Pneumatic radial tire

Abstract: A pneumatic radial tire (11) having good drainage properties and capable of reducing air-column-tube resonance sound in circumferentially extending grooves to decrease noise, comprising: a radial carcass layer (16), a pair of bead cores (14), a belt layer (18) a tread (19), a circumferentially extending groove (20) provided on the surface of said tread and having sidewalls (20a) inclined in opposite directions with respect to a radial direction of said tire, and at least one vibration buffer wall (21) having a substantially constant cross sectional shape with sidewalls inclined with respect to the radial direction of said tire and formed adjacent a sidewall (20a) of said circumferentially extending groove (20) and extending toward a tread surface of said tread, each of said sidewalls of said vibration buffer wall (21) being inclined in the same direction as that of an adjacent sidewall (20a) of said circumferentially extending groove (20), wherein the height of the outside edge of the vibration buffer wall (21) in the radial direction of the tire is lower than the height of the outside edge of said circumferentially extending groove (20) in the radial direction of the tire, and wherein the following relationships are satisfied: 0.50D≤H≤0.95D S≤0.30B 0.01B≤W≤0.30B 0.50D≤L≤1.50D

Description: The present invention relates to a pneumatic radial tire, and particularly to a pneumatic radial tire having good drainage properties combined with low noise for use in high-speed large trucks or automobiles. In automobiles running at high speed on a rainy day, rainwater is penetrated and wedged between the tread of a tire and the surface of a road to cause a phenomenon called hydroplaning in which the friction between the tread and the road surface is lost and the steering and braking do not correctly function and the safety of driving is worsened. Conventionally, the pneumatic radial tire 1 as shown in FIG. 7 of the accompanying drawings is proposed to solve the problem of hydroplaning in automobiles. This pneumatic radial tire 1 is formed in the shape of a loop as a whole with a rubber layer 2, and beads 3, 3 in the sectional ends of the radial tire 1 are provided with a pair of bead cores 4, 4 formed into a ring around the rotating shaft of the radial tire 1. A 2-ply carcass layer 6, consisting of ply cords 5 arranged in the shape of a loop in the sectional direction of the radial tire 1, is provided across a pair of the bead cores 4, 4, and the ends of the carcass layer 6 in the longer direction are turned outside and wound up around a pair of bead cores 4, 4. The radial outside of the carcass layer 6 is provided with a 2-ply steel belt layer 8 consisting of nonstretchable steel cord 7, and on the radial outside of the steel belt layer 8, a thick-wall tread 9 is formed so as to cover the steel belt layer 8. Further, the surface of the tread 9 is provided at predetermined intervals with a plurality of continuous rib grooves 10 circumferentially extending around the radial tire 1 to permit water penetrated between the tread 9 and the surface of a road to be discharged outside via the circumferentially extending grooves 10, thus improving the drainage of the radial tire 1. In the radial tire 1 as proposed above, however, there occur air-column tubes between the circumferentially extending grooves 10 and the surface of a road in the rolling tire, and the air in the air-column tubes causes noise by resonating with the vibration of the radial tire 1 brought about by the uneven surface of a road. If circumferential grooves 10 are enlarged to improve drainage, the noise will be increased because the air-column-tube resonance sounds are increased generally in proportion to the size of the circumferential grooves 10. As a means to solve the problem, there is proposed for example a pneumatic tire having a tread provided with circumferentially extending grooves and in the crosswise direction of the tire with laterally extending grooves inclined with respect to the equatorial plane of the tire, where notches are formed generally parallel to and adjacent to the laterally extending grooves (Japanese Patent Application Laid-Open Publication No. 38412/1991). However, such a pneumatic tire is not effective enough for preventing the noise because both the laterally extending grooves and the notches come into contact with the ground and the sidewalls of both the laterally extending grooves and the notches are simultaneously vibrated. That is, the pneumatic tire disclosed in Japanese Patent Application Laid-Open Publication No. 38412/1991 has not succeeded in solving the above problem. A pneumatic radial tire in which the upper edges of the sidewalls of a circumferentially extending groove are made sloping with an incline to the equatorial plane of the tire is also proposed in for example Japanese Patent Application Laid-Open Publication No. 117414/1995. However, this prior art pneumatic radial tire cannot relieve the lateral vibration of its circumferentially extending grooves and thus cannot reduce air-column-tube resonance sounds satisfactorily. Hence, the pneumatic tire disclosed in Japanese Patent Application Laid-Open Publication No. 117414/1995 has also not succeeded in solving the above problem. There is further proposed a pneumatic radial tire having a tread provided with a rib and with a circumferentially extending wide groove, said rib having circumferentially extending thin grooves formed outside said circumferentially extending wide groove, wherein the edge zone between the circumferentially extending wide and thin grooves is lower than the rib (US Patent No. 4,936,363). However, the pneumatic radial tire proposed in US Patent No. 4,936,363 was structured as above to prevent the edge of the rib from undergoing wear, and said lower edge zone has projecting and re-entrance portions on the sidewalls of the circumferentially extending wide groove, that is the cross-sectional shape of the edge zone is uneven, while the outside surface also has projecting and re-entrance portions. Therefore, this prior art tire may be effective for preventing wear on the rib, but cannot relieve the vibration in the crosswise direction of the circumferentially extending groove of the rolling tire, so that this tire has not attained sufficient prevention of noise resulting from air-column-tube resonance sounds etc. There is further proposed a pneumatic tire comprising main grooves and stepped zones in US 5,445, 201. The present invention was made in view of the above problem and the object is to provide a pneumatic radial tire having good drainage properties and capable of reducing noise by decreasing air-column-tube resonance sounds. The present invention provides a pneumatic radial tire comprising: a radial carcass layer, a pair of bead cores, a belt layer radially outside said carcass, and a tread arranged outside of said belt layer in the radial direction of the tire, a circumferentially extending groove provided on the surface of said tread and having sidewalls inclined in opposite directions with respect to a radial direction of said tire, and at least one vibration buffer wall having a substantially constant cross sectional shape with sidewalls inclined with respect to the radial direction of said tire and formed adjacent a sidewall of said circumferentially extending groove and extending toward a tread surface of said tread, each of said sidewalls of said vibration buffer wall being inclined in the same direction as that of an adjacent sidewall of said circumferentially extending groove, wherein the height of the outside edge of the vibration buffer wall in the radial direction of the tire is lower than the height of the outside edge of said circumferentially extending groove in the radial direction of the tire, and wherein the following relationship is satisfied: 0.50D≤H≤0.95D S≤0.30B 0.01B≤W≤0.30B 0.50D≤L≤1.50D wherein B is the width of said circumferentially extending groove, D is the depth of said circumferentially extending groove, H is the height of said vibration buffer wall from the bottom of said circumferentially extending groove, S is the width of an upper surface of said vibration buffer wall, W is the width of a groove between the sidewall of said circumferentially extending groove and said vibration buffer wall, and L is the depth of the groove between the sidewall of said circumferentially extending groove and said vibration buffer wall. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 is a perspective sectional view of a first example of a pneumatic radial tire of the present invention; FIG. 2 is a plan view of an essential part of the first example of the pneumatic radial tire shown in FIG. 1; FIG. 3 is a sectional view of the first example of the pneumatic radial tire across line X-X in FIG. 2; FIG. 4(a) and (b) show a perspective view of a circumferentially extending groove of a second example of a pneumatic radial tire of the present invention; FIG. 5 show a characteristic sound-pressure level against frequency, of rib grooves in rolling tires; FIG. 6(a) and (b) show characteristic vibration levels of rib grooves in rolling tires in low- and high-frequency ranges, respectively; and FIG. 7 is a sectional perspective view of a prior art pneumatic radial tire. In the drawings, 11, 11' are pneumatic radial tires; 12, rubber layer; 13, bead; 14, bead core; 15, ply cord; 16, carcass layer; 17, steel cord; 18, steel belt layer; 19, tread; 20, rib groove; 20a, 20b, 21c, sidewalls; and 21, vibration buffer wall. In a specific embodiment of the pneumatic radial tire of the present invention, said vibration buffer walls are formed generally parallel to and adjacent to the sidewalls of said circumferentially extending groove, and said vibration buffer walls may have notches. The pneumatic radial tire of the present invention is characterized by having the following relationships (1) to (4): 0.50D≤H≤0.95D S≤0.30B 0.01B≤W≤0.30B 0.50D≤L≤1.50D wherein B is the width of said circumferentially extending groove, D is the depth of said circumferentially extending groove, H is the height of said vibration buffer wall from the bottom of said circumferentially extending groove, S is the width of an upper surface of said vibration buffer wall, W is the width of a groove between the sidewall of said circumferentially extending groove and said vibration buffer wall, and L is the depth of the groove between the sidewall of said circumferentially extending groove and said vibration buffer wall. By forming the vibration buffer walls with a generally identical cross-sectional shape adjacent to the sidewalls of the circumferentially extending groove, the pneumatic radial tire of the present invention constituted as above suppresses transmission of tread vibration from the circumferentially extending grooves in the rolling tire to the air in the circumferentially extending grooves, so that the air-column-tube resonance in the circumferentially extending grooves is suppressed and the generation of noise is thus prevented. That is, the shear strength in the crosswise direction of the circumferentially extending grooves in the rolling tire is reduced, the vibration in the crosswise direction of the circumferentially extending grooves is relieved, and air-column-tube resonance sounds at high frequency of 1.6 KHz or more are reduced. By arranging the vibration buffer walls generally parallel to the sidewalls of said circumferentially extending groove, the capacity of the circumferentially extending grooves is secured thus permitting the circumferentially extending grooves to accommodate a sufficient amount of water to ensure drainage. By making the height of the outside edge of said vibration buffer wall lower than the height of the outside edge of the circumferentially extending groove, the vibration buffer wall receives relatively low pressure from the ground as compared with other portions of the tire. Therefore, the vibration buffer wall itself does not vibrate to such a high level as in other portions and thus it does not cause the vibration of the air in the circumferentially extending grooves. The generation of noise is thereby effectively prevented. Further, when a part or the whole of the outer edge (surface of the tread) of the circumferentially extending groove comes to have the same height as the outer edge of the vibration buffer wall as a result of the spread of wear on the tread, the outer edge of the vibration buffer wall will undergo much more wear than the outer edge of the circumferentially extending groove because the rigidity of the outer edge of the vibration buffer wall is lower than that of the outer edge of the circumferentially extending groove. Therefore, the height of the outer side edge of the vibration buffer wall is always maintained lower than the height of the outer edge of the circumferentially extending groove. Furthermore, the production of tires is facilitated by the presence of notches in the vibration buffer walls. The embodiments of the present invention are further described by reference to the accompanying drawings. Those elements which have the same function have the same symbols in the following descrption of the embodiments. FIG. 1 is a sectional perspective view of a first example of the pneumatic radial tire of the present invention, FIG. 2 is a plan view of an essential part of the first example of the pneumatic radial tire, FIG. 3 is a sectional view of the first example of the pneumatic radial tire across line X-X in FIG. 2, and FIG. 4 is a perspective view of a circumferentially extending groove of a second example as a modification of the first example of the pneumatic radial tire. In the pneumatic radial tire 11 in FIG. 1, the tire size is PSR265/70R16 and the tire has a loop shape in section and is made of a rubber layer 12 as a whole. Beads 13 at the sectional ends of the radial tire 11 are provided with a pair of bead cores 14, 14 formed into a ring around the rotating shaft of the radial tire 11. A 2-ply carcass layer 16, consisting of ply cords 15 arranged in the form of a loop in the sectional direction of radial tire 11, is provided across a pair of the bead cores 14, 14. The ends of the carcass layer 16 in the longer direction are turned outside and wound up around a pair of the bead cores 14, 14. The radial outside of the carcass layer 16 is provided with a 2-ply steel belt layer 18 consisting of nonstretchable steel cord 17, and a thick-wall tread 19 is formed on the outside of the steel belt layer 18 in the radial direction, so as to cover the steel belt layer 18. Further, the surface of the tread 19 is provided at predetermined intervals with a plurality of continuous rib grooves 20 (circumferentially extending grooves) circumferentially extending around the radial tire 11. The rib grooves 20 are provided inside with a pair of thin-wall vibration buffer walls 21 having a generally uniform cross-sectional shape and being generally parallel to and adjacent to sidewalls 20a respectively, and the height of the outside edge of this vibration buffer wall 21 in the radial direction is set lower than the height of the outside edge (surface of the tread 19) of the rib groove 20 in the radial direction of the tire. In this case, the width (B) of rib groove 20 is 13 mm, the depth (D) of rib groove 20 is 10 mm, the height (H) of vibration buffer wall 21 from the bottom of rib groove 20 is 8 mm, the width (S) of vibration buffer wall 21 is 2 mm, the distance (W) between the sidewall 20a of rib groove 20 and the vibration buffer wall 21 is 1 mm, and the depth (L) of the groove between the rib groove 20 and the vibration buffer wall 21 is 8 mm. The rib groove 20 in the second example in FIG. 4 has a different structure from the rib groove in the first example of the pneumatic radial tire in FIG. 1. That is, in FIG. 4(a), the vibration buffer wall 21 is generally parallel to and adjacent to only one of sidewalls 20a of rib groove 20, and in FIG. 4(b) the vibration buffer wall 21 in FIG. 4(a) is provided intermittently with notches 21 a. By providing the vibration buffer wall 21 with notches 21a, the extremely thin vibration buffer wall 21 can be easily vulcanized and molded. The pneumatic radial tire of the present invention was evaluated by comparing it with a conventional pneumatic radial tire as a comparative example. The performance of the first example of the present pneumatic radial tire was compared with that of the comparative example. The measurement results are shown in Table 1. Comparative Example First Example Noise level (overall value) 0 dB (A) Δ0.5 dB (A) (Small value is good) Hydroplaning performance 100 99 (Large value is good) Partial wear 100 95 (Small value is good) These values are relative to those (as 0 dB(A), 100) of the comparative example. As can be seen from Table 1, the performance of the first example is improved: that is, the noise level is reduced, the hydroplaning performance is hardly reduced, and the wear resistance of the tire is decreased. This may be because the vibration buffer wall 21 undergoes relatively much wear work in the circumferential direction upon contact with the ground, by which wear work on other portions is relatively decreased. In this measurement, the noise level was evaluated with an on-bench noise meter drum. To evaluate drainage, a car ran straight in a pool of 10 mm in depth and the lowest speed when hydroplaning occurred was determined and evaluated. The partial wear was evaluated by examining wear work with a machine for measurement of on-bench contact pressure and sliding. It is said that among the air-column-tube resonance sounds in the rib groove 20, sounds of 1 kHz or thereabout occur due to the vibration of the bottom of the groove, while high-frequency sounds of 2 kHz or more occur due to the vibration of the groove walls. The first example of the present invention has effectively reduced high-frequency resonance sounds because the vibration level in the first example is lower by 1.5 to 2.0 dB(A) in each point ranging from 2 to 3.2 kHz than that of the comparative example, as shown in the characteristics of sound pressure level vs. frequency in FIG. 5 and the characteristics of vibration level vs. frequency in FIG. 6 with respect to the circumferentially extending grooves in the rolling tire. In this measurement of vibration level, an acceleration sensor was attached to the rib groove wall in the comparative example and to the vibration buffer wall 21 in the first example of the present invention. Although the first and second examples have been described above in detail as embodiments of the pneumatic radial tire of the present invention, the present invention is not limited to the radial tires described in such examples, and these can be modified in design without departing from the scope of the invention described in the appended claims. For example, a description of straight and continuously extending straight rib grooves was made for the first example of the present pneumatic radial tire, but the grooves may be zigzag-shaped or partially interrupted. As can be understood from the above description, the pneumatic radial tire of the present invention can suppress air-column-tube resonance in circumferentially extending grooves to prevent the occurrence of noise because a vibration buffer wall with a roughly identical cross-sectional shape in section is formed near the sidewalls of the circumferentially extending grooves. Hence, the problem of generation of noise from automobiles can be prevented. In addition, the adequate capacity of the circumferentially extending grooves is secured by arranging the vibration buffer wall generally parallel to the sidewalls of the circumferential extending grooves, thereby preventing drainage from lowering. Further, the vibration buffer wall itself does not vibrate because the height of the outside edge of the vibration buffer wall is designed to be lower than the height of the outside edge of the circumferentially extending groove. Therefore, noise can be effectively prevented, the shear strength in the crosswise direction of the tire in contact with the ground can be reduced, the vibration in the crosswise direction of the circumferentially extending grooves in the tire can be relieved, and high-frequency air-column-tube resonance sounds of 1.6 kHz or more can be decreased. Vibration buffer walls with notches are easy to mold, so it is possible to manufacture an extremely thin vibration buffer wall with good workability.

Claims: A pneumatic radial tire (11) comprising: a radial carcass layer (16), a pair of bead cores (14), a belt layer (18) radially outside said carcass, and a tread (19) arranged outside of said belt layer in the radial direction of the tire, a circumferentially extending groove (20) provided on the surface of said tread and having sidewalls (20a) inclined in opposite directions with respect to a radial direction of said tire, and at least one vibration buffer wall (21) having a substantially constant cross sectional shape with sidewalls inclined with respect to the radial direction of said tire and formed adjacent a sidewall (20a) of said circumferentially extending groove (20) and extending toward a tread surface of said tread, each of said sidewalls of said vibration buffer wall (21) being inclined in the same direction as that of an adjacent sidewall (20a) of said circumferentially extending groove (20), wherein the height of the outside edge of the vibration buffer wall (21) in the radial direction of the tire is lower than the height of the outside edge of said circumferentially extending groove (20) in the radial direction of the tire, and wherein the following relationship is satisfied: 0.50D≤H≤0.95D S≤0.30B 0.01B≤W≤0.30B 0.50D≤L≤1.50D wherein B is the width of said circumferentially extending groove (20), D is the depth of said circumferentially extending groove (20), H is the height of said vibration buffer wall (21) from the bottom of said circumferentially extending groove (20), S is the width of an upper surface of said vibration buffer wall (21), W is the width of a groove between the sidewall (20a) of said circumferentially extending groove (20) and said vibration buffer wall (21), and L is the depth of the groove between the sidewall (20a) of said circumferentially extending groove (20) and said vibration buffer wall. A pneumatic radial tire as claimed in claim 1, characterized in that said vibration buffer wall (21) is formed essentially parallel to the sidewall (20a) which is facing the vibration buffer wall (21). A pneumatic radial tire as claimed in claim 1 or 2, characterized in that a second vibration buffer wall (21) is formed adjacent to another sidewall (20a) of said circumferentially extending groove (20). A pneumatic radial tire as claimed in claim 3, characterized in that said vibration buffer wall and said second vibration buffer wall are formed adjacent and parallel to the sidewall (20a) which is facing the respective vibration buffer wall (21). A pneumatic radial tire as claimed in claim 1 or 2, characterized in that said vibration buffer wall (21) has notches (21a). A pneumatic radial tire as claimed in claim 3 or 4, characterized in that said vibration buffer walls (21) have notches (21a). A pneumatic radial tire as claimed in any of claims 3, 4 or 6, characterized in that said vibration buffer wall and said second vibration buffer wall have substantially identical cross-sectional shapes. A pneumatic radial tire as claimed in any of claims 3, 4, 6 or 7, characterized in that said circumferentially extending groove (20) has a substantially u-shape in cross-section and said vibration buffer wall and said second vibration buffer wall are formed adjacent to and defined by sidewalls (20a) of said u-shape circumferentially extending groove.

Inventors: YOKOTA HIDETOSHI, YOKOTA, HIDETOSHI, YOKOTA, HIDETOSHI, C/O BRIDGESTONE CORP. TECH.CTR.
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1997
Main classification: B60C11
IPC codes: B60C11