Heavy duty tire with improved tire noise

Abstract: A pneumatic radial tire especially for use on trucks and buses comprises a carcass (1) reinforcing a sidewall portion (4) and a tread (6), and a belt (5) comprised of at least two belt layers, wherein when the tire is mounted onto an approved rim (7) and inflated under an internal pressure of 0.5-1.0 kgf/cm 2 , a carcass line of the carcass at a radial section of the tire comprises a curve having a maximum radius of curvature (R) in a region (E) ranging over 10-50% of a tire sectional height (H) and centering around a position (S) of maximum carcass width, and the sidewall portion (4) has a maximum thickness in a zone correspcnding to the region (E).

Description: This invention relates to pneumatic tires, and more particularly to a heavy duty pneumatic radial tire for use in trucks and buses and capable of reducing tire noise. It is well known from such heavy-duty tires to comprise the features of the preamble of claim 1. During the running of a tire, vibrations are applied to the tire due to local variation of rigidity in the tread pattern and unevenness of the road surface, which propagate in air to cause noise. Such a tire noise is closely related to resonance frequency of a tread or a sidewall portion, so that it is particularly effective to improve vibration properties of the sidewall portion for reducing noise in this type of tire. As regards the vibration properties of the sidewall portion, various countermeasures for reducing the tire noise are proposed in tires for passenger cars, while no countermeasure for this type of tire noise is proposed in heavy duty pneumatic radial tires for use in trucks and buses. Attention is also drawn to the disclosures of EP-A-0 640 496 and EP-A-0 614 774 which are both concerned with the problem of noise reduction by modifications of the tire sidewall vibration properties. It is, therefore, an object of the invention to reduce tire noise by improving the vibration properties of the sidewall portion in a heavy duty pneumatic radial tire. The present inventor has observed vibration behaviour applied to the sidewall portion of a tire in detail and found that vibration amplitude is considerably large in a position corresponding to a maximum tire width and in the vicinity thereof. Furthermore, the inventor has made various studies with respect to the shape, thickness and the like of the sidewall portion and found out that it is desirable to optimize the shape of the carcass as a skeleton of the tire and the thickness of the sidewall portion for the reduction of tire noise and as a result the invention has been accomplished. According to the present invention, there is provided a heavy duty pneumatic radial tire comprising a carcass toroidally extending between a pair of bead cores through a pair of sidewall portions, and a belt superimposed outward about a crown portion of the carcass in a radial direction of the tire and comprised of at least two belt layers, characterized in that, when the tire is mounted onto an approved rim and inflated under an internal pressure of 0.5-1.0 kgf/cm 2 , a carcass line of the carcass at a radial section of the tire comprises a curve having a maximum radius of curvature in a region ranging over 10-50% of a sectional height of the tire and centering around a position of maximum carcass width, and the sidewall portion is provided on its outer surface with a rubber layer located around a line segment passing through the position of the maximum carcass width so as to have a maximum thickness in a zone corresponding to the said region. The term "carcass line" used herein means a profile line of the carcass at the radial section of the tire, and the term "maximum carcass width" used herein means that the distance of the carcass ply in the widthwise direction at the radial section of the tire is maximum. In preferred embodiments of the invention, the carcass line in the region ranging over 10-50% of the sectional height of the tire and centering around the position of maximum carcass width consists of a curve symmetrical with respect to a line segment passing through the position of maximum carcass width and parallel to a rotating axis of the tire; and a thickness of a zone of the sidewall portion corresponding to the region ranging over 10-50% of the sectional height of the tire and centering around the maximum carcass width is not less than 1.4 times the minimum thickness of the sidewall portion. The invention will be further described with reference to the accompanying drawings, wherein: Fig. 1 is a diagrammatic left-half radial section of an embodiment of a pneumatic radial tire according to the invention; and Fig. 2 is a graph showing transmissibility in a sidewall portion of the tire. In Fig.1 is diagrammatically shown a left-half radial section of a pneumatic radial tire according to the invention at an inflated state under an internal pressure of 1.0 kgf/cm 2 after mounting onto an approved rim. Of course, the right-half section of the tire (not shown) is symmetrical with the left-half section thereof. Numeral 1 is a bead core, and numeral 2 a carcass comprised of a single carcass ply toroidally extending between the bead cores 1 along an inner wall of the tire and wound around the bead core 1 from the inside of the tire toward the outside to form a turnup portion 2a extending along a bead portion 3 toward a sidewall portion 4. On a crown portion of the carcass 2 are disposed a belt 5 comprised of at least two belt layers and a tread 6 in a radial direction of the tire in turn. Numeral 7 is an approved rim. When the tire having the above basic structure is mounted onto an approved rim and inflated under an internal pressure of 0.5-1.0 kgf/cm 2 , it is important that a carcass profile line of the carcass 2 at a radial section of the tire comprises a curve having a maximum radius of curvature R in a region E ranging over 10-50% of a section height H of the tire (which is defined by 1/2 of a difference between an outer diameter of the tire and a diameter of the rim) and centering around a position S corresponding to a maximum carcass width. Preferably, such a curve is symmetrical with respect to a line segment L passing through the position S of maximum carcass width and parallel to a rotating axis of the tire because the position of maximum carcass width corresponds to a loop portion in mode of tire vibration and further develops an effect of controlling vibration. That is, a portion of the carcass line corresponding to the region E is constituted with a curve having a maximum radius of curvature R, so that when the tire is inflated under a standard internal pressure, tension per unit area at the region E becomes sufficiently large as compared with the other region and hence strong vibrations produced in the zone of the sidewall portion corresponding to the region E are controlled to reduce the tire noise. Furthermore, it is important that the sidewall portion has a greatest thickness at the zone corresponding to the above region E. Specifically a rubber layer 8 is added to the zone of the sidewall portion corresponding to the region E as shown in Fig. 1, whereby a thickening part may be formed in the region E. In this case, the rubber layer 8 may be arranged over the whole of the region E, but it is preferable that at least 20% of the region E is formed by the thickening part. As shown, the sidewall portion 4 is provided on its outer surface with the rubber layer 8 located around the line segment L passing through the position S of maximum carcass width so as to have a maximum thullness in the zone corresponding to the region E. Thus, when the thickness is made maximum at the zone of the sidewall portion corresponding to the region E, rubber mass at this zone increases as compared with the other zone, so that vibrations transmitted from the road surface through the tread surface can be absorbed at the region E to control the application of vibration to the sidewall portion, which brings about a reduction of tire noise. In order to more promote the reduction of tire noise by the above action, it is preferable that the thickness of the zone of the sidewall portion corresponding to the region E is not less than 1.4 times the minimum thickness of the sidewall portion. The following examples are given in illustration of the invention and are not intended as limitations thereof. Pneumatic radial tires for trucks and buses having a tire size of 11R22.5 and a basic structure as shown in Fig. 1 are manufactured according to a specification as shown in Table 1, respectively. Each of these tires is mounted onto an approved rim and inflated under a standard internal pressure, and is run on a drum testing machine at a speed of 50 km/h under a standard load, during which sound pressure of noise from the tire is measured by means of a microphone located at a distance of 1.0 m apart from a contact surface between the tire and the drum. The measured results are shown in Table 1. Invention tire 1 Conventional tire Radius of curvature of carcass line in region E at a state of inflating under an internal pressure of 1.0 kgf/cm 2 (mm) R = 600 R = 200 Thickness of sidewall portion in region E (mm) 12 4 Minimum thickness of sidewall portion (mm) 4 4 Reduction level of sound pressure at 500-800 Hz(dB) Δ1.8 control Remarks Fig. 1 - Furthermore, each of the invention tire 1 and conventional tire is mounted onto a rim having a size of 7.5x22.5 and inflated under an internal pressure of 7.0 kgf/cm 2 and then placed on an indoor drum noise testing machine. Then, excitation (input) is carried out at one point of a central portion in the widthwise direction of the tread and outputs are measured by means of acceleration sensors attached to the sidewall portion at an interval of 1 cm in the radial direction of the tire to obtain results as shown in Fig. 2 in which a ratio of output to input at each position of the sensors is calculated as a transmissibility. As seen from Fig. 2, the transmissibility of the invention tire at the sidewall portion corresponding to the region E is reduced to 2.9 dB from that of the conventional tire.

Claims: A heavy duty pneumatic radial tire comprising a carcass (2) toroidally extending between a pair of bead cores (1) through a pair of sidewall portions (4), and a belt (5) superimposed outward about a crown portion of the carcass in a radial direction of the tire and comprised of at least two belt layers, characterized in that , when the tire is mounted onto an approved rim (7) and inflated under an internal pressure of 0.5-1.0 kgf/cm 2 , the carcass line of the carcass (2) at a radial section of the tire comprises a curve having the maximum radius of curvature (R) in a region (E) ranging over 10-50% of a sectional height (H) of the tire and centering around the position (S) of maximum carcass width, and the sidewall portion (4) is provided on its outer surface with an additional rubber layer (8) located around a line segment (L) passing through the position (S) of the maximum carcass width so as to have the maximum sidewall thickness in a zone corresponding to the said region (E). A pneumatic radial tire as claimed in claim 1, characterized in that the carcass line in the region (E) ranging over 10-50% of the sectional height of the tire and centering around the position (S) of maximum carcass width consists of a curve symmetrical with respect to a line segment (L) passing through the position (S) of maximum carcass width and parallel to a rotating axis of the tire. A pneumatic radial tire as claimed in claim 1 or 2, characterized in that a thickness of a zone of the sidewall portion (4) corresponding to the region (E) ranging over 10-50% of the sectional height of the tire and centering around the maximum carcass width is not less than 1.4 times the minimum thickness of the sidewall portion.

Inventors: NAOI TOSHIKATSU, NAOI, TOSHIKATSU
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1996
Main classification: B60C13
IPC codes: B60C3, B60C13