Pneumatic tyre

Abstract: A pneumatic tyre comprises a carcass ply (9) extending between bead portions (4) and turned up around a bead core (5) in each bead portion to form two turnup portions (9B) and a main portion (9A) therebetween; each of the turnup portions (9B) extends radially outwardly and adjoins the main portion (9A) from a certain height (h) above the bead core (5); a space (8) surrounded by the carcass ply main portion (9A), each turnup portion (9B) and the bead core (5) is filled with a small size bead apex rubber (10) or a gas; and the bead portion (4) is provided between the carcass ply (9A) and the bead core (5) with a bead core cover (19) for preventing the carcass cords from directly contacting the bead core (5).

Description: The present invention relates to a pneumatic tyre, more particularly to a bead structure capable of reducing the weight of the bead portions without deteriorating bead durability. In pneumatic tyres used under relatively heavy loads such as heavy duty tyres for trucks and buses, light truck tyres and the like, a large volume of bead apex rubber is disposed between a carcass ply turnup portion and main portion to increase the bead rigidity and thereby to decrease deformation of the tyre under heavy loads. Recently, in order to decrease tyre weight, bead structures have been re-examined, and many efforts have been made to decrease the weight of the bead portions by decreasing the volume of bead apex rubber. In tyres in which the bead apex rubber is very small, movements and bending deformation of the carcass plies under loads are relatively large. Therefore, as the tension of the carcass cords is large and a large stress concentrates on contacting points with the bead core, the carcass cords are liable to be cut. JP 07108806 A discloses a pneumatic tyre according to the preamble of claim 1. The carcass cords directly contact the bead core and are thus liable to be cut. EP-A-0 492 504 discloses a pneumatic tyre with a bead core formed by metal wire coils. A sheet of elastomeric material is wound loop-wise about the pack of metal coils constituting the bead core. This sheet is covered with a strip of rubberized fabric being reinforced with cords of a heat-shrinkable material. During vulcanizing the tyre, these cords shrink and the sheet of elastomeric material is thus pressed on the bead core. EP-A-0 692 395 discloses a pneumatic tyre with a bandage made of a textile fabric which can be wound around a belt layer of a tyre or around a bead core. It is an object of the present invention to provide a pneumatic tyre, in which the carcass cords are prevented from being cut and the durability of the bead portions is improved. This object is achieved by a pneumatic tyre according to claim 1. Preferably, the bead core cover is made of a textile fabric of organic fibre yarn such as nylon, rayon, polyester and the like. Embodiments of the present invention and alternative embodiments not falling within the scope of the invention will now be described in detail in conjunction with the accompanying drawings in which: Fig.1 is a cross sectional view of a heavy duty tyre according to the present invention; Fig.2 is an enlarged cross sectional view of the bead portion thereof; Fig.3 is a cross sectional view showing the bead core and textile fabric; Fig.4 is a cross sectional view of a light truck tyre according to the present invention; Fig.5 is an enlarged cross sectional view of the bead portion thereof; Fig.6 is a cross sectional view of a heavy duty tyre not being within the scope of the present invention; Fig.7 is an enlarged cross sectional view of the bead portion thereof; Fig.8 is an enlarged cross sectional view showing a sealing structure for a bead cavity; Fig.9 is an enlarged cross sectional view showing another example of sealing structure for the bead cavity; Fig.10 is a diagram for explaining the carcass cord distance in the adjoining part; and Fig.11 to Fig.14 are diagrams for explaining a method of manufacturing a tyre having the bead cavity. Neither a tyre having a bead cavity as shown in figures 8 to 10 nor a manufacturing method as explained with reference to figures 11 to 14 are within the scope of the present invention. Definitions First, the terms used in this application "standard rim", "standard pressure", "standard load", "bead base line" and "radial height" are defined as follows: Standard rim is the "standard rim" specified in JATMA, the "Measuring Rim" in ETRTO, the "Design Rim" in TRA or the like; Standard pressure is the "maximum air pressure" in JATMA, the "Inflation Pressure" in ETRTO, the maximum pressure given in the "Tyre Load Limits at Various Cold Inflation Pressures" table in TRA or the like; Standard load is the "maximum load capacity" in JATMA, the "Load Capacity" in ETRTO, the maximum value given in the above-mentioned table in TRA or the like; Bead base line is an axial line passing the bead heel point at the axially outer end of the bead bottom and corresponding to the rim diameter; and Radial height is a height measured radially from the bead base line. In the drawings, the tyre 1 (1A, 1B, 1C) according to the present invention comprises a tread portion 2, a pair of sidewall portions 3, a pair of axially spaced bead portions 4 each with a bead core 5 therein, a carcass 6 extending between the bead portions 4 and a belt 7 disposed radially outside the carcass 6 in the tread portion 2. The belt 7 comprises at least one ply, preferably at least two crossed plies of parallel cords. For the belt cords, high elastic-modulus cords such as steel cord are preferably used. But, organic fibre cords, e.g. nylon, aromatic polyamide, rayon and the like can be used. The bead core 5 is made of at least one inextensible material, for example, a coiled rubberised steel wire or wires, a coiled high-elastic-modulus organic cord or cords such as aromatic polyamide fibre cord, a wound tape-like material, and the like. For the sectional shape of the bead core 5, a hexagonal shape is preferably used. In the case of heavy duty tyres to be mounted on a 15-degrees taper rim, a hexagonal shape, the aspect ratio of which is low and the major axis which is inclined at substantially the same angle (10 to 17 degrees) as the inclination of the rim seat (15 degrees), is preferably used. The bead core 5 is covered with a bead core cover made of a textile fabric 19 and/or a rubber layer 16 to prevent the carcass cords 21 from directly contacting with the bead wire. The carcass 6 comprises at least one ply 9 of cords 21 arranged radially at an angle of 70 to 90 degrees with respect to the tyre equator CO, and extending between the bead portions 4 through the tread portion 2 and sidewall portions 3, and turned up around the bead core 5 in each bead portion 4 from the inside to outside of the tyre to form a pair of carcass ply turnup portions 9B and a main portion 9A therebetween. For the carcass cords 21, steel cords are preferably used in the case of heavy duty tyres. However, organic fibre cords, e.g. nylon, rayon, polyester, aromatic polyamide and the like can be used. As to the carcass ply turnup portions 9B, the distance from the carcass ply main portion 9A gradually decreases towards radially outwards from the bead core 5, and then, from a certain radial height (h), the distance becomes a substantially-constant minimum value. This part (hereinafter adjoining part 15) in which the distance between the turnup portion 9B and the main portion 9A is minimum and thus these portions adjoin each other has a certain length L2. Further, a part of the turnup portion 9B between a point at which the carcass ply turnup portion 9B comes into contact with the bead core 5 and a point corresponding to the radially inner end of the adjoining part 15 is curved towards the axially inside. But, in the adjoining part 15, it extends substantially straight along the carcass ply main portion 9A. The carcass turnup portion 9B terminates at a position radially inside the maximum tyre width point. As to the carcass ply main portion 9A, a part which extends radially outwardly from a point at which the carcass ply main portion 9A comes into contact with the bead core 5, is formed substantially straight. This straight part Y extends to the radially inner end of the adjoining part 15 at least, usually to the radially outer end of the adjoining part 15, whereby the carcass cord path is minimised to control the axially outward movement or deformation of the carcass when the tyre is loaded. Thus, the deformation of the bead portion can be reduced. A space defined as surrounded by the carcass ply turnup portion 9B and main portion 9A and the bead core 5 is filled with a small size bead apex rubber 10 or a gas (usually air). The bead portion 4 is provided along the bottom and axially outside thereof with a chafer 11. The chafer 11 is made of a relatively hard rubber having a 100% modulus of from 55 to 75 kgf/sq.cm, whereas the sidewall rubber 10 has a 100% modulus of from 10 to 20 kgf/sq.cm. The chafer 11 extends radially outwards from the underside of the bead core 5, with abutting on the axially outside of the carcass 6. The chafer rubber 11 tapered-overlaps the sidewall rubber 10 above the radially outer end of the rim flange Jf. In the overlapped portion, the chafer rubber 11 is positioned on the axially inside of the sidewall rubber 10. On the outer surface of the tyre, the radial height L4 of the radially outer edge of the chafer rubber 11 is preferably set in the range of from 1.2 to 2.5 times the flange height H. If the height L4 is more than 2.5 times H, heat generation increases and cracks are liable to occur on the surface chafer rubber 11, and as a result, the bead durability decreases. If less than 1.2 times H, the radially inner end portion of the sidewall rubber 10 is liable to wear. If the 100% modulus of the chafer rubber 11 is less than 55 kgf/sq.cm, the bead rigidity is insufficient. If more than 75 kgf/sq.cm, heat generation increases and the bead durability decreases. If the 100% modulus of the sidewall rubber 10 is less than 10 kgf/sq.cm, it is difficult to protect the carcass 6 from external injuries. If more than 20 kgf/sq.cm, cracks are liable to occur on the sidewall surface. Fig.1 and Fig.2 show a heavy duty radial tyre 1A according to the present invention, wherein a state of the tyre mounted on a standard rim J (a centre drop 15-degree taper rim) and inflated to an internal pressure of 50 kpa is shown. In this embodiment, the bead core 5 is made of a coiled rubberised wire, the sectional shape of which is a hexagon of a low aspect ratio and the major axis thereof is inclined at substantially the same angle as the inclination of the rim seat (15 degrees). The bead core 5 is covered with a bead core cover made of a textile fabric 19 so as to prevent the carcass cords 21 from direct contacting with the bead wire. The textile fabric 19 is made of organic fibre yarn such as nylon, rayon, polyester and the like. Preferably, the yarn is relatively thin (for example, 940 dtex/2 to 1670 dtex/2) in comparison with the usual tyre cords. It is possible to cover the bead core surface partially, but in this example, as shown in Fig.3, the textile fabric 19 is wound around the bead core 5 in a single layer at least, preferably a double layer, so as to cover all the surface of the bead core 5. The carcass 6 is composed of a single ply 9 of steel cords comprising a pair of turnup portions 9B and a main portion 9A. The distance of the carcass ply turnup portion 9B from the main portion 9A becomes a minimum value from a radial height (h) and the adjoining part 15 extends a length H of from 35 to 70 mm. In the adjoining part 15, the rubber thickness measured from the cords of the turnup portion 9B to the cords of the main portion 9A, is set in the range of from 0.5 to 4.0 mm to effectively mitigate a sharing force therebetween. The space surrounded by the carcass ply turnup portion 9B and main portion 9A and the bead core 5 is filled with a bead apex 10. The bead apex 10 is made of a relatively hard rubber having a JIS-A hardness of 70 to 100 degrees tapering towards the radially outside from the bead core 5. The radial height (h) of the radially outer end 13 thereof is set in the range of 0.1 to 0.3 times, preferably not more than 0.25 times, more preferably not more than 0.20 times the radial height Hk of the outer surface of the carcass 6 at the tyre equator CO. In the straight part Y of the carcass ply main portion 9A and the curved part of the turnup portion 9B, the thickness of the bead apex rubber 10 is decreased. As a result, the turnup portion 9B is positioned near to the stress neutral line thereby greatly decreasing compressive stress in use. The belt 7 in this embodiment is composed of four plies 7A, 7B, 7C and 7D of parallel steel cords disposed in this order from the inside to outside. The cord angle of the first ply 7A is 50 to 70 degrees, and the angles of the second, third and fourth plies 7B to 7D are 10 to 30 degrees with respect to the tyre equator CO. The inclinations of the cords with respect to the tyre equator CO are reversed between the second and third belt plies 7B and 7C. Comparison Test 1 Heavy duty tyres of size 11R22.5 14PR having the structure shown in Fig.1 and Fig.2 were prepared and tested for bead durability. Bead durability test: Using a tyre test drum, each test tyre was subjected to a 600 hour continuous running test under the following conditions, and the running time to any bead damage was measured. Running speed 20 km/h Tyre load 300% of standard load = 9,000 kg Tyre pressure standard pressure of 800 kpa, Wheel rim 22.5X8.25 standard rim The specifications of the tyres and test results are shown in Table 1. Tyre Ref.A1 Ex.A1 Ex.A2 Ex.A3 Ex.A4 Carcass Height Hk (mm) 211 211 211 211 211 Straight part of main portion exist exist exist exist exist Adjoining part length L2 (mm) 40 40 40 40 40 Bead apex rubber JIS-A hardness (deg.) 90 90 90 90 90 Height h (mm) 40 40 40 40 40 Textile fabric - nylon nylon nylon nylon - 940dtex/2 940dtex/2 1670dtex/2 1670dtex/2 Layer - single double single Double Bead durability (hrs.) 500 550 600 580 600 Fig.4 and Fig.5 show a light truck tyre 1B according to the present invention, shown mounted on a standard rim J and inflated to an internal pressure of 50 kpa. The belt 7 is composed of at least two crossed plies, in this example, two cross plies 7B and 7C of high-elastic-modulus cords such as steel cords and the like. The bead core 5 is made of a rubberised steel wire coiled in a hexagonal sectional shape. The carcass 6 comprises one to three plies, in this example two plies 9 and 14 of organic fibre cords 21, e.g. polyester, rayon, nylon, aromatic polyamide and the like arranged at an angle of 75 to 90 degrees with respect to the tyre equator CO. The inner carcass ply 9 consists of a pair of turnup portions 9B turned up around the bead core 5 from the inside to outside of the tyre and a main portion 9A therebetween. The outer carcass ply 14 has however, no turned up portion. The outer carcass ply 14 is disposed on the inner carcass ply 9 so as to cover the outside of the main portion 9A and the outside of the turnup portions 9B, and terminates axially outside or beneath the bead core 5. Similarly to the first described tyre 1A, a substantially straight part Y of the carcass ply main portion 9A, a curved part of the carcass turnup portion 9B, and an adjoining part 15 of the carcass ply main portion and turnup portion are formed. In this embodiment, the space surrounded by the carcass ply turnup portion 9B and main portion 9A and the bead core 5 is filled with a bead apex 10. The bead apex 10 is made of a relatively hard rubber having a JIS-A hardness of 70 to 100 degrees tapering towards the radially outside from the bead core 5. The radial height (h) of the radially outer end 13 thereof is set in the range of from H -15 mm to H +15 mm, wherein H is the rim flange height. The height (h) in this tyre 1B is lower than that of the former tyre 1A. In such a tyre, during building the tyre, the carcass ply turnup portion is liable to come off the outer end of the bead apex rubber 10. In the finished tyre, therefore, adhesive failure is liable to occur and air remains in this position which greatly decreases bead durability. In order to avoid this problem, as shown in Fig.5, a first rubber layer 16 is disposed between the carcass 6 and the axially inner and outer surfaces of the bead apex 10. The first rubber layer 16 has a JIS-A hardness of 50 to 80 degrees which is smaller than the JIS-A hardness of the bead apex rubber and a substantially constant thickness T1 of 1.0 to 3.0 mm. In this example, the first rubber layer 16 extends continuously from the axially inside to outside of the bead apex 10 through the underside of the bead core 5. Thus, the first rubber layer 16 is also disposed between the carcass and bead core, whereby the carcass cords can be prevented from direct contacting with the bead core, and a sharp bend of the carcass cords at the corners of the bead core is prevented. Thus, carcass cord cuts can be effectively controlled. Incidentally, it is possible to use such a rubber layer and the above-mentioned textile fabric 19 at the same time. In this example, further, the first rubber layer 16 extends continuously from both the axially inside and outside of the bead apex 10 to the adjoining part 15. In other words, a second rubber layer 17 having a thickness T2 of 2.0 to 6.0 mm (two times T1) and a JIS-A hardness of 50 to 80 degrees is disposed between the carcass ply main portion 9A and turnup portion 9B in the adjoining part 15. The length L1 of the second rubber layer 17 measured along the carcass 6 is preferably set in the range of from 5 to 15 mm. If the thickness T1 is less than 1.0 mm, it is difficult to prevent the carcass cords from being cut. If the thickness T1 is more than 3.0 mm, the engaging force between the tyre and rim becomes insufficient. If the thickness T2 is less than 2.0 mm, and/or the length L1 is less than 5 mm, it is difficult to eliminate the air and an adhesive failure is liable to occur. If the thickness T2 and length L1 are more than 6.0 mm and 15 mm, respectively, the weight increases against the primary object. In this embodiment, the chafer 11 extends radially outwards, abutting the axially outside of the outer carcass ply 14. Comparison Test 2 Light truck tyres of size 7.00R16 having the structure shown in Fig.4 and Fig.5 were prepared and tested for bead durability. Bead durability test : Using a tyre test drum, each test tyre was subjected to a 600 hour continuous running test under the following conditions, and the running time to any bead damage was measured. Running speed 20 km/h Tyre load 1100 kg Tyre pressure 600 kpa Wheel rim 5.50FX16 standard rim The specifications of the test tyres and test results are shown in Table 2. Tyre Ref.B1 Ref.B2 Ex.B1 Carcass Straight part of main portion non Exist exist Adjoining part length L2 (mm) - 40 40 Bead apex rubber JIS-A hardness (deg.) 90 90 90 Height h (mm) 85 28 28 Flange height H (mm) 12.7 12.7 12.7 Rubber layer 16 Thickness T1 (mm) - - 2 JIS-A hardness (deg.) - - 70 Thickness T2 (mm) - - 4 Length L1 (mm) - - 10 JIS-A hardness (deg.) - - 70 Bead durability (hrs) 400 500 600 A third embodiment is shown in Fig.6 and Fig.7 which is a heavy duty radial tyre 1C mounted on a standard rim J and inflated to a standard pressure but loaded with no tyre load. In this embodiment, the belt 7 is composed of four plies 7a, 7b, 7c and 7d of parallel steel cords disposed in this order from the inside to outside. The cord angle of the first ply 7a is 50 to 70 degrees, and the angles of the second, third and fourth plies 7b to 7d are not more than 30 degrees with respect to the tyre equator CO. The bead core 5 is made of a coiled rubberised wire, the sectional shape of which is a low aspect ratio hexagon as explained in the tyre 1A. And the bead core 5 is covered with a bead core cover made of a textile fabric 19. The carcass 6 comprise a single ply 9 of steel cords arranged at substantially 90 degrees with respect to the tyre equator C. Similarly to the former tyres 1A and 1B, a substantially straight part Y of the carcass ply main portion 9A, a curved part 12 of the carcass turnup portion 9B, and an adjoining part 15 of the carcass ply main portion and turnup portion are formed. The curved part 12 extends axially inside or on a straight line X, the straight line X drawn between the axially outmost point BP of the bead core 5 and the outer end 8e of the cavity 8. In this embodiment, the space surrounded by the carcass ply turnup portion 6B and main portion 6A and the bead core 5 is not filled with a bead apex rubber. The space is filled with a gas, usually air to form a cavity 8. As shown in Fig.7, the cavity 8 tapers towards the radially outside from the bead core 5. The radial height (h) of the outer end 8e thereof is 0.7 to 3.0 times the radial height H of the rim flange Jf. If the height (h) is more than 3.0 times the height H, the bead durability and bead rigidity decrease. The internal pressure of the cavity 8 is set at more than the atmospheric pressure. In order to maintain the internal pressure, the cavity 8 is surround by an airtight rubber layer 20 (20A, 20B). In Fig.6 and Fig.7, along the inside of the cavity 8, a sealing layer 20B is disposed. The sealing layer 20B is preferably made of a butyl rubber containing not less than 30 phr of halogenated butyl rubber. The thickness Ta of the sealing layer 20B is at least 0.2 mm. Especially, when the halogenated butyl rubber content is minimum, it is better to use a thicker layer. Preferably, the thickness Ta (mm) is determined as being not less than 20 times the halogenated butyl rubber content (phr). And, the thickness Ta is not more than 1.5 mm and not more than 50 times the halogenated butyl rubber content (phr). As shown in Fig.8, when the topping rubber layer 20A of the carcass ply and bead core is very thin and/or the topping rubber is a non-butyl rubber whose principal component is diene rubber, the sealing layer 20B is preferably disposed. However, if the topping rubber layer 20A is thick enough to provide airtightness, the sealing layer 20B may be omitted. Incidentally, the thickness of the topping rubber 20A is in the range of 0.15 to 1.0 mm. Fig.9 shows another example of the sealing structure, wherein the sealing layer 20B extends beneath the bead core 5 so as to wrap the bead core therein. The adhesion of the butyl rubber layer 20B is not so good when compared with the topping rubber. Therefore, to prevent separation, inserting length L5 of the sealing layer 20B between the carcass ply main portion 9A and turnup portion 9B is set to be not more than 5 mm. Further, the radial height L6 of the upper end of the sealing layer 20B is preferably not more than 3.0 times the flange height H. As shown in Fig.10, in the adjoining part 15, the rubber thickness N between the carcass cords 21 of the main portion 9A and the carcass cords 21 of the turnup portion 9B is set in the range of from 0.15 to 4.5 times, preferably 1.3 to 3.5 times the diameter K of the carcass cords 21. If the thickness N is less than 0.15 times K, it is difficult to mitigate the sharing force, and there is the danger in which the carcass cords 21 directly contact with each other, and thus a carcass ply separation is caused. If the thickness N is more than 4.5 times K, the turnup portion 9B is liable to be broken by a compressive stress and the heat generation is liable to increase. In this example, to provide the thickness N, a cushion rubber layer 22 having substantially same hardness as the topping rubber is disposed between the carcass ply main portion 9A and turnup portion 9B. However, it is also possible to use the carcass ply topping rubber itself. The length L2 of the adjoining part 15 is in the range of from 0.5 to 5.0 times preferably 1.0 to 4.0 times the maximum section width BW of the bead core 5. If the length L2 is less than 0.5 times BW, the bead durability decreases. If the length L2 is more than 5.0 times BW, it is difficult to improve bead durability, and the tyre surface is liable to undulate and a carcass ply edge separation is liable to occur because the outer end of the turnup portion 9B reaches to a position where the sidewall rubber is relatively thin. In this embodiment, the chafer 11 extends radially outwards abutting the axially outer side of the turnup portion 9B, to a radial height L3, wherein the height L3 is more than the radial height (h) of the cavity. As a result, the bead rigidity is increased, and thereby running performance such as steering stability and the like are improved. Comparison test 3 Heavy duty radial tyres of size 11R22.5 having the structure shown in Fig.6 and Fig.9 were prepared and tested for bead durability, steering stability and tyre weight. The test tyres had a carcass composed of a single ply of steel cords (3X0.17+7X0.20) arranged at an angle of 90 degrees with respect to the tyre equator at a cord count of 21 (/5cm) at the tread centre, and a belt composes of four plies of steel cords (3X0.20+6X0.35) laid parallel with each other at a cord count of 26 (/5cm). The cord angles of the four plies were +67/+18/-18/-18 degrees (from inside to outside). Bead durability test : Using a tyre test drum, each test tyre was subjected to a 10,000 kilometre continuous running test under the following conditions, and the running distance Li to any visible damage was measured. Running speed 20 km/h Tyre load 9000 kgf Tyre pressure 1000 kPa Wheel rim 8.25X22.5 standard rim In Table 3, the ratio of the distance Li to 10,000 kilometres is indicated by an index based on Reference tyre C being 100. Steering stability test : Running a 10-ton truck provided on all the wheels with test tyres on an asphalt road, a test driver evaluated the steering response, rigidity, road grip and the like. The results are indicated by an index based on reference tyre C being 100, wherein the larger the index, the better the steering stability. Tyre pressure 800 kPa Wheel rim 8.25X22.5 standard rim Tyre weight: In Table 3, the tyre weight is indicated by an index based on Reference tyre being 100. The specifications of the test tyres and test results are shown in Table 3. Tyre Ex.C1 Ex.C2 Ex.C3 Ex.C4 Ex.C5 Ex.C6 Ex.C7 Ex.C8 Ex.C9 Ex.C10 Ref.C Cavity height h (mm) 28 40 28 28 28 28 28 28 28 28 - Ratio h/H 2.2 3.1 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 - Sealing rubber layer Thickness Ta (mm) 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 - Thickness T (mm) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 - Inserting Length L5 (mm) 3.0 3.0 6.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 - Carcass Adjoining part Length L2 (mm) 55 55 55 7 55 55 55 55 55 55 55 Ratio L2/BW 3.7 3.7 3.7 0.4 5.2 3.7 3.7 3.7 3.7 3.7 3.7 Rubber thickness N (mm) 1.3 1.3 1.3 1.3 1.3 0.1 3.6 1.3 1.3 1.3 1.3 Ratio N/K 1.7 1.7 1.7 1.7 1.7 0.13 4.7 1.7 1.7 1.7 1.7 Chafer Height L3 (mm) 65 65 65 65 65 65 65 25 25 25 25 100% modulus (kgf/sq.cm) 60 60 60 60 60 60 60 60 54 76 60 Test Results Bead durability 150 105 130 102 150 80 101 75 105 110 100 Steering stability 105 103 105 100 105 103 100 90 95 100 100 Tyre weight 98 97 98 96 103 97 102 98 98 98 100 From the test results, it was confirmed that test tyres according to the present invention were improved in the bead durability and weight wile maintaining the steering stability. Tyre Manufacturing Method Fig.11 to Fig.14 show a method of manufacturing the tyre 1C having the cavity 8. First, an inner liner rubber 30 is wound around a tyre building drum 40. On each side of the inner liner rubber 30, a strip of rubber 31 made up of a chafer rubber 11 and a sidewall rubber 10 connected with each other, is further wound. Further, a carcass ply 9 is wound thereon to form a cylindrical main body 32. A pair of annular bead cores 5 are put around the cylindrical main body 32, and a bead lock 43 is expanded to fix the bead core. Note that the bead core is covered with a textile fabric 19 in advance. Further, a butyl rubber seat for the sealing layer 20B is wound over the bead core 5. Here, the tyre building drum 40 comprises a central former 42 and a pair of side formers 41. The central former 42 can be expanded, for example, by means of inflation of a bladder, and also, the side former 41 can be expanded by means of inflation of a bladder. Further, a tread ring 36 made up of a tread rubber 35 and a belt 7 which are assembled beforehand is put around the carcass main portion. Next, as shown in Fig.13, the central former 42 and side formers 41 are expanded in order that the carcass main portion is shaped in a toroidal shape, and the carcass turnup portions 9B and the rubber strip 31 is fold around the bead core 5 onto the carcass main portion 9A. By the expansion of the carcass main portion 9A, the carcass main portion 9A is pressed against the tread ring 36. The raw tyre 1C built up as above is put in a mould and vulcanised by applying heat and pressure. During the vulcanising process, the cavity 8 is provided with an internal pressure of over an atmospheric pressure. As explained above, the present invention can be suitably applied to heavy duty tyres and light truck tyres. However, it is also possible to apply it to passenger car tyres and the like.

Claims: A pneumatic tyre comprising a tread portion (2), a pair of sidewall portions (3), a pair of bead portions (4) each with a bead core (5) therein, a carcass comprising a carcass ply (9) extending between the bead portions (4) and turned up around the bead core in each bead portion to form two turnup portions (9B) and a main portion (9A) therebetween, each said turnup portion (9B) extending radially outwardly to adjoin the main portion (9A) from a certain height above the bead core so as to form an adjoining part, wherein a space (8) in each bead portion surrounded by the carcass ply main portion (9A), the turnup portion (9B) and the bead core (5) is filled with a bead apex rubber (10) tapering radially outwardly from the bead core (5), the bead apex rubber (10) having a JIS-A hardness of 70 to 100 degrees, characterised in that a bead core cover (19) is disposed between the carcass ply (9) and the bead core (5) for preventing cords of the carcass from directly contacting with the bead core (5), the bead core cover (19) being made of a textile fabric and/or a rubber layer, the height (h) of the bead apex rubber (10) is in the range of H-15 mm to H+15 mm, where H is the height of a flange of the wheel rim for the tyre, and wherein between the bead apex rubber (10) and the carcass (6), a rubber layer (16) having a JIS-A hardness being in the range of from 50 to 80 degrees and being less than that of the bead apex rubber (10) and having a thickness of from 1.0 to 3.0 mm is disposed. A pneumatic tyre according to claim 1, characterised in that the bead core cover (19) is made of a textile fabric of organic fibre yarn.

Inventors: ENDO YUKIO, IKEDA IKUJI, NUMATA KAZUKI, OOHARA YOSHIO, UEYOKO KIYOSHI, ENDO, YUKIO, IKEDA, IKUJI, NUMATA, KAZUKI, OOHARA, YOSHIO, UEYOKO, KIYOSHI
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1999
Main classification: B60C15
IPC codes: B60C1, B60C15