of lightened weight and exhibits anti-airleak property comparable or superior to that of conventional tyres even when it has no inner liner.

Description: The present invention relates to lightened-weight tubeless pneumatic tyres having excellent anti-airleak properties. A typical structure of a tubeless pneumatic tyre is shown in Fig. 10. The tubeless tyre includes a carcass ply 1 defining the carcass of the tyre and comprising a carcass cord ply made of organic fibre such as of nylon, steel wire or the like and a topping rubber covering on both opposite surfaces of the carcass cord web. The carcass ply 1 extends from the tyre centreline from the tread portion through a shoulder portion and sidewall portion to a bead portion, and is turned up around a bead core 2 outwardly from the inside of the tyre in the axial direction. The entire interior surface of the carcass ply 1 is lined with an inner liner 3 mainly made of butyl rubber which is excellent in air imperviousness to prevent leak of the air charge in the tyre, whereby the tubeless tyre maintains its predetermined air pressure therein. As shown in Fig. 10, the tyre further includes a tread reinforcing belt 4 such as a breaker or belt layer disposed on the outer surface of the carcass ply 1, and a rim 5 is used to provide the tyre/wheel sub-assembly for a vehicle. Such a tubeless tyre is of lightened weight compared to previous tubed type tyres because there is no tube and, in recent years, further weight reduction of tyres has been desired for energy-saving automobiles. Japanese Unexamined Patent Publication No. 4-9092 (1992) discloses a tubeless pneumatic tyre which is lightened by separately disposing inner liner components in regions of the right and left sidewall portions thereof, i.e., by providing no inner liner in the region of the tread portion thereof. However, the major part of the interior surface of the tyre is still lined with the inner liner and, therefore, weight reduction of the tyre is not completely successful. On the other hand, Japanese Unexamined Patent Publication No. 6-156007 (1994) discloses a tubeless pneumatic tyre comprising a carcass 9 consisting of a carcass cord ply 7 and a topping rubber 8 of a butyl-based rubber covering both surfaces of the carcass cord web 7, as shown in Fig. 11 (enlarged view of a bead portion) and Fig. 12 (sectional view of the carcass). In Fig. 11, reference numeral 10 denotes a bead core. Since the topping rubber 8 is formed of butyl-based it is rubber excellent in air imperviousness and hence the carcass 9 per se exhibits the function of an inner liner and a separate inner liner can be entirely dispensed with. Thus, satisfactory weight reduction can be achieved. However, butyl-based rubbers have poor vulcanisability and adhesiveness in comparison with diene-based rubbers. If a tyre has a topping rubber 8 entirely formed of a butyl-based rubber, the butyl-based rubber comes into contact with other components and ply layers (e.g., breaker ply, sidewall rubber or the like) disposed outside the carcass. This may cause the component to be readily separated from the carcass, thereby deteriorating the durability of the tyre. It is an object of the present invention to provide a tubeless pneumatic tyre that is lightened by effectively eliminating at least part or all of the inner liner without deteriorating the durability thereof. According to the present invention a tubeless pneumatic tyre comprises a carcass having a carcass cord web and rubber topping layers covering opposite side of the carcass cord web, the carcass extending from a tread portion through a sidewall portion to a bead portion and turned up around a bead core outwardly from the inside of the tyre in the direction axially of the tyre, characterised in that only the inner layer of the rubber topping layers is formed of a butyl-based rubber. The carcass may include a single carcass ply or, alternatively, a plurality of carcass plies. Where the carcass includes a plurality of carcass plies stacked one on another, only the inner one of the topping rubber layers of the innermost carcass ply is formed of the butyl-based rubber. A tubeless tyre having a carcass composed of the plurality of carcass plies stacked one on another may include an innermost carcass ply extending from the tread portion through the sidewall portion to the bead portion and turned up around the bead core outwardly from inside of the tyre in a axial direction of the tyre, and an outer carcass ply extending from the tread portion through the sidewall portion to the bead portion and turned up around the bead core inwardly from outside of the tyre in the axial direction so as to cover the turned-up portion of the innermost carcass ply, wherein only the inner one of the topping rubber layers of the innermost carcass ply is formed of the butyl-based rubber. The tubeless tyre having the carcass composed of the plurality of carcass plies stacked one on another may include an outer carcass ply extending from the tread portion through the sidewall portion to the bead portion and turned up around the bead core outwardly from inside of the tyre, an innermost carcass ply extending from the tread portion through the sidewall portion to the bead portion and terminating at the bead portion without being turned up around the bead core, and a bead apex rubber provided in a portion surrounded by the turned-up portion of the carcass and the bead core, wherein difference Hc between radial distance Hb from the terminating end of the innermost carcass ply to a radially inside edge of the bead core and radial distance Ha from a radially outside edge of the bead apex rubber to the radially inside edge of the bead core is not less than 5 mm, and wherein only the inner one of the topping rubber layers of the innermost carcass ply is formed of a butyl-based rubber. The radial distance Hb from the terminating end of the innermost carcass ply to the radially inside edge of the bead core is preferably not greater than 20 mm. In the tubeless tyre having the carcass composed of the plurality of carcass plies stacked one on another, the innermost carcass ply may be divided into two separate carcass ply portions, which are respectively disposed in regions corresponding to the opposite sidewall portions. The two carcass ply portions of the innermost carcass ply are preferably arranged so as to satisfy the following relation: 0.2 Wb ≤ Wn ≤ 0.95 Wb where Wb is a tread width and Wn is a spacing between the two carcass ply portions of the innermost carcass ply. In the tubeless pneumatic tyre of the present invention, the aforesaid butyl-based rubber preferably includes a butyl rubber or a derivative thereof as a main ingredient in an amount of not less than 60 % by weight. The rubber gauge Y between the carcass cord ply and the interior surface of the tyre may be in the range of 0.8 mm to 2.5 mm. The tubeless tyre preferably includes a reinforcing rubber layer provided outside the turned-up portion of the carcass. Further, the tubeless pneumatic tyre of the present invention may include an inner liner covering the inner surface of the carcass. Alternatively, the topping rubber layer formed of the butyl-based rubber may define the interior surface of the tyre without the inner liner being provided on the inner surface of the carcass. Since the inner topping rubber layer of the carcass is formed of the butyl-based rubber which is excellent in air imperviousness in accordance with the present invention, the tubeless pneumatic tyre has an anti-airleak property comparable or superior to the conventional tubeless pneumatic tyres and offers a lighter weight even when it is not lined with inner liner. The tubeless pneumatic tyre having the carcass composed of the plurality of carcass plies has an excellent anti-airleak property and a lightened weight while ensuring stable steering performance. In particular, the provision of the innermost carcass ply of the separation type realises further weight reduction of the tubeless pneumatic tyre. The lining of the inner topping rubber layer of the carcass with an inner liner further improves anti-airleak property of the tubeless tyre of the present invention. Further, the provision of the reinforcing rubber layer improves the durability of the tubeless tyre without increasing the weight of the tyre so much. These and other objects, and advantages of the present invention will become apparent from the following detailed description of embodiments, by way of example only, in conjunction with the attached diagrammatic drawings in which:- Fig. 1 is a partial enlarged sectional view illustrating the bead portion of a tubeless tyre in accordance with a first embodiment of the present invention; Fig. 2 is a schematic diagram for explaining the structure of the carcass ply of the tubeless tyre of the first embodiment; Fig. 3 is a partial enlarged sectional view illustrating a bead portion of a tubeless tyre in accordance with a second embodiment of the present invention; Fig. 4 is a schematic diagram for explaining the structure of a carcass composed of a plurality of carcass plies; Fig. 5 is a partial enlarged sectional view illustrating a bead portion of a tubeless tyre in accordance with a third embodiment of the present invention; Fig. 6 is a partial enlarged sectional view illustrating a bead portion of a tubeless tyre in accordance with a fourth embodiment of the present invention; Fig. 7 is a partial enlarged sectional view illustrating a tubeless tyre having a carcass of the separation type; Fig. 8 is a schematic diagram for explaining the structure of a carcass ply lined with an inner liner; Fig. 9 is a partial enlarged view illustrating a bead portion of a tubeless tyre provided with a reinforcing rubber layer in accordance with the present invention; Fig. 10 is a diagram illustrating the structure of a conventional tubeless tyre; Fig. 11 is a partial enlarged view illustrating a bead portion of a conventional tubeless tyre; and Fig. 12 is a schematic diagram for explaining the structure of a carcass of the tubeless tyre shown in Fig. 11. Fig. 1 is a tubeless tyre having a single-layer of carcass ply 11. As shown, the carcass ply 11 is turned up around a bead core 14 outwardly from the inside of the tyre in the axial direction. A chafer 15 of an organic fibre ply coated with rubber wraps the bead over the carcass ply 11. As shown in Figs. 1 and 2, the carcass ply 11 comprises parallel cords web 12, e.g., a cord fabric, such as of nylon and topping rubber layers 13 covering the opposite sides of the carcass cord web. The inner layer 13a is formed of a butyl-based rubber, while the outer layer 13b is made of a common diene-based rubber. The carcass ply 11 is fabricated by assembling carcass cords into a carcass cord web 12 of cords, dipping the carcass cord web into an adhesive to improve the adhesiveness between the topping rubber materials and the carcass cord web, and bonding topping rubber sheets to both sides of the carcass cord web 12 by means of calendering. As a result the coverage state of the butyl-based rubber on the carcass cord web 12 varies depending on the thicknesses of the rubber calendered on to the inner side. The boundary between the inner topping rubber layer 13a of butyl-based rubber and the outer topping rubber layer 13b of diene-based rubber may be substantially aligned with the centre line of the carcass cord web 12 as shown in Fig. 2(a), or with the inner surface line of the carcass cord web 12 as shown in Fig. 2(b). Fig. 3 illustrates a tubeless tyre in which the carcass 16 comprises two carcass plies 16A and 16B which are integrally stacked one on the other. The carcass 16 as a whole is turned up around a bead core 17 outwardly from the inside of the tyre in the axial direction of the tyre. Similarly to the first embodiment, the carcass plies 16A and 16B are each composed of a carcass cord web and topping rubber layers covering the carcass cord web (shown in Figs. 1 and 2, but not shown in Fig. 3). Only the inner topping rubber layer of the inner carcass ply 16A is formed of a butyl-based rubber, like the carcass ply 11 of the first embodiment. The outer ply does not have such a butyl-based topping rubber layer. Where the carcass 16 comprises more than two carcass plies stacked one on another, again only the inner topping rubber layer of the innermost carcass ply is formed of the butyl-based rubber, similarly to the aforesaid case. In Fig. 4 which illustrates a carcass 18 composed of three carcass plies 18A, 18B and 18C, the inner layer 19a of the topping rubber layers 19 of the innermost carcass ply 18A is formed of the butyl-based rubber, while the outer layer 19b (on the side contacting the adjacent carcass ply 18B) is formed of a common diene-based rubber. In Fig. 4, a reference numeral 20 denotes carcass cords. Fig. 5 illustrates a tubeless pneumatic tyre having a carcass 22 composed of two carcass plies 22A and 22B. The inner carcass ply 22A is turned up around a bead core 23 outwardly from the inside of the tyre in the axial direction of the tyre, and the outer carcass ply 22B is turned around the bead core 23 from the outside of the tyre in the axial direction of the tyre so as to cover the turned-up portion 24 of the inner carcass ply 22A. The carcass plies 22A and 22B each comprise a carcass cord web and topping rubber layers covering the carcass cord web (not shown). Only the inner one of the topping rubber layers of the inner carcass ply 22A is formed of a butyl-based rubber. With this arrangement, the turned-up portion 24, where the topping rubber layer formed of the butyl-based rubber with poor adhesiveness faces outwards, is covered by the outer carcass 22B having topping rubber made of the diene-based rubber and, hence, the topping rubber of the diene-based rubber of the outer carcass ply 22B contacts the sidewall rubber located outside the carcass 22. Therefore, the topping rubber around the bead portion in the tubeless tyre of the third embodiment exhibits improved adhesiveness in comparison with the tubeless tyre of the second embodiment in which the inner carcass ply and outer carcass ply integrally stacked together are turned up around the bead core outwardly from the inside of the tyre. Though the carcass shown in Fig. 5 is composed of two carcass plies in this embodiment, the carcass may be composed of more than two carcass plies. In this case, either or both of the inner carcass ply 22A and the outer carcass ply 22B may be composed of a plurality of carcass plies stacked one on another. Fig. 6 illustrates a tubeless pneumatic tyre in accordance with a fourth embodiment of the present invention. In this embodiment, a carcass 26 is composed of two carcass plies 26A and 26B. Only the outer carcass ply 26B is turned up around the bead core 27 for coverage thereof, and the inner carcass ply 26A extends from a tread portion through a sidewall portion to a bead portion and terminates at the bead portion without being turned up around the bead core 27. The carcass plies 26A and 26B each comprise a carcass cord web and topping rubber layers covering the carcass cord web (not shown), like the carcass ply of the first embodiment. Only the inner one of the topping rubber layers of the inner carcass ply 26A is formed of butyl-based rubber. As shown in Fig. 6, a rubber bead apex 29 tapering in the radial direction of the tyre is provided on the bead and surrounded by the turned-up portion 28 of the carcass ply 26B and the bead core 27. The difference Hc (= Ha - Hb) between the radial distance Hb from the terminating edge 30 of the inner carcass ply 26A to the radially inside surface (the lower end in Fig. 6) of the bead core 27 and radial distance Ha from the radially outside edge (the upper end in Fig. 6) of the bead apex 29 to the radially inside edge of the bead core 27 is not less than 5 mm. The distance Hb is preferably not greater than 20 mm, more preferably not greater than 10 mm. If the distance Hc is less than 5 mm, the edge 30 of the inner carcass ply 26A is located too close to the radially outside edge of the bead apex 29. This causes stress to be concentrated around the edge 30 and radially outside edge of the bead apex 29 when the tyre undergoes flexure, with the result that the occurrence of damage thereat is likely. If the distance Hb is greater than 20 mm, the edge 30 is positioned in a portion susceptible to the tyre flexure, whereby the edge of the carcass cord ply tends to be readily loosened at its edge 30. The bead apex, in general, is formed of a rubber harder than the sidewall rubber so that the lateral rigidity of the tyre can be enhanced by the co-operation of the bead apex rubber and the turned-up portion of the carcass ply. This feature is not limited to the structure shown in Fig. 6, but is applicable to the tyres of the first to third embodiments. Though the edge of the turned-up portion 28 is located closer to the tyre axis than the radially outside edge of the bead apex 29, i.e., on the side closer to the bead core 27 in accordance with the embodiment shown in Fig. 6, the present invention is not limited to this structure. The edge of the turned-up portion 28 may be located in a position radially more outward of the radially outside edge of the bead apex 29, i.e., on the side closer to the tread portion (see the turned-up portion shown in Fig. 1). As can be appreciated from the foregoing, there is no need to provide an inner liner in the tubeless tyre, because the inner topping rubber layer of the carcass facing the inside of the tyre is formed of the butyl-based rubber which is excellent in air imperviousness. Therefore, the tubeless tyre of the present invention can be lighter than conventional tubeless tyres, and the fabrication thereof can be simplified. Since a joint portion which would otherwise appear between the inner liner and the topping rubber can be eliminated, the integrity of the tyre components can be more enhanced, resulting in a tyre of enhanced durability. In a tyre having a carcass 33 composed of a plurality of carcass plies (e.g., two carcass plies 33A and 33B in Fig. 7), the innermost carcass ply 33A may comprise two separate carcass ply portions, which are respectively disposed in regions corresponding to the opposite sidewall portions 34, in other words, the innermost carcass ply 33A may not be provided in a region corresponding to the tread portion 35. This arrangement reduces the weight of the tyre having a plurality of carcass plies. The tread portion 35, though not provided with the innermost carcass ply 33A, is generally provided with at least one carcass ply (e.g., the outer carcass ply 33B in Fig. 7) and further with a cord layer 36, a belt layer 37 and the like, on which a thick tread rubber 38 is provided. Therefore, airleak problem rarely occurs even if a layer of the butyl-based rubber excellent in air imperviousness is not provided in the tread portion. That is, it is unlikely that airleak problem will occur due to the absence of the innermost carcass ply 33A and thus the absence of the butyl-based rubber layer. Where the innermost carcass ply of this separation type is provided, the two separate carcass ply portions are preferably arranged so as to satisfy the following relation: 0.2 Wb ≤ Wn ≤ 0.95 Wb where Wn is the length of the breaker 37 corresponding to the tread width and Wb is the spacing between the two carcass ply portions of the innermost carcass ply 33A across the tread portion. If the length Wn is less than 0.2 Wb, substantial weight reduction cannot be expected. If the length Wn exceeds 0.95 Wb, the airleak problem becomes likely and the durability of the tyre tends to be deteriorated. Though none of the tubeless tyres of the first to fourth embodiments is provided with an inner liner as shown in Figs. 1, 3, 5 and 6, the present invention does not preclude the provision of an inner liner. As shown in Fig. 8, an inner liner 43 formed of a butyl-based rubber may be provided on an inner surface of the inner-most carcass ply 41 (or the carcass if the carcass is of a single-layer structure) having an inner topping rubber layer 42a of the butyl-based rubber to further enhance the air imperviousness. Since the inner topping rubber layer 42a is formed of the butyl-based rubber exhibiting imperviousness to air, the inner liner 43 can be made thin in comparison with an inner liner of a conventional tyre in which the topping rubber is formed of a diene-based rubber. Hence, some weight reduction of the tyre is still achieved. Next, reference is to be made to butyl-based rubbers to be used in the present invention. The butyl-based rubbers defined herein are meant to include butyl rubbers and derivatives thereof. The butyl rubbers are copolymers of isobutylene (saturated chain polymer unit) and a small amount of isoprene (polymer unit having a double bond). The derivatives of the butyl rubbers include halogenated butyl rubbers such as chlorinated butyl rubbers and brominated butyl rubbers which are obtained by reacting butyl rubber with halogens such as chlorine and bromine to improve vulcanisability of butyl rubber. The butyl rubbers and the derivatives thereof have low unsaturation degrees and, thus, are chemically stable and excellent in air imperviousness. The butyl-based rubber to be used in the present invention preferably contains a butyl rubber or a derivative thereof in an amount of not less than 60 % by weight If the proportion of butyl rubber is less than 60 % by weight, unsatisfactory air imperviousness may result. Other rubber ingredients to be blended with the butyl rubber or derivative thereof include natural rubbers, and diene-based rubbers such as butadiene rubber and styrene-butadiene rubber, but not limited thereto. The topping rubber layer of such a butyl-based rubber is formed so that the gauge Y (see Fig. 2) measured from the interior surface of the tyre to the carcass cord web is preferably in the range between about 0.8 mm and about 2.5 mm, more preferably between about 1.0 mm and about 2.0 mm dependent on the composition of the butyl-based rubber to be used. If the gauge Y is less than 0.8 mm, the inner topping rubber layer is extremely thin, and cracks on the inner surface of the carcass are likely. Such cracks will deteriorate the durability and anti-airleak property of the tyre. If the gauge Y exceeds 2.5 mm, the weight of the tyre cannot satisfactorily be reduced. If lined with an inner liner, the tyre is preferably built so that the sum Y (see Fig. 8) of the thickness I of the inner liner and a gauge K measured from the carcass cord web to the inner liner is in the aforesaid range, that the thickness I of the inner liner is in the range between about 0.5 mm and about 2.0 mm, and that the gauge K is in the range between about 0.3 and about 1.5 mm. To be adequate, an average thickness of the inner topping rubber layer and an average proportion of the butyl-based rubber used therein after vulcanisation moulding of the tyre are within the aforesaid respective ranges. To achieve more stable air imperviousness, however, the gauge Y throughout the interior surface of the tyre is preferably within the aforesaid range. In terms of durability, the thickness X of the outer topping rubber layer (see Figs. 2 and 8) is preferably about 0.5 mm to about 1.5 mm. If the thickness X is less than 0.5 mm, the carcass ply tends to be separated (or loosened) from the breaker ply or the like provided outside the carcass. If the thickness X exceeds 1.5 mm, a substantial increase in the weight of the tyre is unavoidable and, as well, the carcass ply tends to be separated from the breaker ply or the like, resulting in a tyre of poor durability. In the tubeless tyre of the present invention, a rubber rim reinforcing layer 48 made of a diene-based rubber and having a thickness of about 0.5 mm to about 1.5 mm is preferably provided in a position outside a turned-up portion 47 of a carcass 45 turned up around a bead core 46 outwardly from the inside of the tyre in the axial direction, as shown in Fig. 9. The provision of the reinforcing layer 48 prevents the portions of the carcass 45 formed of butyl-based rubber 45 from coming into direct contact with the chafer 49, sidewall rubber 50 and the like, thereby preventing deterioration in durability of the tyre. Also, the provision of the reinforcing layer 48 increases the rigidity of the tyre in the bead portion to ensure enhanced steering performance of an automobile mounted with such tyres. If the thickness of the reinforcing rubber layer 48 exceeds 1.5 mm, the weight of the tyre is undesirably increased without any substantial durability improvement. The rim reinforcing layer 48 provided on the turned-up portion 47 preferably extends from the radially outside edge 51 of the bead core 46 to the radially outside edge 52 of the contact region between the turned-up portion 47 and the chafer 49, as shown in Fig. 9(a), more preferably it extends from the radially outside edge 51 of the bead core 46 to the edge 53 of the turned-up portion 47 as shown in Fig. 9(b). Where the tyre has a carcass composed of a plurality of carcass plies, the rim reinforcing rubber layer may be provided in substantially the same manner as the embodiment shown in Fig. 9 having a single-layer carcass ply. Now the present invention will be described by way of more specific embodiments. The evaluation method of the characteristics of the tyres was as follows. Evaluation (a) Durability Fabricated tyres were mounted on rims (14 x 6 JJ), and the inside pressures thereof were adjusted to 1.9 kg/cm 2 . Then, the tyres were run on test drums having a diameter of 1700 mm. After a 30,000 km test was carried out under predetermined conditions (load: 670 kg or 805 kg, speed: 80 km/h), the tyres were inspected and evaluated according to the following three levels. A: No change B: Looseness occurred after completing 30,000km C: Unable to last 30,000 km (b) Airleak Fabricated tyres were mounted on rims (14 x 6 JJ), and the inside pressures thereof were adjusted to 2.0 kg/cm 2 . After the tyres were allowed to stand at a temperature of 21°C for one month, decrease rates of the inside pressures of the tyres were calculated. For every test sample, three tyres were employed and an average value was calculated. Then, the decrease rate of the inside pressure for every test sample was expressed as an index by assuming the decrease rate of Reference Example 2 to be 100. A greater index value indicates that the tyre had a better anti-airleak property. (c) Weight reduction The weight of every test sample was expressed as an index by assuming the weight of Reference Example 1 to be 100. A greater index value indicates that the tyre is heavier. Rubber compositions Six rubber compositions No. 1 to No. 6 shown in Table 1 were prepared to be employed for topping rubbers and inner liners. Among them, rubber compositions No. 3 to No. 6 are butyl-based rubbers. In Table 1, the value of each component is expressed in parts by weight relative to 100 parts of the rubber component. Rubber composition No. 1 2 3 4 5 6 Chlorinated butyl rubber - - 50.0 60.0 70.0 100.0 Natural rubber 72.0 69.0 50.0 40.0 30.0 0 Styrene-butadiene rubber 28.0 31.0 - - - - Butadiene rubber - - - - - - Carbon black 38.0 42.0 51.0 51.0 51.0 51.0 Process oil 9.8 3.5 0.3 0.3 0.3 0.3 Sulfur 3.0 1.5 1.2 1.2 1.2 1.2 Zinc white 5.0 3.0 5.0 5.0 5.0 5.0 Vulcanisation accelerator 1.0 1.0 1.3 1.3 1.3 1.3 Stearic acid 2.0 2.2 1.2 1.2 1.2 1.2 Tyre having carcass composed of single carcass ply Example 1 A carcass ply was fabricated using polyester fibres (1500d/2,51 ends/5cm) for the carcass cord web, and a butyl-based rubber composition No. 5 and a rubber composition No. 1 for the inner topping rubber layer and the outer topping rubber layer, respectively. With this carcass ply, a tubeless tyre (size: 195/65R14) having no inner liner was built. Specifically, the inside topping rubber layer defined the interior surface of the tyre (see Fig. 2(a)), and the gauge Y measured from the carcass cord web to the interior surface was 0.4 mm. The durability, anti-airleak property, and weight of the tubeless tyre having such structure were evaluated in the aforesaid manner. The results are shown in Table 2. Examples 2 to 13 Carcass plies and tyres were fabricated in substantially the same manner as in Example 1, except that rubber compositions employed for the topping rubbers and the gauges of the inner topping rubber layers were different from Example 1 as shown in Table 2. The durability, anti-airleak property and weight of the tyres thus built were evaluated in the same manner as in Example 1. The results are shown in Table 2. The tyres of Examples 8 and 9 each had a reinforcing rubber layer with a thickness t (shown in Table 2) provided on a turned-up portion of the carcass ply and extending from the radially outside face of the bead core to the radially outside edge of the turned-up portion as shown in Fig. 9(a). Example 14 A tubeless tyre of Example 14 had a carcass ply lined with an inner layer as shown in Fig. 8. The inner liner and inner and outer topping rubber layers were respectively formed of rubber compositions as shown in Table 2. The tubeless tyre having such structure was built, and the durability, anti-airleak property and weight thereof were evaluated. The results are shown in Table 2. Reference Examples 1 to 4 Tubeless tyres of Reference Examples 1 and 2 each had a carcass ply having topping rubber layers formed of a diene-based rubber and lined with an inner liner. A tubeless tyre of Reference Example 3 had a carcass ply having topping rubber layers formed of a butyl-based rubber. A tubeless tyre of Reference Example 4 had a carcass ply having topping rubber layers formed of a butyl-based rubber and lined with an inner liner. Rubber compositions employed for the topping rubber layers and inner liners in Reference Examples 1 to 4 are shown in Table 2. The tubeless tyres having such structures were built, and the durability, anti-airleak property and weight thereof were evaluated. The results are shown in Table 2. In Table 2, "C1" for the durability means that the tyre was not able to travel 30,000 km due to air leak caused by cracks. "B1" means that the tyre was able to travel 30,000 km but looseness occurred. As can be seen from Table 2, the tubeless tyres of Examples 1 to 7 in each of which the inner topping rubber layer was formed of a butyl-based rubber having a thickness greater than a predetermined value and the carcass ply was provided with no inner liner exhibited an anti-airleak property and durability comparable or superior to those of a tyre having a carcass ply lined with an inner liner. However, the tubeless tyres of Examples 1 and 2 in each of which the gauge of the inner topping rubber layer was relatively small exhibited unenhanced anti-airleak property. On the other hand, the tubeless tyres of Examples 6 and 7 in each of which the gauge was relatively large exhibited enhanced anti-airleak property but were heavier than Reference Examples. The tubeless tyres of Examples 10 and 11 in each of which the inner topping rubber layer was formed of a rubber composition containing not greater than 60 % by weight of butyl rubber did not exhibit significant superiority in anti-airleak property over Reference Examples 1 and 2 each having topping rubber layers formed of rubbers other than butyl-based rubbers. It is appreciated that as the content of butyl rubber in a rubber composition used for the inner topping rubber layer becomes higher, the anti-airleak property of the resulting tyre becomes better without significantly increasing the weight of the tyre (see Examples 10 to 13). The tubeless tyre of Example 14 in which the gauge of the inner topping rubber layer formed of a butyl-based rubber was small but an inner liner formed of a butyl-based rubber was provided had an improved anti-airleak property, and yet the weight thereof was comparable to Reference Examples. On the other hand, the tubeless tyres of Reference Examples 3 and 4 in each of which both the topping rubber layers were entirely formed of a butyl-based rubber exhibited improved anti-airleak property, but the durability thereof was deteriorated. It is also appreciated from the comparison of Example 4 with Examples 8 and 9 that the durability of a tubeless tyre can be improved by providing a reinforcing rubber layer. Tyres having carcass composed of plural carcass plies Tubeless tyres each having a carcass composed of a plurality of carcass plies were examined. These tubeless tyres were of the structure in accordance with the fourth embodiment. Rubber compositions No. 1 to No. 6 shown in Table 1 were employed for the topping rubber. Examples 15 to 26 and Reference Example 5 to 8 Rubber compositions employed for the outer and inner topping rubber layers of the innermost carcass ply of each of the tyres are shown in Table 3. Tubeless tyres of Example 26 and Reference Examples 5, 6 and 8 had inner liners, and rubber compositions employed for the inner liners are shown in Table 3. The tyres were of the structure shown in Fig. 6, in which the width Wb of a breaker ply was 144 mm, distance Ha was 40 mm and distance Hb was 5 mm. The durability, anti-airleak property and weight of the tubeless tyres having such structures were evaluated. The results are shown in Table 3. In Table 3, "B2" for the durability means that the tyre was able to travel 30,000 km but a looseness occurred between the turned-up portion of the outer carcass ply and the inner carcass ply. "C2" means that the tyre was unable to travel 30,000 km due to air leak caused by cracks. As can be seen from Table 3, the tubeless tyres of Examples 16 to 21 in each of which the inner topping rubber layer was formed of a butyl-based rubber having a thickness greater than a predetermined value and the innermost carcass ply was provided with no inner liner, like the aforesaid Examples 1 to 7 (single carcass ply), exhibited anti-airleak property and durability comparable or superior to those of a tyre having a carcass ply lined with an inner liner. However, the tubeless tyres of Examples 15 and 16 in each of which the gauge of the inner topping rubber layer was relatively small exhibited unenhanced anti-airleak property. On the other hand, the tubeless tyres of Examples 20 and 21 in each of which the gauge was relatively large exhibited enhanced anti-airleak property but were heavier than Reference Examples. The tubeless tyres of Examples 22 and 23 in each of which the inner topping rubber layer was formed of rubber composition containing not greater than 60 % by weight of butyl rubber did not exhibit significant superiority in anti-airleak property over Reference Examples. It is appreciated that as the content of butyl rubber in a rubber composition of the inner topping rubber layer becomes higher, the anti-airleak property of the resulting tyre becomes better without significantly increasing the weight of the tyre (see Examples 22 to 25). The tubeless tyres of Examples 15 and 26 in each of which the gauge of the inner topping rubber layer formed of butyl-based rubbers was small but an inner liner formed of a butyl-based rubber was provided had improved anti-airleak property, and yet the weight thereof was comparable to Reference Examples. On the other hand, the tubeless tyres of Reference Examples 7 and 8 in each of which the entire topping rubber was formed of a butyl-based rubber exhibited improved anti-airleak property, but the durability thereof was deteriorated. Next, the relationship between the tyre performance and the position of the terminating end portion of the innermost carcass ply was examined. Examples 27 and 28 and Reference Examples 9 and 10 Tubeless tyres of the structure shown in Fig. 6 (width Wb of a breaker ply: 144 mm) were built, in which only the inner topping rubber layers of the inner carcass plies were formed of butyl-based rubbers and distances Ha and Hb were variously changed as shown in Table 4. The distance Hc was not less than 5 mm in Examples 27 and 28, and was less than 5 mm in Reference Examples 9 and 10. The durability, anti-airleak property and weight of the tubeless tyres having such structures were evaluated. The results are shown in Table 4. In Table 4, "B3" for the durability means that the tyre was able to travel 30,000 km but looseness occurred along the radially outside edge of the bead apex. "C3" means that the tyre was not able to travel 30,000 km due to air leak and looseness occurring along the radially outside edge of the bead apex. Tyre Examples Reference Examples 27 28 9 10 Rubber composition Outer topping 1 1 1 1 Inner topping 5 5 5 5 Inner liner - - - - Gauge K (mm) 1.5 1.5 1.5 1.5 I (mm) - - - - Y (mm) 1.5 1.5 1.5.15 1.5 Ha 40 40 40 40 Hb 10 35 40 45 Hc = Ha - Hb 30 5 0 -5 Durability Load 670 kg A A C3 B3 Load 805 kg - - - - Anti-airleak 103 103 102 101 Weight reduction 97 96 96 95 As can be seen from Table 4, tyres in which the distance Hc was less than 5 mm exhibited poorer durability and anti-airleak property. Tyres having plural carcass plies in which the innermost carcass ply is of separation type Tubeless tyres each having a plurality of carcass plies of which the innermost carcass ply was of the separation type were examined. Examples 29 to 32 and Reference Example 11 and 12 Tubeless tyres each having a structure shown in Fig. 7 in which the width of a breaker ply was 144 mm and the innermost carcass ply was of the separation type were built. The spacing Wn and overlapped length Wc (= 1/2(Wb - Wn)) were variously changed as shown in Table 5. In tubeless tyres of Reference Examples 11 and 12, the spacing Wn was greater than 0.95 Wb (136.8 mm). Rubber compositions employed for the outer and inner topping rubber layers of the innermost carcass ply of each tyre and the gauges of the topping rubber layers are shown in Table 5. The durability, anti-airleak property and weight reduction of the tyres having such structures were evaluated ir the same manner as in Example 1. The evaluation results are shown in table 5. In Table 5, "C4" for the durability means that the tyre was not able to travel 30,000 km due to looseness occurring along the breaker ply edge thereof. "C5" means that the tyre was not able to travel 30,000 km due to looseness around the tread portion of the inner carcass ply thereof. Tyre Examples Reference Examples 29 30 31 32 11 12 Rubber composition Outer topping 1 1 1 1 1 1 Inner topping 5 5 5 5 5 5 Inner liner - - - - - - Gauge K (mm) 1.5 1.5 1.5 1.5 1.5 1.5 I (mm) - - - - - - Y (mm) 1.5 1.5 1.5 1.5 1.5 1.5 Wn 134 124 94 64 144 164 Wc = 1/2 (Wb - Wn) 5 10 25 40 0 -10 Durability Load 670 kg A A A A C4 C5 Load 805 kg - - - - - - Anti-airleak 103 103 103 103 103 102 Weight reduction 92 92 94 95 91 89 As can be seen from Table 5, weight reduction increased with increasing spacing Wn. On the other hand, the anti-airleak property was hardly influenced by the presence and the extent of the spacing Wn (see Examples 29 to 32 and Examples 27 and 28). Where the overlap between the breaker ply and the innermost carcass ply, in particular, the portion topped with the butyl-based rubber was absent, the anti-airleak property and durability of the tyre were deteriorated (see Reference Examples 11 and 12). While only certain presently preferred embodiments of the present invention have been described in detail, as will be apparent with those familiar with the art, various changes and modifications can be made in embodiments without departing from the scope of the invention as defined by the following claims.

Claims: A tubeless pneumatic tyre comprising a carcass (11,16,22) having a carcass cord web (12) and rubber topping layers (13a,13b) covering opposite sides of the carcass cord web, the carcass (11) extending from a tread portion through a sidewall portion to a bead portion and turned up around a bead core outwardly from the inside of the tyre in the direction axially of the tyre, characterised in that only the inner layer (13a) of the rubber topping layers is formed of a butyl-based rubber. A tubeless pneumatic tyre as set forth in claim 1, characterised in that said carcass (16) is composed of a plurality of carcass plies (16a,16b) stacked one on another and each comprising a carcass cord web and topping rubber layers covering opposite sides of the carcass cord web, wherein only the inner one (19a) of the rubber topping layers (19a,19b) of the innermost carcass ply (19) is formed of butyl-based rubber. A tubeless pneumatic tyre as set forth in claim 1, characterised in that said carcass (22) is composed of a plurality of carcass plies (22a,22b) stacked one on another and each having a carcass cord web and topping rubber layers covering opposite sides of the carcass cord web, said plurality of carcass plies including an innermost carcass ply (22a) extending from the tread portion through the sidewall portion to the bead portion and turned up around the bead core outwardly from the inside of the tyre in the axial direction, and an outer carcass ply (22b) extending from the tread portion through the sidewall portion to the bead portion and turned up around the bead core (23) inwardly from the outside of the tyre axis in the axial direction so as to cover the turned-up portion of the innermost carcass ply. A tubeless pneumatic tyre as set forth in claims 1,2 or 3 characterised by a rubber bead apex surrounded by the carcass, the turned-up portion of the carcass and the bead core, wherein the difference Hc between a radial distance Hb from the terminating edge of the innermost carcass ply to a radially inside edge of the bead core and a radial distance Ha from a radially outside edge of the bead apex rubber to the radially inside edge of the bead core is not less than 5 mm, and only the inner one of the topping rubber layers of the innermost carcass ply is formed of the butyl-based rubber. A tubeless pneumatic tyre as set forth in claim 4, characterised in that the distance Hb is not greater than 20 mm. A tubeless pneumatic tyre as set forth in claim 2, 3 or 4, characterised in that the innermost carcass ply is divided into two separate carcass ply portions, which are respectively disposed in regions corresponding to opposite sidewall portions. A tubeless pneumatic tyre as set forth in claim 6, characterised in that said two separate carcass ply portions of the innermost carcass ply are arranged so as to satisfy the relation: 0.2 Wb ≤ Wn ≤ 0.95 Wb where Wn is the tread width and Wb is the spacing between the two carcass ply portions of the innermost carcass ply. A tubeless pneumatic tyre as set forth in any of claims 1 to 7, characterised in that said butyl-based rubber includes a butyl rubber or a derivative thereof as a main ingredient in an amount of not less than 60 % by weight. A tubeless pneumatic tyre as set forth in any of claims 1 to 8, characterised in that the rubber gauge Y between the carcass cord web and an interior surface of the tyre is about 0.8 mm to about 2.5 mm. A tubeless pneumatic tyre as set forth in any of claims 1 to 9, characterised in that the interior surface of the tyre is defined by the inner topping rubber layer formed of the butyl-based rubber. A tubeless pneumatic tyre as set forth in any of claims 1 to 10, characterised by further comprising a reinforcing rubber layer provided outside the turned-up portion of the carcass. A tubeless pneumatic tyre as set forth in any of claims 1 to 11, characterised by further comprising an inner liner formed of a butyl-based rubber and covering the inner topping rubber layer formed of the butyl-based rubber.

Inventors: ENDO YUKIO, MINAMI NOBUAKI, SUZUKI KAZUYA, ENDO, YUKIO, MINAMI, NOBUAKI, SUZUKI, KAZUYA
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1995
Main classification: B60C5
IPC codes: B60C1, B60C9, B60C5, B60C15