Pneumatic safety tires

Abstract: A pneumatic tire comprising a cylindrical tread (T), a pair of sidewalls (10), bead rings (20), a radial carcass (30), rubber fillers (40) respectively each arranged between turn-up portions (31) of the carcass and a main body of the carcass and extending from above the bead ring toward the tread portion such that the radially sectional shape of the rubber filler becomes narrower toward the tread portion, and a pair of thick rubber reinforcement layers arranged in the sidewalls (10). Each of the rubber reinforcement layers is constituted by first and second reinforcing rubber layers (50,60), the first reinforcing rubber layer (50) occupying a radially outer side of the sidewall (10) and the second reinforcing layer (60) being continued to a radially inner side of the first reinforcing rubber layer through an inclined joint surface (70) and arranged on a radially outer side of the rubber filler (40) through the main body of the carcass. The Shore A hardness of the rubber reinforcement layer is made greater in the order of the first reinforcing rubber layer (50), the second reinforcing rubber layer (60) and the rubber filler (40), and the rubber volume of the reinforcing rubber reinforcement layer is made greater in the order of the rubber filler (40), the second reinforcing layer (60) and the first reinforcing layer (50).

Description: The present invention relates to pneumatic tires, and more particularly the invention relates to pneumatic safety tires having improved riding comfortability against vibrations (hereinafter referred to as anti-vibration riding comfortability) as well as improved durability in upper regions of sidewall portions. Since safety tires can be run flat over some distance under a reduced inner pressure, even when the inner pressure of the tire decreases due to a puncture, such safety tires have recently become increasingly used because of their safety performance. As structures for safety tires capable of being run flat, a double wall structure, a tire interior-supporting coat structure, and a tire sidewall-reinforcing structure as shown in Fig. 2 of the accompanying drawings are known. Among them, a side-reinforced tire having inner surfaces of the sidewall portions reinforced mainly with rubber layers has been put into practical use due to its lower production cost, ease of rim-assembling and good run-flat running performance. Such a tire is described in EP-A-0005399. Fig. 2 of the accompanying drawings is a sectional view illustrating a conventional side-reinforced safety tire. In this conventional safety tire, a pair of sidewall portions 1 extend substantially radially inwardly from opposite ends of a cylindrical tread T, respectively, bead rings 2 are provided in the end portions of the respective sidewall portions 1, and a carcass 3 consisting of at least one ply having fiber cords is turned up around the respective bead rings 2 from an axially inner side to the axially outer side thereof, and each of turn-up portions 3' of the carcass is formed at a relatively radially low position. A rubber filler 4 is arranged between the main part of the carcass 3 and the turn-up portion 3' thereof. This rubber filler has a triangular sectional shape contacting the bead ring 2 at its base portion, and is made of a relatively hard rubber having, for example, Shore A hardness of 70-98 and a large volume. Further, the tire is reinforced by arranging a thick rubber reinforcement layer on the axially inner side of the carcass 3 in the sidewall portion. The rubber reinforcement layer is divided substantially in the direction of the rotary axis of the tire (hereinafter referred to as "axial direction"), and constituted by a relatively soft first reinforcing rubber layer 5 having, for example, a Shore A hardness of 60-80 and positioned outwardly in the axial direction and a relatively hard second rubber reinforcing layer 6 having, for example, a Shore A hardness of 75-90 and positioned inwardly in the axial direction. A relatively soft rubber chafer 7 having good wear resistance is arranged axially outwardly along the turn-up portion 3' of the carcass from a radially inner end portion of the bead portion which contacts a rim when the tire is fitted to the rim. Following the rubber chafer 7, the sidewall portion is entirely covered with a side rubber 8 having good bending resistance. However, with respect to the conventional safety tire, particularly a conventional high performance tire, having the above construction, not only high running performance but also good comfortability, particularly anti-vibration riding comfortability during ordinary running (no run-flat running), are required. However, since the sidewall portions and the bead portions are entirely reinforced with relatively hard rubber as mentioned above, anti-vibration riding comfortability particularly during ordinary running is unfavourably poor. Since the above-mentioned conventional safety tire largely changes its curvature during run-flat running in the case of puncture, the rubber reinforcing layer becomes cracked on its inner surface in the upper part of the sidewall portion by synergistic effects of stress concentration, heat generation and heat accumulation. Consequently, such cracks are likely to be propagated to damage the carcass. In particular, since the rubber filler 4 has a relatively large volume and is surrounded by the main body and the turn-up portion of the carcass 3, its rigidity, particularly its bending rigidity, becomes extremely high. Consequently, this causes not only stress concentration in the upper part of the sidewall portion but also reduction in anti-vibration riding comfortability. The pneumatic safety tire according to the present invention has been developed through examination and solution of the problems possessed by the above-mentioned conventional pneumatic tires. Therefore, it is an aim of the present invention to provide a pneumatic safety tire which simultaneously improves not only anti-vibration riding comfortability but also durability in the upper parts of the sidewall portions. Attention is also drawn to the disclosure of US-A-4779658, in particular the embodiment of Fig. 2 thereof. The present invention provides a pneumatic tire comprising a cylindrical tread portion, a pair of sidewall portions extending radially inwardly from opposite ends of the tread portion and having respective bead rings in the ends thereof, a radial carcass toroidally extending from one bead ring to the other bead ring through one sidewall portion, the tread portion and the other sidewall portion and reinforcing the sidewall portions and the tread portion, each of the opposite end portions of the carcass being turned up around the respective bead ring axially from the inside to the outside thereof, rubber fillers each arranged between the turn-up portions and the main body of the carcass and extending from above the bead ring toward the tread portion such that the radially sectional shape of the rubber filler becomes narrower toward the tread portion, and a pair of thick rubber reinforcement layers arranged on respective axially inner sides of the carcass in the sidewall portions, wherein each of the rubber reinforcement layers is constituted by first and second reinforcing rubber layers, the first reinforcing rubber layer occupying a radially outer side of the sidewall portion and the second reinforcing layer being continued to a radially inner side of the first reinforcing rubber layer through an inclined joint surface and arranged on the radially outer side of the rubber filler through the main body of the carcass, characterized in that the Shore A hardness is made greater in the order of the first reinforcing rubber layer, the second reinforcing rubber layer and the rubber filler, and the rubber volume is made greater in the order of the rubber filler, the second reinforcing layer and the first reinforcing layer. As mentioned above, according to the pneumatic safety tire of the present invention, the Shore A hardness of the rubber reinforcement is greater in the order of the first reinforcing rubber layer, the second reinforcing rubber layer and the rubber filler, and the rubber volume of the rubber reinforcement is greater in the order of the rubber filler, the second reinforcing layer and the first reinforcing layer. Consequently, the entire rubber reinforcement including the rubber filler is well balanced, so that vibrations applied to the tire from the road are mitigated to enhance the vibration-attenuating effect, and local stress concentration is prevented to reduce cracking, heat generation or heat accumulation in the inner surfaces of the sidewall portions of the tire. Further, since the first and second reinforcing rubber layers are continuous with respect to each other through the inclined joint surface on the radially inner side of the first reinforcing rubber layer, a discontinuous face of high rigidity in the sidewall portion is eliminated to improve the anti-vibration riding comfortability and further to prevent local stress concentration upon the inner surface of the sidewall portion, so that fracture at a boundary between the first and second rubber layers made of different rubber materials can be prevented. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a sectional view illustrating one embodiment of a pneumatic safety tire according to the present invention; and Fig. 2 is a sectional view illustrating a conventional safety tire. The pneumatic safety tire according to the present invention as shown in Fig. 1 includes a cylindrical tread portion T for contacting the road, and a pair of sidewall portions 10 extending radially inwardly from opposite ends of the tread portion T and having bead rings 20 in the end portions thereof, respectively. The tire is reinforced with a radial carcass 30 extending from one of the bead rings 20 to the other through the side wall portions and the tread portion. The carcass 30 is composed of two plies in which organic fiber cords made of rayon or polyester are arranged in a direction crossing the equatorial plane of the tire substantially at right angles. Each of the opposite ends of the carcass 30 is turned up around the respective bead ring 20 from the axially inner side to the axially outer side. The turn-up portion 31 of the carcass 30 is extended up to a position relatively low in the sidewall portion 10, that is a position radially outwardly slightly beyond an upper end of a flange of a rim to which the tire is fitted. A rubber filler 40 is arranged radially outwardly from the bead ring 20 between the turn-up portion 31 and the main body of the carcass 30, and the filler 40 has a substantially triangular cross sectional shape narrowed toward the tread portion T from above the bead ring 20. The tread portion T above the carcass 30 is reinforced with a belt layer 32 and an auxiliary belt layer 33 arranged radially outwardly on the belt layer 32. The belt layer 32 is composed of at least two plies in which non-stretchable cords such as steel cords are inclinedly arranged such that the cords in one ply are crossed with those in an adjacent ply. The auxiliary belt layer 33 is composed of at least two plies in which thermally shrinkable cords such as of nylon are arranged in parallel to the equatorial plane of the tire. A part of the sidewall portion 10 located on an axially inner side of the carcass 30 is reinforced with a thick rubber reinforcement layer. This thick rubber reinforcement layer is constituted by a first reinforcing rubber layer 50 and a second reinforcing rubber layer 60. The first reinforcing rubber layer 50 occupies a radially outer side in the side wall 10. The second reinforcing rubber layer 60 continues to the first reinforcing rubber layer 50 on a radially inner side of the first layer through an inclined joint surface 70, and occupies a radially outer side of the rubber filler 40 through the carcass 30. The first reinforcing rubber layer 50 is located on the axially inner side of the carcass 30, and reinforces the sidewall portion 10 mainly in the radially outer region in an area from a tire shoulder portion to the sidewall portion 10. The thickness of the first reinforcing rubber layer is gradually reduced toward the radially outer and inner portions. The second reinforcing rubber layer 60 reinforces the sidewall portion mainly in the radially inner region located radially inwardly below the first reinforcing rubber layer 50. The radially inner end of the second reinforcing rubber layer 60 is extended to a region within in the height area of the rubber filler 40. The thickness of the radially outer and inner portions of the second reinforcing layer is gradually reduced as in the case with the first reinforcing rubber layer 50. An inner liner 11 made of an ordinary rubber is arranged on the axially inner side of the first reinforcing rubber layer 50 and the second reinforcing rubber layer 60. The axially outer side of the sidewall portion 10 is entirely covered with an outer cover rubber. This cover rubber is constituted by a relatively soft rubber chafer 12 having good wear resistance and a side rubber 13 having good bending resistance. The rubber chafer and the side rubber are extended radially outwardly from a radially inner end portion to be contacted with a rim when the tire is mounted on the rim, and arranged on the axially outer side along the turn-up portion 31 of the carcass. The side rubber 13 covers the entirety of the sidewall portion 10 following the rubber chafer 12. In the above construction, according to the pneumatic safety tire of the present invention, Shore A hardness and the volume are specified with respect to the rubber filler 40, the first reinforcing rubber layer 50 and the second reinforcing rubber layer 60 as follows. That is, the Shore A hardnesses of the rubber filler 40, the first reinforcing rubber layer 50 and the second reinforcing rubber layer 60 are successively decreased from the radially inner side to the radially outer side, that is in the order of the rubber filler 40 > the second reinforcing rubber 60 > the first reinforcing rubber 50. The Shore A hardness is specified in Japanese Industrial Standard (JIS). It is preferable that the Shore A hardness is 74° to 98° for the rubber filler 40, 60° to 90° for the second reinforcing rubber layer 60, and 60° to 85° for the first reinforcing rubber layer. Although the Shore A hardnesses are selected in the above respective ranges for the rubber filler and the first and second reinforcing rubber layers, the Shore A hardnesses must satisfy the hardness relationship of the rubber filler 40 > the second reinforcing rubber layer 60 > the first reinforcing rubber layer in this order. Further, it is preferable that the resilience (specified in JIS) of the first rubber layer 50 is less than that of the second reinforcing layer 60. The volumes of the rubber filler 40, and the first and second reinforcing rubber layers 50 and 60 are successively increased from the radially inner side to the radially outer side, that is, the volume is increased in the order of the rubber filler 40 < the second reinforcing rubber layer 60 < the first reinforcing rubber layer 50. The volumes of the rubber filler 40 and the first and second reinforcing rubber layers 50 and 60 with respect to the total reinforcing rubber of the filler and the first and second reinforcing rubber layers are preferably 10 to 20%, 15 to 35% and 45 to 70%, respectively. The inclined joint surface 70 as a boundary between the first reinforcing rubber layer 50 and the second reinforcing rubber layer 60 preferably satisfies a requirement that an angle  measured on an acute angle side between a straight line T' extended from the joint surface and a center line l-l of the tire is 50° to 80°, the straight line T' being downwardly inclined toward the axially inner side of the tire. When the reinforcing rubber layers are constituted as mentioned above, the total balance of the reinforcing rubber layers including the rubber filler is improved. Particularly, an attenuating effect of the reinforcing rubber layers is improved by mitigating vibrations inputted to the tire from the road, and cracking and heat generation and accumulation in the inner surface of the sidewall portion of the tire become unlikely to occur through the prevention of local stress concentration. Furthermore, since the first reinforcing rubber layer 50 is continued to the second reinforcing rubber layer 60 through the inclined joint surface 70 on the radially inner side, there is no rigid discontinuous face in the sidewall portion 10, thus improving anti-vibration riding comfortability. Moreover, since local stress concentration is prevented from occurring on the inner surface of the sidewall portion 10, boundary fracture of the first reinforcing rubber layer 50 and the second reinforcing rubber layer 60 made of different rubber materials can be prevented. Therefore, the pneumatic safety tire according to the present invention has not only excellent anti-vibration riding comfortability but also durability in the upper part of the sidewall portion. In particular, the pneumatic tire of the invention has good characteristics required for run-flat running. The construction and effects of the pneumatic safety tire according to the present invention will be further explained with reference to the following test examples. The construction shown in Fig. 1 was employed in a pneumatic tire having a tire size of 255/40ZR17, and this tire was subjected to evaluations of durability and anti-vibration riding comfortability. That is, two plies composed of rayon cords 1650d/3 arranged at 90° in the circumferential direction of the tire were used as a carcass 30, and two plies composed of steel cords 1 × 5 × 0.23 arranged at 68° in the tire circumferential direction were used as the belt layer 32 while the cords in one ply were crossed with respect to those in the other ply. As an auxiliary belt layer 33 there was used a ply formed by spirally winding a nylon cord 1260d/2 in a direction substantially parallel to the circumferential direction of the tire. As the first reinforcing rubber layer 50, rubber having a Shore A hardness of 80 and a resilience of 85 was used, and heights h 1 and h 4 of a radially outer end and a radially inner end of the first reinforcing rubber layer were set at 87% and 35% of a height H of the tire, respectively. As the second reinforcing rubber 60, rubber having a Shore A hardness of 85 and a resilience of 80 was used, and a height h 2 of a radially outer end of the second reinforcing rubber layer was set at 50% of the height H of the tire. As the rubber filler 40, rubber having a Shore A hardness of 98 was used, and a height h 3 of a radially outer end of the rubber filler was set at 30% of the height H of the tire. The total volume of the reinforcing rubbers comprised by the rubber filler 40, the first reinforcing rubber layer 50 and the second reinforcing rubber layer 60 was 960 cm 3 , and the volumes of the reinforcing rubbers were 15% (rubber filler 40), 25% (second reinforcing rubber layer 60) and 60% (first reinforcing rubber layer 50), respectively, with respect to the total volume. In addition, the inclined joint surface 70 as a boundary between the first reinforcing rubber layer 50 and the second reinforcing rubber layer 60 was set such that a straight line T' extending along the inclined joint surface 70 formed an angle  = 60° as measured on an acute side with respect to a central line l-l of the tire, the straight line T' being downwardly inclined toward the axially inner side of the tire. On the other hand, a conventional tire having the construction shown in Fig. 2 was obtained for comparison purposes. In this conventional tire, a first reinforcing rubber layer had a Shore A hardness of 80 and a resilience of 85, and occupied a volume of 40% with respect to the total volume of the reinforcing rubbers. A second reinforcing rubber layer had a Shore A hardness of 85 and a resilience of 80, and occupied a volume of 30% with respect to the total volume of the reinforcing rubbers. A filler rubber had a Shore A hardness of 98, and occupied a volume of 30% with respect to the total volume of the reinforcing rubbers. The height of a radially outer end of the rubber filler was set at 40% of the height of the tire. With respect to these two kinds of the tires, durability and anti-vibration riding comfortability were evaluated under the following conditions, and the results are shown in the following table. (1) Durability was evaluated as follows: Each of the tires was fitted under the same fitting conditions: a used rim No. 9J×17, and no internal pressure 0 kg/cm 2 (run-flat condition) and a load of 400 kg. The thus fitted tire was subjected to a running test on a drum having a diameter of 1.7 m with a camber angle of 0° at a speed of 90 km/h. A running distance which caused fracture in an upper part of the sidewall portion due to cracking or the like was measured. Durability was evaluated by an index based on results obtained (the result of the conventional tire was taken as 100, and the larger the index, the the better is the durability). (2) Anti-vibration riding comfortability was evaluated as follows: Six force components were measured when the tire was run on the above drum, and anti-vibration riding comfortability was evaluated by an index based on the six force components thus measured (the result of the conventional tire was taken as 100, and the larger the index, the better is the anti-vibration riding comfortability. Conventional tire Invention tire Durability 100 250 Anti-vibration riding comfortability 100 110 As explained above in detail, the pneumatic safety tire according to the present invention has excellent anti-vibration riding comfortability as well as durability in the upper portion of the sidewall portion. In particular, the invention tire has good characteristics required for run-flat running.

Claims: A pneumatic tire comprising a cylindrical tread portion (T), a pair of sidewall portions (10) extending radially inwardly from opposite ends of the tread portion and having respective bead rings (20) in the ends thereof, a radial carcass (30) toroidally extending from one bead ring to the other bead ring through one sidewall portion, the tread portion and the other sidewall portion and reinforcing the sidewall portions and the tread portion, each of the opposite end portions of the carcass (30) being turned up around the respective bead ring axially from the inside to the outside thereof, rubber fillers (40) each arranged between the turn-up portions (31) and the main body of the carcass and extending from above the bead ring toward the tread portion such that the radially sectional shape of the rubber filler (40) becomes narrower toward the tread portion (T), and a pair of thick rubber reinforcement layers arranged on respective axially inner sides of the carcass in the sidewall portions, wherein each of the rubber reinforcement layers is constituted by first and second reinforcing rubber layers (50,60), the first reinforcing rubber layer (50) occupying a radially outer side of the sidewall portion (10) and the second reinforcing layer (60) being continued to a radially inner side of the first reinforcing rubber layer through an inclined joint surface (70) and arranged on the radially outer side of the rubber filler (40) through the main body of the carcass, characterized in that the Shore A hardness is made greater in the order of the first reinforcing rubber layer (50), the second reinforcing rubber layer (60) and the rubber filler (40), and the rubber volume is made greater in the order of the rubber filler (40), the second reinforcing layer (60) and the first reinforcing layer (50). A tire as claimed in claim 1, characterized in that the Shore A hardnesses of the rubber filler (40), the second reinforcing rubber layer (60) and the first reinforcing rubber layer (50) are 74° to 98°, 60° to 90°, and 60° to 85°, respectively. A tire as claimed in claim 1 or 2, characterized in that the resilience value of the first reinforcing rubber layer (50) is less than that of the second reinforcing rubber layer (60). A tire as claimed in any of claims 1 to 3, characterized in that the volumes of the rubber filler (40), the second reinforcing rubber layer (60) and the first reinforcing rubber layer (50) are 10 to 20%, 15 to 35% and 45 to 70%, respectively. A tire as claimed in any of claims 1 to 4, characterized in that the inclined joint surface (70) is so inclined as to form an angle of 50 to 80° as measured on an acute angle side between a straight line (T 1 ) extended from said joint surface (70) and a center line of the tire, said straight line (T 1 ) being downwardly inclined toward an axially inner side of the tire.

Inventors: KAWABATA MISAO, YAMAGUCHI YUTAKA, YASUDA TAKUO, KAWABATA, MISAO, YAMAGUCHI, YUTAKA, YASUDA, TAKUO
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1992
Main classification: B60C13
IPC codes: B60C5, B60C13, B60C15, B60C17