Pneumatic tire tread

Abstract

A tread for a pneumatic tire in which air column resonance sound is reduced and wear of the groove fences and tread portion are caused to be approximately the same, while drainage performance is maintained, wherein a plurality of groove fences are formed and are installed within at least one circumferential groove, extending from the bottom of the circumferential groove, and block at least 70% of the cross-sectional area of the circumferential groove, and the bending parameter of the groove fences, defined as E.Math.I/(h3l) (where E is the modulus at 10% elongation of the material used for the groove fences, I is the second moment of area of the groove fence, h is the height of the groove fence, and l is the width of the groove fence) is at least equal to 250 Pa and at most equal to 350 Pa.

Claims

1. A tread for a pneumatic tire having at least one circumferential groove having a bottom portion and opposing walls, at least two ribs adjacent to the circumferential groove, and a plurality of groove fences formed within the abovementioned at least one circumferential groove such that the abovementioned circumferential groove is interrupted, wherein the abovementioned groove fences are formed extending from the bottom portion of the abovementioned circumferential groove in a direction perpendicular to the axis of rotation of the tire in such a way that there are gaps to the abovementioned walls, and at least 70% of the cross-sectional area of the abovementioned circumferential groove in which the abovementioned groove fences are formed is blocked, and in that the bending parameter of the groove fences which extend from the bottom portion of the abovementioned circumferential groove in a direction perpendicular to the axis of rotation of the tire, defined as
(EI)/(h.sup.3l), where E is the modulus at 10% elongation of the material used for the abovementioned groove fences, I is the second moment of area of the abovementioned groove fence, h is the height of the abovementioned groove fence, and l is the width of the abovementioned groove fence, is at least equal to 250 Pa and at most equal to 350 Pa.

2. A tread for a pneumatic tire according to claim 1, wherein the modulus at 10% elongation (M10) of the material used for the abovementioned groove fences is at least equal to 2.0 MPa and at most equal to 8.0 MPa.

3. A tread for a pneumatic tire according to claim 2, wherein the thickness of the abovementioned groove fences is at least equal to 0.5 mm and at most equal to 0.7 mm.

4. A tread for a pneumatic tire according to claim 3, wherein the material used for the abovementioned groove fences is the same material as the material of the tread part including the abovementioned at least two ribs.

5. A tread for a pneumatic tire according to claim 3, wherein the material used for the abovementioned groove fences is a different material to the material of the tread part including the abovementioned at least two ribs.

6. A tread for a pneumatic tire according to claim 4, wherein the cross-sectional shape of the abovementioned groove fences is rectangular.

7. A tread for a pneumatic tire according to claim 5, wherein the cross-sectional shape of the abovementioned groove fences is rectangular.

Description

BRIEF EXPLANATION OF THE FIGURES

(1) [FIG. 1] is a diagram illustrating schematically a tread for a pneumatic tire according to an embodiment of the present invention.

(2) [FIG. 2] is an enlarged sectional view of the tread for a pneumatic tire as viewed along line II-II in FIG. 1.

(3) [FIG. 3] is an enlarged sectional view of the tread for a pneumatic tire as viewed along line III-III in FIG. 1.

(4) [FIG. 4] is a diagram which illustrates, similarly to FIG. 2, an enlarged sectional view of the tread for a pneumatic tire as viewed along line II-II in FIG. 1, illustrating schematically a state in which the tire is being driven on a wet road surface.

(5) [FIG. 5] is a diagram which illustrates, similarly to FIG. 3, an enlarged sectional view of the tread for a pneumatic tire as viewed along line III-III in FIG. 1, illustrating schematically a state in which the tire is being driven on a wet road surface.

(6) [FIG. 6] is a diagram which illustrates, similarly to FIG. 3, an enlarged sectional view of the tread for a pneumatic tire as viewed along line III-III in FIG. 1, illustrating schematically a state in which the tread portion has been worn down by approximately 30%.

MODES OF EMBODYING THE INVENTION

(7) A preferred mode of embodiment of the present invention will now be described with reference to the diagrams.

(8) First, a tread for a pneumatic tire according to a mode of embodiment of the present invention will be described based on FIG. 1 to FIG. 3.

(9) FIG. 1 is a diagram illustrating schematically a tread for a pneumatic tire according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view of the tread for a pneumatic tire as viewed along line II-II in FIG. 1, and FIG. 3 is an enlarged sectional view of the tread for a pneumatic tire as viewed along line III-III in FIG. 1.

(10) First, as shown in FIG. 1, reference number 1 indicates a pneumatic tire tread 1 according to the present embodiment, two circumferential grooves 2 having a width W and extending in the circumferential direction of the tire as indicated by XX are formed in the tread 1, and ribs 3 demarcated by these circumferential grooves 2 are formed in the tread 1. It should be noted that the size of the tire in this example is 225/55R16. In the present mode of embodiment, the width W of the circumferential grooves 2 is 14.5 mm.

(11) On the diagram are shown the tread footprint 5 and the tread footprint length L when the tire is inflated to its rated pressure and a rated load is applied. It should be noted that according to the ETRTO Standard Manual 2010 the applicable rim for this size is 7J, the rated pressure is 250 kPa, and the rated load is 690 kg, and in the present embodiment the footprint length L is 143 mm.

(12) When the tire is rolling, air columns are formed between the road surface and each of the circumferential grooves 2 which pass through the tread footprint 5, and since the resonant frequency of the circumferential grooves 2 depends on the length of the air column formed in this way, in order to vary the frequency of the air column resonance sound the length of the air column should be varied.

(13) As shown in FIG. 1, a plurality of groove fences 4 of width l, with which the circumferential grooves 2 can be largely blocked, are formed in each circumferential groove 2 for the purpose of varying the length of the air column. The installation interval P between groove fences 4 formed in the same circumferential groove 2 is provided in such a way that it is a shorter interval than the footprint length L, so that at least one groove fence is always present within the footprint 5 in each circumferential groove 2. In the present mode of embodiment, the width l of the groove fences 4 is 13.5 mm.

(14) Next, as shown in FIG. 2 and FIG. 3, the bottom portion 41 of the groove fence 4 is connected as shown in the diagrams to the bottom portion 21 of the circumferential groove 2, and as shown in FIG. 3, the groove fence 4 is provided in such a way that it extends in the radial direction of the tire (the direction that is perpendicular to the axis of rotation of the tire). Further, as shown in FIG. 2, side surface portions 42 on each side of the groove fence 4 are provided in such a way that there is a prescribed gap between the whole thereof, excluding the connecting portion (41) described above, and opposing walls 22 of the circumferential groove 4.

(15) As shown in FIG. 1, each groove fence 4 is formed such that it extends in a direction perpendicular to the direction in which the circumferential grooves 2 extend. Each groove fence 4 has a rectangular cross-sectional shape, and the rectangular cross section has a width l as described above, and a thickness e (refer to FIG. 3).

(16) Further, as shown in FIG. 2, the groove fence 4 as viewed in the longitudinal direction (front view) of the circumferential groove 2 is formed in the shape of a rectangle, and as shown in FIG. 2 and FIG. 3 it has a height h which is slightly lower than the depth D of the circumferential groove 2.

(17) The groove fence 4 is formed such that it blocks at least 70% of the cross-sectional area of the circumferential groove 2, and is formed such that it collapses under the water pressure of liquids such as principally water that flow within the circumferential groove 2. In the present mode of embodiment, the depth D of the circumferential groove 2 is 8.0 mm, the height h of the groove fence 4 is 7.0 mm, the thickness e of the groove fence 4 is 0.6 mm, and the groove fence 4 blocks approximately 87% of the cross-sectional area of the circumferential groove 2. It should be noted that for example in the case of the tire in the present mode of embodiment the groove fence 4 should be of a rectangular shape having a height h of at least approximately 5.6 mm such that it blocks at least 70% of the cross-sectional area of the circumferential groove 2. It should be noted that without limitation to the present mode of embodiment, if the width W and the depth D of the tire circumferential groove 2 change, the height h of the groove fence 4 should be modified accordingly such that it blocks at least 70% of the cross-sectional area of the circumferential groove 2.

(18) In the present mode of embodiment, the groove fences 4 consist of the same material as the ribs 3 of the tread 1 (the tread part). It should be noted that the groove fences 4 may consist of a different material to the ribs 3.

(19) Further, in the present mode of embodiment the groove fences 4 are formed using a material which has a modulus at 10% elongation (M.sub.10) of 5.8 MPa. Thus in the present invention the bending parameter of the groove fence 4, prescribed (defined) by

(20) $\frac{E.Math.I}{h^{3}l}$
is 304 Pa. The value of this bending parameter 304 Pa is a value such that the groove fence 4 does not collapse when only air is flowing through the circumferential groove 2 when being driven on a normal dry road surface, as a result of which the air column becomes shorter and air column resonance sound is reduced. It should be noted that the same effect is obtained if the value of the bending parameter is at least equal to 250 Pa and at most equal to 350 Pa.

(21) Here, E is the modulus at 10% elongation (M.sub.10) of the material used for the groove fence 4, l is the width of the groove fence 4 projected onto a surface parallel to the axis of rotation of the tire, I is the second moment of area, defined from the abovementioned width l of the groove fence 4 and thickness e of the groove fence 4, as

(22) $\frac{e^{3}l}{12}$
and h is the height of the groove fence 4 in a direction perpendicular to the axis of rotation of the tire.

(23) Next, the condition when a tread for a pneumatic tire according to a mode of embodiment of the present invention is being driven on a wet road surface will be described with reference to FIG. 4 and FIG. 5.

(24) FIG. 4 is an enlarged sectional view illustrating a state in which the tread for a pneumatic tire as viewed along line II-II in FIG. 1 is being driven on a wet road surface, and FIG. 5 is an enlarged sectional view illustrating a state in which the tread for a pneumatic tire as viewed along line III-III in FIG. 1 is being driven on a wet road surface.

(25) As shown in FIG. 4 and FIG. 5, the groove fence 4 having a bending parameter set to 304 Pa as described above collapses or bends under the water pressure generated by liquids such as principally water flowing through the circumferential groove 2 when being driven on a wet road surface, and as a result its height is reduced to h*, the main part of the circumferential groove is released by virtue of the fact that the height is reduced, and drainage is ensured. It should be noted that the same effect is obtained if the value of the bending parameter is at least equal to 250 Pa and at most equal to 350 Pa.

(26) Next, the state after the tread has become worn, in a tread for a pneumatic tire according to a mode of embodiment of the present invention, will now be described with reference to FIG. 6.

(27) FIG. 6 is an enlarged sectional view of a state in which the tread for a pneumatic tire as viewed along line III-III in FIG. 1 has been worn down by approximately 30%.

(28) FIG. 6 illustrates a state in which, after having been driven a prescribed distance, the depth D of the circumferential groove 2 has been worn down to a depth D which is shallower than the original height h of the groove fence 4. After having been driven a prescribed distance, the groove fence 4 having a bending parameter set to 304 Pa as described above has worn down such that its distal end portion which is in contact with the road surface is oblique and its height has been reduced from its original height h to h on the high side and h on the low side, and the height h on the low side is approximately the same height as the depth D of the circumferential groove 2. It should be noted that the same effect is obtained if the value of the bending parameter is at least equal to 250 Pa and at most equal to 350 Pa.

(29) A groove fence 4 of which the bending parameter described above has been appropriately set (although it is 304 Pa in the present mode of embodiment, the value of the bending parameter may be at least equal to 250 Pa and at most equal to 350 Pa.) does not collapse under the pressure of air when rolling while being driven on a dry road surface, and it also does not buckle. Further, although it falls slightly or bends due to reaction forces when it comes into contact with the road surface, an appropriate contact pressure is generated between the distal end portion of the groove fence 4 and the road surface, and it becomes worn through the generation of slippage within the tread footprint as a result of the rolling of the tire. As a result, the groove fence 4 can be caused to wear to a degree equivalent to that of the tread portion.

(30) It should be noted that as variations of the present mode of embodiment, provided that it has the effect described above, the shape of the groove fence 4 across the width l (the cross-sectional shape) may be formed with an undulating shape such that it collapses under water pressure as described above and such that an appropriate contact pressure is generated against the road surface; or the surface of the groove fence 4 as viewed from the longitudinal direction (front view) of the circumferential groove 2 may for example be provided to some extent with an uneven portion which adjusts the degree to which the groove fence 4 can bend; or it may be formed as another shape such as a rectangular or trapezoidal shape with corners that are rounded when viewed from the front.

(31) In such cases, if for example a wave-shaped or protruding body is provided as described above then the second moment of area may be calculated by approximation using the defining equation described above (e.sup.3l/12), using the average thickness e of the groove fence 4, or a suitable second moment of area defining equation appropriate to the cross-sectional shape according to the variation may be used.

(32) A particularly preferred mode of embodiment of the present invention has been described hereinabove, but the present invention may be modified and implemented in the form of various embodiments without limitation to the mode of embodiment shown in the diagrams.

(33) Embodiment

(34) Next, in order to clarify the advantages of the present invention, an explanation will be given of the results of tests performed using a conventional example in which groove fences are not provided, a comparative example provided with groove fences, and a pneumatic tire according to embodiment 1 of the present invention.

(35) The specimen tires according to the conventional example, the comparative example and embodiment 1 were in each case tires of size 225/55R16, the wheel size was 7.0J16, and the pressure was set to 250 kPa.

(36) (1) Wear Performance:

(37) Unused specimen tires were mounted, using the rims and at the pressure mentioned above, onto the four wheels of three identical vehicles (2000 cc displacement FR cars) which were driven in a three-vehicle convoy approximately 7,000 km on a prescribed asphalt test course with one driver in each vehicle, and the depths of the remaining grooves and the heights of the remaining groove fences were measured.

(38) (2) Drainage Performance:

(39) Unused specimen tires were mounted, using the rims and at the pressure mentioned above, onto the four wheels of vehicles (4300 cc displacement FR cars) which were driven, with one driver in each vehicle, on a straight-line course comprising an asphalt road surface provided with a pool of water of depth approximately 10 mm, and the driving speed at which the driver in the vehicle felt that the tires were hydroplaning is presented as an index, where 100 corresponds to the conventional example. A larger index indicates a more satisfactory performance.

(40) (3) Noise Performance:

(41) Unused specimen tires were caused to rotate, using the rims and at the pressure mentioned above, at a speed of 60 km/h on a rotating drum of diameter 2.7 m installed in an anechoic chamber, and the noise level was measured using a microphone installed in the vicinity of the point at which the tire entered the tread footprint. The measured noise is presented as the difference in sound pressure level compared with the conventional example, for the sound pressure level of the frequency band from 0 to 2,000 Hz to which an A filter has been applied. A smaller value indicates a more satisfactory performance.

(42) TABLE-US-00001 TABLE 1 Embodiment Conventional Comparative 1 example example Groove fences? Yes No Yes Groove fence thickness (mm) 0.6 0.6 Initial groove fence height 7.0 7.0 (mm) Modulus (M.sub.10) of groove 5.8 5.8 1.3 fence material (MPa) Groove fence bending 304 68 parameter (Pa) Depth of remaining 5.5 5.5 5.5 circumferential groove (mm) Height of remaining groove 6.0 7.0 fence (high side) (mm) Height of remaining groove 5.5 6.5 fence (low side) (mm) Drainage performance 100 100 100 (index) Noise performance (dBA) 0.0 +2.0 0.0

(43) As shown in Table 1, it can be confirmed that the groove fences in the product according to the embodiment are subjected to an equivalent degree of wear to the wear of the tread portion, while noise performance and drainage performance are maintained.

EXPLANATION OF THE REFERENCE NUMBERS

(44) 1 Pneumatic tire tread

(45) 2 Circumferential groove

(46) 21 Bottom portion of circumferential groove 2

(47) 22 Opposing walls of circumferential groove 4

(48) 3 Rib

(49) 4 Groove fence

(50) 41 Bottom portion of groove fence 4 (portion connected to bottom portion 21 of circumferential groove 2)

(51) 42 Side surface portions on either side of groove fence 4

(52) 5 Tread footprint