High performance pneumatic radial tires

Abstract: A high performance pneumatic radial tire includes a tread surface (1) formed with a plurality of circumferential grooves (2), a radial carcass (3), a belt (4) composed of two belt layers (4a, 4b) of metal cords, an additional reinforcing layer (5) arranged on a radially outer side of the belt and at an axially central area of the tread, and at least two additional auxiliary layers (6a, 6b) arranged at each of widthwise opposite side portions of the tread and composed of organic fiber cords. The additional reinforcing layer (5) is composed of cords crossing the metal cords in the belt layer (4b) adjacent thereto and inclined with respect to the tire-circumferential direction, and has a width (W₂) less than the minimum width (W₁) of the belt (4) but greater than a distance (W) between the circumferential grooves located at widthwise outermost sides of the tread, respectively. The organic fiber cords constituting the additional auxiliary layers (6a, 6b) extend substantially in the tire-circumferential direction, and the additional auxiliary layers have different widths. A tread-widthwise inner end of the additional auxiliary layer (6a) located at the radially inner side of the tire is located adjacent a side edge of the additional reinforcing layer (5), and a tread-widthwise outer end of this additional auxiliary layer (6a) is located at a tread-widthwise outer side of the side edge of the belt layer (4a) having the maximum width. A tread-widthwise inner end of the additional auxiliary layer (6b) located at the radially outer side of the tire is located at an axially inner side of the circumferential groove (2) located at the widthwise outermost side of the tread but at an axially outer side of the center of the tread, and a tread-widthwise outer end of this additionally auxiliary layer (6b) is located at an axially outer side of the belt layer (4a) having the maximum width.

Description: The present invention relates to pneumatic radial tires, and in particular to high performance pneumatic radial tires. Particularly, the invention relates to improvement of the tread-reinforcing structure, and is aimed at prevention of the occurrence of buckling, improvement of the vehicle-cornering stability and reduction in generation of noise. Fig. 2 of the accompanying drawings shows a tread-widthwise sectional view of a part of a tread-reinforcing structure of a tire of this kind. In Fig. 2, a carcass 31 is formed from one ply of cords extending substantially at an angle of 90° with respect to the tire circumferential direction, and a belt 32 is arranged on a radially outer side of a crown portion of this carcass 31 over the entire width of the tread. The belt 32 is formed by two belt layers 32a and 32b constituted from metal cords symmetrically arranged at relatively small angles with respect to a tire-circumferential direction such that the metal cords in one of the belt layers cross those in the other belt layer. On a radially outer side of the belt 32 is arranged an additional layer 33 constituted by a so-called cap and so-called layers, the cap being an additional reinforcing layer 33a composed of organic fiber cords extending substantially in the tire-circumferential direction and having a width, for example, slightly greater than that of the belt, and the layers being additional auxiliary layers 33b composed of similar cords extending in the tire-circumferential direction and covering axially side portions of the belt 32, respectively. In Fig. 2, a tread surface 34 of the tread is formed with circumferential grooves 35 extending in the tire-circumferential direction. In such a reinforcing structure, mainly the additional reinforcing layer 33a prevents a central area of the tread from radially outwardly projecting due to centrifugal forces during high speed turning of the tire, and mainly the additional auxiliary layer 33b prevents the axially side portion of the tread from radially outwardly projecting due to such centrifugal forces during high speed turning. Thereby, durability of the tire at high speeds can be improved. However, in the case of the tire having such a conventional structure, particularly in which the belt layers 32a and 32b are made of metal cords, a so-called buckling phenomenon occurs such that a widthwise central area of the belt 32 is deformed in a ground-contacting area of the tread in direction away from the road upon receipt of a load there. Consequently, the ground-contacting pressure of the tread surface 34 of the tread becomes particularly low at a portion between the widthwise central area and the circumferential groove provided at each of the widthwise outermost sides of the tread. Such a tendency becomes more conspicuous with increase in load. For this reason, when the road-gripping force of the tire becomes lower, the ground-contacting pressure of the tire becomes non-uniform in the width direction of the tread during rotating of the vehicle as mentioned above. Consequently, the road-gripping force rapidly drops, so that tire controllability is deteriorated. Furthermore, in such a conventional tire, since the additional reinforcing layer 33a reinforcing the central portion of the tread increases rigidity of the tread due to its large share of tension load with the cords extending in the tire-circumferential direction, and causes resonance of the tire, undesirably generated noise of the tire becomes greater. The present invention has been accomplished through investigations to overcome the above-mentioned problems posed by the conventional high performance pneumatic radial tires. Therefore, the present invention aims to provide a high performance pneumatic radial tire, particularly a tread-reinforcing structure thereof, which can improve cornering stability of a vehicle, and prevent swelling of a part of a central portion of a tread through effectively preventing the buckling of a belt, and effectively suppress occurrence of resonance of the tire during running at high speeds. The present invention provides a pneumatic radial tire including a tread having a tread surface formed with a plurality of circumferential grooves extending in a tire-circumferential direction, a carcass composed of at least one ply of cords extending substantially at an angle of 90° with respect to the tire-circumferential direction, a belt arranged on a radially outer side of a crown portion of the carcass and composed of two belt layers of metal cords arranged at relatively small angles with respect to the tire-circumferential direction such that the cords in one of the belt layers cross those in the other belt layer, an additional reinforcing layer arranged on a radially outer side of the belt and at an axially central area of the tread, and at least two additional auxiliary layers arranged at each of widthwise opposite side portions of the tread and composed of organic fiber cords, wherein said additional reinforcing layer is composed of cords crossing the metal cords in the belt layer adjacent thereto and inclined with respect to the tire-circumferential direction, and has a width less than the minimum width of the belt but greater than a distance between the circumferential grooves located at widthwise outermost sides of the tread, respectively; the organic fiber cords constituting said at least two additional auxiliary layers extend substantially in the tire-circumferential direction, and said at least two additional auxiliary layers have different widths; a tread-widthwise inner end of the additional auxiliary layer located at the radially inner side of the tire is located adjacent a side edge of the additional reinforcing layer, and a tread-widthwise outer end of the said additional auxiliary layer is located at a tread-widthwise outer side of the side edge of the belt layer having the maximum width; and a tread-widthwise inner end of the additional auxiliary layer located at the radially outer side of the tire is located at an axially inner side of the circumferential groove located at the widthwise outermost side of the tread but at an axially outer side of the center of the tread, and a tread-widthwise outer end of the said additional auxiliary layer is located at an axially outer side of the belt layer having the maximum width. According to the present invention, the following are preferred. (1) The additional auxiliary layer is constituted by a structural body formed by spirally winding a ribbon-shaped member made of a plurality of rubberized organic fiber cords in the tire-circumferential direction. (2) The cords constituting the additional reinforcing layer are aramid cords, and the cords constituting the additional auxiliary layer are nylon cords. (3) The cords constituting the additional reinforcing layer are extended to be substantially symmetrical with the cords of the belt layer adjacent to this additional reinforcing layer, and a relative angle of the cords constituting the additional reinforcing layer with respect to the tire-circumferential direction is substantially equal to that of the cords constituting the belt layer adjacent the additional reinforcing layer. (4) At least said two additional auxiliary layers at at least one of the axially opposite side portions are constituted by a ribbon-shaped member spirally wound from one side to the other in a given overlapped state. In this case, the term "overlapped state" means that the two additional auxiliary layers are wound such that the overlapped amount is zero. In the pneumatic radial tire according to the present invention, the cords of the additional reinforcing layer are inclined to cross the cords of the belt layer adjacent thereto, and preferably the relative angle of the cords of the additional reinforcing layer with respect to the tire-circumferential direction is made substantially equal to that of the cords of the belt layer adjacent thereto. In other words, the relative angle of the additional reinforcing layer with respect to the tire-circumferential direction is set in a range of the relative angle of this belt layer ± 10°. Thereby, bending rigidity is increased at least at a central portion of the belt, more accurately at a portion of the belt sandwiched between the circumferential grooves located at the widthwise outermost sides of the tread, so that buckling resistance is effectively improved. Furthermore, the width of the additional reinforcing layer is made greater than the distance between the circumferential grooves at the widthwise outermost sides of the tread but smaller than the minimum width of the belt, so that increase in rigidity at the widthwise opposite side portions of the tread is suppressed, and difference in rigidity between the widthwise opposite side portions and the central portion of the tread is sufficiently decreased to further improve buckling resistance in a given range. In addition, the buckling resistance is improved by making the rigidity uniform in the tread-width direction even when the tire is slightly deformed (the tire rolls quietly), so that deformation of the tire and vibrations of the tread portion are suppressed. As a result, the resonance of the tire is effectively reduced. Moreover, since the cords conventionally required to extend at the central portion of the tread in the tire-circumferential direction and share large tension are omitted, circumferential rigidity of the central portion of the tread is reduced, and vibrations of the tread are suppressed during rolling of the tire to reduce resonance of the tire. That is, tire sounds can be reduced by effectively suppressing vibrations of the tire in both the tread-width and tread-circumferential directions of the tire. In addition, since at least two additional auxiliary layers composed of the cords extending substantially in the tire-circumferential direction are arranged in each of the axially opposite side portions of the tread, the axially opposite side portions of the tread can be effectively prevented from being radially outwardly swelled due to centrifugal forces during rolling of the tire at high speeds to improve high speed durability. Further, since the widths of at least two additional auxiliary layers are made different from each other, the tread portion can be effectively prevented from being radially outwardly swelled out due to centrifugal forces during rolling at high speeds. That is, although the magnitudes of the centrifugal forces acting upon various widthwise portions of the tread differ depending upon the material of the belt or the gauge of the tread, the swelling-out amount of the tread portion at high speeds can be controlled and high speed durability can be improved by making the widths of the additional auxiliary layers different from each other. Furthermore, according to the tire of the present invention, since the tread-widthwise inner end of the additional auxiliary layer located at the radially inner side of the tire is located adjacent the side edge of the additional reinforcing layer, difference in rigidity between the central portion and the axially side portion of the tread is decreased to improve the buckling resistance. Further, since the tread-widthwise outer end of this additional auxiliary layer is located at the widthwise outer side of the belt layer having the maximum width, the swelling out of the tread during rotating of the tire at high speed can be sufficiently suppressed to a location corresponding to the side edge of the belt to further improve durability at high speed. In addition, the tread-widthwise inner end of the additional auxiliary layer located at the radially outer side of the tread is located at the radially inner side of the circumferential groove located at the widthwise outermost side of the tread but at the radially outer side of the center of the tread, and preferably the additional auxiliary layer is overlapped with the additional reinforcing layer between the axially outermost circumferential groove and the circumferential groove axially inwardly adjacent thereto. By so doing, occurrence of buckling due to the bending of the belt around the axially outermost circumferential groove can be prevented. Further, since the tread-widthwise outer end of this additional auxiliary layer is located at the axially outer side of the side edge of the belt layer having the maximum width, durability at high speed and buckling resistance can be further improved. In the present invention, when the additional auxiliary layer is constituted by a structural body formed by spirally winding a ribbon-shaped member made of plural rubberized organic fiber cords in the tire-circumferential direction, the efficiency of forming the additional auxiliary layers can be largely improved. This is more remarkable when two or more additional auxiliary layers are constituted by a ribbon-shaped member spirally wound from one side to the other in a given overlapped state. When the additional reinforcing layer and the additional auxiliary layer are made of aramid cords and nylon cords, respectively, the weight of the tire can be reduced, necessary tensile resistance can be imparted upon the end portions of the belt, and high bending rigidity can be imparted upon the central portion of the belt. The invention will be further described, by way of example only, with reference is made to the accompanying drawings, wherein: Fig. 1 is a schematically cross-sectional view of a tread of an embodiment of a tire of the present invention; and Fig. 2 is a schematically cross-sectional view of the tread of a conventional tire. Fig. 1 is a schematically cross-sectional view of the tread portion of one embodiment of a tire of the present invention. A plurality (five in Fig. 1) of tire-circumferential grooves 2 are provided in a tread surface 1 of the tread, and extend in a tire-circumferential direction. A carcass 3 is formed from at least one ply (one ply in Fig. 1) composed of cords extending substantially at an angle of 90° with respect to the tire-circumferential direction. A belt 4 is arranged on a radially outer side of a crown portion of the carcass 3. The belt 4 is formed from two belt layers 4a, 4b composed of metal cords arranged at relatively small angles with respect to the tire-circumferential direction such that the metal cords in one belt layer cross those in the other belt layer. An additional reinforcing layer 5 is provided on a radially outer side of the belt 4 in a widthwise central portion of the tread, and two additional auxiliary layers 6a, 6b are provided on the radially outer side of the belt 4 at widthwise opposite sides of the tread. The additional auxiliary layers 6a, 6b are composed of organic fiber cords, and have different widths. The additional reinforcing layer 5 and the additional auxiliary layers 6a, 6b together constitute an additional layer 7. The metal cords of the belt layer 4b adjacent the additional reinforcing layer 5 are set at 22° with respect to the tire-circumferential direction, and the additional reinforcing layer 5 is composed of aramid fibers extending in a direction crossing the metal cords of the belt layer 4b and forming an angle of 30° with respect to the tire-circumferential direction. The aramid cords have fineness of 1500d/2. The additional reinforcing layer 5 has a width W₂= 130 mm, which is smaller than the minimum width W₁ of the belt but greater than a distance W between the circumferential grooves 2 located at widthwise opposite sides of the tread. The additional auxiliary layers 6a, 6b are formed from nylon cords extending substantially at 0° with respect to the tire-circumferential direction. Preferably, each of the additional auxiliary layers 6a, 6b is constituted by a structural body formed by spirally winding a ribbon-shaped member in the tire-circumferential direction. The ribbon-shaped member has a width of, for example, 10 mm, and is formed by rubberizing a plurality of nylon cords. The additional auxiliary layer 6a located at the radially inner side extends over a width from a location adjacent the widthwise side end of the additional reinforcing layer 5 to a location at the widthwise outer side of the belt layer 4a having the maximum width as shown. The other additional auxiliary layer 6b located at the radially outer side extends over a width from a location located at the widthwise inner side of the widthwise outermost circumferential groove and at the widthwise outer side of the center of the tread, preferably from a central location between the widthwise outermost circumferential groove and the circumferential groove inwardly adjacent to the widthwise outermost circumferential groove, to a location at the widthwise outer side of the side end of the belt layer 4a having the maximum width. In order to enhance productivity and increase the yield of the ribbon-shaped member, it is preferable that the additional auxiliary layers 6a, 6b are simultaneously formed by spirally winding the above-mentioned ribbon-shaped member from one side to the other in a given overlapped state. For example, both the additional auxiliary layers 6a, 6b are formed as follows: The ribbon-shaped member is spirally wound from a location corresponding to the tread-widthwise outer ends of the additional auxiliary layers 6a, 6b toward the widthwise inner direction of the tread while the ribbon-shaped member is overlapped by 1/2 of the width of the ribbon-shaped member between the radially inner and outer sides. When the ribbon-shaped member reaches a location corresponding to the side end of the additional reinforcing layer 5, the ribbon-shaped member is further spirally wound up to a given widthwise inner location of the tread to form a remaining portion of the additional auxiliary layer 6b at the radially outer side while side edges of adjacent turns of the ribbon-shaped member are closely contacted to each other in a non-overlapped state. The two sets of the additional auxiliary layers located at the widthwise opposite sides of the tread may be formed by spirally winding a single ribbon-shaped member on one widthwise outer end portion of the tread in the overlapped state as mentioned above, while the ribbon-shaped member is continuously passed from the widthwise inner end of the additional auxiliary layer 6b on this one widthwise opposite side to that of the additional auxiliary layer 6b on the other widthwise opposite side, followed by spirally winding. According to the tire constructed above, the buckling of the belt can be effectively prevented, and cornering stability of the vehicle can be effectively improved as mentioned above. In addition, the cap layer (90°) required in the conventional belt structure is omitted, so that the circumferential tension in the central portion of the belt is reduced to effectively suppress occurrence of resonance of the tire. Comparative Experiment : In the following comparative experiment there will be explained between an invention tire and a conventional tire with respect to high speed durability, cornering stability and generation of tire noise. Test tires : The invention tire and the conventional tire had the tread-reinforcing structures shown in Figs. 1 and 2, respectively, and both had a tire size of 205/55 ZR 15. Test methods : (1) High speed durability: The tire was fitted to a rim having a size of J6-16, and inflated at an internal pressure of 2.55 kg/cm². Then, the tire was pressed to a rotary drum having a diameter of 1600 mm under pressure of 540 kgf, and a high speed durability was measured when the rotation speed was increased by 10 km/h every 20 minutes, starting from 150 km/h, and the results were evaluated by an index taking the result of the conventional tire as 100. In this test, room temperature was 22°C, and a camber angle and a slip angle were both set at 0°. (2) Cornering stability: Each of the above tires was used on a front wheel, and run on Nürnberg circuit in Germany. Drivability and cornering stability were evaluated by drivers's feeling. (3) Tire noises generated: Tire noises generated were evaluated by `measurement of noise on passing in a test course and noise test on a table inside room. Test results : Test results are shown in Table 1. In Table 1, the greater the index value, the better are the results. Conventional tire Invention tire High speed durability 100 100 Cornering stability When the tire exceeded a limit for road-gripping forces during turning, controllability rapidly lowered. Even when the tire exceeded the limit for road-gripping forces during turning, no rapid reduction in cornering power occurred, and controllability was excellent. Tire noises generated 100 95 (reduced by 5%) As is seen from the test results in Table 1, according to the present invention, the occurrence of the buckling of the belt can be prevented, high speed durability can be maintained at a high level, and cornering stability can be advantageously improved. In addition, the resonance of the tire can be effectively prevented by lowering the circumferential tension in the central portion of the belt, and the noises of the tire generated can be largely reduced.

Claims: A pneumatic radial tire including a tread having a tread surface (1) formed with a plurality of circumferential grooves (2) extending in a tire-circumferential direction, a carcass (3) composed of at least one ply of cords extending substantially at an angle of 90° with respect to the tire-circumferential direction, a belt (4) arranged on a radially outer side of a crown portion of the carcass and composed of two belt layers (4a, 4b) of metal cords arranged at relatively small angles with respect to the tire-circumferential direction such that the cords in one of the belt layers cross those in the other belt layer, an additional reinforcing layer (5) arranged on a radially outer side of the belt and at an axially central area of the tread, and at least two additional auxiliary layers (6a, 6b) arranged at each of widthwise opposite side portions of the tread and composed of organic fiber cords, wherein said additional reinforcing layer (5) is composed of cords crossing the metal cords in the belt layer (4b) adjacent thereto and inclined with respect to the tire-circumferential direction, and has a width (W₂) less than the minimum width (W₁) of the belt (4) but greater than a distance (W) between the circumferential grooves located at widthwise outermost sides of the tread, respectively; the organic fiber cords constituting said at least two additional auxiliary layers (6a, 6b) extend substantially in the tire-circumferential direction, and said at least two additional auxiliary layers have different widths; a tread-widthwise inner end of the additional auxiliary layer (6a) located at the radially inner side of the tire is located adjacent a side edge of the additional reinforcing layer (5), and a tread-widthwise outer end of the said additional auxiliary layer (6a) is located at a tread-widthwise outer side of the side edge of the belt layer (4a) having the maximum width; and a tread-widthwise inner end of the additional auxiliary layer (6b) located at the radially outer side of the tire is located at an axially inner side of the circumferential groove (2) located at the widthwise outermost side of the tread but at an axially outer side of the center of the tread, and a tread-widthwise outer end of the said additional auxiliary layer (6b) is located at an axially outer side of the belt layer (4a) having the maximum width. A pneumatic radial tire as claimed in Claim 1, characterized in that the additional auxiliary layer (6a, 6b) is constituted by a structural body formed by spirally winding a ribbon-shaped member made of a plurality of rubberized organic fiber cords in the tire-circumferential direction. A pneumatic radial tire as claimed in Claim 1 or 2, characterized in chat the cords constituting the additional reinforcing layer (5) are aramid cords, and the cords constituting the additional auxiliary layer (6a, 6b) are nylon cords. A pneumatic radial tire as claimed in any of Claims 1 to 3, characterized in that a relative angle of the cords constituting the additional reinforcing layer (5) with respect to the tire-circumferential direction is substantially equal to that of the cords constituting the belt layer (4b) adjacent the additional reinforcing layer. A pneumatic radial tire as claimed in any of Claims 1 to 4, characterized in that at least two said additional auxiliary layers (6a, 6b) at at least one of the axially opposite side portions are constituted by a ribbon-shaped member spirally wound from one side to the other in a given overlapped state.

Inventors: WATANABE SHINICHI, WATANABE, SHINICHI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1992
Main classification: B60C9
IPC codes: G10K11, B60C9, D02G3, D07B1