Pneumatic radial tire

Abstract: A pneumatic radial tire in which both end portions of a plurality of sheets of carcass plies are mounted respectively to left and right bead cores to fold back from an inner side to an outer side of the tire, fold back portions of the carcass plies constituting the outermost sides on inner sides of the bead cores are laminated onto unfolded portions of the carcass plies, carcass cords of the carcass plies are intersected with each other between the laminated layers and a length of the fold back portion is made longer than any of fold back portions of all of the remaining carcass plies.

Description: The present invention relates to a pneumatic radial tire in which a carcass ply (carcass layer) is constructed by a semi-radial structure, particularly to a pneumatic radial tire promoting driving stability without being accompanied by an increase in mass or a reduction in productivity. In pneumatic tires, a tire in which a carcass cord of a carcass ply is arranged by less than 90 degree relative to a tire equator is particularly referred to as a semi-radial tire. Generally, according to a conventional semi-radial tire for a passenger vehicle, as shown by Fig. 3A, two sheets of carcass plies 21 and 22 in which carcass cords are intersected with each other between the plies, are arranged to reach bead portions 25 from a tread portion 23 via left and right side portions 24 and both end portions thereof are folded back to wrap bead fillers 27 from the inner side to the outer side of the tire respectively around left and right bead cores 26. Further, the tread portion 23 is arranged with two sheets of belt layers 28 over the entire periphery of the tire along the peripheral direction of the tire on the outer side of the outer side carcass ply 21. There are many different tires in production, for example, the "centres-off-set" asymmetrical, semi-radial tires of JP-62 205804A and EP-A-0 819 553; and the asymmetrical radial tire of US-A-5 117 888. "Centres-in-line" and "centres-off-set" refers to the relative placement of the individual carcass plies one atop another. A tire according to the preamble of claim 1 is disclosed in EP 0 484 831. In the carcass plies 21 and 22, a fold back portion 21b of the carcass ply 21 constituting the outermost side on an inner side of the bead core 26 in the bead portion 25, is extended to the side of the tread portion 23 along an unfolded portion 21a of the carcass ply 21 (that is, main body portion). Further, a fold back portion 22b of the carcass ply 22 rides over a distal end 21e of the fold back portion 21b to cover a total of the fold back portion 21b and is successively extended to the side of the tread portion 23 along the main body portion 21a. Therefore, a distal end 22e of the fold back portion 22b is disposed on the side of the tread portion 23 relative to the distal end 21e of the fold back portion 21b. According to the above-described conventional semi-radial tire, when the driving stability is intended to further promote, as a general conventional method, a reinforcement layer comprising steel cords or fiber cords are arranged on the outer side of the bead filler 27. However, such an additional arrangement of the reinforcement layer gives rise to an increase in a mass of the tire by that amount, increases also tire fabrication steps and is obliged to submit to disadvantage resulting in a reduction in the productivity. It is an object of the invention, at least in certain preferred embodiments, to provide a pneumatic radial tire promoting driving stability while mass and productivity thereof stay in the same levels as those of a conventional pneumatic radial tire. According to the present invention, there is provided a pneumatic semi-radial tire according to claim 1. According to the invention the length of the fold back portion of the carcass ply constituting the outermost side on the inner side of the bead core and extended from the main body portion (that is, the unfolded portion of the carcass ply), is made longer than any of fold back portions of all of the remaining carcass plies and therefore, a laminated layer region in which carcass cords intersect with each other between laminated layers of the main body portion and the fold back portion can be made wider than that of the conventional tire of Fig. 3A and Fig. 3B. The laminated layer region in which the carcass cords intersect with each other in this way is provided with the flexural rigidity larger than that of the laminated layer region in which the carcass cords are brought into a state in which the carcass cords are in parallel with each other between the layers and therefore, according to the invention, compared with the conventional tire of Fig. 3A and Fig. 3B, the lateral rigidity of the side of the tire can be increased and the driving stability can be promoted. Further, an amount of the carcass plies and tire fabrication steps remain the same as those in the conventional tire and therefore, the tire mass is not increased and the productivity is not deteriorated. For a better understanding of the invention, and to show how the same may be carried into affect, reference will now be made, by way of example, to the accompanying drawings in which: Fig. 1A is a semi-sectional view of a semi-radial tire for a passenger vehicle in a meridian direction thereof showing an embodiment of the invention; Fig. 1B is an explanatory view showing a laminated state of fold back portions in Fig. 1A; Fig. 2 is a semi-sectional view of a semi-radial tire for a passenger vehicle in the meridian direction showing other embodiment of the invention; Fig. 3A is a semi-sectional view showing an example of a conventional semi-radial tire for a passenger vehicle in the meridian direction; and Fig. 3B is an explanatory view showing a laminated state of fold back portions in Fig. 3A. According to a tire forming an embodiment of the invention, as shown by Fig. 1A, two sheets of carcass plies 1 and 2 in which carcass cords are laminated to intersect with each other between the plies, are arranged to reach bead portions 5 from a tread portion 3 via left and right side portions 4 and both end portions thereof are folded back to wrap bead fillers 7 from the inner side to the outer side of the tire respectively around left and right bead cores 6. The respective carcass cords of the carcass plies 1 and 2 are inclined by an angle of less than 90 degree relative to the tire equator. Further, the tread portion 3 is arranged with two sheets of belt layers 8 over the entire periphery of the tire along the peripheral direction of the tire on the outer side of the outer side carcass ply 1. In the carcass plies 1 and 2, a fold back portion 1b of the carcass ply 1 constituting the outermost side on an inner side of the bead core 6 in the bead portion 5, is extended to an inner side of a wing tip 9 at a vicinity of an end portion of the shoulder along a main body portion 1a of the carcass ply 1 and is directly laminated on the main body portion 1a. Further, a fold back portion 2b of the carcass ply 2 is extended to the side of the tread portion 3 along the fold back portion 1b and by directly laminating on the fold back portion 1b. A length of the fold back portion 1b is longer than a length of the fold back portion 2b. That is, a distal end 1e of the fold back portion 1b is disposed on the side of the tread portion 23 relative to a distal end 2e of the fold back portion 2b. Notation 2a designates a main body portion of the carcass ply 2. Due to such a fold back structure of the carcass ply, as shown by Fig. 1B, the fold back portion 1b and the main body portion 1a are laminated to each other such that a carcass cord 1c of the fold back portion 1b and the carcass cord 1c of the main body portion 1a intersect with each other in a region S excluding a portion where the bead filler 7 is interposed. When there is established such a relationship in which the carcass cords intersect with each other between the layers at a portion where the main body portion 1a and the fold back portion 1b are directly laminated to each other, compared with a case in which there is established a relationship in which the carcass cords are in parallel with each other between the layers, the flexural rigidity of the laminated plies can be increased. Meanwhile, according to the conventional tire shown by Fig. 3A and Fig. 3B, when the laminating relationship is investigated, although in a region S' in which the fold back portion 21b is directly laminated on the main body portion 21a, there is established a relationship in which the carcass cords 21c intersect with each other between the layer, in a region S'' in which the fold back portion 22b is directly laminated on the main body portion 21a, there is established a relationship in which the carcass cords are in parallel with each other between the layers (the carcass cord 22c of the fold back portion 22b and the carcass cord 21c of the main body portion 21a are in parallel with each other). Accordingly, in respect of the tires of Fig. 1A and Fig. 3A, when tire sizes thereof stays the same and amounts of using the carcass plies stay the same, S of Fig. 1A is equal to S'+S'' of Fig. 3A and S>S' in the regions S and S' in which the carcass cords intersect with each other between the layers and therefore, the flexural rigidity of the side portion of the tire of Fig. 1A is larger than that of the tire of Fig. 3A, further, the driving stability is more excellent. However, materials of the both tires are quite the same, the fabrication steps also stays the same and therefore, the tire mass and the productivity stay quite the same. Fig. 2 is a semi-sectional view of a semi-radial tire in the meridian direction showing other embodiment of the invention. The semi-radial tire is constructed by a constitution similar to that in the above-described embodiment except that an reinforcement layer 11 is arranged on the outer side of the fold back portions 1b and 2b of the carcass plies 1 and 2. The reinforcement layer 11 comprises reinforcement cords of steel cords or organic fiber cords and the reinforcement cords intersect with the carcass cord 2c of the fold back portion 2b on the outermost side. According to such a tire, the rigidity of the bead portion 5 can further be increased. As carcass cords constituting the carcass plies, it is preferable to use cords comprising organic fiber of nylon, polyester, aramid fiber or rayon. In respect of an angle of arranging the carcass cords, any of angle ranges which have conventionally been used in semi-radial tires are applicable and the angle ranges are preferably equal to or more than 65 degree and less than 90 degree relative to the tire equator, more preferably equal to or more than 65 degree and less than 87 degree. A number of implanting the carcass cords (number of ends) may also fall in a range which has been applied to the conventional semi-radial tire and the number is preferably 45 pieces through 55 pieces / 50 mm at the tire equator. Although the length of the fold back portion of the carcass ply is not particularly restricted, when the distal end is arranged to the tread side rather than a maximum width portion of the tire, the feature of the present invention can fully be utilized and it is preferable that the distal end of the fold back portion of the carcass ply laminated on the outermost side is extended to a vicinity of an edge portion of the tread shoulder, particularly to an inner side of the wing chip. Although a number of sheets of the carcass plies is preferably two, the carcass plies can be laminated up to a maximum of four sheets. EXAMPLES There are fabricated a tire according to the invention and the conventional tire constructed by a common constitution in which the tire size is 225/45R17 and two layers of carcass plies are arranged such that nylon 66 cords of 1260d/2 are inclined by 70 degree relative to the tire equator and a number of ends thereof at the tire equator is 50 pieces / 50 mm and by a constitution in which arrangement of distal ends of two fold back portions differ from each other as respectively shown by Figs. 1A and 1B and Figs. 3A and 3B. S = 50 mm, S' = 30 mm, S'' = 20 mm. When lateral rigidity of side of tire and driving stability are measured under conditions, described below, in respect of the two kinds of semi-radial tires, a result of Table 1 has been obtained. Lateral rigidity of side: The respective tires are filled with air under an internal pressure of 200kPa and a total of the outer periphery of the tread portion is brought into a fixed state, a displacement in an axial direction of tire is applied from the rim and the reaction force is measured as the lateral rigidity of the side. An evaluation is carried out by inverse numbers and is designated by indices with an inverse number of a measured value of the conventional tire as 100. The larger the index value, the more excellent is the lateral rigidity of the side. The result is shown in Table 1. Driving stability : Five professional test drivers run vehicles on a slalom test course erected with pylons at constant intervals and the driving stability is measured by a passing time period. An evaluation is carried out by inverse numbers of average values of passing time periods by the five test drivers and is designated by indices with an inverse number of an average value of a passing time period in the case of the conventional tire as 100. The larger the index value, the more excellent is the driving stability. The result is shown in Table 1. Side lateral rigidity Driving stability Invented tire 115 130 Conventional tire 100 100 As is apparent from Table 1, it is known that the invented tire is more excellent than the conventional tire in both of the side lateral rigidity and the driving stability. As has been described in detail, in the tire having the semi-radial structure in which the carcass cords comprise a plurality of sheets of the carcass plies intersecting with each other between the layers, the fold back portion of the carcass ply constituting the outermost side on an inner side of the bead core, is laminated to the unfolded portion of the carcass ply (that is, main body portion), the carcass cords of the carcass plies intersect with each other between the laminated layers and the length of the fold back portion is made longer than any of the fold back portions of the total carcass plies and accordingly, while making the mass and the productivity of the tire of the present embodiments at the same levels as those of the conventional pneumatic radial tire, the region of laminating the carcass cords to intersect with each other between the layers can be maximized and accordingly, the side lateral rigidity can be increased as large as possible and the driving stability can be promoted.

Claims: A pneumatic semi-radial tire comprising: a plurality of sheets of carcass plies in which carcass cords of the carcass plies are inclined to a tire equator by an angle equal to or more than 65 degree and less then 90 degree and cross over the carcass cords of adjacent plies; and a tread defining left and right tread shoulders between the tread and adjoining tire walls, wherein each end portion of each carcass ply is mounted to fold back from the inner side to the outer side of the tire around a respective one of left and right bead cores, so that both end portions of an individual carcass ply extend symmetrically with respect to left and right bead cores; and wherein the fold back portion (1b) of the carcass ply (1) constituting the outermost side on the inner side of the bead core (6) in the plurality of sheets of carcass plies is laminated on the unfolded portion (1a) of the carcass ply, the carcass cords of the carcass plies cross over the carcass cords of adjacent laminated layers thereof and the length of said fold back portion (1b) is made longer than any of the fold back portions (2b) of all of the remaining carcass plies (2), characterised in that : the distal end (1e) of the fold back portion (1b) of the carcass ply constituting the outermost side on the inner side of one of left and right bead cores (6) is extended to a vicinity of the respective left or lght edge portion of the tread shoulder. The pneumatic semi-radial tire according to Claim 1 wherein: the number of the plurality of sheets of carcass plies is two to four. The pneumatic semi-radial tire according to Claim 1, further comprising: reinforcement layers (11) arranged on outermost sides of the fold back portions of the plurality of sheets of carcass plies; wherein reinforcement cords of the reinforcement layers and the carcass cords of the fold back portions on the outermost sides contiguous to the reinforcement layers cross one another.

Inventors: NOJI HIKOMITSU, NOJI, HIKOMITSU, Noji, Hikomitsu, The Yokohama Rubber Co., Ltd.
Applicants: YOKOHAMA RUBBER CO LTD, THE YOKOHAMA RUBBER CO., LTD.
Application year: 1999
Main classification: B60C15
IPC codes: B60C15, B60C9