Pneumatic tire and method of designing tread pattern thereof

Abstract

A pneumatic tire reduces the columnar resonance noise of the tire while controlling the lowering of wet performances, wherein four circumferential grooves continuously extending in the circumferential direction of the tire are disposed in a treading face and a plurality of lateral grooves each having one end opened to the circumferential groove and terminated in a land portion are formed with respect to two circumferential grooves among the four circumferential grooves, and these lateral grooves and the respective circumferential grooves have such a groove width that both groove walls of the groove do not contact with each other in a ground contact face and one or more lateral groove are always completely included in the ground contact face, and an extending length of a portion of each lateral groove in the ground contact face having a groove width of the lateral groove corresponding to not less than 30% of a groove width of the circumferential groove is made not less than 40% of an extending length of the circumferential groove in the ground contact face.

Claims

1. A pneumatic tire comprising a tread, said tread comprising: at least one first circumferential groove, which extends continuously in the circumferential direction of the tire and which is disposed in a treading face; at least one second circumferential groove, which extends continuously in the circumferential direction of the tire and which is disposed in the treading face; a first plurality of lateral grooves, each of the first plurality of lateral grooves having a first end opened to the at least one first circumferential groove, each of the first plurality of lateral grooves having a second end, which terminates in a land portion, and each of the first plurality of lateral grooves is formed by a single continuous groove wall, respectively, extending from the first end opened to the at least one first circumferential groove to the second end and back to the first end, wherein each of the first plurality of lateral grooves is formed independently of a second plurality of lateral grooves, each of said second plurality of lateral grooves opened to the at least one second circumferential groove and not opened to the at least one first circumferential groove, wherein said at least one first circumferential groove is separated from said at least one second circumferential groove and said at least one first circumferential groove is formed independent of the second plurality of lateral grooves, wherein the at least one first circumferential groove only connects to grooves which have an end terminating in a land portion, said grooves including said first plurality of lateral grooves, wherein each of the at least one first circumferential groove and the first plurality of lateral grooves has a groove width such that groove walls do not contact with each other at a tire posture when the tire is mounted on an approved rim and filled with a maximum air pressure and loaded with a mass corresponding to a maximum load capacity, wherein at least one of the first plurality of lateral grooves is always completely included in a ground contact face of the tread, wherein a portion of the at least one of the first plurality of lateral grooves has a groove width corresponding to not less than 30% of a groove width of the corresponding first circumferential groove to which the at least one of the first plurality of lateral grooves is connected, and the at least one of the first plurality of lateral grooves has an extending length in the ground contact face of not less than 40% of an extending length of the corresponding first circumferential groove, to which the at least one of the first plurality of lateral grooves is connected, in the ground contact face, wherein the second lateral grooves have a groove width such that groove walls do not contact with each other at a tire posture when the tire is mounted on an approved rim and filled with a maximum air pressure and loaded with a mass corresponding to a maximum load capacity, and wherein at least one of the second plurality of lateral grooves is opened to both the at least one second circumferential groove and one ground contacting end of the tread.

2. A pneumatic tire comprising a tread, said tread comprising at least one circumferential groove, which extends continuously in the circumferential direction of the tire and which is disposed in a treading face; a selected plurality of lateral grooves, each of the selected plurality of lateral grooves having a first end opened to the at least one circumferential groove, each of the selected plurality of lateral grooves having a second end, which terminates in a land portion, and each of the selected plurality of lateral grooves is formed by a single continuous groove wall, respectively, extending from the first end opened to the at least one first circumferential groove to the second end and back to the first end, wherein each of the selected plurality of lateral grooves is formed independently of any other lateral groove, wherein the at least one circumferential groove only connects to grooves, which have an end terminating in a land portion, said grooves including said selected plurality of lateral grooves, wherein each of the at least one circumferential groove and the selected plurality of lateral grooves has a groove width such that groove walls do not contact with each other at a tire posture when the tire is mounted on an approved rim and filled with a maximum air pressure and loaded with a mass corresponding to a maximum load capacity, wherein at least one of the selected plurality of lateral grooves is always completely included in a ground contact face of the tread, wherein a portion of the at least one of the selected plurality of lateral grooves has a groove width corresponding to not less than 30% of a groove width of the at least one circumferential groove to which the at least one of the selected plurality of lateral grooves is connected, and the at least one of the selected plurality of lateral grooves has an extending length in the ground contact face of not less than 40% of an extending length of the at least one circumferential groove, to which the at least one of the selected plurality of lateral grooves is connected, in the ground contact face, wherein the tread further comprises at least one shoulder groove having a groove width such that groove walls do not contact with each other at a tire posture when the tire is mounted on an approved rim and filled with a maximum air pressure and loaded with a mass corresponding to a maximum load capacity, and wherein the at least one shoulder groove is opened to both a ground contacting end of the tread and a circumferential groove, which is isolated from the plurality of lateral grooves and which is also isolated from the at least one circumferential groove to which the plurality of lateral grooves open.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a developed view of a tread pattern of a pneumatic tire showing an embodiment of the invention.

(2) FIG. 2 is a view showing a footprint of the tire of FIG. 1.

(3) FIG. 3 is a developed view of another tread pattern.

(4) FIG. 4 is a developed view of the other tread pattern.

(5) FIG. 5 is a view showing a footprint of the other tire.

(6) FIG. 6 is a developed view of a further tread pattern.

(7) FIG. 7 is a developed view of a still further tread pattern.

(8) FIG. 8 is a developed view of a tread pattern of a comparative tire.

(9) FIG. 9 is a schematic view showing a measuring embodiment of the noise.

(10) FIG. 10 is a graph showing a state of a change of the noise level with respect to a change of the length ratio of the lateral groove.

(11) FIG. 11 is a view showing a footprint of another comparative tire.

BEST MODE FOR CARRYING OUT THE INVENTION

(12) Embodiments of the invention will be explained with reference to the accompanying drawings below.

(13) FIG. 1 is a developed view of a tread pattern of a pneumatic tire schematically showing an embodiment of the invention.

(14) Moreover, the inner reinforcing structure or the like of this tire is the same as in a general radial tire, so that the illustration thereof is omitted.

(15) Numeral 1 in this figure is a treading face. In this treading face 1 are disposed two pairs of circumferential grooves 2, 3 located symmetrically with respect to an equatorial line C of the tire and continuously extending straight in a circumferential direction.

(16) With respect to a pair of center-side circumferential grooves 2 located close to the equatorial line C of the tire among these circumferential grooves 2, 3 are disposed a plurality of lateral grooves 5 each extending in a land portion 4 located at a side opposite to the equatorial line C and having one end opened to the circumferential groove 2 and the other end terminated in the land portion 4 so as to extend straight downward to the right in this figure. Each of these lateral grooves 5 is completely independently formed from another lateral grooves capable of disposing so as to be opened to another circumferential grooves 3.

(17) Also, each of a pair of shoulder side circumferential grooves 3 located away from the equatorial line C of the tire and each of ground contact ends E of the tread are communicated with each other by a plurality of shoulder lateral grooves 6 continuously extending between the shoulder-side circumferential grooves 3 and the ground contact end E and opened to both of them. Moreover, each of the shoulder lateral grooves 6 is formed by extending straight in a direction substantially perpendicular to the circumferential groove 3.

(18) In the above tread pattern of the tire, under such a state that the tire is mounted on an approved rim and filled with a maximum air pressure and loaded to a mss corresponding to a maximum load capacity, as seen from a footprint of FIG. 2, the groove widths of the circumferential groove 2 but also the lateral groove 5 have a size that groove walls of each groove do not contact with each other in a ground contact face and an arranging form that one or more of the lateral grooves 5 is always completely included in the ground contact face. Further, an extending length of a portion of the lateral groove 5 having a groove width of the lateral groove corresponding to not less than 30% of a groove width of the circumferential groove 2 in the ground contact face, i.e. a whole length l of the lateral groove 5 shown in FIG. 2 is made not less than 40% of an extending length L of the circumferential groove 2 in the ground contact face.

(19) According to the tire having such a construction, under the formation of the plural circumferential grooves and the like as mentioned above, excellent wet performances can be ensured while simultaneously establishing the steering stability and the limit grip property on the dry road surface, and also the columnar resonance frequencies of the respective circumferential grooves 2, 3 can be made different with each other. For example, the resonance frequency of the circumferential groove 2 can be made considerably small as compared with that of the circumferential groove 3, whereby the peak level of the columnar resonance noise can effectively be reduced and the change to white noise can largely be promoted.

(20) FIG. 3 is a developed view showing another embodiment of the tread pattern. In this embodiment, each of lateral grooves 7 having an end opened to the circumferential groove 2 is extended substantially in a hook form and has the other end corresponding to the tip of the lateral groove 5 added with a bent portion substantially parallel to the circumferential grooves 2, 3, and the other portions are the same as in FIG. 1.

(21) According to this embodiment, a total length of each lateral groove 7 having a sufficient groove width can be lengthened as compared with that of the lateral groove 5 shown in FIG. 1 and the sound-absorbing frequency can be approximated to the columnar resonance frequency as compared with the tire of FIG. 1, so that the resonance noise can be more effectively absorbed to advantageously reduce the overall level of the tire noise.

(22) And also, a crossing angle between the lateral groove 7 and the circumferential groove 2 can be made larger than that of FIG. 1, so that the occurrence of the uneven wear at a corner part of the land portion defined by these grooves can also advantageously be controlled.

(23) In a tread pattern shown in FIG. 4, a lateral groove 8 opened to the circumferential groove 2 has a bent portion substantially parallel to the circumferential grooves 2, 3, an extending length of which is made longer than that shown in FIG. 3, and a sub-groove 9 having an end opened to the bent portion and the other end terminated in the land portion 4 is disposed so as to extend substantially parallel to a connecting portion of the lateral groove 8 to the circumferential groove 2 without crossing with any grooves.

(24) According to this embodiment, the further improvement of the wet performance and the more further reduction of the columnar resonance noise can be realized under a cooperation of the lateral groove 8 and the sub-groove 9 as previously mentioned.

(25) FIG. 5 is a footprint showing another tread pattern of the tire according to the invention, which shows a case that the tire is contacted with ground under the aforementioned conditions.

(26) In this case, with respect to the pair of center-side circumferential grooves 2, lateral grooves 10, 11 respectively extending at both sides of one circumferential groove are arranged so as to have a tendency of substantially a V-shape as a whole, while they are arranged at the other circumferential groove 2 so as to have a tendency of substantially an inverted V-shape. Each of the pair of lateral grooves 10, 11 is opened to the circumferential grooves 2 at substantially the same position in the circumferential direction. Also, each of the lateral grooves 10 extending in a land portion 12 located at a center side from the circumferential groove 2 is formed downward to the right in this figure, while each of the lateral grooves 11 extending in the land portion 4 located at a shoulder side from the circumferential groove 2 is formed upward to the right. Further, each of the lateral grooves 11 is provided with a bent portion extending close to the shoulder-side circumferential groove 3 and substantially in parallel thereto.

(27) In this illustrated embodiment, only the shoulder-side lateral grooves 11 satisfy a given groove-width condition over approximately a full length in the ground contact face and also satisfy a given length condition.

(28) Even in such a tread pattern, the resonance frequencies of the respective circumferential grooves 2, 3 can be made sufficiently different with each other to effectively develop a desired function of noise reduction.

(29) FIG. 6 is a developed view showing the other tread pattern. In this case, two pairs of circumferential grooves 2, 3 extend in the zigzag form, and the same lateral groove 8 as described in FIG. 4 is formed by directly opening to the center-side circumferential groove 2, and the sub-groove 9 is formed by indirectly opening to the center-side circumferential groove 2, and the shoulder lateral groove 6 extending substantially in the widthwise direction of the tread and opened to the ground contact end E of the tread is formed by opening to the shoulder-side circumferential groove 3.

(30) Even in this tire, the improvement of the wet performance and the reduction of the columnar resonance noise can be realized under the cooperation of the lateral groove 8 and the sub-groove 9 as previously mentioned.

(31) FIG. 7 is a developed view of another tread pattern.

(32) In this case, two pairs of circumferential grooves 2, 3 are disposed to extend straight in the circumferential direction, In the land portion 4 defined between these circumferential grooves 2 and 3 are formed the lateral groove 8 directly opening to the center-side circumferential groove 2 and the sub-groove 9 indirectly opening thereto likewise the cases of FIGS. 4 and 6, while a lateral groove 13 and a sub-groove 14 directly or indirectly opening to the shoulder-side circumferential groove 3 are formed in a point symmetry with respect to the lateral groove 8 and the sub-groove 9 therebetween in the land portion 4. The shoulder-side circumferential groove 3 is communicated with the ground contact end E of the tread through sipes 15 each extending substantially in the widthwise direction of the tread at such a width that the groove walls contact with each other in the ground contact face.

(33) In this embodiment, as the groove walls of the sipe 15 contact with each other in the ground contact face, not only the lateral grooves 8 but also the lateral grooves 13 independently exist from another circumferential groove and another lateral groove capable of opening to the ground contact end of the tread, and can effectively contribute to the sound absorption together with the respective sub-grooves 9, 14.

(34) Even in such a tread pattern, the approach form of the respective grooves into the ground contact face of the tread differs between a combination of the center-side circumferential groove 2, the lateral groove 8 and the sub-groove 9 and a combination of the shoulder-side circumferential groove 3, the lateral groove 13 and the sub-groove 14, and the columnar resonance frequencies in the respective groove portions including the respective circumferential grooves 2, 3 also necessarily differ, so that the required dispersion in the resonance frequencies is effectively conducted.

EXAMPLES

Example 1

(35) At a state of mounting an example tire having a tire size of 195/65 R15 on a rim of 6J, filling with an air pressure of 220 kPa and applying a load of 4.25 kN, the columnar resonance noise level (1000 Hz) and the overall level of the noise are measured at a speed ranging from 40 km/h to 100 km/h every 10 km/h according to JASO C606 standard, and the resistance to hydroplaning in the actual straight running is evaluated by entering a vehicle into a road surface having a water depth of 10 mm to measure a vehicle speed floating the tire.

(36) The average values of these measured results are shown in Table 1.

(37) In Table 1, Example tire 1 has a tread pattern shown in FIG. 1, and Example tire 2 has a tread pattern shown in FIG. 2 and Example tire 3 has a tread pattern shown in FIG. 4. On the other hand, Comparative tire 1 has a tread pattern shown in FIG. 8 in which all of the lateral grooves and the shoulder lateral grooves opened to the ground contact end of the tread are opened to the shoulder-side circumferential groove.

(38) In the measurement of the noise, as shown by a side view in FIG. 9, five microphones are arranged not only at a measuring position defined in JASO C606 but also at positions set every 50 cm within a range of 1 m forward and backward from the above measuring position, and the noise level is determined by calculating an average value from the measured waveforms.

(39) TABLE-US-00001 TABLE 1 Comparative tire 1 Example tire 1 (FIG. 8) (FIG. 1) Columnar resonance noise level control 1.6 dB (A) (1000 Hz) Overall level control 0.7 dB (A) Resistance to hydroplaning 100 100 (Index)* Example tire 2 Example tire 3 (FIG. 3) (FIG. 4) Columnar resonance noise level 1.9 dB (A) 3.0 dB (A) (1000 Hz) Overall level 0.8 dB (A) 1.0 dB (A) Resistance to hydroplaning 100 100 (Index)* *Index value shows that the larger it becomes, the more excellent the result is.

(40) As seen from Table 1, all Example tires can advantageously reduce the noise while effectively controlling the lowering of the wet performance and also the effect of reducing the noise is improved in accordance with the increase of the length of the lateral groove

Example 2

(41) Next, the change of the overall level in the noise and the change of the columnar resonance are measured in the same manner as mentioned above under the same conditions as in Example 1 using the ratio of the lateral groove length to the circumferential groove length in the ground contact face to obtain the effect shown by a graph in FIG. 10.

(42) As seen from FIG. 10, the noise level violently lowers when the ratio of the lateral groove length is more than 40%.

Example 3

(43) At a state of mounting an example tire having a tire size of 195/65 R14 on a rim of 6J, filling with an air pressure of 200 kPa and applying a load of 4.9 kN, the columnar resonance noise level (1000 Hz) and the overall level of the noise are measured at a speed of 80 km/h in the same manner as in Example 1, and the resistance to hydroplaning in the straight running is also evaluated in the same manner as in Example 1.

(44) The average values of these measured results are shown in Table 2.

(45) In Table 2, Example tire 4 has a footprint (1/L=0.4) shown in FIG. 5 and Comparative tire 2 has a footprint shown in FIG. 11.

(46) TABLE-US-00002 TABLE 2 Comparative tire 2 Example tire 4 (FIG. 11) (FIG. 5) Columnar resonance noise level 80.2 dB (A) 78.9 dB (A) (1000 Hz) (1.3) Overall level 86.5 dB (A) 86.0 dB (A) (0.5) Resistance to hydroplaning 100 100 (Index)* *Index value shows that the larger it becomes, the more excellent the result is.

(47) As seen from Table 2, the noise level can be reduced without lowering the wet performances, especially a hydroplaning property in question.

INDUSTRIAL APPLICABILITY

(48) As seen from the above examples, according to the invention, the noises generated in the tire, particularly columnar resonance can be effectively reduced while sufficiently highly ensuring the wet performances of the tire.