Pneumatic tires

Abstract: A pneumatic tire having an improved uniformity in a tire-wheel assembled state has a bead portion (3) closely fitted to a standard rim (2) having an inclined bead seat (6), a rounded concave corner portion (7) extending from the bead seat (6) and a flange (8) extending outward from the rounded concave corner portion (7) and having a curved portion (9). In this tire, the bead portion (3) has an expanded heel bringing about close fitting to the rounded concave corner portion (7) prior to contact between the curved portion (9) and the bead portion (3).

Description: This invention relates to a pneumatic tire having an improved uniformity in a tire-wheel assembled state, and more particularly to a pneumatic tire capable of lessening radial runout (hereinafter abbreviated as RRO) and effectively controlling radial force variation (hereinafter abbreviated as RFV) by providing a satisfactory uniformity in a tire-wheel assembled state when the tire is mounted on a rim standardized in accordance with the Japan Automobile Tire Manufacturing Association (JATMA), the Tire and Rim Association, Inc. (TRA) or the like (hereinafter simply referred to as a standard rim) such as a two piece divided type rim, 5 degree full drop center rim, 15 degree full drop center rim, wide flat base rim and the like. As to the reduction of RFV in a tire-wheel assembly after a pneumatic tire is mounted on a rim, Japanese Patent laid open No. 3-189201 discloses that a spacer is interposed between a bead portion of the tire and a flange of the rim at a position corresponding to a large value of RRO measured at a shoulder portion of the tire. In this case, however, it is required to repeat the operation of assembling the tire on the rim and supplying air into the tire, which considerably complicates the operability of the rim assembling, and also there is a danger of causing disorder due to external force applied to the tire-wheel assembly. On the other hand, it is known that a tire after the vulcanization is mounted onto a rim so that a position of maximum peak in a waveform showing the change of RFV measured on the tire itself coincides with a position of minimum peak in a waveform showing a variation of scale deflection separately measured on the outer periphery of the rim. However, such a manner of rim assembling is no longer meaningful owing to the improvement of rim working accuracy. With the advance of studies on ride comfortability against vibration and noise of automobiles, particularly passenger cars, the uniformity in the tire-wheel assembled state becomes important. The term "uniformity in tire-wheel assembled state" does not mean that the tire-wheel assembly is merely a true circle in its shape, but means that the deflection on the periphery of the assembly is equal at any position under the same load or the reaction force is uniform during the rotation of the assembly under a certain deflection because RRO among the measures for the evaluation of the uniformity or the scale deflection of the outer periphery on the tire and rim degrades the variation of radial reaction force or RFV when the tire-wheel assembly is rotated under a certain deflection. The present inventors have discovered that RRO as a tire-wheel assembly does not become small even when a tire having good RRO is mounted on a standard rim having a sufficiently improved working accuracy, which results from the eccentrically assembled state of the tire on the rim. The present invention is based on the above discovery and provides a pneumatic tire having an improved uniformity in a tire-wheel assembled state and capable of effectively controlling RFV as a tire-wheel assembly by improving a bead portion of the tire so as to easily attain a concentrically assembled state when the tire is mounted on the rim. Attention is also drawn to the disclosures of US-A-3203461 and FR-A-2429111. According to the present invention, there is provided a pneumatic tire having an improved uniformity in a tire-wheel assembled state, and having a bead portion closely fitted into an inclined bead seat of a standard rim comprised of a rounded concave corner portion smoothly connected to the bead seat and a flange protrudingly extending outward from the rounded concave corner portion and having a curved portion in a direction opposite to the protruding direction, characterized in that the bead portion has a substantially flat bottom surface and an expanded heel for close fitting to the rounded concave corner portion of the standard rim over the full periphery of said rounded concave corner portion prior to contact between the curved portion of the standard rim and an outer surface of the bead portion facing thereto. The preferable embodiments of the invention are as follows. The bead portion has an annular depression adjacent to the expanded heel and facing the flange near the rounded concave corner portion. The expanded heel is a local torus, which is more preferably reinforced with a ring-shaped core embedded therein. A ratio of an expansion quantity of the expanded heel measured from a line passing through a bead base point and perpendicular to an axis of the tire to a fitted width of a radially inward face of the bead portion is within a range of 0.06-0.30. Further, the bead portion has a chamfered portion facing a hump of the standard rim at a bead toe located at a side opposite to the expanded heel, and more preferably a ratio of an axial length of the chamfered portion to a width of the bead portion is within a range of 0.2-0.4. An annular groove is formed in the bottom of the expanded heel over its full periphery, and more preferably a ratio of an axial width of the annular groove to a width of the bead portion is within a range of 0.2-0.3. The expanded heel is provided with a cord reinforcing layer arranged along a contour of the expanded heel. The invention will be further described, by way of example only, with reference to the accompanying drawings, wherein: Fig. 1 is a schematically partial section view of a first embodiment of a bead portion of a pneumatic tire according to the invention together with a state of mounting the tire on a rim; Figs. 2 to 6 are schematically partial views of other embodiments of bead portions of pneumatic tire according to the invention, respectively; and Fig. 7 is a schematically partial section view of a conventional pneumatic tire together with a state of mounting the tire on a rim. In Fig. 1 is shown a first embodiment of a pneumatic tire according to the invention and a main part for mounting this tire on a standard rim, wherein numeral 1 is a pneumatic tire, numeral 2 a standard rim, numeral 3 a bead portion of the tire, numeral 4 a sidewall portion, numeral 5 a bead core, numeral 6 a slant bead seat (usually 5° ± 1°) of the standard rim 2, numeral 7 a rounded concave corner portion, and numeral 8 a flange having a curved portion 9. In the flange 8, a straight portion raised from the rounded concave corner portion may be omitted in accordance with the kind of the standard rim 2. In the invention, the bead portion 3 is fundamentally characterized by having a substantially flat bottom surface and an expanded heel 10. An expansion quantity α of the expanded heel 10 is determined by using as a standard a vertical line n passing through a bead base point Q determined in the tire vulcanization, which corresponds to an intersect P between a line ℓ extending from the slant bead seat 6 toward the rounded concave corner portion 7 in a sectional profile of the standard rim 2 fitted to the tire and a line m perpendicular to an axial line of the standard rim 2 in contact with the flange 8, and perpendicular to the axial line of the standard rim 2, and is preferably within a range of 2-4 mm. The expanded heel 10 is a local torus 12 as shown in Figs. 2 and 3, or may be a plurality of separate segments facing the rounded concave corner portion 7. As shown in Fig. 1, an annular depression 11 is formed in the bead portion 3 so as to be adjacent to the expanded heel 10 and facing the flange 8 near the rounded concave corner portion 7. Further, the local torus 12 may be reinforced with a ring-shaped core 13 embedded therein as shown in Fig. 3. Furthermore, a ratio of the expansion quantity α of the expanded heel 10 to a fitted width β of a radially inward face of the bead portion 3 is preferably within a range of 0.06-0.30. A height of an expanded top T of the expanded heel 10 is represented by a vertical distance g between a line j extending from the inward face of the bead portion 3 and a line k parallel thereto and passing through the top T, and the vertical distance g is usually within a range of 1.5-10.5 mm. As shown in Fig. 4, a bead toe of the bead portion 3 located at a side opposite to the expanded heel 10 has a chamfered portion 15 corresponding to a hump 14 (Fig. 1) of the standard rim 2, and a ratio of length t of the chamfered portion 15 to a width γ of the bead portion 3 in the axial direction of the tire is preferably within a range of 0.2-0.4. As shown in Fig. 5, the expanded heel 10 is provided at its bottom with an annular groove 16 over its full periphery, and a ratio of width W of the annular groove 16 in the axial direction to the bead width γ is preferably within a range of 0.2-0.3. As shown in Fig. 6, the expanded heel 10 may be reinforced with a cord reinforcing layer 17 arranged along a contour of the expanded heel 10. In any case, at least the expanded heel 10 in the bead portion 3 is preferably made from a hard rubber stock having a JIS-A hardness of not less than 60°, preferably not less than 65°. Moreover, it is desirable that the ring-shaped core 13 is made from an endless band of inextensible cord such as steel cord or organic fiber cord. As the cord reinforcing layer 17, use may be made of cord fabric and plain weave fabric of metal cords such as steel cord or organic fiber cords such as nylon, polyester or the like, in which these cords are arranged at a certain cord angle with respect to a tangent line at the top T of the expanded heel 10. It is desirable that such a fabric is embedded in the expanded heel 10 along the contour of the expanded heel 10 as shown in Fig. 6 or adhered to the outer surface of the expanded heel 10. In general, the bead portion 3 of the pneumatic tire 1 has an adequate interference against a rim diameter D defined by using a distance from the intersect P between the line ℓ and the line m to the axial line of the standard rim 2 as a radius. When the tire 1 is mounted on the standard rim 2, the bead portion 3 is partly and successively ridden over the curved portion 9 of the rim 2 to locate in a drop or well of the rim 2 and then moved toward the flange 8 of the rim as shown by an arrow in Fig. 1. Thereafter, air is supplied to the inside of the tire 1 or a tube housed in the tire (not shown) to increase the internal pressure up to a standard internal pressure defined for this tire. Thus, the outer surface of the bead portion 3 is pushed along the slant bead seat 6 up to the outer surface of the curved portion 9 by such an air pressure. In Fig. 7 is shown such a rim assembling state with respect to a conventional pneumatic tire having no expanded heel. As the interference of the bead portion 3 against the slant bead seat 6 increases, the degree of closely fitting the bead portion to the rim becomes high. However, the friction resistance of the slant bead seat 2 obstructing the movement of the bead portion 3 always becomes non-uniform over the full periphery thereof, so that the outer surface of the bead portion 3 in the tire first contacts with the curved portion 9 of the rim 2 at a certain point on the periphery thereof to cause compressive deformation at this point and the bead base point Q approaches the intersect P while withstanding such a compressive deformation. As a result, the rim assembling operation is frequently stopped while non-uniformly causing a space S between the bead heel 10' of the bead portion 3 and the rounded concave corner portion 7 on the periphery of the standard rim 2. For this end, RRO as a tire-wheel assembly becomes large to cause RFV though the tire itself has a sufficient uniformity after the vulcanization. Under the above rim assembling operation, according to the invention, the expanded heel 10 or the local torus 12 first contacts with the rounded concave corner portion 7 of the standard rim 2 as shown in Fig. 1 to cause compression deformation, through which the outer surface of the bead portion 3 contacts with the curved portion 9 of the flange 8 under an adequate pressure. Therefore, the rotational axis of the tire 1 easily coincides with the rotational axis of the standard rim 2 to lessen RRO as a tire-wheel assembly, whereby RFV can effectively be controlled. In a tire for a conventional passenger car, the expansion quantity α of the expanded heel 10 or local torus 12 is preferably within a range of 2-4 mm and the ratio of the expansion quantity α to the fitting width β of the inner face of the bead portion 3 is preferably within a range of 0.06-0.30. When the bead portion 3 has a chamfered portion 15 at its bead toe, it is well engaged with the hump 14 of the standard rim 2, and it is preferable that the ratio of the axial length t of the chamfered portion 15 to the bead width γ is within a range of 0.2-0.4. Further, when the annular groove 16 is formed at the bottom of the expanded heel 10 over its full periphery, the riding over the hump 14 is facilitated in the rim assembling, so that the annular groove 16 has preferably an axial width W corresponding to 0.2-0.3 of the bead width γ. In order that the bead portion 3 is well fitted to the standard rim 2, the expanded heel 10 should be rendered into adequate shape and size. In this case, the expanded heel 10 is determined by the expansion quantity α. When the fitting width β of the inner face of the bead portion 3 is defined by an inner face length of the bead portion 3 contacting with the slant bead seat 6 of the standard rim 2, if the ratio of the expansion quantity α of the expanded heel 10 to the fitting width β of the bead portion is less than 0.06, the effect of controlling RRO and RFV is substantially lost, while if the ratio exceeds 0.3, the contacting to the rim 2 becomes shallow to lower the contact pressure of the inner face of the bead portion and hence slipping between the tire and the rim (rim slipping) is apt to be caused during the running of the tire. If the bead toe located at a side opposite to the expanded heel 10 of the bead portion 3 does not easily ride over the hump 14 of the standard rim 2, the rim assembling can not be properly achieved, and therefore a chamfered portion 15 is preferably formed in the bead toe of the bead portion. When the axial length t of the chamfered portion 15 is within a range of 0.2-0.4 of the bead width γ, the chamfered portion 15 can properly contribute to the close contact of the expanded heel 10 to the rounded concave corner portion 7 without catching the bead toe by the hump 14. At the initial stage of the rim assembling, the bead portion 3 of the tire 1 locates in a drop or well portion having a diameter smaller than that of the hump 14, so that it rides over the hump 14 from a largely eccentric state with respect to the standard rim to move onto the slant bead seat 6, but the bead portion 3 just before the moving onto the slant bead seat is still eccentric with respect to the rim. When the hump 14 is housed in the annular groove 16 formed in the bottom of the expanded heel 10 over the full periphery, the eccentric state is considerably lessened, so that after the bead portion rides over the hump 14, the expanded heel 10 or the local torus 12 first contacts with the rounded concave corner portion 7 to cause compressive deformation and then the outer surface of the bead portion smoothly contacts with the curved portion 9 of the flange 8 under a proper pressure to complete the rim assembling, whereby the rotational axis of the tire is easily aligned with the rotational axis of the rim. If the axial width W of the annular groove 16 is less than 0.2 of the bead width γ, the recession to the hump 14 is too small and the resistance to riding over the hump 14 in the rim assembling is hardly mitigated to reduce the effect obtained by the formation of the expanded heel 10, while if said ratio exceeds 0.3, the recession to the hump 14 is too large and there is a danger of causing an eccentric state after the fitting of the bead portion to the rim though the bead portion easily rides over the hump 14. At least the expanded heel 10 or local torus 12 in the bead portion 3 is preferably made from a hard rubber stock having a JIS-A hardness of not less than 60°, more preferably not less than 65°, which can advantageously cause an equal contact with the rounded concave corner portion 7 over its full periphery, but the upper limit of the rubber hardness is preferably 80°. The following examples are given in illustration of the invention and are not intended as limitations thereof. Example 1 A tire-wheel assembly is manufactured by using a pneumatic tubeless tire for a small-size passenger car having a tire size of 205/65 R15 and an adaptable rim of 15 x 6JJ (according to JATMA YEAR BOOK 1991). In this case, an expanded heel 10 having various expansion quantities α as shown in Fig. 1 is formed in a bead portion 3 of the tire and has a JIS-A hardness of 70°. Then, RRO (mm) and RFV (kgf) of the tire-wheel assembly are measured to obtain results as shown in Table 1. Control (Fig. 7) Comparative Example Example 1 α (mm) 0 1.0 2.0 3.0 4.0 PRO (mm) 0.53 0.47 0.21 0.18 0.20 RFV (kgf) 8.3 7.8 5.1 4.7 4.6 In the tire-wheel assembly, when the expansion quantity α is 3.0 mm, the expanded heel 10 is compressed by about 1 mm in the rim assembling. Even in the modified embodiments of Figs. 2 and 3, the interference of the bead portion 3 is unified into the conventionally known shape that the radially inward face of the bead portion is inclined at an angle somewhat larger than that of the slant bead seat 6 of the rim to be closely fitted thereto. Thus, the interference of the bead portion 3 is sufficient to be a value according to the conventional technique. For example, the inclination angle of the inward face in the bead portion may be a larger inclination of plural stages at the bead toe. As the bead core 5, use may be made of conventionally known bead cores. For example, the bead core 5 may be formed by spirally winding a single steel reinforcing element thinly coated with rubber to form substantially a rectangle in section as described in Japanese Utility Model laid open No. 61-8804, or may be a so-called cable bead core obtained by using a soft steel filament as a core and winding a single filament of small diameter around the core. Example 2 In the same tire-wheel assembly as in Example 1, when the ratio of the expansion quantity α in the bead portion 3 of the tire to the fitting width β of the radially inward face of the bead portion is varied within a range of 0.06-0.30, RRO is not more than about 0.20 mm and RFV is not more than about 5 kgf. Moreover, when the tire size is varied, it is required to increase the expansion quantity α in accordance with the fitting width β, but if the ratio of α/β exceeds 0.3, the tendency of causing rim slipping becomes stronger. Example 3 In the same tire-wheel assembly as in Example 1, when a chamfered portion 15 is formed in a bead toe located opposite to the expanded heel 10 of the bead portion 3 as shown in Fig. 4 and the ratio of axial length t of the chamfered portion to width γ of the bead portion in the widthwise direction is within a range of 0.2-0.4, even if the expansion quantity α is increased by 2-8 mm, there are obtained results equal to or better than those of Example 1. Example 4 In the same tire-wheel assembly as in Example 1, when an annular groove 16 is formed in the bottom of the expanded heel 10 of the bead portion 3 as shown in Fig. 5 and the ratio of the axial width W of the annular groove to the bead width γ is 0.25, a better result is obtained. Example 5 A cord reinforcing layer 17 comprised of nylon cords of 840 d/2 arranged at a cord angle of 85° with respect to a tangent line at the top T of the expanded heel 10 is arranged along the contour of the expanded heel 10 as shown in Fig. 6. In this case, the same results in relation to RRO and RVF as in Example 1 are obtained. Then, a bead portion durability is evaluated by an occurrence ratio of bead portion failure after the tire is run on a drum testing machine at a speed of 60 km/hr under a load of 450 kgf over a distance of 1000 km when the expansion quantity α is 3 mm. As a result, the occurrence ratio of bead portion failure was found to be 2 tires/50 tires, which is notably lower than the failure ratio of 5 tires/50 tires for bead portions having no cord reinforcing layer. As mentioned above, according to the invention, the exact seating of the expanded heel in the bead portion onto the rounded concave corner portion of the rim is attained in the usually used rim without changing the profile of the rim and taking special care in the rim assembling, so that the value of RRO as a tire-wheel assembly can be reduced and hence the value of RVF can be effectively controlled.

Claims: A pneumatic tire (1) having an improved uniformity in a tire-wheel assembled state, and having a bead portion (3) closely fitted into an inclined bead seat (6) of a standard rim (2) comprised of a rounded concave corner portion (7) smoothly connected to the bead seat (6) and a flange (8) protrudingly extending outward from the rounded concave corner portion (7) and having a curved portion (9) in a direction opposite to the protruding direction, characterized in that the bead portion (3) has a substantially flat bottom surface and an expanded heel (10) for close fitting to the rounded concave corner portion (7) of the standard rim (2) over the full periphery of said rounded concave corner portion prior to contact between the curved portion (9) of the standard rim and an outer surface of the bead portion facing thereto. A pneumatic tire as claimed in claim 1, characterized in that the bead portion (3) has an annular depression (11) adjacent to the expanded heel (10) and facing the flange (8) near the rounded concave corner portion (7). A pneumatic tire as claimed in claim 1 or 2, characterized in that the expanded heel (10) is a local torus (12). A pneumatic tire as claimed in claim 3, characterized in that the local torus (12) is reinforced with a ring-shaped core (13) embedded therein. A pneumatic tire as claimed in any of claims 1 to 4, characterized in that a ratio of an expansion quantity (α) of the expanded heel (10) measured from a line (n) passing through a bead base point (Q) and perpendicular to an axis of the tire to a fitted width (β) of a radially inward face of the bead portion (3) is within a range of 0.06-0.30. A pneumatic tire as claimed in any of claims 1 to 5, characterized in that the bead portion (3) has a chamfered portion (15) facing a hump (14) of the standard rim (2) at a bead toe located at a side opposite to the expanded heel (10). A pneumatic tire as claimed in claim 6, characterized in that a ratio of an axial length (t) of the chamfered portion (15) to a width (γ) of the bead portion (3) is within a range of 0.2-0.4. A pneumatic tire as claimed in any of claims 1 to 7, wherein an annular groove (16) is formed in the bottom of the expanded heel (10) over its full periphery. A pneumatic tire as claimed in claim 8, characterized in that a ratio of an axial width (W) of the annular groove (16) to a width (γ) of the bead portion (3) is within a range of 0.2-0.3. A pneumatic tire as claimed in any of claims 1 to 9, characterized in that the expanded heel (10) is provided with a cord reinforcing layer (17) arranged along a contour of the expanded heel.

Inventors: FUJITA KAZUTO, WADA MITSUNORI, FUJITA, KAZUTO, WADA, MITSUNORI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1993
Main classification: B60C15
IPC codes: B60C15