Pneumatic tyres

Abstract: A pneumatic tire (1) having an aspect ratio of not more than 55% comprises a carcass composed of a carcass ply (3), in which a turnup end portion (5) of the carcass ply is disposed between an end portion of a belt (7) and a crown portion (8) of the carcass ply, and distances L 1 and L 2 from a straight line (m) passing through the central portions of the bead cores (2) respectively to an outer end (10) of the bead filler (4) and to a maximum width (11) of the carcass in the radial direction (9) of the tire satisfy a relationship of L 1 ≧L 2 , and the distance (L 1 ) is within a range of 35-45% of a section height (H) of the tire, and the distance (L 2 ) is within a range of 27-45% of the section height (H).

Description: This invention relates to a pneumatic tire or so-called high-performance tire balancedly satisfying steering stability and ride comfortability with reduction of tire weight and having an aspect ratio of not more than 55%. A high-performance tire is a pneumatic tire particularly attempting improvement of the steering stability by making the aspect ratio small and widening the tread width to increase the ground contact area, and usually uses a carcass comprised of two carcass plies for ensuring sufficient tire rigidity. However, it is increasingly demanded every year to attain low fuel consumption of a vehicle and hence it becomes important to reduce the tire weight, which is also true in the case of the high-performance tire. As a result, it is attempted to develop a high-performance tire using a carcass comprised of a single carcass ply for reduction of the tire weight. In the conventional high-performance tire using the single carcass ply, however, it is liable to be lacking in lateral rigidity and radial rigidity of the tire and hence sufficient steering stability can not be obtained. On the other hand, when a hard rubber is arranged as a bead filler for making up such a shortage, the rigidity in the radial direction of the tire may become too large to degrade the ride comfort. It is, therefore, an object of the invention to solve the above problem of the conventional technique and to provide a pneumatic tire or so-called high-performance tire having an aspect ratio of not more than 55% and capable of balancedly satisfying the steering stability and ride comfort with the reduction of the tire weight by using a single carcass ply, arranging a turnup end portion of such a ply between an end portion of a belt and a crown portion of the carcass ply, lowering the position of maximum width of the carcass ply, and raising the position of an outer end of a bead filler in the radial direction of the tire. A tire corresponding to the preamble of claim 1 is known from US-A-5361820. This tire comprises a turnup end portion disposed underneath the belt edge. According to the present invention, there is provided a pneumatic tire comprising a carcass toroidally extending between a pair of bead cores and comprised of a carcass ply, in which an end portion of a turnup portion of the carcass ply wound around a bead core and around a bead filler located above the bead core from the inside toward the outside is disposed between an end portion of a belt reinforcing a tread portion and a crown portion of the carcass ply, characterized in that said pneumatic tire has an aspect ratio of not more than 55%, and a first radial distance (L 1 ) from a straight line (m) connecting a pair of said bead cores and passing through their central positions at a section of the tire in a widthwise direction thereof up to a position corresponding to a radially outer end of the bead filler is greater than or equal to a second radial distance (L 2 ) from the straight line (m) up to the maximum width position of said turnup portion of said carcass ply, and said first radial distance (L 1 ) is within a range of 35-45% of a section height (H) of the tire, and said second radial distance (L 2 ) is within a range of 27-45% of the said section height (H). Furthermore, the term "section of tire in widthwise direction thereof" used herein means a section of the tire in the widthwise direction when the tire is mounted onto a measuring rim defined by ETRTO and inflated under an air pressure corresponding to a maximum loading ability at a state of applying no load. The invention will be further described with respect to the accompanying drawing, wherein: Fig. 1 is a diagrammatically left-half section view of a typical embodiment of the pneumatic tire according to the invention in a radial direction thereof. In Fig. 1 is sectionally shown a typical embodiment of the pneumatic tire according to the invention, wherein numeral 1 is a pneumatic tire, numeral 2 a bead core, numeral 3 a carcass ply, numeral 3a a turnup portion of the carcass ply, numeral 4 a bead filler, numeral 5 a turnup end portion of the carcass ply, numeral 6 a tread portion, numeral 7 a belt, and numeral 8 a crown portion of the carcass ply. The illustrated pneumatic tire 1 is a high-performance tire having an aspect ratio of not more than 55% and has a so-called envelop structure that the carcass toroidally extending between a pair of bead cores 2 is composed of the single carcass ply 3 and the turnup end portion 5 of the carcass ply 3 wound around the bead core 2 and the bead filler 4 located just above the bead core 2 from the inside toward the outside is disposed between an end portion of the belt 7 reinforcing the tread portion 6 and the crown portion 8 of the carcass. Thus, the rigidity of the tire liable to be lacking when the carcass is constituted with the single carcass ply can be supplemented by sandwiching the turnup end portion 5 of the carcass ply 3 between the belt end portion and the carcass crown portion 8. Moreover, the belt 7 shown in Fig. 1 is comprised of four rubberized cord layers 12-15 and a narrow-width rubberized cord layer 16 covering each of both ends of these layers 12-15. However, the arrangement and the number of these layers and the like may properly be changed, if necessary. The term "end portion of the belt" used herein means an end portion of an innermost rubberized cord layer among the plural layers constituting the belt as shown in Fig. 1. In the pneumatic tire according to the invention, it is an essential feature that when a first radial distance from a straight line (m) connecting between a pair of bead cores 2 and passing through their central positions at a section of the tire in a widthwise direction thereof up to a position corresponding to an outer end 10 of the bead filler 4 in a radial direction 9 is L 1 and a second radial distance from the straight line (m) up to a position corresponding to a maximum width 11 of the carcass in the radial direction of the tire is L 2 , the distances L 1 and L 2 satisfy a relationship of L 1 ≧L 2 . The reason why the distances L 1 and L 2 satisfy the above relationship is due to the fact that since a bending center of a sidewall portion during the running of the tire under loading is approximately the maximum width position 11 of the carcass, tire rigidity can be enhanced by reinforcing the portion corresponding to the maximum width of the carcass as the bending center with the bead filler 4. However, even when the distances L 1 and L 2 satisfy the above relationship, there may be caused a case of balancedly satisfying both the steering stability and the ride comfortability. For this end, the inventor has found that the steering stability and ride comfortability can balancedly be satisfied by properly arranging the distances L 1 and L 2 with respect to a section height H of the tire, or concretely arranging the distances L 1 and L 2 within ranges of 35-45% and 27-45% with respect to the section height H, respectively. The reason why the distance L 1 is limited to the range of 35-45% with respect to the section height H is due to the fact that when it is less than 35%, the bead portion is apt to be damaged under a large loading to degrade the bead portion durability, while when it exceeds 45%, the flex zone in the sidewall portion becomes lacking to degrade the ride comfortability. The reason why the distance L 2 is limited to the range of 27-45% with respect to the section height H is due to the fact that when it is less than 27%, the maximum width position 11 of the carcass as a bending center is located inward from the height of the rim flange in the radial direction of the tire and hence the flex zone becomes lacking to degrade the ride comfortability, while when it exceeds 45%, the maximum width position 11 of the carcass is too separated away from the rim and hence the sharp steering is degraded. In the invention, the rubber hardness of the bead filler is preferably within a range of 80-100. The term "rubber hardness" used herein means A-type spring hardness measured according to JIS K6301. The following examples are given in illustration of the invention and are not intended as limitations thereof. Example A pneumatic tire according to the invention is prepared and the performances thereof are evaluated as follows. The invention tire is a high-performance tire having a sectional shape shown in Fig. 1 and a tire size of 255/40ZR18, in which a carcass toroidally extending between a pair of bead cores 2 is composed of a single carcass ply 3 and a turnup end portion 5 of the ply 3 wound around the bead core 2 and a bead filler 4 located just above the bead core 2 from the inside toward the outside is disposed between an end portion of a belt 7 reinforcing a tread portion 6 and a crown portion 8 of the carcass and the distances L 1 and L 2 are 40 mm and 35 mm (L 1 >L 2 ) and are 45% and 39% with respect to a section height H of the tire, respectively. The belt 7 has such a lamination structure that two wide-width rubberized layers 12, 13 each containing steel cords arranged at a cord angle of 22° with respect to an equatorial plane of the tire are laminated so as to cross the cords of these layers with each other and two wide-width rubberized layers 14, 15 each containing nylon fiber cords arranged in parallel to the equatorial plane are laminated thereon and a narrow-width rubberized layer 16 containing nylon fiber cords arranged in parallel to the equatorial plane is laminated on each of both end portions of the wide-width rubberized layers 12-15. Moreover, the other tire structure is substantially the same as in the conventional high-performance tire. Comparative Example 1 This tire has substantially the same structure as in the example tire except that the distances L 1 and L 2 are 43 mm and 38 mm (L 1 >L 2 ) and are 50% and 44% with respect to the section height H, respectively. Comparative Example 2 This tire has substantially the same structure as in the example tire except that the distances L 1 and L 2 are 23 mm and 20 mm (L 1 >L 2 ) and are 30% and 26% with respect to the section height H, respectively. Comparative Example 3 This tire has substantially the same structure as in the example tire except that the distances L 1 and L 2 are 33 mm and 38 mm (L 1 <L 2 ) and are 40% and 46% with respect to the section height H, respectively. Comparative Example 4 This tire has substantially the same structure as in the example tire except that the distances L 1 and L 2 are 16 mm and 30 mm (L 1 <L 2 ) and are 23% and 43% with respect to the section height H, respectively. Comparative Example 5 This tire has substantially the same structure as in the example tire except that the distances L 1 and L 2 are 43 mm and 50 mm (L 1 <L 2 ) and are 50% and 58% with respect to the section height H, respectively. Conventional Example This tire has substantially the same structure as in the example tire except that the carcass is composed of two carcass plies and the position of the turnup end of the carcass ply is located downward from the maximum width position of the carcass by 10 mm and the distances L 1 and L 2 are 33 mm and 23 mm (L 1 >L 2 ) and are 40% and 28% with respect to the section height H, respectively. o ○ Test Method Each of the above tires is mounted onto a large-size high-performance sedan type vehicle and run on a test course of dry asphalt road surface at a speed of 50-180 km/h, during which the steering stability and ride comfortability are evaluated by a professional driver's feeling. Particularly, the steering stability is evaluated by cornering property and handling progressiveness. Also, the tire weight is measured. The results are shown in Table 1. Each of the cornering property, handling progressiveness and ride comfortability in Table 1 is represented by a numerical value in 10-point process, in which the larger the numerical value, the better the property. On the other hand, the tire weight is represented by an index value on the basis that the conventional example is 100, in which the smaller the index value, the lighter the weight. Cornering property Handling progressiveness Ride comfortability Tire weight Example 7.0 7.0 7.5 95 Comparative Example 1 7.5 7.5 5.5 97 Comparative Example 2 5.5 5.5 6.0 93 Comparative Example 3 6.5 6.0 6.5 94 Comparative Example 4 5.5 5.0 6.0 91 Comparative Example 5 7.5 7.5 5.5 97 Conventional Example 7.0 7.0 6.5 100 As seen from the results of Table 1, when the example is compared with the conventional example using the carcass comprised of two carcass plies, the tire weight can be reduced and the total performance . of the steering stability and ride comfortability is excellent. On the other hand, when Comparative Examples 1-5 are compared with the example, since any one of the relationship between the distances L 1 and L 2 , ratios of the distances L 1 and L 2 with respect to the section height H of the tire is outside the acceptable range defined in the invention, either the steering stability or the ride comfortability is not attained to a satisfactory level, and hence both the performances are not well balanced. As mentioned above, according to the invention, it is possible to provide a pneumatic tire or so-called high-performance tire having an aspect ratio of not more than 55% and balancedly satisfying the steering stability and ride comfortability while realizing a reduction of the tire weight.

Claims: A pneumatic tire (1) comprising a carcass toroidally extending between a pair of bead cores (2) and comprised of a carcass ply (3), in which an end portion (5) of a turnup portion (3a) of the carcass ply (3) wound around a bead core (2) and around a bead filler (4) located above the bead core from the inside toward the outside is disposed between an end portion of a belt (7) reinforcing a tread portion (6) and a crown portion (8) of the carcass ply, characterized in that said pneumatic tire (1) has an aspect ratio of not more than 55%, and a first radial distance (L 1 ) from a straight line (m) connecting a pair of said bead cores (2) and passing through their central positions at a section of the tire in a widthwise direction thereof up to a position corresponding to a radially outer end (10) of the bead filler (4) is greater than or equal to a second radial distance (L 2 ) from the straight line (m) up to the maximum width position of said turnup portion (3a) of said carcass ply (3), and said first radial distance (L 1 ) is within a range of 35-45% of a section height (H) of the tire, and said second radial distance (L 2 ) is within a range of 27-45% of the said section height (H). A pneumatic tire as claimed in claim 1, characterized in that the bead filler (4) has a hardness of 80-100 as a spring A-type hardness according to JIS K6301.

Inventors: HAYASHI KAZUO, HAYASHI, KAZUO
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1997
Main classification: B60C15
IPC codes: B60C15, B60C9, B60C3